Date of Award
Earth and Environmental Sciences
fluid history, fluorite, metal endowment, Sn-W-Mo, trace-elements
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The Mount Pleasant Sn-W-Mo deposit is located in southern New Brunswick, Canada and consists of two zones: the North Zone (NZ) and the Fire Tower Zone (FTZ). The North Zone hosts predominantly Sn with minor W-Mo mineralization, whereas the Fire Tower Zone hosts predominantly Mo and W with minor Sn mineralization. Fluorite is an important gangue mineral as it is ubiquitous throughout the deposit and is used to provide a record of fluid evolution. The complexity of the deposit is apparent from the deposit-scale to micrometer-scale trace-element variations in fluorite crystals such that fluorite is key to understanding the composition of the ore-forming fluids and their relationship to the metal endowment of the deposit. Tungsten- and Mo-related fluorite crystals from the FTZ generally exhibit homogenous to simply-zoned cathodoluminescent (CL) character, whereas Sn-related fluorite from the NZ is complexly zoned. Based on LA-ICP-MS analysis, distinct bivariate trends (most notably between Fe and Rb) that are unique to each mineralization assemblage suggest that three compositionally different fluids were responsible for the three types of mineralization. Intra-crystal trace-element variability in single fluorite crystals define trends consistent with Rayleigh fractionation during fluid exsolution and suggest these three fluids originated from three magmas that underwent pulsed crystallization. The W/Mo ratio in W-related fluorite (~3) is higher than in Mo-related fluorite (~0.5), reflecting precipitation from chemically distinct fluids with metal signatures that in part reflect the associated ore bodies. No Sn was detected in samples of fluorite from Mount Pleasant.
Greene, James, "The Use of Fluorite in Assessing Fluid History and Metal Endowment in Hydrothermal Sn-W-Mo Deposits: An Example from Mt. Pleasant, Canada" (2019). Electronic Theses and Dissertations. 7784.