Park County, Colorado

U. S. Gam.,, .. _ JVEY FP-ld Library Albuquerque, New Mexico Results of Reconnaissance for Radioactivity in Parts of the Alma District, Park County, Colorado

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

Trace Elements Investigations Report 248

UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY

metadc304524

1..._ -

OFFICIAL USE ONLY

Geology and Mineralogy

This document consists of 28 pages, plus 2 figures 0 Series A.

UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

RESULTS OF RECONNAISSANCE FOR RADIOACTIVITY IN PARTS

OF THE ALMA DISTRICT, PARK COUNTY, COLORADO*

Co T. Pierson and Q. D. Singewald

April 1953

Trace Elements Investigations Report 248

This preliminary report is distributed without editorial and technical review for conformity with official standards and nomenclature. It is not for public inspection or quotation0

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

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

OFFICIAL USE ONLY 2

USGS - TEI - 245

GEOLOGY AND MINERALOGY

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Geophysics Branch, Washington 0 0 0 0 0 0 0 O .- 0 1 Alaskan Geology Branch, Washington0 0 0 0 0 0 0 .O .0 1

Fuels Branch, Washington 0 0 0 0 0 0 0 0 0 0 O .O 0 1

D, M. Lemmon, Washington. 3 0 0 0 .: 0. . .O 0 1 L0 R0 Page , Denver0 0 0 0 0 0 0 0 0 0 0 0 0 0 O .O 0 2 R0 P. Fischer, Grand Junction 0 0 0 0 0 0 0 0 . .O .0 1 A. E0 Weissenborn, Spokane0 0 0 0 0 0 0 0 0 0 O O .0 1 C0 B0 Hunt , Plant City 0 . 0 0 0 0 0 0 0 0 O .O .0 1 J 0 F. Smith, Jr.9 Denver 0 0 0 0 0 0 0 0 0 0 0 O O 0 1 No M. Denson, Denver 0 0 0 0 0 0 0 0 0 0 0 0 0 . .O .0 1 R. W0 Swanson, Spokane0 0 0 0 0 0 0 0 0 0 0 0. O O 0 1

Lo So Gardner, Albuquerque. 0 0 0 0 0 0 0 0 0 O O .0 1 M. R. Klepper, Washington 0 0 0 0 0 0 0 0 0 0 O .O .0 1

J. D0 Love 9 Laramie 0 0 0 0 0 0 0 0 0 0 0 0 0 . .O .0 1 A0 H. Koschmann, Denver 0 0 0 0 0 0 0 0 0 0 0 . .O a 1 E0 H. Bailey, San Francisco.0 0. 0 0 0 0 0 0 0 O .o 0 1

J 0 RD Cooper, Denver 0 0 0 0 0 .0 0 0 0 0 0 0 ... O .0 1 W 0 P0 Williams, Joplin0 0 0 0 0 0 0 0 0 0 0 0 O .O .0 1 C 0 E 0 Dutton, Madison 0 0 0 0 0 0 0 0 0 0 0 0 O O .0 1 R0 A0 Laurence, Knoxville 0 0 0 0 0 0 0 0 0 0 O .O a 1 R0 J0 Roberts, Salt 'Lake City 0 0 0 0 0 0 0 0 O .O .0 2 Q0 D0 Singewald , Beltsville .0* 0 .0 0 . 0 O O 0 2 TEPCO, Washington:

Resource Compilation Section .0 0 0 0 0 0 0 0 0 0 0 .0 .0 0 0 .0 0 2 Reports Processing Section.0 0 0 0 0 0 0 0 0 0 0 0 0 .0 0 0 .0 0 0 3 (Including master) 3

CONTENTS

Page

Abstract 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O O O O O 0 0 4

Introduction 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O 0 0 0 0 . 0 5 Field work and acknowledgments 0 . . 0 . 0 .O . .0 0 .0 . 0 5 Location and accessiblity0 0 0 0 0 0 0 0 0 O 0 0 0 0 0 .0 5

General geology and ore deposit s.. 0 0 0 0 0 0 O 0 .0 0 0 . 0 7 Method of reconnaissance for radioactivity 0 0 O 0 .0 .0 0 0 0 9 Radioactivity measurements 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 The uranium occurrences 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 19 Veins in pre-Cambrian rocks 0 0 0 0 0 0 0 0 0 0 0 0 0 0 21

London vein system 0 0 . 0 0 0 0 0 0 0 0 0 .s 0 0 0 0 0 0 21

Veins east of Cooper Gulch fault 0 0 0 0 0 0 0 0 0 0 0 .0 22 Dis equilibria in the uranium occurrences 0 0 0 0 0 0 0 0 23 Non-anomalously radioactive localities 0 0 0 0 0 0 0 0 .0 23 Origin 0 0 0 0 0 0 0 0 0 o. 0 0 0 0 0 0 0 .0 .0 .0 .0 0 0 24

Literature cited. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O .O.O O O 0 0 24

ILLUSTRATIONS

Figure l Index map of Colorado showing location of the

Alma district 0 .. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6

2. Geologic sketch map, part of Orphan Boy mine, Alma mining district, Park County, Colorado,

showing radioactive localities 0 0 0 0 0 0 0 0 o .e In envelope

3. Generalized geologic map of the Alma district, Park County, Colorado, showing areas radiometrically tested. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 In envelope

