Distribution and Abundance of 

Gold and Other Selected 

Elements in Altered Bedrock, 

Empire Mining District, 

Clear Creek County, Colorado

GEOLOGICAL SURVEV BULLETIN 1278-C

Distribution and Abundance of 

Gold and Other Selected 

Elements in Altered Bedrock, 

Empire Mining District, 

Clear Creek County, Colorado

By MAURICE A. CHAFFEE

CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING 

FOR MINERALS

GEOLOGICAL SURVEY BULLETIN 1278-C

A study of the geological and geochemical 

relationships of gold anomalies to those 

of tellurium, tin, bismuth, silver, 

and manganese

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTiON, Secretary

GEOLOGICAL SURREY 

Vt E. McKelvey, Director

Library of Congress catalog-card No. 72-600010

For sale by the Superintendent of Documents, U.|S. Government Printing Office

Washington, D.C. 20402 - PriU 30 cents

Stock Number 2401-2127
CONTENTS

Abstract---.....---..-..--......-.......--......-..-......

Introduction.-...........-------.. ..................

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

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

Alteration-...-......... ..... ....... .

Sampling and analysis........................

Genesis of the elements under study. 

Geochemical distribution maps...........

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

Page

Cl

1

2

2

5

5

7

ILLUSTRATIONS

Page

FIGURE 1. Index maps showing locations of the Empire mining

district and the upper and lower placers........... ......... C3

2. Photographs of the upper and lower placers- .........-.......... 4

3. Geologic map of the lower placer.... ......... ..... ........ 9

4-9. Maps of the lower placer showing distributions of 

metal anomalies and alteration intensities:

4. Gold.............................................................................. 10

5. Tellurium.....-.. .. .. . .. . 11

6. Tin.... .................................................................... 12

7. Bismuth....................................................................... 13

8. Silver.....-. . . .... - .. 14

9. Manganese.... .. ....- ......-.. .... - . 15

10. Geologic map of the upper placer--......--..-.---.....-.-.---.- ---.-. 16

11-16. Maps of the upper placer showing distributions of 

metal anomalies and alteration intensities:

11. Gold..... .. ... .. .. 18

12. Tellurium-.-..-.......-...- - 19

13. Tin. .................................................... 20

14. Bismuth..........-.-....- .. 21

15. Silver.......-..............-....... . 22

16. Manganese........ . .. . ... 23

TABLES

TABLE 1. Correlation coefficients of logarithms of concentrations 

of five selected elements relative to gold........... ............

2. Geochemical parameters for gold and five selected

elements........................... ... ..... ... . .._... . ..

3. Analyses of sulfide concentrates, Tenth Legion minePage 

C6

7

7

in

CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING 

FOR MINERALS

DISTRIBUTION AND ABUNDANCE OF GOLD

AND OTHER SELECTED ELEMENTS IN

ALTERED BEDROCK, EMPIRE MINING

DISTRICT, CLEAR CREEK COUNTY,

COLORADO

By MAURICE A. CHAFFEE

ABSTRACT

A geochemical study was made of altered bedrock samples from two placer 

areas in the Empire mining district, Colorado. Statistical study of the logarithms of the concentrations of 32 elements analyzed in these samples indicates 

that gold has linear correlation coefficients exceeding 0.55 with tellurium, tin, 

bismuth, and silver, and a linear correlation coefficient of 0.46 with manganese. Geochemical distribution maps show a degree of overlap of anomalies 

between these five selected elements and gold; this overlap exceeds 90 percent 

for each of the five elements. The areal distributions of all six of the elements 

studied seem to be related to the degree of alteration intensity that is observed 

in the field.

Analyses of surface bedrock samples suggest that the five selected elements 

are all pathfinder elements that would be useful in the search for gold mineralization in the Empire district. Data from unweathered underground samples 

from the district suggest that the amounts of tellurium, bismuth, silver, and 

manganese are closely related to the amount of hypogene gold. Tin values from 

the same samples, though mostly anomalous, do not show enough variation to 

establish any concentration trend relative to the trend of gold values. All six 

elements apparently behave chemically in a similar manner in the supergene 

environment of the area studied. In this district, tellurium would be the best 

pathfinder element to use in conjunction with gold for widespread reconnaissance exploration. The other four elements would be better suited for detailed 

studies.

