Bulletin No 57 (Low Res) - SJS Resource Management

Transcription

BALI 2013
East Asia:
Geology, Exploration
Technologies
and Mines
non-corporate Sponsors
MEMR
EMD
Geological Survey Indonesia
EXTENDED ABSTRACTS
An Australian Institute of Geoscientists
symposium organised in conjunction with
Geoscientists Symposia
27-29 May 2013
bali, indonesia
Sponsors
Volume compiled by Julian Vearncombe
Bulletin No. 57 - 2013
East Asia: Geology,
Exploration Technologies and Mines
- Extended Abstracts
© Australian Institute of Geoscientists
This booklet is copyright. All rights reserved. No part of this publication may be reproduced or stored in a retrieval system
or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior
permission in writing of the copyright owners.
Bulletin number 57
ISBN 1 876118 42 3
ISSN 0812 60 89
DISCLAIMER
The Organising Committee sought to obtain a broad coverage of this topic. Every effort was made to minimise amendments
in content of the resultant abstracts. Abstracts including references have been reproduced as submitted with changes restricted
to typographic, punctuation and layout only. The opinions and statements within the individual papers comprising the Bulletin
reflect solely the viewpoint of their authors, and are not necessarily shared by the Organising Committee of the Australian
Institute of Geoscientists.
Short quotations from the text of this publication and copies of maps, figures, tables etc (excluding any subject to pre-existing
copyright) may be used in scientific articles, exploration reports and similar works provided that the source is acknowledged
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strictly fair and balanced. Other than for the purposes of research or study the whole work must not be reproduced without the
permission in writing of the Australian Institute of Geoscientists.
ORGANiSING COMMITTEE
• Julian Vearncombe (SJS Resource Management)
• Jocelyn Thomson (Geoscientists Symposia & AIG)
• Bill Hewitt (PT PZC Services, Jakarta}
• Sandy Moyle (Goldminex Resources, Melbourne and Port Moresby)
• Priyo Pribadi (Samindo Resources, Jakarta)
• Wayne Spilsbury (Geoduck, Perth)
Typesetting
Joanne Hamilton, e-type design
joanne@etypedesign.net.au
East Asia: Geology, Exploration Technologies and Mines
Thank you to our sponsors:
non-corporate Sponsors
MEMR
EMD
Geological Survey Indonesia
Sponsors
East Asia: Geology, Exploration Technologies and Mines
Thank you to our trade booths and supporters:
Contents
Author
title
Satriya Alrizki, Rusiana Permana
Investigation of a High Sulfidation Epithermal Cu-Au Deposits Using
Induced Polarization And Magnetic Method in Batang Asai, Jambi
1
Mike Andrews
The Exploration, Discovery and Development of the Way Linggo
Epithermal Gold-Silver Mine in Southern Sumatra
3
Malcolm G. Baillie
The Ingredients of Successful Exploration
5
Kelvin Brown
New Exploration Technologies
6
Rowena Duckworth, Kevin Blake
Petrology and Electron Microprobe Analyses in Target Generation and
Metallurgy
7
KEYNOTE: M. Elias
Nickel Laterites in SE Asia – Geology, Technology and Economics:
Finding the Balance
9
Robert G. Ellis, Barry de Wet, Ian N. Macleod
Inversion of Magnetic Data from Remanent and Induced Sources
12
R. H. Findlay, S. Meffre
The Liamu Complex of the Papuan Peninsula; regional significance for
the tectono-thermal history and discovery within the Papuan Peninsula,
PNG
17
Mark Gabbitus
From Exploration to Extraction
18
KEYNOTE: Steve L. Garwin
Tectonic and Structural Controls to Porphyry and Epithermal
Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the
West Pacific
19
Helen Gibson, John Sumpton, Des
FitzGerald, Ray Seikel
3D Modelling of geology and gravity data:
Summary Workflows for Minerals Exploration
24
Matthew R. Greentree, Gavin Chan
Chinese Minerals Exploration Methods and Philosophy: Implications for
Out-bound Investment
27
KEYNOTE: Graeme Hancock
Realising the Mineral Potential of Mongolia
29
KEYNOTE: Craig J. R. Hart, Richard J. Goldfarb A Framework for China’s Gold Exploration and Endowment
Page
30
Dedy Hendrawan, Gayuh ND Putranto
The Tombulilato Copper Gold Project in Sulawesi, Indonesia ‘Facing the
Challenges and Opportunities’
32
T. Hoschke, S. Schmeider, S. Kepli
Geophysics of the Elang Cu-Au Porphyry Deposit, Indonesia, and
Comparison with Other Cu-Au Porphyry Systems
34
J. M. A. Hronsky
Controls on High-grade Au Ore-shoots: Towards a New Paradigm
36
KEYNOTE: David Isles
Ramping-up Exploration Value from Aeromagnetic Surveys
– More Geological Input Needed!
39
Hashari Kamaruddin, Hartono, Ciputra
Cu-Au Porphyry System of Atlantis Prospect, Papua Province:
A Preliminary Report
42
poster: Imants Kavalieris, Khashgerel BatErdene
Formation of Advanced Argillic Zones
43
David Lawie
Sorting the Signal From the Noise
44
Contents
Author
title
Page
Evgenia Lebedeva, Andrew Riley
Biogeochemistry and Partial Digest Techniques in Mineral Exploration
– a Brief Review
46
poster: Sony Malik, Ferdian Haryadi, Gita
Srikandi
Geothermal Surface Manifestation and Alteration of Conggeang Area,
Mount Tampomas, Sumedang Regency
48
Adi Maryono, Rachel Harrison
Porphyry Copper-Gold Mineralization Styles along the Eastern Sunda
Magmatic Arc, Indonesia
58
D. Menzies, S. Shakesby, J. Wass, D. Finn, N.
Fitzpatrick, G. Morehari, B. Tekeve, B. Alupian,
J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter,
P. Golias
The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration
Zonation, Surface Geochemical Expression and Paragenesis
60
Paul Merriner
Case Study: Discovery and Geology of the Kham Thong Lai Copper-Gold
Deposit, Lao PDR
64
KEYNOTE: AHG Mitchell, Myint Thein Htay
The Magmatic Arc and the Slate Belt: Copper-gold and Tin-tungsten
and Gold Metallotects in Myanmar
66
Chris J. Muller, Kieran Harrington,
Hugh McCullough, Lindsay W. Bandy
Mineralisation Potential of the Kulu-Fulleborn Trend (Whiteman Range),
New Britain Island, Papua New Guinea
68
Yulia Nazimova, Gregory Ryan
Alluvial and Bedrock Platinum, East Asia
71
A. H. (Tony) Osman
The History of Coal Development in Indonesia
73
Rod Paterson
Interpolating Assays and Physical Properties in Folded and Faulted
Layered Geology
74
Rusiana Permana, Sufian Nur Hikmat,
Yosafat P. Simanjuntak, Eratmadji,
Bronto Sutopo
Porphyry Cu-Au Occurrences in Batulicin Area, Batangasai, Jambi
Province, Indonesia
76
C. Querubin, S. Walters, M. Papio, W.
Satiyawan
The Pani Gold Project: Geology and Mineralization
77
Neal Reynolds
Tectonics and Metallogeny of Mainland Southeast Asia
– Framework for New Discovery Opportunities
78
M. P. Roberts, R. A. Armstrong
Age and O, Hf Isotope Systematics of the Yandera Porphyry Rocks Constraints on Magma Sources, Crystallisation History and Crustal
Evolution
80
Stephen Sugden
Field Portable XRF – Good Techniques to Avoid Bad and Ugly Analyses
83
Erric Sukmawan,Yosafat Palty Yudhistira
Simanjuntak, Wanda Ilham Dani, Rusiana
Permana, Bronto Sutopo
A Lithocap in The Bujang Prospect, Jambi Province: Related or not
Related to the Porphyry Cu – Au Mineralisation System
85
poster: Adi Sulaksono, Muhammad A.
Luthan, and Putu A. Andhira
Hydrothermal Alteration Study In Tertiary Volcanism
Ayah Area, Southern Central Java
87
Geoff Taylor, Greg Corbett, Grace Cumming
Cirianiu Epithermal Au, Vanua Levu, Fiji
89
Andrew J. Vigar, Ian Taylor, Greg MacDonald
Resource Estimation for the Aurukun Bauxite Deposit
91
Brad Whisson
Developments in Microwave Digestion for Geochemical Analysis
92
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Investigation of a High Sulfidation Epithermal Cu-Au Deposits Using Induced Polarization and
Magnetic Method in Batang Asai, Jambi
Investigation of a High Sulfidation Epithermal Cu-Au
Deposits Using Induced Polarization and Magnetic
Method in Batang Asai, Jambi
Satriya Alrizki1 and Rusiana Permana2
A detail geological investigation has been carried out
in Batang Asai area, Jambi province for prospecting the
indication of gold mineralization in the area. Geological
investigation has resulted in several mineralization prospect
areas such as Batulicin prospect, Kayuaro prospect, Hulu
Banyak ikan prospect and Gunung Bujang prospect.
Especially in Gunung Bujang prospect, the mineralization
consists of covellite, chalcocite, and enargite in advanced
argilic alteration zone (pyrophyllite-alunite-dickitekaolinite±diaspore) and also siliceous (vuggy-massive
quartz). Based on the evaluation of geological data mineral
alteration in Gunung Bujang prospect, it is concluded that
the mineralization type was Deep HSE (High Sulphidation
Epithermal) with alteration found in the form of quartz
alunite, phyropilite, paragonite, and muscovite.
Induced Polarization (IP)
surveys were conducted
by PT.ANTAM Unit
Geomin in the late 2012.
Approximately 9 lines
for a total 11 kilometres
of 25 m dipole-dipole
was read with 100 metres
between lines over Gunung
Bujang prospect. The
Induced Polarization (IP)
data was inverted using
a 2D algorithm by Earth
Imager AGI to produce a
block model and section of
resistivity and chargeability.
From the IP result it
shows significant anomaly
correlation between high
resistivity from over a
thousand ohm meter and
high chargeability for a
hundred msec, in about 180
m of depth penetration. A
detailed magnetic data was
also collected during that
year, using 5 m spacing between each data point collected,
the magnetic survey covered 16,5 kilometres over Gunung
Bujang prospect. The alteration at Gunung Bujang prospect
is not magnetic destructive, we could still find a magnetic
characteristic mineral such as magnetite,hematite,pyrite
over the outcrop in Gunung Bujang. The magnetic data
was filtered by using Oasis Montaj Geosoft software to
produce RTP (reduce to pole) Map with 25 meters upward
continuation.
The overlay result between RTP (reduce to pole) map
and distribution of alteration by Short Wavelength Infra
Red (SWIR) shows that the minerals pyrophylite, dickite,
alunite, kaolinite (lithocap) and other minerals such as
muscovite, diaspore etc are localized at moderate to high
zone of magnetic anomalies, the same characteristis is found
1. PT. Antam (Persero) Tbk.- Unit Geomin, Jl. Pemuda No.1, Jakarta Timur. Telp. 021-4755380, Fax. 021-4759860 Corresponding author: satriya@antam.com; rusiana.permana@antam.com
East Asia: Geology, Exploration Technologies and Mines - Bali 2013
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Investigation of a High Sulfidation Epithermal Cu-Au Deposits Using Induced Polarization and
Magnetic Method in Batang Asai, Jambi
in the prospects of Elang Prospect in Sumbawa through
measurement of airborne magnetic survey. Airborne RTP
magnetic anomaly pattern in Elang prospect at Sumbawa,
a type of porphyry Cu-Au mineralization is almost
similar to its pattern with the Gunung Bujang prospect
Groundmagnetic RTP anomalies. From Gunung Bujang
magnetic anomalies we could find bull’s eye anomalies
constituted from the RTP Map (high magnetic surrounded
by low magnetic). Even more interesting is the presence
of two high magnetic patterns, one pattern flanking
magnetic low. In addition, to identify potential areas of
alteration, the magnetic data contains a significant amount
of information that may reveal geological and structural
features simultaneously with the Induced Polarization (IP)
data to reveal the distribution and localized conductive
minerals that related to Deep HSE mineralization deposit in
the subsurface.
References
Tim Eksplorasi Emas Jambi, Laporan Eksplorasi Emas dmp - Semester II tahun
2012, Daerah Batulicin dan Gunung Bujang, Kabupaten Merangin, Propinsi
Jambi, Unit-Geomin PT ANTAM (persero) Tbk, 2012
Tim Eksplorasi Geofisika Jambi, Laporan Penyelidikan Geofisika Metoda IP
dan Magnetik - Semester II tahun 2012, Daerah Gunung Bujang, Kabupaten
Merangin, Propinsi Jambi, Unit-Geomin PT ANTAM (persero) Tbk, 2012
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The Exploration, Discovery and Development of the Way Linggo Epithermal Gold-Silver Mine
in Southern Sumatra
MIKE ANDREWS
The Exploration, Discovery and Development of the
Way Linggo Epithermal Gold-Silver Mine in
Southern Sumatra
MIKE ANDREWS1
The Way Linggo gold-silver mine was successfully brought
into production in August 2010 by Kingsrose Mining
(the project’s 85% major shareholder). This marked the
culmination of some 26 years of exploration by seven
different companies over a regional tenement which
originally covered approximately 9,500 sq km.
The Way Linggo mine is situated centrally in the 4th
Generation PT Natarang Mining Contract of Work area
which currently is 100 sq km bounded on the north and
westerly sides by the Bukit Barisan National Park and
to the east by tracts of unprospective recent volcanics.
The tenement is focused on the northern truncation of
the Semangka Graben which western boundary is the
Trans Sumatra Fault and the East side is bounded by the
Semangka Fault. The Trans Sumatra Fault is the major long
lived strike slip fault running the length of the Western
portion of Sumatra which has had a profound regional
influence on the localisation of volcanicity and related
epithermal and porphyry mineralisation on that island.
These two large fault systems converge at the northern end
of this graben and have generated a complex dilational zone
characterised with active pull-apart basins on scales of 10’s
kms down to 100’s metres and dilational splays.
At Way Linggo underground mining is mainly focussed on
the high grade North Vein a low sulphidation epithermal
vein system comprising two en-echelon ore bodies which
are texturally distinct, the A Orebody dominated by a
white Quartz-Adularia-Clay assemblage and B Orebody
characterised by a Quartz- Calcite-Green SmectiteChlorite? assemblage. These zones average approximately
5 m in width and appear to be joined by a link vein system.
The ore bodies at Way Linggo are best developed where
hosted in a porphyritic dacite intrusive host and appear
to loose grade tenor where the bounding structure enters
andesitic tuffs along strike to the north.
Kingsrose Mining has commissioned a 140,000 tpa
Merill-Crowe processing plant fed from the Way Linggo
underground mine from two adit accesses, an external 700
feet railed skipway to haul ore from the main haulage levels
and an internal shaft. The initial JORC compliant resource
on mine start up was 669,000 tonnes @ 8.44 Au g/t, 129 Ag
g/t. Mining is by traditional narrow vein generally hand held
methods, haulage underground by electric locos.
The Contract of Work was signed in December 1986 with
Musswellbrook Energy and Minerals as the foreign partner
who selected the area covering most of the outcrops of
Miocene andesitic volcanics in Lampung province. They
undertook a number of regional geochemical drainage
sampling programmes over the entire 9,500 sq km and
identified the drainages in the Way Linggo area as lower
order geochemical anomalies, no follow up was carried
out. In 1989 Ashton Mining took over the project and
followed up the higher order anomalies elsewhere in the
tenement without success. By chance during a brief follow
up traverse in drainages some 15 km downstream of the
mine two pieces of banded quartz vein float were sampled
however these gave low gold grades (2.3 and 3.4 Au g/t),
the project geologist ( Joel Ivey) recognised the interesting
epithermal textures and instigated further follow up which
lead to the discovery of an extensive epithermal float train
in the drainage 2.5 km to the east of Way Linggo, the
Semung Kecil prospect. Soil surveys identified a well defined
gold, arsenic, silver c-horizon soil anomaly coincident
with some surface outcrops of siliceous sinter, however
trenching an exploration adit and subsequent drilling failed
to confirm significant mineralisation at Semung kecil (It
does still remain an inticing target). During mapping of the
peripheral areas west of Semung Kecil narrow epithermal
veins were found exposed in streams to draining into the
Way Linggo waterfall, a soil grid was undertaken in this area
to the south of the current mine which confirmed a 450 m
by 250 m gold, arsenic soil anomaly and trenching identified
numerous narrow 10 cm to 1 m epithermal gold bearing
veins but generally of low grade. A 1 m wide vein outcrop
exposed due to low river levels river indicated that the
soil grid should be extended over the northern part of the
prospect, although no coherent anomalies were detected, a
single spot high of 6 g/t Au in C-Horizon soil was trenched
uncovering the subcrop of the North Vein.
Ashton Mining and its spin off Aurora Gold refocused
elsewhere in Indonesia, notably on the development of the
Mount Muro Mine in Kalimatan and in 1994 the Project
1. Southern Arc Minerals Inc. (Formerly Director, Kingsrose Mining Ltd), Graha Sentana, Jl. Buncit Raya, Jakarta 12760, Indonesia Corresponding author: mandrews@pacificgoldfields.com
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The Exploration, Discovery and Development of the Way Linggo Epithermal Gold-Silver Mine
in Southern Sumatra
was taken over by Meekatharra Minerals which instigated
discovery drilling. Meekatharra Minerals focus was to prove
up enough ore to sustain a 30,000 oz per annum high grade
gold project so work focussed on completing a feasibility
study on the project, this was completed in 1996. However
the Bre-X scam and collapsing gold price saw Meekatharra,
renamed AuIron Energy refocusing on its Australian
coal and iron ore assets at the time many companies were
exiting Indonesia. A private consortium Advance Concept
Holdings Ltd acquired the project from AuIron in 2000 and
commenced limited underground development to access the
North Vein orebody to enable level development to confirm
grades predicted from drilling. Face sampling revealed
significantly higher grades than the drill core.
The ACH consortium successfully floated Kingsrose Mining
on the ASX in December 2007 and in February 2009
Kingsrose acquired the project and focussed on rapid project
construction. For the Year ending June 2012 Kingsrose
reported a production of 37,650 oz Au and 432,754 oz Ag
from Way Linggo at one of the lowest cash operating costs
per ounce.
MIKE ANDREWS
Kingsrose has undertaken a very extensive exploration
programme of the entire tenement, including using BLEG
geochemistry, airborne magnetics and radiometrics,
and CSAMT coupled with aggressive diamond drilling
campaigns. They have been rewarded with the discovery of
their second mine Talang Santo which is currently under
construction. Kingsrose currently reported a JORC resource
of 485,869 oz Au at grades of 6.91 Au g/t and 45 Ag g/t
(all categories) in their 2012 Annual report.
The Way Linggo project is a good example of the need for
a persistence of exploration effort, requirement for good
geological observation, not to miss the right signs and
blindly follow the assays and corporate commitment to
aggressive drilling campaigns.
The prospectivity northern extent of the Semangka graben
has been highlighted by the discovery the Way Linggo
mine but its potential as a new mineral district has only
been identified by the aggressive exploration and drilling by
Kingsrose Mining.
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Malcolm G. Baillie
Malcolm G. Baillie1
While the primary skill of the Exploration Manager is his
geological knowhow, this alone is not enough to guarantee
success. There are a mass of non-technical issues which he
must manage to avoid failure, even when a good resource is
present. Broadly, these issues relate to good communication
with corporate management, dealing with the environmental
and social issues specific to the project location, relationships
with Government authorities and operating in accordance with
the regulatory regime. This presentation looks at the nature
of these non-technical factors for Indonesian projects, and
how, in many cases they can take up more of the Exploration
Manager’s time than the exploration program itself.
The difficulties in successfully managing these issues have
resulted in the abandonment of more than one project in
Indonesia, and have contributed to the very low level of grass
roots exploration now taking place. Some of the reasons
for this are examined, including what is believed to be a
significant lack of understanding of the nature of exploration
by the public in general, and by regulators specifically.
One of the first responsibilities of the Exploration Manager
is to communicate frankly and in a timely fashion with his
corporate management. This is where the finance originates.
The head office of this organisation is usually based offshore
and its management may not be familiar with the issues
encountered. It has to report to shareholders, who are even less
familiar with the local issues, and confidence in the exploration
team is rapidly lost if shocks are encountered. There is more
than one recent case which illustrates this problem.
Environmental issues are generally minimal during
exploration, but local communities generally expect all
exploration to result in a mine, so it is important to consider
the potential impact at an early stage and to communicate
with local people and improve their understanding. The
establishment of a sound relationship with the local
community from the very beginning is critical. This cannot
be done without thorough profiling of the local community
and the leaders and should precede any field work. Once
trust with the local community is lost, it is very difficult to
recover. Employment policies, land acquisition and dealing
with illegal mining all require a cooperative approach.
Dealing with Government authorities is another critical
matter. Regional, Provincial and Central Government are all
involved. Each considers its role as the most important, and
they may not have a common view on all issues. In recent
months, many new regulations have been issued. Some
of these have a distinctly negative effect on exploration,
and some are not clear. It is essential that the Exploration
Manager fully understands the nature of these regulations
and communicates their impact on the project to corporate
management. While few amongst the mining sector dispute
the Government’s policy to seek an appropriate return
from mining operations, it seems likely that the regulations
actually put into place will have the effect of strangling the
industry.
New mining operations are essential to maintain the
industry, and these are entirely dependent on successful
exploration. Exploration and mining are two very different
activities. Exploration involves high risk with less than
one in a hundred projects leading to a mine. Mining is a
business, subject to feasibility before commitment like any
other. Quite different companies seek involvement in the
two sectors – junior exploration companies dominating
the exploration field. Yet the regulations seek to cover
both activities as if there is an inevitable follow on. It is
more realistic to view exploration as normally leading to
the creation of new geological data and not to a mine.
The Government should seek its return from mines and
encourage exploration companies to spend their precious
funds efficiently on finding them.
The necessary support could be provided within the existing
Mining Law if the difference between exploration and
mining was understood. Approvals for exploration activities
(e.g. Forestry Permits) could be simplified and streamlined
to avoid the unnecessary costs of delay, and if the need for
exploration to be spread over many projects was recognised.
In summary, there are many factors which contribute to
a successful exploration program. Some are technical,
and some are non-technical. All need to be assessed
before starting field work and all need to be continuously
monitored. Excessive difficulties associated with any could
be the basis for not commencing field work or curtailing it
once started. Exploration funds are limited and have to be
directed where there is the best chance of success.
1. Chairman, Forum for Exploration and Mining Development, Indonesia Corresponding author: malcolmbaillie@regional-advisory.com
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Kelvin Brown
Kelvin Brown1
Data Acquisition
Past: A brief look back at how we gathered geological data
during the mineral exploration drilling process.
Present: How data is currently gathered, the improvements
made to date and the shortcomings that still exist.
Future: A look at where we need to take this process by
utilising new technologies & methods in a way that increases
production, reduces costs and improves the data availability.
Data Management
How do we manage this data that is expensive to acquire? Is
it secure? Which data do we need sooner?
Over the recent decade our ability to generate vast quantities
of data has significantly increased but has our capability to
manage this data increased with it?
Here we will look at state of the art systems that can help us
to identify the important information needed to make the
best decisions and how we can get this information quickly
to the stakeholders.
1. Imdex, 8 Pitino Court, Osborne Park, Western Australia 6017 Corresponding author: imdex@imdexlimited.com
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Petrology and Electron Microprobe Analyses in Target Generation and Metallurgy
Petrology and Electron Microprobe Analyses
in Target Generation and Metallurgy
Rowena Duckworth1 and Kevin Blake2
Optical microscopy is a traditional technique for
characterising rocks and describing the mineral textures and
parageneses. However, it is a technique that is not used as
widely as it used to be, despite its ability to provide relatively
factual information about rocks reasonably quickly and
cheaply. Electron Microprobe Analysis (EPMA) is a more
modern analytical technique that utilises X-ray detection
methods to provide definitive mineral chemistries and
element identification. Both of these techniques can be
used on regular polished thin sections (no extra thickness
of thin section is required for microprobe work). These
two techniques combined can, therefore, divulge abundant
information about core, chip and outcrop samples that is
useful for target generation and, down the track, metallurgy
and mineral processing.
One of the most important uses of optical microscopy is to
complement/ contradict the hand specimen descriptions,
especially those generated during routine core logging.
Submitting one or two samples for petrology from
each lithology encountered is recommended, as logging
descriptions can prove to be unreliable, and should always
be groundtruthed before mineralisation models and target
generation plans are developed. An example of this is a
suite of rocks logged as amphibolites that systematically
failed to contain any amphibole when observed using
transmitted light microscopy. This type of hand specimen
mis-identification is common, and can lead to incorrect
mineralisation models.
As well as determining the major, minor and accessory
minerals in a rock sample optical microscopy can identify:
• Primary mineralogy
• Metamorphic minerals, textures, metamorphic facies,
and the degree and sequence of ductile or brittle
deformation events
• Alteration mineralogies and facies
• Vein and selvage mineralogy
• Sequence of events (paragenesis) including the timing
of ore mineralising events: did the ore minerals come in
early or late?
EPMA back scattered electron image showing dark grey pyrite grains
that have been variably brecciated and replaced by several telluride
phases (with differing brightness). At this scale, using reflected light
microscopy there may be just a hint of another phase present in the pyrite
and with the naked eye it may not be apparent at all.
Microscopic description of rocks can also help with the
refinement of stratigraphy and structure, the identification
of geological and hydrothermal processes and assist with ore
grade vectoring from near miss drill holes.
Staining techniques are largely not used these days due to
modern OHS regulations as they utilise hydrofluoric acid.
Hence microprobe analyses can be helpful in determining
carbonate chemistries and feldspar chemistries, which often
cannot be determined optically.
Electron microprobe analysis can additionally provide
crucial information with respect to the location of elements
of interest: e.g. gold? Gold can occur as native gold, bonded
with other elements to form a mineral, e.g. sulphosalts,
as inclusions within a mineral or bound up in the lattice
of another mineral phase. Often assays will indicate
the presence of significant gold, but in hand specimen
and even under the optical microscope, it is difficult/
1. Gnomic Exploration Services, Townsville, Qld 4810 Corresponding author: rowenaduckworth@bigpond.com
2 Advanced Analytical Centre, James Cook University, Townsville, Qld 4814
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Petrology and Electron Microprobe Analyses in Target Generation and Metallurgy
impossible to locate the gold. EPMA imaging and energy
dispersive (EDS) chemical analysis can usually resolve this
problem. The back scattered electron image below is from
a deposit where the company was not sure from the assay
data whether the gold was occurring as free gold or as
telluride complexes. Microprobe analysis showed that there
was native gold as well as a range of telluride complexes
including, gold, gold-silver, silver-gold, iron and mercury
tellurides. This highlights the need to understand the
correlation between assay data and the mineralogy.
For quantitative mineral analysis, EDS or wavelength
dispersive analysis (WDS) can be used depending on the
detection limits of the elements in question. WDS analysis
has a better resolution but is more time consuming, as
it requires calibration for each element to be analysed
(major plus minor elements of choice, F, Cl, Cu, Co, Te,
Ag etc.) and each analysis can take 3-4 minutes depending
on the elements being measured. However, the results
are definitive and can be extremely useful as exploration
vectors. Quantifying and then mapping the amount of a
particular trace element in a particular mineral is a powerful
mineralisation vectoring method.
Microprobe analyses can also be useful in the processing
stage of mining in order to identify any contaminants,
adverse or beneficial, which may affect the final mineral
concentrate.
l
keynote
9
Nickel Laterites in SE Asia – Geology, Technology and Economics: Finding the Balance
M. Elias
Nickel Laterites in SE Asia – Geology, Technology
and Economics: Finding the Balance
M. Elias1
This presentation reviews the nature and genesis of nickel
laterite mineralisation, and describes the relationship
between deposit characteristics (both geological and nongeological) and the successful development of lateritic
deposits as commercial nickel producers. The importance of
nickel laterites lies in their huge resource base, which could
potentially provide a much greater share of global nickel
production than their current level compared to nickel from
sulphides.
Nature of nickel laterite mineralisation
Most of the world’s terrestrial nickel resources are hosted
in nickel laterites. These are products of intense weathering
in humid climatic conditions of Mg-rich or ultramafic
rocks which have primary Ni contents of 0.2-0.4%. The
process of lateritisation involves the breakdown of primary
minerals and release of their chemical components into
groundwater, the leaching of mobile components, the residual
concentration of immobile or insoluble components, and the
formation of new minerals which are stable in the weathering
environment. The combined effects of these processes is
to produce a vertical succession of horizons of differing
chemistry and mineralogy (the laterite profile), the overall
structure of which is governed by the differential mobility of
the elements in the weathering zone. The detailed structure
of the profile varies greatly, and in any one place is the result
of the dynamic interplay of climatic and geological factors
such as topography, drainage, tectonics, structure and parent
rock lithology. Nickel (and typically cobalt) can be enriched
to ore grade in parts of the profile by being incorporated into
the structure of the newly formed stable minerals or into the
alteration products of primary minerals.
Figure 1 is a diagrammatic representation of a typical laterite
profile developed in a tropical environment. At the base of
the profile, initial stages of weathering produces saprolite,
in which the unweathered rock fabric is preserved, although
most of the original minerals may have been altered. As
weathering proceeds, Mg and Si are leached until in the
upper part of the profile only insoluble Fe oxides remain. This is referred to informally as limonite.
Despite the complexity and interplay of controls, there are
a number of broad features of the laterite profile that are
Figure 1. Schematic laterite profile developed on ultramafic rock in a
tropical climate, showing indicative chemical compositions in wt%.
Parts of the laterite profile which are viable sources of feed for the
respective extraction methods are shown.
common to most examples, and it is possible to describe
the range of laterite types formed over ultramafic rocks on a
deposit scale in terms of three main categories on the basis
of the dominant Ni-bearing mineralogy developed in the
profile:
Oxide laterites: comprise largely Fe oxyhydroxides and
oxides (mainly goethite) in the upper part of the profile,
overlying altered or fresh bedrock;
Clay laterites: comprise largely smectitic clays in the upper
part of the profile, and
Silicate laterites: comprise hydrated Mg-Ni silicates
(serpentine, garnierite) occurring deeper in the profile, which
may be overlain by oxide laterites.
Although the detailed morphology and composition of the
deposits can vary greatly on a small scale (tens of metres),
deposit scale and regional scale controls result in broad
consistencies in deposit characteristics over wider areas. For
example, lateritisation of tectonically uplifted ultramafic
massifs which host most of the nickel laterites in New
Caledonia has produced thick silicate laterite deposits, and
physical erosion has removed most of the oxide laterites. A
more subdued topography in the Philippines has resulted
in greater preservation of the oxide zone and generally less
1. Principal Consultant – Nickel, CSA Global Pty Ltd, West Perth Corresponding author: ???
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intense alteration in the silicate laterite zone. Clay laterites
are not represented in the SE Asia-Pacific region as the
climatic and tectonic controls required for their formation
are absent.
Global resources of nickel laterites are estimated to contain
in excess of 150 million tonnes of nickel. Of this total, over
50% is found in New Caledonia, Indonesia, the Philippines
and Papua New Guinea. That such a large proportion of
global resources is found in a relatively small area is due to
the favourable combination of tectonic and climatic factors.
Tectonically active zones typical of the region are often
associated with oceanic or continental plate boundaries and
collision zones, where thrust faulting has obducted slabs
of upper mantle peridotites and associated rocks forming
ophiolite complexes with extensive areas of exposure at
surface. Tectonic processes (i.e. uplift) play a large part in
influencing the type of nickel laterite deposits formed.
Exploration and resource delineation
Exploration for Ni laterites does not present significant
technical problems. The occurrence and distribution of
ultramafic rocks is well known in most, if not all, deeply
weathered terrains. They can be readily and more precisely
delineated at regional to local scales by airborne magnetic
surveys, which can also be used to outline lithological variation,
stratigraphy and favourable structures. Within appropriate
areas, preliminary geomorphological, regolith-landform and
structural maps can be prepared from aerial photography, a
variety of remote sensing techniques and magnetic surveys
to determine the most prospective sites for potential Ni
accumulation. Follow-up by inspection, field mapping and
drilling are used to outline the potential resource.
Diamond core drilling is the most common method of
sampling for resource delineation. Initial drilling on a widespaced grid is followed by progressive infill drilling in areas
of better results. Ni laterite deposits show great variation in
the distribution of Ni and other elements, profile thickness
and other characteristics over short distances. Advanced
exploration for accurate estimation of resources and reserves
and for reliable mine planning therefore relies on having an
adequate drilling density; generally a 25-50 m grid is used. Subsequently, precise grade control and careful blending
of mined ore categories are required to minimize variation
in the composition of plant feed and thus optimize plant
operating conditions. Grade control commonly requires
drilling or sampling on grids of 5-10 m.
M. Elias
• Sample assaying – the most commonly used methods
employ XRF on either fused glass disks or pressed
powder pellets.
• Bulk density and moisture determinations – the porous
nature and high moisture contents of laterites make these
difficult.
Mineral processing and metal extraction
About 50% of primary nickel produced globally is sourced
from lateritic ores.
Methods currently in use on a commercial scale to extract
nickel from laterites comprise three main processing
routes:
• Smelting to produce ferro-nickel or matte, including
nickel pig-iron (NPI),
• Caron process (reduction roast – ammoniacal leach), and
• Leaching using sulphuric acid, under atmospheric or
high pressure conditions.
Due to the requirements of each process and the wide range
in chemical and mineralogical composition in the laterite
profile, each of these processes is only suited to a part of
the profile. No commercially applied process has yet been
developed to economically treat the entire profile, and this
remains the “holy grail” of laterite processing. Thus any
processing method has to be carefully matched with the
mineralogical and compositional range of the deposit it is
intended to treat. Figure 1 shows the applicability of each
process within the profile.
Each of the processes has drivers which influence not only
production cost but also non-economic factors such as plant
location. Some of these include:
• Smelting – highly energy intensive, requires cheap
power; ore chemistry (Si:Mg ratio) is critical; no benefit
from by-product credits; product well suited to stainless
steel production.
• Caron process – highly energy intensive; high capital
cost; poor by-product (Co) recovery.
• Acid leaching – sensitive to acid consumption and
sulphur cost; high capital cost; technology risk; good Ni
and Co recovery; tailings storage and effluent disposal
issues in tropical environments.
Because the processing method is essentially determined by
the type of deposit, it follows that infrastructure and plant
location should be capable of supporting its operation.
Other factors to be aware of in resource delineation
programs and mine planning include:
Ingredients of a successful laterite project
• Drilling should extend at least two to three metres
into bedrock to ensure that the entire profile has been
intersected.
History has shown that new nickel laterite development
projects have a very patchy record of success. Commercial
development of nickel laterite projects is a high risk
undertaking due to the high capital costs involved and
the need for the application of the highest standards of
technology and engineering. However, there are a number
• Core recovery – laterites often comprise a mixture of
hard rock boulders in a soft matrix. HQ-sized core is
generally required to ensure adequate sample recovery.
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of natural attributes of nickel laterite deposits that, if they
applied in new projects, would improve their chances of
successful development and becoming profitable operations.
It helps to have a quality orebody in terms of size, grade,
consistency, and ore and overburden thickness, and the SE
Asian region is well endowed in this respect. Nevertheless,
successful projects clearly also require a favourable
combination of geological, mineralogical and mining factors,
technical and engineering factors related to the process
flowsheet, infrastructure-related factors and environmental
considerations.
