GEOLOGICAL SURVEY CIRCULAR 320

URANIUM OCCURRENCES IN THE 

GOLDEN GATE CANYON AND 

RALSTON CREEK AREAS 

JEFFERSON 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 320

URANIUM OCCURRENCES IN THE GOLDEN GATE CANYON AND 

RALSTON CREEK AREAS, JEFFERSON COUNTY, COLORADO

By J. W. Adams, A. J. Gude 3d, and E. P. Beroni

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., 1953

Free on application to the Geological Survey, Washington 25, D. C.
URANIUM OCCURRENCES IN THE GOLDEN GATE CANYON AND 

RALSTON CREEK AREAS, JEFFERSON COUNTY, COLORADO

By J. W..Adams, A. J. Gude 3d, and E. P. Beroni

CONTENTS 

Page Page

Abstract..................................... 1 Golden Gate Canyon area Continued

Introduction.................................. 2 Ladwig No. 3 ........................... 11

Golden Gate Canyon area...................... 2 Ralston Creek area........................... 11

Union Pacific prospect.................... 4 North Star mine......................... 11

Buckman property....................... 8 Schwartzwalder mine (Ralston Creek)...... 13

Ladwig No. 1 ........................... 10 Nigger shaft (Hoffmeister prospect) ....... 13

Ladwig No. 2 ........................... 11 Literature cited.............................. 16

ILLUSTRATIONS

Page

Figure 1. Index map of central Colorado ................................................................ 3

2. Index map, Golden Gate Canyon area.......................................................... 4

3. Map and section of the Union Pacific prospect.................................................. 5

4. Assay map of walls.......................................................................... 9

5. Geologic map of adit, Buckman property............................... v ...................... 10

6. Index map, Ralston Creek area............................................................... 11

7. Map and section, North Star mine .............................................................. 12

8. Map of the Schwartzwalder mine............................................................... 14

9. Geology of Nigger shaft...................................................................... 15

TABLE

Page

Table 1. Analyses of samples......................................................................... 6

ABSTRACT thickness. The breccias probably are related to the

Laramide faults, or "breccia reefs" of similar trend,

Pitchblende, associated with base-metal sulfides, mapped by Levering and Goddard (1950). The breccias 

has been found at nine localities in the northern part of are composed of fragments of bleached and iron-stained 

Jefferson County, Colo., in shear zones that cut pre- wall rock, usually hornblende gneiss, that have been 

Cambrian metamorphic and igneous rocks, chiefly horn- cut by veins and cemented by carbonate minerals, 

blende gneiss, biotite schist, and granite pegmatite. quartz, and orthoclase( ?). Pitchblende and associated 

The known deposits are in the vicinity of Ralston Creek ore minerals, chiefly copper sulfides, occur in and 

and Golden Gate Canyon, in the foothills of the Colorado along the margins of the breccias and apparently were 

Front Range and about 15 miles east of the pitchblende- introduced at a late stage of the carbonate deposition, 

producing area of the Central City district. Two of the At one deposit, the Buckman, the pitchblende is in 

pitchblende occurrences were found by a local pros- narrow shear zones not closely related to any large 

pector in 1949; the seven other deposits were found by breccia bodies. 

Geological Survey personnel in 1951-52.

Secondary uranium minerals are subordinate

The pitchblende deposits, with one exception, are except at the Schwartzwalder mine, where torbernite 

in major shear zones that contain veinlike bodies of and metatorbernite are common. Some alteration of 

carbonate-rich breccia that ranges from 1 to 5 feet in pitchblende to nonopaque materials, believed to be
hydrated oxides, has been noted in ore from two 

of the deposits.

INTRODUCTION

The recent discovery of nine uranium-bear ing 

vein deposits in pre-Cambrian rocks of northern 

Jefferson County, Colo., indicates a new district favorable for uranium prospecting. The known deposits are 

in two small areas in the foothills of the Colorado Front 

Range, less than 20 miles from Denver (fig. 1) and 

about 15 miles east from the pitchblende-producing area 

of the Central City district.

The initial discovery of pitchblende was probably 

made before 1884, as a note in Mining and Science 

Press (1884) for that year describes its occurrence in 

Jefferson County in thin seams but in "too small quantity to be economically valuable. " No specific location 

for the deposit was given.

In the spring of 1949 samples of pitchblende and 

torbernite ores from the northern, or Ralston Creek, 

area were brought to the attention of the Atomic Energy 

Commission by Fred Schwartzwalder of Golden. In 

1951, the first of the several occurrences in the Golden 

Gate Canyon area was found by members of the Geological Survey. More recently additional discoveries 

in both areas, have been made by members of the Survey; 

this work was done on behalf of the Division of Raw 

Materials of the U. S. Atomic Energy Commission. In 

all the deposits the uranium is associated with copper, 

and most of the occurrences had been prospected for 

metals as early as 1894.

Preliminary studies show striking parallelisms in 

the geology and mineralogy of the several occurrences that 

are suggestive of a common period of deposition and similar environmental conditions. In general, pitchblende 

occurs along the walls of fault zones that contain vein 

fillings of carbonate and potash feldspar rock, presumably 

of hydrothermal origin, and genetically related to the ore. 

The wall .rock is usually hornblende gneiss that has been 

severely bleached adjacent to the veins. Breccia fragments 

in the vein have been wholly or partly replaced bysulfides. 

Copper minerals are invariably present in the veins, and 

include chalcopyrite, covellite, bornite, chalcocite, tetrahedrite-tennantite, malachite, andazurite. Pyriteisless 

abundant than chalcopyrite; galena, has been noted at only 

two localities. Carbonates are generally abundant. Ankerite is the dominant gangue mineral of the carbonate and potash feldspar vein material and is earlier than calcite, which 

probably is largely postpitchblende.

