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Economic Significance

GEOLOGICAL SlfRV&Y £S SlOS AL PA1»EPR 710

Jasperoid in the United StatesIts Characteristics, Origin, and 

Economic Significance

By T. G. LOVERING

GEOLOGICAL SURVEY PROFESSIONAL PAPER 710

Jasperoid consists dominantly of quarts replacing 

older host rocks, commonly limestone or dolomite. 

It is a useful ore guide in many mining districts

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

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY

H. William Menard, Director

First printing 1972 

Second printing 1978

For sale by the Branch of Distribution, U.S. Geological Survey, 

1200 South Eads Street, Arlington, VA 22202
CONTENTS

Page

Abstract .................................................................................... 1

Introduction .............................................................................. 2

Purpose and scope of the investigation ...................... 2

Definition of jasperoid .................................................. 2

Acknowledgments ............................................................ 3

Distribution of jasperoid ...................................................... 3

Geographic distribution ................................................ 3

Geologic distribution ...................................................... 6

Host rock .....................................................,..........._ 6

Structural control .................................................. 6

Geologic age .............................................................. 6

Physical properties of jasperoid ........................................ 7

Megascopic features ...................................................... 7

Color ......................................................................... 7

Texture ...................................................................... 7

Associated minerals ................................................ 9

Microscopic features ...................................................... 9

Grain size ................................................................ 9

Fabric texture ........................................................ 11

Accessory minerals ................................................ 15

Other physical properties ............................................ 29

Density and porosity .............................................. 29

Differential thermal analysis ................................ 30

Composition of jasperoid ...................................................... 30

Major constituents ........................................................ 30

Minor constituents .......................................................... 34

Genesis of jasperoid ................................................................ 35

Source of silica ................................................................ 35

Solution and transportation of silica .......................... 36

Solubility of various forms of silica in pure

water at low temperature and pressure.......... 37

Solubility of various forms of silica in pure

water at higher temperature and pressure .... 37

Solubility of various forms of silica in 

aqueous solutions at low temperature and

pressure ................................................................ 39

Solubility of various forms of silica in 

aqueous solutions at higher temperature

and pressure ........................................................ 40

Summary .................................................................. 41

Composition of natural silica-bearing solutions ........ 41

Deposition of silica ........................................................ 43

Deposition at low temperature ............................ 43

Deposition at high temperature ............................ 44

Genesis of various forms of silica in

jasperoid ................................................................ 45

Replacement of host rock by silica ............................ 46

Physical factors ...................................................... 46

Chemical factors .................................................... 48

Theory of replacement process ............................ 49

Jasperoid as a guide to ore .................................................. 50

Definition of favorable and unfavorable jasperoid.... 50

Methods of data analysis .............................................. 51

Comparison of megascopic characteristics .............. 53

Comparison of microscopic characteristics .............. 54

Comparison of other physical properties .................. 54

Comparison of chemical composition .......................... 55

Jasperoid as a guide to ore Continued

Summary of criteria for evaluation of jasperoid 

samples ........................................................................

Characteristics of jasperoid in major mining districts 

of the United States ......................................................

Tri-State district, Oklahoma, Kansas, and

Missouri ......................................................................

Clifton-Morenci district, Arizona ..............................

Bisbee (Warren) district, Arizona ............................

Ely (Robinson) district, Nevada ..............................

Leadville district, Colorado ........................................

Tintic and East Tintic districts, Utah ......................

Gilman (Red Cliff) district, Colorado ......................

Aspen district, Colorado ..............................................

Eureka district, Nevada ..............................................

Summary of jasperoid in the major districts ..........

Characteristics of jasperiod in other than the major 

mining districts of the United States ..........................

Alabama ................................................................. .. .

Alaska ................................................. ..........................

Southern Seward Peninsula area ......................

Salmon River district ..........................................

Arizona ............................................................................

Banner district ......................................................

Cameron area ........................................................

Courtland-Gleeson district ..................................

Jerome district ......................................................

Pima district ..........................................................

Other occurrences ..................................................

Arkansas ..........................................................................

Northern Arkansas zinc-lead district ..............

California .........................................................................

Darwin district ......................................................

Bidwell Bar district ...............................................

Ivanpah district ....................................................

East Shasta district ...............................................

Other occurrences .................................................

Colorado ...........................................................................

Horseshoe-Sacramento district ..........................

Kokomo district .....................................................

La Plata district ...................................................

Pando area .............................................................

Rico district ...........................................................

Uncompahgre district ...........................................

Other occurrences ...................................................

Georgia ............................................................................

Cartersville district ...............................................

Other occurrences ...................................................

Idaho ..................................................................... ...... 

Illinois, Iowa, Kentucky, and Wisconsin ...................

Upper Mississippi Valley district .......................

Kentucky-Illinois district ......................................

Central Kentucky district .....................................

Michigan .......................................................... .................

Missouri ...........................................................................

Southeastern Missouri district ...........................

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in
IV CONTENTS

Page

Characteristics of jasperoid in other than the major 

mining districts of the United States Continued

Montana ............................................................................ 107

Phillipsburg district .............................................. 108

Nevada .............................................................................. 108

Atlanta district ........................................................ 108

Bald Mountain district ............................................ 110

Boyer district .......................................................... 110

Candelaria district .................................................. 110

Cedar Mountain district ........................................ Ill

Cherry Creek district ............................................ Ill

Contact district ...................................................... Ill

Cortez and Mill Canyon districts ........................ Ill

Delmar district ........................................................ 112

Dolly Varden district ............................................ 112

Dyer district ............................................................ 113

Ferguson district .................................................... 113

Getchell mine area (Potosi district) ................ 114

Gilbert district ........................................................ 114

Goodsprings district .............................................. 114

Groom district .......................................................... 115

Kern district .................... ...................................... 115

Lewis district ............................................................ 115

Manhattan district ............ ................................... 116

Mineral Hill district .............................................. 116

Patterson district .................................................... 116

Santa Fe district ...................................................... 116

Silverhorn district .................................................... 117

Silver Peak district ................................................ 117

Taylor district ....................................................... 117

Tecoma district ........................................................ 119

Ward district and West Ward area .................. 119

White Pine (Hamilton) district .......................... 121

Willow Creek district .............................................. 122

Wyndypah district .................................................. 122

Other occurrences .................................................. 122

New Mexico ...................................................................... 123

Bishop Cap district ................................................ 124

Carpenter district .................................................. 125

Cooks Peak district .................................................. 125

Cuchillo Negro district .......................................... 125

Hadley (Graphic) district .................................... 125

Hermosa (Sierra Caballos) district ................ 126

Hillsboro district .................................................... 126

Kingston district ...................................................... 126

Lake Valley district ................................................ 126

Magdalena district .................................................. 127

Organ district ........................................................ 127

Santa Rita district .................................................. 128

Steeple Rock district ................................................ 128

Tierra Blanca district ............................................ 128

Tres Hermanas district ........................................ 129

	Page

Characteristics of jasperoid in other than the major 

mining districts of the United States Continued

Victorio district ...................................................... 129

Other occurrences ............................................ 129

North Carolina and South Carolina ............................ 130

Pennsylvania and New Jersey .................................... 130

Friedensville district .............................................. 131

Other occurrences .................................................. 131

South Dakota .................................................................... 131

West Lead district .................................................. 132

Ragged Top Mountain district ............................ 133

Carbonate district .................................................. 134

Tennessee .......................................................................... 134

Bumpass Cove district .......................................... 134

Eastern Tennessee zinc district ............................ 134

Central Tennessee district .................................... 135

Other occurrences .................................................... 135

Texas .................................................................................. 135

Shafter district ........................................................ 135

Eagle Mountains district ...................................... 136

Other occurrences .................................................... 136

Utah .................................................................................. 137

Bingham district ...................................................... 137

Bull Valley (Goldstrike) district ........................ 139

Clifton district .......................................................... 139

Drum Mountains (Detroit) district .................... 139

Dugway district ...................................................... 140

Gold Hill district .................................................... 140

Lucin district .......................................................... 142

Mercur and Ophir districts ................................ 142

Mount Nebo district ................................................ 143

North Tintic district .............................................. 144

Rush Valley (Stockton) district ........................ 144

San Francisco district and vicinity .................... 144

San Rafael Swell area ............................................ 145

Silver Islet district .................................................. 146

Tutsagubet district ........................................... .. 146

Other occurrences .................................................. 146

Virginia and West Virginia .......................................... 147

Austinville district .................................................. 147

Howell mine area .................................................... 147

Timberville district .......................................... .. 147

Other occurrences .................................................... 147

Washington ........................................................ ..... 148

Metaline district ...................................................... 148

Other occurrences .................................................. 149

Wyoming .......................................................................... 149

Miller Hill area ........................................................ 149

References cited ............................................... .......... . 149

Index .......................................................................................... 157

ILLUSTRATIONS

Page

FIGURE 1. Map showing jasperoid-bearing localities and provinces of the conterminous United

States ............................................................................................................................................ 4-5

2. Photographs: A, Typical outcrop of jasperoid; B, Hand specimen of jasperoid showing preservation of primary bedding texture ........................................................... ... 8

3. Diagram showing mean size and size range of jasperoid grains in 200 samples .............. 10
CONTENTS

Page

FIGURE 4. Diagram showing frequency distributions of mean size and size range of jasperoid

grains ............................................................................................................................................ 11

5-13. Photomicrographs of jasperoid showing 

5. Typical jigsaw-puzzle texture .......................................................................................... 11

6. Typical xenomorphic texture ............................................................................................ 11

7. Granular texture .................................................................................................................. 12

8. Feathery and fibrous textures .......................................................................................... 13

9. Reticulated texture .............................................................................................................. 13

10. Stages in the replacement of limestone by jasperoid .............................................. 14

11. Typical calcite dust-sized particles ................................................................................ 14

12. Incipient jasperoid in dolomite ........................................................................................ 15

13. Selective replacement of calcite containing dolomite ................................................ 15

14. Photograph (A) and photomicrograph (B) of jasperoid contact with limestone ............ 16

15-31. Photomicrographs of jasperoid showing 

15. Ghost colloform banding .................................................................................................... 17

16. Zoned allophane inclusions ................................................................................................ 17

17. Chert and fine-grained jasperoid cemented by coarser grained jasperoid .......... 17

18. Veinlet of fine-grained quartz cutting coarse-grained jasperoid matrix .......... 18

19. Brecciated chert cut and cemented by coarser quartz ............................................ 18

20. Barite veinlet cutting jasperoid ...................................................................................... 20

21. Chalcedony ............................................................................................................................ 20

22. Goethite lining vugs filled with coarse supergene quartz, in limonite gossan .... 22

23. Hematite pseudomorphous after pyrite in oxidized jasperoid ................................ 22

24. Jarosite inclusion in late coarse quartz, filing fractures and cavities in jasperiod ........................................................................................................................... 23

25. Limonite particles disseminated through aphantic jasperoid .................................. 23

26. Lussatite lining vug in goethite ...................................................................................... 24

27. Fine-grained supergene jasperoid impregnated with manganese oxide ................ 24

28. Opal groundmass cut by hematite veinlets and younger chalcedony veinlet ........ 25

29. Alternating colloform bands of pyrite and chalcedonic jasperoid ........................ 26

30. Small pyrite grains disseminated in Arkansas Novaculite ...................................... 26

31. Quartz grain inclusions in jasperoid, showing accretionary overgrowths in

optical continuity ........................................................................................................ 27

32. Histograms showing distributions of density and porosity in 124 jasperoid samples ...... 29

33. Histograms showing distributions of elements detected in the majority of jasperiod

and chert samples ...................................................................................................................... 32

34. Diagrams showing solubility of quartz in H20: A, At 300 atm pressure; B, at 400°C .... 38

35. Graph showing comparison of scores for megascopic plus microscopic criteria with

scores for chemical criteria on all samples ...................................................................... 58

36-50. Maps showing jasperoid-bearing areas in 

36. Southwest Missouri, Oklahoma, Kansas, and Arkansas .......................................... 59

37. Alaska .................................................................................................................................... 89

38. Arizona .................................................................................................................................. 90

33. California .............................................................................................................................. 95

40. Colorado ................................................................................................................................ 98

41. Georgia, North Carolina, South Carolina, Tennessee, and southwest Virginia .. 103

42. Idaho and Montana ........................................................................................................... 104

43. Illinois, Iowa, Kentucky, Wisconsin, and southeastern Missouri ............................ 105

44. Nevada .................................................................................................................................. 109

45. New Mexico .......................................................................................................................... 124

46. Pennsylvania, New Jersey, northern Virginia, and West Virginia .................... 130

47. South Dakota and Wyoming ............................................................................................ 131

48. Texas ...................................................................................................................................... 136

49. Utah ........................................................................................................................................ 137

50. Washington ......................................................................................................................... 148
VI CONTENTS

TABLES

Page

TABLE 1. Colors of fresh and weathered surfaces of oxidized hypogene jasperoid samples ........ 7

2. Accessory minerals found in jasperoids, showing age relative to silicification of host

rock and approximate abundance ............... ......................................................................... 19

3. Jasperoid-associated minerals reported in the literature, other than those discussed in

the text ..................................................... ......................................................-.............-.-..- 28

4. Analyses of jasperoid and other similar rocks ...................................................................... 31

5. The observed range and average concentrations of the 13 commonly reported oxides 

plus sulfur for 10 representative jasperoid samples compared with those of certain 

other rock types ........................................................................................................................... 31

6. Distribution of minor elements in jasperoid .......................................................................... 35

7. Median concentrations of elements detected in jasperoid samples .................................. 36

8. Composition of some natural silica-bearing waters ................................................................ 42

9. Distribution of megascopic characteristics in 95 favorable and 53 unfavorable oxidized jasperoid samples ............................................................................................................. 53

10. Distribution of microscopic characteristics in 95 favorable and 53 unfavorable jasperoid samples ...................................................... .................... ........................ .................. 54

11. Distribution of density and porosity in 72 favorable and 41 unfavorable jasperoid

samples ........................................................................................................................................... 54

12. Maximum difference in cumulative proportions of characteristic and common elements between favorable and unfavorable samples, and significance of this difference ........................................................................................................................................... 55

13. Distribution of minor elements in 95 favorable and 53 unfavorable jasperoid samples ................................................................................................................................................... 55

14. Evaluation of criteria for distinguishing between favorable and unfavorable jasperoid

samples ........................................................................................................................................... 56

15. Summary of percentages of misclassified samples scored according to various combinations of classifications ......................................................................................................... 57

16. Age relations of minerals in Ely district jasperoid to the jasperoid quartz .................... 69

17. Minor-element distribution in 26 samples of jasperoid from the Ely district, Nevada.. 70

18. Relative abundance of 15 most abundant elements in 26 samples of jasperoid from the

Ely district, Nevada ................................................................................................................... 70

19. Minor-element distribution in 25 samples of jasperoid from the Tintic and East Tintic

districts, Utah ............................................................................................................................. 77

20. Relative abundance of 13 most abundant elements in 25 samples of jasperoid from the

Tintic and East Tintic districts, Utah ................................................................................ 77

21. Characteristics of jasperoid in major districts of the United States ............................ 86-87
JASPEROID IN THE UNITED STATES ITS 

CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

By T. G. LOVERING

ABSTRACT

Jasperoid is a rock composed dominantly of silica, most 

commonly quartz, that has formed largely by epigenetic replacement. It is a common product of hydrothermal alteration 

of carbonate rocks in many mineralized areas.

Although jasperoid in the United States is most abundant 

in limestone and dolomite, it also occurs in shale, mudstone, 

extrusive igneous rocks, and metamorphic rocks. Most bodies 

of jasperoid are localized along faults, fracture zones, and 

shear zones, and they spread laterally from such conduits 

through beds of favorable lithology or permeability, or beneath impermeable caprocks. In many mining districts of the 

Western United States, the jasperoid bodies seem to be both 

spatially and genetically related to siliceous igneous intrusives.

Individual bodies of jasperoid range in size from pods a 

few feet in diameter to masses more than a quarter of a mile 

in their greatest dimension. Many form crosscutting veins or 

reefs; others form concordant mantos or sheets. Some are 

lenticular, and some are extremely irregular in shape with 

many projecting apophyses.

Large masses of jasperoid characteristically form prominent rugged outcrops that shed a talus of angular broken 

blocks. They tend to be strongly brecciated and recemented 

by younger quartz. The rock is fine grained to aphanitic in 

texture; the coarser varieties resemble fine-grained quartzite, 

and the finer varieties resemble chert. Vugs are commonly 

abundant and conspicuous. Jasperoid in most outcrops is 

oxidized and is stained by iron oxides in various shades of 

brown, yellow, and red. Unoxidized jasperoid is predominantly 

gray or black. Some jasperoid retains both the color and texture of the host rock, and is distinguishable only by its 

greater hardness. Some masses of jasperoid have sharp contacts with unreplaced host rocks; others grade into the host 

through a transition zone of tiny irregular quartz veinlets 

and disseminated quartz grains.

Quartz in jasperoid displays a variety of microtextures. 

The two most common are irregularly interlocking grain 

boundaries, comparable to xenomorphic texture in igneous 

rocks, and extremely irregular sinuous boundaries with individual grains interlocking like the pieces of a jigsaw puzzle. 

A less common texture, which seems to be confined to jasperoid 

and which may be used to distinguish it from other forms of 

quartz, consists of randomly oriented euhedral to subhedral 

quartz laths that form a reticulated net, with the interstices 

filled by interlocking anhedral grains.

Although jasperoid is composed predominantly of quartz, 

only a few varieties are composed entirely of quartz. The 

most common of nearly 100 observed accessory minerals are 

allophane, barite, calcite, chalcedony, dolomite, goethite, 

hematite, hydromica, jarosite, kaolinite, limonite, opal, pyrite,

sericite, tourmaline, and zircon. Some accessory minerals are 

unreplaced inclusions in, or remnants of, host rock. A few are 

nearly contemporaneous with the matrix quartz, but most 

are younger than the matrix quartz and form crosscutting 

veinlets, vug fillings, or oxidation pseudomorphs of older 

minerals.

Chemical analyses of selected samples indicate that typical 

jasperoid consists of about 80-99 percent silica; the remainder is mostly iron, aluminum, calcium, magnesium, and water, 

in varying proportions. Forty-three elements were detected, 

by spectrographic analyses, in one or more of 200 samples; 

of these elements, only silicon, aluminum, iron, magnesium, 

calcium, titanium, manganese, barium, chromium, copper, 

nickel, strontium, and vanadium were detected in most of the 

samples.

The prerequisites to the formation of jasperoid are (1) an 

adequate source of silica, (2) solutions that can transport 

silica to the site of deposition, (3) an environment at this 

site that inhibits the solubility of silica and promotes solution of host rock, and (4) reaction rates that cause the host 

rock to dissolve at least as fast as silica precipitates.

Possible sources of silica are (1) a cooling magma at depth 

contributing juvenile siliceous emanations, (2) silica-bearing 

rocks above or below the host rock, and (3) silica disseminated through the host rock itself.

The capacity of an aqueous fluid to transport silica depends 

largely on the form of silica available, and on the temperature, pressure, and chemical composition of the system. 

Although hydrothermal fluids are generally capable of transporting silica in higher concentrations than is cool water, 

ground water can also transport large quantities of silica 

under the proper conditions during a longer period of time.

Ionic solubility of silica varies directly with the fluid density of the solvent. At low temperature, saturation with respect to ionic silica is low in strongly acid solutions, increases 

slightly in weakly acid solutions, declines to a minimum in 

neutral solutions, rises in slightly alkaline solutions, and 

rises rapidly in strongly alkaline solutions. Dispersed silica 

sols tend to be stable at low pH; consequently, acid solutions 

are capable of transporting large quantities of silica.

The silica content of natural waters ranges from a low of 

about 6 parts per million in sea water to a high of several 

hundred parts per million in thermal springs of volcanic 

origin. The concentration of silica in natural water seems to 

be largely independent of the total dissolved solids in the 

water.

Precipitation of silica can result from (1) decrease in fluid 

density, (2) evaporation of the solvent, (3) neutralization of 

acid or alkaline waters, (4) contact with a solid form of 

silica, (5) changes in the concentration of certain dissolved 

salts, (6) the mingling of dispersed sols with opposite elec-
JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

trical charges, or (7) a combination of these factors. Iron 

and aluminum promote precipitation of silica from acid solutions, and barium and fluorine promote its precipitation from 

alkaline solutions. Sodium chloride causes silica to precipitate from supersaturated solutions and to dissolve in undersaturated solutions. Increases in temperature and pressure 

accelerate the conversion of silica gel to quartz.

Although some jasperoid bodies probably result from solution of host rock at an early stage and from precipitation of 

silica in the resulting voids at a later stage, the common 

preservation of original host rock textures in replacing jasperoid furnishes evidence th#t simultaneous solution of host 

rock and precipitation of silica by the same solution must also 

be an important process in the formation of such bodies.

If a hot aqueous silica-bearing fluid containing dissolved 

C0a and NaCl rose under pressure along an insulated conduit 

into a layer of carbonate rocks that was highly permeable, 

the resulting rapid change in physical and chemical environment would be conducive to this type of volume-for-volume 

replacement. Both carbonic acid and sodium chloride increase 

the solubility of carbonate rocks. The rising pH of the solution resulting from reaction with these rocks, and the drop 

in both temperature and pressure as the solution spread from 

the feeding conduit through the permeable zone, would tend 

to supersaturate the solution with silica. The presence of 

sodium chloride would, however, inhibit such supersaturation 

and cause the excess silica to precipitate as the carbonate 

rock dissolved. If the silica precipitated as a gel rather than 

as crystalline quartz, the rate of replacement would decline 

as the reaction became dependent on diffusion of solution 

through the thickening gel layer. However, the higher temperature of solutions on the inlet side of the system would 

promote rapid conversion of silica gel to quartz. The loss in 

volume resulting from such a conversion would open new 

channels for solutions to move toward the reaction interface 

with the host rock. If silica precipitated directly as quartz 

disseminated through the host, solutions could continue to 

flow along intergrain boundaries and tiny fractures in the 

host rock and the growing nuclei of quartz within it.

The appearance, texture, mineralogy, and composition of 

ore-related jasperoid samples from many different localities 

were studied and compared statistically with the same attributes of non-ore-related samples. Characteristics found to be 

significantly more common in ore-related samples include 

phaneritic texture, abundant vugs, brown color, highly variable grain size, reticulated microtexture, the presence of 

goethite, jarosite, pyrite, and >0.00015 percent Ag, >0.0015 

percent Pb, >0.015 percent Zn, >0.003 percent Cu, >0.0007 

percent Mo, >0.15 percent As, >0.0007 percent Ga, > 0.0007 

percent In, >0.0015 percent Sn, >1.5 percent Fe. Characteristics found to be significantly more common in samples not 

associated with ore are red color, jigsaw-puzzle microtexture, 

and the presence of yellow limonite, montmorillonite, hydromica, sericite, and >0.01 percent Mg.

Numerical scores were awarded to each characteristic according to its statistical level of significance, and the scores 

were summed for each sample in both groups. More than 90 

percent of the ore-related samples yielded scores of >5, and 

more than 90 percent of the non-ore-related samples yielded 

scores of <5.

Each of the nine major jasperoid-bearing mining districts 

in the United States has yielded ore worth at least $100 million. These districts, in order of decreasing production, are

Tri-State, Clifton-Morenci, Bisbee (Warren), Ely (Robinson), Leadville, Tintic, Gilman, Aspen, and Eureka. The 

distribution and characteristics of jasperoid in each of these 

districts are discussed in some detail. Information on jasperoid in 99 other mining districts and mineralized areas in 

the United States is summarized more briefly, and 97 other 

occurrences of jasperoid or silicified rock that may be jasperoid are named and located.

INTRODUCTION 

PURPOSE AND SCOPE OF THE INVESTIGATION

The common association of bodies of silicified 

rocks (jasperoid) with replacement ore deposits in 

mining districts of the Western United States 

prompted this investigation. The major objectives 

are twofold: first, to establish criteria for distinguishing jasperoids that are closely associated with 

replacement ore bodies (favorable jasperoids) from 

similar siliceous bodies that are unrelated to ore 

(unfavorable jasperoids and cherts); second, to obtain information on the physical and chemical nature of jasperoid as a rock type and on the environment in which it forms.

Much of the information has been derived from 

geologic literature, and most of the rest, from examination and analysis of jasperoid samples contributed 

by my colleagues.

DEFINITION OF "JASPEROID"

Although the term "jasperoid" has been established in the literature since the late 19th century, 

some confusion still exists as to its exact meaning. 

This confusion is due in part to the many names 

that have been applied to jasperoids. These include 

blout, flint, quartz, jasper, hornstone, chert, secondary chert, hydrothermal chert, limestone quartzite, ozarkite, cherokite, silicified limestone, and 

silicified dolomite.

The term "jasperoid" was first introduced by 

Spurr (1898, p. 219-220), who wrote:

Jasperoid may then be defined as a rock consisting essentially of cryptocrystalline, chalcedonic, or phenocrystalline 

silica, which has formed by the replacement of some other 

material, ordinarily calcite or dolomite. This jasperoid may 

be white or various shades of red, gray, brown, or black, the 

colors resulting from different forms of iron in varying proportions.

Lindgren (1901, p. 678), in his report on metasomatic processes in fissure veins, wrote as follows:

Many tiny quartz grains first appear scattered through 

the rock, chiefly along areas of slight shearing or fracture. 

Here and there appear long slender quartz crystals entirely 

surrounded by fresh limestone. As silicification proceeds, the 

slender crystals multiply, forming a characteristic network, 

sometimes enclosing small areas of calcite which are sprinkled 

with small, irregular quartz-grains of varying size, in which
INTRODUCTION

the retiform structure is still apparent, and which rock resembles a chert or a fine-grained and altered quartzite, and 

is generally somewhat porous, drusy, and also often colored 

red or yellow. In structure, appearance, and origin, this 

cherty rock is identical with the jaspers of Lake Superior. 

Mr. Spurr proposes "jasperoid" as a term for this rock, consisting essentially of cryptocrystalline, chalcedonic or 

phanero-crystalline silica formed by the replacement of other 

rocks, chiefly limestone.

Lindgren did not stipulate an origin due to the 

agency of circulating water, as did Spurr. Further 

confusion regarding the definition of the term 

"jasperoid" is caused by the fact that both Lindgren 

and Spurr regarded the jasper of the Lake Superior 

region as being a jasperoid. Van Hise and Leith 

(1911, p. 124, 556), in their famous monograph on 

the geology of this region, did not commit themselves to a replacement origin for the jasper, and 

regarded the interbedded iron ore as syngenetic. In 

an investigation of the Ironwood Iron-Formation, 

Huber (1959, p. 111-113) stated that the jasper is 

primary.

The characteristic features of jasperoid described 

by Lindgren are evident in much of the jasperoid 

from the type locality at Aspen, Colo., but some of 

them are not apparent in many rocks called jasperoids by later investigators in other areas. Smith 

and Siebenthal (1907, p. 14) applied the term to the 

dense black siliceous rock in the Joplin district, 

Missouri-Kansas, which is commonly associated 

with the galena and sphalerite ore bodies. Soon 

afterward, Irving (1911, p. 630-631) described 

gold-bearing jasperoid bodies in the Black Hills of 

South Dakota whose contacts with the enclosing 

dolomite are knife-edge sharp. Duke (1959) defined 

jasperoid as "any rock which is composed mostly of 

secondary silica."

There seems to be general agreement on two 

points: (1) jasperoids are composed predominantly 

of silica, which in most places is in the form of 

aphanitic to fine-grained quartz, and (2) jasperoids 

form by replacement of the enclosing rock. For this 

study, I return to Spurr's definition (1898) by restricting the usage of the term "jasperoid" to mean 

"an epigenetic siliceous replacement of a previously 

lithified host rock." Jasperoid, thus defined, excludes 

syngenetic or diagenetic forms of silica, such as 

primary chert and novaculite.

ACKNOWLEDGMENTS

I am deeply indebted to H. T. Morris, A. V. Heyl, 

and T. S. Levering, who not only contributed a vast 

amount of valuable information on jasperoid and 

constructive criticism of this manuscript, but also 

provided many of the specimens in my collection.

