Wall-Rock Control of 

Certain Pitchblende 

Deposits in Golden Gate 

Canyon, Jefferson County 

Colorado

GEOLOGICAL SURVEY BULLETIN 1030-G

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

Wall-Rock Control of 

Certain Pitchblende 

Deposits in Golden Gate 

Canyon, Jefferson County 

Colorado

By JOHN W. ADAMS and FREDERICK STUGARD, JR.

CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

GEOLOGICAL SURVEY BULLETIN 1030-G

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 GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956
UNITED STATES DEPARTMENT OF THE INTERIOR

Fred A. Seaton, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 50 cents (paper corer)
CONTENTS

Page

Abstract_________________________________________________ 187

Introduction. _____________________________________________________ 187

Geology________________________________________ 190

Petrography of the wall rocks__________-___--_---_---_--_--____- 191

Hornblende gneiss.____-____-____--___--_-__________-__--_- 191

Quartz-biotite gneiss,______________________________________ 191

Breccia reefs_______-___--________-__-----_-____-______-_-- 194

Ore deposits__________-____-__-____________-__--_-___-____-_-___-- 195

Union Pacific deposit__--_---__--__--_--------_--_-__---------- 195

Mineralogy of the ore.__-____-____-_--------__-_-__---_---_ 195

Ore minerals--___-_---_---_-------_-----_--_------_------- 195

Gangue mmerals_-_-----_--_----_---.-----___-_-_--------- 199

Paragenetic history_____________________________________ 200

Wall-rock control at the Union Pacific deposit_______________ 202

Buckman adit deposit_______-__----_---_---__--___------------- 205

Discussion of pitchblende deposition___-____-____-___-__---_--_-_--_- 206

Conclusions._ _ _ ______-________________-_.________-____-_-_-__---_ 207

Literature cited,-___-.-_____-____-______-________--_----__--__---_ 208

ILLUSTRATIONS

Page 

PLATE 11. Geologic map and section of the Union Pacific deposit,

Jefferson County, Colo__----____----_--_--_--_--_- In pocket

12. A, Photomicrograph of thin section of ore from Union Pacific

deposit; B, Photomicrograph of polished section______ Faces 198

13. Photomicrographs of polished sections_______________ Faces 199

FIGURE 45. Index map of central Colorado showing location of Golden

Gate Canyon and Ralston Creek areas__________________ 188

46. Geologic sketch map showing distribution of uranium occurrences in the Golden Gate Canyon area, Jefferson 

County, Colo___________________________ 189

47. Camera lucida drawing of ore showing localization of tennantite by earlier pyrite_-__-__--___--_________-___-_-____ 198

48. Chemical changes during alteration of gneiss__-_-__-------- 201

49. Paragenesis of the minerals at the Union Pacific deposit.__. 203

50. Geologic map of adit, Buckman deposit ___________________ 205

in
IV CONTENTS

TABLES

Page 

TABLE 1. Rock analyses, Union Pacific deposit, Jefferson County,

Colo... _______ _.___. __.____.__..._..._.....__ 192

2. Spectrographic and uranium analyses of rocks and ore,

Golden Gate Canyon area. . _ _ __ 193
CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

WALL-ROCK CONTROL OF CERTAIN) PITCHBLENDE

DEPOSITS IN GOLDEN GATE CANYON, JEFFERSON

COUNTY, COLORADO

By JOHN W. ADAMS and FREDERICK STUGARD, JR.

ABSTRACT

Carbonate veins cutting metamorphic rocks of Precambrian age in the Golden 

Gate Canyon area, Colorado, contain pitchblende and base-metal minerals. 

The veins occupy extensive faults considered to be of Laramide (earliest Tertiary) 

age, but normally contain pitchblende only where they cut hornblende gneiss. 

At the Union Pacific deposit, which was studied in detail, pitchblende, hematite, 

and some ankerite formed before the sulfide minerals, except possibly for minor 

earlier pyrite. Base-metal minerals and the bulk of the ankerite vein filling 

were deposited after the pitchblende. Chemical analyses show a high ferrous 

iron content in the hornblende gneiss in contrast to low ferrous iron in the adjacent biotite gneiss. It is thought that ferrous iron released by alteration of 

hornblende was partly oxidized to hematite by the ore-bearing solutions and, 

contemporaneously, uranium was reduced and deposited as pitchblende.

In other veins that are not in hornblende gneiss, biotite or iron sulfide may 

have been similarly effective in precipitating pitchblende. Apparently both 

the ferrous ion and the sulfide ion can serve as reducing agents and control pitchblende deposition. Conditions, that seem favorable for uranium deposition 

include those where uranium-bearing solutions had access to rocks rich in ferrous 

iron or preexisting sulfide minerals.

INTRODUCTION

Pitchblende and secondary uranium minerals are found in vein 

deposits in northern Jefferson County, Colo. The deposits, which 

were recently discovered, occur in or near Laramide fault zones that 

cut gneiss, schist, and pegmatite of Precambrian age. They have 

been found in two areas about 6 miles apart (fig. 45); the northern 

or Ralston Creek area contains the Schwartzwalder (Ralston Creek) 

mine now being actively worked, the North Star mine, the Nigger 

Shaft, and several other more recently discovered deposits. Eight 

occurrences of uranium minerals are known in the southern or Golden 

Gate Canyon area and include the Union Pacific, Buckman, and 

Lad wig deposits. Pitchblende is the most abundant uranium mineral

187
188 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

O Jamestown 

BOULDER

RALSTON CREEK AREA \

Visioni^a. o Ley den 

1 GOLDENGATE^

FIGURE 45. Index map of central Colorado showing location of Golden Gate Canyon and Ralston

Creek areas.

in the deposits and is associated with copper minerals in a carbonate 

gangue with quartz and potash feldspar. Lead and zinc minerals 

are present in the ore but are not abundant.

A preliminary investigation of these deposits (Adams, and others, 

1953) was made in 1952-53 as part of the study of uranium deposits 

undertaken by the U. S. Geological Survey on behalf of the U. S. 

