Abstract

The Contact Lake lode gold deposit is situated in northern Saskatchewan within the Proterozoic La Ronge domain of the Trans-Hudson orogen ( degrees 1.9-1.7 Ga). The deposit is associated with a high-angle, reverse shear zone, which crosscuts the central granitic and granodioritic phases of the composite Little Deer Lake pluton. Four temporally distinct stages of veining within the shear zone have been identified on the basis of mineralogical, textural, and crosscutting relationships. The vein mineralogy, the size of the veins, and the extent of alteration distinguishes this deposit from other epigenetic gold deposits in the La Ronge domain. The four discernable vein types (two devoid of gold and two containing gold mineralization) permit the detailed study of fluids responsible for gold mineralization versus barren fluids, which is critical to gold exploration. Stage I veins are the earliest, consist of feldspar and quartz + or - biotite, are devoid of gold, and occur as pods and stringers 3 to 100 cm in width and several meters in length. Stage II quartz-biotite veins are 1 to 100 cm wide, are also devoid of gold, and have a narrow (<1 m) alteration envelope consisting of biotite and epidote. Biotite from stage II veins is chemically distinct from biotite in the pluton. Stage III quartz-muscovite-pyrite + or - gold veins range in size from 0.1 to 100 cm in width, occur as rotated tension fractures, and have a narrow (<1 m) alteration envelope consisting of muscovite and pyrite which overprints the stage II alteration halo. Stage IV quartz-musco-vite-chalcopyrite-sphalerite-gold-galena + or - albite + or - calcite + or - chlorite + or - pyrrhotite + or - pyrite + or - bismuthinite + or - native bismuth veins occur as microfractures less than 1 cm in width and 1 to 15 cm in length that crosscut all other stages of veining. Gold is always associated with several of these minerals, although the mineral assemblage associated with gold is strongly dependent on the environment in which the stage IV veins are emplaced. In the granodioritic phase of the deposit, interaction between the...

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