DEPARTMENT OF THE INTERIOR

FRANKLIN K. LANE, Secretary / ? */ 2~ J o

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, Director

Bulletin 681

THE OXIDIZED ZINC ORES OF LEADVILLE

COLORADO

BY

G. F. LOUGHLIN

WASHINGTON

GOVERNMENT PRINTING OFFICE

1918
o

o

 *? 
CONTENTS.

PageIntroduction. ............................................................. 7

Discovery.....................................................'............ 7

Early accounts of zinc carbonate and silicate............................. 8

Recent discovery of oxidized zinc ore bodies............................. 12

Production................................................................ 13

Literature.................................................................. 16

Mineralogy................................................................... 17

Zinc-ore minerals....................................................... 17

Smithsonite....................................................... 17

Hydrozincite....................................................... 18

Aurichalcite..................................'..................... 19

Calamine......................................................... 20

Hetaerolite....................................................... 21

Chalcophanite..................................................... 24

Zinciferous clay................................................... 24

Deschenite........................................................ 28

Associated minerals.................................................... 28

Iron oxides........................................................ 28

1 Manganese oxides.................................................. 29

Dolomite.......................................................... 29

Manganosiderite............... 1................................... 29

Calcite........................................................... 30

Aragonite and nicholsonite.......................................... 30

Barite.,........................................................... 31

Plumbojarosite..................................................... 31

Opal, chalcedony, and quartz....................................... 32

Sericite........................................................... 33

Kaolin............................................................ 33

Sulphides.......................................................... 33

Native silver...................................................... 34

Paragenesis........................................................... 34

Varieties of ore........................................................'..... 36

Gray carbonate ore.................................................... 36

Occurrence....................................................... 36

Megascopic features:.............................................. 36

Microscopic features............................................... 37

Chemical composition............................................. 39

Brown carbonate ores................................................... 40

Megascopic features................................................ 40

Microscopic features................................................ 42

Chemical composition............................................. 44
4 CONTENTS.

Varieties of ore Continued. Page.

Black zinc ore........................................................ 46

White or "talcy " zinc ore.............................................. 47

Analyses............................................................... 47

Range in metal content of the ores........................................... 48

Zinc content.......................................................... 48

Other contents......................................................... 50

Distribution and mode of occurrence of the ores............................. 51

Geographic distribution................................................ 51

Distribution with respect to kinds of country rock....................... 51

Relations to the different kinds of lead carbonate and mixed sulphide ore

bodies.............................................................. 51

Shapes and sizes of ore bodies........................................... 54

General features.................................................... 54

Carbonate Hill ore bodies.......................................... 57

Character of boundaries of the ore bodies................................. 61

Relations to oxidized iron and manganiferous iron ores .................. 64

Vertical distribution and relation to depths of oxidation and ground-water

level................................................................ 64

Lack of association with secondary sulphides............................. 66

Genesis.................................................................... 68

First stage............................................................ 69

Derivation of materials............................................... 69

Deposition of materials from solution................................ 72

Second stage.......................................................... 80

Third stage............................................................ 81

Summary.............................................................. 83

Prospecting for bodies of oxidized zinc ore................................... 85

Index................................................................... 89
ILLUSTRATIONS.

Page. 

PLATE I. A, Gray zinc carbonate ore; B, Chalcophanite and calamine coating

brown zinc carbonate ore...................................... 18

II. A, Photomicrograph of gray zinc carbonate ore inclosing remnants of 

sulphide ore; B, Photomicrograph of zinc carbonate replacing 

manganosiderite............................................... 19

III. A, Brown zinc carbonate ore with fine druses of smithsonite; B,

Photomicrograph of specimen shown in A ....................... 20

IV. A, Brown zinc carbonate ore with druses of calamine; B, Calamine

druse coating brown zinc carbonate ore......................... 21

V. A, Brown zinc carbonate ore with druses of aurichalcite; B, Photomicrograph showing aurichalcite and calamine filling cavity in 

brown zinc carbonate ore; C, Photomicrograph of vein of calamine, 

aurichalcite, and opaline silica in low-grade brown zinc ore...... 24

VI. A, White zinciferous clay; B, Brown dense zinciferous clay; C, 

Brown banded zinciferous clay; D, E, Aragonite filling cavities in 

brown iron oxide.............................................. 25

. VII. Plan of zinc carbonate ore bodies in workings of Western Mining Co.,

Carbonate Hill................................................. 58

VIII. Sections through ore bodies shown in Plate VII.................... 60

FIGURE 1. Diagram showing percentages of constituents in zinciferous clays,

arranged in order of increasing alumina......................... 27

2. Diagram showing distribution of calamine along bedding planes

and cross fractures in brown zinc carbonate ores............. % .. 42

3. Plan and sections of lead-silver stopes in Belgian mine............ 53

4. Diagrams illustrating relations of oxidized zinc ore bodies to lead

carbonate stopes in the Oro La Plata mine..................... 54

5. Plan and sections showing relation of oxidized zinc ore body on

the Dome claim to old lead carbonate stope..................... 55

6. Plan and section showing relations of oxidized zinc ore stopes to

old lead carbonate stopes, Tucson mine........................ 56

7. Plan and section showing relations of oxidized zinc ore to old lead

carbonate stopes in Chrysolite mine........................... 57

5

THE OXIDIZED ZINC ORES OF LEADVILLE, COLORADO.

By G. F. LOUGHLIN.

INTRODUCTION.

Oxidized zinc ores were first exploited in the Leadville mining 

district, Colorado, after the Geological Survey's field study of the 

other ores had been completed. In the summer of 1913 the writer was 

detailed to study these ores and spent four weeks in the district during July and August. The present report was completed early in 

1914 and transmitted to form a chapter in a monogpaph on the 

geology and ore deposits of the district, but owing to continued delay 

in the completion of the monograph it has been decided to publish 

this chapter in advance.

The mine operators and engineers in the district gave the writer 

till possible assistance in his work. Thanks are especially due to 

Messrs. Nicholson, MacDonald, and Dalrymple, of the Western Mining Co.; Messrs. Platt and Kleff, mine surveyors and lessees of the 

New Dome property; Messrs. Davis and Pendery, of the Yak Co.; 

Messrs. Argall and Aicher, of the Iron Silver Co.; the officers of the 

Ibex Co.; Mr. Warren F. Page, of the Luema Mining Co.; and Mr. 

John E. Curley, State inspector of mines. To the several other 

lessees, foremen, and miners who rendered assistance at different 

times the writer here expresses his hearty thanks. Thanks are also 

due to Mr. E. C. Wells, of the United States Geological Survey, 

for criticism of the discussion of chemical processes involved in the 

deposition of the oxidized zinc ores.

DISCOVERY.

After it was realized, in 1910, that large deposits -of oxidized zinc 

ores were present in the Leadville district, considerable discussion 

arose over the fact that these ores had been so long overlooked both 

by the mining engineers and geologists who had made frequent visits 

to the mines and by the mine officers and assayers who had been 

working in the ore and handling samples of it for several years. It

7
8 OXIDIZED ZINC OKES OF LEADVILLE, COLO.

must be admitted that the ore had been exposed both on dumps and 

'underground and all who have had an opportunity of finding it must 

share the blame of having overlooked it. Very few of those who 

have written on the subject realized that silicate and carbonate of 

zinc had been known to exist from the earliest days, when only a 

comparatively small part of the oxidized lead ores had been worked.

EARLY ACCOUNTS OF ZINC CARBONATE AND SILICATE.

The following paragraph was published as long ago as ^.882: *

Mr. Garrison (of St. Louis) makes the prediction that at an early date 

Colorado will be made tributary to the western spelter industry. Probably 

the first call will be made for carbonates, calcined before shipping. This class 

of zinc ores often so closely resembles limestone that the ordinary prospector 

would not detect its value. If we remember correctly, Prof. Konig, of Philadelphia, has found calamine, or carbonate ore, in the vicinity of Leadville. 

Should a closer search, which we trust will be made at an early date, reveal 

the presence of larger bodies of this ore, zinc mining might soon be added to 

the list of Colorado industries.

It was thus early known, therefore, that oxidized zinc ores occurred 

in the Leadville district, but zinc was then evidently of insufficient 

interest to stimulate prospecting for bodies of high-grade zinc ore.

In 1886 Emmons, in his famous monograph,2 noted the occurrence 

of calamine at Leadville and mentioned zinc blende and calamine as 

accessory minerals. He evidently had considered the problem of 

the disposition of the zinc in the oxidized zone, as he shows in his 

description of the old Iron mine:

In the body of the limestone, on the eighth level, not far from the north 

incline, a natural jointing plane forming one wall of the drift was observed to 

be coated with fine, silky white crystals which chemical examination proved 

to be calamine or silicate of zinc. If the sulphureted ores, which will undoubtedly be found when the mine workings shall have reached the limits of 

the zone of oxidization, are as rich in blende as those which have been found 

in the A. Y. mine, it seems singular that little or no zinc has hitherto been 

found associated with the oxidized ore. This occurrence would seem to show 

that, owing probably to greater solubility, the alteration products of blende 

have been removed during secondary deposition to a greater distance from 

their original location than those of the other sulphurets.

Again, he writes:

Zinc occurs in the lead carbonate ores in very small proportion and probably 

in the form of silicate (calamine), since this is the only mineral of zinc that 

has been observed in the Leadville deposits. It is rarely visible and generally 

form fine, needle-like silky-white crystals, lining drusy cavities and cracks or 

joints in vein material and limestone. There is little doubt that it originally 

occurred as zinc blende, and, from analogy with the Tenmile deposits, it may be 

presumed that it formed a much larger proportion of the deposit than it does

1 Bng. and Mln. Jour., vol. 34, p. 16, 1882.

2 Emmons, S. F., Geology and mining industry of Leadville, Colo.: U. S. Geol. Survey 

Mon. 12, pp. 376, 389, 398, 547, 550, 556, 557, 560, 1886.
DISCOVERY. 9

now. The much greater solubility of its sulphate than that of the other inetals 

would account for its more thorough removal by surface waters.

He noted the absence of zinc in analyses of samples of basic ferric 

sulphate, a feature in accordance with the observation, quoted above, 

that the zinc had been further removed from the original ore bodies 

than the other metals, owing to the more ready solubility of its sulphate, and he states that in spite of the comparative absence of 

zinc this metal was " quite uniformly detected in the products of 

smelting."

The analyses of different vein materials show little or no zinc. 

A siliceous hematite from the Chrysolite mine, carrying 2.56 per cent 

of zinc oxide, was said to contain " a rather unusual percentage of 

zinc." As these vein materials were in large part similar in color 

and other visible features to the reddish-brown zinc ores now mined, 

the absence in all of them of any considerable amount of zinc may

well have diverted Emmons's attention, both then and in later years, 

from such iron-stained bodies as possible oxidized zinc ores. Very 

little drifting or other work beneath the old lead stopes had been done 

at the time, and no ground with abundant pockets of calamine, such 

is characterize much of the oxidized zinc ore now mined, had been 

exposed. Even after some of the extensive zinc ore bodies had been 

exposed along drifts and other workings the strong resemblance of 

the reddish-brown ore to iron ore at one extreme and iron-stained 

limestone at the other and the close resemblance of the gray ore to 

partly leached but unstained limestone were hardly likely to lead one 

to suspect the presence of high-grade zinc ore. These ores are in general so different in color and texture from the more crystalline and 

brilliant specimens from other districts, so common in museums and 

other collections, that failure to recognize them without chemical 

examination is not surprising.

Emmons, however,. did recognize the rather exceptional occurrences of small quantities of the dense white zinc ore that is identical 

in appearance with " Chinese talc," as shown by his discussion of the 

analyses. He regarded this material as a mixture of hydrated silicates, of alumina and silicate of zinc and remarked that " the occurrence of the zinc was somewhat unexpected." In the extensive 

mining of oxidized zinc ores during the last few years, ore of this 

type has been found only in small quantities and of a grade too low 

for shipment except during a short time when the price of zinc was 

abnormally high. It is indeed striking that none of the many specimens of ores and vein matter taken during the extensive study of 

the ores in the earlier days proved to contain any considerable 

quantity of zinc carbonate.

In 1889, after a. period of extensive development, during which 

many of the oxidized lead bodies had been followed down to the
10 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

sulphide zone. Blow 1 called attention to the abundance of zinc blende 

just below the zone of oxidation and offered the conclusion that it 

was the result of downward sulphide enrichment. In his own words,

The zinc sulphides are the most widely disseminated and show plainly the 

result of their more ready solubility than the other sulphides and the redeposition of a large portion of the zinc which has thus been removed from the 

carbonate ores. This fact is cjearly shown in many ways, but most satisfactorily just at the line of transition. The sulphides first encountered are invariably heavy sulphides of zinc, carrying a little iron and very little lead. They 

have a close crystalline structure and lie in a laminated form, the lines of 

fracture being nearly vertical. Upon these cleavage planes crystals of cerusite 

are found, and often a small incrustation of native silver. Such deposits, where 

first encountered in passing from oxidized to unoxidized ores, are always lowest 

in silver. In their further, extension the zinc gradually grows less and the 

laminated structure disappears. Beyond this, again, the zinc sulphides appear 

to predominate along cleavage and contact planes with the gray porphyry, or 

along the lines of minor faults and cracks in the limestone. Such characteristics are also universally observed in other instances besides those of Iron 

Hill. * * *

In advancing further within the ore shoots the zinc appears to lose its preponderance over the other sulphides. * * * It seems probable that a large 

proportion of the zinc, which was totally removed from the carbonate ores, 

has beeen redeposited as a sulphide, and principally just below the line of complete oxidation, by surface waters, and such redeposition has advanced and 

increased pari passu with the limit and extent of such oxidizing action.

As a corollary of the above, it is believed that at the present stage of development in Leadville, the sulphide of zinc forms a larger part of the unoxidized 

ores than will be found in future and deeper exploration.

This conclusion, in view of the fact that no zinc carbonate ore 

bodies had then been discovered or recognized, seemed very plausible 

from the evidence in hand. It was evidently adopted by Emmons 

and Irving,2 who wrote in 1907:

The hydrous zinc sulphate is presumably more soluble and less stable than 

the corresponding iron sulphate. In Leadville, like gypsum, which should have 

been formed by the reaction between iron sulphate and limestone, it is practically absent from the oxidized zone and must have been carried away in solution or redeposited as a sulphide below the zone of oxidation. It has, in fact, 

been observed that the sulphide ores are much richer in zinc blende immediately below the limit of oxidation than elsewhere.

This hypothesis of downward enrichment of zinc blende tended 

to delay the search and discovery of the zinc carbonate ores, as the 

possible existence of such ores must have been dismissed from the 

minds of the geologists and consequently from the minds of the 

operators.

The field evidence, however, on which this hypothesis was based 

may be interpreted in another way, as will be shown later; further1 Blow, A.. A., The geology and ore deposits of Iron Hill, Leadville, Colo.: Am. Inst. 

MIn. Bng. Trans., vol. 18, pp. 168-172, 1890.

a Emmons, 8. F., and Irving, J. D., The Downtown district of Leadville, Colo.: U. 8. 

GeoL Survey Bull. 820, pp. 32-33, 1907.
DISCOVEKY. 11

more, later developments have shown that rich bodies of zinc blende 

are not limited to the top of the sulphide zone; and finally, recent 

experimental evidence and field observations in other parts of the 

world have shown that such deposition of secondary zinc blende is 

very unlikely.

After the large shipments of ore in 1910 had attracted wide attention Emmons addressed a letter from Dinard, France, to the Leadville Herald-Democrat,1 in which he said:

At the time of my first study of the Leadville district, in 1880, I was much 

puzzled to know what had become of the zinc. * * * I assumed then that 

owing to the superior solubility of the zinc sulphate, the oxidation products 

of that metal had been carried much further than those of lead before being 

transformed into the now stable carbonate, and had possibly been entirely removed in the run-off.

Blow's observation that on Iron Hill secondary zinc blende had accumulated 

in the upper part of the sulphide zone seemed to account for some of the

missing zinc, and from accounts published by0 you, it is evident that much of 

it has accumulated as calamine in the zone of change from sulphide to oxide.

Though I have particularly desired to study the zinc of Leadville, I have 

never been able to, because in 1880 mine workings had not yet reached it, and 

when I next visited the district (1890) they had gone beyond it, and owing to 

the soft nature of the ground in that zone the drifts leading to it were for the 

most part caved and inaccessible.

It certainly seems rather strange that those in charge of mines, when this 

zone was exploited, did not notice such bodies of calamine as you describe, 

but it must be borne in mind that calamine is generally a white-brown earthylooking material, which would not attract attention unless especially sought 

for, and that it was pay ore rather than material of only mineralogical interest 

that they were seeking, and at that time zinciferous ores were a particularly 

undesirable product.

Another reason, mentioned by several writers,2 for the failure to 

recognize oxidized zinc ores is the fact that in the earlier days the 

presence of zinc in the lead-silver ores and also in the iron ores was 

a decided detriment, and miners in consequence avoided points where 

assays showed a considerable percentage of zinc. According to G. 0. 

Argall and E. W. Keith, the presence of zinc was especially noticeable in shipments from the Carbonate Hill and Fryer Hill mines. 

The object of search in those days was lead-silver ore, and as there 

was then no market for zinc there was no incentive to look for it, 

even though some of the early operators may have recognized its 

character. Argall further states that it was after the gradual depletion of the sulphide ores and in consequence of the increasing 

expense of deep operations that exploitation turned again to the

1 This letter, dated Oct. 11, 1910, has been quoted by the Engineering and Mining 

Journal (Nov. 12, 1910. p. 954) and by H. B. Burton In Mines and Minerals (February, 

1911. p. 436).

* Mining World, Dec. 17, 1910, p. 1147. Keith, B. W., Leadville Herald-Democrat, 

Sept. 20, 1910, p. 1. Argall, G. O., Oxidized zinc ores at Leadville: Eng. and Mln. Jour., 

Aug. 26, 1911, p. 399.
12 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

upper levels in search of ore that might not have been profitably 

mined when first opened and thus led to the discovery of the character and value of the oxidized zinc deposits.

RECENT DISCOVERY OF OXIDIZED ZINC ORE BODIES.

Accounts of the recent discovery of oxidized zinc ores in extensive 

bodies at Leadville are not in accord.1 Some state that the discovery 

was made through the curiosity of a Leadville assayer, who took the 

time and trouble to determine the contents of a sample of high specific gravity, which had been shown by assays to contain little or no 

lead, silver, or gold; others state that the character of the material 

was recognized by those who had discovered and worked oxidized 

zinc ores elsewhere in the State. According to J. B. McDonald,2

the first silicate of zinc shipped from the State was from the old Madonna 

mine, at Monarch, Chaffee County, in 1902. * * * Several hundred tons of 

the ore were shipped. * * * The first carbonate of zinc ever shipped from the 

State came from the Monarch Pool mine, at Monarch, and the two highestgrade cars of carbonate of zinc ever shipped out of the State to this day came 

from this mine. One car ran 46.7 per cent and the other 47 per cent zinc.

The following year (1903) Mr. McDonald and Mr. Harry Paui 

procured a lease on the Eclipse mine at Monarch and shipped a 

mixed carbonate and silicate ore almost identical in character with 

that discovered in Leadville seven years later. Mr. McDonald states 

that in the spring of 1906 he found the first carbonate and silicate 

of zinc ever found in commercial quantities in the Leadville region. 

This was at the Hilltop mine, in the Horseshoe district, which adjoins 

the Leadville district on the divide between Lake and Park counties.

The first discovery of ore of this kind within the Leadville district in recent years was made in 1909 by W. E. Jones, a lessee in the

Robert E. Lee mine, who found a large body of zinc carbonate. 

Shipments were made from this body and also from the Penrose 

dump but were of too low grade for treatment and failed to arouse 

much interest in oxidized zinc ores. In the following year (1910) 

the first high-grade zinc ore, reported as calamine, was discovered 

by H. E. Burton, H. K. White, and Alfred Thielen in a lease at the 

Hayden shaft of the May Queen mine. This property was the first 

to ship high-grade calamine ore. After this discovery S. D. Nicholson, manager of the Western Mining Co.'s properties, began a search 

for oxidized zinc ores in the old workings of the Wolf tone and 

adjoining claims and discovered in them the largest bodies yet found

»Leadville Herald-Democrat, Sept. 11, 1910, and Jan. 1, 1911; Eng. and Min. Jour, 

Nov. 12. 1910, p. 954, and Aug. 26, 1911, p. 399; Mln. World, Dec. 17, 1910, p. 1147; 

Mines and Minerals, Feb. 11, 1911, p. 436; Mln. Sci., July 27, 1911, p. 85.

2 Personal Interview with the writer. A similar account is given in Min. Sci., July 27, 

1911, p. 85.
PEODUCHON. 13

in the district. This discovery resulted in a general search for the 

ore throughout the district, with the result that smithsonite and 

calamine in varying amounts were found in a number of properties 

from Fryer Hill on the north to Weston Pass on the south.

PRODUCTION.

These discoveries were made at a time when there was an increasing demand for zinc, and although shipments of oxidized zinc ores 

began only at the end of 1910, they became very large in 1911, as 

shown in the table on page 14, offsetting a marked decline in the 

production of zinc sulphide ore and increasing the output of metallic 

zinc in Lake County by 15,243,011 pounds. This increase, in spite of 

a decrease of 7,996 tons in total shipments of zinc ores from the Leadville district, was due to the higher grade of the oxidized ores. At 

first only oxidized ores that averaged 30 per cent or more in zinc 

were shipped, but the increasing price, which culminated at 7 cents 

a pound late in 1912 and early in 1913, allowed profitable mining of 

ore containing as low as 17 per cent, and the production of oxidized 

zinc ores in 1912 greatly increased. Some ore containing as low a? 

15 per cent was shipped but at a loss. Most of the ore shipped, however, averaged about 30 per cent, and some contained as high as 40 

per cent. The average for all shipments was 29.2 per cent.

Owing largely to this increase in price, which allowed several 

small producers of low-grade ore to ship at a profit, many enthusiastic estimates were made of the vast quantity of ore in reserve; but 

the rapid decline in price to about 5 cents a pound in the spring of 

1913 forced most of the small producers to stop work, and the production for 1913 was less than that for 1912. During the writer's 

visit to the district in July and August, 1913, only a few properties 

besides those of the Western Mining Co. at Carbonate Hill were 

being worked. Ore containing as little as 24 per cent of zinc, however, could be shipped at a profit during the summer, and in October of that year it was stated that 22 per cent ore could be marketed.1

In January, 1914, new smelting rates made it possible to ship carbonate ore containing only 18 pe"r cent of zinc. The average content of ore shipped during that .year was 24.3 per cent, and in 1915 

the average was 22.48 per cent. In spite of this opportunity to ship 

lower-grade ores, and in spite of the reported opening of a large 

body of zinc carbonate ore averaging 25 per cent zinc in the upper 

levels of the Wolftone mine in 1915,2 the production of oxidized 

zinc ores, as shown in the accompanying table, continued to decrease 

during 1914 and 1915, the decline more than offsetting substantial

i Eng. and Mln. .Tour., Oct. 18, 1913, p. 761. 

 Mining Press, Mar. 20, 1915, p. 455.
14 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

increases in output of zinc sulphide ore. Owing to the extraordinarily high price of zinc in 1915, however, the total value of zinc 

from Lake County was more than 100 per cent greater than in 1914.

Depletion of the immense deposits in Carbonate Hill was evidently far from compensated during these years by discovery and 

development of oxidized zinc ore bodies elsewhere in the district. 

The production of both zinc carbonate and zinc sulphide ore in 

1916, however, showed an encouraging increase, though the zinc content of the carbonate ore continued to decrease slightly.

The following figures * show the quantities of oxidized zinc ore produced in the Leadville district from the time of the first shipments 

in 1910 to the end of 1916 and the corresponding quantities of zinc 

sulphide shipments in the district, the total zinc for Lake County 

(most of which is from Leadville), and the total zinc for the whole 

State.

Zinc produced in the Leadville district, in Lake County, and in Colorado,

1909-1916.

Year.

1909.........

1910.........

1911.........

1912.........

1913.........

1914.........

1915.........

1916.........

Leadville.

Oxidized ores.

Quantity 

(short 

tons).

8,059 

83,905 

142,782 

135,760 

113,881 

82,592 

85,513

Per cent 

of zinc.

30+ 

31.1 

29.2 

27.45 

24.3 

22.48 

21.52

Sulphide ores.

Quantity 

'(short 

tons).

163, 2i8 

79,376 

104,148 

97,704 

111,947 

136,555 

147,295

Per cent 

of zinc.

23.3 

24 

23 

21.2 

22.09 

21.69

Lake County.

Total zinc 

(pounds, in 

spelter and 

oxide).

56,367,445 

71,610,456 

105,945,783 

93,842,857 

78,763,334 

72,493.170 

76,785,567

Value.

$3,043,842 

4,081,796 

7,310,259 

5,255,200 

4,016,930 

8,989,154 

10,289,266

Colorado.

Total zinc 

(pounds, in 

spelter and 

oxide).

51,210,260 

77,089,648 

94,607,456 

132,222,812 

119,346,429 

96,774,960 

104,594,994 

134,285,463

Value.

$2,765,354 

4,162,841 

5,392,625 

9,123,374 

6,683,400 

4,935,523 

12,969,779 

17,994,252

Most of the ore thus far mined has come from the immense body 

in Carbonate Hill, which extends through the claims controlled by 

the Western Mining Co. and a few adjoining claims. Smaller 

amounts have come from Fryer, Breece, Iron, Printer Boy, and Eock 

hills, showing that the oxidized zinc ores, like the oxidized lead ores, 

are distributed throughout the district. There is, however, a striking contrast between these two classes of ore, for although large 

bodies of oxidized lead ore have been mined in all of these hills, the 

correspondingly extensive bodies of high-grade oxidized zinc ore 

thus far discovered are limited to the northern part of Carbonate 

Hill.

1 Henderson, C. W., Gold, silver, copper, lead, and zinc in Colorado: U. S. Geol. Survey 

Mineral Resources, 1909 to 1916.
PRODUCTION.

Mines producing oxidized zinc ores, 19.10 to 1916.

15

Dolly B...... ..............................................

Eliza.......................................................

Elk........................................................

Highland Chief ............................................

La Plata (Eickard) .'.......................................

Lilian......................................................

Little Ellen.. :.............................................

Mikado ....................................................

Pnlarict

Star Consolidated ....................................... . .

