GEOLOGICAL SURVEY CIRCULAR 345

RADIOACTIVITY RECONNAISSANCE 

OF PART OF NORTH-CENTRAL 

CLEAR CREEK 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 INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

GEOLOGICAL SURVEY CIRCULAR 345

RADIOACTIVITY RECONNAISSANCE OF PART OF NORTH-CENTRAL 

CLEAR CREEK COUNTY, COLORADO

By John D. Wells and Jack E. Harrison

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.
GRA

I

N D j

S B OULDER

r

(

G 1 L P

CITY

lDAHO SPRINGS 1

GOLDEN 

O

GEORGETOWN

CLEAR CREEK

J EFFERSON

i

J 

ARK

)

10 0 i ......... i

20 Miles 

_l

Figure 1. Index map of central Colorado showing area covered by reconnaissance.

ii
RADIOACTIVITY RECONNAISSANCE OF PART OF NORTH-CENTRAL 

CLEAR CREEITCOUNTY, COLORADO

By John D. Wells and Jack E. Harrison

CONTENTS

Page

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

Introduction.................................. 1

Background radioactivity...................... 2

Instruments.................................. 2

Method of reconnaissance ..................... 2

- Surface reconnaissance .................. 2

Underground reconnaissance.............. 3

Radioactivity of dump material................. 3

Page

Abnormal radioactivity........................ 3

Classification........................... 3

Mineralogic data ........................ 3

Relation between mineralogy

and radioactivity....................... 8

Economic significance ................... 8

Literature cited. ............................. 8

Unpublished reports .......................... 9

ILLUSTRATIONS

Page

Figure 1. Index map of central Colorado showing area covered by reconnaissance........................... ii

2. Map of part of north-central Clear Creek County, Colorado, showing

radioactivity of localities examined......................................................... 4

3. Map of part of north-central Clear Creek County, Colorado, showing

distribution of vein types.................................................................. 7

TABLE

Radioactivity and mineralogic data for localities of high, moderate, 

or low abnormal radioactivity.................................

Page 

. 5

ABSTRACT

A radioactivity reconnaissance of 334 localities 

in north-central Clear Creek County, Colo., was made 

during the field seasons of 1951 and 1952. This reconnaissance, made with a portable scintillation counter 

and a portable survey meter with a 6-inch gamma-beta 

Geiger tube, disclosed that seven of the localities contain sufficient uranium to warrant some physical exploration.

Within the area studied, the localities containing 

chalcopyrite have the highest grade and highest percent 

of occurrences of significant abnormal radioactivity. 

Zones of galena-sphalerite veins have approximately 

the same rate of occurrence of significant abnormal 

radioactivity as zones of galena-sphalerite with chalcopyrite. Any locality or zone containing pyritic-type 

veins without chalcopyrite is considered unlikely to contain a uranium deposit.

INTRODUCTION

As a part of the U. S. Geological Survey's investigations of the uranium-bearing deposits in the 

Central City-Idaho Springs region (fig. 1), a radioactivity reconnaissance was carried on in northcentral Clear Creek County in 1951 and 1952. This 

work was done on behalf of the Division of Raw 

Materials of the U. S. Atomic Energy Commission.

The purpose of the reconnaissance was to determine the distribution and economic importance 

of the radioactive occurrences in the region. Three 

hundred and thirty-four localities mine dumps and 

accessible underground workings were examined with 

a portable scintillation counter and a portable survey 

meter with a 6-inch gamma-beta Geiger tube. The 

methods of the reconnaissance are briefly described, 

because they might be of use in similar, future 

studies.
The radioactivity data of this report were collected largely "by Wells; Harrison is responsible for 

most of the information on the Freeland-Lamartine area 

(Harrison and Wells, manuscript in preparation). 

F. B. Moore of the Geological Survey collected some 

of the data on the Fall River area, in the northern part 

of the area covered by this survey. Radioactivity data 

from the northeastern part of the Fall River area, 

published by the Atomic Energy Commission (Smith 

and Baker, 1951, p. 5-10), has been incorporated in 

this report.

As classified by Bastin and Hill (1917, p. 105), 

the veins in the area covered by this report are of three 

general types: (1) pyritic, containing predominantly 

quartz and pyrite, with lesser amounts of chalcopyrite; 

(2) galena-sphalerite, consisting principally of galena, 

sphalerite, pyrite, and quartz, with subordinate amounts 

of chalcopyrite; and (3) composite, consisting of veins 

of type 1 that are crosscut by stringers of type 2. Radioactive minerals are most commonly associated with 

veins of types 2 and 3.

