UBC Undergraduate Research

Petrological Analysis of Mineralization of the Pb-Zn-Ag Treasure Mountain Deposit, British Columbia Armstrong, Jacqueline


Treasure Mountain is an epithermal style lead-zinc-silver deposit situated within the northern extent of the Cascade Mountain range of southwestern British Columbia. Hand sample and thin section analysis of 13 rock samples from the Treasure Mountain property displayed boiling textures, fluid chemistry, ore mineralization, and alteration mineral assemblages consistent with low sulphidation epithermal deposits. Dominant ore minerals observed include sphalerite, galena, chalcopyrite, tetrahedrite, boulangerite and minor arsenopyrite. Local alteration in veins, host rock, and nearby dyke appears dominantly phyllic. Veins hosting the ore are typically zoned and vuggy, and dominantly consist of comb quartz edges, pink carbonate, and central white carbonate. Carbonate vein gangue material that appears to have been emplaced prior to ore mineralization indicates that circulating hydrothermal fluids likely had a neutral pH. A neutral pH may have been achieved by ascending magmatic fluid that has equilibrated with the surrounding country rock mixing with meteoric fluid. The Pasayten group arkose-argillite bedded sequence that hosts the Treasure Mountain deposit was contained detrital pyrite and may have been a significant source of sulfur to circulating hydrothermal fluids. The clastic sedimentary host rock of the Treasure Mountain deposit is not consistent with the classic definition of epithermal deposits, which are hosted in volcanic rock. The silver-lead-zinc vein deposit model best fits the style of mineralization studied. Silver-lead-zinc vein deposits are produced by low sulphidation epithermal systems hosted by monotonous sequences of clastic rocks that have been intruded by gabbro to granitic plutons.

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