Mineral Resources of the 

Illinois-Kentucky Mining District 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 970 

Mineral Resources of the 

Illinois-Kentucky Mining District 

By DARRELL M. PINCKNEY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 970 

Excellent possibilities exist for finding 

deposits of fluorspar, lead, zinc, silver, 

cadmium, rare earths, and niobium in 

Illinois and Kentucky 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1976 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Pinckney, Darrell M. 

Mineral resources of the Illinois-Kentucky mining district. 

(Geological Survey Professional Paper 970) 

Bibliography: p. 

1. Mines and mineral resources-Illinois. 2. Mines--and mineral resources- Kentucky. 

I. Title. II. Series: United States Geological Survey Professional Paper 970. 

TN24.13P56 553'.09769 76-8006 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-02853-1 
CONTENTS 

Page 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Composition of the ore. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Geologic setting........................................... 4 

Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Stratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Significance of the stratigraphic section in controlling ore 

deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Changes in carbonate lithology . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Effect of shales on ore fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Igneous rocks and diatremes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Page 

Mineral deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Minerals of the ore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Structural types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Veins ................................................ 11 

Bedded deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Solution-slump breccias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Diatremes ............................................ 13 

Deposits containing chiefly lead or zinc . . . . . . . . . . . . . . . . . . . . . 13 

Area of mineral potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

References ............................................... 14 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map showing location of the Illinois-Kentucky fluorspar region and nearby structural features . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

2. Geologic map of the Illinois-Kentucky fluorspar region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3. Map showing sources of data used for figure 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

4. Stratigraphic column ofthe Mississippian formations in the Illinois-Kentucky fluorspar district. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

5. Diagram of mineralized breccia of solution-slump origin in Hill mine, Cave in Rock district, Illinois ............................ 12 

TABLES 

Page 

TABLE 1. Content of lead, zinc, and silver in four lots of selected ore from the Illinois-Kentucky mining district. . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

2. Spe~o:trographic analyses for selected elements in sphalerite, chalcopyrite, and galena from the Hill mine, Cave in Rock district, 

Illinois ............................................................................ ······························· 3 

III 

MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY 

MINING DISTRICT 

By DARRELL M. PINCKNEY 

ABSTRACT 

The mineral deposits of the Illinois-Kentucky fluorspar district are the 

major source of domestic fluorspar; they also contain significant amounts 

of lead, zinc, barite, cadmium, and germanium, and some silver. Barite, 

strontium, and a small amount of copper are present, but mostly these are 

not recovered. The ores contain approximately 9.9 tons (9 t) or more of 

lead and 55 tons (50 t) or more of zinc per 1, 102 tons (1 ,000 t) of fluorite. 

The cadmium, germanium, and silver are contained chiefly in the sulfide 

minerals sphalerite and galena. 

The major structural features of the region are a broad arch which 

trends northwestward, ending at Hicks dome, and a system of horsts and 

grabens that cross the arch and trend northeastward to eastward. 

Mineral deposits belonging to four structural types are known: (1) 

veins, which are along normal faults related to the horsts and grabens; (2) 

bedded deposits, which are found in horsts; (3) solution-slump breccias, 

which extend downward below some bedded deposits; and (4) diatremes, 

which are related to the Hicks dome structure. The structural ore control 

of the first three types is the intersection of faults and other fissures with 

certain beds of Mississippian limestone. The mining area, about 540 

square miles (1 ,400 km2), is nearly coextensive with the area of outcrop of 

these beds of limestone. The area of mineral potential is approximately 

doubled in size by projecting the favorable beas outwara rrom the mining 

area and downdip off the flanks and the end of the arch. 

Many square miles of area having mineral potential within the 

structural framework defined here are unexplored. In addition, the 

mineral potential of the diatremes has been largely unrecognized. These 

facts, coupled with a substantial production from the area, indicate a 

large mineral potential in the region. 

INTRODUCTION 

The large mineralized area in southern Illinois and 

western Kentucky is loosely referred to as the 

Illinois-Kentucky fluorspar district because fluorspar has 

been the most important product of the region. The 

location of the area is shown in figure 1; the outline of the 

known mineralized area and the major geologic features of 

the region are shown in figure 2. The known mineralized 

area covers about 540 square miles (1 ,400 km 2) and 

contains many districts. The geology of the area has been 

studied for many years; general references include reports 

by Ulrich and Smith (1905), Bastin (1931), and Weller, 

Grogan, and Tippie (1952). Much of the geologic background for this report is included in reports by Trace 

(1974) and Hook (1974). The emphasis here, however, is 

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0 100 200 MILES 

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APPROXIMATE SCALE 

FIGURE I.-Location of the Illinois-Kentucky fluorspar region and 

nearby structural features (dashed lines). 

on pointing out the enormous potential remaining in both 

the known mineralized area and the surrounding 

region-in structurally controlled deposits that are 

localized by favorable stratigraphic horizons or by 

diatremes. 
2 MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY MINING DISTRICT 

The known mineral deposits occur as four major 

structural types: veins, bedded deposits, breccias of 

solution-slump origin, and diatremes. Deposits of all types 

contain fluorite, sphalerite, galena, chalcopyrite, and 

barite, and at least one diatreme also contains uranium-, 

thorium-, niobium-, and rare-earth-element-bearing 

minerals. Mining activity has concentrated on the vein and 

bedded types, and the solution-slump breccias and 

diatremes are not well known. 

Nearly all the deposits of the region contain large 

amounts of fluorspar and differ significantly from other 

major deposits in the Mississippi valley, which are mined 

mainly for lead and zinc minerals. The lead and zinc now 

produced here are byproducts of fluorspar mining. Lead, 

however, was the first commodity mined (Ulrich and 

Smith, 1905, p. 16- 21; Weller and others, 1952, p. 11), 

starting about 1835. In early mining, fluorite was 

considered to be a gangue mineral, but in the late 1800's 

fluorite became valuable for its use as flux in the 

open-hearth furnaces of the steel plants in the upper part 

of the Ohio River valley. Sulfide minerals were detrimental 

to this use of the fluorspar ore, and ore free of sulfides was 

desired. Milling by selective flotation and by the sink-float 

process came into general use in the area in the late 1930's 

and early 1940's; lead and zinc have been recovered since 

then, and multicomponent ores are now mined. 

The use of fluorspar has steadily increased for many 

years, and, because the Illinois-Kentucky mineralized area 

is the largest source of domestic fluorspar, production can 

be expected to increase correspondingly. Hence, the production of other commodities associated with fluoritechiefly lead, zinc, cadmium, and possibly barite-will also 

increase. Many deposits contain fairly large amounts of 

barite, some of which is now being recovered in 

conjunction with other products; until recently, problems 

of separating the barite from the other components of the 

ore discouraged significant production of barite. 

The area has great potential for the discovery of 

additional deposits of fluorspar, lead, zinc, and barite, as 

well as other commodities (as discussed below); thus far, 

however, exploration has been inadequate to define this 

potential in terms of tons of the various commodities. 

