Preliminary report on uranium in Hardin County, Illinois

5f

no. 200
c>l

STATE OF ILLINOIS

WILLIAM G. STRATTON, Governor

DEPARTMENT OF REGISTRATION AND EDUCATION

VERA M. BINKS, Director

DIVISION OF THE

STATE GEOLOGICAL SURVEY

JOHN C. FRYE, Chief
URBANA

CIRCULAR 200

PRELIMINARY REPORT ON URANIUM
IN HARDIN COUNTY, ILLINOIS

BY

J. C. BRADBURY, M. E. OSTROM, and L. D. McVICKER

PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS

URBANA, ILLINOIS

1955

ILLINOIS ULOLOGICaL
SURVEY LIBRARY

SEP 28 1955

Digitized by the Internet Archive

in 2012 with funding from

University of Illinois Urbana-Champaign

http://archive.org/details/preliminaryrepor200brad

^7

PRELIMINARY REPORT ON URANIUM
IN HARDIN COUNTY, ILLINOIS

by
J. C. Bradbury, M. E. Ostrom, and L. D. McVicker

ABSTRACT

Hicks dome in Hardin County, 111., is an eroded structural
dome whose specific mode of formation is not clear. Associated
with it are explosion breccias and pendotite dikes. The central
part of the dome is an area of about 1 1/2 square miles underlain
by rocks of Devonian-New Albany age, principally limestone and
chert bordered by black shale. The bedrock in the central areas
of the dome, as well as in other adjacent areas, is covered by red
and yellow clays believed to be a residuum resulting from the
leaching of cherty Devonian limestone. Chert breccias, cemented
by secondary silica, also are present.

Tests of about 200 samples taken from the dome and through-
out the county suggest that the residual clays and breccias within
the Devonian-New Albany area of the dome are generally more
radioactive than samples elsewhere, though there are some ex-
ceptions. Samples of fluorspar, zinc and lead ores, and concen-
trates from these ores have little or no radioactivity as measur-
ed by a laboratory Geiger counter. U308 determinations made by
chemical procedures on 25 samples having some of the higher
uranium equivalent values were all lower than the uranium equiv-
a ent values. All the samples analyzed for UjOg contained less
of this compound than the minimum of 0.1 percent for which prices
are quoted by the Atomic Energy Commission.

INTRODUCTION

by J^teV"* SlX mTh3 C°nSiderable Publ- -terest has been aroused

County m Contre8enCe radi°aCtive ™te»*ls on Hicks dome in Hardin

men" Ld s C°f "mn* lntereSt has bee" maintained by reports* that have

4 and tren7leS '™*ln* fr°m °-10% *° °-21% U3°8. and leasing, test pit-
<g and trenching, and sampling has been under way in the area

nois gS CiT °f any "^ POtential min«al resource in the State, the Illi

for th f C dCPOSltS f°r the benefit of owners and prospectors and

:^n"a0f aU citizens °f the state- A large number of a"pi"

"tivity ha t rat,0metHCally and S°me of those that showed higher radio-
!_i^yhave been chemically analyzed for uranium.

Hardin County Independent, March 17, 1955, p. 1.

o Sample

^ Sample from breccia

• Sample from dike

Fig. 1 - Sketch map showing sample locations on Hicks Dome and vicinity ^s are show,
g by solid lines. The approximate limits of the area underlain by rocks of

Devonian-New Albany age are indicated by a dotted line.

URANIUM IN HARDIN COUNTY 3

Because of the widespread public interest in Hicks dome, this progress
report has been prepared to make available the Geological Survey's informa-
tion as of this date. As our investigations are incomplete, all deductions and
hypotheses expressed herein are subject to revision as investigations proceed
further and additional data become available. The basic analytical data pre-
sented here, however, are of more lasting value.

