LIGHTWEIGHT AGGREGATES 



341 



sources is similarly blurred, for the concept of de- 

 posits in mining districts really does not apply to 

 the distribution of argillaceous rocks throughout the 

 United States. Geologic mapping in the United 

 States, at scales adequate to identify the presence 

 of argillaceous rocks, is sufficiently complete to vir- 

 tually rule out the possibility of finding additional 

 units. What remains to be found are those deposits 

 that would be classed as submarginal or, at best, 

 as paramarginal. 



Reserves of expandable clays, shales, and slates 

 are so large that they can be relied upon to satisfy 

 the Nation's needs for many years. If those needs 

 are projected from 1970 through 2000, starting with 

 the estimated actual 1970 production of slightly 

 more than 10 million tons and projecting an annual 

 growth rate of 5 percent, the cumulative production 

 is about 670 million tons. That figure, though im- 

 pressive, is seen in better perspective if it is allo- 

 cated among the 36 States that produced lightweight 

 aggregates in 1970 — an average per State of about 

 ISy^ million tons, or the mining of about 13 stand- 

 ard mining claims to a depth of a little less than 

 20 feet. Put another way, cumulative production 

 through the year 2000 will represent about one- 

 millionth of the tonnage of argillaceous rocks in the 

 48 contiguous States to a depth of 20 feet below 

 the surface. 



For a number of reasons the sum of recoverable 

 reserves cannot be stated with much accuracy, but 

 a reasonable estimate can still be made, based on 



other than strictly geologic reasoning. Between 70 

 and 85 processing plants (both kiln and sinter) have 

 been in operation annually over the period 1965-70. 

 Plant investments are large, ranging from several 

 hundred thousand dollars to more than $1 million. 

 Average annual production in 1970 was about 

 150,000 tons. Plant amortization requirements over 

 about a 10-year period suggest the need for an 

 average raw-material reserve of about 1.5 million 

 tons per plant, about the equivalent of a standard- 

 size mining claim quarried to a depth of 20 feet. In 

 view of the stratigraphic characteristics of the ar- 

 gillaceous rocks, this is a very plausible estimate 

 for almost any of the processing sites. As a rule of 

 thumb, roughly equal amounts can be assigned to 

 the proved, probable, and possible reserves, perhaps 

 about 115 million tons each, or a rounded total of 

 recoverable reserves in the presently known deposits 

 of about 350 million tons. The sum of all reserves 

 plus hypothetical and speculative resources is many 

 times that of the recoverable reserves. 



VOLCANIC ROCKS 



Various volcanic rocks are suitable for use as 

 lightweight aggregates; all are glasses, and they 

 range in composition from mafic to silicic. Scoria, 

 volcanic cinder, pumice, and pumicite make moder- 

 ate- to low-strength structural aggregates, whereas 

 expanded perlite and expanded pumicite are ultra- 

 lightweight materials. The chemical composition of 

 the glasses (table 68) faithfully mirrors that of 



Table 68. — Comparative composition of volcanic glasses 



[Tr., trace; ND, not determined; NA not applicable] 



SAMPLE LOCATIONS AND REFERENCES 



1. Sample JV-6, Pearlette ash, Kansas (Carey and others. 196i2). 



2. Sample NNV-IB, Calvert Ash Bed of Ogallala Formation, Kansas 



(Carey and others, 1962). 



3. Pumicite at Shoshone, Calif. (Chesterman, 1956). 



4. Average of 54 analyses, Kansas (Bauleke, 1962). 

 6. Mono County, Calif. ((Chesterman, 1966). 



6. Italy (Talmage and Wooton, 1937). 



7. Mount Taylor, N. Mex. (Talmage and Wotton, 1937). 



8. Average of 80 analyses (King, 1948). 



10 from Anderson, 



9. Socorro deposit. New Mexico (Weber, 1963). 



10. Deschutes deposit, Oregon (King, 1948). 



11. Average of 21 analyses: 11 from King (1948); 



Selvig, Baur, Colbassani, and Bank (1956). 



12. Shirataki, Japan (Yagi, 1966). 



13. Glass Mountain, Calif. (Chesterman, 1966). 



14. Average of three analyses, Oregon and California (King, 1948). 



15. Red Cinder Mountain, Calif. (Chesterman, 1956). 



16. Average of six analyses, Idaho (Asher, 1965). 



