GEOLOGICAL SURVEY CIRCULAR 707 

Anomalous Concentrations of 

Several Metals in Iron-Formation 

of the Blue Lead Mountain Area, 

Pennington County, South Dakota 

Anomalous Concentrations of 

Several Metals in Iron-Formation 

of the Blue Lead Mountain Area, 

Pennington County, South Dakota 

By William H. Raymond, Robert U. King, and 

James J. Norton 

GEOLOGICAL SURVEY CIRCULAR 707 

1975 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretary 

Geological Survey 

V. E. McKelvey, Director 

Free on application to the U.S. Geological Survey, National Center, Reston, Va. 22092 
CONTENTS 

Page 

Abstract _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 

Introduction _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 

General geology _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 

Stratigraphy _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 

Structural geology _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4 

Mineralization _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5 

Geochemical anomalies _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5 

Summary _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6 

References cited _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6 

ILLUSTRATIONS 

Page 

FIGURE 1. Geologic map of the Blue Lead Mountain area _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

2-9. Maps showing content of -

2. Copper ----------------------------------- 7 

3. Gold ------------------------------------- 8 

4. Silver ------------------------------------ 9 5. Mercury _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10 

6. Molybdenum _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 11 

7. Arsenic _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 12 

8. Zinc _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13 

9. Cobalt------------------------------------ 14 

m 

Anomalous Concentrations of Several Metals in 

Iron-Formation of the Blue Lead Mountain Area, 

Pennington County, South Dakota 

By William H. Raymond, Robert U. King, and James J. Norton 

ABSTRACT 

Geochemical sampling of bedrock has revealed anomalous 

copper, silver, molybdenum, gold, arsenic, mercury, zinc, and 

cobalt in meta-iron-formation in the Blue Lead Mountain area 5 

miles (8 kilometres) north-northwest of Keystone, S.Dak. The 

anomalies are in complexly folded and faulted iron-formation. 

Metal content decreases sharply in the surrounding rocks. The 

extent and intensity of the anomalous areas, despite evidence 

that previous mining had little success, are sufficient to make 

this area an interesting target for exploration. 

INTRODUCTION 

Metamorphosed iron-formation is the host rock 

of many of the gold prospects and small mines as 

well as of the one truly large deposit - the 

Homestake mine - in the Black Hills of western 

South Dakota. The area surrounding the village of 

Keystone, which is 15 miles (24 km) southwest of 

Rapid City in the Mount Rushmore quadrangle, 

has an unusual number of sizable bodies of 

grunerite-quartz iron-formation. In times past, 

Keystone itself has been a center of- gold mining 

and exploration in a northwesterly trending belt 

several miles long, containing mineralized iron-formation, gold-quartz veins, and many folds and 

faults. 

In 1971 W. H. Raymond conducted a 

geochemical sampling program of the Keystone 

region, especially in localities with iron-formation 

and associated rocks, which previously had been 

mapped by J. J. Norton. As might be expected, 

iron-formation near Keystone contains anomalous 

amounts of several metals, and so does ironformation elsewhere in the region. 

This report describes the outcome of work 

around Blue Lead Mountain, 5 miles (8 km) northnorthwest of Keystone, where exploration in the 

past may not have been as comprehensive as is 

warranted. The geology and the outline of the area 

studied are shown in figure 1. Additional samples 

were collected from here in 1973 by Raymond and 

R. U. King. The area is mostly in the Black Hills 

National Forest, but a portion at Sheridan Lake 

and for 2 miles (3 km) south of it is either in a 

recreational area closed to mineral entry or is 

privately owned. 

For information about roads and for more 

geographic detail than is shown in figure 1, the best 

source is the Mount Rushmore topographic map 

(scale1:24,000) in the photorevised edition of 1971. 

The principal roads are U.S. Highway 16, which 

crosses the southeast part of the area shown in 

figure 1, and Sheridan Lake Road, which crosses 

the area near its north border. Roads of lesser 

quality, ranging down to nearly impassable old 

logging trails, make most of the area accessible. A 

few roads were extensively washed out during the 

flood of June 9, 1972, as a result of about 14 inches 

(360 mm) of rainfall. 