INTRODUCTION

A comprehensive geochemical investigation of the distribution 

of selected trace elements in various media was undertaken by the 

U.S. Geological Survey in 1967 in the northern part of the Empire 

mining district, Clear Creek County, Colorado, about 37 miles west 

of Denver in the Front Range of the Rocky Mountains (fig. 1). 

Previous reports of that investigation (Curtin and others, 1968,

Cl
C2 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

1971) discussed the distribution and abundance of trace metals in 

humus-rich forest soil (mull) in the district. This report discusses 

the distribution and abundance of a selected suite of trace metals 

in bedrock in two gold-placer areas in the district (fig. 1).

Much of the Empire district is covered with colluvial or glacial 

deposits. The two placer areas were selected for this geochemical 

study because they have a greater than usual amount of exposed 

bedrock for this region (fig. 2) and are near known mineralized 

structures.

ACKNOWLEDGMENTS

I was assisted in the field by G. C. Curtin, H. W. Lakin, and H. D. 

King. Chemical analyses were made by E. L. Hosier, K. C. Watts, 

A. E. Hubert, W. W. Janes, R. L. Turner, J. R. Watterson, and 

J. G. Frisken. I thank Messrs. H. C. Nelson and E. J. Woodriff 

for granting permission to publish data on samples collected on 

their properties.

GEOLOGIC SETTING

The geology of the Empire district has been most recently described by Braddock (1969). Formations include Precambrian 

igneous and metamorphic rocks that have been intruded by felsic 

to intermediate igneous rocks of Tertiary age. Quaternary glacial 

deposits, alluvium, talus, and solifluction debris cover about onethird of the pre-Quaternary rocks in the Empire quadrangle (Braddock, 1969, p. 45).

Within the two areas studied, exposures of Boulder Creek Granite and biotite gneiss, both of Precambrian age (Braddock, 1969), 

predominate (figs. 3, 10). Except for some minor exposures of 

bostonite porphyry in the upper placer (fig. 10), no Tertiary units 

crop out in either placer.

For this study, four post-Tertiary units have been mapped. These 

are glacial moraine and talus (both Quaternary), placer tailings, 

and mine tailings. Glacial moraine is found around the perimeter 

of the two areas studied; there, no placer mining has been done, 

and the original surface remains virtually undisturbed. Parts of 

the two placers (especially their perimeters) have, as a result of 

the placering, steep slopes on which eroded material derived from 

glacial moraine or weathered bedrock, or both, has locally moved 

downward from the rim of the placer and has partly covered the 

underlying bedrock. Such areas have been mapped as talus but 

actually comprise a mixture of transported and residual materials 

and many small outcrops of bedrock. Areas of both placers mapped 

as placer tailings are covered by piles of glacial boulders remaining
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C3

105°40'30"

1000

I 2000 FEET

CONTOUR INTERVAL 200 FEET

FIGURE 1. Index maps showing location of the Empire mining district and the 

upper and lower placers. Arrows indicate direction of views shown in figure 

2. Rectangles indicate areas shown in figures 3-16.
C4 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

after placer operations. Areas mapped as mine tailings consist 

mostly of material originally mined underground. This material

FIGURE 2. Upper placer (above) and lower placer (below). These two areas, 

still lacking vegetation, were originally covered with natural growth and 

as much as 40 feet of residual oxidized and decomposed bedrock. As a consequence of hydraulic placer mining of this altered bedrock in the 1860's, 

during which the original soil was removed, natural reforestation has been 

greatly inhibited. Orientation of these photographs is shown in figure 1.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C5

now consists of weathered sulftdes and strongly argillized host 

rocks of the various formations found in the district.

