66 



UNITED STATES MINERAL RESOURCES 



asbestos needs. The American asbestos-cement in- 

 dustry has become particularly reliant on crocidolite 

 because a small content of these fibers blended with 

 chrysotile facilitates manufacture. For several dec- 

 ades there was speculation that large resources of 

 crocidolite existed in the remote Hammersley Range 

 of Western Australia. The first significant mining 

 of these deposits began in 1947 ; concurrently inten- 

 sive exploration was done through large parts of an 

 area about 200 miles long by 75 miles wide. Ore 

 seams were found to be thin and not generally ex- 

 tensive, and continuity was difficult to predict. 

 Crocidolite mining was recessed in 1966, apparently 

 because the readily won resources had been largely 

 depleted. Some 400,000 tons of crocidolite are out- 

 lined to be recovered when access and other circum- 

 stances are more favorable. Submarginal resources 

 of crocidolite have been estimated at 2 million tons 

 (Trendall and Blockley, 1970). Thus, some doubt 

 exists that the Australian crocidolite resources can 

 significantly supplement those of the Republic of 

 South Africa. 



Since 1940, the increase in worldwide demand for 

 asbestos has been exceptional ; more remarkable has 

 been the ability of the industry to discover and 

 rapidly develop resources to keep pace. These events 

 are in part depicted on figure 9. Between 1940 and 

 1950, U.S. consumption doubled, paralleling the 

 world trend, then leveled to average about 750,000 

 tons annually. With the impetus provided by the 

 postwar escalation of production capacity and in 

 view of the potential created by universal acceptance 

 of asbestos-cement products, Canadian producers 

 successfully searched out new markets and contin- 

 ued to increase production, thus breaking the long- 

 established pattern of production parallel with 

 U.S. consumption. 



While Canada increased production by more than 

 400 percent, from 375,000 tons in 1940 to 1,650,000 

 tons in 1970, similar expansion occurred in the 

 other major producing areas. Data for the U.S.S.R. 

 are scant; therefore, the production record shown 

 on figure 9 is incomplete. Nonetheless, the order of 

 the increase in U.S.S.R. production, from 100,000 

 tons in 1940 to 1,150,000 tons in 1970 is of the cor- 

 rect magnitude. With due allowance for exports, 

 consumption of asbestos in the U.S.S.R. may have 

 reached a par with U.S. consumption during the late 

 1960's. Rhodesian production of chrysotile asbestos, 

 about 58,000 tons in 1940, apparently tripled by the 

 late 1960's. In the Republic of South Africa, where 

 chrysotile makes up about 15 psrcent, amosite about 

 a third, and crocidolite something over half the out- 

 put, production increased from 27,400 tons in 1940 



Southern Africa 

 product ion* 

 U.S. production..^" 



Figure 9. — World production, production from major sources, 

 U.S. production and consumption of asbestos, 1920-70. 



to about 280,000 tons in 1970. South African output 

 surpassed Rhodesia production for the first time in 

 about 1950. Several nations that mined only small 

 amounts of asbestos or mined only sporadically also 

 have expanded production to significant tonnages in 

 recent years. 



GEOLOGY 



MODES OF VEIN OCCURRENCE 



Asbestos occurs as cross-fiber veins, in which the 

 parallel fibers are about normal to the vein walls ; 

 as slip-fiber, in which fibers lie in near-parallel ar- 

 rangement, commonly somewhat matted together, 

 along the plane of the vein — commonly also an obvi- 



