Depósito Ni-Cu Santa Rita - Bahia

Depósito Ni-Cu Santa Rita - Bahia
Cesar F. Ferreira Filho
IG – Universidade de Brasília
Eurípedes Mariano da Cunha
5° SIMEXMIN
Ouro Preto
23 de maio de 2012
Picture February 2012
Outline
• Overview of the Santa Rita Project
Eurípedes Mariano da Cunha (Exploration Manager)
•The Santa Rita Ni-Cu Deposit
Mirabela Nickel Exploration Team
• Discussion of Recent Data
Sulfur isotopes
LA-ICPMS zircon geochronology
PGE / PGM data
EXPLORATION & RESEARCH
Exploration History
• Mineração Nhambú Limitada 1979-1981 (JV between BP-RTZ)
• Regional and grid exploration culminating in 2 ddh (328.88m)
• Concluded that the Fazenda Mirabela nickel anomaly was of lateritic origin and
unrelated to significant primary mineralization
• Caraíba Metais S/A 1985-1989
• Reconnaissance and grid exploration with 5 ddh (579.70m). 4 holes intersected
intervals of disseminated Ni and Cu sulphides within the Fazenda Mirabela MaficUltramafic Intrusion
• Sulphide resource estimated as 18 Mt @ 0.5% Ni, 0.2% Cu but Caraíba were not
interested due to low Cu grades and the prevailing economic conditions
• Companhia Baiana de Pesquisa Mineral (CBPM) 1989-2002
• Detailed grid exploration, airborne EM survey leading to 5 ddh (1,340.35m)
to confirm the earlier sulphide resource. Auger drilling and 36 ddh totaling 985.8m
defined a laterite resource of 54.7Mt @ 0.78% Ni
• Public tender of project in 2003 won by Mirabela Mineração do Brasil Ltda (MBN)
• MBN began laterite evaluation in Mar. 2004 and sulphide evaluation in Sep. 2004
Exploration History
Ano de 2006
• Dezembro – audiências públicas referente aos Relatório de Impacto
Ambiental (RIMA) .
Ano de 2007
• Novembro – Início das atividades de implantação do Empreendimento.
Ano de 2009
• Início da operação da Mina Santa Rita;
Ano de 2010
• Produção de 10,3 mil toneladas de níquel contido.
• Itagibá-BA passa a ser o município com maior arrecadação de CFEM na
Bahia.
Ano de 2012 (Target)
6.5 Mt ROM
147 Kt concentrado (13% Ni)
Produção - 20.2 Kt – Ni contido
Mercado: VM (Fortaleza de Minas) e Noril'sk (Finland)
Orthopyroxenite Ridge and Tailing Dam - 2004
Exploração & Pesquisa
Orthopyroxenite Ridge and Tailing Dam – 2012
Exploração & Pesquisa
Infrastructure
Exploração & Pesquisa
Environmental Conditioning
Fauna monitoring
Seismograph monitoring
Revegetation
ETE Monitoring
Environmental noise
monitoring
Hedgehog reabilitation
(Chaetomys subspinosus)
Flora monitoring
Fauna monitoring
Air quality monitoring
Waste Management
Seletive gathering
Aquatic Ecosystem
implementation
Source: Environment and Sustainability
9
Sustainability Actions and Environmental Education
Sustainability development
support
Talk Project
Sustainability development
support – Food course
Citizen Mirabela Project
Trail Project
Eco Blitz Project
Mirathlete Project
Pre- University Course
Source: Environment and Sustainability
Mexa-se Program
Trained people in 2010 and 2011 = 150
Hired people = 45
Teacher Training
Supporting the CETEP
with courses
Sow Project
10
Flow Sheet – Plant
Balls Mill II
Primary Crusher
Stockpile
Source: Plant Operation
SAG Mill I
De-sliming
Concentrate Thickener
Flotation
Tailings Thickener
Filtration
Nickel Concentrate – 13% Ni Grade
Tailings Dam
11
Santa Rita Mining Phases
Source: Mine Planning and Control
12
Santa Rita Mining Phases – Phase 1
Source: Mine Planning and Control
13
Santa Rita Mining Phases – Phase 2
Source: Mine Planning and Control
14
Santa Rita Mining Phases – Phase 3
Source: Mine Planning and Control
15
Santa Rita Mining Phases – Phase 4
Source: Mine Planning and Control
16
Santa Rita Mining Phases – Phase 5
Source: Mine Planning and Control
17
Santa Rita Mining Phases – Phase 6A
Source: Mine Planning and Control
18
Santa Rita Mining Phases – Phase 6B
Source: Mine Planning and Control
19
Santa Rita Mining Phases – Phase 07
Source: Mine Planning and Control
20
Santa Rita Ni-Cu Deposit
Cava Norte
March 2010
The largest example of stratiform/stratabound
Ni-Cu sulfide deposit hosted within the interior
of a layered intrusion.
