C- 322:

GEOLOGICAL SURVEY CIRCULAR 322

THE EAST SLOPE NO. 2 URANIUM 

PROSPECT, PIUTE COUNTY, UTAH

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 322

THE EAST SLOPE NO. 2 URANIUM PROSPECT, PIUTE COUNTY, UTAH

By Donald G. Wyant

This report concerns work done on behalf of the 

U. S. Atomic Energy Commission and is published 

with the permission of the Commission.

Washington, D. C., 1954

Free on application to the Geological Survey, Washington 25, D. C.
THE EAST SLOPE NO. 2 URANIUM PROSPECT, PIUTE COUNTY, UTAH

By Donald G. Wyant

Abstract.........

Introduction......

Rock units .......

Structure .......

Uranium deposits 

Character ..

CONTENTS 

Page

1 Uranium deposits Continued

1 Alteration ................

3 Sampling..................

4 Outlook and guides to prospecting.

4 Literature cited................

4 Unpublished reports.............

Page

ILLUSTRATIONS

Page 

Plate 1. Geologic map and cross sections, East Slope No. 2 uranium prospect,

Piute County, Utah ..........................,................................Inside back cover

Figure 1. Index and geologic maps of the Marysvale district, Utah, showing the location

of the East Slope No. 2 prospect ..................................................... . 2

2. Sketch section along west face of the upper cut, East Slope No. 2 uranium prospect,

Piute County, Utah ................................................................... 3

TABLES

Table 1. Spectrographic analyses of samples from alteration zones, East Slope No. 2 uranium 

prospect, Piute County, Utah ................................................

2. Analyses of samples, East Slope No. 2 uranium prospect, Piute County, Utah.......

Page

ABSTRACT

The secondary uranium minerals autunite, 

metatorbernite, uranophane(7), and schroeckingerite 

occur in altered hornfels at the East Slope No. 2 

uranium prospect. The deposit, in sec. 6, T. 27 S., 

R. 3 W., Piute County, Utah, is about 1 mile west of 

the Bullion Monarch mine which is in the central 

producing area of the Marysvale uranium district.

Hornfels, formed by contact metamorphism 

of rocks of the Bullion Canyon volcanics bordering the margin of a quartz monzonite stock, is 

in fault contact with the later Mount Belknap 

rhyolite. The hornfels was intensely altered by 

hydrothermal solutions in pre-Mount Belknap time. 

Hematite-alunite-quartz-kaolinite rock, the most 

completely altered hornfels, is surrounded by 

orange to white argillized hornfels containing" 

beidellite-montmorillonite clay, and secondary uranium minerals. The secondary uranium minerals 

probably have been derived from pitchblende, the 

primary ore mineral in other deposits of the 

Marysvale area.

The two uranium-rich zones, 4 feet and 5 feet 

thick, have been traced on the surface for 60 feet and 

110 feet, respectively. Channel samples from these 

zones contained as much as 0.047 percent uranium.

The deposit is significant because of its position 

outside the central producing area and because of the 

association of uranium minerals with alunitic rock in 

hydrothermally altered hornfels of volcanic rocks of 

early Tertiary age.

INTRODUCTION

Uranium minerals were discovered on the 

East Slope No. 2 prospect by John Henry of Marysvale 

and Don Macintosh of Junction, Utah, in July 1950. The 

deposit is 3£ miles north-northwest of Marysvale in 

sec. 6, T. 27 S., R. 3 W., Salt Lake meridian, Piute 

County, Utah, about 1 mile west of Bullion Monarch 

mine (fig. 1). It may be reached over approximately 

6 miles of good graded road from Marysvale. The 

deposit is one of the few outside the central producing 

area (fig. 1) where autunite, metatorbernite, and
R.3W.

PAPSYS HOPE 

PROSPECT _

^ I

_ A

BULLION MONARCH

KSEEGMILLER MINE 

. MINE

\\i

CENTRAL PRODUCING AREA

MARYSVALE

Geology after Eugene Callaghan, 

U.S. Geological Survey

EXPLANATION

Alluvium and gravel

+Y MOUNTAINS

Quartz monzonite

MARYSVALE 

DISTRICT.

COLORADO 

PLATEAUS

112° 15'

Figure 1. Inde-i and geologic maps of the Marysvale district, Utah, showing the location of the East Slope No. 2 prospect.

