GEOLOGICAL SURVEY CIRCULAR 321 

OCCURRENCES OF URANIUM-BEARING 

MINERALS IN THE ST. KEVIN DISTRICT 

LAKE COUNTY, COLORADO 

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 DEPARTMENT OF THE INTERIQR 

Douglas McKay, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

GEOLOGICAL SURVEY CIRCULAR 321 

OCCURRENCES OF URANIUM-BEARING MINERALS IN THE 

ST. KEVIN DISTRICT, LAKE COUNTY, COLORADO 

By C. T. Pierson and Q. D. Singewald 

This report concerns work done on 

behalf of the U. S. Atomic Energy 

Commission and is published with 

the permission of the Commission. 

Washington, D. C., 1954 

Free on application to the Geological Survey, Washington 25, D. C. 

OCCURRENCES OF URANIUM-BEARING MINERALS IN THE 

ST. KEVIN DISTRICT, LAKE COUNTY, COLORADO 

By C. T. Pierson and Q. D. Singewald 

CONTENTS 

Page 

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

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Purpose, scope, and acknowledgments.... 2 

Geography: . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

.Page 

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

Radioactivity measurements. . . . . . . . . . . . . . . . . . . 4 

The uranium occurrences. . . . . . . . . . . . . . . . . . . . . 16 

Unpublished reports. . .. . . . . . . . . . . . . . . . . . . . . . . . 17 

ILLUSTRATIONS 

Page 

Figure 1. Index map of Colorado. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

2. Geologic map of Sugar Loaf and St. Kevin districts........................................... 3 

3. Adit showing locality 117 . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

4. Adit showing localities 118, 119, 120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

5. Lower Wilkes barre adit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

6. Radioactivity in the St. Kevin district.. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13 

7. Radioactivity in part of St. Kevin district (detailed)........................................... 14 

8. Radioactivity in the Sugar Loaf district. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

TABLE 

Page 

Table 1. Radioactivity anomalies, Sugar Loaf-St. Kevin district....................................... . 7 

ABSTRACT 

Two hundred and seventy-one prospect pits, 

mine dumps, or mine workings within the Sugar Loaf 

and St. Kevin mining districts and vicinity, were 

tested for radioactivity by the U. S. Geological Survey 

in 1951 during six weeks of investigation on behalf of 

the Division of Raw Materials of the U. S. Atomic 

Energy Commission. One hundred and twenty-two 

weak radioactivity anomalies were found in the 

St. Kevin district and vicinity, and eight slight 

anomalies were noted in the Sugar Loaf district, which 

adjoins the St. Kevin district on the south. Most of 

the radioactive anomalies were found in pre-Cambrian 

igneo~s and metamorphic rocks, but some were found 

in metalliferous veins of Tertiary age. Samples of 

altered granite or schist contain as much as 0. 065 percent uranium, -probably in the form of secondary 

uranium minerals. Samples of vein material 

contain as much as 0. 013 percent uranium, also 

probably in the form of secondary uranium 

minerals. 

1 

At only a few localities has the identity of the 

uranium-bearing minerals been determined. Torbernite, 

associated with turquoise, malachite, and chrysocolla, 

occurs as disseminations and fracture coatings in altered granite at the Josie May turquoise mine; 

metatorbernite is disseminated in granite at the 

Turquoise Chief mine. Commonly the limonite-stained 

fractures in the altered granite and schist are radioactive; metatorbernite has been identified in limonite 

stain at one locality. A uranium-variety of florencite, 

a hydrous cerium aluminum phosphate, is disseminated 

in the granite on the dump of a mine just west of the 

St. Kevin district, and autunite(?) is disseminated in 

fine-grained, highly silicified rock in the northeastern 

part of the St. Kevin district. 

None of the uranium occurrences is of commercial 

importance. They are for the most partin nonglaciated 

terrane, which has been subjected to a very long period 

of weathering. Thus, chemical leaching. within the 

zone of weathering may have greatly reduced the 

uranium content of material near the surface, and 
occurrences of even small quantities of secondary 

uranium minerals might be related to stronger 

concentrations of primary minerals at depth. 

INTRODUCTION 

Purpose, scope, and acknowledgments 

A radioactivity reconnaissance of the St. Kevin mining district, an outlying area immediately to the west, and 

the northern part of the adjoining Sugar Loaf mining district, 

Lake County, Colorado, was made in 1951 by the Geological 

Survey on behalf of the Division of Raw Materials of the U. S. 

Atomic Energy Commission. The reconnaissance was 

undertaken because in 1951 torbernite was identified in several samples previously collected by Singewald. Theresults of the reconnaissance provide a preliminary appraisal of the frequency, magnitude, and distribution of 

radioactivity anomalies, and their significance. 

The field work was done during the summer of 

1951 byQ. D. Singewald, C. T. Pierson, J. W. Mytton, 

V. R. Wilmarth, R. C. Vickers, and D. L. Peck. 

Examinations for radioactivity were made of most 

of the prospect pits, mine dumps, and accessible mine 

workings in the St. Kevin district and in the region 

109° 108' 

• 

j 

I 0 0urango 

I 

370 I ,------- ; NEW MEXICO 

50 0 

I I I I I I 

adjoining the district on the west. Fewer tests 

were made in the Sugar Loaf district because the 

general level of radioactivity was low. 

Samples were taken at most localities that 

exhibited radioactivity greater than 3 times backgrounc' 

count, but only a few were taken at the weakly radioactive localities. 

The writers are indebted to J. M. Kleff of 

Leadville for courtesies extended during the 

examination of the Lakewood mine, and also to 

George S. Casey of Leadville, who generously contributed information and a map of the Wilkesbarre mine. 

