U.S. GEOLOGICAL SURVEY BULLETIN 1797 -
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY 

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications 

that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual"Price and 

Availability List" are no longer available. 

Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated monthly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, Box 

25425, Denver, CO 80225. Reports released through the NTIS may be obtaine.d by writing to the National Technical Information 

Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. 

Order U.S. Geological Survey publications by mail or over the counter from the offices given below. 

BY MAIL 

Books 

Professional Papers, Bulletins, Water-Supply Papers, Techniques 

of Water-Resources Investigations, Circulars, publications of general interest (such as leaflets, pamphlets, booklets), single copies of Earthquakes 

& Volcanoes, Preliminary Determination of Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone 

out of print at the Superintendent of Documents, are obtainable by mail 

from 

U.S. Geological Survey, Books and Open-File Reports 

Federal Center, Box 25425 

Denver, CO 80225 

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Detennination of Epicenters) can be obtained ONLY from 

the 

Superintendent of Documents 

Government Printing Office 

Washington, D.C. 20402 

(Check or money order must be payable to Superintendent of Documents.) 

Maps 

For maps, address mail orders to 

U.S. Geological Survey, Map Distribution 

Federal Center, Box 25286 

Denver, CO 80225 

Residents of Alaska may order maps from 

Alaska Distribution Section, U.S. Geological Survey, 

New Federal Building- Box 12 

101 Twelfth Ave., Fairbanks, AK 99701 

OVER THE COUNTER 

Books 

Books of the U.S. Geological Survey are available over the 

counter at the following Geological Survey Public Inquiries Offices, all 

of which are authorized agents of the Superintendent of Documents: 

• WASHINGTON, D.C.--Main Interior Bldg., 2600 corridor, 

18th and C Sts., NW. 

• DENVER, Colorado--Federal Bldg., Rm. 169, 1961 Stout St. 

• LOS ANGELES, California--Federal Bldg., Rm. 7638, 300 N. 

Los Angeles St. 

• MENLO PARK, California--Bldg. 3 (Stop 533), Rm. 3128, 

345 Middlefield Rd. 

• RESTON, Virginia--503 National Center, Rm. 1C402, 12201 

Sunrise Valley Dr. 

• SALT LAKE CITY, Utah--Federal Bldg., Rm. 8105, 125 

South State St. 

• SAN FRANCISCO, California--Customhouse, Rm. 504, 555 

Battery St. 

• SPOKANE, Washington--U.S. Courthouse, Rm. 678, West 

920 Riverside Ave .. 

• ANCHORAGE, Alaska--Rm. 101, 4230 University Dr. 

• ANCHORAGE, Alaska--Federal Bldg, Rm. E-146, 701 C St. 

Maps 

Maps may be purchased over the counter at the U.S. Geological Survey offices where books are sold (all addresses in above list) and 

at the following Geological Survey offices: 

• ROLLA, Missouri--1400 Independence Rd. 

• DENVER, Colorado--Map Distribution, Bldg. 810, Federal 

Center 

• FAIRBANKS, Alaska--New Federal Bldg., 101 Twelfth Ave. 
Geology and Geochemistry of the 

Pitch Uranium Mine Area, 

Saguache County, Colorado 

By j. THOMAS NASH 

Description and interpretation of the geology and 

geochemistry of a new type of uranium deposit that 

occurs chiefly in brecciated dolomite 

U.S. GEOLOGICAL SURVEY BULLETIN 1797 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Any use of trade names is for descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey. 

Library of Congress Cataloging-in-Publication Data 

Nash,). Thomas Uohn Thomas), 1941-

Geology and geochemistry of the Pitch uranium mine area, Saguache County, 

Colorado. 

(U.S. Geological Survey bulletin ; 1797) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1797 

1. Geology-Colorado-Saguache County. 2. Uranium ores-ColoradoSaguache County. I. Title. II. Title: Pitch uranium mine area, Saguache 

County, Colorado. Ill. Series. 

QE75.B9 no. 1797 557.3 s 87-600332 

[QE92.S24] 553.4' 932 
CONTENTS 

Abstract 1 

Introduction 1 

Uranium deposits 3 

Geology 3 

Stratigraphy 3 

Structural geology 5 

Petrology and geochemistry of the Pitch mine 7 

Petrology of host rocks 7 

Petrology of altered rocks and ores 11 

Geochemistry of host rocks 13 

Geochemistry of the Little Indian deposit 26 

Interpretation and discussion 31 

Structural control of ore 31 

Possible role of karst 31 

Importance of Leadville Dolomite 33 

Uranium transport and deposition 33 

Resource implications 36 

Summary: Genetic model 36 

Uranium source 36 

Paleohydrology 37 

Uranium deposition 37 

References cited 37 

FIGURES 

1. Generalized geologic map showing location of Pitch mine, Colorado 2 

2. Preliminary geologic map of the Pitch mine area 6 

3. Schematic cross section A -A ' of the Pitch mine area 7 

4. Cross section B-B' of the Pitch mine area 8 

5. Simplified map of structural features in Pitch mine area 9 

6. Photomicrographs of rocks from the Pitch mine 10 

7. Photomicrographs of ores from the Pitch mine 12 

8. Radiographs showing distribution of uranium in fractured dolomite from 

the Pitch mine 13 

9. Map showing location of analyzed samples and drill holes 14 

10. Plot of uranium versus organic carbon in samples from the Pitch mine 28 

11. Plot of uranium versus total sulfur in samples from the Pitch mine 28 

12. Plot of correspondence-analysis factor scores for factor 1 and factor 2 29 

13. Plot of correspondence-analysis factor scores for factor 2 and factor 3 30 

14. Plot of uranium content versus correspondence-analysis score for factor 

3 31 

15. Generalized geologic map of the Little Indian deposit area 32 

16. Photomicrographs of ores from the Little Indian deposit 33 

Contents Ill 
TABLES 

1. Petrochemical data for host rocks and ores, Pitch mine area, Colorado 15 

2. Statistical summary of chemical data, Pitch mine area, Colorado 27 

3. Correlation of clements with uranium in Leadville Dolomite 28 

4. Analytical data for host rocks and ores, Little Indian deposit, Colorado 34 

5. Statistical summary of chemical data, Little Indian deposit, Colorado 35 

IV Contents 
Geology and Geochemistry of the 

Pitch Uranium Mine Area, 

Saguache County, Colorado 

By J. Thomas Nash 

Abstract 

Uranium ore in the Pitch mine, Saguache County, Colorado, occurs chiefly in brecciated Mississippian Leadville 

Dolomite along the Chester fault, and to a lesser extent in sandstone, siltstone, and carbonaceous shale of the Pennsylvanian 

Belden Formation and in Precambrian granitic rocks and schist. 

Uranium-mineralized zones are generally thicker, more consistent, and of higher grade in dolomite than in other hosts, 

and roughly 50 percent of the reserves are in dolomite. Strong 

physical control by dolomite is evident, as this is the only rock 

type that is pervasively brecciated within the fau It slices that 

make up the footwall of the Chester upthrust fault. Other rocks 

tended either to remain unbroken or to undergo ductile deformation. Chemical controls on uranium deposition are subtle 

and appear chiefly to involve coprecipitation of iron sulfide 

(pyrite or marcasite) with pitchblende and coffinite, suggesting 

that sulfide ion may be the reductant. 

Chemical analyses of 116 rock and ore samples 

demonstrate that ore-bearing dolomites are significantly enriched in Fe, K, S, Mo, Cu, and Ni. Some statistical tests suggest that rocks high in Si, AI, Ba, Sr, Pb, Zn, and V are also 

enriched with uranium. The strong association of uranium with 

sulfur, ferrous iron, and molybdenum is most important 

geochemically. Petrologic studies reveal only minor alteration 

of dolomite adjacent to pitchblende and coffinite. The dark carbonate rocks are not bleached, but minor amounts of very fine 

grained silica were precipitated along with pitchblendecoffinite-pyrite or marcasite. Rocks in near-surface and 

permeable fault zones were oxidized, the uranium was leached, 

and soft ocher-colored dolomite was formed. The rock 

chemistry and the association of pitchblende with marcasite 

and pyrite suggest a hypothesis: uranium was reduced and 

deposited by aqueous sulfide derived from metastable sulfur 

compounds such as thiosulfate or through biogenic reduction 

of sulfate. 

The Little Indian deposit, 2 km north of the Pitch mine, 

is likewise localized along the footwall of the Chester upthrust, 

chiefly in fractured Ordovician Harding Quartzite. The 

mineralogy and chemistry of the Little Indian deposit contrast 

with the Pitch deposit: iron and uranium minerals are oxidized, 

and P, As, Ti, Mn, Sr, Ba, and Mo are enriched in ore. Most 

uranium in the Little Indian was deposited in response to reactions with anions such as phosphate, arsenate, or silicate, rather 

than with sulfur. Some uranium is associated with organic 

pellets, and pyrite was formerly present, suggesting that an older 

period of uranium enrichment by reduction could have been 

important. 

The Leadville Dolomite is the most important host for 

uranium in the Pitch mine, but other units contain important 

uranium resources where fractured along the Chester fault. 

Brittle character is a prime requirement of favorable host rocks. 

Chemical properties of favorable host rocks are also important 

and seem to involve pre-ore sulfides and organic matter. The 

juxtaposition by faulting of blocks of brecciated Leadville 

Dolomite and organic, sulfide-rich shale and fine-grained sandstone of the Belden Formation, may have provided the required 

combination of structural permeability and source of reductant. 

The Laramide age of the Chester fault is a maximum age 

for the uranium deposits. The most likely age is Oligocene, 

when volcanic rocks covered the fault zone, because alteration of volcanic rocks is the most likely source of uranium and 

silica that formed jasperoid bodies in the fault zone. Observed 

and interpreted features at the Pitch deposit suggest a model 

of formation that has wide application to the Western United 

States. Key factors are (1) a wide zone of brecciation, commonly 

produced by upthrusts in brittle rocks; (2) a reductant provided 

by reactive pre-ore sulfide minerals or organic material and 

sulfate-reducing bacteria; and (3) a viable source of uranium, 

such as altered volcanic rocks. Pitch-type deposits can be anticipated to potentially contain 2,000-30,000 tonnes LJ:,08 with 

mixed high and low grades. 

INTRODUCTION 

The Pitch uranium mine is located in the Sawatch 

Range in Saguache County, Colorado, about 60 km east 

of Gunnison (fig. 1). The Pitch mine (formerly known 

as the Pinnacle mine or Erie No. 28 claim) and several 

other uranium prospects were located in 1955. Development of the Pitch mine began in 1959 with the opening 

of two adits. The mine closed in 1962 when its contract 

with the U.S. Atomic Energy Commission expired. About 

100,000 tons of ore averaging 0.50 percent U3Q; 

(1,000,000 lbU3 0 8) were mined, and another 100,000 lb 

U3Q; were recovered by solution mining (Ward, 1978). 

In 1972, Homestake Mining Company acquired the property and began to reevaluate the mine area for additional 

Introduction 
OT 

T 

0 2 4 6 8 MILES T 

0 5 10 KILOMETERS 

EXPLANATION 

~ Quaternary and Tertiary sediments, mainly post-volcanic rocks ~ Mississippian to Cambrian sedimentary rocks 

~ Tertiary intrusive and volcanic rocks Precambrian rocks 

~ Cretaceous and Jurassic rocks Contact 

0 Pennsylvanian sedimentary rocks Fault-BaH and bar on downthrown side 

'X' Mine 

Figure 1. Generalized geologic map showing location of Pitch mine, Colorado (after Tweto and others, 1976). 

reserves amenable to open-pit mining, because the 

previous history had demonstrated that fault offsets of 

ore and unstable wall rocks made underground mining 

costly. 

In the period 1972-77, Homestake Mining Company documented a reserve that was minable by openpit methods of 1.91 million tonnes of ore at an average 

grade of 0.17 percent U3 0 8 (3,245,000 kg U3 0 8

) (Ward, 

1978). Rather than seek high-grade "vein-type" ore, 

Homestake explored for more dispersed ore using vertical rotary drilling supplemented by about 10 percent 

angle and vertical core drilling. Success came in 1973 

when the company recognized a ''new type'' of ore in 

brecciated dolomite of the Mississippian Leadville 

Dolomite. The dolomite was found to be complexly 

faulted between slices of sandstone, siltstone, and shale 

2 Pitch Uranium Mine Area, Colorado 

of the Pennsylvanian Belden Formation. Much of the ore 

mined from 1959 to 1961 also probably was in Leadville 

Dolomite, but was not recognized as such (J .M. Ward, 

Homestake Mining Co., oral commun., 1979). Homestake mined the deposit at a rate of about 600 tons per 

day from an open pit from 1979 to December 1983. 

This study began in 1977 in conjunction with exploration and pre-mine development by Homestake Mining Company, and as a follow-up to geologic mapping 

by J.C. Olson (1983). A small test pit exposed part of 

the ore zone, but most of the study involved drill core 

and cuttings. About 9,000 m of drill core in 73 drill holes 

were logged, and more than 400 samples were taken; 

samples from roadcuts were taken as the best source of 

least altered rocks distant from ore. Major and minor 

elements were analyzed in 135 samples of core and 
outcropping rocks, about 150 thin and polished sections 

were studied on the microscope, and hundreds of samples 

were analyzed by X-ray diffraction. Thin sections were 

stained with alizarin red to impart a red stain to calcite, 

but X-ray diffraction proved most reliable for carbonate 

mineral identification. Some data included in a 

preliminary report (Nash, 1979) are not repeated here, 

but 36 new rock analyses are reported. 

This study was made possible by the full cooperation of the Homestake Mining Company in providing 

base maps, access to the mine area, and samples of drill 

core. J. Mersch Ward, Homestake Mining Company, was 

a cordial host and provided much useful discussion. J .C. 

Olson, J.A. Campbell, N.S. Fishman, and A.R. Wallace 

offered helpful advice and comments on manuscripts. 

URANIUM DEPOSITS 

This report focuses on uranium deposits at the Pitch 

and Little Indian mines, both localized along the Chester 

fault. Uranium deposits occur in five rock types in the 

Marshall Pass area (Malan, 1959; Olson, 1983) and will 

be briefly reviewed here to orient the reader. The following discussions are arranged by decreasing age of host 

rocks; the ages of ores are not known. 

Precambrian biotite schist.-Several prospects and 

small mines occur in the Harry Creek area (Lookout 22, 

Marshall Pass No. 5 prospects) about 2 km east of the 

Pitch mine. Uranium minerals probably include pitchblende and some hexavalent uranium minerals. Near these 

veinlike deposits are high-grade concentrations of 

uranium in alluvium (type 5 below). 

Precambrian pegmatite.-Shears in Precambrian 

pegmatite in the Pitch mine area contain pitchblende, including the discovery outcrop for the Pitch mine (Ward, 

1978). 

Middle Ordovician Harding Quartzite.-

Uranophane and other U+6 minerals fill fractures in the 

quartzite and generally are accompanied by limonite 

(Malan, 1959). A carbonaceous bed containing fish scales 

at the top of the Harding is radioactive. This bed guided 

prospectors to the Little Indian 36 deposit, where the 

Harding is fractured along the Chester fault 2 km north 

of the Pitch mine. Production from the Little Indian 36 

mine from 1957 to 1959 was about 6,180 tonnes of ore 

with a grade of 0.48 percent U30 8 (29,550 kg U30 8

) 

(Ward, 1978). 

Lower Mississippian Leadville Dolomite and Lower 

and Middle Pennsylvanian Belden Formation.-Oxidized 

and reduced uranium minerals at the Pitch mine occur 

in dark-gray dolomite, sandstone, black shale, and coaly 

shale. Oxidation occurs to depths of about 100m. In oxidized zones, disequilibrium is great and radioactivity is 

much in excess of chemical uranium content (Malan, 

1959). Pyrite occurs in most unoxidized rocks, but many 

pyritic rocks have very low uranium content. Fractures, 

shears, and breccia zones host the uranium ores. Past production from the Pitch (Pinnacle) mine was about 500,000 

kg U3Ds (Ward, 1978). Carbonaceous shales of the 

Belden are radioactive in many places, as at the mouth 

of Indian Creek, 6 km southwest of the Pitch mine. These 

radioactive shales apparently first attracted prospectors 

to the Marshall Pass area but no significant uranium concentrations have been found in Belden shales except at 

the Pitch mine. 

Eocene(?) carbonaceous regolith.-Several unusual 

small, but high-grade, concentrations of uranium have 

been mined from "alluvium" (Gross, 1965) and carbonaceous regolith developed in Precambrian gneiss and 

schist and in places overlain by Tertiary volcanic flows 

(Malan, 1959). Mined localities were at the Lookout No. 

22 claim, previously mentioned, and the Bonita claims 

east of the Continental Divide (about 11 km east of the 

Pitch mine). Pitchblende and a number of U+6 minerals 

have been identified from these deposits (Malan, 1959; 

Gross, 1965). Most of the several hundred tonnes of highgrade ore (about 1, 770 kg U3

0 8) produced from these 

deposits was from the pockets in alluvium and a lesser 

amount from veinlike deposits within Precambrian host 

rocks (type 1) (Malan, 1959; Ward, 1978). 

GEOLOGY 

Stratigraphy 

Rocks ranging in age from Early Proterozoic(?) to 

Oligocene(?) are exposed in the Pitch mine area. All units 

except the Oligocene(?) volcanic rocks contain uranium 

deposits, but the Leadville Dolomite is the most important host rock. The following description of rock units 

is primarily from Olson (1983). 

Early Proterozoic(?) rocks.-The chief Early Proterozoic(?) rock type in the area is medium-grained red 

biotite granite. It is weakly foliated and generally friable 

from weathering. Quartz-muscovite-orthoclase 

pegmatites cut the granite in many places. Mica schist and 

hornblende gneiss occur as pendants in the granite. 

Granite and schist exposed in drill core are friable and 

soft. Deep road cuts in the granite along U.S. 50 about 

6 km to the north expose no fresh granite. 

Sawatch Quartzite (Upper Cambrian) and Manitou 

Dolomite (Ordovician).-Cambrian and Ordovician 

sedimentary rocks unconformably overlie the Precambrian basement. The oldest unit, the Upper Cambrian 

Sawatch Quartzite, is a clean, vitreous, medium-grained 

quartzite less than 1 m thick. It occurs in a small area 

just north of the Little Indian mine. The oldest of four 

similar appearing dolomite units is the Lower Ordovician 

Geology 3 
Manitou Dolomite. This 75- to 90-m thick unit of generally massive bedded dolomite was deposited unconformably 

on Precambrian rocks or conformably on the Sawatch 

Quartzite. The color is light gray when weathered and 

somewhat pink on freshly broken surfaces. Chert lenses 

and nodules a few centimeters long are common along 

bedding planes. 

Harding Quartzite (Middle Ordovician).-The 

Harding Quartzite is a distinctive marker horizon in the 

Paleozoic section dominated by dolomitic rocks. The 

lower part consists of about 9 m of indurated mediumand fine-grained quartzite that forms well-exposed ledges. 

The upper 2-3m are black shale and limonitic sandstone 

with distinctive fish scales, asphaltic pellets, and fossil 

trash; this unit is regionally radioactive. The Harding contains scattered low-grade uranium deposits at the Apache 

No.4 prospect on Indian Creek, about 3 km west of the 

Pitch mine, and at the larger Little Indian deposit (Little 

Indian 36) 2 km north of the Pitch mine (fig. 1). 

Fremont Dolomite (Upper Ordovician).-The Fremont Dolomite conformably overlies the Harding. The 

Fremont is about 55 m thick, chiefly massive-bedded 

medium-gray dolomite with lesser amounts of pale-gray 

limestone. Fossils are more common than in the other 

carbonate units. Fremont carbonates yield a distinctive 

fetid or petroliferous odor when freshly broken. Fractured Fremont Dolomite contains some hexavalent 

uranium minerals in the Little Indian deposit. 

Chaffee Group (Upper Devonian and Lower 

Mississippian(?).-Vnconformably overlying the Fremont is the Upper Devonian and Lower Mississippian(?) 

Chaffee Group, consisting of a lower red to gray-green 

shale and coarse-grained sandstone unit, the Parting 

Quartzite, and an upper unit, the Dyer Dolomite. The 

Parting is poorly exposed and only 3-6 m thick, but the 

green glauconitic fragments from it are a good marker. 

The Dyer Dolomite, about 50 m thick, consists of thinbedded shaley limestone and dolomite and some massive 

dolomite. The pale-yellow to tan color on weathered surfaces is distinctive. The Dyer and overlying Lower 

Mississippian Leadville Dolomite are a regressivetransgressive marine sequence in western Colorado and, 

to the north, are separated by the Gilman Sandstone 

(Campbell, 1970). There is no sandstone equivalent to the 

Gilman in the Pitch mine area, which makes it difficult 

to locate the contact of the dolomites. On the basis of 

drilling patterns north of the Pitch mine, the Dyer appears to contain uranium deposits in the footwall of the 

Chester fault. 

Leadville Dolomite (Lower Mississippian).-The 

Leadville Dolomite is about 130 m thick in the area, 

depending upon amount of pre-Belden erosion. The 

Leadville generally is dark-colored massive-bedded 

dolomite, although a few zones of pale-gray limestone 

are known. Some outcrops appear sandy, but under the 

4 Pitch Uranium Mine Area, Colorado 

microscope, quartz sand grains are rarely seen. Much of 

the Leadville is very fine grained dolomicrite that breaks 

with conchoidal surfaces, and some is crystalline with 

dolomite rhombs 100-200 p.m (micrometers) in size. 

Centimeter-scale pods of black chert and intrabed slumps 

and faults are associated with the crystalline dolomite 

zones in some places. Calcite and chalcedony veinlets are 

common and often can be used to distinguish the Leadville from other dolomites. The upper surface of the 

Leadville is gently eroded and cut by caverns filled with 

iron oxides. The ferruginous material, probably karst filling, has the appearance of a gossan and was thoroughly, 

but unsuccessfully, prospected years ago. The limonitic 

filling is faintly radioactive. Leadville Dolomite is the 

most important host rock in the district in the newly 

developed Pitch mine, and because of this, it was investigated in detail in this study. 

Some relations in the area suggest the possibility 

that the Leadville was deposited unconformably on 

Precambrian rocks of the ancient Sawatch uplift 

(DeVoto, 1980). Some drill-core intercepts and a series 

of backhoe trenches at the south end of the mineralized 

zone expose Leadville Dolomite resting on hematitic clayaltered Precambrian granite. The red clay zone is about 

1-2 m thick and is sheared. The hematitic material 

resembles a regolith. There are no terrigenous clastic beds 

near this possible depositional contact, and thin sections 

of dolomite reveal it to be normal dolomicrite with less 

than 1 percent clastic quartz. Also, the Leadville section 

does not thin significantly toward the hypothetical uplift. 

On a regional scale, a large paleoslope would be required 

to permit both Leadville Dolomite and Sawatch Quartzite to have been deposited on the Precambrian. The 

Sawatch depositional contact is 2 km north of the Pitch 

mine and about 250 m lower in the section. The localities 

showing Leadville on regolith are interpreted to be fault 

contacts, even though the faults are not obvious in core. 

Maxiumum thickness of Leadville Dolomite in the mine 

is about 17 m, only a small fraction of the total Leadville section known in the area (about 130m). It is not 

possible to establish the stratigraphic position of the 

Leadville in the mine because the formation is highly 

deformed, and the outlying Leadville displays no obvious 

internal units useful for correlation. 

Belden Formation (Lower and Middle Pennsylvanian).-Unconformably overlying the Leadville is the 

Belden Formation, about 400 m of diverse lithologies including arkose, sandstone, shale, coal, and limestone of 

apparent fluvial-deltaic-marine origins. Facies changes are 

rapid, and surface outcrops suggest different compositions than do drill core because abundant soft clay-rich 

units are very poorly exposed. A lower unit is readily 

recognized by basal white kaolinitic sandstone and 

arkose, coal beds, and black to green-gray mudstone. The 

lower unit is about 90 m thick west of the Pitch mine. 
The middle unit is characterized by pale-gray limestone 

and dark-red shale. The limestone forms discontinuous 

outcrops, but the poorly exposed shale is more abundant 

in drill cores. The middle unit is about 130 m thick. The 

upper unit is characterized by drab green-brown sandstone beds and gray shale. About 200 m of the upper unit 

is exposed near the Pitch mine; the top is not exposed. 

Quartz Latite Tuff (Oligocene?).-The youngest 

rocks in the immediate Pitch mine area are poorly exposed remnants of sandy tuff less than 20 m thick that 

are part of an Oligocene(?) quartz latite ash-flow tuff 

unit. A few kilometers south and west of the mine are 

exposures of younger volcanic units that presumably once 

overlay the quartz latite unit in a volcanic trough coincident with the Chester fault (Olson, 1983). These younger 

units are Oligocene(?) volcanic breccia and conglomerate 

and overlying Oligocene (34 m.y. old) Rowley Andesite 

flows. Reconstructions by Olson (1983) indicate the base 

of the Tertiary volcanic section was about 100 m above 

the pre-mining surface of the Pitch mine. About 6 km 

south of the mine, more than 300 m of Oligocene 

andesitic volcanic rocks of the San Juan volcanic field 

cover Paleozoic rocks. 

Structural Geology 

The major structural feature in the Pitch mine area 

is the Chester fault, which dips east at about 70 ° and 

strikes nearly due north. The fault placed Precambrian 

rocks above and west of Paleozoic rocks (figs. 2 and 3). 

The term upthrust seems best for this fault because there 

is evidence that the fault surface is steep at depth and 

flattens upward (Nash, 1980). Net reverse displacement 

along numerous fault strands is more than 600 m. It is 

important to remember that the Chester fault is a zone 

of faults, not a single surface. The zone of faults is about 

100 m wide in the mine area (fig. 2); it then splits into 

major east and west strands to the north. Within the fault 

zone, coherent, but highly broken, blocks of individual 

formations are bound by faults. Fault planes and shear 

zones could be recognized when core was logged, but it 

was generally not possible to determine the exact magnitude of displacement. Relations shown on figures 3 and 

4 are highly generalized. Some drill holes intersected 

dolomite and Precambrian rocks several times before bottoming in dolomite, indicating complex up-and-down 

relative movement on the individual fault surfaces. Easttrending normal faults offset the Chester fault (fig. 2). 

Paleozoic rocks west of the Chester fault are folded into 

a south-plunging syncline whose east limb is probably 

overturned under the fault zone (figs. 3 and 4). Tops of 

beds could not be identified to prove overturning. Farther west, Paleozoic rocks have a low dip and are gently 

warped into broad folds. Structure in the area is well illustrated by cross sections in Olson (1983). 

Faulting in the Chester fault is of Laramide age. 

Cretaceous rocks about 20 km to the west are displaced 

by similar faults, and upthrusts elsewhere in the Rocky 

Mountains displace Cretaceous rocks. The Chester fault 

does not cut Oligocene volcanic rocks south of the Pitch 

mine (Olson, 1983); but at Marshall Creek, 3 km south 

of the mine, the volcanic rocks are displaced and rotated 

at the fault, probably reflecting some younger renewed 

movement along the fault. 

Uranium deposits at the Pitch and Little Indian 

mines are structually controlled by the Chester fault. The 

selectivity for quartzite and dolomite is unusual among 

uranium deposits. A review of the literature (Nash, 1980) 

indicated that the physical situation could be explained 

by structural observations at other upthrusts and by 

behavior in experimental deformation. Although not well 

exposed, the geometry of faults in the Chester fault zone 

is similar to that observed elsewhere in other Rocky 

Mountain Laramide uplifts (Stearns, 1978). Figure 5 

shows several features of interest. 

In most places the Chester fault dips 60°-70°to the 

east. Good exposures near the old townsite of Chester, 

3 km south of the mine (fig. 5, no. 1) show the fault dips 

60° east, and drilling in the Pitch mine indicates dips of 

60 °-70 ° east. The highest level of the Chester fault is exposed on the ridge north of the Pitch mine (fig. 5, no. 

2). The geometry of the fault trace in this area suggests 

more gentle dip, possibly_ 45 ° or less. 

Paleozoic sedimentary rocks in the footwall of the 

fault zone are folded into a probable overturned syncline 

(fig. 5, no. 3) a style of deformation observed near many 

upthrusts (Berg, 1962). 

South of the mine (fig. 5, no. 4) a thrust slice of 

Precambrian rocks extends west of the main upthrust 

block. Although this thrust may be younger than the upthrust, it might represent a flat split from the main upthrust zone. 

Several features may reflect either compression or 

post-upthrust relaxation. The east-trending faults (fig. 5, 

no. 5) have mostly normal displacement and create a 

series of blocks with relatively small rotation. Northtrending faults in the footwall block (fig. 5, no. 6) have 

apparent normal displacement and may represent subsidence faults as described by Wise (1963). ~orne of the 

offsets within the Chester fault zone also might reflect 

late-stage subsidence upon relaxation. Faults in Precambrian rocks of the uplift block (fig. 5, no. 7) may have 

been produced during arching of the upthrust block. 

However, no "keystope graben" (Wise, 1963) can be 

discerned. 

The Chester fault displays many of the features 

described in other uplifts (Berg, 1962; Wise, 1963) recently explained as products of forced folding and faulting 

(Stearns, 1978). Geologic features (Stearns, 1978) and 

laboratory experiments (Friedman and others, 1976) 

Geology 5 
0'1 

l"'l 

~ 

:r 

Si= 

Col 

:;, 

c:· 

3 

~ :;· 

~ 

~ ~ 

!J 

n 

0 

~ Col 

Q. 

0 

20,000E 

106°18' 

18,000E 

16,000N 14,000N 

0 

0 

~ Quaternary to Tertiary talus and alluvium 

Pennsylvania Belden Formation 

IPbu I Upper Unit 

!Pbm I Middle Unit 

IPbl Lower Unit 

Mississippian Leadville Dolomite 

38°24' 

1000 

300 

EXPlANATION 

u 

D 

12,000N 10,000N 

2000 FEET 

600 METERS 

Precambrian rocks, undivided 

Uranium mineralized zone (>0.01 percent U308), 

projected to surface 

Contact-Approximately located 

Fault-Dashed where approximately located, dotted 

where covered 

~ Overturned syncline-Inferred 

__!f_ Strike and dip of bed 

Figure 2. Preliminary geologic map of the Pitch mine area. Cross section A-A' is shown on figure 3 and cross section 8- 8' on figure 4. Geology in places 

adapted from mapping by Olson (1983) and j .M. Ward, Homestake Mining Co. (unpub. data, 1972- 1977). Grid is mine coordinate system used by Homestake 

Mining Co. 
A A' 

WEST METERS FEET EAST 

10,800 120 400 

90 

60 

30 

10,400 0 

0 30 60 90 120 

Iw 

w 

LL. 

~ 10,000 

z 

0 

i= 

~ w 

_J 

w 

9,600 IPbm !Pbu 

(middle) Pennsylvanian Belden Formation 

(upper) 

9,200 

18,000E 19,000E 20,000E 

Figure 3. Schematic cross section A-A' of the Pitch mine area. Line of section is shown on figure 2. Structure in Chester fault 

zone is known from drilling to be much more complex than shown. Overturned synclinal structure is inferred from sparse surface outcrops showing bedding attitudes. Symbols are same as in figure 2. 

indicate the importance of pressure, ductility, stratigraphic layering, and degree of attachment to the basement. The basement is a massive ram that induces or 

"forces" folding, faulting, or both, in overlying sedimentary rocks. The situation at the Pitch mine is one of "attached, brittle sections" (Stearns, 1978) in which there 

are many local faults and fractures because the attached 

brittle rocks cannot slip along the uplifting Precambrian 

block. For uranium and other ore deposits, the importance is the large volume of brecciated rocks favorable 

for ore deposition (Nash, 1980). 

PETROLOGY AND GEOCHEMISTRY OF THE 

PITCH MINE 

Petrology of Host Rocks 

Petrographic studies were undertaken to describe 

host rock lithologies and alteration effects. A topic of 

particular interest was the mineralogy and textures of 

dolomites produced by diagenesis as compared with later 

alteration effects related to ore formation. In addition, 

petrographic data were used to help determine the 

stratigraphic identity of carbonate rocks in isolated fault 

blocks within the Chester fault. As the study evolved, it 

became evident that attributes such as content of fossils 

and clastic quartz could reliably differentiate carbonate 

units. Although Precambrian rocks contain some ore, 

they were not studied in detail because hand-lens observations suggested there would be little alteration to 

observe in thin sections. The following sections describe 

and contrast lithologies in the Leadville and Belden 

Formations. 

Carbonates of the Leadville Dolomite generally 

contain more than 90 percent dolomite with minor quartz, 

clay, and calcite. Texture of dolomites from the Leadville is distinctive (fig. 6A), but not unique in this area. 

About one third of the samples contain microcrystalline 

dolomite with intergrown grains less than 10 Jlm in 

diameter. Dolomite in other samples has grain sizes ranging up to about 200 JLm, generally as well-formed rhombohedra. The coarser grained dolomites show no spatial 

relation to uranium deposits or to faults. The recrystallization probably occurred in early diagenesis. Many of the 

coarsely crystalline dolomites are in zones with bedded 

chert lenses and intraformational slump and fold features, 

both of which suggest movement of diagenetic pore fluids 

Petrology and Geochemistry of the Pitch Mine 7 
(f) 

a: 

w 

1-

w 

~ 

B 

WEST 

11,000 

~ 

z 

0 i= 10,000 

~ w 

_J 

w 

0 

0 

Md 

Dyer 

Dolomite 

200 

60 

400 FEET 

120 METERS 

349R 

Precambrian 

B' 

EAST 

Figure 4. Cross section 8-8' of the Pitch mine area. Line of section is shown on figure 2. Structure in ore zone is schematic; 

bedding in lower Belden units is near vertical in this zone. Symbols are same as on figure 2. 

during lithification. Other evidence that this is a recrystallization process is the similar composition of the fine- and 

coarse-grained dolomites; both are devoid of clastic terrigenous and fossil detritus. Dolomite in the underlying 

Manitou, Fremont, and Dyer Dolomites generally is 

crystalline with rhombs about 100 I-'m wide that resemble the crystalline dolomite of the Leadville. Carbonate 

"mud" in the Belden Formation is extremely fine grained, 

similar to the Leadville dolomicrites, but it is calcite and 

generally supports fossils and quartz grains. 

Two samples (nos. 37 and 38, table 1) from the 

Leadville collected about 1 km west of the mine are 

notably different from the typical carbonates described 

above. These samples show well-defined bedding and 

crossbedding, show calcite composition, and contain 

30-40 percent fossils supported in very fine grained calcite 

mud (fig. 6B). They are classified as fossiliferous 

biomicrite (Folk, 1962) or packstone (Dunham, 1962). 

The locality 1 km west of the mine appears to be in the 

middle to upper part of the Leadville. The significance 

of these textures is that they testify to moderate current 

or wave energy that was sufficient to move particles but 

8 Pitch Uranium Mine Area, Colorado 

not great enough to winnow out the fine-grained carbonate mud. 

Carbonate rocks in the Belden Formation are compositionally and texturally more diverse than those in the 

Leadville (fig. 6C). It is clear in outcrop, as well as under 

the microscope, that in the Belden a continuum exists 

from essentially pure carbonate rocks through terrigenous 

rocks. Of 29 Belden samples that contain more than 50 

percent carbonate minerals, 60 percent contain more than 

10 percent clastic quartz grains of sand or silt size, 28 

percent contain fossils, 18 percent are bioturbated, and 

12 percent contain intraclasts. Most Belden carbonates 

are composed of calcite only, but 15 percent contain 

dolomite in excess of calcite. Sparry calcite in the rock 

matrix or in fractures is common in Belden carbonates, 

but rare in the Leadville. Many of the Belden carbonates 

have grain-supported texture dominated by clasts of 

coarse-grained quartz or fossils with mud infilling, a texture not observed in the Leadville. Most Belden carbonates are classified as sandy micrite and biomicrite 

(Folk, 1962) or sandy wackestone and packstone 

(Dunham, 1962). Limestone in the Belden contains few 
D 

u 

0 

EXPLANATION 

Location of feature described in text 

Reverse fault showing dip- Hachures on upthrown side 

u ---::~- High angle fault- U, up-thrown side; 

D, down-thrown side 

4 4 4 Thrust fault-Sawteeth on upper plate 

Overturned syncline- Showing direction 

of dip of limbs and plunge 

'X' Uranium mine 

Pitch Mine Ore Zone 

651y 65 (j) ~ 'X' LOOKOUT 22 

DU 

0.5 1 KILOMETER 

Figure 5. Simplified map of structural features in Pitch mine area (modified from Olson, 1983; Nash, 1979). 

Petrology and Geochemistry of the Pitch Mine 9 
Figure 6. Photomicrographs of rocks from the Pitch mine. Photos taken in plane polarized light. A, Faintly laminated Leadville 

Dolomite (sample 298-377) with grains slightly recrystallized to about 30 11m average size; many dolomites have finer grain 

size and are not photogenic. 8, Fossiliferous limestone unit (sample P38) .in Leadville Dolomite; unit has atypical composition 

and is crossbedded in outcrop. C, Jasperoid alteration (sample P25) of Leadville Dolomite with typical veining and variable fine 

grain size; dark material is iron oxides and organic matter. 0, Contact of clay-rich, very fine grained sandstone and oolitic limestone 

(sample P29) in middle unit of Belden Formation. 

open fractures; it tends to make long pieces when cored 

and is rarely mineralized. 

Terrigenous clastic strata are conspicuously absent 

from the Leadville Dolomite in the Pitch mine area. 

Microscopic examination of dolomites that appeared 

"sandy" in the field or drill core, and had been reported 

as such in the literature, did not reveal clastic quartz. A 

few samples contained about 2-5 percent silt-size quartz, 

and a few rare grains of sand-sized quartz were seen. 

Several samples taken at the Leadville-Precambrian contact, where I thought clastic material might be more abundant, did not contain more than 1 percent clastic quartz 

or any feldspar. Partly from this petrographic evidence 

and partly from an interpretation that the red clay at the 

top of the Precambrian is fault gouge not paleosol, these 

contacts were later judged to be fault contacts. A fair 

amount of aluminum, equivalent to about 4 percent clay, 

is present in the Leadville, but clay was not evident in 

10 Pitch Uranium Mine Area, Colorado 

thin sections. Only traces of clay minerals have been 

found in whole-rock X-ray diffraction tests of Leadville 

dolomites. The apparent absence of significant clastic 

quartz, and the presence of aluminum (clay), are consistent with other evidence for sedimentation in water that 

was quiet or protected from a clastic source by distance 

or a barrier. 

Clastic rocks are abundant in the Belden Formation, in contrast to the Leadville. The basal unit of the 

Belden commonly is a medium to very coarse grained 

(0.3- to 2-mm) quartzose sandstone with variable amounts 

of potassium-feldspar, muscovite, plagioclase, and rock 

fragments. These sandstones and arkoses are white, from 

kaolinite matrix, and often contain about 1-4 percent 

pyrite as coarse euhedral crystals. The sandstones seem 

to be fluvial channel deposits. Curiously, these pyritic 

sandstones rarely contain uranium of importance 

by volume or grade even when in fault contact with 
uranium-rich dolomite breccia. More abundant in the 

Belden are 3- to 1O-m-thick massive, soft, very fine grained sandstone and siltstone with abundant green or tan 

clay matrix and variable amounts of calcite cement. Two 

types of quartz grains are present: most are angular 50-

to 100-J.tm grains, and some are about 300 J.l.m in diameter 

and well rounded. The matrix is variable proportions of 

sericite, kaolinite, chlorite, and calcite. Pyrite, in amounts 

from 1 to 5 percent, is present as very fine to coarse grains 

in the matrix. These clay-rich fine-grained sandstones and 

siltstones are essentially unlithified; they are soft and 

plastic when cored. The plastic behavior does not allow 

fractures to remain open, which may explain why these 

sediments are the least likely to contain ore. The rare finegrained sandstones that are mineralized contain lowgrade, disseminated uranium. 

Two types of chert are present as replacements of 

Leadville Dolomite; none has been seen in Belden Formation carbonate. One type is early diagenetic and occurs as discontinuous pods along bedding planes, as 

described by Banks (1970). The other, which I believe to 

be Tertiary in age, occurs in or near the Chester fault zone 

in zones tens of meters wide. The latter type of chert, 

more aptly termed jasperoid (Lovering, 1972), generally 

is brecciated (fig. 6D). Under the microscope, breccia 

textures are evident, but chalcedonic quartz is similar in 

fragments and matrix; the chalcedony seems to have 

cemented a preexisting carbonate breccia. These rocks are 

more than 90 percent Si02 and are composed of chalcedonic quartz with grains less than 15 J.l.m in diameter. The 

chalcedony is speckled with opaque particles of iron oxide 

and possibly carbonaceous matter. Irregular veinlets or 

gradational swaths of more coarsely crystalline quartz 

(50 J.l.m to 1 mm in size) cut the chalcedonic chert. Mineral 

and fluid inclusions are abundant in the quartz, but none 

are multiphase fluid inclusions; thus none could be used 

for thermometry. 

Petrology of Altered Rocks and Ores 

Three types of alteration have occurred in the Leadville Dolomite: (1) oxidation, in places accompanied by 

leaching of carbonate minerals; (2) subtle silicification 

by addition of thin films of silica along fractures; and 

(3) pervasive silicification to produce jasperoid. The first 

two alterations are parts of ore processes, and the last 

is not directly related to ore but may reflect processes 

operating in source rocks. 

Oxidation has occurred to depths of more than 

100m along faults, and some breccia zones are pervasively oxidized to depths of about 60 m. Two extreme cases 

of a continuum are most easily described. Extreme oxidation and acid alteration at shallow levels have created 

porous, cellular rocks in which carbonate is removed, and 

the rock is a lacelike silica boxwork with limonite encrustation. Samples 3 and 612-15 are good examples 

(table 1). The altered rock is essentially a gossan. It tends 

to be highly radioactive but is deficient in chemical 

uranium. This type of disequilibrium indicates leaching 

of uranium in the past million years or localization of 

radium by sulfate (Phair and Levine, 1954). The other 

example is massive or brecciated dolomite having an 

ocher color imparted by hydrous iron oxides. The ocher 

dolomite is slightly softer than the unoxidized equivalent, 

but X-ray diffraction and petrographic studies show 

essentially no change in major minerals. Pyrite was 

destroyed and replaced in situ by iron oxides having cubic 

form, and iron oxides permeated grains and cracks to produce a strong coloring effect. Chemical analyses (table 

1) indicate many of these rocks have gained several percent of iron relative to unoxidized equivalent dolomites. 

Uranium content of most ocher dolomites is only 50-200 

ppm, but it probably was higher before oxidation. This 

oxidative alteration was produced by sulfuric acid 

generated by oxidation of sulfide minerals. The acid had 

a destructive effect on previously reduced ore zones. In 

some places, the leached uranium apparently was 

redeposited recently in zones that have chemical uranium 

in excess of radioactivity (Malan, 1959); one such environment of young uranium enrichment is peat bogs adjacent 

to the deposit (J.M. Ward, oral commun., 1980). 

Subtle silicification of dolomite is best observed on 

newly exposed rocks in the Pitch open pit. Very thin films 

of quartz, sufficiently crystalline to sparkle in sunlight, 

coat breccia fragments in the ore zone. This alteration, 

possibly obscured by mud and dust, was not detected during drill-core logging and is not visible in most thin sections. Many samples of ore contain more than 10 percent 

Si02 (see analyses for samples 298-341, 713-102, 

782-471 on table 1), an enrichment relative to barren 

equivalents. This alteration seems to be related to ore in 

zones of pitchblende and sulfide minerals, but the outer 

limits are not known. 

Pervasively silicified Leadville Dolomite occurs at 

many locations between the Pitch and Little Indian mines. 

Some is preserved as residual boulders more than 3 m 

in diameter, and other examples form craggy outcrops 

along the Chester fault zone. This rock is best termed 

jasperoid; it is dark-gray to reddish-black, very fine 

grained, massive chalcedonic quartz containing streaks 

and patches of red iron oxides. Vuggy crystals are absent, and carbonate minerals are rare. Si02 content is 

generally more than 90 percent. In a few places a replacement interface with dolomite was observed, but in most 

places a replacement of dolomite is inferred from nearby outcrops of unaltered dolomite. The jasperoid is mildly 

radioactive in some outcrops. 

The jasperoid commonly has a breccia texture of 

uncertain origin. The breccia was recemented into a 

Petrology and Geochemistry of the Pitch Mine 11 
strong rock that breaks across the breccia fragments. Individual fragments tend to have slightly different colors, and 

the matrix tends to be darker from higher content of iron 

oxides. The problem is whether this is a brecciated jasperaid or a jasperized breccia. I have not been able to determine if the jasperoid grades out into brecciated dolomite 

because outcrops are lacking at key places. I believe the 

rock was formed by silicification of a brecciated dolomite 

because the breccia is healed and because it is confined 

to the Chester fault zone and subsidiary faults. This 

silicification possibly is related to alteration of Oligocene(?) tuffs that formerly overlay the altered dolomite. 

Uranium minerals in ores are inconspicuous despite 

grades in excess of 1 percent. Primary ores are dark gray 

to black, but they do not look much different from other 

dark dolomite breccias. Uranium, chiefly as pitchblende, 

and iron sulfides fill the matrix of breccias (fig. 7A-D). 

Macroscopic and microscopic studies reveal no alteration 

selvage in dolomite next to uranium minerals. The matrix 

is a dark mixture of comminuted dolomite, some fine 

silica, pitchblende, pyrite, and marcasite (fig. 7 B). Detailed 

probing with a shielded geiger counter and radiographs 

(fig. 8) indicate that the great majority of uranium occurs in breccia matrix; unbroken dolomite contains sparse 

uranium minerals. 

Within the 100-m-wide zone of faulting along the 

Chester upthrust (fig. 2) are fault-bound blocks of 

dolomite roughly 5-20 m wide and deep that carry the 

majority of the ore. Drill core penetrating these blocks 

displays uniform brecciation to centimeter-size fragments, 

and the uranium grade tends to be high (>0.2 percent 

U30 8

) and relatively uniform throughout the dolomite 

breccia. Some sheared and brecciated zones contain tectonically mixed millimeter- to centimeter-size fragments 

of Precambrian, Leadville, and Belden rocks; these zones 

often are rich in clay gouge and tend to have lower 

Figure 7. Photomicrograpb,.s of ores from the Pitch mine. A, Brecciated Leadville Dolomite (sample 298-345) characteristic of 

high-grade ores; opaque matrix is rich in sulfide and uranium minerals; transmitted light. B, Brecciated Leadville Dolomite (sample 298-345), main ore zone; angular fragment in upper center is chert, opaque matrix is ore; transmitted light. C, Ore-bearing 

brecciated dolomite (sample 298-327); pyrite and marcasite (white) and pitchblende (not shown in this field of view) are abundant in matrix; reflected light in oil immersion. 0, Pitchblende-sulfide veinlet in brecciated dolomite (sample 298-327); pyrite 

and marcasite are white, pitchblende is gray; reflected light in oil immersion. 

12 Pitch Uranium Mine Area, Colorado 
2mm 

Figure 8. Radiographs showing distribution of uranium (white) 

in fractured dolomite from the Pitch mine. 

of Precambrian, Leadville, and Belden rocks; these zones 

often are rich in clay gouge and tend to have lower 

uranium content than the monolithic dolomite breccias. 

Belden shales, especially those rich in carbonaceous 

material, are sheared and plastically deformed along fault 

strands; such zones tend to contain lower grade uranium 

(roughly 0.1 percent U30 8). 

Earlier studies (Malan, 1959) described most ore as 

occurring in "limestone and lignitic shale" of a lagoonal 

facies of the Belden Formation. A stockpile of lignitic 

shale ore dumped below the old Pitch adit has been 

sampled by many visitors, but it is not typical of the 

"new" high-grade ore in brecciated dolomite. Carbonaceous black shales and black siltstones generally contain less than 0.05 percent U3

0 8 • 

Microscopic study of dolomite breccia ore revealed 

a relatively simple assemblage of pitchblende, coffinite, 

pyrite, marcasite, and minor quartz. Veinlets of pitchblende and coffinite more than 1 mm wide were rarely 

seen. These minerals filled the breccia matrix (fig. 7C, 

7D) with very little additional gangue other than comminuted dolomite. About half of the black uranium 

minerals had low reflectivity under oil immersion 

reflected light, and some had red internal reflections; 

these observations suggested that the mineral is coffinite, 

but its abundance and age relative to pitchblende could 

not be determined with confidence. FeS2 is both 

isotropic (pyrite) and anisotropic (marcasite). With high 

magnification and oil immersion reflected light, the marcasite is creamy yellow relative to pyrite and tends to form 

rectangular grains. In most samples, marcasite equaled 

pyrite in abundance. Marcasite of similar habit is abundant at the Midnite mine, Washington (Ludwig and 

others, 1981) and in many sandstone-type uranium 

deposits (Goldhaber and Reynolds, 1979). 

Dolomites in the ore zone and in breccias along the 

Chester fault zone showed no recrystallization effects that 

can be related to ore or fracturing. Many are dolomicrites 

with grain size less than 10 J.tm, and dolomite in the matrix 

is also typically finely crystalline (less than 16 ~-tm) and 

generally finer than the dolomite in the breccia fragments. 

Texture of dolomite is uniform within fragments, but differs between fragments in the same thin section, indicating that there has been no post-fault recrystallization. 

Even the edges of dolomite breccia fragments show no 

bleaching or recrystallization adjacent to pitchblende 

matrix-filling. As mentioned before, the greatest observed 

variation in dolomite texture is distant from the ore zone 

in zones of bedded chert and slumping that are interpreted 

to be effects of early diagenesis not related to ore. 

The matrix of many breccias contains fine-grained 

dark material, some of which is fragments of Belden 

black shale in polylithic breccias, but most is simply a 

fine-grained mixture of dolomite, pitchblende and coffinite, and iron sulfides (fig. 7C). Organic carbon analyses 

(table 1) indicate contents in the range of 0.1-0.7 percent, which suggests that part of the dark color may be 

from organic material, but iron sulfides and uranium 

minerals are thought to be the predominant source of the 

color. 

Geochemistry of Host Rocks 

Chemical analyses of host rocks for major and 

minor elements were made to describe their compositions 

and the effects of alteration, to provide evidence for conditions of ore formation, and to determine elements 

useful as exploration guides. Chemical data for 116 

samples of unaltered, altered, and ore-bearing rock from 

the Pitch mine area are in tables 1 and 2; sample locations are shown on figure 9. Unaltered rocks are here 

defined as those showing no recrystallization, mineral 

alteration, or abnormal radioactivity. They were selected 

from unweathered road cuts to minimize effects of ore 

processes and surface leaching. Altered rocks carry 

megascopic evidence of recrystallization or mineral alteration, and ore-bearing rocks are defined as having more 

than 1000 cps (counts per second) radioactivity in the field 

or more than 500 ppm (parts per million) uranium. Major element contents tend to confirm mineralogical observations, although the content of silica is more variable 

than anticipated. Minor element trends are subtle and 

were evaluated by statistical analyses, which were used 

to highlight and simplify the multielement data for geochemical interpretations. Discussion will focus on subsets 

of data based on lithology or ore type to reduce compositional variance and make interpretation more specific. 

Correlation analysis (Davis, 1973) is useful for 

highlighting relations among variables. Several such 

analyses were made. The most effective was a test on 

Petrology and Geochemistry of the Pitch Mine 13 
15,000 N 14,000 N 12,000 N 11,000 N 18,000 N 

448C 

27 

20,000 E 

201C• 25 ~36 0 33 

0 <o 0 24 26 35 

0 

34 

19,000 E 

EXPlANATION 

Approximate limit of uranium mineralized zone 

Surface sample 

.201C Drill core sample N------

18,000 E 

0 400 800 FEET 

o20 I 

030 0 

I I 

100 200 METERS 

Figure 9. Map showing location of analyzed samples and drill holes. 

33 variables describing 73 samples of Leadville Dolomite 

and alteration products. Log transformation of the data 

minimized the effects of lognormally distributed elements 

like uranium and produced higher correlation coefficients. Correlation coefficients for uranium are shown 

in table 3. Correlation coefficients that are significant at 

the 95 percent level of confidence are shown with an 

asterisk; the minimum value for significance depends on 

the number of samples and ranges from r = 0.225 for 

N=73 to r=0.381 for N=27 (Dixon and Massey, 1957). 

Uranium correlates significantly (95 percent 

confidence level) with AI, Fe2 0 3 , FeO, K, H2 0 +, Mn, S, 

Cl, Ba, Sr, Pb, Zn, Mg, Cu, Ni, and Zrl. The very high 

correlations of uranium with S, FeO, Pb, and Mo are 

particularly worthy of note, as is the low correlation 

(r = .12) of U with organic carbon. Correlation analysis 

also shows high mutual correlations ofMg, Ca, FeO, Ba, 

Sr, and C02, presumably as carbonate minerals; 

chlorine correlates with this group, which possibly is 

evidence for dolomitization in high salinity fluids. 

Correlation analysis directs attention to a group of 

associated elements that may occur as clay minerals and 

(or) adsorbed constituents: AI, Fe2 0 3 , K, Ti, P (rather 

than with calcium as apatite), F, Ba, Pb, Zn, Mo, U, Cr, 

1

Chemical references will be to element symbol rather than the 

oxide reported in data tables; for iron in two oxidation states, FeO or 

Fe20 3 will be specified if a specific valence is important. 

14 Pitch Uranium Mine Area, Colorado 

Cu, Ni, V, and Zr. Many of the chalcophile elements 

(such as Pb, Zn, and Mo) are associated with both sulfur 

and Pe-Al oxides rather than being chiefly associated 

with sulfur in sulfide minerals. 

The important relations of uranium with possible 

reductants sulfur and organic carbon are perhaps best 

seen on scatterplots (figs. 10 and 11). The plot of uranium 

versus organic carbon in 116 samples from the Pitch 

deposit (fig. 10) shows near random scatter, confirming 

the very low correlation coefficient. Sulfur and uranium, 

however, show a strong linear trend (fig. 11) that confirms the high correlation coefficient. A plot of molybdenum versus sulfur shows a similar linear trend. These 

plots, combined with petrographic observations, are conclusive evidence for a strong uranium association with 

sulfide minerals. 

R-mode analysis of the Leadville geochemical data 

computed element groups similar to those just discussed. 

Factor analysis (Davis, 1973) in the R mode searches for 

relations between variables. For a simple model, three factors can be used that carry 64 percent of the compositional information, as follows: factor 1-Ti, K, F, AI, V, 

Cr, Sr, P, Zr, H2 0+, and Na (elements in clay minerals or 

adsorbed on mineral surfaces); factor 2-Mg, Ca, C02, 

Cl (the carbonate mineral group; Si has negative loading 

on this factor); factor 3-U, S, Cu, Mo, Pb, Ba, F~~, 

FeO, Ni, and Mn (chiefly sulfur-related elements (chalcophile) or elements localized by reduction). 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado 

[Leaders (--), not determined; OJo, weight percent; Ctotal, total carbon; Corgan, organic carbon; Carbnt, carbonate; ppm, parts per .million; 

XR, X-ray diffraction. Chemical analyses: major elements, including F and S-single solution technique (Shapiro, 1975) by H. Smith; minor 

elements-atomic absorption spectrometry for Ba, Sr, Ag, Pb, Zn, and Hg, specific-ion electrode for C1, and spectrophotometry for Mo by 

E. Campbell; total carbon-combustion thermal conductivity by V.E. Shaw; carbonate carbon determined gasometrically by P.H. Briggs; organic 

carbon determined by difference; U-delayed neutron analysis by H.T. Millard, C. McFee, and C. Bliss; other minor elements-six-step emission 

spectrography by J .C. Hamilton and E. Silk. Mineralogy: semiquantitative estimates of dolomite {dolom XR), calcite (calcit XR), quartz {quartz 

XR), clay (clay XR), and iron oxide (hema XR) content made by X-ray diffraction by J .T. Nash; clays observed were kaolinite and sericite (lOA 

mica); iron oxides observed were hematite and goethite; precision and accunicy about ± 1 part in 10] 

Sample 

3 

7 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

43 

44 

45 

201-69 

298-313 

298-327 

298-334 

298-341 

299-323 

299-334 

299-351 

299-377 

400-174 

402-128 

408-368 

441-109 

441-179 

441-204 

441-209 

Si02 % 

63.00 

.60 

21.90 

6.60 

17.30 

5.90 

2.90 

9.00 

8.60 

96.90 

97.70 

61.00 

17.60 

2.90 

.20 

.20 

22.80 

13.70 

97.00 

27.50 

9.80 

2.50 

17.00 

32.60 

4.50 

.90 

1.40 

97.00 

6.40 

13.60 

.63 

.43 

2.40 

48.00 

3.60 

9.40 

3.90 

27.80 

7.70 

40.90 

21.50 

8.00 

28.60 

35.30 

39.70 

Al203 % 

13.70 

.33 

1.80 

.82 

1.50 

1.00 

.33 

.53 

.03 

.33 

.53 

.03 

1.80 

.33 

.03 

.03 

2.50 

.13 

.13 

.23 

.23 

.13 

.63 

7.80 

1.00 

.03 

.13 

.23 

.13 

3.80 

.34 

.13 

.14 

.90 

.60 

1.60 

.74 

4.40 

.93 

3.70 

2.90 

1.50 

4.30 

4.10 

3.60 

Fe203 % 

9.10 

.59 

.36 

.23 

.26 

.35 

.05 

.49 

.20 

.18 

.21 

.06 

.46 

.07 

.18 

.11 

.94 

.21 

.14 

.21 

.08 

.16 

.20 

46.40 

.87 

.28 

.05 

.80 

.02 

.74 

.48 

4.50 

2.60 

6.30 

.61 

1.10 

1.20 

.99 

2.00 

1.10 

1.50 

4.70 

2.90 

2.20 

1.50 

FeD % 

.04 

.08 

.12 

.08 

.08 

.20 

.16 

.16 

.16 

.01 

.20 

.12 

.12 

.12 

.40 

.44 

.12 

.40 

.12 

.24 

.16 

.08 

.08 

.08 

.08 

.04 

.04 

.08 

.12 

1. 70 

.36 

1.30 

.48 

1.40 

.24 

.52 

.28 

.36 

.32 

.60 

.28 

.04 

.16 

.04 

.08 

MgO % 

.44 

21.00 

16.00 

17.80 

16.10 

.88 

.66 

.45 

18.70 

.18 

.07 

8.30 

.76 

.44 

19.40 

20.80 

10.20 

17.80 

.29 

14.70 

18.80 

.60 

.47 

.27 

17.60 

20.60 

.97 

.10 

19.00 

2.10 

20.60 

18.60 

19.50 

7.20 

19.80 

16.10 

18.70 

13.50 

18.00 

10.30 

14.80 

17.00 

12.10 

10.10 

9.90 

CaD % 

.46 

30.20 

23.90 

31.30 

26.70 

49.40 

53.00 

49.50 

29.50 

.24 

.15 

11.90 

43.50 

53.00 

32.40 

30.50 

28.60 

26.70 

.31 

22.20 

28.00 

53.10 

44.70 

.61 

30.60 

31.00 

52.40 

.43 

29.70 

39.50 

29.60 

27.20 

27.50 

11.40 

29.40 

27.60 

29.30 

19.90 

27.70 

17.20 

23.40 

27.60 

20.00 

19.20 

17.60 

Na20 % 

.07 

.31 

.04 

.03 

.01 

.08 

.07 

.05 

.04 

.06 

.02 

.01 

.05 

.0 

.02 

.01 

.06 

.04 

.0 

.08 

.06 

.01 

.05 

.0 

.09 

.01 

.05 

.0 

.0 

.04 

.0 

.01 

.0 

.0 

.08 

.02 

.0 

.07 

.03 

.04 

.07 

.0 

.10 

.06 

.05 

K20 % 

1.50 

.61 

.68 

.36 

.47 

.21 

.04 

.05 

.01 

.03 

.05 

.02 

.43 

.15 

.01 

.03 

.70 

.06 

.02 

.05 

.01 

.09 

.21 

.61 

.25 

.04 

.05 

.05 

.01 

.72 

.04 

.02 

.0 

.09 

.10 

.29 

.13 

1.20 

.22 

.88 

.81 

.41 

1.30 

.95 

1.10 

H20+ % 

5.10 

.10 

.43 

.41 

.61 

.66 

.47 

.56 

.30 

.47 

.60 

.24 

.87 

.24 

.21 

.28 

1.00 

.35 

.32 

.30 

.30 

.30 

.33 

9.10 

.52 

.22 

.24 

.53 

.30 

1.20 

.28 

.51 

.33 

.59 

.64 

.73 

.68 

1.10 

.28 

.78 

.85 

1.00 

1.60 

1.60 

.26 

H20- % 

5.50 

.24 

.27 

.25 

.14 

.24 

.15 

. 11 

.06 

.09 

.10 

.11 

.33 

.08 

.07 

.09 

.27 

.OS 

.04 

• 11 

.07 

.06 

.13 

2.20 

.10 

.20 

.16 

.05 

.16 

.39 

.06 

.27 

.10 

.51 

.12 

.36 

.26 

.29 

.16 

.36 

.27 

.78 

.65 

.68 

.44 

Ti02 % 

.27 

.01 

.19 

.04 

.14 

.08 

.01 

.03 

.02 

.0 

.02 

.0 

• 11 

.0 

.o 

.0 

. 11 

.0 

.0 

.0 

.0 

.0 

.03 

.17 

.04 

.01 

.02 

.01 

.0 

.17 

.01 

.02 

.01 

.01 

.03 

.07 

.03 

.29 

.04 

.27 

.15 

.07 

.24 

.22 

.25 

P205X 

.09 

.02 

.05 

.02 

.04 

.10 

.10 

.15 

.02 

.02 

.03 

.02 

.20 

.01 

.01 

.02 

.04 

.02 

.02 

.03 

.01 

.02 

.03 

.20 

.02 

.02 

.01 

.03 

.01 

.20 

.0 

.02 

.01 

.04 

.02 

.04 

.04 

.07 

.02 

.09 

.04 

.12 

.09 

.12 

.10 

Petrology and Geochemistry of the Pitch Mine 15 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample MnO % 

3 .15 

7 .10 

18 .06 

19 .03 

20 .05 

21 .07 

22 .06 

23 .07 

24 .11 

25 .04 

26 .04 

27 .07 

28 .04 

29 .04 

30 .14 

31 .06 

32 .03 

33 .21 

34 .03 

35 .15 

36 .08 

37 .02 

38 .02 

39 .08 

40 .03 

41 .01 

43 .03 

44 .04 

45 .02 

201-69 .14 

298-313 .18 

298-327 .19 

298-334 .17 

298-341 .09 

299-323 .07 

299-334 .06 

299·351 .05 

299·377 .02 

400·174 .04 

402·128 .03 

408·368 .03 

441·109 .1 0 

441·179 .12 

441·204 .15 

441·209 .05 

C02 % 

.13 

47.10 

34.40 

43.10 

37.80 

40.90 

42.80 

39.90 

43.50 

.0 

.05 

18.10 

34.40 

42.00 

46.90 

48.20 

31.30 

40.00 

.08 

33.50 

41.70 

41.40 

34.70 

.24 

45.50 

46.80 

43.00 

.06 

45.20 

35.70 

46.80 

41.10 

45.10 

16.00 

44.60 

40.90 

43.20 

29.20 

41.70 

23.10 

33.80 

39.90 

27.80 

25.50 

25.90 

F % 

.06 

.02 

.07 

.06 

.07 

.03 

.02 

.03 

.02 

.0 

.0 

.0 

.07 

.01 

.02 

.01 

.07 

.01 

.0 

.01 

.02 

.02 

.02 

.06 

.05 

.03 

.01 

.0 

.01 

.03 

.01 

.01 

.01 

.01 

.02 

.02 

.02 

.08 

.02 

.03 

.03 

.02 

.06 

.03 

.06 

s % 

.03 

.02 

.06 

.07 

.06 

.04 

.03 

.02 

.02 

.02 

.03 

.02 

.05 

.03 

.02 

.02 

.13 

.03 

.02 

.02 

.02 

.07 

.04 

.04 

.04 

.02 

.05 

.02 

.02 

.14 

.12 

4.30 

1.90 

6.30 

.31 

1.10 

1.00 

.45 

1.50 

.49 

.64 

.04 

.04 

.04 

.06 

16 Pitch Uranium Mine Area, Colorado 

Ctotal % 

.44 

,12. 71 

10.24 

11.63 

12.15 

11.38 

11.65 

10.95 

11.79 

.29 

.44 

5.26 

9.80 

11.81 

12.70 

12.79 

9.45 

11.04 

.23 

9.33 

11.82 

11.72 

9.81 

. 51 

12.31 

13.16 

12.10 

.20 

12.37 

10.12 

12.99 

11.26 

12.33 

4.97 

12.62 

10.99 

12.18 

8.16 

11.63 

6.73 

9.62 

11.07 

7.86 

7.37 

6.80 

Corgan % 

.44 

.0 

.11 

.0 

.19 

.31 

.17 

.20 

.09 

.29 

.37 

.33 

.47 

.12 

.01 

.04 

.79 

.0 

.23 

.0 

.02 

.17 

.15 

.46 

.23 

.09 

.32 

.13 

.07 

.31 

.0 

.03 

.0 

.72 

.41 

.02 

.19 

.11 

.28 

.15 

.43 

.01 

.22 

.06 

.29 

Carbnt % 

.0 

12.71 

10.13 

11.63 

11.96 

11.09 

11.48 

10.75 

11.70 

.0 

.07 

4.93 

9.33 

11.69 

12.69 

12.75 

8.66 

11.04 

.0 

9.33 

11.80 

11.55 

9.66 

.05 

12.08 

13.07 

11.78 

.07 

12.30 

9.81 

12.99 

11.23 

12.33 

4.25 

12.21 

10.97 

11.99 

8.05 

111.35 

6.58 

9.19 

11.06 

7.64 

7.31 

6.51 

Cl ppm 

45 

200 

140 

250 

75 

25 

25 

25 

140 

25 

25 

120 

25 

25 

25 

85 

55 

25 

25 

180 

140 

140 

25 

25 

160 

180 

70 

25 

200 

55 

380 

390 

310 

160 

480 

64 

100 

160 

68 

68 

68 

73 

150 

53 

63 

Ba ppm 

120 

80 

20 

80 

20 

160 

180 

80 

80 

20 

20 

40 

170 

160 

20 

100 

100 

72 

20 

40 

20 

260 

120 

20 

120 

40 

140 

20 

60 

180 

43 

280 

61 

320 

83 

330 

110 

140 

76 

100 

33 

170 

150 

220 

110 

Sr ppm 

160 

20 

66 

130 

130 

350 

500 

330 

20 

10 

10 

10 

325 

300 

20 

10 

110 

20 

10 

20 

20 

210 

310 

10 

56 

10 

130 

10 

10 

360 

28 

31 

31 

21 

57 

83 

180 

190 

110 

180 

110 

230 

180 

300 

180 

Pb ppm 

5.0 

1.3 

1.9 

.8 

2.1 

5.8 

1.0 

2.2 

2.0 

4.9 

15.0 

5.9 

9.5 

1.4 

2.3 

2~6 

11.0 

2.4 

19.0 

5.7 

3.6 

1.9 

1.5 

7.3 

3.6 

3.8 

1.4 

63.0 

1. 1 

5.0 

5.0 

25.0 

33.0 

120.0 

25.0 

65.0 

73.0 

5.0 

80.0 

5.0 

5.0 

57.0 

5.0 

25.0 

5.0 

Zn pptn 

140 

18 

58 

56 

20 

32 

22 

22 

22 

10 

5 

30 

22 

5 

40 

34 

5 

5 

350 

14 

34 

12 

135 

5 

38 

5 

5 

26 

140 

2,600 

17 

5 

35 

34 

78 

29 

48 

44 

140 

44 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample 

3 

7 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

43 

44 

45 

201-69 

298-313 

298-327 

298-334 

298-341 

299-323 

299-334 

299-351 

299-377 

400-174 

402-128 

408-368 

441-109 

441-179 

441-204 

441-209 

Mo ppm 

3.30 

.10 

1.10 

. 70 

3.10 

.20 

.10 

.10 

.20 

2.20 

14.00 

2.50 

.40 

.10 

.50 

.20 

1.50 

8.40 

4.10 

1.40 

3.00 

.10 

.10 

.80 

1.40 

.10 

.10 

.50 

.10 

.50 

1.60 

4.50 

20.00 

88.00 

18.00 

73.00 

48.00 

3.40 

19.00 

15.00 

11.00 

.80 

.60 

1.00 

.40 

Hg ppm 

2.600 

.005 

.005 

.005 

.005 

.010 

.005 

.005 

.015 

.065 

1.150 

.230 

.005 

.005 

.010 

.012 

.005 

.076 

.510 

.180 

.180 

.005 

.005 

.005 

.005 

.005 

.005 

.005 

.005 

.005 

.005 

.020 

.100 

.150 

.039 

.005 

.005 

.005 

.560 

.023 

.005 

.120 

.005 

.015 

.005 

u ppm 

778.00 

.18 

1.86 

.41 

.72 

3.43 

4.10 

3.60 

3.92 

1.05 

14.20 

4.31 

3.00 

1.56 

.89 

1. 74 

1.47 

3.99 

5.11 

2.32 

6.79 

2.65 

2.42 

11.10 

2.16 

.18 

4.13 

13.30 

.76 

19.80 

1,160.00 

31,300.00 

4,160.00 

33,500.00 

1,960.00 

7,720.00 

4,300.00 

56.10 

739.00 

149.00 

151.00 

35.70 

38.50 

26.50 

33.90 

Cr(s)ppm 

14.0 

13.0 

7.5 

3.7 

18.0 

28.0 

.5 

16.0 

4.4 

3.8 

15.0 

13.0 

1.2 

3.3 

50.0 

3.0 

5.0 

30.0 

20.0 

20.0 

20.0 

15.0 

Cu(s)ppm 

.8 

.8 

.8 

.8 

3.4 

1.7 

.8 

4.8 

3.0 

.8 

.8 

2.1 

.8 

.8 

1.5 

1.5 

1.0 

5.0 

7.0 

7.0 

3.0 

15.0 

Ni(s)ppm 

4.5 

5.6 

2.0 

3.3 

1.9 

11.0 

3.4 

14.0 

.8 

4.3 

2.1 

4.9 

.8 

3.3 

3.0 

3.0 

15.0 

15.0 

10.0 

10.0 

20.0 

20.0 

Sr(s)ppm 

140.0 

220.0 

1,200.0 

20.0 

5.6 

830.0 

25.0 

240.0 

1.1 

21.0 

690.0 

130.0 

340.0 

18.0 

300.0 

7.0 

7.0 

70.0 

150.0 

150.0 

300.0 

200.0 

V(s)ppm 

12.0 

10.0 

8.5 

5.2 

2.8 

16.0 

8.0 

32.0 

.5 

3.8 

11.0 

13.0 

4.2 

1.7 

15.0 

4.0 

5.0 

15.0 

15.0 

20.0 

15.0 

10.0 

Zr(s)ppn 

130.0 

37.0 

35.0 

6.2 

9.9 

190.0 

6.8 

32.0 

2.3 

5.9 

180.0 

18.0 

6.0 

2.3 

50.0 

15.0 

10.0 

70.0 

50.0 

200.0 

30.0 

70.0 

Petrology and Geochemistry of the Pitch Mine 17 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample Dolom XR 

3 .0 

7 10.0 

18 6.0 

19 7.0 

20 7.0 

21 8.0 

22 1.0 

23 .5 

24 9.0 

25 .5 

26 .0 

27 5.0 

28 .0 

29 .0 

30 7.0 

31 10.0 

32 6.0 

33 7.0 

34 1.0 

35 1.0 

36 6.0 

37 .5 

38 .5 

39 .0 

40 7.0 

41 9.0 

43 .5 

44 .0 

45 6.0 

201·69 2.0 

298·313 10.0 

298·327 9.0 

298·334 9.0 

298·341 5.0 

299·323 9.0 

299·334 8.0 

299·351 9.0 

299·377 5.0 

400·174 8.0 

402·128 5.0 

408·368 6.0 

441·109 9.0 

441·179 7.0 

441·204 6.0 

441·209 5.0 

CalcitXR 

.0 

.0 

.5 

1.0 

1.0 

.0 

8.0 

8.0 

.0 

.0 

.0 

.0 

7.0 

6.0 

3.0 

.0 

.0 

.0 

.0 

.0 

.0 

10.0 

10.0 

.5 

2.0 

.0 

10.0 

.5 

3.0 

6.0 

.0 

.0 

.0 

.0 

.0 

1.0 

.0 

.0 

.0 

.0 

.0 

.0 

.5 

.0 

1.0 

QuartzXR 

10.0 

.0 

4.0 

2.0 

2.0 

2.0 

1.0 

2.0 

1.0 

10.0 

10.0 

5.0 

3.0 

4.0 

.0 

.0 

4.0 

3.0 

9.0 

9.0 

4.0 

.5 

.5 

8.0 

1.0 

1.0 

.5 

10.0 

1.0 

2.0 

.5 

.0 

1.0 

4.0 

1.0 

1.0 

1.0 

4.0 

2.0 

5.0 

4.0 

1.0 

3.0 

4.0 

4.0 

18 Pitch Uranium Mine Area, Colorado 

Clay XR 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

1.0 

.0 

1.0 

.0 

.0 

.0 

1.0 

.0 

.0 

.5 

.0 

.5 

.0 

.5 

Hema XR 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Stratig 

6 

3 

6 

6 

6 

7 

7 

7 

6 

6 

6 

6 

7 

7 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

7 

6 

6 

6 

6 

6 

6 

6 

6 

7 

6 

6 

7 

7 

7 

7 

Elev Ft 

10,650 

9,040 

10,360 

10,340 

10,320 

10,480 

10,540 

10,775 

10,820 

10,800 

10,800 

10,780 

10,625 

10,510 

10,175 

9,975 

10,160 

10,725 

10,760 

10,760 

10,775 

10,880 

10,780 

10,800 

111130 

11,120 

10,950 

10,900 

10,240 

10,749 

10,271 

10,257 

10,250 

10,242 

10,270 

10,259 

10,242 

10,216 

10,374 

10,428 

10,355 

10,494 

10,436 

10,416 

10,412 

North Ft 

12,360 

9,000 

13,410 

13,450 

13,650 

13,610 

13,660 

14,400 

15,140 

15,050 

15,040 

14,960 

12,060 

11,420 

12,950 

11,620 

12,120 

14,750 

14,820 

14,830 

14,920 

15,000 

14,600 

14,600 

16,600 

16,700 

19,000 

16,500 

8,800 

15,200 

14,090 

14,090 

14,090 

14,090 

14,120 

14,120 

14,120 

14,120 

13,690 

13,850 

14,200 

14,080 

14,080 

14,080 

14,080 

East Ft 

19,82 

5,00 

18,02 

17,90 

17,72 

19,14 

19,34 

19,39 

20,05 

20,04 

20,04 

20,07 

19,61 

19,87 

17,63 

17,13 

17,65 

20,14 

19,89 

20,03 

20,09 

16,00 

16,20 

16,20 

17,00 

16,80 

17,80 

18,30 

15,20 

20,13 

19,97 

19,97 

19,97 

19,97 

19,93 

19,93 

19,93 

19,93 

19,96 

19,99 

20,05 

20,03 

20,07 

20,09 

20,09 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

_sample 

441-219 

441-223 

441-229 

441-230 

441-32 

441-57 

442-84 

443-301 

444-215 

445-28 

446-40 

446-65 

447-131 

447-98 

448-121 

!+48-65 

449-201 

449-33 

449-51 

449-87 

450-166 

451-247 

452-249 

452-265 

452-339 

453-113 

453-94 

453-97 

454-90 

501-196 

506-168 

509-200 

509-206 

610-152 

610-181 

610-228 

610-229 

610-254 

610-51 

612-118 

612-128 

612-15 

612-160 

612-36 

614-159 

Si02 % 

23.00 

92.20 

7.20 

8.20 

29.70 

50.80 

17.40 

10.40 

51.50 

4.30 

18.90 

4.80 

8.70 

9.20 

7.20 

23.80 

76.00 

75.60 

31.60 

7.30 

10.90 

6.70 

8.90 

,_ 10 

68.50 

4.60 

12.90 

12.50 

13.50 

8.20 

2.00 

40.70 

36.00 

22.30 

3.40 

58.60 

16.50 

59.70 

8.00 

10.50 

15.30 

37.30 

15.60 

5.90 

6.10 

Al203 % 

2.00 

.54 

.63 

.84 

5.10 

6.30 

1.10 

1.30 

5.70 

.74 

2.30 

.53 

.73 

1.50 

.43 

3.30 

1.30 

7.40 

2.60 

1.00 

1.20 

.94 

1.20 

.34 

6.50 

.83 

1.20 

,_ 70 

1.20 

.53 

.53 

1.90 

1.90 

1.10 

.33 

11.60 

.82 

13.70 

1.60 

1.30 

1.80 

11.30 

.63 

1.10 

.83 

Fe203 % 

1.60 

1.90 

2.10 

.73 

1.90 

2.50 

4.70 

.58 

.90 

4.90 

1.30 

2.90 

2.50 

6.40 

.44 

2.60 

1.10 

1.60 

,_ 10 

.90 

2.30 

.44 

.50 

.24 

.87 

.39 

3.10 

.56 

,_ 10 

.46 

.88 

.20 

.33 

.24 

.37 

2.60 

.12 

.76 

.34 

1.40 

1.20 

33.90 

.44 

.63 

.38 

FeO % 

.08 

.04 

.36 

.88 

.08 

.20 

.0 

.24 

.44 

.0 

.08 

.12 

.0 

.0 

.16 

.04 

.12 

.08 

.16 

.08 

.04 

.96 

.84 

.44 

.88 

.16 

.08 

.12 

.12 

1.20 

.60 

.08 

.16 

.08 

.76 

.24 

.24 

4.10 

2.50 

.16 

.12 

.24 

.12 

.12 

.20 

MgO % 

14.80 

.69 

18.40 

18.40 

11.60 

7.10 

.35 

18.10 

1.40 

13.20 

15.70 

18.00 

17.10 

16.50 

18.40 

14.50 

4.30 

2.20 

12.40 

19.20 

16.80 

18.80 

18.30 

20.60 

3. 70 

7.30 

2.90 

13.40 

17.40 

3.00 

19.20 

.63 

.40 

.64 

18.50 

1.40 

.53 

1.20 

2.40 

9.70 

8.10 

.61 

13.50 

17.50 

17.00 

CaO % 

23.10 

2.00 

28.50 

27.40 

20.00 

11.40 

41.00 

27.50 

20.00 

34.60 

24.20 

30.00 

27.70 

25.20 

29.90 

20.20 

6.40 

4.30 

21.60 

28.20 

28.00 

28.30 

27.50 

29.40 

6.50 

43.50 

42.40 

32.10 

25.30 

45.80 

30.70 

30.30 

34.00 

41.90 

30.20 

8.70 

44.50 

4.50 

44.20 

37.40 

36.00 

1.90 

30.50 

30.00 

31.60 

Na20 % 

.02 

.01 

.03 

.02 

.05 

.03 

.0 

.02 

.03 

.01 

.02 

.01 

.03 

.02 

.06 

.03 

.01 

.03 

.03 

.01 

.0 

.0 

.0 

.0 

.04 

.01 

.0 

.01 

.01 

.07 

.04 

.04 

.03 

.02 

.04 

.21 

.02 

.16 

.28 

.0 

.07 

.06 

.01 

.07 

.01 

K20 % 

.46 

.13 

.14 

.21 

1.50 

1.30 

.05 

.42 

1.60 

.18 

.50 

.20 

.19 

.34 

.18 

.96 

.25 

1.60 

.73 

.33 

.23 

.19 

.32 

. 11 

1.20 

.23 

.53 

.54 

.50 

.18 

.13 

.60 

.64 

.38 

.11 

3.40 

.29 

3.10 

.35 

.39 

.51 

1.20 

.25 

.26 

.32 

H20+ % 

1. 70 

.31 

.50 

.24 

1.60 

1.80 

.57 

1.00 

.44 

.81 

.16 

.48 

.51 

1.60 

.36 

1.20 

1.00 

1.90 

.92 

1.10 

.82 

.38 

.46 

.33 

1.80 

.50 

.90 

.38 

.93 

.27 

.39 

.46 

.52 

.45 

.27 

2.50 

.38 

4.80 

. 75 

.35 

.65 

7.90 

.30 

.34 

.57 

H20- % 

.37 

.37 

.29 

.12 

.50 

.49 

.76 

.21 

.56 

.54 

.32 

.48 

.34 

.67 

.20 

.55 

.26 

.62 

.23 

.13 

.38 

.09 

.15 

.01 

.50 

.19 

.40 

.21 

.17 

.06 

. 11 

.15 

.14 

.15 

.10 

.89 

.14 

.64 

.24 

.12 

.04 

3.60 

.13 

.01 

.03 

Ti02 % 

.08 

.02 

.05 

.03 

.29 

.35 

.07 

.06 

.45 

.02 

.14 

.03 

.05 

.05 

.05 

.18 

.07 

.53 

.20 

.05 

.06 

.03 

.05 

.02 

.49 

.05 

.09 

.08 

.08 

.03 

.03 

.24 

.14 

.08 

.04 

.69 

.09 

.78 

.08 

.05 

.09 

.25 

.03 

.04 

.06 

P205% 

.04 

.06 

.02 

.02 

.06 

.11 

.13 

.02 

.09 

.0 

.04 

.03 

.03 

.06 

.01 

.09 

.05 

.11 

.07 

.02 

.04 

.01 

.01 

.01 

.10 

.02 

.04 

.03 

.04 

.01 

.01 

.03 

.04 

.03 

.01 

.10 

.02 

.19 

.20 

.04 

.06 

.16 

.03 

.02 

.03 

Petrology and Geochemistry of the Pitch Mine 19 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample MnO % 

441·219 .12 

441·223 .02 

441·229 .13 

441·230 .12 

441·32 .05 

441·57 .03 

442·84 .16 

443·301 .06 

444·215 .03 

445·28 .31 

446·40 .03 

446·65 .08 

447·131 .13 

447·98 .07 

448·121 .07 

448·65 .03 

449·201 .14 

449·33 .03 

449·51 .02 

449·87 .01 

450·166 .06 

451·247 .15 

452·249 .19 

452·265 .05 

452·339 .0 

453·113 .12 

453·94 .14 

453·97 .02 

454·90 .04 

501·196 .08 

506·168 .25 

509·200 

509·206 

610·152 

610·181 

610·228 

610·229 

610·254 

610·51 

612·118 

612·128 

612·15 

612·160 

612·36 

614·159 

.05 

.01 

.10 

.12 

.04 

.19 

.12 

.07 

.05 

.08 

.08 

.04 

.03 

.05 

C02 % 

32.70 

1.20 

42.80 

42.10 

26.50 

15.70 

32.80 

40.20 

15.80 

41.60 

35.10 

43.20 

41.50 

37.80 

42.80 

31.50 

8.70 

3.60 

29.30 

42.90 

40.40 

43.80 

42.40 

47.40 

7.90 

41.40 

35.60 

39.50 

39.20 

39.60 

45.60 

24.70 

26.30 

32.80 

45.50 

6.40 

35.50 

6.30 

39.10 

39.10 

36.20 

.01 

37.80 

44.10 

42.10 

F % 

.02 

.01 

.01 

.03 

.06 

.03 

.04 

.05 

.09 

.02 

.07 

.02 

.04 

.04 

.03 

.05 

.02 

.06 

.07 

.03 

.03 

.02 

.03 

.02 

.07 

.02 

.03 

.03 

.04 

.02 

.02 

.02 

.02 

.02 

.01 

.21 

.02 

.10 

.03 

.04 

.02 

.05 

.03 

.02 

.03 

s % 

.03 

.03 

.05 

.16 

.08 

1.70 

.04 

.34 

.21 

.03 

.08 

.12 

.05 

.06 

.04 

.02 

.03 

.03 

.10 

.05 

.06 

.06 

.07 

.06 

.37 

.20 

.02 

.06 

.03 

.15 

.06 

.04 

.22 

.03 

.06 

1.20 

.07 

.05 

.06 

.21 

.03 

.01 

.03 

.03 

.12 

20 Pitch Uranium Mine Area, Colorado 

Ctotal % 

9.69 

.44 

12.07 

11.90 

7.68 

5.00 

9.11 

11.42 

4.80 

11.66 

9.92 

12.39 

11.59 

10.81 

12.21 

9.09 

2.72 

1.21 

8.44 

12.01 

11.28 

12.20 

12.32 

12.55 

2.50 

11.91 

9.70 

11.14 

11.18 

11.02 

12.79 

6.79 

7. 71 

9.51 

12.40 

2.04 

9.93 

2.15 

10.92 

10.95 

9.88 

.49 

11.06 

12.48 

12.46 

Corgan % 

.31 

.02 

.09 

.45 

.25 

. 73 

.03 

.25 

.30 

.05 

.01 

.54 

.17 

.46 

.34 

.54 

.41 

.16 

.40 

.06 

.0 

.20 

.20 

.01 

.34 

.39 

.02 

.01 

.49 

.0 

.46 

.13 

.69 

.54 

.05 

.26 

.02 

.25 

.06 

.0 

.18 

.28 

.52 

.28 

.70 

Carbnt % 

9.38 

.42 

11.98 

11.45 

7.43 

4.27 

9.08 

11.17 

4.50 

11.61 

9.91 

11.85 

11.42 

10.35 

11.87 

8.55 

2.31 

1.05 

8.04 

11.95 

11.28 

12.00 

11.52 

12.54 

2.16 

11.52 

9.68 

11.13 

10.69 

11.02 

12.33 

6.66 

7.02 

8.97 

12.35 

1. 78 

9.91 

1.90 

10.86 

10.95 

9.70 

.21 

10.54 

12.20 

11.76 

Cl ppm 

100 

120 

150 

130 

75 

25 

25 

90 

46 

80 

93 

78 

93 

63 

550 

110 

100 

25 

130 

110 

130 

130 

190 

240 

160 

85 

25 

68 

110 

170 

240 

48 

38 

78 

56 

25 

47 

41 

110 

130 

68 

45 

62 

135 

230 

Ba ppm 

160 

250 

120 

76 

160 

97 

2,100 

67 

140 

300 

61 

300 

110 

170 

60 

270 

360 

160 

110 

110 

140 

110 

80 

70 

110 

70 

160 

110 

70 

70 

920 

90 

160 

110 

60 

300 

120 

450 

90 

90 

100 

140 

45 

35 

60 

Sr ppm 

77 

65 

65 

49 

130 

180 

420 

50 

250 

63 

150 

57 

61 

76 

80 

220 

90 

270 

130 

75 

90 

80 

75 

43 

250 

390 

50 

120 

170 

260 

120 

210 

260 

420 

75 

350 

310 

130 

310 

210 

400 

230 

100 

65 

120 

Pb ppm Zn ppm 

25.0 610 

160.0 1,000 

41.0 850 

20.0 710 

5.0 92 

5.0 48 

5.0 47 

25.0 79 

5.0 20 

5.0 300 

5.0 68 

220.0 340 

71.0 230 

39.0 99 

14.0 40 

69.0 74 

22.0 120 

5.0 10 

10.0 5 

13.0 250 

42.0 49 

5.0 40 

5.0 5 

18.0 12 

5.0 12 

14.0 310 

12.0 160 

10.0 12 

16.0 24 

5.0 5 

10.0 280 

10.0 

10.0 

22.0 

200.0 

5.0 

10.0 

85.0 

5.0 

14.0 

17.0 

10.0 

5.0 

5.0 

10.0 

5 

41 

29 

36 

110 

37 

14 

57 

540 

10 

89 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample Mo ppm 

441·219 .40 

441·223 .60 

441·229 .40 

441·230 3.40 

441·32 .80 

441·57 

442·84 

443·301 

444·215 

445·28 

446·40 

446·65 

447·131 

447·98 

448·121 

448·65 

449·201 

449·33 

449·51 

449·87 

450·166 

451·247 

452·249 

452·265 

452·339 

453·113 

453·94 

453·97 

454·90 

501·196 

506·168 

509·200 

509·206 

610·152 

610·181 

610·228 

610·229 

610·254 

610·51 

612·118 

612·128 

612·15 

612·160 

612·36 

614·159 

3.70 

.05 

7.80 

1.40 

9.40 

1.00 

1.80 

1.60 

7.40 

.05 

4.90 

1.50 

.80 

1.80 

1.40 

1.80 

1.00 

.70 

5.60 

1.00 

14.00 

1.60 

1.40 

1.00 

.80 

1.60 

.80 

.70 

.70 

1.80 

2.10 

.80 

1.30 

.80 

1.60 

1.30 

14.00 

.50 

.05 

1.60 

Hg ppm 

.010 

.110 

.058 

.010 

.030 

.005 

.065 

.090 

.005 

.005 

.005 

.016 

.010 

.085 

.053 

.045 

.018 

.023 

.005 

.005 

.160 

.070 

.560 

.560 

2.500 

.005 

.060 

.005 

.093 

.005 

.210 

.005 

.005 

.005 

.075 

.039 

.005 

.042 

.005 

.005 

.039 

.005 

.005 

.042 

.005 

U ppm 

50.70 

62.60 

61.80 

256.00 

38.80 

107.00 

38.80 

109.00 

141.00 

107.00 

12.50 

125.00 

97.80 

50.20 

49.50 

49.90 

116.00 

34.30 

20.80 

102.00 

109.00 

26.50 

56.20 

113.00 

24.60 

1,190.00 

53.60 

19.00 

37.90 

64.40 

24.20 

63.40 

19.40 

55.20 

103.00 

395.00 

248.00 

228.00 

111.00 

121.00 

59.20 

241.00 

26.80 

11.70 

33.00 

Cr(s)ppm 

10.0 

15.0 

30.0 

20.0 

7.0 

7.0 

15.0 

5.0 

30.0 

15.0 

10.0 

3.0 

15.0 

15.0 

7.0 

70.0 

3.0 . 

15.0 

3.0 

30.0 

15.0 

20.0 

Cu(s)ppm 

7.0 

3.0 

1.5 

7.0 

7.0 

15.0 

7.0 

7.0 

1.5 

1.0 

3.0 

3.0 

3.0 

3.0 

1.5 

5.0 

1.0 

1.5 

50.0, 

1.5 

3.0 

5.0 

Ni(s)ppm 

20.0 

30.0 

20.0 

7.0 

10.0 

50.0 

20.0 

20.0 

7.0 

3.0 

20.0 

3.0 

30.0 

7.0 

3.0 

2.0 

10.0 

3.0 

7.0 

7.0 

5.0 

15.0 

Sr(s)ppm 

70.0 

30.0 

200.0 

500.0 

20.0 

70.0 

70.0 

50.0 

200.0 

20.0 

50.0 

7.0 

50.0 

70.0 

200.0 

150.0 

30.0 

200.8 

150.0 

500.0 

100.0 

500.0 

V(s)ppm 

15.0 

7.0 

30.0 

15.0 

10.0 

20.0 

15.0 

7.0 

20.0 

7.0 

15.0 

7.0 

15.0 

10.0 

5.0 

15.0 

10.0 

15.0 

30.0 

15.0 

15.0 

20.0 

Zr(s)pPffl 

30.0 

20.0 

70.0 

15.0 

10.0 

20.0 

50.0 

20.0 

300.0 

10.0 

3fLO 

10.0 

70.0 

30.0 

10.0 

2oo~e 

7.0 

50.0 

150.0 

20.0 

20.0 

50.0 

Petrology and Geoch~mistry of the Pitch Mine . 21 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample Dolom XR 

441-219 6.0 

441-223 .0 

441-229 8.0 

441-230 7.0 

441-32 5.0 

441-57 5.0 

442-84 .5 

443-301 7.0 

444-215 5.0 

445-28 6.0 

446-40 6.0 

446-65 8.0 

447-131 6.0 

447-98 7.0 

448-121 7.0 

448-65 6.0 

449-201 6.0 

449-33 2.0 

449-51 4.0 

449-87 9.0 

450-166 8.0 

451-247 7.0 

452-249 8.0 

452-265 10.0 

452-339 3.0 

453-113 4.0 

453-94 3_0 

453-97 4.0 

454-90 7.0 

501-196 .5 

506-168 10.0 

509-200 6.0 

509-206 5.0 

610-152 .5 

610-181 9.0 

610-228 .o 

610-229 .0 

610-254 .0 

610-51 3.0 

612-118 4.0 

612-128 4.0 

612-15 .0 

612-160 4.0 

612-36 9.0 

614-159 6.0 

CalcitXR 

.0 

.0 

.5 

1.0 

2-0 

.0 

5.0 

.0 

.0 

4.0 

4.0 

1. 0 

2_o 

.0 

1. 0 

.0 

.0 

1.0 

3.0 

.0 

1.0 

.0 

.0 

.0 

.0 

.0 

5.0 

.0 

.0 

8.0 

.5 

.0 

.0 

6.0 

.0 

1.0 

6.0 

.0 

6.0 

4.0 

3.0 

.0 

3.0 

.5 

3.0 

QuartzXR 

4.0 

10.0 

2.0 

2.0 

3.0 

4.0 

4.0 

3.0 

4.0 

.5 

.0 

1.0 

2.0 

3.0 

2.0 

4.0 

4.0 

6.0 

3.0 

1.0 

1.0 

3.0 

2.0 

.5 

5.0 

5.0 

2.0 

4.0 

3.0 

2.0 

.5 

4.0 

5.0 

4.0 

1.0 

5.0 

4.0 

5.0 

1.0 

2.0 

3.0 

5.0 

2.0 

1.0 

1.0 

22 Pitch Uranium Mine Area, Colorado 

Clay XR 

.0 

.0 

.0 

.0 

.0 

1.0 

1.0 

.0 

1.0 

.0 

.5 

.0 

.0 

.0 

.0 

.0 

.0 

1.0 

.0 

.0 

.0 

.5 

.0 

2.0 

2.0 

1.0 

.0 

2.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

2.0 

.0 

3.0 

.5 

.0 

.0 

1.0 

1.0 

.0 

.0 

Hema XR 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

4 

0 

0 

0 

Stratig 

7 

7 

7 

7 

7 

7 

7 

6 

7 

6 

6 

6 

6 

6 

6 

6 

7 

6 

6 

6 

6 

6 

6 

6 

6 

7 

7 

7 

6 

7 

6 

7 

7 

7 

7 

7 

7 

9 

7 

7 

7 

6 

6 

6 

7 

Elev Ft 

10,404 

10,400 

10,395 

10,394 

10,557 

10,536 

10,522 

10,283 

10,317 

10,524 

10,506 

10,483 

10,473 

10,497 

10,474 

10,514 

10,378 

10,530 

10,514 

10,481 

10,416 

10,323 

10,283 

10,267 

10,193 

10,486 

10,505 

10,502 

10,565 

10,353 

10,552 

10,279 

10,274 

10,470 

10,445 

10,405 

10,404 

10,382 

10,558 

10,470 

10,462 

10,589 

10,437 

10,532 

10,416 

North Ft 

14,080 

14,080 

14,080 

14,080 

14,080 

14,080 

11,813 

11,520 

11,520 

13,870 

13,869 

13,869 

14,000 

14,000 

13,978 

13,978 

13,978 

13,978 

13,978 

13,978 

13,800 

11,740 

11,650 

11,650 

11,650 

12,802 

12,802 

12,802 

12,377 

13,810 

12,210 

11,120 

11,120 

12,680 

12,680 

12,680 

12,680 

12,680 

12,680 

12,870 

12,870 

12,680 

12,870 

12,870 

11,660 

East Ft 

20,10 

20,10 

20,10 

20,10 

19,99 

20,00 

19,59 

19,93 

19,83 

20,08 

20,07 

20,08 

20,12 

20,10 

20,07 

20,03 

20,07 

20,00 

20,00 

20,02 

20,04 

19,75 

19,75 

19,75 

19,75 

19,81 

19,81 

19,81 

19,59 

19,99 

19,81 

20,02 

20,02 

19,82 

19,84 

19,86 

19,86 

19,87 

19,77 

19,81 

19,82 

19,75 

19,84 

19,76 

19,84 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample Si02 % 

614-186 8.10 

614-209 4.60 

614-219 19.40 

614-225 9.20 

614-263 63.50 

614-84 8.30 

615-261 8.90 

615-270 16.20 

615-297 13.30 

615-308 12.70 

616-231 9.20 

713-102 42.70 

766·137 11.90 

766-165 13.80 

766-183 4.40 

766-190 24.90 

766·199 9.30 

766-218 5.50 

766-220 48.60 

769-130 12.70 

769·218 43.10 

782-047 55.10 

782-336 62.70 

782-355 6.90 

786-133 27.20 

786-138 10.30 

Al203 % 

.63 

.53 

4.20 

.93 

4.40 

3.40 

.73 

1.90 

.23 

2.50 

4.90 

5.40 

1.50 

1.90 

1.20 

1.60 

1.30 

.59 

8.30 

2.00 

3.50 

7.10 

1.00 

.65 

.98 

1.10 

Fe203 % 

.33 

.25 

1.40 

.48 

.65 

4.00 

.21 

.56 

.43 

1.10 

3.80 

1.20 

1.30 

.48 

.61 

2.30 

1.30 

1.40 

1.90 

.81 

.95 

4.10 

4.10 

7.90 

1.40 

.61 

FeO % 

.20 

.16 

.24 

.16 

.56 

.44 

.20 

.32 

.16 

.48 

.36 

1.20 

.60 

.60 

.88 

1.60 

.88 

2.50 

1.60 

.68 

.72 

.84 

.64 

.62 

.12 

.79 

MgO % 

17.60 

18.00 

14.40 

18.10 

2.40 

.88 

18.70 

16.60 

17.30 

16.40 

.81 

8.40 

16.90 

17.20 

17.80 

12.30 

17.10 

16.00 

5.90 

16.80 

9.90 

5.10 

5.80 

15.90 

13.30 

17.40 

If additional factors are added, they carry elements 

with low communalities that make small groups, such as 

Hg with organic carbon, and Zn and Pb withF~0 • 

Factor analysis in the Q-mode (Davis, 1973) was 

performed to search for relations between samples and 

groups of samples with similar character. Several data 

sets were run using different variables, including and excluding non-Leadville samples. The results are fundamentally similar and will be presented only for the Leadville 

subset of log-transformed data for 33 variables in 73 

samples, as in the correlation analysis. Factor 1 carries 

86 percent of the variance, factor 2 carries 3.8 percent, 

factor 3 carries 2.0 percent, and factor 4 carries 1.5 percent; other factors have eigenvalues of less than 1 and 

carry less than 1 percent of the compositional information. In the 3-factor varimax model, factor 1 is headed 

by sample 298-327 and contains 48 dolomite samples; 

uranium content does not seem to be important in defining this group. Factor 2 carries 15 samples and is headed 

by sample 26 (jasperoid) and sample 3 (gossan), which 

have negative loading. Factor 3 carries 10 samples, headed 

by sample 38 (limestone). In the 4-factor model, factors 

CaO % 

29.50 

30.60 

23.60 

27.40 

12.80 

42.40 

27.20 

24.50 

26.70 

24.80 

41.50 

14.70 

27.60 

25.90 

29.60 

22.60 

25.80 

28.60 

10.10 

26.50 

15.70 

7.40 

8.60 

24.50 

23.80 

26.60 

Na20 % 

.0 

.0 

.05 

.04 

.10 

.03 

.01 

.02 

.01 

.04 

.04 

.14 

.02 

.08 

.01 

.08 

.01 

.03 

.09 

.16 

.02 

.04 

.03 

K20% H20+ % H20· % Ti02% P205% 

.26 .33 .07 .03 .02 

.23 .98 .02 .04 .01 

1.30 1.40 .42 .22 .04 

. 39 . 77 . 11 . 06 . 03 

1.30 1.40 .24 .35 .06 

.32 1.50 .24 .18 .63 

.32 .35 .04 .05 .02 

.63 .68 .17 .15 .04 

.15 .40 .06 .03 .02 

.84 1.20 .29 .15 .05 

.40 2.60 .15 .21 .46 

1.60 1.60 .44 .19 .05 

.38 .51 .22 .02 .03 

. 50 . 68 . 19 . 11 . 02 

.10 .40 .18 .03 .01 

.26 . 78 .52 .07 .03 

.21 .41 .25 .05 .02 

.07 .45 .29 .01 .02 

1.60 4.50 .37 .40 .09 

.57 .55 .20 .08 .03 

.91 .99 .30 .20 .07 

1.60 2.70 1.40 .41 .07 

.11 .69 .44 .02 .03 

.47 .50 .02 .04 

.08 .55 .33 .03 .05 

.16 .50 .31 .07 .03 

1 and 3 are essentially the same as those in the 3-factor 

model, but factor 2 is broken up into two new factors, 

one headed by samples 612-15 and 3 (gossan type) and 

a new factor 4 headed by samples 34 and 26 (jasperoids). 

