Lisitsin, Vladimir1, Dhnaram, Courteney1
1Geological Survey of Queensland, Brisbane, Australia
Geological Survey of Queensland (GSQ) has undertaken systematic geochemical and mineralogical characterisation of numerous Iron-oxide copper-gold (IOCG) and affiliated copper ± gold deposits in the Cloncurry district of the eastern Mount Isa Province. This work contributes to and expands a current collaborative project between GSQ and CSIRO, focusing on characterisation of key mineral systems and deposits in the region. The geochemical and mineralogical dataset is based on >1,000 of individual samples from multiple deposits, including Ernest Henry, E1, Great Australian, Mount Elliott – SWAN, Eloise, Little Eva, Blackard, Kalman, Osborne and Starra. Samples from each deposit were generally collected from multiple boreholes, at a spacing from 15 m to 50 m, to characterise the range from high-grade mineralisation to proximal alteration zones and further to relatively distal samples, hundreds of metres away from visible mineralisation. More extensive sampling and analytical work was undertaken around the Ernest Henry and Mount Elliott – SWAN deposits, aiming to better characterise geochemical and mineralogical zonation at a scale of hundreds to thousands of metres.
Major and trace element geochemistry (for up to 67 elements) was consistently characterised using a combination of digestion methods and analytical techniques. All samples were analysed using four-acid digestion and ICP-MS / OES (48 elements), with the majority also analysed by lithium metaborate fusion and ICP-MS / OES (31 elements, to ensure near-total digestion of Ba, REE, Sn, W, U), fire assay and ICP-MS (Au, Pt. Pd), Leco furnace (C, S), KOH fusion – ion chromatography (F) and Aqua regia – ICP-MS (Hg, Se, Te). Prior to geochemical sampling, drill core samples (and often – entire drill cores) were scanned using GSQ’s HyLogger-3 to characterise spectral mineralogy.
Exploratory statistical data analysis (principal component and clustering analyses) highlight a multi-element geochemical signature common for almost all of the sampled copper-gold deposits – Cu-Au-Ag-S-Te ± Co-Bi-Se. There are also significant differences between signatures of individual deposits (and their spatial clusters). In particular, the Ernest Henry and several nearby deposits are characterised by a particularly complex multi-element geochemical signature – Cu-Au-Ag-S-Te-As-Bi-Mo-W-Co-Se-Re ± Pb-Ba-In-U-Sb-Sn-Hg.
In addition to copper and gold, IOCG deposits in the district are also significantly enriched in several critical metals, most notably, Co (commonly hundreds ppm, with smaller deposits and parts of orebodies averaging >0.1% Co), REE (locally >0.5% total REE) and Re (particularly in Mo-rich deposits and orebodies affiliated with IOCG deposits sensu stricto), which could become potentially economically extractable by-products.
Vladimir Lisitsin is the manager of the Mineral System team in the Geological Survey of Queensland. He holds PhD from the University of Western Australia. His current research interests include mineral system analysis, exploration targeting and metallogeny of critical minerals.