The principal workings, as shown in figure 1, are 

at the Blue Lead and Dakota Calumet mines, 

about 1 mile (1.6 km) south of Blue Lead Mountain, 

and at a locality 2 miles (3.2 km) farther to the 

southeast known as the Wealthy mine according to 

Francis Michaud (oral commun., 1974). 

The Wealthy mine, which almost certainly was 

opened for gold, seems to have been mentioned in 

the published record only on a map by Scott (1897). 
' 

0 .5 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

EXPLANATION 

METAIGNEOUS ROCKS 

f;a~ ,j Amphibolite 

METASEDIMENTARY ROCKS 

[Z'n\et~j Mica schist and quartz-mica schist 

n;i<Jf Xl Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

~ Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

'g_iry>j Quartz-mica schist 

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

Inclined 

Vertical 

Shaft 

Caved ad it - Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 1.- Geologic map of the Blue Lead Mountain area, Pennington County, S.Dak. 

2 
It has a shaft at least 100 feet (30m) deep, and the 

size of the dump indicates an additional 200-300 

feet (60-90 m) of underground workings. 

Better information is available for the Blue Lead 

and Dakota Calumet copper mines in reports by 

Connolly and O'Harra (1929, p. 209-210) and the 

U.S. Bureau of Mines (1955, p. 32-33), though both 

of these reports were written long after activities at 

these sites had ended. The Blue Lead mine has a 

1,610-foot (490-m) adit and a 260-foot (80-m) vertical shaft. The Dakota Calumet shaft is 850 feet 

(260 m) deep and has an 1,170-foot (357-m) 

crosscut with nine drifts presumably of modest 

length. Ore was processed in a small matte smelter, 

of which only ruins now remain. Mining operations 

began as early as 1879 and continued intermittently until 1919. 

Prospect pits, small open pits, and short adits 

are common in iron-formation in the area covered 

by the map, though not as common as in most 

other parts of the Keystone region. They are especially sparse on rubble-covered slopes of 

Calumet Ridge. Apparently the early gold prospectors found little cause for enthusiasm, and the evident lack of success of copper mining is also discouraging. Yet a considerable thickness of 

grunerite iron-formation exists over a distance of 

several miles, with only a few thousand feet of exploration workings, no drill holes, and almost no 

record of what was found. These circumstances, 

together with our geochemical results, indicate 

that more work might be worthwhile. 

GENERAL GEOLOGY 

All of the rocks shown on the geologic map (fig. 1) 

are of Precambrian age. Most of them are on the 

east limb of a long narrow syncline that has been 

mapped by Norton for several miles to the southsoutheast. The rocks southwest of the Sheridan 

fault from the center of section 29 to the west limit 

of the map are on the west limb of this same syncline. All the folds shown on the map are subsidiary 

structures superimposed on the main syncline. 

Whether the syncline is in fact a syncline rather 

than an anticline is not certain. Bedding on the two 

limbs is generally parallel in both strike and dip, 

and unambiguous evidence of tops of beds is sparse 

both here and elsewhere in the Keystone region. 

For the purposes of this report the question is unimportant. 

3 

STRATIGRAPHY 

The oldest unit is a lenticular body of quartzmica schist cut off by the Silver Mountain fault 

along the east border of the map. The rock is the 

metamorphic equivalent of an impure sandstone, 

now consisting mainly of quartz, muscovite, 

biotite, and plagioclase, with accessory microcline, 

garnet, and other minerals. 

The succeeding unit consists mostly of mica 

schist and of occasional layers of mica-garnet schist 

in which both muscovite and biotite as well as 

quartz are abundant, but the most prominent outcrops are of massive beds of clastic quartzite. Few 

of the quartzite beds are more than 5 feet (1.5 m) 

thick or can be traced more than 100 feet (30 m) 

along strike; some of the premetamorphic lenses of 

sandstone may have been much longer than this 

but were sheared off by intense folding or were 

separated by the development of boudinage. Most 

of the quartzite is gray, but it ranges to nearly 

white, and some has a bluish cast. The name Blue 

Lead undoubtedly comes from the bluish quartzite 

and the miner's term "lead." 

