Chris Voisey (PGN Geoscience) presents 'Geochemical Modelling for Orogenic Gold: The Centrefold for Ore Genesis and Prospectivity' for the September 2021 GSA SGEG Facets of Exploration Webinar.

Abstract: The most productive orogenic gold fields are often linked to major crustal structures, however, the gold deposits themselves are not directly hosted within them. Although fluid migration is structurally controlled, fluid evolution which destabilizes gold and other metals must be influenced by the chemistry of the system. For example, pressure and temperature changes experienced by hydrothermal fluids that rapidly ascend from deep crustal levels into shallow depths should significantly change the solubility of gold and other elements. However, if this were the case then gold deposits would form on large crustalscale faults where the greatest changes in pressure and temperature occur. Instead, orogenic gold deposits are mostly found on 2nd and 3rd order faults where there is a greater capacity for longlasting fluidrock interaction and gold precipitates in particular mineralogical and geochemical domains. Therefore, reactions during fluidrock interaction must be critical for deposit formation. Here we demonstrate use of reactive mass transport geochemical modeling (HCh software) for interpreting deposit genesis by discussing a published example from the Fosterville gold mine. Additionally, a case study from the Woods Point dyke swarm will be discussed to highlight how such modelling can aid in evaluating the prospectivity of potential host rocks in orogenic terranes which contain multiple lithologies.

Biography: Chris Voisey is an economic geology consultant at PGN Geoscience and an affiliate researcher at Monash University. Chris completed a B.Sc. (Hons.) degree at the Memorial University of Newfoundland, Canada, majoring in Earth sciences. He spent three years working as a field and geochemistry assistant for the Geological Survey of Newfoundland and Labrador. Following this, he conducted exploration on selfowned and contracted mineral prospects. In 2016, Chris moved to Australia to pursue a PhD at Monash University focussing on the genesis of orogenic gold deposits found in central Victoria. Chris’s interest now focuses on integrating geochemistry with structural geology to better understand ore genesis and develop applications toward mineral exploration.