M. Elias
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ROBERT G. ELLIS, Barry de Wet,
Ian N. Macleod
Inversion of Magnetic Data from Remanent
and Induced Sources
ROBERT G. ELLIS 1, Barry de Wet2 and Ian N. Macleod1
Summary
Magnetic field data are of fundamental importance in
many areas of geophysical exploration with 3D voxel
inversion being a common aid to their interpretation. In
the majority of voxel based inversions it is assumed that
the magnetic response arises entirely from magnetic
induction. However, in the last decade, several studies
have found that remanent magnetization is far more
prevalent than previously thought. Our experience with
numerous minerals exploration projects confirms that the
presence of non-induced magnetization is the rule rather
than the exception in base metals exploration.
In this work we show that failure to accommodate for
remanent magnetization in 3D voxel-based inversion can
lead to misleading interpretations. We present a technique
we call Magnetization Vector Inversion (MVI), which
incorporates both remanent and induced magnetization
without prior knowledge of the direction or strength of
remanent magnetization. We demonstrate our inversion
using model studies and field data. Successful application
to numerous minerals exploration surveys confirms that
incorporating remanent magnetization is essential for the
correct interpretation of magnetic field data.
Introduction
The utility of magnetic field data in many areas of
geophysical exploration is well-known as is the application
of 3D voxel inversion to aid in magnetic data interpretation
(for example, Li and Oldenburg 1996, Pilkington, M.,
1997, Silva et al. 2000, Zhdanov and Portniaguine 2002, to
cite just a few). In the majority of voxel based inversions it
is assumed that the magnetic response arises entirely from
magnetic induction.
However, in the last decade, studies have found that
remanent magnetization is far more prevalent than
previously thought (McEnroe et al. 2009) and affects crustal
rocks as well as zones of mineralization. Unfortunately,
remanent magnetization can seriously distort inversion
based on the assumption that the source is only induced
magnetization. The severity of the distortion is due
to the highly non-unique nature of potential field
inversion making it extraordinarily easy for a potential field
inversion to produce a seemingly plausible model which
agrees satisfactorily with the observed data, even when a
fundamental assumption in the inversion is flawed.
Several authors have reported progress toward magnetic
data inversions including remanent effects (for example,
Shearer and Li 2004, Kubota and Uchiyama 2005, Lelièvre and Oldenburg 2009). In this work we report further progress in this direction with a technique we
call Magnetization Vector Inversion (MVI), which incorporates both remanent and induced magnetization
without prior knowledge of the direction or strength of
remanent magnetization. In the following sections,
we extend conventional scalar susceptibility inversion
to a magnetization vector inversion, that is, we allow
the inversion to solve for the source magnetization
amplitude and direction. While this increases the number of
variables in the inversion we will show by example that the
same regularization principles that allow compact targets
to be resolved in highly unconstrained scalar susceptibility
inversion also apply in vector inversion.
Perhaps our most significant finding is that MVI,
or more generally, inversion including all forms of
magnetization, significantly improves the interpretation of
the majority of minerals based magnetic field inversions.
Unfortunately, the surprising degree of improvement
in interpretability cannot be adequately presented in
a paper and can only be verified by direct experience.
Consequently, while we have applied MVI to a large number of magnetic field surveys and find the results
to be significantly superior to conventional scalar based
inversion, in this paper we are forced to limit our attention
to a synthetic case and field data from the Cu-Au Osborne
deposit located approximately 195km SE of Mount Isa, in
Western Queensland, Australia.
Method and Results
Let us begin with the very general assumption that the
magnetic properties of the earth can be represented by a
volume magnetization, M(r) (Telford et al. 1990). We make
1. Geosoft Inc. Suite 810, 207 Queens Quay West, Toronto, ON, Canada Robert. Corresponding author: Robert.Ellis@Geosoft.com 2. Ivanhoe Australia Ltd., Level 13, 484 St Kilda Road Melbourne, VIC, 3004, Australia East Asia: Geology, Exploration Technologies and Mines - Bali 2013
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no assumptions about whether source of the magnetization
is induced, remanent, or otherwise.
From magnetostatics, the magnetic field B at point rj
resulting from a volume V containing magnetization, M(r), is
given by
This expression shows directly that the magnetization vector
M(r) is the natural parameter for inversion. This is a crucial
observation.
If the volume V consists of a collection of N sub-volumes vk
each of constant magnetization mk then
This defines the forward problem: given a set of sources
mk (k =1,..,N) then Bj is the predicted magnetic field
anomaly at points, rj (j=1,..,M). Note that the coordinate
index is summed over indicating that we are free to choose
the most computationally convenient internal coordinate
system. It also suggests that a coordinate invariant quantity,
such as the amplitude, M(r) = lM(r)l will be most robustly
determined from the data.
Ian N. Macleod
Example - Buried Prism
Although the buried prism model is far too simplistic to
have exploration significance, it does make an
excellent pedagogical example, so we follow tradition
and begin by considering the inversion of simulated TMI
data over a buried prism with magnetization vector M
perpendicular to the earth field. The model consists a cube
with side length 40m buried with a depth to top of 20m and
a magnetization vector in the EW direction, (My = 0, Mz = 0)
as shown in Figure 1.
Simulated TMI data are shown in Figure 2 for Earth field
with inclination 90° and amplitude 24000 nT. Cardinal
directions have been chosen only for simplicity of
explanation; any directions could be chosen with equivalent
results. Also for simplicity, the data were simulated at 20m
constant clearance and on a regular 8m grid.
Inverting the TMI data in Figure 2 yields the model
shown in Figure 3 which should be compared to the true
model shown in Figure 1. There is some variability in the
magnetization direction but the predominant direction is
clearly EW, in agreement with the true model.
For conciseness, we will represent Eq (2) simply as
The vector magnetization inverse problem is defined
as solving for m given B subject to an appropriate
regularization condition. Although there are many choices
for the regularization (see for example, Zhdanov 2002), we
choose without loss of generality, the familiar Tikohonov
minimum gradient regularizer. The inverse problem becomes
solving for m in,
where in the first line, the total objective function f is
the sum of a data term fD and a model term fM with a
Tikohonov regularization parameter, l . The second line
defines the data objective function in terms of the data
equation (3) and the error associated with each data point.
ej. The third line gives the model objective function in terms
of the gradient of the model ∂g m and the amplitude of the
model, with weighting terms as required, wgw0 . The fourth
line indicates that the Tikohonv regularization parameter
l is chosen based on a satisfactory fit to the data in a
chi-squared sense, XT2. In addition, other constraints, such as
upper and lower bounds, can be placed on m as appropriate
to the specific exploration problem.
Figure 1.The buried prism model with magnetization vector orientation
(Easterly) shown by the green cones. Side=100m
Figure 2. The TMI data simulated over the magnetization vector model
shown in Figure 1. The axes are in metres.
Vector magnetization models in 3D are difficult to interpret
directly in all the but the simplest cases. In real-world
exploration we need some simpler derived scalars which
highlight the important information in the vector model. As
suggested by Eq(1), the most robust and meaningful scalar
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Ian N. Macleod
Figure 3: The MVI recovered model for comparison with Figure 1. The
magnetization vector orientation shown by the green cones.
is the amplitude of the vector magnetization and this should
be the primary quantity used in interpretation. However,
since the magnetization vector direction is the earth field
direction for induced sources, it is tempting to attempt
to use the directional information recovered in MVI to
generate scalars related to the earth field direction.
There are many possibilities but we have found that three
useful derived scalars for exploration are: the amplitude
of the magnetization, the earth field projection of the
magnetization, and the amplitude of the perpendicular-toearth-field components of the magnetization. In exploration
problems, the amplitude is robust by being independent
on of any assumptions regarding the earth field, while the
amplitude perpendicular is an approximate indicator of
non-induced magnetization. To support our findings, these
three derived scalars are shown in Figure 4b, c, d for an
East-West slice through the model volume bisecting the target in the true model.
In exploration situations it is convenient to present
MVI output normalized by the amplitude of the earth’s
magnetic intensity in the area of interest. That is, our
results are displayed as where is the amplitude of the earth’s
magnetic intensity in the area of interest. By using this
normalization in an area of purely induced magnetization,
the numerical values returned by MVI inversion will be
directly comparable to those of scalar susceptibility inversion,
in our case in SI.
For completeness, and to show the contrast between MVI
and conventional scalar inversion, Figure 5b shows the
equivalent section through a model produced by an
inversion which assumes only induced magnetization. As
should be expected, the recovered model using scalar
inversion is a very poor representation of the true
model, which in real-world exploration ultimately adds
significant confusion to the interpretation process.
This simple prism example demonstrates the power of
magnetization vector inversion and its advantage over scalar
susceptibility inversion in cases where the magnetization
vector direction deviates from the earth field direction.
We argue that this situation predominates in real-world
Figure 4: (a) A cross section through the true model, (b) the recovered
amplitude of the magnetization vector, (c) the amplitude of the
perpendicular-to-earth-field components of the magnetization, (d) the
projection of the magnetization on to the earth field direction. The
colour scales indicate the MVI magnetization in normalized to SI
(see text).
Figure 5: (a) A cross section through the true model, (b) the
recovered scalar susceptibilty. The color bar shows the susceptibility
magnitude in SI.
exploration environments based on experience from many
magnetic surveys, however this cannot be shown here.
Example - Osborne
The preceding pedagogical study of MVI on simulated
data over a prism provides a solid basis for the much more
important application of MVI to field data. As mentioned
in the Introduction, it is hard to appreciate fully the impact
on magnetic data interpretation by including non-induced
magnetic sources. However, to motivate our assertion, we
present typical results taken from TMI data collected over
the Osborne deposit.
The history of the Osborne mine is well described elsewhere,
see for example, Rutherford et al. 2005. Briefly, significant
Cu-Au mineralization beneath 30-50m of deeply weathered
cover was confirmed in 1989. Intense drilling between 1990
and 1993 defined a total measured and indicated resource
of 11.2 Mt at 3.51% Cu and 1.49 g/t Au. Exploration since
1995 has delineated high-grade primary mineralization
dipping steeply East to some 1100 m vertical depth. As of
2001, total mined, un-mined and indicated resources are
reported to be about 36 Mt and 1.1%Cu and 1 g/t Au East Asia: Geology, Exploration Technologies and Mines - Bali 2013
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Ian N. Macleod
(Tullemans et al. 2001). Current exploration is focussed on
mapping the high- grade mineralization to greater depths
and mapping similar structures in the surrounding area. The
geophysics includes total magnetic intensity (TMI) data over
the property, which is shown in Figure 6. The TMI data were
acquired in 1997 flown at 40m clearance on 40m line spacing.
Figure 7: An EW section through the recovered MVI model amplitude
at the Osborne property with the now known mineralization
shown in black. The color bar gives the normalized amplitude in SI.
The axes are in metres.
Figure 6: The observed TMI data acquired over the Osborne property.
The axes are in metres. The color scale shows the TMI amplitude in nT.
Magnetization Vector Inversion of the Osborne TMI data yields the magnetization vector amplitude earth
model shown in Figure 7. Superimposed (in black) is
the subsequently discovered mineralization from extensive
drilling and underground mining. For comparison, Figure 8 shows the corresponding scalar susceptibility inversion.
Comparing Figure 7 and Figure 8 shows that inverting for
the magnetization vector provides a much better model
for interpretation. The scalar inversion fails to represent
reality in this case suggesting, most likely, that the scalar
assumption is violated: a common occurrence in mineral
exploration in our experience. In contrast the MVI model
is consistent with the drilling results, and furthermore,
indicates a steeply dipping volume on the Eastern flank. The
strong near surface anomaly to the west of the dipping zone
is known banded ironstone.
Conclusions
We have argued that remanent magnetization must be included in magnetic field data inversion in order to
avoid seriously misleading interpretations. To support this
argument we demonstrated the value of Magnetization
Vector Inversion using model studies, and field data from
the Osborne property. The degree of improvement
afforded by using MVI in all areas of magnetic field data
inversion may seem surprising, however recent advances
in understanding remanent magnetism suggest that
non-induced magnetization plays a far more important
role than previously thought in the origin of magnetic
anomalies. Successful application to numerous
minerals exploration surveys confirms that incorporating
Figure 8: The same section as in Figure 7 for the scalar model with
drilling and mineralization in black. The color bar gives the susceptibility
in SI. The axes are in metres.
remanent magnetization is recommended for the correct
interpretation of the majority of magnetic field data.
Acknowledgements
The authors would wish to thank Geosoft Inc. and Ivanhoe
Australia Ltd. for permission to publish this work.
References
Butler, R. F., 1992, Paleomagnetism: magnetic domains to geologic
terranes, Blackwell Scientific Publications.
Kubota, R., and Uchiyama A., 2005, Three-dimensional magnetization
vector inversion of a seamount, Earth Planets Space, 57, 691–699
Li, Y., and D. W. Oldenburg, 3-D inversion of magnetic data, Geophysics,
61, 1996, 394-408.
Lelièvre, P. G., and Oldenburg, D. W., 2009, A 3D total magnetization
inversion applicable when significant, complicated remanence is present,
Geophysics, 74, L21-L30
McEnroe, S. A., Fabian, K., Robinson, P., Gaina, C., Brown, L., 2009,
Crustal Magnetism, Lamellar Magnetism and Rocks that Remember,
Elements, 5, 241-246.
Pilkington, M., 1997, 3-D magnetic imaging using conjugate gradients, Geophysics, 62, 1132-1142.
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Rutherford, N. F., Lawrance, L. M., and Sparks, G., 2005, Osborne Cu-Au
Deposit, Clonclurry, North West Queensland, CRC LEME Report.
Shearer, S., and Y. Li, 2004, 3D Inversion of magnetic total gradient data in
the presence of remanent magnetization: 74th Annual Meeting, SEG, Technical Program, Expanded Abstracts, 23, 774-777.
Silva, J. B. C., Medeiros, W. E., and Barbosa, V. C. F., 2001, Potentialfield inversion: Choosing the appropriate technique to solve a
geologic problem, Geophysics, 66, 511 - 520.
Telford, W. M., Geldart, L. P., Sherriff, R. E., and Keys, D. A., 1990,
Applied Geophysics, Cambridge University Press.
Ian N. Macleod
Tullemans, F. J., Agnew P., and Voulgaris, P., 2001, The Role of Geology
and Exploration Within the Mining Cycle at the Osborne Mine, NW
Queensland, in Monograph 23 - Mineral Resource and Ore Reserve
Estimation - The AusIMM Guide to Good Practice, Australian Institute of Mining and Metallurgy, Melbourne, 157-168.
Zdhanov, M. S., 2002, Geophysical Inverse Theory and Regularization Problems, Method in Geochemistry and Geophysics 36, Elsevier Science B.V., Amsterdam, The Netherlands.
Zhdanov, M. S., and Portniaguine, O., 2002, 3-D magnetic inversion with data compression and image focusing, Geophysics, 67,
1532-1541
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The Liamu Complex of the Papuan Peninsula; regional significance for the tectono-thermal
history and discovery within the Papuan Peninsula, PNG
R. H. Findlay, S. Meffre
The Liamu Complex of the Papuan Peninsula; Regional
Significance for the Tectono-thermal History and
Discovery Within the Papuan Peninsula, PNG
R. H. Findlay1 and S. Meffre2
Effective exploration in greenfields terrains requires proper
delimitation of the regional geological and geochronological
architecture of the broad target district to enable efficient
vectoring into the target. Many greenfields areas, such as
those in PNG and Asia, and indeed Australia, have been
mapped only at the broad reconnaissance scales and their
geochronological relationships are usually poorly understood.
The Liamu Complex, in tenements held by Goldminex
Resources Ltd in the Papuan Peninsula, provides a regionally
important case study of discovery by careful attention to
systematic geological mapping, allied to geomorphology,
legacy geochemical data and geochronology.
The Papuan Peninsula is known for its history of very
small-scale alluvial gold and PGE mining, and generally
unsuccessful exploration by industry. The region is underlain
by obducted latest Cretaceous-Palaeocene oceanic basalts
and ultramafic complexes extending for 250km (Papuan
Ultramafic Belt), juxtaposed against low- to high-grade
metasedimentary rocks of probable Cretaceous age to
the south. Until recently the source of the gold in ground
occupied by the Papuan Ultramafic Belt was most uncertain,
despite reconnaissance geological mapping by PNG
government geologists and first-pass regional geochemical
surveys by industry.
In 2009, reinterpretation of the 1:250 000PNG government
geological maps, allied to geomorphological observations
and legacy geochemical surveys in the Liamu River area
of the Musa Valley, highlighted incompatibilities in the
previous interpretation of the geology and led to systematic
regional and detailed geological mapping that has identified
a major 45 sq km plus intrusive and extrusive complex
(Liamu Complex) containing Cu-Au porphyry indications
and evidence for structurally controlled epithermal deposits.
This mapping has also allowed focused and therefore costeffective geophysical surveys that appear to show that the
complex may be as large as 75sq km.
sparse prior K/Ar dating, confirms a very late Miocene to
Pliocene thermal event in the Papuan Peninsula, one that
was involved in production of potassic intrusive bodies and
monzonite intruding the Papuan Ultramafic Complex along
the length of the Papuan Peninsula.
Rocks similar to those in Liamu Complex are reported in
the legacy geochemical data, and geomorphological studies
combined with brief helicopter-supported visits and float
sampling in 2011 indicate the strong probability of several
other such late Miocene-Pliocene intrusive systems along the
Papuan Peninsula and within the Papuan Ultramafic Belt.
These discoveries allow an integrated regional model for
both Cu-Au porphyry/epithermal discovery in the Papuan
Peninsula and also explain the prominent development of
Ni-sulphide occurrences along major fault systems cutting
the ultramafic rocks of the Papuan Ultramafic Belt.
The geochronology, albeit one sample in addition to a very
few prior K/Ar ages, confirms that in late Miocene and
Pliocene times the Papuan Peninsula was host to the same
regional, mineralising, tectono-thermal event that has hosted
such deposits as Porgera (5.2Ma) and Tolukuma (4.6Ma),
among the many others extending from the Wau-Bulolo
goldfields of Morobe to Frieda River in the westernmost
part of PNG.
A recent geochronological study (U/Pb zircon) has yielded
an age of 6Ma for the current drilled target in the Liamu
Complex. Apart from the lithostratigraphic importance
of this age, which demands that this part of the complex
must be tilted by around 20 degrees, it, together with
1. Montagu Minerals Mapping Pty Ltd,44 Riawena Road, Tasmania 7018. Corresponding author: rhfindlay44@gmail.com 2. CODES, University of Tasmania, Sandy Bat, Hobart, Tasmania 7018 Corresponding author: s.meffre@utas.edu.au
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mark Gabbitus
mark Gabbitus1
Technology is increasingly being asked to fill the skills
shortage in mining. Geologists are being asked to do more
in less time with less training and mentoring. Therefore
it is essential that the software used during exploration,
geological modelling, resource modelling and grade control
is capable of quickly, accurately and auditably producing the
results required by the end users of the model, engineers and
miners.
New technologies such as implicit modelling reduces the
time spent by geologists building models and allows for the
rapid generation of multiple block models for a project. Used
alongside estimators of risk, such as conditional simulation,
geologists can present best case to worst case scenarios for
optimisation and scheduling that meets the growing demand
of engineers and, perhaps more importantly, investors.
Beyond feasibility studies and resource modelling it is also
important that the grade control system used at a site is
flexible, can be automated and is able to interface with the
growing level of mining information available today for
accurate reconciliation.
Software companies are responding to these needs and
this paper will detail how MineSight® has approached
this challenge both through the software and the services
provided to ensure that exploration and mining companies
can progress from the first hole drilled to the last truck
extracted in a single system. This single system approach to
geology, engineering and mining ensures that the integrity
of data is maintained throughout the mining value chain
without the need for highly skilled users.
1. Regional Business Development Manager, MineSight Applications Corresponding author: Mark.Gabbitus@minesightapps.com.au
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Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic
Magmatic Arcs of Southeast Asia and the West Pacific
Steve L. Garwin
Tectonic and Structural Controls to Porphyry and
Epithermal Mineralization in the Cenozoic Magmatic Arcs
of Southeast Asia and the West Pacific
Steve L. Garwin
Introduction
Gold and copper deposits in Southeast Asia and the west
Pacific occur largely in middle to late Cenozoic (25 to 1
Ma) magmatic arcs. The region contains
more than 160 deposits, including
porphyry, skarn, epithermal, volcanicassociated massive sulfide, disseminated
sedimentary rock-hosted deposit and
other mineralization styles. The combined
past production and current resources of
these deposits exceeds 15,000 tonnes of
gold and 115 million tonnes of copper
(Garwin et al., 2005). The majority of the
gold and copper are contained in porphyry
and epithermal deposits, many of which
contain resources of more than five
million ounces of gold (Figure 1).
Miocene, Middle Miocene and the Plio-Pleistocene (Barley
et al., 2002; Garwin et al., 2005). Hydrothermal systems
were active for durations of < 100,000 years. Arc-continent
collisions and the subduction of buoyant aseismic ridges
Magmatic Arcs and Tectonic
Setting
Twenty major magmatic arcs and
several less extensive arcs of Cenozoic
age form a volcano-plutonic chain that
extends >17,000 km from Japan in the
northeast, through Taiwan, Philippines,
Indonesia, Malaysian Borneo, and
Papua New Guinea, to Myanmar in
the northwest. The arcs are constructed
on basement formed from continental
and oceanic crust. The geometries of
individual arc segments are complex
and typically the product of subduction,
locally involving polarity reversals,
seamount subduction, obduction, arc-arc
and arc-continent collisions, rifting, and
transcurrent faulting.
Most of the porphyry and epithermal
deposits developed during episodes of
plate reorganization and local variations
in arc stress regimes during the Early
Figure 1. Present-day tectonic features, major Cenozoic magmatic arcs and large porphyry and
epithermal deposits of Southeast Asia and the west Pacific. Only deposits that contain more than
five million ounces of gold are shown. Thick red lines with triangles are subduction zones and
thick black lines are major strike-slip faults (modified from Hall, 2002 and Garwin et al., 2005).
Digital topography and bathymetry models are from the United States National Geophysical
Data Center. Indicated magmatic arcs and seafloor topographic features are described partially
in the text of this abstract and comprehensively in Garwin et al. (2005). The locations of the
magmatic arcs are modified from Hamilton (1979), Hutchison (1989), Yamada et al. (1990),
Mitchell and Leach (1991), Carlile and Mitchell (1994), and Garwin et al. (2005). Several
buoyant aseismic ridges and oceanic plateaux are being, or have been, subducted beneath
overlying arcs, including the Palau-Kyushu Ridge in southwestern Japan, the Scarborough
Seamounts in Luzon, the Ontong Java Plateau in Papua New Guinea – Solomon Islands, the
Roo Rise near Sumbawa, and the Investigator Ridge in Sumatra. The subduction of each of these
seamounts has led to the development of large porphyry and epithermal deposits in the region.
The large deposits in medial New Guinea did not form above an active subduction zone but
within uplifted regions in a fold- and thrust-belt in a convergent setting.
1. Independent Consultant and Adjunct Research Fellow, Centre for Exploration Targeting, School of Earth and Geographical Sciences,
University of Western Australia, Nedlands, WA 6009, Australia Corresponding author: sgar@iinet.net.au
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vary the orientation of predominantly arc-orthogonal stress
fields and induce episodic reactivation of crustal-scale fault
systems in transpressional to transtensional settings.
The distribution of porphyry and epithermal deposits
reflects differences in structural- and tectonic-setting and
composition of the crustal basement (Table 1; Sillitoe
and Hedenquist, 2003; Garwin et al., 2005). Many of the
deposits are spatially and temporally related to intrusions
and volcanic centers in calc-alkaline to alkaline andesiticdacitic arcs. Porphyry, and high- and intermediatesulfidation epithermal deposits occur typically in
contractional to neutral arc settings and are closely related to
shallow intrusions, volcanic centers, and, locally, diatremes.
Low-sulfidation epithermal systems are associated with
intra-arc and backarc grabens and extensional settings
that control bimodal basaltic-rhyolitic volcanism in Japan,
calc-alkaline volcanism focused near dilational jogs in the
Sumatra strike-slip fault system in Indonesia and K-alkaline
magmatism in Papua New Guinea.
Tectonic
Stress-Regime
Probable Causes
Deformation Style
Contraction
Deposit Types
Deposit Examples
Subduction Slab Topology and Seamount
Collisions
The majority of the porphyry and epithermal deposits in
the region lie above subduction slabs. However, the giant
deposits in medial New Guinea (e.g., Grasberg, Ok Tedi and
Porgera) lack an active subduction zone and are the product
of collisional tectonics in a fold- and thrust-belt.
Major changes in the dip of the subduction slabs define
kink zones that plunge obliquely to nearly orthogonal to
the local strike-direction of each slab. The origin of these
slab kinks is, in part, related to the age and density of the
crust that comprises the subduction slabs. Buoyant, aseismic
oceanic ridges (seamounts) have collided with portions of
the subduction zones in several localities (Figure 1). The
seamounts consist of inactive, sea-floor spreading centers;
leaky transform faults and ancient sea-floor volcanic
fields. These seamount collisions enhance the coupling of
Near-Neutral
Extension
arc-arc, arc-continent collision;
buoyant seamount subduction;
fast convergence and high OCR;
subduction of young oceanic crust
most common arc setting; shares
similarities to contractional arc, but
lacks major collisions and typically
is characterized by slab rollback
and episodes of arc-relaxation
orogen-parallel folds, reverse faults
and thrust belts; orogen-transverse
strike-slip to oblique-slip faults
orogen-parallel and orogenorogen-parallel normal faults and
transverse strike-slip to oblique-slip grabens, intra-arc and backarc;
faults; dilational jogs in strike-slip
marginal basins
fault systems
Subduction slab rollback due to
subduction of older oceanic crust
or tearing of slab adjacent to
buoyant ridge; slow convergence
and low OCR
calc-alkaline to K-alkaline andesitedacite
tholeiitic to calc-alkaline bimodal
basalt-rhyolite; K-alkaline mafic to
intermediate rocks
Plio-Pleistocene Medial New
Guinea (CM)
Plio-Pleistocene Luzon Central
Cordillera (IA)
Plio-Pleistocene Southern Ryukyu
(Taiwan, CM)
Pliocene Cotobato (CM?)
Pliocene N. Sulawesi (IA)
Pliocene NE Japan (CM)
Neogene Sunda (CM to IA from
W to E, mildly contractional
between E. Java and W. Sumbawa)
Plio-Pleistocene Philippines (IA)
Early Miocene Central Kalimantan
(CM)
Middle Miocene NE Japan
(backarc, CM)
Pleistocene Ryuku (CM)
Pleistocene Izu-Bonin (IA)
Pleistocene Outer Melanesian
(Tabar-Feni, IA)
Au-rich Porphyry, Skarn, HS, IS
Porphyry, HS, IS, (LS), DS
Grasberg, Ok Tedi, Far South East
Ertsberg, Wabu
Lepanto, Chinkuashih
Porgera pit, Victoria, Acupan-Itogon
(Baguio)
Tujuh Bukit, Batu Hijau, Elang
and Tombulilato district
Martabe, North Lanut, Nalesbitan
Kelian, Toka Tindung, Placer
Lebong Donok (dilatant
jog in SFS) and Pongkor
Mesel, Bau
calc-alkaline to K-alkaline andesiteMagmatic Suite and
dacite; diminished volcanic activity
Style
or volcanic gap
Arc Examples
Steve L. Garwin
VMS, LS
Kuroko deposits in
Hokuroku district (tholeiitic)
Hishikari (tholeiitic) and Ladolam?
(K-alkaline)
Table 1. Summary of tectonic regime, deformation, magmatism and mineralization in Cenozoic magmatic arcs of Southeast Asia and the west Pacific
(modified from Garwin et al., 2005)
Abbreviations: OCR - Rate of convergence orthogonal to magmatic arc; SFS - Sumatra Fault System.
Arc settings: CM, continental margin setting; IA, oceanic island arc setting.
Deposit styles: DS, disseminated sedimentary rock-hosted; HS, high-sulfidation epithermal; IS, intermediate-sulfidation epithermal; LS, low-sulfidation
epithermal; VMS, volcanic-associated massive sulfide.
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Steve L. Garwin
the subducting slab with the overriding arc crust, which
increases the normal stress across this interface (Scholz
and Small, 1997) and promotes uplift of the overlying arc
(Garwin et al., 2005).
Examples of seamount subduction that occur near zones
of significant gold and copper mineralization in the
region include the Palau-Kyushu Ridge near Kyushu in
southern Japan (site of Hishikari, ~ 1 Ma); the Scarborough
Seamounts in northern Luzon in the Philippines (Lepanto
– Baguio, 1.5 to 0.7 Ma); the Roo Rise near eastern Java –
western Sumbawa in Indonesia (Bukit Tujuh, Batu Hijau
and Elang, ~ 4 to 2.7 Ma); and the Investigator Ridge near
northern Sumatra in Indonesia (Martabe, ~ 3 Ma). Similar
relationships between subducted seamounts and the location
of arc-transverse, intrusion-related mineral belts are observed
in the Central Andes (Sasso and Clark, 1998; Sillitoe, 1998;
Kerrich et al., 2000).
In the Southeast Asian collisional sites mentioned in the
preceding paragraph, epithermal or porphyry deposits
formed during a transition in local stress-regime that
developed as a response to seamount subduction (Garwin
et al., 2005). Northern Luzon provides one of the most
dramatic examples of the relationship between the effects
of the topology of the subduction slab on the uplift of the
overlying arc and gold-copper deposit development.
The slab beneath the Luzon arc dips steeply eastward (60
to 80°) beneath the Manila Trench, underlying two parallel
island arcs that extend between Taiwan and Luzon (Figure
2). The accretion of the extinct spreading center of the South
China Sea (Scarborough Seamounts) at the Manila Trench at
about 5 to 3 Ma stalled subduction, and magmatism ceased
in the western arc (Yang et al., 1996; Bautista et al., 2001).
The dip of the Luzon slab flattens to about 30° at the site of
collision (16-18° N), which partly underlies uplifted portions
of the fore-arc basin known as the Stewart Bank and Vigan
High (Hayes and Lewis, 1984; Pautot and Rangin, 1989).
The Baguio-Mankayan region, where Miocene coralline
limestone has been uplifted to > 1500 m above sea-level, lies
near the southern margin of the subducted seamounts, above
an abrupt change in slab-dip from ~ 30° to the north to > 60°
to the south. The subducting slab is suggested to have torn
along the trace of the Scarborough Seamounts at about 2
Ma, which led to the upwelling of underlying asthenosphere
through the torn slab and a migration in magmatism towards
the east (Yang et al., 1996; Bautista et al., 2001). The timing
of this second magmatic pulse correlates with the formation
of porphyry and epithermal deposits in the Mankayan
district (1.4 to 1.15 Ma; Hedenquist et al., 1998, 2001) and
the Baguio region (~1.5 Ma and 0.65 Ma; Sillitoe, 1989;
Cooke et al., 1996).
In contrast to northern Luzon and other arc-trench settings,
the relationship of subduction to alkaline magmatism and
related Plio-Pleistocene mineralization in medial New
Guinea is not clear. Southerly-directed subduction beneath
the New Guinea Trench is too young to explain this
magmatic-hydrothermal event, and subduction related to the
Figure 2. Tectonic framework of the Luzon arc and elements relevant
to the eastward subduction of the South China Sea plate (from Garwin
et al., 2005). The Scarborough Seamounts (SS), the extinct spreading
center of the South China Sea, subducts below Luzon. A buoyant
oceanic plateau, to the north of this aseismic ridge, is also inferred
to have accreted to the base of the Luzon Central Cordillera (LCC;
Bautista et al., 2001). This accretionary process has led to the uplift of
the Stewart Bank (SB) and Vigan High (VH), which segment the fore
arc to form the North Luzon Trough (NLT) and West Luzon Trough
(WLT). The Baguio and Mankayan districts underwent extensive
uplift in the Plio-Pleistocene and lie along the subducted trace of the
Scarborough Seamounts (Knittel et al., 1995). Two parallel island arcs
extend between Luzon and Taiwan. In the Luzon Central Cordillera
and towards the north, volcanic activity was focused in the western arc
(WVC) from the Miocene to middle Pliocene (~ 4-3 Ma) and migrated
to the eastern arc (EVC) in the late Pliocene (~ 2 Ma), which remains
active to the present. PSF = Philippine fault system; COB = margins of
the South China Sea plate. The relative motion between the Philippine
Sea plate and Eurasia (86 km/m.y.) is from McCaffrey (1996).
calc-alkaline Maramuni arc ceased by ~ 10 Ma. However,
the spatial and temporal correlation between large porphyry
and epithermal deposits (e.g., Porgera ~ 6 Ma, Grasberg ~
3 Ma and Ok Tedi ~ 1 Ma) and the southward progression
of fold-and-thrust belt deformation (Davies, 1991) suggests
that crustal thickening and block uplift played a critical
role in metallogenesis. Rapid convergence between New
Guinea and the Caroline plate in the Late Miocene caused
compression throughout the island and uplift of the Papuan
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fold belt (Hill et al., 2002). In the Pliocene, compressional
stresses were reduced and transpression characterized the
New Guinea margin, which is inferred to have facilitated
dilation about the intersections between frontal thrusts
and northeasterly-trending, orogen-transverse faults (Hill
et al., 2002). These dilatant zones served as the loci for the
emplacement of mantle-derived, potassium-rich magmas
and the generation of large hydrothermal systems at shallow
crustal levels.
Crustal-scale, Arc-transverse Faults and
Lineaments
Arc-transverse fault zones are inferred to control the
distribution of many of the intrusion-related deposits in
medial New Guinea, Luzon, Sunda-Banda, and in other
magmatic arcs in the region (Corbett and Leach, 1998;
Garwin et al., 2005). Similar cross-arc distributions of
deposits exists in the central Andes, where arc-transverse
mineral belts coincide with faults, fracture zones and
lineaments defined by deflections in regional structural grain
and geological discontinuities (Skewes and Stern, 1995;
Sasso and Clark, 1998; Sillitoe, 1998; Richards et al., 2001).
In Southeast Asia, arc-transverse oblique- to strike-slip
faults extend on the order of 100 to 400 km across many
of the magmatic arcs, and indicate arc-parallel extension
on the order of about 3 mm/yr locally (e.g., near Timor,
Indonesia; McCaffrey, 1988). Crustal-scale lineaments,
inferred from regional geology, digital topography, satellite
gravity, bathymetry, and satellite imagery, extend at angles of
about 45° to 70° across the Indonesian arcs. Many of these
lineaments coincide with clusters of shallow (< 30 km depth)
earthquake hypocenters along major faults in the arc and
backarc, and coincide with segments of varying earthquake
activity in the underlying Benioff zone (figure 8 in Garwin
et al., 2005). These arc-transverse fault- and fracture-zones
are inferred to extend towards the base of the crust and
create dilatant channels for hydrothermal fluids and the
efficient release of metal-bearing volatiles exsolved from
melts at high levels in the overlying arc (e.g., < 4 km beneath
paleosurface).
District-scale Structural Controls
The major controls to large porphyry and epithermal
deposits and districts in the region typically include
second- and higher-order fault systems that lie adjacent
to arc-transverse fault- or fracture-zones that have
localized Neogene to Pleistocene magmatism and locally,
sedimentation. The most prolific intrusion-related districts
are characterized by areas of uplift and exhumation in
regional-scale, compressional to near-neutral stress-regimes
that have experienced variations or inversions in the local
stress-fields. In contrast, several of the low-sulfidation
epithermal systems typically lack a direct connection to
causal intrusions and occur in extensional settings but may
also be associated with stress-regime inversions.
