Illinois-Kentucky Fluorspar Research Articles

Hydrothermal Fluid Origins in Mississippi Valley-Type Ore Districts: Combined Noble Gas (He, Ar, Kr) and Halogen (Cl, Br, I) Analysis of Fluid Inclusions from the Illinois-Kentucky Fluorspar District, Viburnum Trend, and Tri-State Districts, Midcontinent United States

Samples were selected from three of the classic Mississippi Valley-type districts in the midcontinent area of North America. The Illinois-Kentucky fluorspar district belongs to the fluoritic subtype of Mississippi Valleytype districts, and the Ozark districts of the Viburnum Trend and Tri-State are representative of the Pb-rich and more typical Zn-rich subtypes of Mississippi Valley-type mineralization, respectively. Noble gas (Ar, Kr) and halogen (Cl, Br, I) data have been obtained simultaneously by noble gas mass spectrometry of inclusion fluids released by in vacuo crushing of irradiated fluorite, quartz, carbonate, and sphalerite samples. Additionally, He analyses have been obtained from nonirradiated fluorite from the Illinois-Kentucky fluorspar district. Fluorite from the Illinois-Kentucky fluorspar district has a maximum 3 He/ 4 He ratio of 0.35 Ra (where Ra = atmospheric 3 He/ 4 He ratio of 1.4 × 10 –6 ), higher than values typical of crustal fluids and confirming the presence of a minor mantle component, equal to less than 6 percent of the total He in the fluids of the Illinois-Kentucky fluorspar district. The Br/Cl mol ratios of all the deposits are, with one exception, higher than the value of seawater (1.54 × 10 –3 ), ranging from 1.69 to 3.70 × 10 –3 , and indicating acquisition of salinity by the evaporation of seawater beyond the point of halite saturation. Late quartz from the Tri-State district contains a very minor component of halite dissolution water and has a Br/Cl mol ratio of 1.46 × 10 –3 . The I/Cl mol ratios are typical of oil field brines and are ubiquitously higher than what is attainable by the evaporation of seawater alone. I/Cl mol ratios are in the range of 6 to 270 × 10 –6 , indicating that the fluids have interacted with I-rich organic matter present in sedimentary rocks. In the Ozark districts, 40 Ar/ 36 Ar ratios vary between 320 and 345 in the Tri-State and between 350 and 420 in the Viburnum Trend. In the Illinois-Kentucky fluorspar district 40 Ar/ 36 Ar ratios reach values of 1,200. The corresponding concentrations of 40 Arexcess ( 40 Ar not attributable to radiogenic decay of 40 K or an atmospheric source) are similarly elevated in the main-stage fluorite mineralization of the Illinois-Kentucky fluorspar district (6.8–18.2 × 10 –4 cm 3 cm –3 H2O) relative to the Viburnum Trend and Tri-State districts (mostly 1.3–3.3 × 10 –4 cm 3 cm –3 H2O and 0.3–1.4 × 10 –4 cm 3 cm –3 H2O, respectively). Together the noble gas and halogen data indicate the existence of three brine provinces, (1) a regional TriState brine present throughout the Ozark region, (2) a Viburnum Trend brine, and (3) an Illinois-Kentucky brine. Furthermore, in the Viburnum Trend the halogen composition of main-stage dolomite is distinct from that of the main-stage sphalerite but identical to the regional hydrothermal dolomite seen in the Tri-State district. The data imply that mixing relationships in the Viburnum Trend are highly complex but are compatible with regional models in which the Tri-State brine, present throughout the Ozark region, was sourced in the Arkoma basin.

Hydrothermal Fluid Origins in a Fluorite-Rich Mississippi Valley-Type District: Combined Noble Gas (He, Ar, Kr) and Halogen (Cl, Br, I) Analysis of Fluid Inclusions from the South Pennine Ore Field, United Kingdom

