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T-4518 <br />contact between the Caribou stock and the mica schist unit then served as shear zone <br />boundaries under northeast-trending compression. Between the boundaries, northeast- <br />trending tensional fractures developed under left-lateral differential movement Continued <br />differential movement resulted in the sigmoidal shapes of and minor right-latertl motion <br />on the tensional fractures. East-trending faults then formed at the sheaz zone t~oundaries. <br />Vein mineralization in the tensional structures and east-trending faults occurs in <br />seven stages: 1}fine-grained quartz-pyrite+~rtolybdenite; 2) medium- tocoarse-grained <br />quartz-pyrite+-illite+~tematite±sphalerite_+galena; 3) cazbonate; 4) main base- az~d precious- <br />metal stage sphalerite-galena-electrum-acanthite with three periods of chalcop~rrite <br />deposition; 5) sulfosalt stage tetrahedrite-tennantite-prousdte-pyrargyrite-fama.tinite- <br />stromeyerite-chalcopyrite; 6) dolomite; and 7) supergene stage covellite-chalcocite- <br />digenite-malachite-azurite-gold-silver-goethite-lepidocrocite. Electrum is associated with <br />the second period of chalcopyrite deposition in the base- and precious-meta] stage and <br />commonly replaces earlier pyrite, sphalerite, and galena. <br />Specific alteration assemblages are associated with individual stages of <br />mineralization. The alteration assemblage muscovite-sericite-phengite-chlorin; (MSPC) is <br />associated with coarse-grained quartz-pyrite veins. Adularia alteration occurs with <br />speculaz hematite. Cazbonate alteration is associated with the cazbonate stage. Alteration <br />developed during base- and precious-metal mineralization overprints MSPC alteration <br />with adularia and ankerite. Smectite-kaolinite accompanies latest dolomite mineralization. <br />iv <br />