Other minerals found associated with platinum in alluvial deposits are iridium and osmiridium. The Ural placer deposits contain on the average about 5 dwt. of platinum per ton, but occasionally much richer deposits are found. The most -productive of the Ural placers are those occurring along the Iss and Pura rivers, and these are said to yield about 80 per cent, of the Russian output.
In western Colombia, South America, platinum-bearing gravels occur chiefly in the Choco district ; and platinum is also found to a small extent in the gold-bearing gravels of the Barbacoas district farther south. Platinum is found in gravels at Fifield, in New South Wales; in the gold-bearing gravels and beach-sands of California and Oregon in the United States; in the placers of Goodnews Bay at Seward peninsula, Alaska; and in those of the Tulameen and Similkameen rivers in British Columbia.
Palladium occasionally occurs alloyed with gold. In Brazil, such palladium gold in a limestone close to the contact of an igneous rock.
In Canada, platinum and palladium are obtained from the mattes obtained by smelting the nickel-copper ore of Sudbury, in Ontario. The high-grade mattes contain from 0.2 to 0.5 oz. of platinum metals per ton. The platinum occurs in the Sudbury copper-nickel ore as sperrylite, embedded in chalcopyrite. Platinum-bearing nickeliferous pyrrhotites are known to occur elsewhere, as in the Bushveld complex of the Insizwa Range of Cape Province in South Africa.
Considerable amounts of platinum are obtained from the Sudbury mattes, but the Bushveld deposits yield an even greater amount. Palladium can be found as a free metal alloyed with gold and other platinum-group metals in placer deposits of the Ural Mountains, Australia, Ethiopia, North and South America. Platinum is reported to occur in the highlands of Honda, Malaga province, Spain, where there is an abundant development of serpentinized peridotites.
The platinum is associated with chromite, and is concentrated in the basal layer of the surface gravels. Platinum is associated with gold and osmiridium in the island of Borneo.
In the US, sperrylite, the same mineral found in the superficial zone of some of the Sudbury mines, has also been mined in the Rambler mine in Wyoming where it occurs in copper ores, mainly chalcopyrite and covellite. Here it is probably of igneous origin and forms a lens in a dioritic rock. Much palladium is also present in the Rambler mine. Platinum and palladium are found with gold in ores of the Boss mine, in the Yellow Pine district, Clark County, near Moapa, in eastern Nevada.
The ore minerals here are associated with quartz that replaces dolomite along vertical fractures. Granite porphyry intrudes the dolomite, and no basic igneous intrusive rocks are known in this region. The ore is oxidized and contains a bismuth-bearing variety of plumbojarosite. All metals at the Boss Mine are found in minute division.
The gold is rough, black and spongy, the palladium-platinum appears as microscopic black grains. The platinum metals were probably contained in the primary sulphides and most likely have been concentrated by solutions in which they were present in colloid suspension. Neither the Rambler nor the Boss mines have been important sources of platinum.
At many copper mines across the western US, platinum and palladium are recovered in the electrolytic refining of copper bullion by processing the mud that forms in vats where blister copper is purified. The most important source of platinum group metals in the US has been at Goodnews Bay in Alaska. These placer deposits produced about 545,000 troy ounces by dredging between 1927 and 1975.
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Native Platinum nugget, Ural Mountains, Russia
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