Document nkKMVO2epnzEpdbjaa5NmQmNw

Rcscntuin ultrsmafle bodies. Three small deposits are situated within the Muldersdrlf ultrsmafle hod/ shout 25 km north o( Johannesburg. Chrysotlle production In Swaziland for the /ear 1978 was 48,bOO tonnes -- mainly Iron the Rsvulock nine. South African production of this fiber for 1978 was 113,000 tonnes and cans fron the Type 11 ultranafle deposits described shore, aa well as fron Type lit sedimentary deposits of the Cnrollna district. Zimbabwe. The two principal chrysotlle producing nines In Zlnhabwe are located within the Mashaba and Shabanl Igneous complexes. The Mashnba complex occurs at the western end of the Fort Victoria green stone belt In southern Zlnhabwe. It la a layered ultrsmafle Intrusion which Includes pyroxcnltes and serpentlnlred dunltes and harzburgltes. The Shabanl ultranaflc body, located approximately 100 km west of Fort Victoria aqd Immediately east of the Crest Dyke, la a lenticular ultramafic sill and is suggested to hare Intruded Into the Archcan gneisses at the northeast margin of the Bellngwe schist belt (Anhseusser, 1976). Stall chrysotlle deposits are found In the Fllabusi ultrsmafle com plexes located about 50 kn west of the Shabanl deposits and at the Ethyl deposit at the north end of the Creat Dyke. The Creat Dyke Is an elon gate mass of mafic and altramaflc rocks extending nearly 500 kn across the Rhodesian Croton. It la not a true dike but rather the remelne of four lopollthlc Intrusions. Chrysotlle asbestos is found In the vlclnity of faults where serpentlnlzatlen apparently was ptonoted. In 1978 the Zimbabwean chrysotlle production wag 210,000 tonnes, of which about 60 percent ease fron the Shsbsnl end 35 percent fron the Ksshnba deposits. Type III deposits Comcrdally less Important, yet geologically very Interesting chrysotlle deposits occur In serpentlnlred limestones; two notable localities are in the Globe ares of central Arizona and In the Carolina area of the Transvaal. The Arizona asbestos-bearing strata occur In the Precambrian Mescal limestone formations of the Apache Croup, Vhere dlsbsse sills e few centi meters to a few meters thick have Intruded. The comserclal asbestos is developed by replacement of the limestones by serpentine, usually occurring vlthln 40 meters of the diabase Intrusion (Bateman, 1923; Stewart, 196'. . Although only about 50,000 tonnes of chrysotlle asbestos has been pro* duced from Arizona fron the time the deposits wera opened early IS this ! century to the present, the flbel is ^f very high quality end each eoug- j after for applications In advanced technology. An occurrence very similar to that In Arizona la found in the Transvaal Basin, where dikes and allls of dlabeec have Intruded and altered the Kalmanl Dolomite. The principal asbestos deposits are lo cated In eastern Transvaal vest of Barberton Mountain Land and eet of Carolina. The sills commonly produced a metamorphosed assemblage In the dolomite extending for a meter or more above the upper chilled eontecta with the diabase. The controls on serpentine mineralization Involve dedolomltlzatlon to calclte to furnish magnesium, solution of chert to } furnish silica, and the presence of the diabase sill to furnish 11,0 and J heat (Anhscuspcr, 1976). Fiber la not developed In ekert-free dolomite | but ts seen replacing chert where present ltmedlstely above the sill. As with the formation of amphlbole asbestos discussed previously, it appears that In addition to the necessary chemical controls, a stress environment resulting fron folding, faulting, or differential heating is required to promote the growth of chrysotlle fiber. Anhseusser (1976) suggests that the dominant regional controlling faetor for asbestos development Is folding. REALTH HAZARDS OF ASBESTOS Diseases related to asbestos exposure There are three principal diseases which are related to exposure tr one or more of the coemerclal asbestos minerals. These are: (1) lung cancer, which Includes cancer of the trachea,.bronchus, and lung proper; (2) mesothelioma, a cancer of the pleural and peritoneal membranes which invest the lung and abdominal cavities, respectively; snd (3) asbestosIs, a diffuse Interstitial fibrosis of the lung tissue often leading after long exposure to severe loss of lung function and respiratory failure. The lung cancer of asbostoa workers le also associated vith cigarette smoking, which leads to considerable difficulty in assigning relative risks of asbestos exposure to smokers. Mesothelioma, a disease which Is PRODUCED BY FORD W> 8005 0061 JOt