Yukon Region Alaska Gold Production
The Iditarod district, between lat 62° 10' and 63°00' N. and long 157°30' and 158°30' W., along the upper drainage of the Iditarod River and its tributaries, ranks second among the gold-producing districts in the Yukon basin.
Gold was discovered in 1908 along Otter Creek, a tributary of the Iditarod River (Maddren, 1911, p. 238). Despite its remoteness, the district developed, and in 1910 production was reported at $500,000 (Smith, 1933, table facing p. 96). Productive gravels also were found on Flat and Willow Creeks. The placers have been mined by dredges, mechanical scrapers, and hydraulic equipment (Mertie and Harrington, 1924, p. 110). Total gold production through 1959 was 1,297,500 ounces; nearly all production was from placers.
The underlying bedrock of the district, as described by Mertie and Harrington (1924, p. 12-82), consists dominantly of sandstone, shale, and conglomerate of late Cretaceous and Eocene age. In the western part of the district, west of the Iditarod River, undifferentiated metamorphic rocks of Paleozoic and Precambrian age are exposed; in the central part there are a few small stocks of quartz monzonite and basic intrusives. Unconsolidated deposits of sand, gravel, and silt of Pleistocene and Recent age are in the stream valleys.
Placers are of two types—residual and stream (Mertie and Harrington, 1924, p. 111-115). The stocks of monzonite, which are sheared and mineralized, are the source of the gold for each type.
INNOKO DISTRICT
The Innoko district, in the upper drainage area of the Innoko River between lat 62°50' and 63°15' N. and long 156°10' and 156°50/ W., lies immediately northeast of the Iditarod River. The Beaver Mountains form the drainage divide between the Innoko and Iditarod Rivers.
Gold was discovered in the gravels of Ganes Creek in 1906, and despite its remoteness the new camp attracted permanent settlers (Maddren, 1911, p. 236) who began gold production in 1907 that continued uninterrupted through 1957. Most of the mining was in the Ophir, Spruce, Little, Ganes, and Yankee Creek areas (Maddren, 1911, p. 246). The Innoko is a placer district and through 1959 produced a total of 518,565 ounces of gold. Most of the placers are in the gravels of the present streams or in bench deposits.
Argillaceous beds of Late Cretaceous and Eocene age underlie most of the Innoko district, except for a small area in the northeastern part where several small bodies of quartz monzonite and basic intrusives cut the sedimentary rocks (Mertie and Harrington, 1924, p. 30, 62, 69, pi. 4).
KANTISHNA DISTRICT
The Kantishna district is an area of about 4,500 square miles, between lat 63°25' and 65°00' N. and long 149°00' and 151°10' W., that includes part of the Alaska Range foothills on the south and part of the Tanana lowlands on the north. It is bounded on the east by the Nenana River and on the west by the western tributaries of the Kantishna River.
The Tanana River valley became well populated by miners and prospectors during the early part of the Fairbanks rush, and soon the rich gravels in the Kantishna district were found. In 1904 gold was found along Toklat River and the following year a flood of hopeful gold seekers left Fairbanks for the new district (Capps, 1919, p. 75). Soon several thousand people swarmed into the area, nearly all streams were staked, and several towns were built. It soon became apparent that the deposits, though rich, were shallow and of small area, so that a dismal exodus began and the population of the district quickly dwindled to about 50 (Capps, 1919, p. 76). Those who remained were able to maintain small production from the placers, and the district was still active on that scale in 1957. In 1904-5 lode deposits of lead-silver and antimony were found, and in 1921 gold, copper, and mercury lode deposits were discovered. The antimony deposits were worked sporadically during 1936-55, but the other lode deposits never achieved any significance (Reed, 1961, p. 27-28).' Total gold production from the district from 1905 through 1957 was 45,925 ounces, all from placers. No activity was reported in 1958-59.
The oldest rock in the district is the Birch Creek Schist of Precambrian age (Wells, 1933a, p. 343). This schist is succeeded by younger schists, phyllites, and gneisses, composing the Totatlanika Schist of pre-Devonian age and the Tonzona Group of Devonian or Silurian age. Pre-Tertiary greenstone, Mesozoic limestone, a sequence of Tertiary fresh water sediments, tuffs, and flows, and Quaternary glacial, glaciofluvial, and fluvial deposits complete the sedimentary column in the district (Capps, 1919, p. 22-23). The pre-Tertiary and lower Tertiary rocks have been deformed into east-trending folds parallel to the axis of the Alaska Range to the south of the district (Capps, 1919, p. 22).
The productive placers of the district are along the streams that radiate outward from the higher parts of the Kantishna Hills. The gold was believed by Capps (1919, p. 79) to be derived from erosion of small quartz veins that cut the Birch Creek Schist.