U. S. Smelting, Refining & Mining Co .....................

Western Mining Co.: 

AdaTis ......... ......... .....

Big Chief ...............................................

Btookland ..........................................

Castleview .............................................

Evalyn ............................................. .

Henrietta ...............................................

Maid of Erin. ..........................................

Waterloo ............................................ . Wolftone ..................................... .....

Yak tunnel: 

White Cap....... .....................................

1910

V

1911

y

X

X

y

7

X

?

y

y

?

1912

X

X

y

y

X

x

X

y

y

y

?

y

1913

X

X

x

X

X

y

X

1914

y

X

X

X

x

y

y

X

y

y

X

'

1915

y

X

x

y

y

1916

y

X

X

X

X

X

X

X

X

X

Among recent developments in the district wholly or partly induced by the mining of oxidized zinc ores are the establishment of a 

plant at Leadville for the treatment of low-grade oxidized zinc ores 

and the unwatering of the Downtown, Fryer Hill, and Carbonate Hill 

sections of the district. In the spring of 1914 the Western Zinc Mining & Reducing Co. began the erection of a zinc oxide plant to treat 

the oxidized ores.1 This plant, which had a capacity of 50 tons a 

day and was designed to treat zinc carbonate ore containing 16 per 

cent or less of zinc, was put into operation in the fall of 1914 2 but was 

operated for only a short time. In 1915, however, it was successfully 

operated by the Western Zinc Oxide Co. on low-grade zinc carbonate 

ores, mainly from the Kobert E. Lee mine, and was reported in July 

of that year to be yielding 150 tons a month of a product containing 

70 to 80 per cent zinc and realizing $100 a ton.8 The plant was operated steadily during 1916. In April, 1917, it was reported to be capable

1 Bng. and Mln. Jour., Mar. 28, 1914, p. 676. 

«Mln. and Eng. World, Nov. 14, 1914, p. 92. 

 Mlo. Press, July 24, 1915, p. 144.
16 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

of treating 60 tons of zinc carbonate a day, and the company was said 

to be considering an enlargement of the plant to include equipment 

for roasting sulphide ores.1

The unwatering of the Downtown section of the district was begun 

in 1914 with the installation of pumps at the Penrose shaft. It proved 

an immense undertaking and was not completed until 1916. During 

that year the projects to unwater the Fryer and Carbonate hills sections 

were begun. In 1917 they were completed, and shipments of ore, including zinc carbonate, were made from the newly unwatered ground 

in all the three sections.2 Trial shipments of zinc carbonate ore from 

the Penrose mine yielded 25 per cent of zinc.3

LITERATURE.

Although several short articles, already referred to, have been 

written on the oxidized zinc ores of Leadville, they deal mostly with 

history. Only three papers have discussed the occurrence and-genesis of these ores at any length. G. 0. Argall * in 1911 gave brief descriptions of the mineralogy and occurrence of the ore and discussed 

the process of oxidation by which the zinc ore was concentrated. 

Butler 5 in 1913 described the occurrence and nature of the ore in 

somewhat more detail and announced the occurrence of two mineral 

varieties not previously recognized in the district. One of these was 

an aragonite containing variable proportions of zinc and named by 

Butler nicholsonite, after S. D. Nicholson, manager of the Western 

Mining Co., in whose mine the mineral was found. The other mineral was at first thought to be a new species and was named wolftonite, from its discovery in the Wolf tone mine. Further study, however, proved this mineral to be hetaerolite, although the Leadville 

specimens are different in appearance from the type material.6 Butler also discussed the origin of the ore and the results of experiments 

on the determination of the grade of ore and on its concentration.

Philip Argall visited the deposits on Carbonate Hill a few months 

after the writer's visit and in 1914 published a very interesting 

paper,7 laying special emphasis on the occurrence of gray zinc carbonate ore along fissures in the lower part of the White limestone of

» Min. Press, Apr. 14, 1917, p. 519.

8 Hosklns, A. J., Unwatering projects at Leadville: Bng. and Mln. Jour., Mar. 24, 1917, 

pp. 483-487. Henderson, C. W.,. U. S. Geol. Survey Press Bull. 325, p. 3, July, 1917. 

«Min. Press, Mar. 24, 1917, p. 424. '

4 Argall, G. O., Oxidized zinc ores at Leadville : Leadville Herald-Democrat, Jan. 1, 1911, 

p. 6. The same article in condensed form appeared in Bng. and Min. Jour. Aug. 26, 1911, 

p. 399.

5 Butler, G. M., Some recent developments at Leadville, second paper, The oxidized zinc 

ores; Econ. Geology, vol. 8, pp. 1-18, 1913; reprinted with addendum in Colorado School 

of Mines Quart., vol. 8, pp. 9-21, 1913.

 Written communication by G. M. Butler to the writer.

7 Argall, Philip, The zinc carbonate ores of Leadville: Min. Mag. (London), vol. 10, 

pp. 282-288, 1914.
MINERALOGY. 17

the Maid of Erin mine places not exposed at the time of the writer's 

visit. The zinc carbonate ore there grades into manganiferous 

siderite a short distance from the fissures. Argall's descriptions 

supplement and his conclusions are in accord with those of the 

writer.

A paper of general interest on the formation of oxidized zinc ores 

by Wang 1 was published in 1915, over a year after the present report 

was completed. In this paper several experiments were described, 

some of which confirmed conclusions stated by the present writer 

regarding the genesis of the Leadville ores and none of which offered 

conflicting evidence. Wang's conclusion, however, that there is no 

definite order in the formation of smithsonite and calamine is not 

confirmed by study of the Leadville ores, in which smithsonite everywhere precedes calamine. The only specimen from Leadville described by Wang is one composed mostly of calamine with some 

smithsonite, in which hematite and limonite are concentrated along 

the partings and cleavage cracks of calamine.

MINERALOGY.

The zinc-ore and associated minerals noted in the oxidized zinc 

deposits of the Leadville district are given in the following lists:

Zinc-ore minerals. Associated minerals. 

Smithsonite.

Hydrozincite.

Aurichalcite.

Nicholsonite (zinciferous aragonite).

Calamine.

Hetaerolite (" wolftonite").

Chalcophanite.

Zinciferous clay.

Deschenite.

Iron oxides.

Manganese oxides (?).

Dolomite.

Manganosiderite.

Calcite.

Aragonite.

Barite;

Plumbojarosite.

Opal or chalcedony.

Chert.

Quartz.

Sericite.

Kaolin.

Sulphides.

Native silver.

ZINC-ORE MINERALS. 

SMITHSONITE.

Smithsonite, the zinc carbonate (ZnCO3 ), is by far the most 

abundant of the oxidized zinc minerals. The pure mineral should 

contain 52 per cent of metallic zinc, but owing to the presence of impurities, the percentage in shipping carbonate ore of the better

_______i _ . - 

1 Wang, Y. T., The formation of the oxidized ores of zinc from the sulphide: Am. Inst. 

Min. Fng. Bull., September, 1915, pp. 1959-2012.

52757° Bull. 681 18 -2
18 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

grades is rarely above 40 and commonly not much above 30. Smithsonite occurs in two varieties, deposited in different stages. Both 

may commonly be noted in a single specimen. The older variety 

'(Pis. I, A; II, A) contains isoinorphous mixtures of iron, magnesia, and manganese carbonates. It forms a dense gray to palebrown mass of microscopic grains, in part relatively massive and in 

part containing numerous small cavities or pockets. The younger 

varieties (Pis. Ill, A; IV, A) is a fine drusy growth, colorless to 

white or locally pale greenish where free from foreign matter but 

usually of brown appearance, owing to the brown iron oxide to which 

it is attached. The dusty smithsonite has a weaker absorption and a 

lower index of refraction than the dense variety, properties which 

indicate a higher percentage of zinc, whereas the dense vvariety is 

correspondingly high in iron. Individual grains of the dense material, however, are so extremely fine and so complex in composition that measurements of their indices can not be made with sufficient accuracy to give more than a rough approximation to the 

percentage of zinc. The drusy variety lines small pockets and minute fractures in the dense variety, and close inspection shows that 

in several places it forms minute layers alternating with layers of 

a black manganese mineral (hetaerolite ?) and locally with ferric 

oxide. (See PL IV, A.) Many if not most of the cavities containing calamine have a narrow rim of drusy smithsonite. The 

crystals of the drusy variety have for the most part curved or corroded faces, but here and there minute though nearly perfect unit 

rhombohedrons may be found. Occasionally pockets are found 

containing minute isolated rhombs, more or less corroded, scattered 

over a surface of brown iron oxide.

No coarsely fibrous or botryoidal smithsonite was seen by the 

writer, and only one occurrence in the lower beds of the White limestone in the Maid of Erin mine has been reported, to his knowledge.1 

In this respect the Leadville smithsonite is sharply contrasted with 

that in many well-known deposits of oxidized zinc ores, and the 

absence of these more familar forms of the mineral may go far toward explaining the failure to realize earlier the position and extent of the oxidized zinc ores in the Leadville district.

HYDROZINCITE.

Hydrozincite, a basic zinc carbonate (ZnC03 .ZnO2H2 ), has been reported to occur here and there as a dull-lustered white, soft, earthy 

alteration product of smithsonite.1 In the workings accessible to the

l Argall, Philip, The zinc carbonate ores of Leadville: MIn. Mag. (London), vol. 10, ! 

p. 284, 1914. ]

2 Butler, G. M., Some recent developments at Leadville, second paper, The oxidized zinc 

ores: Econ. Geology, vol. 8, p. 8, 1913; reprinted in Colorado School of Mines Quart, 

vol. 8, April, 1913. 
D. S. GEOLOGICAL SURVEY BULLETIN 681 PLATE I

A. GRAY ZING CARBONATE ORE.

S. CHALCOPHANITE AND CALAMINE COATING BROWN ZINC CARBONATE ORE.
U. S. GEOLOGICAL SURVEY BULLETIN 681 PLATE II

A. PHOTOMICROGRAPH OF GRAY ZINC CARBONATE ORE INCLOSING 

REMNANTS OF SULPHIDE ORE.

B. PHOTOMICROGRAPH OF ZINC CARBONATE REPLACING 

MANGANOSIDERITE.
MINERALOGY. 19

writer, however, the only earthy white material found in the oxidized 

zinc ores proved, on testing, to be the zinciferous clay, described on 

pages 24-28.

ATJRICHALCTTE.

Aurichalcite is a basic carbonate of zinc and copper, 2(Zn,Cu)C08. 

3(Zn,Cu) (OH) 2 , whose zinc content ranges, according to different 

analyses, from 50 to 59 per cent, and whose copper content ranges 

from 15 to 22 per cent. The pure mineral, according to Penfield,1 

contains 53 to 54.4 per cent of zinc and 20 to 21.2 per cent of copper. 

The pure mineral is of pale-green to sky-blue color, of pearly luster, 

and very soft and occurs in drusy coatings or divergent tufts of 

columnar or needle-like crystals.

The only deposits of aurichalcite noted by the writer in Leadville 

were in two small stopes above the first level of the Ibex No. 1 (Little 

Johnny claim). Here the aurichalcite occurs as pale bluish-green 

crystals forming druses or cavity fillings in light-brown zinc carbonate ore. (See PI. V, A.) In thin section (PI. V, B) the pocket 

fillings were found to consist of a mixture of aurichalcite and calarnine. The calamine predominated, forming diverging groups of 

bladelike crystals, in and through which were scattered tufts of fine 

needle-like to fibrous crystals of aurichalcite. A thin rim of drusy 

smithsonite separated the calamine and aurichalcite in places from 

the massive brown ore. One of the pockets was found to have a matrix of nearly or quite isotropic silica, in which the crystals of aurichalcite and calamine were embedded. The silica preserved to some 

extent the granular texture of the massive carbonate ore, proving 

that the " pocket" had grown in part, or been enlarged, by replacement of the massive ore, and indicating that the zinc in the calamine 

and aurichalcite had been, at least in part, derived from the zinc in 

the massive ore. The source of the copper is not apparent. It is 

said that ore of this type from the Ibex No. 1 has run as high as 4 

per cent copper, but that no allowance for the copper is made by the 

ore buyers. Ore of a similar kind is said to have been mined in the 

Battling Jack claim, whose shaft is a short distance southeast of 

the Ibex No. 1 shaft.

A few microscopic needles of aurichalcite were found in a thin 

section (PL V, C) of a calamine-quartz vein cutting low-grade reddish-brown zinc ore in the Belgian mine (Fenton's lease in 1913). 

Here also the aurichalcite grew simultaneously with the calamine; 

the two zinc minerals grew inward from the sides of the vein, and 

their terminations are embedded in a central filling of chalcedonic 

quartz. Some of the aurichalcite needles are bent, and fragments

* Penfield, S. L., One the chemical composition of aurJchalcite: Am. Jour. Sci., 3d ser., 

vol. 41, pp. 106-108, 1891.
20 OXIDIZED ZINC OBES OF LEADVILLE, COLO.

of calamine blades, which may have been broken from the margins, 

are inclosed in the central portion of the vein, suggesting that there 

was a sluggish flowing of fluid (or gelatinous) silica during or just . 

after the growth of the aurichalcite and calamine crystals.

The fact that these were the only occurrences of aurichalcite 

noted in the district indicates that the mineral is a very minor constituent of the general run of the oxidized zinc ores. Its relative 

abundance in the Ibex, which lies in the copper-gold belt, is significant, and its occurrence in considerable quantities is doubtless limited 

to this belt.

. CALAMINE.

Calamine is a hydrous silicate of zinc, whose formula may be 

written H2Zn2Si05 , (ZnOH) 2 .Si03 , or H,0.2ZnO.SiO2 . The pure 

mineral contains 54.2 per cent of metallic zinc. It occurs typically in 

fine to coarse druses of white to colorless bladed crystals (PI. IV), or 

in aggregates of diverging crystal groups, which may partly or 

completely fill cavities (fig. 2, p. 42). Sheaf-like aggregates, composed of crystals welded along their brachypinacoids, are occasionally 

found. The crystals in these cavities are tabular parallel to the 

brachypinacoid, which is vertically striated. Many of the crystals 

are terminated by a blunt point formed by two macrodomes; others 

by a sharper point where the blunt macrodomes are subordinate to 

steep macrodomes. Less commonly the nearly flat brachydomes predominate, producing a blunt chisel-like termination, and in a few 

specimens the " chisel edge " was seen to be truncated by the basal 

pinacoid. One small pyramid face was noted by Butler.1 Prism 

faces are present but not conspicuous. The calamine,also fills small 

fractures, in a few of which it is accompanied by amorphous or microcrystalline silica. In one exceptional specimen, found by E. S. Fitch 

on the dump at the Adams shaft, August, 1913, calamine crystals 

are coated with minute quartz crystals. The calamine crystals have 

grown upon both massive and drusy smithsonite, and on red and 

brown iron oxides and black manganese oxides. (See Hetaerolite.) 

They may inclose small particles of the iron and manganese minerals 

and be correspondingly darkened in color. They are also found in 

pockets or fractures in limestone near zinc carbonate ore bodies, and 

some veinlets cut hetaerolite and zinciferous clay ore, both of which 

are described below. One specimen, found on the May Queen dump, 

was so filled with brown oxide of iron as to have a brown opaque appearance, and only its crystal habit gave a clue to its identity. In 

this and certain other specimens the calamine appears to have grown, 

at least in part, by the replacement of brown massive smithsonite ore

^Butler, G. M., Some recent developments at Leadville, second paper, The oxidized 

zinc ores: Econ. Geology, vol. 8, p. 7, 1913.
U. S. GEOLOGICAL SURVEY BULLETIN 081 PLATE III

A. BROWN ZINC CARBONATE ORE WITH FINE DRUSES OF SMITHSONITE

B. PHOTOMICROGRAPH OF SPECIMEN SHOWN IN A.
U. S. GEOLOGICAL SURVEY BULLETIN 681 PLATE IV

A. BROWN ZINC CARBONATE ORE WITH DRUSES OF CALAMINE.

S. CALAMINE URUSK COATING BROWN ZINC CARBONATE ORE,
MINERALOGY. 21

along cavities or fractures. In still other specimens, where the 

calamine rests upon other drusy minerals or fills a network of fractures inclosing sharply angular fragments of brown carbonate ore, 

the calamine was unquestionably deposited by infiltrating waters 

without detectable replacement.

HETAEROLITB (" WOLFTONITE ").

The mineral hetaerolite was not recognized at Leadville until the 

development of the oxidized zinc ores was begun. It was at first believed to be a new species and was therefore named wolftonite,1 after 

the mine in which it was found, but further study proved it to be 

hetaerolite. It is composed principally of oxides of zinc and manganese, with smaller'amounts of silica and water. Opinions differ 

as to its chemical formula. The mineral was first described by 

Moore 2 in 1877 from a specimen found at the Passaic zinc mine, 

Sterling Hill, near Ogdensburg, Sussex County, N. J. Moore described the physical properties and occurrence of the mineral and 

stated it to be a zinc hausmanite (ZnO.Mn2 03 ) s but published no 

analyses. It occurred in association with chalcophanite in ocherous 

limonite, the chalcophanite usually forming a thin coating over it.

In 1910 Palache 4 studied a new lot of material from Franklin 

Furnace, N. J., and agreed with Moore that the hetaerolite was a zinc 

hausmanite. He assigned it to the tetragonal system of crystallization and stated that it had an indistinct cleavage. The material was 

analyzed by W. T. Schaller, of the United States Geological 

Survey (see column 1 on p. 23), and shown to contain small amounts 

of silica and water, the latter being attributed to a slight admixture 

of chalcophanite.

In 1913 Ford and Bradley 5 published a description and analysis 

of a specimen of the Leadville hetaerolite, taken from the Wolf tone 

mine. They described it as a rare vug-filling mineral, found with a 

radiating mammillary structure, whose outer surfaces are generally 

smooth and rounded. The mineral showed a splintery fracture, and 

individual splinters showed a prismatic structure. Under the microscope the finest fragments were birefringent and had an extinction 

parallel to the prism edges, but no further indication of its crystal 

form could be discovered. Its hardness was found to be between 5.5 

and 6, and its specific gravity was determined as 4.6. Its luster was

1 Butler, G. M., op. cit, p. 8.

2 Moore, G. E., Preliminary notice of the discovery of a new mineral species: Am. Jour. 

Sci., 3d ser., vol. 14, p. 423, 1877.

' The formula for hausmanite is Mn30.i or MnO.MnaOs.

* Palache, Charles, Contributions to the mineralogy of Franklin Furnace. N. J.: Am. 

Jour. Sci., 4th ser., vol. 29, pp. 177-187, 1910.

3 Ford, W. E., and Bradley, W. H., On hetaerolite from Leadville, Colo.: Am. Jour. Sci., 

4th ser., vol. 35, pp. 600-604, 1913.
22 OXIDIZED ZINC ORES OP LEADVILLE, COLO.

submetallic, its color dark brownish to black locally, with a bright 

varnish-like exterior, and its streak dark chocolate-like brown. 

It was infusible, but on charcoal with sodium carbonate gave the 

characteristic zinc oxide coating and with fluxes gave the color reactions indicative of manganese. It was easily dissolved in hydrochloric acid, giving off chlorine gas. In the closed tube it yielded 

water but did not give off oxygen gas. The index of refraction 

of hetaerolite was determined by Ford and Bradley to be above 

1.78. It was determined by E. S. Larsen, of the United States 

Geological .Survey, from material collected by the writer to be 2.19 

and 2.22.

The writer can add to the above description that the mineral is of 

widespread occurrence in the oxidized zinc deposits of Leadville, 

though he found no specimens equal in size to those found in one part 

of the Wolftone mine. It has also been recently found by Philip Argall on the fourth level of the Tucson mine, filling small fractures in 

manganosiderite, well below the levels where oxidized zinc ores have 

been mined.1 The mineral occurs mostly as thin drusy bands, alone 

of alternating with smithsonite, around cavities; also as fillings of 

small fractures, or as linings of fractures that are centrally filled with 

calamine or zinciferous clay. Its surface may be exposed, or it may 

be covered by calamine druses, the crystals of hetaerolite appearing 

to end abruptly where those of calamine begin. In some specimens 

small central clusters of distinct hetaerolite crystals grade outward 

into black stains that spot or mottle a considerable part of the brown 

carbonate ore. This relation leads to the suggestion that all the 

black manganese oxide stains and spots in the zinc carbonate ores may 

be incipient segregations of hetaerolite and not of psilomelane, as 

would at first be supposed. Wherever seen these black stains bear 

the same paragenetic relations to the later smithsonite and to calamine as the undoubted occurrences of hetaerolite. Locally hetaerolite may be the most conspicuous mineral in the ore, giving it a black 

or brownish-black color. In one specimen of this character, from 

the Tucson mine, the hetaerolite crystals are very distinct, having 

grown along intersecting fractures and inclosing dark-brown soft, 

earthy material of low grade. In other specimens of similar color 

the mineral is not visibly crystallized. The Tucson specimen strongly 

indicates that the hetaerolite was formed by the segregation of zinc 

and manganese from the massive carbonate ore, which left a residue 

composed largely of iron oxides. This origin is also suggested by 

several other specimens, some of which contain undoubted hetaerolite 

and others only the black stains.

* Specimen taken in June, 1914, and sent to the writer for identification.
MINERALOGY.

In column 1 below is all analysis made by W. T. S'challer 1 of 

hetaerolite from Franklin Furnace, N. J.; in columns 2 and 3 are 

analyses of the Leadville hetaerolite made respectively by Bradley 2 

and by Chase Palmer, of the United States Geological Survey; and 

in column 4 a partial analysis by Haigh. 3

Analyses of hetaerolite.

MnjOa .......................................................

O.. ..........................................................

FesO«. .......................................................

ZnO.........................................................

CaO.........................................................

SiO,.............................:...........................

H,0- .......................................................

H80-K..... ..................................................

1

60.44

.77

33.43

1.71

2.47

1.42

100.24

2

MnO 50. 34

5.99

37.56

2 AQ

} 4.36 '

100.94

3

49.13

5.50

.67

37.66

Undet.

2 91

3.78

99.65

4

45.9

t Q

07 i

 2.0

4.7

95.6

a Insoluble.

In discussing analysis 2, Ford and Bradley state that the structure 

of the mineral was such as to suggest that the silica is due to the 

presence of calamine, and that if so about 10 per cent of calamine 

is present a large amount to escape discovery; but they thought 

that the fibrous structure of the hetaerolite might well conceal this 

amount. By recalculation, with allowance for the calamine, analysis 

2 is found to correspond closely to the formula 2Zn0.2Mn2 03 .H2O. 

Recalculation of analysis 1, including H2O but not SiO2 , yielded 

the same formula, which Ford and Bradley conclude should be the 

formula for hetaerolite, instead of ZnO.Mn2O3 , as stated by Moore 

and later by Palache; but they add that "it may be that the exact 

composition of hetaerolite can not be settled until purer material 

can be analyzed."

The best specimens collected by the writer show the hetaerolite 

to be a distinctly earlier growth than calamine, and the purest material, when crushed to a fine powder and examined under the microscope, gave no indication of calamine, even fine specks of which 

should be easily distinguishable from the hetaerolite. Chemical 

analysis (column 3 in the preceding table) shows it, however, to be 

practically identical with the material analyzed by Bradley (column 

2). G. M. Butler 4 has expressed the conviction that the silica is an 

essential constituent of the mineral but has not suggested a corresponding formula. Nevertheless, the fact that silica and the excess 

of ZnO over that necessary for the ratio 2ZnO.2Mn2 03 .H2O are in 

the same ratio as in calamine is certainly significant, although just 

what the significance is must for the present be left to speculation.

1 Palache, CharleB, op. clt., p. 180.

8 Ford, W. B., and Bradley, W. M., op. clt., p. 602.

 Haigh, G., partial analysis quoted by Ford and Bradley.

* Written communication.
24 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

CHALCOPHANITE.

Chalcophanite, like hetaerolite, is a manganese-zinc oxide, with the 

formula (Mn,Zn)0.2MnO2 .2H2 0, containing about 21 per cent of 

zinc oxide.1 It is closely associated with hetaerolite, both at Franklin Furnace, N. J., and at Leadville, Colo. It differs from hetaerolite 

in certain physical and chemical properties. In some specimens 

collected by the writer at Leadville it forms druses of minute tabular 

crystals of the rhombohedral system, coating botryoidal surfaces and 

filling occasional cracks in hetaerolite. In others it forms foliated 

crusts coating brown smithsonite and covered in turn by calamine 

druses. (See PI. I, B.) Dana states that it also forms stalactitic 

and plumose aggregates. Its hardness, as given by Dana, is only 

2.5; its specific gravity 3.91. Its luster is metallic and brilliant; its 

color bluish black to iron-black; and its streak chocolate-brown. In 

the closed tube it gives off water and oxygen and exfoliates slowly, 

and its color changes to a golden bronze. Before the blowpipe a 

similar change of color takes place, accompanied by slight fusion 

on thin edges, and it is this bronzy appearance that has given rise 

to the mineral name.

Since the above paragraph was written specimens of Leadville 

chalcophanite collected by F. B. Laney have been studied by Ford,2 

whose description verifies the properties above mentioned. He found 

that very thin plates under the microscope are sufficiently transparent 

to give a negative uniaxial interference figure.

- '' ": / ZINCIFEROUS CLAY. :-'

Three varieties of zinciferous clay have been recognized in the 

Leadville mines white, brown, and black. The white and brown are 

the most abundant. The white clay (PI. VI, A] is very similar in 

appearance to kaolin and is one of the materials included under the 

local name " Chinese talc." The fresh material, however, is harder 

(about 3) and of more waxy luster than kaolin and does not slake 

or become plastic even when immersed in water for several days. Its 

fracture is conchoidal. Weathered or leached portions of it are of 

earthy appearance and slake readily in water. It has been found at 

the base of porphyry sheets in the Waterloo 3 and New Dome mines, 

forming in the latter a layer 1 to 2 feet thick that separates the sill 

from an underlying body of reddish-brown zinc carbonate ore. It 

has also been found in the Yankee Doodle mine, where it forms a 

layer about 2 feet thick immediately beneath a thin bed of silicified

J Dana, J. D., System of mineralogy, 6th ed., p. 256.

