ASBESTOS 



71 



percent; large ill-defined masses of the leathery 

 material that will yield 20-25 percent fiber in the 

 milling process is considered ore. Only fiber of Group 

 7 grade is recovered. Obviously these occurrences 

 cannot be evaluated by conventional techniques, and 

 only a few sites in the sheared serpentine have been 

 outlined as ore bodies. At least 100 million tons of 

 flaky material amenable to processing occurs in 

 masses of proportions suitable for mining. Con- 

 ceivably, resources totaling several times this 

 amount could occur in this 14-mile serpentinite 

 mass. In nearby localities other serpentinite masses 

 rather similar in character remain to be prospected. 

 Obviously this is a significant resource, but of Group 

 7 fiber only, and it will long be the prime source for 

 certain California asbestos fabrication plants and 

 may ultimately supply a much expanded industry. 

 Because these resources are not typical of the con- 

 tent of fibers, and cannot be put to the wider range 

 of uses represented in asbestos resources tabulated 

 for other districts, they are not included in the 

 foregoing tabulation of conventional asbestos re- 

 sources available in the United States. 



Of more than 90 asbestos prospects reported in 

 the serpentinites of California at least half are 

 chrysotile occurrences (Wiebelt and Smith, 1959). 

 About 30 are tremolite or anthophyllite occurrences. 

 Intermittently, small tonnages of weak fiber that 

 has limited use have been mined from some of the 

 amphibole deposits, and occurrences of this type that 

 remain cannot be expected individually to have more 

 potential, in either volume or quality. Most of the 

 little-known prospects for which the mineral species 

 is not reported are likely mere mineralogic occur- 

 rences. Geologic settings with promise of hosting 

 extensive chrysotile stockworks of the Quebec type 

 are most numerous along the western foothills of 

 the Sierra Nevada and in the Klamath Mountains, 

 which is a northern outlier of the foothills belt. 

 Among or in the vicinity of the chrysotile prospects 

 of these areas, it is reasonable to anticipate that at 

 least a few and perhaps several additional deposits 

 comparable to the Copperopolis ore body will ulti- 

 mately be discovered. The possibility of large stock- 

 works of chrysotile in the serpentinite masses west 

 of the Great Valley of California is certainly not to 

 be overlooked, but relatively few of these appear — 

 from sparse information — to be promising in their 

 geologic settings. 



In east-central Oregon, along the presumed offset 

 continuation of the Pacific Coast ultramfic belt, 

 exposures of serpentinite masses are sparse com- 

 pared to the numbers and volume exposed in the 

 California interval. Oregon is thus a less promising 



region to prospect. The most promising known east- 

 ern Oregon chrysotile occurrence has been explored 

 by modern techniques, apparently without outlining 

 significant amounts of asbestos. 



Other domestic occurrences of chrysotile in mas- 

 sive serpentinite receive intermittent attention as 

 possible targets for prospecting. Most noteworthy 

 among these are occurrences at various localities 

 near the Kobuk River in northwestern Alaska 

 (Bowles, 1955, p. 17) and scattered prospects in 

 Wyoming opened during and before World War I 

 (Beckwith, 1939). Past prospecting of the north- 

 west Alaska occurrences was directed mainly toward 

 determining mineral species and whether fibers of 

 textile length existed. Most of the prospected occur- 

 rences are of short-fiber chrysotile; data available 

 provide little hint as to whether or not any are 

 potential targets for outlining extensive deposits. 



In the area prospected for chrysotile a few miles 

 south of Casper, Wyo., rocks other than serpentinite 

 make up the bulk of exposures; many of the ser- 

 pentinite exposures are barren of asbestos, and 

 apparently none exhibit faces extensively veined by 

 asbestos. It is not certain that any of these serpen- 

 tine masses are large enough to contain an asbestos 

 deposit of minable size. Serpentine masses south of 

 Lander, Wyo., are moderately well exposed and 

 obviously large enough to include minable stock- 

 works of chrysotile ; none of the present exposures 

 contain enough asbestos to encourage mining, but 

 chrysotile veining is widespread enough to suggest 

 that the occurrence could be reassessed as a possi- 

 ble target for exploration by modern techniques. 



The chrysotile resources of Arizona are entirely 

 in deposits of the limestone type. At any given time, 

 reserves estimated for the entire district aggregate 

 only a few thousand tons. From considerations of 

 geologic habit and regional distribution, an esti- 

 mated 75,000 to 100,000 tons of fiber remains to be 

 discovered within the depths at which these typically 

 small deposits can be economically mined (Shride, 

 1969). Those resources include a high proportion of 

 long fiber. When available, as in the past, these 

 resources will largely be marketed only for special 

 uses. Chrysotile occurrences of the Arizona type 

 known in the Panamint Mountains of eastern Cali- 

 fornia and near Cliff Lake in the Madison Range of 

 southwestern Montana are erratic in fiber distribu- 

 tion. They do not approach the Arizona deposits in 

 quality of fibers or in continuity of the mineralized 

 zones and cannot be regarded as recoverable re- 

 sources. 



MEXICO 



The search for and mining of chrysotile asbestos 