BACKGROUND RADIOACTIVITY

Background, as defined by Korff (1946, p. 23-24), 

is the instrument reading at a particular time and place 

caused by internal contamination of the counter, cosmic 

radiation, and the natural radioactivity of the surroundings. In precise laboratory determinations of 

radioactivity, the effects of these three factors are 

carefully determined. In the field, however, these 

factors can only be roughly accounted for. A field survey for radioactivity is concerned primarily with the 

measurement and interpretation of variations in the 

natural radioactivity of the surroundings; for this purpose, internal contamination of the instruments is negligible and can be ignored. However, the variation in 

cosmic radiation from day to day and with changes in 

altitude must be reckoned with. In addition, in northcentral Clear Creek County, the variation in the natural 

radioactivity of the rocks must be considered.

The natural radioactivity of the rocks in northcentral Clear Creek County varies widely between preCambrian schistose rocks, mafic rocks, granite gneisses, 

and Boulder Creek granite, which are low in radioactivity, and the pre-Cambrian Silver Plume granite 1 

and the Tertiary intrusive rocks, which are relatively 

high. The natural radioactivity of most of the veins 

is low. Certain veins, even though they contain radioactive minerals, have a lower average radioactivity 

then the Tertiary intrusive rocks and the Silver Plume 

granite.

In order to distinguish the radioactivity that is 

average for the Tertiary dikes and Silver Plume granite 

from the radioactivity that is higher than average for 

the veins, a low background was chosen and the radioactivity readings separated on the basis of source material. Radioactivity from both sources was higher than 

background, but only the readings from veins were considered abnormal. The term "background radioactivity," 

as used in this report, is the average radiation recorded

1 From the analyses of many samples, Phair (1952) found that the 

Tertiary intrusive rocks have an equivalent uranium content ranging from 

0.002 to 0.024, but generally this content is less than 0.020 percent. 

A sample of Silver Plume granite, considered representative, contained 

0.006 percent equivalent uranium.

at a given place and time over material known to be 

low in natural radioactivity. "Abnormal radioactivity" 

is defined for this report as the radioactivity caused 

by a concentration of radioactive material in veins. 

The anomaly recorded from the highly radioactive 

country rocks will not be discussed further in this 

report.

INSTRUMENTS

A portable scintillation detector and a portable 

survey meter with a 6-inch gamma-beta Geiger tube 

were used for the reconnaissance. Although both of 

these instruments measure radioactivity, the characteristics of each instrument are such that one supplements the other.

The portable scintillation detector measures 

gamma radiation only. Gamma radiation is more penetrating than beta radiation and can be detected through 

greater thicknesses of rock and at greater distances 

from the source than beta radiation. In addition, a 

scintillation counter has a much higher efficiency for 

the detection of gamma radiation than does a Geiger 

counter (Brownell, 1950, p. 167).. A scintillation detector is well adapted for field use when the purpose 

is to detect changes in the amount of gamma radiation 

dependent upon quantity or bulk of radioactive -material 

regardless of grade, and was used in this reconnaissance to locate areas of abnormal radioactivity. The 

survey meter, on the other hand, is sensitive to a 

small source area and was used in this reconnaissance 

to isolate the specific mineral or material causing abnormal radioactivity.

Although both instruments will detect the presence 

of radon in a mine, they give little indication of its 

quantity. In the presence of radon, both instruments 

will show a gradual increase in amount of radiation 

recorded, even though the instruments are kept stationary. Even after the instruments are brought out of 

the mine, higher-than-normal readings will continue 

for some time.

METHOD OF RECONNAISSANCE

Radioactivity surveys were made on the surface 

and underground. The general procedure was to determine the background for the instruments, traverse 

the area, record any abnormal radioactivity, and 

sample areas that showed more than twice background on the rate meter.

Surface reconnaissance

The first procedure of surface reconnaissance 

was to determine the local background for the instruments. At the time of the examination, in 

order to eliminate variations in cosmic radiation, 

the background for the scintillation counter was 

determined within a few hundred feet of the area. 

The background for a rate meter with a gammabeta probe was determined by holding the probe 

several feet in the air to eliminate the effect of 

the rock material. The background was found to 

be constant at different places and times for the 

rate meter but variable for the scintillation counter.
The area or dump to be examined was then 

traversed, using the scintillation counter. Traverses were made about 6 feet apart, holding the 

counter a few inches from the ground to obtain 

readings from a maximum depth. The traverses 

were made slowly to allow the instrument time 

to make an average radioactivity count of the material being traversed.

Abnormal radioactivity that was more than 

twice background on the rate meter was considered 

significant, and the radioactive material was sampled. 

Abnormal radioactivity that was less than twice background on either instrument is reported in this paper, 

but the material causing the radioactivity was not 

sampled. Laboratory determinations of uranium and 

equivalent uranium were made for all samples that 

were collected.

Underground reconnaissance

A procedure similar to that for surface reconnaissance was followed for underground reconnaissance. Generally, the background is slightly higher 

underground than at the surface because of the proximity of a greater surface of the radioactive rock. 

The background was established underground by recording the instrument reading at least 50 feet from 

the portal or shaft.