PRODUCTION 

Since 1880 the area has yielded more than 9,500,000 tons 

(8,600,000 t) of fluorspar, 80 percent of the total U.S. 

production (Grogan and Bradbury, 1968, p. 373). Since 

1939 it also has yielded more than 135,000 tons (122,000 t) 

of zinc and more than 60,000 tons (54,000 t) of lead. These 

amounts of lead and zinc constitute only a small part of the 

U.S. production of these metals, but they increase the 

value of the ore significantly. Additionally, small amounts 

of silver and cadmium are recovered in refining the lead 

and zinc. The ores of the area furnish a significant amount 

of the cadmium produced in the United States. 

Average values or grades of the fluorspar ores produced 

cannot be obtained from gross production figures, because 

the production figures are the sums of the tonnage of 

different products that have different contents of fluorite. 

In some years most of the fluorspar shipped was of 

metallurgical grade (60-72.5 percent CaF2), and in other 

years most of the fluorspar shipped was of acid grade (97 

percent CaF2). The value of the ores can be better estimated by analyzing some of the production data in relation to 

the grade of the fluorspar product. 

COMPOSITION OF THE ORE 

The ores differ in composition, but the quantitative 

differences are unknown because ore bodies are not 

systematically sampled. However, the variations are less 

important to mining operations extracting large amounts 

of ore than the average composition of the ore. An 

estimate of the average composition of the ore of the area 

has been obtained from statistics gathered by the U.S. 

Bureau of Mines and is presented in table 1. 

The Bureau of Mines data were critically examined for 

this report, and by using those that show the grade of 

fluorspar, the absolute amounts of calcium flouride is 

calculated. The three major grades of fluorspar product 

are metallurgical (60 -72.5 percent CaF 2), ceramic 

(85- 96 percent CaF ), and acid (97 percent CaF.>). 

Bradbury, Finger, and Major (1968) gave a good summary 

of industrial grades and uses of fluorspar. The values 

for each grade used to compute the total amounts of 

calcium fluoride are shown in table 1. Only a few deposits 

have been mined chiefly for a product other than 

fluorspar. The veins at Rosiclare were first worked mainly 

for lead, several other deposits were mined chiefly for zinc, 

and one deposit produced mainly lead. Production data 

for such operations that produced a single product are not 

included in table 1. 

Table 1 shows the amounts of calcium fluoride, lead, 

zinc, and silver in large samples of ore from Illinois and 

Kentucky. In general, calcium fluoride is concentrated 

about 2- 2 Yi times by milling in order to make the 

fluorspar products; thus, little concentration is required to 

turn large blocks of ore into salable products. In mining, 

CaF 2 content of about 20 percent is usually the cutoff 

grade for ore, but lower grade material is extracted and 
COMPOSITION OF ORE 3 

TABLE I.-Content of lead, zinc, and silver in four lots of selected ore from the Illinois-Kentucky 

mining district 

[All units are metric; tonnes X 1.1023 =short tons; grams per tonne X 0.0202 =troy ounces per short ton. Leaders ( ... ) indicate insufficient 

data or not applicable) 

Metals in crude ore 

Lot Years State Crude ore Pbl znl Ag2 Pb Zn Ag 

produced (tonnes) (tonnes) (tonnes) (grams) (percent) (percent) (gltonne) 

I I953 -56 Ill. I,090,815 7,127 25,098 2,097,992 0.65 2.3 1.9 2 1957-59 Ill. 596,614 2,158 12,222 .36 2.0 

Average metal content ...................................... 0.5I 2.2 

3 I953-55 Ky. 57,557 47 452 0.081 0.78 

4 I956-59 Ky. 57,67I 675 1,520 33,872 1.2 2.7 0.59 

Average metal content ..................................... 0.64 1.7 

Additional data on lots 2 and 4 

Fluorspar (tonnes)3 CaF2 (tonnes)3 Ratio of metal to CaF2 

Lo~----------

M A c M A c Total Pb Zn Ag 

2 31,507 I80,534 39,959 

4 9,900 16,7I2 4,89I 

18,903 175,118 37,163 231,I84 

5,940 I6,210 4,548 26,698 

0.0093 0.053 

.025 .057 

I The amounts of Pb and Zn shown are the amounts reported 

as recovered. The recovered metal is about 95 percent of the total in 

the concentrates. 

2 The amounts of Ag shown are the totals reported from wet 

assay data of concentrates. The amounts reported as actually 

recovered are approximately 12 percent of these totals. 

blended with high-grade ore as long as the desired millfeed 

is maintained. 

The crude ore listed in table 1 contains about 0.5 percent 

lead and about 2 percent zinc. Thus, the deposits of the 

area tend to be near the marginal limit for lead-zinc 

deposits and probably could not be mined economically on 

a sustained basis for lead and zinc alone. The crude ore 

from Illinois contained slightly more zinc and slightly less 

lead than that from Kentucky. However, the production 

data used for table 1 may reflect how the ore was mined 

and was concentrated, and minor differences in the nature 

of the crude ore may not be significant. The ratios of lead 

and zinc to calcium fluoride (table 1) probably show the 

character of the ore more accurately; the Zn:CaF 2 ratio for 

Kentucky ore is nearly three times as high as that for 

Illinois. The differences in the Pb:CaF 2 ratios might reflect 

different types of deposits; most of the ore from Illinois 

was from bedded deposits, and most of the ore from 

Kentucky was from veins. 

Some silver has been recovered from sulfide 

concentrates from both Illinois and Kentucky. Silver may 

occur throughout the area, but for some years no recovery 

3 Grades used for calculating tonnes of CaF2 are: 

M, metallurgical, 60 percent CaF2; 

A, acid, 97 percent CaF2; 

C, ceramic, 93 percent CaF2. 

was reported. Table 2 shows that silver occurs in 

sphalerite, galena, and chalcopyrite in amounts 

comparable to those reported in the production data. 

Therefore, the silver of the district is fully extracted by the 

mining and milling techniques already in use and 

additional recovery of silver will depend upon smelting 

processes. 

The area is a source of cadmium, which is recovered 

from the zinc concentrates during smelting. The cadmium 

is chiefly in the sphalerite, which also contains most of the 

TABLE 2.-Spectrographic analyses (in percent) for selected elements in 

sphalerite (SI), chalcopyrite (Cp), and galena (Gl) from the Hill mine, 

Cave in Rock district, Illinois 

[M, major constituent. Analyst, Harriet G. Neiman, U.S. Geol. Survey) 

Sample 

No. Mineral Fe Ag Cd Cr Cu Ge 

902 .... Sl 0.7 0.0 0.5 0.0003 0.07 0.03 

903 .... Sl 1.5 .002 1.5 .0001 .07 .02 

904 .... Cp M .991 .01 .003 M .01 

905 .... Gl .03 .0007 .0 .0 .02 .0 

906 .... Gl .015 .0005 .0 .001 .005 .0 

907 .... Gl .015 .01 .0 .0002 .003 .0 
4 MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY MINING DISTRICT 

germanium in the district; only a small amount of 

cadmium is in chalcopyrite (table 2), and no other 

cadmium-bearing minerals are known in the primary ore. 

Thus, only normal mining operations are needed to extract 

all the recoverable cadmium from the ground. 

