Shoshone County Idaho Gold Production |
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The age of the intrusions and deformation is not clearly revealed. The rocks were folded and then faulted, but the intrusions may have occurred at any time during or prior to the faulting, as some faults cut the monzonite.
The rocks are thrown into several large asym¬metrical folds which trend west-northwest, north, or northeast. Complicating the structure are smaller folds superimposed on the limbs of the major ones. The rocks are extensively dislocated by normal and reverse faults, the main group of which strikes nearly east and a smaller group, north to slightly west of north. The Osburn, Placer Creek, Big Creek, and White Ledge faults are examples of the first group; the Dobson Pass, Carpenter Gulch, and O'Neil Gulch faults are typical of the second.
Mineral deposits in the Coeur d'Alene region pri¬marily contain silver-lead-zinc ores, and some cop¬per and gold are recovered as byproducts. Gold lodes have been mined near Murray. The silver-lead-zinc ores are mostly in the main part of the region, between Mullan and Kellogg. They are in veins and in tabular replacement bodies most of which are in the Revett and Burke Formations (Ransome and Calkins, 1908, p. 106). Argentifer¬ous galena, pyrite, pyrrhotite, chalcopyrite, sphaler¬ite, and local tetrahedrite are the most abundant metallic minerals; siderite and locally occurring quartz are the dominant gangue minerals (Ransome and Calkins, 1908, p. 107-111).
Gold deposits occur in four different structural environments: (1) mineralized shear zones with steep dips, (2) quartz veins along bedding planes, (3) quartz veins along low-angle thrust faults, and (4) placers (Shenon, 1938, p. 18). Of these, the placers were the most productive, followed by the bedding-plane veins, then by the mineralized shear zones and thrust-fault deposits. All the gold lodes occur in beds of the Prichard Formation. Bedding-plane veins usually are found in argillite. They contain quartz and some ankerite, sericite, albite, chlorite, and apatite. The ore minerals, which form as much as 5 percent of the vein material, are arsenopyrite, pyrite, galena, chalcopyrite, specularite, scheelite, and gold. Selenium is sparse (Shenon, 1938, p. 20). The shear-zone deposits are mineralogically similar to the bedding-plane veins except that they also contain pyrrhotite and sphalerite but no scheelite or specularite (Shenon, 1938, p. 19). The minable thrust-fault deposits are restricted to only one mine, the Wakeup Jim. The mineralogy also is similar to that of the bedding-plane veins.
Although copper deposits in this region are classified as a distinct type occupying an area in the southeast part of the district, they were worked by only one mine, and it was closed in 1915. The ores are disseminations of bornite, chalcocite, and chalcopyrite in the Revett Quartzite (Ransome and Calkins, 1908, p. 150). Gold is a minor constituent.
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