Traverses were made by carrying the instrument 

at waist height. The scintillation counter repeatedly 

recorded anomalies from small areas and thin fractures, 

samples from which commonly assayed as low as 

0.006 percent equivalent uranium.

Traversing of mines that contain radon is impractical because the instrument becomes contaminated. 

Henry Faul (oral communication), of the Geological Survey has eliminated some of this contamination by placing 

the probe of the instrument in a plastic or rubber bag 

before entering a mine containing the gas.

RADIOACTIVITY OF DUMP MATERIAL

The assumption is made that the radioactive materials associated with Tertiary veins are in equilibrium. 

However, results from more than 40 chemical assays 

show that most of the samples, particularly those 

collected from dumps, contain less uranium (U) 

than the radioactivity measurements (eU) of these samples indicates (table, p. 5). Phair and Levlne (1952, 

p. 14) have shown that this disequilibrium can be caused 

by acid solutions that leach uranium and leave a concentration of less soluble radioactive disintegration products of uranium. Because the uranium is leached rapidly 

from mate rial on dump surfaces, the radioactivity of a 

dump sample, rather than the actual uranium content of 

that sample, is probably more representative of the amount of uranium originally present in the material.

The failure to discover radioactive material on a 

dump does not necessarily mean that such material does 

not occur in the mine. The dumps of several inaccessible mines have been reported to show no abnormal radioactivity, but underground examinations following reopening of the mines have revealed significant amounts 

of abnormal radioactivity.

ABNORMAL RADIOACTIVITY

During the reconnaissance the grade of radioactive material could not be determined accurately 

because of the limitations of the instruments and because the measurements were made, of necessity, on 

nonhomogeneous samples of different sizes. Therefore, the laboratory determinations of equivalent uranium and uranium are used in the report. The localities showing abnormal radioactivity are given in the 

table (p. 5).

Classification

The intensity of abnormal radio activity (equivalent 

uranium) is here classified as (1) slight, if the radioactivity is greater than background but less than twice 

background; (2) low, if the equivalent uranium ranges 

between 0.005 and 0.020 percent; (3) moderate, if the 

equivalent uranium ranges between 0.021 and 0.099 percent; and (4) high, if the equivalent uranium is 0.10 percent or more. Localities where abnormal radioactivity 

was noted are shown on figure 2. This classification is 

based upon both field instrument readings and laboratory 

determinations of equivalent uranium, because samples 

were not collected from localities with abnormal radioactivity less than twice background. As determined by 

the writers the percent equivalent uranium that is equal 

to twice background is approximately 0.005. Information 

on localities containing slight abnormal radioactivity is 

not given in the table (p. 5).

The upper limit of low abnormal radioactivity was 

placed at 0.020 percent equivalent uranium, because all 

of the pre-Cambrian rocks and most of the Tertiary intrusive rocks in the area contain less than 0.020 percent equivalent uranium. The range of low abnormal 

radioactivity overlaps the range of radioactivity of 

some of the country rocks (see section on background 

radioactivity). The moderate abnormal radioactivity 

class has more equivalent uranium than the country rocks, but less equivalent uranium than present ore-grade material. The high abnormal radioactivity class has equivalent uranium equal to or 

greater than that of present ore-grade material.

Mineraloglc data

The mineral suites identified at the localities 

included in .this report have previously been recognized by Spurr, Garrey, and Ball (1908) and 

by Bastin and Hill (1917). Bastin and Hill (p. 105) 

have shown that these mineral suites are characteristic of three vein types: (1) pyritic, predominantly pyrite and quartz with minor amounts of 

chalcopyrite; (2) galena-sphalerite, predominantly 

galena, sphalerite, pyrite, and quartz with a subordinate amount of chalcopyrite; and (3) composite, 

veins in which stringers of type 2 crosscut veins 

of type 1. This classification, with modification, 

is used in this report.

Because much of the data in this report were 

obtained from dumps, the detailed relationships between vein types necessary to identify the composite type of vein are unknown. The composite 

type of vein, therefore, cannot be discussed here 

and is not shown on figure 3.
LOCALITIES EXAMINED FOR 

RADIOACTIVITY

UNDERGROUND EXAMINATIONS

A2

High abnormal radioactivity 

0.10 percent or more eU

A?

Moderate abnormal radioactivity 

0.021-0.099 percent eU

A*

Low abnormal radioactivity 

0.005-0.020 percent eU

A

Slight abnormal radiaoctivity. 