Geography 

The Sugar Loaf and St. Kevin districts (figs. 1 

and 2) are separated by Lake Fork Creek, and are on 

the eastern flank of the Sa watch range, and 4 to 7 miles 

west-northwest of Leadville, the county seat of Lake 

County. The districts are reached by good secondar'y 

roads from Leadville, and, within the districts, most 

of the mines are accessible by moderately good 

to poor mountain roads. The relief is about 1, 400 feet; 

altitudes range from about 9, 700 feet to more 

than 11, 000 feet. 

QColorado Springs 

IOOMiles 

I 

Burlington0 

I 

i 

: _____ j 

OKLAHOMA 

Figure 1. -Index map of Colorado showing location of Sugar Loaf and St.. Kevin districts. 

2 
EX PLANATION 

Granite 

W%1J Schist and gneiss 

Contact --between granite, 

schist and gneiss 

DasMd wll~rs int.rrsd 

~0 

Strike and dip of foliation 

'*('75 ... 

Vein showing dip 

Ooshed where in""ed 

+ Comer of section 

Figure 2. -Generalized geologic map of the Sugar Loaf and St. Kevin district, Lake County, Colorado, showing 

vein pattern. 

3 
GEOLOGIC SETTING 

The geology of the Sugar Loaf and St. Kevin 

districts has . oeen studied by Singewald (in preparation), and the following is abstracted from 

his report. The bedrock (fig. 2) is composed 

mainly of pre-Cambrian rocks including schist 

and gneiss of the Idaho Springs formation(?), 

the Silver Plume(?) granite, and minor pegmatites, 

but dikes and irregularly shaped bodies of Tertiary 

igneous rock, tentatively correlated with the 

White porphyry of the Leadville district, occur 

locally. Most of the area is nonglaciated; however, Lake Fork Creek occupies a glacial valley. 

Unconsolidated deposits consist of moraine, outwash 

gravel, alluvium, and gravel. 

Only the schist and gneiss, mapped as a unit, 

and the granite, which approaches quartz monzonite 

in composition, are shown in figure 2. All types of 

bedrock have been intensely sericitized, and, locally, 

silicified adjacent to fissures. One important effect 

of silicification has been the development of chert 

"dikes" and 11 dike 11 zones and also of "chert 

disseminations 11 consisti~g of innumerable chert 

veinlets irregularly distributed through the country 

rocks. 

During the Laramide orogeny the area of 

the Sawatch Range was folded into a broad, 

EXPLANATION 

~ 

60 --

- Fault showing dip, 

dashed where opproxi.mately locoteti 

Outline of workings· 

"-117 

Rod iaactive locality 

and number 

I 

anticlinal arch trending north-northwest, and faulted. 

Because outcrops are sparse within the Sugar Loaf 

and St. Kevin distriats, however, the details of the 

folding cannot be deciphered. The faults in the 

Sugar Loaf and .St. Kevin districts have prevailing 

trends of north-northwest and east-northeast, and are 

indicated by VeinS, Chert 11 dikeS1 II and ZOneS Of Sericitized rock. 

The ore deposits of the Sugar Loaf and St. Kevin 

districts are found in composite veins along fissure 

zones, within which the ore forms films, veinlets, 

and veins. Silver has been the principal metal 

produced, although a few of the deposits have been 

worked for gold, and many contain subordinate 

amounts of zinc and lead. Turquoise occurs in 

several prospects in the south-centra.! part of the 

St. Kevin district, but apparently these do not contain 

silver. Most of the production, which has an estimated 

value of between 10 and 15 million dollars, came during 

the last century; the output since that time has been 

intermittent. 

RADIOACTIVITY MEASUREMENTS 

In the Sugar Loaf and St. Kevin districts and vicinity, 

271 prospect pits, mine dumps, or mine workings were 

tested for radioactivity during 1951. These localities, of 

which 130 were anomalously radioactive, are shown on 

figures 3, 4, 5, 6, 7, and 8. The radioactivity 

1 +-T.ight pyritic fissure in siilclfied granite I 

·1 17 (Only on ore a of ®out . one squore foot 

of the vein ts rodiooctive} 

Crosscut is in pre-Cambrian granite and schist. 

No stoping. 

\Portal; 10,930 feet 5.68°30' from N.W. 

corner of section 7, T.9S., RBOW. 

50 0 

Base by compass and pace traverse. 

50 Feet 

Geology· by C.T. Pierson and J.W.Mytton 

October 1951 

Figure 3.-Map of unnamed ad it west of the St. Kevin district, Lake County, Colorado, showing radioactive locality 117. 

4 
120 

I 

) 

Breccia zone, 

dips steeply SE 

I ' 

Workings are in pre-Cambrian granite 

50 0 50 Feet 

Base by compass and· pace traverse 

--

Fork about 200 feet lang; not mapped; 

no a~omalous radioactivity. 

fissure; not radioactive 

EXPLANATION 

~---­ Fault , showing dip~ 

dashed where approximately located 

~I Outline of workings 

120---........ 

Radioactive locality and number 

\Portal; 10,160 ieet S.66°W. from N. W. 

corner of section 7, T.9S., R.BOW. 

Geology by C. T. Pierson and J. W. Myttan 

October · 1951 

Figure 4. -Map of unnamed adit west of the St. Kevin district, Lake County, Colorado, showing radioactive 

localities 118, 119, and 120. 

5 
Workings are in pre-Cambrian granite 

? 

. 85 

/cav•d 

LPorta 1- 3150 feet N29° E. from S.W. 

corner of Sect ion 6, r. 9S:;R. SOW. 

100 

I I I 

0 

11 1 I I 

100 FMt 

I 

Mine workings from map by F. J. McNair, 

with additions from compass and pace 

trav·erse ~y Q.O. Singew~ld C!nd C_.T. Piers~n. 