In the spillway of the Sheridan Lake dam, near 

the base of this unit, is a large exposure of conglomerate with boulders of quartzite in a matrix of 

mica schist. Similar conglomerate is common 

elsewhere in the Keystone region, but generally its 

nature is obscured by weathering and a cover of 

lichens. At all known localities the conglomerate 

fragments are virtually all of quartzite; close search 

reveals pebbles of schist and occasionally of 

amphibolite, but no vein quartz forming convincing pebbles has ever been detected. Though some 

of the quartzite fragments are round, they 

generally are ellipsoidal, with the long axis plunging nearly vertically, parallel to the predominant 

minor folds of the region. The size of the quartzite 

fragments ranges from small pebbles to masses 

tens of feet long, differing in no obvious way from 

nearby quartzite beds. These observations suggest 

that the rock may be a pseudoconglomerate, 

originating through deformation that separated 

quartzite beds into small pieces. A more plausible 

interpretation, however, is that the rock is in fact a 

true conglomerate, but also contains lenses of sand 

formed from the same source rock as the quartzite 

pebbles. During metamorphism the sand lenses 

would have acquired the same appearance as the 

true pebbles. The contact with the underlying 

quartz-mica schist may be a major unconformity. 
Layers and lenses of meta-iron-formation are 

common features in this part of the stratigraphic 

sequence throughout the Keystone region. The 

thick meta-iron-formation unit that crosses 

Calumet Ridge and extends to the north and south 

borders of the geologic map is merely an unusually 

large example, though it is treated on the geologic 

map as a separate stratigraphic unit because of its 

central importance in the geochemical sampling 

done for this report. Its lithology can be described 

with that of the smaller bodies of meta-ironformation nearby. 

The predominant rock is grunerite schist containing lenses and layers of metamorphosed cherty 

quartzite. At the surface, and perhaps in some 

mineralized segments in the subsurface, the rock is 

generally limonitic and earthy. Most such rock is 

probably a result of nearly lateritic weathering 

prior to Upper Cambrian sedimentation. The ironformation can grade along strike into grunerite 

schist with only a slight amount of quartzite, where 

the iron content may be about 30 percent, or it can 

grade into nearly pure quartzite with streaks of 

graphite, mica, garnet, or other accessory minerals. 

South of the Wealthy mine, just beyond the 

Sheridan fault, is the best example of thickstreaked quartzite in the area shown in figure 1, but 

adjoining areas contain many localities of sucp 

quartzite. The grunerite schist of the Blue Lead 

Mountain area has not been examined in thin section, but observations elsewhere suggest that it 

probably also contains common hornblende and 

possibly actinolite. 

Other rocks interlayered with iron-formation are 

chiefly micaceous and graphitic schists. Gray 

quartzite, possibly of clastic origin, appears in 

places on the west slope of Calumet Ridge, but 

these may represent unmapped infolds of the 

quartzite-bearing unit lying to the east. 

Where iron-formation is of greatest thickness, the 

cause is duplication by tight folding, as can be seen 

on the geologic map just north and south of 

Sheridan Lake. Fault movement along shear zones 

reported in underground workings (U.S. Bureau of 

Mines, 1955, p. 32-33) may increase the exposed 

thickness of Calumet Ridge. The actual structure 

of the iron-formation beneath Calumet Ridge is 

probably far more complicated than is indicated by 

the map of the surface. 

The youngest metasedimentary unit, which occupies the center of the syncline, consists of mica 

schist and muscovite, biotite, quartz, plagioclase, 

and sparse garnet interlayered with massive beds 

4 

that are more quartzose and less micaceous. 

The amphibolite of the region is a hornblendeplagioclase rock of approximately gabbroic composition. Much of it is fine grained and probably a 

metabasalt. The amphibolite in the NW% section 

29 is the northeast extremity of a large body that is 

for the most part so coarse grained that it may be 

called metagabbro. It is, however, probably a 

volcanic pile. Virtually all the amphibolite in the 

Keystone region is within or near the stratigraphic 

level of iron-formations, quartzites, and associated 

rocks that cross Calumet Ridge and Blue Lead 

Mountain. Thus these metasedimentary rocks are 

probably the same age as the metaigneous 

assemblages. 

The valleys of the Blue Lead Mountain area contain only intermittent streams with narrow 

flood plains underlain by a meager quantity of 

Quaternary alluvium. Terrace gravels of older age 

are so sparse that they hardly merit being mentioned; the only sizable one extends for about 1,000 

feet (305m) along a ridge at the border of sections 1 

and 12 east of the meta-iron-formation. 

