Controls on the fertility of magmas for the genesis of associated hydrothermal ore deposits

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Magmatic-hydrothermal ore deposits are our major resources of metals such as Cu, Mo, Au, Ag, Re, Sn and W. Most large ore deposits near the surface have already been discovered and the finding of new major deposits to cover the increasing metal demand of society requires exploration at depth at greatly increased cost. Therefore, the identification of the most prospective regions for ore genesis to focus mineral exploration efforts on is essential. The outcomes of the proposed research will help to identify ore-fertile segments of continental arcs based on geochemical criteria, which may be particularly useful when applied to accreted composite arc terrains with complicated magmatic history and tectonic evolution such as the Canadian Cordillera.***To achieve this goal, I will combine experimental and field-based studies to investigate the fate of sulfur and ore metals during all main stages of magma evolution leading up to ore genesis, including 1) the generation of magmas in the Earth's upper mantle over subducting oceanic plates; 2) the transport of magmas through the Earth's lithosphere, and 3) ore fluid generation by magma degassing at upper crustal depths. Particular attention will be paid to the evolution of the redox state of magmas as this defines the geochemical behavior of sulfur and many ore metals. For example, the presence of sulfur in reduced state may lead to magmatic sulfide saturation, which may greatly affect metal transfer into later exsolving fluids. On the other hand, the presence of abundant oxidized sulfur species in the magmatic fluid phase is a pre-requisite for efficient ore mineral precipitation in porphyry and high-sulfidation epithermal ore deposits. We will therefore: 1) Investigate how subducted slab-derived fluids influence the oxidation state and ore metal budget of arc magmas by using high pressure-temperature experiments and by studying volcanic rocks in the Trans-Mexican Volcanic Belt, a unique continental arc with a great diversity of primitive mantle-derived magmas; 2) Conduct a field-based study in the Andes to constrain how the concentration of ore metals, S and Cl vary during magma differentiation in the crust in tectonic settings particularly favorable for ore genesis, and compare this to arc segments with moderate mineralization potential; 3) Experimentally develop new methods to constrain the evolution of the redox state of magmas and apply these to rock samples collected in the field; 4) Experimentally constrain how silicate melt composition, pressure and temperature affect the efficiency of ore metal and sulfur transfer into exsolving magmatic fluids and use this information to help interpret data obtained from natural samples. The proposed research will take advantage of numerous recent successful experimental and analytical method developments in my group, which will allow us to obtain very powerful and previously inaccessible information to facilitate better understanding of the above processes.**