Caved 

/p 

/ 

2-inch stringer 

of quartz -pyritegouge. 

EXPLANATION 

65 '-L....__ __ _ 

Vefn, showin.o dip 

Dashed where approximately located 

~--- Vertical vein 

Oashed where approximately located 

Outline of working~ 

,.___25 

Ra·dioactive locality and number 

Geology by Q.D. Singewald and C.T. Pierson, 

Augvst 1951 

Figure 5. -Map of lower Wilkesbarre adit, St. Kevin district, Lake County, Colorado, showing radioactive 

localities 24, 25, and 26. 

measurements made with portable survey meters 

equipped with 6-inch beta-gamma tubes, are recorded 

in table 1 in milliroentgens per hour, a unit of measure 

of the relative amount of gamma-ray activity. No data 

are recorded in table 1 for nonanomalously radioactive 

localities shown in the illustrations. 

For each anomalously radioactive locality, the 

maximum radioactivity reading obtained on the most 

radioactive specimen found, and the range of background readings are listed in table 1. The maximum 

readings were obtained by repeated tests during which 

the probe was held directly against the specimens 

6 

tested. The background readings were obtained by 

holding tube at waist level for about 1 minute and recording the range of readings. 

A locality is considered to be anomalously 

radioactive if the ratio of the maximum radioactivity 

reading to the maximum background reading is greater 

than 1. 3:1. The values of the ratios for the localities 

tested range from 1:1 (locality 26) to 125:1 (locality 52). 

Each locality has been assigned to one of three ratio 

groups. A few localities, 21, 36, 61, described in 

table 1 as having a slight fee.ble, or doubtful anomalous 

radioactivity, but for which no radioactivity readings 
.....::] 

Table 1.--Radioactivity anomalies, Sugar Loa~ and St. Kevin mining districts and vicinity 

Maximum 

Locality /radioactivity~ Background no. reading reading 

Jmr per hr) (mr per hr) 

1 I 0.10 I 0.03-0.06 I 

2 .10 • o3- .o6 I 

3 .09 .02- .06 

4 .10 • 03- .o6 I 

5 • 12 .04- .06 

6 .30 .03- .05 

7 I .131 .05- .07 

8 

I 

.101 .05- .07 

9 • 12 .03- .06 

10 .13 .03- .07 

11 I .201 .03- .06 

12 • 121 • o3- .05 I 

13 • 08 .04 

14 . o81 .03- .04 I 

15 .08 .03- .04 

16 .08 .03- .04 

[Chemical and specttographic analyses by Geological Survey Trace E~ements laboratories] 

Equivalent 

uranium 

(percent) 

---

---

---

0.005 

---

.023 

.019 

---

---

---

---

---

Uranium 

(percent) 

Occurrences o~ the radioactive minerals and results o~ mineralogical 

and spectrographic analyses. 

--- ·Limonite-stained ~ractures in ~ine-grained rock, probably granitized 

schist ~rom dump o~ prospect pit . Do. --- ·Limonite-stained ~ractures in slightly silici~ied granite and granitized 

schist ~rom dump o~ caved adit • 

0.0021Relatively ~resh granite ~rom dump o~ caved adit. --- Limonite-stained ~ractures in granite ~rom dump o~ caved sha~t . .013 Autunite(?) as disseminations in ~ine-grained, highly silici~ied, 

limonite-stained rock ~rom outcrop; the ~reshly broken sur~aces o~ 

the rock exhibited nearly as much radioactivity as did the limonitestained sur~aces. Spectrographic analysis shows XX. Si; X. Al, Fe; 

O.X Ti, Ca, Mg; O.OX Mn, Na, Ba, La, Pb; O.OOX Ag, B, Cr, Cu, Ni, Sr, 

V, Y, Zr; O.OOOX Be, Co, Ga, Mo, Sc, Sn. --- ·Limonite-stained, and limonite- and manganese-stained ~ractures in partly 

weathered granite that is partly sericitized and silici~ied. From 

prospect trench. 

--- /Limonite-stained ~ractures in granite ~ro~ dump o~ Amity sh~t. 

--- Limonite-stained ~ractures in granitized schist ~rom dump o~ caved adit • --- Limonite-stained sur~ace o~ ~ragment o~ intensely sericitized and silici~ied granite transected by veinl&ts o~ vuggy quartz with very 

minor sul~ide minerals; also manganese-stained sur~aces o~ granite. 

From dump o~ caved sha~t or prospect pit • • oo81Fracture coatings and disseminations in highly silic.i~ied and sericitized 

granite. Limonite and manganese stain is common, and pyrite and 

galena occur in vuggy quartz. From dump o~ Huckleberry sha~t. The 

material presumably came ~rom within the vein or the walls adjoining it, 

but is not ore. No uranium minerals identi~ied. Spectrographic 

analysis shows XX. Si; X. Al, Fe; O.X Ti, Ca, Mg, Pb, Zn; O.OX Mn, Na, 

Ag, Ba; O.OOX B, Cr, Cu, Mo, Ni, Sr, V, Y, Zr; O.OOX Be, Ga, Sc • 

--- IL1monite-stained ~ractures in granitized schist ~rom dump o~ prospect pit • --- Disseminations(?) in relatively ~resh granite ~loat near bedrock source • Hydrothermaily altered granite and schist, and siliceous vein material ~rom dump o~ adit not anomalously radioactive • 

--- /Limonite-stained ~ractures in silici~ied granite ~rom adit dump. --- Limonite-stained ~ractures in silicified granite ~rom sh~t dump. --- Limonite-stained ~ractures and disseminations in silici~ied granite from sh~t dump. Relatively ~resh granite ~loat nearby read 0.10. 
co 