Thanks are also given to Frank Howd and Arthur 

Rose of the Bear Creek Mining Co., and to D. A. 

Brobst, the late A. H. Koschmann, J. H. McCarthy, 

Jr., Arthur Pierce, J. J. Norton, J. C. Ratte, D. R. 

Shawe, A. F. Shride, Ogden Tweto, E. J. Young, 

and many other geologists of the U.S. Geological 

Survey who furnished jasperoid samples from many 

mining districts. Richard Taylor took many excellent photomicrographs illustrating jasperoid textures. Mrs. Elizabeth Tourtelot carefully searched 

the literature on mining districts and compiled much 

of the information that is included in the district 

summaries. J. C. Hamilton made most of the spectrographic analyses of my jasperoid samples.

DISTRIBUTION OF JASPEROID 

GEOGRAPHIC DISTRIBUTION

Jasperoid bodies have been recognized and reported from more than 200 mining districts and 

mineralized areas in the United States (fig. 1), and 

they undoubtedly occur in many more areas. Bodies 

of jasperoid that are apparently unrelated to commercial ore deposits are also common throughout 

large areas of the Western United States, but because most of them are small, widely scattered, and 

of no known economic importance, they rarely are 

shown on small-scale regional geologic maps. Thus, 

the localities shown on figure 1 probably represent 

less than half the actual jasperoid localities in the 

United States.

Many of the known localities are concentrated in 

certain areas, or jasperoid provinces; others are 

widely scattered. Jasperoid provinces may be of significance in broad-scale economic exploration programs because they represent regions within which 

jasperoid seems to be associated with ore. These 

provinces, shown in figure 1, are: (1) a large area 

in eastern Nevada and western Utah, (2) an area 

west and southwest of Tonopah, Nev., extending 

southward into California, (3) an area in central 

Colorado surrounding Leadville, (4) a long narrow 

area in southwestern New Mexico extending from 

Magdalena southward to the Mexican border, (5) 

the Tri-State "district" (in reality a very large region of many "districts," as the term is used in the 

West) surrounding the common corner of Kansas, 

Oklahoma, and Missouri, and (6) the lead-zinc "district" of northern Arkansas. In each of these provinces are many districts in which jasperoid bodies 

are associated, both genetically, and spatially, with 

sulfide ore deposits. It is also noteworthy that major 

mining districts lie near the center of many of these 

provinces, for example, Ely, Nev., Leadville, Colo., 

and the "Picher Field," Okla.
4 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

48'

46'

44'

42'

40'

38'

36'

34'

32'

30'

28'

26'

24'

22°

128° 126° 124° 122° 120° 118' 116° 114° 112° 110° 108° 106° 104° 102° 100° 98° 96'

I I I I I

NORTH DAKOT

 ,. ^ r

I _______5.

EXPLANATION

TEXAS

Area 

m

of large 

mining district

-- Major district

X

Minor district 

or area

Reported occurrence

_____ Jasperoid province

DISTRICTS WITH ^. 

METAL PRODUCTION \ 

IN EXCESS OF I 

$100 MILLION v\ /~~~~\. 

1. Tri-State ~VN -'' N 

2. Clifton-Morenci N^ crt^" 

3. Bisbee , V N jj& 

4. Ely (Robinson) v. <3f 

5. Leadville ^ ^f 

6. Tintic \ 1| 

7. Gilman (Red Cliff) \^ ^L 

8. Aspen ""v__^^jj 

9. Eureka

/ / / f 1 1 1 1 1

118° 116° 114° 112" 110° 108° 106" 104° 102° 100° 98° 96*

FIGURE 1. Jasperoid-bearing localities and
DISTRIBUTION OF JASPEROID

96° 94" 92° 90 c 86° 84° 82° 80° 78° 76° 74° 72° 70° 68° 66° 64' |48 C

r \ \ \ \ \ \

r-'~\

' ^"^Sf

MINNESOTA

46 c

44 <

42 1

40 c

38'

36 C

34'

32'

30 C

28'

24 c

22'

96° 94" 92° 90° 88° 

provinces of the conterminous United States.

86° 84° 82° 80° 78° 76 C

74'
JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

In the Eastern United States the scarcity of 

jasperoid-bearing mining districts may reflect a 

scarcity of such districts with readily silicified host 

rocks and may also reflect a lack of published information on jasperoid in certain districts where 

jasperoid does exist.

Many jasperoid-bearing mining districts in other 

countries have been reported in the literature. A few 

of these are listed below.

Central and-South America, Antilles

Sierra Mojada district, Coahuila, Mex.

Santa Barbara district, Chihuahua, Mex.

Santa Eulalia district, Chihuahua, Mex.

Colquijirca mine near Cerro de Pasco, Peru

Eastern Cuba

Western Haiti 

Europe

Vosges Mountains, France

Rosia district, Tuscany, Italy

Kostajnika district, Southern Croatia, Yugoslavia 

Africa

Anti-Atlas Mountains, Morocco

Tsumeb district, South-West Africa

Postmasburg district, Cape Province

Pilgrims Rest district, North-East Transvaal 

Australia

Tasmania 

Asia

Tienpaoshan district, Sinkiang Province, China

South Fergana district, Uzbek, USSR

Kara Tau Mountains, Kazak, USSR

GEOLOGIC DISTRIBUTION

HOST ROCK

Rocks vary greatly in their susceptibility to replacement by silica. The most susceptible rocks are 

limestone and dolomite; shale and siltstone are also 

replaceable, although considerably less so than the 

calcareous rocks. Siliceous hypabyssal and extrusive 

igneous rocks and pyroclastics have a susceptibility 

to replacement by silica comparable to that of shale. 

Plutonic igneous rocks and metamorphic rocks, except for marble and metavolcanic rocks, appear to 

be most resistant to siliceous replacement. Sandstones and conglomerates that are impregnated with 

silica and brecciated rocks that are recemented by 

silica are, by definition, not jasperoids.

Most of the jasperoid bodies reported in the geologic literature have formed by the replacement of 

limestone or dolomite. Commonly, other rock types 

that have been jasperoidized are closely associated 

with similarly altered calcareous rocks.

Jasperoids occur in host rocks of all ages, from 

Precambrian to Tertiary; however, the greatest concentration of jasperoid bodies in the Western United 

States is in rocks of Devonian, Mississippian, and 

Pennsylvanian ages. Probably, this concentration

merely reflects the fact that calcareous rocks of 

these ages cover a considerably larger area of the 

Western United States than do calcareous rocks of 

any other age.

STRUCTURAL CONTROL

Most jasperoid bodies are localized along zones of 

structural disturbance, such as breccia zones, shear 

zones, and faults, and this structural control is the 

best criterion for distinguishing jasperoid from 

chert or novaculite. Channelways created by these 

zones of structural weakness provide the plumbing 

system through which the silica-bearing solutions 

gain access to the host rocks. In other localities a 

relatively impermeable caprock has caused widespread lateral migration of silicifying solutions at 

the contact, resulting in a jasperoid blanket conformable with the host rock. Such bodies may closely 

resemble bedded chert on the outcrop, but they can 

be identified as jasperoids by such features as local 

silicification of the caprock, transgression of the 

bedding, or by the presence of feeding channels. 

Layers of jasperoid may also form by selective replacement of certain favorable beds in a carbonate 

series. The jasperoid in this type of deposit closely 

resembles bedded chert, but it can be distinguished 

from chert by the following criteria: (1) jasperoid 

beds are localized in a relatively small area, in contrast to the broad regional distribution of bedded 

cherts, and (2) such jasperoid layers commonly 

grade laterally into larger masses with evident 

structural control. Jasperoid blankets may also form 

in the permeable zone along a buried erosion surface, and jasperoid may replace limestone adjacent 

to old drainage channels and sinkholes beneath such 

a surface.

Jasperoid deposits are most prevalent in the vicinity of intrusive bodies of igneous rocks, to which 

they are genetically related. The presence of an 

intrusive mass, however, is not a prerequisite for 

the occurrence of jasperoid. Large masses of jasperoid are found far removed from any known intrusive stocks for example, in the Tri-State district 

of Kansas, Oklahoma, and Missouri.

GEOLOGIC AGE

The laboratory methods of geochronology that 

have been applied to plutonic and hypabyssal igneous rocks cannot be applied to jasperoids, and their 

age is therefore difficult to determine. Most of the 

jasperoid bodies whose distribution is shown in 

figure 1 are presumed to be of "Laramide" age 

(late Mesozoic or early Cenozoic). Jasperiod masses 

of known Precambrian age have been reported from
PHYSICAL PROPERTIES OF JASPEROID

the Jerome district and the Fort Apache iron district of north-central Arizona, and from Tasmania, 

Australia"; rounded detrital pebbles of jasperoid, 

presumably of Permian age, have been found in the 

Triassic Shinarump Member of the Chinle Formation and in the Jurassic Morrison Formation in the 

northern Colorado Plateau; and jasperoid replaces 

Tertiary marine limestones and associated volcanic 

rocks in Cuba and Haiti (Goddard and others, 1947, 

p. 34-37; Park, 1942, p. 81-82, 92-93). There is a 

suggestion that jasperoid bodies may be forming today beneath some of the hot springs in the Yellowstone Basin. The waters of some of these springs are 

rich in calcium bicarbonate and deficient in silica; 

these chemical characteristics strongly indicate contact with carbonate rocks at depth, and it seems a 

reasonable hypothesis that they lost silica to these 

rocks as they leached calcium carbonate (D. E. 

White, written commun., 1957).

PHYSICAL PROPERTIES OF JASPEROID 

MEGASCOPIC FEATURES

Jasperoid varies widely in physical appearance; 

commonly, a single body contains several distinguishable varieties of jasperoid with distinctive 

colors, textures, and assemblages of associated 

minerals.

COLOR

Many jasperoids range in color from white 

through various shades of gray to coal black; this 

is particularly true of unoxidized varieties. An iron 

content of 0.1-1 percent generally is sufficient to 

impart various shades of brown, yellow, orange, 

and, less commonly, red and pink to most oxidized 

jasperoid outcrops. Less colorful outcrops are common in areas where the iron content of the jasperoid 

is unusually low, or where the jasperoid is so dense 

that little or no oxidation of the iron present has 

taken place. In some jasperoid the pigmentation is 

primary and colors the rock below the zone of surface oxidation.

The relative frequency of various color occurrences in my suite of oxidized jasperoid samples, 

from more than 50 localities, is shown in table 1. 

Most of the samples are mottled, veined, streaked, 

or banded with more than one color, which accounts 

for the total of the various colors being higher than 

the total number of samples. The prevailing colors 

of fresh exposures of oxidized jasperoid are shades 

of gray, followed by light to medium brown and 

orange. The prevailing colors of weathered jasperoid 

are medium brown, light brown, and orange, followed by dark brown, reddish brown, and dark gray.

TABLE 1. Colors of fresh and weathered surfaces of oxidized 

hypogene jasperoid samples from more than 50 localities in 

the United States

[The 12 most common colors are listed, in order of decreasing frequency 

of occurrence]

Fresh surface 

(267 samples)

Weathered surface 

(205 samples)

Number 

Color of 

samples

1.... Medium gray ...... 

2....Medium brown .... 

3.... Dark gray-black.. 

4... .Light brown ........

6....White to light 

gray ..................

7... .Reddish brown .. 

8....Yellow ..................

9....Medium red ........ 

10....Pink ......................

11... .Dark red ............

109 

56 

54 

54 

52

35 

27 

24 

23 

22 

20 

20

Number 

Color of 

samples

l....Medium brown ....

4. ...Medium gray ........

6.... Reddish brown .... 

7 .Dark gray-black .. 

8....Dark red ..............

9....White to light 

gray ..................

10....Yellow ..................

11... .Medium red ..........

68 

47 

40 

25 

23 

22 

20 

16

14 

11 

10 

10

Red and pink jasperoids are relatively uncommon, 

as may be seen in table 1.

My collection contains only 35 samples of unoxidized jasperoid, from 15 localities. Dark gray is 

the predominant color of this suite, followed by 

medium gray and white. Individual specimens also 

show various shades of olive gray, brown, yellowish 

gray, and grayish orange.

I also have 11 samples of supergene jasperoid that 

are gradational into siliceous gossans. These samples 

are a variety of dark colors, including dark gray, 

dark brown, dark yellowish orange, dark reddish 

brown, and dark red.

TEXTURE

Jasperoid bodies are resistant to weathering and 

commonly exhibit prominent rough outcrops (fig. 

2A). Where their distribution is controlled by faults, 

these outcrops tend to stand up as uneven walls or 

"reefs." Jasperoid is both hard and brittle and therefore is commonly highly fractured and brecciated in 

zones of structural instability. This shattering 

causes both characteristic rough outcrops and 

aprons of angular sharp-edged talus blocks below 

such outcrops. Gilluly (1932, p. 98) described 

jasperoid bodies, in the Mercur and Ophir districts 

of Utah, as being cut by many randomly curved 

and slickensided fracture surfaces that terminate 

abruptly at the contact with the country rock, suggesting differential movement of blocks within the 

body after its solidification.

Another distinctive feature of jasperoid exposures in many districts is the abundance of vugs. 

These range in size from microscopic openings to
8 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

~*d^JB&&£j&£:

^K^m^mrnKM-^'^ ^i'f^^l^^Sj^KMp^

:^^?«^rw^««^'y

FIGURE 2. A, Typical outcrop of jasperoid, Lake Valley district, New Mexico (photograph by E. J. Young). B, Hand specimen of jasperoid showing preservation of primary bedding texture.
PHYSICAL PROPERTIES OF JASPEROID

cavities several inches in diameter. The larger vugs 

characteristically are lined with crystals of quartz 

or calcite. Vugs in jasperoid commonly show a random orientation and distribution, but many are 

restricted to well-defined zones. Locally, they have a 

strong preferred orientation, forming lenticular 

voids parallel to the walls of the jasperoid mass in 

which they occur.

Many jasperoid bodies have sharp, well-defined 

contacts with their host rocks. Some have transitional contacts, grading outward through a zone of 

unreplaced fragments of host rock in jasperoid into 

a zone of shattered host rock cut by anastomosing 

veinlets of jasperoid, and finally into a zone of 

quartz grains or slender, doubly terminated quartz 

crystals randomly disseminated through the host. 

Others are bordered by a zone of soft friable carbonate rock, which breaks down on weathering so 

that the contact is not exposed at the surface.

In some places jasperoid differs strikingly in appearance and texture from its host. Elsewhere, the 

color, texture, and primary bedding of the host rock 

are faithfully preserved in the replacing jasperoid 

(fig. 25). Extensive bodies composed exclusively of a 

single homogeneous type and generation of jasperoid are rare. Most jasperoid masses consist of several distinct varieties of jasperoid, in which the 

oldest generation has been fractured or brecciated 

and then recemented by a second generation. This 

second generation, in turn, has been cut by a third 

generation, and so on, so that it is not uncommon 

to find five or more distinct ages and types of jasperoid in large exposures. In most such bodies, only 

the oldest generation is a true jasperoid, strictly 

speaking, formed by replacement of the host. The 

younger generations have merely filled fractures, 

without replacement. It is customary* however, to 

refer to the entire mass as jasperoid.

The typical texture of jasperoid is aphanitic, almost glassy, but fine-grained phaneritic jasperoid 

with a "sugary" texture is common in some areas. 

Locally, jasperoid with an average grain size of as 

much as 1 millimeter is found. In mining districts 

where relatively coarse grained jasperoid forms the 

host rock for disseminated sulfide minerals, or where 

jasperoid is disseminated in a carbonate host rock, 

leaching in the zone of oxidation has produced light 

friable porous masses of "honeycomb quartz." Such 

masses from the Lowell mine at Bisbee, Ariz., were 

described by Ransome (1904, p. 131) and from the 

Bingham district, Utah, by Boutwell (1905, p. 68, 

118,202).

ASSOCIATED MINERALS

Jasperoid that constitutes the host rock for ore 

bodies commonly contains a wide variety of visible 

accessory ore minerals. Considerably fewer minerals, recognizable in hand specimen, are common in 

oxidized jasperoid not closely associated with ore. 

They are chalcedony, calcite, dolomite, hematite, 

limonite, "manganese oxides," and, more rarely, 

pyrite, fluorite, barite, siderite, opal, chlorite, and 

apatite. These minerals occur either disseminated 

through the jasperoid matrix or concentrated in 

veinlets and on the walls of vugs.

Primary jasperoid, produced by hydrothermal alteration, commonly exhibits oxides of iron and manganese as surface stains and fracture coatings, and, 

locally in the zone of oxidation, it contains scattered 

iron oxide pseudomorphs after original sulfides. 

Secondary or supergene jasperoid, produced by 

siliceous alteration from ground water during 

weathering and oxidation of an ore body, commonly 

contains oxides of iron and manganese intimately 

mixed with, and disseminated through, the siliceous 

matrix; it rarely exhibits sulfide pseudomorphs.

MICROSCOPIC FEATURES

Thin sections of jasperoid, examined with a 

petrographic microscope, exhibit considerable variation in grain size, a wide range of textures, and a 

much more extensive suite of accessory minerals 

than is visible to the naked eye. A jasperoid sample 

that in hand specimen appears to be simple, dense, 

and relatively homogeneous may reveal, when examined under the microscope, a complex history, 

starting with replacement, followed by successive 

brecciation and recementation, and ending with 

weathering and oxidation.

GRAIN SIZE

The mean grain size and size range of grains in 

recognizable distinct varieties of jasperoid in 200 

thin sections were recorded and plotted on a scatter 

diagram (fig. 3). Size range was recorded as the 

ratio of the mean diameter of the largest grains 

to that of the smallest. The high concentration of 

points in the lower left corner of this diagram shows 

that jasperoid is commonly very fine grained, having 

a mean grain size of <0.05 mm, and is relatively 

homogeneous, with a ratio of largest grain to smallest grain of <10:1. It is the abundance of this 

type of jasperoid that makes it so difficult to distinguish between jasperoid and chert in hand specimens. The nature of the mean size and size-range 

distributions of these samples is further shown by 

the histograms in figure 4. The class intervals chosen
10 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

>0.2

0.2

0.15

ui

N 0.1 

CO

<0.05

0.01

<0.01

 Dv X

cf x n o

XD D» 

n_* *

Hi * D Q D«X

a x a

1/1 5/1 10/1 15/1 20/1 25/1 50/1 

SIZE RANGE (MEAN DIAMETER OF LARGEST GRAINS/MEAN DIAMETER OF SMALLEST GRAINS)

100/1

FIGURE 3. Mean size and size range of jasperoid grains in 200 samples. Q, unfavorable; , favorable; X, not known.
PHYSICAL PROPERTIES OF JASPEROID 11

40

30

u 20

(3

Ul 

O 

tz 10

<4.6 4.6-<10 10-<22 22-<46 ,>46

SIZE RANGE (MEAN DIAMETER OF LARGEST GRAINS/MEAN 

DIAMETER OF SMALLEST GRAINS)

30

^ 

O

i 20

o

_

-pjpH

liSSli? ^X-^^J

1 1 1

Ssf^-jii -; _ :W"":"--.-. :-'--"-:-" . . 3 ;

s;s

si

:" !' '! ~ 

1 sl

'..'^'. ". - .)-,,,,.,. »..' ..: 1" L '-..... :.!,. :^B|....

<0.01 0.01- >0.022- 0.046- 0.1-C.22 , 3.2- >0.46

0.022 <0.046 <0.1 <0.46 ~

MEAN GRAIN SIZE, IN MILLIMETERS

FIGURE 4. Frequency distribution of mean size and size 

range of jasperoid grains.

for these histograms are approximately equal on 

a logarithmic scale, except for the two open-end 

classes. The resulting distributions after the 

logarithmic transformation still show a pronounced 

positive skewness, thus emphasizing that most jasperoid is extremely fine grained and relatively 

homogeneous.

FABRIC TEXTURE

The shapes of jasperoid grains and their mutual 

boundaries produce several different characteristic 

textural patterns.

One of the most common microtextures in jasperoid consists of highly irregular grains that are 

tightly interlocked in somewhat the same way as 

are the pieces of a jigsaw puzzle (fig. 5). This 

texture is typical of extremely fine grained and relatively homogeneous varieties of jasperoid, and 

probably represents the crystallization of an original 

silica gel into quartz. Relatively coarse grained 

jasperoid may also exhibit "jigsaw-puzzle" texture. 

Such coarse jigsaw-puzzle jasperoid is commonly asFIGURE 5. Typical jigsaw-puzzle texture in aphanitic jasperoid. Crossed polars. X 100.

sociated with masses of fibrous chalcedony, filling 

voids in an older generation of jasperoid.

Jasperoid grains that are somewhat irregular at 

their boundaries but lack the deep sinuous indentations and amoeboid forms that characterize the jigFIGURE 6. Typical xenomorphic texture in coarse-grained 

heterogeneous jasperoid. Crossed polars. X 40.
12 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

saw-puzzle texture produce a textural pattern very 

similar to the xenomorphic texture commonly observed in nonporphyritic igneous rocks. This texture 

is characteristic of many jasperoids that have a 

heterogeneous grain-size distribution in which 

smaller grains form inclusions in, or fill interstices 

between, larger grains (fig. 6), and it may also occur in jasperoids that have relatively homogeneous 

grain-size distribution. Textural gradations from 

jigsaw puzzle to xenomorphic are common within a 

single jasperoid type, and these two textural varieties characterize most jasperoids.

The granular texture that is typical of finegrained detrital sedimentary rocks is also found in 

a few jasperoids of replacement origin. The grains 

are all about the same size, are nearly equant, and 

have smooth, simple boundaries (fig. 7A). Rarely, 

when the individual granules are examined under 

the microscope with crossed nicols, they do not extinguish as a unit but show a peculiar hourglass 

type of extinction in which different quadrants of a 

granule extinguish in different positions (fig. IB). 

Granular texture is relatively rare in jasperoid, although it is characteristic of silicified siltstone, 

which may be indistinguishable from jasperoid in 

hand specimens.

Masses or veinlets of jasperoid quartz that have 

formed from original chalcedony may exhibit a 

peculiar "feathery" texture (fig. 8A) or a "crossfiber" texture, suggestive of chrysotile veinlets in 

serpentine of the type shown in figures SB and C. 

These textures in quartz are rare, however, because 

chalcedony seems to be a stable mineral in most 

jasperoids.

Another type of texture ijat is common in the 

coarser grained varieties of jasperoid consists of 

abundant elongated grains with a length-to-width 

ratio of 3:1 or greater. Such grains are elongated 

parallel to the c axis, and some show crystal faces. 

They are randomly distributed in a matrix of 

smaller, nearly equant, anhedral grains, and commonly give the appearance of a crude mesh or network. This reticulated texture (fig. 9) is useful in 

distinguishing jasperoid from other siliceous bodies, 

such as chert and novaculite, because it seems to be 

peculiar to jasperoid. Unfortunately, only a relatively small proportion of jasperoids has this texture; therefore, its absence in a sample cannot be 

considered as evidence that the rock is not a jasperoid. The origin of reticulated texture in jasperoid 

has been discussed by Lindgren (1901, p. 678; 

quoted on p. 2 of present report). His statements 

therein appear to be valid, except for the implication that all jasperoids form in a manner that proFIGURE 7. Granular texture. A, Granular texture in Precambrian jasperoid. Crossed polars. X 68. B, Granular jasperoid with hourglass extinction. Crossed polars. X 68.

duces this texture; actually, only a small proportion 

of them seem to do so. The presence of reticulated 

texture in jasperoid is evidence of the original 

deposition of silica as crystalline quartz rather than 

as a colloidal gel and is most common in bodies 

whose contacts with the host rock are gradational. 

The first phase in the formation of this type of
PHYSICAL PROPERTIES OF JASPEROID 13

FIGURE 9. Reticulated texture in jasperoid. Crossed polars.

x 68.

jasperoid is commonly a recrystallization or marmorization of limestone that results in the formation of numerous coarse grains of calcite. 

Accompanying, or closely following, this recrystallization is the formation of small grains and slender 

euhedral crystals of quartz randomly scattered 

through the calcite (fig. 10A). As silicification proceeds, there is a selective replacement, outward from 

tiny fractures (fig. 10B), of the smaller calcite 

grains by fine-grained aggregates of anhedral 

quartz. Finally, only irregular remnants of the 

coarse calcite grains remain as inclusions in the 

jasperoid matrix (fig. 10C). The jasperoid quartz 

formed by this process is commonly clouded by tiny 

dust-sized particles of calcite, a few microns in 

diameter (fig. 11). These particles are characteristically round or oval in section, and, rather than 

being tiny unreplaced remnants of the original host 

rock, they appear to have exsolved as the quartz 

crystallized. Such carbonate particles are also found 

in jasperoid that has jigsaw-puzzle and xenomorphic textures. Wherever the particles occur, they 

provide evidence of the origin of the enclosing 

quartz by replacement of a carbonate host rock.

FIGURE 8. Feathery and fibrous textures. A, Feathery texture in jasperoid quartz recrystallized from chalcedony. 

Crossed polars. X 100. B, "Crossfiber" texture in quartz 

veinlet (Q). Crossed polars. X 68. C, Detail of quartz veinlet shown in B. Crossed polars. X 170.
14 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

r

FIGURE 11. Typical calcite dust-sized particles in jasperoid. 

Crossed polars. X 250.

The replacement process just outlined is common 

in limestone, but for some reason the growth of 

euhedral quartz crystals seems to be inhibited by a 

dolomitic host rock, although the recrystallization 

of the host rock and the selective replacement of 

smaller grains by aggregates of anhedral quartz 

(fig. 12) proceed in a manner similar to that outlined for limestone. Dolomite is more resistant to 

replacement by silica than is limestone, and unreplaced original dolomite crystals may be preserved 

in a completely jasperoidized limestone (fig. 13). 

Where aphanitic jasperoid, of the type shown in 

figure 5, comes in contact with a carbonate host 

rock, that contact is normally sharp and well defined (fig. 14), in contrast to the gradational contacts just discussed. Sharp contacts of this type 

probably are indicative of rapid precipitation of 

silica, as a gel, from solutions that were highly 

supersaturated with silica.

Evidence of the colloidal origin of some jasperoid 

may be preserved in delicate repeated colloform

FIGURE 10. Stages in the replacement of limestone by jasperoid. A, First stage, disseminated quartz grains and 

crystals (Q) in a matrix of coarse recrystallized calcite. 

Crossed polars. X 30. B, Second stage, selective replacement 

of smaller calcite grains by fine-grained anhedral quartz 

aggregates (Q). Crossed polars. X 40. C, Third stage, remnants of coarse calcite (C) in a jasperoid matrix. Crossed 

polars. X 100.
PHYSICAL PROPERTIES OF JASPEROID 15

FIGURE 12. Incipient jasperoid in dolomite (note similarity 

to fig. 10£). Crossed polars. X 100.

bands, which bear no relation to existing grain 

boundaries or textural variations and which disappear under crossed nicols (fig. 15). This type of texture has its counterpart in zonally arranged inclusions of allophane or carbonate particles that preserve the euhedral outlines of original seed crystals 

of quartz in a mass composed of an aggregate of 

coarse anhedral grains (fig. 16). These zoned inclusions around euhedral cores provide good evidence that the early jasperoid was deposited directly 

as quartz rather than as a gel. They are most common in late quartz that fills veinlets or voids in an 

older generation of matrix jasperoid, but they may 

also occur within a matrix of coarse jasperoid.

Where more than one generation of quartz is 

present in a jasperoid, as is generally true, the 

younger generations are commonly coarser grained 

and more heterogeneous than the oldest generation 

(fig. 17) ; but in some jasperoids the younger quartz 

is finer grained than the matrix (fig. 18). Some 

chert layers in limestone are locally brecciated and 

recemented by younger quartz (fig. 19).

ACCESSORY MINERALS

The accessory minerals associated with jasperoid 

quartz may be divided into three groups on the basis 

of their age relative to the main period of silicification. These groups are (1) early older minerals, 

remnants of unreplaced host rock or accessory minB PM °-2mm tj

FIGURE 13. Selective replacement of calcite containing dolomite, by jasperoid. A, Dolomite rhomb in coarse calcite 

remnant in jasperoid matrix. Crossed polars. X 100. B, 

Disseminated dolomite rhombs in jasperoid matrix, which 

has replaced calcite (same section as that shown in A). 

