Intrusion-related critical metal deposits throughout the Appalachian orogen: constraining melt fertility and the magmatic-hydrothermal transition

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The eastern margin of Canada is comprised of geological terranes that were "accreted" (material added to the side of a tectonic plate) during mountain building events (the Appalachian Orogeny) beginning more than 480 million years ago. These terranes contain igneous intrusions formed mainly by melting of the crust during accretion. Some of these intrusions host deposits of metals (e.g., tin, tungsten, lithium, cesium, indium, rare-earth elements) that are critical for Canada's continuing transition to a low-carbon, digitized economy. In Nova Scotia and New Brunswick, past research on intrusion-related deposits has historically focused on using bulk (the whole rock) methods of chemical and isotopic analyses to constrain the metal "fertility" of magmas (the likelihood that magmas of specific ages and compositions could form metal deposits). However, information yielded from bulk analyses is often ambiguous because bulk igneous rocks are end-products of multiple geological processes that can erase, or diminish, the original chemical signature of magmas and related fluids at different stages in their evolution. Consequently, current geological models for intrusion-related deposits in the Appalachian orogen require revision. The analysis of melt and fluid inclusions (microscopic samples of formerly molten rock and hydrothermal solutions that transported and concentrated metals, trapped in minerals throughout geological time) is the most robust approach to directly measure the metal content of ancient magmas and related volatiles. The proposed research program will constrain the evolution of variably mineralized igneous rocks in the Appalachian Orogeny through the investigation of melt and fluid inclusions. These inclusions, trapped in relatively physically and chemically robust minerals (e.g., zircon) will be analyzed using a variety of microanalytical methods. Individual projects will advance overall research program objectives by investigating the magmatic history of igneous settings of different ages and varying metal endowments. The objective will be to better understand the relative importance of primary controls (e.g., the magma source composition, crystallization, contamination, fluid degassing) on magma metal endowment and economic potential. Trainees involved in the proposed research will gain valuable skills and knowledge that will be transferable to careers in academia, government and the private sector and generate a range of data products and new knowledge suitable for a variety of end-users. The program will provide important updates to metallogenic models not only in the study areas, but in other similar terranes globally, and more broadly, will address fundamental questions about magmatic processes in the Appalachian orogen, testing the validity of previous studies. The research proposed has clear application to the natural resource field, aiming to provide exploration criteria that will have socio-economic benefit to Canada.