GEOLOGICAL SURVEY CIRCULAR 699 

Gold in the Black Hills, South Dakota, 

and How New Deposits Might Be Found 

Abstract .......................................... . 

Introduction ...................................... . 

Acknowledgments ............................. . 

Geologic setting ................................... . 

Precambrian rocks ............................ . 

Paleozoic and Mesozoic rocks .................. . 

Cenozoic rocks ................................ . 

Production ........................................ . 

Types of gold deposits ............................. . 

Homestake deposit ............................ . 

Other deposits in iron-formation ................ . 

Gold quartz veins ............................. . 

CONTENTS 

Page 

1 

1 

6 

6 

6 

8 

9 

10 

11 

11 

12 

13 

Types of gold deposits-Continued 

Deposits in basal conglomerate of Deadwood Formation ........................................ . 

Replacement deposits in Deadwood Formation ... . 

Deposits in Pahasapa Limestone ................ . 

Deposits in Tertiary igneous rocks .............. . 

Quaternary and Tertiary placer deposits ........ . 

Proposed approach to exploration ................... . 

Exploration target areas ........................... . 

Area north of Lead ............................ . 

Portland and Ruby Basin region ................ . 

Rockerville area ............................... . 

References cited ................................... . 

ILLUSTRATION 

FIGURE 1. Generalized geographic and geologic map of the Black Hills of western South Dakota and adjacent parts of 

Wyoming .................................................................................... . 

TABLE 

TABLE 1. Gold production of the Black Hills, 1875-1971 .................................................... . 

m 

Page 

14 

15 

16 

17 

17 

18 

19 

19 

20 

20 

21 

Page 

4 

Page 

3 

Gold in the Black Hills, South Dakota, 

and How New Deposits Might Be Found 

By James J. Norton 

ABSTRACT 

Of the recorded production of 34,694,552 troy ounces of gold 

mined in South Dakota through 1971, about 90 percent has 

come from Precambrian ore bodies in the Homestake mine at 

Lead in the northern Black Hills. Most of the rest has come from 

ore deposited in the Deadwood Formation (Cambrian) by 

hydrothermal replacement during early Tertiary igneous activity. About 99 percent of the total production has been within a 

radius of 5 miles (8 km) of Lead. Elsewhere, prospecting has 

been intense, both in the Precambrian rocks, which are exposed 

over an area 61 by 26 miles (98 by 42 km), and in nearby 

Paleozoic rocks. 

All the known ore bodies have been found either at the surface 

or in subsurface workings of operating mines. Efforts to find 

totally new deposits have been modest and sporadic; no comprehensive and systematic program has ever been attempted. 

Obviously, any exploration program should be aimed at finding a new deposit resembling the Homestake in the Precambrian, but discovery in the Deadwood of a new group of ore 

bodies containing several hundred thousand ounces of gold 

would certainly be worthwhile. 

Evidence has long been available that the Deadwood deposits 

and the Homestake deposit are somehow related. Current opinion is that (1) the Homestake ore is mainly Precambrian, (2) a 

trivial amount of Homestake ore is Tertiary, (3) gold in 

Deadwood basal conglomerate is largely of placer origin, and 

(4) the gold of replacement deposits in the Deadwood and in 

other rock units came originally from sources similar to the 

Homestake deposit or its parent materials. 

Homestake ore is virtually entirely contained in a unit of ironformation locally known as the Homestake Formation, which 

seemingly had more gold in the original sediments than similar 

rocks exposed elsewhere in the Black Hills. Gold, sulfur, and 

other constituents were subsequently concentrated in ore shoots 

in zones of dilation caused by cross folds that deformed earlier 

major folds. These ore shoots are in metamorphic ro~ks of a 

grade just above the garnet isograd, in a zone where the principal iron-magnesium mineral of the iron-formation changes 

from a carbonate (sideroplesite) to a silicate (cummingtonite). 

This metamorphic reaction would release carbon dioxide to the 

fluid that presumably formed the ore bodies. 

In short, three controls over localization of the ore have been 

identified: (1) the cross folds; (2) the so-called Homestake Formation, which passes beneath Paleozoic rocks north of Lead and 

has not been proved to reappear anywhere else in the Black Hills 

1 

(Other units of iron-formation less enriched in gold might locally become more like the Homestake Formation beneath the 

cover of Paleozoic rocks.); (3) proximity to the garnet 

isograd-nearly all the exposed Precambrian rocks in the Black 

Hills are at a metamorphic grade higher than this isograd-and 

occurrence of this isograd zone mostly beneath Paleozoic rocks. 

In searching for new deposits, one can guess from existing 

data where Precambrian rocks of suitable nature may be concealed. The usefulness of such guesses can be increased if they 

are made with information about the distribution of gold in 

younger rocks. Gold in the Deadwood basal conglomerate would 

be the simplest indicator of a deposit once exposed on the preDeadwood surface. Tertiary replacement deposits in the 

Deadwood or other rocks, which obtained their gold from 

Precambrian sources that may be nearby or far away, can also 

be helpful; they, like anomalies found by geochemical sampling, 

at least outline the regions of mineralizing activity. 

A suitable approach to exploration is to make a 

thorough study of the stratigraphy, the structure, and 

the metals geochemistry of the Deadwood Formation 

and associated rocks, chiefly in the northern Black Hills 

but to a lesser extent elsewhere in localities where the 

Precambrian geology seems promising and where gold 

has been found nearby. Such a program, even if it does 

not yield a new Precambrian deposit, might lead to the 

discovery of buried Deadwood deposits of minable grade 

and size. Areas that, from available information, seem 

worthy of close attention are (1) north of Lead; (2) the 

region including the Portland and the Ruby Basin 

districts, west and southwest of Lead; and (3) the 

Rockerville area, which is on the east flank of the central 

part of the Black Hills. 

INTRODUCTION 

The Homestake gold deposit, at Lead in the 

northern Black Hills, S. Dak., is in Precambrian 

rocks exposed in a Tertiary dome surrounded by 

Paleozoic sedimentary rocks and Tertiary intrusions. The site of the original outcrop of the 

deposit has outliers of the Deadwood Formation 

(Cambrian) in its immediate vicinity, and the edge 

of the main body of Paleozoic cover is as little as 2 

miles (3.2 km) away. Had erosion never removed 
the Paleozoic blanket from a small but critical 

area, the Homestake deposit might still be undiscovered. If, in uneroded circumstances, the 

deposit had in fact been discovered, it would 

probably have been because a small gold mine in 

conglomerate at the base of the Deadwood accidentally led miners to the Homestake lode. 

With the exception of the Homestake mine and 

the Bald Mountain mine, which is in the Deadwood 

Formation 3 miles (almost 5 km) west of Lead, all 

the gold mines in the Black Hills have been closed 

for more than 30 years, and many have not been 

worked since the period of intense gold activity 

near the turn of the century. Few workings are now 

accessible, and opportunities for detailed geologic 

mapping and comprehensive modern geologic investigations have not existed for more than a 

generation. 

As the final draft of this paper is being written 

(Feb. 1974), however, the open-market price of gold 

is about $150 per ounce. Though severe fluctuation 

has been experienced in recent months, partly as a 

consequence of speculation, the price of gold seems 

likely to remain generally high because of demand 

in industry and the jewelry business and because of 

the tendency in many parts of the world to fall back 

on gold at any sign of monetary weakness. 

Renewed gold activity in the Black Hills seems 

inevitable. Old mines will be reopened, though 

most of them are small and have had little or no 

success. AUsman (1940) described nearly 100 gold 

properties, and the Black Hills Mineral Atlas of the 

U.S. Bureau of Mines (1954, p. 19-22, 95; 1955, p. 

24-25, 141) identified 225 properties. These do not 

include the countless ephemeral placer operations 

of the region. Yet, as table 1 shows, very few of the 

many deposits that have attracted the energy and 

funds of their supporters have been important. 

Only one mine-the Homestake-has been large by 

modem standards; two other groups of properties-the Bald Mountain and (though there is uncertainty in the data) the Golden Reward-have 

produced nearly 1 million ounces of gold apiece; 

only four other localities have exceeded the 

100,000-ounce level. 

Obviously, an effective enlargement of Black 

Hills gold production can be achieved only by 

finding deposits at least as large as those of the 

Bald Mountain or the Golden Reward operations 

and preferably of a size approaching that of the 

Homestake deposit. The chief purpose of this 

paper is to argue that geologic investigation of 

the Deadwood Formation can direct the way to 

2 

other Homestake-type deposits if such deposits 

exist beneath the Paleozoic rocks. Perhaps the 

Homestake is the only major gold deposit in the 

Black Hills, but existing evidence, some of it 

recently obtained but most of it long available 

and little noticed, indicates that areas of 

considerable potential have been only slightly 

investigated or totally neglected. 

A resumption, however, of the simple prospecting of the past in rocks at or near the surface is unlikely to result in the discovery of a Homestaketype deposit. Many thousands of prospect pits dot 

the Black Hills. Most gold pits are in locations that 

indicate the prospector knew well enough which 

rocks and perhaps even which structures are most 

favorable; some pits are in unlikely or even absurd 

places) such as the quartz cores of pegmatites and 

ordinary schist with quartz veinlets, whereas others 

were merely dug in handy locations to meet assessment requirements. 

Of course major deposits may have been 

overlooked because mineralization stopped short of 

the present surface or because the gold is very fine 

grained or occurs in such odd minerals that it was 

not readily detected by the panning and assaying 

techniques generally used in the past. These 

possibilities can, and undoubtedly soon will, be 

tested by diamond drilling at old mines or at places 

determined to be favorable by the recent work of 

Bayley (1970, 1972a, b, c). Such work should at the 

very least bring to light the existence of previously 

undetected, but probably small, ore shoots. 

The obvious alternative is to search beneath and 

within the Paleozoic rocks. In recent decades the 

knowledge of the Black Hills Precambrian rocks 

has vastly increased, especi~lly through (1) the 

work of Bayley (1970, 1972a, b, c) in the northern 

Black Hills, (2) the clarification of the origin of the 

gold deposits through work on stable isotopes by 

Rye and Rye (1974), (3) the comprehensive review 

by Shapiro and Gries (1970) of ore deposits in 

Paleozoic sediments and Tertiary intrusive rocks, 

( 4) the modern improvements in exploration 

techniques, and (5) the existence now of largescale topographic base maps. All these can 

facilitate a new and perhaps more effective search 

for concealed gold deposits. 

Figure 1 shows the geography and geology of the 

Black Hills in a generalized way. For additional information, the maps likely to be most useful and 

most easily obtained are those of Irving (1904), 

Darton and Paige (1925), Kleinkopf and Redden 

(1974), and the Lead topographic quadrangle 
TABLE 1.-Gold production of the Black Hills, 1875-1971 

Mine or locality Location 

Principal mines: 

Principal 

source of ore' 

Gold produced 

(in troy OUnC!lS) 2 

Homestake ................. . At Lead, Lawrence County .... . p£if 

£dd 

(;dd 

31,446,~7 

3

950,000 

4

836,000. 

5350,000 

6200,000 

Golden Reward group of mines . 

Bald Mountain group of mines . 

2 mi. (3 km) SW. of Lead .... . 

3 mi. (5 km) W. of Lead ...... . 

Mogul ...................... . 3 mi. SW. of Lead ........... . £dd 

QTp 

£dd 

£dd 

p£q 

Placers of Deadwood region ... . Near Deadwood .............. . 

Maitland (Penobscot) ........ . 3 mi. NNW. of Lead ......... . 147,000 

7 120,000 

86,00o 

56,000 

845,464 I 

43,885 

43,617 

Wasp No.2 ................. . 2 mi. S. of Lead ............... . 

Keystone and Holy Terror .... . At Keystone, Pennington County 

Gilt Edge ................... . 5 mi. (8 km) ESE. of Lead .... . Ti 

Mp 

p£q 

£dd 

Ti 

£dd 

QTpand £de 

SpearfishGold .............. . 7 mi. (11 km) W. of Lead ..... . 

Clover Leaf (or Uncle Sam) ... . At Roubaix, 7 mi. SE. of Lead . 

Lundberg, Dorr, and Wilson ... . 2 mi. WSW. of Lead ......... . 

Hoodoo- Union Hill .......... . 5 mi. ESE. of Lead .......... . 9

30,000 

27,003 

1020,000 

Reliance: ................... . 5 mi. W. of Lead .............. . 

Rockerville placers ........... . Just E. of Rockerville, Pennington County ............ . 

Ragged Top ................. . 6 mi. W. of Lead .............. . Mp 

Mp 

p£q 

15,800 

n.q~~ 

11,500 

Deadwood Standard ......... . 7 mi. W. of Lead .............. . 

J.R ......................... . 3 mi. N. 60° E. of Hill City, Pennington County ............ . 

Hidden Fortune ............. . Just N. of Lead .............. . £dd 10,997 

Other deposits: 11 

Lawrence County (especially 

Alder Creek, Cleopatra, 

Bismarck, Golden Cre~t. 

Monarch, and Kicking 

Horse). 12 

Pennington County (especially 

Empire, Bullion, Standby, 

and Sunnyside). 12 

Custer County ............ . 

£dd 50,000 

p£:fandp£q 30,000 

p£q 4,000 

Total production from identified sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34,536,246 

Production from unidentified sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158,306 

====== 

Total recorded production. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34,694,552 

1 p£if, Precambrian iron-formation; p£q, quartz veins in Precambrian metamorphic 

rocks; £de, conglomerate at the base of the Deadwood Formation; £dd, replacement bodies and veins in dolomite and other rocks of the Deadwood Formation; Mp, 

Pahasapa Limestone; Ti, Tertiary igneous rocks; QTp, Quaternary and Tertiary 

placer deposits. 

'Chief source of information is AUsman (1940); other sources (except for the Deadwood and Rockerville placers) are U.S. Bureau of Mines Minerals Yearbooks, 

Reports of the South Dakota State Mine Inspector, Slaughter (1968, p. 1438), U.S. Bureau of Mines (1954, 1955), Irving (1904, p. 117-118), and Shapiro and Gries (1970, p. 190-194). Many figures are in part estimates, several of which are based on published statements of the probable dollar value of production during years prior to 1900 f<;>r which no exact records exist; other estimates, for years after 1937, were ob- tained by subtracting the published or probable production figures of other mines from the total South Dakota production in that year. 3

Allsman (1940, p. 38-39) recorded production from the Golden Reward for 1901-11 as only 371,382 ounces of gold and 734,223 ounces of silver, but he stated that in- complete records for earlier years suggest a total production of about $21 million in bullion. This large total implies that the Golden Reward gold production cannot have been le~ than the 950,000 ounces used here, which makes the Golden Reward group of properttes the second largest source of gold in the Black Hills. The Bald Mountain group of mines has traditionally been regarded as holding the second ranking position, and tradition may well be correct, for its production of 836,000 ounces is almost completely documented. 

'The production of t~e Bald Mountain group of mines is the total of (1) 487,877 ounces fo_r 1901-37 pubhshed by Allsman (1940, p. 28); (2) about 342,000 ounces for 1938-59 etther known or readily deduced as coming from the Bald Mountain operation from U.S. Bureau of Mines Minerals Yearbook figures and from Slaughter (1968, table 1); and (3) apparently small production prior to 1901, of which only an es- timated 5, 700 ounces from the Clinton and Dividend properties seems to be recorded (Irving, 1904, p. 118). This brings the total, in round figures, to 836,000 ounces. Unfor- tunately, Miller (1962, p. 114-115), whose data should be authoritative, gives figures that (after subtracting the Mogul production, which is here treated separately) total 

3 

only 757,858 ounces. Miller and AUsman are substantially in agreement for the period 1901-37. The main discrepancy lies in the 1938-59 figures, for which Miller seems to use 271,561 ounces instead of the 342,000 ounces used here. 5Allsman (1940, p. 38) recorded production of 212,679 ounces for 1902-17. He also said that scattered records indicate about $3 million in bullion produced in earlier years. This amount, after allowance is made for silver, suggests 138,000 ounces of gold, which brings the total gold production, in round figures, to 350,000 ounces. 6Bergendahi (1964, p. 44). Source of information is unstated, but oral com- munications with him and A.H. Koschmann during the late 1950's, when they were compiling gold production data from many sources, suggest that this figure is based on U.S. Mint records of gold receipts from this region during years when the only large 

production was from placers at Deadwood. 7 AUsman (l940, p. 40) recorded 100,819 ounces for 1901-20 and said that $500,000 or less was produced in earlier years, which indicates a total of about 120,000 ounces. 80mits AUsman's figure of 3,150 ounces for 1899, which according to Shapiro and Gries (1970, p. 167) came mostly or entirely from elsewhere. "The Hoodoo- Union Hill deposits (AUsman, 1940, p. 63) had a production of at least $150,000 in gold, and the company owning the property produced $800,000 from this and other sources. The 30,000-ounce estimate used here is nearer the larger figure than the smaller one. 10Parker (1966, p. 87) seems to be the only author who has ventured an estimate of the Rockerville production, which, without citing a source, he places at $400,000 in 1877 and 1878 and at more than $500,000 within a few years thereafter. The amount of disturbed ground in Rockerville Gulch and along the base of the Deadwood Formation suggests that production was indeed substantial, but it was probably not as large as Parker states. The estimate of 20,000 ounces used here is merely a guess but probably is as accurate as any that can be made now. ''None of the hundreds of small placer deposits mined after the gold rush years are included. ''Mines specifically named are those that have a recorded or estimated production of between 3,000 and 10,000 ounces. 
""" 

4 4 

oo' 

L LAWRENCE co 1 PENNINGTON CO I ..: 

(.')It; 

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::;lti O l :r: 

>-If-. ;;: ;:::> 

0 

til 

I 

I 

EXPLANATION 

Tertiary intrusive igneous tocks 

Chiefly rhyolite, rhyolite porphyry, quartz 

monzonite porphyry, and monzonite porphyry 

D 

Paleozoic, Mesozoic, and Cenozoic sedimentary rocks 

Harney Peak Granite 

D 

Metamorphic rocks 

Chiefly metasedimentary quartz-mica and mica 

schists. Also metabasalt, metagabbro, me

tairon-formation, quartzite, conglomerate, and 

carbonate rocks. In southern Black Hills intruded by pegmatites and satellitic plutons 

of Harney Peak Granite. Small area near 

Bear Mountain intruded by granite of same 

age as Lilt le Elk Granite 

Little -Elk Granite 

Contact 

X 

Mountain peak 

Road 

z 

< 

;:;: 

a:l 

::;;: 

< 

&l 

0:: 

"' 
c.n 

I 

I Bear Mountain I ___ PENN~GTON ~o__ _ x 

r CUSTER CO 

I 

I 

I 

104°00' 

INDEX SHOWING LOCATION 

OF MAP AREA 

Base compiled from U.S. Geological Survey and State 

highway maps 

Geology compiled from Darton and Paige (1925), 

Darton (1905), Bayley (1972c), and from mapping by 

J. A. Redden, J. J. Norton, J. C. Ratte', and P. H. Rahn 

from 1948-73 

0 5 10 15 20 MILES 

0 5 10 15 20 KILOMETERS 

FIGURE I.-Generalized geographic and geologic map of the Black Hills of western South Dakota and adjacent parts of Wyoming. 
(scale 1:24,000) and adjacent quadrangles. The 

literature cited in the list of references is replete 

with other maps and information for the serious 

reader. Because, however, the body of published 

literature and unpublished but obtainable reports 

on the Black Hills is lengthy and often tends to 

obscure rather than clarify the merits and suitable 

methods of exploring for gold, another purpose of 

this paper is to summarize what appears to be the 

critical information and to refer the reader interested in exploration to other reports from which 

he can form his own opinions. 

ACKNOWLEDGMENTS 

Perry Rahn, South Dakota School of Mines and 

Technology, graciously showed me in 1972 the 

Deadwood conglomerate and the Quaternary 

placer deposits at Rockerville, which I had 

previously suspected were far smaller than indicated by published accounts in newspapers and 

in books written for popular consumption. 

GEOLOGIC SETTING 

The Black Hills is a dome consisting of a 

Precambrian core flanked by Paleozoic and 

younger sediments. Tertiary rhyolitic, monzonitic, 

and alkalic intrusions are abundant in the northern 

Black Hills but are absent in the south. Literature 

on all aspects of the geology runs to so many 

thousands of pages that only highlights pertinent 

to the questions at hand can be mentioned here. 

PRECAMBRIAN ROCKS 

The area of exposed Pre cam brian rocks is oval in 

shape, elongate in a north-northwesterly direction, 

and 61 miles (98 km) long and as much as 26 miles 

(42 km) wide. Small bodies of granite in two 

separate localities have been dated at about 2.5 

billion years (Zartman and Stern, 1967; Ratte and 

Zartman, 1970). One of these is the Little Elk 

Granite north of Nemo, which unconformably underlies the small quantity of adjacent Precambrian 

rocks and is otherwise completely surrounded by 

the Deadwood Formation. The other is near Bear 

Mountain, in the west-central part of figure 1; 

there, the granite has intruded metasedimentary 

micaceous schist, thus indicating that sedimentation in this region was exceedingly ancient. 

Another gr~nite, the Harney Peak Granite, which 

with its many pegmatites is a prominent feature of 

the southern Black Hills, is 1, 7 44~ 12 million years 

old (Riley, 1970, p. 716-718). Metagabbro, 

which is modestly abundant, is the only other kind 

6 

of intrusive rock. The Harney Peak Granite is the 

youngest Precambrain rock known in the area, 

though the Sioux Quartzite, of much later age, extends in the subsurface to a point about 100 miles 

east of the Black Hills (Steece, 1964, p. 28-31). 

Approximately three-fourths of the Precambrian 

rocks consist of schist or phyllite derived from 

shale, graywacke, and subgraywacke. Metabasalt, 

not uncommonly having pillow structure, is abundant at several localities from the Lead region to 

the south border of Pennington County. The best 

examples are on maps by Bayley (1970, 1972a, b, 

c), who was in fact the first to recognize the 

metabasalt for what it is; previous authors had 

argued about whether it was metamorphosed carbonate sediment or plutonic rock (for example, 

Berg, 1946, p. 30-41). Other metamorphic rocks include cummingtonite-grunerite iron-formation, 

cherty and clastic quartzites, conglomerate, and 

carbonate rocks. The units of iron-formation, 

though they occur at several stratigraphic levels, 

are insignificant in quantity but are the most 

prominent host for gold. 