GEOLOGIC SETTING 

The mineralized area was formerly part of the 

Illinois-Indiana-Kentucky depositional basin. This basin is 

on the North American craton west of the Appalachian 

trough and was the site of deposition of more than 13,000 

feet (4,000 m) of sediments during Paleozoic times (Bayley 

and Muehlberger, 1968). During the later part of 

Mississippian time, the types of sedimentation in the area 

changed from deeper marine of the continental shelf to 

near-shore marine. The change continued into Pennsylvanian time, and the basin received coastal-type sediments 

that contain large amounts of coal. By Late Pennsylvanian 

time the basin seems to have been completely filled. During 

Mississippian time, the northern and central parts of the 

basin were partly separated into eastern and western basins 

by the rise of the La Salle anticline belt. Later, Hicks dome 

(fig. 2) and the area to the southeast rose, thereby almost 

completing the separation between the Illinois basin on the 

west and Western Kentucky basin on the east. 

The major part of the uplift in the south occurred after 

the deposition of the Pennsylvanian coal beds. However, 

the uplift may have started as early as Early 

Pennsylvanian; Desborough (1961) found beds of the 

Lower Pennsylvanian Caseyville Formation that were 

faulted and then were covered by slightly younger beds of 

the same formation. The map pattern of the MississippianPennsylvanian contact around the mineralized area (fig. 

2) shows that the regional structure is a broad, low arch on 

the south edge of the Illinois and Western Kentucky basins. 

Northward from the Nashville dome and eastward from 

the Ozark dome (fig. 1), the strata dip gently toward the 

Illinois and Western Kentucky basins, and the arch is 

scarcely more than a slight reversal in the dip of these 

strata. 

The north-northwest trend of the arch is apparent in 

figure 2 by the distribution of the Lower Mississippian 

formations. Hicks dome is at the northwest end of the 

arch; the southeastward extent of the arch is not known, 

for it is covered by sediments of the Mississippi 

embayment. The arch is bounded on the north and east by 

synclines. North of Hicks dome the beds dip steeply into 

the Eagle Valley syncline, rise up into an anticline a little 

farther north, and finally dip downward into the Illinois 

basin. Eastward, in Kentucky, along the northeast side of 

the area, the beds dip gently northeastward into the eastern 

extension of the Eagle Valley syncline and the Western 

Kentucky basin. Regional dips are less apparent on the 

southwest side of the arch. In the area north of the edge of 

the Cretaceous and Tertiary formations and west of the 

Ohio River, the regional dip is northward into the Illinois 

basin. South of Carrsville, Ky., between the Ohio River 

and the central part of the arch, the regional dip is obscure 

because of faults. 

The rocks of the arch are broken into many horsts and 

grabens, which are separated by normal faults. The horsts 

are broad, broken by faults, and poorly defined; they are 

separated from the grabens by complicated fault zones that 

include many branches and step faults. (See, for example, 

Moodie and McGrain, 1974, figs. 7, 8, 9.) The grabens are 

narrower and less faulted, and they are seen easily on the 

geologic maps of the region. 

Eleven grabens have been well defined by geologic 

mapping, and they are shown in figure 2; Hook (1974) also 

presents a map showing the grabens that is similar to figure 

2, but of a smaller area. The two maps are independent 

compilations; the names used here to designate the grabens 

either are well established by local usage or are chosen 

from the names of town within the structure. The grabens 

tend to die out to the east or northeast in the 

Pennsylvanian sedimentary rocks, and they are poorly 

known to the southwest where they are partly covered by 

the Cretaceous and Tertiary sediments. Two grabens, the 

Sheridan and the Marion, converge into a complex fault 

zone near the great bend of the Cumberland River. The 

convergence appears to be along the projection of the Tabb 

fault zone. The Dawson Springs graben is well defined in 

its eastern part but is more complex to the west. Near the 

southwest end the structure contains several raised blocks 

between the bounding faults. East of the Tabb fault zone 

the Dawson Springs graben contains Pennsylvanian rocks 

and is bounded on both sides by Mississippian rocks. In 

contrast, to the southwest of the Tabb fault zone, the 

graben contains Mississippian rocks, some of which are 

older and some of which are younger than the 

Mississippian rocks of the adjacent horsts. The oldest 

rocks are toward the southwest. Perhaps the structure has 

been raised toward the southwest and tilted toward the 

northeast. However, according to R. D. Trace (U.S. 

Geological Survey, oral commun., 1974) identification of 

the formations at the surface in the southwestern part of 

the Dawson Springs graben is difficult. 

FAULTS 

The fault structure of the region is dominated by normal 

faults that define the regional framework of horsts and 

grabens. Faults related to other structures include radial 

and concentric faults around Hicks dome, northwardtrending faults in blocks, between the grabens, the 

Shawneetown fault zone, and the Tabb fault zone. 
GEOLOGICAL SETTING 5 

Normal faults having a northeasterly to easterly trend 

are predominant. Most of the northeast-trending faults are 

part of fault zones that bound grabens and horsts. These 

fault zones extend southwestward under the sediments of 

the Mississippi embayment and may be part of the New 

Madrid fault zone. To the northeast they are less well 

known in the Pennsylvanian sedimentary rocks of the 

Illinois basin; much of the area north and northeast of 

Hicks dome is covered with either alluvium or glacial till. 

Some of the northeast-trending faults probably extend into 

the Wabash Valley fault zone. Along their northeasterly 

courses, many of the faults tend to swing to the east. This 

change in strike is very strong in the eastern part of the 

region. A few faults trend northward; these are mostly 

near Rosiclare and are in the horsts between the grabens. 

Their relation to other structures is not clear. Vertical 

movement on the faults that bound the grabens is only 

about 650 feet (200 m) or less in most places, and the 

maximum displacement known is less than 3,000 feet (900 

m) (Trace, 1974, p. 67- 69). 

The radial faults are known only at the northwest end of 

Hicks dome. They lie along both sides of the axis of the 

dome and project inward to a small area that is very close 

to the center of the dome. A few of the radial faults bound 

small grabens. The radial faults resulted from stretching of 

the rocks around the end of the rising dome. Concentric 

faults surround the northwest end of the dome for almost 

180° of arc. They are normal faults downthrown on the 

inside toward the center of the dome. Movement along 

them resulted from collapse of the dome. 

The Shawneetown fault zone passes through the Western 

Kentucky basin, where it is called the Rough Creek fault 

zone, and through the Eagle Valley syncline, where it 

occupies the axial part of the syncline. Both structures 

bend around the northwest side of Hicks dome. The 

syncline dies out in a complex zone of faults that extends 

several miles to the southwest as the northwest side of the 

Dixon Springs graben. Heyl and Brock (1961) and Grogan 

and Bradbury (1968, p. 376) referred to the Shawneetown 

fault zone as a high-angle thrust fault, but they gave no 

evidence. From the original work of Butts (1925, pl. 1) and 

Baxter, Desborough, and Shaw (1967, pl. 1), one can 

conclude only that the fault zone dips at a high angle, and 

on cross sections Butts (1925) showed it as being vertical. 