2
uranophane(?) have been found. It is developed 

by two shallow trenches and by two bulldozer cuts, 

one-the lower cut-at the time of mapping, was covered 

by the dump of the upper. .Similar zones of altered 

and uraniferous rock were seen by the writer in the 

lower cut.

Since the preparation of this report the property 

has been leased to the Magnolia Lead Company of 

Salt Lake City. This company has sold one truck load of 

ore from the property to the Marysvale purchasing 

depot, and has driven a 50-foot adit under the deposit.

The East Slope No. 2 prospect was mapped as 

part of the U. S. Geological Survey's program for the 

evaluation of the uranium resources of the Marysvale 

region (Wyant, 1950) on behalf of the Division of Raw 

Materials of the U. S. Atomic Energy Commission. 

The general geology of the surrounding area has been 

mapped by Callaghan (1939). A plane-table map of the 

mine workings (pi. 1) and a detailed sketch section of 

the exposed workings (fig. 2) were made during four 

days in August.

Acknowledgment is made of the assistance of 

Mr. John Henry and Mr. Don Macintosh in showing 

the writer their property. Mr. F. L. Klinger and 

Mrs. D. G. Wyant assisted in the geologic mapping. 

T. S. Levering of the Geological Survey spent about 

half a day at the prospect and assisted greatly in 

identifying the types of alteration and comparing them 

with similar altered rocks in the Eureka district. 

Eugene Callaghan, also of the Geological Survey, 

visited the property with the writer and discussed the 

identification of the various rock types in relation to 

alunitic and other types of alteration in the Marysvale 

region.

ROCK UNITS

The volcanic rocks of the Marysvale district have 

been divided into an earlier Tertiary group and a later 

Tertiary group by Callaghan (1939,p. 438). His earlier 

Tertiary group consists of the Bullion Canyon volcanics: 

tuff and related volcanic rocks that have been intruded 

by quartz monzonite; his later Tertiary group consists 

of the Mount Belknap rhyolite and related extrusives. 

The two groups are separated by an unconformity and 

the exact ages of the rocks are unknown.

The Bullion Canyon volcanics and the related 

rocks in the area mapped have been converted 

to hornfels. Elsewhere in the Marysvale district they 

are latite, tuff, flows, and agglomerates.

The hornfels is predominately a dark-gray to 

green rock composed of white feldspar prophyroblasts 

in an aphanitic matrix. Subordinately, the hornfels 

is granular and gradational with the porphyroblastic 

variety. The granular hornfels is composed largely 

of fledspars, chlorite, and mica, with minor quartz 

and magnetite. Epidote was observed in this rock at 

a few places. The granular hornfels is charaeteristically gray to red, and weathers brown.

The Mount Belknap rhyolite is in fault" contact 

with hornfels at the' southeast edge of the area mapped. 

It is a red facies of the formation and consists of 

tuffaceous and platy red rhyolite.

Figure 2. Sketch section along west face of the upper cut, 

East Slope No. 2 uranium prospect, Piute County, Utah.

The quartz monzonite is a coarse-grained equigranular rock composed of plagioclase feldspar, orthoclase feldspar, and chlorite, and minor quartz and magnetite. Near 

the margins of the quartz monzonite, migmatitic zones 

have been formed by partial assimilation of hornfels.

The three major types of bedrock in the area 

surrounding the East Slope No. 2 prospect are quartz 

monzonite, hornfels, and red (Mount Belknap) rhyolite. 

Their relationships are illustrated in figure 2. At the 

deposit, hornfels has been altered to hematite-alunitequartz-kaolinite and uraniferous beidellite-montmorillonite 

rocks. Nearby, the hornfels has been altered to a 

silicified hematite-alunite rock. These rocks are overlain by Pleistocene or Recent talus and alluvium.
The East Slope No. *2 prospect is in hornfels near 

the eastern margin of a stock of quartz monzonite. 

This quartz monzonite stock is entirely separate from 

a similar stock that contains the larger uranium mines 

of the district (fig. 1). Hornfels, formed by the contact metamorphism of the Bullion Canyon volcanics, 

borders the quartz monzonite. Mount Belknap rhyolite, 

talus, and alluvium bound the older Tertiary rocks to 

the south, and are the surface rocks in the area between 

the East Slope No. 2 prospect and the quartz monzonite 

stock to the east that contains the principal uranium 

mines of the Marysvale district.

