Uranium-Bearing NickelCobalt-Native Silver 

Deposits, Black Hawk 

District, Grant County 

New Mexico

GEOLOGICAL SURVEY BULLETIN 1009- It

This report concerns work done on behalf 

of the 17. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

T 

L

A CONTRIBUTION TO THE GEOLOGY OF

URANIUM

THE URANIUM-BEARING NICKEL-COBALT-NATIVE

SILVER DEPOSITS IN THE BLACK HAWK DISTRICT,

GRANT COUNTY, NEW MEXICO

By ELLIOT GILLERMAN and DONALD H. WHITEBREAD

ABSTRACT

The Black Hawk (Bullard Peak) district, Grant County, N. Mex., is 21 miles 

by road west of Silver City. From 1881 to 1893 high-grade silver ore valued at 

more than one million dollars is reported to have been shipped from the district. 

Since 1893, there has been no mining in the district except during a short period in 

1917 when the Black Hawk mine was unwatered and reopened.

Pre-Cambrian quartz diorite gneiss, which intrudes quartzite, schist, monsonite, 

and quartz monzonite, is the most widespread rock in the district. The quartz 

diorite gneiss is intruded by many pre-Cambrian and younger rocks, including 

diorite, granite, diabase, monzonite porphyry, and andesite, and is overlain by the 

Upper(?) Cretaceous Beartooth quartzite. The monzonite porphyry, probably 

of Late Cretaceous or early Tertiary age, forms a small stock along the northwestern edge of the district and many dikes and irregular masses throughout the 

district.

The ore deposits are in fissue veins that contain silver, nickel, cobalt, and 

uranium minerals. The ore minerals, which include native silver, argentite, 

niccolite, millerite, skutterudite, nickel skutterudite, bismuthinite, pitchblende, 

and sphalerite, are in a carbonate gangue in narrow, persistent veins, most of 

which trend northeast. Pitchblende has been identified in the Black Hawk and 

the Alhambra deposits and unidentified radioactive minerals were found at five 

other localities. The deposits that contain the radioactive minerals constitute a 

belt 600 to 1,500 feet wide that trends about N. 45° E. and is approximately 

parallel to the southeastern boundary of the monzonite porphyry stock. All the 

major ore deposits are in the quartz diorite gneiss close to the monzonite porphyry.

The ore deposits are similar to the deposits at Great Bear Lake, Canada, and 

Joachimsthal, Czechoslovakia.

INTRODUCTION

Mining began in the Black Hawk (Bullard Peak) district in 1881 

when high-grade silver ore was found at the Alhambra mine. Most of 

the silver produced was native silver associated with nickel and 

cobalt arsenides and sulfides. In 1920 pitchblende was recognized

283
284 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

on the dumps of some of the old mines, and since 1949 the district 

has been of interest as a possible source of uranium, nickel, and 

cobalt ores.

LOCATION, ACCESSIBILITY, AND CLIMATE

The Black Hawk mining district is mostly in sees. 20, 21, 22, 28, 

and 29, T. 18 S., R. 16 W., in Grant County, N. Mex. (fig. 44), and is 

21 miles by road west of Silver City, the terminus of a branch line of 

the Atchison, Topeka and Santa Fe Railway.

The district is in the northeastern foothills of the Big Burro Mountains at an altitude of 5,450 to 6,150 feet. Scattered junipers, scrub 

oak, small pines, and brush cover the hillsides, but no trees suitable for 

use in mining are present. Most of the district is drained by way of

Black Hawk Canyon which bisects the area and flows northward to

Mangas Creek, but the eastern part is drained by tributaries of Silver 

Dale Creek, which flows northeastward to Mangas Creek. Mangas 

Creek flows into the Gila River about 9 miles northwest of the mouth 

of Black Hawk Canyon. All the streams, except the Gila River, are 

intermittent. Annual precipitation at Silver City is about 16 inches, 

most of which comes as heavy thundershowers in July, August, and 

September.

SCOPE AND PURPOSE OF WORK

Fieldwork in the Black Hawk district was done by the writers as 

part ofc the program for investigation of radioactive minerals by the

U. S. Geological Survey on behalf of the Division of Raw Materials of 

the U. S. Atomic Energy Commission. A preliminary reconnaissance

confirmed the presence of radioactive minerals in the district (H. C. 

Granger, written communication). Additional examinations of mine

dumps, pits, and. shafts for radioactivity by A. J. Gu.de 3d, and

Elliot Gillerman during the spring of 1951 resulted in the finding of

small quantities of pitchblende on the dumps of the Black Hawk

and Alhambra mines. About 4 months were spent in the field on the 

present study which was begun in December 1951. The investigations consisted principally of geologic mapping of an area of about

2^ square miles at a scale of 1:6,000. Detailed surface maps of the

Black Hawk and Alhambra mines at a scale of 1:1,200 -were made by

plane table and alidade,

ACKNOWLEDGMENTS

Mr, Ira L, Tfrignt, aeneral Manager or the BiacK nawK consolidated Mines Co., and Mr. and Mrs. A. A. Leach, owners of the 

Alhambra group of claims, made available to the writers old maps and 

reports of the mines in the district and also specimens of ore taken
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 285 

R.I7W. 16 15 R.14W.

30' 21

108°30'

5 Miles

FIOURE 44. Index map showing the location of the Black Hawk raining district, Grant County, N. Mox.

from the Black Hawk and Alhambra mines. Chemical analyses 

were made by the New Mexico Minerals Laboratory of Silver City, 

N. Mex.

OWNERSHIP

The principal deposits in the district are covered by patented claims. 

The Black Hawk group, owned by the Black Hawk Consolidated
286 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Mines Co., Milwaukee, Wis., consists of the Black Hawk, Silver 

Glance, Surprise, Kent County, Little Rhody, Chicago, and Extension 

patented claims. The Alhambra group, owned by Albert A. and 

and Frances I. Leach of Lordsburg, N. Mex., consists of the Alhambra 

and Good Hope patented claims and the Silver King (Hobson) unpatented claim. The Rose claim is owned by Mrs. Elizabeth J. 

McCabe, Pasadena, Calif., and Elizabeth C. (Mrs. William Howard) 

Meade, San Francisco, Calif. The ownership of some of the claims 

in the district is not known.

HISTORY AND PRODUCTION

In 1881 float of high-grade silver ore was found at the Alhambra 

mine, and subsequent prospecting soon resulted in the discovery of 

the Black Hawk, Rose, Silver King (Hobson), Good Hope, and Other 

deposits. Mining began in the district in 1881 and continued until 

1893, when a decline in the price of silver and the depletion of the 

rich silver ore caused the mines to be closed. Nearly all the ore 

produced had a high silver content, and shipments of ore assaying as 

much as 15,000 ounces of silver per ton are reported (Jones, 1904, 

p. 55).

In 1917, when a new owner acquired the property, the Black Hawk 

mine was unwatered and opened to the lowermost levels, where 

undeveloped high-grade ore was reported (W. R. Storms, written 

communication). Some drifting was done on the upper levels to 

search for an ore body that had not been developed during the earlier 

operations. W. H. Weed, (written communication), consulting 

geologist, and A. A. Leach (written, communication), then geologist 

for Phelps Dodge Corporation at Tyrone, N. Mex., examined the 

mine and recommended further work. Shortly thereafter, all work 

ceased. In 1917 there was also a short-lived interest in some of the 

smaller properties in the eastern part of the district. The district 

has been idle since 1917.

Because of the need for additional nickel, cobalt, and uranium, 

interest in the district was revived in 1949. In the spring of 1952

a Government exploration loan was granted to the Black Hawk

Consolidated Mines Co. to explore the Black Hawk mine, and three

diamond core-drill holes were completed by November 1952. The 

three holes were drilled to a depth oi 1,000 leet; iioio 3 imiorSo«to,i

sparse ore minerals in carbonate gangue, btlt the OtheP tWO uOlGS

were barren.