Locality no. 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

Table 1.--Radioactivity anomalies, Sugar Loaf and St. Kevin ~ning districts and vicinity--Continued 

Maximum radioactivity~ Background reading reading 

{mr per hr) {mr per hr) 

O.lE>I 0.03-0.04 

.111 .04- .05 

• 10 I .03- .o6 

.09 .03- .06 

.181 .03- .06 

.20 .03- .o6 

• 16 I .09- .14 

• 16 I .14 

.131 .13 

• oB I .03- .o4 

. 081 .04 • 11 .03- .06 

• 11 I .03- .06 

. osl .o4 

'.05 .04 

• oB I .o4 

Equivalent 

uranium 

{percent) 

o.ooB 

• 013 

.018 

.014 

.014 

.009 

Uranium 

(percent) 

Occurrences of the radioactive minerals and results of mineralogical 

and spectrographic analyses 

0.0041Black, sooty coatings on fractures in pyritized, silicified granite and 

pyritic, siliceous vein material from adit dump. Vugs of the vein 

material contain quartz, galena, and sphalerite(?). No uranium 

minerals identified. Spectrographic analyses shows XX. Si; X. Al, 

Fe; .X Ti, Ca, K, Zn; Q_.OX Mn, Mg, Na, Ba, Cu, Pb; O.OOX Ag, B, Cr, 

Ga, Ni, Sc, V, Y, Zn; O.OOOX Be, Co, Sr. 

---·Soft clay and limonite-stained fractures in highly weathered, silicified and sericitized granite, exposed by a glory hole • --- !Limonite-stained granitic debris from dump of shallow prospect pit. --- Limonite-stained fractures in granite from dump of upper Wilkesbarre 

adit; vein material on dump not anomalously radioactive. 

--- !Dump of caved adit; doubtful anomalous radioactivity. 

.008 Vein material and gouge from dump of lower Wilkesbarre adit . .013 Disseminations(?) in fine-grained, intensely altered rock, probably 

from t-g.e vein zone; from dump of lower Wilkesbarre adit. No uranium 

minerals identified. Spectrographic analysis shows XX. Si; X. Al, 

Fe; O.X Ti, Ca, Mg; O.OX Mn, Na, Ba, Pb, Zn; O.OOX B, Co, Cr, Cu, La, 

Ni, Sc, Sr, V, Y, Zr; O.OOOX Ag, Be, Ga • .Ol31Intensely altered granite intermixed with gouge, and stained by l~onite; 

forms footwall of Arty and Snow vein zone exposed by lower Wilkesbarre 

adit; radon gas present. No uranium minerals identified • .0021Quartz, pyrite, and gouge from 2-inch-thick stringer in hanging wall of 

Arty and Snow vein zone; exposed by lower Wilkesbarre adit. - Radon 

gas caused the exceptionally high background reading. 

.0051Chip-channel sample of crushed and gouge-permeated granite across 5-foot zone of hanging wall of Arty and Snow vein zone, lower Wilkesbarre adit. 

Considerable amount of radon gas present • --- ·Silicified granite cut by quartz-pyrite-sphalerite veinlets; from adit 

dump. Silicified granite, schist, and pyritic vein material from dump 

not anomalously radioactive • --- !Disseminations(?) in relatively fresh granite from outcrop • --- Pegmatitic rock with smooth, limonite-stained surfaces. From dump of 

prospect pit sunk into pe~atite which grades into schist • --- ·Limonite-stained surfaces of partly granitized schist from dump of shaft; 

there is a relatively small amount of anomalously radioactive material 

in dump • --- ·Disseminations(?) in friable, limonite-stained granite from dump of lower 

Griffin adit. Vein material not anomalously radioactive. --- ·Pyritic, siliceous vein material from adit dump feebly radioactive; 

granite and schist not anomalously radioactive • 

--- •Fracture coatings and disseminations(?) in granite and schist from dump 

of shaft. 
34 

35 

36 

37 

38 

39 

4o 

41 

co 42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

.09 

.07 

Feeble 

anomalous 

radioactivity. 

.12 

.18 

.12 

.20 

.o8 

.07 

• 08 

.07 

.10 

• 12 

.10 

.08 

.10 

.12 

• 08 

5.00 

• 08 

.04 

.03;.. .04 

.03- .05 

.03- .05 

.03- .05 

• 04- .06 

.05 

.04 

• 04 

.04 

.05 

.03- .04 

• 03- .04 

.03- .04 

.04- .05 

• 04- .05 

.03- .05 

.03- .04 

.03- .04 

.04 

.011 

.050 

.007 

.043 

Limonite-stained fracture coatings and disseminations(?) in fairly fresh 

granite and schist from dump of Rosse Tunnel; Pyritic-siliceous vein 

material not anomalously radioactive. 

Disseminations(?) in relatively fresh granite from dump of Grand View 

shaft. Hydrothermally altered granite, pyritized granite, relatively 

fresh schist, and pyritic vein quartz not anomalously radioactive. 

Limonite-stained fractures in intensely sericitized granite from dump of 

shallow prospect pit sunk in schist and granite. (Schist is common rock of dump.) 

Pale-yellow, limonite-stained, intensely altered rock, probably from or adjacent to St. Kevin vein. From dump of inaccessible shaft. Highly 

altered schist fragments from the same dump gave weaker readings; 

pyrite-quartz vein material not anomalously radioactive. 

.0091Limonite-stained, rather porous, intensely silicified granite from dump 

of caved shaft . Limonite-stained fractures in granite from dumps of several closely 

clustered shallow prospect pits. 

.028INo uranium mineral identified. The uranium is associated with the biotite 

of coarse-grained, altered granite from dump of shallow pit in granite, 

schist, and jasperoid. Disequilibrium caused by excess radium; no thorium present. 

