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Western Kentucky Fluorspar District

Introduction

The Illinois-Kentucky Fluorspar District is located in Hardin and Pope Counties in southeastern Illinois and in adjacent Crittenden, Livingston, and Caldwell Counties of western Kentucky, within the Paducah 30 x 60 minute quadrangle. The western Kentucky portion of this district is called, appropriately enough, the Western Kentucky Fluorspar District.

Until the 1970's, more than three-fourths of the fluorspar produced in the United States came from the Illinois-Kentucky Fluorspar District, which was the largest producer of fluorite in the United States during World War II. Since about 1970, foreign imports could be acquired more economically. Substantial quantities of zinc and some lead and barite have also been produced in the district, usually as a byproduct of fluorspar mining. The mineralization occurs in vein deposits and in some bedded deposits (called mantos). Most of the mining recovered the surficial residual deposits accumulated above the vein deposits and ore deposits in the shallow subsurface; however, there is still a substantial reserve of fluorspar and zinc in deeper deposits.

KGS has published numerous geologic maps, reports, and cross sections and led many field trips to investigate the district. KGS and USGS mapped the district at a scale of 1:24,000, and KGS has converted these maps into digital format for the Kentucky portion of the fluorspar district. Since 2004, KGS has been scanning thousands of mine maps, cross sections, logs, reports, and other important data for the district and will place this information into a GIS and on an Internet map server for public use in the next few years.

 

fluorspar district

History and Production

The earliest mining in the district was for lead at the Columbia Mine, Crittenden County, in 1835 (Ulrich and Smith, 1905, p. 115). From 1835 to the early 1870's, little fluorspar was mined. Only small amounts were produced from the early 1870's to about 1890, when an expanded market was created by the development of the basic open-hearth steel furnace in which fluorspar was used for flux. Production since 1890 has been erratic, but in general has risen. Production during World Wars I and II and the Korean conflict rose sharply, but because of rising imports during 1935-38, production in the distict decreased. Production rose in 1970, but declined rapidly, and all mine production ceased in Kentucky by 1985. Sporadic milling of recycled government stockpiles continued into the 1990's. Exploration is intermittent in the district, but currently there are no operating mines.

fluorite specimen

Fluorite specimen, Western Kentucky Fluorspar District

Zinc has been produced for many years, and since 1940 the district has become a major source of zinc, some as a byproduct of mining fluorite. Substantial quantities of barite have also been produced. Lead has been a minor byproduct in recent years, as have silver, cadmium, and germanium.

Until the early 1930's, almost the entire production from the district was from vein ores. Since then, the amount of ore produced from bedding-replacement deposits near Cave in Rock, Ill., has risen so that by the middle to late 1960's this type of ore constituted more of the Illinois production than vein ore. The rise in the ratio of bedding-replacement ore to vein ore was in part due to the depletion of some of the large vein deposits near Rosiclare. In Kentucky, practically all production has been from veins, although a substantial deposit of bedding-replacement ore near Joy has been known since the 1950's; production was attempted in the 1970's, but beneficiation problems closed the mine.

Since mining began in 1873, the Western Kentucky Fluorspar District has produced about 3.5 million tons of fluorspar, 70,000 tons of zinc, 12,500 tons of lead, and 45,000 tons of barite concentrate. Some trace elements such as silver, copper, cadmium, and gallium have also been recovered. Thirty percent of the fluorspar came from the Tabb Fault System, a major curvilinear fault in southern Crittenden and western Caldwell Counties (Trace and Amos, 1984).

 

Economic Geology

The major economic minerals of the area are fluorspar, sphalerite, barite, limestone, sand, gravel, and clay deposits. The fluorspar district is situated along the intersection of two major fault systems: the northeast-trending New Madrid Fault System and the east-trending Rough Creek Fault System. The principal structural features in the district are the Tolu Arch (a dominant anticline in northern Crittenden County), and a series of elongate, northeast-trending, complexly faulted horsts and grabens crosscut by northwest-trending igneous dikes and sills. The rocks consist of interbedded limestone and sandstone of Mississippian age, sandstones of Pennsylvanian age, and mafic (iron and magnesium) dikes of Permian age. Detailed information about the geology, stratigraphy, structure, mineralization, and ore deposits of the fluorspar district are available in Trace (1954), Hutcheson (1974), Anderson and others (1982), Trace and Amos (1984), Eidel and Goldhaber (1992), Baxter and others (1992), and Plumlee and others (1995).