Atomic Energy Commission. During this study it was noted that 

most of the occurrences of uranium minerals and of high radioactivity 

anomalies in the Golden Gate Canyon area (fig. 46) were found where 

fault zones crossed a single bed of hornblende gneiss 100-150 feet 

thick. No significant radioactivity has been found along the same 

fault zones where they pass through other rocks.
Contour interval 100 fee

Datum is mean sea leve

Topography from Ralston Buttes quadrangle, 1948 Geology by J.W. Adams and F. Stugord, 

FIGURE 46. Geologic sketch map showing distribution of uranium occurrences in the Golde
190 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

As the preliminary data indicated "favorable" and "unfavorable" 

rock types, further investigations were made to establish, if possible, 

the reason for the apparent wall-rock control. Although the field 

and laboratory studies of this problem were concerned primarily 

with the Golden Gate Canyon area, notably the Union Pacific deposit, the results may be found applicable to uranium occurrences in 

other environments. For the present investigation, a map was 

made on a scale of 1 inch to 1,000 feet (fig. 46) to show the distribution of the known uranium occurrences in relation to the hornblende gneiss beds and breccia zones. A geologic map of the 

Ralston Buttes quadrangle (scale, 1:24,000), which includes the 

Golden Gate Canyon and Ralston Creek uranium areas, is now in 

preparation by the U. S. Geological Survey.

GEOLOGY

The rocks in the Golden Gate Canyon area include Precambrian 

hornblende gneiss, quartz-biotite gneiss, granite gneiss, quartzite, 

and pegmatite. Intrusive rocks of Tertiary age, such as are found 

in the Central City district (Phair, 1952), have not been recognized.

Hornblende gneiss and quartz-biotite gneiss are the rock types 

most closely associated with the uranium deposits. Both are similar 

in outcrop appearance and show distinct foliation that strikes about 

N. 80° E. and dips steeply north. These rocks are cut by several 

northwestward-trending faults characterized by carbonate-potash 

feldspar vein filling. The faults presumably are of Laramide age 

and are related to the highly siliceous breccia "reefs" or "dikes" of 

similar trend mapped by Levering and Goddard (1950). One such 

fault on the west side of Golden Gate Canyon in sees. 24 and 25 

(fig. 46) probably is a southern extension of the Hurricane Hill breccia 

reef, a structure that has been traced for almost 20 miles to the northwest (Levering and Goddard, 1950, pi. 2). The relationship between 

the breccia reefs and the uranium deposits will be discussed in another 

section of this report.

The geology of an area including and extending north of Golden 

Gate Canyon has been mapped by Gabelman 1 on a scale of about 

1 inch to 850 feet. As a result of his work, Gabelman believed the 

granite gneiss to be the marginal facies of a granitic intrusion lying 

south of Golden Gate Canyon and the other metamorphic rocks to 

represent the south limb of a large truncated synclinal fold. The 

other limb of the fold is believed to lie several miles to the north.

« Gabelman, J. W., 1948, The geology of the Oolden Oate-Van Bibber Creek area, Jefferson County, 

Colo.: Unpublished thesis in flies of Colo. School of Mines, Oolden, Colo.
WALL-ROCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 191 

PETROGRAPHY OF THE WALL ROCKS

Field studies indicate that most of the uranium deposits in Golden 

Gate Canyon occur in hornblende gneiss in an area of predominant 

quartz-biotite gneiss; therefore these rocks were studied in detail by 

petrographic, spectrographic, and chemical methods. These two 

types of rocks are described below.

HORNBLENDE GNEISS

In the area studied, hornblende-plagioclase-quartz gneiss occurs 

in two main beds about 100 .feet thick and in a few narrow layers in 

the adjoining quartz-biotite gneiss. The rock, which will be called 

hornblende gneiss, is fine grained and well foliated and in outcrop 

appears black or dark gray. Hand specimens show banding or 

layering of dark and light minerals, but these bands generally do not 

exceed a few millimeters in thickness. Bio tite may be abundant 

along individual foliation planes, but it is a minor constituent of the 

rock. At the Union Pacific deposit, and presumably elsewhere, the 

rock contains small epidote-bearing lenses and a few narrow quartz 

stringers, neither sufficiently abundant to affect the bulk composition 

of the rock. The hornblende gneiss is uniform in composition as 

determined by examination of several thin sections; three typical 

modes are as follows:

Percent by volume 

Hornblende__________________----- 41 48 50

Plagioclase (andesine).--------------------- 42 35 37

Quartz....___________________ 14 14 10

Opaque minerals,_________________________ 222

Others.._______________________ 111

Apatite is the most abundant nonopaque accessory mineral. Biotite, 

as previously noted, is common along some foliation planes and may 

be of secondary origin. Sphene, zircon, and garnet are less common 

than apatite. The opaque minerals as determined by polished-section 

methods and X-ray powder patterns are chiefly ilmenite and magnetite 

containing minor amounts of pyrite and chalcopyrite. The magnetite and ilmenite may be partly altered to hematite.

The results of chemical and spectrographic analyses of channel 

samples of the hornblende gneiss are given in tables 1 and 2.

QUARTZ-BIOTTTE GNEISS

The term quartz-biotite gneiss is applied in this report to the bulk 

of the layered metamorphic rocks adjoining the hornblende gneiss 

beds in the Golden Gate Canyon area. They are, for the most 

part, lighter in color than the hornblende gneiss and tend to be more 

massive with fewer foliation planes per unit thickness. Although 

variable in mineral proportions, all are characterized by the presence

384541 56 2
192 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

of biotite and the absence of hornblende. The fabric of the quartzbiotite gneiss layers commonly is granoblastic but may be locally 

gneissic. The following mode is typical of the granoblastic rock in 

the vicinity of the Union Pacific deposit:

Percent by volume 

_______________________ 30

_______________________ 50

________________ 20

Quartz. _ ________________

Plagioclase (albite-oligoclase). 

Biotite_____________

Others. <1

Apatite is the most abundant accessory mineral in the rock represented by this mode, but, including zircon and opaque mineral grains, 

constitutes less than 1 percent of the total composition. Calcite, 

sphene, clinozoisite, and epidote have been noted in the thin sections. 

In the less common gneissic beds, most of the biotite is restricted 

to thin bands separated and commonly crosscut by layers of quartz, 

plagioclase, and microcline. The laminated rock apparently was 

derived from the injection of silicic igneous material into the granoblastic quartz-plagioclase-biotite gneiss. Thin and polished sections 

show that the biotite rocks contain about one-third as much opaque 

material as the hornblende rocks and that most of this is magnetite 

or magnetite-hematite intergrowths. The results of the spectrographic and chemical analyses of a composite sample representing 

100 feet of the biotite gneiss at the Union Pacific deposit are given in 

tables 1 and 2.

TABLE I. Rock , Union Pacific deposit, Jefferson County, Colo. 

[Lucille M. Kehl, analyst]

Field no.

JWA-64-53...

JWA-77-53...

JWA-82-53...

