220 



UNITED STATES MINERAL RESOURCES 



another producing plant to a consumer who would 

 rather pay more freight than change suppliers. 



Environmental problems of feldspar mining are 

 standard for a nonmetallic mineral mined by open- 

 pit methods. Large dumps may be avoided by better 

 coproduct or byproduct recovery, especially of quartz 

 sand, mica, or feldspar-silica mixtures. Dust hazards 

 also can be avoided. Some open pits may be utilized 

 for lakes or reservoirs ; the impounded water should 

 generally be clear because sources of feldspar usually 

 lack sulfide minerals that produce acid mine waters. 



GEOLOGIC OCCURRENCE 



Commercial deposits of feldspar are found in some 

 pegmatites, many granites and related igneous rocks, 

 and certain beach sands and alluvium. Most pegma- 

 tites are light-colored coarsely crystalline igneous 

 rocks, which are found as lenticular or tabular bodies 

 in metamorphic rocks or in large granitic intrusions. 

 Individual mineral grains and crystals range in 

 length from less than 1 inch to many feet. Pegmatite 

 bodies vary in size from small pods and veins to 

 large masses hundreds of feet thick and thousands 

 of feet long. Feldspar, quartz, and mica are the most 

 common minerals present, but many rare and un- 

 usual minerals are found in some deposits. In many 

 pegmatite bodies the minerals are somewhat evenly 

 distributed throughout, but in others the minerals 

 are segregated into certain layers or parts of the 

 body, called zones. These zones can sometimes be 

 selectively mined to recover the desired minerals by 

 hand sorting and are, therefore, important economi- 

 cally. Most of the feldspar produced in the United 

 States before 1946 was perthite, which commonly is 

 abundant as very large crystals in the intermediate 

 zones or cores of zoned pegmatite bodies. 



The principal pegmatite districts in the United 

 States are in New England, especially Maine, New 

 Hampshire, and Connecticut, in the Appalachian 

 Piedmont from Virginia to Alabama, and in the 

 Blue Ridge Mountains in North Carolina and Geor- 

 gia. Smaller districts are in the Black Hills of South 

 Dakota, the Front Range of Colorado, several areas 

 in northern New Mexico, western Arizona, and 

 southern California; minor districts are in Nevada, 

 Montana, Wyoming, Idaho, and Washington (Cam- 

 eron and others, 1949; Jahns, 1955). 



Granite and related igneous rocks are composed 

 of one or two kinds of alkalic feldspar ; quartz ; and 

 minor amounts of various other minerals, mainly 

 muscovite, biotite, hornblende, or rarely pyroxene. 

 Feldspar content ranges from 50 to 70 percent, and 

 grain size from less than one-fourth inch to about 

 an inch. Deposits range from small masses measured 



in feet to very large masses measured in miles. 

 Granitic rocks such as alaskite, that contain only 

 small amounts of ferromagnesian minerals, locally 

 are mined in bulk and a mixture of potassium and 

 sodium feldspar recovered by milling and flotation. 

 Mixtures of feldspar and quartz are also produced as 

 byproducts of granite quarrying. 



Granites are common igneous rocks that occur 

 widely in the crystalline terranes of the world. Large 

 granitic bodies in the United States are scattered 

 throughout New England ; the older Appalachians 

 from New York to Alabama ; the Llano area, Texas ; 

 northern Wisconsin and adjacent Michigan; north- 

 ern Minnesota ; the St. Francois Mountains, Mo. ; the 

 Black Hills of South Dakota; the Rocky Mountains 

 from New Mexico to Wyoming; and in isolated 

 mountain ranges of Arizona, Utah, and Nevada. 

 Large batholithic intrusions are in California, Idaho, 

 Montana, and Washington. 



Feldspathic beach sands and alluvial deposits may 

 be rich enough to be mined for their feldspar con- 

 tent. The dune sands of Pacific Grove, Monterey 

 County, Calif., which have been worked extensively, 

 contain about 53 percent quartz, 46 percent feld- 

 spar, and less than 1 percent other minerals in an 

 area about 6 miles long and 1 mile wide. Alluvial 

 deposits along the Mississippi, Illinois, Wabash, and 

 Ohio Rivers and dune and beach sands of Pleistocene 

 age in Illinois contain 5-25 percent feldspar, 2-12 

 percent feldspathic rock fragments, 60-80 percent 

 quartz, and some chert and heavy minerals. The 

 alluvial sands are in low river terraces, in present 

 channels, and in sandbars (Hunter, 1965) . Similar 

 deposits along the Kansas, Arkansas, Little Arkan- 

 sas and Republican Rivers in Kansas contain as 

 much as 27 percent feldspar. 



Authigenic potash feldspar has been reported 

 from many sedimentary rocks of various lithologies 

 and ages (Sheppard and Gude, 1965, p. 6) . Feldspar 

 content may range from less than 10 percent in 

 some shales and siltstones to as much as 90 percent 

 in some tuffaceous beds. Recent work on Cenozoic 

 tuffs in saline lake beds in California, Oregon, Ne- 

 vada, and Arizona has shown a definite zonal pattern 

 to these deposits (Sheppard and Gude, 1968; Shep- 

 pard and Walker, 1969). At the margins of former 

 lakes, most of the tuff beds contain unaltered glass 

 and grade into a zeolite facies toward the middle 

 of the lakes; however, near the centers of the lakes 

 in areas of higher salinity nearly pure beds of 

 potash feldspar are found. The deposits studied to 

 date contain more iron and are finer-grained than 

 is desired for glass feldspar. The tuff beds, how- 

 ever, are 2-8 feet thick and may cover tens of square 