Bog iron was exposed by the flood June 9, 1972, 

in a few places scattered along a 0.5 mile (0.8 km) 

stretch of a valley in the N 1

/2 section 20. It probably 

continues northeast into section 17. The maximum 

width is at least 100 feet (30m) and the thickness is 

as much as 6 feet (2 m). 

STRUCTURAL GEOLOGY 

The principal structures are three categories of 

folds, presumably of different ages. One is the main 

syncline. Another consists of the isoclinal folds 

southwest of the Sheridan fault and of the folds 

near Sheridan Lake and north of it. And the third is 

the rather open folds east and southeast of Calumet 

Ridge. 

Though the main syncline has been mapped 

several miles to the south-southeast, its structure is 

inexactly known. Dips are nearly vertical on both 

limbs, and though the strike of bedding can be 

highly changeable from later deformation, the 

overall trend of stratigraphic units on the two limbs 

is nearly parallel or slightly divergent to the north. 

Hence this is an isoclinal fold. Presumably the 

plunge is gentle, although no small folds of gentle 

plunge have been noticed. 

The folds observed in many outcrops plunge very 

steeply - from about 70° south to 80° north. These 

are associated with the set of folds shown on figure 1 

near Sheridan Lake and southwest of the Sheridan 

fault. Such folds tend to be nearly or quite 
isoclinal, and can cause a single unit to be 

overthickened by being folded against itself several 

times, as probably happened in the iron-formation 

crossing Calumet Ridge. A notable characteristic of 

these folds is their right-hand movement pattern 

on the east limb of the major syncline and lefthand pattern on its west limb, which implies that 

they are merely subsidiary folds or "drag folds" 

associated with the syncline. The steep plunge, 

however, argues otherwise: a syncline many miles 

long cannot plunge vertically without causing 

serious geometric problems at depth. More likely 

the small folds were formed in beds that were 

already dipping vertically. Conceivably, in the 

development of the large synclines and anticlines of 

the Keystone region, these small folds represent a 

late stage in which shear forces shifted in orientation to create a nearly horizontal compressional 

effect parallel to the axial planes of the larger folds. 

The last set of folds consists of the rather open 

folds with a left-hand movement pattern east or 

southeast of Calumet Ridge. Folds of this kind, 

though sparse in the Keystone region, have also 

been mapped on the west limb of the major syncline. Strike and dip observations on bedding in the 

large fold in section 20 indicate a nearly vertical 

plunge. 

The Silver Mountain fault, along the east side of 

the geologic map, is one of several large northnorthwesterly striking faults in the Keystone 

region. Younger rocks crop out northeast of the 

fault, indicating that it is downthrown on that side, 

but that it probably also has a large lateral displacement. The Sheridan fault also generally· has 

younger rocks on its northeast side, though it has 

an odd relation to the iron-formation on Calumet 

Ridge, brought about by the crossfolds in section 

20. The faults have steep dips and nearly straight 

traces, showing they are younger than the folds, 

but neither fault shows evidence of being younger 

than the metamorphism. 

MINERALIZATION 

Information about the mineralized parts of the 

Blue Lead and Dakota Calumet mines is meager. 

The chief sources are brief descriptions by Connally and O'Harra (1929, p. 209-210) and the U.S. 

Bureau of Mines (1955, p. 32-33), based on observation of the dumps and on information probably 

originally obtained mostly from men who had 

worked in these mines. 

The Blue Lead adit cut an ore-bearing shear 

5 

zone, 1,400 feet (430 m) from the entry, that strikes 

N. 25° W. and dips 60° to 70° east. The Dakota 

Calumet workings entered a mineralized shear 

zone of similar attitude and 50 to 200 feet wide. 

Presumably it is the same shear zone as in the Blue 

Lead adit. The shear zone has not been recognized 

at the surface, perhaps because it is covered by 

rubble on the west side of Calumet Ridge, and 

whatever surface evidence of shearing one might 

observe would ordinarily be attributed to tight 

folding. 

