Inferred Relationship of 

Some Uranium Deposits 

and Calcium Carbonate 

Cement in Southern 

Black Hills, South Dakota

GEOLOGICAL SURVEY BULLETIN 1046-A

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

Inferred Relationship of 

Some Uranium Deposits 

and Calcium Carbonate 

Cement in Southern 

Black Hills, South Dakota

By GARLAND B. GOTT

CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

GEOLOGICAL SURVEY BULLETIN 1046-A

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956
UNITED STATES DEPARTMENT OF THE INTERIOR 

Fred A. Seaton, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D. C. - Price 15 cents (paper cover)
CONTENTS

Page

Abst ract __________________________________________________________ 1

Introduction. _ ____________________________________________________ 1

Planning of exploration_____________________________________________ 1

Results of exploration._____________________________________________ 5

Conclusions-_ _ _______________________ 8

Literature cited- __________________________ 8

ILLUSTRATIONS

Figure 1. Calcium carbonate cemented sandstone______________________ 2

2. Thermoluminescence of specimen shown in figure 1______.,__^ 3

3. Map showing distribution of carbonate cement and uranium

deposits in channel sandstone, Fall River County, S. Dak___ 4

4. Map showing channel sandstone, distribution of carbonate 

cement, and location of diamond-drill holes in parts of the 

Edgemont XE and Edgemont quadrangles, Fall River County, 

S. Dak_.._.___._____"__._.___.__._.__.____._..____-_-__ 6

CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INFERRED RELATIONSHIP OF SOME URANIUM

DEPOSITS AND CALCIUM CARBONATE CEMENT IN

SOUTHERN BLACK HILLS, S. DAK.

By GARLAND B. GOTT

ABSTRACT

Evidence resulting from geologic mapping in the southern Black Hills indicates 

that the areas marginal to some of the larger carbonate-cemented sandstones 

are a favorable geochemical environment for the localization of uranium deposits. 

To determine whether these favorable environments are predictable, a limited 

experimental core-drilling program was carried out. An extensive deposit was 

discovered in an area marginal to a sandstone well-cemented with calcium carbonate. The deposit has not yet been developed, but from the available data 

it appears that there is a significant quantity of mineralized rock present containing as much as 3.0 percent eU3Og.

INTRODUCTION

The V. S. Geological Survey is currently carrying on geological 

investigations in the southern Black Hills under the sponsorship of 

the Division of Raw Materials of the IT. S. Atomic Energy Commission. Principal emphasis has been placed on determining the interrelationships among; structure, lithology, and geochemical environment 

that favor the localization of uranium, [t is the purpose of this 

report to set forth preliminary information on the possible relationships between carbonate cements and uranium deposits, and the 

possible use of these relationships as a guide for prospecting for concealed deposits in the southern Black Hills. Although any conclusions based on this information must be tentative, the results to date 

are encouraging and, therefore, of interest to those engaged in the 

search for uranium deposits.

The results reported here are in part based on work by R. W. 

Schnabel, E. V. Post, Henry Bell, III, and D. A. Brobst,

PLANNINO OF EXPLORATION

A large proportion of the uranium deposits in the southern Black 

Hills occurs in the areas of maximum change in chemical and physical 

characteristics of the sandstones of the Inyan Kara group of Early 

Cretaceous age. The interrelationships between changes of structure,

1
2 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

lithology, permeability, and geochemical environment appear to have 

been influencing or controlling factors in the localization of many of 

the deposits. As a result of detailed geologic mapping some inconclusive evidence has been found that suggests that one of the favorable 

geochemical environments is in transitional areas between carbonaterich and carbonate-poor sandstones.

The inference that uranium is associated with calcium carbonate 

cements has also been suggested by the pattern of the thermolumiFIGURE 1. Calcium carbonate cemented specimen.

nesceiice of the cements. For a general reference on the techniques 

used in thermoluminesceiice studies see Daniels and others (1953). 

Although much basic work is needed before the significance of this 

phenomenon can be evaluated, the banded and concretionary-like 

patterns in the carbonate cements are suggestive. The pattern of 

thermoluminescence displayed by nodular-shaped masses of sandstone 

tightly cemented with calcium carbonate is illustrated in figure 2; 

figure 1 shows a specimen of tightly carbonate cemented sandstone, 

and figure 2 shows the distribution of thermoluminescence in the
URANIUM AND CALCIUM CARBONATE CEMENT IN BLACK HILLS 3

same specimen. Although in figure 1, the distribution of cement 

seems to be uniform, the banded pattern of thermoluminescence in 

figure 2 indicates that the cementation was brought about through 

various stages of concretionary growth arid finally by coalescing of 

the nodular-shaped masses.