JWA-73-53...

JWA- 3-54 

Field no.

JWA-64-53...

JWA-77-53...

JWA-82-53...

JWA-73-53...

JWA- 3-54...

Description of rock

Biotite gneiss __ _ . _________

Hornblende gneiss. Composite sample representing 25.8-foot chip channel. East side of fault zone.

Hornblende gneiss. Chip channel

across 11.4 feet of gneiss 130 feet west

of fault zone.

Altered hornblende gneiss. Chip

channel across 5 feet of altered rock

underlying JWA-77-53, 

Breccia "reef" material. Composite

sample of fresh rock from mine

dump.

NajO

3.87

3.28

3.32

2.46

.21

KjO

2.52

.79

.67

3.30

7.13

HsO0.10

.30

.27

1.93

.15

HsO+

0.72

1.35

1.33

3 74

.23

TiOj

0.45

1.41

1.68

1.72

.81

SiOs

68.92

54.86

55.78

51.70

32.87

COi

0.09

.05

.04

.17

20.58

AlaOj

1455

14.65

13.82

18.06

9.10

PsOj

0.13

.31

.41

.25

.36

FeiOs

1.95

466

485

12.36

.45

S

0.02

.02

.01

.01

MnO

0.08

.22

.24

28

29

FeO

2.89

7.99

8.55

.16

10.67

Total

100.04

99.96

100.05

99.70

100.38

MgO

1.50

3.40

2.84

1.15

5.60

Less 

OforS

0.01

.01

CaO

2.25

6.67

6.34

2.41

12.03

Adjusted 

total

100.03

99.95
TABLE 2. Spectrographic and uranium analyses of rocks and ore, Golden Gate 

[A single asterisk (*) indicates Spectrographic analysis by G. W. Boyes, Jr. A double asterisk (**) in

Field no. Description of sample eU Al Fe Ti Mn Ca 

JWA-64-53..

JWA-82-53..

JWA-73-53.. 

JW A- 3-54..

JWA-90-53.. 

JWA-92-53..

JWA-94-53-. 

UP- 4-52..

*Biotite gneiss. Composite of chip 

samples at 3-foot intervals for 100 

feet.8

*Hornblende gneiss. Channel sample across 11.4 feet.8

*Altered hornblende gneiss.3 -_---.

* Breccia reef material; 5-pound 

dump sample from Union Pacific 

deposit.8

**Hurricane Hill reef; 12-foot channel 

sample west of Buckman adit. 3

**Reef 750 feet WNW of Union Pacific deposit; 3-foot channel sample.'

**Reef 700 feet NW of Union Pacific 

deposit; 40-inch channel sample.3

* Pitch blende-bearing ore from 

Union Pacific deposit. 3

20.002

4 .001

2.000

s.009 

s.006

5.004

1 0.004

8.001

«.001

XX. 0

XX 

XX

x+

XX 

XX

XX

XX. 0

XX

XX 

X

x+

x+

x+

X

x.o

x+ 

x+

X

x+

X

x+

X

o.x

-X+

-X+ 

.X-

.X 

.X

.X- 

.X

0. OX+ X. 0-

.X x+

.X

.ox+x

x

.XV_tX

. OX+ X+ 

.X x+ 

Field no.

JWA-64-53-. 

JWA-82-53. 

JWA-73-53- 

JWA-3-54... 

JWA-90-53- 

JWA-92-53- 

JWA-94-53. 

UP- 4-52.

Co

O.OOX- 

.OOX- 

.OOX

.oox- 

.oox-

.OOOX+ 

.OOOX+

Cr

o.oox- 

.ooox

.OOOX+

.oox- 

.ooox- 

.oox 

.oox

.OOX+

Cu

O.OOX 

.OOX+

.oox

.ox

.oox

.oox

.ooxX

Qa

Tr.

.oox- 

.ooxTr.

.OOOX+ 

.OOOX+ 

. OOOX+ 

0

La

Tr. 

0 

0 

0 

0

.OOX

.oox

Mo

0 

0 

Tr.

.OOX+ 

0 

0 

0

.OX

Nb Ni

0

0

0

0

.oox- 

.oox

Tr.

O.OOOX+

Tr.

.OOOX+ 

.OOX- 

.OOX- 

.OOX- 

.OOX-

.ooox

Pb

0. OOX0

Tr. 

.OOX 

.OOX- 

.OOX-

.ooxSb

0 

0 

0 

0 

0 

0 

0 

.X

S

0. O

.oo

.oo

.o

.oo

.o

.o

.oo

i The concentrations are reported as elements, not as oxides or compounds. 

The following classification is used for the Spectrographic data, in percent:

XX =>10 

X+=4. 64-10 

X =2.15-4. 64 

X- = 1.0-2.15

.X+=0. 46-1.0

.X =0.215-. 464

.X-=0.10-. 215

Tr. = Near threshold amount.

2 Analysts: J. W. P

8 Other elements loo

Hg, In, Ir, Li, Nd, Os, 

* Analyst: J. W. Pa

6 Analyst: S. P. Fu

6 Analysts: Jesse M
194 CONTRIBUTIONS TO THE GEOLOGY OF TJRANTDM .,-.\r

BRECCIA REEFS

The composition and character of the breccia reefs are of special 

interest because the uranium deposits are believed to be genetically 

related to them. The major reefs are presumably the southern 

extensions of structures along which faulting and silicification took 

place during the Laramide orogeny (Levering and Goddard, 1950, 

p. 216-217). There is, however, a marked difference between the 

composition and appearance of the reefs to the north as compared 

with their presumed southern extensions. The northern reefs are 

highly siliceous and ferruginous and form resistant wall-like outcrops 

composed chiefly of iron-stained quartz. The southern reefs are 

not siliceous but consist of carbonate-potash feldspar as a finegrained groundmass enclosing rock fragments that have been replaced in varying degrees by these minerals. Because of its carbonate 

content, the reef material is subject to more rapid chemical weathering than the country rocks, and good outcrops are uncommon. 

Typical exposures are reddish brown, and breccia fragments stand 

out in relief above the groundmass; the color is the result of the 

oxidation of iron from ankerite. Where unweathered, the rock is 

almost white and is compact and tough.

The chemical and spectrographic analyses of reef material (tables 

1 and 2) show that it contains abundant potash. Part of this potash 

can be attributed to the included wall-rock fragments, but much 

presumably has been introduced. The reef material from the shaft 

at the Union Pacific deposit contains many fragments of the enclosing hornblende gneiss. These fragments retain the fabric of the 

gneiss, but of the original mineral components only quartz remains. 