GEOLOGY OF HICKS DOME

Hicks dome, which is both a structural and a topographic feature, is lo-
cated about 7 1/2 miles north of Rosiclare, centering in sec. 30, T. 11 S., R.
8 E. Although the beds dip outward for several miles from the center of the
dome, for the purposes of this report the term "Hicks dome area" will be given
the approximate geographic limitations shown on the map (fig. 1). The central
part of the dome, referred to in this report as "Hicks dome," is an area of
about 1 1/2 square miles; most of the prospecting for uranium has been con-
centrated there. It is underlain by Devonian limestone and chert identified
from drilling as the Clear Creek formation (Brown et al., 1954). The surface
is now covered by red cherty clay, a residue from the weathering of the cherty
limestone.

A circular belt about 1/4 to 3/8 mile wide around the central part of the
dome is underlain by black carbonaceous New Albany shale, which shows some
radioactivity. Information on the rocks at depth is contained in the log of the
Fricker well on the southeastern side of the dome (Weller et al., 1952) and in
the report by Brown et al. (1954) on the Hamp well, an oiltest on the central
part of the dome.

Exposures of two mica-peridotite dikes and three occurrences of explo-
sion breccia are evidences of igneous activity in the Hicks dome area. In ad-
dition, a well (the Hamp well) was drilled through explosion breccia from 1725
feet to the bottom of the well at 2925 feet. All exposures except a dike on the
Joiner farm are shown on figure 1. The Joiner farm dike is shown on the geo-
logic map in Illinois Geological Survey Bulletin 76 (Weller et al., 1952) as oc-
curring in the SE 1/4 sec. 25, T. 1 1 S., R. 7 E., but it apparently no longer crops
out.

Faults are difficult to recognize because of the nature of the materials ex-
posed on Hicks dome, but it is believed that such faults as may be present are
small and of limited extent. A chert breccia in slickensided wall-like bodies
s found at scattered places. One such outcrop protrudes several feet above
>e ground for a distance of about 75 feet. Most of the slickensided walls had
a general northeast strike, ranging from N. 20 E. to N. 60 E. This is the pre-
vailing trend of the faults in Hardin County.

The exact origin of Hicks dome is not completely known. Its upward arch-
ing may have been associated with the structural movements that produced the
siting that is common in Hardin County and adjacent parts of Kentucky and is
^ly complex. An alternate hypothesis is that the dome reflects the localized
trusxon of a mass of igneous material at considerable depth, from which the
ndotite dikes and explosion breccia are offshoots. A third hypothesis (Brown
H.> 1954) also involves a molten mass at depth but suggests that the doming
caused by gases evolved from the igneous rock or by steam from ground-

4 ILLINOIS STATE GEOLOGICAL SURVEY

water heated by the intrusion. Thus the explosive release of the gases may
r !!d thl breccias found on the dome. However, occurrences of explo-
breccfafn areas away from the dome, for example, near Sparks Hill and
r mile wea8; of Ro^iclarl, throw doubt on the significance of such breccia in
the formation of Hicks dome.

METHOD OF SAMPLE ANALYSIS
The sampled materials, described below, were crushed in a jaw crusher
to approximately 1/8 inch. Radiometric analyses of the samples were made
wi* a laboratory model Geiger counter which had been calibrated again,, : sam
Ties of known U,08 content obtained from the Atomic Energy Commission.
P Dominations of U308 were made according to the Atomic Energy Com-

I', booklet -Manual of Analytical Methods for the Determination of
UrTium ana Thorium in Their Ore's." A Beckman Model DU spectrophotom-
eter with 10 cm. Corex cells was used for the color measurement

A standard curve of transmittance was prepared by analysis °f various
dilutions of a sample of phosphate rock of known U308 content obta ned from
the Atomic Energy Commission. Results of the Illinois Survey analyses of
ftandarT samples compared satisfactorily with the Atomic Energy Commis-
sion's values for the same samples.