Steve L. Garwin
The local structural settings that promote the heat- and
fluid-flow necessary to produce large porphyry and
epithermal deposits in the region include: 1) dilatant
zones in long-lived fault systems; 2) structural highs,
domes, anticlines or horst-blocks; and 3) the margins of
pre- to syn-mineralization plutonic complexes, horst-block
margins and competent blocks in zones of low meanstress. Arc-transverse belts that host thin, young volcanosedimentary cover sequences (with or without mineralized
rock fragments), volcano-sedimentary basins, porphyritic
intrusions and hydrothermally altered magmatic centers
indicate significant potential for the future discovery of large
gold and copper deposits.
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3D Modelling of Geology and Gravity Data: Summary Workflows for Minerals Exploration
Helen Gibson, John Sumpton,
Des FitzGerald, Ray Seikel
3D Modelling of Geology and Gravity Data:
Summary Workflows for Minerals Exploration
Helen Gibson1, John Sumpton1, Des FitzGerald1 and Ray Seikel1
Abstract
Introduction
3D geology modelling coupled with innovative approaches
to interpreting gravity data are combined in a suite
of workflows available to assist minerals exploration.
Challenges facing explorers - such as those relating
to complex geology and structure, and how to achieve
low-cost exploration - are being met with new software
tools. Predicting the continuity of mineralised zones
and faults away from mapped and sampled regions can
now be rigorously constrained using GeoModeller which
offers a highly appropriate 3D interpolation method.
Intrusions, overturned limbs, faulting, and thin & irregular
bodies (e.g., dykes and veins), can be modelled implicitly,
constrained by measured contacts and orientations,
including from drill holes.
GeoModeller is geology modelling software developed
and commercialised in Melbourne, Australia by Intrepid
Geophysics in co-operation with the BRGM, France.
The geophysical methods described in this paper are
implemented in Intrepid software which was developed
and commercialised in Melbourne, Australia – solely by
Intrepid Geophysics.
Why are we interested in potential field data as an aid to
geological resources mapping and exploration? Insufficient
geology observations often exist and so hamper reliable
construction of the full geological and structural story,
particularly at depth. Beyond surficial and drilled geology
data, model constraints can also be derived from ground
or airborne gravity data. Here we introduce one innovative
interpretation workflow: Multi-Scale Edge Detection
(Hornby et. al., 1999) which can facilitate semi-automated
structural interpretation for the model zone, given certain
caveats and uncertainties (see below).
Searching for mineralisation can sometimes be successfully
aided by simplifying the problem to: “Where do we have
excess density clusters that are required by our measured
gravity field, but cannot be explained by our best-known
and modelled host geology?” In this workflow, we describe
a non-deterministic geophysical inversion method which
maintains a link to realistic 3D geology, and references
observed gravity to drive results in terms of (i) geological
uncertainty and (ii) a 3D grid of most-probable variable
density. These inversion-outcomes may be used to again
refine the geological model, and importantly to generate
drilling targets centred on unexplained high-density
clusters which may be a proxy for the location of unmapped
sulphide-hosted mineralisation.
The model-building interpolators
The 3D interpolation method employed by GeoModeller
is based on potential field theory (McInerney et al, 2005).
Uniquely it enables cokriging of two related variables
(geology & fault contact points and orientation data) by
treating them as increments and derivatives of an isopotential surface of a 3D scalar field (Lajaunie et al., 1997;
Fig. 1A). Cokriging therefore enables geology formationboundary positions to be computed in 3D as curvilinear
surfaces which honour coupled dip & dip-direction data
(orientation data are treated as gradients of the
potential field).
Multiple geology surfaces and fault planes can be
interpolated separately – (e.g., of host sediments, intrusives,
veins, dykes, and faults). When interpolating separately,
the final model construction of aggregated volumes and
fault surfaces honours a rule-based approach obeying the
relationships of the pile (i.e., onlapping or erosional) and
also obeying the chronology of the fault network. Both of
these rule-based inputs are important constraints of the
model, and are additional to the fundamental contact and
orientation data.
By this method, computation of the geological model
using all constraining data is rapid, taking only seconds on
a standard PC. Rendering the model in 2D & 3D views
takes longer, depending on required resolution. GeoModeller
models are easily updated and re-computed when new data
becomes available with progressive drilling, sampling and/
or mapping.
1. Intrepid Geophysics, Unit 110, 3 Male Street, Brighton, Victoria 3186, Australia Corresponding author: helen@intrepid-geophysics.com
25
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Multi-Scale Edge
Detection – aiding
structural interpretation
This semi-automated method
implemented in GeoModeller
applies either to gravity or
magnetic data, and relies on
producing unbiased estimates
of sharp lateral changes in
rock properties (FitzGerald &
Milligan, 2013). The aim is to
identify depth, location and shape
of the sources reflected, say in the
gravity data. The assumption is
that the position of the maxima in
the horizontal gradient represents
the edges of the source bodies.
Such maxima can be detected
and mapped as points, and later
converted to poly-lines or “worms”
- potentially providing evidence,
for example, for continuation of
known structures or contrasting
geological units in a model zone
under construction.
The process of mapping maxima
as points can be extended to
many different levels of upward
continuation of the potential field
data. This provides points and
poly-lines that can be displayed
in three dimensions, using the
height of upward continuation as
a pseudo z-dimension. In MultiScale Edge analysis a further
assumption is that lower levels of
upward continuation map nearsurface sources, while higher levels
map deeper sources. Whilst generally
true, this aspect must be treated
with caution due to the non-uniqueness of potential field
solutions.
In recent years efforts to enhance the usefulness of this
technique for fully automated interpretation have focused
on solving the non-uniqueness issue for the estimation
of “true” depth of sources. One candidate lies in the
established Euler/Werner deconvolution technology
(FitzGerald et al., 2004). This technology offers promise,
but a robust technique is still under development.
Nonetheless, the currently available tool can offer a
good semi-automated workflow, offering some structural
mapping constraints when depth-corrections are treated as
qualitative (Fig1B).
Figure 1.
Non-deterministic inversion of gravity data
Next, with our geology model closer to reality than before,
mean densities can be assigned to each geology unit. But
if some are unknown, a property optimization routine can
first be run to determine optimum values. At this stage,
several forward modelling runs are necessary to compute
the gravity response directly from 3D geology and the
coupled properties data. When a fairly close match is
achieved between the modelled and observed gravity – then
preparations for a litho-constrained stochastic inversion
are complete. [Note that property optimisation, forward
modelling and inversion are all performed on a discretised
26
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version of the smooth 3D geology model (Fig. 1C). This
necessary step creates a 3D grid or “voxet” model, for
computation purposes.]
During inversion, as employed in GeoModeller (McInerney
et. al., 2005), each iteration makes a modification to one cell
in the voxet, either in terms of geology-geometry, or the rock
property (density). The revised geophysical response is recomputed following the small change, and assessed against
observed gravity. If the misfit is better than for the last
iteration, the model is kept. If the misfit is worse, the model
is generally (but not always) rejected.
This inversion method is based on a Markov Chain Monte
Carlo formulation. Hence, rather than iterations ceasing
when misfits reach a specified low limit (a deterministic
approach), inversion employed in GeoModeller continues
to iterate, exploring millions of possible models while
converging to an overlap zone representing all models
supported by the available independent data sets (Fig 1D).
Retained models are within tolerance of the known geology
& properties, and these are the basis from which inversion
outcomes are reported in terms of probabilities.
Specific outcomes from inversion of 3D
geology and gravity: Excess density
Performing an inversion on gravity data may have multiple
goals, but here we highlight a workflow which may be useful
in identifying zones of excess density. That is, zones where
the best-known geology model still cannot explain the
observed gravity response, and the driven inversion outcome
in terms of most-probable density voxet, indicates clusters
of high-density cells which are interpreted to indicate
significant sulphide mineralisation (Fig 1E).
In our experience this workflow is best applied in highresolution to prospect-scale models, and uses ground
gravity data. Sometimes our recommended workflow
involves sensitivity testing, using multiple inversion runs
commencing from different initial models, for example, with
and without mapped gossans and their predicted depthextensions into mineralized zones.
A project is deemed to bear results worthy of further
exploration, when inversion outcomes yield cells of
anomalously high density, within a variable density voxet.
A filtered view of the voxet, say at > 3.3 gcm-3, enables
geo-location of high density clusters, and thus targets.
Post-inversion volumetrics and density statistics are also
available for what was usually a poorly constrained zone of
the initial model.
Summary note
Numerous workflows using the software tools available in
GeoModeller and Intrepid aim to offer powerful solutions to
exploration problems (Fig 1).
References
Hornby, P., Boschetti F., and Horowitz F.G., 1999. Analysis of potential
field data in the wavelet domain: Geophysical Journal International, 137,
175-196.
FitzGerald, D. and Milligan P., 2013. Defining a deep fault network for
Australia, using 3D “worming”. ASEG 2013, in prep.
FitzGerald, D., Reid, A., and McInerney, P., 2004, New discrimination
techniques for Euler deconvolution: Computers&Geosciences, 30,
461–469.
Lajaunie, Ch., Courrioux, G., and Manuel, L., 1997, Foliation fields and
3D cartography in geology: principles of a method based on potential
interpolation: Mathematical Geology, 29, 571–584.
McInerney, P., Guillen, A., Courrioux, G., Calcagno, P. and Lees, T., 2005.
Building 3D geological models directly from the data? A new approach
applied to Broken Hill, Australia. Digital Mapping Techniques pp 119130.
27
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Chinese Minerals Exploration Methods and Philosophy: Implications for Out-bound Investment
Chinese Minerals Exploration Methods and Philosophy:
Implications for Out-bound Investment
Matthew R. Greentree1* and Gavin Chan2
Explorers in China rely on a set of prescriptive National
Standards to provide guidance on all aspects of mineral
exploration, which cover Resource and Reserve
Classification, principals of mineral exploration, technical
requirements for field work, reporting and contain guidelines
for individual minerals or mineral types (e.g. Liu and
Zhou, 2003; Bucci et al, 2006). These guidelines leave little
flexibility for exploration personnel to design exploration
programmes that fit with local conditions, local experience,
geology and mineralisation styles. The aim of this paper is
to discuss how the Chinese National Standards (National
Standards) originated and how they influence the way
Chinese companies and State Owned Enterprises (SOE)
approach minerals projects within China and overseas.
During the mid to late twentieth century, the Chinese
mineral industry was tightly controlled by government
policy, operating independently of commodity markets and
instead relying on complex system of quotas used to control
mineral production. Mineral exploration was conducted
by government agencies such as the Geological Brigades
and Gold Squads who were organised at both county and
provincial levels with oversight from National institutes
such as the China Geological Survey. The role of these
groups was to conducted similar work programmes to that
of geological surveys in the west. However, the role of
the geological brigade also included mineral exploration,
development of mineral Resources and mining. These
systems were still largely in place, until reforms began in
the late 1980’s and many of the state owned and operated
organisations were incorporated and became more
autonomous.
China started developing a series of National Standards
for mineral exploration during the 1950’s based on the
standards used within the Soviet Union. By 1959, the
Chinese standards were issued by the State Commission
of Mineral Reserves (SCMR) and again in 1983. The
SCMR issued standards concerning mineral Resource and
Reserve classification, principals of mineral exploration
and exploration codes of individual minerals types. More
recently, the standards have been issued by General
Chinese National Standards
Exploration stage
Work programme
Result
Regional geological assessment
Regional Mapping
Typically regional reconnaissance style geological
mapping at 1:1 000,000 to 1:25,000 scale. May
include soils, stream sediment sampling and rock
chip sampling.
A number of defined targets or prospects
Reconnaissance
Target generation based geochemistry, mapping
and limited drilling. Additional reconnaissance
drilling, sampling and mapping. Work conduced at
1:50,000 – 1:10,000 scale.
Prospecting
Sampling at scales 1:10,000 to 1:5 000. Soils
sampling, trenching and geophysics. Limited
drilling and some
Potential mineralisation assessed by “Preliminary Study”
which covers economic, social or technical factors that
may affect any decision to proceed
Broad spaced drilling of identified mineralisation
General Exploration (resource at inferred level Chinese standards).
Detailed
Exploration
Systematic drill-out (resource at indicated level
Chinese Standards)
Pre-feasibility study including metallurgical testing
carried out by mine design institutes.
Feasibility study and resource to be used for mine design
carried out by mine design institutes and application for
mine license
Table 1 Exploration stages as defined in the Chinese National Standards
1. SRK Consulting Australasia, 10 Richardson Street, West Perth, WA Australia 6160 Corresponding author: mgreentree@srk.com.au
2. SRK Consulting Hong Kong, Suite A1, 11/F, One Capital Place, 18 Luard Road, Hong Kong
28
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Chinese Minerals Exploration Methods and Philosophy: Implications for Out-bound Investment
Administration of Quality Supervision, Inspection and
Quarantine and the China Geological Survey.
The National Standards describe in detail how each phase
of work is conducted. The Standards state specifications for
different commodity types and include specifications for
exploration methods, sample spacing, depth of drilling, assay
schemes and cut-off grades. Exploration work outlined
by the National Standards focuses on surface geochemical
sampling methods including streams sediment, soils, rock
chip, trenching and pitting. Although accesses to airborne
geophysical methods are becoming more common, they are
not routinely used in mineral exploration in China as they
are by western geologists.
The National Standards divided exploration cycle into stages
which are; reconnaissance, prospecting, General Exploration
and Detailed Exploration (Table 1). Each stage is matched
to a level of detail and type of work conducted. Detail
of work is linked to map scale (1:200,000; 1:50 000, 1:10
000 and 1:1 000) and sampling density. At the conclusion
of General Exploration and Detailed Exploration stages
there includes recommendations for mining studies. As
most details of exploration are prescribed in the National
Standards, this provides little encouragement for the
geologist to assess the local geology and assay results
systematically. This differs philosophically and practically
from western exploration methods (e.g. JORC). Western
exploration focuses on the judgement of a competent person,
familiar with the commodity or deposit style, to design
a site-specific/appropriate exploration programme, and
supervise any exploration or Resource development work.
The National Standards have been used successfully in
many exploration programmes across China. However, the
prescriptive approach outlined in the National Standards
has a number of shortcomings particularly if an exploration
programme is designed to follow the National Standards
at the expense of decisions based on technical merit.
Exclusively following these standards is likely to lead to an
inefficient exploration programme in terms of time or cost
and could result in an ineffective exploration programme.
With changes to government policy in 2006 to encourage
direct investment by Chinese companies overseas, China
has become the largest source of investment for Resource
projects worldwide. During 2011 Chinese investment
within the Australian Resource sector reached USD 7.4
billion (Ferguson and Hendrischke, 2012). Increasingly,
Chinese companies tend not to just acquire or invest
in projects with established Resources, but begin
actively exploring and developing greenfield Resource
projects overseas. Many of the professionals within
these organisations will continue to apply the National
Standards on which they base exploration work and
investment decisions.
The additional cost required to bring exploration
programmes designed according the National Standards
to a western standard is difficult for many Chinese
exploration companies to justify. However, exploration
results and Resource estimates based on the National
Standards are generally not accepted for the public
reporting on either Asian (e.g. HKEx or SGX) or
western stock exchanges (e.g. ASX, TSX, AIM). This is
a significant challenge for Chinese organisations if they
move to IPO or attempt to gain obtain funding from
outside of China. This can be overcome with a “hybrid”
of Chinese and western exploration methods. With
the National Standards being followed, thus fulfilling
any obligations to the Chinese parent company and
incorporating aspects of western exploration (sampling,
QA/QC, drill spacing, continuity of mineralisation etc.)
that satisfy a Competent person under JORC. References
Bucci L., Hodkiewicz, Jankowski P., Guibal D., Song X., 2006 JORC and
the Chinese Resource Classification Scheme – an SRK view. AusIMM
Bulletin Feature Exploration July / August pp 24 -27
Ferguson D. and Hendrischke H., 2012 Demystifying Chinese Investment
– Chinese Direct Investment in Australia. KPMG & University of
Sydney China Studies Report pp 20
JORC, 2012. Australasian Code for Reporting of Exploration Results,
Mineral Resources and Ore Reserves (The JORC Code) Available
from: http://www.jorc.org> (The Joint Ore Reserves Committee of The
Australasian Institute of Mining and Metallurgy, Australian Institute of
Geoscientists and Minerals Council of Australia).
Liu R. and Zhou eds. 2003 Compilation of commonly used standards for
geological exploration. Sichuan Metallurgical and Geological Bureau
l
keynote
29
Graeme Hancock
Graeme Hancock1
The land mass of Mongolia is formed from a series of
accreted terranes sandwiched between the North Asian
Craton to the north and the Sino-Korean Craton to the
south. The main accretion events appear to have taken
place during the early to late Paleozoic and the terranes
comprise both island arc sequences as well as blocks of preCambrian basement and granites. These accreted terranes
have subsequently been subjected to a series of intrusive
and volcanic episodes. The accreted formations are overlain
by sedimentary rocks dating from periods of tropical
climate sedimentation creating large basins of coal bearing
sediments. This combination of events has resulted in a
complex and highly prospective geological environment.
Most of the mapping and interpretation of the geology
was done by joint Russian and Mongolian geological teams
during the period when Mongolia was a satellite State of
the Soviet Union. During this time they identified over
8000 mineral occurrences covering 80 different mineral
commodities as well as a significant number of mineral and
coal deposits. The island arc terranes are highly prospective
for copper, gold, uranium and a range of other metals and
rare earth elements. The Permian aged island arcs also
contain significant bituminous coal deposits. To date two
copper deposits have been developed into producing mines
(Erdenet during the socialist era and Oyu Tolgoi now
commissioning) as well as two uranium mines (Dornod
and Gurvanbulag) both of which were developed by Russia
during the socialist era. Early gold exploration focused
mainly on easily exploitable alluvial deposits, with more
recent exploration more focused on hard rock occurrences.
This modern gold exploration has resulted in the
development of one significant gold deposit (Boroo Gold)
and the discovery of a number of other significant prospects.
Coal exploration and development has also received a lot
of attention, particularly in the recent past with Permian
bituminous coals now being exploited from a number of
deposits and exported into the Chinese coking coal market.
Huge deposits of younger lignite and sub-bituminous coals
occur extensively throughout the central, north and eastern
parts of the country providing fuel for the country’s thermal
power and heating plants.
In common with many developing countries Mongolia
faces a number of challenges in realising the development
of this significant mineral potential. A combination of
poorly developed infrastructure, a sometimes unstable
legal and regulatory environment coupled with some
unfriendly foreign investment rules have discouraged many
explorers. When combined with the issues the Mongolian
Government faces as a landlocked country in managing the
geopolitical influences of its two immediate and powerful
neighbours (Russia and China) it all creates a unique set
of interesting challenges and opportunities for mineral
exploration and development.
1. President and Chief Representative, Mongolia, AngloAmerican Corresponding author: graeme.hancock@angloamerican.com
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keynote
30
A Framework for China’s Gold Exploration and Endowment
Craig J. R. Hart, Richard J. Goldfarb
A Framework for China’s Gold Exploration
and Endowment
Craig J. R. Hart1 and Richard J. Goldfarb2
Among the most dramatic change in the global gold
exploration and mining landscape during the past ten years
is the significant development of China’s gold industry to
that of the global leader in gold production. First in gold
production since 2008, China now produces more than 400
t of gold/year representing 10% of global production and
surpassing Australia (250t) and USA (230t). Importantly,
production has been increasing at almost 12% yearover-year which contrasts most other traditional gold
producing countries that now lack growth. Such production
advances have been made with increased investments and
efficiencies in existing mines, consolidation of small mines,
the application of technologies to increase recoveries of
gold from low-grade and refractory ores, and greenfields
and brownfields exploration and discoveries that result
in the development of new mines. However, China’s
gold mines, of which there may be more than 1000, are
typically small in terms of both production and resources
with few approaching world-class status. China’s ‘official’
gold resource has grown to 1900t, but is likely inflated, and
represents only 3.7% of the global resource and would be
exhausted with only five years of production. The influx of
foreign explorers and miners and expertise to China peaking
in 2004 significantly catalysed the industry such that the
benefits are still prominent despite changing policies starting
in 2008 that discouraged foreign investment. The industry
has changed 180 degrees such that Chinese cash is playing
an increasing role to off-shore corporate ownership and
mineral exploration and mining development efforts.
China’s gold mines have traditionally been prominent in
the eastern part of the country where high population
density has ensured that most small deposits were
discovered and exploited by underground methods, and
these mines were important contributors to China’s
historical production. With increased political emphasis
on development of the county’s western frontiers, new
discoveries have been made in regions such as Xinjiang,
Qinghai, Gansu and Tibet. However, the country’s largest
mines are those historical underground producers that
have been consolidated and expanded with infrastructure
capital that was difficult to obtain prior to 2009. Examples
of consolidated and expanded mines are those in the
Shandong province that now have the capacity to produce
>26t Au/year, and Zijinshan high sulphidation epithermal
deposit now generating 15.5t/year. A key step forwards
was the development of large open pit gold mines by
foreign companies. First in this effort was the discovery
and development of the CSH deposit by Canadian junior
explorer Jinshan Gold Mines, which was developed prior
to their takeover by China National Gold Corp and will
expand to more than 8t of annual production by 2015.
Prominent also, are the efforts of Eldorado Gold Corp
who, including their takeover of SinoGold in 2009 for
$2.2B, have put three gold mines into production ( Jinfeng,
Tanjianshan, White Mountain) that are generating ~11t
of annual production. Not all involvement of foreign
companies has been positive, with Southwestern Gold’s
manipulation of resource data at the Boka gold deposit and
failure of the government to provide development permits to
Mundoro Resources for development of their 30t Maoling
deposit, as examples.
China is composed of several Archean cratonic blocks that
were amalgamated in the late Paleozoic to early Mesozoic
to form the Precambrian regions of present-day China. The
assembly of these blocks was associated with numerous
episodes of Phanerozoic tectonic activity that caused
their margins to become deformed and modified. These
Phanerozoic orogenic belts overprint and reworked the
margins of cratonic blocks and overlying sedimentary rocks
and generated magmas that formed plutonic and volcanic
assemblages. Most of China’s orogenic, epithermal, skarn,
porphyry, and Carlin-like gold deposits and resources
are in or proximal to these modified cratonic margins.
Accordingly, China’s major gold provinces are preferentially
located along the northern, eastern and southeastern margins
of the North China craton, along the various margins of
the Yangtze craton, in the Tianshan and Altaishan orogenic
belts adjacent the Tarim and Junggar blocks in northwestern
China. Eastern China was subsequently influenced by
Pacific subduction that generated magmas, porphyry and
epithermal systems in southeastern China, and the collision
with India generated Himalayan orogeny that generated
small orogenic and porphyry systems.
1. MDRU-Mineral Deposit Research Unit, The University of British Columbia, Vancouver, BC, Canada Corresponding author: chart@eos.ubc.ca
2. United States Geological Survey, Box 25046, MS 973, Denver Federal Center, Denver, CO, USA
31
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A Framework for China’s Gold Exploration and Endowment
Three-quarters of China’s gold-only (mostly orogenic)
deposits occur within uplifted blocks of Precambrian
metamorphic basement rocks along the margins of the
North China craton and include those in the Shandong,
West Qingling, Xiaoqingling, Daqinshan, Yan-Lioa and
Changbaishan gold provinces (). However, unlike many
other regions of the world where important enrichments
of gold mineralization are directly related to Archean
or Paleoproterozoic basement terranes, no important
Precambrian gold systems have been recognized anywhere
in China. All of China’s gold endowment formed in
response to Phanerozoic events. This is a globally unique
situation in which significant accumulations of Phanerozoic
gold were deposited in Precambrian rocks. The old rocks
are typically not receptive to younger tectonic, magmatic
or thermal events due to the rigid integrity provided by
their thick, cold and stiff lithosphere. The widespread
distribution of orogenic gold deposits throughout eastern
China appears to be broadly related to subduction beneath
them, which warmed and softened their margins and
allowed heat, magmas and fluids to infiltrate their margins as
early as initial Permo-Triassic amalgamation. Lithospheric
softening of the margins to the North China block, either by
delamination or thermal erosion, was particularly dramatic
Craig J. R. Hart, Richard J. Goldfarb
during the Jura-Cretaceous and resulted in the loss of subcontinental lithospheric mantle (the Archean-Proterozoic
keel) which further destabilized and weakened the craton
margins, leading to Yanshanian orogeny. This process was
initiated by the subduction of three plates beneath eastern
China, with subsequent fluid flow reflecting the changing
stress regimes at ca 125 Ma that is coeval with China’s
largest gold event. This setting is a dramatic departure from
those typically accepted within orogenic gold models.
China continues to overemphasize their already low
resource levels. Most past gold discoveries were acquired
through prospecting and systematic empirically-driven
exploration. Future discoveries of large gold resources
require the application of conceptual targeting and mineral
deposit models, as well as improved understandings of the
significance of regional geological setting and district-scale
ore controls, these exploration approaches have not been
previously widely applied. Future resource success will
require amalgamating small underground deposits into
larger open pits with lower grades. The influx of foreign
explorers contributed new methods and strategies and
ideas to China’s gold exploration and mining landscape and
ultimately contributed to the production boom that China is
currently enjoying.
32
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The Tombulilato Copper Gold Project in Sulawesi, Indonesia ‘Facing the Challenges
and Opportunities’
The Tombulilato Copper Gold Project in Sulawesi,
Indonesia ‘Facing the Challenges and Opportunities’
Dedy Hendrawan1 and Gayuh ND Putranto1
Located in Gorontalo Province, Indonesia, Tombulilato
Cu-Au District is a well known district which has
potential Cu-Au mineralization to develop. The district
is also located in Au-Cu mineralization trend (Figure
1). International Minerals Corp (IMC), a subsidiary of
PT Bumi Resources Tbk that took over share ownership
from BHP in 2005, began an exploration and drilling
program in the south part of the District area in 2006. PT.
Gorontalo Minerals (GM) owned 80% by the IMC and
20% by PT. Aneka Tambang (ANTAM) had continued
exploration program since 2011 and commenced an
extensive drilling program in Sungai Mak and Cabang Kiri
in September 2011.
The geology of the Tombulilato district, North Sulawesi
(Perello, 1993), is characterized by an island arc-type
volcano-sedimentary pile, > 3400 m thick and of late
Miocene (?)–Pleistocene age, which is made up of
submarine to subaerial basic to acid volcanic rocks
interbedded with, marine and continental sedimentary
rocks. The sequence is intruded by high-level stocks and
dikes, and cut by diatreme breccias of late Pliocene and
Pleistocene age, some of which are associated intimately
with porphyry Cu–Au and epithermal Cu–Au–Ag
mineralization. A main compressive deformation event took
place in the Pliocene. Preliminary geologic reconstructions
suggest that these mineralization types in the Tombulilato
area were generated over about 2 M yr (between 2.9 and
0.9 Ma) as part of a district-scale hydrothermal system.
Continuous syn-mineralization uplift and erosion, which
are interpreted to have removed some 2 km of rock in the
last 3 M yrs, were responsible for the progressive un-roofing
of the hydrothermal system and the superposition of
epithermal environments over relics of higher temperature,
deeper-seated mineralization. In the near-surface
environment, intense uplift accompanied formation of a
chalcocite blanket at Sungai Mak.
The structure of the Tombulilato District is characterized
by northerly striking high-angle faults, normally a few
meters wide and containing tectonic breccias, high-tomoderate angle normal faults showing an easterly trend
and of post-mineralization origin, and common low-angle
thrust faults, typically accommodated by ductile sedimentary
intercalations in the Bilungala Volcanics and showing a
random orientation. All intrusive bodies postdate folding
and thrusting (Leeuwen and Pieters, 2011).
Figure 1. Tombulilato District and prospect locations
1. PT Gorontalo Minerals, Gedung Leppin Jln Sawah Besar 300, Bone Bolango, Gorontalo, Indonesia Corresponding author: dedy.hendrawan@brm.co.id
33
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The Tombulilato Copper Gold Project in Sulawesi, Indonesia ‘Facing the Challenges
and Opportunities’
Three main mineralization types are present in the district: 1.
porphyry Cu–Au; 2. high-sulfidation epithermal Au-Cu-Ag;
and 3. low-sulfidation epithermal Au–Ag. Porphyry Cu–
Au mineralization is present at Cabang Kiri (East, North,
Southwest and South), Sungai Mak, Kayubulan Ridge, and
Cabang Kanan. High Sulphidation epithermal Au-Cu-Ag is
present in Motomboto (North, East and West), Mohutango
and Ridho. Low Sulphidation Au-Ag is present in
Kaidundu, Mamungaa, Pombolo, Hulapa, Ombulo, Hupito,
Moota, Waluhu, and Bilolatunga (Figure 1).
Hypogene Cu-Au is 72.2mt @ 0.31% Cu and 0.17gr/t
Au and 3. Sungai Mak Oxide Au is 11.5mt @ 0.51gr/t Au.
Most of resource was fall in measured-classification. Mineral
resource of Cabang Kiri is 124mt @ 0.43% Cu and 0.67gr/t
Au. In order to support and accelerate the completion of FS
and AMDAL, before 2011 and during the resource drilling
period in 2011-2012, GM had also completed numbers
of test and studies including metallurgy, geotechnical,
geohydrology, hydrology, baseline study, health study, social
impact study, flora/fauna study, marine biota study, etc.
SRK Consulting as a main consultant, LAPI ITB,
Simulus and Io Global are some of reputable consultants
that have been involved with GM from the beginning of
recommencement of exploration in 2011. Reputable national
universities (ITB, UNHAS, UNSRAT, UNTAD, UNG,
UG, IPB and UI) and international institution (ANU)
had been involved conducting numbers of baseline studies
to support the Feasibility study (FS) and Environmental
Impact Study (AMDAL). Other consultants are Paradigm
Management Consulting (PMC) and Ernst and Young who
assisted GM in developing Integrated Management System
and QHSE Management System.
Current JORC resource from Sungai Mak and Cabang
Kiri reported in 2012, new resource from Motomboto area
expected to get in 2013, potential additional expansion
from these three prospects and other resources from known
prospects including Kayu Bulan, Cabang Kiri North,
Cabang Kanan, and numbers of clusters in Motomboto
and Kaidundu-Pombolo are very possible that Tombulilato
District will prove to be a world class Copper-Gold District.
Regional exploration program during 2011-2012 assisted
by effective target selection from data collection, data
compilation and data processing of geophysics data (airborne
and IP) and geochemistry data had also successfully located
new large Cu-Au anomalies (Poga, Ridho, Kayu Bulan
Barat, and other cluster at South).
In the Bumi Resources era in between 2006 and 2010, GM
conducted minor scale but systematical exploration program
in the south part of Block 1, especially in Kaidundu prospect
and its surroundings. Started in mid 2011, GM started
running extensive drilling program targeting to bring the
project into production in 2016-2017. This is a challenging
task. Challenges includes legal and permitting, compiling
old analog data, building new team, building new system
and infrastructures, building good relationship with stake
holders, facing public perception, working in remote and
rugged terrain, working together with local miners, financing
the project, maximizing local contractors, implementing
and monitoring HSE aspects, etc. Exploration strategy and
timing is also critical in developing this project to achieve
and fulfill the target and expectation of the government
in line with the exploration stage in the Contract of Work
stage period after long inactive period of exploration. In
the other hand, developing, implementing and maintaining
Health, Safety and Environment (HSE) are very important
to conduct in all aspect of activities.
Expansive drilling program over Sungai Mak and Cabang
Kiri was conducted during 2011-2012, totaling 15197.95m
in Sungai Mak and 5983.05m Cabang Kiri. The drilling
program included twin holes, resource holes metallurgy
holes, and geotechnical holes. Current JORC minerals
resource of Sungai Mak and Cabang Kiri using 0.2% Cu
cut-off grade was reported by competent person of SRK
in July 2012. Sungai Mak resource are divided into 3
mineralization domains: 1. Sungai Mak Supergene Cu-Au
is 84.3mt @ 0.84% Cu and 0.42gr/t Au, 2. Sungai Mak
Significant reduction in numbers of people working in
local artisanal gold mining Au activity in Motomboto from
5000-7000 people in 2011 to approximately 700 people in
End of 2012 has opened access and opportunity to conduct
exploration program in the area. BHP reported in 1997 that
Tulabolo prospect or what we currently call Motomboto
North has high grade Au-Ag-Cu at 3.5mt @ 4.8gr/t Au,
94.3 ppm Ag, 1.67% Cu (BHP and ANTAM, 1992).
Because of these reasons, GM plans to conduct exploration
and resource drilling program over Motomboto North and
Motomboto East in 2013. Motomboto complex has numbers
of clusters located along WNW structures associated with
a multiphase of hydrothermal breccias complex. Main
mineralization occurs in sulphides-cemented breccia and
vuggy silica, both as oxide and sulphide Au-Cu-Ag. Oxide
Au near the surface at Motomboto North is the first priority
to complete followed by higher tonnage and higher grade of
Au-Ag in Main Motomboto East. New resources from both
prospects are expected to get in end of year 2013.
PT. Gorontalo Minerals has successfully overcome the
challenge to get high level confidence of mineral resource
and increase more tonnage and grade in the past 1-2 year
exploration program. The company is now moving to
complete detail Feasibility Study of Motomboto North,
Motomboto East and Sungai Mak in 2013 followed by
Environmental Impact Study (AMDAL) in 2014 and
construction stage in 2015-2016.
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Geophysics of the Elang Cu-Au Porphyry Deposit, Indonesia, and Comparison with Other Cu-Au
Porphyry Systems
Geophysics of the Elang Cu-Au Porphyry Deposit,
Indonesia, and Comparison with Other Cu-Au Porphyry
Systems
T. Hoschke1, S. Schmeider2 and S. Kepli2
Introduction
The Elang porphyry Cu-Au deposit is located in south
western Sumbawa in Indonesia approximately 60 km due
east of the Batu Hijau porphyry Cu-Au mine (Figure 1). It is
a large deposit with a total resource estimate (as at June 2010)
of 2425 Mt at 0.33 g/t Au and 0.31 g/t Cu (Ball, 2011).
A regional stream sediment sampling and mapping program
in 1987 and 1988 led to the discovery of epithermal veins
in the Elang area. Gold mineralisation was intersected in
drill holes, but not enough to be of interest and exploration
ceased until after the discovery of Batu Hijau in 1991. The
area was then reassessed for porphyry Cu potential and a
large low grade resource was discovered, however this was
not considered economic at the time. Another phase of
exploration began in 2002 and significantly added to the
resource to the south under a lithocap up to 200 m thick.
The deposit is associated with a series of tonalite porphyry
intrusions that are hosted by andesitic volcanics (Maula
& Levet, 1996). The geology and alteration are shown in
Figures 2a and 2b, respectively. Mineralisation is associated
with potassic alteration (chlorite-magnetite±biotite)
which grades outward to propylitic alteration. This system
is overprinted by intermediate argillic alteration and an
advanced argillic lithocap, up to 200 m thick, covers much of
the deposit.
The Elang area was covered by an airborne magnetic survey
in 1993 and with ground magnetics and Gradient array
IP/resistivity surveys at about the same time. Pole-dipole
IP/resistivity surveys were conducted from 2003 to 2005,
HoisTEM and NewTEM were flown in 2004 and an
airborne magnetic and radiometric survey in 2012.