Xhe Silver production fzom tKe district. l>eforo isoa Is estimated to

have been between $1,000,000 and $1,500,000 (LffldgM, GratOIl; and 

Gordon, 1910, p. 324; Leach, A. A., 1916). The Black Hawk mine is 

reported to have yielded $600,000 to $650,000 (Jones, 1904, p. 55;
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 287

Leach, 1916); the Alhambra mine about $400,000 (A. A. Leach written 

communication); the Rose mine about $140,000; and the Silver King 

> (Hobson) about $40,000 (A. A. Leach written communication). The 

remainder of the production came from the Good Hope and other 

properties.

GEOLOGY

 The Black Hawk district is within the pre-Cambrian Burro MounA tains batholith, which is exposed over an area of about 400 square 

miles in southwestern Grant County. The batholith is a composite 

body made up chiefly of granite with inclusions of gneiss, schist, 

quartzite, and intrusive rocks. Many stocks and dikes intrude the 

batholith. 

s The predominant rock in the Black Hawk district is pre-Cambrian

^ quartz diorite gneiss part of the batholith that intrudes quartzite, 

schist, monzonite, and quartz monzonite. These rocks are cut by 

many igneous rocks of pre-Cambrian and younger age, the most 

common of which is monzonite porphyry of probable Late Cretaceous 

or early Tertiary age. The Beartooth quartzite of Late(?) Cretaceous 

age overlies the pre-Cambrian rocks. Many faults, most of which

i trend northeast, cut the rocks of the district.

The ore deposits are in fissure veins that are most commonly in the 

quartz diorite gneiss. Native silver is the major ore mineral and is 

associated with nickel and cobalt arsenides and sulfides in a carbonate 

gangue. Pitchblende, associated with the silver, nickel, and cobalt 

minerals, has been identified from the Black Hawk and Alhambra 

mines. The metalliferous deposits are spatially related to the monzonite porphyry and are considered Tertiary in age.

* The rock units and their relationships to one another are shown 

on the geologic map (pi. 14).

IGNEOUS AND METAMORPHIC ROCKS

"* QUARTZITE AND SCHIST

"* Pre-Cambrian quartzite, schist, and other metamorphic rocks are 

shown on the geologic map (pi. 14) as quartzite and schist. These 

rocks form two broad irregular east-trending bands in the southwestern 

part and small isolated patches throughout the southern part of the 

mapped area. The beds strike N. 40° W. to west and dip 37°-64° 

NE. at most places; but locally, near the western edge of the mapped

4 area, they strike N. 50°-65° E. and dip 62° NW. The quartzite is a 

thin-bedded, fine-grained, gray to buff rock consisting mostly of 

angular quartz grains and a few flakes of mica and grains of magnetite. 

Thin mica schist layers that contain some magnetite and quartz,

353745 56 2
288 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

amphibolite, and knotted schist are associated with the quartzite. 

Epidote is present locally in the schist and amphibolite.

MONZONTTE AND QUARTZ MONZONTTE

A rock of monzonitic and quartz monzonitic composition is exposed 

over a wide area in the southeastern part of the mapped area (pi. 14). 

This rock is predominantly homogeneous, fine grained, and equigranular, but near its contact with the quartz diorite gneiss it commonly has a porphyritic texture with phenocrysts of orthoclase as 

much as an inch in diameter. This porphyritic texture is especially 

well developed in areas where there has been lit-par-lit injection of 

gneissic material. Foliation is obscure, but a layering that possibly 

represents relict bedding is present locally. This layering suggests 

that the rocks designated in this report as "monzonite and quartz 

monzonite" may be migmatized sedimentary rocks.

The monzonite and quartz monzonite consist essentially of freshlooking pink and white feldspars, biotite, and hornblende. Some 

quartz is present in places and epidote occurs sparsely.

The age relationships of the monzonite and quartz monzonite to the 

quartzite and schist are unknown; these rocks are found in contact at 

only two localities and the relations at these places are obscure. The 

monzonite and quartz monzonite are cut by the quartz diorite gneiss.

QUARTZ DIORITE GNEISS

Quartz diorite gneiss of pre-Cambrian age constitutes the country 

rock in most of the district (pi. 14). The gneiss is a widespread phase 

of the Burro Mountains batholith and intrudes the quartzite, schist,

monzonite, and quartz monzonite. About equal amounts of plagioclase and biotite comprise 85 to 90 percent of the rock mass. The 

plagioclase is white to pinkish gray and appears to be andesine. It 

OCClirS mostly as anhedral grains averaging 2 centimeters in length, but

subhedral to euhedral crystals as much as 2 inches in length are

common as phenocrysts elongated parallel to the foliation. The 

feldspar is slightly altered to sericite in places. The biotite occurs as 

aggregates of small flakes between the feldspar grains, and some of it

is altered to chlorite. Anhedral quartz, which makes up 5 to 10 percent of the rock, occurs with the biotite, and orthoclase is present in

minor amounts. Hornblende crystals as much as 2 centimeters in

length constitute 2 to 3 percent of the rock, and is found chiefly in the 

biotite aggregates. Zircon and magnetite are present, and some epidote is associated witn tne magnetite,

Both the individual flakes, and the aggregates of biotite are oriented
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 289

parallel or subparallel to the foliation of the rock. The long axes of 

the hornblende crystals are oriented parallel to the foliation but there 

is no preferred linear orientation.

The gneissic structure, believed to be a primary flow structure, 

strikes northeast and dips steeply northwest except in the southeastern part of the mapped area and in areas contiguous to the older 

rocks, where there are local variations from the regional trend (pi. 14).

BIOTITE-QUARTZ DIORITE

Two small masses of biotite quartz diorite crop out along the southern 

edge of the district (pi. 14). The rock differs from the quartz diorite 

gneiss in the following respects: it contains more biotite; it does not 

contain large feldspar phenocrysts; and it has a less pronounced 

gneissic structure. The contacts of the rock with both the quartz 

diorite gneiss and the diorite are obscured by surficial material, and 

the age relations are unknown.

DIORITE

Many small, irregular bodies of diorite have been mapped in the 

southern part of the district (pi. 14). The diorite is a course-grained, 

dark-green to black rock with a characteristic greenish-brown and 

white mottled weathered surface. It consists predominately of 

chloritized biotite and hornblende, anhedral grains of plagioclase 

feldspar, and minor amounts of quartz.

The diorite intrudes the quartzite and schist; also it probably intrudes the quartz diorite gneiss and the biotite quartz diorite, but 

conclusive evidence of an intrusive relation is lacking. At an excellent exposure of the diorite and the quartz diorite gneiss in Black 

Hawk Canyon, slightly more than half a mile southwest of the Black 

Hawk shaft, the diorite appears to intrude the quartz diorite gneiss. 

The age relations, however, are partly obscured by pegmatite dikes 

that have been emplaced along the contact.

SYENITE

Seven small bodies of syenite that range in size from short dikes 

20 to 75 feet wide to masses about 200 feet wide and 450 feet long 

are present about 2,000 feet southeast of the Black Hawk mine (pi. 14). 

The syenite is a medium-grained equigranular brown rock that consisted originally of pink orthoclase feldspar and biotite, but which now 

is highly altered. The biotite commonly is altered to a brown 

limonitic powder and the feldspar is kaolinized. The syenite is intruded by the granite; it intrudes the quartz diorite gneiss, but its 

age in relation to the other pre-Cambrian rocks" is unknown.
290 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

GRANITE

Many irregular bodies and dikes of granite intrude all the older 

rocks throughout the mapped area (pi. 14). The rock is similar to 

the granite that forms the main mass of the Big Burro Mountains 

to the south and constitutes most of the Burro Mountains batholith. 

The granite is a fine- to medium-grained, equigranular, pink rock 

that consists of quartz, orthoclase, and small amounts of plagioclase 

and biotite; apatite, sphene, and an unidentified mineral are minor 

constituents. Many pegmatite and aplite dikes cut the granite and 

the older rocks.

