Magma fertility related to Au-Cu deposits in the northern Bowen Basin

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Robyn Russell
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to asses Cu Au fertility (Sr/Y, V/Sc) (Loucks, 2014) Parameters are based on

1 Magma fertility related to Au-Cu deposits in the northern Bowen Basin Methodology Helge Behnsen1*, Carl Spandler1, Isaac Corral1, Zhaoshan Chang1, Paul H.G.M. Dirks1 1Economic Geology Research Centre (EGRU), James Cook University, Cu Au fertility The Loucks concept Loucks (2014) Proposed WR parameters to asses Cu Au fertility (Sr/Y, V/Sc) (Loucks, 2014) Parameters are based on intrusive rocks related to mineralization Strict sample selection criteria to define fertile field: WR SiO wt% LOI < 3.5 wt% No indications for Plagioclase cumulates (Al2O3 < 20 wt%; Eu/Eu* > 1.3) 2

Enhanced fertility of arc magmas relates primarily to their high water content [ ].

known epithermal Au Cu mineralization (Mt.

2 Enhanced fertility of arc magmas relates primarily to their high water content [ ]. (Richards, 2011; 2012) Plag ± Mgt Moore and Carmichael (1998) Increase in H 2 O content and P changes the crystallization sequence! Modified from Richards (2011) Cu-Au fertility We applied proposed fertility parameters to an area of known epithermal Au Cu mineralization (Mt. Carlton district) in north Queensland, Australia (see Corral et al. and Sahlstroem et al.) tested if these are still an applicable whole rock geochemical exploration tool in volcanic suites.and examined for additional useable, easily accessible parameters

Regional Geology of the Study Area Modified

Carlton district (MTC) and Capsize Porphyry

288 Ma Herbert Creek MCU Pilot Mountain.

ridge Stockyard Creek The Springs Beta BV5

3 Regional Geology of the Study Area Modified from Cross et al. (2012) Modified from Kositcin et al. (2015) Mt. Carlton 8/12/ Sampling strategy: Samples from the Mt. Carlton district (MTC) and Capsize Porphyry (CS) Map courtesy of Ian Withnall (2015) Ma Herbert Creek MCU Pilot Mountain. Quartz Hill Ma Mt Carlton Boundary Herbert Creek Capsize Power Line Castle Strathmore Ortiz BV8 Mt Abbot Matrimony ridge Stockyard Creek The Springs Beta BV5 Delta Bowhunters Otter ridge Euri Creek Bee Hill Motley N Hill Top Southern Collinsville Mount Vista Sansons Delvin Pocket Samples distal to mineralization Mt Pool

4 WR Neodymium isotope compositions Cretaceous (within NEO) CHUR From Blevin et al. (1996) Age (Ma) Lizzie Creek Volcanic Group geochemistry Total alkali vs. silica, after Le Bas et al. (1989) Close to mineralization (MTC & CS) Distal to mineralization (Collinsville)

5 Geochemical evaluation of alteration: Alteration Box Plot (Ishikawa et al., 1976; Large et al., 2001; Williamson & Davidson, 2004) Typical porphyry alteration trend Close to mineralization (MTC & CS) Distal to mineralization (Collinsville) LCV geochemistry Fertile samples are generally more depleted compared to barren samples

$wet fractionation?$ $dry fractionation Close to$

6 LCV geochemistry LCV geochemistry wet fractionation? dry fractionation Close to mineralization (MTC & CS) Distal to mineralization (Collinsville)

7 How to quantitatively identify water rich magmas: Close to mineralization (MTC & CS) Distal to mineralization (Collinsville) Amph ± Cpx After Davidson et al. (2007) Applying Loucks ideas: Cu Au fertility/prospectivity Modified from Loucks (2014) Secondary calcite Loucks fertility criteria: wt.% SiO 2 ; Sr/Y > 35

$(2010) Cu (ppm) Onset of Mgt fractionation 12 FeO + SO 4 2 = 4 Fe 3 O 4 + S 2 Sun et al. (2004) Fertile samples: 58 70 wt% SiO 2 above y = 32.5 0.$

8 Applying Loucks ideas: Cu Au fertility/prospectivity Modified from Loucks (2014) Cu Au fertile reference field Modified from Jenner et al. (2010) Cu (ppm) Onset of Mgt fractionation 12 FeO + SO 4 2 = 4 Fe 3 O 4 + S 2 Sun et al. (2004) Fertile samples: wt% SiO 2 above y = x wt% SiO 2 Free sulfide to scavenge Cu & Au Conclusions Bob Loucks fertility scheme for Cu Au ore productivity works not only for intrusive rocks, but also for extrusive suites with fertile magmas having higher Sr/Y and V/Sc Sr/Y ratios of samples associated with mineralization agree with the global prospective unprospective division of Loucks (2014) The division in the investigated samples based on V/Sc is far more prominent Rare Earth Element ratios (La/Yb, Dy/Yb, Y vs. SiO2 or MgO) might prove to be the better proxies, because (a) they are less affected by alteration and (b) can help to identify hydrous magmas!caution is advised for random application!

9 Thank you very much! Acknowledgments: We thank GSQ and the involved industry partners for funding this large scale project as well as the geologists of Evolution Mining for providing mine access and logistical support at the Mt. Carlton deposit. Thanks go to Dr. Carl Spandler, Dr. Zhaoshan Chang and Dr. Isaac Corral for assistance during the fieldwork and organizing the data, Dr. Robert Henderson for giving helpful insights into the regional geology of NQLD and Dr. Arianne Ford for providing geological maps and GIS data. Assistance of the technical staff of JCU during the preparation and analyses of zircons is gratefully acknowledged. 17

Preliminary results on magma fertility related to Au-Cu mineralization in north Queensland, Australia

Subproject #3: Magma fertility, petrogenesis and geodynamic setting of Carboniferous and Permian magmatic complexes Preliminary results on magma fertility related to Au-Cu mineralization in north Queensland,