Subproject 2 Geology of the Mt Carlton highsulphidation

Transcription

1 Subproject 2 Geology of the Mt Carlton highsulphidation deposit Fredrik Sahlström, Zhaoshan Chang, Paul Dirks, Isaac Corral and Mark Stokes EGRU, JCU fredrik.sahlstrom@my.jcu.edu.au 27 May 2015 Townsville, Queensland, Australia Contents of talk Introduction to the Mt Carlton deposit and the purpose of this project Recent work and preliminary results Forward plan

2 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

3 The Mt Carlton deposit High-sulphidation epithermal (Au- Ag-Cu) deposit Current total resources: g/t Au, 36 g/t Ag and 0.28% Cu (Dec 2013) Open pit mining commenced in 2013 The V2 pit at Mt Carlton The Mt Carlton deposit Map courtesy of Ian Withnall Located in the northern Bowen Basin Lionel Diggings Mt Dillon Matrimony ridge Mt Abbot Stockyard Creek Otter ridge Hosted in the Lizzie Creek Volcanic Group which comprises rhyolitic to andesitic volcanics and terrestrial sediments Pinnacle Gold Creek Sullivans Reward Castle Capsize Strathmore Herbert Creek Boundary Mt Carlton Ortiz BV8 Power Boundary Line Quartz Hill Delta Beta BV5 The Springs Bowhunters Euri Creek Bee Hill Motley Ridge Albion Hill Top Southern Mount Vista Additional LS- and HS epithermal and porphyry mineralisation in the area Oakey Creek Sansons Mt Pool Robard Creek Delvin Pocket

4 Purpose of this project 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) Recent work and preliminary results

5 What has been done? 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) Preliminary cross section From Evolution mining

6 Preliminary cross section - protolith Basement: monzogranite, part of the Urannah batholith (GoQ, 2013) Andesite rhyodacite porphyry andesite-dacite rhyodacite volcaniclastics + sediments andesite-dacite trachyte (not shown) NE-SW profile across A39 and V2 Mineralisation is hosted in the rhyodacite units Limit of drilling Morrison, 2010 Cummings, 2012 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 Limit of drilling Morrison, 2010 Cummings, 2012

7 Alteration strongly controlled by protolith Preliminary cross section - alteration Qtz-alu-py and qtzdick/kao-py alteration confined mainly to rhyodacite units NE-SW profile across A39 and V2 Andesites-dacites show mainly illitemontmorillonitepyrite alteration above and below the AA zone Limit of drilling The basement has illite-chlorite-pyrite alteration Preliminary cross section NE-SW profile across A39 and V2 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

8 Alteration and mineralisation paragenesis Foundation of applying vectors and advanced analytical programs Paragenesis table

9 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 euhedral gypsum, which occur in the advanced argillic zones alu qtz alu gyp

10 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-illite alteration occur illite-chlorite ill qtz-ill py py with qtz-ill halo 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

11 Stage 2a: Au-Cu-Ag mineralisation (HS) 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 qtz en en cct py bor nau ttd en Stage 2a: Au-Cu-Ag mineralisation (HS) The HS mineralisation stage is rich in native gold, mainly associated with enargite native Au How much Au is hosted in e.g. enargite and pyrite? en en native Au

12 Stage 2a: Au-Cu-Ag mineralisation (HS) Silver-dominated minerals include: acanthite Ag2(S,Te) electrum naumannite Ag2(Se,Te) jalpaite Ag3Cu(S,Te)2 electrum?jalpaite goldfieldite acanthite?jalpaite naumannite naumannite Stage 2b: Zn-Pb-Au mineralisation (IS) Stage 2 is an intermediate-sulphidation assemblage dominated by sphalerite Accompanied by galena, pyrite and barite as well as native gold gal sph gal sph gal bar sph

13 Stage 2c: late Cu-Au mineralisation (IS) 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 dic (late) ccp ttt gal Goldfieldite with internal zoning due to variable As-content. White inclusions are galena. sph ttt py ccp Stage 3 post-mineralisation

14 Stage 3 post-mineralisation Stage 3a: bluishtranslucent dickite cuts main-stage alteration as well as mineralisation assemblages Stage 3b: gypsum veins are very common in predominantely the andesitic units. Textures indicate they are tension veins emplaced during postmineralisation shearing dickite enargite Dickite vein cutting mineralisation Gypsum veins in andesite at V2. Photo Paul Dirks gypsum andesite Wall rock and mineralisation ages at Mt Carlton district 265 Zircon U-Pb LA-ICP-MS; this study Below V Zircon, SHRIMP, literature Mo Re-Os; Capsize porphyry; this study Alunite Ar-Ar; V2; this study Trachyte Capsize, late-mineral Age (Ma) Basement granitoid Chang, 2015 Lizzie Creek Volcanic Group Porphyritic intrusions in Lizzie Creek volcanics

15 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 observations 2) 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 breccia 2) Silicic zone 3) Grade zonation (Leapfrog model) DHNARAM Courteney 4) <Courteney.Dhnaram@dnrm.qld.gov.au> 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 zonation 2) (U-Th)/He + fission track thermochronology

16 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!