Mass transfer of volatile and ore-forming elements in the Earth’s lithosphere

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The major goal of this research program is to improve our understanding of the mass transfer of ore-forming and volatile elements in the Earth’s solid crust, leading to the formation of ore deposits. The genesis of several types of mineral deposits is linked to magmatism, and the research proposed here focuses on the understanding of processes leading to the formation of so called “magmatic-hydrothermal” ore deposits. This subclass of mineralizations serves as our primary or major resource of elements such as Cu, Mo, Au, Sn, W, Re, Ag, Pb and Zn. The formation of such deposits relates to the exsolution of a volatile phase from magmas in response to decompression and crystallization, the same process which drives explosive volcanic activity. This is an essential step in ore formation, because this exsolving volatile phase may efficiently extract metals from magmas, and later precipitate them leading to local enrichment of specific ore metals. This exsolving magmatic volatile phase (MVP) is usually dominated by water and smaller amounts of CO2, but also contains S, Cl and various metals in significant concentrations. The concentration and speciation of S and Cl in the MVP exert primary control on the efficiency of ore metal extraction from magmas, and also affect the transfer to, and precipitation at the site of mineralization. The comprehensive research program proposed here addresses this key process of metal extraction from magmas, and also those that control the initial metal endowment of the magmas before the exsolution of a magmatic volatile phase. We will combine observations made directly on natural samples with experimental investigations conducted at high pressures and temperatures simulating the physical-chemical conditions in geologic systems. The experimental studies will first focus on the volatile/melt partitioning of S and Cl, and the solubility and partitioning behavior of Cu and Au, using a range of innovative methodologies. The ultimate goal is to use this experimental dataset along with previously published data to construct a thermodynamic model which can accurately predict the volatile/melt partition coefficients of these elements as a function of pressure, temperature and melt composition. The studies on natural samples will track the co-variation of the concentration of volatile elements and ore forming metals in various magmatic-hydrothermal ore forming systems throughout the magmatic and/or hydrothermal evolution. Most data will be obtained by analyzing silicate melt-, sulfide- and fluid inclusions in minerals. These are tiny droplets of these phases (~10 to 100 µm), which are trapped in crystallizing minerals during the evolution of these systems, preserving a time resolved record of their compositional variation. The analysis of these inclusions poses an analytical challenge; however, a state of the art laboratory will be set up at the University of Toronto for this purpose. This will allow the detection of some element concentrations down to the parts per billion level for optimal samples. All these data will be integrated to construct improved models of magmatic-hydrothermal ore genesis.Improved genetic models of ore formation will allow developing more rigorous exploration criteria for the mining industry and serve as a foundation for the discovery of new ore deposits. Securing the constant supply of mineral resources is essential for economic growth, comfortable human life and global peace. Due to its natural endowment of ore deposits, Canada may play a strategic role in covering the rapidly growing resource demands of society. Therefore, efficient mineral exploration may boost the growth of the Canadian economy, generate wealth for Canadians and increase Canada’s influence in world politics.