OCCURRENCE AND NATURE OF MATERIALS SAMPLED
FROM HICKS DOME AREA
All types of earth materials present at the surface in the Hicks dome are
and in tesTpits and trenches up to 20 feet deep were tested in the field with a
Portable Ge'iger counter and sampled for analysis in the Surve Y Intone. ^
Included in the field examination were red, yellow, and brown clay chert, sar
stone (minor amount), fault (?) breccia, explosion breccia peridotite dikes
black marine shale (New Albany), massive limonite, and calcite and ^ luorite^
Only the clays, some of the fault (?) breccia, and some of the New Albany shj
showed appreciable radioactivity. Some pieces of the explosion breccia sho^
weak radioactivity whereas others showed none. The dikes were very weakl,
radioactive. The rest of the material showed little to no radioactivity.

Clays

Most of the cherts and the clays, which are principally red or yellow, ap
pear to be residual from the weathering of a limestone that contained chert
nodules and beds as much as several feet thick. The red clay present over
of the dome has the typical color and appearance of residual clay from 1 me
X-ray diffraction patterns of the minus 2 micron or clay-size fraction of tw
samples (nos. 18 and 38, table 1) established the absence ^ofanyc ^racterist
cally crystalline clay mineral in sufficient abundance to be identified. Heter
geneous weathered assemblages of this nature are often observed in clays r<
sidual from limestone.* As sample 18 was moderately radioactive and sam

*Bradley, W. F., personal communication.

URANIUM IN HARDIN COUNTY 5

pie 38 was virtually nonradioactive, there is apparently no relationship be-
tween clay mineralogy and radioactivity.

On the central part of the dome, the yellow clay occurs as vertical "veins"
and irregular masses in the red clay and commonly carries much higher val-
ues in radioactivity than the surrounding red clay. The yellow clay is different
in appearance and physical properties from the red clay. It dries to a rather
powdery mass which feels silty; the red clay typically dries to a hard substance
resembling brick. Size analyses of the red and yellow clays (table 2) show that
sample 72, the yellow clay, carries twice as much silt (-325 + 2 microns) as
the two red clays and much less clay-size material than sample 18, a red clay.
The relative scarcity of clay-size particles in the other red clay, sample 38,
is probably due to the fact that a large part of that sample was composed of
chert fragments. Otherwise sample 38 is similar to sample 18 - in color, tex-
ture, and drying characteristics.

An x-ray diffraction pattern of the minus 2 micron fraction of the yellow
material showed the same characteristics as the red clays. The yellow clay
occurring in "veins" probably came from an overlying layer of yellow residual
clay which has been completely eroded. As cracks opened in the underlying red
clay, possibly from slumping into sink holes in the limestone, the yellow clay
was washed into the fissures. As these fissures were also watercourses, ra-
dioactive substances in the groundwater may have become concentrated in the
yellow clay "veins" by adsorption on the clay minerals. The data in table 2
suggest some sort of relationship between the amount of the clay fraction and
radioactivity.

On the eastern flank of the dome, in the vicinity of the Robinson dike (sam-
ple 130), a bulldozer-cut exposed a yellow residual clay overlying Mississip-
pian Osage chert. The yellow clay on the Robinson property was radioactive
only at the contact with the underlying chert bedrock (sample 175), indicating
a concentration by groundwater at the surface of the bedrock. Sample 176 was
taken from a two-foot wide radioactive zone in broken chert at the southeastern
side of the dike as exposed in the trench. The dike itself had been weathered
in place to a soft material that was easily cut by the bulldozer. The material
of sample 176 showed as strong a reading on the portable Geiger counter in the
wall of the trench as did that of sample 175, but when tested five days later by
a laboratory counter it was only weakly radioactive (see table 3). As the ma-
terial had been sampled as soon as it was exposed by the bulldozer, the radio-
activity may have been caused by radon gas.

Another type of yellow clayey material is exposed for about 1000 feet along
a stream and its tributaries on the northwestern flank of the dome in the NW
74 sec. 25 and the NE 1/4 sec. 26 (samples 131 to 133 and 168). It is moder-
tely radioactive in spots and is composed mainly of fragments of weathered
chert, although an occasional fragment of sandstone or shale can be found. The
material is soft except for the few sandstone fragments, and the chert offers no
more resistance to a knife blade than does the interstitial clayey material.
Some stratification can be found and is contorted in places. Apparently the ma-
terial is a strongly weathered chert gravel. No differences in included mate-
rials, texture, or structure could be found between the radioactive and nonra-
noactive portions.