DIABASE ANT) BASALT PORPHYRY

Many diabase dikes have been mapped in the southern part of the 

district (pi. 14). These dikes, generally less than 25 feet wide, trend 

northwestward in most places. A basalt porphyry dike, exposed 

intermittently from near the center of the western edge of the mapped 

area to the southeast corner, has not been distinguished from the 

diabase dikes on the map (pi. 14). A few diabase dikes are present in 

the northern part of the district. The diabase is a fine-grained, darkgray rock that contains laths of plagioclase in a matrix of pyroxene and 

magnetite. The basalt porphyry consists of a dark-gray, fine-grained, 

equigranular groundmass of pyroxene, plagioclase feldspar, biotite, 

and phenocrysts of light-gray feldspar as much as 0.5 centimeter in 

diameter. The phenocrysts constitute from 10 to 15 percent of the 

rock.

RJHYOLITE

A white chalky-appearing, fine-grained rhyolite dike that ranges 

from 5 to 25 feet in width crops out intermittently from east to west

across the mapped area, about midway between the northern and 

southern boundaries (pi. 14). The dike is texturally similar to aplite,

and has a chilled border facies. The rock consists mostly of feldspar,

with some quartz and a few flakes of mica.

Small masses of quartz monzonite have been mapped along the

northern edge of the district and near the southwestern corner (pi, li),

Ttie quartz monzonite in tne northern part is fine-grained, equigranular, and gray, and consists predominantly of white and gray

subhedral feldspar with subordinate quartz and altered euhedral books

of biotite. Hornblende is sparse to absent. The rock in the southern 

part of 'the mapped area'pontains more hornblende. The two types of

quartzVonzonite have not been distinguished on the map. Dikes ol 

monzonite porphyry cut both types of quartz monzonite.
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 291 

MONZONITE PORPHYRY

Monzonite porphyry, the second most abundant rock in the Black 

Hawk district, is present as a stocklike mass in the northwestern part 

of the area and as dikes and irregular masses throughout the rest of the 

area (pi. 14). The rock consists of a grayish-white fine-grained 

groundmass with abundant white anhedral to subhedral feldspar 

crystals as much as 0.5 centimeter in diameter, and black hornblende 

needles as long as 1 centimeter. Small amounts of biotite are present 

in some places; quartz is rare. Locally the long axes of hornblende 

needles are alined to produce a linear structure. In the dikes the 

groundmass is mostly aphanitic, and the feldspar forms conspicuous 

phenocrysts.

In altered monzonite porphyry the groundmass is aphanitic, the 

feldspars are soft and earthy; and the hornblende is chloritized, 

epidotized, or converted to an iron-stained clay. Pyrite, in places 

altered to limonite, is common in the altered monzonite porphyry 

between Black Hawk Canyon and the Silver King mine. The altered 

rock is greenish gray, light gray to white, or reddish brown.

The monzonite porphyry is considered early Tertiary or Late 

Cretaceous in age on the basis of correlation with lithologically similar 

stocks in the Silver City area. No intrusive relations with the 

Beartooth quartzite were observed in the vicinity of the Black Hawk 

district, but some of the other stocks intrude the Upper(?) Cretaceous 

Beartooth quartzite and Colorado shale of Late Cretaceous age. 

Eight or more similar stocks of monzonite, quartz monzonite, and 

granodiorite are known in the Silver City area. All are considered 

early Tertiary or Late Cretaceous in age (Paige, 1916).

The monzonite porphyry stock, known as the Twin Peaks stock, is 

topographically higher than the surrounding country and constitutes 

the high peaks called Twin Peaks (pi. 14).

QUARTZ DIORITE

Several easterly trending dikes of quartz diorite have been mapped 

in the northeastern part of the district (pi. 14). The rock is fine 

grained, equigranular, brown to gray, and consists mostly of plagioclase 

feldspar, horneblende, and quartz. At places scattered grains of 

magnetite and some epidote are present. The quartz diorite dikes cut 

the monzonite porphyry, and are in turn cut by the ore-bearing veins.

ANDESITE

Two small stocklike masses of andesite crop out in the northeastern 

part of the district (pi. 14). Two dikes to the south of these andesite 

bodies and one dike about 1,500 feet to the west of them are believed 

to be of the^same composition. The andesite is fine grained and dark
292 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

gray; it consists mostly of feldspar. A few phenocrysts of feldspar 

and hornblende, altered to a yellow-brown claylike material, are 

present. The andesite intrudes the pre-Cambrian rocks, but its age 

relation to the Beartooth quartzite has not been determined. The 

megascopic appearance of the andesite is similar to the diabase, but 

for the most part it is less altered. The andesite contains abundant 

vertical joints at the edges of the stocks.

SEDIMENTARY BOOKS 

BEARTOOTH QUARTZITE

The Beartooth quartzite of Late(?) Cretaceous age crops out along 

the top of a long ridge in the northeastern part of the mapped area 

(pi. 14). The quartzite overlies the quartz diorite gneiss, granite, and 

quartz monzonite. The formation strikes N. 60° W. and dips from 

15° to 25° N. 30° E. and consists of alternating beds of conglomerate, 

sandstone, shale, calcareous sandstone, and quartzite. The quartzite 

extends both east and west of the area and lies between the older 

igneous rocks to the south and west, and volcanic rocks, probably of 

Tertiary age, to the north and east.

ALLUVIUM

Recent stream deposits, consisting of silts, sands, and gravels, are 

found in Black Hawk Canyon throughout much of its course.

STRUCTURE

Folds are of minor importance in the Black Hawk district, but faults

are common in all parts of the area. Many faults are filled with vein 

material or dikes. Foliation, planar structures, and jointing are common in some of the igneous rocks.

FOLDS

The pre-Cambrian quartzite and schist that occurs as inclusions in 

the quartz diorite gneiss are homoclinal blocks; most of the blocks are

tilted northeast at angles ranging from 37° to 64°. The beds in general

strike N. 40° W. to west. Tne two large east-trending blocks are

Oriented at a Slight angle tO the predominant strike of the strata, and

extend for about a mile west of the mapped area. The dip and 

strike of the beds are consistent throughout the outcropping masses.

The Beartooth quartzite also occurs as a laomoclinal block striking

N. 60° w. and dipping is0 to 25° NE. The inclined beds can be traced

for at least 1 mile east and 2 miles west of the mapped area. The 

homoclinal attitude of the beds is probably the result of faulting and 

the Beartooth quartzite exposed in the district is part of a 

fault block.
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 293

FAULTS

Faults and shear zones are abundant in the Black Hawk district. 

Most of the veins and dikes are along faults, although evidence of 

movement along many of the fractures is difficult to determine. The 

dominant trend is north-northeast to east, but a few of the fractures, 

particularly in the southwestern part of the area, trend northwest. 

Most of the dikes and veins dip 70°-90°; a few dip at angles as low as 

55°. There is no uniformity in the direction of dip of the veins or 

dikes.

Two fairly conspicuous fault systems trend slightly east of north 

across the area. Each system of faults consists of one rather persistent fault, from which branching faults split off to the northeast. 

One extends from the southern boundary of the map at the point where 

Black Hawk Canyon enters the mapped area, to near the northern 

edge. This system of faults passes a few hundred feet west of the 

Black Hawk shaft. Near the northern edge of the mapped area it is 

interrupted by two parallel east-trending vein-filled faults.

Another conspicuous fault system lies about 1,600 feet east of the 

Black Hawk shaft and extends from the southeastern boundary of the 

mapped areas to beyond the northeastern edge of the district. Faults 

of both systems extend into the Beartooth quartzite along the northeast edge of the district, and cut the quartz diorite dikes, which, with 

the exception of the andesite, is the youngest rock unit in the district. 

The easternmost fault system is interrupted by an andesite stock 

through which no evidence of faulting could be traced.

Between the two fault systems and also in the area west of Black 

Hawk Canyon most of the faults and dikes strike northeast, however, 

in the eastern part of the area the dikes and faults trend more nearly 

east.

Within the monzonite porphyry stock the fractures trend northeast 

parallel to the elongation of the stock, and part of the southeastern 

boundary of the stock is formed by the northeast-trending fault and 

shear zone.

