Argentian Cryptomelane and 

Bromargyrite in Volcanic Rocks 

near Silver Cliff, Colorado

GEOLOGICAL SURVEY BULLETIN 1 J 8 2 - C
t J*

»c- H I tV u

ir I

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I t

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Argentian Cryptomelane and 

Bromargyrite in Volcanic Rocks 

near Silver Cliff, Colorado

By FRED A. HILDEBRAND and ELWIN L. MOSIER 

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1382-C

This report describes silver minerals, 

especially a new variety of cryptomelane, 

and explains why unmined silver ores remain 

at the surface in this old mining district

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1974
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 74-600085

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

Washington, D. G 20402,- Price 40 cents (paper cover) 

Stock Number 2401-02509
CONTENTS

Abstract................................................................. Cl

Introduction ............................................................. 1

Location and extent of area .......................................... 2

Acknowledgments .................................................... 2

Mining history ........................................................... 3

Methods of sampling and mineralogical study .............................. 5

Geologic setting .......................................................... 5

Ore deposits ............................................................. 6

Silver Cliff Plateau and Round Mountain .............................. 6

Bromargyrite .................................................... 7

Cryptomelane .................................................... 10

Todorokite and chalcophanite ..................................... 14

Goethite, dickite, fluorite, and barite .............................. 14

White Hills .......................................................... 15

Rosita Hills.......................................................... 21

Fissure veins .................................................... 21

Manganiferous silver ore at Game Ridge ........................... 21

Conclusions ....... . ...................................................... 21

References cited.......................................................... 23

ILLUSTRATIONS

Floats 1. Index map showing location of study area in south-central Colorado

2. Map showing principal mining area of Silver Cliff-Rosita mining 

district and areas of detailed sampling .......................

3. Map showing sample localities in the Silver Cliff area ..........

4. Pace-and-compass map of the Racine Boy and Silver Cliff quarry 

area showing sample localities

Page

C3

11

5. Map showing sample localities in the Rosita area ............... 22

TABLES

 Page

TABLE 1. Occurrences of cryptomelane containing more than 4,000 p/m silver

in the Racine Boy and Silver Cliff quarries .................. C12

2. Major cation constituents of five cryptomelanes from the Racine

Boy and Silver Cliff quarries ................................ 14

3. Minerals of the Silver Cliff Plateau and Round Mountain mines . 16

4. Elemental composition of cryptomelanes from 66 localities in the

Silver Cliff area............................................ 19

5. Minor element's in galena and sphalerite from the Silver Cliff-Rosita

mining district ............................................. 20

ill

CONTRIBUTIONS TO ECONOMIC GEOLOGY

ARGENTIAN CRYPTOMELANE AND

BROMARGYRITE IN VOLCANIC

ROCKS NEAR SILVER CLIFF,

COLORADO

By FRED A. HILDEBRAND and ELWIN L. M OSIER

ABSTRACT

This investigation of silver-bearing manganese veins and breccia fillings in rhyolitic 

rocks of Oligocene age in the Silver Cliff-Rosita mining district of south-central Colorado 

discloses that appreciable amounts of unmined silver ore remain at the surface. The 

remaining silver is mainly in argentian cryptomelane, a new variety identified during 

this study. Associated minerals are bromargyrite, goethite, dickite, fluorite, barite, and 

minor amounts of chalcophanite, todorokite, and birnessite. Although the study was 

directed mainly to the manganiferous silver ores, the base-metal fissure veins were also 

examined for the potential silver content of galena and sphalerite, and an explanation is 

offered for the long-misunderstood nature and processing of the manganiferous silver 

ores.

The amalgamation process of extraction recovered only the silver in bromargyrite, 

whereas mill tailings of manganese oxide containing 10-20 ounces of silver per ton were 

discarded. Argentian cryptomelane in outcrops and in waste materials that were cast 

aside as worthless commonly contains 500-3,000 parts per million silver and, in some instances, 5,000-10,000 parts per million silver.

Vein jarosites, heretofore unrecognized in the area, are associated with base-metal 

fissure veins and are accompanied by silver halides. The silver content of galena and 

sphalerite from the fissure veins was found to be 1,000-3,000 and 50-150 parts per million, 

respectively.

The Silver Cliff area appears to be unique in having appreciable argentian cryptomelane and bromargyrite, rather than chlorargyrite, distributed over a relatively large 

area. The presence of abundant bromargyrite indicates a large source of bromine from 

the volcanic parent rocks.

INTRODUCTION

Base-metal smelting ores were discovered in the Silver Cliff-Rosita 

mining district as early as 1863, and in 1878 manganiferous silver ore 

was discovered that assayed as much as 8,400 ounces of silver per ton. 

The manganiferous silver ores, however, like those in many other mining districts in the Western United States, were handicapped by 

metallurgical problems in processing. Poor recovery of silver from such

Cl
C2 CONTRIBUTIONS TO ECONOMIC GEOLOGY

ores, estimated to be only 65 percent, was a common problem, as illustrated by the presence of 10-20 ounces of silver per ton in the mill 

tailings of amalgamated manganiferous silver ores at Tombstone, Ariz. 

(Church, 1887, p. 605), and at Lake Valley, N. Hex. (Silliman, 1882, p. 

435), as well as at Silver Cliff, Colo. (Irwin, 1881, p. 715). One of the 

principal metallurgical obstacles, apparently, has been the presence of 

a heretofore unrecognized variety of silver-bearing manganese oxide argentian cryptomelane that would not respond to amalgamation or cyanidation treatment. It has been positively identified at Silver 

Cliff (this paper) and at Tombstone,1 but it has not yet been identified 

at Lake Valley. Thus, an understanding of the mineralogy of the ores 

will facilitate the solution of the metallurgical problem.

LOCATION AND EXTENT OF AREA

The area investigated is in the Silver Cliff-Rosita mining district, 

Custer County, Colo. (fig. 1), on the east side of the Wet Mountain 

Valley between the high Sangre de Cristo Range and the lower Wet 

Mountains. One main mining area is north of Silver Cliff, and the other 

is to the southeast around Rosita and Querida.

The manganiferous silver ores occur on the Silver Cliff Plateau from 

the vicinity of Silver Cliff eastward to Round Mountain (fig. 2). The 

Silver Cliff Plateau merges northward into the White Hills, where the 

ores occur mainly as base-metal fissure veins containing cerussite. This 

area was called the Carbonate Belt in some early reports. To the 

southeast the Rosita area contains many large and small base-metal 

fissure veins, a deep gold- and silver-bearing chimney opened by the 

Bassick mine at Querida, and a small area of manganiferous silver ore 

on Game Ridge (fig. 2).

Detailed sample-locality maps of the Silver Cliff and Rosita areas are 

shown in figures 3 and 5, respectively.

The senior author is responsible for the field and mineralogical 

studies and the junior author is responsible for most of the spectrographic data.