Disseminations(?) in weathered but hydrothermally unaltered granite from 

shaft dump. Limonite-stained fractures in the granite are slightly more ~adioactive than unstained surfaces. 

Disseminations(?) in somewhat altered granite from dump of shallow pit • Disseminations(?) in moderately fresh granite from dump of prospect pit • Limonite-stained fractures in granite are slightly more radioactive than 

fresher surfaces. 

Disseminations(?)" in saussuritized granite from shallow trench. 

Hematite- and goethite-stained fractures in silicified granite from dump 

of shaft. Siliceous vein material not anomalously radioactive • Hematite-stained fractures in granite from dump of adit . Hematite- and goethite-stained fractures in silicified granite from dump 

of shaft.· Siliceous vein material not anomalously radioactive. 

Disseminations(?) in pyritized granite; iron-stained, silicified granite; 

and pyritic, siliceous vein material. From dump of adit. · Disseminations(?) in pyritized, silicified granite from dump of adit • .OOliRelatively fresh granite from outcrop; radioactivity readings upon freshly 

broken surfaces nearly as high (0.06-0.10) as on manganese-stained 

surfaces (0.06-0.12) • Limonite-stained fractures in silicified granite from adit dump. 

.Ol81No uranium mineral identified. Uranium is associated with black fracture 

coatings in pyritic vein quartz from dump of caved adit. X-ray powder 

pattern of coating matches quartz and hydromica patterns. Spectrographic analysis show~ XX. Si; X. Al, Fe, K; O.X Na; O.OX Ti, Mp, Ca, Mg, Ba; 

O.OOX B, Cr, Cu, Ga, ~o, Ni, Pb, Sc, Sr, V, Y, Zr; O.OOOX Ag, Co. 

Disequilibrium caused by excess radium; no thorium detected • Tight, unpyritized fissure in granite exposed in adit. Copper-stained 

White porphyry, silicified granite, and silicic vein material on dump 

not anomalously radioactive. Some relatively unaltered granite on dump 

read 0.07. 
I--' 

0 

Table 1.--Radioactivity anomalies, Sugar Loaf and St. Kevin mining districts and vicinity--Continued 

Maximum 

Localitylradioactivityl Background no. reading I reading 

(mr per hr) (mr per hr) 

54 

55 

56 

57 

58 

59 

60 

61 

62-64 

65 

66 

67 

68 

69 

70 

71 

72 

73 

74 

75 

76-1 

0.08 0.01-0.05 

.12 .03- .07 

.16 .03- .06 

• 171 .02- .05 

.15 .02- .05 

• 131 .02- .06 

.13 .02- .06 

.40 I .02- .05 

• 14 .02- .08 

.09 .02- .05 

• 09 .02- .05 

.13 .02- .08 ' 

• 16 .02- .08 

• 19 .02- .08 

• 14 .02- .08 

.09 .02- .05 

.13 .02- .08 

•131 .02- .08 

.12 .03- .05 

Equivalent 

uranium 

(percent) 

0.004 

.024 

.010 

.085 

.010 

Uranium 

(percent) 

Occurrences of the radioactive minerals and results of mineralogical 

and spectrographic analyses 

< 0. 001 I Limonite-stained crushed rock and gouge along minor fissure, in hanging 

wall, several inches away from vein; Lakewood m+ne. --- • Gossan, 1 foot thick, exposed in place just east of portal, upper 

Griffin adit. . 015 I Breccia composed of chert and silicified granite fral?JI!ents, cemented 

by silica and limonite; from dump of workings west of upper main 

Griffin adit. No uranium minerals identified • --- • Limonite-stained surfa.ce in very intensely altered granite from shaft 

dump. (Probably from footwall of vein.) 

.007 I Limonite-stained fractures and disseminations in sericitized, finegrained hybrid rock from dump of shaft, Griffin vein zone. Spectrographic analyses shows XX. Si; X. Al, Fe; O.X Ti, Mg, Pb; O.OX Mn, 

Ca, Na, Ag, Ba, Cr, Cu, La; O.OOX B, Ni, Sc, V, Y, Zr; O.OOOX Be, Ga, 

Sn, Sr . --- Limonite-stained fractures in granite from dump of prospect pit. --- Limonite-stained fractures in granite from dump of shaft. --- Dump of small pit; slight anomalous radioactivity. 

.065 Metatorbernite(?) .in limonite and manganese-stained fracture coatings 

and as disseminations(?) in granite from dumps of three small prospect pits, Griffin vein zone. Spectrographic analysis of sample shows 

XX. Si; X. Al, Fe; O.X Ca, Mg, Na, Ba; O.OX Ti, Mn, Pb, Sr, U; O.OOX 

B, Cr, Cu, Mo, V, Y, Zr; O.OOOX Ag, Be, Ga, Ni, Sc. Disequilibrium 

caused by excess radium; no thorium detected. 

--- \Dump of large pit; doubtful anomalous radioactivity • --- Limonite-staine.d fractures in granite from dump of small trench. --- Limonite-stained fractures in schist from dumps of two shallow prospect 

pits in schist and granite. 

--- !Limonite-stained fractures in schist from dump of shallow prospect pit • --- Limonite-stained fractures in granite and schist from dump of shallow 

prospect pit . --- ·Limonite-stained fractures in granite and schist from dump of shallow 

prospect pit . 

.007 !Limonite-stained fractures in schist from dump of shallow prospect pit 

surik into schist and granite • 

--- 1 _Crumbled granite from dump of shallow prospect pit. --- \Limonite-stained fractures in granite from dump of prospect pit. --- Maximum reading on freshly broken granite was 0.11; limonite-stained 

fractures gave readings of 0.13. Both from dump of shallow prospect 

pit. 

