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The Afton Cu-Au porphyry deposit near Kamloops, B.C. contains high concentrations of platinum-group elements (PGE). PGE mineralization occurs in an unusual alteration zone that developed where a high-Mg basalt subvolcanic intrusion is in contact with a syenite-monzodiorite stock. The samples examined in this study are from the hypogene zone of the Cherry Creek unit, the latest intrusive phase of the Iron Mask Batholith. They were obtained as part of DRC Resources Corporations deep drilling program that is exploring the economic potential for underground mining beyond the pit. The goal of this study is to provide a first and detailed characterization of the alteration mineralogy of the Afton deposit with a particular focus on the effects of the alkali basalt dykes on the alteration styles, and the P-T-X characteristics of the different alteration styles in the deposit in the context of Cu, Au, and PGE deposition. Petrographic characterization of vein crosscut relationships in the samples determined the timing of different alteration stages. Temperatures for the formation of chlorite and biotite were calculated based on the Al content of the tetrahedral site of chlorite and the exchange of F between biotite and apatite. Four sets of veins observed in the samples define four stages of alteration. In order of formation, from earliest to youngest, they are early carbonate, chlorite brecciation, quartz stockworks, and late carbonate. New gold geologists determined that the quartz stockworks are the most significant host to sulphide and PGE minerals. Chlorite veins are the most abundant and are associated with the formation of ore-minerals. Chlorite formed from 497-735^oC +/- 20^oC. After the chlorite had partially crystallized, biotite precipitated out of the SiO₂-rich fluids from 723-1271^oC +/- 41^oC. The high temperatures determined from the biotite composition suggest that the fluid was derived from the basalt intrusion. Therefore, fluid released from the late basalt intrusions would be hot enough to dissolve any minerals hosting copper, gold, and PGE and provide a mechanism to reprecipitate these elements close to the basalt and explain the presence of PGE in the quartz stockwork.

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Pages: 91
Supervisors: J. Hanley, Y. Fedortchouk