ACKNOWLEDGMENTS

We thank the many people of the Westcliffe-Silver Cliff area for 

providing information on mine locations and allowing access to properties and for other disclosures that could only be obtained from them.

We are grateful for the analytical assistance of several U.S. 

Geological Survey personnel, who are acknowledged individually at appropriate places in the report.

'During this study, an old analyzed sample of cryptomelane from Tombstone (USGS No. D-1237 cited by Richmond 

and Fleischer, 1942, p. 610), obtained from W. T. Schaller in approximately 1952, was reexamined and found to contain 

500 parts per million silver. X-ray-diffraction patterns show only a single cryptomelane phase; thus, it is presumed to 

be argentian cryptomelane.
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C3

4

40

39

38'

109° 108°

37'

107° 106° 105° 104' 103° 102°

COLORADO

oDENVER

Leadville

Gunnison

o oSalida

Cripple Creek

o Canon City 

Bonanza o pueblo

Study area (fig. 2)' XUSTER 

COUNTY

. Walsenburg

tAlamosa

FIGURE 1. Location of the study area in south-central Colorado.

MINING HISTORY

The first discoveries of ore were made near Rosita between the years 

1863 and 1877. In 1878, rich "hornsilver" ore was discovered on a bluff 

at the north edge of what later became the city of Silver Cliff. The 

silver halide consisted of solid fist-size pieces of bright-green mineral 

that assayed 8,400 ounces of silver per ton (Wulsten, 1878) and was 

described as occurring in "pores" in the rock. The "pores" can still be 

seen on the uppermost remnants of the Silver Cliff bluff. They are 

partly lithophysae cavities in rhyolite and partly druses in manganese 

veins. The "hornsilver" discovery area near Silver Cliff was developed 

mainly by quarrying and became known as the Racine Boy quarry. A 

little later, the Silver Cliff quarry was developed adjacent to, and west 

of, the Racine Boy quarry. Surprisingly, the workings are virtually unchanged, as can be seen by comparing them with an 1888 photograph 

(Emmons, 1896, pi. 37). Consequently, materials that are comparable 

with the early mined ores can be obtained here to determine the 

mineralogy of the original ores that were processed by the then adjacent mills.

Extensive prospecting of the Silver Cliff Plateau led to many additional discoveries of silver halide there and on Round Mountain. 

Shortly thereafter, base-metal fissure veins similar to those in the 

Rosita Hills were discovered in the White Hills.
FIGURE 2. Principal mining area of the Silver Cliff-Rosita min
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C5

METHODS OF SAMPLING AND MINERALOGICAL STUDY

A method of sampling was chosen for collecting the material from 

veins, breccia, and dumps to give products resembling mill concentrates of manganiferous material containing as little rhyolitic rock and 

gangue minerals as possible. Materials from veins were collected over 

as long an interval as was practical to obtain a representative sample. 

The material from breccias consisted of a representative quantity of 

black matrix, free of rhyolite fragments. Dumps or other waste 

provided manganiferous material consisting of breccia matrix or vein 

material, or both.

Sampling of the Silver Cliff quarry area was directed toward the 

remaining outcrops of breccia and veins of manganiferous silver ore. 

Samples were collected from veins on the highest remaining parts of 

the Silver Cliff bluff and from breccia in the lowest accessible part of 

the Racine Boy quarry at the end of a tunnel that begins in the east 

wall of the Silver Cliff quarry, passes under, and ends beneath the floor 

of the Racine Boy quarry (fig. 4, Iocs. 63 and 64).

In the laboratory, the black manganese materials were handpicked 

and ultrasonically cleaned. From these preparations about 100-200 

pieces of the purest appearing manganese material were then handpicked, crushed in a Plattner diamond steel mortar, and studied by Xray-diffraction patterns and, occasionally, by X-ray fluorescence. 

Elemental determinations were made spectrographically. At first, fireassay and atomic-absorption examinations were also made, but these 

analyses were discontinued after the results were found to agree well 

with the spectrographic method. To insure that all the silver was attributable to the manganese material and that there was no contribution of silver from silver halide, the samples were treated with ammonium hydroxide. Some samples containing unusually large amounts 

of silver, and therefore suspected of containing silver halide, were 

further examined for halogens by X-ray fluorescence; however, none 

was found.

From samples of base-metal fissure veins, tiny cleavage blocks of 

galena and transparent cleavage fragments of sphalerite, free of inclusions, were handpicked and ultrasonically cleaned. Their purity was 

ascertained by X-ray examination, and their silver content was determined spectrographically.

GEOLOGIC SETTING

The rocks of the Silver Cliff-Rosita mining district are of volcanic 

origin and, according to G. R. Scott and R. B. Taylor of the U.S. 

Geological Survey (oral commun., 1972), are of Oligocene age. The 

rocks were first mapped by Cross (1896) and recently by Siems (1967, 

1968).

The rocks of the Silver Cliff Plateau (fig. 2) are mainly flow-banded 

platy rhyolite, spherulitic rhyolite, rhyolitic flow-breccia, and obsidian.
C6 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The White Hills consist mainly of rhyolitic tuffs, tuff breccias, several 

syenite (?) dikes, and small patches of quartz latite. The rocks and ore 

deposits of the Silver Cliff Plateau are different from those of the 

White Hills, partly because the plateau has been dropped considerably 

by faulting, and rocks higher in the geologic section are exposed, but 

also because both areas probably have different sources of mineralizing 

solution.

The rhyolitic rocks of the Silver Cliff Plateau and White Hills are 

bordered on the north and east sides by Precambrian granitic rocks. 

The enclosing rocks on the west and southwest sides are completely 

obscured by valley-fill deposits in the Wet Mountain Valley. The 

rhyolitic volcanic rocks extend southeast from Silver Cliff between 

bordering Precambrian granitic rocks to the Rosita Hills, as shown by 

Cross (1896, pi. 26). Thus, the volcanic rocks of the district have a 

northwest elongation which parallels the northwest trend of the largest 

fissure-vein system in the Rosita Hills, namely, the HumboldtPocohontas vein, bearing N. 50° W. (Siems, 1967, pi. 5). These 

lineaments indicate that the volcanic rocks probably gained access to 

the Precambrian granites along a broad northwest-trending zone of 

weakness.

Siems (1967, p. 161-165) contended that the volcanic rocks around 

Silver Cliff denote a part of a small calderalike structure with 

successive concentric-ring faults and that the rocks within the caldera 

have subsided more than 2,000 feet. Additional evidence observed 

currently, and in support of Siems* ring-fault concept, is the occurrence 

of two additional parallel faults south of an innermost ring fault in 

section 9 (Siems, 1967, pi. 3). This large fault was first noted by Cross 

(1896, p. 400). It bears about N. 70° W. and separates obsidian on its 

south side from rhyolitic tuffs and breccias.