Crossed polars. X 100.

erals from the host rock preserved in the jasperoid;

(2) contemporary minerals formed penecontemporaneously with silicification of the host rock; and

(3) late the large group of minerals that were
16 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

A

FIGURE 14. Jasperoid contact with limestone. A, Abrupt 

contact between jasperoid (J) and limestone (L), showing 

later brecciation and cementation by coarse calcite (C). 

Specimen from the Egan Range, Nev. Natural size. B, Jasperoid (J) contact with limestone (L). Same specimen as 

that shown in figure A. Crossed polars. X 40.
PHYSICAL PROPERTIES OF JASPEROID 17

FIGURE 15. Ghost colloform banding. A, Plane polarized 

light. X 68. B, Crossed polars. X 68.

emplaced after the initial silicification; this group 

includes both minerals deposited from late hypogene 

hydrothermal solutions and strictly supergene minerals formed as a result of weathering and oxidation. The distinction between the two categories of 

minerals included in the third group may be clear 

where both outcrop samples and samples taken from

FIGURE 16. Zoned allophane inclusions outlining original 

quartz crystal nuclei (N) and growth stages (G), in coarse 

xenomorphic jasperoid. Crossed polars. X 170.

FIGURE 17. Chert (ch) and fine-grained jasperoid (F) cemented by coarser grained jasperoid (C), with late coarse 

quartz (Q). Crossed polars. X 40.
18 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

FIGURE 18. Veinlet of fine-grained quartz cutting coarsegrained jasperoid matrix. Crossed polars. X 68.

FIGURE 19. Brecciated chert (ch) cut and cemented by 

coarser quartz (Q). Crossed polars. X 40.

below the zone of oxidation are available from the 

same jasperoid body; however, this distinction becomes much more difficult to make where only the 

outcrop can be sampled. Most of the samples I

studied are outcrop samples; hence, I made no attempt to differentiate between these two categories. 

Table 2 gives the paragenesis, in terms of these 

three groups, of accessory minerals that I identified 

in thin sections of 250 jasperoid samples collected 

from about 40 different mining districts and unmineralized local^ies.

ALLOPHANE

Allophane is a common, though minor, constituent 

of jasperoid quartz. It forms tiny inclusions, a few 

microns in diameter, embedded in the quartz grains. 

Where more than one generation of quartz is present, the allophane is most highly concentrated in the 

oldest generation. Allophane particles may be zoned 

either in hexagonal patterns around original quartz 

crystal cores (fig. 16) or in wavy colloform patterns 

(fig. 15,4). These zonal patterns, where present, 

are useful indicators of the form in which the silica 

was originally deposited; colloform patterns suggest 

crystallization of jasperoid from a colloidal silica 

gel, whereas hexagonal patterns indicate deposition 

of silica directly in the form of quartz crystals.

ANKERITE

Ankerite is very sparse in jasperoid, but where it 

occurs, it is in the form of relict inclusions. It is 

indicative of a hydrothermal carbonate phase of 

host-rock alteration preceding silicification.

BARITE

Barite is relatively common in jasperoids, particularly those associated with ore deposits; however, in regions characterized by abundant barite, 

such as north-central Nevada, it is found in jasperoid bodies far removed from sulfide deposits. It may 

form granular aggregates or euhedral crystals older 

than the quartz, it may be disseminated through 

the matrix in small grains deposited penecontemporaneously with the silica, or it may be present in 

younger masses and veinlets (fig. 20) and as 

crystals that line vugs.

BEIDELLITE (?)

Small aggregates and disseminated particles of a 

mineral belonging to the montmorillonite group, 

tentatively identified as beidellite, were observed in 

a few jasperoid samples. This mineral is approximately contemporaneous with the matrix quartz in 

which it occurs; but positive identification could not 

be made with the petrographic microscope, and the 

mineral is not sufficiently abundant to furnish a 

sample for X-ray identification.
PHYSICAL PROPERTIES OF JASPEROID 19

TABLE 2. Accessory minerals found in jasperoids during the present study, together with their composition, relative age,

and relative abundance

[The minerals were identified, by T. G. Levering, in thin sections of 250 jasperoid samples collected from 

about 40 mining districts and unmineralized localities]

Mineral Composition

Age and relative abundance

Early Contemporary Late

Allophane ...................................... A12O3, SiO2, ?iH2O .............................................................................................. X ..... .....

Ankerite ........................................ CaO- (Mg,Fe)O 2CO2 .................................................................... x ..................................

Barite ............................................ BaO SO3 ............................................................................................ x x x

Beidellite? .................................... Al2O3 ±SiOa 3±H2O .......................................................................................... x ............

Biotite ............................................ K2O 4(Mg,Fe)O 2(Al,Fe) 2O3 - 6SiO2 H2O .............................. x ..................................

Brochantite .................................. HCuO SO3 3H2O ............................................................................................ ...................... x

Calcite ............................................ CaO COa ............................................................................................ X x x

Carbon .......................................... C .......................................................................................................... x x? ............

Cerussite ...................................... PbO CO2 ............................................................................................................ ...................... x

Chalcedony .................................. SiO2 ...................................................................................................... x x x

Chalcopyrite ................................ CuFeS2 ................................................................................................................ x ............

Chlorapatite ................................ 9CaO 3P2O5 CaCl2 .......................................................................... x ..................................

Dickite .......................................... Al2O3 2Si62 2H2O ..^.....!...............!!!^"........................................... x ..................................

Dolomite ........................................ CaO MgO 2CO2 .............................................................................. x x? ............

Epidote .......................................... Ca2 (Al,Mn,Fe) 3 Si3Oi2 (OH) ............................................................. x ...................................

Fluorite ........................................ CaF2 .................................................................................................................... ...................... x

Galena .............................. . . PbS ...................................................................................................................... x x

Glauconite .................................... SiO2,AlaO3 ,Fe2Os,FeO,MgO,K2O,H2O ................................................ x ...................... ............

Goethite ........................................ Fe2O3 H2O + rcH2O ............................................................................................ x x

Halloysite ...................................... A12O3 - 2SiO2 2H2O ............................................................................................ ...................... x

Hematite ...................................... Fe2O3 .................................................................................................... x x x

Hydromica .................................... (Al,Fe) 2 (Al,Si)4 K<-5(OH) 2 nH2O .......................................................... X ............

Jarosite .......................................... K2O 3Fe2O3 4SO3 6H2O ................................................................................ ...................... x

Kaolinite ...................................... A12O3 2SiO2 2H2O ............................................................................ X x x

Limonite ........................................ Fe2O3 ?iH2O ........................................................................................................ x x

Lussatite ...................................... SiOa nH2O ( ?) .................................................................................................. ...................... x

Magnetite ...................................... Fe2O3 FeO .............................. . ..... ... .................. x x ............

Malachite ...................................... 2CuO CO2 H2O ................................................................................................ ...................... x

"Manganese oxide" .................... MnO,Mn2O3,±rcH2O .......................................................................... -- - . ......... ...... X

Microcline .................................... K2O A12O3 6SiO2 .............................................................................. x ...................... x

Montmorillonite .......................... MgO A12O3 4SiO2 nH2O ..................................................................----.. x x

Muscovite ...................................... K2O 3A12O3 6SiO2 2H8O .............................................................. x ..................................

Nontronite .................................... (Ca,Mg)O 2Fe2O3 - 8SiO2 7±H2O .............................................................. ................ x

Opal .............................................. SiO2 ntL2O ............................ . . ................................................. ...................... x

Orthoclase .................................... K2O - A12OS SiO2 ................................................................................ x ..................................

Plagioclase .................................... Na20 A12O3 GSiOz-CaO A12O3 2SiO2 ........................................ x ...................................

Pyrite ............................................ FeS2 ...................................................................................................... x X x

Quartz .......................................... SiO2 ...................................................................................................... x ...................... X

Sericite .......................................... K2O 3A12O3 6SiO2 2H2O ................................................................................ X ............

Siderite .......................................... FeO CO2 ............................................................................................ x ...................................

Smithsonite .................................. ZnO CO2 ............................................................................................................ ...................... x

Sphalerite .................................... ZnS .................................................................................................................... x x

Sphene .......................................... CaO TiO2 SiO2 ....................................................................._......... x ..................................

Stibiconite .................................... Sb2O4 ?iH2O? ..................................................................... .............................. ...................... x

Tourmaline .................................. Na2 0 8FeO 8A12O3 4B2O3 16SiO2 5H2O .................................. x x ............

Tremolite ...................................... 2CaO 5MgO 8SiO2 H2O ................................................................................ ...................... x?

Wulfenite ...................................... PbO MoO3 .......................................................................................................... ...................... x

Zircon ............................................ ZrO2 SiO2 ............................................................................................ x ..................................

1 X, major accessory: x, minor accessory.

BIOTITE

Biotite is very sparse in jasperoid, and where it 

occurs, it seems to be a relict mineral older than the 

enclosing quartz.

BROCHANTITE

Brochantite is present in minor amounts, as a 

late mineral, in veinlets cutting jasperoid in the 

oxidized zone of some copper districts. In one sample 

from the Bisbee district, Arizona, brochantite lines 

the walls of a veinlet that is filled with still younger 

supergene quartz.

CALCITE

Calcite is the major constituent of the most common host rock for jasperoid and is present in nearly 

all jasperoid bodies. Very fine grained limestones 

are in many places recrystallized into coarsely 

crystalline calcite adjacent to jasperoid bodies, and 

relict grains and breccia fragments of unreplaced 

calcite and limestone are common in these bodies. 

Where replacement of the host rock is more nearly 

complete, tiny particles of calcite are locally preserved in the quartz (fig. 11). These particles may
20 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

either pseudomorphs of galena crystals or alteration 

rims around relict grains of galena.

CHALCEDONY

Chalcedony is abundant in jasperoid. It forms 

spherulites and irregular masses that are peneconFlGURE 20. Barite veinlet (B) cutting jasperoid. Crossed 

polars. X 100.

be concentrated in patterns, similar to those for 

allophane, that indicate the form in which the silica 

was deposited, or they may be randomly distributed. 

Late calcite fills veinlets that cut the matrix or 

forms layers that coat vugs. Much of this late calcite may be of supergene origin, deposited in cavities 

by circulating ground water, but some was probably 

deposited by late hydrothermal solutions.

CARBON

Amorphous, opaque, very dark brown or black 

organic material occurs in some jasperoids. It may 

be present as irregular masses or as streaks or 

particles disseminated in the matrix quartz, or it 

may be concentrated along grain boundaries. In 

some places it is concentrated in a zone adjacent to 

the host rock in which abundant relict grains of unreplaced calcite or dolomite remain. Most of this 

organic material in jasperoid represents an inert 

impurity inherited from the host. The carbon particles disseminated in some jasperoids however, may 

have been introduced and deposited by the silicifying solutions.

CERUSSITE

Cerussite, a constituent of lead ore-bearing jasperoid, occurs in the zone of oxidation. It is an 

alteration product of galena, and commonly forms

FIGURE 21. Chalcedony. A, Chalcedony (C) transitional into 

late quartz (Q), lining a vug. Crossed polars. X 40. B, 

Veinlet of fibrous chalcedony cutting aphanitic jasperoid. 

Crossed polars. X 130.
PHYSICAL PROPERTIES OF JASPEROID 21

temporaneous with the jasperoid quartz matrix (fig. 

21A,B), but more commonly it fills veinlets and 

lines cavities (fig. 21A,B) in the jasperoid. Rarely, 

breccia fragments of chalcedony are enclosed in the 

matrix. Sparse and peculiar feathery or fibrous 

forms of jasperoid quartz appear to have formed 

from the dehydration of original chalcedony (fig. 

8A). Chalcedony is more abundant in fine-grained 

jasperoid than in the coarser varieties.

CHALCOPYR1TE

Chalcopyrite, like galena, occurs locally in 

unoxidized samples of productive jasperoid. It is 

characteristically slightly younger than the first 

generation of matrix silica.

CHLORAPAT1TE

Rounded grains of chlorapatite, older than the 

matrix jasperoid, are present in some samples from 

the Ely district, Nevada. An unusual sample from 

the Shirley Basin, Wyo., contains, as a major constituent, an aphanitic uraniferous chlorapatite that 

is associated with veinlets of younger chalcedony. 

This mineral is rarely present in jasperoids.

CHLOR1TE

Chlorite is a sparse relict mineral in jasperoid. 

It also occurs locally as a late hydrothermal mineral 

in the jasperoids of some major districts. T. S. 

Lovering (1949, p. 39) reported abundant younger 

chlorite in some jasperoid from the Tintic district, 

Utah, where it formed close to the mineralizing conduits.

DICKITE

Dickite was sufficiently abundant for identification 

in only one thin section, and there it appeared to be 

older than the matrix quartz. It is highly probable, 

however, that minor amounts of dickite are intimately associated with kaolinite in other specimens, 

but the mineral was not recognized because of the 

similarity of its optical properties to those of 

kaolinite.

DOLOMITE

Dolomite, like calcite, is a very abundant constituent of jasperoid. It generally appears as unreplaced remnant grains and aggregates in jasperoid 

masses that replace a dolomitic host rock. Another 

common mode of occurrence is as tiny euhedral 

rhombs disseminated through the matrix. These 

rhombs may have been deposited at the same time as 

the silica, or they may be relicts from the selective

replacement of limestone in which they were originally embedded (fig. 13). Veinlets of late dolomite 

that cut jasperoid are extremely sparse. Late carbonate, in jasperoid that replaces dolomite, is generally calcite rather than dolomite.

EPIDOTE

Although epidote is a common constituent of the 

higher temperature lime silicate rocks, it is extremely sparse in jasperoid. It was identified in only 

one thin section, where it is present as small corroded grains in a brecciated zone that was later 

silicified.

FLUOR1TE

Fluorite is relatively sparse in jasperoid, but 

where it does occur, it is generally a late hypogene 

mineral in the form of veinlets that cut the matrix, 

or as masses that enclose grains and aggregates of 

early jasperoid quartz. Locally, it lines vugs and 

cavities in the matrix.

GALENA

Below the zone of oxidation, bodies of jasperoid 

that are host rocks for sulfide ore commonly contain disseminated grains and crystals of galena associated with pyrite. In most of these occurrences, 

the sulfides are clearly introduced after the silicification of the host rock. Locally, deposition of silica 

and sulfides may have been contemporaneous. 

Galena is rarely formed before the enclosing quartz.

GLAUCONITE

Glauconite was identified in only one sample, and 

there it is present as tiny rounded grains in a fragment of silicified sandstone incorporated in a matrix 

of coarse quartz.

GOETHITE

Goethite is common in oxidized jasperoids, where 

it forms late veinlets and irregular masses. It also 

rims vugs, or it may be disseminated as tiny grains 

through the matrix quartz. Crystalline orange 

goethite is commonly associated with amorphous 

isotropic brown or yellow limonite with hematite, 

and less commonly, with jarosite. It is generally a 

very late mineral, younger than both the matrix 

quartz and the limonite; however, in the relatively 

few samples in which it is disseminated through the 

quartz matrix it appears to be contemporaneous in 

origin with the silica and is indicative of supergene 

jasperoid. Sharp euhedral pseudomorphs of goethite 

after pyrite are common in jasperoid outcrops in
22 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

FIGURE 22. Goethite (G) lining vugs filled with coarse 

supergene quartz (Q), in limonite gossan (black). Crossed 

polars. X 68.

mineralized areas, but similar pseudomorphs of 

limonite or jarosite are sparse. In some samples, 

vugs, cavities, and veinlets are rimmed with orange 

goethite and are filled with younger coarse xenomorphic quartz (fig. 22). The fact that the introduction of this quartz did not result in the conversion of 

goethite to hematite indicates that such quartz may 

form at low temperatures. Indeed, in many places 

there is strong evidence that it was deposited by 

downward-percolating surface waters during 

weathering and oxidation of the outcrop.

HALLOYSITE

Halloysite is a sparse late mineral that accompanies kaolinite. It lines vugs and fills fractures.

HEMATITE

Like goethite, hematite is abundant in the oxidized 

parts of some jasperoid bodies, to whose outcrops 

it imparts a characteristic deep-red color, it is generally a late mineral that fills fractures and permeates the rock along quartz-grain boundaries, and it 

commonly forms good pseudomorphs after original 

pyrite crystals (fig. 23). Unlike goethite, however, 

hematite occurs in many samples as an early hypogene mineral, either coprecipitated with original 

silica and disseminated through the resulting jasperoid, or as irregular masses cut by later jasperoid

FIGURE 23. Hematite (H) pseudomorphous after pyrite in 

oxidized jasperoid. Crossed polars. X 68.

quartz. In most samples that contain both hematite 

and goethite the hematite is older, but in some samples the two minerals seem to be nearly contemporaneous. Hematite that is definitely younger than 

associated goethite is very rare. According to Tunell 

and Posnjak (1931), goethite is unstable above 

130°C. There is ample evidence, however, that either 

hematite or goethite can form at low temperatures. 

Iron oxide, like silica, apparently may be precipitated at relatively low temperatures either as a 

colloidal hydrosol or directly in anhydrous form. 

Once it is precipitated as hematite it is stable, but 

the hydrosol may crystallize into goethite, maintain 

its amorphous form, and partly desiccate to form 

limonite, or, depending on its environment after 

deposition, it may even undergo complete dessication 

to form hematite.

HYDROMICA

Hydromica is a common constitutent of early 

hypogene jasperoid quartz, through which it may 

be disseminated. Sericite normally accompanies the 

hydromica, and has the same habit of occurrence. 

Most of the hydromica in jasperoid apparently precipitated concurrently with the early silica, but 

locally it occurs in older clay pockets and lenses. It 

is much less abundant in younger generations of 

jasperoid quartz, and has not been observed as a 

late, postsilica mineral.
PHYSICAL PROPERTIES OF JASPEROID 23

FIGURE 24. Jarosite inclusion (J) in late coarse quartz (Q), 

filling fractures and cavities in jasperoid. Crossed polars. 

X 100.

JAROSITE

The oxidation of pyrite in, or adjacent to, jasperoid bodies in arid regions commonly causes the 

precipitation of jarosite from the acid potassiumbearing sulfate waters. Jarosite in veinlets and as 

vug coatings, disseminated granules, and irregular 

masses accompanies goethite, hematite, and limonite in weathered jasperoid (fig. 24). Massive jarosite only rarely forms the matrix for breccia 

fragments of jasperoid. In many places jarosite is 

clearly derived from the alteration of pyrite, but it 

has not been observed as a direct pseudomorph of 

pyrite crystals. Jarosite is a late supergene mineral, 

generally even later than associated goethite.

KAOLINITE

Kaolinite is a major constitutent of relict clay 

pockets and lenses that are incorporated in silicified 

breccias or are inherited from impure argillaceous 

carbonate rocks. It may also be associated, in minor 

amounts, with hydromica and sericite introduced 

contemporaneously with the silica. It is locally a 

late mineral, occurring with halloysite, coating vugs, 

and filling fractures in the matrix quartz. It is not 

abundant in most jasperoids.

LIMONITE

The amorphous isotropic forms of hydrous iron 

oxide that are abundant as stains and fracture coatFIGURE 25. Limonite particles disseminated through aphanitic jasperoid. Crossed polars. X 170.

ings on outcrops, and in the oxidized zone beneath, 

have been lumped together under the heading of 

"limonite." These limonites are normally some shade 

of brown, ranging from a dark chocolate brown to 

light tan, but some are yellow or orange. In some 

supergene jasperoids, limonite particles are evenly 

disseminated through the groundmass and contemporaneous with it (fig. 25). Rarely, limonite inclusions are present in younger jasperoid quartz. In 

most samples, however, it is definitely later than the 

quartz, and it coats fractures and lines vugs. Limonite normally is associated with late hematite, 

goethite, and jarosite, but in many jasperoid samples it is the only iron mineral present. The reason 

for the wide variation in the color of limonite is not 

known, although the dark-brown varieties seem to 

be most commonly derived from the oxidation of 

sulfides, particularly copper-iron sulfides.

LUSSATITE

Lussatite, a very sparse form of silica, has the 

refractive indices of opal and the birefringence of 

quartz (fig. 26). It is fibrous, has positive elongation 

and parallel extinction, and gives a disorder cristobalite pattern on X-ray. Rogers and Kerr (1942, 

p. 190) regarded it as probably a mixture of fibrous 

chalcedony and opal. In Dana's "A textbook of 

Mineralogy, 4th ed." (Ford, 1932, p. 473), lussatite 

is mentioned as having a structure like chalcedony,
24 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

but the opposite sign, and the specific gravity and 

refractive index of opal. According to Frondel 

(1962, p. 280-281), lussatite is a fibrous form of 

low-temperature cristobalite with a composition 

similar to that of opal but containing less water. 

In the present study, lussatite was observed in two 

samples a jasperoid breccia from the Ely LimeFIGURE 26. Lussatite (L) lining vug in goethite, showing 

fibrous character. A, Crossed polars. X 170. B, Same field, 

with stage rotated. Plane polarized light, x 170.

stone in the Ely district, Nevada, and a silicified 

siltstone sample from the Deadwood Formation in 

the southwestern part of the Lead district, South 

Dakota. In the first sample, fragments of jasperoid 

are cemented by vuggy limonite and goethite, in a 

vein about 3 inches wide, between walls of opal; 

open vugs in the limonite are rimmed with orange 

goethite, and the goethite is encrusted with a thin 

film of lussatite. In the sample from the Deadwood 

Formation a succession of narrow bands, suggestive 

of Liesegang bands, consists of goethite and chalcedony. The goethite in these bands is full of microvugs that are lined with lussatite. In both, the 

occurrence of lussatite as a very late incrustation on 

goethite suggests that it was deposited at low temperature, probably from downward-moving1 surface 

waters.

MAGNETITE

Magnetite is a very sparse constitutent of hypogene jasperoids. It occurs as small rounded grains 

and short irregular veinlets in a fine-grained siliceous dolomite, which is locally replaced by jasperoid 

quartz, in the Pahasapa Limestone in the northern 

Black Hills of South Dakota. This magnetite is older 

than the jasperoid.

MALACHITE

Malachite is associated with jarosite, goethite, 

and brown limonite as an oxidation product from

FIGURE 27. Fine-grained supergene jasperoid impregnated 

with manganese oxide (black areas). Crossed polars. x 40.
PHYSICAL PROPERTIES OF JASPEROID 25

the withering of copper sulfide-bearing jasperoid. 

In most places it fills fractures and coats fractures, 

and it appears to be younger than the associated 

supergene iron minerals. Locally, it forms crystals 

embedded in remnant masses of recrystallized limestone or dolomite, in a matrix of jasperoid quartz.

"MANGANESE OXIDES"

Aphanitic, black, opaque, supergene manganese 

oxides are abundant in a few oxidized jasperoids in 

mineralized areas. These normally are too finely 

divided to permit optical identification of the mineral species present. They characteristically impregnate the matrix quartz of supergene jasperoid (fig. 

27), and are associated with limonite and goethite. 

They range in size from thin films to large irregular 

masses containing scattered quartz grains. In some 

places these masses are fractured and veined with 

younger quartz.

MICROCLINE

Most microcline found in jasperoids occurs as 

relict grains or crystals, inherited from the host 

rock, or as small angular breccia fragments. A 

few jasperoids, in the outer part of a contactmetamorphic zone surrounding an intrusive, however, contain younger microcline in veinlets that cut 

the jasperoid. Where this happens, the jasperoid 

matrix normally is impregnated with sericite.

MONTMORILLONITE

Montmorillonite is not a common constituent of 

jasperoid. It is occasionally observed in the form of 

tiny disseminated particles that cloud the matrix 

quartz, or more rarely, as a filling in late veinlets 

that cut the matrix.

MUSCOVITE

Rarely, coarse flakes of muscovite are incorporated in jasperoid breccias, or they are inherited 

from micaceous rocks that have been replaced by 

jasperoid.

NONTRONITE

Nontronite that occurs in jasperoids is, like halloysite, predominantly of supergene origin. Thin 

veinlets of nontronite cut jasperoid quartz in the 

zone of oxidation. The mineral also lines vugs and 

open cavities. In some samples it is associated with 

late calcite and goethite.

OPAL

Opal is a sparse, late, minor constitutent of jasperoid. It fills veinlets and coats cavities in association with chalcedony and goethite, and is commonly

FIGURE 28. Opal groundmass (O), cut by hematite veinlets 

(H) and younger chalcedony veinlet (C). Plane polarized 

light. X 40.

of supergene origin. In one sample of supergene 

jasperoid, opal takes the place of quartz as the 

major silica mineral in the matrix. Here, the opaline 

groundmass contains disseminated red hematite and 

is cut by veinlets of hematite and of chalcedony (fig. 

28). This opal replaced dolomite at the base of a 

volcanic flow.

ORTHOCLASE

Orthoclase, like microcline, locally occurs as breccia fragments, or as unreplaced inclusions, in a 

silicified matrix. It is very sparse, and has not been 

found as a contemporaneous or younger constitutent 

of jasperoid.

PLAGIOCLASE

The remarks made about orthoclase apply equally 

to plagioclase. Where remnant inclusions of plagioclase do occur, they normally show sericitic alteration.

PYRITE

Pyrite is a common but not abundant constitutent 

of unoxidized jasperoids. Most pyritic jasperoids are 

spatially and genetically related to sulfide ore bodies 

in mining districts. However, pyrite also occurs as 

an early mineral in a considerable number of jasperoids that apparently are unrelated to any other 

sulfide mineralization, and therefore its presence
26 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

cannot be regarded as a reliable guide to ore. Pyrite 

is predominantly contemporaneous with, or slightly 

younger than, the oldest generation of matrix 

quartz. In a few samples, pyrite occurs as an 

aphanitic colloidal precipitate, contemporaneous

FIGURE 29. Alternating colloform bands of pyrite and chalcedonic jasperoid. A, Colloform banding. Dark bands are 

largely pyrite. Reflected light. X 40. B, Enlargement showing abundance of chalcedony (C) in some silica bands, and 

quartz (Q) in others. Black bands are largely pyrite. 

Crossed polars. X 100.

FIGURE 30. Small pyrite grains (P) disseminated in Arkansas Novaculite. Crossed polars. X 170.

with the silica matrix (fig. 29). Pyrite in jasperoid 

generally crystallizes in cubic form, and in oxidized 

samples its former presence is shown by masses of 

cubic hematite or goethite or by square pits. In 

aphanitic, "cherty"-looking, barren jasperoid, pyrite 

may occur as tiny well-formed cubes, a few hundredths of a millimeter in diameter, evenly disseminated through the matrix and apparently contemporaneous with it. A similar occurrence of pyrite has 

been observed in fresh drill-hole samples of Arkansas Novaculite, in which both pyrite and quartz appear to have formed from a syngenetic marine 

chemical precipitate (fig. 30). Neither pyrite nor its 

pseudomorphs have been observed in supergene jasperoid.

QUARTZ

The major constituent of nearly all jasperoids is 

quartz. It occurs both as a replacement and as an 

accessory mineral. Older quartz grains, inherited 

after the replacement of a sandy dolomite or limestone, are commonly found in jasperoids. Many of 

these grains show zonal overgrowths of jasperoid 

silica in optical continuity with the grain (fig. 31). 

Quartz of nonreplacement origin commonly fills 

veinlets that cut the matrix, or it forms well-formed 

crystals that line vugs and cavities. Some of these 

crystals are long, slender, and prismatic, but most 

are short and stubby or show only the pyramidal
PHYSICAL PROPERTIES OF JASPEROID 27

FIGURE 31. Quartz grain inclusions (Q) in jasperoid, showing accretionary overgrowths of jasperoid silica in optical 

continuity. Crossed polars. X 68.

terminations. The theory that quartz may be precipitated directly from cold water as relatively 

coarse grained aggregates, or as crystals, is substantiated by its presence in these forms in veinlets 

in, and crusts on, supergene minerals such as 

goethite (fig. 22) and brochantite.

SERICITE

Sericite is a common constituent of the earliest 

generation of hypogene jasperoid quartz. It is characteristically present in the form of tiny shreds and 

flakes which are randomly disseminated through the 

groundmass and which seem to have been introduced 

with the replacing silica. Sericite may also be present in pockets of older clay, or as an alteration 

product in relict feldspar. It is notably less abundant 

in younger generations of quartz that cuts the matrix. It is commonly associated with hydromica and, 

locally, with kaolinite. The prevalence of sericite in 

association with hypogene jasperoid suggests that 

potassium is a major constituent of the silicabearing solutions that are responsible for the replacement by which this jasperoid formed.

