Laser ablation ICP-MS trace element systematics of hydrothermal pyrite in gold deposits of the Kalgoorlie district, Western Australia

The Kalgoorlie district in the Archean Yilgarn Craton of Western Australia containstwoworld-classgolddeposits:thegiant Golden Mile shear-zone system and the Mt Charlotte quartz-vein stockworks. Mineralization occurs in three styles:(a) Fimiston style is characterized by ankerite-pyrite ± hematite-magnetite-gold replacement, (b) Oroya style overprintsFimiston ore in the shear zones and is characterized by silica-ankerite-V-muscovite-pyrite ± pyrrhotite-gold-telluridereplacement and (c) Mt. Charlotte style is characterized by veins with ankerite-sericite ± albite-pyrite-pyrrhotite-goldselvages. Hydrothermal pyrite is ubiquitous in all styles and occurs in several stages. Laser ablation inductively coupledplasma mass spectrometry (LA-ICP-MS) spot analyses (n= 652) were collected on 54 representative samples of pyritefrom three deposits. Smooth sections in the ablation spectra were selected for quantitative analysis excluding peakscaused by micron-sized inclusions. Linear mixed effects (LME) modeling of the analytical results indicates no system-atic differences between the Fimiston, Oroya and Mt Charlotte styles. The variance introduced to the dataset bygeological variability reflected in random differences between samples and deposits is large. This may be a major reasonfor difficulties in distinguishing the differences due to mineralization style. However, there are clear differences betweenpyrites co-existing with different mineral assemblages. These indicate a strong control on pyrite chemistry by thecomposition of the hydrothermal fluids. Finally, Au-Te-As systematics show that a substantial proportion of the analyzedpyrites in all deposits fall into the field of gold saturation consistent with the known metallurgical character of the ores.Mineralogical studies, ultra-fine grinding and recovery by cyanide leach show that > 82% of all gold is present in nativegrains or in Au-Ag-tellurides. The refractory nature of theFimiston pyrite concentrates is due to clusters of micron- tonano-sized inclusions rather thandue to abundant lattice-bound gold.