Pyrite compositions from VHMS and orogenic Au deposits in the Yilgarn Craton, Western Australia: Implications for gold and copper exploration

Abstract

The Archaean Yilgarn Craton (Western Australia) is a world-class metallogenic province, hosting considerable resources of Au, Ag, Ni, Cu, Zn and Fe. Here we present trace element compositions of pyrite from >30 orogenic Au and 5 volcanic hosted massive sulphide (VHMS) deposits across the Yilgarn. Pyrites from VHMS deposits tend to have higher Sn, Se, Cu, Pb, Bi and lower Ni relative to orogenic deposits. VHMS deposit pyrites commonly have Co>Ni, As>100Au, Te>Au, Se>Te. Orogenic gold deposits could be subdivided based on association of Au with As or Te. Pyrites from AuAs ores generally have Pb/Bi>5, Se/Te>5, Pb/Sb<5 and Tl/Te>100 and the majority of Au is refractory (in pyrite structure). At the same time AuTe association pyrites are characterised by lower values of Pb/Bi, Se/Te and Tl/Te, higher values of Ag/Au, Pb/Sb and Au generally resides in inclusions of different compositions. Our data can be used at the exploration stage to distinguish between VHMS vs Orogenic Au signatures. For all studied deposits inclusion populations are summarised with implications for Au and Ag deportment. Orogenic Au deposits from the Yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of pyrites. However, only some deposits record multiple high Au mineralisation events.