The fault zones in which the pitchblende deposits 

occur have a similar trend and possibly are related to 

the extensive Laramide faults, or breccia, reefs mapped 

by Lovering and Goddard (1950). At least one such 

breccia reef is present in the Ralston Creek area, 

250 feet from, and roughly parallel to, a pitchblendebearing vein. The individual reefs have not as yet been 

correlated with those mapped a few miles to the north 

(Loveringand Goddard, 1950). The relationship between breccia reefs and the uranium-bearing veins 

possibly is analogous to that of the reefs and certain 

ore deposits in nearby Boulder County, where the reefs 

are probably served as deep channels for the ore deposited in adjacent fissures (Lovering and Goddard, 

1950, p. 239).

The known uranium deposits will be discussed 

as those of the Golden Gate Canyon area (fig. 2) and 

the Ralston Creek area (fig. 6).

GOLDEN GATE CANYON AREA

The known deposits in the Golden Gate Canyon 

area (fig. 2) are alined along a narrow belt that trends 

N. 75°-80° E. The trend of this belt is essentially 

parallel to the trend of the well-developed foliation of 

the pre-Cambrian metamorphic rocks of the area. The 

individual deposits, however, with the possible exception of the Buckman, are found at the intersection of 

northerly-trending, carbonate-bear ing fault zones and 

the N. 75°-80° E. -trending belt.

The rocks in the vicinity of the deposits are predominantly interlayered gneisses and schists of the 

Idaho Springs formation and include hornblende gneiss, 

biotite schist, and quartz-biotite gneiss. For this investigation they have been differentiated only megascopically. The hornblende gneiss is a. fine-grained 

black rock containing about 50 percent hornblende and 

50 percent quartz and feldspar. It is well foliated and 

is generally fresh and unaltered in outcrops. Interlaminated with the hornblende gneiss are narrow layers 

of biotite schist. These layers, which are soft and 

friable, possibly represent hydrothermally altered 

gneiss. The hornblende gneiss and biotite schist make 

up a rock layer or unit that is about 100 feet thick at 

the Union Pacific prospect.

Stratigraphically above and below this unit the 

rocks are dominantly gray and foliation is not as well 

developed. These lighter colored rocks are chiefly 

fine grained quartz-biotite gneiss in which the quartz, 

biotite, and feldspar content varies considerably from 

layer to layer. A few narrow layers of a black, hornblende-rich rock are interbedded with the gray gneiss.

Field studies indicate that the previously mentioned 

alinement of the pitchblende deposits is due to their 

occurrence in the hornblende gneiss-biotite schist unit. 

This layer is the host rock of the four occurrences of 

pitchblende in section 19 (fig. 2), and probably includes 

the pitchblende vein north of the Buckman adit.

It is not yet known whether the occurrence of the 

uranium deposits in the hornblende gneiss is the result 

of structural control or of some physical or compositional difference. The carbonate-bearing fault zones 

generally show a slight anomalous radioactivity. This 

anomalous radioactivity, together with the proximity 

of the pitchblende to the fault zones, suggests that they 

represent the channelways along which the ore solutions 

moved. Uranium minerals have not been found along 

all the carbonate-bearing faults that cross the hornblende gneiss-biotite schist unit, but all such intersections may be potentially ore-bearing.

About 700 feet north of the hornblende gneissbiotite schist unit, anomalous radioactivity has been 

found at several places along another belt of hornblende 

gneiss and biotite schist which is parallel to the favorable unit. The radioactivity apparently is confined to 

narrow beds of bleached biotite schist cut by carbonatebearing faults. The radioactivity anomalies suggest 

the existence of another zone of favorable host rocks, 

although no uranium or copper minerals have as yet
Jamestown

BOULDER

BOULDER

Clear

Idaho Springs 

?6EOR6ETOWN

CLEAR CREEK

EXPLANATION

Ralston Creek 

area

Golden Gate 

Canyon area

ARAPA HOE

JEFFERSON

^(DOUGLAS

CASTLE ROCK 0

40°

10

L

10 Miles

i i i

Figure 1. Index map of central Colorado showing location of Golden Gate Canyon and Ralston Creek areas.

3
EXPLANATION

Uranium occurrence

1. Union Pacific

2. Buck man

3. Ladwig No. I

4. Ladwig No.2

5. Ladwig No.3

R. 71 W. R. 70 W.

5000 Feet

Figure 2. Index map showing known uranium occurrences in Golden Gate Canyon area, Jefferson County, Colorado.

been observed at these localities. Analyses of samples 

from the Golden Gate Canyon area are shown in table 1.

Union Pacific prospect

Uranium in the Golden Gate Canyon area was 

discovered at the Union Pacific prospect (fig. 2), which 

is on land owned by John Pearce and Thomas Pearce of 

Golden, Colo. Mineral rights to the property are held 

by the Union Pacific Railroad Company. The deposit 

was at one time prospected, presumably for copper, 

by an inclined shaft, 57 feet deep, from which a short 

drift extends a. few feet into the right wall at the 30-foot 

level. In December 1951 the shaft was dewatered by 

the Union Pacific Railroad Company for examination by 

their geological staff. At that time, samples were collected and the walls of the shaft were mapped by the 

Geological Survey.

Pitchblende and copper minerals occur along the 

hanging wall of a 10- to 15-foot fault zone that strikes 

N. 15°-20° W. and dips about 35° NE. The strike of the 

fault zone is approximately at right angles to the foliation 

of the enclosing hornblende gneiss and biotite schist. The 

fault consists of hanging-wall and footwall zones of sheared 

and bleached rock and a central unit of wholly or partly 

cemented breccia. The cemented breccia is composed 

essentially of small bleached fragments of gneiss in a 

fine-grained groundmass ofankerite and minor quantities 

of an unidentified potash feldspar. The ankerite-rich 

breccia is a dense, light-gray rock that oxidizes readily 

to an earthy limonitic gossan. The gossan is well exposed 

along the south wall of the opencut, where it appears as 

the dark band in the lower part of the breccia zone.