Magnetic Response
A helicopter magnetic and radiometric survey flown by
Newmont in 1993 covered a large part of SW Sumbawa,
including the Batu Hijau and Elang areas. The survey was
flown in an east west direction with 200 m spacing between
flight lines. A more recent survey was completed in 2012
with 100m spaced north south lines.
Figure 1. Location of Elang on SW Sumbawa
In the 1993 survey Elang shows up as a discrete magnetic
high of about 700 nT within a magnetically quiet area. The
better resolution of the ground magnetic survey and the
2012 airborne survey shows two discrete highs (Figure 2c).
The magnetic highs are due to magnetite associated with
the potassic alteration zone of the mineralised tonalite
porphyries. This contrasts with a broader zone of magnetite
destructive clay alteration. The low between the two
magnetic bodies is probably due to a less magnetic late
tonalite intrusion (the Echo Tonalite).The larger southern
body lies under the lithocap at a depth of up to 200m
depending on topography.
The magnetic data were inverted in 3D and the potassic
zone, as determined by drilling, correspond well to the zones
of high magnetic susceptibility in the inversion model.
Magnetic susceptibility measurements on drill core confirm
that the mineralised potassic zone is moderately to highly
magnetic.
Electrical Response
IP surveys
Gradient array IP/resistivity surveys were conducted over
Elang with a line spacing of 200 m and an electrode spacing
of 50 m. There are strong chargeabilities associated with the
1. Consulting Geophysicist, Perth, WA Corresponding author: terry.hoschke@gmail.com
2. PT Newmont Nusa Tenggara East Asia: Geology, Exploration Technologies and Mines - Bali 2013
35
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Geophysics of the Elang Cu-Au Porphyry Deposit, Indonesia, and Comparison with Other Cu-Au
Porphyry Systems
Elang alteration system and a corresponding resistivity low.
The lithocap was not detected in this survey.
Pole-dipole IP surveys conducted between 2003 and 2005
covered the deposit and surrounding alteration system. The
line spacing was 100 m or 200 m with a potential electrode
spacing of 50 m reading to N=10. A 3D inversion was
applied to the lines covering Elang.
Very strong chargeabilities are associated with the porphyry
alteration (Figure 2d). The limit of disseminated pyrite
(sulphide shells of Lowell and Guilbert, 1970) is well
defined, and drilling confirms a strong chargeability high on
the eastern side of the survey is due to the pyrite shell of the
porphyry system. A chargeability low immediately to the
east of the deposit relates to a late dacite intrusion. Some of
the more subtle lows may be due to late intrusive phases that
are less mineralised.
chargeabilities both in the ore zone and the pyrite halo.
There is a broad resistive low due to clay alteration and
sulphide veining which is not uncommon in porphyry
systems.
References
Ball, R., 2011. Newmont Mining Corporation Presentation, CIBC Annual
Instutional Investor Conference, Whistler, B.C.
Lowell, J. D. and Guilbert, J.M., 1970. Lateral and vertical alterationmineralization zoning in porphyry ore deposits, Economic Geology 65:
373-408.
Maula, S. and Levet, B.K., 1996. Porphyry Copper-Gold Signatures
and the Discovery of the Batu Hijau Deposit, Sumbawa, Indonesia,
in Australian Mineral Foundation, eds., Conference on Porphyry
Related Copper and Gold Deposits of the Asia Pacific Region: Cairns,
Australasian, August 12-13, 1996, Proceeding, p.8.1-8.13.
The resistivity data clearly show the extent
of the alteration system (~3km x 2km) with
the porphyry alteration being relatively
conductive at 10s of ohm-meters in a
background of fresh volcanics in the 100s of
ohm-meters. The highly resistive lithocap of
1000s of ohm-meters is well defined and the
conductive zones are due to clay alteration
and/or sulphide veining. Chalcopyrite
veining in the potassic zone appears to be
extensive and is probably a good conductor.
This zone is generally too deep to be seen
with the pole-dipole resistivity.
Airborne Electromagnetics
HoisTEM and NewTEM surveys were
flown over Elang in 2004 and show
similar results.
The Elang alteration system clearly shows
up as a NE trending conductive zone in
relatively resistive volcanics. The leached
cap is highly resistive and is clearly
identified by the HoisTEM. There are
other conductors in the area that may
represent alteration zones and there is
a conductive sedimentary unit on the
western side of the area.
Conclusion
Elang is typical of a number of Cu-Au
porphyry systems in that magnetite
is associated with mineralisation and
produces a strong discrete magnetic
anomaly. It has a larger potassic zone
than most systems, which may be due
to more than one porphyry centre. The
Elang system is more pyrite rich than
many porphyries, leading to very strong
Figure 2. Plans showing the geological and geophysical character of the Elang deposit. (a) Elang
geology from mapping and projected from drilling. (b) Alteration.(c) Airborne magnetics – RTP
(2012 survey). (d) Chargeability surface 200m below topography (from 2002-2004 surveys). The
0.3% Cu shell as defined by drilling is outlined in blue.
36
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Controls on high-grade Au ore-shoots: Towards a New Paradigm
J. M. A. Hronsky
Controls on High-grade Au Ore-shoots:
Towards a New Paradigm
J. M. A. Hronsky1
Recent industry challenges associated with the development
of large, low-grade deposits have once again highlighted
the critical role of grade in profitable gold mining. For
this reason and also because much gold exploration is
increasingly focused at depth in known camps, it seems
clear that a robust process understanding of controls on
the irregular distribution of high-grade ore-shoots within a
deposit should be an industry priority.
Interestingly, the current structural targeting paradigm
relating to this topic is seldom explicitly articulated, let alone
challenged. Despite this, it has a strong influence on current
approaches to near-mine targeting. This paradigm recognises
(correctly) that well-mineralised rock volumes represent sites
of anomalous ore-fluid flux. However it implicitly assumes
these anomalous volumes represent localised more dilatant/
permeable rock volumes embedded within a surrounding,
larger-scale, less focused fluid flow system and that they
are generated by dynamic syn-ore deformation (eg Ridley,
1993). Based on the above assumptions, it is assumed that
knowledge of deposit structural geometry and inferred
syn-ore stress field can be used to predict the kinematics of
these structures and hence anomalous dilational sites. This
framework also implies that localised mineralised volumes
hosted by structures such as faults and shear zones are
intrinsically a property of these structures.
The primary problem with this existing paradigm is that
although individual examples of a close association between
mineralisation and inferred dilatant geometries can be
demonstrated, this is not a consistent predictive relationship
and the concept fails in many deposits (eg Lancefield
gold deposit, Hronsky, 1993; Cracow gold Deposit, Mickelthwaite, 2009).
It is proposed here that the solution to this problem is
provided by fundamentally changing our perspective on the
physical relationship between ore-shoots and the fluid flow
systems that host them. Hronsky (2011) proposed that most
ore deposits can be considered as forming in transient fluidexit conduits, associated with the episodic rupture of overpressured reservoirs at depth.
Fluid Exit Conduits are rock volumes that have been
conduits for large amounts of fluid flux, usually over multiple
cyclic events. They represent zones of localized intense
fracturing and extreme crustal permeability. They are
sourced from an overpressured reservoir zone at depth and
are formed when a fluid pressure pulse breaks its way to the
surface, taking the easiest path. This path of least resistance
may involve the reactivation of existing structures but in
many cases results in the formation of pipe-like fracture
zones in previously intact rock. Stress changes associated
with these fluid pulses are large and overwhelm the effect
of the ambient stress field. This is the primary reason for
the predictive failure of the existing paradigm as ore-shoots
are constrained to be restricted to these fluid-exit conduit
volumes, which will have geometries not predictable by
traditional structural analysis.
An important implication of this new perspective is that
fluid conduits may be much more vertically-extensive
features than the pre-existing structures which host them.
A single fluid conduit may move between host structures
as it propagates upward, depending on which pathway
provides the path of least resistance. This may result in
them following quite torturous paths from source to sink,
including right-angled bends in three dimensions.
The key control on conduit localisation (and hence ultimately
ore-shoot location) is the rheological structure of rock mass
above the source reservoir – what is the easiest path upward
for the fluid pulse? In this context, ore-hosting fault and
shear zones are effectively just another rock type. Usefully,
from a predictive perspective, it is clear that some geometric
patterns of rock rheological distribution are consistently
more favourable. One of the most notable of these is where a
steeply-oriented pipe-like volume of more brittle rock occurs
within a weaker wallrock sequence. In this situation, the
brittle pipe behaves like a “lightning rod” and commonly is
preferentially used by the propagating fluid pulse.
Ore-fluid conduits can be divided into two types, with
important implications for near mine targeting. Type
1 conduits occur as pipe-like stockwork bodies, and
are typically associated with large, coherent bodies of
mineralisation of relatively uniform but generally low, grade.
Porphyry-related stockwork deposits are a good example of
Type 1 conduits but they also occur in other ore styles. Type
1. Western Mining Services and Centre for Exploration Targeting Corresponding author: Jon.hronsky@wesminllc.com
37
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J. M. A. Hronsky
2 conduits form complex, linked,
vein arrays, which host local,
smaller, discontinuous lenses of
mineralisation (“ore-shoots”).
In this conduit type, individual
ore-shoots can be much highergrade than background parts
of the host vein system. Most
Low-sulphidation Epithermal
and Orogenic Gold deposits are
hosted by Type 2 conduits.
Type 1 conduits are associated
with the failure of previously
intact rock whereas Type 2
conduits are associated with shear
Figure 1: An example of application of the hierarchical framework of ore-shoot controls proposed in this
failure of pre-existing planes of
model– Mararoa Reef at Norseman. (Diagram modified after Campbell, 1990)
weakness. In the case of Type
2 conduits, ore-deposition is
heterogeneous along the conduit
this reason, exploration must focus on the conduit system,
zone, related to locally enhanced dilation and associated
rather than the immediate local host structure. For example,
pressure drop. This occurs because of the affect of the shear
in a system dominated by near-surface, flat-dipping orecomponent on local structural heterogeneities along the host
hosting structures, there must somewhere be more steeply
structure (ie local “dilational jogs”). Importantly, these local
oriented feeder conduits that bring in fluid flow from depth
dilational volumes are not sites of greater fluid flux than
and these should be a near-mine exploration target.
adjacent segments of their host conduit – instead they are
simply volumes of greater mineral (commonly dominantly
Type 2 (ie Shear zone-associated) conduits will host local
quartz) precipitation. These local heterogeneities represent a
zones of dilatancy and hence are more likely to host local
lower-order scale of control on ore deposition that is absent
higher-grade shoots. In contrast, Type 1 conduits (eg
from Type 1 conduit systems
stockwork zones) will not host local zones of anomalous
From a process perspective, the critical difference between
Type 1 and Type 2 conduit systems is whether fluid-driven
failure is purely extensional (Type 1) or has a shearcomponent (Type 2). It is proposed (following Cox, 2010)
that these different states of fluid-pulse propagation depend
on the ratio of lv (pore-fluid pressure factor) to differential
stress (s1-s3), and that this, in turn, relates to factors such
as paleodepth, fluid pressure (bigger systems more likely
to manifest as Type 1 conduits) and distance from parental
intrusion.
There are a number of important practical implications of
this revised perspective on hydrothermal ore emplacement.
Because all deposits need to form as part of a fluid conduit
system that connects an underlying fluid reservoir with
a near-surface sink zone, exploration needs to focus on
tracing the fluid conduit system (through barren segments)
downward beneath known ore-shoots and prioritising these
volumes for further follow-up exploration. Developing
techniques for recognising such barren linking segments
is therefore an important objective. For example, relatively
subtle alteration in the plane of the lode may be much more
important than stronger alteration elsewhere.
Because the expected vertical extent of the fluid conduit
system is commonly much greater than individual host
structures, we predict conduits will use multiple structures at
different vertical levels as they propagate to the surface. For
dilatancy (at a relevant scale) and therefore will always be
more uniform in grade, forming pipe-like ore volumes.
Importantly for exploration, a Type 2 conduit that hosts
one localised high-grade ore-shoot volume is very likely
to host others. However, these may be separated by barren
segments of the host conduit zone. When targeting these
deeper extensions in Type 2 conduit systems, it is important
to separate out conduit-scale from localised ore-shoot-scale
plunge controls; exploration should focus down the plunge
trend of the conduit not the localised ore-shoot.
The key geological element for targeting in the near-mine
environment is localised rheological heterogeneity (in 3D)
because this is what overwhelming controls fluid conduit
emplacement. Therefore near-mine geology must always be
characterised with reference to rheology (note that in this
context, pre-existing shear zones are really just a special type
of weak rock).
It is important to establish the geological process which
defines the base of an ore-shoot – this will determine follow
up exploration strategies. For example, if the base of the oreshoot is related to the termination of a local dilational zone,
the exploration implications are very different from the case
where the termination is related to the fundamental base of
the zone of ore deposition.
Ore-shoots can be hosted by all pre-existing structures not
just the latest “syn-ore” ones; therefore the age of the host
38
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structure is not necessarily the age of mineralisation (as has
commonly been assumed in the past).
In summary, in the 21st Century, rather than the more
traditional “structure-centric” conceptual approach, a “fluidcentric” alternative is advocated for near-mine targeting. This
approach has very important practical implications and has
the potential to contribute to the more efficient discovery of
high-grade gold ore shoots.
References:
J. M. A. Hronsky
Hronsky J.M.A., 1993. The role of physical and chemical processes in
the formation of gold ore shoots at the Lancefield deposit, Western
Australia. PhD Thesis (unpubl.), University of Western Australia. 205p.
Hronsky J.M.A., 2011. Self-organized critical systems and ore formation:
The key to spatial targeting? Society of Economic Geology Newsletter,
Vol. 84, 14-16.
Micklethwaite S., 2009. Mechanisms of faulting and permeability
enhancement during epithermal mineralisation: Cracow goldfield,
Australia. Journal of Structural Geology 31, 288-300
Ridley J., 1993. The relations between mean rock stress and fluid flow in the
crust: With reference to vein- and lode-style gold deposits. Ore Geology
Reviews 8, 23-37
Campbell J.D., 1990. Hidden gold – The Central Norseman story. AusIMM Monograph 16
Cox S.F., 2010. The application of failure mode diagrams for exploring
the roles of fluid pressure and stress states in controlling styles of
fracture-controlled permeability enhancement in faults and shear zones.
Geofluids 10, 217-233
l
keynote
39
Ramping-up Exploration Value from Aeromagnetic Surveys – More Geological Input Needed!
David Isles
Ramping-up Exploration Value from Aeromagnetic
Surveys – More Geological Input Needed!
David Isles
Aeromagnetic data can add a vast amount of geological
information to a project area. The process of integrating
aeromagnetics with geology, satellite imagery and
radiometrics to produce ‘working project maps’ is
straightforward: it is really an extension of the geological
mapping process and the tasks involved closely parallel
those used in conventional geological mapping. However,
we frequently encounter high quality aeromagnetic data
sets that are very poorly integrated with geology and other
project data. This is partly due to inexperience in working
with the aeromagnetics, partly due to inadequate allocation
of (geologist’s) time to the integration task and partly
due to a pre-occupation with quantitative geophysical
interpretation tools.
High quality acquisition and detailed survey specifications
are the norm in the airborne magnetic industry, and a range
of very good options is readily available for filtering and
image enhancement. Most surveys flown yield excellent and
appropriate imagery for interpretation, and the re-use of ‘old’
(post 1970s) survey data is also made easy by robust software
for stitching and merging new and old surveys. Our ability
to gather, process and present data is very well developed,
but our tendency is to lose momentum after the ‘pretty
pictures’ have been produced. While there are strategies
for optimising the data processing and presentation stage
to give interpreters the most appropriate imagery in the
shortest possible time-frame, these do not cause substantial
improvements to the final, integrated interpretation.
The key ingredients that lead to high quality, high value
interpretation are geological thinking and time.
Aeromagnetic images depict the (3-D) distribution of
magnetic minerals in the Earth’s crust. Almost all rock
types contain sufficient magnetic mineral to be ‘seen’ in a
modern aeromagnetic survey (concentrations of 0.001%
magnetic mineral are usually readily detectable). The
magnetic ‘signature’ of a rock unit will be influenced not only
by its original composition and environment of formation,
but also (and often predominantly) by subsequent events
like diagenesis, metamorphism, alteration and weathering.
Astute interpretation can ‘read’ some or all of these processes
from aeromagnetic imagery. The uniformity of survey
sampling and the very frequent continuity of ‘magnetic
rock units’, also provides the interpreter with a geometric
framework on which structural interpretation can be based.
We ‘know all of this’ but often find the task of integrating
a high quality set of aeromagnetic imagery and the best
available geological information daunting. Where do we
start?
The Integration Process – Layers
In exactly the same way that geological mapping begins,
aeromagnetic interpretation starts with a quite basic
set of factual observations. We observe and record the
locations, shapes and sizes of magnetic rock units and
we record pattern discontinuities and trends in much
the same way as is done for aerial photography. We
produce a ‘factual’ observation layer that can then be
directly compared to available geological information,
be it factual or interpretive. This leads to a period of
integration which very often involves resolving conflicts
between the geophysical and geological data. ‘Successful’
integration is usually a slow and painstaking process. It
requires the best possible local geological input and an
understanding of the way aeromagnetic ‘signal’ relates to
the magnetic mineral distribution in the subsurface. It
does not require sophisticated software, or indeed any
software, if the interpreter so chooses. The outcome of the
integration process is a ‘solid geology layer’ that depicts
‘what rocks are where’ and identifies the main fault and
fracture patterns. This benefits from further geological
interrogation, to consider such things as deformation styles,
timing relationships and alteration, metamorphism or
mineralisation events.
Our third layer in the process is then an integrated,
interpretive solid geology. There are many possible
extensions and embellishments of this interpretive product
including 2-D and 3-D magnetic modelling, production
of geological cross sections and integrated 3-D or even
4-D geological models. None of these can be effectively
done before the basic, qualitative process of integrating the
aeromagnetic imagery and the geology has been solidly
preformed. There no shortcuts!
1. Southern Geoscience Consultants, Belmont, WA Corresponding author: david.isles@sgc.com.au
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Golden Dyke Study Area
The Golden Dyke example illustrates this integration
process in a situation where outcrop is very good, expression
of geological features in aerial photography is very good and
the area has been well mapped by experienced geologists.
The integration of a small amount of aeromagnetic data
(200m line spacing amounting to less than 400 line km
over a study area of 7km x 10km) in this low grade metasedimentary environment would not be expected to add
much to the geological picture- but it does!
David Isles
extraordinary intensities and may not appear ‘anomalous’
in the geophysical sense, but when integrated with the
geology they are very clearly ‘geologically anomalous’.
- There are two ‘alteration zones’ definable from their
magnetic character.
1. The ‘fuzzy’ magnetic zone in the SW part of the
Golden Dyke Dome has a central coherent magnetic
low, and looks like a ‘doughnut’. Visual inspection
of the aeromagnetic images and consideration of the
geological context allows us to propose the nature
Figure 1 shows the mapped geology
and one of the main images used in
the observation and interpretation
process. In this study, a set of five
key images provided all of the
necessary aeromagnetic information.
The observation layer is seen as a
somewhat messy collection of lines,
polygons, measurements and notes.
It is very similar to a geologist’s field
notes and is indeed the record of
our ‘field trip’ to the aeromagnetic
imagery. The observation layer
is the fundamental initial step in
assembling a high quality, high value
interpretation. Without this step we
run the risk of overlooking much of
the subtle information that is often
crucial to understanding geological
and mineralising processes.
The integrated interpretation
incorporates an assessment of
the regional context, both from
published geological studies and the
expanded aeromagnetic coverage. It
looks, at first glance, very similar to
the geology map. We expect this
because the geology is well exposed
and well mapped. On closer
inspection we find a range of quite
important additions sourced from
the aeromagnetics.
- the recognition of magnetic
stratigraphic marker horizons in
three of the sedimentary units
greatly expands our view of the
folding and faulting. The clearer
and more detailed structural
picture is invaluable in the
assessment of the area for gold
potential.
- localised magnetic units in key
structural and stratigraphic
locations constitute exploration
targets. These do not have
Figure 1. Geology, aeromagnetic image, aeromagnetic observations and integrated interpretation over
the Golden Dyke area, Pine Creek Inlier, NT. The area is 7km x 10km. Geology from the published
‘Batchelor-Hayes Creek’ 1:100,000 scale map, aeromagnetics from the GADDS portal (both sourced from
Geoscience Australia) and all images from Isles & Rankin, ‘ Geological Interpretation of Aeromagnetic
Data’ (in press).
41
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of the magnetic mineral distribution and the likely
(alteration) mechanism that caused it. We do not
need modelling or inversion to do this.
2. The quite subtle zone of decreased magnetic intensity
NW of the Golden Dyke Dome (around the Sandy
Creek alluvial workings) is not an outstanding
feature of the image in figure 1, nor in most of the
other images used for the interpretation, but it is
consistently identifiable and when considered in its
geological (especially structural) context it is likely to
be a zone of ‘magnetic mineral destruction’.
The new features added from our integration of the
aeromagnetics sharpen our focus at the exploration targeting
stage. The localised magnetic (geological) anomalies and
the alteration zones discussed above are direct and ‘obvious’
target zones, but of equal importance is the refinement
of the structural picture, allowing us to apply structural
models to the targeting process. If we consider targeting
based solely on the (very good quality) geological mapping,
the value of the (very small amount of ) aeromagnetic data
becomes clear.
Mt Leyshon and Bau Districts
Two further examples illustrate the stages of observation and
integration in different geological environments.
David Isles
- The Mt Leyshon gold district is ‘a dog’s breakfast’
both geologically and in the aeromagnetic imagery.
Integration of the two data sets is a daunting task and
one that does not lead to a clear ‘answer’. However, the
increased clarity of structure and intrusive ‘zonation’
advances the targeting process significantly.
- The Bau gold district in Sarawak (East Malaysia) shows
a number of intriguing aeromagnetic features that have
not, as yet, been well explained in the context of the
known geology. Their possible importance in targeting is
conjectural, but addressing the task of integration is very
likely to be a valuable step forward in understanding the
local geology.
Concluding Remarks
Significant value is added to an exploration project by
the integration of aeromagnetics with geology (and other
key data). The integration process is straightforward and
qualitative but it requires good geological reasoning and,
most importantly, adequate allocation of geologist’s time.
The cost of the geologist’s time is small compared to the cost
of aeromagnetic data acquisition. The value added to the
project by the clearer focus in exploration targeting is the
reward for allocation of this time.
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Cu-Au Porphyry System of Atlantis Prospect, Papua Province: A Preliminary Report
Hashari Kamaruddin, Hartono, Ciputra.
Cu-Au Porphyry System of Atlantis Prospect,
Papua Province: A Preliminary Report
Hashari Kamaruddin, Hartono, Ciputra.
Atlantis exploration project is located in the Star Mountains
Range, at the border of Papua New Guinea and Indonesia,
in the Papua Province of Indonesia. Mountain Star is the
southern flank of the Central Mountain Range along the
prospective Papuan Arc Belt.
Tectonically, Papua is situated within the Pacific “Rim
of Fire”. Geological investigation recorded in Mountain
Star was begun by the Dutch agency in 1938 with a gold
exploration program then followed by two yearly programs
in 1959 and 1961. More systematic exploration was
conducted in 1970-1971 by PT. Kenneccot Indonesia with
a regional exploration survey. In 1989, PT Ingold Antares
acquired the concession in the region, covering some of the
Kenneccot survey area. Antam took the tennement in 2008
after PT Ingols Antares return it to the government.
The Atlantis project commenced with a due diligence
program on some of previously Ingold CHECK concessions
in 2008 and literature review and Landsat imagery
study. Indicators of mineralisation were interpreted from
morphotectonic impression by using SRTM, Landsat
and Aster data that allowed the prediction of dilation and
elliptical stocks. Follow-up work included (1) compass
mapping along streams, (2) creek and ridge traverses
documenting with the colour codes “Anaconda” mapping
method (3) ridge and spur soil sampling program and (4)
ground geophysics acquisition data.
The Atlantis Project is situated in the “blank spot interval”
between two remarkable deposits of Grasberg and Ok Tedi,
in the hihgly prospective mineralisation belt of Papuan Arc.
The exploration activities effectively started in the end of
2010 but, unfortunately, had to postpone in the middle of
2012 waiting for forestry permits. The permits are expected
to be cleared-up in the middle of 2013.
1. PT Aneka Tambang (persero), Tbk; Unit Geomin, Jl. Pemuda No. 1, Jakarta Timur Corresponding author: hashari.kamaruddin@antam.com
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43
Imants Kavalieris, Khashgerel Bat-Erdene
Imants Kavalieris and Khashgerel Bat-Erdene
Advanced argillic (AA) alteration forms large tabular zones
(or lithocaps), commonly up to several km in strike length
and >500 m in thickness. Lithocaps are formed from acid
sulfate fluids that may have several origins, including,
1) magmatic-hydrothermal, related to condensation of
ascending magmatic volatiles, and 2) steam-heated hot
spring alteration, from which acid fluids can descend to
deep levels. Similar alteration assemblages, including sulfides
can form in both environments, as shown from geothermal
studies. Especially in older terrains, poorly exposed and
eroded lithocaps are difficult to classify. The main alteration
mapping guides to the origin of lithocaps are 1) vertical
alteration zonation (mineralogy and texture), 2) nature
of the top of the alteration zone (e.g., sinter or fumarolic
deposits), and 3) volcanic-intrusive environment.
Acknowledgements
The authors would like to thank Shawn Crispin, Exploration
Manager of PT Agincourt Resources for permission to use
data from the Martabe Mine. We are also grateful to our
colleagues formerly of PT Intrepid Mines, Adi Maryono,
Andrias Kristianto, Bruce Rohlach, Steve Williamson and
Rachel Harrison for their support and help, during field
mapping at Tujuh Bukit.
References
Moore JN, Christenson BW, Browne PRL and Lutz SL (2002) The
mineralogical consequences of descending acid-sulfate fluids: An
example from the Karaha Telaga Bodas geothermal system, Indonesia.
Proc 27th Workshop of Geothermal Reservoir Engineering, Stanford
Uni California
Reyes (1991) Mineralogy, distribution and origin of acid alteration in
Philippine geothermal systems, In High-Temperature Acid Fluids and
Associated Alteration and Mineralization, Matsuhisa Y, Masahiro A.
and J Hedenquist (eds) Geological Survey of Japan Report, 277: 59-65
1. Alteration Mapping Consultants, Plus Minerals Corresponding author: imantsk2@yahoo.com
44
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David Lawie
David Lawie1
Modern mineral exploration can avail itself of enormous
volumes of data covering a number of disciplines, with
additional data constantly being generated on a daily basis
during active exploration. This data represents information
on ALL the processes that a particular piece of rock or soil
has been exposed to.
The interpretation of this data is reliant on use of models
that describe these processes and the challenge, in a time
poor exploration environment, is to define the processes
of interest (e.g. evidence of a mineralising event) and
separate them from the irrelevant sources, to allow us to
make decisions (e.g. drill another hole or walk away) in an
efficient way. This paper illustrates the process of sorting the
signal (mineralisation) from the noise (everything else) with
examples from exploration geochemistry.
Exploratory Data Analysis (EDA) methods can be utilised
to define for example:
• the process by which a signal related to mineralisation is
present within surficial materials and then test the data
to see if the hypothesis holds, or to
• define processes not related to mineralisation (noise) and
strip them away so that the signal can be more clearly
seen.
These are illustrated in the following examples.
Surface Exploration in Areas of
Transported Cover
The uptake of elements from the subsurface by vegetation
is one method proposed for the vertical migration of metals
through the regolith profile (Aspandiar et al., 2008). Plants
have the capability of taking up metals such as Zn, Mo,
Se, Au, Ni, Cu As and Pb, storing them and ultimately
releasing them to the surface (Aspandiar et al., 2008). The
key to confident interpretation of this pattern is defining,
in advance, that this migration mechanism is likely to occur
and then vector to the source at depth.
A good example that illustrates this process is the work of
Anand et al. (2007), which tested the use of vegetation in
exploring areas of cover in the Yilgarn Craton, Western
Australia. Several types of vegetation samples (i.e. litter,
roots, etc) were collected in combination with soil samples
and then analysed by different methods including total,
partial and selective digests. Anomalous Au, As and Mo
were detected in several plant organs, with the best anomaly
contrast provided by litter samples (Figure 1a, Anand
et al., 2007). By defining the hypothesis and rigorously
testing it, the movement and accumulation of metals
in and by vegetation is demonstrated and so vegetation
can be confidently used as an exploration method in this
environment.
However an alternative approach commonly seen is the
fitting of an “interpreted signal” to data collected without
consideration of process driving the metal movement and
accumulation. This approach often results in incorrectly
fitting the signal to random noise (Figure 1b) and the
consequent failure to detect mineralisation or the incorrect
identification of a false positive.
Recognition and Removal of Processes
not Related to Mineralisation
In complex terrains, simple patterns dominated by the
mineralisation process (signal) are rarely observed. The
challenge then is to identify and isolate this mineralisation
signal from the noise. In other words, our data contains
information about both the background and the anomaly
and we need to be able to separate them. Sources of noise
may include, sampling error, poor program design, analytical
error, but also whatever patterns result from geological
processes unrelated to mineralisation.
A practical example is the analysis of stream sediment data
from the Robb Lake Pb-Zn deposit in North-Eastern
British Columbia (data from Jackaman, 2008). EDA
commonly starts from the simplest observations, in this
case by identifying and locating anomalous Zn samples
with the aid of univariate plots (Figures 1c and 1d). The
next step in the analysis is to understand if these represent
true Zn anomalies or if there are factors, other than the
mineralization process, that influence the Zn distribution.
For example, adsorption by Fe and different background
1. General Manager – Analyitics, ioGlobal Pty Limited, 369 Newcastle Street Northbridge, WA 6003 Australia. Corresponding author: dave.lawie@ioglobal.net
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David Lawie
Figure 1.
concentrations in different lithologies influencing the Zn
distribution.
A simple scatter plot of Zn vs Fe allows us to quickly
test and confirm whether Fe adsorption is occurring. A
regression analysis of Zn on Fe is then undertaken to
identify Zn residuals (i.e., Zn not controlled by Fe) which
then can be visualised spatially (Figures 1e and 1f ). This
is an example of how the signal (the Zn anomaly) can be
enhanced by removing the noise (Zn related to Fe content).
A similar process can be applied to test if Zn is also
controlled by geology. In this case a regression analysis,
subdivided by geological group, can be undertaken to remove
the effect of geology on the Zn distribution (Figure 1g and
1h). A completely different anomalous population is now
identified compared to just picking the highest values in the
raw data.
References
Anand, R., Cornelius, M., and Phang, C. (2007): Use of vegetation and
soil in mineral exploration in areas of transported overburden, Yilgarn
Craton, Western Australia: a contribution towards understanding metal
transportation processes; Geochemistry: Exploration, Environment,
Analysis, Vol. 7 2007, pp. 267–288.
Aspandiar, M.F. Anand, R. and Gray, D. (2008): A review of mechanisms
of metal dipersion through transported cover: implications for mineral
exploration in Australia; CRC LEME open file report, 246 p.
Jackaman, W. (2008): Regional Stream Sediment and Water Geochemical
Data, Pine Pass (NTS 93O), British Columbia; Geoscience BC, Report
2008-7, 262 p.
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Biogeochemistry and Partial Digest Techniques in Mineral Exploration – a Brief Review
Biogeochemistry and Partial Digest Techniques in
Mineral Exploration – a Brief Review
Evgenia Lebedeva1 and Andrew Riley1
The development of analytical instrumentation has expanded
opportunities for low level geochemistry and its application
in mineral exploration. There is growing interest to such
techniques as biogeochemistry and partial digest. Difficulty
with the interpretation of data from these methods often
prevents people from using them in exploration; however,
these methods could be very useful when exploring blind
or buried mineralization. Such geochemical techniques
combined with ground magnetic surveys, AEM conductivity,
hyperspectral data etc. can significantly improve drill targeting.
Biogeochemistry is particularly useful as a guide to the
underlying geology in areas of transported cover, where the
signature in the vegetation can be better than the soils1. In
arid and semi-arid conditions, due to greater root:shoot
ratios2 in vegetation, roots can penetrate several meters in
depth to reach the permanent water source. For example,
roots of Spinifex have been observed in mine pits at depths
of 30 m and below3. In tropical forests roots can penetrate
up to 18 m deep, while tropical grassland can penetrate
even deeper (up to 68 m)2. There is very limited open data
on biogeochemistry exploration in East Asia. It was found
that species of genera Homalium and Hybanthus were
identified as hyperaccumulators of nickel and can be used
as an indication of nickeliferous (usually ultrabasic) rocks4.
These plants are abundant in Indonesia, in particularly
on Sulawesi and Halmahera Islands. In ultramafic areas,
such as Sabah (Malaysia) and the Philippines, the strong
nickel hyperaccumulator is Phyllanthus balgooyi. For Au
investigations in equatorial regions Astronidium palauense,
a moderate size tree, is widely distributed in the region and
can be successfully used in biogeochemical exploration5. In
the Amazon region (Carajas) geobotanical remote sensing
showed that distribution of vegetation correlated with
variations in geology6.
About 200 published scientific studies on biogeochemistry
in Australia were analysed at Intertek Genalysis. The
majority of studies (46 %) were devoted to identify Au
mineralization. In studies for Au mineralisation the major
plant tissue were leaves and leaflet branchlets (87%), bark
(7.8%), twigs (3.1%) and litter (1.6%). Bark and leaves on
average gave the highest values for gold anomalies. The
most popular species successfully used in exploration studies
Fig.1. Example of samples media that can be collected for biogeochemistry
(leaves, bark, litter and roots) and partial digest (soil).
in Australia are Acacia and Eucalyptus, Spinifex, Tea tree,
Fuschia bush, Monterey pine, Black oak and Cassinia.
Several companies with reports published on the ASX
used biogeochemical sampling techniques to identify drill
targets, to name a few – Australasian Resources Ltd used
vegetation sampling to identify Ni mineralization7, Marmota
Energy Ltd used vegetation to identify U mineralisation8,
PepinNini Minerals Ltd used Spinifex to target Ni/Cu and
base metal mineralisation9, Blaze International Ltd applied
biogeochemistry to target calcrete-hosted and granitehosted U mineralisation10, Cullen Resources Ltd used
vegetation to delineate base-metal mineralisation11.
Partial digest techniques are also used to detect trace
element concentration in the top soil profile, avoiding
complete digest of silicate, iron or calcium-rich minerals.
Complete dissolution of such minerals results in high TDS
(total dissolved solids) content, increasing detection limits
for the trace elements of interest (for example Ag and Au),
which could be associated only with minor fractions (like
1. Intertek Minerals, Jakarta, Indonesia Corresponding author: Evgenia.lebedeva@intertek.com
47
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Biogeochemistry and Partial Digest Techniques in Mineral Exploration – a Brief Review
clay or organic fractions). Partial digests enable preferential
high recovery of these ions in comparison to poor recovery
of ions that are lithologically sourced and more tightly
bound on the mineral surface.
A number of companies have successfully utilised Partial
Digests in exploration. Gold Road Resources utilised partial
leaching techniques over Permian cover in areas with no
previous drilling. The partial leach was performed on -75
micron soil fraction of the top soil profile and this appeared
to be more effective than conventional digest12. Trafford
Resources Ltd successfully used partial digests together
with a geophysical exploration program13 (the soil was taken
within top 20 cm) to identify IOCG (Iron Oxide/Copper/
Gold) target while Investigator Resource Ltd was successful
in utilising partial digest to delineate silver mineralisation14.
