Earth Seminar 01 March - Emeritus Professor Ken Collerson

Cobalt and HREE Mineral Systems in the Eastern Mount Isa Block: IOCG Metal Source and Exploration Opportunities for Battery and Technology Metals

Abstract

In Mesoproterozoic palaeogeographic reconstructions of Laurentia, the Idaho Cobalt Belt (ICB) lies close to the northeast margin of Precambrian Australia. ICB element associations (Co-Ni-Cu-Au-Pt-Pd-F) are broadly similar to Eastern Succession (ES) systems and are HREE enriched (Slack 2012).  A litho-geochemical study of cobalt-rich samples from selected ES deposits was undertaken to constrain the mineral system and evaluate REE prospectivity (Collerson 2018).  In previous studies, the Williams Naraku Granite was inferred to be the metal source of Mesoproterozoic ES mineral systems (Williams et al., 2015). However, the ES element association includes elements not normally concentrated in silicic melts e.g., Co, Ni, Sc and PGE's, thus a more plausible explanation is that the mineral system was derived from an ultramafic to mafic source. Discovery of HREE-rich cobalt mineralisation at Mount Cobalt, hosted by olivine-bearing pyroxenites, confirmed this interpretation. Although highly altered, given the presence pseudomorphs of euhedral igneous pyroxene and serpentinised olivine, the affinity of these ultramafic protoliths is unequivocal.  The ultramafics are interpreted to be plume generated endmembers of the IOCG and ISCG suite of intrusions emplaced during break-up of Columbia Supercontinent.  Majority of ES samples have molar Cu/Au ratios between ~30,000 and 100,000, typical of alkaline igneous systems. Primitive mantle normalized HSE abundance plots are also consistent with the involvement of a mafic/ultramafic alkaline system. Elevated Au in these plots reflects epithermal enrichment. Epithermal textured silica-rich and Fe-rich hydrothermal breccias shows that boiling occurred during deposition. Some outcrops with spherulitic textures of possible biogenic origin are similar to siliceous sinters at Yellowstone (Guidry and Chafetz, 2003).  These epithermal textures show that hot springs occurred above IOCG source intrusions and explain the occurrence of high concentrations of Au. Significant potential exists in the ES for discovery of battery and technology (critical) metals, such as the high-value heavy rare earths, scandium and cobalt in alkaline ultramafic bodies.  Discovery of this system confirms an idea originally proposed by Groves and Vielreicher (2000).

• Collerson K.D. (2018) GSQ Report 159pp.
• Groves, D.I., Vielreicher, N.M.  (2000) Mineral. Deposita 36: 189-194.
• Guidry, S.A., Chafetz, H.S. (2003) Sed. Geol., 157: 71-106.
• Marinova, I., et al., (2013) Mineral. Deposita. DOI 10.1007/s00126-013-0473-4.
• Slack, J.F. (2012) Econ. Geol. 107: 1089-1113.
• Williams, M.R., et al. (2015). Ore Geol. Rev. 64: 103-127.

Biography

Ken Collerson is an Emeritus Professor in the School of Earth and Environmental Sciences at UQ and Principal at KDC Consulting. Prior to appointment at UQ he was Professor of Geochemistry at the University of California in Santa Cruz. Ken is an internationally recognised geoscientist whose research has provided a basis for predictive mineral system exploration. He is a specialist in exploration for technology (HREE, Sc) and battery (Li, Co Mn) metals, as well as PGEs and alkaline-hosted Au-Cu porphyry mineralisation.  His use of spinifex biogeochemistry to explore under cover in western Queensland resulted in discovery of a 2000 km long plume generated Silurian to Devonian age mineral province in Australia.