Metalliferous minerals in unaltered ore include 

pyrite, pyrrhotite, and chalcopyrite. Locally oxidized ore contains azurite, malachite, chrysocolla, 

cuprite, tenorite, and native copper. Analyses of our 

samples indicate as much as 0.3 percent arsenic, 

implying that arsenopyrite is also in the ore. No 

molybdenum or zinc minerals have been 

recognized, even though geochemical samples from 

near these mines contain as much as 70 ppm (parts 

per million) molybdenum and 2,000 ppm zinc. 

GEOCHEMICAL ANOMALIES 

Figures 2-9 show the distribution of geochemical 

an<~malies detected by analyses of 135 samples of 

bedrock or large float blocks. Most of the samples 

came from in or near iron-formation. The maps for 

copper, molybdenum, zinc, and cobalt are based on 

semiquantitative spectrographic analyses; similar 

analyses were made for many other constituents 

but were not sufficiently informative to be recorded 

here. Mercury, gold, and silver were determined by 

atomic absorption, and arsenic was by colorimetric 

analyses. 

Four localities show anomalies. The most 

pronounced concentration of metals is on Calumet 

Ridge. A generally subdued anomaly is in the small 

unit of iron-formation east of this ridge. Another 

place yielding anomalous results is 1 mile (1.6 km) 

north of Sheridan Lake dam, and still another is 

near Eagle Mountain. 

Copper produces a conspicuous anomaly on 

Calumet Ridge, which is not surprising when it is 

considered that this was the site of efforts to mine 

copper. Ten samples have a copper content of2 percent or more, which is the upper limit for determining copper by the analytical method used. 

Most of these samples are in the northwesttrending group along or near the crest of Calumet 

Ridge (fig. 2). Another rich sample (containing 

visible malachite) is from just southeast of the top 

of Eagle Mountain. Elsewhere near Eagle Moun-
tain, copper is rather uniformly distributed in 

amounts of 200-500 ppm. North of Sheridan Lake, 

however, the copper content of iron-formation 

ranges from a few tens of ppm to several hundreds 

of ppm without any conspicuous pattern. 

The gold results are low, but detectable gold has 

the same distribution as other anomalous metals 

(fig. 3). The greatest amount found at Calumet 

Ridge is 0.25 ppm and the greatest amount found 

elsewhere is 0.15 ppm, in a sample from southeast 

of Eagle Mountain. This is in striking contrast to 

the Rochford district, 18 miles (29 km) to the 

northwest, where many samples of similar rocks 

contain more than 5 ppm gold (Bayley, 1972, pl. 2). 

Silver, in amounts of 1-3 ppm, has approximately the same pattern as copper on 

Calumet Ridge (fig. 4). The amount of silver is 

comparable to that at Rochford, though some 

samples there are much richer (Bayley, 1972, pl. 3). 

North of Sheridan Lake the distribution of silver, 

like copper, is uneven, ranging from a trace to 3 

ppm. Near Eagle Mountain several samples have 

0.5-4.0 ppm silver; the rest yield smaller results. 

Mercury, which is commonly used as an indicator of hydrothermal mineralization, is at levels 

of 1-10 ppm in many samples, especially in the 

vicinity of the Dakota Calumet and Blue Lead 

mines. It closely follows the patterns of copper, 

silver, and other metals (fig. 5). The amount of 

mercury is unimpressive north of Sheridan Lake 

and at Eagle Mountain. 

Molybdenum is the only metal that yielded 

wholly unexpected analytical results. More than 40 

percent of all samples contain 10-70 ppm 

molybdenum, and in the Calumet Ridge and Eagle 

Mountain localities nearly two-thirds of the 

samples are in this range. The Calumet Ridge 

anomaly includes six samples which contain 30-70 

ppm molybdenum. Clearly, molybdenum is sufficiently anomalous in the Blue Lead area to justify 

further investigation. Molybdenum was of little 

commercial interest in the years when exploration 

and mining were active in this area, and its existence in mineralized rock of the underground 

workings would probably have been overlooked. 

The remaining maps - figures 7, 8, and 9 -

show anomalies in arsenic, zinc, and cobalt. The 

arsenic content, which commonly is several hundred or a few thousand ppm, suggests the presence 

of arsenopyrite. Zinc attains levels of as much as 

2,000 ppm, thus indicating that some hitherto undetected zinc mineral is probably an accessory constituent of the mineralized rock. Cobalt occurs in 

6 

amounts of 100-500 ppm in 11 samples on Calumet 

Ridge (mainly in samples high in other metals), 

and ordinarily is in amounts of 0-20 ppm 

elsewhere. All three of these metals occur in 

patterns generally similar to other metals discussed 

here. 

