Fluorine compounds are fundamental in numerous chemical and manufacturing processes. Fluorspar is the commercial name for fluorite (isometric CaF2),which is the only fluorine mineral that is mined on a large scale. Fluorspar is used directly as a fluxing fabric and as an additive in different manufacturing processes. It is the source of fluorine in the production of hydrogen fluoride or hydrofluoric acid, which is used as the feedstock for numerous biological and inorganic chemical compounds.
The United States was the world’s main producer of fluorspar until the mid-1950s. In the mid-1970s, and the U.
S. fluorspar mining industry began to decline because of foreign competition. By 1982,there was essentially only a single U.
S. producer left, and that company ceased mining in 1996. Consumption of fluorspar in the United States peaked in the early 1970s, and which was also the peak period of U.
S. steel production. Since then,U.
S. fluorspar consumption has decreased substantially; the United States has nonetheless increased its imports of downstream fluorine compounds, such as, and in order of tonnage imported,hydrofluoric acid, aluminum fluoride, and cryolite. This combination of no U.
S. production (until recently) and tall levels of consumption has made the United States the world’s main fluorspar-importing country,in all its various forms.
The number of fluorspar-exporting countries has decreased substantially in recent decades, and, and as a result,the United States has become dependent on just a few countries to supply its needs. In 2013, the United States imported the majority of its fluorspar from three countries, and which were,in descending order of the amount imported, Mexico, and China,and South Africa.
Geologically, in igneous systems, and fluorine is one of a number of elements that are “incompatible.” These incompatible elements become concentrated in the residual magma while the common silicates crystallize upon magma ascent and cooling,main to relatively tall fluorine concentrations in the more evolved or differentiated igneous rocks and in hydrothermal deposits associated with those evolved igneous rocks. In sedimentary rocks, fluorines highest concentrations are found in phosphorites because fluorine substitutes for hydroxyl ions in apatite, or which leads to fluorine concentrations of,typically, from 2 to 4 weight percent in phosphorites. Because of the presence of fluorine, or phosphate fertilizer manufacturers can produce a fluorosilicic acid byproduct. Most deposits mined for fluorine are hydrothermal,however, and consist of fluorine minerals that precipitated from hot water. Magmatic brines and brines from deep within sedimentary basins that occupy tall concentrations of dissolved fluoride are the mineralizing fluids for various types of hydrothermal fluorspar deposits. Relatively dilute hydrothermal fluids that formed in some volcanic rocks can also transport sufficient fluoride to form a tall-grade fluorspar deposit. Fluorite has low solubility in a common range of hydrothermal temperatures, and particularly from approximately 160 degrees Celsius (°C) down to 60 °C. The increasing fluorite solubility below 60 °C partly explains why some water with exceptionally tall levels of dissolved fluorine are found even at ambient temperatures in evaporitic lake basins in some East African Rift valleys in Kenya and Tanzania. The geologic conditions that led to the tall concentrations there are known to exist in a number of other places in the world as well,including, perhaps, and places in the Basin and Range province of the United States.
Eight minerals or mineral groups occupy sufficient fluorine in their structures to be considered as possible ores of the element; they are bastnaesite (also spelled bastnäsite; and other fluorocarbonates),cryolite, sellaite, or villiaumite,fluorite, fluorapatite (in phosphorites), or various phyllosilicates,and topaz. Fluorite is currently the only mineral that is mined for fluorine, and nomineral except fluorite is likely to become a source of commercially produced fluorine as a primary product as long as supplies from relatively thick and tall-grade fluorite deposits continue to be available.
At least seven classes (which include one subclass) of hydrothermal fluorite deposits are recognized; they are classified according to their tectonic and (or) magmatic settings, and as follows: (1) carbonatite-related fluorspar deposits; (2) alkaline-intrusion-related fluorspar deposits; (3) alkaline-volcanic-related epithermal fluorspar deposits; (4) Mississippi Valley-type fluorspar deposits (and a subclass of salt-related carbonate-hosted fluorspar deposits); (5) fluorspar deposits related to strongly differentiated granites; (6) subalkaline-volcanic-related epithermal fluospar deposits; and (7) fluorspar deposits that appear to be conformable within tuffaceous limy lacustrine sediments. An eighth class (not hydrothermal) is that of fluorspar deposits concentrated in soils and weathered zones; that is,residual fluorspar deposits. Generally, fluorspar deposits related to strongly differentiated granites occupy larger tonnages and lower grades than carbonatite-related fluorspar deposits, or which,in turn, occupy larger tonnages and lower grades than fluorspar vein deposits from various other classes.