6 ILLINOIS STATE GEOLOGICAL SURVEY

Chert and Sandstone
The chert exposed in trenches and as an occasional outcrop does not ap-
pear to be significantly radioactive (table 1) with the exception of sample 72D.
This sample is from a one -foot bed of soft weathered white chert with brown
laminations exposed in the wall of a trench. The only sandstone foundwasa
few blocks in a sinkhole exposed in a trench and one small piece on a hallsade
(sample 88, table 1). None of it was radioactive.

Fault ( ? ) Breccia

The material called fault (?) breccia is composed of chert or other silic-
ified rock fragments cemented by fine-grained to macrocrystalline quartz Th
breccia generally occurs as slickensided wall-like bodies which may protrude
above the ground (sample localities 10 (11) and 25) or be completely covered
bv residual clay (locality of samples 1 through 6 and 77).

The breccia fragments appear to have come from the immediately sur-
rounding rocks, which seem to have been only fractured with none of the grand
ang expectable from a large amount of movement along a fault. No stratagrapl
evidence of faulting was found because of the scarcity of outcrops. However,
we saw no difference in the soil or residuum surrounding the breccia outer opt
from one side of the outcrop to the other, so that movement on the faults was
not sufficient to have brought different kinds of rock into contact

An alternative theory of formation of the breccia is one invoking explosiv
gases. The fault (?) breccia would merely represent a lesser degree of dis-.
turbance than that shown by the explosion breccia. The slickensides, which
transect the cement as well as the rock fragments, could have been caused b>
minor adjustments along the plane of the disturbance after the explosive ac-

tivity had ceased. ,

Appreciable radioactivity in the fault (?) breccia was detected only at th
locality of samples 1 through 6, a ridge exposed in a test pit. One sample <n<
12) from boulders on the opposite side of the same hill also showed moderate
radioactivity, but all samples from other localities showed only weak or no r|
dioactivity The great variation in amount of radioactivity between samples
from the same locality indicates that the distribution of the radaoactaye mate
rial in the breccia is "spotty." It suggests that the lack of appreciable radio
activity shown by samples from the other localities may be due to the chance
missing of radioactive segregations during sampling. Such is not believed tc
be the case because all breccia outcrops were checked with the portable Gel f
counter and only localities of samples 1 through 6 and 12 had shown a count (
more than twice background.

A microscopic examination of the breccia failed to reveal the presence*
uranium minerals, but an ever-present iron-oxide stain could hide any powd.
coatings of normally brightly colored secondary uranium minerals. As tt
chert itself is not radioactive, the radioactivity must be related to the fine-
grained quartz cement. The cementing material is generally vesicular and
here and there is present only as a drusy coating around the chert frag™en '
Generally there is not sharp boundary between the cementing quartz and the
chert, indicating some replacement of the chert by the quartz. Whether

URANIUM IN HARDIN COUNTY 7

quartz of the cement was deposited from hydrothermal solutions related to the
igneous activity or from circulating groundwater cannot be determined at pre-
sent, but the great quantity of silica available in the Devonian chert certainly
makes a hydrothermal source unnecessary. That groundwater is an adequate
carrier of silica is attested by the quartz veinlets and druses associated with
many Siliceous sediments as well as the well-crystallized quartz found in many
geodes. 7

Explosion Breccia

The terms explosion breccia and intrusive breccia have been used in Har-
din County to designate a rock composed of pieces of sedimentary and igneous
rocks in a fine-grained altered matrix which includes fragments of the minerals
feldspar, mica, pyroxene, and apatite (Weller et al„ 1952). Brown et al (1954)
concluded that the breccia in the Hamp well also was an explosion breccia, al-
hough it contained no recognizable igneous material. The breccia at sample
localities 37, 50 (125), and 128 was called explosion breccia in the field because
of its similarity in appearance to described occurrences of that breccia else-
where in Hardin County.

