6 MINERAL RESOURCES, 1916----PART I.
Colombia.—The
price of crude platinum in Colombia, as the Survey is informed, ranged
in 1916 from $50 to $75 an ounce, the average price for the year being
nearer the higher than the lower figure. Colombian crude platinum is
estimated at 84 to 85 per cent fine.
Russia.—Early
in 1916 the Russian Government issued an order prohibiting sales of
crude platinum, but no bill against sales was passed and later in the
year free sale of platinum was allowed. The market was confused by the
contradictory action, but the selling price for the year was in general
nearly double the average for 1915. Petrograde prices for 83 per cent
platinum ranged from $61.14 an ounce in February to $77.42 an ounce in
October, the last quotation available; the Ekaterinburg price ranged
from $61.10 in January to $71.44 in October. Under date of November 11,
1916, the Russian correspondent of the Engineering and Mining Journal1
stated that by Government order the production of platinum had been
taken over by the state banks at a price of $70.56 an ounce, crude
metal 83 per cent pure, and that private trading had stopped.
OCCURRENCE.
With
the exception of a relatively small quantity of platinum and allied
metals obtained by electrolytic refiners of copper, nickel, and gold
all the platinum in the world has been won from placer deposits. Eilers
2 some years ago made a study of the precious metal content
of blister copper, but apparently did not attempt to locate the copper
mines from which the ores were derived. The United States Geological
Survey in 1915 sent inquiries to many of the large producers of copper
in the Western States to ascertain which mines produced platiniferous
ores, but the results were not complete. At many mines no assays had
been made for platinum and at the few mines where such assays had been
made the results were negative. This, however, is not to be wondered
at, for Eilers3 found that the blister copper sent to
refiners contained small quantities of platinum, the highest content
reported by him being 1.825 ounces per 100 tons of blister refined at
the Omaha smelter.
The
mother rocks of platinum are basic igneous rocks, peridotite,
pyroxenite, and dunite. The peridotites and pyroxenites are dark-gray
to black heavy rocks composed principally of black or dark-green
iron-magnesium silicates, pyroxene, augite and hornblende, olivine,
plagioclase feldspar, chromite, ilmenite, and magnetite. Dun-ites are
composed principally of olivine with some chromite. There is every
gradation between these types of rocks and the less basic rocks. A
characteristic of the basic rocks is their tendency to alter to
serpentine, a soft, greasy fibrous mineral of olive-green to black
color that once seen is readily remembered. Attempts to trace platinum
to its source have proved successful in Russia, Spain, and Canada, •but
no deposit of platinum in the mother rock has been found of commercial
grade under normal conditions. It is possible, but does not seem
probable, that bodies of platiniferous rock maybe found in the United
States rich enough in platinum to be worked under present conditions.
It should be recalled, however, by all persons searching
1 Eng. and Min. Jour., Jan. 6,1917.
2 Eilers, A., Notes on the occurrence of some of the rarer metals in blister copper: Am. Inst. Min. Eng. Trans., vol. 47, pp. 217-218,1913.
' Op. cit., p. 217.
