Source to deposit tracing of metals in the lithosphere

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Orogenic gold deposits form in a variety of host rocks with a complex history, and have the potential of forming large districts in which gold source and conditions leading to strong endowment of crustal sections are unresolved. The research program aims at the identification of crustal-scale gold concentration processes that lead to formation of world-class gold mining districts in terms of metallic heritage and geologic evolution. As part of this program, three crustal sections of different age and variable gold endowment are selected for a detailed tectonic and isotopic studies: the Archean Abitibi greenstone belt, and two Phanerozoic orogenic belts, i.e. the North American Cordillera and the Northern Appalachians. Short term objectives are 1) to initiate fieldwork and structural mapping necessary to interpret the geological evolution of the crust in areas of fluid generation to deposit formation, 2) define the radiogenic isotope (Pb-Pb and Re-Os) systematics of ore minerals and crustal host rocks, thus defining the isotopic metal signature of specific deposits and fluid pathways, and 3) use in-situ trace element, and S and Pb-Pb isotopic analyses (Laser ablation ICP-MS) of ore minerals in source rocks for a thorough investigation of gold preconcentration process. A similar scientific approach will be used for selected crustal sections and adjusted according to existing geological data and exposed mineralization. Thematic field work will be combined with detailed sampling of chosen sections for lithogeochemistry and isotope geochemistry. The research program will impact our understanding of crustal scale Archean to Mesozoic auriferous systems, and Precambrian vs Phanerozoic crustal architecture in terms of tectonic evolution and gold endowment. The integration of state-of-the art isotopic tracing (Re-Os; in-situ Pb and S isotopes), quantitative trace element mineral mapping (Laser ablation ICP-MS), and study of orogenic processes as conducted in my ongoing research, will allow to propose new models of gold concentration in the crust, and their influence on forming world-class vs poorly endowed gold belts. A detailed understanding of key components leading to formation of world-class gold districts is paramount when exploring in areas of limited geological knowledge (e.g. northern Canada), especially for highly sought low-grade bulk-tonnage deposits that generally have a discrete geological footprint. Identification of distinct isotopic signature of metals (e.g. provinciality) combined with documentation of favourable structural evolution and timing of fluid generation and circulation, will contribute to the definition of gold fertility assessment and exploration criteria for the industry.