Except within the limits of the opencut, the fault 

is concealed in the mapped area, and its position outside 

the opencut can only be inferred (fig. 3). However,
jT"- -^_ Pitchblende-bearing vein

6610 Quartz-biotite gneiss 

Stippling indicates outcrop

Contact, showing dip 

Dashed where inferred, 

dotted where concealedFault, showing dip 

Dashed where approximately located, 

. dotted where concealed

Strike and dip of foliation

Strike and dip of joint 

Limit of underground working 

-6560' Limit of exposure

Rim of excavation

, IIIHIIIIIIIII

1 Dump

Mopped by J.W. Adams and A.J. Gude 3d 

February 1952

Figure 3. Geologic map and section of the Union Pacific prospect, Jefferson County, Colorado.

5
Table 1. Analyses of samples from Golden Gate Canyon and Ralston Creek area, Jefferson County, Colo

[Channel samples noted. ]

Locality

Union Pacific 

prospect .

Buckman property 

Ladwig No. 2 

North Star mine 

Field 

no.

SA-1 

UP-1

UP-2 

UP-3 

TJP-4 

UP-5 

UP-6 

UP-7 

UP-8 

UP -9 

UP-10 

UP-11 

UP-12 

UP-13 

UP-14 

UP-15 

UP-16

UP-17 

UP-18

OGC-3 

GGC-4 

B-l

RB-4

RB-5 

RB-6

RB-7 

RB-8 

L-l

L-2 

L2-1 

NS-3 

NS-4 

NS-5

NS-6 

NS-7 

NS-8 

MS -9 

NS-10 

NS-11 

AJG-9

AJG-10 

AJG-11

Width o 

channel 

(feet)

(*) 

3.0

3.0 

4.0 

4.0 

4.4 

4.2 

4.0 

4.0 

3-0 

1.0 

2.5 

2.6 

4.3 

4.9

:1

4.0 

1.0

 5 

(V 

 5

.5 

1.0

4.0 

(*)'

( x ) 

( x ) 

1.0

(*)

1.0

.5 

.5 

.5 

.5 

.5

4' 

.2 

.2

Material

Carbonate-breccia with 

pitchblende . 

Altered gneiss and carbonate-breccia.

_£lQ ________ _ _ _

 do 

 do 

 do 

_ ,_do _ . ____ _ __ ___ _ . ____

 do 

Pitchblende in gouge 

Pitchblende in altered 

gneiss. 

Pitchblende in fractured 

quartz . 

Pitchblende in gouge 

Pitchblende in gouge; 

gneiss .

Pitchblende in altered 

gneiss.

Carbonate-breccia with 

pitchblende and copper 

Mineralized breccia 

shear. 

Breccia with pitchblende . 

Mineralized breccia \ 

shear. 

 do - 

 do 

 do 

 do 

Carbonate vein with 

pitchblende. 

 do 

Equivalent 

uranium 

(percent)

0.130 

.006

.006 

.006 

.005 

.009 

.014 

.094 

.230 

.007 

.007 

.006 

.006 

.650 

.014 

5.60 

.015

.008 

.009

.250 

.010 

1.20

1.50

.220 

.072

004

.032 

.980 

.006 

.250 

.370 

.720 

.140

.062 

.023 

.005 

.007 

.011 

' .010 

.010

.320 

.280

Uranium 

(percent)

0.110 

.004

.003 

.004 

.003 

.004 

.006 

.086 

.26.0 

.003 

'.005 

.003 

.004

.810

.011 

5.84 

.006

.003 

.003

.260 

.003 

1.23

.860

.220 

.062

.013 

1.36 

.007

.300 

.510 

.850

.110

.027

.010 

.002 

.002 

.005 

.006 

.004

.220 

.310

Copper 

percent)

0.21

.10 

.49 

 33 

 25

.32

.29 

.20

.16

.08

.10

.08

.16 

.01

8.25 

5-50 

16.83 

3.08

5-7^ 

1.84 

.29 

.02 

.08 

4.12

*.29

Lead 

'percent]

0.01

.005

0 

0

 

.04

.07 

.015

.10 

.11

.10 

.10

.015

Zinc 

[percent)

0.08

.07 

 33 

.50 

 95

 35

 45 

 25

.25

.03 

.05

.10 

.38

.10 

.10

.06

FesOa 

'percent

 -

 

4.04

8.19 

6.29

5.22 

3-81

Manganese 

(percent)

 

 

 

 

Gold 

[oz./ton]

Tr. 

Tr.

Tr.

Tr.

0 

Tr.

Tr. 

Tr.

Tr. 

Tr. 

0 

0 

Tr.

Sil

[oz.

T

T

T

2

T
Schwartzwalder 

mine.

RB-9 

RB-10

RB-11

RB-12 

RB-13 

RB-17

RB-18 

RB-20

RB-21 

RB-22 

RB-23 

RB-24 

BB-27

BB-28 

BB-29

H-651 

H-652

H-653

4 23

4 

4 

t1 )

(i) ( l )

 5 

1 

t1 ) 

1.5 ( x )

1 

t1 )

2 23

Altered breccia with 

torbernite and pitchblende . 

do

Altered breccia with 

torbernite. 

Altered ailicifled 

gneiss. 

Carbonate-breccia with 

torbe.rnite .

- do -- -

Altered breccia with 

pitchblende and 

torbernite. 

