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AN OCCURRENCE OF AUTUNITE,

LAWRENCE COUNTY, SOUTH D AKOTA

By R. C. Vickers

Trace Elements Memorandum Report 559

UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

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otfFICA[ USE ONLY

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Geology - Mineralogy

This document consists of 15 pages, Series A

UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

AN OCCURRENCE OF AUTUNITE, LAWRENCE COUNTY

SOUTH DAKOTA*

R. C. Vickers

January 1953

Trace Elements Memorandum-Report 559

This preliminary report is distributed without editorial and technical review for conformity with official standards and no- menclature. It is not for pub- lic inspection or quotation.

*This report concerns work done on behalf of the Division of Raw Materials of the U. S. Atomic Energy Comission.

When separated from Part II, handle Part I as UNCLASSIFIED.

OFFICIAL USE ONLY USGS - TEM Report 559

GE OLOGY - MINERALOGY

Distribution (Series A) N of copies

American Cyanamid Company, Winchester . . ." . 1 ." Argonne National Laboratory ...... 1 ." Atomic Energy Commission, Washington...... " ." . 1 ." Battelle Memorial Institute, Columbus . . . .e . 1 Carbide and Carbon Chemicals Company, Y-12 Area ." . 1 ." ." Division of Raw Materials, Grants ...... 1 ." ." Division of Raw Materials, Denver ...... " . 1 ." Division of Raw Materials, Hot Springs. . . . ." . 1 ." Division of Raw Materials, New York ...... 0.0.0 ." ." .6 ." Division of Raw Materials, Salt Lake City . . ." ." .1 Division of Raw Materials, Richfield...... " ." .1 ." Division of Raw Materials, Butte...... " .1 ." Division of Raw Materials, Washington . . . . ." ." .e . 3 Dow Chemical Company, Pittsburg ...... 1 Exploration Division, Grand Junction Operations Office ." .1 Grand Junction Operations Office...... " .1 Technical Information Service, Oak Ridge. . . .6 Tennessee Valley Authority, Wilson Dam . . . . .1

U. S. Geological Survey: Mineral Deposits Branch, Washington . . . . . 1 Geochemistry and Petrology Branch, Washington . 1 Geophysics Branch, Washington ...... 1 Alaskan Geology Branch, Washington...... 1 Fuels Branch, Washington ...... a . 1 V. E. McKelvey, Washington...... " .1 L. R. Page, Denver...... 2 ." R. P. Fischer, Grand Junction ...... 1 A. E. Weissenborn, Spokane...... " . 1 J. B. Cathcart, Plant City...... " . 1 J. F. Smith, Jr., Denver...... " . 1 N. M. Denson, Denver...... " . 1 R. W. Swanson, Spokane...... " . 1 L. S. Gardner, Albuquerque...... " .1 J. D. Love, Laramie ...... 1 ." A. H. Koschmann, Denver ...... 1 E. H. Bailey, San Francisco ...... 1 .s A. F. Shride, Tucson...... 1 W. P. Williams, Joplin...... " . 1 ." C. E. Dutton, Madison ...... 1 R. A. Laurence, Knoxville ...... 1 R. J. Roberts, Salt Lake City ...... 1 TEPCO, Washington ...... 5 (Including master)

58 J

CONTENTS

Page

Abstract ...... 4

Introduction ...... 0 0 -* 5

Location and accessibility...... 0 ...... 0 6

History of the property . 6

General geology...... 8 . ." ." ." ." ." ." ." ." ." ." ." ." ." ." ." Uranium deposits . . . . . 8 . ." ." ." ." ." ." ." ." ." ." ." ." ." ." ."

Mineralogy * . . . . . 10

Ore bodies ...... 12

Origin ...... 0 ...... 0 13

Conclusions ...... 0 . . 0 . . 0 . . 0 - 0 13

Literature cited ...... 14

ILLUSTRATIONS

Figure 1. Index maps showing location of the autunite prospect, Lawrence County, South Dakota ...... 7

2. Geologic map and cross section of the autunite prospect, Lawrence County, South Dakota . . . . 9

TABLES

Table 1. Radiometric and chemical analyses of samples from the autunite occurrence, Lawrence County, South Dakota ...... 11

2. Semiquantitative spectrographic analyses of siltstone samples from the autunite occurrence, Lawrence County, South Dakota...... 11 .

AN OCCURRENCE OF AUTUNITE, LAWRENCE COUNTY,

SOUTH DAKOTA

By R. C. Vickers

ABSTRACT

In July 1952 an occurrence of autunite was found in the northern part of the Black Hills, Scuth Dakota, during a reconnaissance for radioactive deposits.

