FLUORINE 



227 



mainly silicic and alkalic rocks and carbonatite com- 

 plexes. The fluorine minerals occur in tactite and in 

 posttactite hydrothermal veins and replacement 

 bodies. Contact-zone fluorspar deposits, mined in 

 Korea and Japan, are generally small podlike bodies 

 about 20 meters long, 10-15 meters wide, and 10 

 meters high. The deposits in Korea are replacement 

 bodies in limestone at the contact with younger 

 "granites" and are of two types : a low-temperature 

 type consisting mainly of fluorite, quartz, and coarse- 

 ly crystalline calcite, and a high-temperature type 

 consisting of epidote and calc-silicates in addition to 

 fluorite, quartz, and calcite (Gallagher, 1963, p. 93). 

 Both types contain some sulfides. 



Fluorspar deposits associated with the Okorusu 

 complex in South West Africa are veins and replace- 

 ment bodies in the contact aureole of carbonatite 

 intrusives. At Amba Dongar, India, the main eco- 

 nomic concentrations of fluorite occur as veins and 

 replacement bodies in carbonate wallrock around 

 late-stage ankeritic carbonatite intrusives which are 

 also fluorite-bearing (Deans and others, 1972, p. 

 B6). Fine-grained cherty quartz and minor amounts 

 of barite, dickite, galena, pyrite, and chalcopyrite 

 are associated with fluorite at Amba Dongar. Meta- 

 somatic phlogopite rocks around carbonatite plugs 

 in Zambia, Malawi, and Rhodesia contain anomalous 

 amounts of fluorine. The fluorine in these dull-gray 

 rocks is contained largely in fluor-phlogopite, but 

 some occurs in sellaite (Deans and others, 1972, 

 p. B6). 



FLUORINE DEPOSITS ASSOCIATED WITH 

 SEDIMENTARY ROCKS 



Some fluorine deposits in sedimentary rocks ap- 

 pear to be genetically related to the enclosing sedi- 

 ments, but some of the deposits may be of hydro- 

 thermal or metasomatic origin. They occur in vol- 

 caniclastic sedimentary rocks; lacustrine deposits; 

 and evaporite, marine-carbonate, and marine-phos- 

 phate rocks. Fluorine minerals generally do not oc- 

 cur in detrital accumulations of economic value. 



Although volcanic ash commonly contains fluorine 

 in glass shards and absorbed on tephra, commercial 

 or potential deposits of fluorine in volcaniclastic 

 sedimentary rocks seem to be either disseminated 

 deposits of probable hydrothermal origin or inter- 

 bedded deposits of lacustrine origin. Fluorite-berylli- 

 um deposits in altered volcaniclastic sedimentary 

 rocks near Spor Mountain, Utah, described later in 

 this chapter, are considered to be of hydrothermal 

 origin. Fluorspar deposits near Rome, Italy, and 

 Rome, Oreg., are lacustrine deposits interbedded 

 with volcaniclastic sedimentary rocks. 



Fluorspar deposits in unconsolidated tuffs near 

 Rome, Italy, are lenses composed of finely crystalline 

 fluorite, barite, calcite, dolomite, apatite, opal, and 

 chalcedonic quartz and minor amounts of detrital 

 minerals and volcanic glass. The fluorite content of 

 some zones averages 55 percent. These lenses are 

 thought to be sedimentary deposits of chemical 

 origin formed in lake basins that were subject to 

 emanations of hydrothermal fluids rich in fluorine, 

 calcium, barium, strontium, silicon, sulfur, and 

 phosphorus (Spada, 1969). 



Near Rome, Oreg., fluorite occurs as submicro- 

 scopic, nearly spherical grains in tuff, tuffaceous 

 mudstone, and mudstone of Tertiary lacustrine de- 

 posits. Fluorite content is generally less than 5 per- 

 cent but is as much as 16 percent in some zones. 

 According to Sheppard and Gude (1969, p. D69) the 

 "fluorite probably formed during diagenesis in sedi- 

 ments that had been deposited in an alkaline, saline 

 lake." 



Some lacustrine brines and evaporites contain con- 

 centrations of fluorine; the best examples are the 

 brines and recent evaporites of lakes in the rift val- 

 leys of Africa, where lake waters contain as much 

 as 1,627 ppm fluorine. The evaporite sequence of 

 Lake Magadi, Kenya, composed largely of trona, 

 locally contains as much as 22 percent villiaumite 

 (NaF), and fluorite is common throughout much of 

 the sequence (Sheppard and Gude, 1969, p. D73). 



In the U.S.S.R., possible economic concentrations 

 of fluorine in marine carbonates and evaporites of 

 the Permian Preurals have been noted (Abramovich 

 and Nechayev, 1960). Fluorite occurs as a fine dis- 

 semination and as crystalline aggregates in vugs in 

 dolomitized limestone. The CaFa content of some 

 zones exceeds 30 percent. In the United States a 

 minor occurrence in Permian dolomitic limestones of 

 the Rocky Mountains contains 12-15 percent CaFa. 

 In marine carbonates of the U.S.S.R., as noted by 

 Kazakov and Sokolova (1950), fluorite is related to 

 the saline facies of relict basins, mainly to dolomite, 

 dolomitized limestones, gypsum, redrocks, anhydrite, 

 potassium and magnesium salts, and celestite. Ac- 

 cording to them (p. 68 of the English translation) 

 the fluorite was precipitated from sea water that 

 had been concentrated three to four times, and con- 

 tinued to precipitate from the brine in a dying sea 

 basin where potassium salts and borates were being 

 deposited. 



The ore mineral of sedimentary phosphate rock is 

 carbonate fluorapatite with ratio of F to P2O5 about 

 1 to 10. Phosphate rock contains as much as 4 per- 

 cent F and 40 percent P2O5, although lower grade 

 deposits are now mined for their phosphate content. 