Sample locality 50 (125) is a small steep-sided rounded hill several hun-
dred feet in diameter liberally sprinkled with boulders of a material composed
of angular fragments of chert in a fine-grained matrix. In places the matrix
appears to be composed largely of iron oxide, but generally the cementing ma-
terial is fine-grained to microcrystalline quartz. The included fragments vary
>n size from about 6 inches down to the granular material of the matrix
1 ,w,?vneral comP°sition the breccia of locality 50 (125) is similar to the
■ault (?) breccia described earlier but differs in degree of brecciation and in
irea and shape of outcrop. The fault (?) breccia appears to be composed of
ragments about 1/2 inch or larger whereas the material of locality 50 (125)
:ontains areas in which the fragments measure no more than a millimeter or
o. The differences in area and shape of outcrop of the two occurrences are
real and appear to suggest different modes of origin. If the hill of locality 50
125) is underlain entirely by the breccia, as would appear to be the case from
he absence of other kinds of rock either as float blocks or outcrops, the brec-
cia has an outcrop area roughly circular in plan and several hundred feet in
uameter. Such an outcrop area would be expected from a pipe -like body. By
ontrast the more typical fault (?) breccia occurs in narrow wall -like bodies
bout 2 to 3 feet wide and up to 75 feet long, suggestive of fault outcrops.

The other two occurrences designated as explosion breccia in figure 1 are
rtermediate in amount of brecciation between the fault (?) breccia and the
reccia plpe. T^y are both chert breccias cemented by sU.ca and .ron ^.^

.eeZTVVi "t' i28 1S Sma"' ^ n°- " iS reP"^d °nly as boulders, so
nof T?fi t^°dXeS iS n0t known- The existence of breccia of the character
Lt ,1', it ! ' ln a S6nSe transiti°nal between the two extremes, suggests

at all the breccia of the Hicks dome area might have originated from the same
rce - explosive release of gases.

The radioactivity of the explosion breccia was found to be low, both in out-
, op measurements and in representative samples tested in the laboratory.
|>wever, analyses of eight 25-foot samples of cuttings from the breccia portion

, ILLINOIS STATE GEOLOGICAL SURVEY

„ ,T> * „i iqc;4t showed four to be moderately radioactiv

^TZr^JTZZl^V™ 0.0!% eU to 0.03% eU. The low leve

^^rrco^ai:: Iferg'ato8: of radioactive material. The generally low
"luefof LT c^mlcJUyses for uranium of the Hamp samples show that
the radioactive material is something other than uranium.

Peridotite Dikes
Two occurrences of mica ^f^^^Z^^O^^
Se^ictl Su°;:eery BulTetm^ (Wel^r ~-l.. 1952). Samples collected by Gro
gan w re ound Jbe hut slightly radioactive (sample 147). On the Robinson
farm on the east side of the dome a weathered dike is exposed in a test pit
simple 130) and in the bulldozer trench from which clay samples 175 and 17
lerTtaken The dike strikes N. 57° E.. in contrast to the northwestward strt
If a 1 other known dikes in Hardin County. The only recognizable mineral re-
manning in this thoroughly weathered dike is mica, in books and plates up to
T/2 inch wide. The weathered material was even less radioactive than the
Joiner dike.

New Albany Shale
The New Albany shale, which encircles the central part of Hicks dome ^
a band 1/2 to 3/8 mile wide, is a black carbonaceous marine shale. Samples
70a tough 70e represent successive 5-foot vertical £«££, -f -« «» out-
crop in the creek just off the bend in the road in the NW 1/4 SE 1/ 1 ••«•«•
A shear zone one foot wide, containing traces of fluonte, showed abnormal ,,
dioactivity in the field, but in the laboratory a sample from this zone tested
no higher than the other shale samples.

Miscellaneous Materials
Boulders of massive limonite up to one foot in diameter (sample 45) and
calcite and fluorite (sample 92) were only weakly radioactive.

