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frA ' 3-4* Mineralogy of tha Coalings Asbestos Deposit by P.A. Mumpton and C.S. Thompson Union Carbide Corporation, I lining and Metals Division. P.0. Sox $79* Niagara Palls, New York 14302, U.S.A. Since 1960 the aebestoe product*on of the United State* has sore than doubled, a phenomenon in large part due. to the development of the Coalings Asbestos deposit in western California. Despite the foot that this deposit is of enormous else and contains over 50 recoverable fiber, it remained unrecognised for over 100 years, einoe its physical appearance ie totally unlike that of almost every other asbestos deposit in tho world. The Coalinga deposit occupies* the southeastern third of the New Idria eerpentlnite, an elongated done-shaped body about 4 miles wide and 12 miles long, which has been Intruded into greywackeo and eh&les of Jurasslo and Cretaceous age. Whereas most asbestos ores consist of cross-fiber veinlets of ehrysotile within massive eerpentlnite, no such velnlete have been found in the Coalinga deposit. , This body has been extensively sheared and pulverised into a gigantic pile of / powdery asbestos. The great bulk of the deposit consists of soft, pov/dery, pellot-liko agglomerates of matter, friable olirysotile, surrounding blocks and fragments of hard, dense, competent serpontinlte. The very nature of this oro has lod directly to its exploitation, slnoe mining can be accomplished with ease, by low-cost, open pit methods, and the fiber content con be easily separated from the coarse, hard rook. At the present time throe oompanles are processing Coalinga ore with on annual production of about $0,000 tons. Four main types of serpentine materials are distinguishable in tho orei (1) fragments and blocks of hard, denso sorpontlnito, ranging in slao from fractions of on inoh to boxcar dluenoionsi (2) large, tough, leathery sheets of matted ehrysotile, up to several square feet in alee; (3) brittle, bladod fragments of green serpentine, up to soveral square inohoe in else; and (4) soft, frlablo, groenish-whlto agglomerates of flaky asbestos, 1/4" to 1" in diameter, which also contain appreciable amounts of both the groen, bladed material and tho htfrd, gritty serpontinlte. The bulk ore consietB predominantly of meubers of the serpentine group, with ehrysotile making up about 75*> of the total. Chrysotlle is almost tho sole oonetituont of both the green bladed material and the leathery shoots. Serpontinlte fragments oonaist primarily of lleardite and antigoritc, with smaller amounts of short-fiber ehrysotile, bruoito, and magnetite. Minor quantities of calclte and'traoos of chromite and uvarovlte are also present. Talo has not been observed. OW 00002 ST07WS829 Coalings chrysotlle has an unusually large surface area, about 70-801i2/g, Dost likely duo to the absence of Inter-fiber material, oonpared with most other ohrysotilee, Although long-fiber, per se, Is not present, fiber lengths up to several microns have been noted in the leathery sheets* Host of the chrysotlle in the ore, however, Is cuoh shorter and is arranged in a swirling mesh of disoriented, tangled fibore, much like cellulose in papor*. Scrpontinito gangue is scattered throughout the soft ore, end contains the bulk jof the platy serpentines present* Petrographioally it is not unlike most other eerpentinitoej however, brucito is a. common constituent and is often found intimately intorgrown with serpentine* The results of chemioal, eleotron probe, and X-ray analyses confirm that the brucito of this oro is iron-rich, having an approximate fomula of (UgiQ?2)(OH)24* The high iron oontont of the bruolte is a critical factor in the susceptibility of the oro to weathering, and brucito-rioh ore invariably dlsoolours- rapidly when exposed*to surface oxidation conditions* Within the 2030* thick surface weathering eons, blocks and fragments of bruclte-rich sorpentinite transform into dark brown, soft, crumbly masses* The weathered eerpcntinlts 'boulders' are enriched in pyroaurite, the new mineral, coallngltc, and amorphous iron oxides, while brucite is almost absent* Laboratory experiments have oonflrmed that in the surfaoo weathering sono,' iron-rich brucito uithor dlssolvos, le'aving behind a residue of brown, amorphous iron oxides, or transforms in situ into pyro&urlte or ooallngite by oxidation and corbonation. The dissolved magnesium later proolpltates as hydromagnesite which . is abundant immediately above the wator table throughout tho doposit* The preeenoe of about 8tf bruolte in the Kew Idria serpentlnite suggests that the parent igneous rock was a dunite, v/hioh. was injeotod into the surrounding sediments during the serpontinisation proooss* Its location, a few miles east of tho famous San Andreas fault sono, prpbably aeoounts for its extremely sheared and fractured nature* The material present in tho mass today nay bo tho result of intensive crushing and pulverisation during or after serpontlnieation, muoh as a thlok paste is ground and smeared in a wot ball mill or mlx-muller* Tho abundaneo of ohrysotlle, especially in the friable , portions of the oro, may bo the result of lleardito and antigorite of the original scrpontinito transforming into tho 'etablo* phase, chrysotlle, during this extensive reworking process* DOW 00003 ST07.48830