72 



UNITED STATES MINERAL RESOURCES 



is just beginning in Mexico. Two widely separated 

 deposits contain the reported reserves. Until more 

 is known of the settings of these occurrences, geo- 

 logic projection of additional resources is not plausi- 

 ble. The expanding asbestos-cement product industry 

 of Mexico will long have first call on any resources 

 that can be discovered in that country. 



PROSPECTING TECHNIQUES 



Quebec-type chrysotile deposits are large enough 

 targets to be searched out by geophysical techniques ; 

 the magnetite ubiquitous in ultramfic terranes deter- 

 mines the prospecting method. Magnetite, most 

 abundant in parts of the ultramfic complexes most 

 intensely faulted, is thus a common constituent of 

 asbestos veins and adjacent wallrock, where anoma- 

 lous concentrations can be outlined by magnetic 

 surveys. Major zones of shearing and bodies of ser- 

 pentinized dunite, both likely to be barren of asbes- 

 tos, can also be expected to exhibit strong magnetic 

 anomalies. Therefore, interpretation of magnetic 

 data is most effective when done with knowledge 

 of the geologic habits of the ultramafics of a given 

 area. Ground surveys have long been a prime 

 method to outline potential asbestos-bearing zones 

 (Low, 1951). Airborne magnetic surveys are espe- 

 cially effective for reconnaissance to locate serpen- 

 tinite masses, and with moderate geologic ground 

 control or local supplementation by ground magnetic 

 surveys, airborne surveys can be used to outline 

 geologic features of possible economic significance 

 (Conn, 1970). 



PROBLEMS FOR RESEARCH 



The reasons for the restriction of large concentra- 

 tions of chrysotile asbestos to certain very limited 

 intervals in an alpine-type serpentine belt are not 

 yet clear. Data of the sort that led to the recent 

 recognition (Irwin, 1964) that serpentinites of the 

 Klamath Mountains of northern California are 

 somewhat older (and the subjects of a different tec- 

 tonic history) than serpentinites contiguous to the 

 west are possibly the kind of field data needed for 

 future evaluations. In this instance the known 

 chrysotile occurrences may be entirely restricted to 

 the older serpentinites. 



The evolution of ideas on the tectonic emplace- 

 ment of alpine-type serpentinites should be given 

 close future attention for hints as to targets for 

 asbestos exploration. The res'criction of asbestos 

 concentrations to only parts of the geosynclinal belts 

 may be related to a certain sequence of structural 

 events, or to optimum pressures or temperatures 

 operative in one tectonic wedge and not in an adja- 



cent mass. Appraisals are being made of the strength 

 and ductility or brittle behavior characteristics of 

 the various serpentinites. Certainly the degree of 

 competence prevailing at the time when energy and 

 solutions were available for the late (local) stage 

 serpentinization was a vital factor in formation of 

 a minable deposit. As a part of the "global tectonics" 

 research, physical properties of the various occur- 

 rences of serpentinite may one day be accurately 

 and readily defined; these data and the techniques 

 used in their determination should be given atten- 

 tion for practical application. As a potential sec- 

 ondary result of such studies, for instance, perhaps 

 magnetic anomalies directly related to asbestos 

 localization may be differentiated from magnetic 

 phenomena that are not so related. 



SELECTED REFERENCES 



Avery, R. B., Conant, M. L., and Weissenborn, H. F., 1958, 

 Selected annotated bibliography of asbestos resources in 

 the United States and Canada: U.S. Geol. Survey Bull. 

 1019-L, p. 817-865. 



Badollet, M. S., 1951, Asbestos, a mineral of unparalleled 

 properties : Canadian Inst. Mining and Metallurgy 

 Trans., v. 54, p. 151-160. 



1953, Asbestos fibers — Production and usage : Cana- 

 dian Inst. Mining Metall. Trans., v. 56, p. 247-249. 



Bailey, E. H., Irwin, W. P., and Jones, D. L., 1964, Fran- 

 ciscan and related rocks and their significance in the 

 geology of western California: California Div. Mines and 

 Geology Bull. 183, 177 p. 



Bailey, E. H., Blake, M. C, Jr., and Jones, D. L., 1970, On- 

 land Mesozoic oceanic crust in California Coast Ranges, 

 in Geological Survey research 1970: U.S. Geol. Survey 

 Prof. Paper 700-C, p. C70-C81. 



Beckwith, R. H., 1939, Asbestos and chromite deposits of 

 Wyoming: Econ. Geol., v. 34, no. 7, p. 812-843. 



Bowles, Oliver, 1955, The asbestos industry: U.S. Bur. Mines 

 Bull. 552, 122 p. 



1959, Asbestos — a materials survey: U.S. Bur. Mines 



Inf. Circ. 7880, 94 p. 



Carroll-Porczynski, C. Z., 1958, Inorganic fibers: New York, 

 Academic Press Inc., p. 169-259. 



Chidester, A. H., 1962, Petrology and geochemistry of se- 

 lected talc-bearing rocks and adjacent country rocks in 

 north-central Vermont: U.S. Geol. Survey Prof. Paper 

 345, 207 p. 



Chidester, A. H., and Shride, A. F., compilers, 1962, Asbestos 

 in the United States (exclusive of Alaska and Hawaii) : 

 U.S. Geol. Survey Mineral Inv. Resource Map MR-17. 



Cilliers, J. J., leR., 1964, Amosite at the Penge asbestos 

 mine, v. 2 of Haughton, S. H., ed.. The geology of some 

 ore deposits in southern Africa : Geol. Soc. South Africa, 

 p. 579-591. 



Cilliers, J. J., leR., and Genis, J, H., 1964, Crocidolite asbestos 

 in the Cape Province, v. 2 of Haughton, S. H., ed.. The 

 geology of some ore deposits in southern Africa : Geol. 

 Soc. South Africa, p. 543-570. 



Coleman, R. G., 1971, Petrologic and geophysical nature of 

 serpentinites: Geol. Soc. America Bull., v. 82, p. 897- 

 918. 