The hornblende has been converted to an extremely fine grained 

material, presumably carbonate, and the plagioclase is replaced by 

potash feldspar, possibly by a base-exchange reaction.

The fine-grained groundmass of the reef material is probably composed of a carbonate having the approximate composition of ankerite, 

and an orthoclase-type feldspar. These two minerals, followed by 

later calcite, apparently are the products of a widespread introduction of hydrothermal solutions into not only the major faults but 

also the many presumably contemporaneous smaller subparallel 

fractures.

It was formerly thought (Adams, and others, 1953, p. 8) that 

the copper and uranium minerals found along the reefs were introduced late in the period of carbonate deposition. The study of the 

Union Pacific deposit now makes it appear more likely that the principal ore minerals were introduced early in the hydrothermal process 

and that the bulk of the fault-filling occurred after ore deposition.
WALL-ROCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 195

The scope of this investigation did not permit more than a limited 

study of the reefs, but it is apparent that a better understanding of 

these structures would be of material aid in the search for additional 

uranium deposits. If the carbonate-potash feldspar reefs are extensions of the siliceous reefs, a significant temperature-zoning pattern 

might be established to delineate areas favorable for uranium 

deposition.

ORE DEPOSITS

Except for some recently discovered occurrences in the Ralston 

Creek area, the known uranium vein deposits in northern Jefferson 

County have been described by Adams and others (1953). For this 

reason mention will be made of the geology of only those deposits 

reexamined for the purposes of this investigation; namely, the Union 

Pacific and Buckman adit deposits.

UNION PACIFIC DEPOSIT

At the Union Pacific deposit (pi. 11), pitchblende and base-metal 

minerals occur along the hanging wall of a carbonate-potash feldspar 

reef which cuts hornblende gneiss. The pitchblende-bearing rock 

exposed in the mine workings is less than half a foot thick but may 

contain as much as 5 percent uranium. Only the leached oxidized 

exposure of the vein is now accessible because the shaft is filled with 

water. So far as is known, the ore is confined to the hornblende 

gneiss, which at the deposit forms a steeply dipping bed about 100 

feet thick. Quartz-biotite gneiss lies above and below the hornblende-gneiss unit.

MINERALOGY OF THE ORE

The ore mineral assemblage at the Union Pacific deposit may be 

representative of the uranium deposits in the two areas. Whether 

the mineralogy of an individual deposit is simple or complex, the 

association of pitchblende with copper sulfide and arsenide minerals 

is persistent. The ore minerals are also characterized by a finegrained texture in which individual mineral grains commonly are 

less than a millimeter in diameter and may require polished-section 

techniques for identification and study.

ORE MINERALS

Pitchblende. Pitchblende is the only uranium mineral that has 

been found at the deposit. In polished section it shows a uniform 

high reflectivity and gray color somewhat lighter than tennantite 

with which it is commonly associated. The pitchblende is seldom 

recognizable to the unaided eye unless it is present in the form of
196 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

films which may be several millimeters thick and occupy fractures 

in iron-stained altered gneiss. These pitchblende films commonly 

include minute euhedral crystals of carbonate and may coat crystals 

of potash feldspar (pi. 12A) that have grown from the walls of fractures. Ore showing pitchblende films contains only sparse sulfides and 

probably formed in the outer edge of the ore zone. In a more common 

type of ore, the pitchblende, which is not discernible without the 

use of the ore microscope, occurs in colloform masses that 

commonly are less than 0.1 millimeter in diameter and densely coat 

crystals of ankerite of comparable dimensions (pi. 125). The pitchblende-ankerite veinlets are irregularly distributed through intensely 

altered wall rock and are replaced in varying degrees by later sulfide 

minerals (pi. ISA). This second type of ore probably formed in 

the fractured wall rock near the central channelway, but this could 

not be confirmed because of the present inaccessibility of the pitchblende-bearing area in the Union Pacific shaft.

Hematite. Finely dispersed hematite gives the hydro therm ally 

altered rocks of the deposit a characteristic brick-red color. It 

appears to be most abundant in the altered feldspar and was formed 

from iron progressively released first from the hornblende and later 

from chlorite. Like pitchblende, hematite was deposited on some of 

the vein orthoclase crystals. This hematite formed aggregates 

of transparent bright-red crystals. Platy intergrowths of hematite 

and pyrite replace hornblende or the opaque minerals of the gneiss. 

These intergrowths are the centers for deposition of late copper 

minerals.

Tennantite. Tennantite, probably the most abundant copper 

mineral in the deposit, occurs in discontinuous veinlets that rarely 

exceed 1 millimeter in width. In polished section the tennantite 

is light gray and gives a red powder when scratched. The mineral 

probably is in the tennantite end of the tetrahedrite series because 

of the 4:1 arsenic to antimony ratio in a typical specimen of the ore. 

As no other arsenic-antimony minerals are known in the ore, the ratio 

is assumed to apply to the tennantite. The identification was confirmed by X-ray powder pattern.

Chalcopyrite. Chalcopyrite, which is next to tennantite in abundance, replaces the earlier pitchblende-carbonate veinlets. The 

textural relationship observed in polished sections indicates that 

Chalcopyrite was deposited both before and after tennantite. The 

early chalcopyrite is found in fine-grained intergrowth with bornite, 

covellite, galena, sphalerite, and emplectite(?). These intergrowths 

appear as isolated patches engulfed by tennantite. The late chalcopyrite commonly occurs as rims or as isolated grains along the 

margins of tennantite areas. Where the rim structure is formed,
WALL-ROCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 197

chalcopyrite has apparently invaded existing interfaces between 

tennantite and pitchblende. Shrinkage of the pitchblende and 

formation of concentric and radial cracks may have afforded channels 

through which the chalcopyrite could migrate and replace the carbonate gangue of the early pitchblende veinlets. Plate 135 shows 

a relatively large carbonate crystal almost completely replaced by 

chalcopyrite.

Bornite, chalcocite, and covellite. Bornite, chalcocite, and covellite 

are the three most abundant minerals of the early sulfide assemblage. 

Except for the presumably supergene replacement of much of the 

bornite and chalcocite by covellite, the relationship is problematical. 

The bornite commonly contains blades of chalcopyrite in a textural 

pattern that has been ascribed to exsolution (Edwards, 1947, fig. 79); 

the chalcopyrite of these intergrowths does not extend beyond the 

grain boundaries of the bornite.

