MSc in Applied Science Thesis Defence

Gabriel Gomez Garcia

'An evaluation of magmatic processes responsible for tungsten enrichment in the Canadian Tungsten Belt: Evidence in melt inclusions of granitoids associated with the Cantung W-Cu deposit'

Abstract: The world class Cantung W skarn deposit in the Canadian Cordillera is spatially, and genetically, related to the 101-Ma Mine Stock monzogranite and aplite dykes of the Tungsten Plutonic Suite. Previous studies suggest that fractional crystallization of the magmas that produced these granitoids enriched melts in W, providing a source for W-rich mineralizing magmatic fluids that formed the deposit. Several questions exist regarding the formation of this deposit, including: (i) What was the W concentration of the granitoid magma associated with the deposit? (ii) Were these granitoids directly responsible for the formation of the deposit? (iii) How did W behave during the crystallization history of the granitoids? (iv) How does the geochemistry of the Cantung causative magmas deposit compared to that of other magmatic systems, including barren intrusions, porphyry (Cu-Mo-Au-Sn-W) and greisen (Sn-W)? To answer these questions, this study focuses on quantifying the major to trace element concentrations of silicate melt inclusions (SMI) hosted in magmatic apatite from the Mine Stock and aplite dykes, and modelling the geochemical evolution of the granitoids during fractional crystallization in order to asses their viability as sources for the W in the deposit. The geochemistry of the SMI shows that the granitoid magmas contained low W concentrations, and are not as geochemically evolved as melts in other intrusions (barren and mineralized settings) that generate Wmineralization. Instead, the data suggest that a very large magma chamber with only modest W enrichment must be located at depth, and that other factors (e.g., long duration of mineralization processes, and/or very efficient metal extraction from the magma and deposition) are mainly responsible for the high grade and tonnage of the Cantung deposit.

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