Seminar by Austin Gion

Abstract

Magmatic volatile phases (MVPs) link deep magmatic processes with the formation of magmatic-hydrothermal ore deposits in transcrustal systems. However, the metal endowment of silicate melts and the efficiency at which metals can be extracted is debated. Fundamental to advancing this discourse is a quantitative understanding of the transfer of metals from silicate melts to MVPs. Such an understanding is elusive because it requires thorough analyses of high-pressure and temperature experiments and sound modelling of the exchange of metals between multicomponent fluids and silicate melts. Here we combine experiments with numerical simulations in order to test if average parental melts can produce ore-forming fluids. We achieve this by experimentally characterizing exchange reactions for 42 elements between H₂O±Cl±F-bearing fluids and silicate melts. Utilizing these data in a thermodynamic framework, we model the degassing and fractional crystallization of a silicate melt. We show that a system with the initial composition of the bulk continental crust can produce fluids and melts that are compositionally equivalent to fluid inclusions from ore deposits and natural melt inclusions. We therefore conclude that pre-enriched magmas are not required for ore formation, which instead are the consequence of repetitive intrusion-fractionation-degassing cycles involving H₂O-rich and Cl-bearing melts.