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Porphyry deposits are natural suppliers of most copper and a significant source of gold for our society. Whereas the Cu-richest (Au-poor) porphyries are related to Andean-type subduction and typical calc-alkaline magmatism, the Au-richest porphyries are associated with high-K calc-alkaline to alkaline magmatism in late to post-subduction or post-collision and extensional settings, and subordinately associated with calc-alkaline magmatism. The reasons for these associations and the large variations in metal endowments of porphyry Cu-Au deposits remain obscure. This webinar will highlight that the porphyry Cu-Au deposits define two distinct trends in Au versus Cu tonnage plots (Cu-rich and Au-rich). Metal endowments for both trends grow larger the longer the mineralization process is. However, Au is precipitated at much higher rates in Au-rich as opposed to Cu-rich porphyry deposits. Using Monte Carlo simulations of petrologic processes, attendees will learn that whereas Cu-rich porphyries require large amounts of magma and water to be formed, Au-rich porphyries are the result of more efficient Au precipitation.

Massimo Chiaradia is a senior lecturer at the Department of Earth Sciences of the University of Geneva (Switzerland). He obtained his M.Sc. degree at the University of Padova (Italy) and a Ph.D. degree in earth sciences at the University of Fribourg (Switzerland). His research focuses on the petrogenesis of arc magmas with implications for continental crust formation and the relationship between magma chemistry, dynamics of subduction zones, and the formation of porphyry-type deposits. To carry out his research, Massimo combines field work with various analytical techniques, including petrography and ore microscopy, mineral and rock geochemistry, light and heavy stable isotopes, radiogenic isotopes, and high-precision radiometric dating.