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27 May 2015Townsville, Queensland, Australia
Subproject 2 Geology of the Mt Carlton high-
sulphidation deposit
Fredrik Sahlström, Zhaoshan Chang, Paul Dirks, Isaac Corral and Mark Stokes
EGRU, [email protected]
• Introduction to the Mt Carlton deposit and the purpose of this project
• Recent work and preliminary results
• Forward plan
Contents of talk
Significance• Best indication for porphyry mineralisation in this region Highest potential to find a porphyry deposit Boost exploration interest in north Queensland
Sillitoe, 2010
The Mt Carlton deposit
• Located ~150 km south of Townsville
From Evolution Mining
• High-sulphidationepithermal (Au-Ag-Cu) deposit
• Current total resources: 20 Mt @ 2.5 g/t Au, 36 g/t Ag and 0.28% Cu (Dec 2013)
• Open pit mining commenced in 2013
The Mt Carlton deposit
The V2 pit at Mt Carlton
• Located in the northern Bowen Basin
• Hosted in the Lizzie Creek Volcanic Group – which comprises rhyoliticto andesitic volcanics and terrestrial sediments
• Additional LS- and HS epithermal and porphyry mineralisation in the area
The Mt Carlton deposit
Mt Dillon
Mt Abbot
Matrimony ridge
Otter ridge
Stockyard Creek
The SpringsEuri Creek
Bee Hill
Hill Top
Motley RidgeAlbion
Southern
Delta Beta
BV5 Bowhunters
Mount Vista
Sansons
Delvin Pocket Mt Pool
Robard CreekOakey Creek
Quartz HillSullivans Reward
Pinnacle
Gold Creek
BoundaryPower
Line
BV8
Ortiz
StrathmoreCastle
Capsize
Mt Carlton
Herbert Creek
Boundary
Lionel Diggings
Map courtesy of Ian Withnall
To help exploration by identifying zoning patterns and through better understanding of the genesis and controlling factors of the deposit
To help locate the surface projection of the linked porphyry by applying vectors in lithocaps (Chang et al., 2011 and others)
Estimate the depth of the linked porphyry (uplift history, vertical zonation)
Feed information and geological understanding to the regional metallogeny analysis (Subproject #1) and prospectivity analysis (Subproject #9)
Purpose of this project
Recent work and preliminary results
• Literature review on regional geology and epithermal-porphyry systems
• First field season at Mt Carlton (2.5 months): Core logging (6.6 km) of 3 sections across the Mt Carlton deposit, with
focus on protolith control, alteration and mineralisation styles Short Wave Infra-Red (SWIR) spectrometry on core to characterise
alteration zonation (1046 analyses) Initial structural observations (next talk)
• Detailed paragenetic study of alteration and mineralisation assemblages, using optical and electron microscopy (42 thin sections)
• Dating of 1 alunite sample (Ar-Ar) and 2 host rock samples (U-Pb)
• O-H isotope analysis of Mt Carlton groundwater (3 samples)
• Sample preparation for dating, fluid inclusions and isotope analysis (samples selected, ongoing)
What has been done?
Preliminary cross section
From Evolution mining
Preliminary cross section -protolith• Basement:
monzogranite, part of the Urannah batholith (GoQ, 2013)
• Andesite rhyodacite porphyry andesite-dacite rhyodacitevolcaniclastics + sediments andesite-dacite trachyte (not shown)
• Mineralisation is hosted in the rhyodacite units
NE-SW profile across A39 and V2
Morrison, 2010 Cummings, 2012
Limit of drilling
Preliminary cross section -protolith• Stratigraphy
similar to previous work (Morrison, 2010; Cummings, 2012; mine geologists)
• however, dome shape not obvious
NE-SW profile across A39 and V2
Morrison, 2010 Cummings, 2012
Limit of drilling
Preliminary cross section -alteration• Alteration strongly
controlled by protolith
• Qtz-alu-py and qtz-dick/kao-pyalteration confined mainly to rhyodaciteunits
• Andesites-dacitesshow mainly illite-montmorillonite-pyrite alteration above and below the AA zone
• The basement has illite-chlorite-pyrite alteration
NE-SW profile across A39 and V2
Limit of drilling
Preliminary cross section
Alunite show low-T compositions throughout the deposit (determined by OH peak at ~1480 nm in SWIR spectra)
however, zonation visible between V2 and A39 (similar to the mines’ observations)
preliminary documentation of hydrothermal breccia distribution indicate that it is localised to V2 and to the NE
NE-SW profile across A39 and V2
Alteration and mineralisation paragenesis
• Foundation of applying vectors and advanced analytical programs
Paragenesis table
Stage 1 – hydrothermal alteration
Stage 1 – hydrothermal alteration• The main alteration
stage show typical assemblages of HS epithermal deposits
• Unusual features include coarse alunite veins (plumose alunite?) and euhedralgypsum, which occur in the advanced argillic zones
alu
qtz
gyp
alu
Stage 1 – deep alteration
• Deep alteration in the granite basement consist of pervasive illite-chlorite-pyrite (SCC) assemblages
• Below the V2 pit pyrite veins with quartz-illitealteration occur
illite-chlorite
py with qtz-ill halo
py
illqtz-ill
Stage 2 – mineralisation
• Stage 2a: high-sulphidation Au-Ag-Cu ore
• Stage 2b: intermediate-sulphidation Zn-Pb-Au ore
• Stage 2c: intermediate-sulphidation Cu-Au ore
• The main high-sulphidation mineralisation stage is dominated by enargite and pyrite
• Occur as hydrothermal breccias and veins (in porphyry host rocks) and disseminations (in tuffaceous host rocks)
• Common minerals include tetrahedrite, galena, sphalerite, bornite, barite, chalcocite, covellite and chalcopyrite
• Typically associated with silicic halos in wall rock
Stage 2a: Au-Cu-Ag mineralisation (HS)
enqtz
en
ttd
py
cct
en
bor
nau
• The HS mineralisation stage is rich in native gold, mainly associated with enargite
• How much Au is hosted in e.g. enargite and pyrite?