2 Ford, W. B., Mineralogical notes: Am. Jour. Sci., 4th ser., vol. 38, p. 502, 1914. 

8 Emmons,/S. F., Geology and mining industry of Leadville, Colo.: U. S. Geol. Survey 

Mon. 12, p. 560, 1886. Hillebrand, W. F., idem, p. 605.
IT. S. GEOLOGICAL SURVEY BULLETIN 081 PLATE V

A. BROWN ZINC CARBONATE ORE WITH DRUSES OF AURICHALCITE.

J?. PHOTOMICROGRAPH SHOWING AURICHALCITE AND CALAMINE FILLING 

CAVITY IN BROWN ZINC CARBONATE ORE.

C. PHOTOMICROGRAPH OF VEIN OF CALAMINE, AURICHALCITE, AND 

OPALINE SILICA IN LOW-GRADE BROWN ZINC ORE.
U. S. GEOLOGICAL SURVEY BULLETIN 681 PLATE VI

D '

A. WHITE ZINCIFEROUS CLAY.

B. BROWN DENSE ZINCIFEROUS CLAY.

C. BROWN BANDED ZINCIFEROUS CLAY.

D, E. ARAGONITE FILLING CAVITIES IN BROWN IRON OXIDE.
MINERALOGY. 25

shale. These occurrences are of sufficient size to be called small ore 

bodies. Here and there are fissure deposits and small patches and 

pocket fillings of clay in the zinc carbonate ore bodies.

One specimen found on the New Discovery dump contains calamine 

veinlets, locally expanded into drusy pockets, so distributed as to 

suggest that the calamine was formed in shrinkage cracks from material extracted from the clay.

Under the microscope the clay from the Yankee Doodle appears as 

an interlocking aggregate of minute fibers, of pale-brown color, nonpleochroic, with rather strong birefringence and positive elongation. 

Its mean index of refraction is a little above 1.58. The general appearance of the fibers is very similar to that of sericite fibers. Clay 

of similar megascopic appearance, from a pronounced fissure in the 

Maid of Erin mine, has optical properties more like those of kaolin, 

being traversed by a network of sericite-like fibers of higher birefringence and containing a few small calamine crystals. These 

features, together with the relatively low specific gravity of the material, suggest that it is kaolin containing a small percentage of zinc, 

mostly in the form of the sericite-like mineral.

The brown variety is more widely distributed but is nearly all 

limited to small deposits, such as the light-brown seams along bedding 

and joint planes and a few cavity fillings. Those along bedding and 

joint planes are of bright waxy luster and of uniform dense texture 

(PI. VI, 5), those filling vugs are of more or less waxy luster and 

may have a pronounced finely banded structure (PL VI, (7), strongly 

resembling that of a sedimentary clay. Both varieties slake rapidly 

in water but lack the high degree of plasticity so characteristic of 

ordinary clays. The bright waxy material slakes into small chips 

or splinters but does not become plastic; material somewhat softened 

and dulled by weathering has a tendency to become plastic but lacks 

the stickiness of ordinary clay, as well as the characteristic odor.

An exceptional occurrence of the brown variety, sufficiently large 

to be called a small ore body, was seen in the Belgian mine (Fenton's 

lease in 1913), replacing limestone along fissures just beneath a sheet 

of Gray porphyry. It was identical in appearance with low-grade 

zinc carbonate ore but yielded no effervescence when immersed in 

hydrochloric acid. In this section it was found to consist of aggregates of the minutely fibrous sericite-like mineral, more or less 

stained and obscured by iron and manganese oxides. Microscopic 

vugs contained growths of the same mineral with radial arrangement 

around the borders. The larger of these vugs, or local enlargements 

of veinlets, contain calamine and the sericite-like mineral so intimately mixed as to indicate that the two must have grown at the 

same time, though the sericite-like mineral evidently began first, 

giving rise to the radial borders. It was traversed by many short
26 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

veinlets of calamine with black borders of manganese oxide. Other 

manganese spots and streaks were also present.

A partial analysis by K. C. Wells shows the presence of 17.8 per 

cent of insoluble matter and 18.7 per cent of zinc oxide (or 15 per 

cent of zinc). The remainder, as shown by qualitative tests, contained a large amount of iron oxide and small amounts of magnesia 

and lime. The insoluble matter doubtless indicates the amount of 

silica in the sericite-like mineral, or zinciferous clay. The zinc oxide 

represents a little calamine as well as the sericite-like mineral. The 

material evidently consists essentially of zinciferous clay, a little 

calamine, iron oxide, and a little manganese oxide.

The black variety was noted in conspicuous amount only at one 

place, where the white clay in the Yankee Doodle mine was locally 

stained by manganese oxide.

The chemical composition of the zinciferous clays is shown by the 

following analyses:

Analyses of zinciferous clays.

SiO................. .................................

AltOt............................:.. .................

FesOs... ............................................

FeO.................................................

MgO..-.. ...........................................

CaO. ................................................

ZnO........................................... ......

PbO.................................................

NasO................................................

KsO.................................................

KiO+. ..............................................

H2O ...............................................

COt.. ...............................................

P205 .- ..............................................

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

1

37.54

24.76

.64

.71

.63

18.43

.36

.66

oll.07

5.03

100. 10

2

35.97

8.81

80

1.87

35.40

o7.20

10.26

100.31

3

35.33

10.38

.71

1.62

33.05

o7.42

11 ' 64

100. 15

4

35.57

10.80

.40

Undet.

.82

.48

31.49

Undet.

Undet.

6.32

Undet.

Undet.

686.88 

25.30

5

36.49

7.09

2.48

Undet.

Q7

33.46

Undet.

Undet.

7.06

Undet.

Undet.

Undet.

88.99 

26.88

0 Hillebrand's analysis as tabulated gave only total water, but the amount of hygroscopic water in each analysis is stated in the text (op. cit, p. 605).

*By comparison with analyses 1, 2, and 3, the deficiency appears to be chiefly hygroscopic water.

1, 2, 3. " Alteration product of porphyry," Lower Waterloo mine. W. F. Hillebrand, 

analyst. U. S. Geol. Survey Mon. 12, p. 603, 1886.

4. White zinciferous clay, Yankee Doodle mine. George Steiger analyst.

5. Brown zinciferots clay, New Discovery mine. George Steiger, analyst.

The first three analyses represent material obtained directly under 

porphyry; the fourth represents the Yankee Doodle deposit, beneath 

a silicified shaly bed; the fifth represents the brown, finely banded 

type. In spite of variations in the mode of occurrence and appearance, the five analyses are very similar to one another in many respects, but attempts to calculate the mineral composition of the ore 

yield varying and only inconclusive results. The Yankee Doodle 

material (No. 4), after kaolin and calamine are calculated,has still an 

excess of silica and zinc, the molecular proportion of the former being a little more than double that of the latter. In the brown banded
MINERALOGY. 27

4O

30

variety (No. 5) the alumina and all the zinc can be assigned to 

kaolin and calamine, respectively, leaving an excess of silica and 

combined water in the approximate ratio of 11 to 2. Attempts to find 

some definite relations between certain constituents by plotting their 

percentages on a diagram (fig. 1) dp not give very definite evidence, 

except that the percentage of zinc oxide (ZnO) varies inversely 

as that of alumina 

(A12O3 ). The birefringence of the clays shows 

that crystalline matter 

is present, and it may be 

suggested that they contain kaolin or some 

closely related aluminum silicate, its optical 

properties changed by 

dissolved impurities, 

but if it were suggested 

that such an aluminum 

silicate held the other 

constituents in solid solution, it would be necessary to assume that 

one molecule of it could 

hold in solution several 

molecules of each of the 

other substances a 

questionable property. 

The low-grade clays, 

furthermore, show in 

thin section that the 

higher birefringent 

mineral forms a network impregnating a 

mass with optical properties like those of 

chalcedonic silica and 

kaolin. If the highly 

birefringent portion 

could be analyzed separately it would probably show as high a ratio of zinc oxide to alumina as the high-grade clays. .The fact that the percentage of 

zinc oxide varies inversely as the percentage of alumina suggests 

replacement by zinc of aluminum in the kaolin molecule. The 

low-grade deposits indicate that such replacement has occurred in

10

±

FIGURE 1. Diagram showing percentages of constituents In zinciferous clays, arranged in order of increasing alumina.-
28 OXIDIZED ZINC ORES OP LEADVILLE, COLO.

clays previously deposited, but at least some of the high-grade 

clays indicate that zinc has taken the place of aluminum in solution 

and that the zinciferous clay has resulted from direct chemical precipitation.

Whatever its true nature, the zinciferous clay has certain relations 

to definite minerals, as is shown by its contemporaneous deposition 

with calamine, described on page 20. This relation may suggest 

that when zinc is above a certain ratio to alumina its excess may 

crystallize as calamine, but analyses of Missouri "tallow clays" 1 

hardly bear out this suggestion. The veinlets and pockets of calainine in the clay, mentioned on page 20, suggest that under favorable 

conditions the clays that were formed first may later separate into 

calamine, silica*, and kaolin, the silica and kaolin remaining as a 

microscopic mixture. The fact that zinc and silica, in the absence of 

alumina, crystallize readily as calamine and opal or chalcedony or 

quartz is demonstrated by the intimate association of these minerals 

 in several places in the Leadville district. The presence of alumina 

therefore seems the critical factor in causing the deposition of the 

clays instead of calamine and other distinct minerals.

DESCHENITE.

According to Emmoris and Irving,2 deschenite, or the vanadite of 

lead and zinc, is found as an accessory and rather rare mineral associated with the ore bodies, but no description of its mode of occurrence is given. This mineral was not. found by the writer.

ASSOCIATED MINERALS. 

IKON OXIDES.

By far the greatest part of the oxidized zinc ores, of both high and 

low grade, are colored brown or reddish brown by oxides of iron: 

The ores contain both limonite and turgite, as suggested by their 

colors and by calculation of the analyses given on page 47, and perhaps also goethite and earthy hematite. Besides coloring the ores, 

these oxides form large masses of siliceous iron ore of varying 

grades, some of which have been found above and others beside 

bodies of oxidized zinc ore. Small masses or segregated deposits of 

brown iron oxide containing negligible amounts of zinc are also 

found here and there within the zinc ore bodies and even, rather 

exceptionally, under them. Iron oxide appears to have been deposited at all stages, from the earliest carbonate ore stage down to

VSeamon, W. H., The zinciferous clays of southwest Missouri and a theory as to the 

growth of calamine of that section : Am. Jour. Sci., 3d ser., vol. 39, pp. 38^12, 1890.

»Bmmons, S. F., and Irving, J. D., The Downtown district of Leadville. Colo.: U. S. 

Geol. Survey Bull. 320, p. 33, 1907.
MINEEALOGY. 29

the present time. In a thin section of a specimen from a zinc stope 

on the Tucson No. 1 level the iron oxide preserves the texture of the 

original dolomite (Blue limestone) and was evidently deposited together with silica before or quite as early as any zinc carbonate ore. 

The bodies of iron oxide accompanied by kaolin and silica, which 

are commonly found in layers from 6 inches to 5 or 6 feet in thickness between overlying lead carbonate stopes and underlying zinc 

carbonate stopes, were also probably deposited during or just before 

the first zinc carbonate stage, but they may be in part residual, having been produced by re-solution and downward migration of the 

topmost parts of the zinc carbonate ore bodies. The iron oxide ores 

of shipping grade, so far as they have been seen in contact with or 

in close proximity to the oxidized zinc ores, appear to have been deposited as early as the first stage of zinc carbonate. The iron oxides 

in the brown zinc ores have been for the most part derived from the 

oxidation of ferrous carbonate, which was a constituent of the zinc 

carbonate of the first stage. There was evidently more or less migration in solution of some of this iron before oxidation, thus accounting 

for the local segregated deposits within and below the zinc ore 

bodies. Gray zinc-iron carbonate ore pay be seen to-day partly 

stained by iron oxide that is evidently still in process of formation.

MANGANESE OXIDES.

Black oxide of manganese occurs in much the same variety of 

ways as the red and brown oxides of iron and needs no detailed 

description. Although much or all of the black manganese oxide 

occurring outside of the zinc ore bodies is psilomelane,' accompanied 

by small amounts of pyrolusite, it seems probable that the black 

stains and coatings in or on the zinc ores is the zinc-manganese 

mineral hetaerolite, accompanied in places by chalcophanite, both 

of which have already been described. (See pp. 21-24.)

DOLOMITE.

Dolomite occurs only as unreplaced portions of wall rock (Blue 

or White limestone), either as inclusions within the zinc ore bodies 

or as incomplete replaced walls. Analyses of different ore samples 

show varying but small amounts of magnesia, usually or always in 

too great a ratio to lime to form dolomite. It appears that during 

the replacement of dolomite, the lime content was nearly or quite 

all removed, whereas a small amount of magnesia remained with 

the ore.

1 - - ' MANGANOSIDERITE.

Manganosiderite, like dolomite, has been found as inclusions or 

replaced remnants in the oxidized zinc ore bodies of the Maid of
30 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

Erin mine. These inclusions are of especial interest, as they prove 

that manganosiderite, as well as dolomite, has been replaced by the 

zinc carbonate ores. Thin sections of specimens from these manganosiderite inclusions show small amounts of chalcedonic quartz 

and sericite accompanied by small grains of pyrite, zinc blende, and 

galena, all of which may be seen preserved in gray zinc-iron carbonate which has replaced the manganosiderite. The manganosiderite can be distinguished from dolomite by its lighter color and 

higher specific gravity and in thin section by its much stronger 

absorption. It differs from the gray zinc-iron carbonate ore in 

its distinctly coarser texture, having a fine to medium grain, whereas 

the zinc-iron carbonate is microgranular.

CALCITE.

Calcite in the oxidized zinc ores occurs for the most part as 

colorless to white crystals, here and there lining pockets in ore of 

all grades and associated iron oxide. Its most common crystal 

form is the flat rhombohedron of disklike appearance, the sharp 

edges lying normal to the walls of the cavity. These crystals rest 

on calamine and in one specimen on hetaerolite and appear to represent the latest mineral growth in the oxidized zinc ore bodies, 

except, of course, any oxides of iron and manganese that may be 

forming to-day. Calcite also occurs in small to microscopic veinlets 

cutting zinc carbonate ore.

ARAGONITE AND NICHOLSONITE.

Aragonite, the orthorhombic form of calcium carbonate (CaC03 ), 

is occasionally found in close association with the oxidized zinc 

ores but has not been noted in direct contact with zinc ore minerals. 

It forms diverging to spherical radiating columnar aggregates, or 

groups of such aggregates (PL VI, E], usually if not invariably 

white. The one occurrence found by the writer formed pockets in 

brown siliceous iron oxide. So far as its general appearance and 

mode of occurrence are concerned, aragonite may be mistaken at 

first glance for calamine; but it lacks the characteristic bladed form 

of calamine and can further be distinguished by its brisk effervescence in very dilute hydrochloric acid.

The aragonite studied by the writer proved to contain little or 

110 zinc, but a variety containing as much as 10 per cent of zinc 

was studied by G. M. Butler, who gave it the name nicholsonite. 

According to Butler,1

1 Butler, G. M., Some recent developments at Leadville, second paper, The oxidized zinc 

ores: Econ. Geology, vol. 8, pp. 8 and 9, 1913.
MINERALOGY. 31

The nicholsonite is identical with aragonite in all but three particulars. 

Those specimens with high percentages of zinc have a higher specific gravity 

than aragonite, show a decided adamantine rather than a vitreous luster, and 

have a better cleavage (good pinacoidal and poor prismatic) than pure 

aragonite. The variety was found in the oxidized iron-manganese ore in the 

blue limestone and was named after S. D. Nicholson, of the Western Mining 

Co., who brought it to the attention of the writer,

BARITE. I

Only one occurrence of barite was noted in connection with the 

oxidized zinc ores. This was in the Little Giant mine, near the 

boundary between that mine and the Yankee Doodle. The barite 

formed a rather coarse grained aggregate of crystals, originally 

white, whose cleavage cracks and boundaries, as well as other fractures, were filled with a yellowish-brown powdery material that 

effervesced weakly in dilute hydrochloric acid. The material was 

said to have a low zinc content, but its noticeably high specific gravity was due to the barite rather than to any iron, zinc, or lead.

1 ? PLUMBOJAROSITE.

I

Plumbojarosite, a hydrous sulphate of lead and ferric iron 

(Pb0.3Fe2 03 .4Si02 .6H2 0), was found in the Yankee Doodle mine 

in the bottom of an old lead stope, just above a small oxidized zinc 

stope. It was called " contact matter" but was known to contain 

considerable lead. The mineral occurs as a yellowish-brown soft, 

earthy mass, with a rather shiny luster and a smoother feel than is 

characteristic of iron oxide or iron-stained lead carbonate. Under 

the microscope the material is essentially homogeneous and consists 

of minute grains, some of which show a partial to complete six-sided 

outline under very high magnification. It is much finer grained than 

the material from Beaver County, Utah, figured by B. S. Butler.1

Material of the same kind was found by Emmons under Gray 

porphyry in the Lower Waterloo mine during the first survey of the 

district aiid was analyzed by Hillebrand 2 as follows:

SiO3 _________________ 0. 36 

FeO3 ._________________ 44. 4 

A12O3 _________________ . 23 

CaO_ _____-_ None. 

MgO____________ _ None. 

K=O_________________ . 15 

Na2O _____________-__ . 37 

H:O _________________ 8. 99 

PbO_________________ 19. 5

RisOa : ____._____ None.

ASsS.________..._______ 0. 39 

P2OB -_ ______________ . 11

RO3 __ _________ 25. 07 

01__________________ . 04 

Ag.____ ________ . 075

99. 685

1 Butler, B. S., Occurrence of complex and little known sulphates and sulpharsenates as 

ore minerals in Utah : Econ. Geology, vol. 8, p. 313, 1913. 

»P. S. Geol. Survey MOB. 12, p. 606, 1886.
32 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

Emmons and Hillebrand, however, did not recognize this material as a distinct mineral species, owing doubtless to its earthy appearance and close resemblance to other materials of varying though 

similar composition. Plumbojarosite was determined as a distinct 

species six years later .by Hillebrand and Penfield.1

OPAL, CHALCEDONY, AND QUARTZ.

Silica, usually in a dense form, has been found in small amounts 

at several different places, usually associated with calamine. The 

occurrence of amorphous (opal) to chalcedonic silica as the middle 

of a veinlet with marginal bands of calamine in the Belgian mine 

and the occurrence of amorphous silica in a vug with calamine and 

aurichalcite in the Ibex mine have already been described (p. 19; 

PI. V, A and B). On the Mikado dump was found a specimen 

containing vugs lined with microscopic to visibly crystalline quartz 

and calamine. A few minute crystals of quartz were seen perched 

en the sides of calamine crystals. R. S. Fitch, of Leadville, found 

p similar but much better specimen in Avhich calamine crystals were 

almost completely coated with fine druses of minute but typical quartz 

crystals.

What appears to be an exceptional microscopic occurrence was 

noted in two thin sections of gray zinc carbonate ore from the Chrysolite dump. Here minute crystals were found in the middle parts of 

veinlets and as central fillings of certain Vugs, in each veinlet 

bordered by smithsonite of the later stage. In a single thin section 

some vugs may be filled with smithsonite and quartz, and others with 

calamine with or without quartz. No explanation is offered to 

account for the failure of silica and zinc to combine in certain places 

when they did in others within an area not more than half an inch 

square.

Silica is also present in considerable amount with the iron oxide 

bodies in or adjacent to the zinc ores. As a rule this silica is completely concealed by the iron oxides, but in one thin section from the 

walls of a zinc stope on the Tucson first level it was found to be 

present as minute quartz grains mingled with the iron oxide and 

also as minute agate-like growths in microscopic vugs.

Microscopic quartz with sericite and sulphide grains has been seen 

in thin sections of gray zinc carbonate which has replaced manganosiderite. It was originally present in the manganosiderite and has 

escaped replacement.

Chert has been found in reddish-brown zinc ore at a few places, 

where it forms the only unreplaced remnants of the original limestone or dolomite. .

1 Hillebrand, W. F., and Penfield, S. L., Some additions to the alunlte-jaroslte group of 

minerals: Am. Jour..Set, 4th ser., vol. 14, p. 213, 1902.
MINERALOGY. 33 

SERICITE.

The only sericite noted in the oxidized zinc ores is the small amount 

which, with quartz and sulphide grains, was originally in manganosiderite and has escaped replacement.

KAOLIN.

Kaolin is present as an abundant constituent of the material that 

separates many lead carbonate stopes from zinc carbonate stopes. It 

is for the most, part stained with iron or manganese oxides but has 

its typical white color in patches away from which the iron and 

manganese oxides have segregated. Kaolin is also present as the 

principal filling of strong fissures, one of which in the Maid of Erin 

mine was found to be bounded on both sides by oxidized zinc ore. 

This kaolin was also more or less stained by iron and manganese 

oxides and was practically identical in general appearance with the 

zinciferous clay ore but differed in its relatively low specific gravity. 

In thin section, as stated on page 25, it was found to contain a net. 

work of streaks and patches of rather high birefringence, resembling 

sericite and also the zinciferous clay, its appearance suggesting that 

a small percentage of zinc had been introduced. A few small calamine crystals were also present in it.

At the base of a porphyry sheet in the Belgian mine was seen a 

kaolin mass which was stained bluish green by some copper salt. 

A low zinc content was also found in this mass, and it seems probable that the presence of both copper and zinc was due to adsorption 

by the kaolin.

SULPHIDES.

At several places in the Western Mining Co.'s workings (Pis. VII 

and VIII) the oxidized zinc ores have been found almost or quite 

in contact with bodies of sulphides, chiefly pyrite, but at no place 

examined by the writer could more than a small face exposure of sulphides be seen. The sulphides where exposed were clean and fresh 

and showed no evidence of having reacted with zinc solutions to produce secondary zinc sulphides.

In the winze about 180 feet .north of the south end of the lower 

Maid of Erin ore body (PI. VII) a small streak of galena was noted 

along a preserved bedding plane within # mass of brown zinc carbonate ore. Calamine crystals, abundant in the brown ore, were 

also present within the galena streak, filling cavities formed by the 

removal of either limestone or zinc blende.

Small amounts of sulphides were also noted in gray zinc carbonate 

ore. These sulphides were originally in manganosiderite but escaped

52757° Bull. 681 18 3
34 OXIDIZED ZINC ORES OP LEADVILLE, COLO.

replacement. They were chiefly pyrite but included a few scattered 

grains of sphalerite (not wurtzite) and galena.

NATIVE SILVER.

The only occurrence of native silver noted was seen in a small stope 

on the Maid of Erin first level, at Crowell's raise. The silver formed 

small flakes and wires in a small mass of siliceous iron oxide veined 

and sprinkled with calcite about 1£ feet in diameter which lay between an old lead stope above and a zinc stope below. The silver 

flakes for the most part were scattered through the iron oxide, but 

some were closely associated with visible spots of calcite.

PARAGENESIS.

The paragenesis of the minerals, or the order in which they were 

formed, may be summarized from the foregoing descriptions as 

follows:

Dolomite or magnesium limestone, manganosiderite, barite, chert, 

the quartz-sericite aggregates, and the sulphides existed before oxidation of the original ore bodies began. The iron oxide and kaolin 

masses that separate the lead carbonate from the zinc carbonate 

bodies may, from analogy with zinc deposits in other districts, have 

been the first of the oxidized minerals to form, but their origin in 

the Leadville. deposits is not so clear. They may also be due in 

part to the leaching away of zinc minerals originally deposited with 

them. They will be further considered in the discussion of the 

genesis of the ores. The one occurrence of native silver noted was 

evidently formed at the same time as the iron oxide.

The first oxidized zinc ore mineral to form was the massive gray 

smithsonite, containing varying but considerable amounts of iron 

and manganese carbonate. This mineral replaced manganosiderite 

and dolomite (Blue and White limestone). It is believed to have 

formed at the same time as or immediately after the iron oxide and 

kaolin masses just mentioned.

Later, through oxidation, the iron and manganese present began 

slowly to oxidize, forming the red or brown iron oxides and the zincmanganese oxide hetaerolite, with a corresponding amount of the later 

and purer drusy smithsonite, which, as shown in thin section, alternated with the iron oxide a*hd the hetaerolite, suggesting a rhythmic 

alternation in deposition. The largest growths of hetaerolite, however, followed the drusy smithsonite. The inconspicuous growths of 

chalcophanite may be the result of the alteration of hetaerolite by 

further oxidation, or they may have been precipitated from solutions 

of different concentration from that which yielded the hetaerolite.
MINERALOGY. . 35

Oxidation of remnants of gray ore and manganosiderite is still in 

progress and doubtless has been to a greater or less extent ever since 

oxidation began.

Calamine and locally aurichalcite and zinciferous clay were next 

formed. The calamine in part was formed at the expense of smithsonite, leaving relatively pure residual iron oxide; in part it was deposited in fractures and. vugs in both smithsonite and dolomite (limestone). Aurichalcite, as shown in thin section, was deposited at the 

same time as calamine. The zinciferous clay in some places appears 

to have been formed instead of calamine in the presence of alumina, 

as it bears the same relations to all the minerals of earlier growth. 

Where calamine and the zinciferous clay are present together, the 

calamine in some places forms the margins and the clay the middle 

fillings of veinlets. In the Belgian mine the clay forms the margins 

of pockets and a parallel growth of calamine and clay the central 

fillings, whereas in one specimen the calamine forms networks of 

veinlets through the clay. These differences may be attributed to 

varying conditions of chemical equilibrium; a relative excess of zinc 

over alumina may have caused calamine to represent the beginning 

of deposition in the first case, and a corresponding excess of alumina 

may account for the marginal growth of clay in the second; the 

calamine veinlets in the clay may be a decomposition product of the 

clay, or a deposit from solutions of a later stage which reached the 

previously dried and cracked clay. The small size and scattered distribution of these occurrences prevent the drawing of a definite conclusion regarding the relations between calamine and zinciferous clay.

Silica, either in an amorphous or a minutely crystallized condition, 

was deposited with or just after calamine and, in most of the specimens studied, appeared to represent the excess of silica over zinc in 

solution. The presence of aurichalcite with calamine and silica is 

interesting in this connection, suggesting a rather delicate balance 

between carbon dioxide and silica that allowed the formation of 

aurichalcite instead of additional calamine and the copper silicate, 

chrysocolla. The replacement of smithsonite by calamine in several 

places and the occurrence of smithsonite in contact with a later 

growth of quartz in at least one place (specimens from the Chrysolite dump) raise another question as to the conditions under which 

zinc silicate may form.

