Placer
platinum has been found in the Slate Creek basin, and osmiridium in the
gravels of Miller Gulch, of the Chistochina district, in the Copper
River basin. The beach placers at Lituya Bay carry small quantities of
platinum, and it is reported, though not confirmed, that there is
platinum in the beach placers of Yakutat Bay and on Kodiak Island.
The
placer gravels of Colorado Creek, in Kenai Peninsula, and of Kahiltna
River, in the Yentna district, carry platinum as well as gold. Samples
of concentrates sent to the Survey from Boob Creek, a tributary of
Mastodon Creek, in the Innoko district, contain platinum.
Placer
miners on Dime Creek, in the Koyuk district, southeastern Seward
Peninsula, obtained several ounces of platinum in 1916 in the ordinary
gold operations, and it would appear from all available information
that this occurrence may prove of considerable importance.
In the northeastern part of Seward Peninsula the gravels of Bear Creek, Fairhaven district, carry platinum.
In
the field season of 1917, J. B. Mertie, jr., Theodore Chapin, G. L.
Harrington, and A. G. Maddren, of the United States Geological Survey,
will visit localities in Alaska in which platinum has been reported
CALIFORNIA.
Sales
in 1916 of 690 ounces of crude platinum obtained from California placer
mines were reported to the Survey. The largest production was made by
the dredges in Butte, Yuba, Calaveras, and Stanislaus counties. As is
well recognized, the gold and platinum in these placers were derived
originally in large part from the Mother Lode country. Along this
remarkable belt of gold veins there are numerous areas of serpentine,
in which chromite has been found at many places and platinum at a few.
Samples
of platinum-bearing ore from the La Plata mine, Liberty Hill district,
Nevada County, have been received by the Survey. The ore is a greenish
siliceous rock, in which pyrrhotite and chal-copyrite are present in
conspicuous quantity. The ore body is reported to occur in gabbro,
lying west of the main serpentine area and east of the slate in the
west-central part of the Colfax quadrangle,1 about 1-1/2 miles
west of Camel Hump, on the Dutch Flat and Lowell Hill road. Outcrops of
serpentine rich in chromite and olivine are said to lie near the vein.
The
Mother Lode region of California has been studied in considerable
detad and the rock formations are mapped in the following folios
published by the United States Geological Survey:
