GEOLOGICAL SURVEY CIRCULAR 224 

VOLCANIC DEBRIS IN URANIFEROUS 

SANDSTONES, AND ITS POSSIBLE 

BEARING ON THE ORIGIN AND 

PRECIPITATION OF URANIUM 

By Aaron 0. Waters and Harry C. Granger 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar L. Chapman, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

GEOLOGICAL SURVEY CIRCULAR 224· 

VOLCANIC DEBRIS IN URANIFEROUS SANDSTONES AND 

ITS POSSIBLE BEARING ON THE ORIGIN AND 

PRECIPITATION OF URANIUM 

By Aaron C. Waters and Harry C. Granger 

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. 

CONTENTS 

Page 

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

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

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Volcanic material included in the 

stratigraphic section . . . . . . . . . . . . . . . . . . . . . . . . 1 

General field characteristics . . . . . . . . . . . . . 1 

Colorimetric tests for montmorillonite . . . . 3 

Chinle formation . . . . . . . . . . . . . . . . . . . 3 

Brushy Basin shale member of 

the Morrison formation. . . . . . . . . . . . 5 

Shinarump conglomerate............. 5 

Salt Wash sandstone member of the 

Morrison formation . . . . . . . . . . . . . . . 5 

X-ray investigations..................... 5 

Petrographic evidence . . . . . . . . . . . . . . . . . . . 6 

Chinle and Brushy Basin units . . . . . . . 6 

Shinarump and Salt Wash units. . . . . . .. 6 

Description of the ores. . . . . . . . . . . . . . . . . . . . . . . . 10 

Features visible in the field . . . . . . . . . . . . . . 10 

Relation of ore to fossil wood. . . . . . . . . . . . . 10 

Relation of ore to clay . . . . . . . . . . . . . . . . . . . 12 

Microscopic features of the ores . . . . . . . . . . 12 

Montmorillonite -vanadium clay 

transition . . . . . . . . . . . . . . . . . . . . . . . . 12 

Secondary enlargement of quartz 

grains ........................... 15 

Solution of quartz grains . . . . . . . . . . . . 15 

Description of the ores--Continued 

Microscopic features of the ores--Con. 

Page 

Relation of vanadium clay to partially 

dissolved quartz grains............ 15 

History of development, and origin of the ores . . 20 

Deposition of sediments. . . . . . . . . . . . . . . . . . 20 

Burial ................................. 20 

Cementation . ; . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Devitrification . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Silicification . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Chemical changes in the connate water of 

the sandstones during devitrification 21 

Addition of alkalis. . . . . . . . . . . . . . . . . . 21 

Addition of uranium, vanadium, 

and other trace elements . . . . . . . .. 21 

Fixation of uranium and vanadium by 

organic matter . . . . . . . . . . . . . .. . . . . . . . . . 21 

Inadequacy of ash leaching...... . . . . . . . . . 22 

~eactivation of ground-water circulation 

by igneous invasion, hydrothermal 

activity, and uplift. . . . . . . . . . . . . . . . . . . . 23 

Supergene changes. . . . . . . . . . . . . . . . . . . . . . . 23 

Suggestions for future work.................... 24 

Geologic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Chemical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Physical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Literature cited ............................. ~ 25 

ILLUSTRATIONS 

Page 

Figure 1. Index map, Colorado Plateaus ............................................................ ;.. 2 

2. Glass shards altered to clay minerals........................................................ 7 

3. Devitrilied pumice lapilli tuff from the Chinle formation, Petrified Forest National Monument...... 8 

4. Altered biotite of volcanic origin in sandstone of the Salt Wash member of the Morrison formation. . g 

5. Sketch showing local fracture control of ore, Dolores group of mines, Uravan, Colo................ 11 

6. Clay galls in sandy matrix, Georgetown group of mines,Slick Rock, Colo......................... 13 

7. Ore, Salt Wash sandstone member of the Morrison formation near Uravan, Colo.................. 14 

8. Vanadium clay pellet derived from a gall of montmorillonite. Section cut from a "trash pile" lens 

at the Dolores group of mines, Uravan, Colo ............................................ .'... 16 

g, Authigenic overgrowths and solution features on quartz grains shown in different parts of a 

single thin section of ore. Salt Wash sandstone member of the Morrison formation.............. 17 

10. Stages in the solution of secondarily enlarged quartz grains in an ore body in the Salt Wash 

sandstone member of the Morrison formation ................................................ 18 

11. Clear quartz grains surrounded by vanadium clay dusted with unidentified uranium-bearing(?) 

mineral. ............................... · ............. · ..................................... 18 

12. Partly dissolved quartz grains surrounded by "ropes" of oriented vanadium clay.................. 1g 

TABLES 

Page 

Table 1. Mineralogy of clay samples from the Brushy Basin shale member of the Morrison formation. . . . . 4 

2. Mineralogy of clay samples from the Salt Wash sandstone member of the Morrison formation . . . . . . 4 

iii 

VOLCANIC DEBRIS IN URANIFEROUS SANDSTONES AND ITS POSSIBLE 

BEARING ON THE ORIGIN AND PRECIPITATION OF URANIUM 

ABSTRACT 

The relationships between uranium-vanadium 

ore deposits on the Colorado Plateaus and volcanic 

material that, in part, make up the host rocks suggest 

that the uranium and vanadium have a complex origin 

and history, and that they were emplaced during the 

structural deformation and igneous intrusion of Tertiary 

time. 

Volcanic debris, now altered to clay minerals, 

has been recognized in the Salt Wash sandstone and 

Brushy Basin shale members of the Morrison formation and in the Shinarump conglomerate and Chinle 

formation. Field studies and microscopic examination 

of the ores indicate a relationship between the ore 

minerals and montmorillonite clay formed by devitrification of volcanic glass. The vanadium hydromica 

formerly called "roscoelite" is believed to be derived 

from montmorillonite. 

A paragenetic sequence of events, shown by 

examination of thin sections of the ore-bearing. sandstones, begins with cementation of the sand by calcite, 

followed by secondary enlargement of quartz grains. 

The new silica deposited as overgrowths on the quartz 

grains was probably released by devitrification of the 

glassy volcanic material. At a later date the quartz 

grains were dissolved and vanadium hydromica and 

uranium-bearing minerals were formed. Deposition 

of the ore minerals was probably related to a change 

in ground-water conditions broughtabout by igneous 

intrusion. 

During devitrification of volcanic ash, ground 

waters may have leached alkalis, uranium, vanadium, 

and other substances from the ash. The absence of 

blanket deposits of uranium and vanadium minerals, 

however, implies either (1) reactivated circulation of 

metal-bearing ground water, or, more probably, (2) 

introduction of metal-bearing juvenile waters into the 

ground-water system. Several additional problems 

must be investigated before final conclusions can be 

reached. 

lliTRODUCTION 

In 1951 the writers visited many of the uraniumbearing localities on the Colorado Plateaus (fig. 1) and 

collected samples of the ores, sedimentary rocks 

associated with the ore, and Tertiary igneous rocks 

that occur as intrusive masses in the sedimentary 

rocks at some localities. These samples were, in 

part, analyzed and studied. 

Early in the work it was recognized that some 

of the Mesozoic sedimentary formations on the 

1 

Colorado Plateaus contain large amounts of vo].canic 

debris; they thus record episodes of volcanism that 

were contemporaneous with the deposition of the 

sediments. 

The uranium deposits of the Colorado Plateaus 

occur chiefly in the upper part of the Salt Wash sandstone member of the Morrison formation, and in the 

Shinarump conglomerate, although they are by no 

means confined to these units. Each of these stratigraphic units contains anpreciable amounts of volcanic 

debris, although their major constituents are 

nonvolcanic. Each is also overlain by a so-called 

"mudstone 11 stratigraphic unit that contains a high 

proportion of altered volcanic ash--the Chinle formation above the Shinarump, and the Brushy Basin shale 

member above the Salt Wash sandstone member. 

It was decided to investigate the beds containing 

volcanic debris in order to ascertain, if pos;sible, 

whether the presence of altered volcanic ash had been 

of any importance in the concentration of the uranium. 

The work is unfinished, but some promising leads are 

outlined in this preliminary report. 

The evidence indicates that volcanism took place 

during, and immediately following the time when the 

host rocks for the 11 Plateau type" uranium ·deposits 

were accumulating but that later igneous activity, 

particularly the intrusion of the laccolithic mountain 

groups, was of primary importance in the origin of 

the ore deposits. 

ACKNOW.LEDG MENTS 

The writers'. knowledge of the geology of the 

Colorado Plateaus was greatly augmented by two field 

excursions, one with C. B. Hunt, the other with 

L. C. Craig. Mrs. Alice Weeks kindly supplied results· 

of her studies of the clay mineral constituents of the 

ore-bearing rocks. An excellent suite of thin sections 

cut from ore -bearing rocks was loaned by R. P. Fischer. 

To these people, and the many others who supplied 

helpful suggestions, the writers are indebted. This 

report concerns. work done by the U. S. Geological 

Survey on behalf of the Division of Raw Materials of 

the U. S. Atomic Energy Commission. 

VOLCANIC MATERIAL INCLUDED rn THE 

STRA TIGRAPIDC SECTION 

General field characteristics 

The Brushy Basin shale member of the Morrison 

formation of upper Jurassic age is a sequence of thinbedded argillaceous sediments with interbedded sandstone lenses. The volcanic origin of much of the 
SALT .LAKE CITY@ 

DENVER @I 

•Albuquerque 

Figure 1. --Index map, Colorado Plateaus. 

argillaceous material (Hess, 1933, pp. 463-464; 

Stokes, 1944)1 is suggested by two features:. (1) the 

fluffy, popcorn-like surfaces developed by the swelling 

of the clay where it is exposed to weathering at the 

surface, and (2) the variegated color of the clay--each 

layer is commonly a different color. The chief colors 

are pastel shades of olive green, blue green, smoky 

white, _pale pink, creamy yellow, blackish purple, 

and maroon. 

In the Chinle forr:r\ation of Triassic age, 

especially in its lower part, are many argillaceous 

beds with characteristics similar to those of the 

Brushy Basin (Camp, 1929; Allen, 1930). Among the 

most St;I"iking examples are the variegated beds of the 

Painted Desert and the Petrified Forest National 

Monument in northeastern Arizona. In some areas, 

however, the Chinle formation consists almost entirely 

of maroon, light red, or yellow beds of sandstone, 

siltstone, and shale whose constituents are chiefly 

quartz sand, silt, and nonswelling clays. 

Both the Salt Wash sandstone member and the 

Triassic Shinarump conglomerate contain typically 

cross-bedded quartz with thin conglomeratic lenses. 

1 See literature cited. 

and layers. Clay is generally present as a prominent 

constituent between the sand grains, and as. tiny 

rounded pellets 2 to 5 times as large as the associated 

sand grains. Locally clay forms abundant galls, 

patches, and angular fragments distributed along the 

bedding of the sandstone. Interstratified with the 

sandstone, especially in the Salt Wash, are thicker 

layers and irregular lenses of argillaceous sediment 

(mudstone). These generally increase in number 

toward the top of the unit. A few of the clay beds 

have the popcorn-like surfaces and typical variegated 

colors; most are maroon or green beds of nonswelling 

·clay. 

Fossil wood is abundant in the Shinarump 

conglomerate, and is also found at many places in 

the Salt Wash sandstone member. In general it has 

been altered to coaly material, but in places it is 

silicified or replaced by carbonates. Some pieces of 

wood show black powdery edges that, in contrast to 

the coaly material, give off little or no volatile 

material when heated in a closed tube. Apparently 

the material is charcoal, though this identification 

has not yet been tested by X -ray methods. If charcoal is present, then some of the wood was partially 

burned prior to deposition. Locally the coaly material, 

and particularly the associated charcoal, are impregnated or replaced with uranium-bearing minerals. 
In many places fossil logs, bits of charred wood, 

abundant 1/2 to 3-inch clay galls, and large angular 

fragments of clay are mixed with the normal sand 

and quartz pebbles in heterogeneous beds that are 

locally called "trash piles." In some of these trash 

piles large and small fragments of fossil bone are 

found. Many of the ore deposits are associated with 

the trash piles. The uranium and vanadium minerals 

have impregnated or preferentially replaced the 

charred wood, certain kinds of clay galls, and bone. 

The individual sandstone beds of the Shinarump 

conglomerate are highly lenticular, and in places lie 

in definite scour channels eroded into the underlying 

Moenkopi formation, or into beds of (he Shinarump 

itself. These scour channels are generally only a 

few feet, or at most a few tens of feet deep. 

Most authors agree that the Shinarump conglomerate was deposited by a system of braided streams. 

These dropped their heterogeneous loads in the stream 

channels, filling them, and later breaking out to scour 

and fill new ones. Thus the streams spread widely 

over the depositional plain in intricate anastomosing 

courses, laying down a thin deposit of dominantly 

coarse debris which shows an interfingering of coarse 

and fine pebbly sandstone lenses, channel unconformities, clay seams, and "trash piles." 

The Salt Wash sandstone member of the 

Morrison is a much thicker stratigraphic unit, and 

consists in large part of normally bedded fluviatile 

sandstones, siltstones, and clays. Nevertheless, 

individual beds within it may show the rapidly developed scour and fill features, and other characteristics 

indicative of swift-flowing over-loaded streams. These 

characteristics are in general more common in the 

upper part of the Salt Wash, where it grades into or 

interfingers with the overlying Brushy Basin. The 

upper' more . heterogeneous portion of the 

·salt Wash isthe- 1favored place for uranium deposits. 

The stratigraphic work of L. C. Craig and 

coworkers (1951} shows that the Salt Wash sandstone 

member was deposited as a broad, .gently-sloping 

alluvial fan which spreads northeastward from a source 

in southern Utah and adjacent Arizona. Craig also 

shows that the sand and pebbles were derived chiefly 

from reworked sedimentary rocks. 

Longwell (1928, p. 56}, Allen (1930, p. 288), 

and others think that the Shinarump and Chinle 

sequence had its source in highlands to the south and 

southeast, and that the sediments were graded toward 

the Late Triassic California sea in broad fans and 

deltas. 

A question often asked concerning the Shinarump 

conglomerate is how a stratigraphic unit of such wide 

areal extent--over 100,000 square miles {Gilluly and 

Reeside, 1928, p. 67)--can be composed of generally less than 100 feet of coarse pebbly sediments that seemingly indicate a flood type of 

deposition from swiftly flowing torrents. 

In the writers' cpinion the heterogeneous 

character of the sandstones of the Shinarump, and of 

those comprising parts of the Salt Wash sandstone 

member, recall the kind of debris carried by streams 

whose headwaters have been showered with fine 

3 

pyroclastics during an episode of explosive volcanic 

activity. After an explosive eruption of ash and 

pumice the ,rivers draining a volcanic area are commonly choked with a slurry of shards, pumice lapilli, 

and fragments of trees destroyed by the ash shower, 

all intermixed with the normal sand and gravel 

constituents that the stream was carrying prior to the 

eruption (Segerstrom, 1950; Anderson, 1933;Wolfe, 

1878). Such streams, armed with abundant cutting 

tools in the form of floating and suspended particles 

of pumice, glass shards, and lava fragments, erode 

the upper part of their courses rapidly (Segerstrom, 

1950, p. 128), but on emerging onto a plain they quickly 

deposit their load, spreading it widely as channel fills 

in braided courses. These interfinger with finer 

deposits formed by bank overflow, and in places with 

thin seams of ash deposited directly from the air. 

The alluvial deposits on the intermontane 

plateaus of the Andes, the water-laid tuffs of the 

Tertiary and Pleistocene just east of the Cascade 

Mountains in Oregon, and the deposits on the alluvial 

plains surrounding the Javanese volcanoes are similar 

to parts of the Shinarump and Salt Wash stratigraphic 

units as far as details of bedding, hetero'geneous 

sizing of particles, and intermixture of old detrital 

material with new volcanic debris and fragments of 

wood and bone are concerned. In rocks as old as the 

Salt Wash and Shinarump, however, these features 

are much more difficult to recognize because volcanic 

glass in the form of shards and pumice has not survived. It has long since been devitrified. mostly to 

montmorillonite clay. 

Colorimetric tests for montmorillonite 

Colorimetric tests for montmorillonite with 

benzidine solution (Hendricks and Alexander, 1940; 

Mielenz and King, 1951) were made in the course of 

the field work. ,In the method used a saturatedwater 

solution of benzidine was dropped on the outcrop. If 

montmorillonite is present the wetted area should 

turn bright blue. However, the benzidine test is subject to considerable error in interpretation (Page, 

1941), chiefly because of of the interferenc~ of certain 

oxidizing or reducing elements present as impurities 

in the clay, the occurrence of "mixed lattice" clay 

minerals, and the lack of control of acidity of the 

sample (Mielenz and King, 1951, pp. 17-21). 

Nevertheless, because of the ease with which 

large numbers of samples can be tested in the field, 

the method merits attention, and from a statistical 

point of view the results of many tests may lead to 

worthwhile generalizations, although the accuracy of 

any individual test is open to question. We were able 

to make many hundreds of tests in widely spaced 

localities but because of the difficulties inherent in the 

method, the following generalizations should be interpreted as of tentative value only. 

Chinle formation 

The widespread light-colored (green, light-blue, 

smoky-white, pale-gray) clays with the popcorn-like 

surfaces that are characteristic of the lower part of 

the Chinle formation in northeastern Arizona and 

southeastern Utah almost invariably react strongly to 

benzidine. They were tested in many widely separated 

parts ofthePlateausfrom Cameron, Arizona, on the 
Table 1.--Mineralogy of clay samples from the Brushy Basin shale member of the Morrison formation 

[Based on X-ray studies by.Alice Weeks] 

Locality 

Woodside anticline, Utah-----------

South of Floy, Utah----------------

Kane Springs, Utah-----------------

La Sal Creek, Utah-----------------

Dry Creek anticline, Colorado------

Dolores group of mines, Colorado---

Unaweep, Colo.---------------------

Escalante Forks, Colo.-------------

! Sample no. 

L537 

L535 

L442 

L443 

L444 

L445 

L446 

L447 

L479 

L474 

L464 

L468 

L469 

L470 

L539 

L455 

L46o 

Minerals 

Montmorillonite, hydromica, quartz, and calcite. 

Do. 

Montmorillonite, quartz, and kaolinite. 

Do. 

Montmorillonite, hydromica, and quartz. 

Montmorillonite, quartz, and calcite. 

Montmorillonite and calcite. 

Montmorillonite, hydromica, quartz, and calcite. 

Montmorillonite and quartz. 

Do. 

Hydromica(?) and quartz. 

Kaolinite, hydromica, and quartz. 

Do. 

Montmorillonite and quartz. 

Montmorillonite. 

Montmorillonite and quartz. 

Kaolinite and quartz. 

Table 2.--Mineralogy of clay samples from the Salt Wash sandstone member of the Morrison formation 

[Based on X-ray studies by Alice Weeks] 

Locality 

Woodside anticline, Utah-----------

South of Floy, Utah----------------

Kane Springs, Utah-----------------

La Sal Creek, Utah-----------------

Dolores group of mines, Colorado---

Unaweep, Colo.------------------~--

Escalante Forks, Colo.-------------

Sample no. 

L534 

L533 

L448 

L449 

L450 

L45l 

L48o 

L475 

L47l 

L456 

L46l 

4 

Minerals 

Hydromica, quartz, and calcite. 

Do. 

Hydromica and quartz. 

Do. 

Hydromica, montmorillonite, kaolinite, quartz, 

and calcite. 

Hydromica, quartz, and calcite. 

Do. 

Do. 

Hydromica, kaolinite, quartz, and calcite. 

Hydromica, quartz, and calcite. 

Hydromica, kaolinite, and quartz. 
southwest to the foothills of the Uinta Mountains on the 

northeast, and from Capitol Reef National Monument, 

Utah, on the west to the Nacimiento uplift of northern 

New Mexico on the southeast. In places, however, 

the Chinle also contains many beds of red or green clay 

that weather to small platy chips instead of developing 

swelling surfaces. Generally these either do not 

react to benzidine, or give faint indefinite colors. The 

nonreactive beds greatly predominate in some areas. 

Brushy Basin shale member of 

the Morrison formation 

Light-colored clays of the Brushy Basin sequence 

reacted strongly to benz'idine at nearly every locality 

where they were tested. Some beds appear to be nearly 

pure bentonites, others are mixed with varying amounts 

of silt, sand, and nonreactive clays. Many of the red 

and purple beds interstratified with the lighter colored 

clay also react, although the blue is partly masked by 

the iron oxides. 

Shinarump conglomerate 

The conglomerate and sandstone of the Shinarump 

generally contain thin clay seams, small clay pellets, 

and, in places, clusters of 1/2- to 2-inch clay galls 

and in places large angular fragments of clay. The formation also contains clay as a matrix between the sand 

grains, but some sandstone beds are free of interstitial 

clay. Marked differences in the reaction of these clays to 

benzidine occur from place to place, and within the 

same outcrop. In general, the matrix clay and the small 

pellets less than 1/4 inch in diameter react, although 

many exceptions were noted. In some outcrops 

two or more kinds of clay galls may be clus.tered 

together in the same lens of sandstone. One 

clay may react to benzidine, another not at all, and a 

third one may react slightly, or may contain small 

highly rea<;:tive pellets in a nonreactive matrix. In 

places it can be established that the nonreactive fragments are pieces of shale and siltstone torn up and 

incorporated from the underlying Moenkopi formation. 

With only a few exceptions the thin clay seams, 

1/4 to 2 inches thick, that locally separate the beds 

of sandstone are strongly reactive. 

Salt Wash sandstone member of 

the Morrison formation 

The sandstones and interbedded shales and 

mudstones of the Salt Wash have been systematically 

tested with benzidine only in the. area directly south 

of the Four Corners and in a few parts of the "Uravan 

mineral belt" (Fischer and Hilpert, 1952). 

In general the prominent beds of red and green 

shale or mudstone interstratified with the pr~vailing 

light-colored sandstones do not react to benzidine, or 

they show only faint indefinite bluish-gray colors. In 

places pellets and small fragments of material within the clay are strongly reactive. In the Four Corners 

area the sandstone contains numerous thin seams and 

partings of light-green clay, generally less than 2 inches 

thick, that react strongly to benzidine. One such 

parting composed the upper half-inch of a 7 -foot bed 

of green shale, the remainder of which was not reactive. 

In the areas studied, clays that are reactive to 

benzidine are both thicker and more numerous in the 

5 

upper part of the Salt Wash than they are in the lower 

part. 

In most places that were tested the matrix clay 

between the sand grains is strongly reactive, but 

exceptions occur. Fragments of clay incorporated 

in sandstone lenses are commonly reactive, although, 

as at many localities in the Shinarump, nonreactive 

fragments are common. 

To summarize and generalize from these 

admittedly inadequate data, it appears that both the 

Shinarump and Salt Wash were derived chiefly fr;om 

a· sedimentary landmass (Craig and others, 1951, 

p. 42) that contributed quartz pebbles, sand, and silt, 

and also clays that do not react to benzidine. In the 

source areas for both formations, however, volcanic 

activity apparently began, and the sands, gravels, and 

clays derived from the erosion of the old sediments 

were diluted and mixed with new accessions of shards, 

pumice lapilli, and fragments of glassy lava which 

have since altered to montmorillonite. 

As·pyroclastics covered a greater extent of the 

source area, the type of sedimentation gradually 

changed to the bentonitic clays and siltstones· characteristic of the lower Chinle and Brushy Basin 

sequences. 

This sequence of events, suggested by field 

characters and the benzidine test, is in part confirmed 

by X-ray and petrographic evidence, as discussed in 

the following paragraphs. 

X -ray investigations 

X-ray studies of clay samples from the formations of the Jurassic and Cretaceous systems at 

several localities in southwest Colorado and Utah 

have been made by Alice Weeks of the U. S. 

Geological Survey. Mrs. Weeks• preliminary results 

with respect to the mineralogy of the clays from the 

Brushy Basin shale and Salt Wash sandstone members 

of the Morrison formation are tabulated below 

(tables 1 and 2). 

As can be seen from these tabulations, all but 

4 of the 17 samples of clays from the Brushy Basin 

shale member contain montmorillonite. Some appear 

to be bentonites, in others the montmorillonite is 

mixed with hydromicas and kaolinite. 

On the other hand the chief clay mineral in the 

Salt Wash samples tested was hydromica. Montmorillonite is reported in only one sample. 

In a general way these results confirm the 

benzidine tests, which indicated that the clays of the 

Brushy Basin shale member are largely bentonitic, 

whereas the thick beds of. red and green clay interstratified with the sandstones of the Salt Wash are 

nonreactive. Benzidine tests showed, however, that 

many of the thin clay seams, and some of the clay 

galls in 11 trash piles" of the Salt Wash sandstone are 

strongly reactive. It will be interesting to obtain 

X-ray data on these highly reactive materials. 

Mrs. Weeks 1 results definitely establish the 

presence of montmorillonite as a prominent constituent 

in some of the ciays of the Brushy Basin shale member. 
It remains to show that the montmorillonite is the 

product of devitrification of volcanic glass. This has 

been done by examination of the clays in thin sections. 

Petrographic evidence 

A few thin sections, ground in oils so that no 

water could touch them, have been cut from the 

samples of the Shinarump, Chinle, Salt Wash, and 

Brushy Basin stratigraphic units. In addition, through 

the kindness of R. P. Fischer, the writers had the 

opportunity to examine a large number of thin sections 

of uranium-vanadium ores from the Salt Wash. These 

were prepared with water in the usual way. 

The thin sections give clear evidence of the 

presence of abundant volcanic debris in each of the 

four stratigraphic units investigated. However, except 

for thin clay seams, and some interstitial clay between 

the sand grains, volcanic material is not abundant in 

the Salt Wash sandstone member exc~pt near its top. 

Chinle and Brushy Basin .units 

Fragments of altered volcanic glass, and bits 

of micro lite -filled lava, intermixed with varying 

amounts of nonvolcanic constituents appear in every 

section cut in oils and more sparingly in the sections 

cut in water. The volcanic glass is completely altered, 

chiefly to rather coarse plates of a clay mineral of 

moderate birefringence, and with indices of refraction 

within the range given for montmorillonite (Ross and 

Hendricks, 1945). Despite complete devitrification, 

the characteristic shapes of shards, and the bubbly 

texture of pumice remain. The textures are beautifully 

preserved in some specimens (figs. 2 and 3), indistinctly 

in others. Small particles of porphyritic lava and 

less commonly pieces of devitrified spherulitic 

obsidian are. better preserved. Even in fragments 

whose feldspar phenocrysts are completely altered to 

clay, their textures are unmistakable (fig. 3). Particles 

of welded tuff. are present in some specimens (fig. 3), 

and fragments of trachytic textured lava that were 

reheated sufficiently during transport in the eruption 

cloud to cause decomposition of the ferromagnesian 

minerals to powdery black aggregates (Williams, 1929, 

pp. 193-198) are seen .ih :o1. few specimens. 

The magmas that produced these pyroclastics 

were apparently highly feldspathic, quartz-free o:r 

quartz-poor types. Sanidine, andesine, albite, and 

biotite are the chief phenocrysts, but in most rocks 

the feldspars are too greatly altered for precise 

identification. Hypersthene and basaltic hornblende 

have been identified in one rock. Quartz occurs as 

phenocrysts in a few bits of spherulitic lava. The 

most common texture is a mat of tiny feldspar microlites in either a hyalopilitic or very fine grained 

trachytic arrangement. About half of the feldspar 

microlites show the nearly square cross sections 

characteristic of sanidine, the rest are sodic plagioclase. 

More work is necessary, but the available evidence 

indicates that the lavas were chiefly biotite latites 

and biotite keratophyres, with perhaps some admixture 

of andesitic and dacitic materials. 

The source of the volcanics cannot be determined 

with the meager data at hand, but the proportion of 

volcanic material in the Chinle appears to increase 

toward the south and southwest. At the Petrified 

6 

Forest National Monument the Chinle formation consists in part of moderately coarse pumice lapilli tuffs 

containing abundant fragments of 11 burned11 lava and 

welded tuff, mixed with particles of pumice ~s much 

as 1 centimeter in size. It seems unlikely that these 

coarse but fragile constituents could have been transported far. 

A few scattered observations suggest that the 

volcanic material of the Brushy Basin sequence thickens 

and coarsens to the west and southwest. 

Shinarump and Salt Wash units 

Thin sections of clayey sandstones from the 

Shinarump conglomerate ana from the ore-~earing 

layers of the Salt Wash sandstone member also show 

volcanic debris, but it is not as easy to recognize as 

in the Chinle and Brushy Basin units. The clayey 

matrix between the sand grains generally shows few 

if any structures characteristic of shards and pumice, 

though in some ·rocks, for example, the basal beds of 

the Shinarump at Fort Defiance, Ariz., small clay 

pellets in the sandstone show well preserved pumice 

sfructure. In a permeable rock like sandstone, it is 

not surprising that the fragile gl~ss textures would 

be largely destroyed. They are obliterated in 

bentonites which have fluffed up by wetting at the 

ground surface, and in a permeable sandstone with 

interstitial ash there would be every opportunity for 

water to enter and destroy the structure after 

devitrification. 

Although the textures characteristic of pumice 

and shards may be destroyed, fragments of altered 

lava can nearly always be found in the clayey sandstones. Furthermore euhedral phenocrysts of biotite, 

sanidine, and plagioclase, some with particles of 

lava still sticking to them (fig. 4), contrast sharply 

with the nonvolcanic constituents of the sandstones. 

The main nonvolcanic constituent is quartz in well 

rounded or subrounded grains. It generally makes up 

85 to 90 percent of the sandstone. Chert and microcline 

are abundant locally, and are present in small amounts in 

nearly every slide. Minor accessories include zircon, 

staurolite, tourmaline, and garnet. Sillimanite and 

apatite are commonlj present as inclusions in quartz 

grains. This assemblage of well rounded, weathering 

resistant minerals contrast strikingly with the easily 

destroyed euhedral books of partiallychloritized biotite 

(fig. 4), the half kaolinized sanidines andplagioclases, 

and the fragile particles of pumice. Obviously reworked 

sedimentary materials prepared by repeated weathering 

and long continued wear have been adulterated with easily 

destroyednew materials of volcanic origin. 

Nevertheless, not all of the fine-grained 

constituents of the sandstones of the Shinarump and 

upper Salt Wash are volcanic. The Salt Wash, particularly, contains abundant beds of clay and silt, 

most of which do not react to benzidine. From the 

little petrographic work that has been done these appear 

to be composed chiefly of a clay mineral of higher 

refringence and birefringence than the montmorillonite 

formed from shards and pumice. Alice Weeks' studies 

indicate that this mineral is hydromica. _ It was 

probably derived from the reworking of older marine 

shales. Hydromica is sometime::: present in pellets 

and flakes, and as a filler between the quartz grains 
...:1 

r---------------------------------------------------------------------------------------------------------------------~ 

h 

JJ 

A. From the Brushy Basin member 

of the Morrison formation 

0 0.1 mm 

B. From the Chinle formation 

Figure 2. --Glass shards altered to clay minerals. 
0 

Tuff fragment 

0.25 mm 

Pumice, altered to 

montmorillonite 

Figure 3. --Devitrified pumice lapilli tuff fr om the Chinle formation, Petrified Forest National Monument. 

8 
0 0.25 mm 

A. - Note slight rounding 

0.25 mm 

B, Biotite phenocryst partly enclosed in' devitrlfied glass matrix 

Figure 4. --Altered biotite of volcanic origin in sandstone of the Salt Wash member of the Morrison formation. 

9 
of the sandstone, but, at least near the ore deposits, 

the common interstitial clay appears to be montmorillonite. 

DESCRIPTION OF THE ORES 

Features visible in the field 

Most ore bodies are small--a few feet thick, 

and a few tens (rarely hundreds) of feet long and wide. 

The larger ore shoots show a rough control determined 

by the bedding, and also tend to cluster in certain 

favorable beds. Although the ore is commonly described 

as lying in "channels, " those deposits for which stope 

maps or geologic maps are available <Fi~cher, 1950A, 

p. 8), rarely show any resemblance to the undulating, 

more-or-less continuous "shoestring" type of ore body 

generally visualized by the word channel. Instead, 

minable ore is generally concentrated in flat ore shoots 

whose long dimension is seldom much greater than 

their width. 

The small but rich ore bodies that occur in and 

around fossil logs, the small ore bodies called "rolls" 

(Webber, 1947, fig. 63), and the ore bodies which 

occur in deep channels in Monument Valley {Witkind, 

1951) are exceptions. These may be many times as 

long as they are wide. 

In detail the or9 cuts across the bedding despite 

the fact that stratification appears to be the dominant 

structural control. In places this cross-cutting relation is a gradational one; a common case is where 

ore penetrates farther along a sandstone bed with a 

high clay content than along an adjoining bed with less 

clay--the ore gradually plays out in the less favorable 

bed. In rolls, however, the ore boundary is generally 

sharp, and transects the bedding in a smooth curve. 

A conspicuous banding of the ore minerals may be 

developed along the edges of the curve. 

In most mines fracture control is not evident, 

but, as it is easily overlooked it may be more comm9n 

than has been recognized. That fractures have, in 

places, served as feeding channels for the ore solutions is demonstrated by the mineralization so well 

displayed along fault gouges in the Rajah mine, by 

the group of closely spaced mineralized joints in the 

White Canyon area (Benson and others, 1952), and on 

a much smaller scal'e by the occurrence of features 

such as those sketched in figure 5 from the Dolores 

group of mines. 

In several rolls that the writers have examined, 

a prominent joint, or series of joints, lined with a 

thin film of white mineral which resembles dickite or 

alunite, lies along the axis of the roll. The sandstone 

adjacent to these joints is commonly bleached and 

softened. In places the shale floor beneath the ore 

body is also cut by a plexus of small fractures that 

show bleaching, films of dickite(?) or alunite(?), 

staining by copper or vanadium minerals, and other 

evidences of mineralization. These features suggest 

that, at least locally, the ore-bearing solutions 

travelled across the beds, emerging from tight fracture channels into permeable beds where the solutions 

could spread out and deposit their ore, and left by 

another series of small fractures on the other side of 

the bed. It should be emphasized, however, that the 

walls of many ore deposits have been well-exposed 

10 

by mining operations, but there is no trace of fracture channels in either floor or roof. For these it 

appears that ore-bearing solutions must have travelled 

along the bed. 

Relation of ore to fossil wood 

Some of the richest ore is closely associated 

with organic matter. Fossil wood enclosed in ore is 

generally richly mineralized except where the wood 

has been strongly silicified or replaced by carbonate 

prior to mineralization. In places,( the Happy Jack 

mine at White Canyon, and the Sevenmile Canyon 

deposits northwest of Moab, for example) the wood is 

replaced by clearly visible masses of pitchblende, or 

by associated sulfides such as pyrite, chalcocite, or 

galena, but more commonly the woody tissues are 

impregnated, replaced,and partially destroyed by 

cryptocrystalline black grains of uranium and vanadiumbearing substances. Commonly the mineralization 

extends some distance from the fragments of wood as 

impregnations in the surrounding sandstone. Orebearing fossil logs commonly have mineralized hulls 

of this J.dgd extending from a few inches to a few feet 

into the sandstone. 

At many places, however, the woody material 

seems to have largely rotted out and its place is now 

filled with clay and calcite mixed with carnotite and 

other ore minerals. Some of the richest ore bodies 

are "logs" of this kind. 

A close relationship between small particles of 

organic material and ore is visible in many deposits 

that do not contain logs or large wood fragments. It 

is possible that ail of the ore-bearing sandstones contain at least a little carbonaceous material. 

Observations at several widely spaced localities 

(for example, Scenic claims at White Canyon, Petrified 

Forest National Monument, Uinta Basin2 and others) 

indicate that charcoal and the charred edges of 

pieces of fossil wood are more strongly mineralized 

than the coaly pieces of wood in the same deposit. 

This relation supports Frederickson•s {1948) idea that 

substances with sheet structures such' as charcoal and 

montmorillonite are able to extract uranium from solution because of the ease with which the large uranyl 

ions can penetrate between the layers of montmorillonite or charcoal. Here they are supposedly trapped 

and held by weak electrical charges. This theory 

may have considerable merit, but much work must 

be done before we understand how uranium minerals 

are accumulated and held by organic materials. 

(McKelvey and Ne1son, 1950; Battelle Mem. Inst., 

1948-49.) 

It has been assumed by many that decay of 

organic m~terial causes a change in the pH of the 

surrounding solution, thus inducing precipitation of 

uranium in and around the wood, but this mechanism 

seems inadequate because of the vast volume of solution that would be needed to precipitate the uranium 

found in even a single richly fossiliferous log. MorE 

promising lead9', per~aps, are humic colloids and 

geochemical sorption phenomena. It is well-known 

experimentally that a number of organic compounds 

and sols have the power of removing uranium almost 

completely from solution (Batt. Mem. Inst., 1948-49.) 
. ' .· " ·. . . . . 

. . . . . . . 

0 

... ·. 

. . '. 

I 

. . . ' .... . . 

2 

.-

3 

. ~ ... 

. : ; :· ': : :.::. :: 

':':' :. · . 

: : -. _: .: •·• ·. ·.: :· :· . . 

. .... . . .. . 

5 6 7 8 Feet l 

Figure 5. --Sketch showing local fracture control of ore, Dolores group of mines, Uravan, Colo. 

11 
In the Shinarump and upper Salt Wash units 

there would be excellent opportunity for the abundant 

particles of wood and other organic materials to 

slowiy decay and produce various kinds of humic 

colloids, resins, and soluble organic compounds that 

might then be distributed widely through the sandstone in ground water. Such potential adsorbants of 

uranium may have been held in these sandstones until 

the igneous intrusion, structural deformation, and 

erosion of Tertiary time, for there probably was 

little opportunity for free circulation of ground water 

through the highly impermeable formations above and 

below these units. In addition to its potentialities of 

precipitating uranium through sorption phenomena and 

straight chemical reaction, the organic-rich connate 

water would also be of strongly reducing nature. 

Perhaps the change of redox (oxidation-reduction) 

potential in a body of ore-bearing solution that might 

enter and mix with such a body of connate water would 

be enough to induce precipitation. 

Relation of ore to clay 

Certain kinds of clay minerals, as well as the 

fossil wood, apparently were able to trap and cause 

precipitation of uranium and vanadium minerals from 

solution. Characteristically the ore minerals occur 

as impregnations or replacements of the clayey 

matrix of impure sandstones. The preferential impregnation or replacement of clay by both uranium 

and vanadium minerals is obvious in the field. Not 

only is the clay matrix of a sandstone mineralized, 

but thin clay seams, and certain kinds of clay pellets 

and clay galls that abound in the so-called trash piles 

have been strongly mineralized (fig. 6). Not all clay 

beds are thus favored, however. The original composition of the clay appears to be a major factor. In 

many ore deposits a thin clay seam, 1/2 to 2 inches 

thick, will be a high-grade ore, whereas another clay 

bed of less favorable composition separated from 

the first by only a few inches of mineralized sandstone, 

is almost completely barren. The c~ay galls in a 

single sandstone bed are differentially mineralized 

also. At many deposits one clay gall may be altered 

to dull, brownish-black, slickensided pellets richly 

impregnated with vanadium and uranium minerals, 

whereas an adjacent clay gall of different composition 

is only slightly mineralized. 

The ore -bearing solutions, however, apparently 

were unable to penetrate deeply into relatively pure 

clay beds and galls even when these were of favorable 

composition. Seams of clay more than 2 inches thick 

are rarely mineralized throughout, unless their 

permeability has been heightened by an appreciable 

content of sand and silt. The edges of clay galls are 

commonly mineralized to depths of only 1/4 to 1/2 

inch, leaving pale colored unmineralized, centers that 

contrast strikingly with the strongly mineralized 

brownish-black rims (fig. 6). 

Chemical experimentation combined with detailed 

field work is needed to determine just what effect both 

fossil wood and clays of different kinds have had on 

the precipitation of uranium. It is obvious from the 

field relations that they have clearly had some effect. 

12 

Microscopic features of the ores 

Most of the ore minerals deposited in the clay and 

fossil wood are of microscopic dimensions; many are 

tiny opaque specks so small that an oil immersion lens 

is needed to see them individually. Hence they are too 

small to identify readily by petrographic methods alone. 

Perhaps a promising method of making progress in the 

identification of these minerals would be a study of the 

ores in thin and polished sections, followed by mechanical separation of the finer-grained minerals by crushing 

and centrifuging in heavy liquids, and study of the concentrates by X-ray and petrographic methods. 

None of this kind of work has been done for this 

report, and only about 40 thin sections have been 

studied in detail, though a fairly large collection loaned 

by R. P. Fischer has been looked over superficially. 

Although the ores are commonly described as 11 carnotite ores, 11 it is the writers' experience that 

carnotite is not a prominent mineral except in deposits 

that have been altered. In these it occurs chiefly as 

joint fillings, and as haloes and impregnations around 

other minerals. In many examples it is clearly derived 

from the fine-grained 11 blue-black 11 ores by secondary 

processes as was pointed out by FrankL. Hess (1913, 

p. 148) in 1913: 

"Faces along many joints of the vanadiferous sandstone are covered with canaryyellow, minutely crystalline carnotite which 

is clearly secondary and has evidently been 

leached from the ore-bearing rock.: ... Here 

(on Fall Creek) all joints, even those that are 

closely spaced, are brightly coated with 

carnotite. The vanadium ore is peculiarly 

black on these claims ..... The carnotite seems 

to be closely connected with the dark or black 

ores. The original mineral from which the 

carnotite was derived is unknown." 

Mineralogic work to date seems to show that the 

original fine-grained blue-black ores are made up 

chiefly of a vanadium clay (the roscoelite or vanadium 

mica of early workers) plus several other minerals, 

chiefly hydrous vanadium and uranium oxides. Pyrite 

(fig. 1) is fairly common in most of the unoxidized deposits, and its former presence is suggested by limonite spots in many of the oxidized ores. Other accessory 

sulfides that appear in places are chalcocite, bornite, 

chalcopyrite, arsenopyrite, covellite, galena, and their 

oxidation products. The copper sulfides are especially 

common .in the Slick Rock district, Colorado and the White 

Canyon area in Utah. 

Certain textural and paragenetic features of 

possible genetic significance were noted during study 

of the thin sections, and will be summarized: 

Montmorillo_nite-vanadium clay transition 

At a group of claims east of the Carrizo Mountains 

of northeast Arizona, thin seams of clay interstratified 
'· ,; . ..' . .. ~ 

,. 

<V"" 

0 ,, 

<> 

.;, .· - ..... ··.-·.···- . ;-. .•·. :. ·~ · ....... ~.. . •. ·: .. :<>· 

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-; . ~ ' 

·' .:. ' ·:: . .,. 

• t / 

•. ~ 0 : ~ 

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-· ·- 0. :~ 

..... ... (..~ .. 

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··· ' , .... ·.,·~ ;-< .. ·;.~.:···:::· .. o.c<-> 

·' .. / } ~=-... . .•, ... 

;o 

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·, a , 

~ <> " ·.,; ... -:.~:·~·;· . 'ilrt.b.. .. . :. ~ .· . .... ;'? .. «: .... \. '; •• ·,,.,:. . • , 

··~ . .. I ' ~ ~,·: ... ,~ . . ....... .. .. · ... ,· 

··.·:·· 

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· .. , c.' I' ·.;:: .~ ... ~ r . . . · .. :; 

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~ . ·':::. ·~:~ .' ·. .· . ·:· · . . ·"'.~\·.· ... • 

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·~':· .. 1:!1._"\, ··,·,. , ·: ;· .,. ·. ,. •, ~ 

. : .,_ ,' '·.c . ·.s · ·~· ' : · . .. ,. ·' ,-o ; 

._:J~ ·~:' .. · . ·.: ~ 

0 l 2 Inches 

Figure 6. --Clay galls in sandy matrix, Georgetown group of mines, Slick Rock, Colo. 
A. B. 

0 Q. , mm 

Figure 7. --Ore, Salt Wash sandstone member of the Morrison formation near Uravan, Col o. 

with the ore- bearing sandstone are composed mainly 

of the dark colored vanadium clay so common in Colorado 

Plateau or~s X- ray studies by Sterlmg Hendricks 

(Fischer, 1942, p. 378) indicate that this mmeral is 

a vanadium hydromica. 

A notable feature of the eastern Carrizo occurrence is that although the thin clay seams are highly 

mineralized, they are separated by only a few inches 

of mineralized sandstone from much thicker beds of 

red and green clay that are almost entirely barren. 

Exposures of the Salt Wash sandstone that occupy an 

equivalent stratigraphic position 1/4 mile to 2 miles 

from the area of mineralization show that the thicker 

clay beds do not react to benzidine, whereas the thin 

clay seams are strongly reactive. The thin clays 

probably represent ash falls that have devitrified to 

montmorillonite, whereas the thicker clays are apparently of a different origin and composition. 

The suggestion immediately arises that the orebearing solutions have converted the montmorillonite 

to vanadium hydromica. This is an expectable transition, 

inasmuch as the space lattices of the two minerals are 

nearly identical (Grim, 1942; Nagelschmidt, 1938; Ross 

and Hendricks, 1945). The transformation may be 

similar to the conversion of montmorillonite to the 

ordinary potassium hydromica ("illite") which Dietz 

(1941) considers to explain the abundance of illite in 

marine shales. 

In the field an attempt was made to trace one of 

the clay seams rich in vanadium outward fr om the 

eastern Carrizo ore into an unaltered montmorillonite 

seam, but because of the discontinuity of the seams, 

the lack of exposures at critlcal points, and a raging 

snowstorm, this was not successful. Such a field 

transition has been found, however, in a thin mineralized layer of clay galls at the Dolores mines near 

Uravan. In this area thickly spaced clay pellets and 

clay galls ranging from 1/100 inch to 2 inches in 

diameter, change from green, unmineralized benzidinereactive clay to dull, black highly mineralized hard 

masses in a distance of 12 feet along the stnke of the 

sandstone that encloses them. The sandstone also 

shows increasing mineralization of the clay matrix. 

Unfortunately thin sections disclose that at least 

two and possibly three kinds of clay galls of different 

origin are mixed together, in this sandstone layer. 

Thin sections in the unmineralized portion show that 

many galls are chips of a previously deposited shale. 

They show bedding, and the clay minerals are oriented 

in minute flakes parallel with the bedding. This clay 

has a high birefrmgence, and X- ray tests made by 

Alice Weeks mdicate that it is hydromica. Another 

kind of clay gall, generally smaller than the shale 

chips, shows tiny but unmistakable alte.red fragments 

of a glassy trachytic textured lava, and particles of 

material preserving shard structures. Both the glass 

and the feldspar microlltes .are completely altered to 

clay, probably the montmorillonite detected by X-ray. 

Successive thin sections taken at 5 points to show 

the increase in mineralization indicate the following 

changes in the clay galls within the sandstone bed. 

The colorless clay (montmorillonite ?) acquires a 

faint sepia color. At the same time shard and other 

structures fade out, and the gall becomes a homogeneous 

mat of cryptocrystalline flakes. With increasing 

mineralization the flakes become more individualized, 

until ultimately the galls consist of a homogeneous mat 

of micaceo us flakes of a deep brown, composed of a 

clay mineral with high birefringence. In a still higher 
stage of mineralization these galls are impregnated, 

particularly along their edges and between the cleavages 

of the clay mineral, by a black, apparently uraniferous 

mineral in tiny rounded grains surrounded by pleochroic 

haloes (fig. 8). 

Changes in the shale galls formed of original 

hydromica are different. Little change is noted at 

first, but ultimately the hydro mica dar kens in a rather 

splotchy manner, apparently because of impregnation 

by the black uranium-bearing(?) mineral. The petrographic work, although not completely definitive, indicates that the original hydromica of the shale has 

not been recrystallized or changed in composition, 

whereas the montmorillonite has been converted to a 

vanadium clay mineral with high birefringence. 

An attempt to study the change from montmorillonite 

to vanadium clay by X-ray methods was only partly\ 

successful because the galls used for X-raying were 

picked from the rock before the petrographic work had 

disclosed that there were chips of sha1e as well as galls 

derived from volcanic debris in the sample. As a 

result the X-ray results cannot be interpreted in terms 

of a possible montmorillonite-vanadium hydromica 

transition, because hydromica is present in all samples. 

A new attempt will be made on more carefully selected 

materials. It is hoped that the change can also be 

demonstrated in the laboratory by experimental methods. 

Spectrographic analyses of four samples involved 

in the transition (unfortunately, separated before the 

petrographic work was done and hence containing 

variable amounts of shale and volcanic pellets in each 

sample) showed the following changes in vanadium, 

uranium, silver, and cobalt contents: 

Thin sections from the Waterfall group of mines 

northeast of Monticello, Utah and from other places 

on the Colorado Plateaus show various stages in the 

disappearance of shard textures and the conversion 

of the original clay to a uniform dark-brown micaceousappearing clay of high birefringence. 

More work is necessary, especially chemical 

experimentation, but these preliminary observations 

suggest that the widespread occurrence of the vanadium 

clay in the ores is because montmorillonite transforms 

to a vanadium hydromica in the presence of vanadiumbearing solutions. < 

Secondary enlargement of quartz grains 

In many thin sections of ate-bearing sandstone 

the quartz grains show authigenic overgrowths in 

optical continuity with the original quartz grains (figs. 

9 and 10). The amount of silica added in this way appears 

to vary from place to place, and is difficult to estimate 

accurately because, as will be shown, the quartz grains 

in many of the ores have later been partially dissolved. 

In some sections, however, from 10 to 20 percent of 

the total bulk of the rock consists of secondary silica. 

In these rocks, overgrowths have filled nearly all the 

spaces between the grains, cementing the sandstone 

into a hard quartzite. 

The silicification, however, seems to be patchy 

and irregular. Our field observations, although meagre, , 

indicate that silicification is more common along the 

edges of the ore bodies and in the wall rocks away from 

15 

the deposits than in the ore itself. It is also more common 

in thin sandstones interbedded with clays of the Brushy 

Basin shale member than it is in the Salt Wash, and 

seems to be best developed in the Salt Wash near the 

Brushy Basin contact. The silicification may follow 

beds, or it may occur in irregular patches that cut 

across beds. In some URmineralized rocks that have 

a clay and calcite cement it is entirely absent. In 

others only a little clay and calcite are left in the 

interstices between the mutually interfering overgrowths. In places small patches of the clay-rich 

groundmass have been completely surrounded and 

appear as tiny islands in the authigenic hull of a single 

grain. 

These relations show that the silicification was 

later than at least an early stage of cementation by 

calcite and clay. The patchy distribution of the areas 

with enlarged grains, however, suggests that the rock 

was only partially cemented prior to silicification, and 

that deposition of silica occurred chiefly in the more 

permeable areas where ,there was only a little clay and 

calcite. 

The silicification appears to be earlier than the 

deposition of the vanadium- uranium ore minerals, as 

shown by the following relations. 

Solution of quartz grains 

Many thin sections of the ores show evidence of 

solution of the quartz grains of the sandstone. The 

solution took place at some stage after the overgrowths 

had formed. Many grains have had the secondary overgrowths partially dissolved, others have had both overgrowths and core deeply indented, and still others have 

been reduced to ragged elongate remnants (fig. 10). 

The solution of quartz has taken place after 

cementation of the rock, and has obviously been influenced by differences in permeability and by fractures. 

This is shown by the variable effects that may be seen 

even in a single thin section~ All drawings in figure 10 

are from a large thin section, about 1-1/2 inches1 square, 

no. U85B in R. P. Fischer's collection. Patches within the section that are tightly cemented by authigenic 

overgrowths show only a little solution along the edges; 

in areas where there is a little calcite and clay as 

cement, mild solution has produced stylolitic iridentations between adjacent quartz grains; in areas where 

there was considerable calcite and clay, solution has 

completely removed most of the authigenic hulls. In 

a few seams that contain a large amount of interstitial 

vanadium clay the quartz grains appear to have lost 

at least half their volume by solution. 

Relation of vanadium clay to partially 

dissolved quartz grains 

In many places where quartz grains show extensive 

evidence of solution the interstitial vanadium clay 

between the grains occurs as a nest of small rope-like 

veinlets that wrap around the quartz grains (figs. 11 

and 12). The plates of the clay, stand at right angles 

to the walls of the veinlet--thus at right angles to the 

edges of the quartz grain. This kind of crystallization 

is typical of minerals that grow in open spaces--gypsum 

plates in small veinlets, comb quartz in veins, ice in 

cracks within frozen ground. Similar groups of oriented 

clay plates can be seen to lie at right angles to the walls 
,__. 

0> 

A. - Note solution features on quartz grains 

B. - Unidentified uranium mineral. Note the pleochroic 

halo it makes in the vanadium clay 

Figure 8. --Vanadium clay pellet derived from a gall of montmorillonite. Section cut from a "trash pile" lens at the Dolores group of mines, Uravan, Colo. 
Chiefly vanadium clay 

0 0.25 mm 

Figure 9. --Authigenic overgrowths and solution features on quartz grains shown in different parts of a single thin 

section of ore. Salt Wash sandstone member of the Morrison formation. 

17 
0 ' 

"1. 

. 

0 0 0~25 mm 

Figure 10. --Stages in the solution of secondarily enlarged quartz grains in an ore body in the Salt Wash sandstone 

· member of the Morrison formation. 

Figure 11. --Clear quartz grains surrounded by vanadium clay dusted with unidentified uranium-bearing{?) mineral. 

18 
0 

Figure 12. --Partly dissolved quartz grains surrounded by "r opes" of oriented vanadium clay. 

19 

0 . 1 mm 
of minute fractures in the minerals or in the matrix 

of the sandstone, and to surround the edges of open 

cavities between the grains. 

Where more than one rope or veinlet appears 

around a quartz grain, the veinlet nearest the grain 

was the last one to be1deposited, as indicated by the 

way it cuts across or merges into ropes that are more 

distant. In a few places these mats of tiny ropes 

apparently preserve the rounded outlines that a quartz 

grain possessed prior to solution. 

The relations show that the solution and filling 

took place in recurring steps, each one giving rise 

to a separate veinlet developed betwee_n its predecessor 

and the retreating quartz wall, and indica'te that solution of quartz grains was followed almost immediately 

by filling of the openings by oriented plates of vanadium 

clay. 

This is good evidence that solution of the quartz 

was accomplished by the same solutions that brought 

in the vanadium. It shows that the ore-bearing solutions 

did not enter the rock until after cementation by !calcite 

and montmorillonite, and until after the quartz grains 

had been enlarged by secondary silica. The widespread 

unidentified uranium(?) mineral that occurs in minute 

black specks seems to have crystallized simultaneously 

with the vanadium clay, but to have continued its crystallization even a little later, for it occurs along the 

cleavages of the vanadium clay and is commonly present as thick clusters on the edges of pellets composed 

of vanadium clay (figs. 8 and 11). 

HISTORY OF DEVELOPMENT, AND 

ORIGIN OF THE ORES 

The field and petrographic evidence may now be 

summarized and certain implications drawn from it. 

Deposition of sediments 

The two principal ore-bearing formations of the 

Colorado Plateaus (Shinarump and upper Salt Wash) 

contain appreciable amounts of volcanic debris, intermixed with weathering-resistant detrital material of 

nonvolcanic origin. ·Some beds contain abundant pumice 

and lava fragments, f9ssil' wood, charcoal, clay galls, 

and in some places fossil bone. This kind of material 

is typical of the pumice-slurry' floods produced where 

volcanic eruption clouds fall into rivers. 

Burial 

Each of the two ore-bearing formations grades 

upward into a thick stratigraphic' unit (lower Chinle 

above the Shinarump, Brushy Basin above the Salt 

Wash) composed in large part of stratified volcanic 

debris. As originally deposited these formations were 

chief ... y ash and pumice lapilli, mixed with varying 

amv~ts\ of sand, silt, and clay of nonvolcanic origin. 

Cementation 

Deposition and burial was followed by cementation 

of the rock, chiefly by calcite and clay. The cemen20 

tation, however, seems to have been somewhat patchy 

and irregular, leaving many places where the voids 

between the grains were unfilled or only partially 

filled. 

Devitrification 

Devitrification of the glassy volcanic debris 

changed the water-laid tuffs in the lower Chinle and 

Brushy Basin to bentonitic shales, siltstones, and 

mudstones. The interstitial ash in the sandstones 

also devitrified, forms a ciay matrix of montmorillonite in some sandstone beds. 

Pleistocene and Recent deposits of volcanic ash 

show little or no devitrification, except adjacent to 

hot springs or fumaroles. On the other hand, glassy 

pyroclastics of early Tertiary time generally are 

almost completely devitrified. It can reasonably be 

assumed, therefore, that devitrification of the glassy 

materials in the Triassic and Jurassic sediments of 

the Colorado Plateaus did not occur until affer burial--

probably to depths of 1, 000 feet or more--and after 

at least partial cementation. 

Silicification 

Probably as a result of the devitrification, widespread, but patchy and irregular silicification occurred. 

Bentonite typically contains less silica than the ash 

from which it was derived. Bramlette (1946, p. 28) 

and Ross, Miser, and Stephenson (1929, p. 186) have 

published analyses of unaltered igneous material and 

of the bentonites derived from them that show very 

considerable losses in silica. Ross, Miser, and 

Stephenson {1929, p. 186) calculate that about half 

the original silica was lost during the transformation 

of an Arkansas trachyte ash to a bentonite. As previously noted, silicification of the sandstones is demonstrated by the widespread occurrence of authigenic 

overgrowths on quartz grains, by the abundant petrified wood, by jaspery and cherty cementation of some 

conglomerates and mudstones, and by abundant thin 

beds of silicified sandstone and shale in the bentonitic 

sediments. Much work remains to be done, but scattered 

field observations suggest that silicification has been 

most extensive in thin, formerly permeable beds of 

sandstone interstratified in the Brushy Basin sequence, 

in the basal conglomerates of the Brushy Basin (for 

example, the jaspery conglomerate of Calamity Mesa), 

and in the sandstones of the upper Salt Wash. 

The obvious source of the silica is from devitrification of the nearby ash beds. Silicification of 

adjacent permeable rocks during the devitrification of 

ash beds has been described by many authors (Rubey, 

1929, p. 160; Ross and Shannon, 1926, p. 79; Bramlette, 

1946, p. 26). Murata (1940) points out the common 

association of silicified wood with devitrified volcanic 

ash, and shows that altered pyroclastics are a rich 

source of. readily available silica for geochemical 

purposes. 

The thin sections indicate that silicification 

occurred simultaneously with devitrification. The 

authigenic overgrowths enclose the calcite cement of 

the rock, and show a strong tendency to fill spaces 

that were not previously filled by calcite, and clay. 

Pieces of carbonatized wood with the carbonate par-
tially replaced by silica were noted on the east side 

of. the Henry Mountains and at the Georgetown claims, 

Sllck Rock, Colo. Thin beds of sandstone interstratlfied 

with bentonites have been silicified to hard quartzite 

at many localities. -

Chemical changes in the 

connate water of the sandstones 

during dev1trification 

The migration of silica during devitrification of 

volcanic ash is shown by the silification of adjacent 

rocks, and by chemical analyses. Certain other chemical changes accompanying devitrification are deducible, 

but are much less susceptible of proof. We have assumed that the rocks were buried deeply during devitrification. Therefore the sandstones of the Shinarump 

and Salt Wash were probably filled with connate water 

which could not circulate freely because of impermeable 

formations above and below. Certain changes may be 

expected in the chemistry of .this connate water body 

and in the enclosmg rocks as a result of devitrification. 

Addition of alkalis 

One obviously deducible fact is that the connate 

waters would be enriched in the alkalis. Chemical 

analyses of bentonites from many areas show that 

potassium and sodium are leached during devitrification; 

m many rocks they are almost completely removed 

(Ross, Miser, and StephensQn, 1929, p. 186). Alkalis 

and alkaline salts are associated with bentonites in 

many areas (Ross and Shannon, 1926, p. 80; Davis, 

1929, p. :?35). 

Base exchange would still further increase the 

alkali content of the connate water, and would decrease 

its content of Ca++ ions. Bentonitic clays tend to extract Ca++ ions from waters passing over them, and 

release Na+ ions (Renick, 1925). Original Mg++ ions 

are similarly removed by base exchange. Magnesium 

is an essential constituent of montmorillonite and it . , 1s doubtful if the original biotite latite and biotite 

kPratophyre contain enough magnesium for complete 

bentonitization. 

By such reactions we may expect the original 

content of calcium and magnesium in the water to be 

almost completely removed, and the content of the 

alkall metals to be greatly increased. 

Addition of uranium, vanadium, and 

other trace elements 

Devitrification of the ash may also be expected to 

result in the redistribution of several other elements 

besides s1lica and the alkalis. The metallic elements 

ordinarily concentrated in pegmatites and hydrothermal 

veins (Rankama and Sahama, 1950, pp. 178-184) would 

presumably not have crystallized during eruption of 

the volcanic materials, and hence would be locked up 

in the glass shards and pumice. On devitrification 

any of these elements ,that ionize readily, or that form 

soluble ionic complexes may .be expected to be partially 

leached from the ash, and to be concentrated in the 

connate water of the adjacent sandstones. 

Two such elements are uranium and vanadium. 

C?the:s are the soluble members of the rare-earth group, 

tltamum, molybdenum, tungsten, copper, bismuth, 

21 

zinc, lead, antimony, mercury, and others. Corresponding nonmetallic elements that would be expected 

to be partially leached and removed are sulfur, selenium, 

tellurium, arsenic, boron, chlorine, and fluorine. 

Theoretically, therefore, all these elements might be 

expected to move into the connate water of the adjacent 

sandstones. However, even if they had thus migrated 

and concentrated, reactivated .circulation of the ground 

water following\ the Tertiary uplift and erosion would 

have flushed out most of those elements that had remained in a soluble form~' 

It is noteworthy, however, that the Salt Wash 

sandstones still contain appreciable !amounts of several 

of these elements. The only known rock that exceeds 

the Salt Wash in selenate content is a tuff of Tertiary 

age near Lysite, Wyo. (Trelease and Beath, 1949, 

p. 69). Because of the- toxic qualities of certain plants 

rooted in seleniferous soils, the distribution of selenium 

in rocks has been widely investigated by agricultural 

agronomists. One such study of the Salt Wash by Beath 

(1943) has given us some extraordinarily interesting 

data. His work, chiefly in the Yellow Cat district, 

Utah, shows the presence of vanadium, uranium, 

chromium, zinc, tellurium, copper, molybdenum, and 

titanium, as well as large amounLs of selenium, in 

rocks from the Sal+ Wash and in the s01ls derived from 

them. · He states (p. 704) that doubtless this list would 

be increased by further investigation. In general, the 

highest concentrations were found in carbonaceous 

vanadium ores, though barren sandy shales also contain high amounts. He reports that vanadium and uranium tend to cluster in zones, whereas selenium and 

other metals are more widely, though not uniformly, 

distributed. 

In view of the .fact that the Salt Wash sandstones 

were not known to contain volcanic matter at the tlme 

Beath wrote, and thatl the volcanic origin of the Brushy 

Basin shales had also been overlooked, his conclusions 

as to the origin of these metals is interestmg (Beath, 

1943, p. 609): 

11The writer finds it difficult to 

visualize clearly how so many different 

minerals were concentrated in the sediments which comprise these poison strips, 

especially if volcanic activity is not believed 

to have been an immed1ate contributing 

factor." 

Beath also reports the presence of selenium in 

the rocks overlying the Salt Wash, but the plants growing on these formations are generally not dangerously 

toxic. His results, therefore, are in accord with, but 

do not necessarily confirm, the hypothesis that many 

of these metals were leached from the over lymg 

pyroclastics of the Brushy Basin and concentrated in 

the connate water of the Salt Wash. Here, of course, 

there would be opportunity for some of the leached 

elements to precipitate m the rock by reactions w1th 

one another and with the minerals of the sandstone. 

Let us look into this possibility a little farther with 

regard to uranium and vanadium. 

Fixation of uranium and 

vanadllim by organic matter 

Assuming that uranium and vanadium were leached 

from the ash and concentrated in the connate water of 
the sandstone as outlined above, perhaps there is a 

possibility that the uranium was extracted from solution 

by organic material present in the sandstones. 

The organic material consists chiefly of fossil 

wood and small amounts of fossil bone. As previously 

noted .some of the fossil wood is in the form of charcoal. 

In the space of time that elapsed between sedimentation 

and devitrification considerable decomposition and 

change in the original plant tissues of the wood are to 

be expected. Humic colloids, organic resins and acids, 

'various hydrocarbon gases such as methane, and many 

other complex organic compounds and sols would be 

released into the grouncl water. Such materials might 

migrate some distance from their point of generation. 

These substances would, of course, change the redox 

pot2ntial of the ground water. 

The remaining parts of the wood would be converted to peat or coal. Charcoal would be expected 

to remain unchanged. Some leaching of the. phosphatic 

material in fossil bone would be expected. 

Several of these organic substances may have 

served to extract and "fix" uranyl ions present in 

solution. The possible role of charcoal as a "fixing 

agent" is emphasized by Frederickson (1948): 

"It is here suggested that the wide 

distribution of uranium throughout the 

sedimentary crust of the earth is due principally to its tendency to form large U02++ 

ions ..... much of the uranium in shales 

may be in the form of adsorbed ions and not 

of discrete minerals. 

"A world-wide association cf certain 

types of carbonaceous material with vanadium and uranium materials has been observed ...... All forms of so-called amorphous carbon, from lampblack and coke to 

charcoal, are graphitic in character. They 

are composed of portions of the graphite 

structure without, however, the regular 

3-dimensional periodicity characteristic of 

crystalline graphite. Because of its structure, with its extensive internal surfaces 

and unsatisfied valencies, charcoal (and 

similar forms of carbon) possesses the property of adsorbing ions to a remarkable extent." 

As previously noted, field tests with a Geiger 

counter show that charcoal is more highly radioactive 

than coaly material when the two occur together in the 

same ore deposit. 

.Another group of fixing agents are the humic 

colloids and other kinds of hydrosols. The possible 

role of geochemical adsorption in removing uranyl 

ion from solution apparently has not been fully investigated. On theoretical grounds, however, the large, 

positively charged uranyl ion with its two attached 

oxygens located on opposite sides of the uranium atom, 

should be attracted and held by the following negatively 

charged sols (Rankama and Sahama, 1950, p. 255) all 

of which were probably present, at least in small 

amounts, in pore fluids of the sandstone: humic colloids, 

hydrate of vanadium pentoxide, metal hydrosols, and sulfide hydrosols. 

22 

Finally, certain organic compounds such as the 

long-chain amines, the ion-exchange resins, and 

various organic compounds of phosphorus and of 

arsenic are known to be remarkably effective precipitants of uranium. (Battelle Memorial Institute 

reports under Contract no. A. T. 30-1-Gen-202, 

especially BMI-JDS-127, 146, and 163.) Whether 

or not any of the particular organic compounds used 

in the Battelle Institute experiments were actually 

present in these natural solutions can only be conjectured, but a source for the materials is available 

in the fossil wood and bone of the sediments, and in 

<iirsenic ions which could have been leached from the 

ash. 

To summarize these admittedly theoretical deductions on the possible results of devitrification: 

We assume that alkalis, uranium, vanadium, and 

other substances were leached from the ash and added 

to the ground water in the adjacent sandstones. Calcium and magnesium were simultaneously removed 

from the water by base exchange and chemical reaction. Humic colloids, hydrocarbon gases, and 

other organic compounds were·generated by decomposition of the fossil wood and bone, and became widely 

dispersed in the pore fluids. These, plus the residual 

coal, charcoal, and fragments of fossil bone may have 

largely removed the uranium and vanadium from solution. 

Does this mechanism explain· the origin of the 

present ore deposits? Could all the uranium in the 

ores have been leached from the overlying ash beds, 

and precipitated in the manner outlined? 

Inadeq~cy of ash leaching 

Some difficulties appear. As Frederi~kson (1948) 

points out montmorillonite has a sheet-lattice structure 

and hence should be as remarkably effective .in adsorbing and fixing uranyl ions as is charcoal. Evidence 

that montmorillonite has played a role in the fixation 

of both vanadium and uranium in the ores of the Colorado 

Plateaus has already been presented und'2r the heading 

"montmorillonite-vanadium clay transition." There 

it was also noted that montmorillonite seams in the 

ore deposits have been converted to vanadium clay and 

are richly impregnated with uranium minerals, whereas beds of hydromica clay are generally :almost, unmineralized. 

Recalling these relations it may justifiably be 

asked: Would uranyl ions ever escape from the ash 

during devitrification? Would they not be immediately 

adsorbed on the newly formed montmorillonite clay 

and thus remain locked in the bentonite? This possibility, plus the overall distribution of the ore deposits themselves convinces the writers that simple 

leaching of ash and precipitation of the leached uranium and vanadium by organic matter is inadequate 

to explain the- genesis of the sandstone-type ores of 

the Colorado Plateaus, though it may be the answer 

for the North Dakota (Denson, 1950) and New Mexico 

(Bachman, 1951) uraniferous lignites. The sandstonetype ores do not occur in a relatively uniform, low-grade 

sheet, as might be expected on this hypothesis. Instead ore shoots are clustered in groups of small relatively high-grade deposits. Over wide areas the 

volcanic sediments of the Brushy Basin and Chinle are 
thoroughly devitrified, but there are no ore deposits 

in the sandstones beneath. 

Thus, although leaching of volcanic ash may have 

been a contributing factor, at least one additional step 

seems to be required to explain the ccr:1centration of 

the metals in the known ore deposits. 

Reactivation of ground-water circulation 

by igneous invasion, 

hydrothermal activity, and uplift 

In Tertiary time widespread igneous activity 

produced the laccolithic complexes and other igneous 

bodies of the Colorado Plateaus area. At approximately 

the same time considerable structural deformation of 

the sedimentary rocks also occurred. 

A spatial grouping of the uranium-1vanadium ore 

deposits in arcs around the edges of the laccolithic 

centers is apparent, and strongly suggests that perhaps the ores are of hypogene origin, derived from 

fluids given off during the crystallization of large 

deep seated magmatic masses that underlie the laccolithic complexes. 

The igneous activity and structural deformation 

of the sediments would certainly reactivate the groundwater circulation in the Shinarump and Salt Wash units. 

Three factors may be considered: (1) te~tonic changes 

in elevation of different areas would supply a hydrostatic head, (2) tectonic movements and igneous intrusion would open joints and faults in the formerly 

impermeable formations above and below the orebearing sandstones, and (3) accession of steam and 

of hydrothermal solutions into the sandstones from 

the crystallizing magmas would reactivate circulation 

of the ground water. The effects produced by the first 

two are obvious. Here we restrict the discussion to 

the possible effects of introducing steam and metalbearing hypogene solutions into the ground water that 

filled the sandstones of the Shinarump conglomerate 

and Salt Wash. 

If, as a result of devitrification and leaching, 

the ground water had evolved to the rather unusual 

compo~ition indicated above, mixing of new magmatic 

water with this material could not help but produce a 

number of effects which should be recorded in the 

rocks themselves. Among the immediate changes that 

may be expect~d are: 

(1) The temperature of the magmatic water 

. would immediately drop. 

(2) The redox potential would be likely to change 

because of the strongly reducing character of the connate water. 

(3) The magmatic waters would be brought into 

contact with coal, charcoal, fossil bone, humic colloids, 

and other organic materials which might act as precipitants or adsorbants of their metals. 

( 4) The magmatic waters would come in contact 

with montmorillonite in thin clay seams, clay galls 

and as interstitial material between the sand grain~. The montmorillonite might selectively adsorb or precipitate some of the metals. 

23 

If the magmatic water contained uranium and 

vanadium any of the four factors mentioned above would 

be likely to 'induce their precipitation; the four of them 

operating together produces a geochemical environment 

in which abundan!_:precipitation would be almost certain. Thus we can explain why the Shinarump and upper 

Salt Wash were especiaHy favored by the ore deposits; 

they have several factors operating to cause precipitation, whereas other stratigraphic units generally 

lack the combination of organic matter and montmorillonite in a permeable rock filled with ground water. 

The structural, mineralogic, and zonal relations 

of the ores favor, or at least are :compatible with the 

idea of hypogene origin, as has been brought out by 

Cater, Shoemaker, Bensori, and others (unpublished 

data and personal co'mmunication). Our studies of 

thin sections bring out still another point. As previously 

noted, the quartz grains of the ore-bearing sandstone 

were being dissolved at the same time the vanadium 

clay and other vanadium-uranium minerals characteristic of the blue-black ores were being deposited. 

What change ensued in the rock to cause solution of 

q!JB.rtz grains, when these same grains had previously 

been enlarged by addition of silica? 

As indicated above, the cause of the original 

silicification was apparently devitrification of the ash. 