Altered breccia with 

pitchblende and sulfides. 

Breccia with torbernite-

_ do__ _ ________ _ __

Altered breccia with 

pitchblende .

Altered breccia with 

pitchblende . 

 do 

.021 

.880

.320

.110 

.039 

.094

.340 

.260

1.40 

.084 

 59 

.13 

.33

4.1 

.018

.44 

2.9

.5

-Oil 

1.07

.360

.082 

.010 

.084

.470 

.330

1.9* 

.058 

 790 

.059 

.43

5-29 

.014

 59 

4.32

.65

 32

.21

 15

.09

2.0

2.67 

 74

 53

.10

.13

.40

.07

 15

.24

,Tr.

 

 

1 Grmb sample.
outcrops of carbonate breccia about 300 feet and 

700 feet northwest of the mapped area, as well as a 

shear zone in rocks on the south side of Golden Gate 

Canyon, probably represent the same structure, and 

indicate that it has a strike length of at least 1,000 feet.

The surface cut and underground workings at the 

Union Pacific prospect are entirely within the fault zone 

in the hornblende gneiss and biotite schist layer previously mentioned as a "favorable bed" for uranium 

deposition. This layer, which is about 100 feet thick 

and dips steeply to the north, apparently has been displaced from 10 to 25 feet to the northwest on the west 

side of the fault.

The southeast wall of the shaft showed anomalous 

radioactivity from the collar to a few feet below the 

stub drift. On the southeast wall of the cut a radioactive 

gossan from 6 inches to 1 foot thick underlies the 

hanging-wall shear zone, and many of the fracture 

surfaces in the shear zone itself show strong radioactivity. Anomalous radioactivity was found in much of 

the soil-covered area between the north rim of the cut 

and a shallow trench about 75 feet northwest of the 

shaft. The anomalies occur within the limits of the 

fault zone as shown on figure 3.

Pitchblende, the only uranium mineral that has 

been observed in the deposit, is associated with chalcopyrite, tetra.hedrite-tennantite, bornite, chalcocite, 

covellite, and pyrite in a zone that ranges from 6 inches 

to 1 foot in thickness along the contact between the 

carbonate-breccia and the hanging-wall shear. The 

ore minerals are largely concentrated in the altered 

and sheared hornblende gneiss, but they are also present in the upper few inches of Uie underlying breccia. 

The pitchblende occurs chiefly as lustrous, black films 

along minor shear planes that are roughly parallel to 

the major structure of the fault. Less conspicuous 

pitchblende, accompanied by the sulfides, is disseminated 

through most of the rock in the ore zone; at least some 

of this pitchblende is a late mineral in carbonate-lined 

veinlets.

Most of the pitchblende observed in the deposit 

was found on the walls of the stub drift; samples taken 

across the shaft walls at points above and below the 

drift showed a rapid decrease in uranium (fig. 4). It 

is possible that the radioactive gossan in the southeast 

wall of the surface cut is an oxidized and leached part 

of the pitchblende-bearing body exposed underground, 

and that both represent the north edge of a lenticular ore shoot whose direction of plunge is a 

few degrees south of the 'direction of the shaft. 

The localization of ore on the crest of rolls in 

the breccia zone is suggested by the relationships 

observed underground.

Copper minerals are abundant in some samples, 

but the copper content of the ore zone is low. Zinc 

was detected in analysed samples, but no zinc minerals 

have been recognized. Gold, silver, lead, nickel, and 

cobalt are present in trace amounts only.

The paragenesis of the minerals from the deposits 

in the area has not been studied sufficiently to be discussed at length in this paper, but it seems probable 

that the pitchblende was formed after the brecciation 

of the wall rocks and during the last stage of carbonate 

deposition.

Buckman property

Pitchblende has been found in an abandoned adit 

about 15 feet .east of the Golden Gate Canyon road 

(fig. 2, locality 2), on land owned by NoraR. Buckman 

of Golden, Colo. About 1916 the adit was driven 

86 feet in a northeasterly direction roughly parallel to 

the foliation of steeply-dip ping pre-Cambrian biotite 

schist and gneiss; presumably the adit prospected 

sulfide-bearing quartz stringers. A winze which is 

now filled with water, had been sunk to a depth of 

25 feet near the heading.

The biotite schist and gneiss exposed in the adit 

is cut by granite pegmatite dikes and discontinuous 

quartz bodies that contain local concentrations of pyrrhotite and chalcopyrite. The quartz bodies, which 

may represent segments of a single quartz vein, 

are cut by the pegmatites and are assumed to be 

pre-Cambrian.

Pitchblende occurs at two places along the south 

wall of the adit (fig. 5). Near the portal, it forms masses 

as much as one-half inch thick in a shattered, ironstained quartz vein. The pitchblende shows colloform 

rim structures around angular quartz fragments. Interstitial to the pitchblende-coated quartz fragments 

are iron oxides, chalcopyrite, uranophane, and an 

unidentified green uranium mineral. A hydrated uranium sulfate, uranopilite, was identified by X-ray and 

optical data obtained by the Geological Survey laboratory. 

Although the relations are somewhat obscure, the 

shattered quartz in which the pitchblende is found apparently lies along a prominent shear that strikes 

N. 15° E., and dips 40° E., but no anomalous radioactivity has been found in the shear away from the" 

quartz body.

About 45 feet along the adit, pitchblende is found 

in an oxidized shear striking N-. 45° E., and dipping 

71° SE. Although this shear cuts a quartz vein, the 

only pitchblende observed occurred a few inches outside of the quartz vein, in the adjacent sheared and 

silicified gneiss. Anomalous radioactivity was not 

detected along the shear except where the pitchblende 

was found.