The diabase and basalt dikes in the Black Hawk district, which 

correspond in composition and in age to similar dikes throughout the 

Burro Mountains, trend northwest. This orientation is characteristic of these dikes throughout the Burro Mountains area, and apparently reflects conditions of regional stress during late pre-Cambrian or 

early Paleozoic tune, which produced northwest-trending fractures 

later filled with the basaltic and diabasic magmas.

Most of the faulting was later than the intrusion of the monzonite 

porphyry stock and probably later than the quartz diorite. Many of 

the faults follow the granite dikes which were intruded during preCambrian tune and suggest a reopening in post-Cretaceous time along
294 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

old pre-Cambrian breaks. The granite dikes fill fractures trending predominantly northeast to east, and this same structural orientation 

characterizes the later intrusions and faults.

Post-ore faults cut some of the veins. In the Black Hawk mine a 

flat-dipping fault, striking N. 75° E. and dipping 25° to 30° NW., cuts 

the vein on the eighth level. The ore in the stopes below this level 

ends sharply against the fault (A. A. Leach, written communication). 

At the Alhambra mine a northeast- and a northwest-trending fault 

cut the vein and displace it (fig. 48). Underground, on the first level, 

fragments of broken and brecciated ore are reported along these faults 

(W. C. Dyer, oral communication). These fragments may have 

resulted from movement along the cross faults after the material was 

deposited in the vein.

FOLIATION, PL.ANAR STRUCTURE, AND JOINTING

The foliation of the quartz diorite gneiss, in general, trends northeast and dips from 60° NW. to vertical. Locally the dips are less

steep. South and southeast of the Rose and Alhambra mines the

foliation trends northwest and dips northeast (pi. 14). At places the 

foliation is parallel to the contacts of the gneiss with the older rocks. 

This, combined with the absence of a regional foliation in the older 

rocks and the absence of a cataclastic texture in the gneiss, is interpreted as indicating that the gneissic foliation is a primary flow 

structure.

The foliation in the quartz diorite gneiss may have been the main 

controlling structure for subsequent igneous instrusions in preCambrian and possibly after pre-Cambrian tunes. Most of the granite

and associated aplite and pegmatite dikes were intruded parallel to the 

foliation. An excellent example of this parallelism of dikes and 

foliation is half a mile southeast of the Black Hawk shaft (pi. 14).

The planar Structure in the northeastern part of the monzomte

porphyry stock strikes parallel to the elongation of the stock and dips 

northwest at steep angles. The stock in this area appears to dip northwest also and at least the upper part of the stock appears to have been 

emplaced as a tabular body. 

Vertical joints parallel the boundaries of the two andesite stocks hi

the northeastern part of the area. The joints are best developed in the

northernmost stock and m COnCCntrically arranged within the stock

(pi. 14),

ORE DEPOSITS

Deposits of uranium-bearing nickel-CObalt-silier ore m the BUU* 

Hawk district occur in fissure veins, most commonly in the quartz diorite gneiss. The veins are numerous in an area about 1 mile wide and 

2 to 3 miles long contiguous to the southeast side of the Twin Peaks
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 295

monzonite porphyry stock. Two intersecting systems of veins are 

present, one striking north to north-northeast and the other striking 

northeast to east. The veins are pitchblende, native silver, argentite, 

nickel and cobalt sulfides and arsenides, pyrite, and small amounts of 

other sulfides, in a gangue of carbonates, and some quartz and barite. 

The veins known to contain pitchblende and the nickel and cobalt 

minerals are closely associated spatially with the monzonite porphyry. 

All except one of the major silver producers are known to contain 

nickel and cobalt minerals and pitchblende.

The ore deposits belong to the nickel-cobalt-native silver ore type 

described by Bastin (1939) and are similar to the major pitchblendeproducing deposits at Joachimsthal, Czechoslovakia, and Great Bear 

Lake, Canada.

MINERALOGY

The vein minerals that have been reported from the Black Hawk 

district are listed m table 1. This list has been compiled in part from 

previous reports; the minerals that have been observed by the present 

writers are indicated in the table.

All the mines were inaccessible in 1951 and 1952 and only a few of 

the ore minerals were found on the dumps. Thus little information 

could be gathered in the field relative to the kind and quantities of the 

vein minerals and their paragenetic relations. Most of this information 

is taken from previous published reports and from personal communications.

Pitchblende is present on the dumps of the Black Hawk and Alhambra mines. Radioactivity was noted on the dumps of the Rose 

and Good Hope mines and at five other localities, but no uranium 

minerals have been identified. The pitchblende at the Black Hawk 

mine, in the specimens observed, occurs as black shiny grains less than 

2 millimeters in diameter, intimately associated with sphalerite, a 

nickel arsenide (probably nickel skutterudite), and other ore minerals. 

The minerals were identified by X-ray and polished-section methods.

Native silver is the most abundant ore mineral in the veins. Masses 

of arborescent silver as much as 60 to 70 feet long, 6 to 18 inches wide, 

and 1 to 2 feet thick are reported (Hess, 1917, p. 753). According to 

Bastin (1939, p. 27), silver in deposits of this type is generally primary.

Argentite, which was a commercially important ore mineral at the 

Black Hawk and Rose mines (written communication, Weed, W. H.), 

is present as fillings in fractures at the Alhambra mine (Leach, 1916). 

According to Leach, crystals of argentite occurred on the niccolite 

and carbonate gangue at the Alhambra mine.

Cerargyrite, proustite, pyrargyrite, and pyrostilpnite are reported 

only from the Rose mine. The cerargyrite was reported in the upper 

levels and the antimonial sulfides of silver on the 200-foot level.

353746 56 3
296 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

TABLE 1. Minerals reported from the Black Hawk district

ORE MINERALS Chemical formula 

Pitchblende 1 ................................____ UO2

Native silver J _____________________________________ Ag

Argentite-________________________________________ Ag2S

Cerargyrite___--------_---_-______________________ AgCl

Proustite. ______-___-------___-____-________--____ 3Ag2S-As2S3

Pyrargyrite__--.-_----__.-._-.--__.__-..___...___. 3Ag2S-Sb2S3

Pyrostilpnite_--_-.-_-__-----------______-_--______- 3Ag2S-Sb2S3

Niccolite 1 . __----__------____---_______________-_- NiAs

Millerite_.____________________________________ NiS

Skutterudite ! _ __-_-________-----___-_-_-___-______ CoAs3

Nickel skutterudite ^............................... (Ni,Co,Fe)As3

Smaltite(?)-_-----------------_------------------_ CoAs2

Chloanthite(?)__-__--_----------_--_____-_______ NiAs2

Erythrite_________________________________ Co3 As2 08 -8H2O

Annabergite______--__-_------_---____-______-_-__ Ni3 AsaOg-SH^O

Rammelsbergite 12_______________________________ NiAs2

Sphalerite >_______________________________ ZnS

Chalcopyrite._____________________________________ CuFeS2

Galena 1 _______________________________ PbS

Stannite______________________________ Cu2S-FeS-SnS2

Bismuthinite._____________________________________ Bi2S3

GANGUE MINERALS

Pyrite '..________________________________________ FeS2

Calcite »__________________________________________ CaCO3

Dolomite »______________________________________ CaMg(CO3 ) 2

Siderite. _______________________________ FeCO3

Rhodochrosite_________._______________ MnC03

Manganoancalcite_________________________________ (Ca,Mn)CO3

Ankerite »______________________________________ CaCO3 -(Mg,Fe,Mn)CO3

Barite ! _........._.......... ...._...._..__.... BaS04

Quartz » _______________ ____ _ _______ Si02

t Minerals observed by tno -writers.

iTentatively Identified as rammelsberglte, but probably nickel skutterudite.

Appreciable amounts of antimony are present in a specimen from the 

Black Hawk dump.