Geological
Setting
• Several mafic and maficultramafic intrusions located
close to the contact between
the Itabuna-Salvador-Curaçá
Orogen and the Jequié Block.
• The Fazenda Mirabela
intrusion is considered to be
emplaced during (or shortly
after) the collision of these
blocks during the ca 2.02.1Ga TransAmazonian
Orogeny (Barbosa et al.
2003).
• Geochronological studies
(zircon U-Pb LA-ICPMS) of
layered intrusions and host
rocks (Fausto Lazarin M.Sc –
UnB) support this
interpretation.
Santa Rita Ni-Cu Deposit
(www.mirabela.com.au)
The stratiform/stratabound mineralization is located
in the transition from dunite in the footwall to
gabbronorite in the hangingwall.
Disseminated sulfides (Pn-Py-Po-Cpy) occur mainly in
harzburgite, olivine opxt and opxt.
Cava Norte (March 2010)
View to from NE to SW
Pxt
Gbrnt
Dunite / Hzb
dyke
Cava Norte (March 2010)
View to from NE to SW
Pxt
Gbrnt
Dunite / Hzb
dyke
View from Cava Norte
SW to NE
Mafic Zone
Peri-Peri
The mafic-ultramafic Fazenda
Mirabela intrusion consists of a
continuously fractionated
sequence of dunite,
harzburgite, olivine opxt, opxt
websterite and gabbronorite.
Gabbronorite
Websterite
Opxt
Minor discontinuities occur in the
stratigraphy. New injections of parental
magma? Convection within the magma
chamber?
Ol Opxt
Hzb
Dunite
Dunite
Ol + Chr cumulate
Harzburgite
Ol+Opx+Chr
Ol Orthopyroxenite
Ol+Opx+Chr
Orthopyroxenite
Opx+Chr cumulate
Websterite
Opx+Cpx cumulate
Gabbronorite
Opx+Cpx+Pl cumulate
The mafic-ultramafic Fazenda Mirabela
intrusion consists of a continuously
fractionated sequence of dunite,
harzburgite, olivine opxt, opxt websterite
and gabbronorite.
Gabbronorite
Opx+Cpx+Pl
Opx+Cpx
The crystallization sequence is:
Opx+Chr
Websterite
Opxt
Ol+Chr > Opx+Ol+Chr > Opx+Chr >
Opx+Cpx > Opx+Cpx+Pl
Ol Opxt
The crystallization sequence and gradational
transition of mafic-ultramafic rocks are
consistent with compositional variations
throughout the stratigraphy.
Ol+Opx+Chr
Hzb
Ol+Chr
Dunite
The Santa Rita deposit is characterized by the lateral continuity of the mineralization
(~ 2 km) and the great thickness of disseminated sulfides (up to 200 meters).
Orthopyroxenite
Ni-Cu sulfide ore
Disseminated sulfide
Disseminated sulfide mineralization occurs mainly from the upper dunite (Ol+Chr
cumulate) to orthopyroxenite (Opx cumulate).
Orthopyroxenite
Ni-Cu sulfide ore
Disseminated sulfide
dunite (Ol+Chr cumulate)
NiS ore
Pn+Po+Py±Cpy
orthopyroxenite (Opx+Chr cumulate)
NiS ore
Pn+Py±Po±Cpy
The Santa Rita deposit is characterized by the lateral continuity of the mineralization
(~ 2 km) and the great thickness (up to 200 meters) of disseminated sulfides (2-5
vol.%), the high nickel tenor of sulfides (ca 16-18 wt.%) and variable Ni/Cu ratios
(average 3-4).
High nickel tenor (16-18 wt.%)
Pn+Py±Po±Cpy
(ca 50-60 % Pn)
High nickel tenor (16-18 wt.%)
~ 50% Pn
Representative data from one drill core
Country rocks of the Fazenda Mirabela intrusion include sulfide-bearing
Neoarchean supracrustal rocks (high grade metamorphosed BIF and
graphite-bearing granulite).