ALTERATION

Bedrock in both placers has been subjected to varying degrees 

of both hydrothermal alteration and weathering; however, most 

of the observed alteration is probably hydrothermal. Where alteration caused by weathering has been superimposed on hydrothermally sulfidized areas, alteration has been accelerated because the 

oxidation of sulfides has produced highly acid ground conditions.

A rough estimate of the intensity of alteration was made at each 

bedrock sample site. Completely unaltered bedrock was not seen 

in either placer. The bedrock was considered weakly altered if the 

dark mafic minerals present in either of the two dominant rock 

types appeared substantially unaltered in a hand specimen. It was 

considered moderately altered if it contained argillized feldspars 

and bleached mafic minerals and strongly altered if it contained 

visible sericite and (or) aphanitic silica in addition to the argillized 

feldspars and the bleached mafic minerals. Alteration intensity 

zones based on these alteration features are shown on all maps 

in figures 4-9 and 11-16.

The lower placer contains extensive exposures of weakly to 

strongly altered biotite gneiss and minor exposures of weakly 

altered Boulder Creek Granite. Alteration intensity seems to be 

crudely zoned around a center near the middle of the placer. (See, 

for example, fig. 4.) Sericite and aphanitic silica are visible on 

fracture surfaces in this central area. The conduit for the hydrothermal fluids associated with this alteration zoning was probably 

one or more of the shear zones forming the Silver Mountain ore 

zone (fig. 1).

Bedrock in the upper placer (fig. 11, for example) is not as intensely altered as it is in the lower placer; sericite was nowhere 

observed, and aphanitic silica is not as widespread. In a crude 

manner, the alteration intensity here also increases gradually 

toward the center of the placer. These intensity zones do not seem 

to be closely related to faults, geologic contacts, or lithology.

SAMPLING AND ANALYSIS

Bedrock samples were collected on an approximately 50-foot grid 

wherever bedrock was available at or near the surface. Care was 

exercised to avoid sampling too near to mine and placer tailings 

and to other obvious sources of sample contamination. Sample sites 

in talus areas are isolated outcrops, most of which are too small 

to show on the geologic maps. Sample sites in the areas of morainal 

deposits are prospect pits that penetrated to bedrock. Sampling

461-835 O - 72 - 2
C6 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

was done at depths ranging from about 0 to 6 inches. The sampled 

bedrock material varied from soft, deeply altered saprolite to dense, 

highly resistant, silicified rock. All samples were ground to pass 

through a 150-micron sieve opening before analysis.

Several techniques were used to obtain the reported analyses. 

Gold was determined by atomic absorption (Thompson and others, 

1968), tellurium by a wet chemical method (Lakin and Thompson, 1963), mercury by atomic absorption (Vaughn and McCarthy, 

1964), and the other elements by a semiquantitative spectrographic 

method (Grimes and Marranzino, 1968). Most of the analyses were 

made in the field.

All samples were analyzed for 32 elements, and all values within 

the limits of determination from these analytical data were used 

as computer input. Output included basic descriptive statistics, 

frequency distributions, and linear product-moment correlation coefficients between pairs of logarithms of all 32 elements. Table 1

TABLE 1. Correlation coefficients of logarithms of concentrations 

of five selected elements relative to gold

Element Coefficient

Te........................................ .............................. 0.64

Sn.......................................................................... .58

Bi........................................................................... .56

Ag.......................................................................... .56

Mn...................................................................... ...-.46

lists the five elements that had correlation coefficients greater than 

an absolute value of 0.45 when compared with gold. Because 26 

of the analyzed elements had correlation coefficients less than an 

absolute value of 0.45 relative to gold, 1 the relationship of these 

elements to gold was arbitrarily considered not significant in terms 

of prospecting value, and these elements were not studied further. 

The concentration ranges, background values, and threshold values 

for the five selected elements and gold are given in table 2.