Metamorphism ranges from moderate to rather 

high intensity. The Lead region, according to 

Noble and Harder (1948, pl. 1), has a biotite zone 

in the west, then a garnet zone, and finally a small 

area in the northeast containing staurolite and extending beneath the Paleozoic cover. Further 

south, in areas mapped by Bayley (1970, 1972a, b, 

c), most localities have at least some garnet, 

though small parts of the region may be in the 

biotite zone. Still further south, on the north flank 

of the Harney Peak Granite dome, both staurolite 

and sillimanite isograds appear. From there to the 

southern border of the Pre cam brian exposures, all 

metamorphic rocks are in the sillimanite zone. 

The rocks have undergone several periods of 

deformation. Tight or isoclinal folds of north to 

north-northwest trend predominate. Refolding has 

been recognized in many places. Dips of bedding 

and schistosity generally exceed 60°, either east or 

west, except on the flanks of granite domes. Even 

the volcanic piles of metabasalt, though of approximately oval form in many places on a geologic 

map, are surrounded by very steep dips. 

Faults are abundant. Some are very ancient, for 

they were healed and deformed during the 

metamorphic and tectonic events accompanying 

intrusion of the Harney Peak Granite. Other faults 

are young enough to displace Tertiary intrusions 

(Irving, 1904, pl. 9). A few faults· that are wholly 

within Precambrian rocks contain breccia of very 
fresh appearance and even slickensides (for example, in the Bullion mine at Keystone) and thus 

seem to be very youthful. 

Two faults require particular attention. One of 

them is the Grand Junction fault in the southwest 

part of the Precambrian area; it was first 

recognized in the Berne quadrangle northwest of 

Custer (Redden, 1968, p. 391) and extends from 

Pringle to Custer and then northwest past Bear 

Mountain toward Deerfield. Neither during the 

Berne work nor during subsequent mapping of 

nearby areas could a persuasive correlation be 

made between the rocks on the two sides of this 

fault, except that the oldest rocks on either side 

belong to the same unit, the V anderlehr Formation 

described by Redden (1968, p. 34 7 -354). 

Presumably the fault has great horizontal displacement, but the stratigraphic discrepancies between 

the two sides can only be explained by causes that 

remain undetermined. 

The other major fault, mapped by Bayley 

(1972b, c), appears from beneath the Paleozoic 

contact southeast of Galena and strikes generally 

south to a point west of N emo and then southeast 

toward Rockerville. Though Bayley correlates some 

of the younger rocks east of the fault with rocks to 

the west, the geologic terranes on the two sides 

appear quite different. Very old and greatly 

deformed metasedimentary rocks, which overlie 

the Little Elk Granite east of the fault are unrepresented elsewhere in the Black Hills, though 

they show some lithologic similarities but little 

resemblance in stratigraphic sequence to old rocks 

west of the Grand Junction fault near Bear Mountain. Metagabbro is more abundant in the Nemo 

area east of the fault than anywhere else in the 

Black Hills, and the younger rocks, possibly correlative with the stratigraphic section at Lead, 

have fewer folds than similar rocks west of the fault 

(Bayley, 1972b, c). 

Most of the area occupied by exposed Precambrian rocks in the Black Hills lies between these 

two faults. At the northern extremity the 

stratigraphic section as presented by Noble and 

Harder (1948, p. 943-952) consists of (1) the Poorman Formation, containing phyllite generally 

carrying ankerite, which is the oldest formation of 

the area and generally is farthest north; (2) the socalled Homestake Formation, a 200- to 300-foot 

(60- to 90-m)-thick unit of iron-formation containing sideroplesite (magnesium-rich siderite) 

where metamorphism is of low intensity and cum7 

mingtonite where metamorphism exceeds the garnet isograd; (3) the Ellison Formation, containing 

phyllite, schist, and dark quartzite; (4) the 

Northwestern Formation, which resembles the 

Ellison except for a lack of quartzite; (5) the Flag 

Rock Formation, of heterogeneous nature, containing phyllite and schist (including pyritic 

graphite schist) and beds of cherty quartzite and 

iron-formation; and (6) the Grizzly Formation, a 

uniform sericitic phyllite. 

Further south, in the Rochford area, Bayley 

(1972a, p. 3, 8, pl. 1) found the structure dominated 

by an anticlinorium having the Ellison, which he 

called the Moonshine Gulch Quartzite, at its core 

and a very great thickness of the Grizzly, which he 

called the Swede Gulch Formation, on its flanks. In 

this area, metabasalt and meta-iron-formation are 

very prominent in the Flag Rock, which Bayley 

raised to group status. 

The Swede Gulch Formation of Bayley is 

lithologically the same as the unit to the south that 

Ratte and Wayland (1969, p. 2-5) called the 

Oreville Formation. The total thickness of the 

Grizzly-Swede Gulch-Oreville rocks amounts to 

tens of thousands of feet. The Oreville Formation is 

succeeded by quartz-mica and mica schists which 

extend to the east and southeast into areas 

mapped by myself. These rocks have within them 

four separate stratigraphic units that, like the Flag 

Rock, contain mica schist interspersed with bodies 

of iron-formation, cherty quartzite, graphitic 

schist, and probable metabasalt. Three of these units 

also have clastic quartzite, and the lowermost 

unit has bodies of conglomerate containing quartzite fragments in a schist matrix. At two localities 

the unit containing conglomerate extends into the 

area mapped by Bayley (1972c); at once place he 

tentatively called it Flag Rock, and at the other he 

considered it a phase of the Grizzly Formation. The 

abundance of folds and faults in the region leaves 

ample room for argument about these correlations, 

and indeed about all the stratigraphy summarized 

in preceding paragraphs; but the pattern of 

Bayley's map (1972c) implies that he too might 

have considered placing these units among his 

youngest rocks. 

The stratigraphic section culminates southeast 

of the Harney Peak Granite in a large area of 

sillimanite schist containing beds of clastic quartzite. This extends all the way to the south end of 

the exposed part of the Precambrian core of the 

Black Hills. 
PALEOZOIC AND MESOZOIC ROCKS 

The Precambrian rocks are surrounded by a 

stratified sequence of Paleozoic and Mesozoic 

sedimentary rocks which dip away from the 

Precambrian rocks. East of the Precambrian exposure the dip is generally moderate but in some 

places forms a decidedly steep monocline. Dips are 

very gentle west of the Precambrian exposure, but 

farther west, in Wyoming, the rocks turn downward 

in a very steep and large monocline. The overall 

configuration of the Precambrian-Cambrian contact is shown by a structure contour map compiled 

by Noble and others (1949, pl. 4). 

The oldest Paleozoic unit, and the only one in 

which ore deposits are abundant, is the Deadwood 

Formation, which is generally called Upper Cambrian but has Lower Ordovician beds near its top in 

the northern Black Hills. The stratigraphy and 

biostratigraphy have been treated in exhaustive 

detail in an unpublished thesis by Kulik (1965); a 

recent· published account is by Lochman-Balk 

(1972). Additional information bearing more 

directly on the relations between the stratigraphy 

and the ore deposits can be found in the report by 

Shapiro and Gries (1970) and in many older 

references. 

The Deadwood Formation consists mainly of 

sandstone and shale, not infrequently containing 

glauconite and being interspersed with many beds 

of intraformational conglomerate. It also has a 

basal conglomerate and calcic to dolomitic carbonate beds, which are the principal hosts for ore. 

Ordinarily the basal conglomerate is a pebble bed 

only a few inches or a few feet thick, but adjacent to 

topographic highs on the Precambrian-Cambrian 

contact it can be several tens of feet thick and contain boulders from nearby sources. Otherwise the 

lower part of the Deadwood consists of sandstone or 

quartzite with occasional lenses of conglomerate. 

The thickness can be as much as 60 feet (18m) but 

is generally less than 30 feet (9 m). Above this are 

interlayered sandstone, shale, limestone or 

dolomite, and intraformational conglomerate. 

These occur in a stratigraphically intricate 

arrangement described and diagramed by Kulik 

(1965, especially pls. 2-4). The topmost unit in the 

formation is the Scolithus sandstone facies, named 

for its abundance of Scolithus borings; this unit exists only in the northern Black Hills. 

The thickness of the Deadwood Formation is 

greatest in the northern Black Hills and diminishes 

to nothing not far south and southeast of the 

8 

southernmost Precambrian outcrops (Kulik, 1965, 

pl. 5; and Lochman-Balk, 1972, fig. 4). The 

thickest measured section, west of Lead near 

Ragged Top Mountain, is 462 feet (141 m) according to Shapiro and Gries (1970, p. 219); to the 

southeast near Rockerville the thickness is about 

200 feet (60 m); 30 miles (48 km) further south the 

formation lenses out (Kulik, 1965, pl. 5). The most 

complete exposure is just north of Deadwood in the 

type section, where the thickness measured by 

Kulik (1965, p. 239-240) is 411 feet (125 m). 

The change in thickness probably results less 

from erosion than from nondeposition in the south 

during north-northwestward regression of the 

Deadwood sea (Kulik, 1965, p. 13, 165). The details 

of the stratigraphy indicate a series of 

transgressions and regressions in which sandstones 

are the nearshore facies followed by shales and then 

by occasional offshore limestones (Kulik, 1965, especially p. 14, 149-151, 204). As a result, limestone 

and dolomite are most abundant in the north and 

west, and the sandstones and shales to the south 

and southeast are only rarely interspersed with carbonate rocks. 

The environment of deposition was one of 

shallow seas, lagoons, and tidal flats (Kulik, 1965, 

especially pls. 14-16). At the onset of sedimentation, however, as the Deadwood sea first advanced 

eastward from Wyoming, there were many islands, 

headlands, and embayments caused by irregularities on the Precambrian surface (Kulik, 

1965, p. 138-139, pls. 14-15). Most such topographic 

prominences were formed of quartzite, granite, or 

amphibolite, but the first island to be identified as 

such in the literature was formed of the Homestake 

lode (Devereux, 1882, p. 473). Generally, however, 

the relief was moderate, probably rarely exceeding 

100 feet (30 m). Nearly lateritic conditions on the 

pre-Deadwood surface are implied by the very common alteration of amphibole in iron-formation to 

iron oxide, by other signs of deep weathering at the 

contact (Redden, 1963, p. 246), and by red stain in 

basal Deadwood rocks. 

Three strata in the Deadwood Formation have 

been of particular importance to mining. One is the 

basal conglomerate, especially near Lead, where 

according to Slaughter (1968, p. 1442) its thickness 

ranges from a few inches to 50 feet (15 m) but is 

generally less than 10 feet (3 m). The other two 

strata are dolomitic units-one is just above the 

basal quartzite and conglomerate and the other is 

20 to 30 feet (6 to 9 m) beneath the Scolithus 

sandstone (Miller, 1962, p. 11-15). Most of the 
Black Hills gold produced from sources other than 

the Homestake mine is from replacement deposits 

in these dolomites. Unfortunately the lower of the 

two dolomite units in the principal gold mining 

area, west and southwest of Lead, does not appear 

in the stratigraphic sections measured by Kulik 

(1965), presumably because surface exposures are 

inadequate and mine workings were not sufficiently accessible. Only a few logs of drill holes and 

shafts obtained from various sources by Shapiro 

and Gries (1970, p. 215-222, 231-232) are helpful in 

reducing this shortcoming. 

