Yukon Region Alaska Gold Production
The Fortymile district, between lat 64°00' and 64°30' N. and long 141°00' and 142°20' W., along the international boundary, includes the upper drainage of Fortymile River, one of the Yukon tributaries that joins the main stream in Canada. It is one of the oldest placer areas in the Yukon region and had uninterrupted output through 1959.
According to Mertie (1938, p. 157), gold was discovered in the district in 1886, but Smith (1933, p. 96) listed small production beginning in 1883. Discoveries of rich stream placers in 1893 in the Sixtymile River area, across the international boundary, drew many prospectors to the Fortymile district as well, and in a relatively short interval all the major gold-producing grounds in the Forty-mile district were found. The placers of Dome, Wade, and Chicken Creeks were all discovered during the 1890's (Mertie, 1938, p. 157). Large-scale mining methods—dredge and hydraulic—have been used with success, which is probably why the district was still active in 1959.
Total recorded gold production of the Fortymile district through 1959 was about 400,000 ounces, all from placers.
The most abundant country rock of the district, according to Mertie (1938, p. 148), is the Birch Creek Schist, but locally other rocks are present. In the Chicken Creek and Franklin Creek areas granite is exposed (Mertie, 1938, p. 171, 182). Small patches of Tertiary conglomerate, shale, and sandstone are known in the Chicken Creek and Napoleon Creek areas, and some lower Paleozoic greenstone and limestone is exposed along Napoleon Creek (Mertie, 1938, p. 184). Basalt, gabbro, and diabase, younger than the granite, are found in the central part of the Chicken Creek basin.
The productive deposits are in gravels of Pleistocene to Recent age. There are also ancient placers in the Tertiary deposits, but none of these contain gold in commercial quantities. On the other hand, these Tertiary deposits, where eroded, contributed their gold to the younger deposits. Quartz veins related to the granite intrusives are the ultimate source of the gold, according to Mertie (1938, p.154).
HOT SPRINGS DISTRICT
The Hot Springs district is between lat 65°00' and 65°20' N. and long 149°40' and 151°20' W. The drainages of Baker, Sullivan, and American Creeks are its major placer areas.
Gold-bearing gravels were discovered in 1898 on Baker and Eureka Creeks by a group of New Englanders known throughout the area as the "Boston Boys" (Mertie, 1934, p. 165-166). When the party returned in 1899 to the new settlement of Rampart, news of their discoveries leaked out and caused a rush to the Hot Springs area. The first production reported was in 1904 (Smith, 1933, table facing p. 96) ; a town was built a few years later (Mertie, 1934, p. 166).
The district maintained a steady output since mining began and was still active in 1959. Opencut, drifting, and hydraulic methods have been used in the mining. Total production through 1959 was 447,850 ounces, all from placers.
As the Hot Springs and Rampart districts are separated by only a narrow drainage divide, their geology can be summarized together.
Consolidated sedimentary rocks that range in age from pre-Ordovician to Tertiary and include sandstone, shale, conglomerate, chert, limestone, and coal-bearing rocks compose the bulk of the bedrock in these two districts (Mertie, 1934, p. 172-173). These are intruded locally by granite of Tertiary age.
Eakin (1915, p. 239) noted that the placers of the Hot Springs district were of several types— bench deposits, reworked bench deposits, irregular discontinuous bodies of auriferous gravel called "spots," and normal stream gravels containing pay streaks.
The gold of the placers was deposited during early and late Tertiary from lodes in and adjacent to granitic intrusives (Mertie, 1934, p. 223).