TABLES

Table 10 Localities tested for radioactivity in the Alma mining district. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

2. Relationship between (1) ratio of maximum radioactivity measurements to average background and (2) percentages of equivalent uranium 0 0 0 0 0 0 0 20 4

RESULTS OF RECONNAISSANCE FOR RADIOACTIVITY IN PARTS

OF THE ALMA DISTRICT, PARK COUNTY, COLORADO

By C. To Pierson and Q. Do Singewald

ABSTRACT

Pitchblende was discovered in July 1951 in the Alma mining district,

Park County, Colo0 , by the U0 S. Geological Survey acting on behalf of the U. So Atomic Energy Commission.

The pitchblende is associated with Tertiary veins of three different geologic environments: 1) veins in pre-Cambrian rocks, 2) the London vein system the footwall block of the London fault, and 3) veins in a mineralized area east of the Cooper Gulch fault. Pitchblende is probably not associated with silver-lead replacement deposits in dolomite0

Secondary uranium minerals, as yet undetermined, are associated with pitchblende on two London vein system mine dumps, and occur in oxidized vein material.Lfrom dumps of mines in the other environments0

Although none of the known occurrences are of commercial importance, the Alma district is considered a moderately favorable area in which to prospect for uranium ore, because twenty-four of the forty-three localities examined show anomalous radioactivity; samples from anomalously radioactive localities, which include mine dumps and some underground workings, have uranium contents ranging from 0.001 to l.66 percent. 5

INTRODUCTION

Field work and acknowledgments

A search for uranium in parts of the Alma mining district, Park

County, Colo, was made during 2-1/2 weeks of July and August 1951 by

the U. So Geological Survey on behalf of the Atomic Energy Commission.

Many mine dumps and mine workings were tested for radioactivity, and

some were sampled, but time did not permit complete coverage even of

the parts of the area examined.

V. R. Wilmarth and R. C0 Vickers of the Geological Survey were members of the field party from July 16 through 19. L. R. Page of the

Geological Survey, and C. Co Towle, Jr., of the Atomic Energy Commission

visited the London Extension and South London mine areas on August l

George Phair of the Geological Survey visited the areas and collected

radioactive samples from London Extension and South London mine dumps

on August 21, 19520

Acknowledgments are due Mr0 Joseph Thibodeau, foreman of the Buckskin

Joe mine, and Mr. G. 0 . Lear at the Sweet Home mine for courtesies extended at the time these mine were examined. The writers are indebted to George Phair of the Geological Survey for providing the results of

chemical and spectrographic analyses made upon radioactive material, handpicked by him, from one of the specimens0

Location and accessibility

The Alma district (fig0 1) is located on the eastern slope of the

Mosquito Range. Elevations range from about 10,500 feet to over 14,000

feet0 Most of the localities examined can be reached by a 4-wheel-drive vehicle0 L'

UNITED STATES DEPARTMENT OF THE INTERIOR TRACE ELEMENTS INVESTIGATIONS GEOLOGICAL SURVEY REPORT 248

108 log* 070 106e050 104 l03 102*

41 WYOMING 41.

r Sterling yvmpo g Croig Greeley

FortMorgan 0 . Boulder 40 -t- Glenwood Denver Spr-ings ALMA DISTRICT 'U - 0 a Burlington \ 0 Leadvilleo E Firplay\

3! 39. Grand Junction__ L I i It a - -- i 0Colorado Springs

Montrose Solidi\ Sz on Prko0

------

30 30 i 1 l 1Silverton

Alamoso

* Duro ngo Trinido q I . _ . . 3T 37. NEW MEXICO OAO

1 109* lose l05 1040 1030 l02*

FIGURE 1- INDEX MAP OF COLORADO SHOWING LOCATION OF THE ALMA DISTRICT.

GPO 82-8000698 7

GENERAL GEOLOGY AND ORE DEPOSITS

The geology of the Alma district has been described in several publi-

cations, to three of which the reader is particularly referred for de-

tails (Singewald and Butler, 19339 1941; Singewald, 1947). The gener-

alized geology of the Alma district, taken from plate 8 of Geological

Survey Bulletin 955 D (Singewald, 1950)9 is shown in figure 3.

The bedrock of the Alma district is composed ofo 1) pre-Cambrian

gneiss, schisb, granite, and pegmatite, 2) pre-Pennsylvanian sedimentary

strata, aggregating 300-600 feet in thickness and comprising the Sawatch

quartzite of Cambrian age, including the Peerless shale member, the

Manitou limestone of Ordivician age, the Chaffee formation (Devonian)

including the Parting quartzite and Dyer dolomite members, and the

Leadville dolomite of Mississippian age; 3) Pennsylvanian sedimentary

strata consisting of interbedded elastic rocks that range from coarse

conglomerate to shale, with a few thin beds of dolomite; and 4) Tertiary (1)

quartz monzonite porphyries, correlated with the White porphyry and the

Gray porphyry group of Leadville, which occur mainly as sills in sedi-

mentary strata, or as dikes in pre-Cambrian rocks. The Buckskin Gulch

stock is composed of igneous rocks closely related to the porphyries.