The Deadwood Formation is succeeded by three 

thin units having an overall thickness of about 30 

to 200 feet (9 to 60 m). These are the Winnipeg Formation, consisting of shale and siltstone; the, 

Whitewood Limestone, consisting of dolomite and 

limestone; and the Englewood Formation, consisting mostly of limestone. The Winnipeg and the 

Whitewood, both of which are Ordovician, appear 

only in the northern Black Hills, whereas the 

Englewood, which is Late Devonian and Early 

Mississippian, completely surrounds the uplift. 

The next major unit is Pahasapa Limestone 

(Mississippian), equivalent to part of the Madison 

Group, which under this and other names is widely 

known in the Rocky Mountains. Its thickness 

ranges from about 200 to 600 feet (60 to 180m), but 

the change is not regular-erosion along its upper 

contact and collapsed solution structures cause 

great local variations. 

The next unit is the Minnelusa Sandstone 

(Pennsylvanian and Permian), generally about 400 

to 500 feet (120 to 150 m) thick. Overlying units 

contain limestone and red beds; the Permian and 

Triassic red beds form the "racetrack" valley circling the Black Hills, and the Jurassic and 

Cretaceous units form the outlying hogback region. 

Any now-foreseeable exploration drilling for concealed gold deposits would start in units no higher 

than the Minnelusa, which extends a sizable distance outward from the Precambrian exposures. 

The thickness to the Precambrian in some 

localities could be about 2,000 feet (600 m), especially where there are large Tertiary sills, but 

more commonly holes could be placed on the 

Pahasapa or Deadwood Formations so as to require 

less than 1,000 feet (300 m) of drilling to reach the 

base of the Deadwood. 

CENOZOIC ROCKS 

The northern Black Hills has an abundance of 

lower Tertiary intrusive igneous rocks in bodies of 

9 

many sizes and shapes. A few very small exposures 

of extrusive rhyolite and obsidian have also been 

discovered (Darton and Paige, 1925, p. 17). 

The intrusive rocks are mainly rhyolite, rhyolite 

porphyry, quartz monzonite porphyry, and monzonite porphyry. Other rocks include grorudite, 

which is allied to the rhyolite porphyry except for 

its abundance of albite and the sodic pyroxene acmite (aegerite), and phonolite (or tinguaite of some 

reports), which consists of orthoclase and albite 

together with acmite, nepheline, and a few more 

rare sodic minerals (Paige, in Darton and Paige, 

1925, p. 16). Phonolites containing quartz are 

gradational into grorudite. The Tinton area also 

contains syenite porphyry, nepheline syenite, and 

pseudoleucite porphyry (Darton, 1905, geologic 

map). 

These rocks form many dikes, sills, stocks, ancl 

probably laccoliths. The term "laccolith," which 

was much more popular a half century ago than today, was applied by Darton ( 1905, p. 10) and by 

Darton and Paige (1925, p. 20-23), as well as by 

other authors, to many of the larger bodies intruding Paleozoic rocks. Noble, Harder, and 

Slaughter (1949, p. 338-340) doubted this usage, 

chiefly because the large intrusions exposed in 

Precambrian surroundings are unquestionably 

stocks. Their structure contour map of the Precambrian surface (Noble and others, 1949, pl. 4) encouraged this doubt by showing domes and other 

irregularities in much the same way as on a structure contour map at the top of the Minnekahta 

Limestone (Permian) (Darton, 1905, fig. 31); 

however, the assumptions that Noble, Harder, and 

Slaughter used in making their map seem to have 

contributed to their conclusions. Recent work by 

Anna (1973) on part of the flank of the large instrusion east of Galena indicates the intrusion is indeed 

a laccolith. 

The only modern studies of the petrology and 

structure of the Tertiary igneous rocks have been in 

three small areas. One study was by Noble (1948) 

in the immediate vicinity of the Homestake mine, 

another was by Mukherjee (1968, p. 48-92, 132-159, 

169-209) in the Galena-Gilt Edge mine area, and 

the most recent was that by Anna (1973) in the area 

east of Galena. A comprehensive investigation was 

started in the late 1950's by H. D. Carlson, then of 

'The bar scale on Darton's figure is in error. The actual scale is 1 inch to about 10.7 

miles instead of 1 inch to about 6.5 miles. A similar map published as figure 6 in Darton and Paige (1925) has a corresponding error; its scale is 1 inch to 27 miles instead of 

16 miles. 
the University of South Dakota, but apparently 

was not completed. 

All other Cenozoic rocks are stream sediments, 

which are unconsolidated except in a few places 

where gravel is cemented by iron oxide. The 

oldest deposits belong to the White River Group 

(Oligocene), which consists of gravel, sand, clay, 

and scattered volcanic ash presumably windblown 

ftom somewhere to the west or south. These are especially widespread on the southeast flank of the 

Black Hills on uplands between stream valleys 

(D~rton and Paige, 1925, geologic map). Even 

~thin the Black Hills, except at high altitudes, 

th~re are scattered outliers of these deposits, some 

of which are assigned only doubtfully to the White 

River because they may be younger terrace gravels 

or may be reworked White River deposits (Darton 

and Paige, 1925, p. 14). 

Modern streams flow generally eastward across 

Precambrian and then younger rocks. Major exceptJons are in the north, where Spearfish and 

Whitewood Creeks flow north, and in the 

southwest, where Pleasant Valley Creek flows 

south. Early Pleistocene drainage seems to have 

been similar (Darton and Paige, 1925, p. 25). 

Alluvium of the generally narrow valley bottoms is 

probably all of Holocene age. Terrace gravels on 

valley walls and still higher gravels, not necessarily 

related to the modern drainage system, are of 

Pleistocene or late Tertiary age. These bodies of 

gravel, many of which contain placer gold, are rarely more than a few hundred feet long. East of the 

Black Hills, however, many tens of square miles of 

such gravel were mapped by Darton and Paige 

(1925). 

PRODUCTION 

Through 1971, the known production of gold 

amounted to 34,694,552 troy ounces. Table 1 gives 

information, chiefly attributable to Allsman 

(1940), as to where most of the Black Hills gold has 

been obtained. More than 90 percent of the gold 

came from the Homestake mine, and about 99 percent came from within a radius of 5 miles (8 km) of 

Lead. The Deadwood Formation has accounted for 

most of the non-Homestake production; placer 

deposits are probably the third largest producer. 

Precambrian iron-formations other than those at 

Homestake have been a very modest source, and 

only a few of the many quartz vein deposits in 

Precambrian rocks have been important. Deposits 

in Tertiary igneous rocks and in the Pahasapa 

Limestone are approximately tied for last place. 

Total silver production through 1971, was 12,-

867,547 troy ounces, of which 7,280,485 ounces, or 

57 percent, came from the Homestake mine (U.S. 

Bur. Mines Minerals Yearbooks; Slaughter, 1968, 

p. 1438). The ratio of silver to gold, by weight, in 

the Homestake mine is 1:4.3 (Slaughter, 1968, p. 

1438), yet the ratio in Deadwood deposits is about 

1:0.6 (Allsman, 1940, p. 26). 

Table 1 is unique in that, unlike previous 

compilations, it reconciles the sum of the 

production from individual sources and the total 

amount of gold known to have come from the 

Black Hills. Other compilers have directed their 

attention mainly to the figures available since 

1900 because these are generally accurate; most 

of these figures were first accumulated in a 

single publication by Allsman (1940). Estimates 

of production in prior years, many of which also 

are in AUsman's bulletin, have tended to be 

overlooked. As a result, about 1 million ounces 

of gold often go unmentioned. In table 1 most 

of this missing gold is assigned to the Golden 

Reward, Mogul, and Bald Mountain operations. 

The reader who is surprised by differences 

between table 1 and widely quoted production 

records will find the major discrepancies 

explained in footnotes appended to the table. 

About 160,000 ounces of gold remain unassignable to a known source; to that figure could 

probably be added a small amount of gold that was 

never entered in any records as coming from the 

Black Hills. Some of the unassigned production 

came from placer operations in the central and 

southern parts of the Black Hills, but the total output from these seems to have been very modest. 

Other gold may have come from Homestake 

properties before their purchase and thus escaped 

entry into Homestake records, but this too seems 

an unlikely cause of major discrepancies. Possibly a 

few tens of thousands of ounces of unrecorded gold 

came from Precambrian deposits of small to 

medium size, for the known history of many of 

these deposits is plainly incomplete. Undoubtedly, 

most of the gold for which a source cannot be determined came from mines in the Deadwood Formation, especially from th~ larger deposits that later 

came under Bald Mountain or Golden Reward 

ownership. 

The production data show clearly enough that a 

prospector who subscribes to the adage that OI)e 

should hunt' for elephants in elephant country 

should direct his most intense efforts to localities 

within a few miles of Lead. His prime objective 

10 
should be to find a new deposit like the Homestake; 

however, discovery of a ;.£~w area of deposits like 

those mined in the Deadwood Formation could also 

be worthwhile. 

TYPES OF GOLD DEPOSITS 

HOMESTAKE DEPOSIT 

The ore shoots forming the Homestake deposit 

are, with a few minor exceptions, confined to the 

Homestake Formation, as used by Noble (1950, p. 

224). Though the literature ordinarily neglects to 

say so except by implication, this is a metamorphosed iron-formation. Its dominant rock 

is cummingtonite schist, which is interspersed with 

a modest quantity of cherty quartz. The optical 

properties of the cummingtonite (Wayland, 1936, 

table 1) commonly place it near or beyond the 

boundary with grunerite, and the mineral has in 

fact been called grunerite in most of the recent 

publications on other areas in the Black Hills. 

Cummingtonite is absent in rocks below (west of) 

the garnet isograd, where sideroplesite (magnesium-rich siderite) is the dominant mineral. 

The change from sideroplesite to cummingtonite begins almost exactly at the garnet 

isograd and is completed within a few hundred feet 

east of it (Noble and Harder, 1948, p. 963-964); the 

Homestake mine is in the zone of this change. 

The ore bodies themselves are groups of pipelike 

southeasterly plunging shoots, some of which 

coalesce with other shoots. They are localized in 

zones of cross folds superimposed on the large 

regional isoclinal folds (Noble, 1950, p. 225-230; 

Slaughter, 1968, p. 1450-1453). Dilation of the 

rocks, which opened channels for movement of 

fluid and for ore deposition, is the supposed reason 

for concentration of ore in these zones. Ore forms 

only a very small, but unestimated, percentage of 

the total amount of Homestake Formation known 

to exist in the northern Black Hills, though 

geologists unfamiliar with the region have occasionally supposed otherwise. 

The ore bodies consist chiefly of chlorite and 

veins and masses of quartz; 7 to 8 percent is of 

the sulfides, pyrrhotite, pyrite, and arsenopyrite 

(Noble, 1950, p. 231; Slaughter, 1968, p. 1455-

1456). The chlorite and quartz can extend hundreds of feet into the adjacent Poorman Formation; 

pyrrhotite can also extend far into the Poorman, 

but the gold and the arsenopyrite with which it is 

commonly associated are generally confined to the 

Homestake Formation. Noble (1950, p. 231-237) 

divided the Homestake mineralization into four 

11 

stages represented by four different mineral 

assemblages in which, from oldest to youngest, the 

principal minerals are (1) quartz, chlorite, and arsenopyrite; (2) quartz (continuing from the first stage), 

ankerite, and pyrrhotite; (3) pyrrhotite (continuing 

from the second stage); and (4) pyrite and calcite.· 

The first three mineral assemblages were formed 

prior to the Tertiary rhyolite dikes, and according 

to R. 0. Rye (written commun., 1974), further 

study has shown that these assemblages can occur 

in any sequence. Veinlets of pyrite and calcite cut 

not only the other three assemblages but also the 

rhyolite. Detectable gold occurs in all four 

assemblages, though it is sparse in veins of massive 

pyrrhotite and in the pyrite-calcite assemblage 

(Slaughter, 1968, p. 1457), and gold is also in nearby unaltered or slightly altered cummingtonite 

schist. Production statistics from Slaughter (1968, 

p. 1438) show that from 1946 through 1965 the mine 

yielded 0.345 ounces of gold and 0.070 ounces of 

silver per ton of ore. 

