The Big Ledge zinc deposit is located 36 miles S of Revelstoke, British Columbia. In this area, the Shuswap metamorphic complex consists of sillimanitegrade marbles, quartzites, and gneisses belonging to the Monashee Group. The rocks are of Lower Palaeozoic (Cambrian[?]) age, metamorphosed in Upper Cretaceous time. The rocks form an east-trending synform, which has been modified by two later stages of deformation.

The sulphide deposit occurs in the Ledge Unit, a highly folded assemblage of marble and diopsidic quartzite. The deposit was formed by replacement, by deposition in fractures and, to some extent, by deposition in breccia zones. The sulphide minerals are sphalerite, pyrite, pyrrhotite, galena, chalcopyrite and marcasite. The gangue consists of the host rock and minor amounts of quartz and calcite.

Pyrite-pyrrhotite temperatures indicate these minerals were in equilibrium at temperatures ranging from 330°C to 400°C. Sphalerite-pyrite-pyrrhotite, and sphalerite-pyrite assemblages equilibrated at temperatures from 330°C to 407°C. The presence of marcasite indicates a maximum temperature of formation of 430°C. Pressures during ore deposition varied from 3350 to 4300 atmospheres.

End_of_Record - Last_Page 207-------