The South Pennine (Peak district) ore field, United Kingdom, is host to several fluorite-rich Mississippi Valley-type deposits and was chosen for study as an analogue to the Illinois-Kentucky fluorspar district, United States. The study was undertaken to test the idea that the large-scale carbonate dissolution and fluorite-rich mineralogy, characteristic of both districts, may require a magmatic source of HF. The data also provide constraints for water-rock interactions and potential fluid sources relevant to the local geology of the South Pennine ore field. Samples were studied from two of the largest and most economically important deposits within the South Pennine ore field, the Hucklow Edge and Dirtlow rakes. In vacuo crushing of irradiated calcite samples released inclusion fluids that were analyzed for noble gas isotopes ( Ar, Ar, Kr) and the halogens (Cl, Br, I). This was achieved simultaneously by noble gas mass spectrometry (Ar-Ar methodology) and was combined with fluid inclusion thermometric salinity data to determine noble gas concentrations. In addition He isotope analyses were obtained from unirradiated fluorite. The He/ He ratio of the Pennine ore fluids (≤0.1 Ra, where Ra = atmospheric He/ He ratio of 1.4 × 10 ) is significantly lower than the maximum value recorded in the Illinois-Kentucky fluorspar district (0.35 Ra: Kendrick et al., 2002, this volume), indicating a crustal fluid source and supporting existing basinal brine models. The low Ar/ Ar ratios with most 50 to 60 percent halite dissolution water (Br/Cl mol ratio = 0.57-0.92 × 10 ). The salinity of fluids included in the main stage of the Hucklow Edge mineralization (avg of 22 wt % NaCl equiv) places an upper limit on the extent of meteoric recharge at 15 vol percent. A secondary vein present at Hucklow Edge has a lower salinity of 40 m.y., a time scale compatible with models in which fluids were derived from small local basins such as the Widmerpool and Edale Gulfs.

Hydrothermal Fluid Origins in Mississippi Valley-Type Ore Districts: Combined Noble Gas (He, Ar, Kr) and Halogen (Cl, Br, I) Analysis of Fluid Inclusions from the Illinois-Kentucky Fluorspar District, Viburnum Trend, and Tri-State Districts, Midcontinent United States

Hydrothermal Fluid Origins in Mississippi Valley-Type Ore Districts: Combined Noble Gas (He, Ar, Kr) and Halogen (Cl, Br, I) Analysis of Fluid Inclusions from the Illinois-Kentucky Fluorspar District, Viburnum Trend, and Tri-State Districts, Midcontinent United States

Lead and sulfur isotope investigation of Paleozoic sedimentary rocks from the southern Midcontinent of the United States; implications for paleohydrology and ore genesis of the Southeast Missouri lead belts

This study utilizes Pb isotope data to identify flow paths and Pb sources for Mississippi Valley-type ores in the midcontinent of the United States with emphasis on the Old and New Lead Belt subdistricts of southeast Missouri. Nearly 150 new analyses are reported which characterize the isotope systematics of both ore samples and Pb hosted by sedimentary rocks away from ore districts. A subset of the samples has been analyzed for sulfur isotopes. The nonore samples contain trace amounts of Pb largely hosted by trace metal- rich FeS 2 (termed trace These metal-rich sulfide phases are constrained by previous petrographic studies to have precipitated from the mineralizing fluids responsible for Mississippi Valley-type ore formation. Sampling was designed to evaluate the role of potential Cambrian and Ordovician aquifers as transport paths for Pb and S in an area broadly surrounding the locus of lead belt mineralization in southeast Missouri. Analyses are also presented for various leach fractions of rocks (termed rock Pb) associated with these same potential aquifer units. Analyses of ore samples establish important benchmarks with which to compare the nonore samples. Ore samples were analyzed from southeast Missouri and include new data for both galena and nongalena phases (chalcopyrite, sphalerite, dolomite) from the New Lead belt subdistrict (Viburnum Trend subdistrict), and galena from the Old Lead Belt subdistrict and the outlying subdistricts of Annapolis and Indian Creek. Also studied were galena samples from the Central Missouri and Tri-State districts. The new data plus published values from the Northern Arkansas and Upper Mississippi Valley districts are nearly collinear on a uranogenic Pb isotope plot ( 206 Pb/ 204 Pb vs. 207 Pb/ 204 Pb). The slope of the linear regression line through this data is consistent with all the ores having been derived from the approximately 1450 Ma basement in the midcontinent area. However, the ores are very clearly separated on a plot of thorogenic isotope data ( 206 Pb/ 204 Pb vs. 208 Pb/ 204 Pb). Ores from either end of the Illinois basin, the Upper Mississippi Valley and Illinois-Kentucky fluorspar...