Siems implied that the mineralized rocks in the White Hills may 

stem from a Jniried rhyolite dome located a short distance northeast of 

Ben West Hill. This concept is important to the current study because 

it affords a new source of mineralizing solution to explain why the ore 

minerals of the White Hills are different from those of the Silver Cliff 

Plateau.

ORE DEPOSITS

SILVER CLIFF PLATEAU AND ROUND MOUNTAIN

Many hundreds of workings, consisting of prospect pits, trenches, 

shafts, quarries, and tunnels, occur in the rhyolitic rocks on the Silver 

Cliff Plateau and eastward to Round Mountain (fig. 3). Most of the 

workings are shallow, and probably none exceeds a depth of 100 feet, 

with the exception of the 2,640-foot-deep exploratory Geyser shaft. 

Inspection o£ many workings disclosed that prospecting and mining 

were directed toward the exploitation of black manganiferous veins, 

stockworks of veins, and fillings around breccia fragments. In a few
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C7

places the manganiferous material is concentrated around spherulites 

or it partially or wholly fills vugs and lithophysae cavities. There is no 

doubt that the sought mineral, which is clearly stated in many early 

reports to be "hornsilver" or "chlorsilver," was directly associated with 

the manganese concentrations of the types just described. One can 

readily see that the largest workings, which were also the best producing mines, were staked out where the manganese mineralization was 

most intense, because there, too, must have been the richest concentrations of silver halide. The most intense mineralization of this type is 

at the Racine Boy quarry and around the Kate mines (fig. 3).

The manganiferous silver ore occurs in flow-banded rhyolite and 

rhyolite breccia. Much of the Racine Boy quarry is in volcanic breccia, 

but the top of the Silver Cliff bluff is a flow-banded rhyolite containing, 

in places, large hollow lithophysae structures. The adjacent Silver Cliff 

quarry is predominantly in flow-banded and massive rhyolite in which 

manganese concentrations are less abundant.

The manganese concentrations in the breccias occur as matrix 

fillings around rhyolite fragments, but they also occur as small vuggy 

zones in both matrix and fragments. In the flow-banded ryholites, the 

manganese concentrations occur as veins and partial fracture fillings. 

The smaller veins have no regular structural pattern, but the larger 

ones trend either northwest or northeast and are generally vertical. 

The veins range in thickness from a hairline width to 5 inches, but for 

the most part they are V2-2 inches wide. Some veins are brecciated and 

contain fragments of rhyolite. In some fractures the manganese veining material does not completely fill the fracture but lines the walls 

and forms vuggy zones with botryoidal surfaces.

BROMARGYRITE

In the summer of 1965, Mrs. James Reilly, a lifetime resident of 

Silver Cliff, loaned specimens of silver ore to the senior author that 

were collected, to the best of her knowledge, from the Racine Boy 

quarry during the early mining days. Because of their rarity, they will 

be described in some detail. The specimens are rhyolite breccia and 

flow-banded rhyolite that contain abundant bright-green euhedral 

bromargyrite crystals. The crystals occur as single crystals and as 

clusters or chains of crystals of several isometric forms. They are most 

common in cavities in the rhyolite, but also occur as thin veinlets that 

cut goethite and the enclosing rhyolite, and, with cryptomelane, fill 

square tabular barite casts. Bromargyrite is intimately associated with 

bluish-black cryptomelane, brown and red goethite, brown and 

colorless fluorite, cloudy white barite, yellow dickite, and a very small 

amount of reddish-brown hematite. Goethite and hematite are partly 

pseudomorphous after a mineral that forms rhombohedrons and 

rosette clusters of rhombohedrons. The rhombohedral mineral 

presumably was ferroan rhodochrosite. It was identified by X-ray dif-
C8 CONTRIBUTIONS TO ECONOMIC GEOLOGY
1 KILOMETE

SAMPLE NUMBERS AND MINE OR QUAR

1

2

22

39

40

41

48

53

Racine Boy 

Silver Cliff 

Defender 

Buffalo

Kate (Silver Bar) 

Vanderbilt 

Buffalo Hunter 

Plata Verde

70 Jay Gould

74 Horn Silver

76 King of the Valley

85 Hecla

120 Immortal

216 Obsidian (Calumet-Victor)

263 King of the Carbonates

267 Ruby Cliff

269 Maxine Elliot

273 Orange

274 L

277 R

278 C

278A K

284 M

B

P

S

286

299

300

FIGURE 3. Sample localities in the Si
CIO CONTRIBUTIONS TO ECONOMIC GEOLOGY

fraction from pieces of cores in which fresh pale-pink rosettelike 

clusters of rhombohedrons occur in vuggy areas. X-ray studies showed 

that these ferroan rhodochrosites have a ratio of Mn : Fe«60 : 40. The 

presence of ferroan rhodochrosite is noteworthy because in an acid environment it could se,rve as a source for manganese and iron. The core 

samples from localities 278 (at 89-ft depth) and 278A (at 586-ft depth, 

fig. 3) were provided by Joe Chelini of Callaghan Mining Co. and by 

Dolf Fieldman of Congdon and Carey, Ltd., respectively.

Some of the silver-bearing manganiferous materials collected from 

the quarries for this study also contain rare tiny pieces of bright-green 

bromargyrite enclosed by cryptomelane or goethite. Some of the 

bromargyrite is coated with a thin layer of elemental silver. The coated 

mineral has a purplish-gray waxy appearance and an adamantine 

luster much like chlorargyrite (silver chloride), but beneath the 

coating, it is bright green. X-ray-diffraction and fluorescence examinations disclosed that it is single-phase bromargyrite in which 

neither chlorine nor iodine can be detected at the lower 0.1 percent 

limit of sensitivity.

Bromargyrite was identified in specimens from outcropping breccia 

in the Racine Boy quarry (fig. 4, loc. 16), an outcropping manganese 

vein northeast of the quarry (fig. 4, loc. 44), an outcropping manganese 

vein on top of the Silver Cliff bluff (fig. 4, loc. 13), and a large dump at 

the south edge of the Silver Cliff quarry (fig. 4, loc. 45). A 10-pound 

sample of rhyolitic dump rock from locality 45 was found by fire assay 

to contain S l/2 ounces silver per ton. A portion of a sample collected 

from this locality and concentrated by wet sluicing in 1962 was given to 

us by Bill Klein of Silver Cliff. It contained bromargyrite and argentian 

cryptomelane and was found by fire assay to contain 390 ounces of 

silver per ton.

