The vast Yukon region encompasses the entire drainage basin of the Yukon River in Alaska. It has the shape of a truncated wedge extending across central Alaska. The region is narrower (80 to 100 miles wide) along the west coast of Alaska at the mouth of the river and wider (200 to 300 miles) along Alaska's eastern border, where it includes the basins of the Yukon and one of its main tributaries, the Tanana. This has been by far the most productive of all the gold-producing regions, with a recorded total through 1959 of 12,282,250 ounces, most of it from placers.
Goodrich's detailed account (in Spurr and Goodrich, 1898, p. 103-131) of the early explorations, the discovery of gold, and the development of the first mining districts is the source of much of the material presented here.
The Yukon region had been traversed rather thoroughly after the 1840's by explorers and traders intent on establishing new posts and opening new country for the fur trade. A lively competition which developed among the Russians, the Hudson Bay Co., and the Americans was terminated by the purchase of Alaska by the United States.
In the 1860's small quantities of gold had been found at several localities in the Yukon basin, but credit for the discovery that led to intensive prospecting goes to George Holt, who made several trips to the Yukon in the 1870's and returned with glowing, if not entirely veracious, tales of gold in the interior. In 1881 a few prospectors panned some gold along the Big Salmon River, one of the tributaries of the Yukon River in the Yukon Territory, Canada. A year later, prospectors working up the Yukon from its mouth found gold in considerable quantities near what is now Rampart, in central Alaska. Discoveries in the 1880's along the boundary between Alaska and Canada in the Fortymile River area were developed rapidly, and by 1893 more than 300 men were working the gravels. Birch Creek in the Circle district next attracted attention and it soon rivaled the Fortymile district. Between 1890 and 1895 gold-bearing gravels were found along the Koyukuk River and additional discoveries were made in the Rampart area and in the adjacent Hot Springs district.
In 1902 gold was discovered in the Fairbanks district (Prindle, 1904, p. 64) which in the succeeding years developed into the leading producer in Alaska. The Fairbanks discoveries stimulated prospecting to the south in the foothills of the Alaska Range, and placers were found in the Bonnifield country in 1903 and the Kantishna district in 1906 (Prindle, 1907, p. 205).
At about the same time, commercial quantities of gold were found several hundred miles to the west in the gravels of the upper valley of the Innoko River and this led to discoveries on the adjacent Iditarod River. In about 1910 placers were found along Long Creek in the Ruby district, about 70 miles east of Koyukuk (Mertie and Harrington, 1924, p. 88, 89, 101). One of the most recently discovered placer districts in the Yukon region is the Tolavana district situated along the Tolovana River, a tributary which joins the Tanana River about 100 miles west of Fairbanks. Mining of these placers began in 1915 (Brooks, 1916, p. 201).
Most of the placer districts of the Yukon, basin remained active after World War II,, through 1959, though production decreased because of the constantly rising mining costs especially since 1950.
Only two districtsâ€”Fairbanks and Nabesnaâ€” have had; any significant lode production, but this is dwarfed by the placer output. The Yukon basin has yielded a total of 12,282,250 ounces of gold, of which 10,776,460 ounces is from placers, 305,560 ounces is from lode deposits, and 1,200,230 ounces is undifferentiated but presumably from placers. It may seem strange that from such a large region so few commercial vein deposits have been exploited; however, several factors must be considered in an analysis of this imbalance. First, the placers are amenable to large-scale dredging methods which means that low-grade material can be mined even at present high costs. Secondly, the remoteness of the areas containing the lode deposits demands large tonnages of high-grade ores for profitable mining.
It is difficult to summarize the geology of a region as large as the Yukon drainage basin, especially in view of the fact that the region has not been completely mapped and the areas that are mapped were done at different scales at different times and by numerous individuals. The upper part of the basin, the Yukon-Tanana area, was mapped first by Spurr (in Spurr and Goodrich, 1898) and then by Mertie (1937), but that part of the basin from the junction of the Yukon and Tanana to the mouth of the Yukon has been mapped in small parcels by individuals investigating only certain districts.
In the upper part of the basin, stratified rocks ranging in age from Precambrian to Recent are exposed. Representatives of every period except Jurassic are present (Mertie, 1937, p. 44-46). Mesozoic and Tertiary granitic intrusive rocks are the most important members of the igneous family in this area, and it is believed that the metalliferous ore deposits are related to them (Mertie, 1937, p. 46).
Farther downstream, in the Ruby area, greenstones and undifferentiated metamorphic rocks of Paleozoic age and older are the predominant country rocks (Mertie and Harrington, 1924, p. 12). In the Innoko and Iditarod districts, which may be considered the lower reaches of the Yukon, Mesozoic sedimentary rocks, chiefly Cretaceous in age, compose most of the country rock. These are inter-layered locally with basic igneous rocks. Granitic intrusions make up the mountain areas, and rhyo-lite dikes are scattered throughout the areas (Eakin, 1913, p. 295).
Throughout the Yukon basing large areas are covered with fluvial deposits that form flats tens of miles wide. The entire region has a complex geomorphic and structural history, much of which is fairly recent in age, but not enough work has been done in the region to interpret the many anomalous features of the present drainage (Mertie, 1937, p. 237).
Page 1 of 10