Laser ablation inductively coupled mass spectrometry of pyrite from the Paleoproterozoic George Fisher deposit and Urquhart Shale Formation (Mount Isa, Australia)

Trace element (TE) analysis of pyrite via LA-ICP-MS can produce large, paragenetically-constrained datasets, which can be used to reconstruct the conditions of pyrite formation in complex mineral systems. The Carpentaria province in northern Australia is host to some of the world’s highest value Zn-Pb (+Ag, Cu) deposits. The genesis of many of these deposits in the southern part of the province is controversial due to tectonic overprinting, with competing models of single- vs. multi-stage ore formation. In this study, LA-ICP-MS analysis of pyrite from the George Fisher Zn-Pb-Ag deposit and correlative unmineralized host rocks has been combined with paragenetic and whole rock lithogeochemical data. Paragenetically constrained pyrite TE data were then evaluated in the context of single- vs. multi-stage ore formation models and compared with recent data from undeformed clastic-dominated (CD-type) deposits of the northern Carpentaria province. Pre-ore diagenetic pyrite is compositionally similar to other Proterozoic diagenetic pyrite, with some evidence of minor hydrothermal anomalism that could help define distal alteration, but requires further analysis. Pyrite from the different ore stages is compositionally distinct, consistent with a multi-stage system. Ore stage 1 pyrite has high concentrations of Cu, Zn, As, Ag, Sb, Tl, and Pb as well as high Co/Ni ratios, whereas ore stage 2 pyrite contains Ni and Co, and ore stage 3 pyrite is dominated by Co with lesser concentrations of Ni and Cu. Ore stage 1 pyrite has a similar composition to hydrothermal pyrite in the undeformed northern Carpentaria CD-type deposits and likely formed syn-diagenesis. Ore stage 2 was syn-deformation, and resulted in replacement and recrystallization of pre-existing pyrite that also resulted in the expulsion of incompatible TEs. Ore stage 3 formed via a later Cu mineralizing event that resulted in a new geochemically distinct generation of Co-rich pyrite. This study demonstrates the value of pargenetically-constrained pyrite TE data for refining genetic models in complex sediment hosted mineral systems. This data publication includes pyrite trace element compositions (in ppm) of 28 samples from the un-mineralized Urquhart Shale Formation and from the George Fisher deposit. Access to drill cores was granted by Mount Isa Mines (MIM) George Fisher operation and Mount Isa Mines Resource Development.