Major structural features are shown on figure 3. The regional

dip of the strata is 100 to 250 east. Departures from this regional

dip occur principally along folds associated with major faults.

There are two major faults in the district, each of which cuts the west limb of an anticline that is overturned to the west. The London

fault is reverse, dips steeply northeastward, and has a throw of about

3,000 feet. The Cooper Gulch fault is reverse, dips 300 eastward, and

has a maximum throw of 450 feet at Mosquito Gulch. The more important ore deposits, which for the most part are within. the "mineralized areas" shown on figure 3, can be classified as follows:

1) gold and silver veins in pre-Cambrian rocks, 2) gold-sulfide veins of the London type, 3) gold veins and replacement veins in Sawatch quartzite, and 4) silver-lead bedded replacement bodies and replacement veins in dolomites. Although mineralized fissures are abundant in the pre-Cambrian rocks, commercial production from them has been limited to a few relatively small to medium-sized mines in Mosquito, Buckskin, and Platte Gulches.

The London vein system, in the footwall block of the London fault, consists of gold-bearing quartz-sulfide veins0 Most of the ore occurred as veins within a zone of porphyry'sills 175-275 feet thick, very close to the base of the Pennsylvanian series, but some were in veins in the upper part of the Leadville dolomite.

Most of the production from deposits in the Sawatch quartzite has been from mines in the mineralized areas (1) east of the Cooper Gulch fault and (2) on North Star Mountain0 Veins along minor faults are productive at certain favorable horizons where thin ore shoots formed by replacement of the wall rock several feet outward from the faults0

Beds containing considerable quantities of carbonate cement, which was more easily replaced than the characteristic siliceous cement, localized most of the shoots.

The silver-lead production has come from bedded replacement bodies and replacement veins from 1) near the London fault at New York

Mountain; 2) the Hock Hocking mine in the mineralized area east of the 9

Cooper Gulch fault and 3) the Mount Lincoln - Mount Bross area. The

bulk of the ore. occurred in the upper part of the Leadville dolomite,

METHOD OF RECONNAISSANCE FOR RADIOACTIVITY

Reconnaissance for radioactivity in the Alma district was carried

out to test the uranium-potentialities of the various types of geologic

environment rather than to systematically cover all mine dumps and ac-

cessible mine workings in the district. The localities visited are

shown on figure 3; the numbers refer to brief descriptions in table lt

Figure 3 does not show mines that were not examined; for the locations

and descriptions of mines not visited, reference is made to the pub-

lications previously cited.

Forty-three localities were tested with Geiger counters, and

twenty-four samples were taken. Sixteen grab samples were selected

from mine dumps, and eight were ship or chip-channel samples from underground exposures or prospect trenches.

RADIOACTIVITY MEASUREMENTS

Table 1 lists anomalous radioactivity measurements in milli- roentgens per hour, taken with survey meters equipped with 6-inch beta-gamma probes0 Readings are, not recorded for localities where no anomalous radioactivity was found. Locality numbers refer to

figure 3, which shows all localities tested.

The maximum radioactivity measurements for a locality is the largest reading obtained by holding the probe directly against the surface of any specimen- or underground exposure at the locality. JO

Table l --Localities tested for radioactivity in the Alma mining district

Maximum radioactivity Locality measure- Background eU U number ment in measurement (percent) (percent) Remarks/ mr0 /hr0 in mro/hr0

1 Dump of caved adit; radioactivity essen= tially equal to back- ground0

2 OO09 O,03-O.05 Limonite-stained fractures in granite and pyritized granite from dump of caved adito

3 o40 0O3-OoO5 OO041 0O022 Pitchblende associated with pyrite in veinlets which cut relatively fresh granite from dump of caved adit0 Spectro- graphic analysis shows XX Si ; X0 Al, ECa, Fe;

XI Mn,P, Mg, %, Ba; 00X U, Y, Zn, Zr, Ti; OOX Ag, B, CurLa, Mo, Ni, Pb, Sr, V; 0 000X Be, Co, Cr, Ga, Sn0

4 009 -Limonite-stained granite from dump of inaccessible adit0

5 009 o03-0005 Limonite-stained granite from dump of inaccessible adit0

6 018 o03-005 0 021 00013 Pitchblende disseminated (?) in relatively fresh granite from hangingwall of tight fissure exposed by adito Spectrographic analysis shows XXo Si; X. Al, Fe, Na; 0X Ca, Mg; .OX Ti, Mn, Ba, Pb; O00X

Ag, B 9 Cu, Mo 9 Ni, Sr, V, Y, Ze; O000X Be, Co, Cr, GA0 J Spectrographic analyses by U. S. Geological Survey Trace Elements Laboratory, Denver, Colo. 11

Table to 'Localities tested for-radioactivity in the Alma mining district-continued

Maximum radioactivity L cality measure- Background eU U number ment in measurement (percent) (percent) Remarks in mr,/hr. mr. /hr. v v v