STRUCTURE

A fault of considerable, but unknown, displacement separates the Mount Belknap rhyolite southeast 

of the EastSlopeNo. 2 prospect from the Bullion Canyon 

volcanics, the quartz monzonite, and the hornfels. 

Other faults within this older group of rocks strike 

west and dip from 54° to 61° south. They are of 

small displacement, erratic in trend, and formed 

either during or after the hydrothermal alteration of 

the rocks. Older faults, if present, may have been 

obscured by the hydrothermal alteration.

The rocks are moderately fractured; fractures 

of dominantly north-northwest strike form a conjugate 

set with fractures of dominantly east strike. The dip 

of the fractures is variable, but generally is steep.

The original structure of the hornfels is not 

readily discernible because planar structures other 

than fractures are generally lacking. The platy 

Mount Belknap rhyolite is essentially horizontal or 

dips gently eastward.

URANIUM DEPOSITS 

Character

Tabular yellow-green uranium minerals, probably autunite, metatorbornite, schroeckingerite, and 

uranophane(?) are sparsely disseminated in two distinct zones: the north and the south uraniferous zones. 

The host rock in these uraniferous zones is white, buff, 

to orange argillized hornfels in which all or nearly all 

of the original textural features have been obliterated. 

The uraniferous zones have an east-west trend and 

dip from near vertical to 54° S. The north zone is 

3 to 10 feet thick and has been mapped a horizontal 

distance of 110 feet and a vertical distance of 70 feet. 

The south zone is 2 to 5 feet thick, at least 60 feet 

long, and has been traced intermittently for a vertical 

distance of 40 feet. Reddish float and altered hornfels 

suggest that both zones may extend over a vertical 

range of more than 100 feet.

The two -zones are incompletely exposed as 

tabular bodies, but geologic relationships indicate 

that they may be connected and form a shell-like body 

around a central alunitic core (see pi. 1 and fig. 2). 

This central core consists of brick-red through purple 

to white, hematite-aluniteTquartz-kaolinite rock in 

which none of the original textural features of the 

hornfels can be recognized. The relationship of these 

zones of alteration to the uranium minerals is illustrated in figure 2.

The uranium minerals form conspicuous, 

euhedral crystals, as much as a quarter of an inch 

across, at the margins of the uraniferous zones; 

here they coat fracture and joint surfaces in the 

weakly altered dense hornfels. This type of occurrence 

is analogous to the well-developed, coarsely crystalline 

uranium minerals that coat the fine-grained dense 

aplite or "granite" exposed in the Bullion Monarch 

open cut. In both places the well-crystallized uranium minerals do not necessarily occur in the highest 

grade ore. The higher grade ore, as in the Bullion 

Monarch open cut, consists, generally, of very fine 

grains of uranium minerals in a white to orange-buff 

clay gangue. By analogy with the operating mines of 

the central producing area, pitchblende may be expected to underly the secondary uranium minerals.

The highest grade material in the north uraniferous zone is in intensely argillized rock. One sample 

from this zone contained 0.043 percent equivalent 

uranium,1 and 0.047 percent uranium. The highest 

grade material in the south uraniferous zone also is 

in intensely argillized rock; one sample contained 

0.032 percent equivalent uranium and 0.034 percent 

uranium.

Alteration

Callaghan (oral communication) has distinguished 

two main types of hydrothermal alteration in the 

Marysvale region: 1, the pyritic type (pyrite, iron 

oxides, clay, alunite, and quartz), and 2, the basemetal-gold type (quartz, carbonate minerals, pyrite, 

and fluorite). Subdivisions of these two types can be 

made according to the proportions of the various 

constituents. All types of alteration recognized at 

the East Slope No. 2 prospect are subdivisions of 

the pyritic type.

Three sub-types of pyritic type alteration that 

are based on mineral composition (determined partly 

by their color) were recognized at the prospect and 

are shown on fig. 3: 1, hematite-alunite-quartzkaolinite rock; 2, beidellite-montmorillonite rock; 

and 3, limonite-quartz rock. The alteration varies 

in intensity and the mineralogic types overlap.