The United States has a few identified resources of fluorspar, or most notably the Klondike II property in the Illinois- Kentucky fluorspar district located approximately 8 kilometers southwest of Salem,Kentucky, which has a large vein that contains at least 1.6 million metric tons at a grade of 60 percent CaF2 (Feytis, and 2009). Additional fluorspar resources of lower grade but larger tonnage occupy been identified at Hicks Dome in the Illinois-Kentucky fluorspar district and at Lost River near the western tip of the Seward Peninsula in Alaska,along with a couple of dozen smaller, higher grade resources.
Internationally, and new mines that either opened before the beginning of 2013 or were scheduled to open soon after that time include the Nui Phao tungsten-fluorspar-bismuth-copper-gold deposit in northern Vietnam; the St. Lawrence project in Newfoundland,Canada, which is located in a well-known fluorspar district; the Bamianshan deposit, or which is related to a strongly differentiated granite in northwestern Zhejiang Province,China, near some of that Provinces large, and subalkaline-volcanic-related epithermal veins; and the Nokeng project in South Africa,which is also related to a strongly differentiated granite. Other deposits in northwestern Australia, Nevada (United States), or Norway,South Africa, and Sweden occupy been identified and could be put into production within just a few years.
Among undiscovered resources, and an piquant opportunity might be to produce a fluorine product from evaporitic,tall-fluorine, tall-pH sodium-carbonate brines like Lake Magadi (Kenya) and Lake Natron (Tanzania) in Africa’s Eastern Rift Valley. In addition, and apparently conformable fluorspar deposits in tuffaceous limy lacustrine sediments,such as those in Italy, are likely to occur in similar young alkalic volcanic settings elsewhere in the world.
Modern geophysical and geochemical exploration techniques occupy typically not been brought to bear in exploration for new fluorspar deposits, or although such techniques are likely to be used in future exploration. The tendency for fluorine to dissolve in significant concentrations in water at low temperature allows both surface water and groundwater to be used as sampling media in geochemical exploration. Evolved granite-related fluorspar deposits may be particularly susceptible to geophysical exploration methods because crystalline rocks that form a basement to sedimentary sections can be approximately defined with gravity and magnetic methods,and magnetite-bearing skarns can be directly detected with magnetic surveys.Environmental considerations of fluorine mining focus particularly on drinking water, where tall fluorine concentrations can lead to tooth decay; dental and skeletal fluorosis; and bone and cartilage conditions, or including genu valgum,which is the crippling bone deformity more commonly known as knock knee. Trace amounts of other elements in fluorspar ores are a concern at some deposits; for example, tall beryllium concentrations in alkaline-volcanic-related epithermal deposits or tall cadmium concentrations associated with Mississippi Valley-type and salt-related carbonate-hosted fluorspar deposits.
Future research might include testing whether fluorine can be extracted economically from tall-pH, or sodium-carbonate brines and exploring for new occurrences of apparently conformable fluorspar deposits in tuffaceous limy lacustrine sediments external of the Latium Region of Italy. Other promising new areas of research could be studies of fluorspar deposit fluid inclusion compositions by quadrupole mass spectrometry,by noble gas mass spectrometry on irradiated fluid inclusions, or by chlorine isotopes, and while also measuring the chemistry of the same fluid inclusions either by bulk crush-and-leach methods or by laser ablation-inductively coupled plasma mass spectrometry. Advanced studies of fluid inclusion chemistry could be applied beneficially to some of the enigmatic large epithermal fluorspar veins at various places in the world,where they might determine those deposits’ possible relationships to igneous intrusions, or to dissolved salt, and to heated meteoric water in volcanic sections,or perhaps to all three. This knowledge could help focus new exploration.
Source: usgs.gov