Q-mode analysis of the complete data set for 135 samples 

from all formations was not very informative. Although 

clay-rich Belden rocks were effectively carried on an 

"aluminum" factor, other rock types were classified according to chemistry, not stratigraphy or alteration. 

Dolomite samples from the Manitou, Fremont, and Dyer 

were grouped logically with Leadville dolomites, and 

Harding Quartzite samples were lumped with jasperoids. 

Correspondence analysis produced more graphic results 

than factor analysis and will be presented in more detail. 

Correspondence analysis (David and others, 1977) 

is a variation on factor analysis in which R-mode and 

Q-mode results are computed simultaneously. Factor 3 

highlights uranium and associated elements. Factor 3 

carries 77 percent of the information on uranium, 90 percent of the information on sulfur, 90 percent on molybdenum, 53 percent on lead, and 31 percent on ferrous 

iron. Factor 1 carries the "carbonate" elements; factor 

Petrology and Geochemistry of the Pitch Mine 23 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample MnO % C02 % F % s % Ctotal % Corgan % Carbnt % Cl ppm Ba ppm Sr ppm Pb ppm Zn ppn 

614·186 .03 43.20 

43.90 

33.50 

41.20 

11.60 

.03 

.02 

.05 

.03 

.04 

.10 

.17 

1.00 

.28 

.21 

11.75 .02 11.73 160 

450 

190 

55 70 5. 0 5 

614·209 .03 12.66 .76 11.90 60 50 5.0 5 

614·219 .05 9.52 .29 9.23 120 150 42.0 36 

614·225 .04 11.42 .0 11.42 65 

25 

60 53 12.0 66 

614·263 .02 3.47 .40 3.07 130 130 5.0 5 

614·84 .07 33.30 

42.40 

39.10 

41.60 

39.40 

.10 

.03 

.04 

.02 

.08 

3.10 

.08 

.36 

.22 

.72 

10.24 .11 9.13 52 

210 

140 

530 

130 

95 550 20.0 50 

615·261 .02 12.21 .62 11.59 60 55 12.0 

615·270 .05 10.37 .06 10.31 60 110 5.0 13 

615·297 .06 11. 46 . 88 1 0 . 58 80 55 16.0 60 

615·308 .14 10.51 .17 10.34 70 220 50.0 220 

616·231 .08 31.50 

20.30 

40.10 

38.70 

44.30 

.07 

.11 

.05 

.06 

.03 

3.00 

1.22 

.74 

.30 

.74 

12.85 4.20 8.65 120 

280 

290 

340 

240 

150 620 14.0 110 

713·102 .03 7.36 1.87 5.49 400 180 

766·137 .03 11.30 .16 11.14 110 57 

766·165 .08 

766·183 .08 

766·190 .21 

766·199 .10 

766·218 .25 

766·220 .09 

769·130 .07 

769·218 .09 

782·047 .07 

782·336 .05 

782·355 .12 

786·133 .15 

786·138 .15 

31.40 

40.90 

41.50 

13.30 

39.60 

22.10 

9.20 

12.70 

36.60 

32.40 

41.40 

.03 

.04 

.02 

.06 

.06 

.07 

.20 

.01 

.01 

.02 

.03 

.29 

1.73 

.71 

1.04 

.43 

.47 

3.29 

3.65 

7.92 

.13 

.40 

10.90 

11.55 

12.18 

9.01 

11.82 

3.91 

11.13 

6.65 

3.06 

3.92 

10.18 

8.84 

11.03 

.18 

.10 

.13 

.47 

.03 

.30 

.15 

.52 

.52 

.56 

.19 

.69 

.03 

2 carries chiefly F~0 , H2 0 +, and P. Factor 4 carries 

chiefly AI, Na, K, Ti, and F, elements probably associated 

with clay minerals. 

Correspondence Q-mode analysis highlights relations between samples. In this analysis the same factors 

(vectors) are used as in the R-mode. Factor I carries dolomites; factor 2 carries hematite-rich gossan-type samples; 

and factor 3 carries samples rich in S, FcO, and U. 

Plots of correspondence factor scores yield additional useful information (figs. I2, 13, I4). It is clear on 

figures I2 and 13 that R-mode scores plot close to the 

Q-mode scores, as they should by this technique. The plot 

of factor I versus factor 2 (fig. I2) breaks out three 

groups: (I) jasperoid-Si, (2) gossan-Fez03, and (3) 

carbonates-Ca-Mg. An interesting trend on figure I2 is 

the spread of sample points between the carbonate cluster 

and the gossan-cluster; these samples are oxidized ocher 

dolomites. The plot of factor 2 versus factor 3 (fig. 13) 

highlights the U-S-FeO-Mo group of variables and 

samples rich in those elements. Again, there is a spread 

of ocher dolomite samples along the gossan-vector. Correspondence analysis classified the oxidized dolomites as 

24 Pitch Uranium Mine Area, Colorado 

10.72 

11.44 

12.05 

8.54 

11.79 

3.61 

10.98 

6.13 

2.54 

3.36 

9.99 

8.15 

11.00 

250 

230 

130 

89 

290 

220 

240 

210 

410 

320 

330 

62 

79 

260 

63 

150 

240 

63 

270 

58 

32 

110 

720 

190 

100 

64 

83 

71 

68 

270 

62 

230 

260 

41 

36 

51 

38 

having properties intermediate between unaltered dolomites and thoroughly altered gossan samples, in good 

agreement with results of petrographic studies. 

A plot of factor 3 scores versus uranium content 

(fig. I4) shows a good linear trend for higher grade 

samples, which also contain more than about I percent 

sulfur. An interesting feature of figure I4 is the cluster 

of samples in the lower left-hand corner; the deviation 

of these samples from the linear trend suggests the interpretation that they have lost not only uranium but also 

other elements (S,FeO, Mo, Pb) that are in factor 3. 

The classification of Leadville samples into four 

groups by factor and correspondence analysis is considered valid because these groups are the same as identified through the logging of core, the mapping of surface 

exposures, and petrographic study. Another test of the 

validity of the classification of samples is by t-tests of 

difference between groups (Natrella, I963). Subsets were 

created according to Q-mode groupings and lithologic 

criteria. These tests examined groups, not individual 

samples. The t-test, comparing data for six samples of 

jasperoid from outcrops with nine normal unmineralized 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample Mo ppm Hg ppm U ppm Cr( s)ppm 

614-186 .80 .160 29.20 7.0 

614-209 2.10 .005 135.00 

614-219 5.30 .110 984.00 20.0 

614-225 2.90 .005 785.00 7.0 

614-263 .80 .020 125.00 

614-84 12.00 .240 9.78 20.0 

615-261 1.30 .005 38.40 

615-270 1.10 .090 106.00 15.0 

615-297 2.10 1.000 1,300.00 

615-308 6.40 .140 330.00 15.0 

616-231 8.10 .160 40.40 

713-102 3,580.00 

766-137 6,260.00 15.0 

766-165 717.00 

766-183 3,410.00 

766-190 7,570.00 7.0 

766-199 21,600.00 

766-218 14,300.00 7.0 

766-220 24,300.00 

769-130 1,090.00 50.0 

769-218 3,110.00 

782-047 10,600.00 70.0 

782-336 9,080.00 

782-355 17,300.00 3.0 

786-133 11120.00 

786-138 16,800.00 15.0 

Leadville dolomites from outcrops, shows that Si is 

significantly enriched in jasperoid (at a 99 percent level 

of confidence) and that Mg, Ca, and Ba are significantly 

depleted. Contents of other elements are not significantly different between these two groups. Comparing the surface jasperoid samples with a group of 10 subsurface 

samples of silicified dolomite shows that the subsurface 

samples (ore-bearing) are significantly enriched in AI, 

Fe.z03,Fe0, S, Ba, Sr, Cr, Ni, V, and U. Some of these 

differences may be due to leaching of the surface samples, 

although the surface samples were selected because they 

were unweathered and the least altered I could locate. 

Comparison of ocher dolomites with unaltered 

dolomites reveals some important differences. For this 

t-test, data for 11 samples of ocher dolomite were compared with the data for 9 unaltered dolomites. Ocher 

dolomites are enriched in the following elements (level 

of significance in parentheses): Si (0.99}, AI (0.99),F~03 (0.99}, K (0.99), Ba (0.95), Sr (0.99), Pb (0.95), Zn (0.99), 

Cu (0.99), Ni (0.99), V (0.99), and U (0.99). The enriched 

elements are those of the ore suite, which suggests that 

the ocher dolomites were mineralized previously, even if 

Cu(s)ppm Ni (s)ppm Sr(s)ppm V(s)ppm Zr(s)ppn 

2.0 3.0 30.0 7.0 7.0 

7.0 15.0 70.0 30.0 20.0 

3.0 3.0 15.0 7.0 7.0 

3.0 15.0 500.0 15.0 20.0 

3.0 3.0 50.0 15.0 50.0 

10.0 20.0 100.0 15.0 20.0 

5.0 20.0 70.0 20.0 70.0 

5.0 10.0 50.0 10.0 70.0 

3.0 10.0 20.0 15.0 50.0 

3.0 20.0 50.0 30.0 20.0 

70.0 300.0 300.0 70.0 100.0 

5.0 100.0 7.0 7.0 30.0 

7.0 20.0 30.0 10.0 100.0 

they are not now ore because of loss of uranium. The 

gossan-type samples number 3 and 612-15 are enriched 

in F~~' Zn, Mo, Hg, and U relative to the ocher 

dolomite subset; this set was not analyzed by t-test 

because the two samples of gossan may not be representative geologically. 

Ores of different grades contain variable concentrations of minor elements in addition to uranium. Three 

subsets were defined by uranium contents: (1) high grade, 

with U greater than 5,000 ppm (N = 12); (2) medium 

grade, U from 500 to 5,000 ppm (N = 26); and (3) low 

grade, U less than 500 ppm (N = 37). The t-test shows that 

the high-grade set is tested as significantly enriched inFcO, 

K, and S relative to the medium grade; data are insufficient for some elements such as Mo and Cu for them to 

be significantly different even though they are enriched 

in three samples of high-grade ore. The medium-grade 

set is significantly enriched inFeO, K, S, Mo, Cu, and 

Ni relative to the low-grade set. 

When the geochemical and statistical results are 

summarized, several statistical tests confirm the association of many elements with uranium. The most important 

Petrology and Geochemistry of the Pitch Mine 25 
Table 1. Petrochemical data for host rocks, Pitch mine area, Colorado-Continued 

Sample Dolom XR CalcitXR QuartzXR Clay XR Hema XR Stratig Elev Ft North Ft East Ft 

614-186 5.0 3.0 2.0 .0 0 7 10,396 11,660 19,86 

614-209 7.0 2.0 1.0 .0 0 6 10,379 11,660 19,88 

614-219 6.0 .0 4.0 .5 0 6 10,372 11,660 19,88 

614-225 7.0 .0 3.0 .0 0 6 10,367 11,660 19,89 

614·263 2.0 4.0 4.0 .0 0 6 10,340 11,660 19,91 

614·84 6.0 .0 2.0 2.0 0 7 10,470 11,660 19,79 

615·261 6.0 .0 4.0 .0 0 7 10,306 11,660 19,87 

615·270 7.0 .0 3.0 .5 0 7 10,298 11,660 19,87 

615·297 7.0 1.0 2.0 .0 0 6 10,274 11,660 19,88 

615-308 8.0 .0 2.0 .5 0 6 10,265 11,660 19,89 

616-231 6.0 .0 3.0 1.0 0 7 10,312 11,660 19,81 

713·102 6.0 .0 4.0 .0 0 

766·137 8.0 .0 2.0 .0 0 

766·165 9.0 .0 1.0 .0 0 

766-183 9.0 .0 1.0 .0 0 

766·190 7.0 .0 3.0 .0 0 

766-199 9.0 .0 1.0 .0 0 

766·218 9.0 1.0 1.0 .0 0 

766-220 5.0 .0 5.0 .0 0 

769-130 8.0 .0 2.0 .0 0 

769·218 5.0 .0 5.0 .0 0 

782·047 4.0 .0 6.0 .0 0 

782·336 5.0 .0 5.0 .0 0 

782·355 8.0 1.0 1.0 .0 0 

786·133 5.0 2.0 3.0 .0 0 

786·138 8.0 .0 2.0 .0 0 

1

Stratigraphy: 1, Manitou Dolomite; 2, Harding Quartzite; 3, Fremont Dolomite; 4, Parting Quartzite; 5, Dyer Dolomite; 6, Leadville 

Dolomite; 7, Belden Formation. 2

Location: coordinates are those used by Homestake Mining Co. For core samples, locations are computed for depth in hole and inclination, but drift of hole is not included. For surface samples, mine grid was extrapolated. 

associations statistically and geologically seem to be S, 

FeO, Mo, K, Ca, and Ni. Silica and aluminum are enriched according to some tests, which is consistent with 

the deposition of small, but important, amounts of quartz 

and clay with uranium minerals. 

GEOCHEMISTRY OF THE 

LITTLE INDIAN DEPOSIT 

The Little Indian deposit, located 1 km north of 

the Pitch mine, was discovered in 1955 and brought into 

production in 1957. The mine was in production for two 

years and yielded 6,180 tonnes of ore grading 0.48 percent U3 0 8 (29,500 kg U3 0 8) (Ward, 1978). The mine 

workings totaled about 275m generally along the strike 

of the Harding Quartzite (fig. 15). 

Most uranium at the Little Indian deposit occurs 

in sandstones of the Harding Quartzite (fig. 16A). The 

26 Pitch Uranium Mine Area, Colorado 

quartzite zone in the lower part of the Harding is typically 

barren. Some uranium also occurs in dolomites of the 

Fremont Dolomite and Manitou Dolomite (fig. 16B), 

stratigraphically above and below, respectively, the Harding. My observations of rocks in the Little Indian area 

and in three drill cores were limited and possibly not 

representative. I was impressed by the following uranium 

associations: (1) Only hexavalent uranium minerals were 

observed in core and identified in the laboratory. (2) 

Uranium always occurs in association with iron oxides 

of brown (''limonite'') to red (''hematite'') color. Some 

pyrite was observed under the microscope; it occupies the 

matrix of poorly sorted sandstone, is highly altered to 

iron oxides, and is older than the hexavalent uranium 

minerals. (3) Uranium and iron oxide minerals occupy 

gash fractures in sandstone and dolomite and are 

disseminated in the matrix of coarser, poorly sorted sandstone (fig. 16A). Other than the oxidation of pyrite, 

previously mentioned and possibly related to ore, there 
Table 2. Statistical summary of chemical data, Pitch mine area, Colorado 

[XR, X-ray diffraction] 

Consti- Geometric Geometric Valid 

tuent Minimum Maximum mean deviation value 

Major elements, in weight percent 

Sio2 0.20 97.7 12.26 3.58 116 

Al2o3 .03 13.7 1.03 3.78 116 

Fe2o3 -02 46.4 .so 3.64 116 

FeO .oo 4.1 .23 3.00 116 

MgO .07 21.0 6.18 4.39 116 

CaO .Is 53.1 19.47 3.07 116 

Na2o .oo -31 .033 2. 35 113 

K20 .oo 3.40 • 25 3.67 115 

H o+ .10 9.10 .64 2-22 116 2 - H20 .01 s.so .36 .64 116 

Tio2 .oo -78 .069 2.96 116 

p2os .oo .63 .037 2.42 116 

MnO .oo -31 .062 2.11 116 

Co2 .oo 48.2 22.70 4.52 116 

F .oo .21 .030 1. 99 116 

s .01 7.92 .12 4.86 116 

c (organic) .oo 4.20 .18 3.38 116 

c (carbonate) .oo 13.07 7.32 2. 7 9 116 

Minor elements, in parts per million 

Cl 8.91 550. 29.8 17.4 116 

Ba 20. 2100. 101.4 2.28 116 

Sr 1 o. 620. 92.0 2.84 116 

Pb o. 220. 9.67 3.42 101 

Zn s. 2600. 33.2 4.50 101 

Mo o.s 88. 1.38 4.91 101 

Hg 0.05 2.6 .022 5.58 101 

u 0.18 33500. 7 5. 3 16.7 116 

Cr .5 70. u.o 2.60 57 

Cu .a 70. 3.02 2. 72 57 

Ni .a 300. 8.18 3.03 57 

v .5 70. 10.9 2. 17 57 

Zr 2.3 300. 28.1 3.11 57 

Mineralogy, in parts per ten 

Dolomite XR o. 100 49 

Calcite XR o. 100 22 

Quartz XR o. 100 24 

Clay XR o. 30 2 

Hematite XR o. 40 0.3 

are few signs of reaction next to uranium minerals. The 

disseminated uranium probably in part replaces small 

amounts of clay minerals in the matrix. (4) Small amounts 

of organic trash and epigenic hydrocarbon in veinlets are 

present but are only slightly radioactive. 

The Little Indian deposit is structually controlled 

by the zone of fracturing below the Chester fault zone. 

The major upthrust surface, the contact between Precambrian granite and sedimentary rocks, was not the locus 

of uranium deposition. The setting (fig. 15) is similar to 

that in the Pitch mine, but I have insufficient informa22 116 

26 116 

22 116 

6 116 

4 116 

tion to document details. Paleozoic sedimentary rocks 

strike west to northwest and dip about 30 ° south. The 

north-striking Chester fault displaces Precambrian rocks 

upward and westward over the Paleozoic section. The 

Paleozoic rocks appear to continue with relatively minor 

change in attitude under the upthrust, judging from my 

sparse drill hole observations. The rocks intersected in 

drill core below the upthrust plane are fractured, but not 

thoroughly brecciated as at the Pitch deposit. The 

sedimentary rocks do not seem to be complexly sliced into 

fault blocks as in the Pitch area, but core from drill hole 

Geochemistry of the Little Indian Deposit 27 
Table 3. Correlation of elements with 

uranium in Leadville Dolomite 

[Computed for 73 samples; *, coefficient significant at 95 percent level of confidence] 

Variable Correlation 

Si .10 

Al • 41* 

Fe2o3 .56* 

FeO .68* 

Mg .20 

Ca .o7 

Na .o8 

K .32* 

H o+ 2 .33 

Ti - .02 

p .22 

Mn .39 co2 • 04 

F .oo 

s .82 

C (organic) .12 

C (carbonate) .o2 

Cl .45* 

Ba .43* 

Sr -28* 

Pb .67* 

Zn .31* 

Mo .64* 

Hg • 21 

Cr .2 6 

Cu .51* 

Ni . ss* 

v .30 

Zr .33* 

Dolomite XR .34* 

Calcite XR • 22* 

Quartz XR - • 03 

775 indicates that about one third of the Harding section was removed by faulting. 

Uranium minerals identified in this study and by 

Malan (1959) include uranophane [Ca(U02)2(Si03)2 

(OH)2 · SH20], autunite [Ca(U02)2 (P04 )2 · nH20], 

kasolite [Pb(U02)2 (Si03)2 (OH)2], and probable 

novacekite [Mg(U02)2(As04)2 · 9H20]. Uranium is 

hexavalent in all of these minerals. No quadrivalent 

uranium minerals have been observed. Most of the 

uranium minerals observed in thin sections are honeyyellow, slightly pleochroic, moderately birefringent, with 

platelike form, all characteristics of autunite. A yellow 

mineral with an X-ray diffraction pattern close to that of 

novacekite drew attention to a possible role of arsenate 

ion. However, subsequent chemical analyses showed 

only moderate arsenic contents with arsenic consistently 

lower than uranium, indicating the arsenate could have 

been only partially responsible for localizing uranium. 

Chemical data for 19 elements in 19 samples taken 

from three drill cores are in table 4, and data for 38 

28 Pitch Uranium Mine Area, Colorado 

10 I I 

Iz 

w . 0 

a: 

w 

a_ 

1-

:r: 

C) 1.0- - w 

~ ! .. ~ ~· . . . .. . z ... 

.. 0 ~· m ,, a: 

<( ~· .. 0 •. . 0 ~· 0.1 ,!! -

z 

<( •.. C) 

a: ·:· 0 

C) •• 0 

...J .. 0.01 ~ • • I • I 

0.01 0.1 1.0 10 

LOG U, IN WEIGHT PERCENT 

Figure 10. Plot of uranium versus organic carbon in samples 

from the Pitch mine. 

10~~~~~~~----------~----------~ ,ll •:• • ,~ • I • • I 

1--

z 

UJ • 0 • a: 

~ 1.0 r-

. . 

.. .. 

.... 

. . . . . ...J • 

0 ;:; 0.1 ~ •• l . 1-- • • • 

CJ ::1: 

9 f~: J "ss Samples <0.01 percent U are not plotted 

.. 

.. 

-

-

0.010L-----------.L____I _____ ll _____ ___l10 

0.1 1.0 

LOG U, IN WEIGHT PERCENT 

Figure 11. Plot of uranium versus total sulfur in samples from 

the Pitch mine. 

elements are summarized in table 5. Fourteen of the 

samples were analyzed by X-ray fluorescence (XRF), 

which may yield somewhat different data than the wetchemical methods employed on 121 other samples; for 

this reason and the fact that this is a small suite of grab 

samples that may not be representative, no statistical 

significance is given to these data, although the data are 

considered to be reliable. Correlation analysis on the data 
+2.0 

+ 1.6 

+1.2 

ff3 +0.8 a: 

0 

0 

(f) 

C\1 

a: 

0 b +0.4 

it 

.612-15 

EXPlANATION 

x Element 

• Sample 

298-327 

/...--.--, 

/ 'yOcher oxidized dolomites 

\ .442-98 :\.. 

\ 445-28 \ e I 

sx ' , ___ --/ ---......... xU MnO .... --e• 43,, I ....x-/ ' x x XMo /,.. MgO : 37 \ 

0 txBa • x • • \ 

Siliceous altered\ ,.. ..... -.--;-;y•- ......... , x x><x ' Ca.o CaO •41 1 

dolomites / ' '-........ • / / . \ '..... / 

( Six• xHg • j ---\N~:n::dolomites and limestones 

~ ..... ___ !._61~-~~--_..../ -0.4 

·ot>. ---.-.... "' ..... --.-:~~ 27 J / .~c~~ / , s\~~ / 

(26. •44 ,......--/ 

-0.8 ~~-----..... --~Surface jasperoid 

-1.2L_ ______ _L ________ L_ ______ _i ________ ~--------L--------L--------~------~ 

-1.6 -1.2 -0.8 -0.4 0 +0.4 +0.8 +1.2 +1.6 

FACTOR 1 SCORES 

Figure 12. Plot of correspondence-analysis factor scores for factor 1 and factor 2. 

from 19 samples indicates that six elements correlate 

strongly with uranium: Ti, Mn, Ni, Sr, Ba, and Mo. For 

this sample suite sulfur and uranium are independent 

(r = 0.008). Computed correlations of phosphorous and 

arsenic with uranium are negative; however, in some 

samples phosphorous and arsenic are enriched with 

uranium. 

A comparison of the average composition of 12 

Harding Quartzite samples with data for the Pitch mine 

suite indicates that contents of Mg, Ca, Fe, S, Mn, and 

Sr are lower in the quartzites and that Si, AI, P, Ba, and 

Pb are higher. Mean contents of P, S, Ba, Mn, Pb, and 

Sr are lower in seven samples of carbonate rocks from the 

Little Indian deposit as compared with carbonates in the 

Pitch mine. Contents of Fe, P, and Sr are higher in quartzite samples than in carbonates from the Little Indian. 

The predominant mineralogic and chemical feature 

of the Little Indian mineral deposit is oxidation, in contrast to the Pitch mine, which has predominantly reduced 

minerals and associated elements. Elements enriched in 

the Little Indian deposit are logically explained by 

transport and deposition under oxidizing conditions; the 

anions phosphate, arsenate, and silicate are important in 

localizing metals and uranium. 

Oxidation at the Little Indian extends to more than 

130 m below the present land surface. The oxidation 

Geochemistry of the Little Indian Deposit 29 
+2.0 

+ 1.6 

+ 1.2 

en 

~ +0.8 

0 

0 

en 

C\1 

a: 

0 

b +0.4 

Lf 

612-15. 

EXPlANATION 

X Element 

• Sample 

,. ...... -.---....... ,,,.... 298-327''-....... / ,, /// \ 

/ M \ / X 0 \ Ore trend •. 298-341. 1 Or---------------------------------~~~~~~------~=----------------+--------------~ 

FeOx xPb / 

-0.4 

,-

/ 

Hg/x 

Silicified dolomites--{-

'--? / 

• I 

I 

I 

I 

/ 

............................. _.../>(High grade ore samples ........... ____ ,782-355 

/27 I 

/ 44 • '1--- Surface jasperoid 

{ 26•34) 

-0.8 \ / ,__ _./ 

Silicifica ion 

-1.6 -1.2 -0.8 -0.4 0 +0.4 +0.8 +1.2 +1.6 +2.0 

FACTOR 3 SCORES 

Figure 13. Plot of correspondence-analysis factor scores for factor 2 and factor 3. 

extends a few meters below the uranium minerals. This 

is not difficult to explain, however, if one considers the 

presence of the Chester fault zone and the ground-water 

outlet in Agate Creek 1 km to the north at an elevation 

about 100 m below the zone of oxidation and uranium 

enrichment. Tertiary ground-water regimes are more difficult to interpret, but the distribution of volcanic rocks 

suggests that the valley of Marshall Creek was a paleovalley and would have been below the Little Indian in 

the Oligocene. Oxidation seems to be most pervasive in 

30 Pitch Uranium Mine Area, Colorado 

the vicinity of sandstone-carbonate rock contacts. This 

may reflect structural and lithologic control of groundwater flow. The regional radioactivity of a bed in the 

Harding that contains fish scales, hydrocarbon pellets, 

and pyrite (now hematite) suggests there may have been 

an older zone of reduced uranium, possibly produced by 

early diagenetic processes. This uranium might have been 

remobilized and redeposited to form the Little Indian 

deposit, or there could have been other sources in granitic 

or volcanic rocks. 
.298-341 

.298-334 

3.0 

2.5 

.766-220 

1-

z 

w 

0 

a: 

w 

a_ 2.0 II 

C) 

w 

3: 

~ 

~- 1.5 :::) 

z 

z 

~ :::) 

1.0 

0.5 

• 766-199 

• 782-355 

FACTOR 3 SCORES 

Figure 14. Plot of uranium content versus correspondence-analysis score for factor 3. 

INTERPRETATION AND DISCUSSION 

Structural Control of Ore 

The most important factor in producing the 

uranium deposits is the Chester fault. The Pitch orebody 

is within the zone of multiple fault strands, and the richest 

ore zones are in thoroughly brecciated Leadville 

Dolomite. The brittle character of the dolomite is an important contributing factor. The Little Indian deposit is 

also along the Chester fault where brittle quartzites are 

fractured. Drilling in the area between these two ore 

deposits reveals additional uraniferous zones in brecciated 

rocks along the Chester fault zone. 

More specifically, the structural mechanism is 

forced faulting of brittle rocks above a rigid basement 

block in an upthrust (Stearns, 1978; Nash, 1980). In 

theory, experiment, and nature, brittle rocks (such as 

dolomite) develop abundant fractures and breccia when 

they occur immediately above upthrust basement blocks. 

At the Pitch mine, as in experiments (Friedman and 

others, 1976), maximum fracturing occurs where brittle 

beds intersect the reverse fault plane at angles near 70°. 

At lower angles of intersection, deformation is less intense, probably due to deflection of shears onto bedding 

planes. Exploration for zones of maximum brittle 

deformation should focus on brittle beds and changes in 

dip where beds are folded next to the fault zone. Concavedownward curvature of the fault surface should be 

anticipated. 

Possible Role of Karst 

Karst is well known in the Leadville Dolomite in 

central Colorado. Iron-stained karst in the Pitch mine 

area has been prospected for metals (many have been excavated or blasted) and are shown as prospect pits on the 

Interpretation and Discussion 31 
118,000E 

119,000NL---------~--------~--L_ __ _L~i_--~------~------~~~-- L_~c_~------~~ 

Base from Homestake Mining Company 

0 500 FEET 

0 150 METERS 

EXPIANATIOS 

ML Leadville Dolomite (Mississippian) 

Dd Dyer Dolomite (Devonian) 

Of Fremont Dolomite (Ordovician) 

Oh Harding Quartzite (Ordovician) 

Om Manitou Dolomite (Ordovician) 

p£ Precambrian rocks, undivided 

40 Strike and dip of beds 

_ _.... __ Fault-Dashed where approximately located; 

bar and ball on downthrowm side 

_ ..____ • ... ,_ Reverse fault-Hachure on upper plate 

--?--- Contact-Dashed where approximately located; 

Queried where uncertain 

Figure 15. Generalized geologic map of the Little Indian deposit area. 

topographic map of the area. Recently Dupree and 

Maslyn ( 1979) proposed that uranium at the Pitch mine 

''largely occurs in the black organic-rich matrix material 

of carbonate breccias''. They added that ''these breccias 

have previously been described as Pennsylvanian Belden 

Formation fault breccias. The carbonate breccias formed 

32 Pitch Uranium Mine Area, Colorado 

by surface karst weathering, as washed-in cave and 

sinkhole fill, and by sinkhole collapse." My observations, 

particularly in the ore zone, do not agree with those interpretations. The carbonate rock breccias are classic tectonic breccias very clearly related to the complex faulting 

along the Chester fault. The breccia and uranium grade 
Figure 16. Photomicrographs of ores from the Little Indian 

deposit. Photos taken in plane polarized light. A, Sandstone 

unit (sample 775-374) having clay-rich matrix and organic 

material (black) within Harding Quartzite. Note bimodal grain 

size of quartz grains. 8, Autunite in fractured Manitou Dolomite 

(sample 762-494). 

die out below and to the west of the faults. After inspecting numerous cores, new open pit exposures, and thin 

sections, I found no evidence for the "organic-rich 

matrix'' or ''washed in clayey sinkhole fill,'' postulated 

by Dupree and Mastyn (1979). Chemical analyses did not 

indicate abundant organic carbon or aluminum in 

uranium-bearing breccias. Close inspection and microscopic examination revealed black portions of some core 

as fragments of black shale of the Belden; their presence 

is consistent with tectonic mixing of breccia in a complex fault zone. Karst features that I have observed outside the mine are characterized by iron oxide fillings, not 

black clays; and they are only slightly radioactive. 

Importance of Leadville Dolomite 

The fact that most of the reserves at the Pitch mine 

occur in the Leadville Dolomite raises a question: Why 

is the Leadville Dolomite important? This question is 

underscored by two other facts: (1) most of the high-grade 

ore at the Pitch mine is in dolomite, and (2) no other 

significant uranium deposit in the United States occurs 

in dolomite. I cannot definitively answer the question, 

but offer the following speculation. 

The Leadville Dolomite is a favored host because 

of its brittle character and structural position, as described 

earlier. The uniformity of die dolomite, with no shale interbeds, and very fine grain size may have made the Leadville section especially susceptible to the pervasive 

fracturing and brecciation needed to prepare ground for 

an economic volume of uranium minerals. 

The Leadville Dolomite is clearly not the only brittle 

host rock. The Little Indian deposit occurs in the Harding Quartzite and partly in dolomites of the Fremont 

Dolomite and Manitou Dolomite, where these rocks are 

fractured. Judging from the drill pattern between the 

Pitch and Little Indian deposits, I infer that other 

uranium zones occur in Paleozoic dolomites along the 

Chester fault, but I do not have specific information to 

evaluate the importance of that resource relative to 

uranium in the Leadville. Precambrian granitic rocks also 

host veins of uranium where fractured. My conclusion 

from these general observations is that several types of 

rocks can host uranium if they fail by brittle fracture. 

Fractured rock alone obviously does not make an 

ore deposit; chemical factors also must be conducive to 

ore deposition. The chemical data show a strong association between sulfur, iron, and uranium in the Pitch 

deposit. The Leadville Dolomite may have been enriched 

in iron and sulfur as FeS2 during diagenesis. The role of 

tidal-flat sedimentation and diagenesis of dolomicrite in 

causing iron and sulfur enrichment were discussed 

elsewhere (Nash, 1979), and no specific conclusions could 

be made because of the paucity of literature on these 

topics. I favor the concept that FeS2 and also organic 

carbon were enriched in the Leadville during tidal-flat 

sedimentation and early diagenesis. This FeS2 and 

organic carbon then would have been available to play 

a direct or indirect role in chemically localizing uranium 

in the Leadville after it was fractured and uranium was 

introduced. 

Uranium Transport and Deposition 

Chemical and petrologic data both indicate a close 

association of uranium with ferrous iron and sulfur. 

Other elements such as lead and molybdenum, enriched 

with uranium, are presumed to have been localized by 

sulfur. The lack of wallrock alteration adjacent to pitchblende in dolomite suggests that the transporting fluids 

were roughly in equilibrium with dolomite and that the 

solutions were not very acidic. The transport of silica 

could have occurred if conditions were more alkaline than 

Interpretation and Discussion 33 
Table 4. Analytical data for host rocks and ores, Little Indian deposit, Colorado 

[Leaders(--), not determined; L, less than value shown in parentheses; N, not detected. Chemical analyses same as for table 1, except first 

14 samples were analyzed by X-ray fluorescence for major elements by J .E. Taggart. Total iron reported as Fe20 3] 

Major elements in weight percent 

Sample No. Sio2 Al203 Fe2o3 MgO CaO K20 Ti02 P2o5 s Stratigraphy 1 

1 7S8-3S3 2.0 .5 .1 0 11.6 33.0 .07 L(.OS) L(l.O) .10 1 

2 7S8-3S9 88.0 3.0 2.7 .30 1. 1 1. 0 .20 L(l.O) .OS 2 

3 758-361 82.0 5.4 3.S .so 1. 2 1.7 .30 1. 0 .07 2 

4 7S8-367 96.0 2.0 1.4 .30 .so .20 L(.OS) 1. 0 .09 2 

s 7S8-377 90.0 2.0 1.6 .30 1. 3 .30 .09 2.0 .10 2 

6 762-428 97.0 1. 0 .06 .10 1(.10) .30 .08 L(l. 0) .07 2 

7 762-S14 S.3 .80 .30 s.o 33.0 .20 L(.OS) L(l.O) • 10 3 

8 726-469 14.0 .80 l.S 8.3 24.0 .20 L(.OS) L(l.O) • 10 

9 77S-360 1.0 L( .OS) .30 s.o 3S.O .03 L(.OS) L(l.O) .1 0 3 

10 77S-371 90.0 2.0 1.0 .10 1.8 .20 .09 2.0 .30 2 

11 775-374 83.0 4.0 3.2 .30 2.0 1. 0 .30 2.0 .30 2 

12 77S-381 94.0 3.0 .30 .30 .so .98 .20 L(l.O) .06 2 

13 77S-409 97.0 2.0 .62 .10 .20 .20 L(.05) L(l.O) .06 2 

14 77S-431 2.0 • 60 .30 8.3 3S.O .10 L(.OS) L(l. 0) .1 0 1 

1S 758-349 2.0 .03 .1 7 20.7 30.3 .14 .02 .01 .02 3 

16 7S8-3S2 2.2 .43 .22 20.6 29.6 .2S .03 .01 .02 3 

17 7S8-3S7 84.3 4.S 2.7 .63 3.0 1. 4 .29 .90 .04 2 

18 7S8-361 83.9 4.7 2.9 .87 2.0 1.S .33 .64 .04 2 

19 7S8-363 9S.O 1.4 .67 .41 1.S .42 .12 .12 .02 2 

Minor elements in parts per million 

Sample No. As Ba Cr Cu Mn Ni Pb Sr u v 

1 7S8-3S3 L(2.0) 2.0 2.0 s.o 1SO.O N 20.0 10.0 13.7 s.o 

2 7S8-3S9 108.0 70. 1S.O so.o 70.0 30.0 100.0 30.0 219.0 70.0 

3 758-361 237.0 100.0 30.0 so.o 30.0 10.0 200.0 150.0 S330.0 100.0 

4 78S-367 2S.O 70.0 1. 0 30.0 10.0 5.0 70.0 so.o 81.4 N 

5 758-377 62.0 50.0 2.0 50.0 3.0 s.o 700.0 30.0 52.4 L 

6 762-428 8.0 20.0 3.0 15.0 s.o s.o 30.0 100.0 10.8 L 

7 762-514 L(2.0) s.o 2.0 3.0 150.0 5.0 10.0 s.o 11.5 N 

8 762-469 308.0 100.0 3.0 7.0 soo.o 200.0 300.0 30.0 73700.0 N 

9 775-360 2.0 2.0 2.0 5.0 300.0 5.0 20.0 7.0 107.0 7.0 

10 77S-371 12.0 30.0 3.0 100.0 20.0 5.0 100.0 1SO.O 216.0 L 

11 77S-374 S2.0 100.0 10.0 100.0 20.0 so.o 200.0 300.0 104.0 20.0 

12 77S-381 2.0 1S.O 15.0 10.0 7.0 s.o 10.0 so.o 8.39 30.0 

13 77S-409 3S.O 70.0 s.o 7.0 so.o 20.0 30.0 10.0 13700.0 30.0 

14 77S-431 1(2.0) s.o 3.0 3.0 300.0 L N 7.0 1S.7 N 

IS 7S8-349 1 s.o 400.0 40.0 89.4 

16 7S8-3S2 3S.O 300.0 S5.0 18.3 

17 7S8-3S7 80.0 1S.O 30.0 80.0 7.0 130.0 346.0 70.0 

18 7S8-361 90.0 20.0 30.0 80.0 7.0 120.0 4800.0 70.0 

19 7S8-363 30.0 3.0 10.0 N 2.0 87.0 807.0 10.0 

1stratigraphy: 1, Manitou Dolomite; 2, Harding Quartzite; 3, Fremont Dolomite. 