CRYPTOMELANE

Cryptomelane, essentially potassium manganese oxide, is the most 

abundant mineral of the manganiferous veins and breccia fillings. It is 

hard and brittle and adheres tightly to the rhyolitic wallrock of veins and 

to rhyolitic breccia fragments. The cryptomelanes have a dull submetallic to shiny metallic luster, a bluish-black to grayish-black color, 

and a rough, uneven to smooth conchoidal fracture. X-ray and spectrographic examinations of many cryptomelanes with these variable 

physical properties disclosed, surprisingly, that they are all of a single 

phase and vary only slightly in degree of crystaHinity and elemental 

composition. Approximately 50 cryptomelanes from the Silver Cliff 

quarries have identical X-ray interplaner spacings. A silver content of 

10,000 p/m (parts per million) produced no observable structural 

change.

Cryptomelanes from outcrops near and in the Racine Boy quarry and 

on the Silver Cliff bluff contain from 500 to as much as 10,000 p/m 

silver; the average silver content of 45 cryptomelanes is 2,500 p/m.
/ Geyser 

* mine

Water 

tank

>

I : Slope to ;

Silver Cliff / /, 

Plateau | / 

I Geyser mina dump //

V I

 

K

0 250 500 METE

FIGURE 4. Pace-and-compass map of the Racine Boy-Silver Cliff 
C12 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Other samples from the northwest corner of the Silver Cliff quarry, 

however, contain only 100-200 p/m silver.

The localities and source data of cryptomelanes containing more 

than 4,000 p/m silver are presented in table 1.

The maximum amount of silver in cryptomelane from the Silver 

Cliff quarries, as shown in table 1, is 1 percent. Cryptomelane containing 1 percent silver was also found at other mines on the Silver 

Cliff Plateau and at Round Mountain, cited later in this report. The 

silver-bearing cryptomelane of this area is argentian cryptomelane, 

reported here as a new variety.

The compositional and structural properties of cryptomelane which 

has the«Mn02 structure were studied in considerable detail by Gruner 

(1943) and Bystrom and Bystrom (1950). Barium, lead, and silver 

cations, which have large ionic radii similar to that of potassium, can 

proxy for potassium as in the high-barium mineral hollandite and the 

high-lead mineral coronadite. No correspondingly high-silver cryptomelane has, to our knowledge, been reported to occur. The presence 

of such large cations, especially potassium, apparently is necessary for 

the formation of cryptomelane and to prevent the structure from

TABLE 1. Occurrences of cryptomelane containing 4,000 p/m or more silver in the Silver

Cliff quarry area

Locality 

(fig. 4) Nature of occurrence

Number of 

pieces

Silver 

content 

(p/m)

11........... J/2-inch-wide veinlike concentration 5

from topmost part of Silver Cliff

bluff. 

16........... Quarried block (B-3) from waste pile 20

on floor of Racine Boy quarry. 

15........... Dump near northeast corner of May 3

shaft. 

51........... 1-inch-wide veinlike concentration 50

from upper south face of Silver Cliff

bluff. 

63 ........... Matrix of rhyolitic breccia from 30-ft- 200

long interval at end of tunnel

beneath floor of Racine Boy quarry. 

49........... From 30-ft-long interval of IVfe-inch- 40

wide vertical vein trending N. 45°

W. along quarry bench. 

16........... Quarried block (B-l) from waste pile 25

on floor of Racine Boy quarry. 

44........... From 50-ft-long interval of trenched 1- 20

to 2-inch-wide vertical vein trending

N. 15° W. in outcrop. 

16........... Quarried block (B-2) from waste pile 20

on floor of Racine Boy quarry.

4,000

4,000 

>4,000 

4,000

5,000

5,000

7,000

7,000

10,000

'Content of each piece.
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C13

collapsing. The composition of the cryptomelane that forms depends 

upon what elements are available in the solutions at the time of formation, and, mainly for this reason, the K +1 , Ag +1 , Pb +2 , and Ba +2 content can vary, as shown by compositional data from the Silver Cliff 

area cited later in this report.

Gruner (1943, p. 503) stated that numerous cation substitutions are 

possible including some between manganese ions of different sizes and 

ionic charge. The states of oxidation of manganese partly determine 

how much K +1 , Ba +2, Pb +2, and Ag +1 can enter the structure at the 

time the minerals form. Supposedly, more silver, which has a onepositive charge, can enter the structure than barium and lead, each of 

which has a two-positive charge. The substitutions cause some lattice 

distortion and instability, especially in the cryptomelanes with the 

larger cations.

Gruner (1943, p. 500, 504) synthesized a cryptomelane containing 

13.7 percent silver from an artificial reagent manganese oxide that 

was structurally cryptomelane and initially contained 3.1 percent 

potassium oxide but no silver. To explain the introduction of the large 

amount of silver into the structure, Gruner presumed that only some of 

the potassium ions were replaced by silver and that some silver entered 

"open positions" or "holes" in the structure, but some may have just 

been adsorbed. He further postulated that some monovalent silver may 

be reduced to metallic silver by Mn +2 ions. As an atom, it could fit into 

the "open positions" or "holes" which are sufficiently large to store 

water, as in the zeolite minerals.

If silver, lead, and barium partly proxy for potassium, cryptomelanes containing larger amounts of these elements should contain 

lesser amounts of potassium. To ascertain these relationships the 

potassium and silver contents of five cryptomelanes from the Racine 

Boy and Silver Cliff quarries were determined and are shown in table 2. 

This table shows that cryptomelanes of high silver content contain less 

potassium than cryptomelanes of low silver content and that as the 

silver increases, the potassium decreases. Also noteworthy in table 2 is 

the observation that the cryptomelane with the least potassium has the 

greatest total cation content, consisting of the cations silver, lead, 

barium, and strontium totaling about 73,000 p/m, whereas the cryptomelane with the most potassium has the least total cation content of 

about 2,300 p/m.

Several cryptomelanes with higher than average barium and lead 

were noted from the Racine Boy quarry. Most notable is one containing 

about 7 percent barium and 0.7 percent silver and another containing about 7 percent lead and 1 percent silver. These cryptomelanes 

do not contain sufficient barium or lead for them to be called hollandite 

or coronadite, but their X-ray-diffraction patterns are somewhat 

different from those of normal cryptomelane in that some lines show 

shifting and intensity differences.
C14 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 2. Major cation constituents of five cryptomelanes from the Racine Boy and

Silver Cliff quarries

[Potassium determinations were made by Kam Wo Leong, all other determinations were made by Elwin L. Mosier, 

both with the U.S. Geological Survey]

Approximate total

Loc. K Ag Ba Sr Zn Pb Fe major cations' X-ray phases

shown

Agl5-B ....

Ag 16-A-l . . .

Ag ll-D-5 . . .

Ag 16-B-l . . .

...15

...14

...16

...11

...16

cent)

3.6

3.3 

2.8 

2.0 

1.3

100

1,000 

1,000 

4,000 

7,000

1,000

1,000 

> 30,000 

20,000 

-60,000

1,000

2,000 

1,500 

3,000 

1,000

5,000

7,000 

10,000 

30,000 

15,000

200

2,000 

200 

> 20,000 

5,000

cent)

2.0

1.5 

.7 

1.0 

10.0

(p/m) (percent)

7,300

13,000 

> 42, 700 

> 77,000 

= 88,000

0.7

1.3 

4.3

7.7 

8.5

Cryptomelane, 

trace of goetWte 

and quartz. 

