Mineralization
Ore deposits of the Coeur d’Alene Mining District and USSC are hosted by slightly metamorphosed Precambrian sedimentary rocks of the Belt Supergroup. Belt strata are composed primarily of fine-grained quartz and original clay (now metamorphosed to fine-grained white mica, or sericite). Although the composition of these metasediments varies widely, three major rock types are generally recognized. These rock type definitions were first applied in the district to the Revett Formation (White and Wilson, 1982) but have since been used in describing other Belt formations as well. The rock types are; vitreous quartzite, sericitic quartzite, and siltite-argillite.
The ore bodies at USSC's property occur as steeply dipping fissure filling veins. The veins cut through the rocks of the Revett Formation and are found along major fracture systems and major faults. The veins generally strike east west and northeast southwest and range in thickness from a few inches to over fifteen feet. Two different ore bearing sulfide assemblages are found at the Galena, a silver-copper ore and a silver-lead ore. Grades of the silver-copper veins range from a few ounces of silver to over a thousand ounces of silver per ton and since 1953 have averaged over 22 ounces per ton. Copper grades range from tenths of a percent to over two percent and since 1953 have averaged 0.83 percent per ton. Grades of the silver-lead ores average approximately 13 ounces of silver and 16% lead per ton.
The cross-section shows the Revett Formation in the core of the Big Creek anticline and the position of the productive veins discovered to date on the north limb of the anticline. The beds dip steeply to the north and the faults dip steeply to the south. On a local scale the Revett Formation consists of interbeds of hard (brittle) and soft (ductile) units; the interbed can be from inches thick to over 100 feet (30 m) thick.
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