Silver Valley (Idaho)

The Silver Valley is a region in the northwest United States, in the Coeur d'Alene Mountains in northern Idaho. It is noted for its mining heritage, dating back to the 1880s. Silver Valley is a narrow valley about in length, east of the city of Coeur d'Alene. The South Fork of the Coeur d'Alene River flows through the valley and Interstate 90 traverses the valley between Fourth of July Pass to the west and Lookout Pass on the Montana border. Several towns are located in the valley, all in Shoshone County. These include (from west to east) Pinehurst, Smelterville, Kellogg, Wardner, Osburn, Silverton, Wallace, and Mullan. The Silver Valley has also been referred to as the Coeur d'Alene Valley and the Coeur d'Alene Mining District. The Coeur d'Alene (Silver Valley) Mining District is located in Proterozoic metasediments. The mined portion of the stratigraphic column in the Silver Valley, known as the Belt series, can be divided into six main formations, three of which have upper and lower parts. These are, from oldest to youngest: the Prichard Formation (lower and upper), Burke Formation, Revett Formation, St. Regis Formation (lower and upper), Wallace Formation (lower and upper), and Striped Peak Formation. Of these, all but the Striped Peak are ore-bearing. All six of these formations are primarily composed of quartzite and argillite. Some limestone and dolomite also occur in the Wallace and Prichard, and a smaller amount of carbonate occurs in the St. Regis. Ripple marks and mud cracks occur throughout the series. Together, these imply a shallow marine depositional environment. The mining district occurs along the intersection of two major regional structural features. A large anticline extends through the district, running in a north-northwesterly direction. The Lewis and Clark line – a series of strike-slip faults running across the Pacific Northwest – crosses this anticline, generally trending in an east-west direction. Within this mining district, the major structure of the lineament is the Osburn fault, which runs directly through the district’s most successful silver belts.