Crustal evolution and implications for mineralisation processes

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Ore-bearing hydrothermal systems have been intensively studied, but the geochemical processes controlling the formation of hydrothermal calcite, barite and associated metals, and their links to fluid/magma sources, are poorly constrained. My long-term goal is to demonstrate how magmas and fluids from crustal and mantle reservoirs contribute to the tectonic and metallogenic evolution of our planet. The objective of this proposal is to investigate how fluid/magma compositions and precipitation rates affect the geochemical and isotopic composition of hydrothermal calcite and barite. Deciphering these parameters requires new and novel investigative tools and approaches. My research has demonstrated that geochemical and isotopic fingerprinting of hydrothermal calcite can be used to model magma/fluid sources and compositions. I propose to study the origin of hydrothermal systems by comparing the isotopic composition of calcite (and secondly barite) precipitated in controlled conditions with hydrothermal calcites from natural environments. These experiments will study how variations in temperature, fluid composition and precipitation rates affect the stable isotope composition of the calcites. This novel experimental and multi-isotopic approach will combine radiogenic and stable isotopes at the whole rock and mineral scale in order to examine the sources of, and processes controlling, hydrothermal fluids and their interaction with wall rocks and magmas. My toolbox includes the novel combined radiogenic/stable Sr isotope system as well as traditional radiogenic (Nd, Hf) and stable (O, C) isotopes. The radiogenic/stable Sr isotope technique provides both an isotopic tracer (radiogenic 87/86Sr), and process monitor (stable 88/86Sr) that is sensitive to changes in fluid composition (Ca/Sr ratio) and the precipitation/dissolution of carbonates from the fluid. This research has the potential to transform our understanding of metal/mineral sources by modeling fluid sources, compositions and precipitation rates. This potential will be tested first in relatively simple low temperature carbonate systems to provide a basis to study more complex high temperature silicate/carbonate systems. At low temperatures, the precipitation experiments will study how fluid composition and precipitation rates affect the formation of calcite using tufa deposits, and carbonate-hosted gold (Carlin-type) and Pb-Zn deposits. At higher temperatures, the hydrothermal calcite experiments and petrological investigations will help constrain mantle/crustal sources, and mineralizing processes in more complex carbonate-silicate hydrothermal systems such as 1) carbonatite-syenite suites and 2) gold-carbonate-quartz veins in intrusion-related gold systems. This research program will constrain the origin of gold and rare metal deposits of interest to the Canadian and global mineral exploration industry, and produce highly qualified personnel with the skills to advance geoscience research.