Calcite was distinctly the latest of all the common minerals of the 

oxidized zinc deposits, except, of course, iron and manganese oxides, 

which may still be forming. Its period of growth may have slightly 

overlapped that of calamine, but it is for the most part distinctly 

later. The exact position of aragonite and nicholsonite in the paragenesis can not be stated. Both have formed in pockets in iron or
36 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

iron and manganese oxides, but their relations to the different zinc 

minerals have not been ascertained.

< VARIETIES OF ORE.

So far as appearance and differences in composition are concerned, 

four varieties of oxidized zinc ore may be distinguished, but these 

are so intimately associated that all may enter into a single carload^ 

The four varieties are (1) gray carbonate ore, (2) reddish-brown to 

brown carbonate ore, compact or filled with calamine pockets, (3) 

brownish-black to black carbonate-oxide-silicate ore, and (4) white 

to brown dense silicate ore (zinciferous clay or " talc "). The brown 

varieties, Nos. 2 and 3, are by far the most abundant.

GRAY CARBONATE ORE. 

OCCURRENCE.

Gray carbonate ore was noted at a few different places in the Maid 

of Erin mine and on the dump of the Chrysolite mine. At least two 

of the occurrences in the Maid of Erin were found immediately 

below pyritic sulphide ore. The others had not been developed, and 

their relations to other ores was not definitely known. An occurrence of grayish-brown to yellowish-brown ore on and below the 

Henriette fourth level, although not found immediately in contact 

with other ores, is doubtless below lead carbonate ore, as only lead 

carbonate ore has been found at so high a level in the vicinity. (See 

PI. VII and section AA, PL VIII.) One of the deposits of gray 

ore contained an inclusion of manganosiderite, which had evidently 

escaped replacement. Further evidence of this replacement is given 

in the description of the microscopic features of the ore (pp. 37-38).

MEGASCOPIC FEATURES.

The ore is of medium to light gray color where quite free from 

oxidation, but some specimens show more or less yellowish-brown 

iron oxide stains in places, and by increase in the amount of staining 

the gray ore grades into the reddish-brown to brown variety. The 

texture of the gray ore is very fine grained to dense (microgranular) 

for the most part, but small cavities or vugs ranging from minute 

pores up to holes an inch or two in diameter are irregularly scattered through it. In places these cavities are small enough and 

regularly enough distributed to suggest shrinkage accompanying 

replacement of the original rock; in others they appear to be enlargements of fractures; and in still others they are clearly the result of 

the leaching out of the more permeable portions of the ore. Cavities 

of the first two kinds have rounded edges where the carbonate ore
VABIETTES OF OEE. 37

has developed microscopic drusy surfaces. Those of the last kind 

have rough, corroded surfaces. No minerals of megascopic size 

were seen in the fresh gray ore, except a few specks of pyrite, zinc 

blende, and possibly galena, which were noted in two specimens. 

These sulphides occur in minute veinlets and scattered grains, just as 

they do in the manganosiderite. In the brownish-gray partly oxidized ore from the Henriette workings the fine-grained carbonate 

aggregate is traversed by veinlets of calamine.

MICROSCOPIC FEATURES.

In thin section (PI. II, A) the gray carbonate ore is composed 

mostly of a uniform aggregate of very fine carbonate grains of high 

relief, typically high birefringence, and cloudy appearance. This 

aggregate is cut by veinlets of smithsonite that are characterized by 

a somewhat coarser grain and freedom from cloudiness. Smithsonite, optically similar to that in the -veinlets, also forms minute 

rhombohedrons lining small cavities. A few minute diverging aggregates and single grains of calamine were noted filling small cavities, but the total amount is negligible so far as the amount of zinc 

in the ore is concerned. Incipient oxidation is marked by faint 

brown and black stains of iron and probably manganese oxides. " A 

veinlet of calcite, distinguished from smithsonite by distinctly lower 

index of refraction, was noted.

The ore incloses small veinlets and patches consisting of varying 

proportions of quartz, sericite, pyrite, and locally zinc blende and 

galena. It also incloses scattered single grains of the same minerals. 

Many of these inclosed veinlets have a marked " wriggling " shape. 

Some are distorted and even appear to have been pulled apart. Some 

are penetrated or cut by veinlets of smithsonite. Small aggregates 

of pyrite also appear to have been pried apart by smithsonite veinlets. The quartz-sericite-sulphide veinlets and aggregates have the 

same features, except for the distortions just described, as in the 

manganosiderite and are evidently all that is left of the manganosiderite body originally present.

Under high magnification the fine aggregate proves to be composed 

of countless anastomosing rows of clear, transparent granules inclosing small rounded bunches of clouded (morestrongly absorptive?) 

granules. The anastomosing rows are so arranged as to indicate the 

' outlines of former manganosiderite grains. In some thin sections the 

small clouded bunches have been removed by leaching and, perhaps, 

in part during grinding of the section, leaving a porous mass of anastomosing rows of smithsonite. These pores may also be in part due 

to removal of grains or minute aggregates of quartz, sericite, and
38 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

pyrite, but removal of these minerals certainly can account for only 

a minor part of the entire pore space. As this finely porous texture 

has been noted in specimens as well as thin sections, there is no doubt 

that it has resulted mainly from leaching.

This anastomosing structure indicates that the zinc solutions permeated the manganosiderite (or dolomite in some places) along the 

boundaries of grains and replaced the grains from their margins inward. The replacement was not strictly pseudomorphous, as the texture of the ore is markedly finer than that of the manganosiderite, 

even including the clouded bunches of granules inclosed among the 

anastomosing grains. An attempt to prove the assumption that the 

clouded bunches have stronger absorption and are therefore probably 

higher in iron than the anastomosing portions was unsuccessful, owing to the extremely fine grain of the ore.

If manganosiderite corresponding to analysis 1 (p. 47) was completely replaced by gray zinc carbonate ore corresponding to analysis 

2, the replacement should have been accompanied by about a 15 per 

cent shrinkage; 1 but evidence of shrinkage is obscured by different 

factors other than the effects of partial leaching of the ore. The recrystallization that accompanied replacement may have distributed the 

amount of shrinkage so as to render it inconspicuous, or it may have 

readjusted the material so that shrinkage was expressed by numerous 

small fractures. The fractures in the ore, whether due to shrinkage 

or to other causes, are now filled with the smithsonite veinlets, which 

may represent material recrystallized practically in place, or additional material introduced after the direct process of replacement had 

practically ceased. Furthermore, deposition of the smithsonite veinlets appears to have caused expansion in certain places. The conclusion that the theoretical amount of shrinkage took place rests on 

the assumption that the zinc was introduced as some salt, presumably 

sulphate, which could react with manganosiderite (or dolomite) and 

deposit an amount of zinc carbonate exactly equivalent to the amount 

of manganosiderite replaced. It is probable that the zinc was largely 

introduced as sulphate, but the veinlets of second-stage smithsonite 

show that a part of it was introduced as carbonate and that deposition was not entirely the result of simple molecular interchange. The 

amount of shrinkage can therefore not be determined from the porosity of the ore in its present state, nor can it be closely estimated 

from the texture and structure of the ore.

1 Specific gravities were not determined, as the zinc ore Is much more porous than the 

manganosiderite. Porosity was not determined, as the pores and other cavities in the 

ore are obviously due In part to other causes than shrinkage. Published specific gravities 

of the several carbonates represented In the analyses vary according to impurities, and 

15 per cent shrinkage Is an approximate average based on these varying data. Theoretically the shrinkage may have amounted to as much as 17 or 18 per cent.
VARIETIES OF ORE. 39

CHEMICAL COMPOSITION.

The chemical composition of the gray ore is shown by analysis 2 

(p. 47), made by R. C. Wells, of the United States Geological 

Survey, from material collected in the narrow stope on the first intermediate level above the second in the Maid of Erin mine, about 

100 feet south of the New Maid (Maid Combination) shaft. The ore 

lay beneath a sulphide body and contained small stringers of sulphides ; but these were avoided in the material analyzed, as were portions showing brown or black stains.

The silica and alumina in this analysis represent quartz and sericite, which together amount to about 2 per cent. The total absence 

of ferric oxide (Fe2O3 ) is noteworthy when this analysis is compared with analyses 3 and 4, of brown zinc ores. The ferrous oxide, 

magnesia, lime, manganese oxide, and zinc oxide are present as carbonates, but the total of their molecular ratios is a little in excess 

of the total carbon dioxide. If the excess is placed wholly in the 

manganese oxide, there remains an excess of 0.2 per cent, which is 

decidedly high in view of the color and microscopic composition 

of the material analyzed. No trace of any mineral containing phosphorus was noted, and the phosphorus pentoxi'de (P2 0c) can not be 

definitely accounted for. If it were combined with enough lime to 

form apatite, a corresponding reallotment of carbon dioxide (C02 ) 

would almost balance the excess of manganese oxide (MnO); but 

this arrangement would demand the presence of 0.67 per cent apatite, 

whereas none was found in thin section. The water driven off above 

110° C. (H2O+) is also in excess over the amounts necessary to enter 

into sericite and possible hydrous manganese oxide, and the excess 

is interpreted as being so intimately inclosed in the ore that it is not 

driven off until temperatures above 110° are reached. In this jconnection it is interesting to note that all the P2 06 and more than half 

the H2 0+ shown in the manganosiderite analysis are in similar excess. Their presence both before and after replacement implies that 

they, like the quartz and sericite, were not affected by the solutions 

that introduced the zinc.

The approximate mineral composition of the gray ore, based on 

microscopic study and the chemical analysis, is as follows:

Carbonates:

ZuCOs ______________ 76.5 

FeCOs __________ 14.5 

MnCO3 ___________ 3.2 

MgCOs________ 1.0 

CaCOa __________ - .5

Quartz 1.1

Sericite_ ___________ 0.8

Excess MnO_____________ .2

Excess PzOs- ________ .3

Excess H2O+ ____________ .9

Excess H2 0 _ ________ .5

99.5
40 OXIDIZED ZINC OEES OP LEADVILLE, COLO.

If the carbonates are recalculated to 100 per cent, and the carbonates of the manganosiderite are similarly recalculated from 

analysis 1, the following comparative results are obtained:

Recalculated composition of manganosiderite and gray zinc ores.

.

FeC03 .... ................................................................

MnC03 ...................................................................

MgCO3 ..... ................................... ...........................

Manganosiderite.

51.49

OQ 1 C

10.12

.24

100.00

Gray ore.

79.88

1 C 14

3.36

1.06

.56

100 00

Difference (per 

cent).

+100.0

- 70.6

- 91.2

- 89.5

+ 57.1

The percentage differences that is, the gain or loss of the different constituents during the replacement process are given in the 

third column, which shows that manganese and magnesia were very 

largely removed in nearly equal proportions, whereas iron was removed in less but still very considerable amount. The increase in 

calcium carbonate is attributed to the presence of a few microscopic 

veinlets in the gray zinc ore. The chemistry of replacement is considered further in the discussion of the genesis of the ores (pp. 

68 85).

BROWN CARBONATE ORES. 

MEGASCOPIC FEATURES.

The brown carbonate ores vary considerably in character. In 

some places they are hard and compact, without conspicuous vugs 

or with only very small vugs lined with fine druses of smithsonite 

(PL III, A) ; in others they are softer and may be filled with vugs 

of varying size lined or nearly filled with white calamine (PL IV, 

A). Their color ranges from chocolate-brown to dark brick-red. 

The only minerals of megascopic size are present in vugs and veinlets. As a rule, where the vugs are small and relatively scarce, they 

are lined with fine druses of second-stage smithsonite, which may alternate with films of hetaerolite or iron oxide. In the larger vugs 

similar linings of smithsonite are covered by typical growths of 

calamine, or in places by exceptionally large growths of hetaerolite or 

chalcophanite (PL I, B), which in turn may be covered by calamine. 

Aurichalcite may accompany the calamine, as in the Ibex mine. 

(See PL V, #.)

The compact body of the ore is not to be distinguished at first 

glance from much of the iron ore or iron-stained manganosiderite, 

dolomite, or limestone. It may be of uniform brown color or may be 

spotted with stains of black manganese oxide (hetaerolite?). In
VARIETIES OF ORE. 41

some places it preserves rather thin bedding planes and breaks into 

layers; in others it has a marked conchoidal fracture. It may be 

hard, or it may be soft and crumbly. Although compact brown zinc 

ore even of rather low grade may be readily distinguished from ironstained dolomite or limestone by its higher specific gravity and finer 

grain, it can not be so distinguished from dense forms of iron ore. 

Again soft porous ore can not in some places be surely distinguished 

from either porous iron ore or decomposed wall rock, owing to the 

relatively light specific gravity of all three materials. Calamine 

growths in vugs are not an absolutely sure indication of good ore, as 

one of two samples of similar appearance may prove to be excellent 

ore and the other to be of too low grade to ship. The latter variety 

is due in part to a leaching of the brown carbonate to form the silicate, or to the deposition of calamine in cavities of stained and partly 

decomposed limestone. In one sample the soft brown material 

around the calamine pockets was found by Mr. Wells to contain only 

14.1 per cent of zinc oxide (11.3 per cent of zinc), which on close inspection proved to be largely in the form of minute calamine crystals 

that had grown within the porous mass. Nearly all the zinc carbonate had been leached, and almost the entire zinc content of the 

material was contained in the calamine druses. In other specimens, 

where the carbonate ore was not leaehed and the calamine was introduced from elsewhere, the value of the ore, already of good grade, 

was increased.

Of the many specimens of compact ore collected, one, said to represent ore containing 22 per cent of zinc, proved on microscopic 

study to be composed almost entirely of iron oxide and silica. Another, which was said to contain 30 per cent of zinc but whose texture gave it a close resemblance to the altered manganosiderite that 

borders some of the ore bodies, was found by George Steiger to 

contain 50.69 per cent of zinc oxide (40.72 per cent of metallic zinc), 

2.38 per cent of insoluble (probably quartz and sericite), only 0.63 

per cent of magnesia, and no lime. The specimen had a rather high 

specific gravity, but that could easily have been attributed to iron 

originally in manganosiderite.

The brown ore may include small bodies, patches, or seams of the 

zinciferous clay colored by a small amount of iron oxide. This clay 

may be distinguished from the brown carbonate by its characteristic 

properties described on pages 24-28.

Where the original bedding is preserved, thin streaks or bunches 

of calamine are distributed along the bedding planes and also along 

short cross fractures that connect bedding planes, as shown in 

figure 2. This distribution of the calamine, which is well exhibited 

at several places in the Maid of Erin mine, is of interest in showing 

the courses followed by the zinc-bearing solutions, which evidently
42 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

percolated along bedding planes, cross joints, and minor (microscopic) fractures and were thus able to react uniformly throughout 

a body of great horizontal and vertical extent. The. process was 

evidently entirely metasomatic at first, and any resulting shrinkage 

may have served to widen the openings along bedding planes and 

fractures, and perhaps also to develop new contraction fractures, 

thus allowing percolation of additional solution through already replaced rock to lower levels and affording openings for the deposition of second-stage smithsonite and calamine. The gradation of 

linear fracture fillings of calamine into vugs, especially at junctions 

of fractures with one another or with bedding planes, points to the

FIGURE 2. Diagram showing distribution of calamine along bedding planes and cross 

fractures in > brown zinc carbonate ores.

origin of the vuggy ore as the extreme development of the structure 

just described crisscross fractures and bedding planes having enlarged into vugs,,and the smithsonite having been more or less converted into calamine.

A few vugs have evidently resulted from replacement by smithsonite only along the immediate walls of fractures and the subsequent 

removal of the unreplaced rock, leaving a cellular ore which is 

usually of very good grade. Material of similar appearance, however, has been found to be composed chiefly of silica and iron oxide.

MICROSCOPIC FEATURES.

In thin section the brown carbonate ore consists of a very fine, 

even-grained aggregate of carbonate grains stained by iron oxide 

but with many microgeodes lined or filled with transparent carbonate grains. (See PL III, B.) The transparent grains under high 

magnification show characteristic acute rhombic terminations.' Some 

of them appear pure, some of them have zonal inclusions (or alternating growths) of black manganese oxide (hetaerolite?), and
VARIETIES OF OEE. 43

others have similar inclusions of brown iron oxide. The last two 

occurrences indicate a breaking down of the ferruginous gray zinc 

carbonate of the first stage and its recrystallization as purer smithsonite of the second stage and iron or manganese oxides. Some of 

the vugs of second-stage smithsonite are surrounded by what appears, 

 to be pure iron or manganese oxide, a relation which also points 

to a breaking down of the impure zinc carbonate of the first stage, 

accompanied by segregation of the different products. Throughout 

the mass of the ore the iron and manganese oxides show this tendency 

to segregate, the iron oxide having a weak tendency to form a network of hairlike veinlets and the manganese mineral a much stronger 

tendency to gather into spots or to fill distinct fractures.

The relations of the calamine to the rest of the ore may be illustrated by two contrasted examples. In one a small group of diverging calamine crystals filling a vug was seen to be surrounded by iron 

oxide, which was opaque except along the edges of the vug, where 

it formed translucent pseudomorphs after acute smithsonite rhombs. 

Here the zinc in the calamine was evidently formed largely in place 

at the expense of smithsonite. In the other example a calamine veinlet cut through a black spot of manganese oxide, proving that it 

was formed after the breaking up of the impure first-stage carbonate ore was well advanced; but there was no uniform accumulation 

of iron or manganese oxides along the vein, and the margins of the 

vein were lined with clear smithsonite rhombs. Inclusions of brown 

carbonate ore in the vein showed no evidence of leaching. The calamine, therefore, must have been wholly deposited by infiltrating 

solutions.

One thin section of a specimen of brown ore, taken beneath a sulphide body and very near a mass of gray carbonate ore that contained an inclusion of manganosiderite, is of especial interest in 

showing the relation of the brown to the gray ore. This section contained within.the typical fine-grained carbonate a relatively coarse 

grained remnant having a texture quite like that of the manganosiderite but showing a relatively weak absorption, presumably due 

to partial or complete oxidation of the iron. The same section contained quartz-sericite veinlets in both the gray ore and the manganosiderite, and there seems no occasion to doubt that the brown ore at 

this place is the oxidized product of the gray ore.

The great extent and uniformity of oxidation of the brown ore 

is a striking feature, as the few small bodies of gray ore appear to 

be the only remnants of the original zinc carbonate ore that have 

escaped oxidation. The ore as a whole must have been easily and 

uniformly permeable by oxygen, a character which indicates a very 

finely porous structure. It may be suggested that the porosity was
44 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

developed during replacement of the original rock by gray zinc ore, 

but are already pointed out (p. 38) the factors influencing porosity 

in the present gray ore are too varied and opposite in their effects 

to permit a definite conclusion on this point, q,nd the effects of oxidation add one more obstacle to its determination in the brown ore.

CHEMICAL COMPOSITION.,

In the light of microscopic evidence chemical analyses of the brown 

ores are not difficult to interpret. In the table on page 47 analysis 3 

represents the sample of high-grade ore from the Maid of Erin mine 

which contains the microscopic quartz-sericite veinlets above mentioned and is clearly an oxidized product of gray ore, and analysis 

4 an ore of lower grade beneath a Gray porphyry sheet and between 

walls of dolomite (Blue limestone), from the first level of the New 

Dome No. 2 mine. Sample 3, in comparison to the gray zinc carbonate ore, represented by analysis 2, contains a larger amount of 

quartz and sericite. It also contains considerably more iron, and 

the iron is completely oxidized to the ferric state. Magnesia and 

lime are each a little higher, whereas zinc oxide and carbon dioxide 

are correspondingly lower. The absence of phosphoric acid is noteworthy, suggesting its removal in solution during the oxidation and 

breaking down of the gray carbonate ore. In the material for analyses 2 and 3 calamine druses were avoided. As the irregular distribution of calamine and of iron and manganese oxides renders strictly 

representative analyses out of the question, the determinations are 

only made to tenths of 1 per cent.

The calculated mineral composition of the ore represented by 

analysis 3 is as follows:

Carbonates:

ZnCOs _____________ 71.3 

FeCOs _____________ 0.0 

MnCOs _____________ 3.0 

MgCO8 ____________ 1-3 

CaC08 __________ .7

Quartz ________________~ 2.9 

Sericite _________._:___ 2.5 

Limonite _______________ 15.7 

Excess MnO ___________ 1.1 

Excess H2O+ ___________ .1 

Excess H2 0 ___________ .9

99.5

The excess MnO and H2 0-f- are present as black oxide, which is 

probably hetaerolite, but as the formula of that mineral is in doubt 

(p. 23) no attempt is made here to estimate its small percentage. 

Comparison with the mineral composition of the gray ore (p. 39) 

shows that whereas all the iron has been oxidized, the manganese remains mostly as carbonate. The magnesia and lime carbonates also 

have remained unaffected during the process of oxidation.
VARIETIES OF ORE. 45

Analysis 4 represents an ore of lower grade and one deposited under somewhat different conditions. The ores represented by analyses 

2 and 3 were deposited directly beneath sulphides, by replacement of 

manganosiderite, but that represented by analysis 4 was deposited directly beneath Gray porphyry, by replacement of dolomite (Blue 

limestone). The ore is of dark-red color and is too soft to permit the 

grinding of a thin section, but it contained small vugs of drusy smithsonite and calamine, and so far as could be seen, the only essential 

difference between it and sample 3 was the presence of a small amount 

of light-brown zinciferous clay. The silica and alumina in the analysis are accounted for by calamine and zinciferous clay. The ferric oxide is much greater than in analysis 3 and indicates either that 

the waters which introduced the zinc carried a great excess of iron or 

that the ore was deposited by different solutions, one, carrying the 

zinc and some iron, migrating along the bedding planes of the Blue 

limestone, and another, carrying iron but little or no zinc, working 

downward through the overlying porphyry. (See fig. 5, p. 55.) The 

impossibility of learning the exact geologic conditions surrounding 

this deposit leaves the matter in doubt. The softness of the ore suggests that there has been a downward leaching of zinc, but hard ore 

directly below the soft contains no more than 30 per cent of zinc, and 

mere leaching of zinc is far from enough to account for the excess of 

iron. Another explanation is that after zinc carbonate ore had been 

formed ferric sulphate solutions, with excess of acid derived by decomposition of pyrite, could redissolve the zinc carbonate, and after 

they had become neutralized the ferric sulphate in them could become 

oxidized and be deposited as ferric oxide. The dissolved zinc carbonate could be transferred downward through the ore and replace 

the dolomite walls, thus extending the original lower limit of the ore 

body. This hypothesis could also be applied in explaining the layers 

of iron oxide that are commonly found between lead carbonate and 

zinc carbonate stopes.

The magnesia in analysis 4, though low, is about three times as 

high as in analyses 2 and 3, an excess corresponding approximately 

to the proportional difference between the magnesia in dolomite and 

in the manganosiderite represented by analysis 1. The lime, however, is quite as low as in analyses 2 and 3, although its difference in 

the two rocks replaced was decidedly greater than that of magnesia. 

Manganous oxide is somewhat greater than in analysis 3, but little 

significance can be attached to the difference, owing to the irregular 

distribution of manganese oxide stains. The zinc oxide, though 

much lower than in analyses 2 and 3, is in excess over the available 

carbon dioxide. The excess, as will be shown presently, in the calculated mineral composition, indicates the proportion of calamine 

and zinciferous clay present. The higher percentage of combined
46 OXIDIZED ZING ORES OF LEADVILLE, COLO.

water (H2 0-|-) is insufficient to hydrate all the large amount of 

ferric oxide to the composition of limonite. The absence of phosphoric acid, in contrast to its presence in analysis 2, is again noteworthy.

The following calculation of the mineral composition of the ore 

is less satisfactory than those made from the other analyses, owing 

to the indefinite composition of the zinciferous clay and the uncertainty of the exact formula for hetaerolite:

Carbonates: Kaolin__________.____ 5.9 

ZnCO8 37. 5 Calamine ______________ 5. 0 

MgCOa-, / 3.6 Excess ZnO____________ 2.4 

CaCO8 ' .5 Excess MnO____________ 3.3

Limonite______________ 15. 3 

Hematite ______________ 24. 2 

_________________ 1. 7

99.4

The kaolin and calamine are of course arbitrarily separated. A 

little calamine is undoubtedly present, but how much of the calculated calamine is in reality present as zinciferous clay is.not known. 

The excess zinc oxide is for the most part accounted for by the reasonable assumption that all the manganous oxide is present as 

hetaerolite, but there is a small excess (nearly 0.6 per cent) of zinc 

oxide over the ZnO: Mn2O3' ratio demanded by either of the proposed formulas for hetaerolite, and this excess may also be,regarded 

as belonging to the zinciferous clay. The total absence of manganese 

carbonate can not be proved, but in view of the relatively low 

carbon dioxide any error in the assumption that all the manganese 

is oxidized is negligible. The iron oxide is figured so far as possible 

as limonite, for convenience in comparison with the other analyses, 

and the excess of iron oxide over water is recorded as hematite. The 

ratio of water to iron oxide is slightly in excess of that for turgite 

(2Fe2O3 .H2O). The red color indicates the presence of a considerable amount of either hematite or turgite.

BLACK ZINC ORE.

The black or brownish-black zinc ore is found only in small quantity and varies considerably in composition. In part it is essentially 

of the same character as the brown vuggy ore, except for its greater 

content of a black manganese oxide, which in some specimens has 

the crystalline structure of hetaerolite or chalcophanite.' The vugs 

are commonly lined with calamine, and some cellular specimens may 

be found consisting almost entirely of calamine and hetaerolite or
VARIETIES OF OEE. 47

chalcophanite, accompanied by a small amount of iron oxide. This 

silicate-oxide variety of black ore is clearly derived from the carbonate ore. Other samples of black ore are composed chiefly of zinciferous clay stained black by a manganese oxide. The occurrences of 

this variety seen by the writer were all said to be of low grade. Specimens of the black ore, especially of the silicate-oxide variety, whether 

of high or low grade, are likely to have a surprisingly low specific 

gravity, owing to their vuggy or very porous character. No chemical analyses of the black ore were made, as they would serve only 

to show to what extent manganese and silica had been locally concentrated and carbon dioxide eliminated.

WHITE OR " TALCY » ZINC ORE.

The zinciferous clays, described on pages 24-28, may occur in 

masses large enough to be considered ore bodies. .It is questionable 

whether they could be smelted at a profit.

ANALYSES.

In the following table are given chemical analyses of the more important varieties of zinc ore discussed above:

Analyses of sine carbonate ores.a

Si02 ..................................................... ......

A\aOt ..... ..................................... ................

FeO...........................................................

MgO......... ..................................................