MATERIAL SAMPLED IN OTHER HARDIN COUNTY LOCATIONS
In an attempt to find whether or not there is any definite association **•
dioactive anomalies with specific types of geologic phenomena, such as faul
ing or igneous activity, materials were sampled at various localities througl
out the Fluorspar -producing district of Hardin and Pope counties. The samp
included clays and shales from fault zones, residual clays from -disturb ed
limestone and sandstone, peridotite dikes and explosion breccias and ^clay.
overling them, ores of fluorspar, lead, and zinc, and concentrates from
ores. Results of tests on these samples are shown in table 3.

In general, of the types of clays sampled, only *ose from fault zone. •
ed more than very slight radioactivity. Clay sample 66 from the Rosiclare

URANIUM IN HARDIN COUNTY 9

system, clay sample 55 and shale sample 54 from t h~ td ♦

its outcrop along Route 146, a„d Mack shale slZ f S, ^ T?'
fluorspar prospect shaft on the Wolrab Mill fault near S™S \- n P * a

nearly twice background on the laboratorv d P *"" registe"d

sample 65 from the Rosiclare vein syttZ S?!,* C°Unt6r- ?°WeVer' Clay
side near the junction of the Wa^'lST^w/rtS h "? ** ^
radioactivity. otewart taults showed very slight

One occurrence of radioactive residual clav is «„ =>
burg sandstone on the Karbers Ridge road ThJ V "* '" *e Hardins

in a zone 6 to 12 inches thick in thT u radioactivity was concentrated

bedrock. Apparently this was a con ^ °yeS'duaI ^ *' fte t0? °f the sh^
that the source of the ra dioTtiv mat' , ¥ gr°Undwater- " « Possible
beds that occur at intervals in &eT r^ **' ^^^ ™S the black sl>ale
known in the ^ "^nit ^^t^^"™ .1 N° ^ *"

A bulldozer-cut in the M11«mT 1,1 W6re V1Sible in the outcrop.

from a stream cut on the strike of th, AT' P red °lay' no- 110>

of the outcrop was only ^tl^J^l^^ "8 ** 15° *« •«— •

.ng themZweTL^rto1:: r^ft^^8 ^ "" - *« cla^ overly-
table 3, the outcrrp tocaHties of Z ? Y' ■ addm°n t0 *' SampleS Sh°™ *
- Oeiger counter' ^^A^^^n.*:^^ *?«"*« ^

"tL-rrr burrows and by -^ ^ » -- rdneyP:hdditionai

Hot, the CavT;„ R0 lU°dL^Parct°reSdar C°"ateS '«« the Rosiclare dis-

- tested but sho::rv;ra^r ^io\uSyEmpire district in p- c°^

SUMMARY OF RESULTS OF ANALYSES

-al JetlmiL^ns T^^f^ S^ ^^ ^ *"" "* «*""

*al radioactivity of the sarnies e™ "ramum equivalent data indicate the

hus they indicate th anZn of uT " '"^ °f U3°8 (UraniUm °*ide>-

stances present. The cheLi a" det '■ T^ PlUS ^ ^ radi°active
dde. e chemical determinations of U308 show only uranium

\^Z£z^ix>5£r?? types of materiais tested a-

Ua underlain by Devoman ' ' J T»" fr°m exPosures *«hi. the

< u) those outsrd° hTs a;er TLrifr tAlbany shaie on Hicks dome <««• o.

* Albany area often is referred * ^T * 1S made because the Devonian-
'> dome." referred to popularly as the "dome" or as being "on

10 fLLINOIS STATE GEOLOGICAL SURVEY

The most radioactive materials are generally red and yellow clays It
^t the clays and breccias within the Devonian area are somewhat
appears that the clays and d elsewhere in the county, though

more radioactive *an "mUar ma teria J- ^ and lead ores> and

there are °°™^™J*™1 " £f™ J radioactivity. The U308 con-

rT:fa?isam;rststed0for both uranium equivalent and U308 was consid-
tent of all samples te , d algo was below the minimum

erably below the -^^^23^ Atomic Energy Commission,
of 0.1 percent on which prices are quoteu y

SOURCE OF RADIOACTIVE MATERIAL

The source of the radioactive material is an unsolved problem at the pre -
The source ° possible sources exist - sedimentary and hy-

Tth rTal The NewTlbany sha'le, which encircles and at one time covered
£S^p5%V -e offers a ^^-^1.
™?^^;^^7^^ of samples^ thro.

rderate ffisrss - jsr^s^^ - -^ -- i

?r» c".* a" Rol^clare fault systems may well be due to Hydrothermal

directly related to fluorspar mineralization.