Radioactivity less than twice background

A 

No abnormal radioactivity

DUMP EXAMINATIONS

.32 

High abnormal radioactivity

®5 

Moderate abnormal radioactivity

09

Low abnormal radioactivity

O 

Slight abnormal radioactivity

O 

No abnormal radioactivity

Note: Numbers refer to list of localities

' M I I I I TTT

Approximate boundary between areas 

containing predominantly pyrltic veins 

and galena-sphalerite-chalcopyrlte 

veins. Dashed where inferred

Approximate boundary between areos 

containing predominantly galenasphalerite veins and areas containing predominantly galena-sphalritechalcopyrlte veins. Broken where inferred

R 

Radon gas present in underground workings

14

Base mop from U.S.Geological Survey 

Central City and Georgetown quadrangles

I. Gold Quarti 

2 Almoden tu

3. Golconda t

4. Standard i

5.'(Nome unki

6. ; Pennsylvonio I nnel

7. (Name unknown tunnel 

e. Gold Chlor

LOCALITIES SAMPLED 

(Mineralogy and percent U shown on table, p.5)

a Albra shaft

1. .Golden Calf tunnel

2. MojorC. and Little colonial tunnel*

3 Big Chief tunnel

4 Old Settler tunnel

5 {Old Settler shaft 

6lSunnyside tunnel 

7 Little Johnie group loner tunnel 

8. Little Johnle group middle tunnel

19.'Lane Tree tunnel 

"20. Poor Man tunnel

Zl.feraill lover tunnel 

52. Bel I of the Welt tunnel

23. Harrisburg shaft

24. Craiy Girl sh«ft

25. Ariotfne shaft

26. Miller tunnel

27. Belle Creole tunnel

28.,0lomond Mountain la 

29.Corner snalt 

SOJMortho E. tunnel 

} (.(Name unknawi) 

32 Orinoco tunnel 

SS.Silver Bjnj tunnel

34.|Eclipse tunnel

35.Muscovite upper turn 

3.&Alpine shaft

37. Blockwaod shaft 

M.'Arao tunnel 

S3. 7alland County tunnel 

40,iBoltic tunnel

41. Humbalt lower tunnel

42. tOiiie tunnel

43. Silver link tunnel

44. Kitty Emmet shaft 

49. (Name unknown)shaft 

46. Two Brothers tunnel

Figure 2. Map of part of north-central Clear Creek County, Colorado, showing radioactivity of localities examined.

4
Radioactivity and mineralogic data for localities of high, moderate, and low abn

[Explanation of abbreviations: ga, galena; sp, sphalerite; cp, chalcopyrite; py, pyrite; qtz, quartz; 1m, limonite; pbd, pitchblende; to, totfaernite; aut, a

az, azurite; ma, malachite; cr, carbonate; gos, goslarite; fl, fluorite]

Mine and locality no. 

(fig. 2)

Source of 

mineralogic data

Minerals

ga sp 1 cp 1 py Iqtz 1 1m Ipbd 1 to aut 1 ur 1 ba cc az 1 

High abnormal radioactivity

Almaden (2) 

Golconda (3) 

Golden Calf (11) 

(Lanagan) . 1

MQTJ+-VIQ T? ( ~z,Ct\

Orinoco (32) (Golden

Glen). 1 

Baltic tunnel (40) 

Smith and Baker (1951)-

- __rir>- _ _ - ___ _ _ _ -

Harrison (1952, p. 4-5)-

Dump; also Spurr and

others (1908, p. 377). 

Smith (1952) Y

Y

Y

Moderate abnormal radioactivity

Gold Chloride (8) 

Sunnyside tunnel (15) 

Middle tunnel, Little

Johnie group (l8). 

Poor Man (20) 

Brazil (21) 

P-pa^-w fUrO ( l?li'\ - _ ___

AT>1ar?nf fpR^ ---------

Belle Creole (27) 

ftrrtn£iT» ( PQ^ _ ___-.

Silver (33) (Silverine) . l

Dump 

tion.

. doUnderground 

Dump; also Spurr and

others (1908, p. 575- 

376).

Ar~i

Y

Y

Y

Y

Y Y

Y Y 

Low abnormal radioactivity

Gold Quartz (l) 

Standard (4) 

Dump 

Smith and Baker (1951,

p. 5-10); Bastin and

Hill (1917, P. 312-

313).

Y

See footnote at the end of table.
Radioactivity and mineralogic data for localities of high, moderate, and low abnorma

Mine and locality no. 

(fig. 2)

Source of 

mineralogic data

Minerals

ga sp cp | Py|qtz| lm|pbd| to aut I ur ba cc az 

Low abnormal radioactivity Continued

Pennsylvania (6) 

Name unknown (9) 

Alhrn Mo^ _ ______ -

Major C and Little 

Colonial (12). 

Big Chief (13) 

Old Settler tunnel

(1*0.

Old Settler shaft

(15). 

Lower tunnel, Little 

Johnie group (17)-

T.oni= Tripa flQ^__ _ __

Bell of the West 

(22). 

Harrisburg (23) -

Miller (26) -

Name unknown (31) 

TnVI 11-1=11= (~*ill\ -

Alpine (36) -

R~l nr>lnjnr>r1 f^T^ _ ____-

Ar>crn (^R} _ - ________ -

Tolland County tunnel

(39). 

