MICA 



421 



acre of schist would be 145,000 tons and of granite, 

 35,000 tons. 



In areas where geologic and mining data are avail- 

 able, good estimates of resources can be made. Thus, 

 reserves of primary scrap or flake mica in the 

 Spruce Pine district have been estimated as 45-50 

 million tons in material similar to that currently 

 being mined (Brobst, 1962, p. 15-16). Conditional 

 and hypothetical resources of scrap mica in that 

 district may be several times greater than reserves. 

 Hypothetical resources of scrap mica in mica schist, 

 weathered pegmatite, and granite in the rest of the 

 Blue Ridge Mountains and Piedmont in the south- 

 eastern States must equal or be many times greater 

 than the reserves in the Spruce Pine district. 



Similarly immense hypothetical resources of scrap 

 mica are present in pegmatites, granites, and mica 

 schist in metamorphic and igneous terranes in New 

 England; the Black Hills of South Dakota; the 

 Llano area of Texas ; the Rocky Mountains ; isolated 

 mountains in Arizona, Utah, and Nevada; parts of 

 California; and other areas of the United States. 

 However, projected annual demand in the United 

 States for flake mica by the year 2000 ranges from 

 280,000 to 550,000 tons (Petkof, 1970, p. 1096) ; 

 thus, the resources of just the Spruce Pine district 

 seem adequate to meet the expected demand for 

 years to come. 



World resources of scrap mica in pegmatite, mica 

 schist, and granite are probably at least of the 

 same order of magnitude as the U.S. resources. 

 Production of scrap mica outside the United States 

 has come mostly from mine scrap, and deposits of 

 flake mica are largely undeveloped. Scrap-mica re- 

 serves and resources in India must be very large; 

 about 10 million tons of scrap were heaped near 

 mines and factories in 1965 (W. R. Griffitts, written 

 commun. ) . The other sheet-mica-producing countries 

 must have similar supplies of scrap because world 

 demand has generally been much less than United 

 States demand. 



SPECULATIVE RESOURCES 



Even less can be said about speculative resources 

 of sheet mica than about reserves and hypothetical 

 resources. Commercial sheet muscovite is found 

 only in pegmatite deposits, and most of the pegma- 

 tite districts in the world have probably been 

 found. The chances of finding a large previously 

 undiscovered district seem negligible because peg- 

 matite minerals are coarse grained and so unusual 

 that they are not easily ignored. The distribution 

 of phlogopite deposits is probably less well known, 

 but again, chances of finding a large undiscovered 



district seem poor. Speculative resources of sheet 

 mica, therefore, are probably not large. 



In contrast to speculative resources of sheet mica, 

 those of flake mica are probably large. Large areas 

 of metamorphic rock known to exist throughout the 

 world have not been studied in enough detail to 

 outline mica schist deposits that might be a source 

 of flake mica. Deposits of hydrothermally altered 

 rock containing fine-grained muscovite like that 

 being mined in South Carolina may be widespread 

 but have not been evaluated as a mica resource. 

 Deposits of detrital mica similar to that mined in 

 Davy Crockett Lake, Tenn., represent another type 

 not exploited to any great extent. All such deposits 

 may be very widespread and may represent large 

 speculative resources of flake mica. 



PROSPECTING TECHNIQUES 



Most sheet-mica mines are in pegmatites that 

 were found because they were exposed at the sur- 

 face. Chips of coarse mica in the soil, exposures of 

 massive quartz, or white clay weathered from a 

 feldspar-rich zone are good signs of a potentially 

 mica-bearing pegmatite. Prospecting consists of 

 trenching, digging shallow pits, or sinking shafts 

 or inclines in a pegmatite. The pegmatite is tested 

 for mica concentrations along the contacts with 

 wallrocks or in the different zones. In the past 20 

 years some drilling has been done, but generally, 

 drilling only proves the presence or absence of peg- 

 matite and reveals little about any mica that it may 

 contain. Only by mining a large enough sample of 

 mica-bearing pegmatite can the miner establish, 

 from the size, quantity, and quality of the mica, 

 feasibility of development of the pegmatite. Geo- 

 logic mapping to determine structure and meta- 

 morphic grade of the country rock may help out- 

 line potential areas for prospecting. Most sheet- 

 mica-bearing pegmatites not in granitic rocks are 

 in metasedimentary rocks that are products of 

 medium- to high-grade (kyanite- or sillimanite- 

 grade) regional metamorphism. If there has been 

 later deformation, the pegmatite may contain mica 

 that is deformed and good only for scrap. Mapping 

 and detailed study of pegmatites begun during 

 World War II proved that reserves and resources 

 can be calculated in zoned pegmatites if the geologic 

 details are known (Cameron and others, 1949; 

 Jahns, 1955; Norton and Page, 1956). Study of the 

 use of geophysical or geochemical techniques in 

 looking for concealed deposits should be made. Small 

 positive geochemical anomalies of various trace ele- 

 ments have been found in gneiss and schist within 



