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Chasing Footprints of an Elusive Quarry

Hydrothermal Ni-As-PGE haloes around the Miitel komatiite-hosted nickel sulfide deposit, Yilgarn Graton, Western Australia - a new exploration tool

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Remobilization of metals during post-deposition hydrothermal alteration of magmatic sulfide ores has the potential to produce distinct haloes far greater in scale than the source ore body. Recognition of such dispersed signatures may dramatically enlarge the detectable footprint of this ore type. Characterisation of the geochemical halo around the Miitel komatiite-hosted nickel sulfide deposit in Western Australia provides an excellent example of the potential of this approach. Anomalous enrichments of base metals, gold and platinum group elements (PGEs) are found in country rocks up to 250 meters away from the primary ore zones of this deposit. This enrichment can be resolved using portable X-Ray Fluorescence analysis, and occurs in both the Mount Edwards footwall basalt and the overlying Widgiemooltha komatiites. The anomalous metal signature is hosted in nickel arsenides concentrated within small quartz and carbonate veinlets. These are interpreted to have formed by circulation of arsenic-rich hydrothermal fluids through the pre-existing nickel sulfide ore, stripping out and remobilizing the concentrated metal content of the system. The presence of such Pt and Pd enriched trace arsenide phases in country rocks and shear zones may offer a widely applicable proximity indicator for nickel sulfides in hydrothermally altered terranes.