Cryptomelane, 

trace of quartz. 

Cryptomelane, 

trace of quartz. 

Cryptomelane, 

trace of quartz. 

Cryptomelane, 

moderate amount 

of goethite.

'Excluding K and also Fe, most of which is assumed to be in goethite.

TODOROKITE AND CHALCOPHANITE

Todorokite (Mn, Ba, Ca, Mg)Mn3 07-H20was tentatively identified in 

one specimen of vein cryptomelane from the Silver Cliff quarry. 

Chalcophanite (Zn, Mn, Fe)Mn205 -2H20 associated with zinc-bearing 

cryptomelane was tentatively identified in a specimen of breccia filling 

from the Racine Boy quarry. Apparently, todorokite and chalcophanite 

are of sparse occurrence in the quarry area, and they, could be tentatively identified in only the two specimens cited above.

GOETHITE, DICKITE, FLUORITE, AND BARITE

Goethite, dickite, fluorite, and barite are coevally associated with 

cryptomelane and bromargyrite, and all these minerals are believed to 

be of volcanic hydrothermal origin. They occur in vugs of breccia 

fillings and in elongated vugs that parallel the wallrock contact of 

manganese veins.

Goethite varies widely in color from black, brown, tan, and red to 

orange-yellow and yellow. Goethite accompanying bromargyrite is 

commonly bright shiny red and shows internal reflections. 

Pseudomorphs of goethite after a rhombohedral mineral are uncommon, as in the Reilly specimens described earlier in this report. Minor 

amounts of goethite as thin iridescent films are probably the result of 

recent weathering.

Dickite is abundant and is fine grained, sugary, and tan to orange 

yellow and yellow and cannot be distinguished from geothite in the 

field. Presumably, because of the identical appearance of the two 

minerals, much dickite in this area has formerly been misinterpreted 

to be goethite.
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C15

Fluorite occurs as clear, brown, green, and, more rarely, purple 

clusters of cubes embedded in cryptomelane, goethite, or dickite. In 

some places it has been leached, leaving only casts, some of which still 

contain remnants of unleached fluorite. Barite occurs most commonly 

as aggregates of tabular crystals, some trending toward prismatic 

habit with a length of as much as IVfe inches. Some of it has been 

leached leaving tabular-shaped casts, and, in some casts, small remnants of solution-pocked barite still remain.

Other ore deposits of the Silver Cliff Plateau and Round Mountain, 

as seen in the mines and exploratory workings, are so similar to those 

of the Silver Cliff quarry area that their descriptive mineralogy will 

not be repeated; instead, it is tabulated (table 3). The studied cryptomelanes contain 100 p/m or more of copper, antimony, vanadium, 

cadmium, and bismuth, and lesser amounts of minor elements, as 

shown in table 4. Their average elemental composition is in the range 

shown for analyzed cryptomelanes, as cited by Richmond and Fleischer 

(1942, p. 610).

WHITE HILLS

The base-metal fissure veins of the White Hills supplied refractory 

silver ores that contributed to the early silver production of the district. The ore minerals containing silver, lead, zinc, and smaller 

amounts of copper occur in stringer zones in veins that range in width 

from less than 1 to 10 feet.

Mineralogic studies were made of fresh specimens from two recently 

operated mines, the Maxine Elliot and the Reveille (fig. 3). Specimens 

from the 100-foot level of the Maxine Elliot, kindly supplied by the 

owner, James Turner of Silver Cliff, disclose that the mineral 

assemblage is mainly pyrite, galena, 2M-type sericite mica, barite, 

anglesite, cerussite, sphalerite, goethite, and quartz. The silver contents of bright silver-gray and dull black sooty galena are reported in 

table 5.

Specimens from the Reveile mine, kindly supplied by the owner, Pete 

Cowan of Westcliffe, came from the 100-foot level of a new drift along 

the original Reveille vein. The vein had not been previously mined 

westward beyond an intersecting syenite dike. By trenching the unexplored area west of the syenite dike, Cowan exposed the vein just a few 

feet below the surface, where it is 4-6 feet wide and contains stringers 

of solid galena 4-6 inches wide. Surprisingly, this area, with ore just 

beneath the surface, apparently had not been explored even during extensive prospecting of the early mining days. The mineral assemblage 

is like that of the Maxine Elliot vein cited previously. Black galena, 

thought by the miners to possibly be acanthite, was found to have a 

normal unit-cell size. The silver contents of black and silver-gray 

galena from the Reveille mine are shown in table 5.
C16 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 3. Minerals of Silver Cliff Plateau and Round Mountain mines

Mine Locality 

(fig. 3)

Mineral Remarks

Ruby Cliff ......... 267

Kate 

(Silver Bar).

40

Obsidian quarry 

(Calumet-Victor).

216

Hecla(trench)...... 85

Fluorite 

Dickite .

Bromargyrite ..

Argentian Dull black cryptomelane in veins and vuggy zones 

cryptomelane. in fine-grained platy rhyolite.

Chalcophanite..... Brilliant black radiating-fibrous fanlike masses 

and spherical forms with structureless gray 

centers. Also as cross-fiber bands and pimply 

botryoidal crusts. Occurs sparsely with 

todorokite and cryptomelane. Non silver bearing.

Todorokite ........ Dull or shiny radiating bundles and plumose

masses with confused fibrous leafy structure and 

silky sheen. Non silver bearing.

Goethite .......... With cryptomelane in pseudomorphs after rhombic

ferroan rhodochrosite (?). Also with cryptomelane and in pseudomorphs after cubic 

fluorite in which remnants of fluorite still remain.

Colorless, brown, and purple; cubic forms. 

Sugary orange-yellow coatings on fluorite. Also as

veins cutting through fluorite cubes. 

Found in three specimens as bright-green pellets, 1- 

2 mm in diameter, and as purple-coated euhedral 

isometric crystals or clusters of rounded crystals 

associated with reddish-brown goethite and tan 

dickite in cryptomelane veins in flow-banded and 

platy rhyolite. Also found as a bright-green 

pellet, 1 mm in diameter, enclosed by a thin 

radial-fibrous layer of brilliant reddish-black 

chalcophanite, both enclosed in a '/4-inch-wide 

vein of black cryptomelane containing 1 percent 

silver.

Argentian Hard brittle black '/^-inch-wide vein of crypcryptomelane. tomelane containing 1 percent silver.

X-ray fluorescence shows there is no contribution 

of silver from bromargyrite. 13 other specimens 

show silver values ranging from 500 p/m for 

pieces containing goethite as a diluent to 5,000 

p/m for pieces of pure cryptomelane. The 

arithmetic mean of 14 determinations is about 

3,000 p/m silver.