In spite of the localization of the pitchblende 

in and adjacent to the quartz veins, it is doubtful that 

they are genetically related, and a pcstquartz vein 

origin seems more probable.

The pyrrhotite and chalcopyrite sparsely disseminated in and along the margins of the quartz veins 

probably are essentially contemporaneous with the 

quartz.

About 300 feet northwest of the adit, a pitchblendebearing vein is exposed in a road cut at the east edge 

of the highway. The vein is 1 to 3 inches thick, strikes 

approximately north, and is essentially vertical." Although the radioactive part of the vein is less than 

2 feet long, it is remarkably rich, containing surfaces 

of hard, botryoidal pitchblende one-eighth to one-fourth 

inch thick that coats a carbonate mineral tentatively 

identified as calcite. Minor amounts of chalcopyrite 

also are present in the vein. The vein cuts hornblende 

gneiss at approximately right angles to the foliation. 

The gneiss is almost completely bleached for a width 

of an inch or more along the contacts. Beyond the
0.006 

CX003

EXPLANATION 1-0.004

Sample, showing 

percent uranium

Bearing sections approx. N.65°E.

(UP-15

\ 0.3 ft 

P-13 |5-84 percent

SOUTH WALL

UP-3

UP-f

Pin

NORTH WALL

Figure 4. Assay map of walls of inclined shaft at Union Pacific prospect, Jefferson County, Colorado.
Water-filled winze, 

7i \ approximately 25 ft deep

Pitchblende in shear 

0.062-1 ft, 0.26-0.5ft

Pitchblende in sheared quartz 

0.040-ift, 0.86-0.5ft

Portal of adit

10

Quartz vein

76

Contact, showing dip; 

dashed where inferred

20 Feet

Vertical contact

Limit of exposure on surface

72

Strike and dip of foliation

6£ 

Strike and dip of joints

Head of winze

0.62-lft

Percent uranium and length 

of channel sample

Geology by J.W. Adams, August 1952

Figure 5. Geologic map of adit, Buckman property, Jefferson County, Colorado.

pitchblende-bearing area, only a barren fracture marks 

the course of the vein.

Because of its proximity to the adit, the vein is 

included in the description of the Buckman property, 

but its location, so far as can be determined, is so 

near the north edge of the property that its ownership 

is uncertain.

The black hornblende-gneiss layer in which the 

small pitchblende vein occurs may be a westward extension of the favorable bed previously described. This 

gneiss, where exposed along the highway, is about 

100 feet thick, strikes N. 80° E., and dips 62° to 85° N. 

It has been traced for about 300 feet west of the road 

to a northwest-trending fault zone that contains large 

bodies of carbonate-cemented breccia. Anomalous 

radioactivity is widespread along the fault near its intersection with the gneiss, and although no uranium 

minerals have been found west of the road, the geologic 

environment, by analogy with the deposit at the Union 

Pacific prospect, would appear favorable for an ore 

body. The small occurrences of pitchblende at the 

Buckman adit and in the road cut differ from the other 

known deposits in Golden Gate Canyon in that they show 

no close relationship to the carbonate-bearing faults, 

the nearest known fault of this type is at least 300 feet

to the west. This variance with the mode of occurrence 

of the other deposits suggests that the Buckman occurrences may be indicative of a strong uranium mineralization capable of depositing pitchblende at some distance from the faults.

Ladwig No. 1

Strong anomalous radioactivity was detected at 

the Ladwig No. 1 property (fig. 2) by a gamma scintillation detector. The radioactivity, which is traceable 

over an area of about 50 square feet, is caused by uranium minerals in rocks concealed under 1 to 3 inches 

of soil. Torbernite, which coats foliation planes of 

altered biotite schist, was noted in the few samples 

that could be collected. A few small fragments in the 

soil appear to be carbonate breccia, and contain minute 

grains of pitchblende and an altered yellow uranium 

mineral that resembles uranophane. Secondary copper 

minerals are also present. Float of carbonate breccia 

and exposures of altered rock indicate that the occurrence of uranium minerals is related to a northwesterlytrending fault.

The relative positions of the contacts of the favorable bed of hornblende gneiss with the quartz-biotite

10
gneiss indicate that the fault has an offset of about 

100 feet, the west block moving south relative to the 

east block.

The anomaly is about 330^feet N. 50° W., of a 

water-filled prospect shaft showing copper minerals 

on the dump. The shaft was sunk in altered biotite 

schist cut by a. carbonate breccia 1 to 2 feet wide that 

strikes north and dips about 70° E. Much of the material 

on the dump is quartz associated with pyrite and limonitic material, and some bornite, covellite, and copper 

carbonates. In spite of the close association of uranium 

with copper in the area, no appreciable uranium has 

been found in ore samples from this locality. It may 

be significant that although the copper prospect lies 

along a carbonate-bearing fault, it does not lie within 

the favorable hornblende gneiss layer.

Mineral rights to the Ladwig No. 1 and two other 

localities are held by Lyman C. Ladwig of Golden, Colo.

Ladwig No. 2

At the Ladwig No. 2 property (fig. 2), uranium 

minerals have been found on the dump of an abandoned 

prospect shaft and in a small trench 100 feet to the east. 

The shaft, which is now 12 feet deep but may have been 

considerably deeper, was sunk in a radioactive carbonate 

breccia, zone, 1 to 2 feet wide, that strikes north and 

dips steeply to the east. The breccia zone cuts the 

hornblende gneiss-biotite schist layer that, in the vicinity of the shaft, is extensively sheared and bleached for 

several feet on the hanging-wall side of the contact. 

No uranium minerals were found in place, but specimens 

collected from the dump of the shaft contain pitchblende 

and torbernite in limonite-stained breccia host rock. 