--- !Limonite-stained fractures in granite from dump of shallow prospect pit. -~- Weathered, moderately dark granite exposed along abandoned road. Radioactive throughout zone 50 feet thick. 
I-' 

I-' 

76-2 

77 

78 

79 

80 

81 

82 

83 

84 

85 

86 

87 

88 

89 

90 

91 

92 

93 

94 

95 

96 

97 

98 

99 

100 

101 

102-105 1 

106 

107 

108 

109 

110 

lll 

112 

113 

.13 

.11 

.10 

.14 

.15 

.17 

.14 

.16 

.16 

Not recorded 

.08 

1.00 

(1) 

• 08 

• 08 

.08 

• 13 

• 11 

.15 

.12 

.40 

• 11 

.16 

.19 

.14 

.11 

.09 

.13 

.40 

.07 

.07 

.08 

.02- .05 

.04- .06 

.04- .06 

. 03- .08 

.02- .08 

.03- .05 

.03- .08 

.02- .10 

.03- .05 

.03- .04 

.02- .10 

.03- .04 

.03- .04 

.03- .04 

.02- .08 

.02- .04 

.02- .08 

.02- .08 

.02- .08 

• 02- .08 

.01- .06 

.01- .06 

.( 1) 

.03- .07 

.03- .06 

.03- .06 . o3-/.o5· 

.02- .10 

.02- .04 

. 02- .04 

.02- .04 

/ 

. 004 

.005 

• 005 

.• 010 

.011 

• 004 

(1) 

.005 

.017 

.007 

.001 

.002 

.001 

.005 

.006 

.002 

(1) 

.001 

.009 

• 004 

Limonite-stained fractures and disseminations(?) in dark-colored granite 

from dump of shaft. · Limonite-stained surface of one block of silicified granite float in 

abandoned road. - Unconsolidated granular material at surface, derived from granite in 

abandoned road. 

Limonite-stained fractures in granite from dump of caved shaft(?) • Limonite films on fractures in granite and in partly silicified.White 

porphyry from dumps of two shallow prospect pits, near caved shaft. 

Limonite-stained fractures in granite from dump of prospect pit. 

Limonite-stained fractures in granite from dump of prospect pit. 

Turquoise and chrysocolla(?) coat fractures in granite exposed by trench • Iron-stained fractures in granite from western part of bull-dozer-cut 

200 feet long. Turquoise found in middle part of cut. 

Visible torbernite on surfaces of granite from two shallow pits. 

Limonite-stained fractures in granite from dump of shallow prospect pit. 

Disseminations and fracture coatings of visible torbernite associated 

with turquoise, malachite, and chrysocolla in granite, schist, and 

hybrid granite from dump of Josie May shaft • Limonite-stained fractures in granite from dumps of three shallow prospect pits • Limonite-stained fractures in granite from dump of shallow prospect pit. 

Limonite-stained fractures in granite from dump of shallow pit. 

Do • Limonite-stained fractures in granite from dump of prospect pit • Pyritic, limonite-stained, silicified granite from dump of caved shaft • Limonite-stained fractures in granite from dump of shallow prospect pit. 

Dump of pit: doubtful anomalous radioactivity. 

Limonite-stained fractures in schist exposed by prospect pit, which also 

exposes granite . Limonite-stained fractures in granite from dump of shallow prospect pit • Disseminations and fracture coatings in muscovite-chlorite schist from 

dump of shallow prospect ~it, which also contains granite • Limonite-stained, slickensided surfaces in chloritic schist which came from within or nearby a prospect pit. 

Dump of pit: doubtful anomalous radioactivity. 

Do. 

(1) 

Films on fractures in both granite and amphibolite(?) from dumps of 

several shallow prospect pits. (Composite sample 102-105.) 

Limonite-stained fractures in granite from dump of caved adit. 

Unconsolidated granular material at surface; derived from granite • Small chunks of soft limonitic gossan, slightly manganese-stained. From 

dump of shaft. 

Metatorbernite(?) disseminated in granite exposed by opencut, Turquoise 

Chief mine. Spectrographic analysis shows XX. Si; X. Al, Fe; O.X Ca, 

Mg, Na; O.OX Ti, Mn, Ba, Cu, La; O.OOX B, Cr, Ni, Pb, Sr, V, Y, Zr; 

O.OOOX Ag, Be, Co, Ga, Sc, Sn • Turquoise(?) and chrysocolla(?) coatings on fractures in granite from 

dump of caved adit. 

Limonite-stained fractures in.granite from dump of shallow prospect pit • Iron-stained surfac& of granite fragment from dump of prospect pit. 
...... 

1:\:) 

Table I.--Radioactivity anomalies, Sugar Loaf and St. Kevin mining districts and vicinity--Continued 

Maximum 

Locality,radioactivityl Background no. .reading reading 

( mr per hr) (mr per hr). 

114 

115 

116 

117 

118 

119 

120 

121 

122 

123-1272 

128 

129 

130 

1 See 106. 2 See 122. 

(2) 

0.06 

.30 

.19 

.90 

1.00 

.18 

.18 .. 

.20 

.15 

.12 

.09 

• 08 

0.02-0.04 

. 03- .06 

.02- .08 

• 04 

.09 

.09 

.09 

• 03- .04 

• 03- .08 

( 2') 

.03- .05 • 03- .04 

.03- .04 

Equivalent 

uranium 

(percent) 

0.021 

( 2) 

.004 

.069 

.015 

.034 

.005 

Uranium 

{percent) 

Occurrences of the radioactive minerals and results of mineralogical 

and spectrographic analyses 

0.014 

Granite exposed by trench-like erosion of about 60 feet of old road • Limonite-stained, weathered schist from dump of shallow prospect pit. 