7 0.19 0.03-0. 05 0.070 0.057 Disseminations in limonite-stained, sooty- black material which occurs as a 4=-inch-thick vein in a 4-6 foot-thick fissure ,zone in relate ti rely fresh granite and pegmatitic granite; exposed by shallow trench. No uranium minerals identified. Spectrographic analysis shows XX. Si, Mn; X. Al, Pb5, Fe; .X Ca, Na, Cu, Mo, Zn; .oOX Ti, Mg, Ag, Ba, U; 00X B, Bi, Co,Cr, Sr, VY, Zr; .000X Be, Ga, Ni,

8a .50 o0-Oo.18 .14 .062 Pitchblende, not visible megascopically, as disseminations in gouge and crushed rock from a 4- inch to 6-inch thick breccia zone in granite and pegmatite; exposed by Kentucky Bell adit. Disequillibrium caused by excess radium; no thorium detected. 12

Table l.--Localities tested for radioactivity in the Alma mining distri ct,- continued

Maximum radioactivity Locality measure- Background eU (U number ment in measurement (percent) (percent ) Remarks mr./hr. in mr./hr.

,09 .03-0.05 .008 0001 Disseminations in limonite-gossan from dump of Kentucky Belle adit. No uranium minerals identified

X010 003-0.05 0008 .004 Pitchblende as disseminations (?) in greenish-gray, highly altered rock from dump of Kentucky Belle adit.

9 013 o03-0.08 .006 .002 Disseminations in fresh granite exposed by Wyandotte adit. No uranium minerals identified0 Radioactivity of Wyandotte vein essentially equal to. background.

10 --- Dump of caved adit; radioactivity essentially equal to background.

11 Dump of Sonny Boy adit; radioactivity essentially equal to background.

12 --- Shaft dump; radioactivity essentially equal to background

13 0.18 0.05-0.10 0.011 0.002 Disseminations (?) in limonite-stained schist and amphi- bolite from hanging 13

Table 1t--Localities tested for radioactivity in the Alma mining district--continued

Maximum radioactivity Locality measure- Background eU U number ment in measurement (percent) (percent) Remarks

mr v / /hr v in mr./hr.v / v 0 o o

wall of narrow fissure zone containing quartz and pyrite; exposed by Sweet Home adit0 Radon present0

14 Dump of caved adit; radioactivity essentially equal to background0

15 0.13 0O0-0.07 --- Disseminations (?) and limonite-stained fracture coatings in fresh granite from dump of caved shaft (?)o

16 015 .02-0.09 O.006 0.005 Disseminations (?) in pyritic, siliceous vein material from dump of main Champaign adit.

17 019 .002-0.09 0005 0003 Disseminations (?) in limonite-stained vein material from dump of caved adit.

.07 Disseminations in pegmatite exposed by adit.

19 Schist and granite exposed by adit; radioactivity essentially equal to background. 14

Table l,--Localities tested for radioactivity in the Alma mining district--continued

Maximum radioactivity Locality measure- Background eU U number ment in, measurement (percent) (percent) Remarks

mr./hror y y

20 0p50 0.05 0.010 0.013 Disseminations (?) in pyritic, siliceous vein material from Champaign fissure; exposed by adit0 21 0.15 0.05-0.10 0.004 0.002 Disseminations (?) in limonite and manganese oxide-stained vein material exposed by adit0

Dumps of several adits and shafts which previc ously exploited silver- lead replacement deposits in Leadville dolomite; radioactivity essentially equal to back ground0 27 Dump of caved Oliver Twist adit; radioactivity essentially equal to background0

28 0.13 0.01-0. 07 0. 008 0.002 Disseminations in brownish-black Penn- sylvanian shale from shallow prospect trench adjacent to Hard-To-Beat workings. Similar material from the dump of a nearby caved shaft is mildly radioactive 0 No uranium minerals identified. 29 013 .01-0.08 o006 .001 Disseminations in sheared, brownish-yellow Pennsylvanian shale from dump of caved Hard- To-Beat adito No uranium minerals identified0

30 015 .05-0.10 0007 .005 Sheared, dark-colored Pennsylvanian shale from dump of North London mine. 15

Table l;-Localities tested for radioactivity in the Alma mining district--continued

Maximum radioactivity Locality measure- Background eU U number ment in measurement (percent) (percent) Remarks in mrr/hr. mr++ oV /hr oV v v

31a 050 o50-007 044 0044 Yellow fault-gouge (?) from dump of South London mine0

31b o05-0.07 0021 o024 Rock fragment coated with secondary uranium minerals; from dump of South London mine0

31c 0050 0.02-005 --- Pitchblende (?) associated with galena, pyrite, and chalco- pyrite in vein material from dump of South London mine0

31d* 6.7 6011. Colloform pitchblende (?) in fine-grained, dark-colored, sulfide vein material from dump of South London mine. Spectrographic analysis shows XX U, Pb; X. Zn; 0X, Mn, Cu, V, Ba, Ca, Au; 0 0X Co, Y, Ag; 000X Be, Cr. (Chemical and spectrographic analyses made upon hand-picked radioactive material.)

32 Dump of American shaft; radioactivity essentially equal to back= ground

33a 0010 005-0007 00004 0.002 Dark-blue, gouge-like material from dump of London Extension mine. 16

Table l--Localities tested for radioactivity in the Alma mining district --continued

Maximum radioactivity Locality measure- Background eU jU number ment in measurement (percent) (percent) Remarks mr /hr. in mr./hr. i ..

