36-8 Constraining the Magmatic-Hydrothermal Evolution Using Magnetite Trace Elements and Oxygen Isotopes from Ore-Forming Breccias at the Mount Polley Porphyry Cu-Au Deposit, Canada

Session: Cordilleran Mineral Systems: Interdisciplinary Perspectives on Critical Metal Ore Deposits (Posters)

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The Canadian Cordillera hosts several world-class porphyry Cu deposits (PCDs) that are important Cu sources for Canada’s transition to a net-zero economy. Within these PCDs, magnetite is a ubiquitous mineral that forms in both magmatic and hydrothermal environments, where its abundance, resistance to weathering, and chemical composition make it a robust and informative mineral for understanding ore-forming processes. Existing trace- and major-element discrimination methods are not consistent in distinguishing igneous from hydrothermal magnetite. However, complementary stable isotope systematics can assist in constraining the timing and conditions of ore formation. Here, we investigate the textures, trace element trends, and d18O of both igneous and hydrothermal magnetite from the well-characterized Mount Polley porphyry Cu-Au deposit in British Columbia, Canada. Preliminary results show moderate to strong positive correlations between trace elements with varying diffusivities (i.e., Mg, Al, Si, Sc, Ti, Cr, Mn, Co, Ni, Zr, Nb, and Hf) and d18O in igneous magnetite. Conversely, hydrothermal magnetite shows no correlation between trace elements and its surprisingly enriched d18O values (+2 to +3‰), suggesting instead an orthomagmatic origin. Our preliminary results indicate that magnetite from hydrothermal breccias in PCD systems can retain magmatic isotopic signatures even when proximal to the ore-forming system. Further work will expand the coupled study of isotopes and trace elements in other magnetite-bearing deposits in British Columbia to refine the use of this indicator mineral as a fertility index or exploration tool.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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