Clear, brown, and purple cubic forms. 

Sugary orange-yellow coatings. 

Brown, red, and black masses closely associated 

with cryptomelane.

Chalcophanite..... Occurs as a coating around kernel of olive-green 

bromargyrite, the whole enclosed by argentian 

cryptomelane in the '/2-inch-wide vein specimen 

cited above. Has brilliant luster, radial-fibrous 

habit, and deep red internal reflections. Closely 

resembles goethite.

Birnessite Small black soft fragile nodular masses of irregular 

(AMn02> shape intimately mixed with cryptomelane in 

montmorillonitic clay in the outer margin of a 

large spherulite, 7 ft in diameter, in obsidian.

Cryptomelane ..... Poorly crystalline and intimately associated with 

birnessite described above. No silver could be 

detected in a mixture of the cryptomelane and 

birnessite.

Montmorillonite ... Formed by devitrification of glassy obsidian.

Birnessite (?)...... Closely associated with argentian cryptomelane

and goethite. Manganese minerals occur as a 

matrix filling around silica fragments in 

spherulitic rhyolite.

Fluorite , Dickite .. 

Goethite ,
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C17 

TABLE 3. Minerals of Silver Cliff Plateau and Round Mountain mines Continued

Mine Locality 

(fig. 3)

Mineral Remarks

JayGould ..........70

Buffalo 

(trenches).

39

King of the Valley ...76

Vanderbilt ..........41

Buffalo Hunter ......48

Argentian

cryptomelane. 

Goethite .......

Botryoidal

silica. 

Galena .........

Argentian

cryptomelane. 

Lead, manganese

oxide. 

Bromargyrite ...

Argentian 

cryptomelane.

Barite .........

Argentian 

cryptomelane.

Goethite .......

Barite .........

Dickite .......

Bromargyrite ..

Argentian 

cryptomelane.

Barite .........

Dickite or 

goethite. 

Bromargyrite ..

Argentian 

cryptomelane.

Hard, brittle, smooth, bluish black. Contains 1,500

p/m silver. 

Orange yellow. Closely resembles dickite. Vug

fillings. 

Creamy brown. Lines walls of vugs.

See table 5.

Contains 500 p/m silver.

Unidentified. Not coronadite or quenselite.

Tiny irregularly shaped bright-green pieces found 

in ultrasonically cleaned samples of black 

botryoidal cryptomelane from veins, about 8 inches wide, in platy rhyolite.

2- to 4-inch-wide veins with large botryoidal surfaces in some places. Some botryoids are nearly 3 

inches in diameter. 13 specimens contain 20-700 

p/m silver and average 200 p/m silver. Five 

specimens contain 1,000-2,000 p/m silver.

Local concentrations in cryptomelane.

Smooth, bluish black. In thin veinlets and as thin 

coatings on spherulites in rhyolite. Aggregate of 

20 pieces contains 300 p/m silver.

Smooth, shiny, black.

Colorless plates.

Sugary, orange yellow.

Small olive-green-, bright-green-, or purplishcoated masses associated with dark-red goethite 

in 12 specimens from bluish-black cryptomelane 

veins in rhyolitic tuff.

Thin veins in fine-grained rhyolitic tuff. Six 

samples contain 200-700 p/m silver. Five samples 

contain 2,000-4,000 p/m silver. There was no contribution of silver from bromargyrite. One 

specimen containing 4,000 p/m silver and much 

greater than 2 percent lead is comparable to a 

high-lead cryptomelane from the Racine Boy 

quarry cited elsewhere in this report. Specimen 

also contains an unidentified lead manganese oxide structurally related to the unidentified lead 

manganese oxide from the Jay Gould mine cited 

above. Emmons (1896, p. 452) cited a Vfe-inch-wide 

manganese oxide vein containing 60 ounces (2,000 

p/m) silver per ton.

Abundant in all Vanderbilt ore.

Orange yellow. Identity not established.

Tiny irregularly shaped bright-green pieces in two 

ultrasonically cleaned samples of bluish-black 

cryptomelane from small veins in flow-banded 

rhyolite.

Samples from 20-ft-deep open trench trending N. 

22° E. for about 600 ft. Widens into open-pit area 

at nprtheast end and presumably was trenched 

along a vein system. Mostly flow-banded 

rhyolite, but south end of trench is in spherulitic 

rhyolite, and the argentian cryptomelane from 

there contains 30 p/m silver. Eight specimens of 

smooth black botryoidal cryptomelane from 

flow-banded rhyolite north of the spherulite zone 

contain 1,000-10,000 p/m silver and have an
CIS CONTRIBUTIONS TO ECONOMIC GEOLOGY 

TABLE 3. Minerals of Silver Cliff Plateau and Round Mountain mines Continued

Mine Locality 

(fig. 3)

Mineral Remarks

Plata Verde .........53 Argentian 

cryptomelane.

Exact 

location 

unknown.

Horn Silver .........74

"Psilomelane" 

cryptomelane.

Barite .......

Goethite .....

Bromargyrite

Argentian 

cryptomelane.

Barite ... 

Goethite .

average silver content of 3,000 p/m. A loose slab 

of cryptomelane vein material measuring 4x12x1 

inches from floor of trench near north end of 

zone contains 2,000 p/m silver.

Clevenger and Caron (1925, p. 9, 22, 80) concluded 

from gas-reduction experiments on 

manganiferous silver ores, including Buffalo 

Hunter ore, that an unidentified refractory silver 

manganite compound is uniformly disseminated 

throughout a higher oxide of manganese, which 

they thought was psilomelane in the Buffalo 

Hunter ore. The current study shows, however, 

that only one silver-bearing manganese mineral, 

namely argentian cryptomelane, occurs in the 

ore.

Stockwork of manganese veins trending northeast 

and northwest. Samples and average silver content as follows: 17 pieces of smooth black cryptomelane from a dump, 1,000 p/m (a single piece, 

2,000 p/m); 9 pieces of smooth black roughtextured cryptomelane from waste rock in a 

small quarry, 300 p/m; 200 pieces of smooth 

black cryptomelane from a small vein bearing N. 

80° E., 300 p/m; 50 pieces of hard brittle bluishblack cryptomelane from a small vein bearing N. 

20° W., 600 p/m; 25 pieces of hard brittle bluishblack cryptomelane from trenched veins, 200 

p/m; 6 pieces of smooth black cryptomelane from 

around the collar of a shaft in trench, 400 p/m.

Emmons (1896, p. 451) cited a sample of manganese 

oxide from south of Round Mountain. The 3.4 

percent K2O reported indicates to us that the 

mineral is cryptomelane and not psilomelane, in 

agreement with Hewett and Fleischer (1960, p. 

21).

White.

Black and brown.