Humbolt (41) 

n-t-v-tp ( h.p\ _____ __ _

Silver Link (43) 

Kitty Emmet (44) 

Two Brothers tunnel 

(46).

Smith and Baker (1951, 

p. 5-10); Bastin and 

Hill (1917, P. 312- 

313).

Hodo 

____ H n ________ ________ __ _

 do 

Underground 

Dump 

Underground 

 do 

Dump; also Spurr and 

others (1908, p. 333).

 do 

Dump; also Spurr and 

others (1908, p. 370- 

371).

Dump; also Spurr and 

others (1908, p. 374).

_ ____ H n _____ __ _,__ ____ ____

 do 

X

X

X

X 

X

X 

X

X 

X

X 

X

.X

X

X

X

X 

X

X 

X

X 

X

X 

X

X 

X

X

X 

X

X 

X

X 

X

X 

X

___

X

X 

X 

X

X 

X

X 

X

X 

X

X 

X

X 

X

X 

X

X

X

X

X 

X 

X

X 

X

X 

X

X 

X

X 

X

X 

X

X 

X

X

X

X

X 

X 

X 

X

X 

X

X 

X

X 

X

X 

X 

X 

X 

X

X 

X 

X

X

X 

X

X 

X 

X

X

X

1Name in parentheses used in earlier U. S. Geol. Survey publications.
EXPLANATION

O 

Pyritic vein

O

Pyritic vein containing 

chalcopyrite

a 

Galena-sphalerite vein

GJ

Galena-sphalerite vein 

containing chalcapyrite

Limonitlc vein material 

identified;rw primary 

sulfides noted

Approximate boundary between areas containing predominantly pyritic veins 

and galena-sphalerltechalcopyrite veins. Dashed 

where inferred

Approximate boundary between areas containing 

predominantly galenasphalerite veins and areas 

containing predominantly 

galena-sphalerite veins 

with chalcopyrite. Broken 

where inferred

35

14

Base mop from U.S Geological Survey 

Central City and Georgetown quadrangles

2 Miles

Figure 3. -Map of part of north-central Clear Creek County, Colorado, showing distribution of vein types.

7
Leonard (19 52) suggests that in the Central City 

area appreciable quantities of chalcopyrite may occur 

in the intermediate zone between areas of predominantly pyritic-type veins and areas of predominantly 

galena-sphalerite-type veins. The vein type occurring 

at each locality examined during this study is shown on 

figure 3. The area where veins of the pyritic type predominate has been outlined on figure 3. In the southwestern part of the area of this report, in the vicinity 

of Ute Creek, galena-sphalerite-type veins that do not 

contain chalcopyrite predominate. An approximate 

boundary has been drawn between this part of the area 

and the part around Freeland, in which galena-sphalerite - 

type veins that contain chalcopyrite predominate.

Relation between mineralogy and radioactivity

Of the 334 localities investigated, 80 were found 

to have abnormal radioactivity. Seven of the 80 have 

high, 12 have moderate, 27 have low, and 34 have 

slight abnormal radioactivity (fig. 2). The mineralogy 

of all localities having significant abnormal radioactivity 

is given in the table (p. 5).

The relation of significant abnormal radioactivity 

to vein mineralogy is shown in the following tabulation:

Vein type 1

Percentage of localities

with significant 

abnormal radioactivity

Pyritic 

Galena-sphalerite 

Chalcopyrite with both pyrite 

and galena-sphalerite 

Chalcopyrite with pyrite 

Chalcopyrite with galenasphalerite-----------------;

15.5

2k.0 

21.0

2k.1

1 Localities showing only limonite are included with the vein type of 

the geographic area in which they occur.

From the data presented in the preceding tabulation, three observations can be made: (1) The localities where pyrite was the only ore mineral identified 

have a small percentage of significant abnormal radioactivity. (2) The localities where chalcopyrite has 

been identified have the greatest percentage of significant abnormal radioactivity. (3) Approximately the 

same percentage of localities where chalcopyrite and 

pyrite were identified and where galena-sphalerite and 

chalcopyrite were identified have significant abnormal 

radioactivity.

to

The relation of significant abnormal radioactivity 

mineral zones is as follows:

Type of mineral zone 1

Percentage of localities

within zone with 

significant abnormal 

__ radioactivity

Pyritic-type veins 

Galena-sphalerite veins 

Chalcopyrite with galenasphalerite veins 

Area of galena-sphalerite-type 

veins with or without chalcopyrite (zones not delimited 

6.3 

22.9

22.1

10.1

1 Localities showing only limonite are included with the vein type of 

the geographic area in which they occur.