Southward dip and thrusting seem to be conjectural. The 

only evidence for reverse movement apparently is a group 

of relatively upthrown blocks on the north and west sides 

of Hicks dome. However, these blocks are within the fault 

zone, and during the collapse of Hicks dome they probably 

failed to move downward as much as the adjacent blocks. 

No outliers have been found. This author concludes that 

thrusting probably did not occur to any significant extent 

and that movement on the Shawneetown fault zone is 

normal rather than reverse. 

The Tabb fault zone is an arcuate complex zone of faults 

extending more than 35 miles (56 km). The extent of the 

zone to the southeast is not fully known. The fault zone 

intersects three grabens; downthrow is on the north, and 

the western part of the fault zone clearly separates younger 

Mississippian rocks on the north side of the fault from 

older rocks on the south side of the fault. The vertical 

displacement may diminish to the south. 

STRATIGRAPHY 

The Illinois-Kentucky fluorspar region is underlain by a 

thick section of Paleozoic strata. The oldest formation 

exposed, the Hunton Limestone of Silurian and Devonian 

age, crops out in the central part of Hicks dome. Nearly all 

the central part of the region is underlain by Mississippian 

formations at the surface, and these formations are 

bordered to the east and north by Pennsylvanian 

formations. The extreme southern part of the region is 

partly covered by a veneer of unconsolidated sediments of 

Cretaceous and Tertiary age. These sediments are the north 

edge of the great prism of sediments in the Mississippi 

embayment, and they overlie an unconformity that cuts 

across the Mississippian rocks. 

The exposed rocks in the area of figure 2 are more than 

5,800 feet (1,700 m) thick, yet almost all the ore has come 

from a relatively thin section of Mississippian rocks that 

comprises the upper part of the Meramecian and lower 

part of the Chesterian Series. A generalized section of 

Mississippian formations is shown in figure 4. 

During the Mississippian Period, a major change 

occurred in the conditions of sedimentation, from deep 

marine to nearshore marine. The Lower Mississippian 

rocks, below the productive section, are chiefly very fine 

grained limestones which contain, in some places, chert. 

They represent a deepwater marine environment. The 

productive section consists chiefly of nearly pure limestone 

composed of well-sorted clastic oolites and fossil 

fragments. This part of the section also contains some 

well-sorted and fine-grained sandstone and a minor 

amount of shale. A large proportion of the upper part of 

the Mississippian section above the productive beds is 

sandstone and shale interspersed with limestone. The 

productive section also changes gradually upward in 

lithology and composition. The lowest part is chiefly 

dark-gray, fine-grained, and impure limestone of the lower 

part of the St. Louis Limestone (fig. 4). This grades 

upward into limestone that is cherty in part, medium to 

light gray, and generally fine grained, but that contains 

oolitic beds. 

The St. Louis Limestone is overlain by the Ste. 

Genevieve Limestone, which is divided into the Fredonia 

Limestone, Rosiclare Sandstone, and Levias Limestone 

Members. The Fredonia Limestone Member is much 
6 MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY MINING DISTRICT 

LIST OF MINES 

1. Hill 

2. North Green 

3. Patrick 

4. Hickory Cave 

5. Old Jim 

6. Hutson 

37°00'L_ ______________________________ __ 

FtoURE 2.-Geologic map of the Illinois-Kentucky 
GEOLOGICAL SETTING 

EXPLANATION 

1:··:::.< . : · .. : ..::_:~ Quaternary alluvium 

- Tertiary and Cretaceous 

formations 

f::}~~::~~:~~::~:::~<:~~j Pennsylvanian formations 

D Mississippian formations younger 

than the base of the Bethel 

Sandstone 

D Mississippian formations older 

than the base of the Bethel 

Sandstone 

0 5 

0 5 10 

!.\\ :u\1 Devonian formations 

-----Contact 

--.,..---Fault- Dotted where concealed; 

bar and ball on downthrown side 

--f---- Syncline - Dotted where concealed 

,----... \ I Area in which mineral deposits 

...., __ ,; have been mined 

10 20 Ml LES 

fluorspar region. Sources of data are shown in figure 3. 

7 
8 MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY MINING DISTRICT 

88° 45' 30' 15' 37°,-----------T----------_:_: ____ , 

45' 

B 47 

30' r------,------1 c 413 c 385 c 342 

Rl 60 

Rl 60 Rl 60 MF-2 GQ-206 

15' 

MF- 2 Ri11er 

'""' -..lvo,s c 360 

KJ':Ivl'u~' /(y ' 

~>$>: "o ..... _ 

37° 

00' 

0 Marion 

GQ-547 

MF-2 

EXPLANATION 

Publication series of Illinois Geological Survey 

B, Bulletin 

C, Circular 

R I, Report of Investigations 

Publication series of the U.S. Geological Survey 

GO, Geologic Quadrangle Maps 

MF, Minerallnvestigations,Field Studies Map 

45' 

G0-491 G0- 777 

GQ-880 G0-490 GQ-629 

GQ-607 G0-742 GQ-573 

Princeton 

GQ- 385 G0-1032 G0-1061 

GQ-360 

GQ-346 

G0-674 

0 10 20MILES 

0 10 20 KILOMETRES 

FIGURE 3.-Sources of data published by Illinois Geological Survey and U.S. Geological Survey used in compilation of figure 2. 

lighter in color than the St. Louis Limestone. Limestone in 

the Fredonia tends to be oolitic, contains numerous fossil 

fragments, and is nearly pure calcium carbonate that 

contains little chert. The Fredonia contains scattered thin 

and discontinuous beds of marine shale. In some places, 

especially in the Cave in Rock district, Illinois, it also 

contains a thin and fine-grained sandstone, an economic 

unit known as the Sub-Rosiclare ore zone. This sandstone 

is commonly very calcareous, crossbedded, and 

discontinuous. It changes facies from calcareous sandstone 

to sandy and oolitic limestone within a short distance, but 

it can be identified by a distinctive sequence of beds 

(Pinckney and Rye, 1972). Its stratigraphic position has 

been stated (Brecke, 1962) as ranging from 40 to 60 feet 

(12 -18 m) below the base of the Rosiclare Sandstone 

Member. The Fredonia Limestone Member beneath the 

Sub-Rosiclare ore zone is characterized by large oolites, 

fossil fragments, and current bedding, suggestive of a bank 

of reworked lime in shallow water. The features of the 

overlying Sub-Rosiclare ore zone are suggestive of a 

shifting channel that extended across the bank. The source 

of the sand was probably to the northeast in the 

Precambrian terrane of the North American craton 

(Pinckney and Rye, 1972). 