The potential role of magmatic gases in the genesis of Illinois-Kentucky fluorspar deposits; implications from chemical reaction path modeling

In this paper, we present results of reaction path calculations using the chemical speciation and reaction path programs SOLVEQ and CHILLER to model possible fluorite deposition mechanisms in the Illinois- Kentucky fluorspar district. Input to the reaction path calculations were the temperatures, salinities, and concentrations of major cation and anions (Na, K, CI, SO 4 , etc.) and dissolved gases (H 2 S, CO 2 , etc.) in the hydrothermal fluids, based on published fluid inclusion data and unpublished fluid inclusion gas compositions. Fluid pH values and concentrations of fluorine and various metals were then calculated assuming saturation with observed hydrothermal minerals. We assumed saturation with fluorite, dolomite, quartz, muscovite (approximating illite), anhydrite, sphalerite, galena, and pyrite. Fluorite ore deposition mechanisms which we initially modeled include (1) simple cooling (from 150 degrees - 140 degrees C, based on data and conclusions of Richardson and Pinckney, 1984), (2) reactions of the hydrothermal fluids with limestones (based upon the observed extensive replacement of limestones by fluorite), (3) combinations of cooling and limestone reaction, (4) isothermal or near-isothermal boiling of the fluids in response to pressure drops, and (5) mixing of two fluids with different Ca and F contents. Using the assumed initial fluid composition discussed above, the modeling predicts that none of these mechanisms accurately reproduces the observed fluorite-dominant mineralization stages and limestone replacement features. We then modeled how interactions of the hydrothermal fluids at 300 degrees C with HF and CO 2 (approximating a CO (sub 2 and HF-bearing gas phase expelled from a crystallizing alkalic magma) might affect fluid chemistries and results of the above deposition mechanisms. The influence of alkalic magmatism on Illinois-Kentucky fluorspar district mineralization is probable based on the geologic relations of the district. Titration of 0.5 g HF and 0.5 g CO 2 into 1 kg of a fluorspar fluid composition produces extensive fluorite precipitation and acidic (pH 2.5 or lower), F-rich, Ca-poor fluids. Cooling of these fluids to 150 degrees C leads to further fluorite precipitation. Other possible magmatic gas compositions were modeled and yielded generally comparable...

Paleomagnetism and the Late Jurassic genesis of the Illinois-Kentucky fluorspar deposits

The Illinois-Kentucky fluorspar district has yielded most of the United States fluorite production. The fluorspar ore occurs as epigenetic replacement deposits in Mississippian limestone and as vein deposits. Paleomagnetic analysis was done on 324 specimens from 33 sites in fluorspar ore and in host limestones and cap-rock sandstones both adjacent to and remote from ore using alternating field and thermal step demagnetization. Saturation isothermal remanence methods were used to identify magnetization carriers in typical specimens and mineral crystals. An A characteristic remanent magnetization (RM) component was found outside the district in stratigraphically equivalent limestones that record a Pennsylvanian Kiaman remagnetization, and a C characteristic RM was found in surface weathered specimens that records the Recent earth9s magnetic field. At 28 sites in ore and nearby host rocks a B characteristic RM was found that gives a Late Jurassic pole position of 152.4 degrees E, 78.0 degrees N (dp = 3.0 degrees , dm = 4.4 degrees ). Late Jurassic genesis for the fluorspar fits within the permissible geologic window from Early Permian to Late Cretaceous and agrees with fission track and strontium isotope dating on the fluorites but does not agree with a recent Sm/Nd date. It is suggested that a Late Jurassic hydrothermal here termed the Rosiclare event, formed the fluorspar deposits, probably remagnetized Kiaman-remagnetized host rocks, probably was controlled geographically by faults of the Reelfoot-Wabash rift system, and probably coincided with the substantial uplift in the region that formed the Pascola arch.