33b 0'80 .05-0.07 1.5 1.66 Pitchblende associated with banded gold-silver-lead= zinc ore from dump of London Extension mine. The pitchblende occurs in veinlets which cross- cut the quartz and sulfide minerals. Secondary uranium minerals coat fractures0 34 Dump of London Butte mine; radioactivity essentially equal to background.

35a 0050 0.01-0.04 0.072 0.033 Pitchblende, not visible megascopically, in iron= stained, pyritized, friable rock from remnant of ore stockpile at former Phillips mill. Dis- equilibrium caused by excess radium; no thorium detected.

35b 0.13 Q.01-0.04 0.013 0.005 Disseminations in unoxidized quartz- pyrite sphalexite- galena-bearing vein material from site of former Phillips mill. No uranium minerals identified. 17

Table 1t--Localities tested for radioactivity in the Alma mining district -- continued

Maximum radioactivity Locality measure- Background eU :U number ment in measurement (percent) (per cent) Remarks mr /hr in mr./hr V, 0

36 Dump of caved adit; radioactivity essentially equal to background0

37 0.o18 0.0l-0.04 00010 00009 Disseminations in rock from the footwall of a pyrite- sphalerite=dolomite vein in quartzite; exposed by Buckskin Joe adit0 No uranium minerals identified. Radioactivity of vein essentially equal to background.

Dumps of main and surrounding shafts, Shelby mine; radio= activity essentially equal to background 0

39a 0003 0.001-0.02 Wall of minor branch fissure exposed by' Shelby adit0

39b 004 .01-0.03 Small area of gouge in minor branch fissure exposed by Shelby adit0

40 Dumps of 4 shafts n near Shelby adit; radioactivity essentially equal to background0

41a 100 0-0.04 0091 1000 Pitchblende as fracture coatings Table l 0-Localities tested for radioactivity in the Alma mining district--continued

Maximum radioactivity Locality measure- Background eU U number ment in measurement (percent) (percent) Remarks Mr./hr.o in mr.o/hr.o

in pyritized, silicified quartz monzonite porphyry from ore pile in Orphan Boy mine.

41b O0.l8 0-0.04 -- --- Disseminations in footwall of gold- base metal vein in quartzite; exposed by Orphan Boy adito The radioactivity occurs at the top of an ore shoot and within or immediately below a Tertiary quartz monzonite porphyry sill which caps the ore shoot.

42 --- m-r=------Dump of caved Brownlow adit; radioactivity essentially equal to background.

43 ------Dump and that part of underground workings traversed, Hock Hocking mine; radioactivity essentially equal to background. 19

A locality or specimen is considered to be anomalously radioactive

if the ratio of the maximum radioactivity measurement to the average background is equal to or greater than 1.7. The average background is taken, for convenience, as the arithmetic mean of the background measurement. Localities at which the ratio is less than 1.7 are not regarded as anomalously radioactive. The anomalously radioactive category has been divided into two classes, as follows: 1) ratio of maximum radioactivity measurement to.average background lies in the range 1.7-30; and 2) ratio is greater than 3.0.

With three exceptions out of twenty-two samples, as indicated in table 2, the percentages of equivalent uranium obtained by laboratory analysis ranges from 0004 to 0.008 in samples from localities at which the ratio of the maximum radioactivity measurement to average background is 107-3.0, and more than 0.0 08 where the ratio is greater than 30.

The percent equivalent uranium for localities at which the ratio is less than 1.7 doubtless is less than 0.004. Accordingly, the percent equivalent uranium may be roughly estimated for occurrences for which no laboratory analyses are-available (e.g., locality 18). Ratios are not available for 31b and 31d, but these occurrences have been assigned to the third group because of their relatively high uranium contents.

THE URANIUM OCCURRENCES

In the Alma district, uranium minerals are associated with Tertiary vein deposits of three different geologic environments: 1) veins in pre-Cambrian rocks; 2) veins of the London vein system; and 3) veins in a mineralized belt east of the Cooper Gulch fault. The known occurrences, although not of immediate commercial importance, offer moderate encouragement for further search. 20

Table 2.--Relationship between (1) ratio of maximum radioactivity

measurements to average background and (2) percentages of

equivalent uranium l/

Range of Symbol used for Number of localities Percent equivalent ratios figure 3 or occurrences uranium for analyzed

specimensV v y

1.7-3.0 cr6ss-in-square 9 OOO4-OOO8 2/ 3.1-50.0 solid square 13 OOO8-15 /

l/ Percent equivalent uranium has not been determined for the 19 localities at which the ratios are less than 17, nor for 9 occurrences for which the ratios are equal to or greater than 1.7. Ratios are not available for 2 occurrences for which per= cent equivalent uranium has been determined.

2/ Except for Locality 13 (0.011%) where radon in adit caused ratio of maximum radioactivity measurement to background to be exceptionally low.

/ Except for Localities 17 (0.005%) and 28 (o.0oo%)0 21

Veins in pre-Cambrian rocks

At localities 2 to 9, 13, 15 to 18, 20, 21 (fig. 3) veins or

material from veins in the pre-Cambrian rocks of the Alma district

were found to be anomalously radioactive. Localities 1, 10 to 12, 14,

and 19 show no abnormal radioactivity. Localities 11 and 12 are in

quartz monzonites of Tertiary age intruded into pre-Cambrian rocks.