The age of Homestake gold mineralization has 

long been disputed; vigorous arguments have been 

set forth in support of both Precambrian and Tertiary ages. The supposedly detrital (Precambrian, 

Homestake-derived) gold at the base of the 

Deadwood and the apparently deep-seated nature 

of the Homestake mineralization indicate a 

Precambrian age. The existence of a small percentage of Homestake ore cutting Tertiary igneous 

rocks and the nearness of the Homestake to the 

main Deadwood deposits suggest a Tertiary age. 

Actually the question was never of a clearcut yesor-no kind; the widespread, though sparse, gold in 

many units of Black Hills iron-formations can be 

plausibly interpreted only as Precambrian, and the 

ore cutting Tertiary igneous rocks is obviously 

youthful. Thus the real question was whether the 

Homestake ore is mainly Precambrian or mainly 

Tertiary. 

The problem seems now to have been settled by 

Rye and Rye (1974) through work on stable 

isotopes, especially of sulfur and oxygen. They 

show that the sulfur was almost certainly an 

original constituent of the sediments and that the 

nature of both sulfur and oxygen isotopes indicates 

the ore bodies obtained their concentrations of sulfur and quartz from nearby sources during 

metamorphism. Much of the vein quartz of the ore 

bodies may be merely dissolved and reprecipitated 

cherty quartz from the Homestake Formation. 

Other data cited by Rye and Rye are compatible 

with the theory of ore deposition from fluids 

migrating into zones of dilation during 
metamorphism. A key element in the process may, 

in their view, have been the alteration at the garnet 

isograd sideroplesite to cummingtonite, which 

would have released carbon dioxide to the fluid. 

They suggested that the metamorphism was the 

1, 700-million-year-old event of the Black Hills, as 

did Kulp and others (1956) as a result of a lead-lead 

age determination. 

Trace amounts of metals, including gold, are 

widespread in iron-formations of the Black Hills, 

and the Rye and Rye results leave little doubt that 

the same processes affected them. Rye and Rye 

likened the depositional environment of the 

Homes take Formation to the hot brine deeps of the 

Red Sea. 

Noble (1950, p. 247-248) was puzzled about why 

gold is localized in the Homestake Formation and 

is scarce or absent in chemically similar nearby 

rocks. He suggested only that some slight 

difference in the chemical properties of the 

Homestake rock made it more receptive to 

hydrothermal mineralization. The now probable 

reason is that the Homestake Formation had more 

gold at the beginning. One must keep in mind that 

Noble was constrained by the theories of his time, 

which was before the large body of information now 

available on syngenetic metals deposits and their 

subsequent history had been amassed. The 

Homestake deposit, with its structural complexities, was no place for the invention of drastic 

changes in theories of origin of hydrothermal· 

deposits. Noble (1950, p. 245-248) had the 

prudence to classify both the question of age and 

the question of ore localization in the Homestake 

Formation as "unsolved problems." 

Three separate ore controls for the Homestake 

deposit have now been identified: (1) the 

Homestake Formation itself, because at least part 

of the original sediment contained gold and 

because most of this gold remained in the formation during later events; (2) the cross folds; and 

(3) the zone of metamorphic change, in rocks just 

above the garnet isograd, where sideroplesite gives 

way to cummingtonite. 

Any locality where these three controls appear 

likely to come together is an exploration target 

worthy of considerable- attention. The cross folds 

may be less important in exploration than the other 

ore controls, for metalliferous fluids passing 

through any available channels may well have~ 

found other dilated structures in which to drop 

their load in a concentrated form. 

Interestingly enough, S. F. Emmons (in Irving, 

12 

1904, p. 78-79), after brief examination of the 

Homestake mine 75 years ago, concluded that the 

deposit is at the juncture of a N. 30° W. line of 

"major crushing" and a N. 10° W. line of "minor 

movement" (presumably what is now called 

crossfolding), that there were both Precambrian 

and Tertiary periods of mineralization, and that 

the metals were derived by leaching from rocks at 

lower levels by percolating waters. At that time the 

science of economic geology, of which Emmons was 

one of the founders, and the mining of the 

Homes take deposit were not far beyond infancy. 

OTHER DEPOSITS IN IRON-FORMATION 

Units of iron-formation in many parts of the 

Black Hills are pockmarked with prospect pits, 

most of which probably were dug because the early 

prospectors found gold in pan concentrates; but 

some pits may reflect their knowledge that ironformation on iron-stained rock was a good place 

to look for gold. Analyses for the Rochford area 

published by Bayley (1972a, pl. 2) confirm the 

presence of gold. Places where iron-formation is 

thickened by folding seem most favorable; these 

localities contain the mines having a record of 

production, the diggings of sufficient extent to have 

once been called mines even though their history 

may now be vague or untraceable, and the groups 

of prospect pits that apparently achieved no fruitful result. The principal localities are near 

Rochford and at various places near Keystone, especially in a belt of iron-formation that goes northnorthwest through the village (Norton, 1960). 

Interest in the Rochford district, which has long 

been considerable, is likely to be enhanced by the 

analyses of Bayley ( 1972a) and by his geologic map 

of the area and descriptions of the rocks and the 

principal mines and prospects. Recorded gold 

production is only a few thousand ounces, and unrecorded production cannot increase the total 

beyond a very few tens of thousands of ounces. Part 

of the reason for the modest productivity may have 

been low mill recoveries. 

The Rochford area has three units of quartzgrunerite schist that very closely resemble the 

Homes take Formation (Bayley, 1972a, p. 6). One of 

these units, which Bayley (1972a, p. 5-6) named 

the Rochford Formation, was in fact long regarded 

as Homestake Formation on the southerly plunging 

upside down nose of a syncline (Noble and Harder, 

1948, p. 954-955; Harder, 1934). Bayley, however, 

found that the structure is anticlinal, that the supposed Homestake Formation is a part of the Flag 
Rock, which he raised to a group, and that the real 

Homestake Formation must be deeply buried, if indeed it exists in the area at all. Bayley's evidence is 

sufficiently persuasive to allow little room for the 

possibility that any iron-formation in this area is 

actually the Homestake Formation. Yet the 

lithologic nature and gold content of the rock point 

to a similarity in origin, as do the isotopic data of 

Rye and Rye (1974). The area may indeed contain 

sizable gold deposits in suitable structural and 

metamorphic environments, if not at Rochford 

then in places to the north beneath Paleozoic cover. 

In the Keystone region most if not all the 

mineralization in iron-formation is Precambrian. 

At Keystone itself, however, a series of deposits 

from the Bullion mine to the Bismark mine is 

alined along a breccia zone containing slickensides 

of such fresh appearance as to indicate a very 

youthful age. The breccia may have formed after 

the mineralization, but the coincidence of the two 

suggests that the mineralization was, at least in 

part, a result of redistribution of metals in the Tertiary. 

The most curious aspect of deposits in ironformation is that exploration for gold or other 

metals has been remarkably unrewarding except at 

Homestake. Perhaps these other iron-formations 

had less gold in the original sediment, but another 

explanation lies in the probability that one of the 

ore controls of the Homestake deposit is its position 

slightly above the garnet isograd. Nearly all the 

Black Hills Precambrian rocks are above the garnet 

isograd. The only known exception is west of Lead, 

though there may be others in the northeast part of 

the Precambrian area. The southern Black Hills is 

mostly above the staurolite and sillimanite 

isograds. Deposits may have formed in rocks of 

lower metamorphic grade once overlying the 

region, but if so they were eroded away later in the 

Precambrian, and the gold was carried to places 

now unknown and undeterminable but surely 

buried deeply beneath Paleozoic cover. 

GOLD QUARTZ VEINS 

Quartz veins having gold in the quartz or in 

the wallrock have been found in many places in 

Precambrian rocks, mostly in quartz-mica schist, 

but probably only because that is the most 

abundant kind of rock in the region. Vein quartz 

in iron-formation or in associated rocks is of 

course excluded here, as it belongs with the 

deposits described on preceding pages. 

Workings range from the smallest of prospect 

13 

pits to mines of moderate size, of which the Holy 

Terror and the Clover Leaf yielded the most gold. 

Most of the so-called mines, however, are more 

properly described as large exploration openings, 

for they never matured into productive and 

profitable operations. Of the 51 square miles of 

Precambrian rocks north of Custer in the Berne 

quadrangle, which is representative of the southern 

Black Hills and perhaps of the entire Black Hills, 

Redden (1968, p. 402) lists nine small gold quartz 

mines in mica schists(9 deposits in 51 sq mi 

is representative abundance). 

Four mines had enough production to warrant 

particular mention; the host rock is quartz-mica 

schist at each of these localities. The Clover Leaf 

(formerly Uncle Sam) mine at Roubaix is a saddle 

reef in a minor anticline plunging 40° SE.; the 

thickness of quartz is about 10 feet (3 m) in one 

limb, 20 feet (6 m) in the other, and considerably 

greater in the crest (Irving, 1904, p. 92-93). Mining 

was from a vertical shaft 750 feet (227 m) deep 

(Allsman 1940, fig. 3). Ore can be expected to continue to greater depths (Bayley, 1970, p. 9), but excessive water, modest ore grade, and low mill 

recoveries seem to have been the causes for discontinuing the operation. The Holy Terror mine at 

Keystone, mined to a depth of 1,200 feet (366m) 

(Allsman, 1940, p. 91), is on a quartz vein of steep 

dip and N. 35° W. strike. The Empire mine, 5 miles 

(8 km) northwest of Keystone, is a combination of 

two older mines on two separate quartz veins, each 

of N. 30° W. strike and steep southwest dip, 

opened to a depth of 650 feet (198 m) (AUsman, 

1940, p. 75-77). The J. R. mine, 3 miles (almost 5 

km) N. 60° E. of Hill City, is on a north-striking 

vein of moderate west dip in which the quartz and 

mineralized wall rock have a thickness of 3 V2 to 4 

feet (1 m) (Allsman, 1940, p. 80). 

It is generally assumed, probably correctly, that 

most of the gold quartz veins formed in the 

Precambrian. Not only has no similar mineralization been recognized in younger rocks, but also the 

occasional particles of gold reputed to have been 

found at the base of the Deadwood on the 

southwest side of the Precambrian rocks seem likely to have come mostly from quartz veins, for these 

are virtually the only gold deposits nearby. 

Nevertheless, a surprising feature of several of 

these deposits is that they are near breccia zones of 

remarkably fresh appearance, which is a rare 

feature in the Precambrian rocks. The movement 

along faults containing these breccias may well 

have been mainly in the Precambrian, but some 

youthful movement, perhaps accompanied by 
mineralization, seems indisputable. Ratte and 

Wayland (1969, p. 13) mentioned such breccia accompanied by gold along the Burnt Fork fault. 