References
2. Canadell, J. et al, 1996. Maximum rooting depth of vegetation types at
the global scale. Oecologia, 108, pp. 583–595.
3. Reid, N., Hill, S., Lewis, D., M., 2008. Spinifex biogeochemical
expressions of buried gold mineralisation: The great mineral exploration
penetrator of transported regolith. Applied Geochemistry, 23, pp. 76-84.
4. Brooks, R.R. et al. 1997. Detection of nickeliferous rocks by analysis
of herbarium specimens of indicator plants. Journal of Geochemical
Exploration.
5. Mclinnes, B. I.A. et al. 1995. Biogeochemical exploration for gold
in tropical rain forest regions of Papua New Guinea. Journal of
Geochemical Exploration.
6. Paradella, W.R. et al, 1994. A geobotanical approach to the tropical
rain forest environment of the Carajas Mineral Province. International
Journal of Remote Sensing, Vol. 15, 8, pp. 1633-1648.
7. ASX Announcement 30 July, Australiasian Resources Ltd.
8. ASX Managing Director’s Presentation, Marmota Energy Ltd.
9. ASX Financial Report 31 December 2010, PepinNini Minerals Ltd.
10.ASX Announcement 31 January 2012, Blaze International Ltd.
1. Anand, R.R., Cornelius, M., Phang, C. Use of vegetation and soil
in mineral exploration in areas of transported overburden, Yilgran
Craton, Western Australia: a contribution towards understanding metal
transportation processes. Geochemistry: Exploration, Environment.
Analysis, 7, pp. 267-288.
11.ASX Announcement 28 November 2011, Cullen Resources Ltd.
12.ASX Announcement 22 November 2012, Gold Road Resources Ltd.
13.ASX Announcement 14 March 2012, Trafford Resources Ltd.
14.ASX Presentation 7 December 2012, Investigator Resources Ltd.
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48
Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas,
Sumedang Regency
Sony Malik, Ferdian Haryadi,
Gita Srikandi
Geothermal Surface Manifestation and Alteration
of Conggeang Area, Mount Tampomas, Sumedang
Regency
Sony Malik1, Ferdian Haryadi1, Gita Srikandi2
The research area is administratively
located on Conggeang Distric,
Sumedang Regency, West Java
Province. Physiographically, the
research area is located between
Bogor Zone and Quaternary
Volcanic Zone. Stratigraphy units
of the research area are divided into
three lithological units, from old to
young, i.e., Claystone Unit, Volcanic
Breccia Unit and Andesitic Unit.
Geothermal systems have three
important elements, i.e., reservoir,
fluids, and heat sources. The Geothermal systems in the
research area triggered by volcanic activity associated
with Quaternary volcanism and magmatic intrusion.The
geothermal fluid type is mixing between chloride water
and bicarbonate water. Located in the outflow zones whit
high relief. Reservoir temperature between 200-210⁰C. The
Geothermal systems is flowing through fracture and cause
alteration in the surface of research area that form of sinter
travertine, vein and kaolinite.
Figure 1. Geological map at geothermal research area, Conggeang Area,
Sumedang Regency, West Java.
Regional Geology
According to Bemmelen (1949), physiographically, West
Java region divided into four zone which has west-east
trending, i.e., Jakarta Beach Plain, Bogor Zone, Bandung
Zone, and Southern Mountains Zone. Research area is
located in the boundary between Bogor Zone and Volcanic
Quaternary Zone. Eastern slope of Tampomas Maountain,
also the western side of Arjawinangun Sheet (Djuri, 1973).
Research area is located at high topography with elevation
range 625 – 1.684 meter above sea level. Regionally, research
area has Java pattern stress (Fig 3). There is thrust fault,
dextral strike slip and anticline at the south east of the
research area. Thrust and fold relatively has north westsouth east trending, which occur in Subang Formation and
other sediment tertiary. Young tectonic activity showed by
two trend of fault, north-south trending to north east-south
west (NNE-SSW), which cross cut Tampomas Mountain
volcanic sequence, but both fault not related to any thermal
activities.
Figure 2. Physiographic of West Java, the research area is located at
the boundary between Bogor Zone with Quaternary volcanic zone
(Bemmelen, 1949 in Martodjojo, 1984)
Regional Stratigraphy
Research area located between Arjawinangun and Bandung
sheet. Lithological unit from younger to older are (Fig 4):
1. Alluvial
2. Young Volcano Product consist of lava (Qyl) and
disheveled volcanic rock (Qyu)
1. Departemen Teknik Geologi Insitut Teknologi Bandung Corresponding author: sony.jomul@yahoo.com
2. PT.PERTAMINA East Asia: Geology, Exploration Technologies and Mines - Bali 2013
49
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Sumedang Regency
Gita Srikandi
3. Old Volcano Product consist of lava (Qvl), breccia
(Qvb), disheveled volcanic rock (Qvu).
4. Citalang Formation (Pt), consist of bedding of tufaceous
sandstone, conglomerate, and tufaceous claystone
5. Kaliwangu Formation (Pk), consist of tufaceous
sandstone, conglomerate, claystone, and bedding of
calcareous sandstone
6. Subang Formation, consist of claystone, marl, and
limestone.
Geological Setting
Stratigraphy
There are three lithological units in the research area, which
are Claystone Unit as the oldest rock unit, Volcanic Breccia,
and Andesite as the youngest rock unit.
Figure 3. Regional stress pattern on Java Island, the research area is
located in the Java pattern (modified from Punggono and Martodjojo,
1994)
Claystone Unit
Claystone Unit is composed of Claystone lithology with
intercalation of tuffaceous sandstones. The unit’s appearance
in the field characterized by grey colored claystones,
calcareous, massive, have been undergoes conchoidal
weathering, and can be found nodules in some area (Image
2). According to petrography analysis, claystones in this
unit containing calcite, small foraminifera shell’s shards, and
glass shards. Micropaleontology analysis showed that this
unit was Upper Miocene Aged (N16 - N 18) based on Blow
Biozone (1969).
Volcanic Breccia Unit
Appearances of this unit characterized with volcanic breccia
with intercalation of lava flow and piroclastic. Breccia
with brown color, grain size of gravel to cobble, poor to
medium sorted, angular to sub-angular rounded, clay to
sand matrixed, non-calcareous cement, basalt fragment,
andesite, crystalline tuff, compact, open fabric, poor porosity
(Image 1). Has a spotted claystone matrix with a rounded
to sub-rounded grain shape. According to petrography
analysis, fragments inside the breccia contain crystalline tuff,
pyroxene andesite, and basalt.
Pyroxene Andesite Unit
This unit appearance in the field characterized by bright
grey colored andesite, aphanitic-porphyritic with pyroxene
as fenocryst inside smooth matrix, massive (Image 3).
Based by petrography observation, the andesite that found
in the research area is a pyroxene andesite with plagioclase
microlite dominated matrix.
Geological Structure
Geological structure that existed in the research area is
Cipicung fault and Cikujang fault.
Figure 4. Arjawinangun Stratigraphic
Cikujang Fault
The fault that cut the breccia unit and the claystone unit
observed by brecciation appearance off set contact between
breccia unit and claystone unit. The brecciation that lay on
the Cikujang River’s Cliff heading towards main direction
N 213 E. Based on structural analysis (Fig 6), Cikujang fault
is a right lateral-normal fault with N 330 E/730 strike and
dip fault plane. Cikujang fault contain breccia alteration that
altered to clay mineral.
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Gita Srikandi
Cipicung Fault
Cipicung fault at Cipicung River observed
based on shear appearance on the riverside.
Beside, fault existence can be shown by the
offset contacts between claystone unit and
breccia unit with an approximately 10 meters
long so the fault cut the claystone unit and
breccia unit. Apart from the existence of shear,
there is also N 93 E brecciation trending. Based
on structural analysis (Fig 6), Cipicung fault
is a right-lateral-normal fault with N 95 E/58
strike and dip fault plane. Similarly as Cikujang
fault, Cipicung fault also contain breccia
alteration that altered to clay mineral.
Geothermal System
Geothermal system has three important
elements which are: reservoir, fluid, and heat
source (Goff and Janik, 2000). Characteristic
from this geothermal system’s elements
determined by water-chemical analysis from
three water samples that taken from the field,
those are: Cipanas 1, Cipanas 2, and Cileungsing which are a
hot water manifestation from the geothermal system around
the research area.
Figure 5. Mudstone unit profile at Cikujang River, indicate a change in
lithology and sedimentary patterns due to changes in the environment
Geothermal Fluid Type
Based on Cl, SO4, and HCO3 anion, hot water type in the
research area is a chloride-bicarbonate and bicarbonate
(Figure 8). Cipanas-1 sample derived from seepage along
Cipanas River that coming out through a fracture at
the volcanic breccia. Cipanas-1 hot water is dominated
by HCO3 anion (bicarbonate). Cipanas-2 classified as
a bicarbonate water (HCO3) that dominated by HCO3
anion. Cileungsing’s water sample classified as a chloridebicarbonate because the water consist a higher chloride
concentration which is 635.30 mg/L compared to HCO3
(519.50 mg/L) and SO4 (2.22 mg/L). Cileungsing’s hot
water is predicted derived directly from the geothermal
reservoir under the surface although it is affected by HCO3
(bicarbonate) and sulfate (SO4) ion.
Reservoir and Source
Relatively higher Cl concentration compared to Li and B
(Fig 9) showed that the hot water in the research area came
from the same reservoir and affected by volcano-magmatic
activity. And the high concentration of Mg-44 to 60 ppm-in
the research area showed that there been a mixing between
geothermal fluid and ground water near the surface.
Figure 6. The kinematics analysis and faults dynamic that show common
patterns of fault is dextral-down and down-dextral in the research area
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Gita Srikandi
Hot Water Flow Pattern
Bicarbonate water type that present showed that the fluid
reservoir had been condensed and mixed with surface water.
This thing indicate that the hot fluid undergo lateral flow
(outflow zone). Figure 9 shows that the hot water in the
research area contains high Cl concentrate compared to
B and Li. This thing shows that the hot water affected by
volcano-magmatic activity. Comparison of Na/K and K/
Mg that showed by Fig 10 indicate that three of the spring
is inside the outflow zone. By that we can conclude that
in this area occur a reaction between hot water, ground
water, and rocks near the surface. According to Hochstein
and Browne (2000), volcanogenic manifestation which
present in the geothermal system is highly affected by
reliefs and topography of the volcano (Fig 11). At the top
of area, manifestation that present can be a fumarole and
solfatara that consists uncondensed steam and gas. Beside,
manifestation that could possibly present is sulfate spring
which is a result from a steam condensation that mixed
with shallow meteoric water so H2S oxidized become
H2SO4. Chloride water is located deeper than sulfate water
(Hochstein and Browne, 2000). Because of the topography
and hydrology gradient chloride spring usually found far
from the heat source and the main reservoir. Thus, on the
geothermal system in the research area is a high relief in
a form a mountain range, chloride water will be found in
the outflow zone, not in the up flow zone like a plain relief
geothermal system. Conceptual model that describe the
emersion of surface manifestation can be used as a reference
to knowing Tampomas Mountain’s geothermal system.
Surface manifestation present in Tampomas Mountain
foothill took form in a bicarbonate and chloride-bicarbonate
hot spring at the outflow. Referring to the conceptual
model, chloride water that came directly from the reservoir
is possibly located in Tampomas Mountain foothills which
has lower elevation and farther than the peak. Thus, to get
chloride water sample that directly came from the reservoir
and haven’t mixed with the ground water can be done in the
foothills.
Image 1. Breccia vulcanic unit at side of cipanas stream, poor sorted
Image 2. Claystone unit
Manifestation location that took form of warm-chloride
water spring might be located a few kilometer from the
warm water manifestation that being currently observed.
Hot Water Isotope
This study is only observes a stable isotope concentrate.
Stable isotope that generally used in geothermal study is
hydrogen isotope (1H, 2H or D-deutrium), carbon (12C,
13C), oxygen (16O, 18O), and sulphur (32S, 34S). Those
isotopes used for knowing the processes or the origin of
water or gas. δD content on geothermal fluid is the same as
δD that consist in meteoric water. On the other hand, the
value of δ18O on geothermal fluid will be more positive
compared to meteoric water (Craig, 1956; Craig, 1963 in
Nicholson, 1993). Alteration of δ18O value is caused by an
exchange reaction with a heavier isotope.
Image 3. Andesite stone unit
Some of the isotope value shows that magmatic-fluid
contribution on geothermal fluid is minor (5 to 10 percent
from total) while the rest derived from meteoric water.
The effect of magmatic fluid will show geothermal fluid
δD value will not be the same with meteoric water δD
value (Nicholson, 1993). Stable isotope that used for warm
water sample in the research area is D-Deutrium and
18O. Both isotope values are used to finding out that the
52
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Sumedang Regency
Gita Srikandi
Figure 7. Map of sampling location
hot fluid in the geothermal system in the research area is
derived from meteoric water or magmatic fluid. Based on
deuterium isotope and Oxygen-18 value (Table 2), all three
of the hot spring located around the blue line which is a
global meteoric water line (Fig 12). This shows that the
geothermal system at Tampomas Mountain recharge from
meteoric water.
Geotermometer
Geotermometer is a method to calculate fluid temperature
in the reservoir. Geotermometer that used were adjusted
with character of the geothermal system. Reservoir fluid
temperature has error tolerance up to 10⁰C. Based on
temperature, the geothermal system can be divided into
three categorize, those are: high temperature geothermal
system (T ≥ 2500C), medium temperature geothermal
system (T=125-250⁰C), and low temperature geothermal
system (T ≤ 125⁰C).
High temperature geothermal systems generally associated
with volcano activity. Temperature can reach ≥ 2000C
(Hochstein and Browne, 2000). Thus, geotermometer
that suitable with high temperature is K-Na geothermal
and Si02, because the geotermometer is valid with high
temperature condition (Nicholson, 1993). Formulas for the
calculation of K-Na geotermometer are:
toC = 1217/ [log (Na/K) + 1.483] – 273 (Fournier, 1979 in
Nicholson, 1993)
toC = 1390/ [log (Na/K) + 1.750] – 273 (Giggenbach, 1988
in Nicholson, 1993)
The geotermometer have some limitation, those are:
1. Used for water that has >180 0C reservoir temperature.
Image 4. A. Cipanas-2 Warm Pool B. Cileungsing Hot Pool C. Springs
2. Used if water contain low Ca based on the calculation
(log (Ca1/2 / Na) + 2,06) and the result is negative.
3. Used to chloride water approach neutral pH.
Silica geotermometer used were adiabatic quartz
geotermometer and conductive quartz. The formulas for this
two geotermometer are:
Adiabatic Quartz (Maximum Steam Loss): toC = 1522/
(5,75-log SiO2) – 273 (Nicholson, 1993)
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Sumedang Regency
Gita Srikandi
Conductive Quartz (No Steam Loss): toC =
1309/ (5,19-log SiO2) – 273 (Nicholson, 1993)
Quartz geotermometer is useful for the > 1500C
reservoir temperature condition. For example
geothermal system that were triggered by
magmatic activity. This geotermometer also have
some limitation, those are:
1. Adiabatic quartz geotermometer useful for
well and boiling hot spring or pond with ≥ 2
kg/s water discharge especially 50 that have
sinter silica. Maximum temperature has been
calculated by this geotermometer for spring
manifestation is ~ 2100C.
2. Conductive quartz geotermometer useful for
sub-boling temperature spring.
Hot water type that can be used for
geotermometer calculation is chloride water type
(Cl), because chloride water has pH of about
neutral which has the best condition to shows
the reservoir condition. In the research area,
geotermometer only used for Cileungsing hot
water, because that area is the only place which
has Cl anion dominated rather than HCO3 and
SO4 anion.
Table 1. The results of chemical analyzes of water sampling Cipanas-1, Cipanas-2
and Cileungsing
Based on geotermometer calculation, the
temperature we got are about 200-2100C
from K-Na geotermometer and 1050C from
conductive quartz geotermometer. And based
on some K-Na geotermometer requirement,
with (log (Ca1/2/Na) + 2,06) = -1,9 and silica
geotermometer, the most suitable geotermomter
is K-Na geotermometer with 200-2100C
reservoir termperature. Thus, fluid reservoir
temperatures at Tampomas geothermal system
are about 200-2100C.
Surface Alteration
Alteration in the research area can be found
at Cipanas River and fault zone. At Cipanas
River, the alteration existed around hot water
manifestation, especially at the edge of fracture
which hot water coming through. At the fault
zone, alteration in a form altered matrix and
fragment volcanic breccia. Matrixes altered
become white and bluish grey colored clay
mineral.
Hot Water Seepage at Cipanas River
Figure 8. The type of geothermal fluid is water mixturing between chloride water
with bicarbonate water
Hot water seepage around Cipanas River were
associated with fracture existence at Volcanic
Breccia Unit (Image 5). This seepage caused the
breccia were undergoing altered, not only at the
surface but also in the matrix and its fragment.
Unlike the other breccia, this altered breccia
54
l
Sumedang Regency
Figure 9. Comparison of B, Li and Cl indicate warm water in the
research area associated with the activity
Gita Srikandi
Figure 10. Comparison of the relative content of Na-K-MG showed
warm water in the research area is an immature water
Figure 11. Conceptual Model geothermal system triggered by andesitic stratovolcano
Table 2. Isotope values of detrium and oxygen-18
55
l
Sumedang Regency
had some character, those are red colored at the surface that
contact with hot water, also had calcite vein with 0,1-0,5
cm width and 5-20 cm long that filled the fracture and
weak plane between matrix and fragment Breccia outcrop
that found around the hot spring relatively more compact
compared to the other breccia and relatively had close fabric
which contact with hot water.
Hot Pond
Gita Srikandi
Table 3. The temperature of the reservoir based on the calculation of
various geotermometer
Hot pond at Cipanas Riverside form naturally
and left sinter travertine residue (Image 9). This
travertine has white colored, smooth texture, and
lamination shows that the depositional happen
iteratively. Massive and compact is the main
character of this deposit.
Fault Zone Alteration
There is altered rock become white and grey at the
area around fault (Image 10). Those altered rock
consist of variety of mineral, like quartz, albite, analsime, and
kaolinite. Kaolinite existence indicated that altered processes
in acid pH condition (Lawless, 1993).
Alteration and Geothermal Pattern
Altered process that occurred at the research area caused by
hot water coming through along fractures. Those showed
by contact of hot water and made the appearance of breccia
become altered. Whereas alteration pattern at the fault zone
also associated with fracture
that caused hydrothermal flow at the fault zone even though
weren’t found hot water manifestation at the fault zone.
Figure 12. Shows the source of the fluid in the research area derived from
meteoric water
Image 5. A. infiltration of warm water from the river through the cracks
B. Some of the hot springs in the riverbed (G11.14)
Existence of kaolinite mineral at the fault zone indicated
this alteration pattern.
Manifestation and alteration at the research area in a form
sinter travertine and calcite vein. Both of this product
alteration is composed by calcite. The differences between
this two are subsurface formed for calcite vein, while sinter
travertine formed at the surface. Two of this mineral will
form at CO2 rich condition based on the reaction:
Ca2+ + CO2 +H2O → CaCO3 + 2H+
This reaction also showed that calcite (CaCO3) will occur
if Ca2+ rich and react with CO2. Kaolinite is alteration
mineral that formed at acid condition (Lawless, 1993).
While sinter travertine is surface deposit that formed
relatively more alkali condition compared to kaolinite
(Nicholson, 1993). Those two manifestations showed that
there is a change of fluid character at the research area. Acid
conditions become more alkali. Kalonite existence which
Image 6. Calcite veins in volcanic breccia at Cipanas Stream (G11.12)
56
l
Sumedang Regency
Gita Srikandi
occurred at acid pH conditions could cause by condensation
process at the steam zone. Condensation near the surface
caused H2S oxidized became H2SO4 and pH rises. In
addition, kaolinite existence also associated with claystone
lithology at the research area.
Conclusion
1. Stratigraphy at the research area those are Claystone
Unit Upper Miocene aged (N16-N18), Volcanic Breccia,
and Pyroxene Andesite as the youngest rock unit.
2. Geological structure that existed in the research area
is Cipicung right-lateral normal fault and Cikujang
normal fault. This two of fault occurred in one phase of
deformation.
3. Geothermal fluid types are mix of chloride water and
bicarbonate.
4. Research area is an outflow zone. Kaolinite existence also
showed lateral flow and formed at CO2 rich condition at
the atmosphere.
Image 7. Thin section of vulkanic breccia matrix with calcite vein filling
fracture (G11.12)
5. Tampomas geothermal reservoir temperatures are about
200-210⁰C. This high temperature geothermal system
generally associated with volcano activity.
6. Altered process that occurred at the research area
caused by hot water coming through along fractures.
Manifestation and alteration at the research area in
a form sinter travertine and calcite vein. Those two
manifestations showed that there is a change of fluid
character at the research area. Acid conditions become
more alkali.
References
Bemmelen, R.W. van, 1949, The Geology of Indonesia, Martinus Nyhoff, The
Haque, Nederland
Blow, W.H., 1969, Late Middle Eocene to Recent Planktonic Foraminifera
Biostratigraphy. Proceedings First International Conference on Planktonic
Microfossils, Geneva
Hochstein, M. P. and Browne, P. R. L., 2000, Surface Manifestations of
Geothermal Systems with Volcanic Heat Source. In Encyclopedia of xiv
Volcanoes (editor: Sirgudsson, H., Houghton, B., McNutt, S. R., Rymer, H., Stix, J.), Academic Press, San Diego
Image 8. Thin section of travertine sinter deposite on vulcanic breccia
(G11.15)
Lawless, J. V., 1993, Epigenetic Magmatic-Related Mineral Deposits
Exploration Based on Mineralization Model, Kingston Morrison Mineral
Services, Auckland
Martodjojo, S., 1984, Evolusi Cekungan Bogor, Jawa Barat, ITB Press,
Bandung
Muhardjo, Nasution, A., Yusup, R. dan Yuhan, 1985, Laporan Penyelidikan
Geologi Daerah Panasbumi Gunung Tampomas, Kabupaten Sumedang,
Jawa Barat. Volcanology Directorate, Bandung
Nicholson, K., 1993, Geothermal Fluids Chemistry and Exploration
Techniques, Springer Verlag, German
Image 9. Travertine Sinter deposite at side of hot pool (G11.15 location)
57
l
Sumedang Regency
Image 10. Alterated rock at G7.3 location, white colour
Figure 13. Geothermal system model in research area (without scale)
Gita Srikandi
58
l
Porphyry Copper-Gold Mineralization Styles along the Eastern Sunda Magmatic Arc, Indonesia
Porphyry Copper-Gold Mineralization Styles
along the Eastern Sunda Magmatic Arc, Indonesia
Adi Maryono1 and Rachel Harrison2
Porphyry mineralization has played a significant role in
contributing gold, silver and copper endowment to the
1,800km E-W striking Eastern Sunda Magmatic Arc,
part of the 3,940 km-long Sunda-Banda Arc (Setijadji et
al. 2006, Maryono et al. 2012). With a world class goldsilver-copper endowment currently estimated at 92.44
million ounces of gold, 279.17 million ounces of silver
and 61.92 billion pounds of copper, the Eastern Sunda
Magmatic Arc has emerged as one of the most prospective
gold-copper belts in the world. The recently discovered
world-class porphyry deposit at the Tujuh Bukit Project
with 30.1 million ounces of gold and 19 billion pounds
of copper (Intrepid Mines Ltd., 2012) has now joined
two known world-class copper-gold deposits at Batu
Hijau and Elang to confirm the Eastern Sunda Arc as an
emerging, economically important magmatic belt. Other
known porphyry prospects and related epithermal prospects
identified along the belt offer promising future resource
potential.
Three world-class porphyry Cu-Au deposits at Batu
Hijau, Elang and Tujuh Bukit and high sulfidation
epithermal deposits at Pangulir, Sane, Gapit, Sabalong,
Pelangan, Mencanggah and Tujuh Bukit (Oxide Zones) are
tectonically confined to the eastern segment (East Java to
Sumbawa) that was constructed on thinner island arc crust
bounded by Australian continental crust further east in
Sumba and Timor (Hamilton, 1979; Carlile and Mitchell,
1994; Hall, 2002; Setijadji et al., 2006; Maryono et al.
2012). In contrast, the sub-economic porphyry prospects at
Selogiri, Ciemas and Cihurip with dominant low sulfidation
epithermal deposits at Pongkor, Cikotok, Cibaliung,
Cikondang and Arinem occur in the western segment of the
arc (West to East Java) that developed on thick continental
crust on the southern margin of Sundaland.
The whole metal endowment of the Eastern Sunda Arc
is related to the Neogene magmatic stage, one of 5 stages
of magmatic activity identified along the belt. Dating of
mineralization age and/or related intrusion age shows similar
features to the magmatic host rocks where mineralizing
intrusions have been dated as Neogene in age, 3.7 Ma at
Batu Hijau, 2.7 Ma at Elang, 7.5 Ma at Selodong, 2.5 Ma
Figure 1. The Eastern Sunda Magmatic Arc with three world classporphyry Cu-Au deposits discovered along the belt, making it one of
world’s most prospective magmatic belts.
at Pongkor and 3.0 Ma at Arinem (Marcoux and Milési,
1994; Garwin, 2000; Maryono et al. 2005; Roe pers. com,
2012; Yuningsih et al., 2012). This is consistent with the
Western Pacific region where the largest gold endowment
(about 45.1% or 321.2 million ounces) is hosted in Neogene
magmatic arcs (Maryono and Power, 2009). In spite of
similarities to those in typical island arc settings, e.g. the
Philippines, PNG, Solomon Islands and Fiji, porphyry
gold-copper mineralization styles in the Eastern Sunda
Magmatic Arc display some unique characteristics. Coppergold mineralization is spatially and temporally developed
within and around small, multiple, nested, tonalitic porphyry
intrusions (<1km2 with +1km vertical extent) as apophyses
to precursor underlying large, more equigranular texture,
dioritic intrusive bodies (+4 km2). Intrusion ages range
from 2.7 Ma at Elang, 3.7 Ma at Batu Hijau to 7.5 Ma
at Selodong with latest intrusive activity marked by postmineralization diatreme breccia bodies which are developed
at the margin or adjacent to the porphyry systems and
disrupt the mineralized bodies. Host stratigraphy is generally
characterized by Miocene volcanic rocks and associated
volcaniclastic rocks as a volcanic edifice. The volcaniclastic
rock sequence contains thin calcareous sedimentary rocks
and limestone, which form thin skarn mineralization, e.g. at
Elang, Batu Hijau and Tujuh Bukit.
1. PT Buena Sumber Daya, Jl. Radin Inten II No 2, Buaran Duren Sawit Jakarta Timur Corresponding author: adi.maryono@buena.co.id
2. Independent Geologist, Sading, Sempidi ,Badung Bali. Email:racharrison@gmail.com
59
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Porphyry Copper-Gold Mineralization Styles along the Eastern Sunda Magmatic Arc, Indonesia
Hypogene mineralization at the three world-class deposits,
as marked by the 0.3% Cu zones in surface projections
of drill hole data, measures on average more than 1 km
in diameter and around 1km vertical extent. Hypogene
alteration, veining and sulfide mineralization developed
in three main temporally and spatially overlapping events,
termed as Early, Transitional and Late (Mitchell et al. 1998,
Clode et al. 1999, Maryono et al. 2005 and Harrison, 2012).
The gold and copper mineralization is directly related to
quartz veining, classified as “A’,”A-family”, “EDM”/”EB”,
“B”, “C” and “D” of Gustafson and Hunt, 1975, Brimhall,
1977 and Clode et al., 1999 .The copper-gold mineralization
forms an annular or inverted shell that lies within and
around the margins of tonalite intrusive bodies. The Early
“A” veins contain the bulk of hypogene chalcocite, digenite,
bornite solid solution (chalcocite-bornite and digenitebornite) and bornite. These veins are estimated to constitute
majority of quartz veins and copper content in the deposits.
The transitional veins (“B” and “C”) contain chalcopyrite
with minor or trace bornite. Bornite and chalcopyrite are
the dominant copper sulfide minerals which form sulfide
zones, namely a central bornite dominant core, large
chalcopyrite-dominant middle zones and marginal pyrite
shells. Supergene copper mineralization is limited, developed
beneath goethitic leached caps only at Batu Hijau and
Elang. A weak chalcocite blanket averaging 40m thick and
0.5 to 0.7 % Cu has been intercepted in drill holes. The
copper enriched zone measures in excess of 500m by 750m
in plan view with variable thickness and is characterized by
an overlying goethite-hematite leached cap at the surface.
Very thin supergene copper mineralization (0.3 to 0.5% Cu,
10 to 20m thick) has been intersected at Brambang but does
not form a significant chalcocite blanket.
Porphyry mineralization in the Eastern Sunda Arc is
typified by gold-rich porphyry systems with only Tujuh
Bukit having significant molybdenum content (90 ppm)
at 0.2% cut-off. Majority of gold was deposited during the
formation of early “A”, ‘A-family” and “EDM/EB” veins
and is dominantly associated with bornite rather than
chalcopyrite (Clode et al., 1999, Arif and Baker, 2004;
Maryono et al., 2005 and Harrison, 2012). Gold mostly
occurs in bornite-rich ores within copper sulfide grains as
invisible gold and other forms along quartz-silicate grain
boundaries as native gold or free gold. The native gold grains
are generally 1 to 12 µm. Higher free gold abundance
develops in chalcopyrite-rich ore than bornite-rich ore (Arif
and Baker, 2004). It’s similar to other gold-rich porphyry
systems e.g. Alumbrera and Cadia.
(+20 km2) as a product of late alteration events above
porphyry mineralized centers. The large lithocap bodies
have undergone various erosion intensities to expose
porphyry deposits from very shallow or totally preserved at
Hu’u, Brambang and Tujuh Bukit to deeply eroded at Batu
Hijau and Elang. High sulfidation epithermal gold-silver
mineralized systems are developed within lithocap bodies
associated with quartz ledges at Elang, Brambang and Oxide
Zones of Tujuh Bukit to form a telescoped system. Biotite
and shreddy chlorite (chlorite after secondary biotite) are the
dominant alteration minerals in ore-bearing alteration zones.
Actinolite is an important alteration mineral as part of orebearing alteration assemblages along with biotite, chlorite,
oligoclase, k-feldspar and magnetite which develop during
early phase hydrothermal events. Abundant shreddy chlorite,
actinolite and minor or lack of k-feldspar marks notable
differences with regards to alteration at other deposits.
Zones of early alteration contain porphyry vein types “A”,
“EB”/’EDM” and “A-family” with dominant chalcopyrite
and bornite mineralization.
References:
Arif,J. and Baker, T. 2004, Mineralium Deposita; 39, 523-535, Brimhall,
G.H., Jr., 1977, Econ. Geo. 72, 37-59
Carlile, J.C., Mitchell, A.H.G., 1994, Jour. Of Geochemical Explor., 50,
Clode, C.H. et al. 1999, Proc. Pac-Rim Cong, 485-498
Garwin, S., 2002, Indonesian Society of Economic Geologists, Special
Publication 9: 333-366
Guilbert, J.M., Park Jr., C.F., 1986, The Geology of Ore Deposits, W.H.
Freeman and Co., NewYork
Gustafson, L.B. and Hunt, J.P., 1975, Economic Geology 70, 857-912
Hamilton, W.B., 1979, Professional Paper 1078, U.S. Geol. Surv.,
Washington, DC, 345
Hall, R., 2002, J. Asian Earth Sciences, 20: 353-431
Harrison R.L. 2012, MGEI Proc 4, 89-90
Intrepid Mines Ltd, 2012, Intrepid Mines Limited: http://intrepidmines.
com.au/investor-relations/news-and-announcements
Marcoux, E. and Milési, J.-P., 1994, J. Geochem. Explor. 50, 393-408
Maryono, A. et al.2005, IAGI Indonesian Minerals and Coal Discoveries,
Maryono, A. and Power, D., 2009, Maryono et al. 2012, MGEI Proced
4, 23-30, Mitchell et al. 1998
Inter PT Newmont Nusa Tenggara report, 164pp, Newmont Mining
Corporation, 2012, http://newmont.q4web.com/files/doc_presentations/
Diggers & Dealers.pdf
Setijadji, L.D. et al, 2006, Resource Geology 56 (3): 267-292
Ulrich T and Hendrich C.A. 2001, Econ. Geo. 96, 1719-1742
Yuningsih et al. 2012, Resource Geology 62 (2); 140-158
Surface alteration at district to deposit scale is typically
manifested by large overlying lithocap alteration bodies
60
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The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration Zonation,
Surface Geochemical Expression and Paragenesis.
D. Menzies, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick,
G. Morehari, B. Tekeve, B. Alupian, J. Kur, N. Kulinasi,
G. Miam, J. Larsen, D. Peter, P. Golias
The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation
and Alteration Zonation, Surface Geochemical
Expression and Paragenesis
D. Menzies1, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick, G. Morehari, B. Tekeve,
B. Alupian, J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter and P. Golias
Introduction
The Miocene Wafi-Golpu gold-rich porphyry Cu-Au
deposit, and associated epithermal Au mineralisation is
located in the Morobe Province of PNG, and has a currently
published resource of 28.5 million ounces of gold, 9.06
million tonnes of copper and 50.6 million ounces of silver
(Newcrest, 2012; Harmony, 2012). The Wafi Au prospect
was originally discovered in the late 1970’s with the Golpu
porphyry Cu-Au mineralisation uncovered in the 1991, and
later considerably upgraded in size during 2009 (Mueller
et al., 2011). The Wafi-Golpu porphyry Cu-Au system is
bounded by a NE to SW trending fault zone known as the
Wafi Transfer, and intrudes a basement sequence of weakly
metamorphosed well-bedded siltstones and conglomerates
of the Oligocene Langimar Formation (previously
interpreted to be the Owen Stanley Metamorphics). The
Langimar Formation dipping between 50-80° to the E-NE
has been intruded by several copper-gold mineralised
hornblende phyric to feldspar phyric diorite porphyry bodies
(Harris, 2010, 2011) and a late phase pheatomagmatic
diatreme breccia. The diatreme breccia is 800 x 600m in
diameter, bounded by pebble dykes, and is inferred to have
vented due to the presence of accretionary lapilli in layered
bands at surface.
Mineralisation and Alteration Zonation
Four discreet mineralising systems have been identified to
date including: the Golpu porphyry Cu-Au system; the
Nambonga porphyry Cu system; the Wafi Zones A and B
high sulphidation epithermal Au mineralisation; and later
Au-bearing Mn-carbonate veined and Au-rich, As-bearing
pyrite epithermal mineralisation within Link Zone and
Northern Gold Zone. The Golpu porphyry mineralised
system exhibits a concentric alteration zonation consisting
of a K-feldspar rich core (330 x 760m in diameter), grading
out into a biotite–magnetic rich zone (650 x 1000m in
diameter), an actinolite rich zone (640 x 1030m in diameter),
grading out into a chlorite dominated zone. Strong sericite
alteration overprint occurs at the eastern and western edges
of the Golpu porphyry and also centrally within cross
cutting fault/shear zones. The first appearance of actinolite
alteration correlates with the first appearance of chalcopyrite
and is coincident with the 0.1% Cu shell. A zone of intense
silicification and quartz veining occurs on the upper northwestern margin of the Golpu porphyry mineralised system,
where pyrite is dominant over chalcopyrite mineralisation.