Nickel and cobalt minerals are reported from all mines for which

records are available, namely the Black Hawk, Alhambra, and Rose

mines. Leach (1916) describes millerite at tne AHiambra mine as

tiny capillary crystals containing some silver. Niccolite associated

witn native silver and argentite is reported from, the Black Hawk and 

Alhambra mines. Hess (1017, p. 753) reports that "in one place in the Alhambra rein a shoot, from 2 to 3 feet wide is saia to have

carried from 15 to 20 percent nickel, in the form of niccolite, and the 

ore was rich in silver." In general nickel-skutterudite and skutterudite appear to be the major primary nickel and cobalt minerals in the 

district. The only other occurrence of skutterudite in the United
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 297

States listed by Ford (1932, p. 437) is at Franklin, N. J., and nickelskutterudite is known in the United States only from the Black Hawk 

district, its type locality. According to Waller and Moses (1892), 

who first described this mineral, nickel-skutterudite from the Black 

Hawk mine is a silver-gray granular mineral with a tubercular structure, the interior of the tubercle being commonly filled with carbonate. 

Waller and Moses (1892), and Krieger (1935) state that native silver 

also fills the tubercle. Smaltite and chloanthite have been reported 

from the Rose and Alhambra mines (Leach, 1916), but probably were 

confused with skutterudite and nickel-skutterudite (Northrop, 1942, 

p. 283). The rammelsbergite is only tentatively identified and may 

be nickel-skutterudite. Erythrite and annabergite, the hydrous 

cobalt and nickel arsenates, form crustiform masses at the Alhambra 

mine (Leach, 1916) and have been found on some of the dumps (W. R. 

Storms and I. L. Wright, oral communication).

Sphalerite may be present in appreciable quantities in the lower 

levels of the Black Hawk mine (W. H. Weed, written communication). 

The other ore minerals are of minor importance, and little is known 

of their occurrence and characteristics.

The principal gangue minerals reported in the veins are calcite, 

dolomite, siderite, and ankerite; less abundant gangue minerals 

include barite, quartz, rhodochrosite, and manganoancalcite. The 

quartz is either crystalline quartz, dull cherty quartz, or pale-greenish 

waxlike cryptocrystalline quartz. Black manganiferous oxide, containing some iron, is present on some of the dumps (W. R. Storms, 

written communication).

DISTRIBUTION OP THE VEINS

Veins are abundant within the Black Hawk district and they may 

be traced for a short distance south and southwest of the mapped 

area. In general they are limited on the northwest edge of the 

mapped area by the stock of monzonite porphyry in the vicinity of 

Twin Peaks, and on the northeast by the Beartooth quartzite. The 

veins are younger than both these rock units and a few veins cut them.

Most of the veins in the district are confined to an area about 1 mile 

wide that lies contiguous to the southeast side of the Twin Peaks 

monzonite porphyry stock (fig. 45). Several of the mineralized veins 

(pi. 14) are in faults in the quartz diorite gneiss close to its contact with 

the monzonite porphyry of the Twin Peaks stock, with the small stocklike body at the Rose mine, and with the small stocklike body near the 

Alhambra mine, which is probably a cupola on the Twin Peaks stock.

The veins are most common in the quartz diorite gneiss and in the 

granite. They are generally absent in the quartzite and schist, and in
298 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

R. 16 W.

17

T 

18 

S.

15

T. 

18 

S.

Monzonite porphyry

Radioactive locality

1QOO 2OOO Feet

FlfiUBE 45. KfldlOflCtiVB lOWlitleS tQ the Black Hawk district, N. Mei., and their relationship to the

main mass of the monzooitO POfphyiy

the monzorxite and quartz monzonite. ftfC tO

alfflOSt entirely confined to the gneiss.

The veins occupy faults and fractuTeS Mid tteiebj reflect the structural pattern of the district. An examination of the vein pattern 

roTeate two intersecting sets of veins, one trending north to northnortheast, and the other trending norttieasTi to e»sx, TK« ^ortu_ 

northeast set of veins is best developed along the two north -north east 

belts of faulting, but the Albambra vein and tbe subparallel veins 

soutb and southwest of the Alhambra mine probably also belong to
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 299

this set. The northeast-trending "veins are arranged in three major 

belts: one that lies along the southeast side of the Twin Peaks stock, 

and widens northeastward to include the Black Hawk vein; another 

that extends from the Rose mine to just south of the southernmost 

andesite stock in the northeastern part of the area; and a third in the 

southern part of the area. These are not continuous belts, but are 

zones of many discontinuous parallel and subparallel veins. Toward 

the northeast the veins trend more easterly, particularly in the 

southern belt.

The ore minerals are mostly confined to the northeast set of veins, 

but the Alhambra vein, one of the most productive, is a north-northeast 

vein. There appears to be no correlation between the intersection of 

the two sets of veins and the presence of ore minerals. The northeasttrending veins, which in general parallel the laminations of the gneiss, 

appear to be cut by the north-northeast veins, but the relationships 

are obscure in many places.

The distribution of the uranium-bearing veins in a zone contiguous 

to the southeastern side of the Twin Peaks stock suggests there may be 

a similar zone on other sides of the stock, and prospecting in these 

areas might be productive. Prospecting to the southwest along the 

continuation of the mineralized zone might result in the landing of 

additional deposits containing nickel, cobalt, and uranium minerals.

CHARACTER OF THE VEINS

The veins in the Black Hawk district are fissure fillirgs along faults 

and fractures with only minor replacement of the wall rock. They 

are similar throughout the district, and differ only in the presence or 

absence of some of the ore minerals. On the geologic map (pi. 14) 

the veins are divided into three groups: veins known to contain 

uranium, silver, nickel, and cobalt minerals; veins known to contain 

nickel, silver, or cobalt minerals (oral communication Leach, A. A.); 

and veins not known to contain any ore minerals. This division is 

based only on the known presence of the specific metals. Many of 

the veins containing nickel, cobalt, or silver minerals may also contain 

uranium minerals, and many of the veins mapped as barren veins may 

contain ore minerals in unobserved portions. A single vein may in 

part belong to one group and in part belong to another group. The 

information on the character of the veins and tbe mineralogy, except 

that deduced from surface observation, was obtained from written 

communications by W. H. Weed, E. D. Lidstone, and A. A. Leach.

Many of the veins are only a foot or less in width but they may open 

up suddenly into ore shoots 3 to 10 feet wide. The veins are wider 

in the quartz diorite gneiss and granite and pinch noticeably upon 

entering the monzonite porphyry. Many of the veins can be followed
300 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

for more than 1,000 feet, but others are only a few hundred feet long. 

The greatest vertical extent known is in the Black Hawk vein which 

has been mined to a depth of 600 feet vertically below the collar 

of the shaft and which crops out to the northeast on ground 175 feet 

higher than the collar of the shaft.

The veins are inconspicuous in the outcrop and are marked generally 

by soft brown-stained carbonate fillings. In places a crude banding 

is developed but most commonly the vein filling lacks any definite 

structure. Oxidation is not deep, and primary minerals are found 

within a few feet of the surface. The boundary between barren 

gangue minerals and ore shoots rich in silver is sharp. The oreshoots 

within the veins are reported to be poddy and lense-like in character 

and conform to no known pattern.

Carbonates make up most of the vein filling and are associated 

with some quartz, fragments of the country rock, and locally, ore 

minerals. The carbonates, which are chiefly calcite, dolomite, siderite, 

and ankerite, weather brown in the outcrop. The quartz is generally 

a dull waxlike yellow-green chert or chalcedony; the rock fragments 

are mostly altered gneiss. The ore minerals are chiefly native silver, 

argentite, and nickel and cobalt minerals, with a small amount of 

base metal sulfides present. On the surface small specks of galena, 

some pyrite, and small amounts of native silver make up the metallic 

minerals. In the major mines the pyrite was common only in the 

waste, and galena was reported to be scarce.

Native silver was abundant in the veins in the upper parts of the

mines and constituted the major portion of the ore. Argentite 

increased in the lower levels, and nickel and cobalt minerals appeared 

below 100 feet. Pitchblende in the veins is probably associated with

the nickel and cobalt minerals.