SUMMARY 

Though the reason for undertaking this 

geochemical investigation was to find evidence for 

a gold deposit, the results give little cause for optimism on this score. Any gold deposits are likely to 

be small and of modest grade. 

Nevertheless, one can be optimistic about the existence of some kind of metal deposit. Mercury 

analyses yield results that imply sulfide 

mineralization in the area, and anomalous 

amounts of other metals in a similar pattern indicate that mineralization may have been of considerable magnitude. Molybdenum is perhaps the 

most promising of the constituents analyzed, but 

copper and silver, despite the lack of success of early 

exploration, are not beyond hope. The body of ironformation crossing Calumet Ridge has an 

average thickness of about 0.4 miles (0.6 km) for a 

distance of 1.5 miles (2.4 km). Shafts and crosscuts 

having a total length of only about 4,000 feet (1,200 

m), with few surviving records of the results, seem 

insufficient to explore a body of rock of this size. 

The Blue Lead adit, except at its caved portal, 

probably is open for most of its 1,610 feet (490 m), 

and thus could be rehabilitated sufficiently well for 

geologic mapping and sampling. Trenching to 

bedrock is also likely to be informative, especially 

on the west slope of Calumet Ridge. Because much 

of the ridge is so thickly covered with rubble and 

with a dense growth of pine trees, both our geologic 

mapping and sampling probably give oversimplified results. 

Eventually subsurface exploration will be required for adequate evaluation of the mineral 

potential of the Blue Lead Mountain area. 

REFERENCES CITED 

Bayley, R. W., 1972, A preliminary report on the geology and gold 

deposits of the Rochford district, Black Hills, South Dakota: 

U.S. Geol. Survey Bull. 1332-A, 24 p [1973]. 

Connolly, J.P., and O'Harra, C. C., 1929, the mineral wealth of 

the Black Hills: South Dakota School Mines Bull. 16, 418 p. 

Scott, Samuel, 1897, Map of the Black Hills of South Dakota 

and Wyoming with full descriptions of mineral resources, 

etc.: Philadelphia, E. P. Noll and Co., 40 p. 

U.S. Bureau of Mines, 1955, Black Hills mineral atlas, South 

Dakota - Part 2: U.S. Bur. Mines Inf. Circ. 7707, 208 p. 
103 27'30" 

R.5E. R.6E 

EXPLANATION 

COPPER CONTENT - In 

parts per million 

<50 

• 50-500 

• >500 

0 .5 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

29 

EXPLANATION 

METAIGNEOUS ROCKS 

G Amphibolite 

METASEDIMENTARY ROCKS 

Mica schist and quartz-mica schist 

Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

a Quartz-mica schist 

-+-

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

Inclined 

Vertical 

~ Shaft 

>-+- Caved adit- Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 2. - Copper content, by semiquantitative spectrographic analyses. 

7 
EXPLANATION 

GOLD CONTENT - In 

parts per million 

None detected 

• <0.05-0.05 

• >0.05 29 

mqs 

0 .5 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

EXPLANATION 

METAIGNEOUS ROCKS 

G Amphibolite 

METASEDIMENTARY ROCKS 

~ 

~ 

Mica schist and quartz-mica schist 

Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

EJ Quartz-mica schist 

Contact- In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

_L__ Inclined 

-r- Vertical 

~ Shaft 

>-+- Caved adit- Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 3. - Gold content, by atomic absorption analyses. 

8 
R 

~/ 

ri-. 

I 

I ·I;;<",.,.' I ,.~ I Y..,.-.1 

n Afi 

i I 

I 

* 

T: 

1 I S.! 

EXPLANATION 

SILVER CONTENT- In 

parts per million 

<0.5 

• 0.5-1.0 

• >1.0 

0 ~ 1 MILE 

0 .5 1 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

EXPLANATION 

METAIGNEOUS ROCKS 

G Amphibolite 

METASEDIMENTARY ROCKS 

EJ Mica schist and quartz-mica schist 

~ Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

~ f Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

EJ Quartz-mica schist 

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

_L_ Inclined 

-t- Vertical 

~ Shaft 

>-+-- Caved adit- Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 4. - Silver content, by atomic absorption analyses. 