This zone also displays minor crenulated and layered quartz
veining exhibiting unidirectional solidification texture
as reported by Seedorff et al. (2005), who proposed this
texture represents the transition between magmatic and
hydrothermal conditions and demonstrates that fluids
accumulated in the apex of a porphyry stock during
crystallisation. The Golpu porphyry Cu-Au sulphide
species have a concentric zonation from a bornite rich core
grading out into chalcopyrite rich then pyrite rich zones.
Au:Cu ratios are typically 0.6:0.9, and in several drill holes
(WR416, WR426) Au has a positive correlation with
observed bornite mineralisation (r=0.21, n=1890). This
relationship is consistent with experimental work by Simon
et al. (2000) who proposed bornite can accommodate one
order of magnitude more gold than chalcopyrite. However,
hand-specimen samples show evidence to suggest that Cu
and Au may have been remobilised in zones of intense
sericite alteration, where chalcopyrite is observed rimming
bornite with appreciable Au grades, a relationship similar
to that reported at Batu Hijau by Arif and Baker (2004). Molybdenite mineralisation is typically found on the
margins and lower portions of the porphyry Cu-Au systems
often associated with potassic alteration within quartzanhydrite veins, and occurs strongly in K-feldspar altered
zones with later sercite overprint. Statistically analysis of
drill core assays demonstrates a strong positive Pearson
correlation between Cu and Au (r= 0.607, n=32653),
a negative correlation between Mo and Au (r=-0.024,
n=32653) and a neutral correlation between Cu and Mo
(r=0.031, n=32653). Similarly the Golpu block model
shows Cu+Au rich zones off-set from Mo-rich zones. On
the south-eastern margin the Golpu porphyry A and B
stockwork mineralisation is overprinted by a telescoped
high sulphidation covellite-enargite-pyrite epithermal
mineralisation and associated advanced argillic alteration.
This high sulphidation epithermal Au-Cu mineralisation
1. Wafi-Golpu Services Ltd. Corresponding author: douglas.menzies@morobejv.com
61
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Plaate B.
Plate A
A. Plate C
C. Plate EE. D. Menzies, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick,
Plaate D.
Plaate A. Sttruccturral em
mpla cem
ment of o G
Golpu and Nam
mbo
ongaa po
orph
hyryy inttrussion
ns asso
a ociatted with left‐ste
eppiing sinistrral faul
f t jogg, sho
owin
ng zon
nation of f blue po
otasssic (b
biotite‐K‐feeldssparr‐
Maagnetitte) to greeen pro
opy liticc altteraation (chlo
orite‐acctinolitte+//‐ ep
pidote) pro
oducce b
by hypeer‐saaline flu
uidss ricch in
n K, Na,, Fe chlorid
des.. Plaate B. IIntrusio
on o
of th
he d
diattrem
me d
due to meteoric incu
ursio
on o
on aa on oveerprint on porrphyyry due
maagm
maticc so
ourcce. Sericitte aalteratio
e to meteoricc draw
w‐do
own
n. De
epossitio
on of chaalco
opyrrite‐‐borrnite
e miinerralissatio
on by b a a lo
ow den
d sityy S‐rrich and Cu‐A
C Au‐b
bearringg ph
hasee, and laaterr molyb
bdenitee byy hyypersalline Fe, K and
d Cll ricch brin
b e as oxoch
hloriide com
mpleexess. Plaate C.. High
H su
ulph
hidaatio n epittherrmaal vugg
v gy siliica‐aalun
nitee‐
pyyrop
phyllite to dickitee‐kaaolinnite altteration
n prroduceed by b an a early
e y + volatile riich eveent rresu
ultin
ng frrom
m the diisso
ociattion
n of H2S0
S 4 tto H
H . A A
latter liqu
uid‐rich
h evventt caarryying Au
u‐Cu
u‐Ass prroducin
ng a a zo
onaation
n fro
om enaargitte‐lu
uzonitee, teenn antite‐tetrraheedriite tto ccove
ellitee (ZZone
e A, B, C
C).
Plaate D. Quaartz‐carrbonatee‐baase meetal + q
quarrtz‐A
As‐p
pyrite‐rrich low
w sulphiidattion epitheermal m
mineerallisattion
n pro
odu
uced
d byy the
e m
mixin
ng o
of preegn
nantt Au
u‐Ass‐Pb
b‐Zn
n beearinng mag
b rbon
nate
e m gmaatic fluiids with bicar
surfacce w
wateers ((Link Zo
one, Noorth
hern
n Zo
one and
d up
pperr Naamb
bongga).
Plaate E. P
Postt minerral tthru
ust ffaulltingg du
uring th
he P
Plioccene (C
Cloo
os eet al., 20
010)) offf‐settin
ng th
he p
porpphyry m
mineeralisattion. FFigu
ure 1. A parrageeneetic mo
odeel fo
or the
t formaatio
on of o tthe Wafi‐‐Go
olpu
u po
orphyrry Cu‐A
C Au min
neraalissatio
on, an
nd h
high
h an
nd low
w ssulp
phid
dation Au minerralissation using fielld o
obse
ervaatio
ons, workk byy (Errcegg ett al.., 1991
1) aand Rya
an aand
d Vigarr (19
999
9), pettrologyy b
9977) and draawing on mo
odeels from SSilliitoe
e (2
2010
0), Corbeett and
a d Leeac h (199
98), Ulrich
h and Maavro
ogeeness by Zha
Z ng et al. (19
(200
08) and
d Li et al. (20012). East Asia: Geology, Exploration Technologies and Mines - Bali 2013
62
l
exhibits a zonation from a vuggy (or residual) quartzalunite bearing core, out to alunite-dickite, dickite-kaolinite
with lesser pyrophyllite and diaspore, then illite-smectite
alteration. Advanced argillic alteration dips to the east, subparallel to dominant bedding, is indicative of a lithological
control to the alteration and mineralisation producing
fluids (Erceg et al, 1991). This style of mineralisation
exhibits sulphide species zonation from enargite-luzonite,
to tennantite-tetrahedrite, covellite and As-bearing pyrite
(Erceg et al, 1991). This high sulphidation mineralisation
is cut by later Au-bearing Mn-carbonate bearing (Zhang et
al., 1997) and As-bearing pyrite veins, interpreted to have
affinities with Carbonate Base Metal Au mineralisation
as defined by Corbett and Leach (1998). Zhang et al.
(1997) interpret the occurrence of Au associated with
Mn-carbonate (rhodochrosite) in the Link Zone core to be
indicative of Au deposition associated with the mixing of
bi-carbonate bearing meteoric waters with pregnant Aubearing magmatic fluids.
Surface Geochemical Expression
Surface geochemical data describes a broad annulus 2.94km
x 2.7km which contains >140ppm Zn rimming the entire
system, centred on the diatreme and is broadly coincident
with the propylitic alteration zone. Zone A and B high
sulphidation epithermal Au mineralisation occurs (manifests
at surface) as a zone of anomalous Au values in soil samples
(1.0 x 0.4km @ > 0.48 g/t Au). The southern portion of
the Golpu porphyry Cu-Au mineralisation is identified
at surface by spotty Cu (>150ppm) and Mo (>35ppm)
anomalism in soil samples. The surface geochemical
expression for both the Golpu and Nambonga porphyry Cu
deposits is well defined using the multi-variant statistical
analysis method, Principle Component Analysis (PCA). The
PCA Cu-Mo and Au-Cu-Mo factors are the best indicator
of both the Golpu and Nambonga porphyry Cu-Au
mineralisation at depth.
Paragenesis of Wafi-Golpu Mineralisation
Wafi-Golpu porphyry Cu-Au and associated epithermal
Au mineralisation are localised within a zone of extension
associated with a left stepping sinistral fault jog, as part of
the Wafi transfer structure as described by Corbett (1994). The porphyry mineralisation is interpreted to have been
introduced by a two-phase fluid as proposed by Fournier
(1999) comprising a hypersaline liquid rich in Fe, K and
Cl and a low density S-rich and Cu-Au-bearing phase
(Sillitoe 2010, Corbett and Leach, 1998). The negative
correlation between Mo and Au-Cu is indicative of a
separate transportation method for Mo into the system,
possibly associated with the hypersaline Fe, K and Cl rich
brine as oxochloride complexes as suggested by Ulrich
and Mavrogenes (2008) and Li et al. (2012) or a separate
intrusion phase of the complex. It is believed the diatreme
intruded and vented due to a phreatomagmatic eruption
resulting from the ingress of meteoric water onto a high
level intra/late mineral porphyry during rapid uplift
(Corbett and Leach, 1998). Current drill hole WR457
shows a transition from hydrothermal breccia (diatreme)
to a more magmatic-hydrothermal breccia with an apliticquartz-silica matrix, and eventually to a quartz lacking
feldspar-biotite-hornblende phyric porphyry at depth below
the diatreme. The lithologically controlled Zone A and
B high sulphidation epithermal Au mineralisation then
overprinted both the Golpu porphyry mineralisation and the
diatreme, and were followed by later Au-bearing carbonatebase-metal and Au-As pyrite epithermal mineralisation
commonly known as the Link Zone (Ryan and Vigar, 1999;
Erceg, 2008). Recently observed cross-cutting relationships
in Northern Gold Zone core (WR392) and petrological
analysis of core from the Link Zone by Zhang et al (1997),
as well as discussions by Ryan and Vigar (1999), indicate
this is the latest mineralising event to have resulted from the
mixing of pregnant metal bearing fluids with bi-carbonate
bearing meteoric waters (Zhang et al., 1997; Corbett and
Leach, 1998). Post-mineral thrust faulting is believed to
be part of a Pliocene (5.0 - 2.5Ma) E-W compressional
event (Reid, 2012, and Cloos et al., 2010)) and has offset the
Golpu porphyry mineralisation to the NW. Figure 1 shows
schematic diagrams of this paragenetic sequence. Copper
mineralisation has undergone later supergene enrichment
forming a chalcocite-rich zone with associated supergene
kaolinite and alunite.
References
Arif, J. and Baker, T. 2004. Gold paragenesis and chemistry at Batu
Hijau, Indonesia: implications for gold-rich porphyry copper deposits. Mineralium Deposita 39:523-535.
Cloos, M., Sapiie, B., Quarles van Ufford, A., Weiland, R.J., Warren P. Q.
and McMahon, T. P., 2010. Collisional delamination in New Guinea:
The geotectonics of subducting slab breakoff. Geological Society of
America Special Papers 2005;400;1-51
Corbett, G.J., 1994, Regional structural control of selected Cu/Au
occurrences in Papua New Guinea, in Rogerson, R., ed., Proceedings
of the Papua New Guinea Geology, Exploration and Mining
Conference 1994: Melbourne, Australasian Institute of Mining and
Metallurgy, p. 57−70.
Corbett, G. J. and Leach, T. M. (1998) Southwest Pacific Rim Gold-Copper
Systems: Structure, Alteration and Mineralization. Economic Geology
Special Publication 6, 240p.
Erceg, M. M., Craighead, G. A., Halfpenny, R., Lewis, P. J. 1991. The
exploration history, geology and metallurgy of a high sulphidation
epithermal gold deposit at Wafi River, Papua New Guinea. PNG
Geology, Exploration and Mining Conference, 1991, p. 58 – 65.
Erceg, M., 2008. Terry Leach: Contribution to the understanding of the
hydrothermal ore-forming processes of the Wafi High Sulphidation
Epithermal Gold Deposit and his role in the discovery of the Wafi
Porphyry Copper Deposit. AIG Bulletin 48 – Terry Leach Symposium.
Fournier, R.O., 1999, Hydrothermal processes related to movement of fluid
from plastic into brittle rock in the magmatic-epithermal environment:
ECONOMIC GEOLOGY, v. 94, p. 1193−1211.
Harmony, 2012. Golu gold equivalent reserve ounces significantly
enhances value of Harmony’s assest portfolio. (http://www.harmony.
co.za/investors/news-and-events/company-announcements-2/
announcements-2012/641-golpu-gold-equivalent-reserve-ouncessignificantly-enhance-value-of-harmony-s-asset-portfolio)
63
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Harris, A., 2010. Petrology Report; v.2: Summary of Petrological
Observations from Drill holes WR315, WR316, WR318, WR320,
WR321, WR323 (66 Samples). Internal unpublished report to MMJV.
CODES ARC Centre of Excellent in Ore Deposits, University of
Tasmania pp. 40 Harris, A., 2011. Petrology Report; v.3: Summary of Petrological
Observations from Drill holes WR327A, WR328, WR331,
WR331-W1, WR333 (36 Samples) - INTRUSIVE PHASES. Internal
unpublished report to MMJV. CODES ARC Centre of Excellent in
Ore Deposits, University of Tasmania pp. 26 Li, N., Chen, Y., Ulrich, T. and Lai Y. 2012. Fluid inclusion study of
the Wunegetu Cu-Mo deposit, Inner Mongolia, China. Mineralium
Deposita, 47:467-482.
Muller, C., Bandy, L., Finn, D., Golias, P., Hayward, S., Menzies, D.,
Shakesby, S., Tekeve, B., and Wima, M. 2011. Unveiling a hidden
giant: discovery of the Golpu Gold-Copper Porphyry Deposit, Papua
New Guinea. NewgenGold Conference Perth, 2011.
Newcrest, 2012. Golpu Pre-Feasibility Study and Reserve Announcement.
(http://www.newcrest.com.au/media/resource_reserves/2012/
August_2012_Golpu_Pre-Feasibility_Study_and_Reserve_
Announcement.pdf )
Reid, R., 2012. Report on the Structure Modelling Completed on the WafiGolpu Project and Decline Route. MMJV Internal report.
Ryan, S. J. and Vigar, A. 1999. Discovery of the High-Grade Link Zone
at Wafi, PNG. PACRIM 99 Congress, 10-13 October Bail Indonesia. The Australian Institute of Mining and Metallurgy Publication Series
No 4/99.
Seedorff, E., Dilles, J.H., Proffett, J.M., Jr., Einaudi, M.T., Zurcher, L.,
Stavast, W.J.A., Johnson, D.A., and Barton, M.D., 2005. Porphyry
deposits: Characteristics and origin of hypogene features: ECONOMIC
GEOLOGY 100TH ANNIVERSARY VOLUME, p. 251−298.
Sillitoe, R. H., 2010. Porphyry Copper Systems. Economic Geology,
105:3-41.
Simon, G., Kesler, S.E., Essene, E.J., and Chryssoulis, S.L., 2000,
Gold in porphyry copper deposits: Experimental determination of
the distribution of gold in the Cu-Fe-S system at 400° to 700°C:
ECONOMIC GEOLOGY, v. 95, p. 259−270.
Ulrich, T., and Mavrogenes, J., 2008, An experimental study of the solubility
of molybdenum in H2O and KCl-H2O solutions from 500°C to
800°C, and 150 to 300 MPa: Geochimica et Cosmochimica Acta, v. 72, p.
2316−2330.
Zhang, L., Leach, T., and Merchant, R., 1997. Petrographic investigations
of drill core samples from holes WR158, WR159, and WR160, Wafi
River Prospect, Papua New Guinea. Terry Leach and Co Unpublished
report for CRA Exploration Pty Ltd. Report number 97128.
64
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Case Study: Discovery and Geology of the Kham Thong Lai Copper-Gold Deposit, Lao PDR
Paul Merriner
Case Study: Discovery and Geology of the Kham Thong
Lai Copper-Gold Deposit, Lao PDR
Paul Merriner
The Kham Thong Lai (KTL) deposit is a stratabound
porphyry-skarn style copper gold system located
approximately 8km ESE from the provincial town of
Phonsavan in Xiengkhouang Province, Lao PDR (Fig.
1). It lies within the Mineral Exploration and Production
Agreement granted to Phu Bia Mining. The deposit is
situated proximal to the confluence area of the northern
Loei Fold Belt (LFB) and Truongson Fold Belt (TFB)
and lies within a complex and deformed arrangement
of magmatic arc and rift volcano-sedimentary rocks
and intrusives overlying Khorat type continental clastic
sediments. Exploration work within the LFB and TFB
has led to the discovery of several ore
deposits including Phu Kham Cu-Au,
Ban Houayxai Au-Ag, Sepon Cu-Au
and Chatree Au-Ag. Orogenic activity
associated with the development of the two
belts has involved widespread plutonism
and volcanic activity throughout the belt
regions. It is this magmatism which has
played a fundamental role in the formation
of the KTL deposit. broad Au and Cu BLEG anomalies which ultimately led
to the rediscovery of the KTL deposit. It was around this
time that the name KTL was adopted by Normandy Anglo
workers, which in Laotian translates as abundant gold
and copper.
Follow-up of this early work comprising geological mapping,
gridded soil geochemical sampling and ground and airborne
magnetics assisted in locating and defining KTL and
directed Normandy Anglo to undertake a scout drilling
campaign over the most prospective geochemical targets.
This drilling consisted of 31 diamond drill holes, many of
which returned significant gold and copper intercepts along
Historically, copper at KTL was probably
first identified by the local people of the
area who referred to the site as Phu Thong,
a name which is still in use today and
literally translates as Copper Mountain in
Laotian. Archaeological finds of bronze
artefacts and the discovery of smelting
furnaces in Laos confirm that metal
production technologies were available
and it may be that copper was mined
and produced from KTL centuries ago,
although this is unconfirmed. In more
recent times during the French colonial
administration small scale mining was
undertaken at KTL from 1951 until 1953.
In 1994 until 1996 Normandy Anglo
Asian Pty Ltd, who were the original
owners of Phu Bia Mining, undertook
regional stream sediment sampling over
the Phonsavan area. This work returned
Figure 1. Location Map
1. Phu Bia Mining, Laos Corresponding author: peter.leaman@pbm.panaust.com
65
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Case Study: Discovery and Geology of the Kham Thong Lai Copper-Gold Deposit, Lao PDR
a 2.3 kilometre long E-W trending zone. At completion
Normandy Anglo reported KTL as a significant resource
of low-grade copper and gold and concluded that that the
metal grades were not high enough to justify further work at
that time. Exploration at KTL consequently ceased.
In 2001 PanAust, then operating as Pan Australian Resources
NL, took an 80% stake in the Phu Bia Contract Area in Laos.
The remaining 20% of PBM was later acquired by PanAust
from Newmont in 2005. Between 2004 and 2005 PanAust
commenced a review of all previous work completed at KTL
by its former owner. PanAust geologists also re-logged the
Normandy Anglo drill core and remapped the prospect
area. Based on this work PanAust recognised potential in
the project and a decision was made to conduct further
exploration work, which included gridded soil sampling,
trenching and ground and airborne geophysics. Encouraging
results consequently led to the resumption and continuation
of exploration drilling from 2006 onwards. To date a total of
290 drillholes have been completed by PanAust, defining an
indicated and inferred mineral resource (at 0.25% Cu cut-off )
of 89 MT @ 0.44% Cu, 0.18g/t Au and 1.7g/t Ag containing
approximately 390,000 tonnes of copper, 515,100oz of gold
and 4,864,400oz of silver. The majority of the stated mineral
resource is primary mineralisation.
The host sequence at KTL consists of an E-W trending,
moderate south dipping, weak to moderately foliated
sedimentary package of Late Carboniferous–EarlyPermian age which contains alternating sequences of
strongly deformed interbedded siltstone, sandstone, micritic
limestone and carbonaceous shales of passive shallow marine
and volcaniclastic origin. The volcano-sedimentary sequence
is intruded by rift related calc-alkali stocks that occur as
elongated bodies and lobes showing a west to northwest
trend. Late quartz-feldspar rhyodacite porphyry dykes
intrude both the diorite and host sediments.
At district scale the Phonsavan area lies at the margin of a
south verging fold-thrust belt of probable late Permo-mid
Triassic age. Evidence of the fold-thrust system is observed
at KTL as localised brittle-ductile and ductile shear in the
core. Statistical analysis of shear data indicates the shear
fabric dips moderately south. Late WNW and NE structures
also occur and appear to have formed after the timing of
mineralisation. This faulting is responsible for disruption
Paul Merriner
and truncation of the deposit but not to a significant extent,
based on recent modeling.
Alteration styles within the host geology are complex and
comprise diverse and localised alteration packages associated
with different lithologies. Diorite and microdiorite intrusions
exhibit propylitic (chlorite/carbonate/± epidote) alteration of
varying intensity with strong development associated with
stockwork zones and increasing in intensity toward skarn
contacts. Weak to strong phyllic alteration is also widespread
and occurs as sericite-silica-pyrite alteration within the
diorite and sediments. Stockwork vein associated sulphide
phases within intrusive bodies are also associated with weak
to strong sericite-silica alteration. No significant potassic
alteration is associated with the KTL deposit and only minor
secondary biotite is observed in the core. Prograde altered
calc-silicate skarns contain mainly garnet and pyroxene and
typically show an outward progression from diorite to brownred garnet skarn to green-yellow garnet skarn to marble to
limestone. Massive magnetite skarn occurs when the host
rock has undergone complete replacement of the original
mineral assemblage by magnetite.
Base and precious metal mineralisation at KTL is
considered to be coeval with stock emplacement. Re-Os
age dating from vein hosted molybdenite returned an
age of 289.4 ± 1.0 Ma. Mineralisation occurs as several
styles. Low to moderate grade Cu-Mo-Au mineralisation
is typically hosted in multi-phase stockworks and sheeted
quartz-sulphide veins, and as disseminated and aggregate
mineralisation within and proximal to intrusive stocks. High
grade Cu-Au is associated with banded and semi-massive to
massive sulphides hosted within prograde and more typically
retrograde altered calc-silicate and magnetite-pyrrhotitepyrite exo-skarn. Skarn hosted mineralisation is more
common and significantly higher in grade within exoskarn
compared with endoskarn, the latter typically comprising
mainly garnet skarn varieties. Dominant sulphide minerals
for both styles are pyrite, chalcopyrite and pyrrhotite with
less common molybdenite, bornite, sphalerite and galena.
Secondary copper within the supergene profile is weakly
developed throughout the deposit and occurs mostly in the
form of malachite with lesser chalcocite and rare chrysocolla.
The deposit is at the pre-feasibility evaluation stage with
additional drilling to upgrade the resource base.
l
keynote
66
The Magmatic Arc and the Slate Belt: Copper-gold and Tin tungsten and
Gold Metallotects in Myanmar
AHG Mitchell, Myint Thein Htay
The Magmatic Arc and the Slate Belt: Copper-gold and
Tin-tungsten and Gold Metallotects in Myanmar
AHG Mitchell1 and Myint Thein Htay1
Myanmar can be divided into a Western province or arc
system, comprising the Popa-Loimye magmatic arc and
associated basins and ridges, and an Eastern province. The
Eastern province consists, from west to east, of the Mogok
Metamorphic belt; the Slate belt; the Paunglaung- Mawchi
zone; and the Shan Plateau which was accreted to Asia
in the Triassic. The Popa- Loimye magmatic arc and the
Slate belt each host distinctive types of mineralisation and
include, at Monywa and Mawchi, two of Myanmar’s four
world- class mineral deposits (Fig.1).
The Popa- Loimye magmatic arc is a discontinuous belt of
intrusive and volcanic rocks extending from Mt Popa north
and northeastwards through the extinct stratovolcanoes at
Taungthonlon and Mt Loimye to near Bumba- bum south
of Chaukan Pass. A forearc basin (Win Swe, 1972) and the
Indo- Myanmar Ranges lie between the arc and GangesBrahmaputra delta in Bangladesh (Steckler et al., 2008)
where the seismic Benioff zone dips very gently east.
Three segments of the magmatic arc are separated by
sedimentary cover. In the largest or Wuntho- Banmauk
segment (United Nations, 1978) basement greenstone is
overlain by a sequence of marine basalts and andesites,
mudstones, dacites and mid- Cretaceous limestones.
Calc- alkaline I- type plutons comprising the Kanzachaung
batholith intrude the sequence below the limestones, and
are mostly early Upper Cretaceous but locally Palaeogene. Mineralisation includes the Shangalon porphyry coppergold prospect in an Oligocene intrusive complex (United
Nations, 1978), numerous mesothermal quartz - gold veins
within the batholith and its host rocks, epithermal quartzgold veins, pyritic low-temperature replacement quartz
bodies, and recently discovered occurrences of volcanogenic
massive sulphide.
To the south, in the Monywa- Salingyi arc segment, midCretaceous (95 to 105 Ma) I- type diorites and granodiorites
intrude pillowed basalts and are overlain by late Tertiary
sediments and in the north by small extinct basaltic
stratovolcanoes (Chhibber, 1934a). At the Monywa copper
mine ( Kyaw Win and Kirwin, 1998; Mitchell et al., 2011) sandstones, overlying stratified diatreme deposits, and midMiocene quartz andesite porphyry intrusions are cut by pebble dykes. Chalcocite-digenite and covellite occur with
Figure 1. Map of Myanmar showing Popa- Loimye magmatic arc and
Slate belt. Fa Falam, Ka Kalaw, Ky Kyaukse, Mc Mawchi, Me Mergui,
Mk Mogok, Ml Meiktila, Mo Moulmein, Mt Myitkyina, Mu Mong
Hsu, My Monywa, Na Namhkan, Ng Ngapali, Pd Padatgyaung,
PMZ Paung Laung- Mawchi zone, Pu Putao, Sh Shinmataung, Ta
Tavoy (Dawei), Tg Tagaung, Tk Tachilek, Ty Taunggyi.
1. Myanma Precious Resources Group, Yangon, Myanmar Corresponding author: andrewmitch999@aol.com
67
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The Magmatic Arc and the Slate Belt: Copper-gold and Tin tungsten and Gold Metallotects
in Myanmar
pyrite in veins and pebble dykes, and as disseminations, in
four high sulphidation epithermal deposits. Hydrothermal
alteration assemblages which include quartz, sericite,
pyrophyllite and alunite within more regional chlorite are
overprinted by supergene kaolin. Barren leached caps up
to 200 m thick overly the chalcocite and covellite which
are partly hypogene but largely products of supergene
enrichment. The pre- mining resource was over 2 billion
tonnes containing 7 million tonnes copper. Nearby auriferous
quartz veins occur in rhyolites and silicified sandstones.
In the southernmost arc segment the Mt Popa stratovolcano
overlies mid- Miocene and younger andesitic lavas which
host widespread bodies of copper and gold- anomalous
replacement quartz-pyrite-alunite within pyritic clays, and
rare breccia dykes.
Northeast of Taungthonlon, arc volcanics of Tertiary age
underlie the Mt Loimye stratovolcano, and are reported
at Kawt-a-bum and Bumba- bum (Chhibber, 1934a), the
probable sources of alluvial gold in the Hukawng valley. The
regional Sagaing dextral fault (Win Swe, 1972) offsets the
arc’s speculative former continuation northeastward from
Bumba- bum through the Tagaung-Myityina belt.
The Slate belt in Myanmar (Fig.1) continues SSE for
2000km to Banka Island in Indonesia (Mitchell et al.,
2012). It consists largely of Carboniferous to early Permian
mudstones or argillites and quartzites, with thick diamictite
beds implying glaciation in Gondwana. To the east the
narrow Paunglaung- Mawchi zone of late Mesozoic
sedimentary and volcanic rocks and older flysch may be an
early Permian suture on which the Slate belt and western
Myanmar collided with the Shan Plateau following
eastward subduction of a Palaeotethys ocean.
Within the Slate belt orogenic quartzgold veins
were discovered in 1999 by Ivanhoe Mines at Modi
Taung northeast of Nay Pyi Daw. Gold here is in
steeply- dipping narrow but high- grade stylo- laminated
book- and -ribbon quartz veins within a 30 km long
NNW-trending district. The veins, mostly tabular but
with rare isoclinal folds, are hosted by argillites, intruded
by calc- alkaline porphyritic dykes, extend for over 530 m
vertically, and provide a resource grading over 30 g/ t Au.
Gold values at Modi Taung exceed those of Ag, As, Cu,
Pb and Zn, but veins 12 km to the north have higher base
metal content. Since no veins occur in granites, we infer
gold deposition from metamorphic fluids, perhaps during
early Permian orogeny.
AHG Mitchell, Myint Thein Htay
Wolframite from several hundred tin and tungsten
mines in the Slate belt accounted for 29 percent of global
tungsten production in 1914. Deposits are associated with
the apices of S-type, or reduced ilmenite series I- type
peraluminous biotite- muscovite granites. Cassiterite is
mined from alluvial deposits, pegmatites and quartz lodes,
and wolframite from quartz lodes and bordering greisen
(Chhibber, 1934b). Much production was from weathered
material. Most of the wolframite is from the Mawchi mine,
from Padatgyaung east of Nay Pyi Daw, and from the Tavoy
(Dawei) region in southern Myanmar.
Zircon U-Pb and the few Rb/Sr isotopic ages on the
mineralised granites indicate late Cretaceous to Eocene
ages (Cobbing et al.,1992, Mitchell et al., 2012), implying crustal melting younger than generation of the orogenic
quartzgold veins in the Slate belt. Many of the more
productive tin- tungsten lode deposits are at high elevations,
suggesting limited erosion and a stable landmass since the
late Cretaceous.
References
Chhibber, H.L., 1934a. The Geology of Burma. Macmillan, London, 538p.
Chhibber, H.L., 1934b. The Mineral Resources of Burma. Macmillan,
London, 320 p.
Cobbing, E.J., Pitfield, P.E.J., Darbyshire, D.P.F. and Mallick, D.I.J., 1992.
The Granites of the South-East Asian Tin Belt. British Geological
Survey, Overseas Memoir 10, H.M.S.O., London, 369p.
Kyaw Win and Kirwin, D., 1998. Exploration, geology and mineralization of the
Monywa copper deposits, central Myanmar. In Porphyry and Hydrothermal
Copper and Gold Deposits: a Global Perspective. Proceedings of the
Australian Foundation Conference, Perth, Australia, 61-74.
Mitchell, A., Sun-Lin Chung, Thura Oo , Te-Hsien, and Chien-Hui Hung,
2012. Zircon U-Pb ages in Myanmar: Magmatic- metamorphic events
and the closure of a neo-Tethys ocean. Journal of Asian Earth Sciences
56, 1-23.
Mitchell, A.H.G., Win Myint, Kyi Lynn, Myint Thein Htay, Maw Oo and
Thein Zaw, 2011. Geology of the high sulphidation copper deposits,
Monywa mine, Myanmar. Resource Geology 61, 1-29.
Steckler, M.S., Akhter, S.H. and Seeber, L., 2008. Collision of the GangesBrahmaputra Delta with the Burma arc: implications for earthquake
hazard. Earth and Planetary Science Letters 273, 367-378.
United Nations, 1978. Geology and Exploration Geochemistry of the
Pinlebu-Banmauk area, Sagaing Division, northern Burma. Technical
Report no. 2, Geological Survey and Exploration Project, United
Nations Development Programme, DP/UN/ BUR-72-002, United
Nations, New York, 69p.
Win Swe, 1972. Strike-slip faulting in Central Belt of Burma. In: Haile,
N.S. ( Ed.), Regional Conference on the Geology of Southeast Asia.
Geological Society of Malaysia Newsletter 34, Annex, Abstracts, Kuala
Lumpur, p.59.
68
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Mineralisation Potential of the Kulu-Fulleborn Trend
(Whiteman Range), New Britain Island,
Papua New Guinea
Chris J. Muller1, Kieran Harrington1, Hugh McCullough1 and Lindsay W. Bandy1
Introduction
Papua Mining plc controls exploration licences over an
area of some 2,600 square kilometres along the Whiteman
Range of New Britain Island, which stretches for 150
kilometres from Eleonora Bay on the north coast to the
village of Fulleborn on the south coast. The geological
setting is favourable for porphyry Cu-Au-Mo, high and lowsulphidation epithermal Au/Ag, high-grade skarn-type and
volcanogenic massive sulphide mineralisation.
Following the discovery of the Panguna deposit on
Bougainville island in the mid-1960’s Conzinc Rio Tinto
of Australia (CRA) commissioned a research vessel the
CRAEStar to carry out a wide reaching survey of the
Western Pacific Rim to explore for porphyry copper/gold
deposits. The survey included reconnaissance geochemical
surveys of New Britain Island and a series of stream
geochemical anomalies were identified across the island
including a number along the Whiteman Range. Since then sporadic follow-up exploration has been
undertaken on New Britain by a number of companies.
In 1968 Placer (PNG) Exploration Pty discovered a
mineralised porphyry system at Plesyumi which it drilled
in the early 1970’s. Subsequently, significant copper/gold/
molybdenum deposits were discovered at the Mt. Nakru and
the Simuku areas. Most of the mineralisation discovered
historically occurs within the Kulu-Fulleborn Trend, a
corridor of Upper Oligocene-Pliocene intrusives and
volcanics which follows the strike of the Whiteman Range
(Fig 1.).
The area has now emerged as one of the most prospective
belts for Cu/Au mineralisation in Papua New Guinea. In
recent years Australian junior Coppermoly Limited have
reported a mineral resource at Simuku of 200 million tonnes
at 0.36% copper, 61 ppm molybdenum, 0.06 g/t gold and
2 g/t silver. At the Nakru-1 deposit the same company has
reported a resource of 38.4Mt at 0.82% copper equivalent. In July 2012 another junior explorer, Foyson Resources
Figure 1. Map of New Britain Island, showing location of Papua Mining tenements with respect to deposits and
prospects within the Kulu-Fulleborn Trend.
1. Papua Mining plc, Kula’s Place, Section 35 Alotment 13, Hibiscus Street (off Wards Road), Hohola, Port Moresby, National Capital District Corresponding author: chris@papuamining.com
69
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Limited, reported that drilling by the company confirmed
the presence of a significant mineralised porphyry system at
Atui Prospect near Fulleborn.
The exploration licence areas controlled by Papua Mining
plc encompass approximately 70 percent of the KuluFulleborn Trend.
Regional Geologic Setting
The basement rock in the Kulu-Fulleborn Trend comprises
Eocene – Oligocene Baining Volcanics, mainly consisting
of andesitic lava flows and pyroclastic rocks interbedded
with conglomerates and sandstones. The Kapuluk Volcanics
(Oligocene – Miocene) are extensively exposed andesitic and
dacitic lava flows and form the central Whiteman Range.
The basement rocks were intruded by a series of gabbroic
to dioritic stocks and plugs ranging in age from 29 – 22Ma
(Page & Ryburn, 1977). The smaller dykes and plugs
occur as elongate bodies aligned with regional NW and
NE lineaments, suggesting a structural control during
their emplacement. Simuku rocks possess arc tholeiite
characteristics, while those from Plesyumi range from mafic,
high-K gabbros to felsic, medium to low-K granodiorites
(Horne, 2011).
The Yalam Limestone was deposited around the flanks of
the basement during a period of reduced volcanic activity in
the Upper Miocence (22 – 10Ma) (Lindley, 1998). During
a period of uplift and renewed volcanic/plutonic activity
in the Pliocene period, the Mungu Volcanics and Kapiura
Bed sedimentary sequences were laid down mainly to the
north of the Whiteman Range. Volcanism continued
intermittently from the Pliocene to present times.
The Kimbe Volcanics (Pleistocene-Recent), consisting of
ash and lapilli tuff, can blanket all lithologies including
the basement rocks especially on the northern side of the
Whiteman Range. In particular in lower areas several meters
of cover could at times potentially mask the geochemical
signature of mineralised bodies.