Stage 2a: Au-Cu-Ag mineralisation (HS)
en
native Au
en
native Au
• Silver-dominated minerals include:
acanthite Ag2(S,Te)
naumannite Ag2(Se,Te)
jalpaite Ag3Cu(S,Te)2
electrum
Stage 2a: Au-Cu-Ag mineralisation (HS)
acanthite
naumannite
naumannite
?jalpaite
goldfieldite
?jalpaite
electrum
• Stage 2 is an intermediate-sulphidationassemblage dominated by sphalerite
• Accompanied by galena, pyrite and barite as well as native gold
Stage 2b: Zn-Pb-Au mineralisation (IS)
sphgal
sph
bar
sph
galgal
• Stage 2b base metal mineralisation is cut by a later Cu-Au mineralisation stage dominated by tennantite
• Common minerals in this stage are chalcopyrite, galena, chalcocite and barite
• Minor amounts of goldfieldite(Cu12Te4S13) and native gold
Stage 2c: late Cu-Au mineralisation (IS)
gal
ttt
ccpdic(late)
tttpy
sph
ccp
Goldfieldite with internal zoning due to variable As-content. White inclusions are galena.
Stage 3 – post-mineralisation
Stage 3 – post-mineralisation
• Stage 3a: bluish-translucent dickitecuts main-stage alteration as well as mineralisation assemblages
• Stage 3b: gypsum veins are very common in predominantelythe andesitic units. Textures indicate they are tension veins emplaced during post-mineralisation shearing
Dickite vein cutting mineralisation
Gypsum veins in andesite at V2. Photo Paul Dirks
dickite
enargite gypsum
andesite
265
270
275
280
285
290
295
300
305
Ag
e (M
a)
Zircon U-Pb LA-ICP-MS; this study
Zircon, SHRIMP, literature
Mo Re-Os; Capsize porphyry; this study
Alunite Ar-Ar; V2; this study
Wall rock and mineralisation ages at Mt Carlton district
Basement granitoid
Lizzie Creek Volcanic Group
Porphyritic intrusions in Lizzie
Creek volcanics
Trachyte
Capsize, late-mineral
Below V2
Chang, 2015
Preliminary observations• Stratigraphic logging conforms well with previous work – but the lack of dome
shape needs to be investigated
• Hydrothermal alteration show typical assemblages of HS deposits, and is strongly controlled by protolith
• Vectors developed using alunite composition and hydrothermal breccia distribution suggest that A39 is distal to V2
• Three distinct mineralisation stages in the deposit
• 1. high-sulphidation Au-Ag-Cu ore (enargite-pyrite) 2. intermediate-sulphidation Zn-Pb-Au ore (sphalerite-galena-pyrite) 3. intermediate-sulphidation Cu-Au ore (tennantite)
• Preliminary dating (Ar-Ar of alunite vein) give age of 284 +/- 2 Ma – overlap with host rocks and Capsize porphyry. More detailed dating work to come.
Upcoming work Purpose Method
Refine stratigraphy 1) Core logging, field observations2) Whole rock data – F content
Age of deposit 1) Ar-Ar dating of alunite (vein and disseminated type) from both V2 and A39.
Surface vectors to porphyry 1) Hydrothermal breccia2) Silicic zone3) Grade zonation (Leapfrog model)4) Mineral chemistry (e.g. alunite and pyrite
composition, texture)
Fluid temperature zonation 1) S isotopes in pyrite-alunite pairs 2) Fluid inclusion microthermometry
Fluid composition zonation 1) O-H isotopes (alunite, dickite-kaolinite, groundwater)2) S isotopes (alteration & mineralisation)3) Fluid inclusion composition by LA-ICP-MS
Depth to porphyry 1) Vertical alteration zonation2) (U-Th)/He + fission track thermochronology
DHNARAM Courteney <[email protected]>DHNARAM Courteney <[email protected]>
Acknowledgements
• Evolution Mining; Roric Smith, Genesio Circosta, David Hewitt, Mick Pocock, Tyron Edgar, Jim Dugdale, Ned Howard, Matthew Obiri-Yeboah
• Geological Survey of Queensland
• JCU Mineral Separation Lab (MSL) and Advanced Analytical Centre (AAC), U Michigan Ar-Ar lab and U Alberta Re-Os lab
• JCU research team
Thank you for listening!
