PRECIOUS METALS KM 



of platinum; it occurs in covellite, which is a sulphide of copper. 

 CuS; and in laurite, which is the sulphide of ruthenium, I, 



Geographical Distribution. Platinum occurs in small quan- 

 tities in the gold-bearing sands of California and Oregon. It 

 occurs in limited quantities in Arizona, Colorado, Georgia, Idaho, 

 a nil Montana. It is reported from Mexico, Santa Domingo, 

 Brazil, and in placer deposits in Colombia. The world's prim i- 

 pal supply of platinum comes from the Siberian side of the Ural 

 Mountains. In Brazil at the Congo Soco mines it occurs in the 

 decomposed schistose rocks associated with gold. It is also 

 found in small quantities in the placer gravels of Alaska. 



The platinum production in the United States has come 

 from the placer mines in Butte, Humboldt, Siskiou, Trinity, 

 Calaveras, Sacramento, and Del Norte Counties, California. 

 Three-fourths of the amount has been obtained from Butte 

 County alone. 



The most noteworthy event of the platinum industry in recent 

 years is the discovery of the comparatively new mineral, sperry- 

 lite, the arsenide of platinum, PtAsa, which occurs in association 

 with nickel-bearing ores of Sudbury, Ontario, and in the Rambler 

 mines, Wyoming. 



Importance is also attached to the discovery of the metal in 

 association with several copper minerals, as covellite, the sulphide 

 of copper, CuS. This result may lead to the discovery of plat- 

 inum of commercial importance in other members of the copper 

 group. 



With the present high price of platinum, more than twice the 

 value of gold, we may expect a persistent search for platinum ores : 

 (1) Among the placer gravels of the serpentine rocks, especially 

 those resulting from the metamorphism of large masses of per- 

 idotite; (2) in the members of the copper group, and (3) in 

 the nickeliferous peridotites. 



Geological Horizon. Platinum is associated with the pre- 

 Cambrian, Cambrian and Ordovician terranes. The origin of 

 the ore bodies is largely through the decomposition of the 

 superincumbent rocks, which allows platinum to be carried into 

 the valleys where it sinks to the lower portion of the gravel and 

 into the cracks and the crevices of the upper portion of tho 

 underlying rock. It is, therefore, intimately associated with 

 gold in placer deposits, and may be reclaimed by the same 

 method as gold. The common parent rock is the ultro-basic 