The oresent radioactive concentrations give little hint as to the orig
the rad oa ^materials. As virtually all the ^o^^^J^
work the only radioactive materials exposed are clays and weathered chert
recci- Ve radioactivity in the clays is almost certainly due , toc«c« Ra-
tion by groundwater, judging from the concentrations in fissures and at ^ .u
face of the bedrock. The one occurrence of radioactive fault (?) breccia re
larded by some observers as the weathered outcrop of a hydrothermal vein
couMhav'e acquired its radioactivity from E"^"*^^^^
vesicular quartz cement or even from groundwater that may have deposited

"""The best evidence for a hydrothermal origin is in the distribution of : th.
mor f radioactive samples. Those inside the ring of ^^ ^Zs^Z
their radioactivity from the weathering of the shale but the three tSide (a
above) the shale more reasonably would be assumed to have ^T^"^
A8 there is no black carbonaceous shale within 1000 feet «*£*^^ ^ .
the lower Mississippian formations at the three localities, the weathering
drothermal veins is a likely source of the radioactivity

Only prospecting at deeper levels will determine whether there is any
ward exLLJof suspected veins, or whether the radioactive ~c«.«*^
merely concentrations by groundwater from the weathering of weakly

tive rocks.

URANIUM IN HARDIN COUNTY

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20

ILLINOIS STATE GEOLOGICAL SURVEY

Table 4. - Summary of Data for Samples within the
Devonian-New Albany Area

Uranium equivalent

u3o8

Material

No.
samples

Range

Av.

No.
samples

Range

Av.

Red clay

37

.000-. 144

.011

8

.002-. 014

.006

Yellow clay

5

.048-. 155

.108

5

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.010

Red and yellow

clay

2

.079

2

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Gray clay

1

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1

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Black shale

6

.005-. 024

.015

3

.005-. 007

.00*

Chert

4

.000-. 061

.018

1

.001

Chert breccia

14

.004-. 030

.010

4

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.00!

Explosion breccia

3

.002-. 008

.005

Peridotite dike

1

.003

Limonite

1

.008

URANIUM IN HARDIN COUNTY

Table 5. - Summary of Analyses of Samples outside the
Devonian-New Albany Area

21

Material

Red clay*

Yellow clay

Red and yellow clay

Black shale

jreen shale

3hert

"hert breccia

Explosion breccia

>eridotite dike

luorspar ore

inc ore

luorspar concentrate

inc concentrate

2 ad concentrate

Uranium equivalent
No. Range Av.

samples

.000-. 019 .003
.000-. 072 .019
.000-. 050 .010
.008
.002-. 008 .005
.000-. 002 .001
.000-. 008 .004
.000-. 007 .002
.000-. 021 .006
.000
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.000
.000

43

10
7
1

3

3

8
10

8

1

3
3
2
2

No.
samples

U3°8

Range Av.

.013

fitting sample 162, which was so high as to distort other data.

REFERENCES

Brown, J. S., Emery, J. A., and Meyer, P. A., 1954, Explo-
sion pipe in test well on Hicks dome, Hardin County,
Illinois: Econ. Geol., v. 49, p. 891-902.

Weller, J. M., Grogan, R. M., and Tippie, F. E., 1952, Ge-
ology of the fluorspar deposits of Illinois: Illinois Geol.
Survey Bull. 76.

ILLINOIS

jCaxd ofjCisicofri/

\

CIRCULAR 200

ILLINOIS STATE GEOLOGICAL SURVEY

URBANA