9 

z 

< ;:: 

a:l 

~ 

< u 

~ 

c.:: 

ll.. 
T. 

s 

~ I ', sqc 

EXPLANATION 

MERCURY CONTENT - In 

parts per million 

<0.25 

• 0.25-1.0 

• >1.0 

0 .5 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

- mqs 

EXPLANATION 

METAIGNEOUS ROCKS 

G Amphibolite 

METASEDIMENTARY ROCKS 

B Mica schist and quartz-mica schist 

~ Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

~ f Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

a Quartz-mica schist 

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

____L__ Inclined 

-r- Vertical 

!I Shaft 

>-+- Caved adit -Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 5. - Mercury content, by atomic absorption analyses. 

10 

z 

<r: 

;2 

j:Q 

:g 

<r: 

u 

~ 

Q::; 

j:l.; 
EXPLANATION 

MOLYBDENUM CONTENT - In 

parts per million 

< 10 

• 10-30 

• >30 

0 lh 1 Ml LE 

0 .5 1 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

EXPLANATION 

METAIGNEOUS ROCKS 

G Amphibolite 

METASEDIMENTARY ROCKS 

8 Mica schist and quartz-mica schist 

8 Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

Quartz-mica schist 

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

---'-- Inclined 

-I- Vertical 

~ Shaft 

>--+- Caved adit- Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 6. -Molybdenum content, by semiquantitative spectrographic analyses. 

11 
103 .27'30" 

R. 5 E'. R 6 E. 

I _I 

~· '\ 

h. 

k 

EXPLANATION 

ARSENIC CONTENT - In 

parts per million 

<50 

• 50-500 

• >500 

0 .5 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

EXPLANATION 

METAIGNEOUS ROCKS 

G Amphibolite 

METASEDIMENTARY ROCKS 

B Mica schist and quartz-mica schist 

8 Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

~ Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

6 Quartz-mica schist 

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

~ Inclined 

-t- Vertical 

rJ Shaft 

>-+-- Caved adit - Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 7. - Arsenic content, by colorimetric analyses. 

12 
T 

S. 

EXPLANATION 

ZINC CONTENT - In 

parts per million 

None detected(< 100 ppm) 

• 100-700 

• >700 

0 .5 KILOMETRE 

CONTOUR INTERVAL200FEET 

EXPLANATION 

METAIGNEOUS ROCKS 

G Amphibolite 

METASEDIMENTARY ROCKS 

B Mica schist and quartz-mica schist 

G Meta-iron-formation, quartzite, 

mica-graphite schist, and 

mica schist 

~ Mica schist, mica-garnet schist, 

quartzite, and conglomerate 

if, meta-iron-formation 

EJ Quartz-mica schist 

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

Inclined 

-t- Vertical 

!I Shaft 

>-+-- Caved adit - Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 8. - Zinc content, by semiquantitative spectrographic analyses. 

13 
1 

S. 

EXPLANATION 

COBALT CONTENT - In 

parts per million 

<10 

• 10-100 

• >100 

0 .5 KILOMETRE 

CONTOUR INTERVAL 200 FEET 

EXPLANATION 

METAIGNEOUS ROCKS 

B Amphibolite 

METASEDIMENTARY ROCKS 

B Mica schist and quartz-mica schist z 

<: 

;: 

~ lXI 

Meta-iron-formation, quartzite, ::?1 

mica-graphite schist, and <: 

u mica schist w 

e:::: 

ll-o 

~ Mica schist, mica-garnet schist, f 

quartzite, and conglomerate 

if, meta-iron-formation 

EJ Quartz-mica schist 

Contact - In part approximately 

located; dotted where concealed 

Fault - In part approximately 

located 

Strike and dip of beds 

_..J.._ Inclined 

--+- Vertical 

~ Shaft 

>-+- Caved adit- Many small pits, 

shafts, and adits are omitted 

Sample site 

Geology by J. J. Norton, 1963 

Base from U.S. Geological Survey, 

Mount Rushmore, 1954 

FIGURE 9. - Cobalt content, by semiquantitative spectrographic analyses. 

14 -tr U.S. GOVERNMENT PRINTING OFFICE:" 1974-677-307/23