Additional fluid inclusion data for the Illinois-Kentucky fluorspar district; evidence for the lack of a regional thermal gradient

Fluid inclusion and paragenetic studies were undertaken on fluorite samples in bedded replacement, vein, and breccia-hosted deposits in the Illinois-Kentucky fluorspar district. Paragenetic relationships show that color bands in fluorite can be correlated from one crystal to another within a bedded replacement deposit, among bedded replacement deposits in the same subdistrict, and among subdistricts. Although the paragenetic sequence of vein deposits superficially resembles that of bedded replacement deposits, it is difficult to correlate the paragenetic sequence of minerals between these two deposit types because of the general lack of color banding in most vein deposits and because fluorite of only one color may be present in a given vein deposit.Fluid inclusion homogenization temperatures (T h ) for primary, aqueous, liquid-vapor inclusions in bedded replacement deposits range from 98.4 degrees to 150.3 degrees C, whereas those in vein deposits range from 60.2 degrees to 143.9 degrees C. T h values of primary, organic liquid-vapor inclusions in the Minerva bedded replacement deposit range from 88.5 degrees to 116.6 degrees C. Secondary inclusions in several bedded replacement and vein deposits exhibit T h values that exceed those of primary inclusions (up to 157.9 degrees C). The highest homogenization temperatures were obtained from the Rose breccia-hosted deposit at Hicks Dome (155.5 degrees -168.4 degrees C). Salinities of primary inclusions in fluorite from bedded replacement (prepurple 7 band), vein, and breccia-hosted deposits range from 17.1 to 22.7, 17.7 to 21.7, and 19.7 to 20.7 wt percent NaCl equiv, respectively. Data obtained here are in general agreement with those reported previ ously from the district.Salinity-T h relationships for the Annabel Lee, Minerva, Hill, and Denton deposits suggest that bedded replacement deposits formed from at least three fluids. A lower temperature higher salinity connate fluid (F1: <125 degrees C, 23 wt % NaCl equiv) and a higher temperature-lower salinity connate fluid (F2: approx 150 degrees C, 19 wt % NaCl equiv) mixed at the site of deposition. These fluids were followed by a lower temperature-lower salinity meteoric water-dominated fluid during the waning stages of purple 6 and 7 (P6 and P7), calcite, and barite deposition. F1 dominated during the precipitation of early fluorite, whereas F2 dominated during the late-stage (but pre-P7) fluorite mineralizing event. Fluid mixing identified during fluorite deposition in the Illinois-Kentucky district is similar to that reported previously in other mid-continent Mississippi Valley-type deposits.By combining T h measurements of fluid inclusions in this study with data obtained from other fluid inclusion studies, it is apparent that there is no evidence for a systematic regional temperature variation throughout the Illinois-Kentucky district, as has been proposed by Rowan et al. (1991) and Taylor et al. (1992). Although T h values in fluorite are highest near Hicks Dome, ranges of T h values for individual deposits can exceed 30 degrees C, with average temperatures for individual deposits that appear to show a random distribution throughout the district.

Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins

Cleat and clastic dikes of Middle Pennsylvanian-age coal beds of the Illinois and Forest City basins of Illinois, Iowa, Missouri, and Kansas locally contain appreciable amounts of sphalerite within a kaolinite-pyrite-sphalerite (+ or - pyrite)-calcite paragenetic sequence. The sphalerite and associated minerals are of interest as a partial record of the history of fluids in the sedimentary basin and as possible indicators of Mississippi Valley-type mineralization. Moreover, zinc from the sphalerite may represent an exploitable by-product of coal mining and combustion.Pyrite is abundant in these coals both as fine-grained disseminated framboids that formed during early diagenesis and as coarser grained cleat fillings, etc., that formed much later. The delta 34 S values of this later pyrite, the sphalerite, and the coal organic matter range from -12 to 19 per mil. Within individual samples, however, pyrite, sphalerite, and organic matter sulfur delta 34 S values are nearly identical. This similarity strongly suggests related origins. The delta 34 S values of pyrite, sphalerite, and organic matter from coals of the Illinois basin and the central and southern Forest City basin range from -12 to 0 per mil. This range is not unique to the sphalerite-bearing coals; pyrite and organic matter from sphalerite-free high sulfur coals have similar delta 34 S values (Price and Shieh, 1979). We believe that sulfur produced by the breakdown of organosulfur compounds in the coal is incorporated into the epigenetic sulfides. In the northern Forest City basin, however, many samples have delta 34 S values between 8 and 19 per mil. These are similar to the delta 34 S values of sphalerite and pyrite from the Upper Mississippi Valley Zn-Pb district which lies northeast of the Forest City basin and north of the Illinois basin. This similarity suggests input from a Mississippi Valley-type hydrothermal system.Cleat kaolinite has delta D values of -36 to -24 per mil and delta 18 O values of 19.2 to 20.2 per mil. Assuming that clearing postdated the lignite rank of coalification implies that kaolinite was deposited between 40 degrees and 100 degrees C. At the lower temperatures, the kaolinite fluid would have had an isotopic composition similar to seawater; at the higher temperatures, it would have had a composition similar to the sphalerite-depositing fluid. Sphalerite was deposited from a fluid that was chemically and isotopically similar to the fluids responsible for the main-stage ores of the Upper Mississippi Valley Zn-Pb district (75 degrees -113 degrees C, approximately 21 equiv wt % NaCl, delta D = -65 to -3ppm, and delta 18 O = -0.9-9.9ppm). The isotopic compositions (delta 13 C = -12.4 to -2.7ppm and delta 18 O = 21.1-25.8ppm) and paragenetic positions of the cleat calcite samples are similar to those of the late-stage calcite of the Upper Mississippi Valley Zn-Pb and Illinois-Kentucky fluorspar districts. Calcite inclusion fluids had delta D (sub H 2 O) values of -80 and -58 per mil, implying a meteoric water source. At probable temperatures of 15 degrees to 75 degrees C, this calcite formed from fluids having calculated delta 18 O (sub H 2 O) values of -9 to 1 per mil, implying slight to moderate exchange with sedimentary rocks. The diagenetic-epigenetic history of fluids recorded by the cleat minerals probably began with a slightly evolved seawater, followed by a metal-bearing deep basin brine, and concluded with a cooler, slightly evolved, meteoric-water fluid.

A hydrothermal system in the Midcontinent region

The Mississippi embayment syncline is proposed as a source of mineralizing solution for several mineral districts around the periphery of the embayment.Information developed by various forms of investigation in the Illinois-Kentucky fluorspar district has established certain requirements to form the mineral deposits of that district. The structural system of the fluorspar district is well known. Lateral migration of solutions is suggested in many of the deposits. The temperature range and chemical composition of the ore solution have been determined. Extensive solution of limestone in the area indicates that large volumes of solution were required to produce the deposits.Several features of the embayment suggest that it was the source of the ore solution for the fluorspar district. The structural system of the embayment appears to be related to the structure of the fluorspar district. The presence of evaporites and metal-rich brines in the embayment could account for the chemistry of the ore solutions. Evidence of extensive igneous activity in the embayment during Upper Cretaceous times suggests that this was the source of thermal energy for heating and propelling the solutions. The age and period of development of the embayment indicate that it may have been the source of large volumes of solution within the time period of formation of the deposits.Mineral zoning in three of the mineral districts indicates a common source of the base metal and barium minerals and a northerly direction of migration is indicated.

Sulfide and sulfur occurrences of the Illinois-Kentucky fluorspar district

The occurrence of sulfides in the fluorspar deposits has been noted previously. This paper presents details of occurrence that may define factors that could have influenced the nature and sites of deposition. The physical relationships of sulfide deposits to structure and indicated routes of solution movement are described. Host rock composition and sources of indigenous reduced sulfur are discussed. The contents of the paper are based on a large number of occurrences, many of which are no longer available for study.

A possible source of solutions of the Illinois-Kentucky fluorspar district

Abundance of fluorine and possible contemporaneity of mineralization with igneous and tectonic activity in the Mississippi Embayment suggest that mineralization in the fluorspar district may represent a transition between a magmatic type and the more subtle Mississippi Valley type.

Barite zoning in the Illinois-Kentucky fluorspar district

The evidence of zoning of barite as presented in this paper suggests that barite was deposited in the part of the mineralized area that is most remote from the source of solution. Deposits are described that indicate a zoning phenomenon is present in single ore bodies, around centers of mineralization and in the district as a whole. The zoning is vertical and lateral.

