Alaska Gold Rush History and Genealogy





Placer Deposit of Alaska GEOLOGICAL SURVEY BULLETIN 1374

The Yentna district includes the area drained by western tributaries of the Susitna River between Alexander and Sunshine and by its eastern tributaries from Sunshine to and including the Taikeetna River.

Most of the placer mining in the district was in the Cache Creek area on streams draining the Peters and Dutch Hills and near Fairview Mountain (41, 42) about 20 miles to the southwest.

The Peters and Dutch Hills are largely underlain by graywacke and finer clastic rocks, predominantly Mesozoic in age. Tertiary continental rocks, including auriferous conglomerate, occur in the Dutch Hills and are exposed in many creek valleys. Alaskite dikes and small plutons and at least one mafic or ultramafic dike, now altered to silica-carbonate rock, cut the Mesozoic sequence (Clark and Hawley, 1968). Some of the dikes and many quartz veins in the Mesozoic rocks contain a little magnetite, scheelite, various sulfide minerals, and native gold, but none of these occurrences has been developed into a mine. Except in parts of the Dutch and Peters Hills, Quaternary glacial and alluvial deposits blanket bed¬rock in most of the area. Placers include stream and bench deposits of the present streams, glaciofiuvial deposits of Pleistocene age, and Tertiary conglomerates. On the basis of recent work by Clark and Hawley (1968), auriferous quartz-rich conglomerates and breccias on Dollar (3), Thunder (7), and Willow (14) Creeks, once considered to be extensively weathered deposits that were buried on an old erosion surface, are now thought to be the result of erosion of hydrothermally altered zones that follow northeastward-striking steep faults. Most of the gold mined in the Cache Creek area probably came from dredging operations on Cache (2) and Peters (11) Creeks. Streams draining the southeast flank of the Dutch Hills were extensively mined by hand and nonfloat methods. Falls

US Geological Paper 610

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 goldbearing 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 Tertia!Y 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


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