Additional radioactive samples, probably derived from 

another breccia zone, were found in the debris from 

the lower of two shallow cuts about 100 feet east of the 

shaft. Copper minerals, notably carbonates, are conspicuous on the dump where the uranium minerals are 

found.

The radioactive breccia zone is also exposed at 

the caved portal of an adit 125 feet south of the shaft. 

Here the breccia zone is 6 feet thick and contains altered 

but recognizable wall-rock fragments that are several 

inches in diameter. No uranium or copper minerals 

were noted at the adit or in the shallow cut that exposesthe breccia zone about 40 feet north of the shaft.

Ladwig No. 3

A single specimen of pitchblende and associated 

copper carbonates was found on the dump of the lower 

of two small prospect pits at the Ladwig No. 3 property 

(fig. 2). As at the previously described deposit, the 

pitchblende and copper minerals occur in or near a 

north-trending breccia zone. This occurrence is poorly 

exposed, and at present is chiefly of interest as another 

example of uranium mineralization along the favorable 

zone.

RALSTON CREEK AREA

Three pitchblende-bearing deposits are known in 

a small area in the vicinity of Ralston Creek (fig. 6), 

about 6 miles north-northwest of the prospects in

11

Figure 6. Index map showing known uranium occurrences in the Ralston Creek area, Jefferson County, 

Colorado.

Golden Gate Canyon. The deposits are similar to those 

in Golden Gate Canyon as they are related to north or 

northwest-trending breccia zones; they do not, however, 

show a similar alinement in a northeasterly direction. 

None of the deposits are easily accessible. The North 

Star and Nigger Shaft deposits can best be reached 

from the north by a private road to the A. G. Brumm 

ranch from Coal Creek Canyon. From the end of the 

ranch road, it is possible to drive 4-wheel drive vehicles to within walking distance of the workings. The 

Schwartzwalder mine, on the southwest side of Ralston 

Creek, can be approached by 4-wheel drive vehicles 

via an access road leading up the creek from Ralston 

reservoir 5 miles north of Golden. Analyses of samples 

from this area are shown in table 1.

North Star mine

Pitchblende was discovered at the abandoned 

North Star mine in April 1952 by geologists of the 

Geological Survey. The mine is on the ranch of 

A. G. Brumm and is probably in the south half of 

section 23, mineral rights of which are held by the 

Union Pacific Railroad Co. According to Brumm, 

4 tons of copper ore was taken from the mine in 1894, 

and another 12 tons was shipped in 1916.

The mine was worked by a short upper level 

(fig. 7) and a lower level connecting with a stope that
Hornblende gneiss, 

schist and pegmatite

i41

NS8-0.002-0.5 ft 

'-0.01-0.5 ft

Mineralized shear zone, 

showing dip; dashed 

where covered

xxxxxx 

Edge of backfill

-NS6-0.027-0.5 ft

Map level / 

7390 :

\/:! ) C^Sl'l-0.006-0.5M \T°P afst °Pe /'

/ -A.. 1 i >

Map level 

7404

Lagging

7400-

7390-

20 Feet

I

Portal, partly caved Datum assumed

Outline af workings above 

and below map levels

Inclined workings, 

chevrons point down

 NS7-O.OI-0.5 ft 

Sample number, percent

uranium, and length

of sample

Figure 7. Map and section of underground workings, North Star mine, Jefferson County, Colorado.

at one time was open to the surface. The portal of the 

lower level is badly caved, and a backfilled area in the 

workings makes access to the stope quite difficult. 

Several other small prospect workings, apparently not 

on ore, are in the general vicinity of the mine.

The rocks exposed in the area are pre-Cambrian 

hornblende gneiss, quartz-biotite schist, and granite 

pegmatite. The foliation of the metamorphic rocks 

strikes northeast and dips steeply southeast; the pegmatites show a. similar northeast trend but are locally 

discordant. These rocks are cut by a carbonateorthoclase(?) vein that strikes northwest and dips from 

25° to 45° NE. Much of the vein exposed in the mine 

is altered to a limonitic gossan, but, where fresh, it 

shows streaks and patches of incompletely incorporated 

wall-rock fragments, and is a breccia-filling similar 

to those in the Golden Gate Canyon area.

Uranium and copper minerals occur throughout 

the vein as fracture fillings and as interstitial material 

surrounding breccia fragments. The ore minerals are 

not consistently present along the vein, and the small 

tonnage of copper ore that was mined probably came 

from narrow lenses of which little evidence remains. The 

best copper and uranium ore now showing'in the mine 

(fig. 7) constitutes a zone 6 inches to 1 foot thick above 

the carbonate vein exposed at track level near the face 

of the lower adit. Some of the ore observed underground is comparable to the pitchblende-bear ing rock 

found on the upper-level dump. This ore is made up

largely of reddish-brown rock fragments, generally 

less than 1 inch in diameter, cemented by primary and 

secondary copper and uranium minerals that include 

bornite, chalcocite, covellite, malachite, azurite, 

pitchblende, uranophane, and several unidentified uranium minerals. Some of the breccia fragments apparently are hornblende gneiss and granite, but the 

alteration, particularly the hematite(?) staining; makes 

identification of the original material difficult. This 

ore probably came from the small workings of the 

upper level, where, according to Brumm, the richest 

copper ore was found. In addition to uranium and 

copper, the ore contains an appreciable amount of 

silver (table 1), but no silver minerals have as yet 

been recognized.

A microscopic study of pitchblende at the North 

Star mine shows alteration from the opaque isotropic 

mineral to a brown transluscent to transparent material 

that is very weakly anisotropic and has an index of 

refraction of about 1.87. The brown mineral, which 

is locally abundant in some specimens of the ore, has 

a radial structure reflecting the original rounded or 

spherical surfaces of the original pitchblende. It is 

thought to be a hydrated uranium oxide, but its identity 

is still uncertain.