The beidellite-montmorillonite rock was recognized in the field by the use of benzedine, a reagent 

that gives a distinctive color to the beidellitemontmorillonite group of clay minerals blue when 

wet, yellow when dry (T. S. Levering, oral communication). The benzedine reaction is a useful field 

test, but exact mineral identification requires more 

precise methods. The hematite-alunite-quartz - 

kaolinite rock is faintly banded in places; white kaolinitic and alunitic rock forms poorly defined bands in the 

red or purple, more hematitic rock. The limonitequartz rock is orange to buff and contains varying 

amounts of fine-grained quartz and limonite stains 

and spots in a clay matrix. The arrangement of these

1 Equivalent uranium is a measure of the total amount of radioactivity emitted by the sample, and is expressed as if all the radioactivity were due solely to uranium in equilibrium with the products in 

its disintegration series. The radioactivity of all radioactive substances, 

such as thorium, potassium (K*°), or uranium, would therefore be included 

as the percent equivalent uranium, if they were present. The equivalent 

uranium content of these samples was determined by Geiger-Mueller counters 

in the laboratory.
three types o' alteration products is concentric, the 

hematite-quartz-alunite-kaolinite rock forms the core, 

the beidellite -montmorillonite rock forms the inner 

shell, and the limonite-quartz rock forms the outer 

shell.

The preliminary results of X-ray studies of 

specimens from the deposit are not conclusive 

(Theodore Botinelly, oral communication),but appear 

to indicate th- % t all three types of altered rock contain 

alunite, and that feldspar occurs with the beidelLtemontmorillo ite rock. Spectrographic analyses made 

by C. L. Waring of the Trace Elements laboratory, 

U. S. Geological Survey, are given in table 1. Of 

particular interest is the barium and vanadium content 

0. Ito 1.0 pe-cent in all samples, the increase in 

magnesium content from the core outward toward less 

altered rock, and the low content of iron in the 

beidellite-montmorillonite rock. These analyses, as 

well as those in table 2, indicate that the uranium content can be closely correlated with the beidellite - 

montmorillonite type of alteration which, in general, 

is outside the more intensely alunitized rock.

Sampling

Thirteen chip samples were taken in the upper 

bulldozer cut. They were cut at approximately right 

angles to the structure and represent each type of 

altered rock across the entire mineralized body. Another sample, DW-10-34, of white clay containing 

uranophane( ?) was taken from the.short trench above 

the upper bulldozer cut. The analyses of these samples 

are shown in table 2 (see also fig. 2). Of particular 

interest is the localization of the highest grade uranium in the beidellite-montmorillonite rock.

OUTLOOK AND GUIDES TO PROSPECTING

. The eastern and western limits of the two uraniferous zones on the East Slope No. 2 prospect have 

not been determined. Trenches to bedrock along the 

6670, 6660, and 6560 contours (pi. 1), across the 

areas covered with talus, might be expected to extend 

the known limits of these uraniferous zones, as well 

as to indicate where to do additional trenching. Because

Table 1. Spectrographic analyses of samples from alteration zones, East Slope No. 2 uranium

prospect, Piute County, Utah

Rock type More than

10.0 

(percent)

Hematite-alunite-quartzl -- Si, Al Pe 

kaolinite rock.

Beidellite-montmorillonite Si, Al K, Na

rock. 

Limonite-quartz rock Si, Al Pe, K, Mg

Spectrographic analyses

1.0 to 10.0 0.1 t.c 1 0 0.01 to 0.1 

(percent) (percent) (percent)

Less than

0.01 

(percent)

Ti, Ba, Cr, \ Sr, Mg, Ca, B Cu, Y, Ni. 

Pb, Na, Mn, 

Zr. 

Pe, Mg, V, U, Cr, Zr, Sr, Pb, Mn, Ni.

Ti, Ba. Ca, Cu. 

Na, Ca, Ba, Cr, Mn, 'Ni, Y 

Ti, V. Zr, Cu, Sr

Table 2. Analyses of samples, East Slope No. 2 uranium prospect, Piute County, Utah

[Type of altered rock: A, hematite-alunite-quanz-kaolinite rock; B, beidellite-Montmorillonite rock; C, limonite-quprtz rockj

Locality

and Length

sample (feet) 

no.

rw-io-21 5.5

-22 5.1

-23 8.6

-24 4.3

-25 5.2

-26 3.8

-27 2.6

-28 2.2

-29 4.5

-30 4.7

-31 ^.0

-32 11.5

-33 10.0

-34 3.6

Description

Orange-red altered rock . 