RADIOACTIVITY

Almost all pits, shafts, adits, and dumps that were accessible in

the Black Hawk district in 1952 were examined with a geiger counter, 

equipped with a 2- by 20-inch copper probe. Many of the deeper

shafts were tested by lowering the probe, attached to a 100-foot cable, 

into the shaft. The localities that show anomalous radioactivity

are listed in table 2 and ai-e slao'wn in figure 45-

A black shiny mineral in a specimen from the dump of the Black

Hawk mine (loc. 6) was identified in the field as pitchblende. This 

identification was later confirmed by X-ray powder analyses. An

orange incrustation tnati coats tne surface of one of me specimens

from the dump of the Alhambra mine (loc. 9) was identified in the 

field as a secondary uranium mineral. Pitchblende was later identified by the laboratory in this and another specimen from this locality.
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 301

No uranium minerals were identified in the specimens from localities 

4 and 7. Table 3 shows chemical analyses of some of the radioactive 

samples.

TABLE 2. Localities showing anomalous radioactivity

Scale reading

No. 

on

figure

45 

1

?,

3

4

5

6

7

8

Q

10

11

Locality 

Pit, 450 feet N. 45° W. of southeast corner sec. 16.--_. _-_

Pit, 1,600 feet S. 68° W. of northeast corner sec. 11........

Dump, Hunecke shaft, Black Hawk vein. ________________

Dump, Copper vein, Black Hawk mine _ ________________

Vein outcrop at shaft, Black Hawk mine. ______________ _

Dump, Black Hawk mine __ _ __________ _____________

Dump, Good Hope mine. -_----____-__________---__---_

Shaft and pit, 750 feet N. 22° W. of Alhambra new shaft, sec. 

20. 

Dump, Alhambra mine__-__-________--____-_-_----_-_-_

Dump, Red vein adit, Rose mine. _________________ _____

Dumo. Main shaft. Rose mine. _________________________

Radio- Noractive mal 

mate- backrial ground 

(0.2 (0.2 

scale) scale)

3 1J_

2/2 1-1/2

31/2-4 iy.

3/2 Ifc

4-5 l/2

5-6 1/2

8 1/2

3 1/2

5-6 1/2

3 1-1/2

3 1-1 1.

TABLE 3. Chemical analyses of specimens from localities showing anomalous

radioactivity

[See fig. 45 and pi. 14 and table 2 for location of localities listed]

U3 08 Ni Co Ag As Sb Cu

Locality- (per- (per- (per- (ounces

cent) cent) cent) per ton) (percent) 1 (percent) 1 (percent) 1

No. 6 2

No. 7 2 

No. 9 2

tine dump 4 _

bra mine

0.09

.24

.07

. 15

1

4

1

0

0

0.

-,r 3

23

58

35

07

18

tr.3

0.22

.48

.27

.08

. 10

?,

8

8,

3

10

34.

15

80

40

45

55

70

1. 0-10.

1. 0-5.

0

0

0. 1-1.

1. 0-10.

tr.8

0 0. 1-1. 0

0 _______

dump 4

' Percents are approximate.

8 Samples analyzed by the New Mexico Minerals Laboratory, Silver City, N. Mex.

3 Indicates less than 0.001 percent.

4 Samples collected and analyzed by the U. S. Bureau of Mines.

COMPARISON WITH FOREIGN DEPOSITS

Nickel-cobalt-silver deposits have been described from many places 

throughout the world (Bastin, 1939, p. 3-19). In some of these deposits, pitchblende occurs with the nickel, cobalt, and silver minerals. 

A brief comparison is made between the Black Hawk deposits and the 

deposits of two notable districts, namely, Great Bear Lake, Canada, 

and Joachimsthal, Czechoslovakia.
302 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

The mineral assemblages, both ore and gangue minerals, in the three 

districts are remarkably similar in that a predominance of silver in the 

ores with appreciable quantities of nickel and cobalt arsenides and 

minor amounts of sulfides and pitchblende are common to all. Iron 

and manganese oxides are also common.

The veins in the three districts cut foliated rocks of pre-Cambrian 

age, and most are short and narrow opening abruptly into wide, 

high-grade ore shoots. Ore in all three districts fills open spaces, and 

has replaced little or none of the wall rock.

DESCRIPTION OF MINES AND PROSPECTS 

BLACK HAWK MINE

PRINCIPAL FEATURES

The Black Hawk mine, the largest mine in the district, is along the 

Black Hawk vein, which is the largest vein on the Black Hawk property (pi. 15).

The workings in the Black Hawk mine are inaccessible. The Black 

Hawk No. 1 shaft is in the bottom of a dry gulch and is filled with sand 

and debris. Only a few pipes sticking up above the sand show its 

location. Information on the underground workings and the nature 

of the vein has been obtained in written communication from Weed, 

Leach, and Lidstone.

The Black Hawk No. 1 shaft (pi. 15), the principal opening on the 

Black Hawk vein, was sunk on the vein to the eighth level, a depth of 

497 feet. The shaft is vertical above the second level and is inclined 

60° N. 20° W. below that level. An aggregate of about 3,000 feet of 

drifts were cut on eight levels; most of these workings are east of the 

shaft. At the east end of the eighth level a winze, inclined about 85° 

S., was sunk for a distance of 150 feet (fig. 46), The ninth and tenth 

levels, 50 feet vertically apart, were driven from the winze. A crosscut on the second level extends about 120 feet north to the copper 

vein.

The Black Hawk No. 2 shaft (pi. 15), also filled, is about 300 feet 

southwest of the Black Hawk No. i shaft, it is 100 foot dooP ^itt 

snort workings on the 100-foot level and probably is not On the BlftCK

HaWk Vein. The H\inecke Shaft (pi. 15), 800 feet northeast of the

Black Hawk No. 1 shaft, IS on the Black Hawk vein, but is not connected with the otter working*. TKo sl,^t. i» « a a *ao toformaflon on tne underground workings is available.

The Black Hawk vein strikes N. 70° E. and dips 60°-70° NW. 

According to the mine maps the dip flattens with depth. The vein

was followed lor more than 1,000 feet on the surface and has been 

followed underground for as much as 700 feet (fig. 46 and pi. 15). Ore 

has been mined in the vicinity of the No. 1 shaft for about 500 feet
FIOUBE 46. Underground workings of the Black H
304 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

along the strike and at least 600 feet down dip and also at other 

localities along the vein.

The vein for the most part, ranges from an inch to about a foot in 

width but the ore shoots are 3 to 10 feet wide. The vein consists of a 

series of imbricate and subparallel fractures. The high-grade ore 

within the ore shoots is in streaks and bunches separated by low-grade 

ore.

On the eighth level a fault that strikes N. 78° E. and dips about 30° 

NW. appears to displace the vein 30 feet to the south and to the left. 

The vein segment below the fault dips about 85° S. The winze, sunk 

from the eighth level, is along this segment of the vein. The correlation of the veins above and below the flat-dipping fault is uncertain 

because the two segments dip in opposite directions.

The mine workings indicate that although the ore shoots in the upper 

levels do not persist downwards, other ore shoots of as great or 

greater length and width were found on the lower levels (W. H. 

Weed written communication).

According to W. H. Weed and A. A. Leach (written communications) 

the ore occurs as fissure fillings, and there is only minor replacement of 

the wall rock. Included fragments of country rock are common, but 

crusts of ore around the fragments are rare. The vein contains a 

central core of carbonate and quartz bordered by a few inches of altered 

wall rock and opens abruptly into the wide ore shoots without any 

apparent change in the general character of the vein. The ore within 

the shoots was mainly altered gneiss netted with tiny veinlets of ore 

minerals. The high-grade ore -was in streaks and bunches, principally 

along the footwall.

Native silver constituted 80 percent of the value of the ore that 

was mined. Appreciable quantities of argentite were present, and 

galena, pyrite, chalcopyrite, and sphalerite {were minor] constituents. 

Niccolite and smaltite are recorded, but most of the nickel and cobalt 

arc probably present as nickel skutterildite (NorthTOp, 1942, p. 283). 