The data in the preceding tabulation are based 

upon the zones as outlined in figure 3, without regard 

for the mineralogy at any particular locality. The 

percentage of the localities with significant abnormal 

radioactivity in the pyritic zone is lower than that for 

the remainder of the area studied. Of the 8 localities 

within the pyritic zone showing significant abnormal 

radioactivity, 3 have chalcopyrite with the pyrite. The 

lack of significant abnormal radioactivity in the central 

part of the pyritic zone is further -emphasized by the 

fact that 6 of the 8 localities are near the margin, and 

no localities with high and only one with moderate abnormal radioactivity occur within this zone.

Consideration of the localities, either individually 

or as they are distributed in mineral zones, leads to the 

conclusion that localities that have the pyritic type of 

vein without chalcopyrite are poor prospects for radioactive materials. The pyritic zone is favorable for 

localities showing significant abnormal radioactivity 

only at its margin. The localities containing chalcopyrite have the highest grade as well as the highest 

percent of occurrence of significant abnormal radioactivity. Five of the seven localities with high abnormal radioactivity contain chalcopyrite. The other two 

localities have galena-sphalerite-type veins. No locality with a pyritic-type vein has high or moderate abnormal radioactivity. If the presence of chalcopyrite 

defines the intermediate zone between the pyritic and 

galena-sphalerite types of veins, then the intermediate 

zone, as suggested by Leonard (1952), appears to be 

the most favorable area for pitchblende prospecting in 

this part of the Front Range.

Economic significance

Only the 7 localities showing high abnormal 

radioactivity contain uranium of ore grade; these 

localities are worthy of at least some exploration. 

As of May 1954, the Golconda and Almaden mines 

were being explored, but no uranium ore had yet 

been shipped." In the Martha E., a 100-foot winze 

was sunk and some drifting done at its foot, but 

only small pods of ore were discovered; further 

exploration is being considered by the owners. The 

owners of the Diamond Mountain mines are considering exploration. No information is available as to 

the possibilities of exploration in the Orinoco mine 

and the Baltic tunnel.

A more objective evaluation of the potentialities 

of uranium production from this region awaits the 

results of detailed studies of the uranium occurrences. 

Additional information from producing mines is necessary to determine the economic significance of the 

various amounts of abnormal radioactivity and the 

pattern of its distribution.

LITERATURE CITED

Bastin, E. S., and Hill, J. M., 1917, Economic geology of Gilpin County and adjacent parts of Clear 

Creek and Boulder Counties, Colorado: U. S. Geol. 

Survey Prof. Paper 94.

Brownell, G. M., 1950, Radiation surveys with a 

scintillation counter: Econ. Geology, v. 45, 

p. 167-174.
INTERPRETING GROUND CONDITIONS 

FROM GEOLOGIC MAPS

Prepared by the Geologic Division

Intelligent planning for heavy construction, water supply, or other 

land utilization requires advance knowledge of ground conditions in the 

area. It is essential to know:

1) the topography, that is, the configuration of the 

land surface;

2) the geology and soils, that is, the deposits that 

compose the land and its weathered surface; and

3) the hydrology, that is, the occurrence of water 

whether under or on the ground.

These elements usually are considered in planning land developments that involve much investment; detailed surveys generally are made 

of the topography, geology, soils, and hydrology at the site selected for 

development. Such detailed surveys are essential, but equally essential 

and often overlooked is the need for general surveys prior to site selection.

Only if the general surveys have been made is it possible to know 

that a particular site is most suitable for the purpose and that no situations in the tributary areas that might affect the project have been overlooked. Moreover, the general regional relations must be known in order 

to properly interpret the geology, soils, and hydrology at a particular 

locality. In brief, both the general and the specific are needed in order 

to avoid costly mistakes either during or after development.

The accompanying maps illustrate how a general geologic map can 

be used for interpreting ground conditions during a planning stage prior 

to site selection. The topographic and geologic maps, which provide the 

basic data, have been simplified from some existing ones. The interpretive sheets are intended to provide some examples of the kinds of 

information that trained persons can read from such basic maps.

UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY ALPINE QUADRANGLE

5 Mil** 

_J

Topographic maps show quantitatively the configuration of the 

land surface. This is accomplished by drawing contours that 

represent level lines on the earth's surface. Irregularities in the 

contour lines reflect the ground plan shape of the land formst 

the spacing between the contours measures the amount of slope. 

In addition, topographic maps show the works of man, such as 

roads, railroads, and buildings, and drainage features such as 

perrenial streams, intermittent streams, springs, and marshes.

TOPOGRAPHIC MAP
UNITIO ITATtS DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY ALPINE QUADRANGLE

 v&&xxxx. ?//, ////j '//"/"% rss/sss///. r//// '//"S//'/. ''^^^mmm f'''ffiff&'>^'W%y''fj&& m^&^mm^ '""//// 

. . xxxx,

xxxx XXXXXXXXy/- -'' '

f/i//lU//. '/t tSS/SS/:

5 Miles

EXPLANATION

"c 

 

o

<r

Meistocene

cUpoii Bonncvillt ok«

j^ Gi

Si

in 

CO

/vxOR^x W////W,

(Qbgg

Touag fan deposits} gravol, with adaflyad 

aaadf silt, and clay.