.001 

.003 

.005 

.004 

Goethite contains the uranium. Spectrographic analysis shows XX. Si; 

X. Al, Fe; O.X Ti; Mn, Ca, Mg, Na; O.OX Ba, Cr, La, Pb, V, Zn; O.OOX 

B, Mo, Ni, Sc, Sn, Sr, Zr, Y; O.OOOX Ag, Be, Co, Cu, Ga. 

Limonite-stained films on fractures in granite, and disseminations in · silicified White porphyry and jasperoid from dump of prospect pit • 

Disseminations in pyritized, silicified granite from tight fissure ex- posed by adi t·. No uranium mineral identified. Disequilibrium caused 

by excess radium; no thorium detected. 

Disseminations in silicified granite from footwall of a pyritic vein 

l foot wide, about 3 feet from the vein. {Vein material 0.15-0.18 mr per hr); exposed by adit.) No uranium mineral identifie~. Spectrographic analysis of sample shows XX. Si; X. Al, Fe; O.X Pb; O.OX Ti, 

Mn, Ca, Na, Ba, Cu, Zn; O.OOX Ag, B, Ga, Sn, Sr, V, Zr; O.OOOX Mg, 

Cr, NL 

Pyritic veinlets exposed by adit • Breccia zone in granite, 6 feet thick; exposed by adit • Florencite, the uranium-bearing mineral, occurs as disseminations in 

pyritized granite from adit dump • < .001 Limonite-stained fractures in sericitized granite from several dumps and 

exposures along road. {Composite of 123-127.) {2) 

--- I Granite from dump of prospect pit • --- Manganese-stained fractures in silicified granite from shaft dump. 

Limonite-stained, silicified granite; pyritized, silicified granite; 

and pyritic, siliceous vein material not anomalously radioactive • --- • Iron- and manganese-stained fractures in silicified granite from shaft 

dump. Granitized schist and silicic vein material not anomalously 

radioactive. 
f-' 

w 

EXPLANATION 

X 

Small prospect pit or open cut 

1!'1 

Shaft 

--< 

Adit 

.... 'tl\\\~ 

Mine dump 

LOCALITIES TESTED FOR RADIOACTIVITY 

A 

Maximum radioactivity less than 

1. 3 times maximum background 

.II. 

Maximum radioactivity 1. 3-3 

times maximum background 

... Maximum radioactivity greater 

than 3 times maximum background 

Number refers to description in table 1 

Localities 55-116 sbown on fig 7 

..,.., 

!,~ 

S:ri 

31 32 

T..BS. 

T.9S. 

39°17'30" "'~}!?~<iE ±~;;;.Js.-,:z;~-~~t?lfiTUNII£i.Sl x~ 4( tJ. 11 ~ . , \:Aer • '\:u 

1o6•lz~· 

1~. 9 I I ~Feet 

Contour Interval 250 feet Datum is mean sea level 

TURQUOISE 

1os"lzz' 30" 

Surveyed by 0.0. Singewold, C.T. Pierson, 

J.W. Mytton, and D.L.Peck. 1951 

Figure 6. -Localities tested for radioactivity in the St. Kevin district and vicinity, Lake County, Colorado. 
1000 

X 

Small prospect pit or opencut 

.. Shaft 

Ad it 

1/tllfl\\~' 

Mine dump 

TESTEO FOR RADIOACTIVITY 

e. Maximum radiaactiv.ity less than 1.3 tin~es 

maximum background 

A 

Maximum radioactivity 1.3- 3 times maximum background 

A radioactivity greater than 3 times 

maximum background 

lllurrrber refers to description in table I 

· locality IOe,not shown on mop, is a 

composite o_f 102-10.5. 

----·-...---e-.-:-......-:.:. ..... __., _ _.__ __ ~~ 

Surveyed by Q.D.Singewcild, C.T.-Pier.san, D. L.Peck, V. R. Wilmarth, and R. C. Vickers __ :__1951. 

2000 Feet 

Contour interval 50 feet 

.f!atum is mean sea level 

Figure 7. --Localities tested for radioactivity in part of St. Kevin district, Colorado, traversed in detail. 

14 
---

T9S 

14'20' 

EXPLANATION 

Small prospect pit or opencul 

Shalt 

Ad it 

Mine dump 

LOCALITIES TESTED FOR RADIOACTIVITY 

Maximum radioactivity less than 1. 3 limes maximum background 

A 

Maximum radioactivity 1.3-3 t1mes maximum background 

Number refers to description in table 1. 

Locality 122, not shown on map, is 

a composite of 123-127. 

Contour interval 250 feet 

Datum is m~an sea level 

3000 Fut 

Surveyed by 0. D. Singewald and C. T. Pierson, 1951 

106°22' 30 

Figure 8. -Localities tested for radioactivity in the Sugar Loaf district, Lake County, Colorado. 

are recorded, are shown on figures 6 and 7 

as belonging to the second ratio group (weak 

anomalous radioactivity). Localities 24, 25, and 

26, where the ratios are low because of the 

unusually high background readings caused by 

radon gas, are assigned to the third category 

(stronger anomalous radioactivity). Locality 85, 

for which radioactivity readings are not recorded, 

15 

is also assigned to the third category because 

of the presence of torbernite in some of the 

specimens. 

Besides providing a quick visual method of 

distinguishing between nonanomalously radioactive 

localities, and the two categories of anomalously 

radioactive localities, the foregoing ratios give a 
rough indication of the percent equivalent uranium 

existing at localities where this percentage has 

not been determined by laboratory analysis. As 

indicated below, the percentages of equivalent 

uranium for 24 of the 33 localities for. which 

laboratory analyses are available fall into two 

distinct groups when. arranged ac·cording to the 

magnitude of their associated ratios. 