According to Leverenz (1950), thermoluminescence of crystals is 

proportional to radiation damage. However, the significance of 

alternating thermoluminescent and nonthermoluminescent bands

FIGUKE 2 Thermoluminescence of specimen shown in figure 1.

seems to be open to two interpretations. First, if trace amounts of 

other elements are present in the calcite crystal lattice, the electron 

banding in the lattice may be so changed as to permit greater radiation 

damage for a given amount of radiation. Thus, the intensity of 

thermoluminescence might reflect the distribution of impurities in 

the calcite. Alternatively, if the intensity of thermoluminescence is 

proportional only to the distribution of the radiation source uranium 

and (or) its decay products - the banded pattern of thermoluminescence shown in figure 2 could reasonably be interpreted to mean
4 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

that the solution depositing the calcium carbonate cement also precipitated variable amounts of uranium and (or) its decay products 

Thus, calcium carbonate cement that exhibits variable or banded 

thermoluminescence would suggest that the original solution from 

which carbonate was precipitated also carried uranium, and further 

that such thermoluminescent calcium carbonate, whether banded or 

not, characterizes rocks through which uranium-hearing solutions 

have moved.

EXPLANATION

Channel boundary, covered 

in part by younger rocks

FIGVBE 3. Map showing distribution of carbonate cement and uranium deposits in channel sandstone,

Fall River County, S. Dak.

To test the inference that a significant concentration of uranium 

should be found marginal to a sandstone that is tightly cemented with 

Calcium carbonate, limited exploration by core drilling was done 

where detailed geologic mapping showed an area in which carbonaterich sandstone graded into a carbonate-poor sandstone.

A sandstone-filled channel in rocks of the Iiiyan Kara group had 

been delineated by detailed surface mapping over a distance of about
25 miles from the southern part of the Flint Hill quadrangle to the 

southeastern part of the Harney Peak 3 SW quadrangle (fig. 3). 

Throughout this distance the channel has been scoured as much as 

100 feet through or into a sequence of varigated impervious mudstones. 

The sandstone is fine- to coarse-grained, normally noncarbonaceous, 

poorly sorted, of extremely variable texture, and cross stratified. 

The normal type of cross stratification consists of tabular sets of very 

thinly bedded cross strata from a few inches to two or three feet thick 

separated by 1- to 2-inch thick horizontal strata. The cross strata 

generally dip to the northwest. Along most of the length of this 

channel evidence has been found that indicates that the deepest 

scour was completely filled and that the stream-borne material was 

then spread out over a relatively wide plain, in some places several 

miles wide.

As shown on figure 3 the channel sandstone is in places cemented 

with calcium carbonate, the most extensive cementation being in the 

southwestern part of the Edgemont NE quadrangle (fig. 4). Because 

of the extent of the carbonate cement, this area was selected for the 

experimental drilling. The sandstone is well cemented where exposed 

in the northwestern part of this area in sees. 26, 27, and 35, T. 7 S., 

R. 2 E., but for a distance of 3% miles to the southeast it is buried 

beneath younger rocks. Where the sandstone is again exposed in 

sec. 8, T. 8 S., R. 3 E., it is relatively free of carbonate cement. The 

immediate objective of the core-drilling, therefore, was to determine 

the limits of the abundant carbonate cement and the inferred presence 

of uranium in the area marginal to the area of abundant carbonate.

RESULTS OF EXPLORATION

As a result of exploration within this area, the buried portion of the 

channel and the extent of the carbonate-rich part of the sandstone 

were approximately delineated (fig. 4). Within the buried portion of 

the channel the sandstone was found to be carbonate-free or carbonatepoor through sec. 1, T. 8 S., R. 2 E. Drilling at GS-5, GS-16, and 

GS 17 penetrated the channel sandstone in the carbonate-poor 

segment. GS-16 penetrated ore-grade uranium in the top part of the 

channel sandstone and GS-5 and GS-17 were barren. GS-10 evidently penetrated the channel sandstone near the southeast margin 

of the carbonate-poor segment and showed low-grade uranium of 

similar mineralogy to that found in GS-16. GS-11, GS-13, and GS14 farther to the east penetrated heavy carbonate cementation and 

were barren. GS-18 penetrated only an insignificant amount of 

carbonate cement and was also barren of ore-grade material although 

very sparsely disseminated black uranium minerals were found in the 

core. The results of the drilling are summarized in the table below.
EXPLANATION

Outcrop of channel sandstone

Area of carbonate cement

Boundary of deepest part of channel, 

dashed where approximately located

Fault, dashed where approximately located.; 