The Fredonia Limestone Member above the distinctive 

sequence of the Sub-Rosiclare ore zone is similar to that 
SYSTEM SERIES 

Pennsyl - Lower 

vanian Pennsylvanian 

c: 

·;: "' 

Q) 

ti 

Q) 

.c 

u 

c: 

·c::; "'

Q) 

E 

~ Q) 

~ 

c: 

Q) "' 

en 

lJl 

0 

Miss. and Lower Miss. and 

Devonian Upper Devonian 

GEOLOGICAL SETTING 9 

APPROXIMATE 

STRATIGRAPHIC UNIT LITHOLOGY THICKNESS, DESCRIPTION 

IN FEET (METRES) 

Caseyville Formation 

Kinkaid Limestone 

Degonia Sandstone 

~ {;:r. 40(12) Limestone and shale· as much as 130ft (40 m) thick where not eroded. -;. ·..:... : \,j..."F......,!:;. ::::..;=!-----=:::3~0~(9;;)!......_ __ +-....;S~a.:.:.n.:.::d:.::st~o~n.:.::e:..c, ::.:si~lt~s~to.!.!n~e~a:!!:n~d,!.!s~h""a,.le~;""d""a""rk""-'-!..!.glre e...:.n""is...:.h.:..:.-g'-lr.!.!a-'=yb"'ed~s"". "'-"-~'-"--'~=""--1 

Clore 

Limestone 

Palestine Sandstone 

Menard 

Limestone 

- 1--1- 112(34) Shaly limestone, limy shale, and minor sandstone. 

56(17) Sandstone, thin-bedded and shaly. 

135(41) Limestone, argillaceous to shaly; some beds of shale. 

Waltersburg Sandstone :-:-:::.;....-:;:.::.--: .:....: 36( 11) Shaly sandstone; interbedded shale; bottom part is shale and arenaceous 

t=v~ie~n~n~a~LJi~m~e~s~to~n~e=~~S~~~t===]1[ID 6115[51==={~ or shaly limestone. 

Tar Springs Sandstone :~: .. ??:_:·:· ... ·r: .. ·:. 1611491 '\Limestone, impure, siliceous, dark-gray; locally shaly. 

_ _ _ Shale and shaly sandstone at top; fine-grained crbssbedded to even-bedded 

Glen Dean Limestone 

Hardinsburg 

Sandstone 

Golconda 

Formation 

Cypress Sandstone 

Paint Creek Formation 

Bethel Sandstone 

Renault Formation 

----

_-_-_-

75(23) 

98(30) 

125(38) 

200(61) 

79(24) 

Q) Levi as Ls Mbr -+- 20(6) ·~ ~ 1---=-=-:R::=o=-:si.:::.c;=la....:re..:..:..:.:_;__...../}..,.:::::..:· i'r_.··c..::~:_:_··j+' ·....;· .,._,.-1i·, ·.;;····;;,· f..--~ 30 (9) 

~ ~ 1---S_s_M_b_r _ _.~/ 1

1 : 11 ° ... ~ <.9 E ai :J Fredonia Limestone 

Member 

Upper 

member of 

St. Louis 

Limestone 

Lower 

member of 

St.Louis 

Limestone 

and Salem 

Limestone 

Warsaw 

Limestone 

Fort 

Payne 

Formation 

Chattanooga 

Shale 

I= l.o I= 

= = = = = 

0 0 0 

= = = 

= = = 

= = = = = 

c> 

= = = 

= = = = 

226(69) 

230(70) 

374(114) 

200(61) 

558(170) 

"- sandstone in middle; shale at bottom. Thin coal locally. 

Limestone, shaly at top and bottom . 

Shaly sandstone and shale in upper part; fine-grained crossbedded sandstone in lower part. 

Upper part: fossiliferous and oolitic limestone; shale in places. 

Middle part: chiefly shale; some limestone. 

Lower part: silty to sandy limestone. 

Sandstone, fine-grained; shaly in upper and lower parts. 

Sandstone, limestone, and shale. 

Fine- to medium-grained thick-bedded quartz sandstone; contains some 

pebbles and fragments of fossils; carbonaceous material at base. 

Limestone, light-gray, oolitic; shaly in middle part; conglomeratic at base. 

!'..... Limestone, oolitic and clastic. 

""'Sandstone, fine-grained quartz; thin shale at base. 

Limestone, chiefly oolitic and clastic, white to light-gray; contains lenses of sanqstone and sandy limestone. One prominent lens of sandstone (SR) about 40.ft (12m) below the 

i

\ top of the Fredonia is called the Sub-Rosiclare ore zone, an 

economic term. 

\..______ ____ _ 

Limestone, gray, medium- to fine-grained; some beds of oolites 

and fossil fragments; chert common, especially in upper part. 

Limestone, gray to dark-gray, dense to fine-grained; locally impure and petroliferous; locally contains some oolites and 

fossil fragments; corals common in some beds; chert nodules common to abundant in many beds; dolomitic in part. 

Limestone, light- to medium-gray, very fine grained to mediumgrained; some calcarenite; some shale beds; chert in some 

beds. 

Limestone and chert in interlayered beds. Limestone is dark 

gray, dense, siliceous, and argillaceous. Chert makes up 

1 0-35 percent of the rock. 

F 1GURE 4.-The Mississippian formations in the Illlinois-Kentucky fluorspar district. The chief ore-bearing beds are shown by solid bar. 
10 MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY MINING DISTRICT 

beneath it, consisting dominantly of oolites and fossil 

fragments, except that it contains beds of sandy limestone. 

The Rosiclare Sandstone Member is in the upper part of 

the Ste. Genevieve Limestone. Fine grained, calcareous, 

and locally shaly, the Rosiclare ranges in thickness from 

about 20 to 40 feet (6- 12 m). It represents the first major 

influx of clastic material, which was spread in a thin 

blanket across the entire region. In places the Rosiclare 

contains lenses of limestone or shale, and a thin shale is 

commonly found at its base. 

The Levias Limestone Member is the uppermost part of 

the Ste. Genevieve Limestone and the Meramecian Series. 

It is medium to light gray, fairly thick bedded, and oolitic, 

and it contains some thin shale partings and many 

fragments of fossils. The Levias ranges in thickness from 

about 10 to 35 feet (3 -11 m), and in places it contains a 

basal conglomerate. 

The Renault Formation is the basal formation of the 

Chesterian Series and overlies the Ste. Genevieve 

Limestone. It consists dominantly of limestone andd shale 

and ranges in thickness from about 70 to 125 feet (21 -38 

m). Some of the limestone is oolitic and crossbedded. The 

limestone is not as pure as that of the Ste. Genevieve, and 

some is carbonaceous and locally contains pyrite. In 

general, the lower part of the formation is limestone or 

shaly limestone, the middle part is shale, and the upper 

part is fairly pure limestone. In many places the Renault 

Formation rests unconformably on the Levias Limestone 

Member. 

The Bethel Sandstone, though dominantly sandstone, 

varies in lithology across the region. To the south and 

southeast, the formation thins and contains siltstone and 

shale. To the north, especially in Illinois, it is thicker and 

consists largely of fine to medium sand but also contains 

coarse and angular grains, and even pebbles. In many 

places the Bethel is unconformable upon the Renault, and 

to the southeast the Bethel has been found, probably as a 

channel deposit, resting on Ste. Genevieve Limestone 

(Trace and Kehn, 1968). The Bethel probably represents a 

Mississippian delta; bottomset and foreset beds are present 

in some of the mines of the Cave in Rock district. 