Background and threshold values were primarily determined 

from a study of cumulative frequency distributions constructed on 

log-probability paper. Plots were made and interpreted in a manner similar to that described by Lepeltier (1969). Where determination of the background and threshold values of a given element was 

not clear from this plot, arbitrary values were assigned after additionally considering observed field relationships and areal distribution patterns of analyses of the given element. For five of the six 

elements, the background value is below the sensitivity of the analytical method used.

1 These 26 elements are Fe, Mg, Ca, Ti, As, Sb, B, Ba, Be, Cd, Co, Cr, Cu, Hg, La, Mo, Nb, 

Ni, Pb, Sc, Sr, V, W, Y, Zn, and Zr.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C7

TABLE 2. Geochemical parameters (in parts per million) for gold and five

selected elements

Element

Au. ...............................

Te. ....... . .. ......... .

Sn.. ..... .......................

Bi...... ...........................

Ag....... ........................

Mn... ............................

Concentration 

range

........................ <0.04- 36

....................... <.l - 85

...................... <10 - 150

.......................<10 - 200

........................ <.5 - 70

.............. ........<10 -5,000

Background 

value

n\

n\

0)

( ] )

( 1 )

200

Threshold 

value

0.06

.3

10

10

.7

70

1Below the limit of analytical detection. The limits are: Au, 0.04 ppm (parts per million); 

Te, 0.1 ppm ; Sn, 10 ppm ; Bi, 10 ppm ; and Ag, 0.5 ppm.

GENESIS OF THE ELEMENTS UNDER STUDY

To determine whether the gold and the five selected pathfinder 

elements had a common hypogene ancestry, four virtually unweathered sulfide samples were collected between 30 and 200 feet 

below the surface in the Tenth Legion mine, just north of the 

lower placer (fig. 1). Analyses of sulfide concentrates from these 

samples show, relative to their respective contents in the country 

rock (table 2 background values), a common enrichment of gold, 

silver, bismuth, tellurium, and, perhaps, tin and a corresponding 

depletion of manganese (table 3). These results suggest that the

TABLE 3. Analyses (in parts per million) of sulfide concentrates, Tenth Legion

Sample 

No.

U-7 .

11 .. ...

73

62 .. . . ..

Au1

.....230

.. 160

90

. .. 60

Te21

12

14

11

Sn3

20

30

( 4 )

30

BP

>1,000

1,000

150

50

Ag=

200

30

30

2

Mn3

10

15

30

150

Sample 

description

Pyrite and minor

amounts of

chalcopyrite.

Do.

Do.

Virtually all

pyrite.

'Atomic absorption analysis by A. E. Hubert.

-Atomic absorption analysis by R. L. Turner.

 'Spectrographic analysis by E. L. Hosier.

4 Bdow the limit of analytical detection (10 ppm).

initial concentrations of at least five (excluding tin) of these 

particular elements are related to the hypogene gold mineralization. Tin values do not show enough variation to establish any 

concentration trend relative to the trend of gold values. The high 

correlation coefficient values and coincident areal distributions for 

gold and the five selected elements as determined from the surfacesample data further suggest that these six elements behave chemically in a similar manner in the supergene environment of the 

area studied.
C8 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

GEOCHEMICAL DISTRIBUTION MAPS

Geochemical maps (figs. 4-9, 11-16) show that (1) the distributions of anomalies of gold and the five selected elements have a 

high degree of overlap (90-100 percent) ; (2) both positive and 

negative anomalies in the lower placer are generally associated 

with bedrock which has been at least moderately altered; this association is similar but not as pronounced in the upper placer; (3) 

the distributions of gold and the five selected elements have no obvious correlation with rock type; and (4) tellurium has a broader 

anomaly pattern than the other pathfinder elements.

Because of the wider distribution of its anomalies, tellurium 

seems to be the best pathfinder element to use in conjunction with 

gold for widespread reconnaissance work. The more restricted distributions of tin, bismuth, silver, and manganese anomalies seem 

best suited for more detailed studies. The use of negative anomaly 

maps, such as those of maganese in this study, should be considered 

in other geochemical studies.