At the Kentucky Belle mine (8) disseminated pitchblende, not visible megascopically, occurs in the crushed rock of a 4-inch to 6-inch thick

breccia zone in granite and pegmatite. A sample from the dump of a

nearby caved adit (3) contains pitchblende and pyrite in a narrow

vein that cuts granite. As much as 0013 percent uranium is contained

in pyritic, siliceous vein material from the Champaign fissure (20).

Radon was detected in the Sweet Home mine (13).

No secondary uranium minerals have been determined but one or more are probably present in such oxidized samples as 8a and 21.

London vein system

Anomalously radioactive material from the dumps of mines along the

London vein system was found at localities 28 to 31, an'd 33, but not at

localities 27, 32, 34 (fig. 3).

Slightly radioactive, gouge-like material, as well as specimens that contain pitchblende associated with banded gold-silver-lead-zinc ores were found on the dump of the now inoperative London Extension mine (33). The hard, lusterous pitchblende occurs in veinlets that

cross-cut the quartz and sulfide minerals. Secondary uranium minerals

coat fractures in these specimens. Pitchblende associated with sulfide 22 vein material, and secondary (?) uranium minerals associated with yellow fault-gouge (?) were found on the dump of the South London mine (31).

Slightly radioactive shale, presumably from the lowermost 150 feet of the Pennslyvanian series, was found on dumps and in a prospect trench at the Hard-to-Beat mine and vicinity (28, 29). It probably came from a shear zone in the west wall of the London fault. Some Pennsylvanian shale on the dump of the North London mine (30) is mildly radioactive.

Veins east of Cooper Gulch fault

In the mineralized area east of the Cooper Gulch fault, veins or vein material from localities 35, 37, 39 and 41 (fig. 3) show anomalous radioactivity. Localities 36, 38, 40, 42, and 43 are not anomalously radioactive.

At the Orphan Boy mine (41; and fig. 2) anomalous radioactivity, probably caused by'pitchblende, was detected in the footwall of the gold-base-metal vein in Sawatch quartzite of Cambrian age. The radioactivity occurs at the top of an ore shoot (41b), and within or immediately below a Tertiary quartz monzonite porphyry sill that caps the ore shoot0 -A sample of pyritized and silicified quartz monzonite porphyry (41a) from an ore pile in the this mine contains pitchblende as fracture coatings.

In the Buckskin Joe mine (37) a sample from the footwall of a pyrite-sphalerite-dolomite vein in Sawatch quartzite contains 0.009 percent uranium, but the other parts of the vein are not anomalously

radioactive

Other localities at which anomalous radioactivity was noted are 23

a remnant of an ore stockpile at the former Phillips mill (35), and the

underground workings of the Shelby mine (39)0

Disequilibria in the uranium occurrences

Inspection of the laboratory analyses for uranium and equivalent uranium (table 1) shows that the ratio of percent uranium to percent

equivalent uranium in samples from the Alma district ranges from a minimum of 0013 (locality gb, fig. 3) to a maximum of 1,30 (20).

The ratio is equal to or less than 100 to 20 of the 24 analyses.

Two of the samples (8a, 35a), which exhibit ratios of less than

0054, were analyzed for radium and thorium contents. No thorium was detected, and radium and other daughter products of uranium are in

excess with respect to the uranium present in the samples. It is

probable that the disequilibria in all or most of the samples where the ratios are less than 10 have been caused by removal of uranium by supergene processes.

The four causes where the ratio is greater than 1.0 probably re-

sulted from the combination of analytical errors and loss of radon during sample grinding.

Non-anomalously radioactive localities

Some non-anomalously radioactive localities, previously listed,. have been found in each of the three geologic environments discussed.

Silver-lead replacement deposits irn dolomite, where tested for radioactivity at New York Mountain in (localities 22, 26, fig. 3) and at the Hock Hocking mine (43) were not anomalously radioactive. The 24

silver-lead dolomite replacements of the Mount Lincoln-Mount Bross area

have not been tested0

Origin

Because of its close association with the Tertiary base-and precious- metal veins, the pitchblende of the Alma district is believed to have been deposited by hypogene processes. The secondary uranium minerals

resulted from supergene alteration of the primary pitchblendeo

LITERATURE CITED

Singewald, Q. D., and Butler, B. S., 1933, Suggestions for prospecting in the Alma district, Colorado: Colorado Sci. Soc0 Proco, vol. 13, no. 4, pp. 89-131.

, 1941, Ore deposits in the vicinity of the London fault of Colorado: U. S. Geol, Survey Bull. 911, 74 ppo

Singewald Q. Do, 1947, Lode deposits of Alma and Horseshoe districts, Park County, Colorado, in Vanderwilt, J. W., editor, Mineral resources of Colorado; State of Colorado Mineral Resources Board, pp. 336 341.

