Regional metamorphism and alteration in the Nymagee area of New

Regional metamorphism and alteration in the Nymagee area of New

AESC 2016 | 26-30 June 2016 – Adelaide Convention Centre
Regional metamorphism and alteration in the Nymagee area of
New South Wales – a HyLogger study
David Tilley, Meagan Clissold, Peter Downes & Joel Fitzherbert
Geological Survey of New South Wales, Maitland and Londonderry
Nymagee Project
Location
• centralpartoftheLachlanOrogen – southofCobar,
incentralNSW;including,theMountHopeTrough,
Winduck Shelf,SouthernCobarBasin,Mouramba
Shelf,Kopyje ShelfandRast Trough
Aims
• tosystematicallydescribechangesinalteration
mineralogyforanumberofselectedmineralised
zones
• tocomparethealterationresponseofdiffering
mineralisationstylestotheirhostrockpackage
• toassistmineralexplorerstobettertarget
mineralisation
Mount Hope Trough
MountAllen
Great Central Mine
GDDH5
DDHQDH4
CometMinearea
DDH3
QuarryHill
DDH5
GCS-1
1km
GreatCentral
GreatCentralSouth
GCS-2
BackgroundResponse
•
Quartz–muscovite–phengite–chloritewithzonesoffeldspar
(bothK- andNa-richvarieties)
•
Feldsparsconsistentwithhostrockmineralogy
Great Central Mine
Adjacenttomineralisedzone
•
Chloritecontentincreases&changesfromFe- toMg-richchlorite
Ø
zone40mwideatGreatCentral,10matQuarryHill
•
AtGreatCentralSouth,whitemicabecomesmorephengitic
•
Analterationzoneassociatedwithapossiblebrecciaatthe
bottomofDDH5(GreatCentralminearea)hasnotbeenfully
assayed
Ø spectralresponseshowsanincreaseingoethiteandFe-rich
chlorite
Ø goethitesuggestsanincreaseinoxidisedsulfides inthiszone
Ø However,nogoethitedetectedbyXRD- thereforepoorly
crystallineironoxideslikely
Winduck Shelf
Manuka/Wonawinta
Manuka / Wonawinta
Gossanousmaterial
Blackcarbonaceous
shaleunit
Legend
Theprimarysulfide-rich
mineralisationhostedby
theupperfossiliferous unit
oftheBoothLimestone
Arkosic sandstone
ThuleGranite
N
S
E
Southern Cobar Basin
MayDay
May Day
315m
Legend
Alteration
•
Talc–carbonate(calcite),
phengite,Mg-chloriteandbiotite
withminoramphibole
•
K-feldspardestructive– ore
formingfluidsMg-rich
350m
Mouramba Shelf
Nymagee Coppermine
Nymagee Copper Mine
Lithology
•
Westfacingandsteeplydipping(80°)turbidite sequenceofmudstone,
siltstone,sandstoneofthelowerAmphitheatreGroup.
Easternside- metamorphosedclay-richunit
•
Regionallymetamorphosedsiltstoneandclay-richsandstone– foliated.
•
Sedimentarystructures- ripplecrossbedding,gradedbedding,cutand
fillstructuresetc.
Westernside- quartzo-feldspathic unit
•
Arkosic-lithicsandstone- derivedfromgraniticparentmaterial.
Orezone
•
Easternzone- relativelywide,Cu-rich.Thinmineralisedveinswithin
cleavageplanes.
•
Westernzone- narrowandbrecciated,Zn-Pb-rich.
Nymagee Copper Mine
Chlorite composition
NMD053W1
Fe-chlorite
Mg-chlorite
=mineralisedzone
NMD047
Fe-chlorite
Mg-chlorite
Nymagee North
West
East
DistinctivelydifferentfromNymagee CopperMine
• actinolite,grossular andsulfides withinaAg-richzone
at209m
• anomalousCuandAupresent
• separateorezonetothemainNymagee CopperMine
Hera - Kershaws
White mica composition vs Cu
HRD003– oregradeCu
DD87KW3A– anomalousCu
NMD068
HRD019– narrowCu-richzone
DD84KW1– anomalousCu
Hera - Kershaws
Chlorite composition vs Cu
HRD003
Fe-chlorite
Mg-chlorite
Kopyje Shelf
Yellow Mountain
YD13
BackgroundResponse
•
Dependentonhostrock
mineralogy
•
Quartz–K-feldspardominantwith
variableplagioclase,minorwhite
micaandvariableminorchlorite
•
Consistentwithfelsic
volcanic/volcaniclastic hostrock
YD16
Yellow Mountain
YD16
YD16
YD13
YD13
Adjacenttomineralisedzone
YD16
Changefromphengitic toan
intermediatewhitemicacomposition
abouta2.1mmineralisedzonewithvery
minorMg-richchloritepresent
YD13
29mwidemineralisedzonewhereKfeldsparislessabundantandthereisan
increaseinintermediatewhitemica
abundance
Thesesubtlechangesareprobablyalterationrelatedbutthedominantspectralresponsein
theseholesarehostrockrelated
Mineral Hill
BackgroundResponse
Pearce
ParkerHill
Thedepositishostedby
felsicvolcanicrocks,
limestoneandsiltstones
EasternSouthern
OreZone
Mineral Hill - Pearce
KMHDD001
Chlorite composition
KMHDD003
Adjacenttomineralisedzone
Alterationconsistsofachlorite-quartz-whitemicaassemblagewithintensezonesofargillic
alteration,someofwhichareassociatedwithmineralisation
Mineral Hill – Parker Hill
Distal
• quartzandtalc,minorFe-chlorite,feldspar,
amphiboleandtracewhitemica
Proximal
• Mg-chloriteassociatedwithtalc
• silicification andK-feldsparalteration
mainmineralisationzone
Mineral Hill - ESOZ
•
Hostrockcomposedofquartz–chlorite–whitemica(notalc)
•
BothMgandFe-Mgchloritepresent
•
Al-OHabsorption feature(2175-2200nm)indicatespossible
paragonite (notvalidated)
Rast Trough
Browns Reef
Mineralisedzone
Standsoutfromthebackground
spectralresponseduetoitsaspectral
nature,adecreaseinthewhitemica
abundanceandlackofchlorite
Ø probablyduetosilicification
and/orsulfides
Nodiagnosticshiftinwhitemica
compositioncorrelatingwith
mineralisation.
Outcomes
HyLogger datacanbeusedto:
Proximalalteration
Mineralisation
•
definethedegreeandextent
ofalterationproximaland
distaltomineralisedzones
•
determinetheregional
metamorphicgrade
•
pointtowardshighergrade
zones,therebyfocussing
explorationefforts
Distalalteration
Hostrock1
Hostrock2