Associated ratios 

1.3:1-3.0:1 

Percent equivalent uranium 

0,004-0.013; 13 localities, 

excluding 56 (0.024). 

Greater than 3.0:1 Greater than 0.013;11 localities, excluding 99 (0,004), 

87 (0.005), 17 (0.008), 

96 (0.010), and 38 (0.011) •. Note: Localities 24, 25, and 26 do not fall into the above groups because 

of the unusually high background readings caused by radon gas. 

THE URANIUM OCCURRENCES 

Uranium minerals in the St. Kevin district 

and vicinity, are found in metalliferous veins of 

Tertiary age and as disseminations and fracture 

coatings in pre-Cambrian igneous and metamorphic 

rocks that were hydrothermally altered in advance 

of vein formation. Descriptions of the occurrences 

are found in table 1. 

Anomalously radioactive vein material was 

found in the St. Kevin district at 11 mine dumps 

(locality 11, Huckleberry vein; and locality 37, 

St. Kevin vein) and, also, at several places 

within the few underground workings now accessible 

(localities 24 to 26, Arty and Snow vein zone; 

and 117 and 119, unnamed veins). The radioactive vein material consists of gouge and intensely 

sericitized and silicified granite transected by 

. veinlets of vuggy quartz containing minor amounts 

of sulfide minerals. Samples of the vein material 

contain as much as 0. 013 percent uranium, but 

the radioactive mineral, which probably is 

secondary, has not been identified. Vein material, 

however, is low in radioactivity at some localities 

where radioactivity anomalies were found on 

fracture coatings of wall rock (localities 13, 20, 

31, and 34). 

Torbernite,. associated with turquoise, 

malachite, and chrysocolla, occurs as disseminations and fracture coatings in altered granite 

at the Josie May turquoise mine (locality 87) 

in the south-central part of the St. Kevin district. 

At locality 85, near the Josie May mine, torbernite is found on surfaces of granite from two 

shallow prospect pits. Metatorbernite is disseminated in granite at the Turquoise Chief mine · 

(locality 110). 

Disseminations of radioactive minerals are 

present at several places in the St. Kevin district, 

most commonly in sericitized granite (localities 13, 16, 

28, 31), but at a few localities (localities 33, 98) in 

schist. The uranium minerals in most of the disseminated occurrences. have not been identified, but 

autunite(?), metatorbernite, and uranium-bearing 

16 

flor:encite have been identified at localities 6, 64, and 

121, respectively. These and perhaps also other 

secondary uranium minerals probably account for most 

or all of the radioactivity anomalies resulting from · 

disseminated uraniferous minerals. 

The limonite-stained fractures in weathered 

granite and schist from the dumps of many ·of the mines 

and small prospect pits in the St. Kevin district are 

anomalously radioactive (localities 1, 7, 39). Except 

for metatorbernite at locality 64, uranium minerals 

that could account fo" the radioactivity have not been 

identified. 

Although no primary uranium minerals 

have been found, it is probable that the uranium 

minerals in vein material in the St. Kevin district formed as a result of supergene alteration 

of primary pitchblende. The secondary uranium 

minerals that coat fractures may have resulted 

from the supergene redistribution of primary 

uranium minerals in the igneous rocks, fresh 

samples of which (localities 4 and 50) contain 

as much as 0. 007 percent equivalent uranium, 

and 0. 002 percent uranium; yet these occurrences 

are mostly restricted to rocks that were hydrothermally altered during Tertiary time, and 

therefore the secondary uranium minerals may 

be derived from pitchblende that was deposited 

by hydrothermal solutions. 

The uranium occurrences in the St. Kevin 

district are largely in nonglaciated terrane that 

has been subjected to a very long period of 

weathering; and, accordingly, nearly all the rocks 

containing the uranium are weathered. Thus, 

chemical leaching within the zone of weathering 

probably has greatly reduced the uranium content of material near the surface, and occurrences of even small quantities of secondary 

uranium minerals might be related to stronger 

concentrations of primary minerals at depth. 

However, if stronger concentrations are present 

at depth, their size and grade may be much 

less than would be required for exploitation. 

Data from which to estimate the depth to 

unweathered rock are exce~dingly. me~?-ger. Complete oxidation probably extends to depths ranging 

from a few feet to not more than 60 feet throughout the district, but partial oxidation along some 

fractures may extend to depths of several hundred feet. 

All the analysed samples from the Sugar LoafSt. Kevin districts and vicinity are in a state of 

disequillibrium, that is, the percent equivalent uranium is greater than the percent uranium. In some 

samples as at localities 40; 52, 64, and 117, the 

differences are reiatively large. Laboratory analyses 

show that the difference between total radioactivity 

and the radioactivity due to uranium is caused by 

surplus radium and other daughter products of uranium. 

As Phair and Levine ( 1952) have shown in their 

studies of the leaching of pitchblende, the most 

probable cause of this disequillibrium is the 

leaching of uranium by supergene processes. 
UNPUBLISHED REPORTS 

Phair, George, and Levine, Harry, 1952, Notes on 

the differential leaching of uranium, radium, and 

lead from pitchblende in H2S04 solutions: TEI-262, 

1952, U. S. Atomic Energy Comm., Tech. Inf. 

Service, Oak Ridge, Tenn. 

17 

Singewald, Q. D., in preparation, Sugar Loaf 

and St. Kevin mining districts, Lake County, 

Colorado, with a section on Petrology of the 

bedrock, by John G. Broughton, U. S. Geol. 

Survey Bull. 

INT.-DUP. SEC •• WASH •.• D.C .. I~Iitl