Yukon Region Alaska Gold Production |
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EAGLE DISTRICT
The Eagle district is between lat 64° 35' and 65° 15' N. and long 141°00' and 142°40' W., along Seventymile, American, and Fourth of July Creeks, all tributaries that enter the Yukon River near Alaska's eastern boundary.
Placer gold was first found in 1895 along American Creek, and production began the following year (Mertie, 1938, p. 190). Although it attracted few miners, the Eagle district maintained a small annual production even through the difficult post-World War II years. Production data before 1906 cannot be found and was probably reported under some other district. Total recorded production for the Eagle district from 1906 through 1959 is 40,220 ounces, all from placers.
The district is underlain in the southwest by a large mass of granite of Late Jurassic age that has intruded and thrust upward a series of Precambrian and Paleozoic sedimentary rocks that are now exposed in northwestward-trending bands in the central and northern parts of the district. Lower Cretaceous marine rocks are exposed in the northern part of the district and these are succeeded by a thick series of freshwater deposits of Late Cretaceous and Eocene age (Mertie, 1930, pi. 12). Post-Eocene uplift caused much of this covering to be removed. Unconsolidated deposits of sand and gravel of Pleistocene and Recent age are in the stream valleys. These sediments reflect a complex geomorphic cycle involving local glaciation, climatic changes, and changes in base level (Mertie, 1930, p. 147-148).
The gold placers are in present stream gravels. The gold in these deposits came originally from small veins related to the granitic mass in the southwest part of the area, but much gold also came from ancient placers in the Upper Cretaceous and Eocene elastics (Mertie, 1930, p. 161-162).
FAIRBANKS DISTRICT
The Fairbanks district, about 300 square miles between lat 64°40' and 65°20' N. and long 147°00' and 148° 10' W., has produced more gold than any other district in Alaska. It is predominantly a placer district, although it also ranks high among the lode districts.
Fairbanks was slow to develop. Placer gold was known in the area as early as 1878 (Mertie, 1937, p. 4), but the active districts of Fortymile, Rampart, and Circle kept all but the most restless away from the Fairbanks area. In 1901 the town of Fairbanks was founded as a trading post, not as a consequence of gold mining (Prindle and Katz, 1913, p. 86). The following year some workable placers were found along Pedro Creek. This discovery brought a rush of miners and prospectors to the district, most of whom became discouraged and left after learning that the rich, easily accessible placers were few and that the large, lower grade deposits were buried and required processing large volumes of material with special machinery. Large investments were needed to purchase and construct hoisting machinery, large dredges, and machinery for thawing the frozen overburden. But gradually, as the obstacles were overcome, it was found that the buried gravels could be mined profitably, and the district prospered as the dredges chewed through huge reserves of auriferous gravels on Dome, Ester, Vault, Cleary, and Chatanika Creeks. Production continued at a high level even after World War II, but in 1959, activity began to diminish. The Fairbanks Daily News-Miner reported (Sept. 15, 1959) that gold dredging was gradually ceasing in this area. Two dredges were closed in 1959 and a third was transferred to the Fortymile district.
Interest in lode mining began after the placers were developed. Small-scale operations were under way in 1910 in Skoogy Gulch and upper Cleary and Fairbanks Creeks (Hill, 1933, p. 51). The peak of lode mining was reached just before World War II. The Pedro Dome and Ester Dome areas contain the most productive lode deposits.
The total gold production of the Fairbanks district through 1959 was 7,464,167 ounces—7,239,696 ounces from placers, 224,471 ounces from lodes.
The Birch Creek Schist, of Precambrian or early Paleozoic age, underlies most of the district (Hill, 1933, p. 41). This includes a variety of rock types, among which quartz schist and quartzite are dominant. Masses of crystalline limestone are present locally. Small bodies of biotite granite and quartz diorite believed to be of Mesozoic age (Hill, 1933, p. 43) intrude the Birch Creek. In the northeast corner of the district is a small patch of Tertiary sandstone and conglomerate, and in the same general area are a few small isolated areas of Tertiary basalt (Hill, 1933, p. 42-43).
The lode deposits of the Fairbanks district are fissure veins in the Birch Creek Schist in the vicinity of bodies of intrusive rock. The trends of both the veins and intrusives seem to be controlled structurally, but the trends are not consistent throughout the district (Hill, 1933, p. 63-64). All the major intrusives trend eastward; the veins in the Pedro Dome area also trend eastward, but the veins in the Ester Dome area trend more northward. The veins consist of quartz with small amounts of the sulfides arsenopyrite, pyrite, sphalerite, jamesonite, and stibnite, and free gold which is associated either with quartz or with the sulfides. Cervantite is widespread as an oxidation product of stibnite, and its yellow-green stain is a guide to high-grade gold ore in this district (Hill, 1933, p. 64-73).
The gold placers occur along stream valleys in unconsolidated gravels. The most productive layer is normally a few inches to 8 feet above the bedrock ; the bedrock from 1 foot to several feet below the gravel is usually gold bearing. A thick mantle of barren material consisting of sands, clays, and muck covers the deposits (Prindle and Katz, 1913, p. 92-98).