SIDERITE

Siderite, like ankerite, is very sparse in jasperoid. 

It locally occurs in the form of relict grains and 

masses in the matrix, indicating an iron carbonate 

phase of rock alteration that preceded silicification. 

Rarely, it fills veinlets younger than the jasperoid 

quartz.

SMITHSONITE

Grains of sphalerite in ore-bearing jasperoid are 

locally replaced by smithsonite in the zone of oxidation, but, more commonly, the sphalerite either 

remains in its original form or is leached away entirely or is replaced in part by hemimorphite and 

jasperoid.

SPHALERITE

In many mining districts hypogene jasperoid 

forms a siliceous gangue for sphalerite ore. Normally, sphalerite is slightly younger than the quartz, 

but it may also be of about the same age. It is most 

commonly associated with pyrite and galena.

SPHENE

Small rounded detrital grains of sphene, originally 

present in the host rock, at places occur as relict 

inclusions in the replacing jasperoid.

STIBICONITE (?)

An aphanitic yellowish-brown antimony mineral 

that has a high index of refraction is a major constitutent of a jasperoid sample from the Taylor 

district, Nevada. It forms irregular massive inclusions in a jasperoid breccia that shows several 

periods of silicification. The mineral appears to be 

approximately contemporaneous with the youngest 

generation of quartz, and is probably a supergene 

alteration product of stibnite, which is relatively 

common in this district, although none was observed 

in the sample. This mineral has been tentatively 

identified as the hydrous antimony oxide stibiconite, 

which was reported from the Mercur district, Utah, 

by Gilluly (1932, p. 116), and from Kostajnika, 

Yugoslavia, by Beck (1905, p. 581) under the name 

"antimony ochre."

TOURMALINE

Tourmaline, like sphene, in most places occurs in 

the form of rounded detrital grains inherited from 

the host rock. In a few places, however, tourmaline 

appears as tiny slender euhedral crystals that seem 

to have formed at about the same time as the quartz 

matrix in which they are embedded.

TREMOLITE

Tremolite, in association with diopside and coarsegrained calcite, is locally found in the outer fringe 

of contact metamorphic zones surrounding intrusive 

rocks, in veinlets that cut dense aphanitic siliceous 

rocks. Some of these siliceous rocks may be jasperoid, but most of them probably are chert.
28 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE 

TABLE 3. Jasperoid-associated minerals reported in the literature other than those discussed in the text

Locality

Mineral Composition Reference

District State or country

Aragonite .............................. CaO'COa ........................................ Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Organ ........... . New Mexico .......... Dunham (1935, p. 126-129).

Tri-State ...... Oklahoma, Kansas,

Missouri. Weidman (1932, p. 68).

Argentite ...................... AgaS .............................................. Georgetown ........ ......... New Mexico .......... Anderson, E. C. (1957,,p. 67).

Horseshoe-Sacramento.. Colorado .................. Butler and Singewald (1940, p. 809).

Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Mineral Hill .................. Nevada .................... Emmons, W. H. (1910, p. 97).

Phillipsburg .................. Montana .................. Emmons and Calkins (1913, p. 213-219).

Arsenopyrite ........................ FeAsS ............................................ Gold Hill ........................ Utah .......................... Nolan (1935, p. 102-103).

Manhattan ......... . Nevada .................... Ferguson (1921, p. 15).

Aurichalcite .......................... 7(Zn,Cu)O«3CO2»4H2O ............ Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Azurite .................................. 3CuO«2CO2«H2O ................................ do ............ .. ...... do ........................ Do.

Mineral Hill .................. Nevada .................... Emmons, W. H. (1910, p. 97).

Phillipsburg .................. Montana .................. Emmons and Calkins (1913, p. 213-219).

Pilgrims Rest ................ South Africa .......... Beck (1905, p. 576-577).

Tutsagubet .................... Utah .......................... Butler, Loughlin, Heikes, and others (1920, p. 595).

Bismite (Bismuth Ochre).. Bi2O3«3H2O( ?) ............................ Pilgrims Rest ................ South Africa .......... Beck (1905, p. 576-577).

Cerargyrite ............................ AgCl .............................................. Georgetown.. New Mexico .......... Anderson, E. C. (1957, p. 67).

Lake Valley ........................ do ........................ Harley (1934, p. 176-178).

Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Mineral Hill ........ .. Nevada .................... Emmons, W. H. (1910, p. 97).

Phillipsburg .................. Montana .................. Emmons and Calkins (1913, p. 213-219).

Chalcocite .............................. CuaS ................................................ Ely .................................. Nevada .................... Spencer (1917, p. 99).

Phillipsburg .................. Montana .................. Emmons and Calkins (1913, p. 213-219).

Chrysocolla ............................ CuO«SiO2«nHaO( ?) .................. Lucin .............................. Utah .......................... Butler, Loughlin, Heikes, and others (1920, p. 493).

Mercur-Ophir ...................... do ........................ Gilluly (1932, p. 116).

Phillipsburg .................. Montana .................. Emmons and Calkins (1913, p. 213-219).

Cuprite .................................. CuzO .............................................. Lucin .............................. Utah .......................... Butler, Loughlin, Heikes, and others (1920, p. 493).

Enargite ................................ CuzS^CuS'AsaSs ........................ Colquijirca .................... Peru ........................ McKinstry (1936, p. 622).

Freibergite ............................ 5(Cu,Ag)2S«2(Cu,Fe)S»2Sb2Ss .. Phillipsburg .................. Montana .................. Emmons and Calkins (1913, p. 213-219).

Gold ........................................ Au ............................ ................. Bull Valley .................... Utah .......................... Butler, Loughlin, Heikes, and others (1920, p. 598).

Kingston ........................ New Mexico .......... Harley (1934, p. 98).

Pilgrims Rest ................ South Africa .......... Beck (1905, p. 576-577).

Terry .............................. South Dakota ........ Irving (1911, p. 631).

Gypsuu. .................................. CaO«SOs«2H2O ............................ Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Luzonite ...___.................. Cu2S»4CuS«As2Ss ........................ Colquijirca .................... Peru ........................ McKinstry (1936, p. 622).

Manganite ............................ MiaOa'SsO .................................. Postmasburg .................. South Africa .......... Du Toit (1933, p. 113).

Manganocalcite .................... (Ca,Mn)O»CO2 ............................ Kingston ........................ New Mexico .......... Harley (1934, p. 98).

Ouray .............................. Colorado .................. Burbank (1940, p. 207).

Manganosiderite .................. (Fe,Mn)O»COa ................. .. . Leadville .......................... . do ........................ Emmons, Irving, and Loughlin (1927, p. 218).

Marcasite .............................. FeSa ................................................ Colquijirca .................... Peru ........................ Lindgren (1935, p. 334).

Tri-State ........................ Oklahoma, Kansas,

Missouri. Weidman (1932, p. 68).

Melaconite ............................ CuO ........................... ...... Mercur-Ophir ............_.. Utah .......................... Gilluly (1932, p. 116).

Orpiment .............................. AsaSs ....................... . ....... Manhattan .................... Nevada .................... Ferguson (1921, p. 15).

Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Pearceite ................................ 8Ag2S»As2Sa .................................. Ouray ............................. Colorado .................. Burbank (1940, p 207).

Plumbojarosite .................... PbO«3Fe2Os«4SOs«6H2O ............ Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Tutsagubet .................... - do ........................ Butler, Loughlin, Heikes, and others (1920, p. 598).

Pyrargerite ............................ 3Ag2S»SbsS3 ................................. Ouray .............................. Colorado .................. Burbank (1940, p 207).

Pyromorphite ...................... 9PbO.3P2Os«PbCl2 ......... .... Mineral Hill .................. ...... do ................... Emmons, W. H. (1910, p. 97).

Pyrrhotite .............................. Fei-*S ............................................ Ely .................................. Nevada .................... Spencer (1917, p. 116).

Realgar .................................. AsS .................................................. Manhattan .......................... do ........................ Ferguson (1921, p. 15).

Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 99).

Rhodochrosite ........................ MnO'COa ...................................... Bingham .............................. do ........................ Boutwell (1905, p. 160).

Kingston ........................ New Mexico .......... Harley (1934, p. 98).

Ouray .............................. Colorado .................. Burbank (1940, p. 207).

Phillipsburg .................. Montana ... Emmons and Calkins (1913, p. 213-219).

Rhodonite .............................. (Mn,Mg,Fe,Ca)MnSi2Oe .......... Diadem Lode ................ California ................ Turner (1899, p. 389).

Scorodite ................................ Fe2Os»As2O5»4H2O ... ............ Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Senarmantite ........................ SbaOs .............................................. Kostajnika .................... Yugoslavia ................ Beck (1905. p. 578-580).

Rosia .............................. Italy .......................... Do.

Silver ...................................... Ag .................................................. Colquijirca ..............._... Peru ........................ Lindgren (1935, p. 334).

Georgetown .................... New Mexico .......... Anderson, E. C. (1957, p. 67).

Lake Valley ........................ do ........................ Harley (1934, p. 176-178).

Stibnite .................................. Sb2Sa .............................................. Cortez .............................. Nevada .................... Emmons, W. H. (1910, p. 103-104).

Kostajnika .................... Yugoslavia .......... . Beck (1905, p. 578-581).

Manhattan .. ........... . Nevada .................... Ferguson (1921, p. 15).

Mercur-Ophir ................ Utah.......................... Gilluly (1932, p. 99).

Rosia .............................. Italy .......................... Beck (1905, p. 581).

Stromeyerite ........... ...... (Ag.CuJaS .................................... Colquijirca .................... Peru .......................... Lindgren (1935, p. 334).

Cortez .............................. Nevada .................... Emmons, W. H. (1910, p. 103-104).

Sulfur .................................... S ...................................................... Kostajnika .................... Yugoslavia ................ Beck (1905, p. 578-581).

Mercur-Ophir ................ Utah .......................... Gilluly (1932, p. 116).

Rosia ................................ Italy .......................... Beck (1905. p. 581).

Sylvite .................................... KC1 ................................................ Ely .................................. Nevada .................... Spencer (1917, p. 63).

Tennantite ............................ 6Cu2S«2(Cu.Fe) S«2As2&- .......... Cartersville .................... Georgia .................... Kesler (1950, p. 48).

Colquijirca .................... Peru .......................... Lindgren (1935, p. 334).

Horseshoe-Sacramento.. Colorado .................. Butler and Singewald (1940, p. 809).

Tetrahedrite .......................... 5Cu2S«2(Cu,Fe)S»2Sb2Ss .......... Bingham ........................ Utah .......................... Bqutwell (1905. p. 160).

Cortez .............................. Nevada .................... Emmons, W. H. (1910, p. 103-104).

Gold Hill ........................ Utah .......................... Nolan (1935, p. 153).

Mineral Hill .................. Nevada .................... Emmons, W. H. (1910, p. 97).

Ouray .............................. Colorado .................. Burbank (1940, p. 207).

, . . , . Stockton .......................... Utah .......................... Butler, Loughlin, Heikes, and others (1920, p. 372).

Wittichemte .......................... SCuzS'BLiSs .................................. Colquijirca .................... Peru .......................... Lindgren (1935 p. 334).
PHYSICAL PROPERTIES OF JASPEROID 29

WULFENITE

Wulfenite has been observed in jasperoid from 

only one locality, the Seventy Nine mine in the Banner district, Arizona. Here, it forms crystals, associated with goethite, that line vugs in a jasperoid 

body that crops out near the entrance to the mine.

ZIRCON

Small rounded grains of zircon, associated with 

tourmaline, sphene, and other detrital minerals, are 

commonly preserved in jasperoid that has resulted 

from the silicification of siltstone and impure carbonate rocks.

OTHER MINERALS

Other minerals which are locally associated with 

jasperoid and which have been reported in the literature are listed in table 3. It is noteworthy that most 

of these minerals are those characteristic of shallow 

epithermal deposits. They consist largely of salts of 

Ag, As, Bi, Cu, Mn, Pb, and Sb.

OTHER PHYSICAL PROPERTIES

Studies were made of the density, porosity, and 

response to differential thermal analysis of some 

representative jasperoid samples in order to (1) 

estimate the nature of the distribution of these 

properties in jasperoid and (2) ascertain whether 

variations in any of them could be useful in distinguishing barren jasperoid bodies from those related 

to ore. The results of this second phase of the investigation will be discussed in a subsequent chapter 

of this report.

DENSITY AND POROSITY

Bulk and powder density determinations were 

made on 124 jasperoid samples representing 19 

districts. The porosity of the sample (in percent) 

was calculated from the equation,

f / Bulk density \ 1

Porosity = I 1 - I -^ -= -= ^ I I X 100. I \ Powder density / I

The observed range of powder densities is 2.50-3.61; 

that of porosities is from <1 to 17 percent. The 

frequency distributions for both density and porosity are distinctly skewed with modes in the low 

values (fig. 32). The sample frequency distribution 

for density approximates a log normal distribution, 

truncated in the low values. The distribution of 

sample porosity data is highly irregular.

The relatively large number of jasperoid samples 

with powder densities in the range 2.5-2.6 is surprising, because the major identifiable minerals in 

jasperoid (quartz, chalcedony, calcite, dolomite,

2.6 2.7 2.8 2.9 3.0 

POWDER DENSITY

J.2 >3.2

ARITHMETIC MEAN

46 8 10 12 

POROSITY. IN PERCENT

FIGURE 32. Histograms showing distributions of density and 

porosity in 124 jasperoid samples.

limonite, kaolinite, sericite) all have specific gravities >2.6.

Many of the extremely fine grained cherty varieties of jasperoids may contain appreciable quantities 

of air or water trapped in submicroscopic pores, 

along fractures and grain boundaries, and in fluid 

inclusions, or the anomalously low birefringence of 

some of these varieties may reflect, in part, the 

presence of cristobalite or opal granules too small 

for identification but sufficiently abundant to lower 

the density of the rock. However, differential thermal analysis of some of these low-density samples
30 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

did not confirm the presence of abundant pore 

water, opal, or cristobalite.

The experimental error factor in these density determinations was appreciable, and may have been 

sufficient to account for the low-density values. The 

likelihood that these low values are due entirely 

to experimental error is considerably reduced, however, by the fact that some of them are based on independent determinations on replicate splits of the 

same sample made in different laboratories. The 

porosity values calculated from the ratios of two 

separate density determinations, both of which were 

subject to considerable analytical error, must be regarded as rough approximations. It is doubtful, 

however, that refinements in the determination of 

sample porosity would alter the general observation 

that dense jasperoid of low porosity is considerably 

more abundant than jasperoid of high porosity.

DIFFERENTIAL THERMAL ANALYSIS

Differential thermal analyses (hereafter referred 

to as DTA) were made on 12 selected jasperoid samples and on two chert samples in order to (1) test 

the theory that chert and aphanitic cherty jasperoid 

may contain appreciable quantities of opaline silica,

(2) determine whether the DTA curves for syngenetic chert differed from those for jasperoid, and

(3) ascertain whether the presence of finely divided 

sulfides, or their alteration products, in jasperoid 

would produce diagnostic peaks on the curves. All 

samples were run on a portable DTA apparatus, 

after calibration of the cells with a standard montmorillonite sample.

Most of the jasperoid samples and one chert sample gave endothermic peaks at various temperatures 

between 100° and 800°C, but no consistent pattern 

was apparent. One jasperoid sample known to contain opal as a major constitutent showed, as expected a strong endothermic peak at about 100°C. 

A pyritic sample showed an endothermic peak at 

about 650°C, and a sample containing much 

sphalerite showed a similar peak at about 750°C. 

Some samples that consist predominantly of aphanitic silica proved to be inert, but other samples of 

similar composition gave a pronounced isolated 

endothermic peak in the range of 500°-550°C. This 

range is too broad, and the peak too strong, to mark 

the inversion of a quartz to ft quartz. The presence 

of this peak is difficult to interpret in terms of the 

known mineralogy of the samples. It comes at too 

high a temperature to mark the dehydration of clay 

minerals or hydrous iron oxides, and at too low a 

temperature to be caused by the breakdown of calcite or dolomite. Alunite could give such a peak, but

no alunite is visible in thin sections of these rocks.

Neither the "cherty" jasperoid samples nor the 

two samples of true chert showed any marked endothermic inflections in the range 80°-300°C. This 

casts considerable doubt on the theory that opal or 

well-crystallized cristobalite is present in any appreciable amount. The DTA curves of cristobalite, 

reported by Eitel (1957, p. 148), all show strong 

single endothermic peaks between 230° and 260°C.

This small sampling indicates that many jasperoids and some cherts do give pronounced inflections 

on DTA graphs, but that these two rock types cannot be distinguished from each other by this method.

COMPOSITION OF JASPEROID

The connotation of a rock composed principally 

of fine-grained or dense replacement silica has' been 

either stated or implied in the various definitions of 

jasperoid since the term was first introduced by 

Spurr in 1898. However, jasperoid grades into 

partly silicified mudstone, dolomite, and limestone 

with increasing alumina and carbonate content and 

decreasing silica content; into siliceous iron and 

manganese ore with increase in the oxides of these 

metals; and into siliceous sulfide ore with increasing 

sulfide content. The boundaries are vague and ill 

defined. They commonly have been established arbitrarily at the discretion of individual investigators 

in individual districts. Jasperoid that is minable for 

one or more metals is designated by the mining industry as siliceous ore. I consider that a rock matrix 

must consist of at least 50 percent replacement silica 

to be called a jasperoid.

MAJOR CONSTITUENTS

The few available complete analyses of jasperoids 

show considerable range in the concentration of 

major constituents, and do not differ notably from 

analyses of other similar rocks of different origin, 

with the exception of iron-formation jaspilites 

(tables 4, 5).

Any attempt to draw general conclusions as to 

characteristic differences in composition between 

jasperoids and the other silica rock types, with the 

possible exception of jaspilite, from the limited 

amount of data given in tables 4 and 5 is unwarranted. Some apparent differences in the sample 

data suggest the possibility of corresponding tendencies in the rock types, but, until considerably more 

analytical data become available for comparison, 

these differences must be regarded as suggestive 

only. Jaspilite samples contain about half as much 

silica and several times as much ferric oxide as the 

jasperoid samples, and somewhat less water. These
COMPOSITION OF JASPEROID 31

TABLE 4. Analyses of jasperoid and other similar rocks

[I.L., ignition loss; ......... no analyses]

Jasperoid

Chert, flint, and 

novaculite Silcrete

Siliceous 

sinter

10 11 12 13 14 IB 16 17 18 19 20

SiOs..........

AlzOs........

Fe2O3.......

FeO........

MgO.......

CaO..........

NazO........

KzO..........

HsO +.......

HsO ........

TiO2........

PsOs.........

................ 96.79

.................. .52

................. 1.02

................. .17

.... .. . .16

................. .14

................. .01

................. .09

................. .35

................. .05

................ .04

................. .01

95.75

1.12

.36

.19

.01

.00

.00

.09

.75

.05

.03

.06

93.28

1.01

1.29

.37

.04

.14

.03

.07

.31

.06

.03

.08

81.70

3.24

5.41

.28

.16

.44

.12

1.10

2.16

.29

.20

.05

96.27

.26

.26

.19

.19

1.16

.05

.11

.42

.03

79.11

3.82

.44

.69

1.19

.62

.31

.54

2.68

.81

.81

.42

95.26

.57

,.00

.69

.05

.25

...... 1

...... |

95.77

1.84

.24

.54

1.17

97.33

1.89

.09

.11

1

| .77

97.07

1.05

.53

Trace

.51

.04

97.32

.521

.so;

.02

.02

.52

; .02

I .03

.491

.16f

.02

.02

98.17 95.50

no J -10 83 1 1.95

.15

.01 Trace

.05 ......

...... Trace

.78} 1.43

I.L.f I.L.

98.19

.00

.02

.21

.30

.08

.03

1.111

.33f

.03

99.47

.17

.12

.05

.09

.15

.07

.12

I.L.

95.10

2.03

.53

.20

.16

.461

I.Lf

1.58

97.05

.95

.14

.0

.0

.471

I.Lf

1.43

94.92

2.32

.31

1.381

l.L|

1.14

72.25 '

10.961

.76f

.31

.10

.74

3.55

1.66

9.021

I.L{

92.67

.0V

.05

.14

,75

.18

5.45

I.L.

MnO.......................... .03 .03 .03 ...... ...... ...... ...... ...... ...... Trace .02 ......

CO°............................ .09 .16 .05 ...... .96 ...... ...... ...... ...... ...... .38 ...... ...... .24 ......

S................................ .00 .08 1.05 l 2.97 .05 2 3.01 ...... ...... ...... ...... .00 ...... ...... .00 ...... ...... ...... ...... 1 .4B

BaO........................... .00 .00 .00 .43 .06 ...... ...... ...... ...... ...... .00 ...... ...... ...... ...... ...... ...... ...... ......

Subtotal-..--- 99.47 

Other................ ......

98.68 97.84 98.55 100.01 94.45 96.82 99.56 100.19 100.19 99.84 

a -.04 3 -.53 4 1.42 2.11 5 5.19 ...... «.04

99.84 99.13 100.54 100.24 100.06 100.04 100.07 99.80 100.04

7.36

Total............. 99.47 98.64 97.31 99.97 100.12 99.64 96.82 99.56 100.19 100.23 99.84 99.84 99.13 100.54 100.24 100.06 100.04 100.07 100.16 100.04

1 As SOa. a Au+Ag+Te. a Oxygen correction. * SbaOs+A&sOs. 5 Cu+Fe as sulfides. « Cu+Zn+Ni+Co. 7 NaCl.

No. Description Locality

1........ Oxidized jasperoid .................... Minturn quadrangle, Colorado

2........ ........do .......................................... Tintic district, Utah .................

3........ - ~ ~ -

4........

5 

6........

1........

Unoxidized jasperoid ................ Tri-State district, Oklahoma....................

Oxidized jasperoid .................... Mercur district, Utah ................................

Unoxidized jasperoid ................ Black Hills, S. Dak ....................................

Composite jasperoid sample.... Ely district, Nevada ..................................

Jasperoid .................................... Joplin, Mo . . ...................................... ..

S........ ........do .......................................... Joplin district, Missouri ............................

9... .. ........do .......................................... Galena, Kans ................................................

10. .... ........do .......................................... Bull Frog mine, Chitwood, Mo ................

11........ Chert ............................................ Custer County, S. Dak ..............................

12........ ........do .......................................... Belleville, Mo ..............................................

13 . . Irish chert .................................. Ireland ..........................................................

14 ..... English flint ................................ England ........................................................

15. Arkansas novaculite ................ Arkansas ......................................................

16 . Silcrete ........................................ Albertina, Cape Province, South Africa..

17........ ........do .......................................... ........ do ..........................................................

18........ ........do .......................................... ........ do ..........................................................

19 . Siliceous sinter .......................... Yellowstone Park, Wyo ............................

20........ ........do .......................................... Steamboat Springs, Nev ............................

Source of data

Present study (E. L. Munson, analyst).

Do.

Do.

Gilluly (1932, p. 114). 

Irving (1911, p. 647). 

Spencer (1917, p.117). 

Bain (1901, p. 121). 

Cox, Dean, and Gottschalk (1916, p. 16).

Do.

Do.

Present study (E. L. Munson, analyst). 

Clarke (1924, p.551).

Do.

Weymouth and Williamson (1951, p. 580). 

Clarke (1924, p. 551). 

Frankel (1952, p. 179).

Do.

Do. 

Clarke (1924, p. 207).

Do.

TABLE 5. The observed range and average concentrations, in percent, of the 13 commonly reported oxides plus sulfur 

for 10 representative jasperoid samples compared with those of certain other rock types

[Leaders (......) indicate no information]

Jasperoid

Range Average

SiOa ...................

AW), .................

Fe203 .................

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

MgO ...................

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

Na20 .................

K2 0 .....................

H20 (total) .......

TiOa ...................

P20B ...................

C0a .....................

S .........................

BaO ...................

..... 80 -97

.3-4

..... 0-5

.15- .7

..... 0-1

..... 0-1

..... 0 - .3

.1-1

.4 - 3.2

.03- .8

.01- .4

..... 0-1

..... 0-3

...... 0 - .4

92.8 

1.4 

1.3 

.4 

.2 

.4 

.1 

.3 

1.2 

.2 

.1 

.3 

1.2 

.1

Chert

Range .# Average

95.5 -99.5 

0 - .5 

0-2 

0 - .15 

0 - .2 

.05- .5 

0 - .15 

0 - .07 

.1 - 1.5

0 " -" .4 

0 

0

97.7 

.2

.6

.08 

.06 

.25 

.06 

.04 

.8

"J

0 

0

95 

1

0 

0

1

Silcrete

Range Average

-97 

- 2.3 

.1 - .5 

...... ^

- .16

.45-1.4 

.1 - 1.6

95.7 

1.8 

.3 

..-.

.08

"".6"

1.4

Siliceous sinter

Range Average

72 -93 

.8 -12

.05-" .1 

.15 - .75 

.8 - 3.5 

.2 - 1.7 

5.5 - 9

82.5 

6.2

""67

.4 

2.1 

.9

7.2

Jaspilite

Range

34.3 -61.4

0 - 4.6 

30.6 -53.1 

.4 - 5.7 

0 - 2.7 

0 - 4.2 

0 - 1.7

.07- 1.9 

0 - .3 

.05- .6 

.06- 2.9 

0 - .2

Average

47.3 

1.2 

45.2 

2 

.5 

1.3 

.6

.7 

.1 

.3 

1.3 

.09
32 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

IRON

n=200

M

30-i ALUMINUM 

M

71=190

ddodddd^cor-.'

MAGNESIUM

71=200

n=20 7i=20

40-1 BARIUM

40-

Z 30-j

20-

10-

71=200

CHROMIUM

»i=20

o o o * c*> r^ r^ 

ddddddddo'd d

A

COPPER

I I I

g

rt co rv m 

80808 

d ddddddd

V

M

n=200

888S

FIGURE 33. Distributions of elements detected by semiquantitative spectrographic analysis in most of the jasperoid (black) 

and chert (stippled) samples. M, median, ~x arithmetic mean. Distribution in parts per million, n, number of samples 

analyzed.
COMPOSITION OF JASPEROID 33

40-i TITANIUM

71=200

MANGANESE 

w=200

NICKEL

71=200

M

o 1-1 f> r*. in

8 8 8 § 8 S 8

o d d o d d d

VANADIUM

7i=200

71=20

V
34 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

differences reflect the fact that jaspilite consists of 

alternating layers of hematite and jasper.

The silica content of the jasperoid samples is 

slightly lower than that of the cherts and silcretes; 

Fe2O3 and A12O3 are higher in the jaspercids than 

in the cherts, but lower than in the siliceous sinters. 

Differences in MgO and CaO contents between the 

rock types are minor; K2O is higher than Na2O in 

jasperoid samples, but the reverse is true in chert 

and siliceous sinter samples. Data for combined 

water versus free water are available only for the 

jasperoids, so no direct comparison can be made of 

these components; ignition loss in the chert and 

silcrete samples is comparable to the sum of H2O+ 

and H2(X in the jasperoid samples, but it is considerably higher in the siliceous sinter samples. 

TiO2 is nearly an order of magnitude higher in 

samples of silcrete than in those of jasperoid, but 

the silcretes all came from the same area, and therefore, they may not be truly representative of this 

type of rock. It would be interesting to ascertain 

whether other representatives of ground-waterprecipitated silica, such as the duricrusts in Australia and the silica-cemented gravels elsewhere, 

show the same tendency toward high titanium content.

MINOR CONSTITUENTS

Semiquantitative spectrographic analyses for 64 

elements were made on about 200 samples of jasperoid and 20 samples of chert and novaculite by 

J. C. Hamilton of the U.S. Geological Survey, using 

a method described by Myers, Havens, and Dunton 

(1961). Only 43 elements were detected in one or 

more of the samples, and only 13 are present in detectable concentrations in most of the samples. These 

13 are Si, Al, Fe, Mg, Ca, Ti, Mn, Ba, Cr, Cu, Ni, Sr, 

and V; Si, of course, is a major constituent of all 

the samples. Frequency distributions of the other 12 

elements in the jasperoid and chart samples are 

shown in figure 33.

