FLUORINE 



229 



low, but the reserves may be substantial. 



In the Western United States many areas of hydro- 

 thermally altered volcanic rock, agglomerates, vol- 

 caniclastic sediments, and unconsolidated clastic 

 sediments contain dispersed fluorite. The fluorite- 

 beryllium deposits near Spor Mountain, Utah, and 

 the Honey Comb Hills, Utah, are good examples 

 (McAnulty and Levinson, 1964). Altered water-laid 

 tuff near Spor Mountain, Utah, contains commercial 

 amounts of beryllium and about 4 percent CaFj. 

 Microscopic fluorite occurs dispersed through altered 

 tuff and in a iine-grained intergrowth with opal and 

 chalcedony in nodules as much as 30 centimeters in 

 diameter. Part of the fluorite in these deposits proba- 

 bly represents redeposition of fluorine leached from 

 the included volcanic ash. However, much of the 

 fluorine, along with beryllium, gallium, lead, lithium, 

 niobium, cesium, and yttrium, seems to have been 

 introduced with laterally spreading hydrothermal 

 solutions (Staatz and Griffitts, 1961 ; D. A. Lindsey, 

 oral commun., 1972). 



Hydrothermal fluorspar deposits in general 

 formed under a wide range of conditions, from high 

 pressure and temperature at depth to low pressure 

 and temperature near the surface, and were pre- 

 cipitated from solutions of varied chemical composi- 

 tion. Nevertheless, each individual deposit formed 

 under a relatively small range of conditions. Fluorite 

 at the Tyrny-Auz skarn complex. North Caucasus, 

 U.S.S.R., formed from pneumatolytic and hydro- 

 thermal solutions at temperatures in excess of 500° 

 C. The initial hydrothermal solutions were highly 

 supercharged with chlorides and fluorides of sodium, 

 potassium, calcium, and other elements (Lesnyak, 

 1965, p. 484). At Jamestown, Colo., fluorite in a 

 stockwork next to an alkalic intrusive formed from 

 solutions that varied in composition with time and 

 space. The main-stage fluids were highly saline (26- 

 32 percent equivalent NaCl) and near 350 °C, though 

 the fluids at times were alternately supersaline, CO2 

 rich, or relatively dilute and cool (J. T. Nash and 

 C. G. Cunningham, oral commun., 1972). Fluorite in 

 veins not closely associated with igneous rocks in 

 southern New Mexico formed from solutions that 

 changed with time. As the temperature decreased 

 from about 200 °C to about 140 °C over several sub- 

 stages of deposition, the salinity increased from 

 about 10 percent equivalent NaCl to about 15 percent 

 equivalent NaCl (Roedder and others, 1968, p. 336). 

 Fluorite in banded and crustified epithermal veins, 

 common throughout the world, formed from very 

 dilute solutions at temperatures ranging from 50° 

 to 200°C (Ermakov, 1965, p. 197; Steven, 1960, p. 



410). The nature of near-surface fluorite deposits, 

 such as at Spor Mountain, Utah, suggests that the 

 fluorite must have been deposited from very dilute 

 and low-temperature (50°-100°C) solutions. Strati- 

 form lead-zinc-fluorine-barium deposits of the Eng- 

 lish Pennines and the Illinois-Kentucky district were 

 formed from relatively high-salinity solutions (20 

 percent equivalent NaCl) at temperatures ranging 

 from 75° to 200°C (Sawkins, 1966, p. 385). 



Many fluorine deposits can be attributed to late 

 stages of igneous activity. The solutions depositing 

 the fluorine in many places seem to have had a com- 

 mon source with the magmas that formed related 

 fluorine-bearing igneous bodies and carbonatite com- 

 plexes. The common source was probably a differen- 

 tiating magma deep in the crust or a zone of frac- 

 tionation in the upper mantle. The partitioning of 

 fluorine between the hydrothermal solutions and the 

 late siliceous magma must have been nearly equal. 



The source of the ore-forming solutions for some 

 fluorine deposits, such as the stratiform deposits of 

 the English Pennines and the Illinois-Kentucky dis- 

 trict, is much debated. Most workers agree that these 

 deposits formed from slow-moving, relatively hot 

 (75°-200°C), dense, sodium-calcium-chlorine-fluo- 

 rine brines containing abundant organic matter. 

 Davidson (1966) suggested that the brines were de- 

 rived from the diagenesis of overlying evaporites 

 and that they concentrated their metals from the 

 limestone and other rocks traversed. Dunham 

 (1966), pointing to the low sodium/potassium ratios 

 of the brines, as little as 6:1, compared with 39:1 

 for normal sea water, suggested that the relative 

 enrichment in potassium appears to rule out purely 

 connate solutions as the source of the brines. He 

 preferred nonevaporitic connate water, reinforced 

 by juvenile fluids associated with an igneous heat 

 source below, as the origin of ore-forming brines. 

 Grogan and Bradbury (1968) suggested that the 

 brines were magmatic, connate,' and meteoric in 

 origin, and that the fluorine and metals were of mag- 

 matic origin. 



Probably in most fluorine deposits the materials 

 making up the ore-forming solution came from more 

 than one source. The ultimate source of the fluorine 

 needed to form the deposits is generally unknown; 

 the relationship of fluorine deposits to major struc- 

 tures points to a deep-seated origin. Still, the re- 

 gional distribution of fluorine in the Western United 

 States through geologic time suggests that once a 

 specific region becomes enriched in fluorine, it re- 

 mains so through several geologic cycles and episodes 

 of mineralization (Peters, 1958, p. 685). 



