LIGHTWEIGHT AGGREGATES 



351 



Piedmont province of South Carolina (one-third of 

 the production), the Blue Ridge province in Vir- 

 ginia, North Carolina, South Carolina, and Georgia, 

 and scattered deposits in Wyoming, Texas, Colorado, 

 California, Nevada, Arizona, Washington, and Ore- 

 gon. The almost invariable association of vermicu- 

 lite with Precambrian rocks allows Hawaii and vir- 

 tually all the central part of the country from the 

 Rocky Mountains east to the Blue Ridge to be dis- 

 missed from consideration, except possibly the 

 Wichita Mountains and the Ozark Mountains. 



All the recoverable reserves of venniculite in the 

 United States are in one deposit in Montana and in 

 several deposits in the Enoree and Enoree-Waldrep 

 districts of South Carolina. Inasmuch as almost all 

 of them are controlled by a single company, and the 

 rest by two other companies, it is not appropriate to 

 publish a quantitative estimate. However, in 1952 

 a mining publication in London (Mining Jour., 1952) 

 estimated that reserves at the Libby deposit ranged 

 from 25 to 100 million tons. No grade was given, so 

 the amount of vermiculite mineral that was available 

 is uncertain. As a measure of the United States 

 position, we can again estimate the cumulative out- 

 put needed to satisfy the demand through the year 

 2000, using a 5-percent rate for the annual growth. 

 Based on the 1970 production (Fulkerson, 1972) of 

 about 285,000 tons of crude and 220,000 tons of 

 exfoliated vermiculite, about 19 million tons of crude 

 will be required. Since 1952 about 4.3 million tons 

 of crude has been produced from all U.S. deposits. 

 The total is less than the smaller estimate for the 

 Libby deposit as published in 1952. 



The remainder of the identified resources of ver- 

 miculite must be classed as submarginal, for it is 

 unlikely that any of the other known deposits can 

 be brought into operation at 1.5 times the present 

 price. They are too small, or too low grade, or too 

 poorly located to be able to compete at that price; 

 thus, they cannot be considered paramarginal re- 

 serves. The total tonnage that can be estimated as 

 submarginal reserves is on the order of 2-3 million 

 tons in North and South Carolina, Texas, Wyoming, 

 Colorado, and Nevada. 



Hypothetical resources in the known districts are 

 probably on the order of IV2-2 million tons — it is 

 unlikely that a new Libby will be found in the 

 known districts, but discovery of new deposits of 

 the Enoree type can be expected. It is also unlikely 

 that there is only one Libby deposit in the conter- 

 minous United States, and so a projection of 25 to 

 100 million tons in the classification of speculative 

 resources seems reasonable. 



Where and how are the hypothetical and specula- 



tive resources to be found ? Most of the hypothetical 

 resources, in deposits of the 20,000- to 100,000-ton 

 size, are likely to come from deposits of the Enoree 

 type in the Inner Piedmont region of South Caro- 

 lina. Possibly a combination of airborne and ground 

 geophysical surveys and detailed geologic mapping 

 can locate these deposits. We should be able to 

 distinguish the zones of ultramafic rocks from the 

 granitic rocks by airborne magnetic surveys, and 

 possibly we may be able to identify magnetic anoma- 

 lies the size of the target vermiculite deposits. At 

 present there are virtually no guides to favorable 

 ground and ore deposits, other than the relationship 

 to ultramafic rocks. 



Deposits of the Libby size, which would contain 

 most of the speculative resources, have geologic 

 relations that are intriguing and encouraging for 

 additional discoveries. The association of ultramafic 

 plutons with syenites, alkalic rocks, and carbonatites 

 is too common to be happenstance; the association 

 of these rocks is known from several deposits in the 

 United States (Rocky Boy, Mont.; Gem Park- 

 McClure Mountain and Powderhorn, Colo.), in the 

 U.S.S.R., and, in particular, in many parts of the 

 African continent. Several generalized clues to 

 places where these rocks may be found together 

 are (1) the rocks are usually in Precambrian ter- 

 ranes, (2) they may be related to Precambrian 

 structural trends, (3) they may exhibit significant 

 magnetic anomalies, and (4) they may be character- 

 ized by ring-dike structures. 



Several problems deserve investigation. What is 

 the environment in which mafic minerals are altered 

 to vermiculite? What are the temperature-pressure 

 conditions and the role of solutions and volatiles 

 from pegmatites, alkalic rocks, and carbonatites? 

 What is the mineralogenic sequence — the need for 

 formation of a micaceous mineral as an intermedi- 

 ate step between diospide and vermiculite, for ex- 

 ample? What role does the composition of the 

 ground water play in the formation of vermiculite, 

 and what climatic factors affect the alteration, and 

 in what way? In a broader context, where the 

 answers are of importance to resources besides ver- 

 miculite, what are the guides to the localization of 

 ultramafic rocks, of syenites and carbonatites and 

 other alkalic rocks? 



SELECTED REFERENCES 



Aase, J. H., 1967, Lightweight aggregates — Expansion prop- 

 ties of selected Michigan shales: U.S. Bur. Mines Kept. 

 Inv. 7055, 23 p. 



Anderson, F. G., Selvig, W. A., Baur, G. S., Colbassani, P. J., 

 and Bank, W., 1956, Composition of perlite: U.S. Bur. 

 Mines Kept. Inv. 5199, 13 p. 