CaO...... ......................................................

MnO...........................................................

ZnO................... ........................................

PbO.. .........................................................

Ai.................... ......................................... coj............................................................

P2 06 . ..........................................................

S08 .. ..........................................................

PI

H2Q+..... ....................................................

H3 0 .........................................................

NaaO..........................................................

KSO............................... ............................

BaO...........................................................

TiOj...........................................................

FeS2 ... ........................................................

1

10.08

3.16

26.80

4.04

.08

19.71

Undet.

Undet.

Undet.

33.14

.47

Undet.

Undet.

.89

.22

.57

.08

.84

100. 08

2

1.5

.3

9.6

.5

.3

2.2

49.6

34.4

.3

1.0

.5

Undet.

Undot.

Undet.

Undet.

Undet.

99.6

OQ Q

3

4.1

1.0

13.4

.6

3.0

46.2

27.2

9 H

.9

Undet.

Undet.

Undet.

Undet.

Undet.

99.3

07 i

4

4.0

2

0

3fi Q

1.7

Q

3.3

qn 9

15.3

3

0

1.7

Undet.

Undet.

Undet.

Undct

Undet.

99.6 

24.2

« U. S. Geol. Survey Bull. 591, p. 240,1915.

1. Manganosiderite, seventh level Tucson mine (collected by J. D. Irving). J. O. Fairchild. analyst.

2. Gray zinc carbonate ore, Maid of Erin mine, first intermediate above second level. R. C. Wells, 

analyst.

3. Brown zinc carbonate ore. Maid of Erin mine, "high line" level. R. C. Wells, analyst.

4. Red ainc carbonate ore, New Dome mine, first level (at No. 2 shaft). R. C. Wells, analyst.
48 OXIDIZED ZINC ORES OF LEADVTLLE, COLO.

RANGE IN METAL CONTENT OF THE ORES. 

ZINC CONTENT.

The zinc content of the ores varies greatly from place to place. In 

some stopes bodies running over 40 per cent of zinc have been mined, 

and many others, especially in the Carbonate Hill workings, have 

yielded much ore averaging 30 per cent of zinc. In fact, up to the 

end of 1913 the Western Mining Co.'s great shipments did not run 

below 28 per cent. These high-grade bodies, however, are bordered 

and separated by large quantities of lower-grade ore, averaging about 

20 per cent of zinc, and these in turn may grade into iron ore or 

altered dolomite, in which the percentage of zinc drops to practically 

nothing. In some places the transition from pay ore into low-grade 

material is gradual; in others, pay ore is rather sharply bounded by 

unaltered rock, an altered zone a few inches or a foot or two in 

thickness separating the two.

In some places it is a rather easy matter to distinguish between ore 

and waste, but in others distinction is possible only after frequent 

and careful sampling. Two of the most influential factors causing 

this difficulty are the varying degree of porosity and the varying 

though usually considerable percentage of iron in the ore. Some 

high-grade ore closely resembles altered manganosiderite or dolomite 

in color and texture, but its microscopic porosity would lead to an 

underestimate of its zinc content. Another sample of similar appearance and approximately equal specific gravity may prove on analysis 

to contain a large amount of iron, either as ferrous carbonate or as 

ferric oxide. Some brown zinc ores of moderate to high grade may 

be practically identical in appearance with very low grade zinc ore, 

or even to iron and iron-manganese ores. High-grade brown vuggy 

ore with calamine druses may have the same appearance as leached 

brown earthy material with similar druses. Considerable experiencemay give the ability to detect inconspicuous though critical differences between ore and waste, but the principal result of experience 

tends rather to make one more cautious than ever, and to depend on 

frequent sampling and assaying as the only reliable means of distinguishing ore from waste.

This question of the grade of the ores was experimentally investigated by Butler,1 who aiialyzed and determined the specific gravity 

of nearly 50 specimens and found that they all absorbed water 

slowly, but at varying rates, for many hours. In order to procure 

comparable data, he allowed particles weighing about 1 gram to soak 

15 minutes before weighing, his determinations thus representing the 

specific gravity of the samples with their pores nearly filled with

1 Butler, G. M., Econ. Geology, vol. 8, pp. 14-15, 1913.
RANGE IN METAL CONTENT. 49

air. He states that in consequence of these and many other tests, it 

can be said that an ore with a specific gravity of less than 3.3 as determined in this way is in all probability of too low grade (under 27 

per cent) to be mined profitably when the market price of zinc averages about 5 cents a pound, as it did during the greater part of 1913, 

when Butler's paper was written. The following table gives the 

results of Butler's determinations, together with calculated specific 

gravities of seven of the samples based on chemical analyses:

Data on oxidized sine ore of .various grades from Leadville.

Ore.

1. Light gray, granular, with cavities; considerable 

pyrite and other sulphides visible.

5. Brown, cryptocrystalline; many cavities lined with

druses of smithsonite crystals, some of them underlaid with psilomelane. 

6. Light gray, very finely granular, cavernous, a few

druses or scalonohedral calcite. 

7. Dark brownish-red, cryptocrystalline; many cavities with druses of smithsonite crystals; some psilomelane and calamine. 

8. White, with a brownish tint, very finely granular,

with a spongy appearance; microscopic drusy cavities. 

9. Same as No. 7 but contains no calamine or psilomelane.

11. Yellowish brown, microscopically spongy to very 

finely granular and compact. 

12. Brown and white, cryptocrystallino to earthy,, with

a cavernous appearance; cavities wholly or partly 

filled with calamine. 

13. Same as No. 12 except that some hydrozincite is

recognizable. 

14. Yellowish brown, very cavernous, with thin, plane

walls. 

15. Light yellowish brown, finely granular, cavernous....

Per 

cent 

of 

zinc.

17.7 

20.9

99 A

23.7

30.4

31.4

31.5

32.4

32.7 

38.4

41.6 

45.4

45.4

46.0

46.4

Observed 

specific 

gravity.

3.5 

2.7

9 7

2 0

3.8

3.9

3.9

3.9

3.9 

4.0

3.9 

3.7

3.9

3.9

4.0

Calculated 

specific 

gravity.

3.8 

3.6

3.6

' 4.0 

4.1

4.1

4.2

Effervescence 

in dilute 

hydrochloric . 

acid.

Very slight.

Do.

Do.

Considerable.

VPTV *sli(r}ii'

Considerable. 

Do.

Do.

Considerable.

Butler's analyses of seven of these samples are given in the following table:

Analyses of oxidised zinc ores from Leadville.

Silica.......................................................

Manganese. .................................................

1

17.7

8

8

4 0

17 0

.6

.4

11.2

2

20.9

.3

1.1

22.4

14.7

9 9

2.1

24.8

4

23 7

.ft

.7

33.6

5.4

2

0

2.0 

34.6

9

32.7

2.2

3.3

199

"3.8

10

OQ A

9 ft

3 8

5 1

.2

6.0 

4,2

11

41.6

' .4

8.7

3

C

2.8

9 fi

15

46.4

g

.5

9 9

2

9 9

Sample 1 is evidently a partly replaced manganosiderite and has 

a specific gravity nearly as high as those of the high-grade samples. 

The other low-grade specimens show a much greater discrepancy 

52757° Bull. 681 18 4
50 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

between observed and calculated specific gravities than the high-grade 

ores and, evidently possess a much higher degree of porosity. The 

relation between specific gravity and the zinc percentage in the highgrade samples, however, shows that specific gravity is not a closely 

accurate indication of the grade of ore.

The degree of effervescence of fragments in dilute hydrochloric 

acid (3 parts water to 1 of acid), as determined by Butler, is 

given in the first table on page 49 and, as he states, is not of 

much avail as an indication of the grade of ore. Similar tests by the 

present writer confirm those of Butler. Gray zinc, carbonate ores, 

which contain considerable amounts of iron carbonate, and also the 

manganosiderite yield little or no effervescence, as shown by samples 

1, 6, and 8. Even when partly stained by oxidation, they effervesce 

very slightly. In the more thoroughly oxidized samples, where fine 

drusy or second-stage smithsonite is abundant, effervescence is more 

pronounced.

Blowpipe tests by Butler on all grades of the material yielded 

similar results, regardless of the percentage of zinc, low as well as 

high grade ores giving the characteristic sublimate of zinc oxide.

In concluding his discussion of the grades of the ores, Butler outlined the following method for quick determination of the grade: 1

Probably the simplest method for quickly ascertaining the approximate grade 

of oxidized zinc ore is to place about a teaspoonful of the finely powdered material to be tested upon a piece of iron or steel barrel hoop, 1^ to 2 inches in 

width. This charge should be introduced into the incandescent coals of a 

blacksmith forge which has been blown until little black smoke is evident. 

The iron should be sunk into a depression in the glowing coals so that they 

stand a half inch or so above the sample on all sides. Then the draft should be 

increased until the iron is heated white hot. Oxidized zinc ore will take fire at 

this point, burning with a bluish flame and emitting white fumes of zinc oxide. 

The density of these fumes varies with the grade of the ore. Experience enables one to judge within 5 per cent of the zinc content by this method, which, 

although long known and practiced in some places, is unfamiliar to those in 

other localities. The scheme can be applied to ore of any grade, as material 

assaying 5 per cent zinc will yield visible fumes.

OTHER CONTENTS.

If the percentages of zinc oxide and carbon dioxide are subtracted 

from analyses 2, 3, and 4 on page 47, and the remainder recalculated 

to 100 per cent, the iron oxides will range from 50 to over 65 per 

cent. The residues, therefore, after extraction of the zinc become possible iron or manganiferous iron ores. The content of silver in each 

of the ores analyzed is less than 0.001 per cent. As 1 ounce per ton 

of 2,000 pounds equals 0.0034 per cent, it is doubtful whether the residues from ores corresponding to these analyses would contain enough

i Op. cit, p. 17.
DISTBIBUTION AND MODE OF OCCUBKENCE. 51

silver to pay for its extraction. Although these samples analyzed 

are believed to represent typical oxidized zinc ores of the district, 

there may be exceptions, for it has been stated that early shippers of 

rich silver ore appear to have purposely broken the zinc ore in some 

places. 1

DISTRIBUTION AND MODE OF OCCURRENCE OF THE

ORES.

GEOGRAPHIC DISTRIBUTION.

Oxidized zinc ores have been found in practically all the hills of 

the district, as far east as the Resurrection mine, near the head of 

Evans Gulch, and as far south as the Continental Chief mine, at 

Weston Pass, 9 miles south of Leadville. Thus far, however, although 

extensive low-grade bodies have been reported from several places, 

all the high-grade deposits in the other hills have proved very small 

in comparison with the immense bodies in Carbonate Hill.

DISTRIBUTION WITH RESPECT TO KINDS OF COUNTRY ROCK.

The oxidized zinc ore bodies thus far found are limited to the 

horizons of the two limestones. The small bunches of red siliceous 

zinc material found in fissures cutting a porphyry sill in the Belgian 

mine are the only deposits noted that were not within or along a 

contact of one of the limestones. Porphyry and quartzite in different 

places form rather sharply defined roofs or floors to ore bodies of considerable size.

RELATIONS TO THE DIFFERENT KINDS OF LEAD CARBONATE 

AND MIXED SULPHIDE ORE BODIES.

The ore bodies thus far worked are all closely associated with 

blanket bodies of lead carbonate ore. For the most part the zinc 

bodies underlie the lead bodies, but in some places they have replaced 

the same strata, either down the dip or even along the strike. Those 

in the Ibex No. 1 (Little Johnnie), although they are in the vicinity 

of lode fissures and magnetite-pyrite bodies, are immediately associated with old blanket stopes. The only apparent reason to account 

for this association is that the lode fissures and magnetite-pyrite 

bodies in this vicinity have not as a rule been subjected to oxidation, 

and their original zinc content accordingly has not been removed to 

form a body of oxidized ore. The Luema vein contains a considerable 

quantity of zinc blende, and as its upper part is oxidized, a corresponding quantity of oxidized zinc ore could be expected somewhere 

along the vein, below the level of oxidation. None, however, has been

* Eng. and Min. Jour., Feb. 14, 1914, p. 396.
52 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

found, and the only apparent explanation is that the strong kaolin 

("talc") selvages along the vein have prevented any considerable 

quantity of zinc solutions from penetrating into the limestone walls. 

It is also possible that the great amount of kaolin has absorbed the 

meager amount of zinc from the solutions, giving rise to zinciferous 

clay; but this point has not been tested.

One feature that is of great annoyance to miners and prospectors 

and is difficult to explain satisfactorily is the lack of uniformity in 

the relations between the oxidized zinc bodies and the associated 

blanket lead bodies. At the north end of Carbonate Hill large 

bodies of both have been mined, but in Fryer and Iron hills, where 

large blanket deposits of lead ore have been mined, only small bodies 

of zinc ore have thus far been found among a great amount of ironstained " contact matter," and some of these bodies have not been of 

very high grade. In some places, although blanket lead stopes are 

of considerable size, associated zinc ore has been found only in small 

bunches from a few inches to 3 or 4 feet in diameter.

The causes of this variation are probably several and can be best 

discussed in connection with the genesis of the ores. (See pp. 68-85.) 

It may be stated here, however, that the size of a zinc body depends 

on the amount of zinc in the original ore body, the kind and distribution of openings through which the waters transferring the zinc 

had to pass, the composition and texture of the rocks through which 

the waters passed, and the materials that accompanied the zinc in 

solution. Consideration of these factors, in places where the zinc 

ores have been mined or searched for, may yield a satisfactory explanation; but without a knowledge of them it is impossible to make a 

definite prediction as to the size and position of oxidized zinc bodies 

that may be associated with old blanket bodies of lead carbonate.

As none of the old blanket stopes were accessible to the writer, 

predictions regarding the location and extent of undiscovered bodies 

are not warranted here. It may be said that the amounts of " vein 

matter" shown in the cross sections by Emmons 1 suggest the probable presence of good oxidized zinc bodies in the northern part of 

Carbonate Hill other than the bodies already worked and of goodsized bodies on other hills; but experience in Fryer and Iron hills 

proves that the thickness and extent of "vein matter" shown in 

Emmons's sections are far from being good indicators of the amount 

of zinc ore present.

In two places noted by the writer bodies of oxidized zinc ore of 

rather low grade are not closely associated with old lead-silver stopes. 

In the Cord Mining Co.'s workings (Page lease, 1913) a small body 

of red zinc carbonate ore has been mined, which" is 150 to 200 feet 

away (down the dip) from the nearest known lead-silver stope of

»U. S. Geol. Survey Mon. 12, atlas, 1886.
DISTRIBUTION" AND MODE OP OCCURRENCE. 53

any considerable size. The ground in the immediate vicinity, up 

the dip, has not been prospected, and it can not be stated whether 

the zinc was carried in solution for an unusually long distance before 

being deposited, or whether there may be an undiscovered lead-silver 

body nearer the zinc carbonate body.

BCLQtAN SHAFT 

NW.,

Old lead carbonate 

stope, approximate

BELGIAN SHAFT

Elevation of collar

/Q976.3*

Line of section B-B'

Level

LEGEND

Old stope level (exact elevation not known) 

Level B ^^.r^L=; 170 feet above Yak tunnel level 

Level C':=-- = --: I60feet above Yak tunnel level 

Level D ssrssss 131 feet above Yak tunnel level

====== Yak tunnel level (elevation 1Q354 feet) T0 OTHER MATER1AL8

^~S " Fissure

FIGURE 3. Plan and sections of lead-silver stopes In Belgian mine. Oxidized zinc ore 

occurs chiefly along the three fissures nearest to these stopes. Section A A', shows 

relation of zinc ore to lead-silver stopes. Section B-B' shows siliceous Iron oxide immediately below lead-silver stopes and small deposit of low-grade zinc material in the 

angle between converging bodies of Gray porphyry. Fissures in the lower body of 

porphyry contain small bunches of siliceous zinc material. The sketch (D) shows 

relations of siliceous zinc ore, clay, and chalcedony in fissure Just below porphyry 

contact, 170 feet east-southeast of Belgian shaft.

In the Belgian mine (Fenton lease, 1913) small bodies of lowgrade siliceous oxidized 'zinc ore were formed by the replacement of 

limestone at the base of a complex Gray porphyry sheet, which separated the zinc ore below from silver-lead bodies above, as shown in 

figure 3. Fissures containing small amounts of very low grade red
54 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

siliceous zinc material pass through the porphyry, and some of them 

certainly connect zinc bodies with lead-silver bodies, although the 

largest of the zinc ore exposures appears to have the most remote 

connection. There seems, however, no reason to doubt that the zincbearing solutions were able to travel for considerable distances 

through unfavorable porphyry to a more favorable place before 

depositing any considerable quantity of zinc.

SHAPES AND SIZES OF ORE BODIES. 

GENERAL FEATURES.

The ore bodies, as shown in the different plans and sections 

(figs. 3 to 7 and Pis. VII and VIII), are for the most part very

FIGURE 4. Diagrams illustrating relations of oxidized zinc ore bodies to lead carbonate 

stopes in the Oro La Plata mine: A, Replacing beds beneatb a blanket stope; B, replacing rock along fissure and beds beneath a blanket stope; C, replacing walls of a 

fissure stope.

irregular. Nevertheless, they show in several places structural features that go far toward indicating their origin. The simplest examples are represented in the sketches in figure 4, illustrating the 

mode of occurrence in the Oro La Plata mine. Figure 4, C, represents zinc carbonate ore of shipping grade forming borders or casings to a lead stope that had replaced the wall rock along a fissure. 

The zinc on oxidation of the primary (sulphide) ore evidently moved 

downward, at the same time permeating the limestone for a distance 

of 2 feet or more. Figure 4, B, illustrates a place where the zinc 

solutions, descending from a blanket sulphide body, found the easiest 

course along a fracture plane, replacing the fracture walls and infiltrating to some extent along the more open bedding planes. Occurrences in the Maid of Erin mine similar to these have been described by Philip Argall.1 Figure 4, J., illustrates what is probably

1 Argall, Philip, The zinc carbonate ores of Leadville: Min. Mag., vol. 10, p. 284, 1914.
DISTRIBUTION AND MODE OP OCCURRENCE. 55

, JX>tte</ ovt/tne ofsiooe <f from 3d up to £d /eve/

 A

Vein material ^^'t\ Gray 

Blue limestone m!£\ PorPhyry

 10.500'

SECTlON^ol

Blue limestone 

' (dip toward observer)

SECTION B-J3'

190 .9 '9° 200 Feet

FIGURE 5. Plan and sections showing relation of oxidized zinc ore body on the Dome 

claim to old lead carbonate stope. Section A-A', an east-west section through the 

Dome No. 2 shaft, shows concentration of ore in shattered ground along fissures; 

Section B-B' shows northward pitch of ore body.
56 OXIDIZED ZINC ORES OF LEADVILLE, C6L6.

the most common mode of deposition, in which the zinc solutions 

worked down into the beds just beneath a blanket stope and then 

tended to migrate downward along the dip. Ii\ one of the stopes 

in the Ibex mine the zinc solutions migrated outward and replaced 

the same strata as the original ore body, the silver-lead and the zinc 

stope lying side by side.

Other ore bodies represent some combination of the conditions 

just described. The New Dome deposit, represented by figure 5,

No. I.

{SECTION ON LINE A-A'

FIGURE 6. Plan and section showing relations of oxidized zinc ore stopes (shaded) to 

old lead carbonate stopes, Tucson mine.

illustrates the downward migration of the zinc solutions along bedding planes just beneath a Gray porphyry sill as far as a fissured 

zone, which then afforded the readiest channel. The shattering of 

the rock along the fissure zone permitted the replacement to extend 

over a rather great width in proportion to length and depth.

The plan and section of the Tucson first level (fig. 6) also illustrates the development of the oxidized zinc ore bodies along fissures, 

with local spreading along bedding planes and minor fractures. The 

scattered distribution of these small bodies beneath a large continuous old silver-lead stope is in marked contrast to the extensive 

bodies of the northern part of Carbonate Hill.
DISTRIBUTION AND MODE OF OCCURRENCE. 57

CARBONATE HILL ORE BODIES.

The enormous size and the details of outline of the Carbonate Hill 

bodies can be explained to some extent, but the surrounding ground 

is so thoroughly altered and soft and in large part so inaccessible 

that a complete explanation of all the details is out of the question. 

The plan of these ore bodies is shown in Plate VII and cross secA'

UTTLE CHIEF N0.4 

'. SHAFT

^ White limestone 100 ZOO 300 400 FEET

FIGURE 7. Plan and section showing relations of oxidized zinc ore to old lead carbonate 

stopes in Chrysolite mine. Outlines of lead carbonate stopes copied from atlas sheet 31, 

U. S. Geol. Survey Mon. 1.2. Outlines of zinc stopes only approximate. Surface east 

of tho outcrop of vein matter is all White porphyry except the dike of Gray porphyry 

In the central part of the area. Section adapted from section B-B, atlas sheet 32, 

U. S. Geol. Survey Mon. 12.

tions in Plate VIII. The outlines of stopes in the plan are not 

everywhere indications of the boundaries of the ore body. In several places the narrow stopes, which might be interpreted as branches 

of ore along fissures, merely represent beginnings of stopes or exploration drifts to block out ore. Other boundaries represent the 

limits of high-grade ore without giving any idea of the large amount
58 OXIDIZED ZINC ORES OF LEADVILLE, CGLO.

of adjacent low-grade ore (averaging near 20 per cent oi zinc). 

The vertical sections throw more light on the dimensions of the ore 

bodies, but it must be remembered that the outlines of these sections 

are for the most part approximations, as the boundaries of the ore 

bodies in most places either had not been reached or were no longer 

accessible. The sections are somewhat generalized to include important features near but not exactly on the lines of the sections.

In sections A-A and F-F, Plate VIII, the maximum thickness, 

about 130 feet, of the ore body beneath the Parting quartzite is shown, 

the ore extending in places down to the Cambrian quartzite. Evidence pointing to the cause of this unusual thickness is very scanty but 

suggests a plausible explanation. Data on the size and distribution of 

associated old lead stopes, which have been exposed at a number of 

points, are scarce and indefinite. Such exposures beneath the Parting quartzite represent comparatively thin blanket bodies. A large 

stope has been exposed in a raise through the quartzite, but little is 

known of its extent and thickness. Comparison with the stope map 

of the monograph on the Leadville district of which this paper is 

to form a part will show that these old stopes lie close to the area 

of extreme metallization, but, although this fact indicates that there 

was an abundance of oxidized lead-silver ore in the immediate vicinity, there is no means of knowing whether the bulk of the zinc migrated vertically downward through the Parting quartzite, or down 

along the dip beneath the Parting quartzite. Both processes no 

doubt took place, but it can not be said which predominated.

Although the immediate sources of the zinc ore are very obscure, 

there is some evidence in the location of faults and open structure 

of the rocks to account for the great thickness of some of the ore 

bodies. The southeastward dip of the strata is interrupted by a fault 

of west-northwesterly trend (section F-F), with relative down-slip on 

its south side. This fault was exposed at only one place, on the first 

Wolftone level, and its length and exact course are not known. 

The amount of displacement where the fault is exposed must be at 

least 25 or 30 feet, according to the positions of exposures of the 

Parting quartzite on either side; but the Parting quartzite does not 

appear to have been displaced to the east, along the " high line ' ? 

drifts connecting with the Deener raise, and it is therefore concluded that the fault stops against one of north-northeasterly trend, 

as suggested in Plate VII. A strong clay-filled fissure, corresponding in position to the suggested north-northeasterly fault, was exposed on the " high line" 90 feet east of the McKean raise. The 

ground on both sides of it consisted of ore or thoroughly altered 

carbonate rock, and no idea of the amount of displacement could be 

gained. It is significant, however, that ore of shipping grade was 

not being mined on the east side of this fissure.
U. S. GEOLOGICAL SURVEY BULLETIN 681 PLATE VII

i

Wo/ft one 

shaft

O-y.

Solid lines, stopes and drifts above farting quartzite 

Dashed lines, stopes and drifts below Parting quart-Lite

IOO ZOO

PLAN OF ZINC CARBONATE ORE BODIES "IN WORKINGS OF WESTERN MINING CO
DISTRIBUTION AND MODE OF OCCURRENCE. 59

This fissure with its heavy clay filling evidently served as an 

effective barrier, at least locally, against the spreading of the zinc 

solutions. The Parting quartzite, as may be inferred from sections 

A-A and F-F, Plate VIII, could also have served in places along 

both faults as a barrier against circulation along the bedding, 

although in the planes of both sections it happens that blocks of 

unreplaced carbonate rock are exposed on the up-slip sides of the 

fault. Just what protected these masses from replacement can only 

be inferred from the evidence presented in the next paragraph. The 

distribution of the quartzite on both sides of the fault would tend to 

impound the solutions and to deflect them downward to some point 

where they could escape from the fault block.

At several places in the stopes of this thick ore body the generally 

open structure of the replaced carbonate rock is well preserved, as 

illustrated in figure 2 (p. 42). The bedding planes are mostly open 

and connected by short cross fractures, thus allowing the impounded 

solutions to permeate the rock throughout a vertical range bounded 

only by the top and bottom of the White limestone. The inclusions 

and bordering masses of carbonate rock found here and there, including those represented in sections A-A and F-F, Plate VIII, owe 

their preservation, to judge from their small exposures, to the local 

absence of this characteristic open structure. Most of these inclusions and masses are now stained by oxidation, and no tests of their 

composition were made, but the inclusion represented in section A-A 

proved to be typical manganosiderite. A specimen of this inclusion 

proved to be surprisingly porous for a crystalline rock, a character 

which, if common to the rock as a whole, would afford more complete permeation when once the zinc solutions had gained access 

along the numerous bedding and fracture planes. The porosity 

alone, however, was evidently not sufficient to allow extensive permeation.

The great thickness of the ore body therefore appears to be due 

to a combination of three conditions the distribution and local impounding influence of two faults, the distribution "of the Parting 

quartzite, and the open structure of the carbonate rock in the block 

bounded by the faults. That the faults were not effective barriers 

at all points is shown in sections F-F and B-B, Plate VIII, which 

represent the ore body extending across the lines of faulting. So 

far as underground study is concerned the principal factor in determining the shape of the ore body as far south as the line of section 

C-C, Plate VIII, was the open structure of the rock. From this 

line southward the ore body gradually assumes a narrow elongate 

outline (sections D-D and E-E) and at its southern extremity is 

limited to a width of 5 feet or less, replacing the dolomite walls of a 

fissure. The relation of the preserved bedding planes on each side of
60 OXIDIZED ZINC ORES OF LEADVILLE; COLO.

this fissure indicate faulting but give no idea of the amount of displacement. The occurrence in the fissure of a small amount of dense 

white quartz inclosing microscopic grains of a decomposed ferruginous carbonate and perhaps also of pyrite indicates a presulphide 

age for this fissure. The zinc ore along this fissure, as along those 

in other mines already described, tends to spread for short distances 

along the bedding and in one place was found to inclose a small bedded layer of sulphide ore, consisting chiefly of galena with cavities 

partly filled with calamine to mark the probable former presence of 

zinc blende.