1l950, Gold placers and their geologic environment in north- western Park County, Colorado: U. 5 Geol. Survey Bull. 955-.D, pp. 103-172. OFFICIAL USE ONLY

.25

TEI-248 - Part II

PLANS AND RECOMMENDATIONS

The Alma district is considered a moderately favorable area in which to prospect for uranium ore because twenty-four out of forty-three localities tested are anomalously radioactive; samples from these localities have uranium contents that range from 0.001 to 1.66 percent. One analysis of handpicked radioactive material, showing 6.11 percent uranium (locality

3ld, fig. 3) was made.

The Geological Survey has no plans for further work in the Alma district at this time. If in the future, however, it is desirable to- resume work in the district, the following localities are considered most favorable for further investigations by reconnaissance and by physical exploration.

Additional reconnaissance for radioactive materials

Reconnaissance for radioactive materials is warranted in the areas which are listed below by geologic type. The first three areas are about equally promising; the fourth is decidedly less promising than the other

three.

1. Mines of the London vein system: Underground traverses should be made in all accessible workings of the London Extension (locality 33, fig. 3), American (32), Havighorst, Ophir, Mosher, North London (30), and

South London (31) mines in the attempt to find pitchblende in place. The chances of favorable results are minimized, however, because the pitchblende so far observed occurs with high-grade ore, which for the most

OFFICIAL USE ONLY OFFICIAL USE'ONLY

26 part has been mined out. A traverse for radioactive material of the

London Butte mine (34) by King J, of the Geological Survey, during

j King, R. U0 , Personal communication,

February 1951 did not reveal a significant amount of radioactivity, but this does not necessarily condemn the mine, because the workings then accessible were mainly in non-productive ground, rather than in ground from which the bulk of the gold ore had been mined,

2. Pre-Cambrian rocks: The results of testing the dumps and the very limited underground workings now accessible at the Kentucky Belle (8),

Champaigne (16), and Sweet Home (13) mines justify additional reconnaissance for radioactive materials at the many mines and prospects in pre-

Cambrian rocks of the Alma district that were not tested during the 1951 investigation. Mines and areas, shown on plate 1 of Geological Survey

Bulletin 911 (Singewald and Butler, 1941) that should be examined, are

1) the workings above the Sweet Home mine (13, radon gas), 2) Platte

Gulch, 3) Lower Mosquito Gulch (secs. 8 and 16, T. 9 S, R. 78 W.), and 4) North Mosquito Gulch (sec. 6, T. 9 S, R. 78 W.).

3. Mineralized area east of Cooper Gulch fault: The rather high uranium content of specimens from two localities (35, and 41) among mines'within a mineralized area along the east side of the Cooper

Gulch fault makes desirable additional reconnaissance for radioactive material of untested mines and mine dumps, including the Paris, in this geologic environment. The principal mines and prospects are shown on plate 1 of Geological Survey Bulletin 911 (Singewald and Butler, 1941).

OFFICIAL USE ONLY OFFICIAL USE ONLY

627

In addition, the older workings of the Buckskin Joe (Phillips) mines,

traversed only in part during 1951, should be tested for radioactive

material because pitchblende was found in the remnant of an ore stock-

pile at the ancient mill site0

4. Silver-lead replacement deposits in dolomite in the Mount

Lincoln-Mount Bross area The Russia, Moose, Dolly Varden, and many

lesser mines and prospects on Mounts Lincoln apd Bross that have yielded

silver-lead ore from replacement deposits in dolomite remain untested

for radioactive material and, therefore, should be investigated. They

are not considered favorable, however, because the bulk of the ore came

from oxidized, or partly oxidized ground, and because somewhat similar

deposits at New York Mountain (22-26) and at the Hock Hocking mine (43)

apparently are not anomalously radioactive0

Physical Exploration

Physical exploration is probably the best way to determine the

extent of radioactive occurrences at the following localities:

l1 Kentucky Belle mine (8): Portal of adit is 1910 feet N. 52 W

from NW, corner of sec0 28, To 8 So, R0 78 W. Exploration is suggested along a 4 to 6-inch breccia zone that strikes N0 200 W. and dips

750800 SW0 from which a sample (8a) was taken approximately 273 feet

from the portal0 Bad air encountered at about 400 feet from the portal precluded adequate reconnaissance even of the exposed part of this zone0

Concurrently, as the bad air is cleaned, examination of radioactive material should be extended into ground from which most of the commercial ore was obtained, i.e., within and near a White porphyry dike which apparently was cut by the adit less than 1,000 feet from the portal0

OFFICIAL USE ONLY OFFICIAL USE ONLY

2. Shallow trench (7): 2260 feet No 290 30' W. from NW. corner

of sec. 2g, To g S., R. 78 W. Exploration is recommended along a 4 to

6-foot thick fissure 9 which strikes No 350 W. and dips 750 SWo

3. Prospect adit (6): Portal of adit is 2270 feet N. 240 30' Wo

from NW0 corner of sec,, 28, To S , R0o78 W. Exploration is recommended along a radioactive fissure trending N. 330 Wo, 660 SWo, which the adit follows.