Tiny irregularly shaped bright-green masses from 

two specimens of bluish-black cryptomelane containing 1 percent silver.

Small veins in rhyolite and bedded tuff. Samples 

and average silver content as follows: 2 pieces of 

black cryptomelane from a large dump, 50 p/m; 5 

pieces of black and bluish-black cryptomelane, 

100 p/m; 4 pieces of black cryptomelane, 450 p/m; 5 

pieces of bluish-black cryptomelane, 1,800 p/m; 1 

piece of bluish-black cryptomelane, 7,000 p/m, 

and another shiny black piece, 1,000 p/m; 1 loose 

piece of black cryptomelane from the shaft 

collar, 2,000 p/m. This cryptomelane is from a 

mirrorlike surface of a slickensided fault plane. 

The cryptomelane is polished by the movement. 

It shows plucking and is impure with grains of 

fault gouge in places. There was no contribution 

of silver from bromargyrite. The cryptomelane is 

obviously of prefault age.

Large tabular crystals.

Brown and black. Probably contaminates and 

dilutes some cryptomelane samples and causes 

an apparent reduction in silver value.
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C19

TABLE 4. Elemental composition of cryptomelanes from 66 localities in the Silver Cliff

area

Element 1

Pb ..............

Zn ..............

Ba ..............

Sr ..............

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

Bi (high values only)2

Cu ..............

Sb ..............

V...............

Cd ..............

Y........ .......

Ti ..............

Mo .............

La ..............

Nd .............

Nd .............

Zr ..............

Co ..............

Ni ..............

Number 

of samples

193

195

196

195

200

27

170

21

194

194

195

97

194

41

27

27

79

74

191

Average 

content

percent

1.5

1.0

0.7

0.15

0.15

p/m

500

200

200

150

100

70

70

70

30

30

30

20

20

20

Element1

Ce. ................

Nb .............

Ti3 ..............

W ..............

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

Se4 .............

Ge

Yb .............

Sc ..............

Be ..............

In3 ..............

Hg5 ............. Te6

An 7

Ta3

Pt3 .............

Number 

of samples

27

41

27

194

IfiQ

194

27

127

27

78

168

27

27

97

oq

27

27

Average 

content

p/m

15

15

15

<50

<20

<10

<10

10

7

5

2

<fl 9

o

'All determinations by semiquantitative spectrographic analysis by E.L. Mosier, except as noted.

2The two high- and low-value groups for Bi were not averaged together, because of their distinctly different values. 

The high-value group came from near the boundary between the Silver Cliff Plateau and the White Hills, close to the 

base-metal fissure veins. The low-value group came from the Silver Cliff Plateau.

3Semiquantitative spectrographic analyses by Nancy M. Conklin.

'X-ray-fluorescence analyses by J. S. Wahlberg.

'Atomic-absorption analyses by W. W. Janes.

6Catalytic Te analyses by R. L. Turner.

'Atomic-absorption analyses by E. P. Welsch, J. R. Watterson, and A. E. Hubert.

'Not detected at 200 p/m.

9 Not detected at 30 p/m.

Mineralogically, the fissure veins of other mines in the White Hills 

are very similar to the Maxine Elliot and Reveille veins. Galena from 

dumps of other mines contains comparable amounts of silver (table 5).

During the investigation of fissure veins, many occurrences of 

associated jarosite, a heretofore unrecognized mineral in the district, 

were found. It was positively identified from 12 mines (fig. 3): Ben 

West, Thames River, Moultrie, Passiflora (south), Herman, Songbird, 

Gray Eagle, Valley, Keystone, Sunrise, Black Friday, and Orange. 

Brown jarosite is still unrecognized by present miners, and for many 

years it has been referred to by them as "jasper" and "brown carbonate." At some mines it can be plainly seen in the upper part of the 

shaft as stringers in the fissure veins. A detailed study of a 2-foot-wide 

jarosite vein on Ben West Hill disclosed that jarosites with a wide 

range of composition and several stages of multiple injection occur in
C20 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 5. Minor elements' in galena and sphalerite from the Silver Cliff-Rosita mining

district

[Data shown in italic refer to sphalerite samples; all other data refer to galena samples. N, not detected at limit of 

detection N(Bi) = 10 p/m, N(Sb) = 150 p/m, N(Zn)s= 200 p/m]

Sample Minor element content (p/m)

Mine Sample2

(Ag-) Number of 

pieces

Source and remarks Ag Bi Sb Zn Pb

Silver Cliff area mines (fig. 3)

Defender ............

Jay Gould ...........

King of the Carbonates

(south shaft).

King of the Carbonates

(north shaft).

Passiflora (north) .....

Herman .............

Songbird ............

Gray Eagle ..........

Reveille .............

Immortal smelter site .

Bull Domingo ........

Sunrise ..............

Lady Franklin ........

22-A

-B

70-A-l

263-A-l

B-2

263-B-l

299-A

308-A

-B

305-A

-B

309-A

-B

269

67-A

277-1

-2

120

261-A

300-A

274-A-l

-A-2

-A-3

150

50

10

50

100+

110

60

100

SO

100

50

100

50

100

1

100

100

1

20

15

8

1

1

Ore shoot ...............

...do ..................

Dump ..................

'.. .do ...................

...do ..................

...do ..................

Loading dock; some trapped

pyrite and sphalerite.

Dump ..................

...do ..................

...do ..................

...do ..................

...do ..................

...do ..................

100-ft level; silver gray . . .

Drift at 100-ft level;

bluish black. . Drift at 100-ft level;

bright silver gray. .

Dump ..................

...do ..................

... do ..................

Loading dock ............

... do ..................

...do ..................

1,500

150

1,000

1,500

15

1,500

700

700

70

300

100

1,500

150

400

550

700

2,000

2,000

1,000

300

3,000

700

200

1,000

N

20

15

15

30

20

30

30

... > ..

N

N

N

N

N

300

N

N

N

1,500

1,000

1,500

1,500

700

300

N

1,000

700

1,500

1,500

1,000

N

1,500

500

N

700

3,000

<200

N

3,000

15,000

N

7,000

N

30,000

N

N

3,000

15,000

N

700

N

N

300

100

150

300

700

Rosita-Querida area mines (fig. 5)

Senator (Maverick) ... 128

Maine No. 2 .......... 250

Vulcan .............. 218

Ben Franklin ......... 249-A

-C-2 

-E

-C-l

Bunker Hill (northeast 215 

slope).

4 Dump; bluish black ...... 1,500 300

1 Shaftcollar ............. 1,500 N

1 Dump .................. 3,000 N

18 Shaft collar; some 5,000 <15 

trapped pyrite and 

sphalerite. 

50 Dump .................. 70 .....

210 Shaft collar ............. 5,000 N

1 ...do .................. 3,000 N

25 Dump; slightly impure with 1,500 300 

pyrite and sphalerite.

