228 



UNITED STATES MINERAL RESOURCES 



Plants in eight countries are recovering fluorine as a 

 byproduct (Wood, 1972). The fluorine in phosphate 

 rock could have been part of the original precipitate, 

 or, inasmuch as calcium phosphate or calcium 

 hydroxy-phosphate can collect fluorine from very 

 dilute solutions, it could have been introduced later. 

 (See also the chapter in this volume entitled 

 "Phosphates.") 



FLUORINE DEPOSITS ASSOCIATED WITH 

 METAMORPHIC ROCKS 

 Topaz and tourmaline are common in metamor- 

 phic rocks and may represent future sources of 

 fluorine. For example, a Precambrian topaz-quartz- 

 sillimanite gneiss in the central part of the Front 

 Range, Colo., contains major amounts of topaz 

 (Sheridan and others, 1968). This unit, part of a 

 high-grade metamorphic gneiss and granitic plutonic 

 complex, is 11-100 feet thick and crops out along 

 strike for 7,000 feet. Three composite chip samples 

 of this unit vi'ere found to contain 67, 23, and 36 

 weight percent topaz and 4.2, 3.9, and 2.2 weight 

 percent rutile. The gneiss may warrant investigation 

 as an ore of rutile, especially since it might also yield 

 topaz or topaz and sillimanite as byproducts (Sheri- 

 dan and others, 1968) . 



FLUORINE IN HYDROTHERMAL DEPOSITS 



Historically, the dominant commercial sources of 

 fluorine have been fluorspar deposits of hydrother- 

 mal origin. Hydrothermal fluorspar occurs in a wide 

 variety of types of deposits formed in many geologic 

 environments under a wide range of physical-chemi- 

 cal conditions. Fluorite is generally the only fluorine 

 mineral in these deposits, and its abundance ranges 

 from nearly 100 percent down to trace amounts. 

 Other common minerals are quartz, chalcedonic 

 quartz, opal, barite, manganese oxides, calcite, clay 

 minerals, and lead and zinc sulfides. The following 

 elements are commonly, but not universally, present 

 in these deposits, and at many places they are in 

 trace amounts only: silver, gold, beryllium, iron, 

 manganese, molybdenum, lead, the rare earths, tin, 

 tellurium, uranium, vanadium, tungsten, and zinc 

 (Worl, 1971). Hydrothermal fluorite occurs in al- 

 most any type of host rock but especially in carbon- 

 ate, silicic igneous, and silicic metamorphic rocks. 



The form of hydrothermal fluorspar deposits is 

 the standard basis for their classification. Most 

 common forms are veins and mantos, which are 

 abundant in well-defined regions of the world. Indi- 

 vidual veins range in thickness from millimeters to 

 several meters and are as much as several kilometers 

 in length. Fluorspar mantos, or blanketlike replace- 



ments of rock, are generally confined to marine car- 

 bonate rocks and commonly extend outward from 

 veins. Mantos are irregular lenticular or wedge- 

 shaped bodies and are not layered concordantly with- 

 in a stratigraphic sequence. Fluorspar in many veins 

 and mantos is characterized by monomineralic band- 

 ing, crustification, and mammillary textures. Mas- 

 sive crystalline material, breccias, and fine-grained 

 earthy material are also common. Most fluorspar 

 veins and mantos contain at least 35 percent CaFa ; 

 many contain at least 70 percent CaFa; and some 

 contain as much as 98 percent CaFj. 



Although host-rock compositions were important 

 in localizing many individual deposits, regional 

 structures controlled the location of most hydrother- 

 mal fluorspar districts. Fluorite veins and mantos in 

 many areas are confined to large faults and subordi- 

 nate fissures of deep-seated regional tensional na- 

 ture, as in India (Deans and others, 1972), in 

 Eastern Mongolia (Khasin and Kalenov, 1965), in 

 the Western United States (Worl, 1971), and along 

 the rift valleys of Africa. Regional domes and arches 

 helped localize fluorspar mineralization in the Illi- 

 nois-Kentucky district of the United States (Heyl 

 and Brock, 1961) and in the North Pennine ore field 

 of the United Kingdom (Sawkins, 1966). Hydrother- 

 mal fluorspar veins and mantos have been docu- 

 mented all over the world, some of the best known 

 occurring in Mexico (Van Alstine, 1961), the 

 United States (Grogan and Bradbury, 1968), Spain 

 (Marin and deLis, 1945), Brazil (Abreu, 1960), 

 South Africa (DeKun, 1965), the U.S.S.R. (U.S. 

 Bur. Mines, 1958), Korea (Gallagher, 1963), Canada 

 (Van Alstine, 1944), Italy (Spada, 1969), France 

 (Chermette, 1960), Pakistan (Bakr, 1965), and 

 Thailand (Gardner and Smith, 1965). 



Some districts characterized by veins and mantos 

 contain individual hydrothermal fluorspar deposits 

 best described as stockworks and pipelike bodies. 

 Fluorspar pipes mined in the Thomas Range, Utah, 

 and near Beatty, Nev., are circular to elliptical in 

 plan and range in diameter from 5 to about 45 

 meters (Peters, 1958, p. 672). Much of the fluorspar 

 at Jamestown, Colo., and the Buffalo mine, Union of 

 South Africa (DeKun, 1965, p. 409), is in the form 

 of stockworks of veins and veinlets. Fluorspar pipes 

 and stockworks commonly occur at fault intersec- 

 tions and are generally associated with stocks and 

 hypabyssal bodies of igneous rock. Fluorspar pro- 

 duction from Jamestown, Colo., has been from brec- 

 cias containing 50-90 percent CaFj within the stock- 

 work. Fluorspar in stockworks generally is diffused 

 through large bodies of rock so that the ore grade is 