STATISTICAL SUMMARY

The class intervals of the histograms are those in 

which the analyses were reported. Some replicate 

samples were submitted to check the precision of the 

analyses. About 60 percent of the reported concentrations of the elements in these check samples 

duplicated the original determinations; about 90 percent came within one reporting interval of the original value.

All the jasperoid sample distributions are positively skewed, with an arithmetic mean higher than 

the median, and all but Ba, Ca, and Sr are unimodal.

Ba and Ca display a single intermodal class which 

is only slightly lower than the adjacent modal 

classes; thus, the bimodality of the sample distributions may reflect a slight analytical or sampling bias 

in samples from populations with platykurtic distributions. Cumulative frequency-distribution plots 

on logarithmic probability paper reveal four different types of sample distributions of these 12 

elements in jasperoid. Al, Fe, Mg, and Ni display 

straight-line plots closely approximating single log 

normal distributions; Ca, Mn, Ba, Cu, and V all display plots in which the low values fall close to one 

straight line and the high values close to another 

straight line with lower slope, with a pronounced 

breakpoint where the two lines intersect. This suggests that for these five elements the samples represent a mixture of two populations one of low 

values with relatively small dispersion and one of 

high values with greater dispersion, both populations being approximately log normal. Cr and Ti 

also display plots characterized by two straight lines 

with a breakpoint, but the high values have a greater 

slope than the low, suggesting a smaller dispersion 

in the high values. Sr displays a very irregular 

cumulative frequency-distribution curve with three 

breaks in slope. The medians of the cumulative distributions for all the elements in which these distributions show a break in slope fall below or nearly 

on this break; thus, the sample median values are 

probably the best representative measures of central tendency for the concentration of these elements 

in jasperoid. The arithmetic-mean concentrations of 

many of these elements are strongly influenced by 

the presence of a few samples in which the elements 

are present in abnormally high concentration, and it 

is doubtful that the proportion of such samples in 

the suite of 200 samples analyzed is adequately 

representative of the proportion of jasperoids containing this high a concentration of these elements. 

Thus, for the elements Ca, Mg, Ba, and Cu in which 

the arithmetic mean is an order of magnitude or 

more higher than the median, the mean does not 

furnish a good representative value for the normal 

concentration of these elements in jasperoid.

The number of chert samples for which comparable analyses are available is so small (12 for Al 

and Ca; 20 for the other elements) that any general 

conclusions drawn from a comparison of these sample frequency distributions with the corresponding 

ones for jasperoid are of dubious validity. In all but 

three of the elements the mean and median values 

for chert either are bracketed by those for jasperoid 

or correspond closely to them. These three exceptions are Fe, Cu, and Sr; for Fe and Cu, both the
COMPOSITION OF JASPEROID 35

mean and median values for chert are below the 

median for jasperoid. The sample data suggest, 

therefore, that iron and copper concentrations are 

characteristically higher in jasperoid than in chert, 

but a considerably larger number of representative 

chert sample analyses would be needed to establish 

this hypothesis. The median value for strontium in 

chert is slightly lower than in jasperoid, and the 

arithmetic mean in chert is slightly higher than the 

jasperoid median; however, in view of the highly 

irregular frequency distributions of this element in 

the samples of both rock types and the small number 

of samples involved, it is doubtful that any general 

significance can be ascribed to this fact.

Frequency distributions and estimated median 

values for the remaining 30 elements detected in one 

or more of the jasperoid samples are given in table 

6. The median values of all 42 elements in the 200 

jasperoid samples are given in table 7. The average 

abundance of these elements in igneous rocks is also 

shown for comparison (Rankama and Sahama, 

1950, p. 39-40). Most of the elements seem to be 

deficient in jasperoid as compared with igneous 

rocks. Only Ag, As, Bi, In, and Sb are significantly 

enriched in jasperoid, and all five of these are 

chalcophile elements. This apparent tendency toward enrichment of chalcophile elements in jasperoid is reasonable, because most jasperoid is a

product of hydrothermal alteration and chalcophile 

elements are likely to have been most concentrated 

in such solutions.

Concentrations of chalcophile elements in jasperoid may provide diagnostic criteria for distinguishing jasperoids from syngenetic and diagenetic chert. 

As shown in table 6, however, there is a wide variation in content of the chalcophile elements in jasperoid. Thus, their presence in abnormally high 

concentration may indeed be indicative of jasperoid 

rather than chert, but low concentrations are not 

indicative of chert.

GENESIS OF JASPEROID

The existence of a body of silicified rock (jasperoid) implies the existence of the following: (1) An 

adequate source of silica; (2) fluids capable of dissolving and transporting the silica to the site of 

deposition; (3) conditions at the site of deposition 

that caused silica to replace the host rock, and (4) 

reaction rates at this site such that host rock dissolved at the same rate or a little faster than silica 

precipitated. Any theory that seeks to explain the 

genesis of jasperoid must, therefore, account for 

each of these conditions.

SOURCE OF SILICA

The silica emplaced in jasperoid bodies may have

TABLE 6. Distribution of minor elements in 200 selected jasperoid samples

[J. C. Hamilton, analyst. Numbers in parentheses ( ) indicate number of samples in which element is present in trace amounts. Leaders in figure 

columns (......) indicate no data (no samples in group). Query (?) indicates estimate for elements detected in 5 percent or less of the samples]

Element Number of samples in which element detected in parts 

in first entry in figure columns

Na ..............

K ..................

P ..................

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

As ................

B ..................

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

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

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

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

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

Ga ................

Ge ................

In ................

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

Li ................

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

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

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

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

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

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

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

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

U ..................

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

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

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

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

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

>0.07 0.7 0.3 0.15 0.07 0.03

.................. 3 ...... 2 5 17 (12)

.................. 3 7

.................. 2 4

.................. ...... ...... 1 ...... 4 5

.................. 13 ...... 962

.................. ...... ...... 1

2 1 H

3

.................. ...... ...... ...... ...... ...... 5

.................. ...... ...... ...... ...... ...... 1

.................. ...... 1 ...... 1

.................. 10 4 7 7 11 12

.................. 1 114 4 10

.................. ...... ...... ...... 2 ...... 1

.................. ...... ...... ...... 1

.................. 4 4 7 11 23 21

.................. ...... ...... ...... ...... 1 8

0.015

10

5 

1 

(1) 

1

1

14 

10

2 

1

2 

1

2

10

0.007

6

3

4 

3

1 

1 

2 

3

5

7

22

5

1

(23) 

27

0.003

22

28

10

1 

1 

2 

3 

(10)

17

19

5

12

39

Number of 

samples in 

per million shown which element not 

detected

0.0015 0.0007 0.0003 0.00015

14 11 13 12

6

3 5 13 25 

1 1 ti\

4 (11)

3 12 (15) 

2

(17)

28 21

(6)

(14)

3 6

(15)

37 (3)

1 ...... 10 39

48

161 

190 

194 

102 

170 

162 

154 

157 

193 

194 

182 

168 

194 

176 

185 

199 

125 

194 

199 

80 

169 

191 

170 

199 

199 

197 

147 

150 

105 

67

Abundance 

Estimated in igneous 

median 1 rocks 2

(ppm) (ppm)

0.003 

.02? 

.005? 

.0001 

.001 

.0005 

.00002 

.00005 

.00001 ? 

<. 00001 

.00005 ? 

.00003 

.000001 ? 

.0001 

.0001 ? 

<. 00001? 

.0002 

<. 000001? 

<. 000001? 

.002 

.0006 

.00005 ? 

.00005 

< .000001 ? 

<. 00001? 

.000001 ? 

.0004 

.00004 

.002 

.001

2.8 

2.7 

.12 

.00001 

.0005 

.0003 

.0006 

.00002 

.00001 

.005 

.002 

.0015 

.0007 

.00001 

.002 

.0065 .0005 + 

.002 

.002 

.0016 

.0001 

.0005 

.004 

.0001 

.0004 

.002 

.003 

.0003 

.013 

.02

1 Median estimated by extrapolation of truncated cumulative frequency distribution. 8 Data from Rankama and Sahama (1950, p. 39-40).
36 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

TABLE 7. Median concentrations of elements detected in the 

200 jasperoid samples studied during the present investigation compared with average concentrations in igneous rocks 

as given by Rankama and Sahama (1950, p. 39-40)

Element concentrations 

(in percent) in 

Element 200 jasperoid Igneous rocks

samples (average)

(median) 2 (from Rankama and

(present study) Sahama, 1950, p. 39-40)

Fe .............................................. 0.7 5

Al .............................................. .25 8.1

Ca .............................................. .18 3.6

Mg .............................................. .03 2.1

K ........................................... (.02)? 2.7

Ti .. ............................................ .016 .4

Mn .............................................. .011 .1

Ba ..... ............. .......... .008 .025

P ................................................ (.005)? .12

Cu . .... .003 .007

Na .............................................. (.003) 2.8

Pb .............................................. (.002) .0016

Zn . ............ ......................... (.002) .013

As . ...... . ... .. ......... (.001) .0005

Sr .............................................. .001 .03

V . .. .... .001 .015

Zr .............................................. (.001) .02

Cr ............................................. .0008 .02

Ni . ............ ......................... .0006 .008

Sb ............ . ............ ......... (.0006) .0001

B . .... ......... (.0005) .0003

Y ................................................ (.0004) .003

Mo .............................................. (.0002) .0005±

Ag .............................................. (.0001) .00001

In .... ....... ...... ............. .......... (.0001) .00001

La .............................................. (.0001)? .002

Bi ................................................ (.00005) .00002

Co .............................................. (.00005) .002

Sc .................. .............. ......... (.00005)? .0005

Sn ................................................ (.00005) .004

Yb .............................................. (.00004) .0003

Ga .............................................. (.00003) .0015

Be .............................................. (.00002) .0006

Cd .............................................. (.00001)? .00001

Ce .............................................. K.OOOOl)? .005

Li ................................................ K.OOOOl) .0065

Ge .............................................. K.OOOOl) .0007

Nb .............................................. K.OOOOl) .002

Nd ............................................. K.OOOOl) .002

Tl ................................................ K.OOOOl) .0001

U ................................................ K.OOOOl) .0004

W ................................................ K.OOOOl) .002

1 Elements are given in order of decreasing abundance in jasperoid.

3 Medians that are estimated by extrapolation from censored distributions 

are in parentheses; those for rarely detected elements, reported in 5 percent or less of the samples, are in parentheses followed by a question mark.

been derived from one or more of four major 

sources: (1) the silica-rich residual fluids emanating 

from a cooling magma; (2) silica released by reaction of a hypogene mineralizing solution with wallrock minerals en route to the site of silicification; 

(3) silica in the form of chert, siliceous organisms 

such as diatoms and sponge spicules, or siliceous 

shale beds and argillaceous and siliceous fractions 

already present in the host rock, and (4) silica released by weathering of overlying or adjacent rocks. 

Silica, in minor amounts, may also be released during the alteration of silicate minerals, such as the 

conversion of montmorillonite to kaolinite by diagenetic or hydrothermal alteration or by weathering. Only the four principal sources just listed, 

however, seem adequate to supply the hundreds of 

thousands of cubic feet of silica commonly contained 

in the larger jasperoid bodies.

There is some question as to whether masses of 

siliceous rock composed of silica derived from 

ground water and furnished by sources 3 and 4 

should be included under jasperoid, or whether the 

term "jasperoid" should be restricted to bodies composed of silica derived only from hydrothermal solutions. Examples of bodies that originated from silica 

in ground water include (1) silicified erosion surfaces in the Apache Group in north-central Arizona 

(Leith 1925, p. 515-516; A. F. Shride, oral commun., 1961), (2) the silcretes of South Africa 

(Frankel, 1952, p. 181-182), the duricrusts of 

Australia (Woolnough, 1928, p. 32), and certain 

silicified rocks from Tanganyika (Bassett, 1954), 

(3) some epigenetic "chert" bodies and the "casehardened" limestone which are common in many 

arid and semiarid regions, and (4) highly silicified 

gossans replacing sulfides and host rock at and near 

the surface. Undoubtedly, a great many siliceous 

replacement bodies that have been designated as 

chert or hydrothermal jasperoid really belong in the 

category of bodies that originated from silica in 

ground water; however, there is at present no inclusive genetic term by which to designate the category. Furthermore, many "hydrothermal jasperoids" 

may have formed from juvenile solutions mixed 

with heated ground waters. Because of the practical 

difficulty in distinguishing between siliceous replacements derived from hot water and those derived 

'from cold water, it seems best, for the present, to 

retain the term "jasperoid" as originally used by 

Spurr (1898, p. 219-220) to include all epigenetic 

siliceous replacement bodies, of whatever origin.

The primary source or sources of silica for most 

jasperoids cannot be conclusively established. In 

many mining districts there is strong field evidence 

that silicifying solutions rose from depth along 

faults and fractures, but whether this silica emanated directly from a cooling magma or was leached 

from siliceous rocks by upward-moving solutions is 

indeterminate. In a few places, such as the Oilman 

district of central Colorado and the Upper Mississippi Valley district, there is evidence that silica 

has been leached in quantity from rocks beneath the 

host rocks for the jasperoid.

SOLUTION AND TRANSPORTATION OF SILICA

The solvent properties of aqueous fluids for silica 

depend on the form in which silica is available, the
GENESIS OF JASPEROID 37

temperature and pressure of the system, and the 

nature and concentration of other chemical components in the solution. Once silica is taken into the 

fluid and begins to move, it tends toward a dynamic 

equilibrium between ionic (monomeric) silica, and 

polymeric silica in true solution, and colloidally dispersed silica in the form of a peptized sol if the solution is supersaturated with respect to ionic and 

polymeric silica. Changes in any of the factors that 

influence release of silica to the solution also influence this equilibrum. Under controlled laboratory 

conditions, where all factors are held constant, days 

or even months may be required to establish such an 

equilibrium; thus, it probably is very rarely attained 

in moving hydrothermal solutions.

Considerable experimental data have accumulated 

on the solubility of silica under various conditions. 

These data may be divided roughly into four main 

categories: (1) solubility of various forms of silica 

in pure water at low temperature and pressure; 

(2) solubility of silica in pure water at higher 

temperature and pressure; (3) solubility of silica in 

various aqueous solutions at low temperature and 

pressure; and (4) solubility of silica in various 

aqueous solutions at higher temperature and pressure. Each of these categories may be further divided 

into (1) thermodynamic investigations of equilibrium solubility and (2) investigations of rates of 

solution and of equilibration.

SOLUBILITY OF VARIOUS FORMS OF SILICA IN PURE 

WATER AT LOW TEMPERATURE AND PRESSURE

Data on the solubility of quartz, powdered silica 

gel, and opal in water at 25°C and 1 atm (atmosphere) are given by Siever (1962, p. 129-133). He 

found that quartz particles on the order of 5 microns 

in diameter showed no measurable solubility in 3 

years, but by extrapolating quartz solubility at 

higher temperatures downward, he calculated an 

equilibrium solubility of quartz at 25°C of about 10 

ppm. Solubility of opal under these conditions is reported as about 120 ppm; that of powdered silica 

gel, about 140 ppm. On the other hand, quartz* grains 

sized to 100, +200 mesh put under pressure of a 

steel rod in water at 25°C and 1 atm gave a solubility close to that of amorphous silica. Quartz grains 

kept in motion in a rotating polyethylene vessel at 1 

atm and room temperature gave values that increased gradually to a maximum of 80 ppm at 386 

days, then dropped abruptly to 6 ppm due to precipitation of quartz (Morey and others, 1962, p. 

1036-1037). Krauskopf (1956, p. 5) gave the solubility of quartz in pure water at low temperature 

and pressure as 6 ppm; Her (1955, p. 9) stated that

solubility of quartz increases with diminishing particle size below 100 microns from about 7 ppm at 

100 microns diameter to about 930 ppm at 3 microns 

diameter.

Experimental data on the equilibrium concentration of dissolved (monomeric) silica in pure water 

at 25°C and 1 atm in solutions supersaturated with 

total silica are not in complete agreement, possibly 

because silica can also form polymeric ion complexes. Her (1955, p. 11-12) reported 100 ppm; 

Siever (1962, p. 129-130), 120-140 ppm; Alexander, Heston, and Her (1954), 120 ppm; and Correns (1951, p. 51), about 250 ppm. In an experiment that I conducted (Levering and Patten, 1962, 

p. 790), the monomeric silica content of a solution 

that contained 1,000 ppm total silica in pure water 

at room temperature and pressure dropped from an 

initial value of 270 ppm to 90 ppm within a week. 

The silica in solution remained at 90 ppm for 2 

months, but when the experiment was discontinued 

at the end of 5 months, it had risen to 100 ppm.

SOLUBILITY OF VARIOUS FORMS OF SILICA IN PURE 

WATER AT HIGHER TEMPERATURE AND PRESSURE

Many problems are associated with the study of 

silica solubility in aqueous fluid at higher temperature and pressure.

1. Solubility varies as a function of the form of 

silica available; in general, it is lower for 

quartz at any given temperature and pressure 

than for the various forms of amorphous silica.

2. Equilibrium solubility at moderate temperature 

and pressure is established very slowly; 

Gruner (1930, p. 702) obtained a solubility for 

quartz at 200°C and 15 atm of 30 ppm after 

24 hours, whereas Kennedy (1950, p. 636) 

reported its solubility under these conditions as 

240 ppm after 230 hours.

3. Solubility does not vary directly with pressure at 

constant temperature nor with temperature at 

constant pressure; instead, it is a function of 

solution density at high temperature and pressure.

4. The reported "solubility" of amorphous forms of 

silica, such as silica glass, commonly is not a 

true equilibrium solubility; a change in conditions of the system that results in solution of 

silica may not, if reversed, cause precipitation 

of silica because of the tendency of solutions to 

remain supersaturated (Morey and Hesselgesser, 1951, p. 830).

5. Early investigators reported solubility of amorphous forms of silica equal to the total silica 

content of the aqueous phase, whereas more
38 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

1000

900

800

700

600

500

400

300

200 -

Morey and Hesselgesser (1951)~

Kennedy (1950)

 Siever (1962): Vapor pressure 

/ only, 2-11 atmospheres

100

100 200 300 400 500 

TEMPERATURE, IN DEGREES CENTIGRADE

5000

2000

1000

500

Q- 200 

co

a 100

z

J 50 

g in 

LL. 

O

> 20

Zi

5

3 10 

o

CO

Ellis and Fyfe (1957).

"Kennedy (1950)

Morey and Hesselgesser (1951)

10 20 50 JOO 200 500 1000 2000 

PRESSURE, IN ATMOSPHERES

5000

recent investigators report only the ionic solubility, recognizing that much of the silica is 

present in the form of dispersed submicroscopic colloidal particles in a sol, a colloidal 

solution.

The solubility of quartz in H20 has been investigated over a wider range of temperature and pressure than that of any other form of silica, and the 

data obtained by various investigators are more 

nearly in agreement. A large part of the solubility 

field of quartz was systematically studied by Kennedy (1950), and his work has since been supplemented by that of Morey and Hesselgesser (1951), 

Ellis and Fyfe (1957), Morey, Fournier, and Rowe 

(1962), and Siever (1962). Kennedy covered the 

region around the critical point of water, from 

200° to 500°C at 200-1,000 atm pressure; Ellis and 

Fyfe obtained some solubility data for temperatures 

of 500° and 600°C at 1,000-3,000 atm pressure. 

Morey and Hesselgesser partly duplicated the field 

covered by Kennedy, obtaining nearly the same 

values, but they also obtained some critical information on solubility at high temperature and relatively 

low pressure. Morey, Fournier, and Rowe investigated quartz solubility in H20 at 1,000 atm pressure 

in the temperature range of 45°-300°C; Siever investigated quartz solubility in the range of 100°- 

200°C at low pressure (the vapor pressure of the 

system). Data from these various sources have been 

combined in figures 34A and 345 showing the isobaric solubility of quartz as a function of temperature at 300 atm pressure and the isothermal solubility of quartz at 400°C as a function of pressure. 

The marked inflection point on the isobaric solubility curve (fig. 34A) in the vicinity of the critical 

point, with decreasing solubility at higher temperatures, is a characteristic feature of these curves up 

to a pressure of about 700 atm; at pressures higher 

than this, solubility increases directly with temperature. If solubility is plotted at a constant specific 

volume of H2 0 rather than at constant pressure, it 

increases steadily with temperature in the twophase fields (quartz plus liquid and quartz plus 

gas), with no inflection at the boundary between 

these fields (Kennedy, 1950, p. 639, 642). The attenuated S-shaped isothermal solubility curve (fig. 

345) shows the marked effect of moderate pressure 

changes on quartz solubility at relatively high temperature in the range of 100-500 atm; a threefold 

increase in pressure (100-300 atm) results in a 

hundredfold increase in solubility of quartz at

FIGURE 34. Solubility of quartz in H20. A, At 300 atm 

pressure. B, At 400°C.
GENESIS OF JASPEROID 39

400 °C. Thus, even a moderate throttling of a hydrothermal conduit could result in undersaturation below the constriction with solution of quartz and in 

a high degree of supersaturation with Si02 in the 

hydrothermal fluid above the constriction.

Published data on Solubility of other forms of 

silica in aqueous fluid at various temperatures and 

pressures are difficult to compare, because many of 

them represent unique metastable equilibrium conditions. Some investigators report total silica, and 

others report ionic silica. In much of the early work 

it is questionable whether the stated conditions of 

the experiment were maintained long enough for 

equilibrium to be established. Kennedy's paper 

(1944), in which he summarized earlier work by 

Lenher and Merrill (1917) and Gruner (1930), is 

one of the most systematic studies of this difficult 

experimental field. His data suggest that the solubilities of various noncrystalline forms of Si02 conform to much the same solubility curves as quartz 

at intermediate conditions of temperature and pressure, but are commonly somewhat higher than those 

of quartz under the same conditions. Siever (1962, 

p. 133) stated that the solubility versus temperature 

curves for quartz and amorphous silica converge 

toward higher temperature.

The rate of solution of quartz is extremely slow 

in water at low to moderate temperature and pressure. Kennedy reported that 230 hours was required 

to achieve saturation at 200°C and 15 atm pressure. Carr and Fyfe (1958, p. 913-914) determined 

that quartz dissolves at the rate of 1 mg per hr 

(milligrams per hour) at 270°C and 1,000 atm, 

which increases to 18 mg per hr at 500 °C under 

the same pressure; at 400°C, an increase in pressure 

from 345 to 1,725 atm increased the solution rate 

from 2 to 12 mg per hr.

SOLUBILITY OF VARIOUS FORMS OF SILICA IN AQUEOUS

SOLUTIONS AT LOW TEMPERATURE AND PRESSURE

ACID SOLUTIONS

The amount of monomeric silica in equilibrium 

with colloidal silica in slightly acid solutions does 

not differ appreciably from that in pure water, but 

it declines in strongly acid solutions. Her (1955, p. 

11-12) reported 140 ppm Si02 at a pH of 1, rising 

to a maximum of 150 ppm at about a pH of 3 and 

then declining to 110 ppm at a pH of 5.7. Elmer and 

Nordberg (1958, p. 518-519) found 160 ppm Si02 

in solution in O.OOLZV HN03 as opposed to 115 ppm 

in 0.8AT HN03 . Lenher and Merrill (1917, p. 2636) 

reported that Si02 content of sulfuric acid solutions 

containing less than 5 percent H2S04 is virtually the 

same as that in pure water; also, that concentrated

HC1 will dissolve only 8 ppm of Si02 , but that 3 percent HC1 solution will dissolve 140 ppm. Levering 

and Patten (1962, p. 789) obtained 320 ppm of 

monomeric silica in H2S04 solution at a pH of 2.3, 

and 220 ppm at a pH of 3.6 after 1 month. In dilute 

carbonic acid solution with a pH of 5.2 they found 

110 ppm of ionic silica in equilibrium with colloidal 

silica, virtually the same as that in pure water. 

Siever (1962, p. 132) reported that humic acid solutions repress the solubility of silica gel to about 15 

ppm of monomeric silica.

Moore and Maynard (1929, p. 277) recognized 

that much of the silica transported by natural acid 

water is in the form of a dispersed hydrosol. The 

decline in true solubility of silica in highly acid 

solutions is counteracted by the stabilizing effect of 

such solutions on dispersed silica sols. This stabilizing effect will prevent the precipitation of silica 

from highly supersaturated solutions, even in the 

presence of strong electrolytes; a solution containing 2,000 ppm of total silica in the form of sodium 

silicate remained perfectly clear for a month at a 

pH of 2.3, although the monomeric silica content of 

the solution after that time was only 320 ppm 

(Levering and Patten, 1962, p. 789). On the other 

hand, solutions highly supersaturated with silica 

become unstable in weakly acid solutions and tend 

to precipitate excess silica. This precipitation is accelerated by the presence of strong electrolytes, but 

it will occur even in their absence. Frondel (1938, 

p. 10) noted that the addition of HC1 to a colloidal 

silica sol reverses the negative charge on the sol. 

The reversal of charge probably accounts for the 

buffering effect of strong acids against precipitation 

by electrolytes.

The solubility of silica derived from common silicate rocks and minerals in acid solutions has not 

been systematically investigated.

Gruner (1922, p. 435) reported that the solubility 

of silica from silicate minerals in acid solutions is 

inversely proportional to the silica content of the 

silicate. According to T. S. Levering (1950, p. 237, 

240), the attack of acid solutions on silicates results 

in solution of their bases, causing decomposition, 

although actual solution of silica is minor. He listed 

the common rock silicates in order of decreasing 

susceptibility to attack by acid solutions as follows: 

Zeolites, feldspathoids, calcic plagioclase, augite, 

hornblende, biotite, oligoclase, orthoclase, albite, 

muscovite, and quartz.

ALKALINE SOLUTIONS

The ionic solubility of silica, in equilibrium with 

colloidally dispersed silica, rises slowly in alkaline
40 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

solutions from a minimum of about 100 ppm at a 

pH of 7 to about 200 ppm at a pH of 9.8, and then 

rapidly to about 500 ppm at a pH of 10.3, 1,100 ppm 

at a pH of 10.6, and 5,000 ppm at a pH of 11 (Her, 

1955, p. 11-12; Alexander and others, 1954). This 

rapid increase in solubility at a high pH is due to 

an increase in the concentration of polymeric silica 

Si(OH) 4 + (OH)--»(HO) 8SiO- + H20. Near the 

neutral point, supersaturated silica solutions become 

unstable in the presence of electrolytes, and excess 

silica readily precipitates. Above a pH of about 8, 

however, highly supersaturated solutions may remain stable for a considerable length of time, even 

in the presence of a moderate concentration of electrolytes. A solution containing 2,000 ppm total 

silica, 120 ppm ionic silica, and 1,650 ppm sodium 

remained clear for a month at a pH of 9 (Lovering 

and Patten, 1962, p. 789). Her (1955, p. 48) reported 

that the stability of colloidal silica sols in the pH 

range 7-10 depends on the SiC>2: Na20 ratio; an increase in this ratio increases the sizes of particles 

in the sol, which favors nucleation and precipitation. 

He (p. 14) also stated that the presence of sodium 

chloride and alkaline carbonates accelerates the solution of colloidal silica in alkaline solutions.

The solubility of quartz, opal, chalcedony, actinolite, and glauconite in NaOH, Na2C03 , CaH2 (C03 )2, 

and MgH2 (C03 )2 solutions was investigated by T. S. 

Lovering (1923, p. 528-531). He found that opal 

and chalcedony are strongly attacked by dilute 

NaOH solutions and that Na2C03 is an even 

stronger solvent for opal; MgH2 (C03 ) 2 is a moderately effective solvent with nearly uniform effect on 

all the silicates including quartz; the effect of 

CaH2 (C03 ) 2 is similar to, but much weaker than, that 

of magnesium bicarbonate. Later, Lovering (1950, p. 

