Yukon Region Alaska Gold Production |
BONNIFIELD DISTRICT
The Bonnifield district is between lat 63°30' and 64°50' N. and long 145°40' and 149°20' W. It extends from the Tanana flats on the north to the north slope of the Alaska Range on the south, and it is bounded on the west and east by the Nenana and Delta Rivers, respectively.
The first gold was mined from the gravels of Gold King Creek in 1903. During the early years there were high hopes that the Bonnifield would become a major district, but only small amounts of gold were produced annually, and after 1949 the district was idle. Total production through 1959 was about 36,600 ounces, all from placers.
The geology, as outlined by Capps (1912, p. 17-19), is as follows. The oldest rocks in the district are metasedimentary rocks of Precambrian or early Paleozoic age—the Birch Creek Schist, consisting of quartz and mica schist, phyllite, and quartzite. Mertie (1937, p. 46) considered the Birch Creek to be Precambrian in age. The Birch Creek Schist is overlain by quartz-feldspar schists forming the Totatlanika Schist of Silurian or Devonian age. A sequence of Tertiary sediments beginning with Eocene fresh-water deposits unconformably overlies the schists. The freshwater deposits are followed by the Nenana Gravel of middle Miocene to early Pliocene age (MacNeil and others, 1961, p. 1806) and Pleistocene and Recent glaciofluvial deposits. The schists are highly contorted, and as the Alaska Range rose in Tertiary time the Tertiary beds were subjected to considerable folding and faulting immediately after their deposition. Intrusive rocks of granitic to dioritic composition cut the schists at various localities. These bodies are older than Eocene and younger than Silurian or Devonian (Capps, 1912, p. 41-42).
The placer deposits are in the foothills between the Tanana Flats to the north and the high slopes of the Alaska Range to the south. Present streams have cut through valleys previously filled with alluvium and have reconcentrated and redeposited the detrital gold of the older alluvium.
CHANDALAR DISTRICT
The Chandalar district, between lat 67°00' and 68°10' N. and long 147°00' and 150°00' W., includes the upper drainage of the Chandalar River.
The Chandalar district, which began producing placer gold in 1906, is one of the small producers of the Yukon basin. Total placer production through 1959 was 30,708 ounces. Cobb (1962) indicated small but undisclosed lode production from the district.
Lode deposits, which have been known in the district for many years, have recently received renewed attention. In 1961 the Little Squaw Mining Co. reported blocking out an ore body worth $1,013,000 in gold (Mining World, 1961).The geology given here is generalized from a more detailed account by Mertie (1925, p. 223-252). Schists, resembling the Birch Creek Schist, of Precambrian or early Paleozoic age are the oldest rocks in the district and are found in the southern part. Other schists and phyllites of early Paleozoic age compose the bedrock in the central part of the district, north of the area underlain by Birch Creek (?) Schist. Silurian limestone and dolomite and Devonian slate occur still farther north. In the southwest corner, Devonian or Mississippian rocks unconformably overlie the schists, and a small patch of Upper Cretaceous sandstone caps the sequence. Igneous rocks in the district consist of granite, granodiorite, and basic lavas, that range in age from Late Silurian or Early Devonian to Tertiary.
The schists contain numerous small auriferous quartz veins and stringers that no doubt were the source of the gold in the placers. Both preglacial and postglacial gravels have been productive.