Geologic and economic significance of the Hutson zinc mine, Salem, Kentucky; its relation to the Illinois-Kentucky fluorspar district

A zinc sulphide deposit, almost unique for the district, is being worked at the Hutson mine in the Southern Illinois-Western Kentucky fluorspar district. A lode-fissure with flanking massive replacement deposits is present. The ore is remarkably high-grade with no fluorspar or galena values and is associated with mica-peridotite dikes.There is evidence that the sphalerite mineralization at the Hutson mine was later than the main calcite-fluorite-sulphide mineralization in the district. Some late sphalerite and galena are found in the major fluorite veins in the district but deposits of late sphalerite only, which are of economic importance, have been exceptionally rare.The Hutson mine offers a key to the structural and mineralogical history of the Illinois-Kentucky fluorspar district. A six-fold sequence of geologic events is indicated and is supported by evidence in other mines of the district.

Lithologic Character of Chester Rocks in Illinois-Kentucky Fluorspar District

This paper describes the lithologic character of the formations of the Chester series in the Illinois-Kentucky Fluorspar district from a study of cores obtained by diamond drilling. This study has extended over a period of more than 9 years and during the course of the work nearly 350,000 feet of core have been examined from an area about 20 by 30 miles in extent. Lithologic details not discernible in ordinary exposures are detectable in the cores. The Chester rocks vary notably in lithologic character and thickness. In parts of the district the lithologic variations are nearly uniform in a given direction but in general there is no apparent uniformity of change for any appreciable distance. The variations in thickness are not uniform either parallel with, or at right angles to, the strike and are the result of non-uniform deposition and differential erosion during the Chester epoch. The Renault formation consists of four well defined and persistent zones, a basal limestone and overlying shale, the Shetlerville member, and an upper limestone and overlying shale, the Downeys Bluff member. The Renault ranges from about 40 to 137 feet thick, the thickest sections occupying a triangular area with its apices at the Beard, Skelton, and Royal properties (Fig. 1). The thicker Renault sections are generally characterized by a prominent upper shale. The Shetlerville member in the western part of the Fluorspar district exhibits a rather uniform increase in limestone and a decrease in shale toward the south. Elsewhere there is no uniform directional variation. The Bethel sandstone contains less shale than other Chester sandstones. Its thickness is between 55 and 105 feet, the thickest sections occupying a belt from northwest to southeast across the center of the district. The Paint Creek is one of the most variable Chester formations both in lithologic character and thickness. The thickness ranges from 0 to 63 feet; the thickest sections are in the northwest and southeast parts of the district. It is almost entirely interbedded thin shale and sandstone layers in the northern and western areas. The most conspicuous lithologic change is the increase in calcareous sediments, especially limestone, toward the southeast. The Cypress sandstone, 70-125 feet thick, is similar to the Bethel except for a greater amount of shale especially in the southern and southeastern parts of the district. The shale beds do not occupy a consistent position in the section. The Cypress-Golconda contact is transitional, with a shale zone between the top sandstone of the Cypress and the lowest limestone of the Golconda in many localities. This zone is in most places non-calcareous and even sandy and might well be called Cypress rather than Golconda as has been done in this paper. The Golconda, 100-200 feet thick, consists of interbedded limestones and shales without lithologic zones which are persistent throughout the district. The Barlow sand which occurs in places in the northern and eastern parts of the district is cons stently near the middle of the formation. The Hardinsburg is a quartz sandstone with variable amounts of shale and ranges in thickness from 68 to about 140 feet. The shales occur in different parts of the sections in different localities but in general are in the middle and upper parts. It is thickest in the southeastern part of the district. The Glen Dean consists of interbedded shales and limestones much like the Golconda but generally with purer limestones than other Chester formations. It is 45-75 feet thick; the greatest thickness is in the south-central part of the district. Considerably less information about the upper Chester has been obtained by drilling. The Tar Springs consists of interbedded sandstone and shale 65-145 feet thick. The Vienna limestone and shale vary from 30 to 106 feet in thickness. The Waltersburg, 40-87 feet, consists of sandstone and shale; the shale is most conspicuous in the middle part of the formation. The Menard, 75-120 feet thick where drilled, consists of interbedded limestones and shales, which do not occur as persistent zones. Complete sections of the higher Chester formations have not been drilled. It is concluded that many of the clastic Chester sediments are of continental origin and that the marine parts of the section were deposited in relatively shallow water. End_Page 1777------------------------------