The narrow stope extending northeastward from the east side 

of the lower ore body between the lines of sections B-B and A-A, 

Plate VIII, has no apparent connection with a pronounced fissure 

and is not necessarily a close indication of the limits of the ore. It 

deserves special mention, however, because it has yielded gray zinc 

carbonate ore, clearly formed by the replacement of manganosiderite, 

directly underneath a mass of sulphides. The existence of this ore is 

evidently due to the migration of zinc solutions chiefly along bedding 

planes east of the line of the fissure described on page 59. The geology was too much obscured by timbering here to warrant a more 

definite statement.

The upper ore body of Carbonate Hill, above the Parting quartzite, extends obliquely down the dip from a point near the old 

Henriette or " Old Maid" shaft to the southwest boundary of the 

Big Chief claim, a distance of about 1,050 feet. Its boundaries, however, are sharply defined at only a few points, and the factors influencing its outline can only be inferred rather than determined. The 

branch stope that extends a little west of south, just crossing the Big 

Chief northeastern boundary, underlies old silver-lead stopes that 

have been exposed at different points. It has at one place on its 

west side a nearly vertical dolomite wall opposite a wall of low-grade 

(10 per cent) ore. No strong fissures were exposed in the ground 

accessible to the writer, but the trend of the higher-grade ore and the 

position of its walls strongly, indicate replacement along a fractured 

zone. At one place just south of the Big Chief line the ore narrowed downward to a fissure filling only a few inches wide.

Northeast of this branch stope, about 50 feet south of the line of section C-C, Plate VIII, the zinc ore, with an inclusion of manganosiderite, was seen directly underlying a mass of pyritic sulphide ore. 

There was no indication of distinct fissuring in the ground accessible. 

The inclusion of manganosiderite, however, would, from analogy 

with the evidence obtained in the thick portion of the lower ore body, 

warrant the inference that the rock replaced by the ore was of open 

structure.
U. S. GEOLOGICAL SURVEY TlJ? G81 PLATE VIII

ELEVATION NW. 

IN FEET

Henrietta 4th I,

SE.

40,000-

9,900-

9,800-

9,700-J

'10,000-

9,900-

NW.

*tfT.. '

Section

Wolf tons shaft

iZSfcetSE.

* from cross

SECTION A-A

Section

NW

. Se'ction

V/olftone shaft (projecte 

.80 feet SE. from cross

SECTION B-B SECTION C-C

 , Parting - quartz.ite .'/ ' "-'!'

JJJ '^?/-?i'-' "" ' ~ *:?~'-~^V^'-4

ELEVATION 

SE IN FEET 

-IO.OOO

- 9,900

- 9,800

L 9.70O

LEGEND

Zinc sulphide

Lead carbonate

Zinc carbonate 

Stdped area shaded

9,800- ( u 9, soo

projected from'west 

of section line

SECTION F-F

SECTIONS THROUGH ONE P.ODIES SHOWN IN PLATE VI[

100 100 zoo

'ELEVATION* 

SE . N FEET

 10,000

- 9,500

L .9,7.00

30O FEET
DISTRIBUTION AND MODE OF OCCURRENCE. 61

About 100 feet south of this point, in the Banquet Hall stope, the 

ore body attained a thickness said to be 50 feet, and still farther 

south, a.short distance beyond the line of section E-E, it was as thick 

or thicker. The ore was worked out in the former place, but in the 

latter it was seen to preserve the open structure of the original rock. 

This thick body underlay old silver-lead stopes, but nothing is known 

of their dimensions. The body diminished rapidly in thickness eastward, and on the east side of the main third level drift, along the line 

of section E-E, had dwindled to a bedded replacement deposit only 

2 or 3 feet thick.

The most reasonable inference to account for the shape of the upper 

ore body, based on the scanty evidence presented, is that the rock had 

become more or less shattered along certain zones characterized by 

anastomosing fractures rather than pronounced fissures. The zinc 

solutions, descending from the oxidizing blanket bodies (now the old 

silver-lead stopes), found the easiest courses along these zones, with 

the result that bodies of relatively great thickness in proportion to 

their width were formed by replacement of the carbonate rock. The 

width of the ore body was limited by the extent of the openings in 

the rock; the depth, as shown in sections D-D and E-E, was limited 

by the Parting quartzite, which in places has been exposed as the 

approximate floor of the stopes. Whether or not these zinc solutions 

found their way in any considerable amount downward along fractures through the Parting quartzite has not been demonstrated by 

mining. It seems doubtful, however, in view of the size of the ore 

body and its depth with respect to oxidation, if any considerable 

amount of zinc carbonate or silicate ore can be expected beneath it, 

on the under side of the Parting quartzite.

Comparison of the position of the Carbonate Hill bodies and the 

slopes on the surface fails to show a concordant relation. The depths 

of oxidation as recorded in Emmons's notes are likewise independent 

of the topography, and it is evident that the depth and circulation of 

ground water has been governed rather by the rock structure that 

is, the trends of the open portions of fissures, minor fractures, and 

bedding planes.

CHARACTER OF BOUNDARIES OF THE ORE BODIES.

The character of the boundaries of the ore bodies, as has already 

been mentioned, varies in different places, and little additional description is necessary. It seems desirable, however, to summarize 

the variations and to check them with certain chemical data. The 

simplest case includes the rather sharply defined nearly vertical walls 

along nearly vertical fissure bodies. The west wall of the fissure 

stope near the south end of the lower Carbonate Hill body is sharply
62 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

bounded by soft, sandy dolomite, a specimen of which was found by 

K. C. Wells to contain 1.28 per cent of zinc oxide, or 1.59 per cent of 

zinc carbonate. At the northwest end of the small fissure stope in the 

New Dome mine (fig. 5) similar but more rusted soft material bordering the stope was found by George Steiger to contain 19.22 per 

cent of insoluble matter, 0.36 per cent of magnesia, 0.53 per cent of 

lime, and 6.33 per cent of zinc oxide. The zinc here showed a 

stronger but still not great tendency to permeate the wall rock, which 

elsewhere in the mine is Blue limestone (dolomite). The insoluble 

material appears to be chiefly silica intimately associated with brown 

iron oxide and possibly combined with the zinc as zinciferous clay. 

This material, only a few inches thick, passed into unstained dolomite. Similar siliceous material was found along the main body of 

the New Dome mine on the first level. The occurrences in the Maid 

of Erin mine, described with assays by Argall,1 are of similar character, though the transition from ore to country rock is more gradual.

Some of the bedded zinc carbonate bodies have rather clearly defined floors, though not nearly so sharply defined as the fissure walls 

just described. Two specimens taken from the floor of a small bed 

stope in the Ibex mine, one at the very contact of the stope and the 

other 5 inches below it, were found by Mr. Wells to contain respectively 27.4 and 14.9 per cent of zinc oxide, or 22 and 12 per cent of 

metallic zinc. These figures indicate a gradual change from ore into 

country rock within a zone between 1 and 2 feet thick. The bottom 

of the upper ore body of Carbonate Hill is in places abruptly 

bounded by the Parting quartzite, the top layers of which have been 

deeply stained by iron and manganese oxides, which may be accompanied by a little zinciferous clay. The lower ore body is said to be 

similarly floored by the Cambrian quartzite at a few places. At one 

place in the lower ore body, about 230 feet west-northwest of the 

Deener raise (PI. VII), the high-grade ore passes downward into a 

decomposed low-grade material consisting chiefly of silica with minor 

amounts of iron oxide and clay, which appears to be the residue of a 

siliceous or silicified carbonate rock. In other places the ore passes 

downward into unaltered carbonate rock. Such variations evidently 

depend on the composition of the rock replaced and on the amount 

of leaching that has been possible since the deposition of the zinc ore.

The sides of the bedded bodies may be rather abruptly bounded, 

but much more commonly they are marked by a gradual decrease in 

zinc content so that the high-grade ores merge into large bodies of 

ore averaging near 20 per cent in zinc. How extensive such lowgrade bodies are has not been definitely stated, but they are said to 

constitute large reserves in several different places.

1 Argall, Philip, The zinc carbonate ores of Leadville: Min. Mag. (London), vol. 10, 

p. 284, 1914.
DISTRIBUTION AND MODE OF OCCURRENCE. 63

The main factor determining the character of the boundary is evidently rock structure. Where permeable rock is abruptly limited, as 

along clear-cut fissures or impervious beds, either of quartzite, shale, 

or porphyry, the contact is also abrupt; where the rock bordering 

the main ore channels is of more open structure, there is likely to be 

a gradation from high-grade ore through a large extent of lowgrade ore into barren rock. In the latter case the degree to which 

zinc is concentrated in the solution may -be an important factor, solutions above a certain strength readily replacing the rock, whereas 

solutions below that strength but otherwise under similar conditions 

could react only slowly and to a small extent. No experimental data 

are at present available to throw light on this matter.

The upper contacts of the ore bodies are marked for the most part 

by layers of siliceous iron oxide and clay in varying amounts, which 

separate the zinc ore from overlying lead-silver bodies. These layers 

range in thickness from a few inches to 6 feet or more. They are 

characteristic of oxidized zinc deposits in several mining districts 

and are subject to more than one interpretation. They may represent 

the first substances deposited by the solutions that transferred material downward from the oxidizing sulphide bodies; they may represent the oxidized residue of a largely insoluble material which 

formed a casing to the original sulphide bodies; they may be the 

insoluble residue left by the leaching of the topmost part of the 

zinc carbonate body; or they may consist principally of material 

leached from the original ore bodies at a relatively late stage and 

deposited at the same time that the topmost part of the zinc carbonate was being leached. Partial evidence in different places suggests one or another of these processes, and it is possible that a combination of processes took place. It is also possible that one process 

may have been of relatively great influence in one district and of 

relatively slight influence in another, owing to differences in chemical 

conditions. The chemical conditions are considered in the discussion of ore genesis (pp." 68-85).

Where the oxidized zinc bodies have been seen immediately underlying porphyry or shale, their upper contacts are marked by a layer 

of zinciferous clay that may be 2 or 3 feet in thickness. The presence of the clay is evidently due to the alumina and silica leached 

from or residual after the porphyry or shale. In some places it seems 

that the alumina must have been precipitated with the zinc; in others 

it seems probable that the clay, already present, has adsorbed zinc 

from solutions which have come into contact with it.

At a few places bodies of oxidized zinc ore have been found in 

contact with bodies of iron or manganiferous iron ore. These contacts are considered in the following paragraph.
64 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

 4

RELATIONS TO OXIDIZED IRON AND MANGANIFEROUS

IRON ORES.

The oxidized zinc ores have been found beside and beneath 

oxidized iron and manganiferous iron ores and have also been reported to occur above them. The evidence obtained by the writer, 

while affording some explanation of these variations in distribution 

and occurrence, does not point to any systematic association. The 

lack of systematic association may be appreciated when it is realized 

that the iron ores may have originated from the complete oxidation 

of either pyrite or manganosiderite masses, and that the zinc ore 

may have been deposited directly either beneath or beside masses of 

either of these materials; also that the primary shoots of zinc blende 

from which the oxidized zinc ores were derived were irregularly 

scattered through the sulphide bodies or were in places underlain 

by manganosiderite. The evidence as a whole indicates that if either 

an oxidized iron or zinc ore body is present a body of the other may 

be present close by; but the relative position of the two bodies can 

not be predicted. In view of the relative abundance and distribution 

of the primary minerals, pyrite, manganosiderite, and zinc blende, 

it is evident that the presence of the iron ore is not a certain indication of the presence of the zinc ore, for large bodies of almost pure 

pyrite bordered by manganosiderite are known to exist with no noteworthy amount of zinc blende in the immediate vicinity. Oxidation 

of such a body would yield a large deposit of iron and manganiferous iron ore, with no associated body of zinc ore.

VERTICAL DISTRIBUTION AND RELATION TO DEPTHS OF OXIDATION AND GROUND-WATER LEVEL.

Oxidized zinc ores have been found in a few places close to and 

even at the surface and at varying depths down to 750 feet. The 

depths at different places depend as a rule on the depths of the contact of the White porphyry and Blue limestone, as most of the zinc 

bodies have been found in association with the " first contact" ore 

bodies of this horizon. The deepest deposit in the northern part of 

the Maid of Erin mine is associated with a series of ore bodies including "second contact" bodies (below Gray porphyry) and with 

bodies just above and just below the Parting quartzite. It is in the 

White limestone, extending in places from the base of the Parting 

quartzite even down to the top of the Cambrian quartzite. This is 

the thickest and one of the largest two oxidized zinc ore bodies thus 

far worked in the Leadville district. It is associated with the 

thickest as well as one of the most continuous bodies, or series of 

bodies, of lead-silver ore in the district, and general conditions
DISTRIBUTION AND MODE OF OCCURRENCE. 65

appear to have been favorable to concentration rather .than dispersion of the zinc.

All the zinc carbonate and silicate thus far mined have been found 

in the zone o'f complete oxidation, except the Ipwest parts of the 

great Carbonate Hill bodies. These, as indicated in sections A-A to 

F-F, Plate VIII, in places underlie sulphide ore. In some of these 

places the zinc ore is practically in immediate contact with the sulphides and may even inclose small amounts of them and of associated manganosiderite. Here the zinc ore has been deposited below 

the local depths of oxidation.

These exposures of sulphides over or within the zinc ore have 

been made at depths of about 640 to 700 feet and more below the 

collar of the Wolftone shaft. Old lead carbonate stopes were 

noted as far down as about 650 to 660 feet below the shaft collar. 

These figures, based on observations at several places in the 

Western Mining Co.'s ground, place the average local depth of 

complete oxidation about 640 to 650 feet below the collar of the 

Wolftone shaft, or at an elevation of about 9,950 feet. They 

correspond closely with figures in Emmons's notes, for he found 

the depths of oxidation to be at an elevation of 9,936 feet (660 feet 

below the surface) in the Wolftone mine, 9,941 feet (639 feet 

below the surface) in the Brookland, and 9,981 feet (667 feet below 

the surface) in the Upper Henriette. Emmons's notes, however, 

show that the depth of oxidation fluctuates considerably in the 

northern part of Carbonate Hill.

The relation of the oxidized zinc ores to ground-water level can 

not be definitely shown, because the original water levels in different 

places have been-greatly disturbed by underground operations. All 

the ore bodies studied, except those in the northern part of Carbonate Hill, are well above the original ground-water level, so far 

as can be learned from available data. It is stated that in northern 

Carbonate Hill water to-day would rise to a level about 300 feet 

below the surface in the Wolftone shaft were pumping operations to 

cease. This is over 300 feet above the average depth of complete 

oxidation and well above all the oxidized zinc bodies thus far mined. 

It can not, therefore, be considered as any indication of the original 

ground-water level. Neither can the average depth of complete 

oxidation be considered a close indication of the original groundwater level, as oxidation is known to extend somewhat below that 

level in some places and considerably below it in excessively fractured zones. On the other hand, sulphide bodies of small to con- 

.siderable size are found, in more protected ground, above groundwater level. The depths at which the zinc carbonate and silicate 

are found are also unreliable indications, for the reason that they

52757° Bull. 681 18 5
66 OXIDIZED ZINC ORES OF XEADVILLE, COLO.

may be deposited by the replacement of limestone below as well as 

above ground-water level. The composition of the zinc carbonate 

ores is such as to indicate that they were deposited in the absence 

of free oxygen, a condition that may exist in the lower part of the 

ground above the water level as well as below it.

The zinc carbonate ores also show that they themselves have certainly, to a large extent, undergone considerable oxidation and leaching, a fact which proves the downward migration of the oxidized 

zone since the bulk of the carbonate ores were deposited. The groundwater level also doubtless migrated downward, keeping pace with 

surface erosion. It is obvious, therefore, that no exact relations can 

be determined between the distribution of the oxidized zinc ores and 

the ground-water level. The evidence as a whole, however, indicates 

that the zinc carbonate ores were deposited close to if not in part 

below the water level that then existed, and it is possible that their 

lower portions were still below the natural water level that existed 

just prior to the disturbances caused by mining.

LACK OF ASSOCIATION WITH SECONDABY SULPHIDES.

No evidence of secondary sulphides of any kind was found in connection with the oxidized zinc ores, and no positive evidence of 

secondary zinc sulphide was noted anywhere in the district. The 

sulphide ore exposed in contact with the zinc carbonate ores had all 

the characteristics of primary ore. Even small grains of pyrite, 

zinc blende, and galena found inclosed in the ore proved under the 

microscope to be intimately associated with veinlets and patches of 

quartz and sericite, the typical gangue minerals of primary sulphide ore. The three sulphides, as well as the quartz and sericite, 

were evidently unaffected by the zinc-bearing solutions that replaced 

the carbonate rock.

The sulphide masses adjacent to the zinc carbonate ore are all 

composed largely, if not entirely, of pyrite, but no sign of zinc sulphide, either sphalerite or wurtzite, upon pyrite was found. This 

is a point of some significance in view of the conclusions expressed by 

Blow and Emmons (see p. 10) that the zinc removed from the 

oxidized zone had been precipitated just below water level and had 

thus migrated downward at equal pace with the limits of oxidation. 

The only available agents for the precipitation of zinc as a sulphide, 

on the assumption that the zinc was in solution as sulphate, were 

a very small quantity of organic matter and a large quantity of 

pyrite.

It has been assumed by some writers that pyrite or marcasite has 

precipitated secondary zinc sulphide, especially in deposits of the
67

Mississippi Valley; but experiments with the two minerals have not 

confirmed this assumption, at least in a convincing way. The experiments of Schuermann x and Weigel 2 lead to the conclusions that 

under certain conditions zinc has a slightly stronger affinity for 

sulphur than iron has in other words, that zinc, sulphide is slightly 

more insoluble than iron sulphide but that the two metals are so 

very nearly equal in solubility that any precipitation of zinc sulphide at the expense of an iron sulphide would not be nearly so 

marked as a precipitation of silver or copper sulphide by the same 

agent. The conditions of these experiments by no means duplicate 

the conditions governing the secondary deposition of zinc minerals 

at Leadville. So far as they go, they may suggest that if pyrite can 

precipitate zinc sulphide from the ground waters in question, it 

does so very slowly and can hardly precipitate large quantities of 

zinc blende just below the zone of oxidation.

The only experiment, to the writer's knowledge, in which zinc sulphide has been precipitated by pyrite or marcasite is one by Stokes 3 

who treated pyrite and marcasite each with an excess of zinc carbonate and potassium bicarbonate in sealed tubes filled with carbon 

dioxide for 24 hours at 180° C. Other experiments under similar 

conditions, also by Stokes, on the action of alkaline solutions alone on 

pyrite and marcasite show that the alkaline solutions, including potassium bicarbonate, decompose pyrite and marcasite. It therefore 

seems probable that the potassium bicarbonate was the influential 

factor in making the precipitation of zinc sulphide possible. In the 

Leadville deposits the secondary zinc solutions, whether sulphates or 

carbonates, evidently found the surrounding carbonate rock to b(e 

more readily replaceable than the pyrite. After the zinc carbonate 

had been thus precipitated the conditions, including low temperature 

as well perhaps as absence of a sufficient amount of alkali in solution, 

were not right to convert it to secondary sulphide at the expense of 

pyrite.

Experimental evidence is thus negative, and local field evidence 

shows that conditions were not favorable for the precipitation of 

secondary zinc sulphide. Local evidence furthermore accords with 

general evidence, which has been discussed by W. H. Emmons,4 who 

says:

It has frequently been stated that zinc sulphide has been precipitated at the 

expense of iron sulphide and that zinc has driven iron out of its sulphide com1 Schuermann, Ernest, Ueber die Verwandtschaft der Schwermetalle /urn Schwefel: 

Llebig's Annalen, vol. 249, p. 326, 1888.

2 Weigel, Oskar, Die Losllchkeit von Schwermetallsulphlde im reinem Wasser: Zeltschr. 

physlkal. Chemle, vol. 58, pp. 293-300, 1907.

3 Stokes, H. N., Experiments on the action of various solutions od pyrite and marcasite : 

Econ. Geology, vol. 2, p. 17. 1907.

* Emmons, W. H., The enrichment of sulphide ores; U. S. Geol. Survey Bull. 529, p. 86, 

1913.
68 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

bination, but no examples of the pseudomorphous replacement of pyrite or marcasite by zinc blende 'are available. On the other hand, Hintze * notes a pseudomorph of marcasite after.zinc blende.

Lindgren 2 states that " zinc is not, as a rule, deposited as a secondary sulphide, and no authentic case has been recorded where it replaces pyrite, as chalcocite so often does." In his discussion of Bain's 

conclusion that secondary zinc and other sulphides have been deposited at Joplin, Mo., below the zone of oxidation, he states 3 that 

" possibly this has taken place on a small scale, but most of the ore 

immediately below the oxidized zone appears to be of primary 

origin."

In a few places, the most recently discovered of which has been 

described by B. S. Butler,4 wurtzite, the hexagonal form of zinc sulphide, occurs as a probable secondary mineral. Butler, while suggesting that the replacement of pyrite by zinc sulphide may be possible, remarks that 

in none of the ore examined can the zinc sulphide be seen replacing the iron, 

but there are abundant specimens that show wurtzite surrounding sphalerite, 

apparently as a later growth on it. This suggests that the precipitation has 

been effected by agents other than the pyrite, and that the attraction of the 

sphalerite had caused the secondary sulphide to be added to it. * * * E. T. 

Alien and J. L. Crenshaw have suggested that acid solutions containing zinc 

sulphate and hydrogen sulphide in solution on having their acidity reduced 

would precipitate zinc sulphide. That such solutions are formed in the zone 

of oxidation there can be little doubt, and as they pass to lower levels their 

acidity may be reduced either by solutions from the adjacent limestone or by 

reaction with alkali silicates that form a part of the gangue of the ore.

From this evidence it would seem possible that wurtzite could be 

found crystallized upon zinc blende in some of the Leadville deposits 

at or below the downward limit of oxidation, but no such occurrence, 

to the writer's knowledge, has been reported. So far as positive 

evidence is concerned, no bodies of secondary zinc sulphide have been 

formed. The bodies of zinc blende just below the zone of oxidation, 

referred to by Blow and Emmons, can doubtless be interpreted as primary and can be shown to differ in no essential way from other 

segregated deposits of zinc blende found well below the zone of 

oxidation, such as have been found in the Cord mine below the level 

of the Yak tunnel.

GENESIS.

That the oxidized zinc ores of the Leadville district are believed 

to have been derived through oxidation of zinc blende in the original

1 Hintze, Carl, Handbuch der Mineralogie, vol. 1, p. 481.

2 Lindgren, Waldemar, Mineral deposits, p. 811, 19.13. 

3Idem, p. 834.

4 Butler, B. S., Geology and ore deposits of the San Francisco and adjacent districts, 

Utah : U. S. Geol. Survey Prof. Paper 80, p. 154, 1913.
GENESIS. 69

sulphide ore must be apparent to all who have read the foregoing 

pages. Below are considered the chemical processes involved in the 

derivation. Some of the evidence afforded by study of the specimens 

and underground workings may not accord perfectly with all the 

experimental data available, and such discordances necessarily leave 

some doubt as to the exact conditions of chemical equilibrium which 

existed and which exerted a greater or less influence on the reactions 

that took place. The genesis of the ores may be conveniently considered in three stages.

FIRST STAGE. 

DERIVATION OP MATERIALS.

The original ore bodies consisted essentially of the ore minerals 

pyrite, zinc blende, and galena, with small amounts of chalcopyrite 

in places and .of the gangue minerals manganosiderite, quartz, and 

sericite, the gangue minerals for the most part forming a casing 

around the ore' bodies. The zinc blende was the ferruginous variety, 

marmatite, composed of about 3 parts zinc sulphide and 1 part iron 

sulphide, as shown by the following analyses:

Analyses of zinc ore from Leadville district.11 

[A. W. Warwick, analyst.]

Zinc 6........................... ...............................................

Adams.

52.8

34.7

12.1

o

99.8

Colonel 

Sellers.

47.6

35.7.

14.8

98.5

Yak.

41 i

^fi 4

17 8

99.5

a, Bain, H. F.. U. S. Geol. Survey Mineral Resources, 1905, p. 384,1906. 

& Includes cadmium, which varied from 0.1 to 0.35 per cent. 

e Includes manganese, which varied from 1.3 to 3.7 per cent.

Study of the sulphide ores in the Leadville district and of similar 

ores in other districts shows that the zinc blende is the first of the 

ore minerals to be removed by oxidation and may be nearly or 

quite all removed before the other sulphides are attacked to any 

considerable extent. The rapidity and thoroughness of removal 

would obviously depend on the degree to which oxidizing solutions 

could permeate the ore of the three sulphides. Galena is the most 

protected from oxidation, owing to the insolubility of the sulphate 

which forms around it. The writer has seen very little chalcopyrite 

in place at Leadville and has no definite data at hand regarding its 

position in the order of oxidation. His observations of ores in 

other districts would lead him to favor the view that chalcopyrite
70 OXIDIZED ZINC OEES OF LEADVILLE, COLO.

underwent oxidation before the pyrite and after the zinc blende 

a view which accords with the occurrence of copper in the oxidized 

zinc ores at Leadville and with the interpretation of their genesis 

but which does not harmonize with certain experimental data.1 . The 

conditions of these experiments, however, do not approach very closely 

the natural conditions under which the Leadville ores were oxidized.

These experimental data have been summarized and discussed by 

W. H. Emnions, who makes the following concluding statement: 

"All these experiments and observations seem to indicate that in 

the zone of oxidation in many deposits the sulphides are dissolved 

in the following order: Sphalerite (?), chalcocite, pyrrhotite, chalcopyrite, pyrite, galena, enargite." The positions of sphalerite, chalcopyrite, pyrite, and galena in this order accord with the writer's 

observations.

The ore bodies are covered by a greater or less thickness of porphyry, through which the oxidizing waters must have descended. 