34 Pitch Uranium Mine Area, Colorado 
Table 5. Statistical summary of chemical data, Little Indian deposit, Colorado 

Geometric Geometric Valid 

Element Minimum Maximum mean deviation values 

Major elements, in weight percent 

Si02 1.00 97.9 

Al2o3 ·03 5.40 

Fe2o3 .06 3.50 

Feo .04 1. 60 

MgO .41 20.7 

CaO .20 35.0 

Na2o .oo -12 

K2o .Q7 1-70 

H o+ .36 2.10 2 - H2o .os .60 

Ti02 .02 .33 

P2os ·01 2.00 

MnO .oo .os Co2 .Q2 47.0 

F .Q2 .40 

s .Q2 .30 

Minor elements, 

Ag(s) 2. 10. 

B(s) 20. 150. 

Ba(s) 2. 100. 

Be(s) 1. 5 3. 

Co(s) s. 100. 

Cr(s) 1. 30. 

Cu( s) 3. 100. 

Mn(s) 3. soo. 

Ni(s) 2. 200. 

Pb(s) 1 o. 700. 

V(s) s. 100. 

Zr( s) 100. soo. 

As 2.0 308. 

Cl 25. 365. 

Ba 15. 90. 

Hg .10 .39 

Mo .s 4.5 

Pb s. 130. 

Sr 35. 150. 

Zn s. 220. 

u 8.39 73700. 

pH 9, and deposition could have occurred upon neutralization by carbonate rocks. However, deposition of silica 

more commonly occurs in response to cooling (Holland 

and Malinin, 1979). The transport of silica is quite unlike 

the transport of uranium because the anionic complexes 

that carry uranium are not effective for silica. The 

association of uranium with FeS2, in particular with 

marcasite, yields the greatest amount of information on 

conditions of uranium transport and deposition. 

Research by Goldhaber and Reynol<fs has documented the important role of marcasite in roll-type 

uranium deposits (Goldhaber and others, 1978; Goldhaber and Reynolds, 1979; Reynolds and Goldhaber, 

58.35 42.9 19 

2-12 1.63 18 

1.24 1-19 19 

.096 .061 5 

8.64 10.9 5 

13. OS 15.3 18 

.046 .045 5 

.s6 .54 18 

1.14 • 81 5 

.28 .21 5 

.17 .11 12 

.97 .81 10 

.022 .022 5 

18.6 25.5 5 

.15 .17 5 

.092 .079 19 

in parts per million 

s.s 3.31 4 

58.9 43.1 9 

45.6 38.8 14 

2.20 .76 5 

32.5 45.2 4 

78.8 8.31 17 

29.7 31.4 17 

us. 4 151.4 14 

24. 1 50.3 15 

137.7 191.7 13 

41.2 33.5 10 

253.8 124.9 13 

77.4 102.7 11 

161. 186.2 5 

50.0 32.9 5 

.026 .011 5 

2.02 1.95 5 

69.4 60.9 5 

n. o 47.0 5 

79.0 87.9 5 

5243.0 16913. 19 

1983). Marcasite also is closely associated with pitchblende in the hardrock deposit at the Midnite mine, 

Washington (Ludwig and others, 1981). Experimental, 

isotopic, and paragenetic data on marcasite strongly support the hypothesis of formation from metastable sulfur 

oxyanions such as thiosulfate (Granger and Warren, 

1969; Goldhaber and Reynolds, 1979). An important 

property of these sulfur oxyanions is that they spontaneously break down into sulfide and sulfate ions; sulfide 

ion so generated is an excellent reductant. and also would 

be present to form FeS2 • Mechanisms described by 

Granger and Warren and by Goldhaber and Reynolds 

seem appropriate for the Pitch mine. First, pre-ore 

Interpretation and Discussion 35 
sulfides in the Leadville Dolomite and in the Belden Formation were oxidized, possibly by uranium bearing solutions, in the near-surface environment. Oxidation of 

pre-ore pyrite created thiosulfate or similar ions that 

moved down the hydraulic gradient of the Chester fault 

zone where they disproportionated and caused reduction 

of uranyl ions. Additional reduction could have been 

caused by bacterial sulfate ions. Sulfur isotope analyses 

of marcasite could place constraints on the sulfur cycle 

and substantiate which reduction mechanism was active. 

(See Reynolds and others, 1982, for details.) 

The low uranium content of most pyritic Belden 

sandstones is not easily explained. Low permeability 

caused by high clay content may explain why some 

localities are barren. Other localities adjacent to faults 

and ore-grade dolomite breccia are especially puzzling. 

One possible explanation is that the pyrite in these sandstones was nonreactive under reducing conditions, thus 

did not provide sulfur oxyanions capable of reducing 

uranium. Partial oxidation of pyrite creates reactive 

sulfur species capable of reducing uranium (Granger and 

Warren, 1969). 

Resource Implications 

The Pitch deposit, as understood from drilling and 

mining over the past ten years, constitutes a ''new'' type 

of deposit with the potential to carry significant resources 

in other areas. A somewhat similar deposit occurs at Copper Mountain, WY. (Yellich and others, 1978), and exploration possibilities along Laramide upthrusts of 

Colorado have been reviewed by Nash (1980). For 

regional-scale exploration and resource assessment, the 

key factors are presence of a major structure, such as an 

upthrust; brittle rocks; a potential source of uranium, 

such as altered tuffaceous rocks; and a reductant, generally not known from surface exposures. 

A grade and tonnage model based on one deposit 

is not reliable, but for this deposit, structural control is 

so strong that good estimates can be extrapolated from 

structural information. The following comments are 

based on the announced reserve of 3,245,000 kg U3 0 8 at 

an average grade of 0.17 percentU3 0 8 (Ward, 1978), my 

logging of drill core, and my observations on drilling patterns in the Pitch mine area. The geometry of the deposit 

is shown on figure 2. More generally, without regard to 

economic factors, the resource zone along the Chester 

fault zone is roughly 100 m wide, 200 or more meters 

deep, and at least 3 km long. Important parts of the Pitch 

deposit (brecciated dolomite) contain more than 0.2 percent U3 0 8 , but there are also large volumes of slightly 

brecciated rock (granite, siltstone, sandstone, carbonaceous shale) with grades in the range 0.02-0.10 percent. 

Extensive development drilling of the Copper Mountain 

deposit also indicates major amounts of low-grade (<0.05 

36 Pitch Uranium Mine Area, Colorado 

percent U3 0 8) mineralization. It is thus known that this 

type of deposit contains both high grade and low grade 

zones of uranium which can only be evaluated by careful 

drilling. The Pitch and Copper Mountain deposits are 

assumed to be relatively large examples of their type. 

Judging from the volume of favorably prepared rocks at 

the Pitch deposits and the known large size of other upthrust zones, a rough estimate of potential resources in 

one of these deposits is in the 10,000 to 30,000 tonnes 

U3 0 8 range, only part of which would ever be economic 

to recover, if found. 

SUMMARY: GENETIC MODEL 

Information presented in this paper is consistent 

with, but does not prove, a near-surface genesis for the 

Pitch uranium deposit in the Oligocene(?), shortly after 

volcanism. The following discussion and speculation are 

directed to the Pitch deposit, but may be pertinent to the 

Little Indian deposit also. Preparation for ore emplacement included sedimentation and diagenesis of brittle 

rocks, some containing diagenetic pyrite, and brecciation 

in the Laramide along the Chester fault. The uranium 

deposits are conclusively post-Chester fault as the structural permeability along that fault zone is a key ore control. A post-volcanic Oligocene(?) age is postulated for 

the following model. 

Uranium Source 

Quartz latite welded tuff of Oligocene(?) age containing pumice and glass was deposited above the Chester 

fault. This unit, and other volcanics, were probably several hundred meters thick; thin relicts are exposed between 

the Pitch and Little Indian mines (Olson, 1983). These 

tuffs would have been highly reactive shortly after deposition and would have undergone reactions similar to those 

described by Zielinski (1981). This alteration of volcanic 

rocks is believed to have been the source of silica to form 

the jasperoid along the Chester fault in brecciated carbonate rocks below the volcanic pile. Volcanic rocks within 

10 km of the Pitch mine are more radioactive today than 

other rocks, such as Precambrian granite; and freshest 

samples contain an average of 10.5 ppm uranium and 

35.2 ppm thorium (two freshest samples). This most 

radioactive volcanic unit is the Rowley Andesite; it is not 

exposed along the Chester fault but is stratigraphically 

younger than the quartz latite tuff. The quartz latite is 

more silicic than the Rowley Andesite2, thus it quite possibly contained more uranium, particularly before 

alteration. 

2Chemical analysis (J. T. Nash, unpub. data, 1980) of two samples 

of Rowley Andesite shows an average of 64.6 percent Si02, 4.1 percent 

Na2

0, and 5.3 percent K20 which suggest the unit sampled is a highpotassium dacite. 
Paleohydrology 

In the Oligocene(?), the Pitch mine area was 

beneath a volcanic trough and about 600 m above the 

Marshall Creek paleovalley (Olson, 1983). Some lakes 

probably existed at times and were filled by tuffaceous 

rocks. Ground water in the Pitch mine probably flowed 

southward along the Chester fault toward Marshall 

Creek, beneath a cover of volcanic rocks. Volcanism in 

the area would probably have heated the ground water, 

possibly to 50-75 °C. At a depth of a few hundred meters, 

in a permeable fault zone, the ground water probably 

would have been oxygenated or partially oxygenated. 

Conditions would have been excellent for uranium 

transport. 

Uranium Deposition 

Laterally or downward moving fluids carrying 

uranium, molybdenum, silicon and possibly sulfur oxyanions (Reynolds and others, 1982) deposited uranium 

and silica when they encountered structurally prepared 

traps that promoted reducing conditions. Reduction could 

have been caused by sulfate-reducing bacteria or by 

disproportionation of sulfur oxyanions in the fluid that 

transported uranium. Silica is not responsive to reduction, but possibly it precipitated in response to cooling 

(Holland and Malinen, 1979). There are no criteria to 

define temperature, but presumably it was below 100 °C 

at the postulated shallow level. 

The essential ingredients are postulated as upthrust 

faulting and brecciation, brittle rocks containing pyrite, 

and a volcanic source containing leachable uranium. 

Details of the ore-forming process need refining, but the 

proposed, largely empirical model can expedite uranium 

exploration. 

RE FE RE NCES CITED 

Banks, N.G., 1970, Nature and origin of early and late cherts 

in the Leadville Limestone, Colorado: Geological Society 

of America Bulletin, v. 81, p. 3033-3048. 

Berg, R.R., 1962, Mountain flank thrusting in Rocky Mountain foreland, Wyoming and Colorado: American Association of Petroleum Geologists Bulletin, v. 46, p. 2019-2032. 

Campbell, J.A., 1970, Petrology of Devonian shelf carbonates 

of west central Colorado: Mountain Geologist, v. 7, 

p. 89-97. 

David, Michael, Dagbert, Michel, and Beauchemin, Yves, 1977, 

Statistical analysis in geology-Correspondence analysis 

method: Colorado School of Mines Quarterly v. 72, no. 

1, 60 p. 

Davis, J.C., 1973, Statistics and data analysis in geology: John 

Wiley and Sons, 550 p. 

DeVoto, R.H., 1980, Mississippian stratigraphy and history of 

Colorado; in Kent, H.C. and Porter, K.W., eds., Colorado 

geology: Denver, Rocky Mountain Association of Geologists, p. 57-70. 

Dixon, W.J., and Massey, F.J., Jr., 1957, Introduction to 

statistical analyses: New York, McGraw-Hill, 488 p. 

Dunham, R.J., 1962, Classification of carbonate rocks according to depositional texture; in Ham, W.E., ed., Classification of carbonate rocks: American Association of 

Petroleum Geologists Memoir 1, p. 108-121. 

Dupree, J.A., and Maslyn, R.M., 1979, Paleokarst controls on 

localization of uranium at Pitch mine, Sa watch Range, Colorado [abs.]: American Association of Petroleum 

Geologists Bulletin, v. 63, no. 5, p. 826. 

Folk, R.L., 1962, Spectral subdivision of limestone types; in 

Ham, W.E., ed., Classification of carbonate rocks: 

American Association of Petroleum Geologists Memoir 1, 

p. 62-84. 

Friedman, M., and others, 1976, Faulted drape folds in 

multilithologic layered specimens; Pt. 3 of Experimental 

folding of rocks under confinine pressure: Geological Society of America Bulletin, v. 87, p. 1049-1066. 

Goldhaber, M.B., and Reynolds, R.L., 1979, Origin of marcasite and implications regarding the genesis of roll-type 

uranium deposits: U.S. Geological Survey Open-File 

Report 79-1696, 40 p. 

Goldhaber, M.B., Reynolds, R.L., and Rye, R.O., 1978, Origin 

of a south Texas roll-type uranium deposit; II, Sulfide 

petrology and sulfur isotope studies: Economic Geology, 

v. 73, p. 1690-1705. 

Granger, H.C., and Warren, C.G., 1969, Unstable sulfur compounds and the origin of roll-type uranium deposits: 

Economic Geology, v. 64, p. 160-171. 

Gross, E.B., 1965, A unique occurrence of uranium minerals, 

Marshall Pass, Saguache County, Colorado: American 

Mineralogist, v. 50, p. 909-923. 

Holland, H.D., and Malinin, S.D., 1979, The solubility and 

occurrence of non- ore minerals; in Barnes, H.L., ed., 

Geochemistry of hydrothermal ore deposits (2d ed.): New 

York, John Wiley and Sons, p. 461-508. 

Lovering, T.G., 1972, Jasperoid in the United States-Its 

characteristics, origin, and economic significance: U.S. 

Geological Survey Professional Paper 710, 164 p. 

Ludwig, K.R., Nash, J.T., and Naeser, C.W., 1981, U-Pb 

isotope systematics and age of uranium mineralization, 

Midnite mine, Washington: Economic Geology, v. 76, 

p. 89-110. 

Malan, R.C., 1959, Geology and uranium deposits of the Marshall Pass district, Gunnison, Saguache, and Chaffee Counties, Colorado: Denver, Colorado Mining Association, 

National Western Mining Conference, p. 1-20. 

Nash, J.T., 1979, Geology, petrology, and chemistry of the 

Leadville Dolomite-Host for uranium at the Pitch mine, 

Saguache County, Colorado: U.S. Geological Survey 

Open-File Report 79-1566, 51 p. 

___ 1980, Supergene uranium deposits in brecciated zones 

of Laramide upthrusts-Concepts and applications: U.S. 

Geological Survey Open-File Report 80-385, 36 p. 

Natrella, M.G., 1963, Experimental statistics: U.S. Bureau of 

Standards Handbook 91, p. 36-37. 

Olson, J .C., 1983, Geologic and structural maps and sections 

of the Marshall Pass mining district, Saguache, Gunnison, 

References Cited 37 
and Chaffee Counties, Colorado: U.S. Geological Survey 

Map 1-1425, scale 1:24,000. 

Phair, George, and Levine, Harry, 1954, Notes on the differential leaching of uranium, radium, and lead from pitchblende in H2S04 solutions: Economic Geology, v. 48, 

p. 358-369. 

Reynolds, R.L. and Goldhaber, M.B., 1983, Iron disulfide 

minerals and the genesis of roll-type uranium deposits: 

Economic Geology, v. 78, p. 105-120. 

Reynolds, R.L., Goldhaber, M.B., and Carpenter, D.S., 1982, 

Biogenic and non- biogenic ore-forming processes in the 

south Texas uranium district- Evidence from the Panna 

Maria deposit: Economic Geology, v. 77, p. 541-556. 

Shapiro, Leonard, 1975, Rapid analysis of silicate, carbonate, 

and phosphate rocks (revised ed.): U.S. Geological Survey 

Bulletin 1401, 76 p. 

Stearns, D.W., 1978, Faulting and forced folding in the Rocky 

Mountains foreland; in Matthews, Vincent, III, ed., 

Folding associated with basement block faulting in the 

western United States: Geological Society of America 

Memoir 151, p. 1-~8. 

Tweto, Ogden, Steven, T.A., Hail, W.J., Jr., and Moench, 

R.H., 1976, Preliminary geologic map of the Montrose 

38 Pitch Uranium Mine Area, Colorado 

1 °X2°quadrangle, southwestern Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-761, 1 

sheet, scale 1:250,000. 

Ward, J .M., 1978, History and geology of Homestake's Pitch 

project, Saguache County, Colorado [abs.]: American Institute of Mining, Metallurgical, and Petroleum Engineers, 

Program of the 1 07th annual meeting, Denver, Colorado, 

February 26-March 2, 1978. 

Wise, D.U., 1963, Keystone faulting and gravity sliding driven 

by basement uplift of Owl Creek Mountains, Wyoming: 

American Association of Petroleum Geologists Bulletin, 

v. 47, p. 586-598. 

Yellich, J.A., Kramer, R.T., and Kendall, R.G., 1978, Copper Mountain, Wyoming, uranium deposit-Rediscovered: 

Wyoming Geological Association Guidebook, 30th annual 

field conference, p. 311-327. 

Zielinski, R.A., 1981, Experimental leaching of volcanic glassImplications for evaluation of glassy volcanic rocks as 

sources of uranium; in Goodell, P. C. and Waters, A. C., 

eds., Uranium in volcanic and volcaniclastic rocks: 

American Association of Petroleum Geologists Studies in 

Geology, no. 13, p. 1-11. 

* U.S. GPO: 1989 673-Q47 /86,070 


SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly) .. 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Reports 

Professional Papers are mainly comprehensive scientific reports of 

wide and lasting interest and importance to professional scientists and engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic. 

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the results 

of resource studies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic. 

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrogeology, 

availability of water, quality of water, and use of water. 

Ch'culars present administrative information or important scientific 

information of wide popular interest in a format designed for distribution 

at no cost to the public. Information is usually of short-term interest. 

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS publications series. Copies are reproduced on request unlike formal USGS 

publications, and they are also available for public inspection at 

depositories indicated in USGS catalogs. 

Open-Flle Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at 

depositories. They are a nonpermanent form of publication that may be 

cited in other publications as sources of information. 

Maps 

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 7 1/2- or 15-minute quadrangle formats (scales mainly 1 :24,000 or 1 :62,500) showing bedrock. surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only. 

Geophysical Investigations Maps are on topographic or planimetric 

bases at various scales; they show results of surveys using geophysical 

techniques, such as gravity, magnetic, seismic, or radioactivity, which 

reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology. 

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photo geologic maps on planimetric bases 

which show geology as interpreted from aerial photographs. Series also 

includes maps of Mars and the Moon. 

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource areas. 

Oil and Gas Investigations Charts show stratigraphic information 

for certain oil and gas fields and other areas having petroleum potential. 

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic dataofboth regular and irregular areas; principal scale 

is 1:24,000 and regional studies are at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

the conditions indicated below from the U.S. Geological Survey, Books 

and Open-File Reports Section, Federal Center, Box 25425, Denver, 

CO 80225. (See latest Price and Availability List) 

"Publications of the Geological Survey, 1879- 1961" may be purchased by mail and over the counter in paperbaek book form and as a 

set of microfiche. 

"Publications of the Geological Survey, 1962- 1970" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche. 

"Publications ofthe U.S. Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche. 

Supplements for 1982,1983, 1984, 1985,1986, andforsubse~uent 

years since the last permanent catalog may be purchased by mml and 

over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State}," may be purchased by mail 

and over the counter in paperback booklet form only 

"Price and A vallability List of U.S. Geological Survey Publications," issued aJUlually, is available free of charge in paperback booklet form only. 

Selected copies of a monthly catalog "New Publications of the U.S. 

Geological Survey" available free of charge by mail or may be obtained 

over the coun~ in paperback booklet form only. Those wishing a free 

subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 

National Center, Reston, VA 22092. 

Note.--Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect Therefore, the 

prices charged may differ from the prices in catalogs, announcements, 

and publications.