Alaska Gold Rush History & Genealogy
Mining District Alaska
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.