Progress Reports
E-7*: Fluorspar in silicified rocks in
New Mexico
by W. N. McAnulty, Sr., 1972, 3 p.
(*The first 7 in this series were designated "target exploration" reports)
More than 200 occurrences of fluorite (CaF2) are known in 12 counties in New Mexico; approximately 650,000 tons of fluorspar, an aggregate of rock and mineral matter containing enough fluolite to make a commercial deposit, have been mined from 91 deposits in 11 counties. Most of the fluorspar procl~icecl came from relatively narrow veins enclosed in a wide variety of sedimentary and igneous roclcs. Most of the fluorite in these veins was precipitated from hydrothermal fluids emanating from magma chambers at depth, filling or partially filling open spaces avdable in fractures along faults, joints, and shear zones. Cornmonly the fluorite cemented rock fragments (fault breccia) formed along active faults before the fluorine-bearing fluicls were introduced. Some of the fluorite, usually only a minor part of the total amount present, was formed by replacement of fault breccias and wall rocks. Open-space, void-filling, or precipitated fluorite is commonly medium-to coarse-grained and relatively pure, whereas replacement fluorite is finer grained and often impure. However, vein material of a mineable thiclcness generally includes varying anlounts of calcite, quartz, iron oxides, unreplaced rock and other impurities which lower the grade of the fluorspar. Few deposits yield co~nmercial ore without some form of beneficiation.
Fluorspar is marketed in three grades--metallurgical, ceramic, and acid. Metallurgical grades, used chiefly in steelmalung, specify a certain number of effective units of CaF2 calculated by subtracting 2% times the percentage of silica (Si02) from the percentage of CaF2, in the ore or concentrate. For example, an ore or concentrate assaying 85 percent CaF2 and 5 percent Si0, contains 72% percent effective CaF2. Ceramic and acid grades are expressed in percentage of CaF,. Ceramic grades range from 85 to 96 percent CaF2. Acid grade, used chiefly in the aluminum and chemical ind~istries, must contain 97 percent or more CaF2. Some consumers place rigid restrictions on the amount and kind of inlpurities in ceramic and acid grades.
Because silica (SiO2,), chalcedony, and other fine-grained varieties of the quartz family of minerals is particularly undesireable in fluorspar, many deposits with a high silica content were not commercial in the past. Therefore, little or no attention was given to such deposits in prospecting. In fact, prospectors steered away from them. Most metallurgical uses require fluorspar in lump form, and a concentrate cannot be used unless it is pelletized. Silica is a common impurity in fluorspar deposits; few deposits yield metallurgical grade without selective mining; little or no metallurgical ore can be produced profitably from most deposits without concentrating and pelletizing.
Producing a salable product from most fluorspar deposits requires processing by heavy media (sink-float) or froth flotation, or both; and large capital expenditures are required for the beneficiation plants. Large reserves are required if the costs are to be amortized--at least one million tons for a medium-sized plant. Obviously, with a total production of only about 650,000 tons from 91 different deposits in New Mexico, the known fissure vein deposits within the state are small. Few fissure vein deposits contain large reserves anywhere. However, Inany large, lowgrade, siliceous deposits in New Mexico could be developed and profitably exploited. The purpose of this paper is to direct attention to these deposits.
New Mexico Bureau of Geology & Mineral Resources
New Mexico Institute of Mining & Technology
801 Leroy Place
Socorro, NM 87801-4796
information: (575) 835-5420
fax: (575) 835-6333
http://geoinfo.nmt.edu
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