The position -and attitude of the vein in the stope 

and at the same map level (fig. 7) in the lower adit 

indicate either that there are two veins or that postvein 

faulting has taken place. Geologic mapping of the

12
underground workings, although not complete, indicates that the vein is probably faulted.

Anomalous radioactivity was found at a small 

prospect trench on the hillside about 600 feet southeast 

of the North Star workings. The few radioactive samples 

found on the dump contain secondary copper minerals.

Schwartzwalder (Ralston Creek) mine

The Schwartzwafder (Ralston Creek) mine 

(fig. 6) is on a heavily wooded, steep slope southwest 

of Ralston Creek, at an altitude of about 7,000 feet. 

Surface and mineral rights to the property are owned 

by Paul White of Golden, Colo. The uranium deposit 

at the mine currently is being explored by Fred 

Schwartzwalder of Golden, who discovered secondary 

uranium minerals at a caved adit on the property early 

in 1949.

The deposit was investigated for the Atomic 

Energy Commission by Anderson 1 and Baker 2.

The caved adit and three shallow pits nearby remained from earlier attempts to mine copper at the 

locality by the Golden Mining Company, during and 

before October 1897. Mr. Schwartzwalder has excavated the caved adit as an opencut and has driven a 

new adit and incline (fig. 8). The new workings were 

begun where the secondary minerals were found and 

continued in rocks showing abnormal radioactivity and 

concentrations of secondary ura,nium minerals.. Pitchblende was first found about 40 feet from the portal, 

where the adit intersects a fault zone which trends 

northwest and dips at a low angle to the southwest. 

The fault was followed downdip by an incline to the 

present (1953) extent of the workings.

The rocks at the Schwartzwalder property are 

quartzose gneiss and mica schist of the pre-Cambrian 

Idaho Springs formation. The foliation of the schist, 

as noted in the underground workings, strikes N. 80° E. 

and dips 77° S. The gneiss and schist exposed in the 

workings have been highly altered and faulted, and 

appear to have been invaded by a large body of massive 

quartz. Much of the quartz is distinctly smoky in color. 

The gneiss, schist, and massive quartz have been cut 

by a fault that is marked by an iron-stained breccia 

consisting mostly of shattered quartz.

The uranium minerals are mostly concentrated 

in the fault zone that is as much as 5 feet thick where 

exposed in the incline. Pitchblende is found almost 

exclusively in the shattered quartz of the fault zone, 

whereas secondary uranium minerals are common in 

all the fractured wall rocks. The pitchblende is finely 

disseminated and partly sooty. Secondary uranium 

minerals identified from the deposit include torbernite, 

metatorbernite, and autunite. Associated with the uranium minerals are minor quantities of chalcopyrite, 

tetrahedrite-tennantite, bornite, galena, pyrite, limonitic material, malachite, aziirite, ankerite, calcite,

1 Anderson, J. P., 1950, Preliminary reconnaissance, Atomic Energy 

Comm. Kept. 35. [Unpublished.]

2 Baker, K. E., 1953, Preliminary report on uranium occurrence at 

the Ralston Creek mine, Jefferson County, Colo. [Report in files of the 

Atomic Energy Commission.]

barite, and an unidentified potash feldspar. The sulfides and associated gangue minerals generally are 

extremely fine grained.

A strongly radioactive, northerly-trending quartz 

breccia similar to that exposed in the mine is exposed 

in a shallow pit 34 feet above and a short distance 

southwest of the portal of the adit. This breccia, which 

is about 4 feet thick, contains visible torbernite and 

malachite along fracture surfaces.

A third exposure of radioactive quartz breccia is 

in an old excavation 52 feet above the mine adit. About 

100 feet above and 150 feet south-southeast of the mine 

adit, an old shaft 18 feet deep also exposes similar 

radioactive rock. All these exposures of radioactive 

breccia probably represent a single fault zone. Continuation of this zone south of the prospected area is 

indicated by breccia float, in which fine-grained rock 

fragments are cemented by carbonates. Relationships 

of uranium minerals to a breccia reef in the Schwartzwalder mine area are analogous to most of the other 

deposits described. The quartzose character of the 

breccia is probably due to local composition of the wall 

rocks rather than to a more siliceous ore-bearing 

solution.

Pitchblende (?) associated with base-metal sulfides 

and secondary copper carbonates was noted in another 

breccia shear zone on the east side of Ralston Creek, 

about 1,000 feet northeast of the Schwartzwalder 

(Ralston Creek) mine. This shear zone trends northwest and dips steeply to the northeast. Two samples, 

RB 27 and RB 29, from this locality contained 0.43 and 

0.014 percent uranium respectively.

Nigger shaft (Hoffmeister prospect)

Pitchblende was first recognized in the Ralston 

Creek area in 1949 at an abandoned copper prospect, 

locally known as the Nigger shaft. The discovery was 

made by Fred Schwartzwalder of Golden, Colo., who 

submitted samples of the radioactive rocks to the 

Atomic Energy Commission. The prospect, worked 

between 1912-14 by Hoffmeister, consists of a 20-foot 

inclined shaft connected to a small stope (fig. 9). A 

short adit was driven from a point about 130 feet southeast of the shaft, presumably to intersect the vein below 

the shaft level.

The ownership of the deposit is unknown because 

the workings are situated on or very close to the 

boundary line between sections 23 and 26. If the deposit is in section 23, the mineral rights are owned 

by the Union Pacific Railroad Co. Surface and mineral 

rights to the adjacent land in section 26 are owned by 

Oscar Dahlberg of Golden.