REFERENCES CITED

Braddock, W. A., 1969, Geology of the Empire quadrangle, Grand, Gilpin, 

and Clear Creek Counties, Colorado: U.S. Geol. Survey Prof. Paper 616, 

56 p.

Curtin, G. C., Lakin, H. W., Neuerburg, G. J., and Hubert, A. E., 1968, Utilization of humus-rich forest soil (mull) in geochemical exploration for gold: 

U.S. Geol. Survey Circ. 562, 11 p.

Curtin, G. C., Lakin, H. W., Hubert, A. E., Hosier, E. L., and Watts, K. C., 

1971, Utilization of mull (forest humus layer) in geochemical exploration 

in the Empire district, Clear Creek County, Colorado: U.S. Geol. Survey 

Bull. 1278-B, 39 p.

Grimes, D. J., and Marranzino, A. P., 1968, Direct-current arc and alternatingcurrent spark emission spectrographic field methods for the semiquantitative analysis of geologic materials: U.S. Geol. Survey Circ. 591, 6 p.

Lakin, H. W., and Thompson, C. E., 1963, Tellurium A new sensitive test: 

Science, v. 141, no. 3575, p. 42-43.

Lepeltier, Claude, 1969, A simplified statistical treatment of geochemical data 

by graphical representation: Econ. Geology, v. 64, no. 5, p. 538-550.

Thompson, C. E., Nakagawa, H. M., and VanSickle, G. H., 1968, Rapid analysis 

for gold in geologic materials, in Geological Survey research 1968: U.S. 

Geol. Survey Prof. Paper 600-B, p. B130-B132.

Vaughn, W. W., and McCarthy, J. H., Jr., 1964, An instrumental technique 

for the determination of submicrogram concentrations of mercury in 

soils, rocks, and gas, in Geological Survey research 1964: U.S. Geol. 

Survey Prof. Paper 501-D, p. D123-D127.
QUATERNARY

o 

o 

r 

o> 

2o

o

H 

ffiM »

M

rM§M 

2H 

,M

WS'-a t (

g

g t ( 2; i i 

2o

o i i 

cc

so

H

PRECAMBRIAN

o
CIO CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

-Approximate limits 

of placer area

EXPLANATION

Approximate boundary between areas of 

different alteration intensity 

W, Weakly altered bedrock 

M, Moderately altered bedrock 

S, Strongly altered bedrock

 

Sample site

> 1.0 ppm gold

o

0.08-0.99 ppm gold

Adit

E 

Shaft

FIGURE 4. Distribution of gold anomalies and alteration intensities 

in bedrock, lower placer.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. Cll

 Approximate limits 

of placer area

EXPLANATION

Approximate boundary between areas of 

different alteration intensity 

W, Weakly altered bedrock 

M, Moderately altered bedrock 

S, Strongly altered bedrock

 

Sample site

o

> 0.3 ppm tellurium

> B 

Adit Shaft

FIGURE 5. Distribution of tellurium anomalies and alteration intensities in bedrock, lower placer.
C12 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

 Approximate limits 

of placer area

EXPLANATION

Approximate boundary between areas of 

different alteration intensity 

W, Weakly altered bedrock 

M, Moderately altered bedrock 

S, Strongly altered bedrock

 

Sample site

o

>10 ppm tin

> B 

Adit Shaft

FIGURE 6. Distribution of tin anomalies and alteration intensities 

in bedrock, lower placer.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C13

CONTOUR INTERVAL 50 FEET

 Approximate limits 

of placer area

EXPLANATION

Approximate boundary between areas of 

different alteration intensity 

W, Weakly altered bedrock 

M, Moderately altered bedrock 

S, Strongly altered bedrock

Sample site

o

> 10 ppm bismuth

Adit

B 

Shaft

FIGURE 7. Distribution of bismuth anomalies and alteration intensities in bedrock, lower placer.
C14 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

