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Paragenesis and evolution of Ba-silicate mineralization in Devonian strata at the Gun occurrence, the Yukon, Canada Macquistan, Mary Grace


This dissertation investigates the mineralogy, mineral chemistry, and paragenetic sequence of the Gun occurrence, a contact metasomatic barium silicate rare mineral locality adjacent to the Gun Pluton in the Sheldon Lake map area (105J-016) in the eastern Yukon, Canada. The mineral assemblage of the Gun occurrence was updated to include pabstite, cymrite, kinoshitalite and kampfite. A potential new mineral “notwalstromite” is described and the new mineral ronpetersonite (IMA 2023-36) was discovered and characterized as part of this research. The mineral chemistry of the units present at the Gun occurrence indicate that at least two chemically distinct host-rock facies were contacted by the intrusion with one being silica-rich and the other carbonate-rich. Additionally, mineral chemistry and textures within these units provide indicators for the relative degree of exposure to the magmatic fluids and thermal signature of the pluton. Subsequent hydrothermal alteration affecting the mineral assemblages is also observed and discussed. The intrusion of the Gun pluton triggered the dissolution/destabilization of baryte and quartz in the contacted host rock to form a suite of anhydrous barium silicate minerals. Subsequent cooling led to the formation of kampfite and sulfides. The system was then hydrated and carbonated. Celsian altered to cymrite, edingtonite and other Ba-zeolites, and cerchiaraite-Fe and cerchiaraite-Al formed at the expense of celsian, gillespite and pellyite, and kampfite destabilized to witherite. Very late baryte mineralization is observed in veins which crosscut all other features and are interpreted to be from later fluid activity.

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