Does assimilation of sulfides from crustal rocks is significant for the origin
of the Santa Rita deposit?
Graphite-bearing gneiss – Po-Py
Santa Rita Pn-Py-Cpy-Po
Country rocks of the Fazenda Mirabela intrusion include sulfide-bearing
Neoarchean supracrustal rocks (high grade metamorphosed BIF and
graphite-bearing granulite).
Does assimilation of sulfides from crustal rocks is significant for the origin
of the Santa Rita deposit?
1. S isotope data for the Santa Rita deposit (Lazarin 2011) do not provide
evidence for crustal contamination.
2. Contrary to what is generally accepted world class Ni-Cu sulfide deposits may
be formed without addition of crustal sulfides.
The preferred petro-tectonic setting of world-class intrusion-related Ni–Cu sulfide
deposits are controversial. Some studies suggest that they are typically
associated with extensional tectonics in the crust, including rifted continental crust
or continental margins. (Naldrett 2004; Barnes et al. 2005).
The Santa Rita deposit is an example of world-class Ni-Cu sulfide
deposit hosted within an intrusion emplaced during (or shortly after)
an orogeny (TransAmazonian - Barbosa et al. 2003).
Geological
Setting
LA - ICP-MS zircon ages.
Lazarin (MSc, 2011 - UnB).
Fazenda Mirabela - 2050±17 Ma
Palestina - 2079±16 Ma
Granulite facies metamorphism in the
southern ISC belt is 2086 ± 7 Ma
(Peucat et al. 2011).
Fazenda Mirabela and Palestina
show minor tectonism and
recrystallization under high grade
metamorphism.
Intrusion were emplaced shortly
after peak metamorphism in the
ISC belt (tardi orogenic intrusions)
Distribution of PGE
Two distinct association (vertically offset profile)
1. PGE associated with BMS (Santa Rita ore). High Pt/Pd.
2. PGE (low S) associated with footwall dunite. Low Pt/Pd
Ni
Cu
S
Cr
Pt
Pd
800
900
Santa Rita
Ni-Cu sulfide
1000
Footwall (low S)
dunite
Distribution of PGE
Two distinct association (vertically offset profile)
1. PGE associated with BMS (Santa Rita ore). High Pt/Pd.
2. PGE (low S) associated with footwall dunite. Low Pt/Pd
Ni
Cu
S
Cr
Pt
Pt
Pd
Pt
800
Pd
900
Santa Rita
Ni-Cu sulfide
Pt
1000
Footwall (low S)
dunite
Pd
Barnes et al. (2010) – EconGeol
Mixing model – U-type (ultramafic magma) and G-Type (mafic magma)
"Sulfide PGE tenors range from less than 100 ppb to greater than 10 ppm of both Pt and Pd, with
maximum values in S-poor rocks at the base of the sulfide-bearing interval. PGEs become
significantly more depleted toward the top of the Santa Rita zone. We attribute these features,
along with ....., to mixing of an initially S-undersaturated, moderately Ni enriched resident magma
with a relatively low Ni, PGE-depleted replenishing magma charged with suspended sulfide liquid
droplets"
PGE and PGM distribution in the Santa Rita deposit.
1. Is the mixing model the best explanation for the distribution of PGE in the Fazenda
Mirabela intrusion?
2. Several layered intrusions (Great Dyke, Serra da Onça, Rincon del Tigre, etc) have
distributions of PGE and BMS characterized by vertically offset profiles. These offset
profiles may be interpreted as the result of fractionation processes in the magma
chamber.
Santa Rita Ni-Cu sulfide deposit
(www.mirabela.com.au)
The largest example of stratiform Ni-Cu-dominant sulfide mineralization hosted
within the interior of a layered intrusion (159Mt@0.53Ni - potential for
significant increase considering deep resources).
Layered intrusions were usually considered as poor targets for Ni-Cu sulfide
deposits.
Cava Norte
March 2010
November 2011
Santa Rita Ni-Cu sulfide deposit
(www.mirabela.com.au)
Layered intrusions were usually considered as poor targets for Ni-Cu sulfide deposits.
Stratiform/stratabound Ni-Cu sulfide mineralization is a common feature in layered intrusion.
The Santa Rita deposit is unusual for the combination of:
extension (up to 2 km), thickness (~ 200m) and metal tenor (16-18% Ni).
Layered intrusions should be considered for high tonnage and low grade Ni-Cu sulfide deposits.
March 2010
November 2011
THANK YOU
Instituto de Geociências
Universidade de Brasília