240) reported that mildly alkaline solutions are relatively ineffectual in causing decomposition of rock 

silicate minerals, although the cation present in 

highest concentration in such solution tends to be 

exchanged for any different soluble cation in the 

mineral; however, Si02 may be leached if the solution is undersaturated with silica. Van Lier, De 

Bruyn, and Overbeek (1960) established that dilute 

NaCl greatly accelerates the equilibration of Si02 

in solution, resulting in precipitation of silica from 

supersaturated solutions and accelerated solution of 

quartz in contact with undersaturated solutions. 

Sodium chloride does not appreciably affect the solubility of silica unless present in concentrations 

greater than 0.1N". Such concentrated brines increase the solubility of silica (Van Lier and others, 

1960, p. 1675, 1681-1682).

SOLUBILITY OF VARIOUS FORMS OF SILICA IN AQUEOUS

SOLUTIONS AT HIGHER TEMPERATURE AND PRESSURE

ACID SOLUTIONS

Systematic studies of the monomeric silica content of acid solutions supersaturated with colloidal 

silica thus far have been limited to 1 atm pressure 

and temperatures below 100 °C. Within this restricted range, silica in solution increases with 

temperature for any given composition of solution. 

For any given acid, solubility declines with increasing acid concentration above Q.IN at higher temperatures. Approximate equilibrium solubilities in 

parts per million at 90 °C for common acids of comparable concentrations are as follows:

Solvent

Concentration 0.1 N ...........

Prt TiPT* PPTli"

HCli

.........420

.........320

......... 60

HNOs2

415

350

140

HsSO.i

425

410

190

iLenher and Merrill (1917, p. 2636). 

2 Elmer and Nordberg (1958, p. 518).

The solubility of silica in pure water at 90 °C is 

about 430 ppm (Okamoto and others, 1957, p. 124).

Equilibrium solubility is attained more rapidly, at 

constant temperature, in strongly acid solutions 

than in weakly acid solutions. Elmer and Nordberg 

(1958, p. 518-519) found that at 90°C, 96 hours is 

required to reach equilibrium in Q.IN HNOs, but 

only about 48 hours in Q.SN HN03 .

A few studies have been made of the leaching of 

silica from rock silicates in acid solutions at elevated temperature and pressure. Lenher and 

Merrill (1917, p. 2636) reported that about 320 

ppm of silica was leached from weathered chert and 

200 ppm from fresh chert in a 4.6 percent HC1 solution held at 90 °C for 2 days. Blanck, Passarge, 

Rieser, and Heide (1925, p. 75) leached about 4.6 

percent of the SiC>2 out of fresh Egyptian granite 

in boiling concentrated hydrochloric acid in 1 hour. 

White, Brannock, and Murata (1956, p. 52) proposed that hot waters highly charged with C02 will 

attack silicate minerals and will dissolve silica in the 

monomeric form. Ingerson (1947, p. 560) stated, 

however, that the presence of C02 in aqueous fluid 

at high temperature and pressure decreases the 

solubility of Si02 , and his statement has been confirmed in the laboratory by Robert Fournier (written commun., 1962). These statements are not necessarily incompatible, because equilibrium solubility 

is achieved more rapidly in highly acid solutions 

than in dilute solutions, even though the saturation 

concentration is lower. The solubility of silica in 

boiling concentrated HC1 is less than 100 ppm, yet 

such a solution leached more than 4 percent of the 

silica out of fresh granite in only 1 hour.
GENESIS OF JASPEROID 41

ALKALINE SOLUTIONS

Equilibrium solubility of monomeric silica in 

supersaturated alkaline solutions, of a pH of at least 

10 and a temperature of 200°C, has been studied by 

Okamoto, Okura, and Goto (1957). They found that 

solubility increases in linear fashion independent 

of pH up to 100°C in the range of pH 7-pH 9 (from 

about 100 ppm at 0° to about 500 ppm at 100°C). 

From 100° to 200°C solubility increases with increasing alkalinity as well as increasing temperature in this range; at 200°C, solubility increases 

from about 920 ppm at pH 7, 980 ppm at pH 8, to 

1,150 ppm at pH 9. At a pH of 10, the solubility is 

considerably higher at all temperatures from 0° to 

200 °C than it is at a pH of 9, but the solubility 

versus temperature curve is nearly parallel to that 

for a pH of 9 (about 800 ppm at 100°C, about 1,400 

ppm at 200°C). The pressure was not specified by 

Okamoto, Okura, and Goto, but presumably it was 

equal to the vapor pressure of the system. T. S. 

Lovering (1950, p. 234) reported that the solubility 

of colloidal silica in Na2C03 solution at 100°C increases from about 3,500 ppm in 0.25A7" solution to 

about 8,000 ppm in IN" solution. Its solubility in 

0.1A7" NaOH at this temperature is about 12,500 

ppm. Gruner (1930, p. 702) ran some experiments 

on the solubility of quartz and gabbro in sodium 

bicarbonate solutions maintained at 300°C in sealed 

metal bombs for 24 hours. He obtained 742 ppm of 

Si02 from the quartz and 64 ppm from the gabbro, 

which is less for both quartz and gabbro than the 

solubility in pure H2 0 under the same conditions. 

Carr and Fyfe (1958, p. 916) maintain, however, 

that alkalies in aqueous solutions at high temperature and pressure accelerate the solution of silica; 

and Her (1955, p. 161) stated that in alkaline solutions under these conditions a high concentration of 

Na+ in the system causes the precipitation of excess 

colloidal silica. Thus, the main effect of alkalinity on 

silica solubility with increasing temperature and 

pressure probably is to maintain equilibrium solubility. Solutions undersaturated with Si02 should 

rapidly dissolve silica until they become saturated, 

and solutions that were supersaturated should precipitate the excess silica.

SUMMARY

The solubility of amorphous silica at low temperatures and pressures is highly dependent on pH; the 

solubility is greatest in strongly alkaline solutions 

and moderately high in weakly acid to neutral solutions. Solutions supersaturated with silica are 

metastable in highly acid and moderately acid solutions; unstable in weakly acid, neutral, and weakly

alkaline solutions; and metastable in moderately alkaline solutions. Increasing pressure at low temperature increases solubility at any pH, but no data are 

available on the effect of pressure versus pH on 

stability of supersaturated solutions at low temperature. With increasing temperature at low pressure, 

solubility increases to the boiling point, then drops 

sharply in the vapor phase. Just below boiling, the 

solubility rises gradually from about 350 ppm at a 

pH of 0.1 to about 500 ppm at a pH of 9.2; then it 

increases rapidly in more highly alkaline solutions. 

At high temperature and pressure, solubility is highest in nearly neutral solutions; it drops off in both 

alkaline and acid solutions. Under these conditions, 

supersaturated solutions are unstable in alkaline 

systems, but no data are available on their stability 

in acid and neutral systems. Solubility is very low 

at low pressure in neutral solutions at supercritical temperatures, and it does not surpass roomtemperature solubility until the pressure reaches 

about 300 atm. At still higher pressures, solubility increases rapidly with pressure. Solubility of silica in 

high pressure-temperature neutral aqueous systems 

varies directly with fluid density, or inversely with 

specific volume of the fluid phase.

COMPOSITION OF NATURAL SILICA-BEARING SOLUTIONS

Silica content of natural water is lowest in the 

oceans, < 10 ppm; in river water, it ranges from 

a trace to about 60 ppm and averages about 10 ppm; 

and in nonvolcanic lake water it ranges from a trace 

to about 150 ppm, although, like river water, it 

averages about 10 ppm. Hot springs of nonvolcanic 

origin can carry as much as 250 ppm silica; however, the most siliceous of the naturally occurring 

waters are found in hot springs, pools, and geysers 

emanating from regions of recent volcanism. Most 

of these contain more than 300 ppm silica, and a few 

contain nearly 1,000 ppm. White, Brannock, and 

Murata (1956, p. 29-30) reported that total silica 

content of supersaturated hot spring water from 

Yellowstone Park and Iceland ranged from 500 to 

700 ppm. They found that at 100°C about 400 ppm 

of this is dissolved (monomeric) silica, and that the 

remainder is in dispersed colloidal form. They (p. 

51) also found that the silica content of calcium 

bicarbonate hot springs that deposit travertine is 

very low (about 50 ppm) ; this fact, they suggest, 

may be due to the exchange of silica for calcium 

carbonate at depth. Thus, such springs at the surface may indicate formation of jasperoid replacement bodies below.

Clarke (1924) reported many analyses of various 

types of natural water. Table 8 gives a few of the
42 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE 

TABLE 8. Composition, in parts per million, of some samples of natural silica-bearing waters

Cold waters

Rivers

COa.........................

SO*.........................

Cl............................

Ca...........................

Mg..........................

Na..........................

K.............................

AbOa+FeaOa........

Total 

dissolved 

solids.. ....... .

1

... 89

... 67

7

... 48

... 11

... 24

7

^^

... 48

... 302

2

58 

24 

7 

29 

5 

161 

2f 

5

66 

212

3

145 

53 

30 

69 

14

57 

3

48 

422

4

124 

164 

304 

82 

26 

(251 

I 24

48 

1,023

5

25 

8 

9 

9

16 

5 

4

42 

118

Lakes

6

112 

190 

9 

44 

48 

37 

5 

2

107 

554

7

180 

9 

3 

42 

25 

62

<1

57 

379

8

1,529 

85 

115 

249 

215 

589

33

150 

2,966

Nonvolcanic 

hot springs

9

30 

18 

11 

3

56 

5

95 

218

10

2,963 

43,579 

356 

4,759 

8,220 

1,865 

218 

12 

1 137 

262

62,371

11

5,781 

2 

577 

76 

102 

19 

1,158 

2 157 

131

8,150

12

4,572

"22 

313 

32 

5 

161

362 

5,467

Hot waters

Volcanic hot springs and geysers

13

5,330 

34,549 

132 

612 

12,455 

1,819 

3,950 

3 438 

738

60,023

14

3

34 

670 

7 

1 

394 

81

580 

1,830

15

122 

18 

439 

2

367

27

383 

1,388

16

115 

102 

153

223 

21

510 

1,131

17

75 

550 

8 

2 

700 

21

700 

2,064

18

136 

1,030 

71 

5 

665 

10

820 

2,735

19

145 

131 

998

7

865 

108

* 253 

325

2,850

19a

312 

129 

949 

12

707

75

* 192 

317

2,508

1 NH*. a HsAsO*. 3 POi. * BaOs.

Source of samples:

1. Platte River at Fremont, Nebr.

2. Laramie River 20 miles north of 

Laramie, Wyo.

3. Republican River at Junction, Kans.

4. Gila River at head of Florence Canal, Ariz.

5. Yellowstone Lake, Wyo.

6. Bigstone Lake, Minn.

7. Silver Lake, Oreg.

Source of Data:

Samples 1-19, Clarke (1924, p. 80-87, 164, 189-190, 196-197, 200-201); 19a, Brannock (1948).

8. Moses Lake, Wash.

9. Pyrenees Mountains, France

10. Bitter Spring, Laa, Austria

11. Roncegno, Southern Tyrol, Italy

12. Acid Spring, California Geysers, Sonoma 

County, Calif.

13. Green Lake, Taal Volcano, Luzon, Philippine 

Islands

14. Coral Spring Norris Basin, Yellowstone 

Park, Wyo.

15. Old Faithful Geyser, Yellowstone Park, 

Wyo.

16. Great Geyser, Iceland

17. Te Tarata, Rotorua, New Zealand

18. Otukapurang, Rotorua, New Zealand 

19-19a. Steamboat Springs, Nev.

most siliceous representatives of these waters and 

the content of their major components, converted 

from percent of total salinity to parts per million 

to facilitate comparison. Sample 19a, a thermal 

spring water, is from the same area as sample 19, 

whose analysis was quoted by Clarke. The general 

agreement between the two analyses is remarkably 

good, considering that they were made more than 50 

years apart and by different methods, and that they 

probably do not represent the same spring.

The data given in table 8 seem to indicate that 

silica content of natural water is largely independent of the nature of the principal anion complex and 

also of the relative abundance of the alkalies (Na 

and K) versus the alkaline earths (Ca and Mg). The 

volcanic hot springs and geysers form a possible 

exception to the rule, inasmuch as all but one of 

them contain Na +1 and Cl" 1 as the most abundant 

constituents other than silica. However, sample 12, 

from the California geysers, is a high sulfate water 

with no chlorine and a Ca + Mg to Na + K ratio 

of almost 10:1. Another generalization suggested by 

the data in table 8 is that, for any given type of 

water, the silica content is largely independent of 

the total dissolved solids. The Platte River sample 

(1) has 48 ppm Si02 out of a total of 302, as compared with one from the Gila River (4), which has 

48 ppm Si02 out of a total of 1,023. One volcanic 

thermal water (17) has 700 ppm SiO2 out of 2,064, 

another (13) has 738 ppm Si02 out of 60,023. Iron 

and alumina are negligible in, or absent from, most 

of these waters, but in two of the thermal water

samples (11, 13) Fe203 + A1203 exceeds 1 gram per 

liter, which is considerably more than the silica 

content of any of the samples. The presence of appreciable quantities of ammonia, phosphate, arsenic, 

and boron as accessory constituents in some thermal 

waters is also noteworthy. Each of these constituents is normally not detectable, yet each may, under 

unusual circumstances, be transported along with 

silica in considerable quantities by hot aqueous solutions.

The total composition of a natural water seems to 

have relatively little effect on its ability to transport 

silica. A relatively pure water in which silica is a 

major constituent may carry about the same amount 

of silica as a highly saline one in which silica is a 

minor constituent. Clarke (1924, p. 96-97) mentioned the high proportion of silica to dissolved salts 

(46-56 percent) carried by some South American 

rivers, yet the total amount of silica in these waters 

is less than 40 ppm.

The aqueous fluid in primary fluid inclusions in 

quartz is another type of natural solution; its composition may be close to that of the solution from 

which the quartz was deposited. Fluid from a quartz 

crystal in a vein cutting rhyolite contained 0.047 

percent Na, 0.011 percent K, 0.006 percent Ca, 0.063 

percent Cl, and 0.063 percent S04 (Roeder and 

others, 1963, p. 368). Fluid inclusions in quartz 

from the Cave-in-Rock fluorite district of Illinois, 

which was deposited just before the ore sulfides, 

may bear an even closer resemblance to those from 

which ore-related jasperoids are deposited. This
GENESIS OF JASPEROID 43

fluid contained 1.73 percent Na, 0.43 percent K, 

0.84 percent Ca, 0.28 percent Mg, 4.7 percent Cl and 

1.29 percent S04 (Hall and Friedman, 1963, p. 898).

Laz'ko (1965, p. 384-386) summarized some information on the composition of fluid inclusions 

from quartz veins in Russia. He found that Na> 

K>Ca in these inclusions and further stated (p. 

384) that "The calculated dissolved Si, as Si03 "~ 2 

(assuming its quantitative preponderance in the 

solution) indicates its total concentrations as high 

as 6-12 percent."

Laz'ko also reported that C02 is present in appreciable amounts in some inclusions, and he concluded that the mineralizing solutions, from which 

quartz is deposited, are primarily aqueous alkali 

chlorides.

DEPOSITION OF SILICA

The ability of natural waters and hot aqueous 

fluids to transport vast quantities of silica, in both 

monomeric and colloidal form, has been well established. We now consider the factors that induce 

precipitation of silica, the form in which silica is 

precipitated, and the causes of the conversion of a 

precipitated silica gel into the more stable forms of 

silica found in nature.

DEPOSITION AT LOW TEMPERATURE

Cold-water solutions that are supersaturated with 

respect to colloidal silica may, for a variety of reasons, precipitate some or most of this excess as hydrated amorphous silica; however, solutions that 

are just saturated or unsaturated with respect to 

colloidal silica, though highly supersaturated with 

silica relative to quartz, tend to maintain their 

metastable equilibrium and do not precipitate 

quartz under normal conditions. Geologic field evidence, on the other hand, strongly supports the conclusion that quartz can be precipitated directly from 

solution at relatively low temperatures. The evidence is in quartz crystals in geodes in unmetamorphosed limestone and shale, quartz-cemented surface 

gravels, and coarse quartz veining and lining cavities in limonite gossans. Murray and Grovenor 

(1953) reported that X-ray spectrometer and 

powder-photograph analyses of oceanic muds and 

the fine fractions of the insoluble residues of limestone and shale reveal abundant quartz particles 

less than a micron in diameter. They suggested that 

these particles may have been precipitated directly 

from solution.

The works of Siever (1962) and Morey, Fournier, 

and Rowe (1962) show that quartz subjected to 

abrasion or differential pressure in cold water will

eventually supersaturate the solution as much as 

tenfold relative to its theoretical solubility, and that 

after a long time quartz will spontaneously precipitate from such a solution to reestablish equilibrium. 

The same process might occur more rapidly in dilute 

sodium chloride solutions, according to the evidence 

presented by Van Lier, De Bruyn, and Overbeek 

(1960).

According to Boydell (1927, p. 51), the precipitation of colloidal silica from supersaturated solutions 

can result from (1) mixing with solutions that contain a high concentration of electrolytes; (2) the 

mixing and reaction with a dispersed sol of opposite charge, such as a metal hydroxide sol; (3) the 

chemical removal of a protecting (peptizing) agent, 

such as fluorine in acid solutions; and (4) decrease 

in pressure or temperature of the system.

Evaporation. One other way in which silicabearing solutions may be induced to precipitate 

silica is by evaporation of such solutions under arid 

conditions. Clarke (1924, p. 366) stated that evaporation of acid siliceous waters forms opal. Rankama 

and Sahama (1950, p. 553-554) reported that the 

silica in alkaline solutions concentrated by evaporation precipitates as an amorphous silica gel. The 

siliceous duracrust of the Australian desert is 

thought by Woolnough (1928, p. 32) to have formed 

by the evaporation of siliceous ground water drawn 

to the surface by capillary action during dry cycles.

Neutralization. Another factor that might contribute to the precipitation of dispersed colloidal 

silica is a change in pH; peptized sols that are stable 

under either strongly acid or strongly alkaline conditions become unstable as they are neutralized. Her 

(1955, p. 45) wrote that gelation or precipitation 

of colloidal silica takes place most readily in the 

pH range 5-6. Levering and Patten (1962, p. 789) 

found that supersaturated sodium silicate solutions 

that contain 1,000 ppm Si02 become unstable and 

precipitate colloidal silica in the pH range 4-8. 

These solutions remained clear and free of precipitate for a period of 2 months both in acid solutions 

with a pH lower than 4 and in alkaline solutions 

with a pH higher than 8. Solutions with the same 

silica content, from which sodium had been removed, 

remained clear at a pH of 7 for 3 months. Thus, the 

neutralization of a strongly acid or alkaline solution 

highly supersaturated with silica may not cause silica to precipitate unless some other agent that 

favors precipitation is also present.

Contact with solid phase. Contact with a solid 

silica phase may also induce precipitation of colloidal silica. Nutting (1943, p. 220) observed that 

particles of solid silica will cause the precipitation
44 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

of excess colloidal silica from supersaturated solutions in a few days and that "certain clays" will do 

the same thing in a few hours. The efficacy of opaline sinter, quartz, and chalcedony in causing the 

precipitation of amorphous silica from siliceous hot 

spring waters was noted by White, Brannock, and 

Murata (1956, p. 49). The effectiveness of various 

forms of solid silica in causing such precipitation 

must depend in part on the nature of the surface 

area that is in contact with the solutions, inasmuch 

as it is possible to keep supersaturated silica solutions in silica glass bottles for years without any 

precipitation.

Soluble salts. Many investigators have commented on the precipitation of colloidal silica 

caused by the introduction of various soluble compounds, both electrolytes and nonelectrolytes, into 

supersaturated silica solutions or dispersed silica 

sols. Her (1955, p. 14, 41-45, 93) reported that the 

addition of soluble salts causes gelation or flocculation of supersaturated silica solutions; sodium salts 

increase the viscosity of dispersed sols and, if present in high concentration, cause silica to precipitate. 

Boydell (1924, p. 89) stated that the addition of an 

electrolyte also increases the rate of diffusion of dispersed sol particles, and Gruner (1922, p. 445) believed that colloidal silica in acid solutions is precipitated on contact with alkaline chloride or alkaline 

carbonate solutions. Boydell (1924, p. 7) and Cox, 

Dean, and Gottschalk (1916, p. 6) agreed that calcium bicarbonate is one of the most effective natural 

electrolytes in causing precipitation of colloidal 

silica. Levering and Patten (1962, p. 791-795) 

showed that relatively dilute carbonic acid solutions 

will precipitate colloidal silica from highly supersaturated solutions, even in the absence of cation 

electrolytes. Bassett (1954) mentioned the precipitation of silica from ground water in African freshwater lake marls as disseminated grains of amorphous silica, deposited with calcite and dolomite.

According to Her (1955, p. 14), aluminum in solution inhibits the solubility of silica, and some experiments conducted by Okamoto, Okura, and Goto 

(1957, p. 129) indicate that soluble aluminum added 

to dispersed silica sols in concentrations as low as 

10 ppm will precipitate as much as 90 percent of the 

excess colloidal silica from acid solutions with a pH 

of 4-5, provided the ratio of colloidal silica to A1+3 

in solution is not greater than 50:1. At a pH lower 

than 4 or higher than 5, soluble aluminum has little 

effect on these sols. Okamoto, Okura, and Goto 

(1957) also found that aluminum in solution, if 

present in excess of 200 ppm, will precipitate dissolved (monomeric) silica from solution most effectively in the pH range 8-10. Harder (1965) has also 

shown experimentally that aluminum will precipitate silica from natural waters, and that the excess 

silica in the precipitated colloid will crystallize as 

quartz. The silcretes of South Africa are thought to 

have formed by replacement of selected clay layers 

by ground-water silica derived from adjacent shale 

or tillite (Frankel, 1952, p. 180-182); such an 

origin would substantiate the effectiveness of A1+3 

as a silica precipitant. Okamoto, Okura, and Goto 

(p. 131) also stated that the action of Fe+3 ion is 

similar to that of A1+3 . Harder (1919, p. 73) wrote 

that ferrous sulfate solutions will react with alkaline silicate solutions in a reducing environment to 

precipitate ferrous silicate and colloidal silica, but 

that such solutions will also precipitate ferric hydroxide in an oxidizing environment.

Mixing of sols. Neither ferric iron nor aluminum can exist in ionic form in high concentration 

except in moderately acid waters, because both tend 

to hydrolyze in near-neutral and alkaline solutions 

Fe+3 at a pH of 3 and A1+ 3 at a pH of 5, according 

to Rankama and Sahama (1950, p. 228). Dispersed 

hydrosols of these metals in neutral or alkaline solutions may, however, on mixing with dispersed silica 

hydrosols, react to precipitate both silica and the 

metal hydroxide in colloidal form. The mutual precipitation of silica and metal hydroxide on mixing 

of dispersed hydrosols is caused by neutralization 

of the charges on the sols, silica being negative and 

metal hydroxide positive; such mutual precipitation 

begins at a slightly lower pH than that at which 

the metal hydroxide would precipitate alone. The 

completeness of flocculation and precipitation, as 

well as the relative proportions of the two colloids 

in the precipitate, depends upon the concentrations 

of the two sols that are mixed, and the pH, Eh, and 

temperature at which mixing takes place. When 

alkaline silicate is present in excess, it tends to form 

a protective layer of colloidal silica on the metal 

hydroxide particles, inhibiting precipitation (Rankama and Sahama, 1950, p. 235; Her, 1955, p. 182- 

183). Moore and Maynard (1929, p. 284) found 

that mixing of ferric hydroxide and silica hydrosols 

precipitates most of the iron but only a little silica 

unless the Si:Fe ratio is greater than 3:1.

DEPOSITION AT HIGH TEMPERATURE

Because the solubility of silica at low pressure increases only slightly with temperature as high as 

the boiling point of water, the chief effect of increasing temperature in this range on supersaturated 

silica solutions is that it allows the various factors 

summarized in the preceding section to act more
GENESIS OF JASPEROID 45

rapidly in causing precipitation of the excess silica. 

Her (1955, p. 161) reported that precipitation of 

silica from supersaturated hot alkaline solutions is 

promoted by the presence of Na+1, Ba+2 , and F" 1 

ions in the solution. Thus, it is probably no accident 

that barite and fluorite are relatively common accessory minerals in'jasperoids.

Colloidal silica can be converted readily to quartz, 

particularly in alkaline solutions, at supercritical 

temperatures and moderate to high confining pressures. Siever (1962, p.' 133) reported that above 

200°C quartz precipitates readily as amorphous 

silica dissolves, and Boydell (1924, p. 15-16) reported that quartz crystals have been obtained by 

heating silica sol or gel in closed tubes at a temperature of 250°C. In alkaline solutions near the critical 

point, fused silica rods dissolve and quartz crystals 

precipitate. The maximum growth rate of these 

crystals was obtained in 0.3N" NaHC03 solution, in a 

period of 6 hours. Then the growth declined, and 

after 20 hours it ceased owing to the growth of a 

layer of porous quartz needles on the nutrient glass 

rods (Walker, 1953, p. 250-251).

The mechanism of the conversion of silica gel to 

quartz at high temperature and pressure was investigated by Ellis and Fyfe (1957, p. 270) and by 

Carr and Fyfe (1958, p. 909). They found that this 

transformation proceeds through two intermediate 

metastable phases; thus, silica gel » crystobalite » 

silica K (keatite) » quartz. Quartz will not form in 

the presence of crystobalite, but once keatite is 

formed it inverts rapidly to quartz. The reaction 

rate increases with both temperature and pressure, 

but it is more sensitive to pressure than to temperature; the presence of alkaline solutions also speeds 

the reaction. These conclusions corroborate the findings of Wyart (1943, p. 483), who converted silica 

glass to crystobalite at 374°C and 220 atm in pure 

H2 0, but in similar experiments with 0.05M KOH 

solutions he obtained quartz instead. On short runs 

with aqueous fluid, Wyart got a mixture of silica 

gel and crystobalite, but in none of his experiments 

did he obtain crystobalite-quartz mixtures. The conversion of colloidal silica to jasperoid in nature 

would thus be facilitated by alkaline solutions in an 

environment of increasing temperature and pressure.

The temperature at which the fine-grained quartz 

of jasperoid has formed may be susceptible to geothermometric measurement, because quartz that is 

known to have formed at low temperatures is richer 

in O18 than quartz that formed at high temperatures 

(Keith and others, 1952). Fluid inclusions might 

also provide information on the formation temperature of jasperoid quartz, were it possible to find 

any in such a rock that has an average grain diameter of less than a tenth of a millimeter.

GENESIS OF VARIOUS FORMS OF SILICA IN JASPEROID

Relatively little is known of the natural conditions under which the various common types of silica found in jasperoid are formed. Silica deposited 

in colloidal form is metastable and commonly converts in time to some other form, normally quartz 

or chalcedony, yet the presence of opaline silica in 

some jasperoid shows that, under some conditions, 

it can remain amorphous for a long time.

Quartz. The natural conditions under which 

quartz precipitates directly from solution at low 

temperature are still largely unknown, although at 

high temperature the deposition of silica in this 

stable anhydrous form proceeds readily. Quartz is 

probably deposited from solutions undersaturated 

with silica relative to colloidal silica but supersaturated with silica relative to quartz itself at the 

temperature of deposition (White and others, 1956, 

p. 55; Morey and others, 1962, p. 1036-1037). Its 

deposition at low temperature must require a long 

span of time under stable conditions. According to 

Adams (1920, p. 640), variety of form and heterogeneity of grain size are characteristic of quartz 

that originated at shallow depth. The conversion of 

various forms of amorphous silica, including silica 

gel, into quartz has been accomplished in the laboratory by simply raising the temperature in a closed 

system to about 250° C. Presumably, the same thing 

happens in nature at a lower temperature over a 

longer period of time. Folk and Weaver (1950) 

found that ordinary chert consists of a mixture of 

quartz and chalcedony, with no opal or other noncrystalline forms of silica, yet the extremely fine 

texture and prevalence of colloform banding in 

chert and in many jasperoids are evidence that these 

rocks were originally colloidal silica. Indeed, such 

textures in jasperoid give indirect evidence of its 

deposition at relatively low temperature, because 

at high temperature silica tends to deposit directly 

as quartz. Boydell (1924, p. 57-58) expressed the 

opinion that crystalline aggregates may be produced 

from a gel either by strain (which implies pressure) or by increasing temperature. White, Brannock, and Murata (1956, p. 55) found evidence at 

Steamboat Springs, Nev., of the replacement of opaline sinter by quartz and chalcedony at relatively 

shallow depth (50+ ft) ; they also found complete 

gradations from fine-grained mosaic-textured quartz 

to chalcedony, a feature that has also been observed 

in jasperoid samples.
46 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

Chalcedony. Folk and Weaver (1950) have 

shown that chalcedony is a fibrous, spongy variety 

of quartz that contains abundant submicroscopic 

bubbles filled with trapped water. These bubbles 

impart to chalcedony its distinctive optical properties. The nature of chalcedony also explains its 

gradation into ordinary" quartz. Adams (1920, p. 