Htel Qbsi

«,Tel Maibart Saad aaaberi Silt aMaitarj 

mrel and aand elaan aand| fonv lake bottoB 

delta deposita. offabore bara a»d deposit. 

3>SO,yLCl dalta dapiaita. CO, =SO,^C1

'XXXXXXXy

^Qbc-g 

r/ssss//A

COmj aaliiii-t 

lake bottoa

Old fan dapoaitai beoldarj 

 teixed and, silt, clay. 

callaha in upper larara.

with

Bedrodc) anatlj liaestone, ooartzite.

Faulti dattod vtera conoaalad. 

GEOLOGIC MAP
UNITCO JTATII DCPARTMCNT OP THC INTtHlOH 

OCOLOOIOAL lUHVtY ALPINt QUADRANtLC

y//^^^^/^//^y//^//.

FIFTH EVENT* 

This fault again 

aetiv»{ 20 f««t 

of diBplae«B«iit*

THIRD KVEJJTl

This fault bacaBW aetiv*}

5-10 fact of oTanaat before

Lake BonnerLlle timf fault

extends under lake beds and

 ay haw recurrent Bovemnt

anytime.

FIRST EVENT! 

These ancient rooks 

folded and faulted 

upward to form 

mountains.

SECOND EVENTt 

This fan built of 

gravel etc. eroded 

from mountain.

FOURTH EVENTI

Valley inundated by glacial Lake 

Bonneville. Delta of grarel (Qbg) 

built at mouth of Alpine Canyon. 

Shore currents moved sand (Qbs) westward on delta and in bars in front of 

delta. Silt (Qbsi) deposited nearshore | clay (Qbc) deposited offshore* 

These lake depoeits are underlain by 

the pre-Bonnerille fans which represent 

the second event*

SIXTH SVEMTi

This fan and the email one 

3 miles vest were built en 

top of Lake Boaneville 

deposits after the lake had 

disappeared. These pest* 

Boaneville fans are still 

being built.

READING GEOLOGIC HISTORY FROM THE GEOLOGIC MAP
UNHID t TAT It DIPARTMINT OP THI IMTIRIOM 

tlOLOaiOAL tURVIY ALPINf QUADNANCLI

^^^K^^y/, ' ' //////''**it j u'>'/ ////*

'//<<^<^^/x/x>,/^<^^<^//.///^/;^^//x

B Mil**

Hard rook*. Good souroe for llnostone or ouartxite for building atone, riprap. Quarry 

operations would require drilling and blasting. Usjostone suitable for ewmt.

 2 This graTel well rounded and well graded but contains considerable line; not suitable for 

conerote aggregatet excellent road netal.

A This gravel poorly graded | fraaaente in part angular and in part veil rounded( deposit is 

free of secondary 11an best source for concrete aggregate.

g Clay deposit contains live and other water-soluble saltsi fair source for structural clay) 

good souree for seal clay} not suitable for high grade oeraaic purposes.

THE GEOLOGIC MAP AS A GUIDE TO CONSTRUCTION MATERIALS
UNHID STATd DIPAftTMINT OP THI INTIRIOR

OIOLOOIOAL unvrv ALPINI QUADNANOLt

'Mmum8tf>''mM&:-.

a MII*> _j

A Clay ground} poor surface drainage} no aubaurfaoa drainagai road Metal and fill for subgradas 

Bust ba haulad fron araa B or C. Ground aaaily excavated by powar shovel or doiar operation. 

Will require aubdrains.

p Gravelly and ailty ground) fairly adaquata surfaoa and subaurfaoa drainaga. Good foundation 

for roade or buildings. Basement excavations Bust ba aballow to avoid intarsaoting tha groundwatar parehad on tba undarlying impermeable Lake Bonneville bads, 

projaotion of ona of tha recently active fault (see E).

This area lies across the

Gravelly ground with excellent aubaurfaoa drainage} ground easily excavated by power shovel 

or docer. Excellent road foundation} tba deposit rests against ona of the recently active 

faults so buildings should be constructed to withstand shocks of intensity 8, R-F scale (eee E).

Sandy ground underlain by silt at depths less than 8 feet) good surfaoa drainaga down to the 

silt. Easily excavated by hand toela. Basement excavations aust be shallow to avoid intersecting groundwatar perched on the silt. Good foundation for roads but clay is needed for 

binding eand.

Two recently active fault*. Haveaent on either one Bay be renewed at any tiae causing earthquakes. Buildings within a Bile or so of the faults or their projaotion should be constructed 

to withstand shocks of intensity 8, R-F scale. Five Biles from the faults tha shocks would 

not ba expeeted to exceed intensity 5.