The autunite occurs as fracture coatings and disseminations in siltstone of the Deadwood formation of Cambrian age and is concentrated mainly in the lower 2 feet of the siltstone at the contact with an intrusive rhyolite porphyry; the radioactive zone is exposed in two old workings which are 90 feet apart. An 18-inch vertical channel sample of the autunite-bearing siltstone contained 0.048 percent uranium. The gangue minerals are fluorite and limonite.

The uranium is believed to have been introduced into the siltstone by solutions of magmatic origin that migrated along the lower contact of the siltstone after or during emplacement of the porphyry. 5

INTO ODUCTICN

Uranium minerals have been reported in the northern Black Hills by several authors. Uranium was first mentioned by Scott (1897), who reported a uranium mineral with the composition of zeunerite from the

Poisoned Ox mine near Pactola, Pennington County, S. Dak. and along

Annie Creek at Carbonate, Lawrence .County. O'Harra (1902, p. 78) states:

"Uranium rinerals have been observed in various places, par- ticularly in the Poisoned Ox mine near Pactola and in the Davier mine on Anna Creek near Portland. Uranium is also reported as occurring near Carbonate. At the Poisoned Ox mine:the minerals occur with copper in slates. In the Anna Creek property it is intimately associated with porphyry. At the latter place effort has been made to obtain the mineral in commercial quantities, but as yet success has not been attained".

Ziegler (1914, p. 206) described autunite from an occurrence in the phonolite porphyries on Annie Creek west of Portland, Lawrence County,

S. Dak. His description follows:

"...crystals are very rare, and the autunite usually occurs as a very thin micaceous coating or a series of thin irregular shaped flakes or as a number of small partially radiating moss- like aggregates, coating minute fissures in the porphyries. The cleavage is excellent, yielding thin brittle laminae of a lemon-yellow color which are weakly transparent. The luster varies from dull silky to adamantine, while an occasional square crystal shows pearly luster. The streak is deep yellow, the hardness about equal to the finger nail, and the specific gravity 3.07. It is associated with limonite and a little fluorite."

Although specimens of autunite from the northern Black Hills may be seen in the museum at the South Dakota School of Mines, Rapid City, S. Dak., no mention has been made of the Annie Creek occurrence, so far as known, since Ziegler's report in 1914.

Because of these reported occurrences of radioactive minerals, a radiometric reconnaissance of the mining districts of the northern Black Hills was conducted by the U. S. Geological Survey during July 1952 on behalf of the

Division of Raw Materials of the U. S. Atomic Energy Commission. During this investigation an occurrence of autunite was found in the Annie Creek area near

Trojan, Lawrence County, S. Dak.

The autunite observed by O'Harra (1902, p. 78) and Ziegler (1914, p. 206) is described as occurring as thin coatings on fissures in porphyry, whereas the autunite described in this report is in siltstcne. It is the writer's belief, therefore, that although both occurrences are in the same general area, they probably are not the same deposit.

Location and accessibility

The autunite occurrence is 5 miles west of Lead in the Bald Mountain mining district, Lawrence County, S. Dak., in sec. 3, T. 4 N., R. 2 E.,

Black Hills Meridian (fig. 1). The property may be reached by following the abandoned Chicago, Burlington, and Quincy railroad grade north from Elmore,

S. Dak., about 2 miles to the end of the railroad fill that crosses Annie

Creek, and then proceeding by foot along the abandoned Annie Creek road for a distance of about two-thirds mile to the first gulch on the right northeast of Lost Camp Gulch. From there proceed N. 700 E. up the bare ridge, on the southeast side of Annie Creek, a distance of about one-third mile to the prospect (fig. 1).

History of the property

The property was located about 1890 for gold and silver. Fluorite, and to a lesser extent uranium minerals, are associated with some of the gold ores 7 UNITED STATES DEPARTMENT TRACE ELEMENTS MEMORANDUM OF THE INTERIOR REPORT 559 GEOLOGICAL SURVEY

SOUTHHLAWRENCE L LAWRENCE Deadwood I T Lead DAKOTAA AREA OF LI__MD E TA ILED COUNT Y

T5N . T5N. T 4 N. Trojan

PROSPECT4.' 6 6 FOLEY MTN C PEAK sc.0TERRY

Elmore

0 I Mile Lead SCALE To Cheyenne Crossin US585 5 miles

Figure I-Index maps showing location of the autunite prospect, Lawrence County, South Dakota.

GPO 82-8000898 of Tertiary age in the Bald Mountain mining district, and the presence of fluorite and autunite on the property probably encouraged the owners to explore the prospect further. There is no reported production from the property, and the workings were probably abandoned soon after the underground work failed to show any gold or silver.

The prospect is on patented ground believed to be owned by the Annie

Creek Mining Company, but it was relocated for uranium by L .J. Bisch,

R. B. Sherman, 0. B. Sherman, and F. S. Budzynski on July 4, 1952. The re-location consists of a claim notice posted at the portal of the adit.

