YENTNA-CACHE CREEK DISTRICT
The Yentna-Cache Creek district includes about 2,000 square miles on the southeast slope of the Alaska Range and is located roughly between lat 61°55' and 62°45' N. and long 150°25' and 151°5/ W. It includes the upper drainage of the Yentna River and its tributaries, the best known of which, from the standpoint of gold mining, are Cache, Mills, Peters, and Long Creeks.
Gold was discovered in this district in 1905 in gravels in the basins of Peters and Cache Creeks. During the first few years most of the production was from these placers. In 1911 additional placers were discovered on Dollar Creek and a few years later on Thunder Creek and Upper Willow Creek (Capps, 1925, p. 54-55). The district, although not a tremendous producer, had a steady output, entirely from placers, and was active through 1957. From 1905 through 1959, about 115,200 ounces was recorded; data for 1931-46 are not available.
The geology and placer deposits were described by Capps (1913; 1925, p. 53-61). Intensely folded slates and graywackes of Mesozoic age compose most of the bedrock. Masses of granitic and dioritic rocks were intruded into the metasedimentary rocks, and Capps believed that the numerous gold-bearing quartz veins in the slates and graywackes were derived from solutions emanating from the cooling intrusives. Poorly consolidated lignitic sand and clay of Oligocene age (MacNeil and others, 1961, p. 1904) unconformably overlie the folded older rocks. The sand and clay are overlain by younger Tertiary gravels.
The placers were derived by weathering and erosion of the auriferous veins in the metasedimentary rocks, first by Tertiary streams which deposited the gold in channels in the Tertiary gravels, then by postglacial streams which reworked the glacial debris and Tertiary deposits and concentrated gold from these earlier deposits into placers in the present stream channels. Minable placers occur in the Tertiary deposits as well as in the Recent gravels.
