OCCURRENCE.
The
geological relations and distribution of platinum and associated metals
has been very thoroughly discussed by Prof. J. F. Kemp in Bulletin No.
193 of the United States Geological Survey." This paper is
authoritative, but, as it appeared in 1902, a few supplementary notes
as to the extension of the then known platinum-bearing areas together
with new localities may not be out of place.
united states.
The
exhaustive tests and examinations of black sands commenced early in
1905 and still being carried on at Portland, Oreg., by the United
States Geological Survey, have done much toward placing platinum mining
in this country upon a stable footing and developing it into a
permanent and profitable industry. Not only have many discoveries of
platinum in new localities been made and the limits of the known
platinum-bearing areas been extended, but the tests have revealed the
fact that there are in this country districts which contain surprising
quantities of platinum, and they have also given much valuable data as
to the best methods of obtaining it. A description of these methods
will be given later.
Platinum
is now known to exist in 15 counties in California: Butte, Calaveras,
Del Norte, Humboldt, Mendocino, Nevada, Placer, Plumas, Santa Barbara,
San Luis Obispo, San Bernardino, Shasta, Siskiyou, Trinity, and Yuba;
in 9 counties in Oregon: Baker, Coos, Curry, Douglas, Jackson,
Josephine, Lincoln, Linn, and Union; in 8 counties in Idaho: Ada,
Bingham, Boise, Elmore, Idaho, Nez Perce, Oneida, and Shoshone; in 4
counties in Colorado: Chaffee, Park, Saguache, and San Miguel; in 3
counties in Washington: King, Skagit, and Whatcom; in 2 counties in
Montana: Custer and Granite; in Utah, in Garfield County; in Arizona,
in Yavapai County; and in Wyoming, in Albany County. The metal is also
found in Alaska and in the gold-bearing sands of the Corozal River,
Porto Rico. Isolated occurrences of single nuggets or mere traces of
the metals have been found in many other counties in the States
mentioned, as well as in four of the eastern States, namely, New York,
Pennsylvania, North Carolina, and Georgia. In many of these localities
the metal occurs but sparingly. The most promising fields are in the
counties of southern Oregon and northern California. Here the metal has
been proved to exist in commercial quantities, and, with a proper
knowledge of methods of obtaining it, there is no reason to doubt that
an output of considerable proportions could be made annually.
The
platinum metals are obtained in most cases as a by-product in working
gold placers, especially where the gravels are derived from
peridotites. The pyroxenites, gabbros, diorites, and sometimes the
syenites also furnish favorable associations for the metal. In most
cases the platinum is accompanied by chromite, ilmenite, and magnetite
sands. In rare instances it is also found in veins, generally
associated with the copper sulphides, as in the Rambler Mine, Wyoming,
and in North Carolina. It also occurs disseminated, in the native
state, through certain basic eruptive rocks, -especially the
peridotites; and all formations where chromite or serpentine occur in
any quantity should be carefully examined for the metal. A very
interesting occurrence of platinum in massive chromite from Anacortes,
Skagit County, Wash., was discovered by the United States Geological
Survey in the course of the tests already referred to. A more detailed
description of the occurrence of the metal in the United States will
not be attempted, as the subject will be fully discussed in a special
report of the Geological Survey.
a
Kemp, J. F., The geological relations and distribution of platinum and
associated metals: Bull. U. S. Geol. Survey No. 193, 1902.