They also (1969, pl. 1) mapped a zone of breccia 

and silicified rock, 1 mile long and as much as 550 

feet wide (about 1,600 by 165 m), that at its 

northeast end, according to my own findings, 

branches into two breccia zones. One branch is 

near one of the quartz veins and the other near the 

second of the quartz veins in the Empire mine. One 

of these breccia zones can be seen in what is known 

as the Climax adit. The very similar breccia zone at 

the Bullion mine, which has already been 

described, is parallel to another such zone in the 

Keystone mine 500 feet to the southwest, and only 

500 feet farther southwest is the Holy Terror quartz 

vein. 

Little is known about the geology of the Keystone 

mine except that a major Precambrian fault goes 

through or near the workings (Norton, 1960). A 

small area at the entry of the main adit, which was 

found to be open and was entered in 1970, contains 

a breccia zone of N. 48° W. strike and 70° NE. dip 

that is close to or exactly on the large fault. A map 

published by AUsman (1940, p. 95) indicates that 

the mine workings are parallel to this breccia zone. 

Nevertheless, it remains unknown whether the gold 

is with vein quartz, is in mineralized breccia, or 

replaces narrow beds of iron-formation corresponding to those exposed about 1,500 feet ( 460 m) to 

the northwest. 

DEPOSITS IN BASAL CONGLOMERATE 

OF DEADWOOD FORMATION 

The only truly productive deposits at the base of 

the Deadwood Formation are at a few localities 

where Cambrian rocks cap hilltops on the west, 

north, and east sides of the original outcrop of the 

Homestake deposit. The best ore was mined in very 

early years (about 1876-81). For descriptions, one 

must depend chiefly on Irving (1904, p. 98-111, 181-

184), whose work followed the abandonment of 

most of the mines, and on Devereux (1882), whom 

Irving himself quoted at length. According to 

Irving (1904, p. 109-111), the gold takes three forms: 

(1) detrital gold, "Apparently***the most important source of value in the ores," of which he found 

many well-rounded examples, one of them a nugget 

"nearly ~ne-half inch in diameter***of undoubted 

detrital origin"; (2) gold subsequently dissolved 

and reprecipitated nearby, some of it in underlying 

schist; and (3) gold introduced with pyrite, 

presumably in Tertiary time. Pyrite, or more com14 

monly iron oxide derived from pyrite, is abundant 

in the matrix of the conglomerate virtually 

everywhere that gold is present and absent where 

gold is absent (Irving, 1904, p. 99, 107-108). This 

circumstance calls to mind the oxidized and pyritic 

phases of replacement deposits higher in the 

Deadwood and raises doubt that any of the gold is 

detrital-a deficiency not mentioned by Irving but 

which was repaired for him by Noble (1950, p. 246). 

Noble had the workings reopened and in his subsequent examination found no obvious detrital 

gold. 

Nevertheless, early observations made at the 

time of mining should not be casually passed over. 

Gold of apparently detrital origin surely was 

observed (Irving 1904, p. 109; Devereux, 1882, p. 

468-469). Devereux (1882, p. 473) pointed out that 

the durability of the Homestake outcrop would 

enable it to form an island in the Deadwood sea 

around which gold-bearing conglomerate would accumulate. Irving (1904, p. 99-104) elaborated on 

this thesis with a description of the apparent preDeadwood topography and its relations to 

stratigraphic units within the Deadwood. Gold was 

most abundant in the deepest depressions and conglomerate _is thickest in these depressions. 

Conglomeratic fragments, especially large 

fragments of schist, diminish in abundance away 

from the Homestake lode, indicating they were 

derived locally. Overlying quartzite and the still 

higher dolomites and shales lap onto the supposed 

island, and only the higher horizons are 

represented near the site of the Homestake outcrop. 

The conglomerate is thick at other localities adjacent to inferred pre-Deadwood topographic highs 

(Kulik, 1965, especially pls. 2, 3, 6, 14), but 

evidence that they contain gold is sparse. 

Elsewhere the conglomerate is generally thin and 

unproductive or absent. A few mines that operated 

chiefly in replaced dolomite also contained gold in 

the underlying quartzite or conglomerate; Shapiro 

and Gries (1970, p. 30, 31, 124) and Irving (1904, p. 

144) cited several examples but showed that nearly 

all such gold was of replacement rather than placer 

origin. 

At Rockerville, in the east-central part of the 

Black Hills, the conglomerate is perhaps 20 feet or 

more (about 6 m) thick. Old workings scattered 

along the Precambrian-Deadwood contact 

northeast and east of Rockerville are large enough 

to verify the presence of gold but too small to indicate that mining was of more than modest 
success. According to Perry Rahn (oral commun., 

1972), surficial material overlying nearby Precambrian rocks has many pits in what appear to be 

relicts of the pre-Deadwood surface. These 

presumably contained placer gold that had worked 

its way into underlying weathered rock. 

Nevertheless, most of the Rockerville mining 

appears to have been in Quaternary gravels to the 

east. 

REPLACEMENT DEPOSITS IN DEADWOOD FORMATION 

Most of the gold from the Deadwood Formation 

has come from replacement bodies in dolomite just 

above the quartzite near the base of the formation 

and from dolomite high in the section, a few feet 

below the Scolithus sandstone. These are known as 

the "lower contact" and "upper contact" ores, 

though these terms have no reference to any 

geologic contact. 2 A few replacement deposits have 

been mined in the basal quartzite. 

Aside from the Maitland and Wasp No. 2 mines 

(table 1), virtually all the mined ore bodies are 

within a rectangle about 5 miles (8 km) long in a 

westward direction and 3 miles (5 km) wide, having 

Lead at its northeast comer. Much of this rectangle 

is occupied by Tertiary igneous rocks, Mississippian units, and Precambrian rocks, but a sizable 

share of it has outcrops of the Deadwood Formation. Most of the Deadwood production has come 

from two small areaa: the Ruby Basin district, 

about 11!2 square miles (6 km2) in extent, 21/2 miles 

west-southwest of Lead; and the Portland district, 

about 1 square mile (2 1/2 km2) in extent, centered 

near Trojan 3 miles (almost 5 km) west of Lead. 

The mining region has many hills and valleys 

which expose rocks from well below the Precambrian surface upward to the Pahasapa Limestone 

(Mississippian). The most abundant rocks belong 

to the Deadwood Formation or to Tertiary intrusions, which are common on the higher mountains and as sills within the Deadwood Formation. 

The topography has facilitated tracing the orebearing horizons of the Deadwood. Most of the discoveries were undoubtedly made by prospecting in 

this way. 

2 Shapiro and Gries (1970, p. 29) suggested that this odd usage originated in a mine 

that had ore at the lower and upper contacts of a thick sill; this is plausible, except 

that Shapiro and Gries based their statement on Crosby (1888), who said nothing to 

indicate that these terms were in use during his time. Even more illogical is use of the 

term "intermediate contact" for ore at intermediate levels. Moreover, the name 

"Bald Mountain," from one of the prominent peaks of the region, has been applied in 

three different ways to Deadwood mining areas: (I) to the whole of the 

Portland-Ruby Basin area; (-2) to the Ruby Basin district alone; and (3) to the most 

important mining company in the area, which, adding further to the confusion, 

operated chiefly in the Portland district. 

15 

The replacement deposits are at the edge of a 

dome which encompasses the whole 

Deadwood-Trojan region and which has near its 

center a Tertiary stock of several square miles, 

known as the Cutting stock, which is 2 miles (3 

km) northwest of Lead. The principal deposits 

are along the south and northeast sides of the 

stock. Elsewhere in the vicinity of the stock, 

Deadwood outcrops are sparse or absent, and 

thus Deadwood gold deposits are necessarily 

absent also. 

Ore occurs where vertical mineralized fractures 

or groups of fractures intersect beds of dolomite, 

which are replaced outward from the fractures. The 

first comprehensive description of the structure of 

these elongate ore bodies, or "shoots," was by Irving (1904, p. 124-136, pl. 11), who said that common dimensions are 100 to 800 feet (30 to 240m) in 

length, 5 to 100 feet ( 1.5 to 30 m) in width, and 1 to 

10 feet (0.3 to 3 m) in thickness. According to 

Miller (1962, p. 31), maximum dimensions are 

somewhat more than 5,000 feet (1,525 m) in 

length, 100 feet (30 m) in width, and. as much as 

22 feet (7 m) in thickness. But greater lengths 

and widths are attained where closely spaced 

vertical fractures cause ore bodies to coalesce. 

Some ore bodies are also controlled by contacts 

with Tertiary intrusions (Shapiro and Gries, 

1970, p. 48), which undoubtedly increase the 

geometric complexity. 

The geologic map by Irving (1904, pl. 9) and 

maps of mine workings compiled by Shapiro and 

Gries (1970, pis. 9-11) show that the dominant 

strike of the ore shoots is due north in the Ruby 

Basin district, where most of the ore is in the 

"lower contact" zone, and N. 45°-55° E. in the 

Portland district, where both the "upper contact" 

and the "lower contact" have been productive. 

Northwesterly and westerly trending ore shoots are 

also common. Less significant vertical fractures 

trend in many other directions and either widen the 

ore bodies or cause branching and anastomosing 

shapes. 

The northerly and northeasterly trends of the 

larger ore bodies suggest control by radial fractures 

around the Cutting stock (Slaughter, 1968, p. 1444, 

fig. 1), but the results of more detailed fracture 

studies of Shapire and Gries (1970, p. 45-48, pl. 8) 

indicate that this appearance is misleading. Fractures having northeast and northwest strikes are 

common throughout the region, so they probably 

are older than the Tertiary igneous rocks and are 

unrelated to any individual intrusion. The 
northerly trend in the Ruby Basin district seem to 

be associated with faults of the same strike, which 

are in part older and in part younger than the Tertiary intrusions. Irving (1904, p. 132-133) suggested 

a less simple scheme but showed clearly that some 

fractures and the ore accompanying them are older 

and some younger than the associated intrusions. 

The Deadwood replacement ore in an unaltered 

state, as first comprehensively described by Irving 

(1904, p. 136-144), is a very fine grained siliceous 

pyritic rock; gold had been identified only in 

telluride form until Connolly (1927, p. 77-90) 

showed that most of the gold is included in pyrite. 

Much of the ore has undergone oxidation, which 

has destroyed the pyrite and made the gold more 

readily obtainable; this "red" or "brown" ore, as it 

was called, was the source of most of the gold 

mined before the late 1920's. Oxidation occurred 

along contacts between ore and adjacent dolomite 

and -along fractures and bedding planes (Irving, 

1904,p. 140;Connolly, 1927,p. 93). 

The ore has always been classed as refractory, 

though technical developments over the years have 

greatly increased recoveries. By ordinary cyanide 

procedures of the early years (Connolly and 

O'Harra, 1929, p. 164) the unaltered or "blue" ore 

yielded no more than one-third of the gold present. 

Even the oxidized ore was difficult to treat, for the 

gold is very finely divided and it required correspondingly fine grinding. Oxidation diminishes 

the refractory nature of the ore probably by 

shattering the quartz as well as breaking down the 

sulfides and tellurides (Connolly, 1927, p. 94). The 

depletion of oxidized ore and the necessity of 

depending on unaltered ore encouraged the use of 

roasting to break down the ore, and recovery ultimately attained about 85 percent (Connolly, 

1927, p. 89-91; Leaver and Woolf, 1928, p. 23-52; 

Miller, 1962, p. 49; AUsman, 1940, p. 45). Mter 

World War IT, cyanide techniques had improved so 

greatly that similar recoveries could be obtained 

from much of the "blue" ore without roasting 

(Miller, 1962, p. 48). Probably most of the "blue" 

ore has now been mined or is inaccessible (D. T. 