U, upthrown side; D, downthrown side

Diamond-drill hole

DECLINATION I95O

Geology by G.B.Gott, R. W. Schnabel and J. D. Ryan, 1953 to 1956 

1 Mil?

O5

FIGURE 4. Map showing channel sandstone, distribution of carbonate ccrnont, and location of diamond-drill holes in parts of Edgcmont NE and Edgcmont quadrangles, Fall

River County. S. Dak.
URANIUM AND CALCIUM CARBONATE CEMENT IN BLACK HILLS

Gamma-ray log interpretation 

[No casing used]

OS hole no.

2. _..-__ _______ _________ _________

4. _ ______

6__ ___________________ _ _ _________

10 - . - -- -- -::-

15 __________________________________

16 ---- -_- -_----_ - -

17.._ ____________________________

Hole logged 

at depth 

indicated 

(feet)

11.0-157.3

10. 4-183. 0

Anomaly 

detected 

at depth 

indicated 

(feet)

118.3-121.5

124. 5-125. 2 

128. 1-129. 0 

129.0-133.3

114.6-115.4 

116.0-117.5 

117. 5-120. 7 

120. 7-121. 9 

123. 3-124. 3 

124.3-125.5 

125. 5-128. 2 

169.1-170.4

Zone of 

anomaly 

(thickness 

in feet)

3.2

.7 

.9 

4.3

.8 

1.5 

3.2 

1.2 

1.0 

1.2 

2.7 

1.3

Counts per 

minute

300

300 

200 

1,300

800 

2,400 

540 

1,300 

7,900 

1,000 

300 

800

Grade 

(percent) 

eUsOs

<0. 005

<.010 

<.005 

.026

040

.029 

.058 

.011 

.030 

.35 

.023 

<.010 

.022

Polished thin sections of the mineralized core from GS-16 contain 

fine-grained uraninite in aggregates 1 2 mm in length associated 

with pyrite, iron oxides, calcite, and clay minerals. The aggregates 

of uraninite are concentrated around pods of green pyritic clay in a 

quart zose sandstone. The pyrite near the margins of the pods is 

euhedral in contrast to the massive pyrite within the pods. The relations of the minerals suggest that the pods of pyritic clay were formed 

in place before deposition of the uraninite. The occurrence of massive 

and euhedral pyrite suggests two generations of pyrite, the euhedral 

type originating, perhaps, at the time of deposition of the uraninite. 

The relative ages of the pyrite and calcite are not clear. The iron 

oxides were deposited after the pyrite. The close association of all of 

these minerals interstitial to the quartz grains suggests that they are 

essentially contemporaneous.

In addition to the minerals listed above, black prismatic crystals 

of a uranium mineral were found in rotary cuttings from a privately 

drilled hole located near GS-16. The crystals are less than 1 mm in 

length and yield a positive reaction in the flux test for uranium. 

Under the microscope, the crystals are seen to be dark red, and to have 

high birefringence, an index of refraction greater than 1.80 and parallel 

extinction. The crystals are combustible and are insoluble in acid. 

The X-ray diffraction pattern is not similar to those of the wellknown dark uranium minerals. Quantitative spectrographic analyses 

show that the material contains 3 percent of uranium and 44 percent 

of vanadium. The combustibility of this mineral indicates that it is 

most probably one of the organo-metallic compounds.
8 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

After completion of government exploration, private drilling in the 

vicinity of core hole GS-16 (fig. 4) extended the deposit found by the 

Geological Survey, and revealed two additional deposits, one of which 

contains a significant amount of mineralized rock with as much as 3.0 

percent eU3O8 .

CONCLUSIONS

A possible relationship between the relative abundance of calcium 

carbonate as a cementing material and the concentration of uranium 

seems to have been confirmed by the results of this preliminary 

exploration. As inferred, uranium is concentrated in carbonate-poor 

sandstone marginal to sandstone tightly cemented by calcium carbonate.

If this relationship has a general validity, it should be possible to 

locate similar deposits by selecting areas for prospecting where poorly 

cemented and friable sandstone grades into hard, tightly cemented 

calcareous sandstone.

LITERATURE CITED

Daniels, Farrington, Boyd, C. A., and Saunders, D. F., 1953, Thermoluminescence

as a research tool: Science, v. 117, p. 343-349. 

Leverenz, H. W., 1950, Introduction to the luminescence of solids: New York,

John Wiley and Sons.

o