4. Adit (20): Portal of adit is 200 feet No 820 E. from NW.

corner of sec0 6, To 9 So, Ro 78 Wo Exploration is suggested along the Champaigne fissure which is exposed by the adit0 The attitude of the fissure is No 300- 350 E0 9 500- 700.NW0

5. Orphan Boy mine (41): Portal of adit is 4360 feet No 690 30' W. from SEo corner of sec0 109 To 9 So, R 78 W. Exploration is in the drift from which samples 41a and 41b were taken (fig. 2)9 and in any other favorable localities that may be found through additional re-

connaissance for radioactive materiAl; in the old workings0

OFFICIAL USE ONLY UNITED STATES DEPARTMENT OF THE INTERIOR TRACE ELEMENTS INVESTIGATIONS GEOLOGICAL SURVEY REPORT 248

+80 feet to fork, +another 375 feet EXPLANATION to breast of western fork: porphyry 41 . all the way; no anomalous radioactivity. 70 L 4/b Adlevel Gray porphyry Quartz monzonite

Porphyry forms 9 M- N top of stope 4 O LiJ U Sawatch quartzite : pile c a 80 z Q~ 4cr 0 6 ' 3' Schist and gneiss

Large stope Porphyry forms 40 top of stope Contact showing dip Dashed where inferred

Stope inclined down to 70 " p NE and also downdip Vein showing dip Dashed where inferred Adlee j Porphyry forms -e level ' 1.Asa top of stop 90 #75"-/14020' i75 -\- Vertical vein Dashed where inferred

55-8 0 . WaterZ 30 70 ** /ase Strike and dip of beds 0 z--- 4/a ( Chute Radioactive locality; Base of Sawatch I Q number refers to quartzite I description in table I. 45-80-

1- . Inclined workings, chevrons point down Portal

Base by compass and pace traverse Geology by Q.D. Singewold and C.T. Pierson, August 1951 FIGURE 2 -GEOLOGIC SKETCH MAP, PART OF ORPHAN BOY MINE, ALMA MINING DISTRICT, PARK COUNTY, COLORADO, SHOWING RADIOACTIVE LOCALITIES.

200 0 200 400 Feet I I I I- I PO 82-8000698 vrv oc ovvvo7o LJfTrJ rrJfJVT :77F777~rTriT fl TL <77 77711U

UNITED STATES DEPARTMENT OF THE INTERIOR TRACE ELEMENTS INVESTIGATIONS GEOLOGICAL SURVEY REPORT 248

106010' R. 78W. 106005' EXPLANAT ION T ~ ----- 7

__ SUMMIT CO. C' LAKE CO. Bartlett North Star Mtn. to I- Quartz monzonite stocks U, 0 01 heler Lake CE PCu -Q0 W 12 < - wai Sedimentary rocks 0 Undifferentiated ttHooser Uo P 9P l154L 13e46Traver Peak PAL

4 13 Pre-Pennsylvanian sedimentary rocks z -14020 inCo CE -/ 4284 m T 8S. V / Mt Cameron -Q 1 '423 T. 8 S. Schist -injection gneiss series LU Whitish-gray granite and pegmatite CE o Mt.Democrat ' / a. z 2E3 \-23 w 3 a 8 c Kentucy elle CC zW r -'- anaotte ~~ML14169 Contact 39020' 39 20' Dashed where approximately located Mkeosqit /1 s ma/Lakes 1 Sny Major fault _.y/- u2-/ P~u 25 Dashed where approximately located

M.Buckskin Inferred fault

/ 04PALS30r3 ampa'gn/6kHome Mineralized area 6~j 5/ r I3 Note- Early Tertiary intrusive porphyries occur abundantly as sills, dikes and laccoliths MosquSho P ot2d - (0/a/ /ndo . a*weab (EI30353 New York tn.-24 / in all formations. 26 5 4 3-2/1 a257 e12 26 Mine, mine dump,or prospect pit radiometrically tested Hard-To-Beat 93 - 'r Number refers to description in table /

I LoLodon 103a5,b (E1.10353) see by M37 Bu kskin Joe Alma MAXIMUM J /40 1 rphan RADIOACTIVITY b39a b9 41a b Boy1 //32 American 1 II o ;3I ,b,c,d /1 112rA~t 0 r ' X11 ~South Lodon/ Less than 1.7 times average background

Ldon 33a®8 33b0 o Extension 34 London Btte 1.7-3 times overage background

f QSouthPennsyfvania Brown ow 42Q15 % 4 13/ 18 Mtn-1 6043 Hc okn Greater than 3 times average background

T9S. P-A 1Mt. Evans T.9S.

/ 1 9~7 12 201 P 9

39015' 39015' I0 6 0'0 R. 78 W. 1 6 5'

ami Geology reproduced from plate 8,U.S.Geological Survey Bull.955-D, 1950 Geology by Q.D.Singewald,J.W. Vanderwilt, Base from Geological Survey maps R.E.Landon,and B.S.Butler, 1928-1932 Radiometry by Q.D.Singewald,C.T. Pierson, V.R.Wilmarth,and R.C.Vickers,1951

FIGURE 3 -GENERALIZED GEOLOGIC MAP OF THE ALMA DISTRICT, PARK COUNTY, COLORADO, SHOWING AREAS RADIOMETRICALLY TESTED.

Scale 1:62,500

0 i 2 3 4Miles . . . . . | i _

5000 0 5000 i0,000 15,000 Feet GPO 82-8000698 Datum is mean sea level w _ w

_ l