Old reports state that the nickel minerals were found below the 100-

foot kvd (Waller and Moses, 1892; p. 49). An analysis of a 100- 

pound sample taken by E. D. Lidstone (written commumCfttlOu) irOfll

tke bottom of the winze and analyzed by Smith, Emery and Co.,

§ftfl Francisco, Calif., is as follows:

Bismuth.......______._____._.__________________ Present, small amounts

Arsenic_______________________________---------- Present, large amounts

Antimony ________________________________________ TraCGS

Copper_..______-__---------------------- ------ Trace

Nickel....________._.________...____.__.____._ - 8.92 percent

Cobalt-._..__.___________-___._____-_-__------- 0.90percent

Zinc.___________________________________________ 8.81 percent

Silver____________________________________________ 2,542.00 ounces per ton
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 305

No analysis for uranium was made on this sample, but two specimens of high-grade massive silver from the mine were tested and found 

to be radioactive. These samples were from the mineral collections 

of Messrs. Ira L. Wright and William Rowlee of Silver City; their 

source in the mine is unknown. Pitchblende from the dump is associated with a nickel arsenide and sphalerite. One of the specimens 

of high-grade silver and the specimen of ore containing pitchblende 

from the dump were examined with a geiger counter equipped with a 

6-inch probe. A count of 10 on the 0.2 scale was recorded for the 

high-grade silver specimen and a count of 5 on the 2.0 scale was recorded for the specimen of ore from the dump. The background 

count was 1 on the 0.2 scale. The specimen from the dump contained 

0.24 percent U3 0g (table 3, specimen 6). Radioactive material also 

was found on the dump of the Hunecke shaft (fig. 45 and table 3).

The Copper vein on the Black Hawk property strikes N. 50° E. and 

dips about 80°-85° NW. It may intersect the Black Hawk vein to the 

west of the Black Hawk No. 1 shaft (pi. 15). It is explored by surface 

trenching, shallow shafts, and by a 100-foot drift from the second level 

of the Black Hawk No. 1 shaft. The Copper vein did not contain 

silver in the underground workings, according to W. H. Weed (written 

communication); however, radioactive material was found on the 

dump of the westernmost of the surface workings (table 3 and fig. 45).

RESULTS OF DRILLING

In May 1952 the Black Hawk Consolidated Mines Co. began a 

program of diamond drilling at the Black Hawk mine. Three 1,000- 

foot holes were drilled to intersect the Black Hawk vein below the 

mine workings. Holes 1 and 2 were directed N. 20° W. and inclined 

70°; hole 3 was directed N. 20° W. but was inclined 63° (pis. 15 and 16). 

The three holes were alined parallel to the strike of the vein. The 

position of underground workings was determined from mine maps 

made from a Brunton-and-tape survey by A. A. Leach (written 

communication.)

Diamond-drill holes 1 and 2 were drilled at angles calculated to 

intersect the vein at depths of about 750 feet and 800 feet, respectively. 

However, the holes were drilled to 1,000 feet without intersecting any 

vein material recognizable as the Black Hawk vein. Hole 3 passed 

through a vein containing carbonate gangue minerals and a few specks 

of galena, pyrite, and native silver between 641 and 651 feet. Assays 

showed a trace of silver but no cobalt or nickel. The samples were not 

assayed for uranium and no anomalous radioactivity of the vein 

material was detected. Near 750 feet the hole passed through 6 

inches of carbonate gangue containing galena, pyrite, and niccolite. 

This material was not assayed and it showed no anomalous radioactivity.
306 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

All three holes penetrated quartz diorite gneiss cut by dikes of 

monzonite porphyry, pegmatitic granite, and diabase. Pyrite was 

abundant in seams and disseminated in the gneiss, and narrow calcite 

veinlets were present throughout the core. None of the core was 

anomalously radioactive.

In February 1953, the three holes were probed with a Geiger-Mueller 

tube but no anomalous radioactivity was found.

The failure of holes 1 and 2 to intersect the vein may have been due 

to deflection of the hole or to the inaccuracy of the underground maps 

upon which the location, inclination, and direction of the drill holes 

wero based. Although hole 3 intersected two carbonate veins, the 

thicker of which resembles the Black Hawk vein, attempts to correlate 

the intersection with the position of the Black Hawk vein as shown on 

the underground maps were unsuccessful.

ALHAMBRA MINE

The Alhambra mine (fig. 48) has been worked by at least four shafts 

and an adit driven along the vein (W. R. Storms and A. A. Leach, 

written communications). The New shaft is reported to be 420 feet 

deep, with short levels at 25, 50, 100, and 150 feet (fig. 47). A total of 

about 750 feet of drifts on these levels is shown on old maps. Deeper 

levels that do not appear on available maps are reported. The : shaft 

is cayed around the collar, and water stands about 40 feet below the 

surface.

The Alhambra vein strikes N. 15° E., dips 80°-85° SE., and is from 

1 to 5 feet wide at the surface. The vein cuts quartz diorite gneiss near 

a large easterly trending monzonite porphyry dike. The vein can be

traced south from the New shaft for about 500 feet. A weakly

mineralized vein, possibly an extension of the Alhambra vein, is found

about 400 feet north of the shaft and can be followed northeasterly for

about 300 feet.

Massive native silver, similar to that mined at the Black Hawk

mine, was the chief ore mineral in the Alhambra vein. Mr. Alex

Woodburn, the mine superintendent at the time of abandonment,

reported there was good ore on the 350-foot and 400-foot levels of the

mine when it was shut down (A. A. Leach, written communication).

Niccolite is reported to be associated with the silver. Pitchblende

was found on the dumps (fig. 45, tables 2 and 3) by the writers, and

had previously been reported by Leach.

ROSE MINE

The Rose mine is in the northeastern part of sec. 29, in the southwestern part of the mapped area (pi. 14). The mine has not been 

operated since 1889 and the shaft is now filled. High-grade silver ore,
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 307

and ore containing nickel and cobalt minerals were reported^to remain 

in the lower workings when the mine was abandoned. The mine was 

worked from a shaft sunk near the intersection of two veins, the Red 

vein and the Spar vein, and by an adit driven on each vein. The shaft 

is reported to be 200 feet deep, and to have levels at 50 feet and 100 feet 

on the Spar vein and levels at 150 feet and 200 feet on both veins. 

The most extensive workings were on the 150-foot level.

-f

LEVEL 3

EXPLANATION

E 

Shaft

CD

Shaft going above 

and below levels

Adit

B

CARR TUNNEL

100 Feet

Modified from A. A. Leech 

FIOURE 47. Underground workings of the Alhambra mine.
308 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Topography by Elliot Gill

FIOURE 48-Geologic map of the Alhambra mine and vicinity, Grant County, N. Mex.
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 309

Both veins at the Rose mine cut granite, quartz diorite gneiss, and 

monzonite porphyry (pi. 14). The Spar vein strikes about N. 75° E. 

and dips 75° to 80° NW. At the surface it can be traced for about 

700 feet east and 400 feet west of the old Rose shaft. The Red vein 

strikes N. 30° E. at the shaft, but at a point 200 feet northeast it turns 

N. 70° E. and is mappable in this direction for about 250 feet. It dips 

60°-75° SE. The veins range from 2% feet to 4 feet in thickness; they 

have well defined hanging walls and irregular footwalls.

The ore consisted of native silver, argentite, and cerargyrite in a 

quartz and carbonate gangue. High-grade silver ore that contained a 

large proportion of nickel and cobalt was mined on the 150-foot level. 

On the 200-foot level the argentite was associated with pyrargyrite, 

proustite, and pyrostilpnite.

Radioactive material was found on the dumps of the main Rose 

shaft and at the portal of the adit on the Red vein (fig. 45 and table 2).

SILVER KING (HOBSON) MINE

The Silver King mine, formerly known as the Hobson mine, is about 

1,300 feet north of the Black Hawk mine (pi. 14). According to R. J. 

Holmquist and M. J. Sheridan (written communication), the vein was 

worked from an adit 300 feet long and an inclined shaft. A raise and 

a winze about 200 feet from the portal of the adit explore the vertical 

extent of the vein. Part of the adit is accessible.