626) reported that chalcedony forms only in nearsurface deposits, whereas White, Brannock, and 

Murata (1956, p. 54) found that at Steamboat 

Springs, Nev., chalcedony formed only at depth as 

a replacement of opaline sinter or as bands lining 

the walls of cavities in this sinter. These bands are 

thicker on the bottom than on the sides of such 

cavities, and the bottom layers are horizontal. Such 

textures suggest precipitation of silica under the 

influence of gravity, even though the available evidence does not indicate whether chalcedony deposited directly or whether colloidal silica precipitated 

and was later converted to chalcedony. The difference in the opinions expressed by Adams (1920) 

and by White, Brannock, and Murata (1956) as to 

the environment in which chalcedony forms is more 

apparent than real, because Adams was discussing 

forms of silica characteristic of deep-seated hightemperature vein deposits as contrasted with those 

found in veins formed at shallower depths, whereas 

White, Brannock, and Murata were dealing with 

forms of silica deposited from hot springs at, or 

about 200 feet below, the surface. Chalcedony apparently forms in a rather restricted environment, 

characterized by low to intermediate conditions of 

temperature and pressure.

White and Corwin (1959) reported the successful 

synthesis of chalcedony by replacement of silica 

glass in alkaline solutions at 400°C and 340 atm 

pressure. They believed that natural chalcedony 

forms not by precipitation from solution but by replacement of amorphous silica in an alkaline environment.

Opal. According to Clarke (1924, p. 366), opal 

is formed by the evaporation of acid siliceous water, 

and White, Brannock, and Murata (1956, p. 53-54) 

expressed the opinion that opal generally forms by 

direct precipitation of monomeric silica, or small 

polymeric molecules of silica, from the rapid evaporation of near-boiling water. They also reported 

that opal may form as an end product of the nearsurface leaching of silicate minerals by hot acid 

solutions. Opal apparently is stable in the presence 

of H20 only at low pressure and at a temperature 

not much above the boiling point. A sample of opal 

in a drill core taken from a depth of 220 feet, temperature 140°C, in- the Norris Basin of Yellowstone

National Park, showed incipient conversion to 

chalcedony.

REPLACEMENT OF HOST ROCK BY SILICA

The term "jasperoid" implies replacement of host 

rock by silica, and in many localities jasperoid 

bodies faithfully preserve the original textural 

features, the delicate fossils, and even the color of 

the rocks they replace (fig. 2B). This type of replacement requires (1) that solution of host rock and 

precipitation of silica must have taken place simultaneously in a thin layer at the contact; (2) that 

the silica, in whatever form deposited, must have 

been sufficiently competent to withstand the existing 

pressure without deformation and yet be sufficiently 

permeable to allow diffusion of solutions through 

it, carrying silica toward the replacement interface 

and host rock in solution away from it; (3) that the 

composition of these solutions must have been such 

that the host rock was soluble and that silica at the 

contact was less soluble; and finally (4), that these 

conditions must have persisted long enough to allow 

replacement of many thousands of cubic feet of rock. 

Considering the stringency of these requirements, 

it is not surprising that the mechanism of volumefor-volume siliceous replacement is a riddle that has 

baffled geologists for years, and that no one has yet 

succeeded in duplicating this phenomenon in the 

laboratory.

Another common type of siliceous replacement 

that results in courser grained jasperoid, commonly 

with reticulated texture, destroys the primary textural features and fossils of the host rock. Formation 

of this type of jasperoid does not require strictly 

simultaneous removal of host rock and deposition of 

silica. Neither does it require diffusion of solutions 

through an advancing silica layer; the silica can be 

deposited directly as quartz disseminated in the host 

rock.

PHYSICAL FACTORS

Although the silicification of host rocks by silicabearing water was known to many early investigators, it was not until after 1900 that the physicochemical environment or the manner in which this 

process takes place was discussed. Church (1862, p. 

109) described an experiment that resulted in the 

substitution of CaC03 for Si02 in solution at room 

temperature, and Spurr (1898, p. 217-220) recognized the epigenetic replacement origin of jasperoid 

at Aspen, Colo., and described the macroscopic and 

microscopic features of this rock.

Lindgren (1901), one of the first geologists to 

speculate seriously on the mechanism of siliceous re-
GENESIS OF JASPEROID 47

placement, stated (p. 602) that "waters containing 

carbon dioxide and silica deposit the latter, while 

simultaneously dissolving a corresponding proportion of calcite." Lindgren (1925, p. 258) later recognized that such replacement can produce either 

crystalline quartz disseminated through the host or 

amorphous silica that replaces the limestone completely and advances as a wave through the host 

rock. Irving (1904, p. 173; 1911, p. 630-631) described the replacement of carbonate rocks by jasperoid in the Black Hills, preserving original 

textures and colors and having sharp contacts with 

the unreplaced host rock. Later, Lindgren (1933, p. 

91) wrote the famous equal-volume law of replacement:

Replacement is the process of practically simultaneous 

capillary solution and deposition by which a new mineral of 

partly or wholly differing chemical composition may grow in 

the body of an old mineral or mineral aggregate * * *. The 

most fundamental changes in rocks take place with practical 

constancy of volume.

Lindgren (1933, p. 173, 176-177) also discussed the 

mechanism by which the reacting solution reaches 

the replacement interface. Penetrating solutions 

under heavy pressure permeate the rocks; such 

rocks then act as semipermeable membranes through 

which electrolytes and gases diffuse rapidly but 

colloids and slightly ionized compounds diffuse very 

slowly. Diffusion takes place in response to concentration gradients, but it is a slow process, does not 

act over long distances, and ceases after a certain 

time. Thus, in the formation of large replacement 

deposits the mechanism of diffusion must be supplemented by solution movement along openings.

The maximum distance from such channels at 

which replacement by diffusion can be effective is 

not known. Irving (1911, p. 538) stated that, in exceptional cases, replacement may extend outward as 

much as 100 feet from feeding channels; however, 

he was probably referring to large trunk channels 

rather than small fractures that could act as subsidiary feeding channels. According to Holser (1947, 

p. 395), transport of material in solution occurs 

mainly by bodily flow in any openings of largerthan-capillary size, but in capillary and subcapillary 

openings such transport is largely by diffusion. Such 

diffusion transport at the replacement interface is a 

necessary prerequisite to completing fine-grained replacement. These conclusions of Lindgren and 

Holser that large-scale complete replacement is dependent on transport by moving solutions supplemented by local diffusion over short distances were 

corroborated by Garrels and Dreyer (1952, p. 374- 

375). They calculated that a minimum of 3,000 years

would be required for the replacement of the most 

permeable limestone beds in the Tri-State district 

by a layer of galena 1 cm thick deposited by dilute 

lead-bearing solutions in which the lead moved only 

by simple diffusion in response to concentration 

gradients. Thus, the ideal conditions for replacement occur in shatter zones characterized by numerous small closely spaced fractures.

The replacement product, as well as the host rock, 

must be permeable to the solutions; otherwise, replacement would cease as soon as a thin layer of 

this product had formed, for it would seal off and 

protect the host rock from further attack. Garrels 

and Dreyer (1952, p. 352) concluded that such a 

situation would occur if the volume of the guest 

mineral precipitated were greater than the volume of 

host mineral dissolved, and that the total amount 

of rock replaced depends only on this volume ratio 

of guest to host, not on solution concentration or 

rate of reaction. Solutions moving in response to a 

high pressure gradient might force their way 

through a somewhat thicker layer of reaction product, however, before the host rock became completely sealed by precipitation. Such a conclusion 

is logical regarding the advancing-wave type of massive replacement, but it would not necessarily apply 

with equal force to the disseminated type, in which 

replacement proceeds outward from a number of 

isolated nuclei scattered through the host. Even in 

this type, however, replacement by a larger volume 

guest mineral should eventually stop when the individual replacement fronts near the main supply 

channel coalesce. Ames (1961d, p. 1443-1444) also 

recognized the importance of the host-guest volume 

ratio in a continuing replacement process, though he 

pointed out that

Volume relationships are a result of a given replacement 

reaction, but do not initially cause or prevent the reaction 

* * *. Starting with equivalent experimental conditions such 

as surface area, the initial significant correlation is between 

ion fraction reacted and activity product ratios. As the reactions proceed, the significant correlation tends to be between ion fraction reacted and molar volume change.

He concluded that replacement reactions resulting 

in a negative theoretical volume change may show 

little actual volume change due to changes in bulk 

density, whereas reactions involving a positive 

theoretical volume change decrease the permeability 

of the host, forcing replacement to become diffusion 

dependent and hence very slow, but the larger 

volume replacing mineral tends to occupy the same 

actual volume as the mineral replaced.

If the volume ratio theory of replacement is 

strictly valid, then it would seem to follow that
48 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

large-scale volume-for-volume replacement with 

preservation of original texture could proceed only 

if the guest mineral has a density equal to, or 

greater than, that of the host. This would preclude 

the replacement of limestone by any form of silica 

lighter than quartz, and it would preclude the replacement of dolomite by any form of silica at,all! 

Such a conclusion is at variance with the field evidence in many districts that dolomite as well as limestone has been silicified, and furthermore, that the 

silica was originally deposited in the form of silica 

gel, which would have a specific volume nearly twice 

that of the carbonate it replaces (Nolan, 1935, p. 94; 

Gilluly, 1932, p. 100; Cox and others, 1916, p. 11; 

Lindgren, 1925, p. 258; and many others). The replacement of large volumes of carbonate rock by 

silica probably proceeds both by diffusion of the reaction products through the gel layer and by movement of silica-bearing solutions along fractures.

Chemical reactions involving the movement of ions 

through a silica gel from an aqueous solution have 

been carried out successfully in the laboratory for 

more than half a century (Hatschek and Simon, 

1912, p. 452) ; hence, there is experimental support 

for the theory that replacement can be accomplished 

in this manner. Furthermore, as pointed out by 

Garrels and Dreyer (1952, p. 347-348), the rate of 

diffusion increases with temperature.

CHEMICAL FACTORS

Ames (1961b, p. 528; 1961c, p. 737; 1961a, p. 

1022, 1024) conducted many experiments on the replacement of limestone by minerals containing a 

common ion (either Ca+2 or C03 ~ 2 ). In all of these 

he concluded that the dominant prerequisite t6 replacement was that the guest mineral is less soluble 

in the system than the host. In complex systems in 

which several possible alteration products are less 

soluble than the host, only the least soluble of these 

will form.

If, as stated by Ames, replacement can take place 

only in a system in which the guest compound is less 

soluble than the host, then siliceous replacement of 

limestone requires greater solubility of CaC03 than 

of Si02 in the solution at the replacement interface. 

The same requirement also applies to the siliceous 

replacement of other rock types, but consideration 

of the chemical processes involved is much simplified 

by limiting discussion to the replacement of calcite 

by silica.

CaC03 is less soluble than Si02 in pure H2 0 at all 

temperatures above the freezing point, and the discrepancy between the relative solubilities of these 

compounds becomes greater as the temperature increases. Although the solubility of calcite does increase slightly with increasing pressure (a threefold 

increase in solubility for an increase in pressure 

from 1 to 1,000 atm, according to Garrels and 

Dreyer, 1952, p. 339-341), that of silica increases 

much more rapidly with pressure at constant temperature (fig. 34J5). Thus, the replacement of limestone by silica derived from an aqueous fluid containing no other components should be impossible. 

The same thing is true of hot alkaline solutions, 

in which calcium carbonate is even less soluble than 

it is in pure water. However, as the pH of a solution 

decreases below the neutral point, the solubility of 

calcite rises rapidly; 100 times for each pH unit, 

according to Garrels and Dreyer (1952, p. 339-341). 

The ionic solubility of silica is relatively low in acid 

solutions, but such solutions are capable of carrying 

many times their saturation concentration of silica 

in the form of a dispersed sol.

Another factor that increases the solubility of calcite is increasing salinity of the solution (Siever, 

1962, p. 145). Miller (1952, p. 173-175) ran a 

series of experiments on the solubility of calcite in 

water and in 0.5M NaCl solutions at various temperatures as high as 100 °C and under various partial 

pressures of C02 from 1 to 100 atm. He found that 

CaC03 solubility increased steadily with increasing 

C02 pressure at constant temperature and decreased 

steadily with increasing temperature at constant 

C02 pressure; furthermore its solubility in the NaCl 

solution was 50-100 percent greater than in water 

at any given temperature and C02 pressure within 

the range of his experiment. The effect of salinity on 

silica solutions is to greatly accelerate the equilibration of these solutions without appreciably affecting 

the silica solubility (Van Lier and others, 1960, p. 

1675). Thus, a warm siliceous brine should be saturated, or nearly saturated, with ionic silica under 

the prevailing conditions of pressure, temperature, 

and pH, and any change in these conditions that 

would decrease its solubility should cause the excess 

silica to precipitate, rather than to supersaturate, 

the solution.

The importance of C02 in promoting the simultaneous solution of calcite and deposition of silica 

has long been recognized. The increase in carbonate 

solubility with increasing C02 content of the solution 

is due to the increasing acidity caused by the formation of carbonic acid. Garrels and Dreyer (1952, p. 

341) found that the solubility of calcite actually decreases with increasing C02 content of the solution if 

the pH is held constant. The pH of solutions saturated with volatile acid-forming gases such as C02 

or H2S is strongly pressure dependent. C02 under
GENESIS OF JASPEROID 49

pressure corresponding to the hydrostatic pressure 

at a depth of 2,000 feet would cause the pH of water 

to drop to a value of 3.2 (Carrels and Dreyer, 1952, 

p. 371-372).

Solubility versus temperature curves for calcite 

and silica trend strongly in opposite directions, and 

at any given temperature the pH of the system, in 

the acid range, has a great effect on carbonate solubility but has relatively slight effect on silica solubility. Thus, at 1 atm C02 pressure, calcite is more 

soluble in H20 than is silica up to a temperature of 

about 65°C; in 0.5M NaCl solution up to a temperature of about 90°C; at 100 atm C02 pressure the 

extrapolated solubility curves would cross at about 

125°C for pure H20 and at 150°C for 0.5M 

NaCl solution. These data, taken in conjunction with 

Ames' observation that replacement cannot occur 

unless the replacing substance is less soluble in the 

system than the material it replaces, suggest that the 

silicification of limestone must be a relatively lowtemperature phenomenon. Such a conclusion is 

further substantiated by the field evidence, in many 

districts, that silica was originally deposited as a 

gel. As stated previously, silica will precipitate in 

the anhydrous form at temperatures above 200°C.

If a carbonated, silica-saturated brine attacked 

and dissolved calcium carbonate, this would tend to 

neutralize the solution at the reaction interface and 

thus promote the precipitation of silica, because the 

ionic solubility of silica is lower in a neutral solution 

than in an acid solution, and the presence of NaCl 

would prevent the excess silica from supersaturating.

THEORY OF REPLACEMENT PROCESS

We can now speculate on a hypothetical mechanism by which silica may replace limestone, which 

is consistent with the various observations previously discussed. Let us assume that hot emanations 

saturated, or nearly saturated, with silica, and also 

containing appreciable quantities of dissolved C02 , 

H2S, and possibly HC1 are rising along a deep conduit, such as a major fault, into a thick sedimentary 

series containing abundant limestone beds, and that 

this conduit penetrates the zone of ground water but 

does not, initially, extend directly to the earth's 

surface. At great depth, where the rocks are tight, 

solution movement will largely be confined to the 

main conduit, the wallrocks will be hot, and changes 

in temperature and pressure within the solution will 

be slight. Such a solution will, in all probability, be 

out of chemical equilibrium with the wallrock of the 

conduit, and we can expect initial alteration of these 

rocks adjacent to the channel, such as silication of

carbonate rocks and argillic alteration of other rock 

types. This will result in the formation of an alteration envelope around the conduit insulating the rock 

beyond it from further attack by the upward-moving 

solutions.

As the system approaches to within a few thousand feet of the earth's surface, the juvenile solutions will begin to mingle with connate brines and 

ground water, and numerous subsidiary fractures, 

minor faults, and other secondary channels will begin to tap the main line of the plumbing system. 

This will cause a relatively rapid drop in both temperature and pressure of the system as well as a 

change in its chemical composition, so that in place 

of a superheated aqueous fluid moving along a major 

channel, hot, acid, silica-bearing water with added 

alkaline chlorides is seeping upward through a 

broad fracture zone. Such a change will result in 

supersaturating the system with silica; however, so 

long as the pH remains low, this silica will not necessarily precipitate but will be carried as a dispersed 

colloidal sol. As soon as the solution enters a 

brecciated bed of limestone, the limestone will begin 

to dissolve, and this reaction will tend to neutralize 

the solution. The presence of dissolved alkaline 

chlorides will increase the solubility of the limestone, and at the same time cause the colloidal silica 

to become unstable as the pH of the solution rises. 

Thus, silica will precipitate as limestone dissolves. 

As the acid solutions penetrate and permeate the 

limestone, the initial solution of this rock must proceed slightly faster than the precipitation of silica 

from the more nearly neutral solutions resulting 

from the reaction. This may be the explanation for 

the commonly observed selvage of sanded limestone 

or dolomite intervening between jasperoid bodies 

and fresh host rock.

If the precipitated silica is in the form of colloidal 

particles or a gel, it coats the walls and fills the 

fractures; the rising pH of the solution tends to 

reduce the host-rock solubility on the outlet side of 

the fractured limestone. Both processes tend to inhibit further replacement. However, solutions can 

still diffuse through the aqueous gel, and this diffusion can be speeded by the development of a gas 

phase as C02 and H2S come out of solution in response to decreasing pressure. Furthermore, the decline in carbonate solubility resulting from a rising 

solution pH is offset, at least in part, by an increase 

in carbonate solubility, as calcium bicarbonate, 

caused by the temperature drop resulting from exsolution of the acid gases.

As the gel layer thickens close to the point of 

entry of solutions into the limestone, the hot rising
50 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

solutions increase the temperature of this gel and 

thus tend to promote its conversion to quartz. Such 

a conversion results in a considerable decrease in 

volume of the silica, accompanied by a corresponding 

increase in porosity and permeability, thus allowing 

continued movement through it of silica-bearing 

solutions toward the replacement interface, in response to both pressure and concentration gradients.

If silica precipitates directly in the anhydrous 

form as either quartz or cristobalite, rather than as 

a hydrous gel, the result will be either a layer of 

fine-grained crystals along the openings resulting 

from solution of calcite or a number of isolated 

quartz or cristobalite nuclei disseminated through 

the host, growing slowly by accretion. In either case, 

reacting solutions can continue to move through the 

replacement product along intergrain boundaries toward the replacement front.

Replacement eventually ceases as a result of one 

or more of the following conditions:

1. The pH of the solution at the replacement interface rises to the point where limestone is less 

soluble than silica under the prevailing temperature and pressure.

2. The whole rock body becomes too hot for the reaction to continue.

3. The silica layer becomes too thick or too impermeable to permit further diffusion of the 

reacting substances through it.

4. The supply of silica becomes depleted.

5. The main conduit breaks through to the surface 

along a different route.

If silica is initially deposited as a gel, this gel will 

rupture as it shrinks and inverts to quartz. Solutions 

circulating through the fractures thus formed will 

cause local solution and reprecipitation of silica, 

thus forming the veinlets and vug linings of late 

coarse quartz that are common in jasperoid bodies.

Low-temperature replacement of limestone by 

silica-bearing ground water and connate brines below the water table must largely be a pressuredependent process. Such waters at depth are probably alkaline chloride solutions containing sufficient 

carbonic acid in solution to prevent the precipitation 

of excess silica. Movement of such solutions under 

pressure gradients into fracture zones in limestone 

decreases their ability to retain silica, both by decreasing silica solubility because of decreasing 

pressure and by neutralization caused by reaction of 

carbonic acid with limestone. Thus, silica precipitates as limestone is dissolved.

The replacement theory just outlined still does 

not account for replacement of rocks other than 

carbonate rocks by jasperoid. Neither does it entirely account for the replacement of limestone by 

supergene jasperoid during the oxidation and 

weathering of silica-bearing sulfide ore bodies nor 

the formation of younger jasperoid matrix, cementing fragments of older jasperoid. The chemical nature of the solutions involved in these processes is 

so complex that more research is required before 

they can be fully explained.

JASPEROID AS A GUIDE TO ORE

In many mining districts, bodies of jasperoid are 

both genetically and spatially related to replacement 

ore deposits. In other districts, jasperoid shows no 

such relationships, and is not useful as a guide to 

ore. Not uncommonly, both types of jasperoids are 

found in the same district, and methods of distinguishing between them are important for effective 

exploration.

DEFINITION OF FAVORABLE AND UNFAVORABLE 

JASPEROID

In this study, jasperoids are divided into two 

categories: (1) jasperoid related to, and associated 

with, ore (favorable jasperoid) ; (2) jasperoid unrelated to ore (unfavorable jasperoid). As in most 

rock classification systems, some borderline rock 

types are difficult to classify. The jasperoid may 

have been deposited from mineralizing solutions that 

later brought in ore metals, but, if the jasperoid 

bodies formed as an outer alteration zone at a considerable distance from the later ore deposits, a 

genetic relationship would be difficult to establish. 

Such jasperoids, even though genetically related to 

ore, could not be classed as favorable, inasmuch as 

they are not helpful in locating ore. This kind of 

jasperoid occurs in the Oilman mining district of 

central Colorado. Here, the major sulfide-replacement ore bodies show little or no silicification of carbonate host rock adjacent to the ore. Yet these rocks 

have been converted to dense aphanitic jasperoid, 

commonly preserving original textures, that extends 

along major fractures from half a mile to several 

miles updip from the ore bodies on the outlet side 

of the hydrothermal plumbing system. Conversely, 

silicification may be younger than the ore stage of 

mineralization and genetically unrelated to it. Where 

such late silicifying solutions pass through ore 

bodies they may become contaminated by the ore 

metals, and the resulting jasperoid bodies may be 

favorable for effective exploration. Possible examples of this type of jasperoid are present in the 

Clifton-Morenci district of Arizona.

The criteria for distinguishing favorable jasperoid from unfavorable jasperoid were developed from
JASPEROID AS A GUIDE TO ORE 51

the comparison of samples taken from, or adjacent 

to, mine workings with samples taken more than a 

quarter of a mile from any mine workings. For this 

study, the first group was designated as favorable, 

the second, as unfavorable. Such a classification, 

based entirely on the presence or absence of spatial 

association with developed ore deposits, inevitably 

results in the misclassification of some samples in 

both categories. A further assumption, implicit in 

any attempt to reach general conclusions on the 

basis of sample investigation, is that the samples 

chosen for study are reasonably representative of 

the bodies from which they were taken. The samples 

included in this study were not selected according 

to a statistically randomized sampling plan; instead, 

an effort was made to obtain "typical" samples at 

each locality. Some samples of unfavorable jasperoid 

bodies that happened to be near, or penetrated by, 

mines are classified as favorable; some samples of 

favorable jasperoid related to undeveloped ore bodies 

are classified as unfavorable. The assumption was 

made that the number of such erroneously classified 

samples would be so small in proportion to the total 

that they would not obscure any significant differences that could be used as criteria for distinguishing between the two groups. After diagnostic 

criteria evolved from the initial study they were 

applied to each sample in both original groups to 

locate and reclassify samples that had been misclassified on the basis of field association alone; they 

were also applied to samples not included in the 

original study groups because their field relations to 

ore either were unknown or were not diagnostic.

METHODS OF DATA ANALYSIS

The characteristics of jasperoid specimens chosen 

for study were initially divided into two groups: (1) 

discontinuously distributed properties those that 

may be either present or absent, such as a specific 

color, texture, or accessory mineral; and (2) continuously distributed properties those that may be 

measured on a continuous scale, such as porosity, 

density, or concentration of a specific element. These 

two groups of properties require different statistical 

tests to appraise the significance of differences between the two categories of jasperoid samples.

For discontinuously distributed properties, the 

number of samples in each category that exhibits a 

specified property is recorded; also recorded is the 

number of samples that do not exhibit the property. 

This generates a 2X2 contingency table of the form

Positive (+) 

Negative (-)

Favorable Unfavorable

A B

C D

with entries in each of the cells, A, B, C, and D. The 

data in these cells are then substituted in the formula 

for chi square given by Siegel (1956, p. 107-109).

N

( (\AD -BC

A (A + B) (C+D) (A + C) (B+D) 

where N=A+B + C+D.

The value of chi square thus obtained is then 

checked against a table of critical values of chi 

square with 1 degree of freedom, such as table C in 

Siegel (1956, p. 249). Values of chi square less than 

the tabulated value for a probability of 0.10 

(x2 = 2.71) are considered to indicate no significant 

difference in the frequency of occurrence of the 

property between the favorable and unfavorable 

sample groups.

As an example of the calculations, let us consider 

the distribution of vuggy texture between the favorable and unfavorable sample groups. Of 95 favorable samples, 55 were vuggy, and of 53 unfavorable 

samples, 18 were vuggy. This gives the following 

2X2 contingency table distribution:

Favorable Unfavorable

Positive (+) 

Negative ( )

A55

L/10

Bis 

D35 N = 148

148(| (55X35) - (40X18) |-74) 2 

(55 + 18) (40 + 35) (55 + 40) (18 + 35)

148 (1925 -720-74) 2

73X75X95X53

189,315,828

27,566,625 = 6.87.

Reference to a table of critical values for x2 with 

1 degree of freedom shows that the probability level 

associated with this value of x2 is slightly less than 

0.01 ( X2 0.01 = 6.64). This means that there is only 

about one chance in a hundred of obtaining such a 

great discrepancy between the favorable and unfavorable sample distributions if, in fact, the property of vugginess were equally common in both types 

of jasperoid. Thus, we may conclude that favorable 

jasperoids are more likely to be vuggy than unfavorable ones; consequently, vugginess becomes one of 

our significant criteria for favorable jasperoid.

For continuously distributed properties, the 

Kolmogorov-Smirnov two-sample test (Siegel, 1956, 

p. 127) may be used. This tests the null hypothesis 

that there is no significant difference between the 

parent populations (favorable and unfavorable jasperoids) with respect to the measured property 

under consideration. The test compares the cumula-
52 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

tive frequency distributions of the property in the 

two groups. If the greatest discrepancy between 

these distributions is sufficiently large to be significant at the chosen probability level, the null 

hypothesis of no significant difference is rejected. 

As with the chi-square test, we may use a probability level of 0.10; that is, if a maximum discrepancy 

between the cumulative distributions as great as, or 

greater than, the one observed may be expected to 

occur by chance as frequently as one time out of 10, 

in samples drawn from the same population, then 

we will assume that there is no significant difference.

The data for both sets of samples are tabulated 

in frequency distributions, using the same class intervals. It is convenient to use the same intervals 

in which the data are reported for grouped data 

such as semiquantitative spectrographic analyses 

(Myers and others, 1961). Ungrouped raw data 

such as density measurements, may be grouped in 

any convenient classes that will adequately define 

the frequency distributions.

The number of samples in each class is first tabulated for both groups, with the class representing 

the highest magnitude of the variable at the top of 

the table, and the class representing the lowest magnitude at the bottom. The number of samples in each 

class (frequency) is then converted to a proportion 

of the total samples in the group in a second parallel 

column (P), and the cumulative proportion is recorded in a third column ($P). The difference between the cumulative proportion values for the two 

groups is then recorded, class by class, in another 

column headed "Difference," and the maximum difference in this column, together with the class to 

which it belongs, is recorded at the bottom of the 

table as D. The value of D thus obtained may then 

be tested for significance (Siegel, 1956, p. 127-135, 

279). The formula used is

where K is a constant dependent on the level of significance desired, and ni and n2 are the total numbers of samples in each of the two categories.