Classification of Mineral Deposits

There are three classes of mineral deposits in the Paducah 30 x 60 minute quadrangle, some of which are considered Mississippi Valley-type (MVT) hydrothermal mineral deposits. The first type is MVT, as described by Ohle (1980). They are very narrow, vein mineral deposits that extend vertically and horizontally for hundreds of feet and consist of fluorite, sphalerite, calcite, barite, and galena. The second type is stratabound or bedded deposits, also classified as MVT, and containing fluorite, which occurs mainly in the Joy and Carrsville, Ky., area, and possibly bedded sphalerite in other areas of the quadrangle. The third type is similar to Hicks Dome, an igneous intrusive carbonatite complex (Mariano, 1989) located in Hardin County, Ill., which is also a host for fluorite mineralization. There are other alkalic intrusives in the district, one example being an ultramafic intrusive called the Coefield Ultramafic Complex in Crittenden County. Associated mineralization is uncertain in the Coefield Ultramafic Complex, but could include fluorite or sphalerite. There could also be other mineralization, and if determined to be kimberlite, it may contain diamonds.

The vein and stratabound deposits were formed during the Permian Period by upward-migrating, fluorine-rich hydrothermal fluids that flowed along the fault planes of the northern New Madrid Fault System, extending north and east to Illinois and Indiana. Basinal hydrothermal fluids mixed with magmatic gases, and fluids generated by the Hicks Dome intrusive event were the dominant source of mineralizing fluids. Vein deposits occur along faulted areas, and most veins are lenticular and trend northeast in Mississippian carbonate rocks. Veins varying in width from 3 to 10 feet swell along strike for several hundred feet, and have been mined to a depth of 800 feet. Fluorite is the dominant mineral deposited in the district, but barite, sphalerite, and galena have been produced in smaller quantities. Some sphalerite mineralization is associated with mafic dikes at the Hutson Mine along the Big Sandy Creek Fault System, and smithsonite, a zinc oxide, occurs at the Old Jim Mine near the Crittenden Springs Fault System. Zinc has been produced for many years, and since 1940 the district has become a major source of zinc, some as a byproduct, some as a main product. Substantial quantities of barite have also been produced at the Mico, Ainsworth, and Pgymy Mines. Other major fault systems with associated fluorite are the Dyer Hill, Levias-Crittenden Springs, Commodore, Moore Hill, Claylick, and Tabb. Lead has been a minor byproduct in recent years, as have silver, cadmium, and germanium.

Bedded (manto) deposits occur along the Rock Creek Graben near Carrsville, and are generally 5 to 200 feet wide, and can be 20 feet thick. Lengths range from 200 feet to 2 miles, and ore averages 20 to 35 percent fluorite (Goldhaber and Eidel, 1992). Until the early 1930's, almost the entire production in the Illinois-Kentucky district was from vein ores. In Kentucky, practically all production has been from veins, although the bedded deposit near Joy and Carssville has been known since the 1950's and was put into production in 1970. Only minor production occurred because of milling problems, but there are still substantial reserves.

The Coefield Ultramafic Complex was discovered by Billiton Minerals in the early 1980's. It is characterized by a large magnetic anomaly and has been identified as both a lamprophyre and kimberlite ultramafic intrusive. Numerous companies have examined the area for diamond potential, but no diamonds have been found. This intrusive is located southeast of Hicks Dome in northern Crittenden County, and there is another magnetic anomaly south of Coefield near Maple Lake in southern Crittenden County. Some exploration has been conducted on the site, but there has been no recent mining. These ultramafic and carbonatite complexes are characterized by igneous alkalic explosive breccia bodies and are discussed in Plumlee and others (1995) and Heck and others (2006).

Origin of Deposits

The vein and bedded deposits were formed by a release of fluorine-rich fluids from deep-seated alkalic intrusive rocks and by the intersection of these magmatic fluids with hydrothermal basinal fluids that were rich in base metals such as sphalerite, galena, and barite. These interactions of magmatic and hydrothermal fluids generated an acidic hydrothermal fluid and the fluorite mineral deposits (Plumlee and others, 1995). At the time of the initial Hicks Dome explosive magmatic event, northward-migrating hydrothermal brines intersected with hot, fluorine-rich magmatic gases, resulting in precipitation along isothermal reaction paths in the fault systems (Plumlee and others, 1995). Paragenetic studies by Hayes and Anderson (1992) suggest that these magmatic/hydrothermal fluids were part of a regional system of mineralization that correlates with the Central Tennessee Zinc District and the Central Kentucky Mineral District.

Museum Displays

Many museum-quality specimens of fluorite and calcite have been obtained from the mines in the district and are some of the best in the world. Secondary minerals such as smithsonite, cerrusite, celestite, hemimorphite, greenokite, and pyromorphite also occur in the deposits (Anderson, 1994). The Clement Museum in Marion, Ky., contains some of the finest fluorite specimens in the world. The lobby of the Mining and Mineral Resources Building on the University of Kentucky campus contains fluorite specimens from many of the old mines, including some of the Clement collection on loan to KGS.