Pre-Miocene structural deformation is dominated by
almost orthogonal sets of NW to NE trending faults. The
regional alignment of the basement and associated plutonic
rocks closely relates to these prevailing trends, supporting
structural control during igneous emplacement. PostMiocene deformation is dominated by NW-SE trending
high angle horst and graben fault blocks. The Pre-Miocene
faults seem to have been reactivated in most cases.
Genetic Model for Intrusions and Associated
Au/Cu Mineralisation
Many Upper-Oligocene and Pliocene dioritic intrusives
are localized in the Kulu-Fulleborn Trend and host
porphyry copper, skarn and gold mineralisation (Titley,
1978). Significant zones of mineralisation include, from the
northwest, Kavola East Prospect, Kulu-Simuku, Plesyumi
and Mt. Nakru (Mackenzie, 1975; Hine and Mason, 1978;
Titley, 1978). Local structural controls, superimposed on
the prominent northwest trend, have clearly controlled
Upper Oligocene emplacement. There is a general decrease
in age of igneous activity in a northwest direction along
the trend. This corresponds with a shallowing in the depth
of formation of mineralization, from the deeper porphyry
coppers at Kulu-Simuku and Plesyumi, to relatively shallow
epithermal mineralization at Kavola East (Lindley, 2003).
The two main recognised intrusive complexes at Simuku
and Plesyumi are located approximately 70km from each
other and are unlikely to have been separated by significantly
greater distances in the past. However the complexes appear
to be magmatically unrelated, being geochemically and
isotopically distinct. The more felsic rocks of the Plesyumi
Intrusive Complex possess geochemical characteristics
that are typical of adakites. These differences may be
explained through magma mixing, as opposed to fractional
crystallisation (Horne, 2011). Slab melting formed adakitic
melts and caused a pulse of melting in the aqueous fluidhybridized mantle wedge. K-rich magmas are commonly
associated with Au deposits (e.g., Müller and Groves, 1993;
Sillitoe, 2002; Blevin, 2002) and their presence as an end
member in the Plesyumi mixing process raises the possibility
that these magmas were the source of Au.
Based on compilations of isotopic compositions for the
western Pacific, the Oligocene to Miocene magmas of New
Britain were derived from variable contributions of the mantle
source of Pacific MORB (rather than Indian MORB) and
ocean floor sediments comparable to Solomon Sea sediments.
Exploration Strategy and Definition of
Drill Targets
From 2009-2010 Papua Mining plc completed a
comprehensive historical technical data compilation exercise,
collating all available geological, geochemical and remote
sensing data. A study was completed on data from a 1982
Esso aeromagnetics and radiometrics survey which had
covered the majority of the Kulu-Fulleborn Trend. Reduced
to Pole (RTP) magnetic images highlight the KuluFulleborn Trend as several parallel structural linears and
the known mineral occurrences are located on or proximal
to these major lineaments. Most of the known porphyrystyle occurrences occur within well-defined magnetic low
zones on the residual RTP magnetic image. Such zones
may be related to hydrothermal activity associated with
porphyry systems. These findings are significant in terms of
exploration targeting, specifically for determining known
mineralised trends from outside the concession area and,
secondly, identifying new potentially mineralised areas. 3D
inversion models were generated on subsets of the dataset
for the known mineralised areas.
The compiled exploration data was used to generate ranked
prospective target lists and the company embarked on a
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major field exploration program along the Whiteman Range
during 2010, with teams carrying out rock chip and soil
sampling, geological mapping and topographic surveys.
a strongly positive correlation with the IP results, with a
well-developed zone of high conductivity within the high
chargeability zone.
More than 40 km2 in the Nakru area was geologically
mapped, by experienced geologists with a knowledge of
the surface expressions of porphyry and porphyry-related
systems. Lithology, alteration and structure were classified
and mapped along all drainages and other exposures,
with the aim of recognizing favourable host lithologies,
hydrothermal alteration related to porphyry development
and conducive plumbing and dilational environments,
respectively.
References
To date more than 10,000 soil geochemical samples have
been collected. Typically the soil grid spacing used is 400
x 50 metres. Substantial copper in soil anomalies (>100
ppm Cu in soils) were identified at Nakru (the Tripela and
Flying Fox Anomalies), at Kori-Dagi five kilometres east of
the known Simuku deposits, and at Plesyumi South in the
vicinity of the known Plesyumi porphyry system.
The mapping data revealed a range of porphyritic intrusives,
amid intercalated volcanic tuff and pyroclastic packages, to
some degree with breccia development along the contact
zones. Zoned alteration is obvious in the Nakru area
( Junction anomaly), where a silica cap is surrounded by
intermediate argillic alteration characterized by dickitekaolinite-pyrite. Distally, these alteration assemblages give
way to sericite and finally chlorite dominated country rocks.
Simultaneous rock chip sampling (for a total of more
than 2,500 samples) was carried out with outcrop samples
returning assays as high as 29% copper at Flying Fox and
25% copper at the Tripela prospect, both areas feature the
occurrence of extensive diorite intrusives with associated
hydrothermal, heterolithic, milled breccias. Several trenches
have been excavated within the mineralised zones and results
are pending.
Induced Polarisation (IP) and Electromagnetics surveys
(EM) have been completed at the Junction target. IP results
there have outlined a resistive, low chargeability core, flanked
by an annulus of high chargeability, typical of the response
one might expect from a porphyry body. The EM data shows
Several strands of the exploration work completed by
the company to date therefore point to the presence of a
number of porphyry systems within the exploration area.
Drill testing of the most advanced target is scheduled to
commence in March. The company anticipates an initial
drilling programme at Junction of three or four diamond
core drillholes to test the chargeability/conductivity target.
Blevin, P. L. (2002). The petrogenic and compositional character of variably
K enriched magmatic suites associated with Ordvician porphyry CuAu mineralisation in the Lachlan Fold Belt, Australia. Mineralium
Deposita, 37, 87-99.
Hine, R., Mason, D.R. (1978). Intrusive rocks associated with porphyry
copper mineralisation, New Britain, Papua New Guinea. Economic
Geology, 73, 749-760.
Horne, P. (2011). The Plesyumi and Simuku Intrusive Complex, New
Britain (PNG): Contrasting Magma Sources and Evolution in a
Subduction Zone. MSc (unpublished).
Lindley, I.D. (1998). Mount Sinivit gold deposits. In: Berkman, D.A. and
Mackenzie, D.H. (Eds), Geology of the mineral deposits of Australia
and Papua New Guinea. Australasian Institute of Mining.
Lindley, I. D. (2003). Echinoids of the Kairuku Formation (Lower
Pliocene), Yule Island, Papua New Guinea: Spatangoida. Proceedings of
the Linnean Society of New South Wales.
Mackenzie, D.H. (1975). Uasilau and Kulu porphyry copper occurrences,
New Britain, in Economic Geology of Australia and Papua New
Guinea, 1. Metals, edited by C.L. Knight (Australasian Institute of
Mining and Metallurgy, Melbourne), Mono. 5, 845-850.
Müller, D., Groves, D. I. (1997). Potassic Igneous Rocks and Associated
Gold-Copper Mineralization. Lecture Notes in Earth Sciences, v. 56,
(2nd, updated and enlarged ed.). Spring-Verlag, Berlin Heidelberg.
Page, R. W., Ryburn, R. J. (1977). K-Ar ages and geological relations of the
intrusive rocks in New Britain. Pacific Geology, 12, 99-105.
Sillitoe, R. H. (2002). Some metallogenic features of gold and copper
deposits related to alkaline rocks and consequences for exploration.
Mineralium Deposita, 37, 4-13.
Titley, S.R. (1978). Copper, molybdenum and gold contents of some
porphyry copper systems of the southwestern and western Pacific.
Economic Geology, 73, 977-981.
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Yulia Nazimova1 and Gregory Ryan2
The most productive economic deposits of
alluvial platinum in the world are associated with
ultramafic zoned complexes of Ural-Alaskan
(UA) type. While a number of deposits ranging
up to 180 tonnes of metallic platinum have been
mined very profitably in Russia, Canada, Alaska
and Australia, only in the Russian Far East
(Kondyor and Galmoenan) are such deposits
still being mined. Alluvial and bedrock platinum
deposits associated with the Galmoenan and
Kondyor UA intrusions are the main topic under
consideration.
Bed-rock Platinum Deposits
UA complexes are pipe-like, concentrically
zoned, ultramafic-mafic intrusions of dunitepyroxenite-gabbro formation, typically ranging
in size from 12 to 80 sq km. They occur in two
distinct geological settings. The majority occur
within mobile belts close to continental margins
(eg Galmoenan). Such intrusions are more or less
deformed, and may also be partially tectonically
dismembered. More rarely, UA complexes
intrude the stable continental platform. In this
case, the zonal structure and the pipe-like shape Figure 1. Locations of the Galmoenan and Kondyor intrusions and their satellite images.
are normally perfectly preserved (eg Kondyor).
Both the Galmoenan and Kondyor intrusions exhibit a zonal
structure with a well-developed dunite core (about 75-80% of
the volume), surrounded by a clinopyroxenite rim 50-500m
wide and some gabbroid occurrences. In the case of Kondyor,
a later phase of alkaline rocks has developed, forming a
network of veins in the dunite and clinopyroxenite.
The Late Cretaceous Galmoenan intrusion is located in
the north of the Kamchatka peninsula, Russia (Fig.1). The
intrusion is elongate in a northeasterly direction, being 14
km long and 2–3 km wide. Based on gravimetric data, the
intrusion represents a tectonic outlier, which is estimated to
have been displaced some 8–15 km from the main thrust [1].
The Kondyor intrusion is located in the Russian Far East,
about 1100 km north of the city Khabarovsk. Forming a
circular, chimney-like structure about 8 km in diameter and
at least 10 km deep (Fig.1), the massif has a dunite core
5.5 km in diameter. Age determinations are inconclusive,
ranging from Mesozoic to Archean–Early Proterozoic
(about 2.5 Ga) [4].
The main source of platinum is the dunite core, particularly
the coarse-grained part containing chromite accumulations.
Several mineralised zones have been delineated on both
Galmoenan [7] and Kondyor [unpublished company
reports]. These zones are characterised by centimeter to
metre-scale chromite segregations occurring sporadically
within the dunite. Platinum distribution within the
chromite segregations is very irregular, with variations up to
340% having been encountered in individual samples. The
“nugget effect” (isolated assays up to 100s of ppm Pt) is very
characteristic of this style of mineralisation.
1. Director/Principal Consultant, NZ Exploration Ltd, 33 Richmond Road, Takaka 7183, New Zealand Corresponding author: jul_nz@yahoo.com
2. Director/Principal Consultant, NZ Exploration Ltd, 33 Richmond Road, Takaka 7183, New Zealand Corresponding author: pacificgeological@hotmail.com
72
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At both Galmoenan and Kondyor, Fe-Cu-Pt alloys comprise
more than 90% of PGM, with isoferroplatinum (Pt3Fe)
strongly predominant. Numerous publications describe the
PGE mineralogy of both complexes [3, 5, 7-9].
Detailed applied PGE mineralogy has been carried out
on bulk samples from strongly mineralised zones of the
Galmoenan intrusion [7, 9]. Similar work is currently
being carried out on Kondyor. In samples with low and
“background” Pt content, PGM (mainly isoferroplatinum)
are finely disseminated, commonly in a cubic crystal form,
whereas high-grade samples exhibit clustered aggregates
(up to several centimetres) of Pt–Fe alloys, cementing the
chromite grains. The average grain-size of the PGM in the
mineralized zones is 175 µm. Despite the presence of large
quantities of small inclusions of PGM (50%, <0.05 mm), the
bulk (70%) of the actual metal content is composed of grains
>0.4 mm [7, 9].
There is potential for economically mineable platinum
deposits to exist within UA intrusions, particularly in Kondyor
and Galmoenan. Such deposits are likely to comprise
aggregates of many mineralised clusters, occurring with
sufficient density and grade to be viable. Using appropriate
exploration techniques in such settings would be critical to
success. In particular, the trench and drill samples should be
no less than 250 kg per 1m interval, in order to give reliable
and repeatable results [7, 9]. It is also necessary to generate
average grades over relatively large blocks. Pilot processing of
bulk (several tonnes) samples should be part of this process.
A very positive feature of such intrusions is that the platinum
can be recovered by simple gravity separation [2].
While considerable bedrock exploration has been carried
out in the past at Galmoenan, exploration is currently in
progress only at Kondyor.
Alluvial Platinum Deposits
Since 1993, eight platinum placers have been delineated
at Galmoenan. Of the seven currently being mined, the
biggest, Ledyanoy and Levtyrinvayam, have produced about
25 tonnes of platinum each. The Ledyanoy placers formed
in several creeks close to the intrusion, with productive
horizons typically 2-3 km long, 20-130m wide and 0.45m thick, with average grade varying from 0.4-7 g/m3.
Overburden thickness varies from a few metres to 60m.
Interestingly, the Levtyrinvayam placer commences 10km
from the intrusion. Various theories have been proposed to
explain this but none has been substantiated. With a length
of 9 km, width of 250-400m and thickness of 2.5-4m, the
average grade of the productive horizon varies from 0.8-5.2
g/m3. Overburden thickness is typically 7-8m [1, 6].
The Kondyor placers occur both inside the ring structure
(Kondyor River and its tributaries) and beyond the gorge
through the ring, where the Kondyor flows into the
Uorgalan River (Fig.1). Platinum placers are known to
extend for 70 km downstream. Mining began in 1984 and
annual production is still 3-4 tonnes. The average platinum
grade varies from 0.5-5 g/m3 (up to 60-80 g/m3 in some
parts) [3, 5].
At both Galmoenan and Kondyor, 70-95% of the platinum
occurs in the basal wash, with minor quantities on “false
bottoms”. Isoferroplatinum comprises 97% of the PGM,
with grain size varying from 0.2-5mm close to the intrusion
and from to 0.05-0.5mm more distant from the intrusion
[1]. Grains also become more rounded with increasing
distance from the intrusion.
Typically 2.5% of the concentrates are composed of nuggets.
Kondyor has produced more than 20 nuggets weighing more
than 1 kg, the largest being 3.5kg [10]. The largest nugget
from Galmoenan was 1.2 kg. Chromite and magnetite are
also present in the concentrate and minor gold occurs at
Kondyor.
Alluvial platinum exploration employs similar techniques
to those used for alluvial gold. Modern or fossil river
channels must be delineated and then explored using bulk
sampling methods, usually churn drill, cable tool rig or
similar, or excavator, depending on depth to bedrock and
ground conditions. Entire 1m samples are processed through
a gravity separator such as goldsaver or small alluvial
processing plant. The results are used to generate gradethickness contours and cross sections, to enable resource
determination.
Literature
1. Koryaksko–Kamchatsky region – a new platinum province of Russia.//
Saint-Petersburg Cartographic Factory, VSEGEI Press, 283-315 (in
Russian).
2. Bogdanovich A.V., Petrov S.V., Nazimova Yu.V., Vasilyev A.M.,
Urnysheva S.A. (2010): Peculiarities of processing minerals with high
non-uniformity of valuable components distribution (example of platinum
ores).// Obogashcheniye rud, 2, pp 3-8 (in Russian).
3. Mochalov, A.G. & Khoroshilova, T.S. (1998): The Kondyor alluvial placer
of platinum metals.// Proc. Int. Platinum Symp. Theophrastus Press,
Athens, Greece, pp 206-220.
4. Malitch K. N., Efimov A. A., Badanina I. Yu. (2012): The Age of Kondyor
Massif Dunites (Aldan Province, Russia): First U–Pb Isotopic Data //
Doklady Earth Sciences, Vol. 446, Part 1, pp. 1054–1058
5. Malitch, K.N. (1999): Platinum-Group Elements in Clinopyroxenite–
Dunite Massifs of Eastern Siberia (Geochemistry, Mineralogy, and
Genesis).// VSEGEI Press, St. Petersburg, Russia (in Russian).
6. Melkomukov V.N., Zaytsev V.P. (1999): Platinum placers of Seynav–
Galmoenan knot (Koryak–Kamchatka province).// Platinum of Russia,
III, pp 143-149 (in Russian).
7. Nazimova Yu.V., Zaytsev V.P., Petrov S.V. (2011): The Galmoenan massif,
Kamchatka, Russia: geology, PGE mineralization, applied mineralogy and
beneficiation// Canadian Mineralogist, v.49, 6, pp 1433-1453
8. Nekrasov I.YA., Lennikov A.M., Oktyabrsky R.A., Zalishchak B.L.,
Sapin B.I. (1994): Petrology and Platinum Mineralization of the
Alkaline-Ultramafic Ring Complexes. Nauka, Moscow, Russia (in
Russian).
9. Petrov S.V., Nazimova Yu.V., Bogdanovich A.V. (2010): Applied PGE
mineralogy and ore beneficiation of the Galmoenan deposit, northern
Kamchatka.// Proc. 11th Int. Platinum Symp. (Sudbury).
10. Sushkin L.B. (1996): Characteristic features of native metals from the
Kondyor deposit.// Geology of Pacific Ocean, Vol. 12, pp 915–924.
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A. H. (TONY) Osman
A. H. (Tony) Osman
The story of coal development and reconstruction in
Indonesia over the past 150 years or so is one of the most
remarkable that can be told today. Indonesia came from
nowhere to its place in 2013 as the world’s largest exporter
of thermal / energy coal.
The narrative divides easily into several phases which are...
1. First beginnings to the Japanese occupation during the
Pacific War 1942
2. Destruction and decline- 1942-1967
3. Reconstruction and the groundbreaking laws of 1/1967
(the foreign investment law) and 11/1967 (the general
mining law) under the administration of President
Soeharto. Emergence of Kalimantan as the location of
export quality steam coal and discovery of high quality
coking coal in Central Kalimantan. Sumatra with lower
quality steam coal.
4. The concept of coal Cooperation Agreements, later to
become Coal Contracts of Work. First, second and third
generation, 1981 onwards.
5. Regional Autonomy legislation and the new mining law
of 2009.
The presentation outlines some of the present day challenges
to coal investment by foreign investors especially the smaller
companies.
1. PT Carsurin, Askrindo Building, Jln Angkasa, Block B-9, Kav.8 - Kemayoran, Jakarta 10601 Corresponding author: tony@carsurin.com
74
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Interpolating Assays and Physical Properties in Folded and Faulted Layered Geology
Rod paterson
Interpolating Assays and Physical Properties in Folded
and Faulted Layered Geology
Rod Paterson
The GeoModeller Domain kriging algorithms, Guillen et
al, 2011, implement two new methods for interpolating
petrophysical properties (porosity, permeability, density,
magnetic susceptibility) or chemical grades (Fe, Cu, Pb,
Zn…) while honouring the geometry and internal structure
of the host geological units.
Traditional distance weighting interpolation methods that
calculate the distance between samples using Cartesian
coordinates (east, north and elevation) are not satisfactory
in a folded and faulted stratigraphic unit or banded ore
horizon. The distance between samples is no longer a
straight line, Figure 1, Guillen et al, 2011. Current methods
used to solve this problem involve unfolding prior to
interpolation followed by reconstruction back to the original
geometry. This can be a very difficult process in complex
structural environments.
Figure 1: Curvilinear distance between two points A and B: Point A
is on the isovalue potA, point B is the isovalue potB. The distance dg (A,
B) is the length of the arc AmBm (in blue) at isovalue potM = (potA +
potB)/2. The distance dg (A, B) is therefore defined as dg (Am, Bm).
The GeoModeller Domain Kriging algorithms are described
below, Guillen et al, 2011.
1. When the variability of the parameter to study is mainly
correlated with the pot coordinate (a metal deposited by
a sedimentary process), the variogram in the space (pot,
dg, q) is in reality a function of pot and we have:
g(pot,dg,q) = g(pot)
The normal coordinate to the isovalues, Figure 1, defines
the potential coordinate (pot); it represents the value of
the potential field function. Computation of potential
distance (orthogonal to potential isovalues) between the
two points A and B, pot (A, B) is very easy: it is the
absolute value of the difference between pot (A) and pot
(B). This can be thought of as a measure of formation
thickness between points A and B.
In this case, we have pure “zonal anisotropy”
This algorithm is fast to compute due to its relative
simplicity.
2. The General case: g(pot,dg,q) = g(pot,dgu,dgv)
Where:
• dgu,dgv represent respectively the geodesic distances
along the u axis and the v axis, which are the axes
representing the anisotropy in the xy plane.
• dgu and dgv are the projection on the principal axes u
and v of the geodesic distance dg and u and v are the
directions of anisotropy on the plane xy rotated with
an angle q from axis x and y.
We may have a geometric anisotropy on the plane xy
and zonal anisotropy along the pot coordinates and two
pot
different nugget effects for pot coordinate (C 0 ) and xy
dg
plane (C 0 ).
Further work is required to improve the performance of
this second domain Kriging algorithm in GeoModeller
as it is computationally heavy.
Data Import Storage, Validation and Kriging
Procedures in GeoModeller
GeoModeller allows the user to load 3D numeric drillhole
data as from/to intervals attached to 3D drillhole
desurveyed path objects where they can be viewed and
compared with logged geology and the interpolated geology
model computed by the dual co-kriging method, Lajaunie
et al. 1997.
A procedure to regularize (composite) irregular from/to
sample intervals is available and should be used. Regularised
drillhole numeric data is then transferred to a 3D vertex
mesh for statistical/neighbourhood/variogram analysis and
1. B.Sc (Geology/Geophysics), FAusIMM, Intrepid Geophysics, Melbourne, Australia Corresponding author: rod@intrepid-geophysics.com
75
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Interpolating Assays and Physical Properties in Folded and Faulted Layered Geology
interpolation. Alternatively 3D numeric point data derived
from sources other than drillholes may be loaded directly
into a GeoModeller 3D vertex mesh for analysis (surface
and underground sampling, seismic velocity …).
Geostatistical procedures follow the normal sequence
of variogram analysis and cross validation followed by
interpolation using the chosen Kriging method (1D, 2D,
Domain Pot, Domain uvPot) or Sequential Gaussian
simulation. An Inverse distance interpolator is also available.
The Domain Kriging algorithms, by following the geology
gradients, produce a tighter more natural distribution of
interpolated physical values.
Examples of the Application of Domain
Kriging
A folded and faulted resource example is presented to
demonstrate the improvements that the new Domain
kriging algorithms can make to more traditional classical
Kriging interpolation results in this environment.
The Domain Kriging method has also been used in
the interpolation of physical properties (density and
susceptibility) where the explorer wishes to determine
whether his drilled resource target fully explains the
observed geophysics (gravity and magnetic surveys). The
interpolated physical property 3D grids or voxets are used as
inputs to GeoModeller’s geophysical forward modeling and
stochastic inversion. This is considered to be a more robust
alternative to single property modeling of the resource
geology. An ability to estimate geological uncertainty at all
points in the 3D resource model is an extra independent
capability of these techniques.
Rod paterson
Acknowledgements
This work has been carried out on behalf of Intrepid
Geophysics who is responsible for the commercialisation of
GeoModeller through an agreement with BRGM, France.
Many thanks to Antonio Guillen of the BRGM for his
work in developing these new algorithms.
References
Guillen, A., Courrioux, G., Bourgine, B. (2011). 3D Kriging using potential
fields surfaces, Proceedings IAMG 2011 conference September 5-9
2011, Salzburg, Austria
Bertoncello, A., Caers, J.K., Biver, P., Caumon, G. (2008). Geostatistics
on stratigraphic grids in Ortiz J et Emery X, Proc. 8th Geostatistics
Congress, 2, 677-686
Calcagno, P., Chilès J.P., Courrioux G., Guillen A. (2008): Geological
modelling from field data and geological knowledge: Part I. Modelling
method coupling 3D potential-field interpolation and geological rules.
Physics of the Earth and Planetary Interiors, Volume 171, Issues 1-4,
December 2008, pp. 147-157
Chilès, J.P., Delfiner, P. (1999): Geostatistics: Modeling Spatial Uncertainty.
John Wiley & Sons, New York, NY., 2nd Edition includes a proper
introduction to the geology co-kriging estimation, at the core of
Geomodeller technology.
Jayr, S., Gringarten, E., Tertois, A.L., Mallet, J.L., Dulac, J.C. (2008): The
need for a correct geological modelling support: the advent of the UVTtransform. First break 26.
Lajaunie, C., Courrioux, G., Manuel, L. (1997): Foliation fields and 3D
cartography in Geology 29, 571–584.
Mallet, J.L. (2004). Space-time mathematical framework for sedimentary
geology. Mathematical Geology 36, 1–32.
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Porphyry Cu-Au Occurrences in Batulicin Area, Batangasai, Jambi Province, Indonesia
Rusiana Permana, sufian nur hikmat,
Yosafat P. Simanjuntak, Eratmadji,
bronto sutopo
Porphyry Cu-Au Occurrences in Batulicin Area,
Batangasai, Jambi Province, Indonesia
Rusiana Permana1, sufian nur hikmat1, Yosafat P. Simanjuntak1, Eratmadji1 and Bronto Sutopo1
Batulicin and Bujang prospect are located in Batang Asai
district of Sarolangun region, Jambi province, Indonesia.
The mineralization in Batulicin prospect is typified by CuAu comprising chalcopyrite in biotite-magnetite±Kspar
alteration. Intermediate sulfidation epithermal overprint
around Batulicin prospect produces quartz vein with galena,
covellite, sphalerite and tennantite. Batulicin geology
consists of volcanic and intrusive rocks. Volcanic andesite
units, tuffs units (ash, accretionary lapilli, lapilli tuff-tuff
breccia), crystal tuff, dacite porphyry, phreatomagmatic and
phreatic breccia. There are three major intrusion consisting
of diorite, porphyritic diorite and hornblend-quartz diorite
(low altered-unaltered). The alteration is dominated by
kaolinite. Weak sericitic-illite-kaolinite and illite-smectite
appear in the west side of Batulicin, sericitic-illite±chlorite,
chlorite-shreddy chlorite-sericitic±epidote, chlorite-biotitemagnetite±Kspar, sericite
(muscovite-paragonite)illite-chlorite, advance
argillic (pyrophyllite-alunitedickite-kaolinite±diaspore)
and siliceous (massive-vuggy
quartz) alteration appear in
Batulicin upstream which
forms Bujang lithocap.
The porphyry veining is
dominated by D vein,
M vein, A vein, B vein,
C vein also banded quartz
vein which is overprints
early vein. Meanwhile,
the mineralization in
Bujang prospect is typified
by Cu-Au comprising
covellite, chalcocite, and
enargite in advanced argillic
(pyrophyllite-alunite-dickitekaolinite±diaspore) and
siliceous (vuggy-massive
quartz) alteration. ASD Terra
Spec™ used to delineate
alteration zonation specially
clay minerals (neutral to acid clays, low temperature to
high temperature clays) as one of the vectors in fluid
source interpretation. Bujang geology related to domediatreme complex which consist of coherent volcanic rocks
(crystal tuff, volcanic andesite and dacite) also clastic rocks
(phreatomagmatic breccia and hydrothermal breccia). The
major mineralization in Bujang deep level of high sulfidation
epithermal emerge in hydrothermal breccia and vein. The
geophysics data like ground magnetic used to delineate high
magnetic anomaly which is interpreted as biotite-magnetite
alteration (prograde), low magnetic anomaly is interpreted
as advance argillic and sericite alteration (retrograde). The
resistivity used to delineate high resistivity anomaly which
is interpreted as high silica alteration and the chargeability
used to delineate high chargeability anomaly which is
interpreted as pyrite shell.
1. PT. Aneka Tambang (Persero) Tbk. - Geomin Unit, Jl. Pemuda No.1, East Jakarta, Indonesia. Phone 021-4755380, Fax. 021-4759860 Corresponding author: rusianapermana@gmail.com, bronto.sutopo@gmail.com
Figure 1.
Interpretative
Geology-Alteration
Map of Batulicin,
Tangkui
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C. Querubin, S. Walters,
M. Papio, W. Satiyawan
C. Querubin, S. Walters, M. Papio, W. Satiyawan
The Pani Gold Project is located in the central section
of the north arm of Sulawesi, Indonesia, situated within
the township of Hulawa, district of Buntulia, regency of
Pohowatu, province of Gorontalo.
The morphology within the area is typified by NE to NW
trending ridges converging towards a central NW-SE
oriented massif. Gunung Pani is viewed as a northeast
trending ridge emanating from the central portion of this
massif.
Within the region, underlying Lower Miocene units are
capped by sub-aerial rhyodacitic volcanics, which were later
intruded by a Pliocene flow dome complex. Multi-phase
emplacement of felsic magma in Pani is inferred to have
been localized by Pliocene back-arc extensional rifting.
The main lithologies within Pani comprise porphyritic
to banded rhyodacites, lapilli tuffs, and fragmentals.
Silicification is the type of alteration commonly observed
and is exemplified by pervasive silica replacement of the
rhyodacite groundmass. Pyroclastic units are generally
argillized whereas heterolithologic volcanic breccias and
porphyritic rhyodacites within the lower sections in the
dome complex are mostly chloritized.
Mineralization is strongly influenced by structural controls
(i.e., extensional fractures) as well as by lithology (i.e., silicasericite altered porphyritic rhyodacites and pyroclastics,
breccia fill, quartz-adularia-limonite veins, or disseminations
in permeable volcanic lithologies and contacts).
Concentric fractures rimming a 4 km wide diatreme towards
the NW are assumed to represent sites most favourable for
mineralization, especially at their intersections with district
scale faults.
1. ???
2. ???? Corresponding author: ???
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Tectonics and Metallogeny of Mainland Southeast Asia – Framework for New Discovery
Opportunities
Neal Reynolds
Tectonics and Metallogeny of Mainland Southeast Asia
– Framework for New Discovery Opportunities
Neal Reynolds
The mineral industry of mainland Southeast Asia is
underdeveloped and its mineral potential remains largely
unrealised and generally not well understood. This reflects a
range of factors from geological to historical and
political. The present day operating and investment
environment remains challenging in most
jurisdictions; investment in exploration should
minimise exploration risk through optimised
understanding of metallogeny and discovery
opportunities.
From the Neoproterozoic into the Early Proterozoic,
Southeast Asia was located on the northern Gondwana
margin in the region of northern Australia. Mineral
Southeast Asian metallogeny is intimately related
to the long and complex history of accretion of
Gondwanan terranes that formed the eastern part
of the Asian continent. Due to substantial recent
improvements in understanding, a metallogenic
approach incorporating tectonic models and timespace reconstruction can provide a framework for
regional- to belt-scale metallogenic targeting and a
context for project assessment. Although significant
uncertainties still exist, this understanding of
metallogenic provinces can point to high priority
areas with potential for new discoveries.
The collage of cratonic and accretionary terranes
that comprise Southeast Asia was derived from
Gondwana in the Palaeozoic and amalgamated
in the Mesozoic during Asian accretion. The
Cathaysian terranes of South China and Indochina
separated from Gondwana in the Early Palaeozoic,
while the Sibumasu terranes separated in the
early Permian. The Indochina and Sibumasu
terranes are separated by accretionary arc belts
developed on the active margin of Indochina from
the Carboniferous to the Triassic. The Triassic to
Jurassic Indosinian orogeny saw amalgamation
of these terranes, together with North China
and Tarim which accreted with Siberia across
the Mongolian arc terranes forming the present
day Asian continent. Post-Indosinian evolution
of Southeast Asia reflects the development
of fringing arcs, arc collision events, and the
Cainozoic collision with India that had extensive
far-field effects across the region.
Figure 1: Summary terrane map of mainland Southeast Asia showing location of
significant mineral deposits.
1. CSA Global, Perth, WA Corresponding author: neal.reynolds@csaglobal.com
79
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Tectonics and Metallogeny of Mainland Southeast Asia – Framework for New Discovery
Opportunities
Neal Reynolds
systems in the Early Palaeozoic include Irish-type zinclead-silver and polymetallic VHMS in the Late Cambrian
to Early Ordovician of the Sibumasu terrane, and Irishtype and SHMS zinc-lead in the Devonian of the South
China terrane. SHMS zinc-lead mineral systems are also
associated with rift and drift of Sibumasu from Gondwana
in the Carboniferous.
A-type in a continental arc setting and was associated with
an evolving range of mineral systems including epithermal
gold, intrusive-related gold, porphyry and skarn coppergold, carbonate-replacement zinc-lead-silver, sedimenthosted gold, and tin- and tungsten-polymetallic skarns and
greisens.
Indosinian orogenic gold is best seen in the Raub-Bentong
zone of Malaysia. The culmination of the Indosinian
orogeny in the Late Triassic saw development of the first
phase of the Southeast Asian tin-tungsten belt related to
late orogenic granites.
Reactivation of old subduction zones in response to Indian
collision saw development of Eocene to Miocene porphyry
copper and epithermal mineral systems, especially in a belt
from western Yunnan into Vietnam.
The Late Carboniferous to Triassic saw development and
accretion of arc and back-arc belts fringing the Indochina
block. This is the most important metallogenic period in
Southeast Asia with a range of mineral systems including
VHMS, porphyry and skarn copper-gold, iron skarn,
epithermal gold, and sediment-hosted gold.
On the western Sibumasu margin, a second Late Cretaceous
phase of tin-tungsten mineralisation in the southeast Asian
tin-tungsten belt is associated with A-type magmatism in
the Late Cretaceous. Porphyry copper-gold and epithermal
systems developed in the central Myanmar arc belt in the
Oligocene to Miocene with sediment-hosted gold systems
in the back-arc in the Mio-Pliocene.
Re-initiation of subduction outboard of the collision
zones occurred along the western Sibumasu margin and
eastern Indochina-South China margin in the Late Triassic
to Jurassic. In South China and Indochina, JurassicCretaceous ‘Yanshanian’ magmatism evolved from I-type to
The range of mineral systems in mainland Southeast Asia
is broad and reflects the diverse and complex tectonic
history of the region. The more-developed mining industry
in contiguous belts in neighbouring southwest and south
China provides a good indication of the remaining potential
for discovery in Southeast Asia.
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Age and O, Hf Isotope Systematics of the Yandera Porphyry Rocks - Constraints on Magma
Sources, Crystallisation History and Crustal Evolution
Age and O, Hf Isotope Systematics of the Yandera
Porphyry Rocks - Constraints on Magma Sources,
Crystallisation History and Crustal Evolution
M. P. Roberts1 and R. A. Armstrong2
The Yandera Cu-Mo-(Au) porphyry deposit located on
the northern flanks of Mount Wilhelm in the Papua New
Guinean highlands is well-known (Figure 1). Exploration
has been more or less on-going since ca 1965 and results
covering such issues as structure and mineralisation have
been published (Titley, 1978; Watmuff, 1978). Age dating
using 1970s state-of-the-art Rb-Sr & Ar-Ar have also
been of great help in unravelling the relationship between
porphyry intrusions and country rock as well as the thermal
effects on the latter (Page, 1976). In working with the
Yandera porphyry rocks different companies have developed
complex lithological classifications to deal with things such
as bodies of breccia, rocks that look very similar to one
another, contradictory cross-cutting relationships, textural
variation and changes in mineralogy from the hydrothermal
effects of overprinting mineralisation. Add to this the
complexities from intrusion and crystallisation in an active
structure, and the problems
with lithological assignment
are obvious.
came from fresh core and surface exposures. It is worth
pointing out that zircon chemistry is unaffected by surficial
weathering processing and hence there is no prerequisite
for fresh material although any contamination must be
stringently avoided. Whole rock major and trace element
analysis was also carried out on the fresh material as well as
detailed petrology.