Sphalerite. Sphalerite is sparse in the ore, appearing as irregular 

grains that have a brown, mottled, nonmetallic appearance with 

crossed nicols. The largest sphalerite grain seen in polished specimens of the ore was approximately 0. 3 millimeter in maximum dimension. Sphalerite probably was one of the early suite of sulfide 

minerals, more abundant before replacement by tennantite and late 

chalcopyrite.

Galena. Galena is commonly associated with sphalerite but is 

the less abundant of the two minerals. Like sphalerite it is considered one of the early-formed minerals.

Emplectite. Emplectite (CuBiS2) was tentatively identified in 

the ore. The mineral occurs intergrown with chalcopyrite in irregular 

patches in tennantite. The emplectite(?)-chalcopyrite intergrowths 

are extremely fine grained and, without high magnification, appear 

as a single mineral resembling chalcopyrite but of a somewhat paler 

color. Under high magnification, the chalcopyrite is seen to be 

intergrown with a mineral that is pale cream-yellow and shows 

brownish-green and violet interference colors. The mineral has a 

hardness about that of chalcopyrite and stains brown with HN03.

Material removed from the pale yellow areas gave a microchemical 

reaction for bismuth. The powder tested unavoidably included 

some of the surrounding tennantite, but when tennantite apparently 

free of these minerals is similarly tested it reacts for antimony rather 

than bismuth. Spectrographic analysis of ore from the deposit 

indicates that bismuth is present in the same relative abundance as 

arsenic (table 2). As little emplectite(?) was found in the polished 

sections studied, it is probable that some bismuth may be contained 

in the tennantite.

Pyrite. Pyrite is not abundant in the ore, and where present is 

found in minute grains intergrown with hematite. These intergrowths
198 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

EXPLANATION

Pyrite partly replaced by 

chalcopyrite and tennantite

Altered gneiss

Chalcopyrite Carbonate vein let

FIOUBE 47. Camera lucida drawing of ore showing localization of tennantite by earlier pyrite.

probably are relics of some of the original iron-bearing minerals of 

the hornblende gneiss. The shape of many of these intefgrowths 

suggests that they were originally hornblende, but others may represent 

ilmenite or magnetite grains; these are commonly associated with 

leucoxene. The pyritization was probably an early reaction between the host rock and the first solutions introduced into the fault 

zone. Where the pyrite-hematite grains are transected by veinlets 

containing copper minerals, replacement of the pyrite is discernible
GEOLOGICAL SURVEY BULLETIN 1030 PLATE 12

r,*?*" ,

 V f .>.__ ' "'-^ - *' '-frM-t -' 

^''&*f£l-M - i'£A',

f**"iZ.~ 

^f*tA. PHOTOMICROGRAPH OF THIN SECTION OF ORE FROM UNION PACIFIC DEPOSIT 

Shows pitchblende (p) coating orthoclase (o) crystals formed on altered wall rock (ivr). Plain light, X 80.|

B. PHOTOMICROGRAPH OF POLISHED SECTION

Shows typical pitchblende (p) ankerite (a) intergrowth, containing tennantite (t) and 

chalcopyrite (cp). X 1190.
GEOLOGICAL SURVEY BULLETIN 1030 PLATE 13

A. Shows pitchblende (p) coating ankerite (o), both replaced by tennantite (t) and chalcopyrite (cp). X 580.

B. Shows replacement of ankerite crystal (a) by chalcopyrite (cp) marginal to tennantite (t). 

Gray areas are pitchblende (p). X 580.

PHOTOMICROGRAPHS OF POLISHED SECTIONS
WALL-BOOK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 199

(fig. 47), and no additional pyrite appears to have been deposited 

until the end of hydrothermal activity.

Very small grains of pyrite, probably deposited after the bulk of 

the ore minerals, are found throughout the main mass of the ankeritic 

breccia filling. These pyrite grains surround small calcite-filled 

cavities and fractures and probably represent the final stage of metallization. Deposition of pyrite rather than chalcopyrite, and calcite 

rather than ankerite, indicates that the solutions had become impoverished in copper and iron.

GANGUE MINERALS

Only a few gangue minerals of hydrothermal origin have been 

recognized in the ore. These include the carbonate minerals, ankerite 

and calcite, potash feldspar, chlorite, and minor sericite. Although 

quartz is a common constituent in the ore, and to a lesser degree in 

the carbonate vein filling, the rounded or fragmental grams are 

presumably derived from the wall rocks. Some vein quartz, however, 

has been noted in the Ralston Creek deposits.

Carbonate minerals. A carbonate mineral close to ankerite in 

composition is common in the ore and breccia and for the most part 

was introduced after the ore minerals. Together with potash feldspar 

and pitchblende, ankerite makes up the early pitchblende-bearing 

veinlets. Little gangue was deposited with the copper minerals, 

and replacement of earlier carbonate minerals by chalcopyrite and 

tennantite is common. After deposition of the copper minerals, 

ankerite was formed abundantly until the reef filling was nearly 

complete. Then minor amounts of calcite were deposited. The 

ankerite was identified by X-ray powder pattern and is readily distinguished from calcite by staining with potassium ferrocyanide. 

Hydrothermal alteration of the hornblende in the wall rocks has 

produced an extremely fine grained white aggregate believed to be 

largely carbonate minerals.

Potash feldspar. Potash feldspar is a characteristic mineral 

of the breccia and the associated pitchblende deposits. The exact 

nature of the feldspar has not as yet been determined, but it is presumably a variety of orthoclase, possibly adularia. Some grains, 

however, show an optic angle (2V) estimated to be between 20° 

and 30° so that an unusual type of feldspar may be present. Birefringence of the mineral is very low. The widespread distribution 

of potash feldspar in the altered wall rock and breccia filling is strikingly shown by staining rock slices or uncovered thin sections with 

sodium cobaltinitrite solution (Gabriel and Cox, 1929) and is further 

confirmed by the potash content of these rocks (table 1).
200 CONTRIBUTIONS TO T#iJ GEOLOGY OF URANIUM

The orthoclase occurs both as replacements of anhedral plagioelase 

grains in the hornblende gneiss and as small cfyst>als formed on 

fragments of brecciated gneiss. The crystals surrounding the breccia 

fragments are clear and transparent by comparison with the cloudy 

orthoclase (pi. 12,4) formed by replacement. No euhedral orthoclase 

crystals have been recognized in the main mass of the carbonate vein 

filling, but the rock contains innumerable fragments of altered gneiss 

in which orthoclase is abundant. TJje observed relationship of 

orthoclase in the deposit leads to the conclusion that potash was 

introduced during the early stage of hydrothermal activity.