SIGNIFICANCE OF THE STRATIGRAPHIC SECTION 

IN CONTROLLING ORE DEPOSITION 

CHANGES IN CARBONATE LITHOLOGY 

Carbonate deposition that formed marine limestone, 

dominantly, throughout much of Mississippian time ended 

with deposition of the deltaic sandstone of the Bethel 

Sandstone. Marine limestone does occur higher in the 

section, but it is interspersed with thick beds of clastics, 

chiefly shale and sandstone. Prior to the incursion of the 

clastic sediments, the depositional environment of the 

lower part of the St. Louis Limestone was a marine shelf in 

fairly deep water. Gradually, the environment shifted to 

shallow-water facies, especially during deposition of the 

Ste. Genevieve and Renault Formations. 

The shallow nearshore environment of deposition of the 

Ste. Genevieve Limestone and Chesterian Series is briefly 

described by Fraunfelter and Utgaard (1973, p. 35 -37). 

They report the oolitic limestone of the Ste. Genevieve 

Formation as representing deposition on a shallow marine 

shelf, similar to the one currently existing in part of the 

Bahama Islands region. Klein (1974, table 1) suggests that 

the Aux Vases Sandstone, which is represented by the 

Rosiclare Sandstone Member in the mining area, was 

deposited in water that was only about 8 feet (2.5 m) deep. 

The clastic and oolitic nature of the limestone of the 

productive section indicates that these rocks were very 

porous at the time of deposition and burial. The author 

believes that some of the rocks of the productive section 

were still very porous when mineralization occurred. 

Indeed, some zones in the same part of the section are still 

very porous and permeable. For example, the McClosky 

sand zones, which are good producers of oil in the Illinois 

and Western Kentucky basins, consist ·of uncemented 

oolites and are highly permeable. High permeability in 

some of the carbonate rocks probably influenced mineral 

deposition strongly. 

EFFECT OF SHALES ON ORE FLUIDS 

Above the Bethel Sandstone the stratigraphic section 

contains much shale, and, in general, the amount of shale 

increases upward. The shales are incompetent, and many 

of them deformed plastically during and after faulting. 

Many faults, not shown on the areal maps, were important 

channels for the solutions that formed the bedded mineral 

deposits, even though the vertical displacement on these 

faults is only a few feet or less. These faults tend to 

terminate upward within beds of shale or shaly limestones, 

the movement along the faults having been taken up within 

the plastic shale. In many other faults that continue 

through a shale bed, shale squeezed into the fault and 

closed it to the further upward movement of the ore 

solutions. The effect of the shales was to seal, or partly 

seal, many fissures above the Bethel Sandstone and to 

restrict the formation of fissures through the shales. This 

effect prevented ore-bearing fluids from reaching the 

limestones of the Chesterian Series. Instead, a large part of 

the fluid probably moved through the porous beds of the 

productive section, which is below the Bethel Sandstone. 

IGNEOUS ROCKS AND DIATREMES 

The region contains many small bodies of igneous rocks 

and several diatremes. These have aroused much 

speculation about their relation to the origins of both the 

structure of the region and the mineral deposits. Clegg and 

Bradbury (1956) showed nearly 80 occurrences of intrusive 
MINERAL DEPOSITS 11 

rock in southern Illinois, and possibly as many exist in 

Kentucky, but no compilation of the intrusive rocks in 

Kentucky has been made. The exposed igneous rocks form 

dikes, small plugs, and a few thin sills. The igneous rocks 

are highly altered; the freshest specimens are mica 

peridotites (Clegg and Bradbury, 1956). 

An aeromagnetic study (McGinnis and Bradbury, 1964) 

showed a magnetic high centered about 5 miles (8 km) 

northeast of the center of Hicks dome. The magnetic 

pattern is consistent with a model of a body of basic 

igneous rock at a depth of between 11,000 and 15,000 feet 

(3,350 -4,570 m) and having a horizontal diameter of 

about 12 miles (19 km). The depth of the basement 

northeast of Hicks dome (Bayley and Muehlberger, 1968) 

is approximately 12,000-13,000 feet (3,700-4,000 m). 

The edge of the body of igneous rocks may pass under 

Hicks dome, but McGinnis and Bradbury (1964) concluded 

that the structure of Hicks dome is not due to intrusion of 

a laccolith centered under the apex of the dome. 

The known diatremes are in the vicinity of Hicks dome. 

They are known to be as much as 800 feet (250 m) across 

and consist chiefly of fragments of sedimentary rocks in a 

matrix of finely ground rocks and minerals. Some contain 

fragments of peridotite. The diatremes are poorly known 

because of poor exposures. Brown, Emery, and Meyer 

(1954) described what is surely a diatreme from data of an 

exploratory oil well, Henry Hamp, Jr., 1, which was 

drilled in the center of Hicks Dome. The Hamp well 

encountered breccia from a depth of 1,815 feet (533 m) to 

the bottom of the hole at 2,944 feet (897 m). Trenches (not 

described by Brown and others, 1954) several hundred feet 

west of the drill hole expose beds that are broken and are 

jumbled. These facts suggest either that the diatremes may 

be considerably larger than indicated on the geologic maps 

by Baxter and Des borough ( 1965) and Baxter, 

Desborough, and Shaw (1967) or that the diatremes are 

surrounded by broken and deformed beds. 

MINERAL DEPOSITS 

NDNERALSOFTHEORE 

The chief minerals of the ore are fluorite, sphalerite, 

galena, and calcite. Barite, strontianite, and quartz are 

abundant in some deposits. Chalcopyrite is present in 

nearly all the deposits, but only in small amounts. 

Marcasite and pyrite have been reported from a few places. 

Smithsonite was abundant at the surface in some deposits, 

since mined out. 

Fluorite, sphalerite, and galena are recovered in nearly 

all the mining operations. Some barite is being recovered 

now by one company. In most deposits, however, barite is 

treated as a gangue mineral. A large amount of limestone is 

extracted with the ore; some is sold as road metal. 

STRUCTURAL TYPES 

The deposits are of four major structural types: (1) veins 

and associated replacement bodies, (2) bedded deposits, (3) 

solution-slump breccias, and (4) diatremes. 

VEINS 

Veins occur throughout the area and have been worked 

for more than 100 years. The veins occupy faults, chiefly 

those bounding grabens and horsts. The veins are largely 

open-space fillings, but replacement of the wallrocks and 

fragments of rock commonly occurred. The amount of 

stratigraphic displacement on the faults seems to have been 

unimportant as an ore control, though it is often 

mentioned as an influencing factor. The type of wallrocks 

in the faults appears to be an important ore control. The 

most productive veins have at least one wall consisting of 

clastic limestones, as described previously, regardless of 

the amount of displacement on the fault. 

The veins differ greatly in size. The largest known veins 

are at Rosiclare, where three exceptionally large veins were 

mined. One vein there was mined for 5,700 feet (1,740 m) 

along the strike, more than 900 feet (275m) downdip, and 

to as much as 45 feet (14 m) in width (Grogan and 

Bradbury, 1968). More generally the ore shoots in the veins 

are 300 feet (100m) long, 100-200 feet (30-60 m) high, 

and several feet wide. Throughout the area the largest veins 

are where the major northeast-trending fault zones change 

strike or branch. These places, characterized by many 

faults, are considered promising for future exploration. 

