Geologic descriptionThe headwaters of Dry Gulch are in the southeast border zone of the Red Mountain ultramafic pluton, where clinopyroxenite and hornblende-bearing rocks are dominant (Alaska Earth Sciences, 2000). Dry Gulch is only about 1/2 mile long, and placer tailings are present along about 1/4 mile of its lower length. Small-scale mining took place as early as 1927 or 1928, and continued intermittently until 1934, when the Goodnews Bay Mining Company started larger-scale dragline operations in the area (Mertie, 1940; 1976). The placer deposit probably has general characteristics like those on nearby Platinum Creek (HG014) and Fox Gulch (HG028). Locally derived gravels were coarse and bouldery, up to 12 feet thick but thinning upstream; PGMs were concentrated on or near bedrock. Bedrock along the mined part of Dry Gulch is part of an assemblage that includes sheared argillite, graywacke, and mafic to intermediate, fine-grained igneous rocks that are difficult to identify because of their decomposed character where exposed in mining cuts (Mertie, 1940). These rocks are included in a regional sedimentary and volcanic assemblage that ranges in age from Paleozoic to Mesozoic (Hoare and Coonrad, 1978). Platinum in Dry Gulch was probably discovered at about the same time that mining started on Platinum Creek (1928, Mertie, 1940). Dry Gulch was probably worked out by 1941. |