Chlorite. A green mineral presumed to be a member of the chlorite 

group forms very fine grained aggregates in the ore and is relatively 

abundant below the zone of oxidation in the altered gneiss of the 

hanging wall. In a specimen of this gneiss containing pitchblende, 

the chlorite is confined to the pitchblende-coated gneiss fragments 

that have been isolated by carbonate veinlets. The chlorite and 

associated sericite are evidently products of a propylitization-type 

of rock alteration that preceded the introduction of uranium. Gneiss 

fragments in the carbonate breccia underlying the chlorite-bearing 

gneiss contain no chlorite, and it is assumed that the minerals of the 

earlier propylitization were largely destroyed by chemical action of 

concentrated carbonate-bearing solutions.

PARAGENETIC HISTORY

Studies of thin and polished sections of the rocks and ores indicate 

that a complex series of events was effective in the formation of the 

deposits.

Formation of the major faults and many other subsidiary fractures, 

such as that at the Union Pacific deposit, presumably took place 

during early Tertiary time. Open parts of these structures then 

became channelways for the migration of alkalic solutions of unknown 

source but of sufficient volume to deposit carbonate throughout 

fault zones miles long and from 1 to 20 feet wide. The effect of these 

solutions in regard to the ore deposition and wall-rock alteration will 

be considered here.

The first process in the formation of the ore is thought to have been 

propylitization of the hornblende gneiss. This resulted in the partial 

conversion of hornblende to chlorite and some sericitization of plagioelase. The sulfide ion concentration of the solutions was probably 

low as only a very little pyrite was formed from the breakdown of 

the iron-bearing minerals, thus permitting any excess iron to deposit 

as hematite.

The extent of the original propylitization is indicated by the outcropping zone of bleached gneiss, 2-5 feet thick, lying above the
WALL-BOCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 201

11.02

Iron oxides || '"" ^-^ " I \ ?*° 

Percent

 > . 0.45

1

,,03

CaO 

Percent

Nd20 3-32 

Percent ^Dl ~ _O2i

K 2 0 

Percent Qg7 __^ - 

- «

1

C0 2 

Percent

0.04________ _ -.'0.17

FIGURE 48. Chemical changes during alteration of gneiss.

central carbonate breccia filling; the footwall bleached zone is not 

as well exposed but is probably of comparable width.

Following, or perhaps during, propylitization, solutions were introduced that raised the potash content of the gneiss from less than 1 

to more than 3 percent (fig. 48). The added potash is in part contained in small clear crystals of orthoclase that line fractures in the 

rock, but as much or more of the potash may be replacing the soda 

of the original plagioclase. This alteration of the plagioclase is shown
202

by the distribution of potassium as indicated by staining and also 

by the decreased soda content of the gneiss after alteration (fig. 48). 

The replacement of plagioclase by potash feldspar has been described 

by Fenner (1936) and Steiner (1953) as a process of rock alteration 

resulting from hot-spring activity.

The precipitation of uranium followed potassic alteration and 

coincided with the beginning of a carbonate phase. This is shown 

by the deposition of pitchblende on orthoclase crystals and its intergrowth with ankerite. The reduction of U+6 ions to U+* by the 

Fe+2 ions released by the breakdown of (1) hornblende and (2) chlorite probably caused the precipitation of uranium. Gruner (1952) 

has experimentally produced pitchblende and hematite by reduction 

of U+6 by Fe+2 ; hematite formed only when the pitchblende was 

synthesized in an H^S-free environment. In the ore deposit, pitchblende and hematite (later ankerite) were deposited at essentially 

the same time and before the formation of the sulfide minerals with 

the exception of the very minor pyrite formed during propylitization.

After depletion of the available uranium, several simple copper 

sulfide minerals, sphalerite, galena, and emplectite(?) were deposited 

in an intricate network of fractures that only in part follow the 

original pitchblende-bearing veinlets. Deposition of these sulfide 

minerals was followed by tennantite replacement. It is questionable 

whether this replacement was part of a continuous period of sulfide 

deposition or whether a "rest interval" took place. Polished-section 

relationships favor discontinuity with a new wave of solution containing arsenic and antimony in addition to copper and iron migrating 

along the margins of preexisting veinlets. On the depletion of the 

arsenic and antimony, sufficient copper remained so that chalcopyrite again formed locally throughout the tennantite and along grain 

boundaries of tennantite and other minerals. With the deposition 

of chalcopyrite the sulfide mineralization waned, and a vigorous 

carbonate phase began which was to continue until the close of 

hypogene activity. The bulk of the carbonate deposited was extremely fine grained ankerite, succeeded at the last by somewhat 

coarser grained calcite. The calcite, which is sparse, forms veinlets 

and fills cavities in the ankerite. Minute pyrite crystals that formed 

along the edges of the calcite-filled openings indicate that a very 

weak sulfide phase marked the transition between the two carbonate 

minerals. Figure 49 is a graphic representation of the paragenesis of 

the deposit.

WALL-ROCK CONTROL AT THE UNION PACIFIC DEPOSIT

The ore occurrence at the Union Pacific deposit is, so far as is known, 

confined to hornblende gneiss wall rocks. This localization, repeated
WALL-ROCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANTON 203

Minerals\Propylltization/ Vein stage 

\ staae /

Pyrite

Chlorite

Leucoxene

Ankerite

Potash feldspar

Pitchblende

Hematite

Chalcopyrite

Bornite

Chalcocite

Sphalerite

Galena

Emplectitef?)

Tennantite

Calcite

-

-

.

? m

? 

?--- 

 

-

 ?o

 $ 

1-

<0 1-

-

-

 

Covellite Presumably supergene

Malachite Supergene

Azurite Supergene

FIGXJEE 49. Paragenesis of the minerals at the Union Pacific deposit.

at several other uranium occurrences in the area, seems to be a result 

of the composition and texture of the wall rock.

As discussed under "Paragenetic history," the deposition of uranium probably was effected by the oxidation of ferrous to ferric iron. 

Analyses of the two rock types (table 1) show that the hornblende 

gneiss contains almost four times as much ferrous iron as the biotite 

gneiss. Field observations and thin section studies indicate that 

the hornblende gneiss was readily altered by the solutions introduced 

along the fault, and that hornblende, the dominant iron-bearing 

mineral of the rock, was especially subject to attack. The writers 

believe that the release and subsequent reprecipitation of iron from 

hornblende provided an effective mechanism for uranium deposition.