THE GEOLOGIC MAP AS A GUIDE TO FOUNDATION 

AND EXCAVATION CONDITIONS
UNItID STATIC MPANTMINT Of TIM INtlNlOH 

0IOL00IOAL 0UNVIY ALPINE OUADHAIMLt

A

This old fan 

deposit underBoanovlll* 

deposit*. It

is an aquifer 

that can be 

reached by 

drilling in 

the south part 

of the

B

groundemter is 

perched on the 

fcqpemeable lake 

bods 10-15 f Mt 

below the *wfaee of this 

young fan 

deposit. This 

freundv»ter 

however i> 

subject te 

pollution by

Zone of seep* 

at odgo of 

yeunffan

deposit* 

 hallow 

water (see box 

B) Misrgis ail 

surface. 

Seep*

available at 

base of this 

delta deeeeit, 

about 40 feet 

 lew rarfaee.

THE GEOLOGIC MAP AS A GUIDE TO PROBLEMS OF UNDERGROUND 

WATER SUPPLY AND SANITARY ENGINEERING
UNITED STATES DEPARTMENT Of THE INTIHIOR 

OfOLOOIOAL SURVEY ALPINE QUAOHAN8LE

w^^mm^?m

Area.

Permeability and 

elope of ground

Runoff 

conditions

Flood control, drainage and 

canal problems

\

2

3

4

5

Impermeable f 

alopee steep.

Moderately 

permeable | 

elopes moderate

Highly permeable, 

gentle slopes*

Moderately 

permeable | 

low slopes.

Impermeable 

and ground 

nearly flat.

Maximum 

eoeffieieat 

of runoff.

Little runoff 

during moderate 

storms j considerable 

runoff during severe

atoms.

Practically no 

runoff even 

following most 

seTere storms*

Moderate runoff 

during severe 

stones*

Water stands in 

pools for long 

periods after rains.

Principal source of floods that 

would be hazardous in valley.-

Subject to floods from canyon} 

during severe storms may discharge 

floods from surface runoff. Moderate 

seepage losses can be expected from 

canals.

No flood control problem* 

Reservoirs and sanals require 

sealing to avoid excessive 

seepage losses.

Subject to flash floods from 

canyon. Moderate seepage losses 

can be expected from reservoirs 

and canals.

Qround readily flooded and 

difficult to drain. No ssspage 

losses from reservoirs or canals*

X Lower limit of perennial flow in stream draining mountain.

THE GEOLOGIC MAP AS A GUIDE TO SURFACE WATER PROBLEMS SUCH AS 

FLOOD CONTROL, DRAINAGE, CANAL CONSTRUCTION ETC
UNIT ID STATES DfPAHTMfNT OF THI INTIHIOR 

OfOLOSICAL SURVEY ALFIHI OUADNANOLt

ww&zwzm

/xxxxxxxx

/XXXXXXXX

XXXXXXXXX'XXXXll

8 Milo ..J

C. w

7

HetmtalnouB «na| roil flams-ally thin and «tm«y. Uoally tter* 1« a f Mail Mil haviaf 10 f««t 

of loaehod «lay (aa oxoollont aooroo of truetural alay). Priaeipal «at«r«h»d mpplyiac mlloy 

area. Foroated.

Stoney aad ia part bouldory grand. Li plaeoa eoTorod by foaail aoil (Boo 1)| locally tba 

loaehod clay baa boon orodod oxpooiag atraagly lia* anriebod graval aad ailt*

Stonoy grooad. Top foot ia brow viadbloav ailt eoataiaing vail rotadod gravolt eoaawa larg* 

aiso 1-2 iaohtta diaawUr. Fivo to tan foot of llM-a*riob*4 graval bafinaiaf a foot balow 

tbo aurfaoo.

Cloan quarts aaa«| graiaa i-i wm diaMtor, woll rouadod, ataimrf by iroa-«zido. la ailt afttrlx, 

aoaw liaw oarboaata oaaoat. Looally bloan into low duaoa.

Stoney grouad, ailt aatrix. Sligbtly li«o anriebod soao loaa tbaa a foot tbiak aaior aarfaaa 

layor of loaobad ailt and gravol 6 iaohoa thick.

Silt ground. Coataiaa about tf of vator-aolHplo aalta \.5% of aaloiaa aarbaaata and l.# 

of aulfatoa and ebloridaa of aodiwa and potaaaia*. Thaaa aalta loaabod fraa top o iaabaa, aad 

radopoaitad ia aaxt foot*

Clay groaad. Coataiaa about 4% of aator-aolublo aalta 1^ of oalaiua aarboaata aad & of 

aulfatoa and ehloridoa of aodiaa and potaaaiaa. Tboao aalta looally f om aarfaaa oraata araaai 

 oiat doproaaioaa.

THE GEOLOGIC MAP AS A GUIDE TO SOILS AND 

LAND UTILIZATION PROBLEMS