GENERAL GOLOGY

The autunite occurrence is in an area of widespread Tertiary igneous activity in the northwestern part of the Black Hills uplift. The rocks in the vicinity of the property are sandstones, siltstones, and shales of the

Deadwood formation of Cambrian age, which have been intruded and displaced by several sills and laccoliths.

In the immediate vicinity of the prospect a 30-foot thick bed of nearly flat-lying siltstone of the Deadwood formation is overlain by rhyolite and underlain %gy rhyolite porphyry (fig. 2). The siltstone is composed mainly of angular to subangular quartz grains, averaging 0.05 mm in length, and interstitial carbonate, which is distributed unevenly through the rock.

URANIUM DEPOSITS

A radiometric traverse of the property using a Geiger counter showed abnormal radioactivity on the dump of the underground workings and at the two prospect pits northwest of the adit. Autunite was observed in the q/ UNITED STATES DEPARTMENT OF THE INTERIOR TRACE ELEMENTS MEMORANDUM GEOLOGICAL SURVEY REPORT 559 \+ + + + + EXPLANATION + + + + tkr \ + 4- 6' 6?O Rhyolite + + + ai \Prospect SL-77-52 6N2 + + o ' Pit No. 1 0.037; 0.016 0 ' Q Rhyolite porphyry '0

6 Dump ro U a o -a LI Deadwood formation -v \o S L-76 -52 Siltstone 0.012; 0.004 0 p O \ ;L SL-75-52 o , ,0.059; 0.048

4 O ~~Under ground ,;.,' 6 work ingsi SL-78-52 Approximate contact S0.00 8; 0.004 SL-74-52 0 6rospe ct 0. 03; 0.02 N Pit No.2 6? 0' O Portalofodit Sample location Leader dashed where underground Shows percent Q Dum p equivalent uranium and percent uranium.

-SL-74-52 0.030; 0.020 Strike and dip of beds

o6260611'

Tape and compass map, July 1952 Geology by R.C.Vickers and Jacob Freedman. SL-77-52 A Pit No. I 0.037; 0.016 Inferred autunite- bearing zone A' SL-75-52, 0.059;0.048

0 lj'- p O - 0.008; 0.004 0 30 Feet Contour interval 20 feet. Deb ris ;a. Datum is assumed

Figure 2.-Geologic map and cross-section of the autunite prospect, County, South Dakota. Lawrence GPO 82-8000898 10 underground workings and on the large dump. The results of radiometric and

chemical analyses of the samples collected are given: in table 1. The sample

localities are shown in figure 2.

The workings consist of a partly caved adit, about 45 feet long, a 10-

foot winze, and several prospect pits. The adit was driven about 1 foot

above, and parallel to, the contact of the Cambrian siltstone with the underlying porphyry. The winze, now partly filled with debris, extends

through the siltstone and into the porphyry.

Mineralogy

Autunite, the only uranium mineral recognized at the property, is apple-

green and highly fluorescent; it forms finely crystalline masses and well-

crystallized plates as much as 5 mm in length. The gangue minerals are purple fluorite and limonite. Semiquantitative spectrographic analyses of four samples (table 2) indicate that minor quantities of cesium, cobalt, molybdenum, niobium, lanthanum, and tin are concentrated in the mineralized

siltstone relative to their concentrations in unmineralized siltstone.

Thin sections of the autunite-bearing siltstone show that the quartz grains and the interstitial carbonate have been corroded and embayed by autunite and fluorite. The fluorite occurs mainly as small veinlets as much as 3 mm thick that cut the siltstone and as small irregular replacements with distinct crystal outlines. 11

Table 1.--Radiometric and chemical analyses of samples from the autunite occurrence, Lawrence County, South Dakota. *

Equivalent Field uranium Uranium number (percent) (percent) Remarks

SL-74-52 0.030 0.020 Composite dump sample

SL-75-52 0.059 0.048 18-inch vertical channel sample of autunite- bearing siltstone

SL-76-52 0.012 0.004 Rhyolite porphyry from winze, Grab sample

SL-77-52 0.037 0.016 Grab sample of siltstone from dumo of prospect pit iael -

SL-78-52 0.008 0.004 Grab sample of siltstone, prospect pit no. 2

* U. S. Geological Survey Trace Elements Laboratory, Denver, Colorado.

Table 2.--Semiquantitative spectrographic analyses of siltstone samples from the autunite occurrence, Lawrence County, South Dakota.*

Field Chemical number Ce Co io Nb La Sn uranium

SL-74-52 00x o.ox .ox 0.020 SL-75-52 OX 000x ...00x 000x ox .oQox .048

SL-77-52 .ooox ox .000x 00x .016 SL-78-52 .004

* U. S. Geological Survey Trace Elements Laboratory, Denver, Colorado. 12

The abundance of limonite associated with the fluorite and autunite

suggests that pyrite is present in the unoxidized material and that the

autunite has resulted similarly by the oxidation and alteration of a

primary uranium mineral, possibly pitchblende.