BEDDED DEPOSITS 

Bedded deposits have been extensively worked for about 

40 years and are known chiefly in two areas: (1) the Cave in 

Rock district, Illinois, and (2) near Carrsville and Joy, Ky. 

Bedded deposits have also been found next to some of the 

veins. 

The bedded deposits in the Cave in Rock district are 

large and have been continuously mined since the 1930's. 

They are in a horst southeast of the Rock Creek graben and 

lie in a belt parallel to the side of the graben on the 

northeast side of the arch. The belt is about 1 mile (1.5 km) 

wide and at least 6 miles (10 km) long; the downdip 

(northeast) end has not been reached, and the updip 

(southwest) end, where the belt crosses the axis of the arch, 

is eroded. The deposits were found where the belt crops 

out, northwest of Cave in Rock, and they were followed 

downdip by churn drilling. Exploration for the belt down 

the dip of the beds has not exceeded a depth of 1,200 feet 

(370m). 

The structure and shape of the bedded deposits were 

illustrated by Weller, Grogan, and Tippie (1952), Brecke 

(1962), and Grogan and Bradbury (1968). In general the 
12 MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY MINING DISTRICT 

deposits have the shape of very long lenses; they are several 

times as long as they are wide and several times as wide as 

they are thick. The stratigraphic position of the major 

deposits is shown in figure 4. They are all in oolitic 

limestone, and the larger ones are in the Sub-Rosiclare ore 

zone or below the base of the Rosiclare or Bethel 

Sandstone. These sandstones each contain a thin shale at 

the base. 

Mapping by this author of the structure and mineral 

distribution in several ore bodies has shown that the 

bedded deposits are zoned. Each bedded deposit overlies 

one or more fissures and is elongate in the direction of the 

fissure. In some deposits, sphalerite occurs near the 

fissures or in the central part of the ore body, and barite is 

more abundant toward the edges and ends of the ore body. 

In many ore bodies, fluorite occupies a central position 

and calcite occupies a peripheral position. 

The fissures below the Cave in Rock ore bodies are faults 

of small displacement or joints in well-defined sets which 

may be marked by steeply dipping veins. Because these 

fissures occur under the ore bodies and are parallel to the 

long axes of the ore bodies, the fissures are thought to be 

the controlling structures through which the ore-bearing 

solutions reached the favorable beds. Most of the fissures 

strike northeast, about parallel to the edge of the Rock 

Creek graben, and they probably formed at the same time 

as the faults between the horsts and grabens and by the 

same means. The author believes that fissures of a similar 

nature may occur in many places bordering the major 

faults that bound the grabens. Thus, the structural setting 

of the very productive Cave in Rock district may well be 

duplicated in belts about 1 or 2 miles (1.6 or 3.2 km) wide 

along the edges of the horsts beside the grabens. Such belts 

of bordering fissures may occure in areas that total more 

than 200 square miles (518 km2). In addition, similar 

structural settings probably occur in the grabens as well as 

in the horsts, but the grabens have not been explored at all 

for bedded deposits. 

SOLUTION-SLUMP BRECCIAS 

In the 1960's several bodies of mineralized breccia were 

found associated with bedded deposits in the Cave in Rock 

district. The largest bodies are in the Hill and North Green 

mines. Smaller bodies of similar breccia are known in other 

mines. The breccias do not extend to the surface; they are 

of solution and slump origin, and their lower limits are not 

known. Some breccias are potentially large ore bodies, 

though of low grade. 

Figure 5 is a map of one of the larger bodies of breccia 

found in the Hill mine. This large body of breccia is along 

and between two fissure zones which strike northeast and 

dip steeply. The beds bend down progressively from 

EXPLANATION 

~ BRECCIA 

Large blocks of limestone Syncline 

ORE 

D Small blocks of limestone ~ High-grade .. and sandstone Low-grade B Crushed and recrystallized Vein ' limestone 

c ((( Trough-shaped body 

of bedded ore 

Fault y Cave 

Monocline ~ Winze 

FIGURE 5.-Mineralized breccia of solution-slump origin; Hill mine 

(1, fig. 2), Cave in Rock district, Illinois. 

southwest to northeast toward the breccia and finally are 

broken and collapsed. All rocks are below their normal 

stratigraphic position. Blocks from the upper part of the 

Renault Formation are now well below the position of the 

Rosiclare Sandstone Member outside the solution-slump 

structure. 

Toward the edges of the slumped area huge blocks of 

limestone are bounded by faults or veins; toward the center 

the blocks are somewhat smaller and are separated by 

strands of breccia that consist of sandstone fragments as 

much as 3 inches (8 em) across and pieces of clay or shale. 

Finely brecciated limestone is rare in the central part of the 

body. The largest blocks of limestone in the central part 

are scarcely tilted; they apparently moved vertically 

downward. Finer material moved downward into spaces 
AREA OF MINERAL POTENTIAL 13 

between the large blocks. Caves were dissolved in the 

limestone along the southwest side of the breccia. 

The fine breccia was mineralized throughout; the large 

blocks of limestone in the central part of the slump-breccia 

contain ore along their edges. The clay and sandstone 

breccia between the blocks in the central area is filled with 

fluorite and is low-grade ore. Many of the large blocks 

surrounding the central area are separated by wide streaks 

of high-grade ore, and some of these blocks contain pods 

of ore. Sphalerite and galena are more abundant in this 

outer part than in other places. 

The vertical extent of the breccia is not fully known, but 

it exceeds 250 feet (75 m). The breccia extends upward 

above the Rosiclare Sandstone Member and includes 

fragments of limestone from the upper part of the Renault 

Formation. It extends downward through the Ste. 

Genevieve Limestone into the St. Louis Limestone. 

Abundant stylolites, caves, and small cavities indicate 

that large amounts of limestone were dissolved. The 

downward movement of all breccia fragments indicates the 

breccia is of solution-slump origin and is not a diatreme. 

Mineralization and slumping were contemporaneous, at 

least in part (Pinckney and Rye, 1972). Therefore, the 

breccia in the Hill mine and similar breccias elsewhere 

are considered to have been major channels for the 

mineralizing solutions. As such, they may contain large 

bodies of ore. 

DIATREMES 

The exploratory hole that was drilled into the center of 

Hicks dome encountered mineralized rock from a depth of 

1,605 feet (490 m) to the bottom of the hole at 2,944 feet 

(897 m). The chief minerals reported were fluorspar and 

small amounts of sphalerite and galena (Brown and others, 

1954). Trace (1960) reported small but noteworthy 

amounts of beryllium, niobium, thorium, and rare-earth 

elements in samples from the exploratory hole. An outcrop 

of breccia, shown by Baxter and Desborough (1965, pl. 1) 

in sec. 30, T. 11 S., R. 8 E., near the top of Hicks dome, 

contains a large amount of jasperiod, which had not been 

reported previously. These facts are evidence of hydrothermal activity in the central part of the dome. From the data 

about breccias and from observations in the field, this 

author thinks that all the central part of Hicks dome, 

shown as Devonian formations in figure 2, may be a 

breccia. If it is, the central part of the dome is probably a 

huge diatreme and merits extensive exploration for mineral 

deposits. 