Devitrification also caused the connate water to be 

enriched in the alkalis. If hot magmatic water then 

entered this environment, mixed with the ground water, 

and induced a dynamic system of active circulation instead of the essentially static condition of water movement that had formerly prevailed, solution of quartz 

would be an almost certam result. Quartz dissolves 

in an alkaline solution. Any acidity that the magmatic 

waters may have had would be neutralized by passing 

through calcite-rich rocks below the ore-bearing sandstone, or by reacting with the carbonate cement of the 

sandstone itself. In the Uravan area the solutions may 

also have picked up salines in passing along the edges of 

the salt intrusions. The widespread bentonitization of 

the ash beds· of the Mesozoic supplied an abundance of 

soluble alkalis to be leached and incorporated into the 

magmatic water. The change from a static water body 

to a hotter one, circulating within the sandstone would 

enable this alkaline solution to attack the quartz and 

carry away the dissolved silica. 

Was all of the uranium and vanadium supplied 

from the magmatic source or was some, possibly most 

of it, supplied by devitrification of volcanic ash, and 

then merely rearranged and reconcentrated into the 

present ore deposits by the reactivated ground-water 

circulation set up by igneous invasion, hydrothermal 

activity, and uplift? No completely satisfactory answer 

can be given to this problem as yet. Possibly the 

anomalous lead isotope relations that Lorin Stieff (1949) 

has found to be characteristic of the ores of the Colorado 

Plateaus may indicate a double source, part of the 

uranium coming from devitrified ash of the Mesozoic, and, 

part from hydrothermal solutions of the Tertiary. 

Supergen~ changes 

In some deposits weathering and recent circulation of ground water appears to have changed the 

mineralogy of the ores considerably since they were 

originally deposited. Other deposits;appea:r to be 
fresh and unmodified. As noted earlier carnotite 

appears to be a supergene mineral developed at the 

expense of the blue-black ores. It is found chiefly as 

haloes around earlier uranium minerals, as coatings 

of fractures, as fillings or replacements of fossil wood, 

and as impregnations in sandstones. Many other 

secondary uranium and vanadium minerals appear. 

BeGause of the bright colors of the secondary minerals 

they are much more GOnspicuous than the original uranium-vanadium constituents of the blue-black ores. 

Th1s is probably responsible .for the deposits being 

called 11 carnotite ores. 11 Hess (1933, p. 471), states: 

11 Pintadoite, pascoite1 and carnotite 

form on the walls of canyons and caTnotite 

or a similar yellow mineral is inclosed in 

gypsum filling recent cracks. There can 

be no doubt of the present day migration 

of the minerals of the deposits, and this 

movement is, in general, away from fossilized vegetal matter, which means that 

plant material was the nucleus of original 

deposition. 11 

Some of the secondary minerals develop very 

rapidly. Fossil wood replaced by pitchblende occurs 

at the Happy Jack mine. Within a few months after 

it is exposed on the moist walls o~ the drifts by mining 

operations it acquires a coat of bright yellow secondary 

products-. 

SUGGESTIONS FOR FUTURE WORK 

The prevailing view that has guided most of the 

exploration on the Colorado Plateaus is that the ore 

deposits are of syngenetic or of penecontemporaneous 

origin. The concepts and ideas presented in this report are at variance with this \Conclusion, but they are 

only in preliminary form and are based on inadequate 

data. Much work remains to be done. The true answer 

to th~ origin of the ores, however, is of much economic 

significance. 

If the source of the uranium is really in hydrothermal solutions of Tertiary age, or even if the 

principal source is from the leaching of ash of Mesozoic 

age followed by redistribution of the uranium due to 

reactivation of the ground water by Tertiary igneous 

activity and orogeny, the problem of finding ore is 

rather different than if the ores are assumed to be of 

penecontemporaneous origin. 

A concerted attack on the origin of the ores, including field work closely tied to mineralogic studies 

and experimentation along chemical and physical lines 

should be made to solve the problem and thus open the 

way to the development and application of new concepts 

in ore finding and exploration. The following studies, 

or lines of approach for studies already begun, are 

suggested for guidance in further investigation of the 

origin of the ores of the Colorado Plateaus. 

Geologic 

1 Carry out a detailed program of mine mapping 

closely tied to pet;rographic work, X-ray studiesJ and 

other laboratory techniques. The mapping and lab24 

oratory work should be directed to definitely ascertaining the space and time relations of the ore to 

fractures, silicification, quartz leaching, mixing of 

ground-water bodies, cementation, and other features. 

Only a little mine mapping has been done and th1s has 

not been closely tied to laboratory studies. 

Continue and expand the investigation of zoning 

and mineral ratio relations within the metallic deposits surrounding' laccolithic centers on the Colorado 

Plateaus. 

Make a detailed geologic map, and a thorough 

spectrographic ana mineralogic investigation of the 

stocks of the La Sal laccoiithic complex with special 

reference to the content of uranium in (1) the igneous 

rock of the stock, (2) the deep seated inclusions that 

occur in the igneous rock, (3) the base metal and other 

ore deposits found as veins in the stocks and in the 

immedhtely adjacent wall rocks, and (4) the portions 

of the stocks that have been altered by hydrothermal 

solutiqns~ 

Similar studies. should be made of the igneous 

bodies near Placerville, Colo. , and in other areas. 

Make a detailed stratigraphic, mineralogic, and 

spectrographic investigation of the bentonitic clays of 

the lower Chinle and Brushy Basin with special reference 

·to ascertaining the original volume of volcanic material, 

and determining its uranium content. In particular 

determine, if possible, the uranium content of any of 

the igneous components that have not been devitrified, 

and compare with the uranium content of the derived 

bento_nite, with that of weathered and 11 f1uffed" material 

on bentonite outcrops, and with that of ground water 

in contact with the bentonite. Also determine whether 

the uranium in these samples is in equilibrium. 

Determine by petrographic studies, stripping 

film, ··and other laboratory, techniques the manner in 

which uranium is distributed in radioactive clays and 

carbonaceous materials in the sandstones. In particular, 

attempt to determine its relation to the kind of clay, 

and to the composition and history of the carbonaceous 

material. 

Attempt to establish the temperature ·a,t_ which the 

ore minerals were deposited by pyrite decrepitation, 

studies of clay alteration, and other,methods. 

Chem1cal 

Investigate the relation of organic material to 

the precipitation of U02++ ion. Controlled experiments 

should be made with wood, rotten wood, humic col' oids, 

peat, coal, charcoal, and asphaltic materials. 

Investigate the effect of montmorillonitic clays 

in adsorbing and precipitating uranium and vanadium 

from solution at various temperatures as much as 

200° C. This should be coupled with a detailed study 

of the base exchange relations between both vanadium 

and uranyl ions with K+, Na+, Mst+-+, and Ca++ ions in 

montmorillonite and related clays. 

Similar investigations with silica qel, humic· 

colloids, and sulfide hydrosol should be tried. 
Physical 

Continue work in an attempt to obtain reliable 

age determinations of the carnotite ores of the Colorado 

Plateaus. Investigate the possible reasons why many 

specimens investigated are out of equilibrium, and 

determine the nature of the leaching (or enrichment) 

that has occurred. 

By scale model experiments simulate the penetration of a hydrothermal water body of different 

density and chemical properties into an essentially 

static body of water, the "static" body being the porefiller in a permeable "sandstone. " 

Investigate the physical changes in wood, charcoal, 

~nd related substances when immersed in sol1.1tions 

approximating hydrothermal conditions, and when subjected to radioactive bombardment. 

LITERATURE CITED 

Allen: V. T., 1930, Triassic bentonite of the Painted 

Desert: Arr .. Jour. Sci., 5th ser., val. 19, pp. 283-

288. 

Anderson, C. A., 1933, The Tuscan formation of 

northern California: Univ. California Publ. , Bull. 

Dept. Geol. Sci., vol. 23, pp. 215-276. 

Bachman, G. 0., and Reed, C. B., 1951, Results of 

recent reconnaissance investigations of uranium in 

coal, black shale, and related deposits, Sandoval 

and Rio Arriba Counties, N. Mex.: U. S. Geol. 

Survey, Trace Elements Mem. Rept. 309. 

[Unpublished. ] 

Battelle Memorial Institute, 1948-49, Organic precipitants and complexing agents for uranium, reports on contracts No. AT 30-1-Gen-202 (especially 

nos. BMI-JDS-127, 146, and 163). 

Beath, 0. A., 1943, Toxic vegetation growing on the 

the Salt Wash sandstone member of the Morrison 

formation: Am. Jour. Botany, vol. 30, pp. 698-707. 

Benson, W. E., Trites, A. F., Jr., Beroni, E. P., 

and Feeger, J. A., 1952,Preliminary report on the 

White Canyon Area, San Juan County, Utah: U. S. 

Geol. Survey Circ. 217. 

Bramlette, M. N., 1946, Monterey formation of 

California and the origin of its siliceous rocks: 

U. S. Geol. Survey, Prof. Paper 212. 

Camp, C. L. , 1929, History of the Chinle Triassic 

formation in the Southwest (abstract): Bull. Geol. 

Soc. Am., vol. 40, p. 165. 

Craig, L. C., Holmes, C. N., Cadigan, R. A., 

Freeman, V. L., Mullens, T. E., and Weir, G. W., 

1951, Preliminary report on the stratigraphy of the 

Morrison and related formations of the Colorado 

Plateau region: U. · S. Geol. Survey, Trace Elements 

Inv. Rept. 180. [Unpublished.] · 

Davis, C. W., 1929, Geology of bentonite, Pan-American Geologist, vol. 41, pp. 333-336. 

Denson, N. M. Bachman, G. 0., and Zeller, H. D., 

1950, Surr,mary of new information on uraniferous 

lignites in the Dakotas: U. S. Geol. Survey, Trace 

Elements Mem. Rept. 175. [Unpublished. ] 

Dietz, R. S., 1941, Clay minerals in recent marine 

sediments: Univ. Illinois. [Unpublished Ph. D. 

dissertation] . 

Fischer, R. P., 1942, Vanadium deposits of Colorado 

and Utah: U. S. Geol. Survey Bull. 936-P, pp. 363-

394. . 

25 

Fischer, R. P., and Hilpert, L. S., 1952, Geology 

of the Uravan mineral belt, u; S. Geol. Survey 

Bull. 988-A, pp. 1-13. 

, 1950A, Uranium bearing sandstone 

--,;d-e-po_s_i:-:-t-s-o-;:f,..-;t-,he Colorado Plateau: Econ. Geol.. 

vol. 45, pp. 1-11. 

Frederickson, A. F., 1948, Some mechanisms for 

the fixation of uranium in certain sediments: Science, 

vol. 108, pp. 184-185. 

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111'1'.-00P. $EC .• IM'SJI., D.C. J:., 18