N N .....

700 3,000 .....

7,000 15,000 .....

10,000 20,000 .....

7,000 7,000

3,000 3,000

1,000 10,000

'Semiquantitative spectrographic analyses by Nancy M. Conklin of the U.S. Geological Survey. 

2Sample localities are shown in figures 3 and 5, except for the Bull Domingo sample 261, which is 3,800 ft N. 34° E. of 

locality 120 (fig. 3) and is shown in figure 2.

the same vein. Most of this vein was mined for its silver content during 

World War I. Silver halides were tentatively identified in remnants of 

this vein, collected from near the borders. They consist of iodiar 

bromargyrite iodyrite and two others containing large amounts of 

iodine and smaller amounts of bromine and chlorine. The discovery of 

iodine-bearing silver halides supports oral statements by local miners
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C21

concerning soft grayish-yellow clayey masses that occurred in mines 

from the Thames River southeastward toward the Defender mine. According to the miners, the clayey masses were yellow when freshly 

mined, but upon exposure to the sunlight for some time, they turned 

pale blue. The miners attribute the color change to an iodine content.

ROSITA HILLS

FISSURE VEINS

The volcanic rocks in the Rosita Hills are more andesitic and appear 

to consist of fewer rhyolitic flows and breccias than the volcanic rocks 

of the Silver Cliff area. Hydrothermal alteration is extensive over 

several broad areas, and there is only a small amount of manganese 

mineralization. The ore deposits are mainly base-metal fissure veins, 

as in the White Hills north of Silver Cliff, but here the veins are larger, 

and the mines are deeper. The large Humboldt-Pocahontas vein, for example, was mined for a distance of about 4,000 feet along its strike, and 

the Humboldt mine was 800 feet deep. Because the Rosita mines are 

now abandoned, specimens of galena and sphalerite for silver determinations (table 5) were collected mainly from dumps.

MANGANIFEROUS SILVER ORE AT GAME RIDGE

On the basis of early mining reports which state that "free milling," 

"hornsilver"-type ore occurs at Game Ridge, northeast of Rosita (fig. 5) 

(Irwin, 1881, p. 716; Engineering and Mining Journal, 1880), specimens 

from the Tecumseh mine were collected and studied. Cryptomelane and 

bromargyrite were identified from veins in what appears to be altered 

trachyandesitic rock. Dull black cryptomelane occurs as small veins 

and as weak botryoidal coatings on the walls of small vugs. X-raydiffraction patterns show that the cryptomelane has good crystalUnity, and spectrographic analyses disclose that it contains 4,000 p/m silver 

and is, therefore, argentian cryptomelane. The bromargyrite is olive 

green and occurs in the argentian cryptomelane, as well as in reddishtan goethite and between tabular plates of white barite. The 

bromargyrite has a slightly smaller cell than normal, presumably 

because of small amounts of iodine and chlorine which were detected 

by a closed tube test. Goethite also occurs as reddish-brown 

pseudomorphs after a rhombohedral mineral similar to that previously 

described from the Silver Cliff Plateau.

CONCLUSIONS

The long-misunderstood nature of manganiferous silver ores and the 

difficulties experienced in their processing, at least at Silver Cliff, can 

now be explained on the basis of their mineralogy.
C22 CONTRIBUTIONS TO ECONOMIC GEOLOGY

105°15'

1 KILOMETER

FIGURE 5. Sample localities in the Rosita area. Mines: 31, Tecumseh; 128, Senator 

(Maverick); 215, Bunker Hill; 218, Vulcan; 249, Ben Franklin; 250, Maine No. 2.

The first mined ore from the Racine Boy quarry was mostly handcobbed bromargyrite,2 was almost unquestionably free milling, and

2Computations based upon 2-year production figures for silver, obtained by raw amalgamation from 

bromargyrite from^he Racine Boy quarry area, which measures about 255 X 500 feet, disclose that about 11.6 

tons of bromine was associated with the silver. This large quantity of bromine from such a small area certainly 

shows that a large volcanic source of bromine was concentrated in this quarry area.
CRYPTOMELANE AND BROMARGYRITE, SILVER CLIFF, COLO. C23

was processed locally by raw amalgamation. As mining progressed and 

the bromargyrite content decreased, the ores contained relatively more 

nonamalgamating argentian cryptomelane and were actually a mixture of free-milling and smelter fluxing ores. If the ores were 

processed by smelting, all the silver was recovered, but if they were 

processed by amalgamation, only the silver from bromargyrite was 

recovered, and the argentian cryptomelane passed into the mill 

tailings. This explains why full recovery of assay values was obtained 

from those ores shipped and smelted outside the district, whereas only 

partial recovery of the assay values was obtained if the ores were 

processed locally by raw amalgamation. Large smelters in the Western 

United States at that time mixed manganiferous silver ores, which also 

commanded a premium as a smelter flux, with silver-bearing lead sulfide smelting ores, whereby the manganese fluxed the lead ores, and 

the lead served to collect the silver from both. We conclude, therefore, 

that if, instead of amalgamating mills, there had been one first-class 

smelter of the Argo (Denver) type at or near Silver Cliff, local smelting 

of all the silver-bearing ores of the district could have been successful, 

and the district might have prospered longer.

REFERENCES CITED

BystrSm, Anders, and Bystrdm, A. M., 1950, The crystal structure of hollandite, the 

related manganese oxide minerals, andaMnCta Acta Crystallographica, v. 3, p. 146- 

154.

Church, J. A., 1887, Concentration and smelting at Tombstone, Arizona: Am. Inst. Mining Engineers Trans. v. 15, p. 601-613.

Clevenger, G. H., and Caron, M. H., 1925, The treatment of manganese-silver ores: U.S. 

Bur. Mines Bull. 226, 110 p.

Cross, Whitman, 1896, Geology of Silver Cliff and the Rosita Hills, Colorado: U.S. Geol. 

Survey 17th Ann. Rept, pt. 2, p. 263-403.

Emmons, S. F., 1896, The mines of Custer County, Colorado: U.S. Geol. Survey 17th Ann. 

Rept., pt. 2, p. 405-472.

Engineering and Mining Journal, 1880, General mining news Colorado; Custer County: 

v. 29, May 8, p. 324.

Gruner, J. W., 1943, The chemical relationship of cryptomelane (psilomelane), hollandite, 

and coronadite: Am. Mineralogist, v. 28, p. 497-506.

Hewett, D. F., and Fleischer, Michael, 1960, Deposits of the manganese oxides: Econ. 

Geology, v. 55, no. 1, pt. 1, p. 1-55.

Irwin, Richard, 1881, History of Custer County, in History of the Arkansas Valley, 

Colorado: Chicago, 0. L. Baskin and Co., Historical Publishers, p. 689-739.

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* U.S. GOVERNMENT PRINTING OFFICE: 1974 543 58S/ia6