Baxter and Desborough (1965, fig. 3) listed 10 breccias 

that may be diatremes. Very little is known about these 

breccias, but, in view of the mineral content of the breccia 

found in the Hamp drill hole, they should be considered as 

potential sources of base metals and fluorite and as 

possible sources of other metals, including niobium. 

DEPOSITS CONTAINING CHIEFLY 

LEAD OR ZINC 

A few deposits have been worked chiefly for lead or zinc 

and contain little fluorspar. Examples are deposits at the 

Old Jim mine (Ulrich and Smith, 1905, p. 176 -180), the 

Hutson mine (Oesterling, 1952), the Patrick mine (Weller 

and others, 1952, p. 130), and the Hickory Cane mine 

(Trace, 1954, p. 53). The Old Jim, Hutson, and Hickory 

Cane deposits are veins of high-grade zinc ore; some ore 

was oxidized to smithsonite. The Hutson deposit also 

contained several bodies of replacement ore. According to 

Osterling (1952), replacement ore at the Hutson mine was 

largely along tension fractures that connect two parallel 

fissure veins. The replacement bodies were fairly large, 

massive, and high grade. They contained about 25 percent 

zinc, but very little lead or fluorite. 

A moderately large deposit at the Patrick mine near 

Cave in Rock consisted chiefly of galena and cerussite and 

contained only a little fluorite or zinc. The ore was in 

replacement bodies and narrow veins in the St. Louis 

Limestone (Weller and others, 1952, p. 130) and was mined 

from an open pit. 

AREA OF MINERAL POTENTIAL 

The area in which mineral deposits have been found and 

mined is very large and it has been only superficially 

explored. Reasonable projections indicate that the area of 

potential production is more than twice as large as the area 

of known production. 

The incentive to explore for new deposits was low during 

the 1950's and 1960's. Exploration lagged because of the 

low price of fluorspar and the abundance of fluorspar 

from foreign sources. With the rise in the price of fluorspar 

during the last few years, exploration activity has 

increased. Even so, only a small part of the area having 

production potential has been thoroughly explored. 

Most exploration has been limited to fairly shallow 

depths. The bedded deposits in the Cave in Rock district 

have been followed downdip by mining and drilling to a 

depth of only 1,200 feet (370 m). The large veins near 

Rosiclare, along the southeast side of the Carrsville 

graben, were explored to a depth of more than 900 feet 

(275 m) north of the Ohio River, but very little is known of 

the same structures south of the river. Exploration 

conducted south of the Ohio River found bedded deposits 

along the southeast side of the Carrsville graben, where the 

structural setting is probably similar to that of the bedded 

deposits near Cave in Rock. Nearly all the old mining 

centers have been partly explored in recent years by 

diamond drilling, and the success of such exploration is 

reflected partly in increased production. 
14 MINERAL RESOURCES OF THE ILLINOIS-KENTUCKY MINING DISTRICT 

The major ore control of deposits in the bedded, vein, 

and solution-slump structures is the intersection of fissures 

with the Ste. Genevieve and Renault Formations. These 

formations crop out throughout much of the axial part of 

the arch in the area shown in figure 2 as older Mississippian 

rocks. Indeed, the mining area and the outcrop area of 

these beds largely coincide. These beds extend downdip off 

the arch into the adjacent basins. Between the north edge 

of the Cretaceous and Tertiary sediments and the 

Mississippian-Pennsylvanian contact, these beds underlie 

an area of more than 1,100 square miles (2,800 km2

), and, 

of course, they extend at depth beyond the Pennsylvanian 

contact. The depth to the base of the Bethel Sandstone at 

the outer edge of this area is approximately the thickness of 

the Chesterian Series, which is about 1,200 feet (360 m) in 

most places. Within this area the length of intersections of 

iissures and favorable beds is hundreds of miles and the 

intersections extend beyond the area. 

The outermost extent of mineralization is not known. 

The areas in which all mines and prospects are located are 

shown within the dashed lines in figure 2. However, Trace 

and Palmer ( 1971) reported the occurrence of sphalerite 

disseminated in siderite east of the Mississippian-Pennsylvanian contact. The minerals are in the Caseyville 

Formation of Pennsylvanian age, within the Shady Grove 

graben. Obviously, the dashed lines in figure 2 do not show 

the limits of mineralization. Instead, the position of lines is 

based on the faults and the outcrop pattern of the 

favorable beds. 

CONCLUSIONS 

The Illinois-Kentucky mining area probably will 

continue to be the major source of domestic fluorspar and 

a small but important source of lead, zinc, and cadmium 

for many years. Mining operations, on a long and 

sustained basis, can expect to recover about 9.9 tons, or 

more, of lead and about 55 tons of zinc for each 1 ,000 tons 

of calcium fluoride produced, as well as small amounts of 

silver, germanium, and cadmium. Barite has potential 

value, but only a little of it is recovered now. Some 

deposits contain strontium, chiefly in strontianite, but little 

use exists now for this metal. 

Most ore has come from veins and bedded deposits, and 

deposits of these types will continue to be important. The 

veins are along known fault zones that are well shown on 

existing geologic maps. Additional ore can be found by 

thorough exploration of those parts of the fault zones 

where one or both walls are the productive beds. The 

intersections of faults and favorable beds are unexplored 

throughout many miles of their length. The large known 

bedded deposits are in horst blocks beside grabens, and 

many hundreds of miles of this favorable setting are 

unexplored. Similar structural settings in the grabens also 

remain unexplored. More deposits in solution-slump 

structures may be found associated with bedded deposits. 

The diatremes are especially intriguing, inasmuch as they 

may contain large deposits at depth. Some of these 

structures can be seen on the surface and followed 

downward. All the known diatremes are in the vicinity of 

• Hicks dome. A search for other diatremes around the 

dome and exploration of the known ones seems 

worthwhile. 

The intersection of fault zones with certain beds below 

the Bethel Sandstone is the most important structural ore 

control and extends throughout most of the entire region. 

Erosion has removed these beds in only a few small areas. 

Many places within the mining area where this relation is 

present are still unexplored. This structural relation also 

extends down the flanks of the arch, under the area shown 

in figure 2 as Upper Mississippian rocks. This additional 

area, if extended out only to the base of the Pennsylvanian 

beds, is approximately as large as the known mining area. 

The Illinois-Kentucky mining area has yielded a 

substantial amount of fluorspar, lead, zinc, silver, and 

cadmium for many years. Some of the barite present is 

now also being recovered. The ore deposits are moderately 

large and of good grade. The known area of mineral 

potential can be considerably expanded, and the newly 

recognized diatreme deposits should be thoroughly 

explored. In short, the mineral potential of the region is 

considered to be very large. 

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Illinois Geol. Survey Circ. 385, 40 p. 

Baxter, J. W., Desborough, G. A., and Shaw, C. W., 1967, Areal 

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Butts, Charles, 1925, Geology and mineral resources of the EqualityShawneetown area (parts of Galletin and Saline Counties): Illinois 

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Fraunfelter, George, and Utgaard, John, 1973, Depositional 

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lC?U.S. GOVERNMENT PRINTING OFFICE: 1976-677-340/91