Delicate, oral commun., 1973). In the mining 

methods used in the region, pillars were robbed on 

retreat, and waste rock was commonly backfilled 

(Miller, 1962, p. 77-78, 82). 

According to Miller (1962, p. 48) the grade of all 

ore mined by the Bald Mountain Mining Co. and 

its predecessors from 1912 to 1959 was 0.186 ounce 

of gold and 0.617 ounce of silver per ton, though 

data from AUsman (1940, p. 28) for the years 1901-

16 

37 indicate that 0.237 ounce of gold and 0.354 ounce 

of silver were recovered per ton of ore. Corresponding figures for the Golden Reward mine between 

1901 and 1922 are 0.388 ounce of gold and 0. 767 

ounce of silver, and for the Mogul they are 0.234 

ounce of gold and 0.485 ounce of silver. At the 

prices of 1973 and early 197 4, these yields would 

amount to about $20 to $60 per ton of ore. Under 

modem economic conditions, ore near the lower 

end of this range, especially in small and irregular 

ore bodies, may be as marginal as it was under the 

conditions when mining 'was most active, but the 

richer and larger ore bodies would clearly be 

attractive. 

The Deadwood replacement ores have been universally regarded as Tertiary in age and as related 

to the Tertiary intrusions. The chief dispute has 

been whether the Homestake deposit is of similar 

age and origin, and this question has now been 

settled in the negative by Rye and Rye (1974), who 

show that the isotopic properties of the two kinds of 

ore are distinctly different. Their work on Tertiary 

deposits was more on the Tertiary minerals of the 

Homestake mine and on lead-silver ores of the 

Deadwood Formation and Pahasapa Limestone 

than on the gold deposits, thus perhaps leaving 

room for further investigation of the nature of gold 

mineralization in Paleozoic rocks. Nevertheless, 

their data indicate that Tertiary ore minerals were 

deposited by hydrothermal fluids associated with 

the igneous activity of that time, and that the sulfur and presumably the gold were obtained from 

Precambrian rocks. Though they say the proximity 

of the Tertiary and Precambrian deposits may not 

be a result of chance, the question remains open 

about whether the Deadwood replacement gold 

came from the so-called Homestake Formation or 

whether the two have a more remote relationship. 

Though the results are not as satisfying as clear 

proof, they do allow the Deadwood deposits to be 

regarded as a traditional geochemical anomaly in 

that they indicate exploration of underlying rocks 

is worthwhile. 

DEPOSITS IN PAHASAPA LIMESTONE 

Except for a few examples of mineralization 

noted in the Whitewood Limestone by Shapiro and· 

Gries (1970, p. 50, 100, 196), none of the 

stratigraphic units between the Deadwood Formation and the Pahasapa Limestone are likely sources 

of gold. Deposits in the Pahasapa resemble those in 

the Deadwood except for their much smaller abundance and productivity. The principal deposits are 
east and northeast of Savoy, especially on the 

flanks of Ragged Top Mountain, which is formed 

from a Tertiary intrusion; the Carbonate district 

northeast of Ragged Top is mainly a lead-silver 

area. The Ragged Top ore bodies were formed by 

lateral replacement of limestone along northeaststriking vertical fractures. They are thus similar to 

deposits in the Deadwood Formation, but there is 

no obvious reason why one bed is selected for 

replacement in favor of another (Irving, 1904, p. 

172-177). The replaced beds are highly silicified. 

Sulfides are virtually absent, but tellurium has 

been detected. 

Most of the mining in the Ragged Top area was 

done after Irving's visit there, and Darton and 

Paige (1925, p. 29) added little to Irving's account. 

Evidently, no geologist has published observations made while the mines were in full operation. 

The supposition that mineralized vertical fractures in the Pahasapa are a sign of ore at depth has 

long been a source of encouragement to deep exploration in the Ragged Top and Carbonate region. 

More concrete evidence of ore at depth lies in the 

existence of modest amounts of ore in Deadwood 

dolomite at the Cleopatra mine (Shapiro and 

Gries, 1970, p. 183-185), which is 2 miles (about 3 

km) north-northeast of Ragged Top and near the 

southwest edge of the Carbonate district. According to AUsman (1940, p. 52) exploration at Ragged 

Top through a 500-foot (150-m) shaft and a 500-foot 

drill hole extended to the lower Dead wood, but, 

though ore was said to have been found, work was 

discontinued. Two nearby diamond drill holes to 

explore the Pahasapa and the Deadwood also had 

small results (Shapiro and Gries, 1970, p. 156-157). 

DEPOSITS IN TERTIARY IGNEOUS ROCKS 

The only significant deposits thus far found in 

igneous rocks are in and near the Gilt Edge 

and Hoodoo-Union Hill mines, northeast of 

Strawberry Ridge, 5 miles (8 km) east-southeast of 

Lead. Small amounts of ore, part of it very rich, 

have been found elsewhere: some at Mineral Hill, 

just across the state line in Wyoming (Darton, 

1905, p. 11); some northwest of Lead (AUsman, 

1940, p. 56); some on Squaw Creek, 4 miles (6 km) 

or less northeast of Savoy (Irving, 1904, p. 97); and 

some, of course, in rhyolite in the Homestake mine 

itself. Adjacent Paleozoic or Precambrian rocks are 

also commonly mineralized. 

According to Irving (1904, p. 97), the ore at 

and near the Gilt Edge mine, which he visited in 

17 

1899 prior to the principal period of mining 

(1900-1908), is in limonitic fracture fillings and 

adjacent weathered porphyry near the surface 

and in pyritic rock doWnward from the surface. 

AUsman (1940, p. 57) confirmed this but added 

that at the intersection of fractures most of the 

ore bodies are in breccia. 

QUATERNARY AND TERTIARY PLACER DEPOSITS 

In the earliest gold-rush years, placer deposits 

were the scene of nearly all mining; the Deadwood 

Gulch area was by far the most productive. It soon 

became obvious, however, that placer mining was 

going to be only a minor activity. Nevertheless, 

placer operations, generally on only a small scale, 

continued sporadically through later years and intensified during the 1930's. Even today some gold is 

taken from placer deposits, but more as recreation 

for amateurs than as profitable enterprise. 

Attempted dredging operations and use of other 

mechanical equipment have been marked more by 

optimism than success. 

Most of the placer mining was at or near valley 

bottoms, where water was readily available. 

Streams that drain a large area of Precambrian 

rocks have been most favored (Connolly, 1933, p. 

14). One important exception is Rockerville Gulch, 

which drains only about 3 square miles of Precambrian rocks and which obtained most of its gold 

from basal conglomerate of the Deadwood Formation. Because Rockerville Gulch contained insufficient water, a 17-mile (27-km) flume was built to 

bring water to this deposit. 

Gold in attractive amounts has been found in 

many terrace gravels on the walls of present-day 

stream valleys, but these deposits tend to be small 

and sparsely distributed, and easily available 

water is lacking. Other gravels have little readily 

apparent relationship to the modern drainage 

systems. High-level gravels may have received less 

attention than they deserve. 

Oligocene sands and gravels, mapped by Darton 

and Paige (1925), occur even at rather high 

altitudes and indicate that much of the Black Hills 

became covered at Oligocene time. Whether gold 

that eroded from older rocks was concentrated 

anywhere in these sediments or whether virtually 

all of it was dissipated is unknown. The Homestake 

lode cannot have been a contributor to such 

deposits, for it was only slightly eroded between 

Cambrian and modern times, and whatever placer 

gold it did yield went, with gold from the nearby 

Cambrian deposits, into the gravels mined in the 

Deadwood Gulch area. Thus, the most obvious 
sizable source for gold in Oligocene sediments is the 

many square miles of Deadwood Formation eroded 

from the northern Black Hills. A site in the 

southern Black Hills that has attracted some attention is the Pleasant valley, 9 miles (14 km) 

southwest of Custer, where about 200 acres of 

Oligocene sediments was mapped by Redden (1963, 

p. 274, pl. 21). Perhaps an effort to decipher the 

Oligocene drainage pattern of the Black Hills 

region would lead to the discovery of gold concentrations, but the investigation would be difficult 

and probably fruitless. 

PROPOSED APPROACH TO EXPLORATION 

The known facts about the distribution of ore indicate that exploration for new major gold deposits 

should be chiefly in the northern Black Hills. 

Production figures indicate that the primary objective should be to find a new deposit of the 

Homestake type, but discovery of a new area of 

Deadwood deposits might be worthwhile. 

The large amount of prospecting in the past virtually eliminates hope that sizable deposits of any 

kind can now be found at the surface. All discoveries to date have been made either at the outcrop or through exploration within existing mines. 

No truly new deposit has been found in the Black 

Hills since shortly after the gold-rush years. Yet 

unmistakable evidence shows that concealed 

deposits may exist in unexplored localities. 

The long-standing belief by Noble ~d his 

associates that the Homestake deposit is of 

Tertiary age must have led them, as it did me 

some years ago, to the conclusion that deposits 

in the Deadwood and younger rocks are a sure 

sign of ore in nearby Precambrian rocks. Yet 

exploration directed by them based on this 

thesis seems to have been meager, probably 

because gold mining, even at Homestake, was 

marginal for a long time. 

Furthermore, few efforts have been made by 

others to find concealed deposits, even though the 

appeal of making the attempt was noticed long ago. 

Of the many drill holes through the Deadwood Formation, few have penetrated more than 20 feet (6 

m) into Precambrian rocks (Shapiro and Gries, 

1970, p. 215-222). A considerable effort was made 

at the Maitland mine between 1912 and 1915 to 

find ore by searching for underlying Homestake 

Formatron (Shapiro and Gries, 1970, p. 124). In 

retrospect, one recognizes that the failure of any of 

the vertical fractures in Deadwood deposits to lead 

to underlying ore was a very discouraging sign. This 

failure was also evidence that the Deadwood 

18 

replacement deposits and the Homestake deposit 

are of different age and that the presence of one 

does not require the nearby presence of the other. 

The Deadwood conglomerate ores can be 

viewed differently. Whether the Homestake 

deposit is Tertiary or Precambrian and whether 

the gold in the conglomerate is introduced or is 

fossil placer, gold in any conglomerate would 

seem to indicate that gold is close at hand in 

Precambrian rocks, and in fact the two did occur 

together at the outcrop of the Homestake lode. 

The view that the conglomerate should be 

thoroughly investigated has long appealed to me 

but apparently has had no other proponents, 

probably because it seemed more practical and 

useful to obtain other kinds of geologic 

information beforehand. 

The assurance now that mineralization was of 

both Pre cam brian and Tertiary age adds complications to the exploration problems, but at the 

same time it explains the absence of simple 

relationships and the lack of discoveries of Precambrian deposits directly beneath deposits of Tertiary 

age. The distribution of Tertiary ore is still useful 

information, for its gold did come originally from 

Precambrian sources, whether close by or far away. 