The Yandera deposit is currently in advanced stages of
exploration in the hands of Marengo Mining Limited with
first production scheduled for 2016. The current resource
comprises ca 5.2 billion Ibs Cu, 140 million Ibs Mo
and 1.1 million oz Au. Chalcopyrite and bornite are the
principal Cu-bearing species and molybdenite for Mo. The
mineralisation occurs in well-defined structural domains
along which the effects of alteration have been concentrated,
and in certain areas within bodies of breccia. The importance
In an effort to better define
classification of the porphyry
suite, an U-Pb zircon dating
study using SHRIMP
was undertaken. This was
later extended to include
Lu-Hf and O isotopes.
The results of the dating
and Hf-O isotope analysis
and their petrogenetic and
tectonic implications are
presented here. It should
be pointed out that this is
work in progress and one
of a plethora of different
investigations currently
underway.
A suite of samples was
collected covering the
principal lithologies defined
in the classifications
under test. These samples
Figure 1. Location of the Yandera deposit relative to other noteworthy deposits in Papua New Guinea.
1. Principal Geologist, Marengo Mining (Australia) Limited, 9 Havelock Street, West Perth, Australia Corresponding author: MalcolmR@marengomining.com
2 RSES, Australian National University, Canberra, Australia East Asia: Geology, Exploration Technologies and Mines - Bali 2013
81
l
of ground preparation for mineralisation cannot be overemphasised and are part of ongoing research and modelling.
The country rock for the Yandera deposit is the Bismarck
Intrusive Complex, the most prominent member of which
is a typical equigranular calc-alkaline I-type granodiorite
with biotite and hornblende as its mafic minerals; some
microgranular enclaves are present. An U-Pb zircon age of
10.42 Ma was obtained and no older inherited components
were found in zircons from this rock.
In contrast, U-Pb zircon ages from the Yandera porphyries
are younger and define 3 groups spanning 7.1 to 6.3 Ma.
The first group has ages between ca 7.1 to 6.9 Ma and are
“equigranular” porphyries (plagioclase-phyric granodiorite)
and one body of diorite, which may be an enclave from
one of these contemporary granitoids. One sample hosts
dessiminated chalcopyrite and may be evidence for an early
stage of mineralising porphyry intrusion. The second group
fall at ca 6.6 Ma and make up the bulk of the rock types
sampled. These rocks cover a wide range of textural types
from relatively equigranular porphyries (mistakenly assigned
to the earlier phase in previous classification schemes) to
quartz-phyric leucodacites. The former type have been found
to underlay and form the matrix to some bodies of breccia.
The youngest suite of dacitic porphyries have fragmental
textures and date at ca 6.4 Ma. These rocks are cross-cut
by mineralisation the age of which is unconstrained as
yet. It is worth noting that no appreciably older inherited
components apart from one Mesozoic age were found in
zircons from these rocks.
The major and trace element geochemistry of the
porphyries show that these, like their country rock host,
are typical calc-alkaline I-type granitoids. However, the
younger group appear to have more tholeiitic chemistry.
Overall, all of the porphyries are adakitic and there is a
broad increase in Sr/Y ratio from oldest to youngest within
the porphyry suite. The reason for this is unclear and may
be due to any number of petrogenetic processes operating
in the source region. The Lu-Hf and O isotopic analysis
by SHRIMP, on the same spots in the zircons from which
the ages were obtained, point to this source region as
being juvenile, mantle-like in characteristic with a tight
dispersion of eHf values and a looser mantle-like cluster
for dO18. This feature of the O isotopes is most probably
attributable to interaction with meteoric water in some
cases and surficial weathering in others.
Comparison of the Lu-Hf and O isotopes of the Yandera
porphyries with those of the Ok Tedi Cu-Au deposit (Figure 2) (data from Van Dongen et al., 2010) show that
the latter has a much greater crustal contribution and
old inherited ages indicating that the source region for
the Ok Tedi magmas was very different to that for the
Yandera rocks. Crustal composition, thickness and depth
to melting are important contributing factors to the metal
budget observed at or near surface in porphyry systems.
Van Wyck & Williams (2002) present U-Pb zircon data
from the Omung metamorphics and Goroka formation
Figure 2. InitialeHf vs d18O for the Yandera 1st and 2nd intrusive
event rocks. Also included are the Hf and O isotopic compositions of zircons
from Ok Tedi porphyries taken from Van Dongen et al. (2010) - data
shown are those with intrusive ages and not Proterozoic inherited cores.
also indicating Proterozoic contributions to rock formation.
These authors suggest that the Markham Valley represents
a major structural break separating older craton from newly
accreted crust. The new data from the Yandera rocks dispute
this and point to the break as lying to the south of the
Bismarck range along the Bismarck fault.
Timing of the Yandera magmatism appears to be at a similar
age as the collision of the Ontong Java plateau with the
Solomon Islands Arc postulated at ca 6 Ma (Petterson et
al., 1997). This collision event could have caused the switch
in motion sense of top to the SE to top to the NW along
the Ramu-Markham and adjacent faults. A change in plate
motion direction would cause the regional realignment
of the stress field leading to rotation and dilation of preexisting structures, which are apparent from regional
magnetic data over the Papua New Guinean highlands.
These in turn could have formed the focus of magmatism
and associated hydrothermal activity, and must have
extended to lower crust - mantle depth to produce magmas
of the type evidenced at the surface.
Acknowledgements
This abstract represents part of a technical paper in
preparation. It forms one of a number of different research
avenues currently underway and would not have got to this
stage without input from the team of geologists currently or
previously involved at Yandera - they are many.
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References
Page, RW, 1976. Geochronology of Igneous and Metamorphic Rocks in
the New Guinea Highlands. Bureau of Mineral Resources, Geology and
Geophysics. Report No: 162,117pp.
Petterson, MG, Neal, CR, Mahoney, JJ, Kroenke, LW, Saunders, AD,
Babbs, TL, Duncan, RA, Tolia, D and McGrail, B, 1997. Structure and
deformation of north and central Malaita, Solomon Islands: tectonic
implications for the Ontong Java Plateau-Solomon arc collision, and the
fate of oceanic plateaus. Tectonophysics, Volume 283: pp. 1-33
Titley, SR, Fleming, AW, Neale, TI, 1978. Tectonic evolution of the
porphyry copper system at Yandera, Papua New Guinea. Economic
Geology, Volume 73: pp. 810-828.
Van Dongen, M, Weinberg, RE, Tomkins, AG, Armstrong, RA, and
Woodhead, JD, 2010. Recycling of Proterozoic crust in Pleistocene
juvenile magmas and rapid formation of the Ok Tedi porphyry Cu-Au
deposit, Papua New Guinea. Lithos, Volume 114: pp. 282-292.
Van Wyck, N, and Williams, IS, 2002. Age and provenance of basement
metasediments from the Kubor and Bena Bena blocks, central
Highlands, Papua New Guinea: constraints on the tectonic evolution
of the northern Australian cratonic margin. Australian Journal of Earth
Science. Volume 49: pp. 565-577.
Watmuff, G, 1978. Geology and alteration-mineralisation zoning in the
central portion of the Yandera porphyry copper prospect, Papua New
Guinea. Economic Geology, Volume 73: pp. 829-856.
83
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Field Portable XRF – Good Techniques to Avoid Bad and Ugly Analyses.
Stephen Sugden
Field Portable XRF – Good Techniques to Avoid Bad and
Ugly Analyses
Stephen Sugden
Field portable XRF (FP-XRF) instruments are a rapidly
maturing technology which is revolutionising the
exploration and exploitation of mineral deposits. The
instruments offer a number of significant advantages to the
geologist including:
• Real-time, non destructive analysis in the field, reducing
analysis turnaround times.
• Integration of the instrument with GPS, mobile GIS
devices and geochemical EDA packages such as ioGAS,
enabling fast efficient interpretation of the analyses.
• Results of interest and interpretations can be
immediately acted upon, enabling program decision
points to be brought forward.
• Screening of samples to reduce analysis costs and
prioritisation of shipment to remote laboratories.
• The potential to undertake real time alteration and
lithological mapping.
To realise these benefits it is critical that users understand
the limitations of FP-XRF instruments. These include:
• Not all elements can be analysed, for example Na, while
other light atomic mass elements such as Mg and Al may
not be analysable on all instruments.
• Analysis of some elements can be problematic due to
spectral interferences. For example Fe with Co and Pb
with As.
• Limits of detection are often significantly higher
compared to laboratory analyses. Depending on the
instrument, detection limits for chalcophile elements
such as Cu range between 5-30ppm, while lithophile
elements such as K and Al range between 30ppm->1%.
• The accuracy and precision of analyses are generally
lower compared to laboratory analyses. It is rare that
accurate readings are obtained without the application
of calibration factors and reduced precision will be seen,
depending on the degree of preparation undertaken.
• Reductions in accuracy and precision are compounded by
poor practises (e.g. short reading times and inadequate
sample preparation).
• Instruments have a number of modes of operation
which are optimised for different suites of elements and
concentration ranges (e.g. soil and mining) and some
modes are not suitable for the analysis of geological
samples (e.g. Alloy). The user therefore needs to select
the mode/s most appropriate to their situation. Again
reduced accuracy and precision will be seen if an
inappropriate mode is used.
A further consideration is compliance. The Table 1 checklist
of the recently released 2012 JORC code now specifically
mentions FP-XRF instruments, their calibration and reading
parameters. Should analyses be released to the market then
supporting discussion, detailing the underlying instrument
set-up and analysis methodology will be required under the
new “if not, why not” reporting requirements of the code.
Many of these limitations however can be mitigated by
completing a test and optimisation program to improve the
accuracy and precision of the analyses and so demonstrate to
the recipients of the analyses and regulatory bodies that they
are “fit for purpose”.
A typical test and optimisation program, used by ioGlobal,
detailing issues to be considered is described below.
1. Selection and preparation of samples and/or standard
reference materials for analysis.
• Sample homogeneity. More homogenous samples
will give more consistent results. The area measured
by the instrument is around 1cm2 and the depth of
penetration is generally limited to the surface for all
except the lightest sample matrices. Biases therefore
will result when analysing materials that are coarse
grained and pulverising to produce a homogenous
fine grained sample for analysis is almost always
necessary.
• Short cuts at this stage are the greatest source of
error in FP-XRF analyses and ioGlobal considers
good sample preparation to be a critical component
in generating quality analyses and robust instrument
calibrations.
• Moisture content. Generally automatically corrected
for by the instrument unless present in significant
amounts. However moisture can cause dilution of
1. Principal Consultant, ioGlobal Pty Ltd, 369 Newcastle Street Northbridge, WA 6003 Australia. Corresponding author: steve.sugden@ioglobal.net
84
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Field Portable XRF – Good Techniques to Avoid Bad and Ugly Analyses.
results and impedes the ability to properly prepare
samples. Laboratories always dry samples before
analysis, so differences will be seen between field
assays and check laboratory analyses when moisture
is present.
2. Precision Assessment and Optimisation.
• Instrument read time. XRF instruments measure the
energy (KeV) and intensity (Counts/Second) of the
secondary X-ray Fluorescence produced as a result
of striking the sample with high energy X-rays. The
energy emitted is characteristic for each element. As
the intensity of the energy is measured in counts/
second, longer read times will generate a larger
sampling set improving the ability to better resolve
the energy spectrum produced, resulting in better
precision and the ability (within limits) to analyse to
lower concentrations.
• Trials undertaken by ioGlobal have found that
increasing read times often has the greatest impact in
generating interpretable data.
• Precision is assessed by analysing paired samples
at different reading times and assessing the relative
differences of the sample pairs.
3. Detection Limit Assessment.
• The paired data is assessed using the detection limit
calculation routine in ioGAS.
• Ideally the majority of values for the elements of
interest should be above the calculated detection limit
and low enough that true background or grade cut off
values can reliably be determined.
• Should the detection limits not be suitable by either
criterion, then reanalysis using longer reading times
should be made.
• It may not be possible to achieve suitable detection
limits in which case the FP-XRF instrument analyses
may not be “fit for purpose”. 4. Accuracy and Bias Assessment.
• A selection of standards are analysed which:
- cover the expected grade range,
- have a similar sample matrix to the samples being
routinely analysed,
- are certified by a total analysis method for the
elements of interest and
- have concentrations for the elements of interest
above the limits of detection limits previously
determined.
• Each standard should be analysed a number of times,
using the reading time previously determined. The
Stephen Sugden
analyses are then compared to the certified value and
ideally should be the same.
• If there is an observed bias and the analyses have a
suitable precision then a custom calibration factor
may be calculated to improve accuracy.
5. Custom Calibration Factor Calculation.
• Custom calibrations can be calculated by plotting
either
- a group of samples which have been analysed
both by the FP-XRF instrument and a laboratory,
using a total or near total analysis method,
- or a set of standards which have been analysed
using the FP-XRF.
• The paired results are plotted on a scatter plot and
a line of best fit calculated which is forced through
the origin. The slope of the line (correction factor)
is applied to the FP-XRF data to derive a corrected
value.
6. Sample Packaging Signal Attenuation and
Contamination Assessment.
• Analysis of samples through plastic, fabric or paper
bags, can impact on the accuracy of results and
potentially introduce contaminants. Once the effect
has been quantified then appropriate corrections can
be applied to improve the ultimate accuracy of the
analyses.
• It has been noted (Innov-X 2010) that analysis
through thin plastic bags can result in Cr, Ba and V
values being lower by 20-30%. Test work by ioGlobal
has also shown that for light atomic elements,
analysing through plastic can degrade results by over
90%. Paper packets can also attenuate analyses and
introduce contamination, for example Ti from paper
whiteners. It has also been reported that some paper
sample packets have high S contents.
• To assess the effect of the packaging on accuracy, a
series of samples are analysed in their packaging and
by the laboratory.
• Contaminant assessment is made by analysing a
blank and noting if any contaminant elements are
present. If the contaminant is an element of interest
then a different packing material should be assessed
to find a suitable replacement.
References:
Joint Ore Reserves Committee (2012). Australian Code for Reporting of
Exploration Resullts, Mineral Resources and Ore Reserves. (The JORC
Code 2012 Edition).
Innov-X Systems (2010). User Manual, Delta Family: Hand Held XRF
Analyisers.
85
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A Lithocap in the Bujang Prospect, Jambi Province: Related or not Related
to the Porphyry Cu – Au Mineralisation System
Erric Sukmawan, Yosafat Palty Yudhistira
Simanjuntak, Wanda Ilham Dani,
Rusiana Permana, Bronto Sutopo
A Lithocap in the Bujang Prospect, Jambi Province:
Related or not Related to the Porphyry Cu – Au
Mineralisation System
Erric Sukmawan1, Yosafat Palty Yudhistira Simanjuntak1, Wanda Ilham Dani1, Rusiana Permana1 and Bronto Sutopo1
The Bujang prospect is an island arc setting located in the
Southwest corner of Jambi Province in the Sunda Banda
archipelago of Indonesia. The prospect is hosted in middle
Tertiary volcanic and intrusive rocks within the Great
Sumatran Fault Zone. Locally, sequence of andesitic dacitic
volcanic and volcaniclastics breccias was cut by hydrothermal
and phreatomagmatic breccias.
Lithocaps exhibit heterogeneous distributions of mineral
assemblages with each mineral showing a distinctive type
of mineral deposition style. In Bujang Prospect, Jambi
Province, the presence of massive-vuggy quartz indicates
the development of epithermal - high sulphidation systems.
This indication was followed by alteration mapping using
short wavelength infrared (SWIR) reflectance spectroscopy
methods that allows rapid identification of clay minerals
which involves some key characteristics of these clays such
as crystallinity and wavelength peak. This leads to a better
understanding of the projects deposits systems, especially
to interpret vector towards higher temperature zone of the
systems and towards the proximal zone of the mineralisation.
The host rocks are completely altered to advanced argillic
and silicic alteration (lithocap) while low temperature, near
neutral argillic is in the peripheral area. Lithocap in Bujang
Prospect is dominated by acid alteration minerals formed
in high temperatures such as alunite, pyrophyllite, kaolinite,
dickite, diaspore. Four alteration zones lineated by these
minerals, i.e., vuggy silica, advanced argillic, intermediate
argillic dan sericitic zone hosted in andesitic to dacitic
volcanic rocks and breccias. Hydrothermal breccia is one
of the most intense mineralized host rocks that relate
to high grade of Au, while phreatomagmatic breccia is
related to high temperature pyrophyllite alteration that
content juvenile-magmatic origin clast. Petrographic and
mineragraphic studies of some selected mineralised host
Figure 1.
1. PT. Aneka Tambang Tbk.- Unit Geomin, Jl. Pemuda No.1, Jakarta Timur Telp. 021-4755380, Fax. 021-4759860 Corresponding author: erric.sukmawan@antam.com
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A Lithocap in the Bujang Prospect, Jambi Province: Related or not Related
to the Porphyry Cu – Au Mineralisation System
rock shows the presence of enargite, pyrite and covellite
associated with massive/vuggy silica. High grade Au is
associated with partialy oxide rock that produces minerals
such as jarosite, hematite and goethite. Advanced argillic
zone associated with topaz showing the possibility of
porphyry – related high sulphidation systems and then
confirmed by the evaluation of several parameters, such as
alunite wavelength peak and high magnetic anomaly in
the center of Bujang Prospect. The identification of clay
minerals in the surface by short wave length infra-red
(SWIR) reflectance spectroscopy analysis shows alunite
wavelength peak shifting from 1475 nm and reaching
1494.48 nm near JR 1 hill. Recent studies shows that the
alunite wavelength peak shifts towards longer wavelength
when it gets closer to the intrusive center (Arribas et al.,
1995). Geophysics surveys in the Bujang lithocap shows
Erric Sukmawan, Yosafat Palty Yudhistira
Simanjuntak, Wanda Ilham Dani,
Rusiana Permana, Bronto Sutopo
several signatures where high resistivity is related to silicic
alteration while low chargeability is barren, low sulfide
content. First scout drilling in Bujang Prospect shows several
mineral assemblages including pyrophyllite – paragonite,
illite – smectite and kaolinite – smectite. These assemblages
correlate with geophysics results, resistivity and chargeability,
where each assemblages reflects certain colour in resistivity
and chargeability sections.
Two high magnetic anomalies (± 600 m width) that have
a top of about 300 m below the surface were interpreted as
intrusions that may host porphyry Cu systems in the center
of Bujang diatreme complex. Further data and analysis
from alteration mapping and test drilling will help with the
understanding whether the high sulphidation systems in
Bujang Prospect related to porphyry Au-Cu or not.
l
poster
87
Hydrothermal Alteration Study In Tertiary Volcanism Ayah Area, Southern Central Java
Adi Sulaksono, Muhammad A.
Luthan, Putu A. Andhira
Hydrothermal Alteration Study in Tertiary Volcanism
Ayah Area, Southern Central Java
Adi Sulaksono1 ,†, Muhammad A. Luthan1, and Putu A. Andhira2
The Ayah Area is located in Kebumen
Regency, Southern Central Java as a part of
the Tertiary volcanism site in Sunda arc ( Java
Island) Indonesia. Observations based on the
aerial photographs show that more than 60%
of the research area is volcanic terrain that
controlled by geological structure indications
with NW-SE relative trending. This situation
becomes important because in many cases,
hydrothermal alteration is mostly controlled by
volcanic activity and geological structures. Many
epithermal deposits are regionally associated
with volcanic-related structures (Rytuba, 1981).
Stratigraphically, the research area is composed
by Late Oligocene – Early Miocene andesite
intrusive unit as a feeder of paleovolcanism, Late
Oligocene – Early Miocene volcanic breccia
unit of Gabon Formation and disconformity
Middle Miocene limestone unit of Kalipucang
Formation (Asikin, 1994). Structural control
of the research area such as NW-SE strike slip
faults and joints (including sheeting joints in
the intrusive rocks). In this condition, the role
of joints is very important as the porous zone in
hydrothermal system that cause strongly altered
andesite. Some of faults are important as the
pathways or porous zones for hydrothermal
fluids that affect the pattern of alteration and
alteration zoning. Several locations showed
that along the river (fault zone) is the strongly
altered rocks.
The geological heritage of paleovolcanism
is shown by the presence of volcanic activity
products, include: intrusive rocks (andesite and
basalt), vent breccia, andesitic lava, tuff breccia,
lapilli tuff, laharic breccia, and pebbly sandstone. Referring to
the volcanic depositional environment scheme by Bogie and
Mackenzie (1998), Ayah area is the central to distal facies of a
paleovolcanic system. This setting becomes interesting because
the character of volcanic settings which host epithermal
deposits is most commonly central to proximal, with volcanic-
Figure 1. Surface alteration map (A) and cross-section (B) of the Ayah
area, Kebumen Regency, southern Central Java.
hosted deposits typically occurring with effusive or pyroclastic
rocks (Sillitoe and Bonham, 1984). The end of Tertiary
volcanic activity showed by Middle Miocene carbonate rocks
of Kalipucang Formation. Because it was occurred after
1 Student of University of Pembangunan Nasional ”Veteran” Yogyakarta
2 Student of Padjajaran University
† Author and presenter of poster
88
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Hydrothermal Alteration Study In Tertiary Volcanism Ayah Area, Southern Central Java
the Tertiary volcanism activity, disconformity Kalipucang
Formation is a barren zone.
Evaluation based on hand specimen observations,
petrographic analysis, and powder X-Ray diffraction analysis
of some Gabon Formation’s altered rock samples show
three hydrotermal alteration types (refer to Thomson and
Thomson (1996)); chlorite - calcite ± epidote ± pyrite zone
(propylitic type), quartz - montmorillonite ± sericite ± pyrite
zone (argillic type), and kaolin - alunite - cristobalite zone
(advanced argillic type).
The outcrops of propylitic type is characterized by green to
gray color. In the Ayah area, this altered rock zone has more
extensive coverage than other types (> 60%). Based on field
interpretation the propylitic zone is located on the outside
of argillic zone. The argillic type is characterized by the
presence of stockwork zones and quartz vein that show some
Adi Sulaksono, Muhammad A.
Luthan, Putu A. Andhira
textures including: crustiform, banded, massive chalcedonic,
vuggy quartz, sugary texture, and comb structure. Vein type
mineralization associated with pervasive alteration of this
type. In some locations, the pattern and distribution of this
alteration zone is controlled by strike slip fault. The presence
of advanced argillic alteration type is overprinting on the
argillic zone. This alteration is characterized by the mineral
assemblage: kaolin - alunite - cristobalite. The origin of
alunite or this acid-sulfate alteration is formed by atmospheric
oxidation of H2S in the vadose zone over the water table,
associated with fumarolic discharge of vapor released by
deeper boiling fluids (steam-heated) (refer to Bethke (1984)
and Rye et al. (1992)). In the other hand, the presence
of boulder vuggy silica at the surface of the research area
confirms that there is an involvement of acidic hydrothermal
condition that also forms advanced argillic type.
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Geoff Taylor, Greg Corbett,
Grace Cumming
Geoff Taylor, Greg Corbett and Grace Cumming
Introduction
Detailed Geology
Fiji is an isolated nation in the South Pacific Ocean
approximately 3,000 kilometers north east of Australia.
Vanua Levu is the second larger of the two major islands.
North east Vanua Levu hosts a number of polymetallic
and Au occurrences localized within a 15 km long graben
formed by extension along the Nubu Fault, which is a
major north east trending basement structure. The Cirianiu
prospect which lies in the center of the graben comprises
low sulphidation epithermal Au mineralization currently
under investigation by Kalo Exploration. Previous explorers
used vertical drilling to evaluate a model based upon flat
lying replacement mineralization,
whereas steep faults are now
interpreted to have introduced
mineralization which has been
remobilized into a flat lying
supergene blanket.
The stratigraphy at Cirianiu has been divided into four
recognizable units including: The Upper Sandstone Package,
The Upper Qiriyaga, The Lower Qiriyaga and Lower
Sandstone Package. Although most prominent in the Upper
Quiriyaga Unit, allochthonous limestone blocks occur
erratically throughout the sequence. The Upper Qiriyaga
is dominated by lithic fiamme tuffs and breccias passing
downwards to the Lower Qiriyaga boulder breccias and
andesite fiamme breccia. A massive flat lying feldspar phyric
andesite sill has gradational contacts into fractured andesite
and in situ and clast rotated andesitic breccias. Hydrothermal
Geological Setting
The coalesced Mio-Pliocene
volcanic fields which make up
north eastern Vanua Levu are cut
by the NE trending Nasavu and
Nubu Faults formed as arc-parallel
graben bounding faults. At Cirianiu
NNE trending dilatant fractures
have developed by a component
of sinistral strike-slip movement
during extension on the Nubu
Fault. The volcanic vents erupted
above and below sea level and were
accompanied by the resedimentation
of volcanic facies in a shallow
marine environment. Large volume
explosive eruptions are probably
related to caldera collapse. A period
quiescence followed evidenced
by the deposition of fine grained
sedimentary facies.
Figure 1. Cross section 500N showing the development of high grade supergene Au overlying feeder
structures. Note the exact dip on these structures remains unknown.
1. Geoff Taylor, Consultant, Savusavu, Fiji. Corresponding author: geofftaylor@connect.com.fj 2. Greg Corbett, Consultant, Sydney, Australia
3. Grace Cumming, Consultant, Hobart, Australia
90
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breccias are fault related, steep dipping and flare upwards as
funnels. The main hydrothermal breccia, the 17 breccia occurs
on the F1 fault and parallel faults F1, F2, F3 and F4 all host
supergene enriched high grade gold mineralization.
Alteration
Argillic alteration, illite-chlorite with variable silica
pervasively floods the permeable volcanic and volcaniclastic
rocks and commonly reduces the rock competency.
Manganese is common and occurs as mounds and
pervades the mudstones and fiamme tuffs and breccias.
Silicification associated with argillic alteration floods
along the flat bedded fracture planes and most importantly
as intense silicification within the silica injection phase
of the breccia pipes. The intense silicification makes the
host rocks competent and amenable to cracking during
Au mineralization. The silicified bedded sediments and
coral clasts suggest this silicification has been formed by
replacement of limestone and carbonate breccias. Inner
propylitic alteration recognized as epidote veins and outer
propylitic as chlorite-carbonate on the margins of the
alteration system, are indicative of intrusion activity.
Mineralisation
Low grade Au mineralisation with hypogene grades of < 1.0
g/t Au occurs within pyritic illite altered breccias. It is mostly
of the low sulphidation epithermal quartz - sulphide Au
style. Gold is contained within the coarse cubic pyrite. The
low grade ore is similar to Round Mountain (Nevada) style
Au deposits and is amenable to heap leaching. Higher Au
grades occur on faults at depth within more competent host
rocks. Carbonate base metal Au mineralisation contains low
temperature yellow sphalerite, galena and minor chalcopyrite
which formed by the mixing of ore fluids with bicarbonate
waters at low temperatures. Primary bonanza Au grades have
not been recognized yet, but could develop in the cooler
portions of the poorly eroded hydrothermal system.
Geoff Taylor, Greg Corbett,
Grace Cumming
Supergene Gold Enrichment
Significant supergene Au enrichment has concentrated
collapsing down steep dipping faults and breccias to
concentrate at the base of oxidation by both chemical and
mechanical processes. The Ag: Au ratio is lower within
supergene ores and displays a higher Au fineness than the
hypogene mineralisation. Significant drill hole intersections
in this zone of supergene enrichment include 86.0m @
5.19g/t gold including 6.75m @ 37.8g/t gold and up to 2m
@ 102g/t gold.
The Model
• Dilatant structures localize ore zones and are best
recognized by northerly flexures within the major north
east trending graben.
• Parallel near vertical faults, F1, F2, F3 and F4 localize
the ore bearing fluids and provide conduits for Au
mineralization.
• Both flat bedded silicification and fracture controlled
silicification allow mineralizing fluids to crack the
competent hosts and contain higher Au grades.
• Significant supergene Au enrichment occurs at the base
of oxidation and above the water table in these funnels.
• The supergene high Au grade zones can contain
exploitable heap leachable Au on the parallel structures
and could represent a mineable gold resource.
• Hypogene carbonate-base metal Au and quartz-sulphide
Au mineralization has not been fully explored and low
temperature sphalerite here indicates possible bonanza
gold at higher levels of a poorly eroded hydrothermal
system.
• I.P. and resistivity surveys are likely to indicate
coincident anomalies as drillable targets.
91
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Andrew J. Vigar, Ian Taylor, Greg
MacDonald
Andrew J Vigar, Ian Taylor, Greg MacDonald
The resource estimation of lateritic deposits, such as
Aurukun, presents specific issues related to the lateral
changes in thickness and elevation of the various horizontal
layers (or zones) within the deposit where the x and y
dimensions are orders of magnitude greater than the z
dimension. The objective was to develop a three dimensional
(3D) block model that retained the vertical and lateral
variation inherent in deposits of this type to allow full
optimisation of the production plan without prior selection
of an economic portion (enriched bauxite layers) of the
profile at the resource estimation stage.
The Aurukun bauxite deposit was held by Chalco Australia
Pty Ltd (Chalco) until it withdrew from the agreement
with the Queensland government in 2010 and it is now
open for tender. The deposit forms part of the world class
Weipa bauxite province, Cape York Peninsula, Queensland,
Australia. The bauxite is predominantly pisolitic with an upper
boehmite-rich zone and lower gibbsite-rich zone. The bauxite
consists of both in-situ and reworked domains, is overlain by
a thin soil horizon and has kaolinite clay as a transitional base.
A Portable Infrared Mineral Analyser (PIMA) was utilised
on site, in additional to elemental assay, on each drill sample
to determine the mineralogy, in particular levels of boehmite,
gibbsite, kaolinite and reactive silica.
As part of the scope of work, a field program was undertaken
using large diameter Boart Longyear Sonic drilling to
acquire detailed density measurements across the deposit
to allow compliance with Joint Ore Reserves Committee
( JORC) reporting requirements.
Interpretation of the stratigraphy was conducted on a hole
by hole basis with definition of the zone layering based
on stratigraphy, geochemistry and mineralogy. The zone
boundaries were then modelled as 3D surfaces and used to
constrain a block model.
The block model estimation used the Ordinary Kriging
method, with the estimation done in unfolded space and
then refolded, therefore maintaining the zones irrespective
of thickness or orientation. The unfolding process converts
the real-world positions for both blocks and informing
samples to a scaled position relative to the roof and floor of
each zone.
Analysis of the data and variography were also undertaken
in unfolded space. The x and y dimensions are unchanged,
but the z dimension is a relative position. The effect of the
unfolding and limits on number of samples per hole is to
“push” the informing sample search sideways but within the
stratification, rather than vertically. This honours the strong
vertical zonation within the bauxite profile.
The JORC code requires that the stated resource must have
“reasonable prospects for economic extraction”. This is a
qualitative rather than quantitative definition. A number
of selection criteria to define a resource roof and floor
were developed in consultation with the project engineers
and owners to meet these criteria. The vertical selection of
material to include in the resource highlights the variation
in the development (and destruction) of the bauxite profile
from area to area within the deposit.
1. ???
2. ???? Corresponding author: ???
92
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Brad Whisson
Developments in Microwave Digestion for
Geochemical Analysis
Brad Whisson1
Digestion of mineral samples in acid has traditionally been
regarded as a “low-tech” process, and there has been little
development in this field over the past 30 years, prior to the
advent of microwave digestion systems.
The rapid energising of molecules and consequent
acceleration of chemical reactions by absorption of
microwave radiation has logically led to the use of
microwave heating in chemical applications such as synthesis
and digestion. Microwave-assisted digestion of mineral
samples has been developed to a usable technique over the
past decade, with several manufacturers continually refining
their approaches and equipment.
Samples are digested in sealed, PTFE-lined, microwavetransparent pressure vessels, and digest conditions are
monitored via infra-red sensors and internal sensors.
Digestions can be controlled with respect to microwave
power, vessel temperature and pressure, which enables
achievement of reproducible digestion conditions across
a wide range of sample materials. Microwave-assisted
digestion techniques have now been accepted by the
scientific community in many areas, and are incorporated
into various USEPA methods.
A microwave-assisted digestion will typically reach
completion in one tenth of the time taken by an equivalent
hotplate method, which largely mitigates the capacity
limitation of the equipment. The approach offers excellent
recoveries for most mineral matrices when compared
to other acid digest techniques. Microwave digestions
are performed in sealed vessels at temperatures typically
around 200°C and pressures of approximately 20 Bar,
which has technical, environmental and operational
benefits. As the oxidising power of acids generally
increases with temperature, the oxidising effect of the
acids is far greater in the microwave-assisted digestion
than in atmospheric pressure digests. Microwave
digestions are therefore very effective at decomposing
sulphides, silicates and other resistant matrices. The use
of sealed vessels in these digestions has the additional
benefits of retaining volatile elements such as mercury
and germanium in the digest vessel, and preventing
cross-contamination from spitting.
Although the technique is limited to sub-1 gram sample
aliquots for practical purposes, modern sample preparation
techniques reliably reduce particle size to the point where
multielement analysis can be satisfactorily performed on a
few tenths of a gram of sample. The sample size limitation
precludes routine analysis for gold, due to sampling and
detection limit constraints.
LabWest adopted microwave assisted digestion as its
primary decomposition technique from the start, developing
methods that reliably catered for a wide range of geological
materials, and has now analysed some 150,000 geochemical
samples in its microwave systems. These have covered
a wide range of sample types, and valuable insights to
the strengths and potential of the technique have been
gained. The analytical strengths of ICP-Optical Emission
Spectrometry (ICP-OES) and ICP-Mass Spectrometry
(ICP-MS) combined with microwave-assisted digestion
enable determination of most metallic elements down to low
detection limits.
Aqua-regia-based, microwave assisted digests give
consistently high recoveries for base metals, readily
decomposing sulphides and most organic matter, and
provide a cost-effective means of obtaining a wide range of
information for the explorer. Hydrofluoric acid (HF) based
digests are used where total decomposition of the host rock
matrix is necessary, and good whole-rock approximations
can be achieved with these digests.
The ability of microwave-assisted digestion techniques to
achieve high recoveries of the metals that are traditionally
harder to extract by acid digestion (eg. Hf, Nb, W, Zr, RareEarths) lends itself nicely to litho-geochemical studies. A
single digest solution can therefore be determined by combined
ICP-OES and ICP-MS for suites of up to 63 elements,
including base and trace metals, major rock-forming oxides
and rare-earths. This has significant cost-saving implications,
and enables exploration geologists and geochemists to gather
a very detailed picture of the mineral environment in one step.
Uranium exploration is particularly well catered for.
Microwave digestion, when coupled with ICP-MS, offers
very good recoveries of the rare-earths with typical detection
1. LabWest Minerals Analysis Pty Ltd, Perth, Western Australia Corresponding author: b.whisson@labwest.net
93
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limits of 0.05ppm or better. Parallel analysis of standard
materials against the traditional techniques shows excellent
recoveries for REEs and the more refractory elements.
Microwave-assisted digestion offers a well-priced alternative
to alkaline fusion or XRF for whole-rock analysis. Under
microwave digestion conditions, appropriate acid mixtures
containing HF completely dissolve most common rockforming minerals. The major oxide forming elements (Na,
K, Ca, Mg, Fe, Al, S, P, Si) are determined from low levels
(0.01%) up to high percentage levels in the rock.
Brad Whisson
Microwave digestion is also well suited to analysis of plant
materials for trace elements. Plant materials are readily
analysed for the full range of elements determined on
mineral samples, including gold, and the very low detection
limits required by geochemical exploration applications are
achieved with ICP-Mass spectrometry.
Future research and development directions will be
discussed.

Bulletin No 57 (Low Res) - SJS Resource Management

Transcription

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