Those bodies which are exposed at the present surface were once 

covered by porphyry, or in some places by the Parting quartzite and 

porphyry, and oxidation in all probability began before these overlying rocks were removed. Possible exceptions may have existed 

locally where sulphide bodies unusually well protected from preglacial oxidation were exposed by glacial scouring and were later 

oxidized by waters that had not previously passed through porphyry ; but study of the geologic sections in the atlas accompanying 

Monograph 12 shows convincingly that in practically all the places 

where oxidized zinc ore bodies have been found the oxidizing waters 

must have descended for considerable distances along major and 

minor fractu res through porphyry.

The porphyries which the writer has studied, both White and Gray, 

are extensively altered to aggregates of pyrite, quartz, and sericite, 

and it is most probable that alteration of this type extended for a 

considerable distance above the " first contact " bodies. The descending waters, therefore, already containing oxygen and carbon dioxide 

from the air, attacked and decomposed the pyrite, taking ferric and 

ferrous sulphates and sulphuric acid into solution. In the earliest 

stages of oxidation the supplies of oxygen as well as of free sulphuric 

acid and ferric sulphate may have become exhausted through further 

reactions before reaching the ore bodies, but as the erosion surface 

and the limits of complete oxidation were gradually lowered these 

active reagents persisted until the ore bodies were reached. The 

waters at this stage probably contained in solution considerable 

quantities of alkalies, alkaline earths, carbon dioxide, and oxygen, 

but larger quantities of the two iron sulphates and sulphuric acid.

1 Emmons, W. H., The enrichment of sulphide ores: U. S. Geol. Survey Bull, 529, pp. 

76-78, 1913.
GENESIS. 71

The presence of alkalies and alkaline earths may have exerted some 

influence in accelerating the processes of solution and deposition, as 

suggested by Nishihara.1 Minor quantities of alumina and silica 

also were doubtless present in solution, as indicated by the composition of many mine waters that have percolated through pyritized 

siliceous rocks.2

Of these constituents sulphuric acid, ferric sulphate, and oxygen 

had the most influence on oxidation and the removal of the sulphides. It is doubtful if carbon dioxide could have exerted much 

solvent action on zinc blende, so long as these three constituents were 

present in excess, owing to the much higher degree of solubility of 

zinc sulphate than that of zinc carbonate. This statement is supported by the fact that where descending waters have locally evaporated in the Leadville mines, desposits of goslarite, the zinc sulphate, 

have been found, but none of a zinc carbonate. Experiments by 

Gottschalk and Buehler 3 have shown that although zinc blende alone 

when leached by water is oxidized very slowly, the process is hastened 

if the water has first descended through pyrite or marcasite that is, 

if it has first become charged with sulphuric acid and ferric sulphate. 

They have shown also that oxidation is much more rapid if the blende 

is in contact with galena or especially with pyrite, the oxidation 

being accelerated by electrolytic action. The water used in these 

experiments is not strictly analogous in composition to the ground 

waters that had descended through the pyritized porphyries of Leadville, but the results of the experiments accord with those of the 

natural process. Whatever the exact reactions were, the zinc blende 

was oxidized before the other two sulphides, and there is little doubt 

that the zinc and iron of the zinc blende were removed as sulphate.

The supply of free oxygen in these solutions probably became exhausted at an early stage of the process, and it may be that more or 

less sulphuric acid and ferric sulphate were still available for further 

reactions. Experiments by K. C. Wells * have shown that sulphuric 

acid, out of contact with air, dissolves zinc blende more readily than 

it dissolves either galena, pyrite, or chalcopyrite, converting the zinc 

to sulphate and setting free hydrogen sulphide. The hydrogen sulphide, if free to escape upward, could finally reach the zone of free 

oxygen, oxidize, and thus tend to renew the supply of sulphuric acid; 

if not free to escape it could, after the sulphuric acid had become exhausted, possibly succeed in reprecipitating some of. the zinc as the 

hexagonal sulphide, wurtzite, but no evidence has been found to

1 Nishihara, G. S., Geology and ore deposits of the Tetiuxe district, Russia: Econ. 

Geology, vol. 12, pp. 277-278, 1917.

8 Analyses of 37 such waters are tabulated and discussed by W. H. Bmmons (U. S. 

Geol. Survey Bull. 529, pp. 60-74, 1913).

8 Gottschalk, V. H., and Buehler, H. A., Oxidation of sulphides: Econ. Geology, vol. 5, 

pp. 28-36, 1910 ; vol. 7, pp. 15-34, 1912.

'Emmons, W. H., op. clt., pp. 59, 76.
72 OXIDIZED. ZINC ORES OF LEADVILLE, COLO.

show that this reaction has taken place in the Leadville deposits. 

Ferric sulphate, out of contact with air, could also convert the zinc 

and iron in zinc blende to sulphates, setting free sulphur and 

itself changing to ferrous sulphate. The disposition of the free 

sulphur under these conditions is questionable, but there is nothing to 

indicate that it played a conspicuous part in the genesis of the oxidized zinc ores. The results of these reactions which may have taken 

place after the free oxygen in the descending waters had become exhausted served to supplement those of the reactions which had taken 

place before in other words, to increase the amount of zinc sulphate, 

and also of ferrous sulphate, already in solution.

After the reactions that produced zinc and iron sulphates in solution had been completed, the carbon dioxide in solution may have 

aided to a minor extent in the further decomposition of zinc blende 

by uniting with some of the zinc in solution as bicarbonate, leaving 

a corresponding amount of sulphuric acid to continue attack on the 

sulphide. The original amount of carbon dioxide in solution may 

have been considerably increased if the descending waters passed 

through any carbonate rock, either manganosiderite or dolomite, before their supplies of sulphuric acid and ferric sulphate had become 

exhausted.

The reactions outlined above are believed to include all that appear 

to have been important in the decomposition of zinc blende,and the 

provision of a supply of zinc available for deposition as oxidized 

ore. The materials that were taken into solution, or left in solution, 

as a result of such reactions are principally zinc sulphate, ferrous sulphate, and more or less zinc and iron carbonate, with corresponding 

amounts of lime, magnesia, and manganese sulphate.

DEPOSITION OF MATERIALS FROM SOLUTION.

Deposition in the oxidized zone may take place by processes of 

hydration and oxidation of the solutions, desiccation or evaporation, 

reaction or metasomatic interchange with the wall rock, and reaction between different solutions. The first two of these processes 

have resulted in deposition of some iron sulphate, goslarite (the 

hydrous zinc sulphate), hetaerolite, hydrozincite, some smithsonite, 

and calamine. Reaction between different solutions may have caused 

deposition of some of the zinciferous clays, waters descending 

through porphyry with alumina and silica in solution reacting 

with zinc-bearing waters that percolated along the lower contact 

of the porphyry and depositing the layers of zinciferous clay along 

the bottom of the porphyry. Metasomatic interchange with the wall 

rock, however, has been the chief agent in producing the deposits 

of commercial grade, although these deposits have been more or less 

reworked by one or more of the other processes.
GENESIS. 73

The disposition of the materials can most conveniently be discussed by following the different courses which the water may have 

followed after its leaching of the zinc from the sulphide bodies. 

Where the water, after taking zinc sulphate into solution, became 

locally supersaturated through desiccation, while still in the sulphide body or in a porphyry sill beneath the sulphide body, goslarite 

was formed (and is being formed), lining fractures and other openings. The only occurrence of goslarite seen by the writer in his study 

of the Leadville sulphide ores was a coating on pyritic sulphide ore 

along a drift on the sixth level of the Tucson mine. The mineral 

here formed white, soft, fine, hairlike crystals associated with relatively thick prisms of epsomite, a hydrated sulphate of magnesia, 

the two minerals forming a parallel fibrous growth. Such deposits 

are only temporary, being redissolved sooner or later by unsaturated 

waters which reach them.

Where the waters pass through the sulphide bodies into underlying 

rocks two sets of conditions may be considered, according to the kind 

of rock (porphyry or carbonate rock). Each of these sets of conditions may be subdivided into two phases one in which the free sulphuric acid and ferric sulphate have not been exhausted and the other 

in which they have been exhausted. If the underlying rock is 

sericitized porphyry, and sulphuric acid and ferric sulphate are 

present, either or both of these reagents will tend to decompose the 

sericite and any unaltered feldspar in the porphyry, taking into solution silica and sulphates of alumina and alkalies. The alumina and 

silica will tend to be precipitated again, perhaps without having 

traveled for any considerable distance, as kaolin, or material of 

similar composition and appearance. This process will also cause the 

deposition of an indefinite amount of zinc and result in zinciferous 

clay. Whether the zinc is deposited simultaneously with the other 

materials as a primary constituent of the clay or through the replacement of aluminum in clay previously deposited is an open question. Where the percentage of zinc in such clay is very high it could 

be regarded as a primary constituent; where the percentage of zinc 

is low it could be regarded either as the result of replacement or as 

a primary constituent of clay deposited from a solution poor in 

zinc. The origin of the iron and manganese oxides locally present 

in these clays is obscured by their segregation, since their deposition, 

into red, brown, and black patches and streaks. They, like the zinc, 

may have been original or secondary (adsorbed) constituents of the 

clay. Under all these suppositions the precipitation of aluminum and 

zinc compounds from solution may imply the liberation of a corresponding amount of sulphate radicle and the renewal of sulphuric 

acid capable of dissolving new portions of the rock and tending to
74 OXIDIZED ZINC OEES OF LEADVILLE, COLO.

repeat the process until the water itself should become exhausted 

or should reach ground-water level.

Where the entire process has taken place within the porphyry 

mass, the zinciferous clays are scattered along fissures and minor 

fractures in the porphyry; where the waters containing the constituents of the clay in solution passed through the porphyry into 

carbonate rock, the clay was deposited through metasomatic replacement, the size and shape of the deposit depending on the relative 

openness of fractures and bedding planes and on the amount of 

clay material introduced. The chemical reactions involved in this 

replacement are not simple, but the replacement of carbonate rocks 

by masses of kaolin is not an uncommon occurrence.

It is believed0 that the process outlined above goes far toward 

explaining the occurrence of low-grade siliceous and argillaceous 

zinc ore like that at the base of a porphyry sill in the Belgian 

mine. (See fig. 4, p. 54.) This ore contains veinlets and vugs 

lined or filled with calamine, which was deposited with and just 

after the clay and appears to represent the excess of zinc over that 

which could be contained by the clay. The opal and chalcedony 

closely associated with the calamine represent a further excess of 

silica. The presence of calamine appears also to indicate that sulphuric acid and ferric sulphate had become exhausted, and that zinc 

sulphate in the neutralized solution, concentrated by depletion of 

the water, could not remain in solution in the presence of an excess 

of silica. The absence of any conspicuous amount of smithsonite 

in this deposit is noteworthy as an indication that carbon dioxide 

was a very minor constituent of the solution which introduced the 

zinc. The presence of a few miscroscopic needles of aurichalcite 

associated with the calamine and chalcedony also points to the 

scarcity of carbon dioxide, as it is probable that the basic carbonates 

of zinc are deposited when there is no excess of carbon dioxide.

It is known that sodium carbonate produces a basic carbonate of 

zinc, when added to zinc sulphate; on the other hand, sodium bicarbonate yields a normal carbonate. Raikow x showed that an excess 

of carbon dioxide transforms the hydroxide of zinc into the normal 

carbonate.

If the descending waters on passing from the sulphide body into 

underlying porphyry have been depleted of their free sulphuric 

acid and ferric sulphate, it is doubtful if any considerable replacement of the wall rock can occur, at least until the waters become concentrated through depletion or adsorption by wall rock material. 

It seems unlikely that the difficultly soluble minerals of the porphyry 

can be readily replaced by interchange with the easily soluble sul1 Raikow, P. N., Weitere Untersuchungen fiber die Einwirkung der Kohlensaure auf die 

Hydrate der Metalle: Chem. Zeitung, vol. 31, p. 55, 1907.
GENESIS. . 75

phate of zinc, and no indication of such a process has been noted. 

It seems probable, on the other hand, that such a solution will pass 

through the porphyry until ground-water level is reached, .or until 

concentration by the above-mentioned factors causes the deposition 

of goslarite, or of calamine in the presence of sufficient silica, or of 

zinciferous clay in the presence of alumina and silica. The alumina 

and silica would presumably have been derived chiefly from gangue 

material within the sulphide body and from porphyry above the ore 

body. Workable deposits of calamine with more or less zinciferous 

clay could be formed in this way where excessive fracturing of the 

porphyry would afford an opportunity. It is possible also that in 

such places some replacement of the shattered porphyry by these 

minerals could be effected if the solutions were sufficiently concentrated, but no such deposits in porphyry have been noted at 

Leadville. 

If the solution with a high content of zinc should pass through

the porphyry into carbonate rock, deposition of the zinc as carbonate by replacement would be possible, and the process would be 

analogous to that described below.

None of the Leadville deposits can be attributed chiefly to this set 

of conditions, although the occurrence of zinc carbonate bodies separated from parent sulphide bodies by a sheet of porphyry is a 

possibility. If the solution were low in zinc and in consequence 

relatively high in silica and alumina, calamine and zinciferous clay 

could be expected, as the conditions would be similar to those illustrated by the occurrence in the Belgian mine.

Where the solution passed directly from the sulphide body into 

carbonate rock, either manganosiderite or dolomite, and contained 

an excess of sulphuric acid and ferric sulphate, the sulphuric acid 

would at once be neutralized by reaction with the carbonates. If 

free oxygen were also present in solution, a corresponding amount of 

ferrous sulphate formed by the reaction would be oxidized to ferric 

sulphate, and this together with ferric sulphate already in solution 

would react further with the carbonate rock and be precipitated as 

ferric hydrate, according to the following equation: 1

Fe2 (SO4 ) 8+3(Fe, Mn, Mg, Ca)CO3+3H2 0=2Fe(OH3 )+3(Fe, 

Mn,Mg, Ca)SO4+3C02 .

The ferric hydrate thus formed would, by gradual loss of a part of 

its water, be gradually transformed into one of the hydrous oxides 

and thus account for a part of the iron oxide in the layers that separate the lead-silver stopes above from the zinc carbonate stopes

*The action of sulphuric acid and ferric sulphate on limestone has been studied by 

W. Melgen (Beltriige zur Kenntnls des Kohlensauren Kalkes: Naturforsch. Gesell. Freiburg 1m Breisgau Ber., vol., 13, p. 76, 1903). The equation given above Is adapted from 

one given by Melgen, In which CaC08 is the only carbonate represented.
76 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

below. The carbon dioxide formed by this reaction would augment 

the small amount already present in solution.

If aluminum sulphate were present in considerable amount it may 

have reacted in the same manner as the ferric sulphate and have 

been precipitated in the presence of sufficient silica to form kaolin. 

The greatest argument for this reaction is the intimate association of 

kaolin with iron oxide in the layers just mentioned. There is also 

evidence that small amounts of alumina, now present as pockets of 

zinciferous clay in zinc carbonate ore, were formed at a later stage. 

The precipitation of the silica in the kaolin may be attributed *o the 

mutual absorptive tendencies of colloidal silica and ferric and aluminum hydroxides. More or less zinc may have been removed from 

solution by the same influence at this time. The solution, after being 

depleted of free sulphuric acid and ferric sulphate, would meet the 

same conditions as those considered in the next paragraph.

Where the solutions had become depleted of free sulphuric acid 

and ferric sulphate before reaching the carbonate rock, no layer of 

ferric oxide and kaolin would be formed at first, but replacement of 

the carbonate rock by zinc carbonate would occur. This reaction has 

usually been explained by the simple equation

ZnSO4+CaCO3 =ZnCO3 -f-CaSO4,

zinc carbonate being precipitated as smithsonite and calcium sulphate 

passing off in solution. This reaction, however, although it plays an 

important part in the process, is not sufficient to explain the entire 

metasomatic process involved in the deposition of the Leadville zinc 

carbonate ores. Direct replacement of calcium, magnesium, and manganese carbonates by zinc carbonate involves a high percentage of 

shrinkage; similar replacement of iron carbonate involves less but 

still considerable shrinkage. Some of the Leadville zinc carbonate 

ore of the first stage, as shown on page 38, presents some indications 

of shrinkage, but the amount is so much obscured by later processes 

of leaching and cavity filling that it can not be even approximately 

measured. Other specimens of the gray ore which show little or no 

evidence of leaching contain no pore spaces large enough to be detected with the high powers of the microscope, and the only evidence 

of shrinkage is the presence of microscopic fractures containing veinlets of smithsonite. The metasomatic process in this material, as shown 

on page 38, evidently proceeded by infiltration of the solution along 

the boundaries of the original carbonate grains and replacement of 

them from the boundaries inward, leaving a very small amount of indeterminable material (unreplaced carbonate?) in the center of each 

grain. The only conclusion warranted by such inconsistent evidence is that some shrinkage may have been developed during replacement but did not develop everywhere in an amount sufficient
GENESIS. 77

to correspond to the effects of a direct molecular replacement of 

dolomite or manganosiderite by the gray zinc carbonate ore.

This problem in metasomatism has been discussed by Lindgren,1 

who states:

Replacements of limestone by smithsonite within the rigid rocks are quite 

common, and in this case the mineral often reproduces exactly the texture of 

the original rock, even to the most minute details; the resulting secondary zinc 

mineral is compact and at least not more porous than the original limestone. 

If this replacement were effected according to a chemical equationfbe it by substitution of zinc for calcium in carbonate or by interchange of zinc sulphate 

and calcium carbonate, a reduction in volume should necessarily be expected. 

It does not take place provided the metasomatic action goes on within the 

mass of the rock itself.

It is therefore necessary to look to the mineralogic evidence in the 

ores for suggestions as to the metasomatic processes that took place. 

This evidence, presented in the ore descriptions, shows that both 

manganosiderite and dolomite were replaced by the gray zinc ore, 

also that after replacement of manganosiderite by ferruginous smithsonite had ceased fractures and other openings were partly or completely filled by smithsonite relatively free from iron.

The descending zinc solutions, depleted of free sulphuric acid and 

ferric sulphate and most or all of their alumina, contained principally 

zinc and ferrous iron, with minor amounts of manganese, alkalies, 

and alkaline earths, chiefly as sulphates and to a minor extent as 

bicarbonates. Silica was also present. The conditions of chemical 

equilibrium that exist when so complex a solution attacks the complex carbonate rock manganosiderite can be only roughly inferred 

from experimental data on relatively simple solutions and compounds. Lack of solubility is the predominating factor in determining the order of separation of the products of such a reaction.2 The. 

composition of the gray ore is proof that under the conditions here 

discussed zinc carbonate was the least soluble product. It is therefore concluded that the zinc in solution as sulphate replaced the 

bases of the manganosiderite, and that the zinc in solution as carbonate was also precipitated. Precipitation of zinc as smithsonite 

thus proceeded either until the manganosiderite was completely replaced or until the total zinc in solution became exhausted.

Any shrinkage due to replacement by reaction between zinc sulphate and manganosiderite is believed to have been compensated by 

simultaneous precipitation of the zinc carbonate from solution, as 

long as the supply of zinc and the carbonate radicle remained. If 

the supply was insufficient to compensate fully for shrinkage, a corresponding amount of shrinkage space in the gray ore must have '

1 Lindgren, Walclemar, The nature of replacement: Econ. Geology, vol. 7, p. 530, 191.2. 

2 Johnston, John, and Nlggli, Paul. The general principles underlying metamorphic 

processes: Jour. Geology, vol. 21, p. 506, 1913.
78 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

resulted. This space may later have been filled by precipitation from 

a new supply of solution, or modified, if not obliterated, by the effects 

of oxidation.

The constituents removed from the manganosiderite by this process, 

thus became, with the sulphate radicle, the principal constituents in 

solution and were presumably removed from the manganosiderite 

zone. Whether or not they could have reacted with and replaced 

dolomite is a question on which the writer has no definite evidence. 

The manganese and magnesium in the manganosiderite were evidently more soluble, or replaceable, than the iron, as shown by comparison of the analyses on page 47.

The replacement of iron carbonate by zinc carbonate is not in accordance with certain experimental data. Knopf,1 in his description 

of zinc carbonate deposits at Cerro Gprdo, in the Inyo Mountains of 

California, cites experiments by K. C. Wells that showed ferrous carbonate to be less soluble than zinc carbonate; but more recent experiments by Mr. Wells 2 have shown that the relative solubility or precipitability of the two carbonates differs according to the precipitant used. Thus if sodium carbonate is used in a sulphate solution 

of the two metals, zinc (carbonate) is precipitated before iron (carbonate) ; if sodium bicarbonate is used, the order is reversed. The 

precipitants, or replaced compounds, of the Leadville zinc ores were 

carbonates, not bicarbonates, and this fact in the light of Wells's 

experiments may be of some significance.

That both zinc and iron and possibly manganese are similarly precipitated by magnesium and calcium carbonates is shown by the composition of the zinc carbonate ores which have replaced dolomite.3 

In this case zinc, iron, and manganese carbonates were precipitated 

together, in varying proportions, which depended no doubt on their 

proportions in the solution.

This isomorphous character of the carbonate ore is of interest. 

The fact that the gray carbonate ore, although free from visible 

microscopic inclusions of manganosiderite, contains about 14 per cent 

of ferrous carbonate and smaller amounts of manganese, magnesium, 

and lime carbonates suggests that replacement of these carbonates 

by zinc carbonates can extend up to a certain limit but not to their 

complete elimination. The same feature may have been shown by the 

ore that replaced dolomite or limestone, but oxidation has obscured 

the evidence. The ratio of calcium carbonate to other carbonates in

1 Knopf, Adolph, Mineral resources of the Inyo and White mountains, Cal.: U. S. Geol. 

Survey Bull. 540, p. 107, 1914.

3 Personal communication.

8 No unoxidized carbonate ore replacing dolomite was seen by the writer at Leadville, but 

the ferric and manganese oxides in the brown ore are mostly or wholly the result of 

oxidation in place of gray (ferrous) zinc carbonate. In the Tintic district, Utah, the 

writer found gray zinc-iron carbonate ore replacing practically pure limestone (Econ. 

Geology, vol. 9, pp. 2-3, 1914).
GENESIS. 79 /

these ores is misleading, owing to the presence of calcite fillings of 

fractures and vugs of later origin than the replacement ore.

The progress and behavior of the solutions after deposition of the 

zinc carbonate could not be adequately studied underground, as the 

mine workings do not generally follow watercourses beyond the 

limits of ore bodies. The few such watercourses seen were stained 

by iron and manganese oxides, but these could hardly have been deposited directly from the waters that deposited the gray zinc ore. 

The waters after the replacement of manganosiderite must have' been 

sulphate waters containing principally iron and manganese, with 

some magnesium and small amounts of several other elements. It 

seems quite possible that they could cause a replacement of dolomite 

by manganosiderite, but no such replacement is known, and it is 

doubtful if such a secondary manganosiderite could be distinguished 

without microscopic study from the primary manganosiderite, which 

is clearly an intimate associate of the sulphide ores. It is doubtful 

if the neutral sulphate waters could cause any other chemical action. 

They would presumably pass on to ground-water level, if they had 

not already reached it, enriching the ground water in sulphates.

The relation of ore deposition to ground-water level is discussed on 

pages 64-66, where it is concluded that the gray zinc carbonate ore 

was deposited close to if not below water level. In this connection 

the following statement by Lindgren 1 is of interest:

Replacement by equal volume demands the nicest balance between solution 

and precipitation and takes place when the rock is permeated by stagnant or 

slowly moving solutions.

These conditions are satisfied below ground-water level and probably in the zone just above it. In arid regions similar replacement 

deposits are found well above the present ground-water level and are 

to be attributed either to the existence of a higher water level when 

replacement occurred, to local impounding of water above an impervious stratum, or to gradual exhaustion of the descending waters 

by permeation of the rock, with resulting slow movement and supersaturation, thus producing conditions of chemical equilibrium essentially the same as those already considered. The abundant precipitation at Leadville and the presence of sulphide bodies above gray 

zinc carbonate ore favor the conclusion that deposition of the zinc 

carbonate bodies on Carbonate Hill below the surface of ground 

water was quite possible. The ground-water level in fact may have 

aided the geologic structure in the concentration of these great bodies. 

In other places for example, in Iron and Rock hills deposition 

took place above the water level, the concentration and the size of 

the ore bodies being determined by the amount of zinc and other ele1 Lindgren, Waldemar, The nature of replacement: Econ. Geology, vol. 7, p. 531, 1912.
80 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

ments°in solution and by the rock structure, which influenced the slow 

or rapid movement of the descending solutions and the degree to 

which they cpuld permeate the rock.

SECOND STAGE.

It is not to be supposed that the processes of solution, transfer, and 

deposition already described were sharply separated in all respects 

from those that remain to be considered. The oxidation of zinc 

blende was accompanied by simultaneous oxidation of some pyrite 

and a little galena, arid the greater the amount of pyrite oxidized the 

greater the amounts of iron sulphates that took part in the different 

reactions; but the much greater susceptibility of zinc blende to oxidation caused its practically complete removal while large amounts 

of the other two sulphides remained. The first stage, marked by 

transfer and redeposition of the zinc, is thus distinct from the second stage, which was characterized by oxidation of the remaining 

pyrite and galena and by a working over of the newly formed zinc 

carbonate bodies.

The oxidation of the remaining pyrite, as before, caused generation 

of sulphuric acid and ferric sulphate; the oxidation of galena-to sulphate and finally to carbonate generated additional sulphuric acid. 

The presence of considerable amounts of jarosite and plumbojarosite, 

however, gives proof that a part of, the iron sulphates were deposited 

without further reactions of present significance and that not all the 

galena was finally changed to carbonate. The amount of sulphuric 

acid and ferric sulphate which succeeded in reaching the zinc carbonate bodies therefore represented only a part^of the quantity of 

pyrite and galena oxidized.

The sulphuric acid, on attacking the ferruginous zinc carbonate 

decomposed it, taking zinc and iron sulphates into solution. The 

iron sulphate, if free oxygen were present, oxidized to ferric sulphate, which, with the ferric sulphate already in solution, in turn 

attacked and replaced more of the zinc carbonate and was deposited 

itself as hydrate or hydrous oxide, thus forming or adding to the 

layer of iron oxide and kaolin at the top of the ore body. The zinc 

thus removed was carried in solution until it could again attack and 

replace manganosiderite or dolomite.

The principal work of the second stage, therefore, was a slight 

downward migration of the zinc carbonate bodies, material removed 

from their upper parts being added to their lower parts. The extent 

of migration obviously depended on the amounts of pyrite and 

galena oxidized.
GENESIS. 81 

THIRD STAGE.

