Yukon Region Alaska Gold Production |
KOYUKUK DISTRICT
The Koyukuk district, between lat 67°00' and 68°00' N. and long 149°00' and 150°50' W., drained by the north, middle, and south forks of Koyukuk River, is often considered to be one of the most northerly in the world.
Some time between 1885 and 1890 placer gold was first found in this district on the sand bars along the Koyukuk River. Maddren (1913a, p. 76) reported that by 1898 at least $4,000 in gold had been mined from them; however, Smith (1933, p. 96) did not report production from the Koyukuk district until 1900. Nearly all the upper reaches of the Koyukuk tributaries have been prospected, and the results have been rewarding. The district was still active in 1959, though only on a small scale. Total production from the district through 1959 was about 278,000 ounces, all from placers. Promising lode deposits of gold have not been found in this district.
The most abundant bedrock in the district is the ubiquitous Birch Creek Schist of Precambrian or early Paleozoic age. The schist is exposed in two belts—one in the southern part of the Endicott Mountains and the other in the Hodzana highland area, between the Yukon River and the Koyukuk valley. Numerous dikes and small intrusives of granitic composition, probably Mesozoic in age, cut the schist (Maddren, 1913a, p. 34-36). Exposed in the central and northern parts of the district are two sequences of Paleozoic rocks: one is of Devonian (?) age and consists of greenstone, slate, chert, and limestone; the other is a section of crystalline limestone and mica schist of Carboniferous (?) age. Underlying the western part of the district are Mesozoic sedimentary rocks represented by Cretaceous limestone and calcareous sandstone inter-bedded with basic flows and pyroclastics (Maddren, 1913a, p. 50-55).
Pleistocene gravel covers large areas in the district, including all the major stream valleys. Recent deposits include gravels along present stream courses.
The placer deposits are in present stream gravels and bench gravels; some of them are buried. Maddren (1913a, p. 83) considered that the gold in the placers was derived from the Birch Creek Schist. Auriferous pyrite occurs in carbonaceous phyllite facies and free gold is found in quartz veinlets and stringers that cut the micaceous quartz schist facies. The gold was transported by streams and glaciers and later concentrated by further stream action into the placer deposits.
MARSHALL DISTRICT
The Marshall district is between lat 61°40' and 62°00' N. and long 161°30' and 162°10' W., along the lower Yukon River.
During the early days, just after the discoveries at Nome, the port of St. Michael was the terminus and supply center for prospectors embarking on trips up the Yukon River or along the coastline of the Seward Peninsula. A portage to the upper Anvik River, one of the Yukon tributaries, greatly shortened the trip to the goldfields at Dawson and elsewhere on the upper Yukon by eliminating travel along several hundred miles of meanders on the lower Yukon River. Thus, except for a few itinerant prospectors and traders, the Marshall district was rather thinly settled and sparsely prospected.
In 1913, however, gold was discovered on Wilson Creek in the Marshall district (Harrington, 1918, p. 56). The usual rush followed. Additional placers were found on Willow Creek, and the first production was in 1914. Lode deposits were found in 1914, and a small shipment was made that same year (Harrington, 1918, p. 57). The quartz veins did not warrant extensive development; at any rate, lode production for the district is unrecorded.
After the first few years of near-bonanza placer production, activity slackened, was rejuvenated briefly in the late 1930's, then declined after World War II. In 1957 there was only small-scale activity in the Marshall district. Total recorded gold production through 1957 was 113,200 ounces, all from placers. The district was idle in 1958 and 1959.
Much of the bedrock in the Marshall district is greenstone and intercalated sedimentary rocks of Carboniferous age (Harrington, 1918, p. 22-26). These rocks are cut by several stocks and dikes of granite, quartz diorite, and dacite of possible Jurassic or Tertiary age (Harrington, 1918, p. 45-46). Cretaceous sandstone and argillite, somewhat metamorphosed, occur adjacent to the greenstone throughout much of the district. The most abundant rock type exposed in the district is the unconsolidated material deposited during Quaternary time by the debris-laden streams issuing from the huge glaciers of the interior of the Yukon River basin (Harrington, 1918, p. 36-44).