The nature of the iron-bearing mineral probably was of little consequence, providing it was reactive and present in sufficient quantity. 

Thus a rock rich in biotite might be just as effective a precipitant as
204 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

one containing its iron equivalent as hornblende. In the Joachimsthai District, Czechoslovakia, pitchblende has been observed to be 

more abundant where the wall rocks of the veins were rich in biotite 

(Everhart and Wright, 1953).

A direct comparison of the iron content of rocks as a measure of 

their effectiveness in uranium deposition should be qualified by a 

consideration of the availability of the iron-bearing mineral to contact with the vein fluids. This availability will be a function of 

(1) the degree to which the rock is shattered and hence its surface 

area, (2) the relative solubility of the other mineral components, 

and (3) the texture of the rock.

No opportunity was afforded to compare the shattering of the two 

rock units at the deposit as the biotite gneiss is not well exposed in 

the vicinity of the fault zone. Comparison may be made, however, 

between the rocks in regard to their relative solubility and texture.

The persistence of quartz in highly altered hornblende gneiss indicates that quartz was not readily attacked by the hydrothermal 

solutions. Modal analyses show that the biotite gneiss contains 

from two to three times as much quartz as the hornblende gneiss, 

and hence, in spite of a somewhat higher plagioclase content, the 

biotite gneiss should be the more resistant of the two rocks.

While the rocks classed as biotite gneiss in this report contain layers 

that are markedly gneissic, they are for the most part granoblastic. 

In contrast, the hornblende gneiss is uniformly foliated and contains 

closely spaced layers of light and dark minerals. It would seem 

reasonable that where vulnerable minerals are alined in almost continuous planes, as in the hornblende gneiss, they would be more 

accessible to the invading solutions than where randomly distributed 

throughout the rock.

The relative abundance of metallic minerals, chiefly ilmenite, in 

the hornblende gneiss was first considered by the writers as a possible 

factor in the localization of uranium. Ilmenite, and some magnetite 

and hematite, constitutes about 2 percent of the unweathered gneiss 

but is not found in the altered gneiss of the ore zone. Instead, the 

ore contains intergrowths of pyrite and hematite, and white opaque 

grains of leucoxene. Many of these probably were derived from the 

ilmenite, although some of the pyrite-hematite intergrowths may 

represent earlier hornblende. As ilmenite contains ferrous iron, 

its oxidation to hematite would favor uranium deposition, but probably 10 times as much ferrous iron was available from the more abundant hornblende. Although the ilmenite probably was of negligible 

importance in the deposition of uranium, the pyrite-hematite intergrowths were to some extent effective in precipitating copper.
WALL-ROCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 205

BUCKMAN ADIT DEPOSIT

The occurrence of pitchblende and secondary uranium minerals 

at the Buckman adit deposit (fig. 46) differs from others in the Golden 

Gate Canyon area in that it is not in hornblende gneiss and is not 

known to be closely associated with a carbonate-potash feldspar 

reef. Instead, the uranium minerals occur in narrow shears that cut 

biotite gneiss, pegmatite, and a discontinuous sulfide-bearing quartz 

vein. The pitchblende is most abundant where a fault sheared the 

quartz vein and it is only sparsely present in the adjoining gneiss. 

The locality is about 300 feet east of a wide carbonate-potash feldsparbearing structure that is presumed to be the southern extension of 

the Hurricane Hill reef.

This apparently anomalous occurrence is probably the result of 

the interaction of uranium-bearing solutions with the sulfide-bearing 

quartz vein, the vein supplying both the structural and chemical 

control for ore deposition.

Movement along small faults sheared the gneissic rocks to some 

extent, whereas the vein was shattered into a breccia of angular 

quartz fragments in which sulfide grains were embedded. This 

zone of brecciated quartz, by reason of its greater permeability, 

provided a favored channelway for the uranium-bearing solutions.

The quartz vein is exposed in the adit as two major segments about 

20 feet long (fig. 50) and small intervening stringers or lenses all 

roughly concordant to the enclosing biotite gneiss. Pyrite, chalcopyrite, and molybdenite occur sparsely in the central part of the

Contact showing dip, 

dashed where inferred

Vertical contact

Fault showing dip, dashed 

where approximately located

Limit of exposure on surface

J4

Strike and dip of foliation

_63 

Strike and dip of joints

Geology by J W. Adams, August 1962

FIGURE SO. Geologic map of adit, Buckman deposit, Jefferson County, Colo.
206 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

quartz bodies but are relatively abundant along their margins in 

selvage zones containing biotite and magnetite. Some of the sulfide 

minerals adjoin magnetite grains from which they may have been 

derived in part. Hematite and an iron-bearing carbonate replace 

some of the sulfide grains. The pyrite, chalcopyrite, and molybdenite probably represent a period of mineralization unrelated to 

the uranium-bearing veins, and possibly of Precambrian age.

The pitchblende-bearing breccia differs from the ore found at the 

Union Pacific deposit; copper minerals are sparse and carbonate 

minerals have not been noted. Pitchblende and hematite are the 

most abundant metallic minerals in the ore. Pitchblende, showing 

typical colloform structures, occurs as rims around the brecciated 

quartz fragments, many of which were later sheared and offset. 

Hematite is interstitial to the pitchblende-coated grains, replaces 

quartz and sulfide, and veins the pitchblende.

Chalcopyrite, pyrite, and covellite occur in small residual grains 

in the hematite. Minute grains of an unidentified mineral that may 

be tennantite are present in some quartz fragments and in the interstitial material. Whether any of these sulfides are relics of the 

original quartz-vein minerals has not been determined, but, in any 

event, only a little copper was introduced with the uranium.

Radial aggregates of uranophane crystals line cavities in the hematite and fill fractures in quartz grains; the fractures appear to have 

been enlarged by uranophane replacement of the quartz.

By comparison with the Union Pacific deposit, the occurrence at 

the Buckman adit deposit may represent only the first stages of the 

complete sequence of metallization possible from the solutions that 

invaded the faults. Mineral deposition did not progress far beyond 

the pitchblende-hematite stage, as shown by the relative paucity of 

copper minerals and the absence of the ankerite phase after ore deposition. This relatively brief "life cycle" probably resulted from an 

early choking-off of the narrow channelway by pitchblende and 

hematite.

Precipitation of the pitchblende is thought to have been effected 

by the iron-bearing minerals in and adjacent to the quartz vein. 