Ore Bodies

The autunite is concentrated mainly in the lower 2 feet of the Deadwood

siltstone exposed in the adit and is believed to form a tabular, essentially

flat-lying deposit in the siltstone just above the porphyry contact (fig. 2).

An 18-inch vertical channel sample (SL-75-52), cut just above the porphyry-

siltstone contact, contained 0.059 percent equivalent uranium and 0.048

percent uranium. A grab sample of porphyry from the winze (SL-76-52)

contained 0.012 percent equivalent uranium and 0.004 percent uranium, which

is similar to the radioactive content of other similar porphyries in the northern Black Hills.

Prospect pit 1, 90 feet northwest of the portal, may be an old caved

shaft that reached the autunite zone. (See cross section, fig. 2.) A grab

sample of siltstone from the dump of this prosect (SL-77-52) contained 0.037 percent equivalent uranium and 0.016 percent uranium. No autunite was observed on this dump, but abundant limonite and fluorite were present.

Slight abnormal radioactivity was detected in siltstone at prospect pit no. 2, 20 feet east of the portal, and a grab sample (SL-78-52) analyzed

0.008 percent equivalent uranium and 0.004 percent uranium.

The difference between equivalent uranium and chemical uranium in the siltstone samples suggests that some oxidation and leaching have occurred and that the near-surface samples analyzed are probably lower in uranium content than unoxidized material. 13

The extent of the autunite zone is not known accurately becase of the lack of suitable exrosures in the area. The zone probably extends continuously from the exposures in the underground workings to the mineralized siltstone encountered in pit no. 1.

Origin

The writer believes, because of the spatial relations of the uranium minerals to the porphyry sill, that the uranium was introduced into the siltstone by hydrothermal solutions that moved along the contact between the siltstone and the underlying prophyry. The fractured siltstone near the contact with the lower porphyry, which may be the result of movement along the contact produced after or during the emplacement of the porphyry, formed a permeable zone through which the ore-bearing solutions could migrate. These solutions probably were related to a late stage of hydrothermal activity that accompanied the intrusion of the porphyries.

CONCLUSIONS

The occurrence of autunite associated with the Tertiary intrusive activity in the northern Black Hills suggests that the area should be considered as a possible source of uranium deposits. Although the deposit described in this report is not of ore grade, additional prospecting. in the area might disclose higher grade deposits or sufficient tonnages of lower grade material to make mining profitable.

This occurrence of autunite confirms one of the uranium mineral localities mentioned in the literature, and additional prospecting could very well confirm other uranuim-bearing localities that have been reported in the literature on the northern Black Hills mining area before 1915. 14

LITERATURE CITED

O'1arra, C. C., 1902, Mineral resources of South Dakota including mineral wealth of the Black Hills: South Dakota Geol. Survey Bull. 3.

Scott, S. E., 1897, Map of the Black Hills of South Dakota and Wyoming with full descriptions of mineral resources; Philadelphia, E. P. Noll Company.

Ziegler, Victor, 1914, The minerals of the Black Hills: South Dakota School of Mines Bull. 10. OFFICIAL USE ONLY

USGS TEM - 559 Part II

RESERVES

Because of the lack of geologic data and exposures, the reserve estimates are in the inferred category. Inferred reserves are estimated at 100 tons of autunite-bearing siltstone containing 0.05 percent uranium and 1,000 tons containing 0.02 percent uranium. The ore reserves are based upon an assumed thickness of 2 feet; the autunite-bearing layer is assumed to extend from the underground workings to prospect pit no. 1, a distance of 90 feet, and to extend an average of 90 feet laterally into the hill (fig. 2). A factor of

14.5 cu. ft. of siltstone per short ton was used in the computation.

PLANS AND RECOMMENDATIONS

The presence of autunite in the northern Black Hills indicates a potential new area of uranium deposits. Because little is known concerning this type of deposit in the northern Black Hills and because of the possibility of finding higher grade deposits or large tonnages of lower grade material, geologic mapping will be carried on at a scale of 1/1200 in the 1/2 sq. m. surrounding the deposit in order to appraise the tonnage and grade of the autunite-bearing rock present, to study the geologic relationships of the occurrence in order to apply the geology to other favorable areas in the northern Hills, and to make a detailed radiometric reconnaissance in the vicinity of the occurrence to extend the limits of the autunite zone and to find new deposits.

This work is covered in our Work Plan and Budget for fiscal year 1954.

No physical exploration is planned at this time.

OFFICIAL USE ONLY