Chemical fingerprinting of hydrothermal ore deposit systems

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The research undertaken in this program will address truly fundamental questions about how important types of gold deposits form. Until now, geologists have understood the fluids that carry and deposit gold in both metamorphic and magmatic gold deposits to be `low-salinity aqueous-carbonic fluids' (H2O-CO2±CH4). This description is extremely simple, grossly oversimplifies the complexity of the ore fluids that have been proven to be involved in specific examples of each of the deposit types, and ignores subtleties of fluid composition that may be critical to ore formation. More problematically, this description encourages the assumption that these ore deposit types are similar, even though their fundamental tectonic settings are clearly entirely different. Is it really possible that the ore-depositing fluids in strikingly different geologic settings are so similar and so simple? Answering this question will help geologists understand the fundamental processes behind the formation of gold deposits, a significant part of the Canadian economy for past century, much better, and will also help mineral exploration companies focus their work and their expenditures more efficiently.*******The work proposed will compare two well known gold terranes in Canada of vastly different age, geological setting and gold endowment: one dominated by metamorphic deposits (Meguma; Nova Scotia) and one having mixed metamorphic -magmatic deposits (Abitibi; Ontario). The methods employed will be a novel combination of analytical approaches that has not hitherto been used on such deposits (or any others). Gold-bearing and associated non-gold-bearing minerals form at the same time and contain information about where the gold came from and the conditions under which it was deposited. Importantly, quartz veins hosting the gold traps minute volumes of the mineralising fluid, called fluid inclusions, which can be sampled and analysed using both common and highly specialised methods. These methods permit quantifying the fluid chemistry and a direct means to assess its origin, which has never been done before, and will then provide a basis to reassess the genetic models for these gold deposits. The associated sulphide minerals (e.g. arsenopyrite) also record the fluid chemistry much like rings in a growing tree. Elemental mapping of these sulphides allow one to reconstruct the fluid history and indirectly assess the origin of gold and its time of entrapment.*******The combination of the methods employed in two very contrasting settings will provide for the very first time absolute data on the fluid chemistry in gold mineralized systems. These data will form the basis for reassessing the genetic models used to explore for these precious resources. The methodology employed will also provide a foundation for similar studies to be applied to other hydrothermal ore-forming systems in order to address similar outstanding issues.******