 Approximate limits 

of placer area

EXPLANATION

Approximate boundary between areas of 

different alteration intensity 

W, Weakly altered bedrock 

M, Moderately altered bedrock 

S, Strongly altered bedrock

Sample site

o

> 0.7 ppm silver

Adit

B 

Shaft

FIGURE 8. Distribution of silver anomalies and alteration intensities 

in bedrock, lower placer.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C15

 Approximate limits 

of placer area

Approximate boundary between areas of 

different alteration intensity 

W, Weakly altered bedrock 

M, Moderately altered bedrock 

S, Strongly altered bedrock

Sample site

o

<70 ppm manganese

Adit

r>

Shaft

FIGURE 9. Distribution of manganese anomalies and alteration intensities in bedrock, lower placer.
C16 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

100

I

200 FEET

CONTOUR INTERVAL 50 FEET

FIGURE 10. Geologic map of the upper placer.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C17

EXPLANATION

Placer tailings

Predominantly glacial boulders 

remaining after placer mining

Biotite gneiss

Contact

Dashed where approximately 

located; dotted where inferred

Fault

Dashed where approximately 

located

Adit

B 

Shaft
C18 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

EXPLANATION

Approximate boundary between areas of

different alteration intensity

Weakly altered bedrock

Moderately altered bedrock

Strongly altered bedrock

 

Sample site

>1.0 ppm gold

o

0.08-0.99 ppm gold

> B 

Adit Shaft

Approximate limits 

of placer area

FIGURE 11. Distribution of gold anomalies and alteration intensities in 

bedrock, upper placer.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C19

Approximate limits 

of placer area

EXPLANATION

. / . * /( Approximate boundary between areas of 

different alteration intensity 

W, Weakly altered bedrock 

M, Moderately altered bedrock 

Strongly altered bedrock

Approximate limits 

of placer area

FIGURE 12. Distribution of tellurium anomalies and alteration intensities 

in bedrock, upper placer.
C20 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Approximate limit 

of placer area

EXPLANATION

 // Approximate boundary between areas of 

. /\^ different alteration intensity 

l|| * \ ^V W, Weakly altered bedrock

\ Vo'x ^' Moderately altered bedrock 

* I * ' %. \ S, Strongly altered bedrock

 

Sample site

>10 ppm tin

Adit Shaft

Approximate limits 

of placer area

39°47'

105-41'

FIGURE 13. Distribution of tin anomalies and alteration intensities in 

bedrock, upper placer.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C21

Approximate limits 

of placer area

EXPLANATION

Approximate boundary between areas of

different alteration intensity 

F ( »\ \ ^' Weakly altered bedrock 

j v^\ M, Moderately altered bedrock 

' \1*,\ S, Strongly altered bedrock

Sample site 

> 10 ppm bismuth

Approximate limits 

^\ of placer area

FIGURE 14. Distribution of bismuth anomalies and alteration intensities 

in bedrock, upper placer.
C22 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Approximate limits 

of placer area

EXPLANATION

^. * // Approximate boundary between areas of 

3-M \ / V. different alteration intensity 

lo'l ( \ ^V W, Weakly altered bedrock

 vc" \ M, Moderately altered bedrock 

 /=», \ S, Strongly altered bedrock

1 Sample site

o > 0.7 ppm silver

85 

Adit Shaft

" -Approximate limits 

\t of placer area

FIGURE 15. Distribution of silver anomalies and alteration intensities in 

bedrock, upper placer.
GOLD AND OTHER ELEMENTS, EMPIRE MINING DISTRICT, COLO. C23

Approximate limits 

of placer area

EXPLANATION

* " jl Approximate boundary between areas of 

\ /\ different alteration intensity 

 (" \ \ W, Weakly altered bedrock

j . V/»\ M, Moderately altered bedrock 

 "% \ S, Strongly altered bedrock

Sample site

 ! \ < 70 ppm manganese 

> K 

Adit Shaft

Approximate limits 

of placer area

FIGURE 16. Distribution of manganese anomalies and alteration intensities 

in bedrock, upper placer.

U.S. GOVERNMENT PRINTING OFFICE: 1972 O 461-835