The rocks in the vicinity of the Nigger shaft are 

pre-Cambrian hornblende gneiss, biotite schist, granite 

pegmatite, and aplite. These rocks are cut by a 

northerly-trending breccia reef that probably is an 

extension of one of the major Laramide fault zones 

mapped three-quarters of a mile to the north by Levering 

and Goddard (1950, pi. 2). The reef, bordered by 

sheared and altered rocks, crops out 250 feet northeast 

of the shaft, and can be traced by float and outcrops 

for 1, 000 feet or more to the northwest.

13
Mica schist 

contains same quartz stringers

Contact showing dip 

Dashed where inferred

EXPLANATION

Fault showing dip 

Dashed where inferred

Strike and dip of foliation 

37

Strike ond dip af joints

Open cut

. Dump

Inclined workings 

Chevrons point down 

R.a-9,0.0ll-4feet

Sample number, percent uranium,and lenqth 

of sample

Sample number,and length af channel sample

^8.-28,0.29-l foot

^J_ower part of incline projected 

"~ ~ to map level

10 2O Feet Geology by J.W.Adams, F. Stugord.Jr., 

and E.R Beroni, August 1953

Figure 8. Geologic map and section of the Schwartzwalder mine, Jefferson County, Colorado.

14
Q
The pitchblende deposit of the Nigger shaft is in 

a shear zone that is roughly parallel to the breccia 

reef. The shear exposed in the workings strikes 

N. 3° E. and dips 50°-60° E., but the surface exposures 

and radioactivity data indicate that the general trend of 

the shear is northwest. The shear zone is from 4 to 

8 feet thick and consists of brecciated and sheared 

hornblende gneiss that is cut by an irregular body of 

carbonate-rich rock which contains the ore. This rock, 

which averages about 2 feet in width, apparently represents that part of the shear zone that was invaded by 

the ore-bearing solutions. It is made up of bleached 

and altered gneiss fragments intricately cut by veins 

and cemented principally by carbonates; it constitutes 

a stockwork of dense, hard, light-brown rock that in 

surface exposures appears as a brick-red gossan.

The sheared gneiss along the hanging wall of the 

vein has been bleached by hydrothermal action for as 

much as 2 feet outward from the vein, but the brecciated 

gneiss in the footwall of the shear zone appears to be 

relatively fresh.

The vein has been traced by radioactivity for 

100 feet to the northwest, but it is almost entirely concealed by soil. Pitchblende and copper minerals were 

recovered from the soil in an area of high anomalous 

radioactivity about 50 feet from the shaft.

Pitchblende occurs in the deposit chiefly as thin 

seams in carbonate veinlets along the margins of the 

stockwork. The seams of pitchblende which range 

from 0. 05 to 0. 5 millimeter in thickness, form rims 

around earlier crystals of carbonate and orthoclase(?). 

Later carbonate and sulfides fill the center of the veinlets. The botryoidal upper surface of the seams 

suggests that they were developed by the coalescence 

of many individual hemispherical bodies, such as occur 

singly or in groups where the seams are discontinuous.

Sulfide minerals, including covellite, chalcopyrite, 

bornite, chalcocite, pyrite, and galena, have been 

identified in polished sections of the ore. Except for 

pyrite and some chalcopyrite, they occur within the 

carbonate veinlets. Most of the sulfides appear to have 

been deposited later than the pitchblende. Detailed 

mineragra.phic studies have not been made, however, 

to determine the paragenetic sequence of the ore 

minerals.

Calcite, ankerite, and quartz are the dominant 

gangue minerals in the pitchblende-bearing veins. The

sequence of their deposition has not been definitely 

established, but preliminary studies show that the ironrich carbonate formed both before and after the deposition of the pitchblende. Calcite is interstitial to ankerite 

and quartz and apparently is the last gangue mineral to 

be formed. All the quartz, so far as known, is younger 

than the pitchblende.

Crystals of a nearly uniaxial mineral of negative 

sign and low birefringence occur along the edges of the 

pitchblende-bearing veinlets. These crystals, thought 

to be orthoclase, were deposited before the pitchblende. 

A dark-green mineral, tentatively identified as chlorite, 

forms radial aggregates in the postpitchblende vein 

filling.

Most of the pitchblende in the veinlets is surrounded 

by an orange-brown layer, about 0.02 millimeter wide that 

may be in direct contact with the pitchblende or is developed entirely in the adjacent gangue minerals. The 

layer may end abruptly at an interface between two 

carbonate crystals or between a carbonate crystal 

and quartz. The material forming the layer has not 

been identified, but its distribution and color suggest 

that it is made up of finely dispersed iron oxides 

formed in ankerite as a product of radiation from the 

pitchblende. It has not been observed in quartz, and, 

where present in one carbonate and not another, it is 

assumed that the barren carbonate is calcite.

A mineral tentatively identified as a hydrated uranium oxide occurs sparsely in oxidized and leached 

breccia. It is light to dark brown, transparent, isotropic, 

and has an index of refraction of about 1.75. Qualitative 

texts show that it contains uranium and lead. This 

mineral was probably derived from pitchblende exposed 

to supergene solutions by the partial removal of enclosing carbonates, and is analogous to the brown material 

found in more abundance at the North Star mine.

Several secondary copper minerals are present 

in the ore; they are not abundant and are chiefly confined to cavities in the veinlets.

LITERATURE CITED

Anonymous, 1884, Mining and Science Press, v. 48,

no. 11, p. 195. 

Levering, T. S., and Goddard, E. ,N., 1950, Geology

and ore deposits of the Front Range, Colorado:

U. S. Geol. Survey Prof. Paper 223.

16 INT.-DUP. SEC., WASH., D.C.J 3