Alaska Gold Rush History & Genealogy

McGrath Mining District Alaska


Map

The McGrath district (fig. 16) is the area drained by the Kus¬kokwim River above the Stony River. All the placer mining in the district has been on streams that cross contacts between small plutons, commonly near quartz monzonite in composition, and Paleozoic limestone or Cretaceous sandstone and shale. The sources of most of the heavy minerals in the placers are mineralized quartz veins in the contact zones and in the plutons, but only in the Nixon Fork and Eagle Creek areas (5, 6, fig. 16) were any of the lodes mined (Berg and Cobb, 1967, p. 96—97).
Gold was discovered on Moore Creek (1, fig. 16) in 1910 and was mined intermittently until at least as recently as 1967. Both stream and bench placers were worked, mainly by hydraulic methods. The principal minerals in the concentrates were cinnabar and chromite, neither of which was saved; accompaning minerals were zircon, magnetite, pyrite, and scheelite in smaller amounts. The chromite was probably derived from a mafic igneous rock, pebbles of which are in the creek gravels. There was a little mining and prospecting on Fourth of July Creek (2, fig. 16), which rises near the head of Moore Creek, where a small pluton intrudes Cretaceous clastic rocks.
The most productive stream in the McGrath district probably was Candle Creek (4, fig. 16), where gold was discovered in 1913 and was mined until World War II. The only dredge in the district operated there from 1917 until 1926. The gold, some of which was in nuggets weighing one or two ounces, was derived from quartz veins in quartz monzonite and Cretaceous sandstone and shale adjacent to the intrusive body. Cinnabar was so abundant in concentrates that for several years it was saved and retorted and the mercury produced was sold locally. Other heavy minerals in concentrates included magnetite, scheelite, and monazite (?). Alder Creek (3, fig. 16) is geologically similar to Candle Creek, but mining was on a small scale and was carried on for only a few years. Between 1929 and 1933 about 65 ounces of gold was recov¬ered from a cut about 13,600 square feet in area. Large boulders hampered the hand-mining operation. No cinnabar was reported in the concentrates, which contained considerable scheelite and some magnetite, stibnite, and bismuth.
Placer gold was discovered on Hidden and Ruby Creeks (6, fig. 16) in 1917 and soon thereafter on neighboring streams, all of which drain an area in which a quartz monzonite stock had in¬truded Paleozoic limestone. By following placer deposits upstream, prospectors discovered lodes that yielded several tens of thousands of ounces of gold. The stream placers were mined on a small scale until the middle 1930’s, but the total production from them was much less than that from the lodes. Native bismuth, a constituent of the lodes, was also common in placer concentrates. Other heavy minerals included magnetite, scheelite, cassiterite, hematite, ilmenite, sphene, zircon, and thorianite. Eagle Creek (5, fig. 16), a few miles to the southwest, is in a similar geologic setting and drains an area where there was a small lode-gold mine. The stream was mined on a small scale in the 1920’s and early 1930’s. Bismuth was not reported, but a concentrate sample contained allanite, garnet, ilmenite, scheelite, thorianite, and a trace of sphene. Colors of gold have been reported from other streams in this part of the McGrath district, but there is no record of suc¬cessful mining on any of them.

 

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