Pink altered rock, south of Sample 

no. EW-10-21.

Hematite-alunite-quartz-kaolinite rock 

 do ____.

South raniferous zone, orange to buff clay;

some quartz.

Orange to brown clay, south of no. EW-10-25 

White -o orange clay, north of no. EW-10-21-- 

Gray spotted hornfels, north of

no. DW 10-27. 

North uraniferous zone, white clay with

uranium minerals.

Orange, altered hornfels; sparse torbernite-- 

Mauve "potted hornfels; visible torbernite 

Brown to gray spotted hornfels - 

Silver to gr-ay spotted hornfels 

White clay with yellow stains from trench

west of (above) upper cut.

Equivalent 

uranium 

(percent)

0.016

.009

. .002 

.007 

.032

.018

.009

.014

.043

.017

.032

.006

.004

.021

Type

Uranium of 

(percent) altered 

rocks

0.018 C, B 

.007 C, B

.002 A 

.006 A 

.034 B, C

.018 C 

.011 B 

.020 

.047 B, C

.021 C 

.040 B 

.004 C 

.002 

.005
of the irregular distribution of uranium minerals in 

secondary deposits these trenches might be expected 

to uncover rock of appreciably different uranium 

content.

In other parts of the Marysvale district, pitchblende, which may constitute higher grade ore, underlies secondary uranium minerals; therefore, exploration 

by drilling or drifting at levels 100 to 200 or more 

feet below the present exposures offers the possibility 

of finding better-grade ore. The absence of information about the vertical extension of the known deposits 

at this prospect, however, makes such exploration 

economically hazardous.

The occurrence of secondary uranium minerals 

with beidellite-montmorillonite rock in zones peripheral to hematite-alunite-quartz-kaolinite rock suggests 

that prospecting of this general type of altered rock 

in the surrounding area might be fruitful. The 

beidellite-montmorillonite rock weathers readily and

therefore forms inconspicuous outcrops. The use 

of the benzedine test should aid in the field identification of this rock.

LITERATURE CITED

Callaghan, Eugene, 1939, Volcanic sequence in the 

Marysvale Region in south west-central Utah: 

Am. Geophys. Union Trans., part 3, p. 438-452.

UNPUBLISHED REPORTS

Callaghan, Eugene, Unpublished maps of the Marysvale, 

Sevier, Monroe, Delano Peak, and Beaver quadrangles, 

Utah.

Wyant, D. G., Stugard, F., Jr., and Kaiser, E. P., 

1950, Uranium resources in the Marysvale region, 

Utah, An Interim Report: U. S. Geol. Survey, 

Trace Elements Memorandum Rept. 169.

INT.-DUP. SEC.. WASH., D.C. 51,557
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEO.OGICAL SURVEY CIRCULAR 322 PLATE I

Mount Belknap rhyolite. ed facies

( uffaceous nd platy)

Quartz monzonite ?nd partly

(dark-gray and equigranular

jHornfels

Contact- metamorphosed latite of Bullion Canyon 

..lea'-, c aia assoc-'ated m'can'c rocks-predomi antly 

da-k-gray to green aphantti.-. roc'f wi-h feldspar 

p ophyrcblasts, bu* also '^eludes granular :roi n 

10 gray o red unfbliated recrysta'l 'zed rock

Inferred fault.showing dip

Dot ed wh-~e -oncssledV, upthrown side,

D. downthrown side

Breccia, showing fault 

zone and dip

Strike and dip of foliation

Uranium minerals

Uranophane, autunite, metatorbernife, 

schroeckingerite in white to buff or orange 

argill <ed rock

Hematte-aiunite-quartz-kaolinite ock

Altered hornfels 

Bleached, kaolmized, or limonitized

Geology and topography by 

D. G. Wyant, August 1950

GEOLOGIC MAP AND CROSS SECTIONS, EAST SLOPE NO. 2 URANIUM PROSPECT, PIUTE COUNTY, UTAH