The vein is along a fault that strikes N. 50°-65° E. and dips 65° 

NW. and cuts quartz diorite gneiss. The fault intersects the main 

body of the monzonite porphyry stock 200 feet northeast and 150 

feet southwest of the shaft. Northeast of the shaft a quartz diorite 

dike is along the contact of the monzonite porphyry and the quartz 

diorite gneiss.

In the adit the vein has a well-defined hanging wall and extends 

along a strong shear zone for 200 feet northeast of the portal, and 

along an irregular series of branching fractures for an additional 100 

feet. The width varies from 2 to 4 feet and is reported to have been 

followed for 300 feet down the dip. Argentite, associated with some 

native silver, was the principal ore mineral. No nickel, cobalt or 

uranium minerals are recorded, and none were found on the dumps.

GOOD HOPE MINE

The Good Hope shaft, now filled, is about 1,900 feet S. 82° W. of 

the Black Hawk no. 1 shaft (pi. 14). Lindgren, Graton, and Gordon 

(1910, p. 325) state that the workings attained a maximum depth of 

about 120 feet. The vein, which strikes N. 65° to 75° E. and dips 

65° SE., is in quartz diorite gneiss, about 400 feet south of the monzonite porphyry stock. Radioactive material, which could not be
310 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

identified mineralogically, was found on the dump. Chemical 

analysis of the radioactive material shows uranium, nickel, silver, 

and cobalt (fig. 45, and tables 2 and 3).

OTHER PROSPECTS

Many other veins in the district have been explored by surface 

cuts and shafts (pi. 14). Waste rock on some of the dumps shows 

some ore minerals, but production of ore has probably been small. 

Cobalt bloom has been reported (W. K. Storms and I. L. Wright, 

oral communication) on the dump of a shaft 1,100 feet south of the 

Black Hawk shaft. Radioactive material was found at two small 

pits, 3,550 feet N. 30° E. and 2,200 feet N. 18° E. of the Black Hawk 

No. 1 shaft. Radioactive material was found also in a shallow shaft 

and pit, 750 feet N. 22° W. of the Alhambra New shaft.

SUGGESTIONS FOB PROSPECTING

Should any future investigations be undertaken in the Black Hawk 

district, the pinching and swelling of the veins along the strike 

and with depth must be kept in mind. At the Black Hawk and 

Alhambra mines, the veins generally are from a few inches to a foot 

in width, but they are reported to swell abruptly into ore shoots 3 to 10 

feet Wide. Because Of the discontinuous nature of the ore in the veins 

and the absence of geologic data to determine where ore shoots are

localized, results of diamond drilling would be inconclusive. Therefore, it is suggested that any further work should commence with 

shaft unwatering and reconditioning of the larger mines in the district 

and then by mapping and sampling of veins.

SELECTED BIBLIOGRAPHY

Bain, G. W., 1950, Geology of the fissionable materials: Econ. Geology, v. 45.

p. 273-323.

Bastin, E. S., 1939, The nickel-cobalt-native silver ore type: Econ. Geology, v. 34,

p. 1-40. 

Clarke, P. W., 1915, Analysis of rocks and minerals from the laboratory of the

United States Geological Survey: U. S. Geol. Survey Bull. 591, 376 p. 

Everhart, D. L., and Wright, Robert, 1953, The geologic character of typical

pitchblende veins: Econ. Geology, v. 48, p. 77-96.

Ford, W. E., 1932, Dana's Textbook of Mineralogy, 4th ed. ( 851 p., New York, 

John Wiley & Sons.

Furman, H. Van F., 1885, Notes on two ore deposits of southwestern New Mexico;

School Mines (Columbia Univ.) Quart., v. 6, p. 138-142.

Hess, F. L., 1917, Nickel, in Mineral Resources of the United States, 1915, part 1;

U, 8, Geol, Survey, p. 743-766.

Hiiiebrand, w. F., 1889, Mineralogical notes: Colorado Sci. Soc. Froc., v. 3,

p. 38-47. 

Jones, F. A., 1904, New Mexico mines and minerals; Santa Fe, 349 p.
URANIUM-BEARING DEPOSITS, BLACK HAWK DISTRICT, N. MEX. 311

»

( Krieger, Philip, 1935, Primary native silver ores at Batopilas, Mexico, and

Bullard's Peak, N. Mex.: Am. Mineralogist, v. 20, p. 715-723. 

Leach, A. A., 1916, Black Hawk silver-cobalt ores: Eng. and Min. Jour., v. 102,

p. 456. 

Leach, F. I., 1920, Radium ore discovered in White Signal district, N. Mex.:

Eng. and Min. Jour., v. 109, p. 989. 

s Lindgren, Waldemar, Graton, L. C., and Gordon, C. H., 1910, The ore deposits of

New Mexico: U. S. Geol. Survey Prof. Paper 68, 361 p. 

' Lindgren, Waldemar, 1933, Mineral Deposits, 4th ed., 930 p., New York, McGrawHill Book Co., Inc. 

"^ Northrop, S. A., 1942, Minerals of New Mexico: N. Mex. Univ. Bull. 379, Geol.

ser., v. 6, no. 1, 387 p. 

Paige, Sidney, 1916, Description of the Silver City Quadrangle, N. Mex.: U. S.

Geol. Survey Geol. Atlas, folio 199.

* Waller, E., and Moses, A. J., 1892, Mineralogical notes: A probably new nickel 

arsenide: School Mines (Columbia Univ.) Quart., v. 14, p. 49-51.

INDEX

Page

Abstract.. - - 283

Acknowledgments...__... . ..._ 284-285 

Alhambramine __.__. _____----- 306 

Alluvium..... . ....... ... 292

Analyses, ore samples from Black Hawk mine. 304-

305 

radioactive samples-.--....-------- 300-301,310

Analysts... - 285,304

Andeslte- 291-292

Basalt porphyry.._______...___._ 290 

Beartoothquartzite. 287,292

Bibliography..... ... ..- 310-311

Biotite-quartzdiorite.---------------------- 289

Black Hawk canyon..___.______ 284 

Black Hawk district, location.------.----.-.-. 284

Black Hawk mine.------------ 302-304, 310; pi. 15

Burro Mountains batholith..--.-- --- 287,290

Carbonates____________...____ 300 

Claims ownership.. ....................... 285-286

Cobalt bloom ... 310 

Comparison with foreign deposits... _. __ 301-302

Diabase. 290

Dikes... 290,291,292,293-294

Dlorite - - ---- 289

Drilling... 286, 305-306, 310; pi. 16

Faults 293-294

Folds......- 292

Foliation - .. . 294

Oangue minerals__------_. .__. 297

Geology. 287-294; pi. 14

Good Hope mine ._____________ 309-310 

Granite. ___._______._______ 290

Hobson mine.--..-.--..---__________ 309 

Igneous rocks......______.._____ 287-292

Jointing. 294

Page 

Metamorphic rocks.... ^ .... __... 287-292

Mineralogy 295-297

Mining, Black Hawk district.....-..--.-... 283

history and production_ ...... 286-287 

Monzonite....__________._____ 288

Monzonite porphyry.__.______.... 291,295

Nlccollte... 296

Nickel.... 296

Ore deposits....__ 294-295

Pitchblende.... 283-284,287,295,296,300,301-302,305

Planar structure_....._._____...... 294

Prospecting suggestions.... . .... 299,310

Purpose of work covered by report.. ...__ 284

Quartz dioritc gneiss. .. 288-289 

Quartz monzonite.______._____ 288,290

Radioactivity.. 300-301

Replacement____________.__._ 299 

Rhyolite. _... .... .......... 290

Rose mine ....._ .. 306-307,309

Scope of work covered by report....-__-..-. 284

Sedimentary rocks- . . _.... 292

Silver.... 283,286,287,295,300,304,306

Silver King (Hobson) mine.._________ 309 

Sphalerite. 297

Syenite 289

Twin Peaks Stock 291,297

Veins. 294-295

Alhambra.__ 299,306

Black Hawk.... 302,304,305

character...________.______.. 299-300 

distribution.-.-..-..-.-. 297-299 

fissure 287,294-295

Red. - 307,309 

Spar,.. 307,309

313

U. S. GOVERNMENT PRINTING OFFICE: 1956