The third stage includes the operation of those processes which 

have been active since the decomposition of the original sulphides. 

The principal agents were oxygen and carbon dioxide, which, as lowering of the surface by erosion progressed, became more and more 

abundant.

Oxygen on reaching the gray carbonate ore oxidized the iron and 

manganese, causing the formation of red or brown ferric oxide and 

the zinc-manganese oxide, hetaerolite, the zinc carbonate recrystallizing in a relatively pure state. The iron oxide, to judge from the 

many specimens of brown ore studied, tended to remain in place, 

while the new smithsonite and hetaerolite migrated short distances to 

fractures and other openings to form druses or complete fillings.

This process shows that the smithsonite and hetaerolite were to 

some extent soluble in the solutions, and that although they were for 

the most part quickly redeposited, small amounts of them may have 

been carried for considerable distances. The free carbon dioxide in 

the water also had a tendency to dissolve the carbonate ore and carry 

the zinc as bicarbonate, the iron and manganese separating out as 

oxides. The combined effect of the oxygen and carbon dioxide was to 

induce a slow downward migration of the zinc carbonate bodies and 

a corresponding thickening of the layers of iron oxide and clay at 

their tops.

After the exhaustion of carbon dioxide to a certain degree silica 

became the active acid radicle, uniting with zinc to form calamine, 

the latest of the more abundant zinc minerals. The character of different calamine aggregates shows that the zinc and silica were for 

the most part carried in solution and the calamine was deposited in 

openings as a result of supersaturation; on the other hand, replacement of smithsonite by calamine shows that a part of the zinc was 

derived in place and the silica introduced in solution. The source of 

the silica is to be referred especially to the porphyry overlying the 

original sulphide bodies. Small amounts of silica may also have 

been derived from the gangue of these ore bodies and from the original carbonate rocks.

The conditions of equilibrium governing the deposition of calamine are not well understood.1 It is evident from paragenetic study 

that calamine can not form until smithsonite (the late drusy form) 

has finished crystallizing; on the other hand, it is also evident that

1 Since this paragraph was written experiments to throw light on the conditions affecting the deposition of calamine have been made by Y. T. Wang (The formation of the 

oxidized ores of zinc from the sulphide: Am. Inst. Mln. Eng. Bull., September, 1915, 

pp. 1988-1991). He found that calamine is soluble In water containing carbon dioxide 

and even more soluble in water containing bicarbonate of zinc as well. These results 

agree with the fact that calamine at Leadvllle is deposited after smithsonite.

52757° Bull. 681 18 6
82 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

calamine can, under certain conditions, replace smithsonite. Why. 

smithsonite is the less soluble in one case and the more soluble in the 

other is not clear. There is no reason for supposing that silica was 

not present while the smithsonite was being deposited. A reasonable 

inference is that crystallization of smithsonite, once started, continued for a time after the equilibrium point was passed, and that 

the smithsonite was later redissolved by the now more stable calamine. Another conjecture is that, as the solution, through prolonged permeation, became more concentrated, silica superseded carbon dioxide as the stronger acid radicle in other words, whereas 

smithsonite was the more insoluble mineral in the dilute solution, 

calamine was the more insoluble in the concentrated solution.

The occurrence of small amounts of zinciferous clay closely associated with calamine shows that the two were deposited at about the 

same time. These small amounts of clay may be attributed to alumina, which is commonly present with silica in mine waters of the 

oxidized zone and was derived from the same sources; but in this 

case the occurrence of the clay as one of the latest minerals is rather 

surprising, especially as the waters that deposited it appear to have 

been pratctically free from sulphates. Some of the clay however, has 

evidently resulted from chemical precipitation and suggests that 

aluminum can be held in solution until the waters become concenQ

trated by depletion, when, in the presence of silica and zinc, it is 

precipitated as zinciferous clay.

Another interpretation is that the clay was in reality precipitated 

at an earlier stage and carried in suspension for indefinite distances 

until finally it was deposited in openings where the waters became 

stagnant, the zinc content being due to replacement of the aluminum 

in the clay. This suggestion could be applied to the clay fillings in 

fractures and fissures. Such fillings may have been formed during 

the first two (sulphate water) stages, and if they were the chemistry 

of deposition could be regarded as generally similar to the processes 

outlined in the preceding pages.

Failure to find any conspicuous occurrences of hydrozincite prevents an adequate discussion of its place and significance in the 

genesis of the Leadville deposits. The writer, in his study of the 

Tintic zinc ores,1 found that hydrozincite as a rule followed the 

drusy smithsonite and therefore belonged to the same period of 

crystallization as calamine. This paragenetic relation is in accord 

with experimental evidence,2 which shows that when carbon dioxide

1 Econ. Geology, vol. 9, pp. 3, 7, 1914. Where hydrozincite in the Tintic district 

alternated with drusy smithsonite, the later smithsonite was evidently deposited from a 

new supply of solution, and this was in turn followed by renewed deposition of hydrozincite.

2 Raikow, P. N., Weitere Untersuchungen ttber die Einwirkung der Kohlensaure auf die 

Hydrate der Metalle: Chem. Zeitung, vol. 31, p. 55, 1907.
GENESIS. 83

is present in the solution in excess the carbonate of zinc, smithsonite, 

will crystallize, but that when carbon dioxide is not in excess the basic 

carbonate, hydrozincite, will crystallize. This principle applied to 

the waters at Leadville would imply that as the solutions diminished 

in volume, owing to their spreading along fractures or to permeation 

through the ore bodies, they lost their excess of carbon dioxide. 

Smithsonite therefore would cease to form, and the remainder of 

the zinc carbonate would crystallize as hydrozincite. According to 

this principle, hydrozincite should be found coating druses of smithsonite and lining fractures below the limits of smithsonite deposition, also as a local alteration product where water containing no free 

carbon dioxide succeeded in causing recrystallization of smithsonite.1

The aurichalcite in the Ibex mine accords with this interpretation. 

The aurichalcite was deposited at the same time as calamine, and 

both were formed later than drusy smithsonite. Evidently the solution, locally impounded in cavities in the ore, lost its excess of carbon dioxide. The copper and a corresponding amount of zinc then 

crystallized as the basic carbonate, aurichalcite, and the rest of the 

zinc went to form calamine. Any excess of silica over that required 

to form calamine was deposited as opal, chalcedony, or quartz coating or inclosing the calamine crystals.

After the waters had become depleted of zinc carbonate and silicate calcite was deposited in small amount, though only in a few 

places, as the final product of the third stage. As nicholsonite and 

aragonite were not found within the ore, they can not be assigned 

to a definite place in the sequence. Both minerals crystallized in 

openings in limonite, and from their mode of occurrence would 

appear to belong to the later part of the third stage of deposition 

that is, to the calamine-calcite period but their relations to calamine, hydrozincite, aurichalcite, and calcite are not known.

The third stage of transfer and redeposition is still in progress. 

Remnants of gray carbonate ore are undergoing oxidation, and the 

other zinc minerals are doubtless slowly forming at their expense. 

These minerals also are being subjected to further leaching and 

redeposition, and even calamine, the latest of the abundant zinc 

minerals, may be found in places with corroded surfaces, which 

signify that slow leaching and continued downward migration are 

still going on.

SUMMARY.

The detailed discussion of genesis may be briefly summarized as 

follows:

1 Since this statement was written Philip Argall (Min. Mag., vol. 10, flg. 4, p. 285, 1914) 

has published an illustration of a specimen taken from a flssure cutting the lower beds of 

White limestone in the Maid of Erin mine. The specimen consisted of fibrous (drusy) 

smithsonite covered by a coating of hydrozincite an eighth of an inch thick.
84 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

In the first stage ferruginous zinc blende (marmatite) was decomposed by sulphate waters, which also contained carbon dioxide. 

Where the solutions containing zinc and iron sulphates and smaller 

quantities of other salts passed through porphyry any free sulphuric 

acid and ferric sulphate decomposed sericite and feldspar and later 

deposited the alumina, silica, and zinc as zinciferous clay, either 

along fissures in the porphyry or by replacing limestone just beneath 

the porphyry. Where the zinc solutions passed from the sulphide 

body into limestone any free sulphuric acid at once became neutralized and ferric sulphate was precipitated as ferric hydrate, which 

replaced the limestone and formed part or all of the characteristic 

layers that separate the zinc from the lead-silver stopes. If no free 

sulphuric acid or ferric sulphate was present, no such layer was 

formed at this time. The neutral solution, then caused replacement 

of carbonate rock, both manganosiderite and dolomite, by gray 

smithsonite. In the manganosiderite greater proportions of magnesia and manganese than pf iron carbonates were replaced. Deposition of the smithsonite took place, at least in part, not so much by 

direct reaction between the carbonates and a molecularly equivalent 

amount of zinc sulphate as by a volume for volume interchange. 

In the replacement of dolomite the magnesia and lime appear to 

have been replaced simultaneously by zinc and iron carbonates. The 

replacement of the carbonate rocks was effected by stagnant or 

slowly moving solutions, which in the northern part of Carbonate 

Hill may-have been close to or even below the level of ground water. 

Elsewhere the replacement occurred well above the water level.

The second stage was characterized by decomposition of the pyrite 

and galena that survived the first stage. The resulting sulphuric acid 

and ferric sulphate that reached the newly formed zinc carbonate 

bodies tended to leach and replace their upper portions, with, a 

corresponding thickening of the iron oxide layers at their tops, and 

to remove the dissolved materials to the lower ends of the ore bodies, 

where additional replacement of carbonate rock could occur. The 

final result of processes active during the second stage was a greater 

or less downward migration of the zinc carbonate bodies, the extent 

of migration depending on the amount of sulphuric acid and ferric 

sulphate available at any particular place.

The third stage includes the changes that took place after the 

sources and supplies of sulphuric acid and ferric sulphate had become practically exhausted, leaving carbon dioxide and oxygen as 

the principal active agents. These attacked the gray zinc carbonate 

ore, oxidizing its iron to red or brown ferric oxide and its manganese 

and some zinc to hetaerolite and recrystallizing a part of the remaining zinc carbonate into drusy smithsonite. Although these changes 

were mostly brought about with very little transfer of material,
PROSPECTING. . . 85

there was probably a slight tendency to downward migration of the 

ore bodies and corresponding thickening of the overlying iron oxide 

layers. After the work of oxygen and carbon dioxide had been 

mostly accomplished and the excess of carbon dioxide had escaped, 

small amounts of aurichalcite and hydrozincite were formed. At 

about the same time silica succeeded carbon dioxide as the dominant 

acid radicle and caused the deposition of calamine, mostly as cavity 

fillings but to a minor extent replacing smithsonite. Where aluminum was locally an abundant constituent of the solutions at this 

period small amounts of zinciferous clay were deposited in cavities 

along with or in place of calamine. If silica was present in excess, 

small amounts, of opal, chalcedony, or quartz were deposited after 

the'calamine. Calcite and probably also aragonite and nicholsonite 

were deposited later than the calamine, representing the latest of the 

succession of minerals in the oxidized zinc ore bodies. Oxidation of 

the third stage, however, is still in progress.

PROSPECTING FOR BODIES OF OXIDIZED ZINC ORE.

The more consideration one gives to the factors chiefly concerned 

in the genesis and distribution of the oxidized zinc ore bodies, the 

more hesitant is he likely to become in any attempt to predict the 

location of undiscovered bodies. It is obvious that the zinc bodies 

are intimately associated with the old lead-silver stopes, but their 

exact positions, shapes, and sizes depend upon too many variable 

factors to be determined without actual prospecting. In the 'first 

place, the distribution of zinc blende in the original sulphide 'bodies 

was very irregular, as it is in the sulphide bodies now being mined.

In some ore bodies zinc blende although abundant, may have been 

accompanied by even more abundant pyrite, as in most of the present 

sulphide bodies. In such deposits the effects of the first and second 

stages of oxidation may have removed the bulk of the zinc a considerable distance from the corresponding lead-silver body, the intervening space being occupied by iron oxide or " contact matter." 

Whether such prolonged transfer would result in greater concentration or dispersion of the zinc would depend upon local structures. 

Local concentrations may be represented by some of the Chrysolite 

bodies (fig. 7, p. 57) found a considerable distance below the stopes 

shown in Emmons's sections and just above the upper contacts of 

porphyry sills.1

In other ore bodies .a shoot of zinc blende may have existed side 

by side with one of pyrite, and oxidation with downward migration 

may have resulted in the formation of zinc carbonate and iron oxide

1 Emmons, S. P., Geology and mining Industry of Leadvllle, Colo.: U. S. Geol. Survey 

Mon. 12, atlas sheets 31 and 32, 1886.
86 OXIDIZED ZINC ORES OF LEADVILLE, COLO.

bodies side by side. Oxidation of manganosiderite beside or even 

beneath the zinc carbonate bodies may also have yielded iron oxide 

or manganese-iron oxide bodies, but oxidation beneath the zinc ores 

was doubtless of relatively infrequent occurrence and small extent.

At some places the rock underlying original sulphide bodies may 

have contained much siliceous matter and correspondingly little' 

carbonate material. In such places the smithsonite, deposited by 

replacement of the carbonate content, may have formed low-grade 

ore bodies of considerable extent or local shoots where fissuring or 

shattering permitted thorough permeation of the elsewhere relatively impervious rock. Descending solutions from siliceous ore 

bodies may have been unusually rich in silica and alumina and deposited them in some form along with the zinc, thus giving ore of 

low grade. Such conditions may account for the characteristics of 

the ore bodies in the Tucson mine and of some ore bodies in the 

Chrysolite mine.

The influence of local structure has been illustrated on pages 54-56, 

and only summarized statements need be made here. Faults and 

strong fissures, if filled with impervious material or if bringing impervious or nonreplaceable beds opposite replaceable beds, may serve 

to impound the solutions and develop an ore body of unusual thickness; faults and fissures of similar magnitude, if open and very 

pervious, may serve to concentrate the flow of solutions along them 

and give rise to deposits of general veinlike form. If solutions 

traveling along open fissures pass beyond the limits, of the carbonate 

rocks before effecting much replacement, it is probable that no workable deposits will be formed by them. Impervious rock layers, such 

as the quartzites and porphyries, may confine replacement to the limestone above them; but the same rocks, if fractured, may 'allow the 

solutions to pass into or through them. Where solutions penetrate 

Cambrian quartzite or thick masses of porphyry in this manner their 

zinc contents are not likely to be concentrated into workable deposits. 

If solutions find their way into a large body of rock which is chemically replaceable but only slightly permeable and which is not immediately underlain by some impervious bed, the solutions are likely to 

become dispersed and to yield an extensive body of low-grade ore or 

a series of shoots too small for profitable mining.

These many and varying conditions should convince operators that 

the more they know of the significance of structural details of their 

ground the more intelligently can they prospect for zinc ores. They 

should realize that large bodies of high-grade ore are to be found 

only where the original supply of zinc, local structural conditions, 

and the composition of the country roek have all been favorable. 

The area covered by the numerous and extensive oxidized lead-silver
PROSPECTING. 87

stopes in the district, extending from the western edge of the Downtown section eastward to Ball Mountain and from Fryer Hill southward to Rock Hill, is legitimate prospecting ground for oxidized zinc 

ores, but it remains for those most familiar with the details of 

individual mines or claims to formulate the best methods of prospecting. Furthermore, especially where ground has been abandoned for 

a long time and detailed knowledge of it is slight, prospectors should 

be ever on the lookout for new and unexpected evidence and should 

modify their methods accordingly.

INDEX.

Page.

Acknowledgments for aid 7 

Alkalies, solution and deposition accelerated by_ _ 70-71 

Aragonite, genesis of_ _ 83 

in brown Iron oxide, plate showing _ 25 

occurrence of_ _ 30 

paragenesis of 35-36 

Argall, G. 0., paper by___ 16 

Argall, Philip, paper by 16-17 

Aurichalcite, deposits of, with brown 

zinc carbonate «. ore, 

plates showing ____ 24 

description of____ _ 19-20 

genesis of _ 83, 85 

paragenesis of_____ _ 35

Barite, occurrence of___ 31 

paragenesis of_ __ 34 

Belgian mine, oxidized zinc ore in__ 53-54 

Bibliography. See Literature. 

Blanket stopes, relation of, to oxidized zinc ore 51-52 

Blow, A. A., cited_____ ___ 10 

Bradley, W. M., analysis by 23 

Ford, W. E., and, on the properties of hetaerolite 21-22 

Breece Hill, oxidized zinc ore from_ 14 

Butler, B. S., cited __ 68 

Butler, G. M., analyses by 49 

cited___________ 30-3.1, 50 

on determination of the grade

of ores_____ 48-50 

paper by 16

Calamine, deposits of, with brown 

zinc carbonate ore, 

plates showing- 18, 21, 24 

description of_____ _ 20-21 

genesis of ________ 81-82, 85 

paragenesis of 35 

relations of, to other ore minerals- ___ 43 

Calcite, genesis of ____ __ 83 

occurrence of 30 

paragenesis of 35 

replacement of, by zinc carbonates 78-79 

Carbonate Hill, oxidized zinc ore

from________ 11,13,14 

position and shape of ore bodies

in_____________ 57-61 

zinc in wall rock of .... 61, 62

Page. 

Carbonate Hill section, unwatering of __________ 15, 16

Carbonate ore, deposition of_____ 74, 75 

failure to recognize_______ 8-9 

replacing manganosiderite, photomicrograph of____ 19 

reworking of _________ 80, 84 

brown, analyses of___^___ 49 

chemical composition of- 44-46, 47 

megascopic features of__ 40-42 

microscopic features of_ 42-44 

plates showing__ 18, 20, 21, 24 

gray, analyses of_ _____ 49 

chemical composition of- 39-40, 47 

genesis of _ _____ 76-79

Inclosing sulphide, photomicrograph of ____ 19 

megascopic features of __ 36-37 

microscopic features of__ 37-38 

occurrence of ________ 36 

plate showing________ 18 

red, analysis of________ 47 

Chalcedony, genesis of ________ 83

occurrence of ____________ 32

Chalcophanite coating brown zinc 

carbonate ore, plate 

showing-- ______ 18 

description of ______ _ 24 

paragenesis of __________ 34 

Chert, occurrence of___ __ _ 32 

paragenesis of __________ 34 

Chinese talc, zinc ore resembling__ 9 

Chrysolite mine, position of ore

bodies in________ 57

Clay, zinciferous, analyses of____ 26

deposition of_________ 73-74,

76, 81, 82, 84, 85 

description of______ __ 24-28

paragenesis of _ __ _ 35 

plate showing _ _ 25 

Cord Mining Co.'s workings, oxidized

zinc ore in ____ 52-53 

Curley, John R., acknowledgment to_ 7

Deposition of oxidized materials _ 72-80

Depth of oxidation ____ ______ 64-6«

Deschenite, occurrence of______ 28

Discovery of oxidized zinc ores __ 7-13

Distribution of zinc ores ____ 51-68

Dolomite, occurrence of _____ 29

paragenesis of ___.__ _ 34

89
90 INDEX.

Page. 

Dome mine, position of ore bodies

in_____ 56 

Downtown section, unwatering of 15, 16

Emmons, S. F., cited___ 8-9,11

and Irving, J. D., cited-- _ 10

Emmons, W. H., cited _____ 67-68, 70

Fairchlld, J. G., analysis by 47 

Ford, W. E., and Bradley, W. M., on 

properties of hetaerolite.___________ 21-22 

Fryer Hill, oxidized zinc ore from_ 11,14 

Fryer Hill section, unwatering of 15, 16

Galena, occurrence of_ 33-34 

Genesis of oxidized zinc ores _ 68-85 

Goslarite, deposition of 72, 73 

Grade of ores, determination of_ 48-50 

Ground-water level, deposition above

and below____ 79-80, 84 

relation of ore bodies to 65-66

Haigh, G., analysis by 23

Hetaerolltc, analyses of - 23

description of ________ 16, 21-23

genesis of _ ____ 81, 84

paragenesis of __ : 34 

Hillebrand, W. F., analyses by 26, 31 

Horseshoe district, oxidized zinc ores

In_____________ 12

Hydrozlncite, description of 18-19

genesis of _______-___82-83, 85

Ibex Co., acknowledgment to_ 7 

Ibex mine, position of ore body in__ 56 

zinc in waif rock of 62 

Iron, content of, in zinc ores _ 50 

Iron carbonate, replacement of, by

zinc carbonate ___ 78, 84 

Iron Hill, oxidized zinc ore from_ 14 

Iron ores, manganlferous, relation

of zinc ore bodies to_ 64 

oxidized, relation of

zinc ore bodies to 64 

Iron oxide, brown, aragonite in cavities in _ 25 

deposition of ___ 75-76 

genesis of ___ 80, 81, 84 

origin and occurrence of 28-29 

paragenesis of __ : 34 

Iron Silver Co., acknowledgment to_ 7 

Iron sulphide, oxidation of 80/84

Kaolin, genesis of _ _ 73-74, 76, 80 

occurrence of__ _ ___ ' 33 

paragenesis of 34

Kleff, John, acknowledgment to_ 7

Lead carbonate deposits, relation of,

to oxidized zinc ore__ 51-54 

Lead sulphide, oxidation of _____ 80, 84 

Lindgren, Waldemar, cited------ 68, 77, 79

Literature of the subject 16-17

Page.

McDonald, J. B., cited________ 12 

Maid of Erin mine, position of ore

bodies in________ 54 

zinc in wall rock of_______ 62 

Magnesium carbonate, replacement

of, by zinc carbonates. 78- 

79, 84 

Manganese carbonate, replacement

of, by zinc carbonates. 78- 

79,84 

81 

29 

34 

47 

29 

34

Manganese oxide, genesis of______

occurrence of____'______

paragenesis of ______ 

Manganosiderite, analysis of___ 

occurrence of_________ 

paragenesis of _________

replacement of, by zinc carbonate________ 76-79, 84 

photomicrograph showing_ 19 

Marmatite, composition of______ 69 

May Queen mine, oxidized zinc ore

from___________ 12 

Minerals associated with oxidized

zinc ores-_____ 17, 28-34 

Minerals of oxidized zinc ores __ 17-28 

Monarch, Colo., zinc ores from___ 12 

Moore, G. E., discovery of hetaerolite by _______ 21

New Dome mine, zinc in wall rock

of ______ 62

Nlcholsonite, description of_____ 30-31 

genesis of ______ 83 

paragenesis of _______ 35-36

Opal, genesis of ___i__ 83 

occurrence of ________ 32

Ore, black, features of _______ 46-47

high-grade, location of_____ 86-87

low-grade, formation of____. 86

prospecting for ________ 85-87

relations of, to lead carbonate

and mixed sulphide

deposits__________ 51-54

resemblance of waste to____ 48

varieties of___________ 36-47

white, nature of_ __1____ 47

Ore bodies, original, constituents of_ 69 

rocks bounding _'!' ___ 61-63 

shapes and sizes of_______ 54-61 

upper contact of ________ 63

Oro La Plata mine, position of ore

bodies in ___ _ 54

Oxidation, depth of _________ 64-66

Oxidation of sulphides, order of__ 69-70

Page, Warren F., acknowledgment to 7 

Palache, Charles, on the properties

of hetaerolite _____ 21 

Palmer, Chase, analysis by__'____ 23 

Paragenesis of the minerals- _ 34-36 

Penrose mine, zinc carbonate ore

from, tenor of_L_____ 16 

Platt, , acknowledgment tb"l«___, 7
INDEX. 91

Page.

Plumbojarosite, features and occurrence of______ 31-32 

Porphyry, ore bodies covered by 70 

oxidizing agents derived from 70 

sericitized, action of oxidizing

solutions on 73, 84 

Printer Boy hill, oxidized zinc ore

from . 14 

Prospecting, suggestions for 85-87 

Production of oxidized zinc ore 13-16 

Pyrite, influence of, on redeposition

of zinc_ 85

Quartz, genesis of 

' occurrence of 

paragenesis of_

83

32

34

Reduction of oxidized zinc ores,

plant for________ 15-16

Robert E. Lee mine, zinc carbonate

from_ ' VL

Rock Hill, oxidized zinc ore from 14

Schaller, W. T., analysis by ___ 23

Sericite, occurrence of 33

paragenesis of 34

Shrinkage, compensation of 77-78

small amount of _ 76-77

Silica, metamorphlc action of 81-82, 85

occurrence of 32

opaline, in brown zinc ore, plate

showing _ 24 

paragenesis of 35 

Silver, content of, in zinc ores 50-51 

native, occurrence of 34 

paragenesis of 34 

Smelter products, zinc in 9 

Smithsonite, description of 17-18 

druses of, on brown zinc carbonate ore, plates showing 20 

genesis of _______ 76-79, 81-82, ts4 

paragenesis of 34 

Specific gravity of ores, determinations of _ 48-49 

Stelger, George, analyses by 26 

Stokes, H. N., experiments by, on 

the precipitation of 

zinc sulphide 67

' Page.

Sulphide, zinc, precipitation of, by

iron sulphide 66-68 

Sulphides, occurrence of 33-34 

order of oxidation of__ _ 69-70 

paragenesis of _ 34 

relation of, to oxidized zinc ore_ 51-54 

secondary, lack of association

with oxidized ores____ 66-68 

solution of, by descending

waters ____ 71-72

Talc, ore, occurrence of 47 

Tucson mine, position of ore bodies

in ____ ________ 56

Unwatering

Wall

of Downtown, Fryer 

Hill, and Carbonate 

Hill sections______ 15, 16

rock, replacement of, by 

oxidizing solutions 

zinc in_ _ _______

Wang, Y. T., paper by_____________

Warwick, A. W., analyses by_______

Waste rock, resemblance of. to ore 

Wells, R. C., acknowledgment to___

analyses by_________

Western Mining Co., acknowledgment to _ 

ainc carbonate ore bodies in 

workings of, plates 

showing __ _ 

Western Zinc Mining & Reducing 

Co., plant of _____

Western Zinc Oxide Co., operation 

by- _ ______

Wolftone mine, oxidized zinc ore 

from________________

" Wolftonite." See Hetaerolite. 

Wurtzlte, secondary deposition of _

74-75

61-63

17

69

48

7

26,47

58,60 

15

15-16

12,13

68

Yak Co., acknowledgment to

Zinc, content of, in ores_______ 48-50 

Zinc blende, decomposition of by

oxidizing solutions__ 71-72

downward removal of ___ 8-11

Zinc ores, leaching of ___ 8-11

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