The problem now arising is how to use the 

younger rocks as guides to the locations of Precambrian deposits. A buried deposit that once was exposed on the pre-Deadwood surface offers the least 

difficulty, or so it would seem in theory, for one 

should be able to find its approximate location by 

determining the distribution in basal Deadwood 

rocks of gold and other metals useful as 

geochemical tracers and, by ascertaining enough 

about the pre-Deadwood topography, to guess the 

positions of hills of quartzose mineralized rock and 

channels that might have brought gold from a 

mother lode. Any deposit whose top is below the 

pre-Deadwood surface will be very hard to find. 

Helpful hints can be obtained by determining the 

distribution of introduced gold and other metals in 

the Deadwood and by learning where the so-called 

Homestake Formation or similar iron-formations 

are likely to be found in a suitable metamorphic 

and structural environment. An unavoidable conclusion is that quick and cheap methods of exploration will not suffice unless, of course, exceptional 

good luck prevails. A comprehensive and costly investigation should be regarded as necessary. 

The program I favor would require a new and 

detailed geologic investigation of an approximately 

120-square-mile (300-km2

) area roughly bounded 

by Spearfish Peak on the north, Savoy on the west, 
Cheyenne Crossing on the south, and the Galena 

lead-silver district on the east. A geologic map of 

this area that would be satisfactory in most 

respects can be compiled at the 1:24,000 scale of 

available topographic maps from existing information, but full field study to increase the detail 

would be required. Paleozoic rocks and some of the 

younger rocks in much of the area have recently 

been mapped by Shapiro and Gries (1970, pls. 2-6). 

Maps by Bayley (1972c) and by Noble, Harder, and 

Slaughter (1949, pl. 1) show the main Precambrian 

features. Mukherjee (1968, pl. 1) mapped about 10 

square miles near Galena. The entire area is 

covered by a map at a scale of 1:62,500 by Darton 

and Paige (1925). These maps are not in all 

respects reconcilable with one another. 

Geologic mapping of perhaps 40 square miles 

(100 km2 ) straddling the South Dakota-Wyoming 

State line at Tinton, or at last a thorough examination of this area, would be worthwhile. Reputedly 

rich placers worked in early years have no obvious 

source for their gold; this peculiarity calls for 

a search for the explanation. 

The physical stratigraphy, structure, and 

geochemistry of the Deadwood For1nation 

should receive close attention. Unfortunately, 

outcrops of the Deadwood are sparse in many 

places, both because of its own weathering 

characteristics and because cliffs of Pahasapa 

Limestone shed rubble over older rocks. A truly 

detailed study is likely to require short core-drill 

holes, which perhaps can be made from a 

truck-mounted rig. The Deadwood Formation 

should also be examined for about 30 miles ( 48 

km) southward, to Rockerville on the east and 

Bear Mountain on the west, to supplement the 

stratigraphic work of Kulik (1965) and to test 

by geochemical sampling the possibility that 

gold deposits are concealed nearby. 

A reexamination of the petrology and structure 

of the Tertiary igneous rocks is desirable and 

perhaps essential. The absence of any comprehensive report on them since the time of Darton and 

Paige (1925, p. 16-17, 19-24) seems a serious shortcoming, for the repeated references to a connection 

between Tertiary mineralization and igneous activity leave little doubt of the need for a fuller understanding of this subject. 

Precambrian rocks, though also occupying a 

sizable share of the area, have been so closely 

mapped in the past (Noble and others, 1949, pl. 1; 

Bayley, 1972c) that they should cause few 

problems, though the rocks west and northwest of 

19 

the Lead area should be mapped in more detail 

than-heretofore. 

Organizations in a hurry, and with the funds to 

indulge their impatience, might be justified in starting deep-hole diamond drilling in the most obviously favorable areas at an early date. Plans for 

such a program should allow for many thousands of 

feet of drilling over an area of several square miles 

to test the structure, stratigraphy, and metals contents in both Cambrian and Precambrian rocks. A 

vertical hole collared near the top of the Deadwood 

Formation could require 400 to perhaps 900 feet 

(120 to 270 m) to reach the Precambrian contact, 

depending on the thickness of Tertiary sills encountered (Shapiro and Gries, 1970, p. 58). 

Inclined holes might be more informative in many 

places, for they will cut across vertical veins in the 

Deadwood Formation and will also yield a cross 

section of the Pre cam brian rocks, which generally 

have a steep dip. 

One may ask why no program of the kind advocated here has ever been attempted, even though 

the need for it has been recognized. The most obvious reason is that the price of gold became attractiv~ only recently. Other reasons lie in shortcomings in knowledge of Black Hills geology, 

sevetal of which have been eliminated in the last few 

years. The question of the age of Homestake 

mih.eralization now seems to have been settled by I 

Rye:and Rye (1974); the need for geologic mapping 

of Precambrian rocks south of the Lead region has 

been eliminated by Bayley (1970, 1972a, b, c); and 

the absence of any comprehensive study of the ore 

· bodies in Deadwood and younger rocks since the 

time of Irving has been eliminated by the work of 

Shapiro and Gries (1970). All these recent reports, 

however, while helpful in planning the kind of work 

here proposed, have enhanced rather than 

diminished the obviousness of the need for further 

investigation. 

EXPLORATION TARGET AREAS 

Existing data suggest that three areas are 

suitable for exploration. A possible fourth, the area 

from Deadwood southeast to the Gilt Edge mine 

and the Galena lead-silver district, will not be discussed here because little can be said beyond the 

obvious statement that ore has been found at the 

surface. 

AREA NORTH OF LEAD 

The so-called Homestake Formation on both 

limbs of the anticlinorium at Lead disappears to 

the north beneath the Deadwood Formation or is 
cut off against Tertiary intrusions; it is not known 

with certainty that it reappears at the 

Precambrian-Cambrian boundary anywhere in the 

Black Hills. 

On the west limb of the Lead anticlinorium, the 

Homestake Formation trends toward the Maitland 

mine and goes through a series of tight folds 

(Bayley, 1972c). The garnet isograd is headed in 

this same direction (Noble and Harder, 1948, pl. 1). 

That this locality is an obvious place to search for 

ore of the Homestake type led to the previously 

mentioned unsuccessful exploration in the 

Maitland mine. 

Deadwood outcrop trends in a generally 

northwesterly direction from Maitland (Darton 

and Paige, 1925, geologic maps). Immediately to 

the northeast it is covered by the thin Whitewood 

and Englewood Formations, followed by a broad 

blanket ofPahasapa Limestone. A few square miles 

of Oligocene sediments as well as Tertiary intrusive 

rocks- also occupy the area. Surface indications of 

underlying ore would obviously be negligible or 

nonexistent. Yet the likely presence in the Precambrian rocks of the Homestake Formation, the 

presence of tight folds and the garnet isograd, and 

the existence of Deadwood ore in the Maitland 

mine all indicate that this area is an exploration 

target worthy of intensive investigation. 

PORTLAND AND RUBY BASIN REGION 

The Portland and Ruby Basin districts in the 

Trojan area contain the historically most productive Deadwood ore bodies, and that count alone 

justifies curiosity about what lies in underlying 

Precambrian rocks. The Deadwood Formation 

predominates at the surface for many miles to the 

south and southeast (Darton and Paige, 1925, 

geologic maps), where it undoubtedly has been 

thoroughly prospected with little or no success. 

Thus it appears that, until more encouraging 

evidence is discovered, areas of exposed Deadwood 

rocks far removed from old mines are not of immediate interest. Pahasapa Limestone occupies the 

higher hills, and Tertiary intrusions are common. 

Still farther south, the Precambrian is exposed in 

an anticlinorium in which the oldest rock is 

probably equivalent to Noble and Harder's Ellison 

Formation (Bayley, 1972a, p. 3, pl. 1). The strike of 

this anticlinorium would carry it beneath the 

Portland and Ruby Basin districts. Just north of 

these districts, Noble and Harder's Ellison 

reappears (Bayley, 1972c) in a manner that implies 

that the anticlinorium continues beneath this en20 

tire region of Paleozoic cover. Whether the 

Homestake Formation exists at all in this region 

and whether, if it does exist, it is ever at the 

Precambrian-Cambrian contact is unknown. If it is 

at or not far below this contact, the Portland and 

Ruby Basin region is as good a place as any to look 

for it. 

The literature does not record what happens to 

the garnet isograd south of where it was mapped at 

Lead (Noble and Harder, 1948, pl. 1). Rocks in the 

Rochford region, however, are above the garnet 

isograd, and so also are most or all of the Precambrian rocks along the east side of the Paleozoic 

rocks between Rochford and the Portland and 

Ruby Basin districts. One must, therefore, conclude that the garnet isograd extends from Lead 

southwest and perhaps west somewhere not far 

from Portland and Ruby Basin. 

In short, this target area possesses Deadwood ore 

bodies, it may have so-called Homestake Formation beneath it, it may be near the garnet isograd, 

and it almost certainly has a tightly folded Precambrian anticlinorium. These facts, taken as a group, 

imply that exploration for a concealed Precambrian deposit may be rewarding. 

ROCKERVILLE AREA 

Deadwood conglomerate east of Rockerville has 

gold of apparently placer origin, and Quaternary 

placers to the east have been extensively worked. 

No one, however, seems ever to have been curious 

about where the gold came from originally. 

The interpretation by Kulik (1965, p. 138-139, pl. 

14) of the paleogeography at the start of Deadwood 

sedimentation attributes conglomerates mainly to 

wave action near islands and steep headlands. 

Kulik seems unaware of the conglomerate at 

Rockerville, but this is a small oversight in view of 

the breadth of area he studied. 

One could suppose that the gold was washed in 

from Keystone, 6 miles (10 km) to the southwest. 

Another possible source area is Silver Mountain, 3 

miles (5 km) to the west, where an island must 

have existed, but the rock there is mostly 

amphibolite, and such iron-formation as is present 

has prospect workings suggestive of only sparse 

gold. All in all, the exposed gold-bearing rocks west 

of Rockerville are unprepossessing as mother lodes 

for the gold in the Deadwood Formation. 

Northwest of Rockerville is a unit called Ellison 

Formation on Bayley's open-file map (1972c) and 

by another name on his N emo map ( 1972b). A body 

of iron-formation near the unit's northeast side is 
tentatively correlated with the so-called 

Homestake Formation (Bayley, 1972c), but it 

lenses out 13 miles (21 km) northwest of Rockerville. The supposed Ellison shows few folds in the 

N emo region, but it becomes intricately folded to 

the southeast before it passes beneath Paleozoic 

cover (Bayley, 1972b, c). Folding of Precambrian 

rocks is also complex near Rockerville; 1.3 miles 

(2.1 km) to the southwest on U.S. Highway 16, J. 

A. Redden and I have seen three sets of folds of 

different shape and attitude in a single outcrop 

over a width of about 10 feet (3 m). 

The strike of the presumed Ellison of Bayley 

should bring it within 1 mile (1.6 km) of the exposed conglomerate. Possibly, gold-bearing ironformation is also nearby, for hematite pebbles in 

Deadwood conglomerate have been observed in the 

Stratobowl just north of Rockerville (Kulik, 1965, 

p. 21). Furthermore, the sparsity and size of garnet 

near Rockerville suggest that the garnet isograd 

may not be far away. An investigation to evaluate 

the possibility that a concealed mother lode of 

Pre cam brian gold lies to the east is clearly 

justified. 

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*u.s. GOVERNMENT PRINTING OFFICE: 1974-!543-!586/1154