Pyrite, chalcopyrite, biotite, and magnetite were all available to the 

solutions moving up the pipelike channel afforded by the sheared 

vein and provided a source of ferrous iron which, through oxidation 

to hematite, could precipitate uranium.

DISCUSSION OF PITCHBLENDE DEPOSITION

Wall-rock control similar to that at the Union Pacific deposit was 

probably effective at all the pitchblende occurrences in the hornblende gneiss beds (fig. 46) in Golden Gate Canyon.
WALL-ROCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 207

The formation of such pitchblende-hematite-carbonate deposits 

apparently requires an environment relatively free of sulfide ions so 

that Fe+2 can be oxidized to Fe+3. In comparing the pitchblende 

deposits of the Theano Point area, Ontario, with that of the Caribou 

mine in Colorado, Wright (written communication, 1950) states:

The predominance of calcite gangue in the uranium-bearing veins of the Theano 

Point area and the virtual absence of sulfides suggest that the oxidizing action of 

carbon dioxide in the mineralizing solutions, and the small amount of sulfur which 

could act as a reducing agent may provide a partial explanation for the abundance of hematite adjacent to the vein. The almost complete absence of hematite 

in the wall rock of the Caribou occurrence, which is rather rich in sulfides and 

where the gangue is predominantly silica rather than calcium carbonate, is in 

agreement with this explanation.

In the Ralston Creek area (fig. 45) two of the known deposits, the 

Nigger Shaft and North Star, are associated with hornblende gneiss. 

The pitchblende deposit at the Schwartzwalder (Ralston Creek) 

mine, currently being worked, was not studied in detail during these 

investigations, but the writers believe that pitchblende localization 

may be related to the distribution of a tourmaline-garnet skarn-type 

rock that accompanies the more abundant quartz-muscovite schist 

or phyllite of the mine area. The skarn rock, severely bleached and 

altered in the ore zone, may have provided ferrous iron either from 

tourmaline or from primary sulfide minerals.

The role of early sulfide minerals in uranium deposition has not 

been established by this investigation, but these minerals are thought 

to have been contributory at the Buckman adit deposit and may have 

been important at the Copper King deposit in northern Colorado 

described by Sims and Phair (1952). At this deposit, pitchblende 

of Tertiary age occurs in a pyrite-sphalerite ore body genetically 

related to Precambrian granite. Gruner (1952) describes the synthesis of pitchblende by the reaction between iron sulfide and a 

solution of uranyl sulfate. In these experiments, performed at temperatures of about 200° C and under acidic conditions, oxidation of 

sulfur but not iron was detected. "Sooty" pitchblende is commonly 

associated with pyritic ore, such as that found at the Copper King 

deposit, and may be the result of a sulfur oxidation reaction. Where 

hematite has been coprecipitated with pitchblende, as at the Buckman adit deposit, iron oxidation and uranium reduction is indicated 

as the more probable process for uranium deposition.

CONCLUSIONS

The detailed study of the Union Pacific deposit indicates that the 

abundance and availability of oxidizable iron-bearing minerals in 

the wall rocks may determine whether uranium deposition will take
208 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

place. Hornblende has been shown to be an effective source of ferrous 

iron, but other minerals, such as biotite, may serve equally well.

Pitchblende, accompanied by hematite and minor early ankerite, 

was deposited in advance of all sulfide minerals except for possible 

minor amounts of pyrite at the Union Pacific deposit. During the 

period of sulfide mineralization, pitchblende was not deposited; 

and locally it was replaced. Evidence indicates that the requirements for uranium deposition were fully met only during the initial 

stage of mineralization where the sulfide ion concentration of the 

incoming solutions was low.

The studies made during this investigation lead to the conclusion 

that pitchblende-bearing veins of the carbonate type may be expected 

where ample ferrous iron is available in the wall rocks. The difference in the available ferrous iron of the hornblende gneiss and biotite 

gneiss beds is thought to have resulted in the localization pattern 

exhibited by the pitchblende occurrences in the Golden Gate Canyon 

area.

This conclusion may be of some value in prospecting for uranium 

in areas of comparable geologic environments; the nature of the ferrous iron-bearing mineral is probably unimportant so that no special 

significance should be placed on the presence of hornblende. Biotite, 

magnetite, tourmaline, and iron sulfide minerals may be equally 

effective where present in sufficient quantity. In a sulfide environment, conditions resulting in the oxidation of either iron or sulfur 

may precipitate pitchblende. This implies that conditions favorable 

for uranium deposition are presented where uranium-bearing solutions 

have access to sulfide-bearing rocks.

LITERATURE CITED

Adams, J. W., Gude, A. J. 3d, and Beroni, E. P., 1953, Uranium occurrences in 

the Golden Gate Canyon and Ralston Creek areas, Jefferson County, Colo.: 

U. S. Geol. Survey Circ. 320.

Edwards, A. B., 1947, Textures of the ore minerals and their significance: Australasian Inst. Min. and Metallurgy, Melbourne, 185 p.

Everhart, D. L., and Wright, R. J., 1953, The geologic character of typical pitchblende veins: Econ. Geology, v. 48, p. 77-96.

Fenner, C. N., 1936, Borehole investigations in Yellowstone Park: Jour. Geology, 

v. 44, no. 2, pt. 2, p. 225-315.

Gabriel, Alton, and Cox, E. P., 1929, A staining method for the quantitative 

determination of certain rock minerals: Am. Mineralogist, v. 14, no. 8, 

p. 290-292.

Gruner, J. W., 1952, New data of synthesis of uranium minerals: U. S. Atomic 

Energy Comm. Tech. Inf. Service, RMO-983, Oak Ridge, Tenn.

Levering, T. S., and Goddard, E. N., 1950, Geology and ore deposits of the Front 

Range, Colo.: U. S. Geol. Survey Prof. Paper 223, 319 p.
WALL-ROCK CONTROL OF PITCHBLENDE, GOLDEN GATE CANYON 209

Phair, George, 1952, Radioactive Tertiary porphyries in the Central City district,

Colo., and their bearing upon pitchblende deposition: U. S. Atomic Energy

Comm. Tech. Inf. Service, TEI-247, Oak Ridge, Tenn. 

Sims, P. K., and Phair, George, 1952, Geology of the Copper King mine area,

Prairie Divide, Larimer County, Colo.: U. S. Atomic Energy Comm.

Tech. Inf. Service, TEI-311, pt. 1, Oak Ridge, Tenn. 

Steiner, A., 1953, Hydrothermal rock alteration at Wairakei, New Zealand:

Econ. Geology, v. 48, no. 1, p. 1-13.

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