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996
MINERAL RESOURCES.
of the gold belt of the Sierra Nevada, but in no place is the metal so abundant that the deposit can be worked for platinum alone. The source of the metal is undoubtedly in the serpentine and peridotite or pyroxenite, which occur as intrusive masses throughout the gold belt. In many places small silvery white scales of iridosmine are more common than the platinum itself. Little or no platinum was recovered until the beginning of dredging operations on a large scale along the foothills of the mountains. In the black sand from the sluice boxes of the dredges the platinum metals accumulate, and the
E platinum sand is recovered by panning the black sand after the gold has been removed by amalgamation. The quantity of platinum recovered would only constitute a small fraction of a cent in value by the ton of sand treated, and its recovery would be out of the question except for the presence of gold. Platinum is now recov­ered at the dredges in Butte, Yuba, Sacramento, Calaveras, and Merced counties. The platinum occurs in very small scales and grains, as a rule somewhat finer than the gold which in the dredg­ing fields generally passes through a 100-mesh screen. Day l and Kemp 2 have summarized the occurrences of platinum in California and Oregon.
Another region in which platinum is recovered includes the gold belt in northwestern California in Siskiyou, Trinity, Humboldt, and Del Norte counties. A few ounces are recovered annually in some of the placer mines in these counties. Serpentine and peridotite are abundant in this region and the platinum is undoubtedly derived from these rocks. As far as known there are no localities which con­tain enough platinum for profitable mining for this metal alone.
The presence of platinum is characteristic of the beach sands along the Pacific coast from San Bernardino County northward to the mouth of the Columbia. The principal beaches where platinum has been reported are Santa Barbara, Lompoc, Santa Cruz, and occa­sionally between Santa Cruz and the Golden Gate. The richest beaches are farther north in Humboldt and Del Norte counties and in Coos County, Oreg. Bullard in Coos County and Port Orford in Curry County have proved, perhaps, the richest beaches. It is very difficult to give the percentage of platinum occurring in the sand, as the fine scales are concentrated into very thin pay streaks on the beach. The determination by Day gives in some cases values as high as $1 or $2 per ton, but ordinarily much smaller values are reported, ranging from a few cents up to 20 or 30 cents. Some production is obtained annually from the beach placers in the vicinity of Port Orford. It has been proposed by D. T. Day and R. H. Richards to use the shaking table for the treatment of these low-grade sands, but thus far the results do not seem to have been satisfactory.
In the interior of Oregon platinum is widely distributed in the southwestern counties, including Josephine and Douglas counties. The richest places appear to be near Kirby, along Josephine, Connor, and Succor creeks, from which during 1911 platinum sands to the value of about $1,000 are said to have been recovered. It is certain, at any rate, that most of the sands are very poor in platinum.
i Day. D. T., Trans. Am. Inst. Min. Eng., vol. 30,1900, p. 704; Day, D. T., and Richards, R. H., Black sands of the Pacific slope: Mineral Resources U. S. for 1905, U. S. Geol. Survey, 1906, pp. 1176-1268.
2 Kemp, J. F., Bull. U. S. Geol. Survey No. 193,1902, p. 52. See also Ann. Rents. California State Min­eralogist, as follows: Vol. 4,1884, pp. 309, 311 (iridium, p. 231); vol. 8, p. 217, Humboldt County; p. 584, Siskiyou County; vol. 9, p. 717, Trinity County; vol. 12, p. 408, Trinity County.