As an example, let us test the significance of iron 

concentration in the two categories of jasperoid. 

The data and calculations are as follows:

Class midpoint

Percent Fe

>io

7 ...............

3 ...............

1.5 .............

.7 .............

.3 .............

.15 ...........

.07 ...........

Total.........

F

....... 8

....... 16

....... 14

....... 13

....... 17

....... 12

....... 11

....... 4

....... 95

Favorable

P= F

SF

0.084 

.168 

.147 

.137 

.179 

.126 

.116 

.043

SPr

0.084 

.252 

.399 

.536 

.715 

.841 

.957 

1.000

Unfavorable Difference

F

1

0 

3 

14 

13 

13 

7 

2

53

P = Jp SPu SPr-SPu

0.019 

.000 

.057 

.264 

'.245 

.245 

.132 

.038

0.019 

.019 

.076 

.340 

.585 

.830 

.962 

1.000

0.065 

.233 

.323 

.196 

.130 

.011 

.005

= 0.323 at 3 percent Fe.

95 + 53

K 0.10 = 1.22 

K .05 = 1.36 

K .01 = 1.63

D 0.10 = 0.027 

D .05= .231 

D .01= .277

 The numbers in the "Class midpoint" column are 

the figures reported in grouped (three-step) spectrographic analysis (Myers and others, 1960) and 

represent the midpoints of three class intervals for 

each order of magnitude. The intervals are approximately equal on a logarithmic scale.

The D value of 0.323 at the iron concentration of 

3 percent is significant at the 0.01 probability level, 

which can be interpreted as indicating that iron 

concentrations of 3 percent or more occur With significantly greater frequency in favorable jasperoids 

than in unfavorable jasperoids.

Although each of the properties vugginess and 

high iron content (given as examples in the preceding discussion) shows a statistically significant association with jasperoids of the favorable type, 

neither one by itself furnishes a diagnostic criterion 

for distinguishing between the two types. Of the 

favorable samples, 58 percent were vuggy and 42 

percent were not, whereas of the unfavorable samples, 34 percent were also vuggy. Iron content was 

significantly high in about 40 percent of the favorable samples and also in about 8 percent of the unfavorable samples.

The application of these statistical tests to all the 

observed properties in both categories of samples revealed a number of properties significantly associated in varying degree with either favorable or 

unfavorable types of jasperoid. Each of these properties was then listed as a criterion and given a 

rank depending on its level of significance; 1 for the 

0.1-0.01 level, 2 for the 0.01-0.001 level and 3 for 

the > 0.001 level; plus (+) if associated with favorable samples and minus ( ) if associated with 

unfavorable samples. Many of the chemical elements 

show significant differences at relatively low con-
JASPEROID AS A GUIDE TO ORE 53

centrations; for these elements an additional scoring 

point was added arbitrarily for each order of magnitude of concentration above the one at which the 

significant value occurred. Thus, lead showed a D 

value that is significant at the 0.001 level, corresponding to a concentration of 0.0015 percent lead; 

so a sample containing 0.015 percent lead would 

have a score of +4 for this property instead of +3. 

All the criteria were applied to each of the samples in the collection, and final classification of the 

sample was made on the basis of its total score. This 

last operation, although empirical rather than 

statistical, resulted in the separation of a large 

majority of the samples in the collection into those 

with distinctly favorable characteristics and those 

with distinctly unfavorable characteristics. It 

changed the classification for some samples in the 

original study groups, and it suggested a classification for many samples not included in these groups

because their field relations to ore either were unknown or were not diagnostic.

COMPARISON OF MEGASCOPIC CHARACTERISTICS

The megascopic characteristics that were recorded for comparison between the favorable and 

unfavorable groups of jasperoid samples were color, 

based on the National Research Council "RockColor Chart" (Goddard and others, 1948), and 

macrotexture, including phaneritic, brecciated, and 

vuggy. Table 9 shows the frequency of occurrence 

and nonoccurrence of these characteristics in both 

sample groups, the computed value of x2> and the 

level of significance associated with this value.

From table 9, it seems that light- to moderate-red 

colors are more characteristic of unfavorable jasperoid, and a dark-brown color, of favorable jasperoid. The latter association was also noted by 

Locke (1926) and by Blanchard and Boswell (1928)

TABLE 9. Distribution of megascopic characteristics in favorable and unfavorable oxidized jasperoid samples

[Rock-color designations are from Goddard and others (1948)]

Favorable Unfavorable

+ - + - Computed value Significance level 2

Color

Pink and light red (5.R ).......................................... 0 2-6 '

Medium red and grayish red (5# ) - - 

Dark red (5R M ) ..........................................................

v 2-6 '

Orange pink (WR |=|) ..................................................

Reddish brown (10/2 44) ..............................................

v 2-6

Dark reddish brown (WR )....................................

v 2-6 7

Grayish pink (5Y# ^=1) ................................................

Light brown and medium brown (5YR )............ 2 6

Dark brown (SYR -|=?) ......................................

v 2-6'

Light brownish gray (5YR^-) ..................................

Grayish orange (WYR 7~8 )..........................................

Yellowish brown (WYR^-) ........................................

x 2-6

Dark yellowish brown (WYR )..............................

Olive gray (5Y 8~6 ).........................................................

White and light gray (Nl-9).. ....................................

Medium gray (2V4-6) ....................................................

Dark gray and black (2V3-1) ......................................

.................... 0

................... i

.................... 6

.................... 2

......... ...... 4

.. .... ........ 10

.................... 5

.................... 24

.................... 7

.................... 6

.................... 14

.................... 19

.................... 4

.................... 10

.................... 30

.................... 25

............... 11

94 

93 

88 

92 

90 

84 

89 

70 

87 

88 

90 

75 

90 

84 

64 

69 

83

10 

17 

5 

5 

8 

5 

5 

5 

2 

5 

12 

16 

3 

17 

34 

32 

15

97 

90 

102 

102 

99 

102 

102 

102 

105 

102 

95 

91 

104 

90 

73 

75 

92

7.35 

11.70 

.05 

.35 

.43 

1.78 

.01 

15.96 

2.42 

.05 

.09 

.63 

.03 

.77 

.02 

.23 

.08

0.001-0.01 

<.001

N.S. 

N.S. 

N.S. 

N.S. 

N.S. 

<.001 

.05-.! 

N.S. 

N.S. 

N.S. 

N.S. 

N.S. 

N.S. 

N.S. 

N.S.

Macro texture

Brecciated ........ ................................................................

Vufferv .. . . ... .. . ... . .. .... ..... . ........

.................... 66

.................... 33

.................... 55

29 

62 

40

22 

23 

18

31 

30 

35

9.91 

.74 

6.87

0.001-0.01 

N.S. 

.001- .01

1 Plus ( + ) indicates frequency of occurrence; minus ( ) indicates frequency of nonoccurrence.

2 N.S. indicates not significant.
54 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

in connection with leached outcrops overlying sulfide 

ore bodies. Coarse grain and vuggy texture also 

seem to be considerably more common in productive 

jasperoid than in barren jasperoid. Brecciated texture is common in all jasperoids, but it is not significantly more abundant in either type.

COMPARISON OF MICROSCOPIC CHARACTERlM ic,s

The microscopic characteristics chosen for comparison between favorable and unfavorable categories of jasperoid samples were microtexture and 

the presence of various accessory minerals (table 

10). The sulfide ore minerals, such as galena, 

sphalerite, and chalcopyrite, and their oxidation 

products have been excluded from the lists in table 

10 because these minerals are present only in favorable jasperoid, and no statistical test of their significance is needed. 

A heterogeneous texture, characterized by a wide 

range in grain size of quartz, and a reticulated texTABLE 10. Distribution of microscopic characteristics in 95 

favorable and 53 unfavorable jasperoid samples

Favorable 1 Unfavorable J x 2

Characteristic Computed Significance 

+ + value level 2

Microtexture 3

Size range of quartz

Granular .............................. 16 80 5 48 .69 N.S.

Reticulated .......................... 31 64 5 48 8.73 .001- .01

Accessory minerals that are generally older than, or contemporaneous with, 

jasperoid silica

Barite .................................... 16 80 3 50 2.39 N.S.

Calcite .................................. 12 83 8 45 .03 N.S.

Carbonate dust .................... 26 69 16 37 .03 N.S.

Chalcedony .......................... 9 86 7 46 .18 N.S.

Clay (kaolinite group) .... 33 62 12 41 1.82 N.S. 

Clay (montmorillonite 

group) .............................. 0 95 3 50 3.01 0.05 -0.10

Dolomite .............................. 5 90 1 52 .32 N.S.

Hematite .............................. 11 84 8 45 .13 N.S.

Pyrite .................................... 29 66 6 47 5.93 .02 - .05

Sericite or hydromica ........ 25 70 22 31 2.96 .05 - .10 

Tourmaline .......................... 4 91 0 53 .97 N.S.

Zircon .................................... 2 93 0 53 .10 N.S.

Accessory minerals that are generally younger than jasperoid silica

Calcite .................................. 15 80 17 36 4.41 0.02 -0.05

Chalcedony .......................... 7 88 3 50 <.01 N.S.

Clay (kaolinite group) .... 4 91 0 53 .97 N.S. 

Clay (montmorillonite 

group) .............................. 1 94 1 52 .10 N.S.

Fluorite ................................ 5 90 0 53 1.50 N.S.

Goethite ................................ 45 50 12 41 7.77 .001- .01

Hematite ................................ 20 75 14 39 .29 N.S.

Jarosite ................................ 23 72 3 50 6.85 .001- .01

Yellow-orange limonite .... 1 94 5 48 4.18 .02 - .05

1 Plus ( + ) indicates frequency of occurrence; minus ( ) indicates frequency of nonoccurrence. 

2 N.S. indicates not significant. 

3 See pages 11-15 for definitions of textural designations. 

4 The ratio of the diameter of the largest common quartz grains in the 

groundmass to the diameter of^the smallest common quartz grains is >10.

ture seem to be significantly associated with favorable jasperoid, whereas jigsaw-puzzle texture shows 

a significantly greater association with unfavorable 

jasperoid. Pyrite is the only older mineral given that 

is more characteristic of favorable than of unfavorable jasperoid, but older sericite and montmorillonite clay are more common in the unfavorable 

variety. Among the younger minerals, goethite and 

jarosite are suggestive of favorable jasperoid; calcite and yellow-orange limonite are suggestive of 

unfavorable jasperoid in the oxidized zone.

COMPARISON OF OTHER PHYSICAL PROPERTIES

The only physical properties other than color and 

texture determined for representative groups of 

favorable and unfavorable jasperoid samples were 

density and porosity; the porosity was computed 

from the ratio of bulk density to powder density. 

These properties were tested on the theory that 

favorable jasperoid samples might tend toward 

greater density because of incorporated ore element 

compounds, or that higher porosity might increase 

permeability of jasperoid for mineralizing solutions. 

The results of the Kolmogorov-Smirnov two-sample 

test on 72 favorable samples and 41 unfavorable 

samples are given in table 11. 

The marked similarity in distributions of both 

powder density and porosity in the two groups of 

jasperoid samples suggests that these properties are 

of no use as criteria for distinguishing favorable 

jasperoid from unfavorable jasperoid. Furthermore,

TABLE 11. Distribution of density and porosity in 72 favorable 

and 41 unfavorable jasperoid samples

[Density determinations by R. F. Gantnier]

Cumulative 

Frequency Proportion proportion

Favor- Unfavor- Favor- Unfavor- Favor- Unfavor- ence 

able able able able able able

Density distribution (percent)

[#-0.080 at 2.65 <2.70; Ds (0.10) -0.237; D<Ds(0.1Q) , is not significant 1 ]

Density: 

<2.60 17 9 0.236 0.219 0.236 0.219 0.017 

2.60-<2.65 19 14 .263 .342 .499 .561 .062 

2.65-<2.70 4 3 .055 .073 .554 .634 .080 

2.70-<2.75 11 4 .153 .098 .707 .732 .025 

2.75-<2.80 5 4 .070 .098 .777 .830 .053 

2.80-<2.85 2 1 .028 .024 .805 .854 .049 

>2.85 14 6 .195 .146 1.000 1.000

Porosity distribution (percent)

[Z)=0.127 at 3-<5 percent; £>s(0.10) =0.237; 

D<Z>s(0.10), is not significant1 ]

Porosity: 

<1 97 0.125 0.171 0.125 0.171 0.046 

l-<3 22 10 .306 .244 .431 .415 .016 

3 <5 15 4 .208 .097 .639 .512 .127

5-<7 9 7 .125 .171 .764 .683 .081 

7-<9 6 8 .083 .195 .847 .878 .031 

9-<ll 4 2 .056 .049 .903 .927 .024 

>11 7 3 .097 .073 1.000 1.000

1 Z>=greatest difference in cumulative proportions; Ds (0. 10 )= difference 

required for statistical significance at 10 percent level.
JASPEROID AS A GUIDE TO ORE 55

a series of check determinations on replicate subsamples from the same original specimen showed 

variations of as much as 0.2 in both powder-density 

and bulk-density determinations. This heterogeneity 

of density distributions within a sample, coupled 

with the narrow range of density values for both 

groups of samples, suggests that density and porosity measurements on jasperoid serve no useful purpose beyond indicating the general range of these 

properties in this type of rock. 

A few selected samples of favorable and unfavorable jasperoid were subjected to differential thermal 

analysis. The resulting curves showed no distinctive 

patterns that would 'be useful for distinguishing between the two types except for one highly favorable 

unoxidized sample that contained much visible 

pyrite and sphalerite. 

Although none of the three physical properties 

investigated proved useful in distinguishing between 

the two types of jasperoid, it is possible that other 

such properties, which were not determined, might 

do so.

COMPARISON OF CHEMICAL COMPOSITION

Semiquantitative spectrographic analyses for 69 

elements were made on 95 favorable jasperoid samples and 53 unfavorable jasperoid samples (most of 

them from the oxide zone) . Only 42 of these elements 

(other than silicon) were present in detectable concentrations in any of the samples analyzed, and only 

28 were present in detectable concentrations in more 

than 10 percent of the samples analyzed. The sensitivity of the analytical method varies considerably 

for different elements. 

These elements may be classified, according to the 

proportion of samples in which they occur in detectable concentrations, as follows:

Percent of samples 

Elements Classification in which elements 

of elements occur in detectable 

concentrations

Al, Fe, Mg, Ca, Mn, Ti, 

Ba, Cr, Cu.......................... Characteristic .... >90

Ni, Pb, Sr, V, Zr.................. Common .............. 50-90

Na, Ag, As, B, Be, Bi, 

Ga, In, Mo, Sb, Sn, Y, 

Yb, Zn ................................ Minor .................. 10-50

K, P, Cd, Ce, Co, Ge, La, 

Nb, Sc ................................ Sparse .................. 2-10

Li, Nd, Ta, U, W.................. Very sparse ........ <2

Significant differences in the distributions of characteristic and common elements between favorable 

and unfavorable jasperoid samples were also tested 

statistically by the Kolmogorov-Smirnov two-sample 

test, as summarized in table 12. Among the elements

TABLE 12. Maximum difference in cumulative proportions of 

characteristic and common elements between favorable and 

unfavorable samples, and significance of this difference

[Data from semiquantitative spectrographic analyses by J. C. Hamilton]

SP at concentraConcentration tion C Difference Significance

occurs Favor- Unfavor- | SPr SPu 1 

(percent) able able

Al .................... 0.3 0.725 0.515 0.210 N.S.

Fe .................... 1.5 .605 .905 .300 0.01-.0001

Mg .................. .015 .375 .130 .245 .05-.02

Ca ............ .15 .560 .450 .110 N.S.

Mn . . ...... .007 .370 .275 .095 N.S.

Ti .................... .015 .450 .540 .090 N.S.

Ba .................... .007 .535 .440 .095 N.S.

Cr . . ......... .0007 .395 .535 .140 N.S.

Cu .................... .003 .355 .830 .475 .001

Ni .................... .0003 .420 .350 .070 N.S.

Pb ...... ............ .0015 .210 .760 .550 .001

Sr .................... .0015 .505 .595 .090 N.S.

V ......... .......... .0007 .460 .280 .180 N.S.

Zr ................... .0015 .235 .350 .115 N.S.

1 N.S. indicates not significant.

of this group, concentrations of > 0.003 percent copper, > 0.0015 percent lead, and >1.5 percent iron 

are characteristic of favorable jasperoid. Magnesium in concentrations > 0.015 percent shows a 

barely significant association with unfavorable jasperoid. 

The minor elements, which were detected in less 

than half the samples analyzed, require a somewhat 

less conservative statistical test to evaluate significant differences between the two groups of samples, because the Kolmogorov-Smirnov test requires 

a difference of 0.23 between the cumulative proportions for the two groups in order to attain the 

threshold significance level of 0.10. Thus, an element 

that was detected in 20 percent of the favorable 

samples and in none of the unfavorable samples

TABLE 13. Distribution of minor elements in 95 favorable 

and 53 unfavorable jasperoid samples

[Data from semiquantitative spectrographic analyses by J. C. Hamilton]

Favorable 1 Unfavorable 1 x2

Element limit Computed Significance 

(percent) + + value level 2

Na .............. 0.03 17 78 9 44 0.007 N.S.

Ag ................ .00015 65 30 6 47 42.183 0.001

As ................ .15 21 74 1 52 9.450 .01

B .................. .003 15 80 10 43 .063 N.S.

Be ................ .00015 19 76 15 38 .897 N.S.

Bi ................ .0007 32 63 0 53 20.833 .001

Ga ................ .00007 21 74 4 49 4.151 .05

In ................ .0007 20 75 0 53 11.163 .001

Mo ................ .0007 49 46 7 46 19.696 .001

Sb ................ .015 18 77 5 48 1.677 N.S.

Sn ................ .0015 23 72 0 53 13.404 .001

Y .................. .0007 21 74 13 40 .017 N.S.

Yb ................ .00007 25 70 15 38 .005 N.S.

Zn ................ .015 62 33 10 43 27.485 .001

1 Plus ( + ) indicates frequency of occurrence; minus ( ) indicates 

frequency of nonoccurrence. 

2 N.S. indicates not significant.
56 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

would fail of significance by this test, although, 

logically, such an element would certainly be considered as characteristic of favorable jasperoid.

Differences between minor-element distributions 

for the two groups can be tested for significance 

by returning to the chi-square test which was used 

for the evaluation of color, texture, and accessory 

minerals. For this test the two sample groups "are 

dichotomized into those samples in which the element was detected and those in which it was not, as 

shown in table 13. The minor elements whose presence in detectable concentrations shows significant 

differences in frequency .between the two groups 

are: Ag, As, Bi, Ga, In, Mo, Sn, and Zn. All these 

elements are more commonly detected in favorable 

jasperoid than in unfavorable jasperoid.

No statistical test can evaluate the significance of 

the sparse and very sparse elements in jasperoid. 

Some of these (Cd, Co, Ge) appear only in analyses 

of samples showing high concentrations of zinc, 

lead, silver, or copper, such that the sample would 

clearly fall in the favorable category on the basis

of its content of these more common metals. Others 

(W, U) suggest areas of abnormally high concentration of these metals, which could be of economic 

interest. The detection of a sparse element in a 

jasperoid sample is highly significant if deposits 

containing that element are of commercial interest.

SUMMARY OF CRITERIA FOR EVALUATION OF 

JASPEROID SAMPLES

The criteria for distinguishing favorable jasperoid from unfavorable jasperoid, together with the 

scoring points for each criterion, are summarized in 

table 14, in which the criteria are divided into three 

categories megascopic characteristics, microscopic 

characteristics, and chemical composition. The 

theoretical range for megascopic characteristics is 

from +8 to 5; for microscopic and megascopic 

characteristics it is from +17 to 11; and for 

chemical composition it is from + 52 to 3. Thus, 

the highest possible combined score is + 77, and the 

lowest is 19. The observed range in the two groups 

of samples was from +5 to 3 for megascopic

TABLE 14. Evaluation of criteria for distinguishing between favorable and unfavorable jasperoid samples

[Rock-color designations are from Goddard and others (1948). >, greater than or equal to]

Megascopic characteristics Microscopic characteristics

Criterion Significance level Score Criterion Significance level Score

6-8, Color

Pink and light red (5R^ 

Medium red and grayish red

Light brown and medium brown

Unfavorable.. 0.01 -2

........do............ .01 -3

Favorable...... .001 +3

Dark brown (5YR)

Texture

Phaneritic ....................

Vuggy ............................

.do. .1 +1

Favorable...... .01

.do. .01

+ 2 

+ 2

Texture

Size range of quartz grains >10X.. Favorable...... 0.01 +2

Reticulated ............................................ ........do............ .01 +2

Jigsaw puzzle ...................................... Unfavorable.. .01

Older minerals

Clay, montmorillonite group ............ Unfavorable.. .10

Pyrite .................................................... Favorable...... .05

Sericite or hydromica ........................ Unfavorable.. .10

Younger minerals

Calcite .................................................... Unfavorable..

Goethite ................................................ Favorable......

Jarosite .................................................. ........do............

Yellow-orange limonite ...................... Unfavorable..

.05 

.01 

.01 

.05

_ o

 1

+1

 1

 1

+2 

+2

 1

Chemical composition

Element

Fe ........................

Mg ........................

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

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

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

As ........................

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

Ga ........................

In ..........................

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

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

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

Significant 

concentration 

(percent)

>1.5

.... > .015

> .003

> .0015

> .00015

> .15

> .0007

> .00007

> .0007

.... > .0005

> .0015

> .015

Higher concentration scores

Significance

Favorable........ 

Unfavorable.... 

Favorable........ 

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

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

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

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

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

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

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

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

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

0.01 

.05 

.001 

.001 

.001 

.01 

.001 

.05 

.001 

.001 

.001 

.001

Score

+ 2 

-1

+ 3 

+ 3 

+ 3 

+ 2 

+ 3 

+ 1 

+ 3 

+ 3 

+ 3 

+ 3

Concentration 

(percent)

>0.15 

> .03 

> .015 

> .0015

> .'007 

> .0007 

> .007 

> .007 

> .015 

> .15

Score

-2

+ 4 

+ 4 

+ 4 

+ 3 

+ 4 

+ 2 

+ 4 

+ 4 

+ 4 

+ 4

Concentration 

(percent)

>1.5 

> .3 

> .15 

> .015

> .07 

> .007 

> .07 

> .07 

> .15 

>1.5

Score

-3

+ 5 

+ 5 

+ 5

+ 5 

+ 3 

+ 5 

+ 5 

+ 5 

+ 5

Concentration 

(percent)

>3 

> !l5

> .7

Score

+ 6 

+ 6 

+ 6

+ 6
JASPEROID AS A GUIDE TO ORE 57

characteristics, from +13 to 7 for microscopic 

and megascopic characteristics, and from +36 to 

 2 for chemical characteristics; the combined scores 

ranged from a high +44 to a low of 8.

By comparing, the frequency distributions associated with total scores for samples in the two 

groups, it is possible to decide the total score at 

which to draw the line between favorable and unfavorable samples in the various categories so as 

to minimize the number of samples that are misclassified. The sample frequency distributions for 

megascopic characteristics are as follows:

Score

Frequency Proportion

Cumulative 

proportion

Favor- Unfavor- Favor- Unfavor- Favor- Unfavorable able able able able able

Difference

<o

0

+1

+ 2

+ 3

+ 4

+ 5

1

13

4

40

12

18

7

2

27

2

19

1

2

0

0.011

.137

.042

.421

.126

.189

.074

0.038

.510

.038

.357

.019

.038

0.011

.148

.190

.611

.737

.926

1.000

0.038

.548

.586

.943

.962

1.000

0.027

.400

.396

.332

.225

.074

Evidently the lower the score at which the line is 

drawn between presumably favorable and presumably unfavorable samples the larger will be the 

proportion of actually unfavorable samples that will 

be misclassified as favorable. In a field reconnaissance investigation of jasperoid bodies, however, one 

would normally be more concerned about overlooking favorable bodies than about needlessly sampling 

unfavorable ones, and so the line might reasonably 

be drawn between a score of 0 and a score of +1, 

the point of maximum difference between the two 

distributions. If the samples included in this study 

had been classified on this basis, according to megascopic criteria alone, only about one favorable sample out of seven would have been misclassified as 

unfavorable, but nearly half (45 percent) of the 

unfavorable samples would have been thrown into 

the potentially favorable category. If all samples are 

classified on the basis of the combined megascopic 

and microscopic criteria, the maximum difference 

between the two sample distributions comes at a 

score of +2; if this is taken as the cutoff between 

unfavorable and favorable, about one sample out of 

five will be misclassified either way. By lowering the 

cutoff to +1, the number of favorable samples misclassified as unfavorable will be cut to about one in 

10, and the number of unfavorable samples called 

favorable will increase to about one in three. The 

changes in the proportions of misclassified samples 

using various combinations of classification at the

TABLE 15. Summary of percentages of misclassified samples 

scored according to various combinations of classifications

Classification

Megascopic alone ........................

Megascopic plus microscopic ..

Cutoff 

score

.. >0

.. >+l

.. > + 5

.. > + 5

.. > + 5

Favorable 

misclassified 

(percent)

14.8

10.6 

10.5

7.3

5.3

Unfavorable 

misclassified 

(percent)

45.2

37.7 

13.2

13.2

7.6

appropriate cutoff scores are summarized in table 

15.

Table 15 illustrates how the discrimination between favorable and unfavorable jasperoid samples 

improves as the number of criteria increases. It also 

shows that a classification based on chemical criteria 

alone is considerably better than one based on a 

combination of megascopic and microscopic criteria; 

and one based on a combination of megascopic and 

chemical criteria is very nearly as good as one based 

on a combination of all three categories. Figure 35 

illustrates the relationship between scores for megascopic plus microscopic criteria and scores for 

chemical criteria on 148 samples. This classification 

system may be further refined by grouping samples 

on the basis of their combined scores as follows: 0 

and <0 = unfavorable, +1 to <+5 = probably unfavorable, + 5 to < +10 = probably favorable, +10 

to <+15 = favorable, and >+15 = highly favorable.

The practical evaluation of jasperoid bodies as ore 

guides in an exploration program could be done in 

three stages: (1) field sampling of jasperoid outcrops that revealed at least one favorable megascopic criterion, (2) analysis of these samples for 

the 12 elements given in table 14, and (3) scoring 

of these samples on their combined megascopic and 

chemical criteria. In drill core and mines, a distinction between oxidized and unoxidized jasperoids 

should first be made and then the evaluation continued as above.

If thin sections of jasperoid samples can be procured more quickly and cheaply than chemical 

analyses, microscopic criteria can also be used with 

some gain in discrimination; however, in most cases 

this gain would be offset by the cost of procuring 

and studying the samples.

CHARACTERISTICS OF JASPEROID IN MAJOR 

MINING DISTRICTS OF THE UNITED STATES

This chapter contains brief resumes of the available information on the characteristics of jasperoid 

in each of the major mining districts where it is 

prevalent. Much of the information has been ab-
58 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

+ 15

+ 10

+ 5

0

-5

-10

\

\

xx\

- X

X

xxx

XXX )

XX

X

XX

xxxx

XX

xxxx

X

X 

All

5 (

1 

2

§sD

\

\

\ 

 \ \ xx v

\ \ V- -\

\~^

X X \ X

\x

XX \

XX \

\

unfavorable

) +5

 1 

0)

£t

£

> .

<a

. . 

\ ....

\ " .....'

V ' .' \* ...;.'

. . v . X . . *

x . \ .- . . .

\ ..... Favorable

L * \ *

^ . \ . Unfavorable

\ \

- A X | \ | 1 1 1 1 

\ .. \

\ . \

\ \

\ ^ o. \ \ \ \

\ \ \ \

\ <- \ \

\ \ \ \ x 9^ \Mostly favorable \ All favorable

\ % \ \ 

\ \ \

i 1 1 1 1 1

+ 10 +15 +20 +25 +30 +35 +4

CHEMICAL CRITERIA SCORES

FIGURE 35. Comparison of scores for megascopic plus microscopic criteria with scores for chemical criteria on all samples.

Field classification: X, unfavorable; », favorable.

stracted from the literature; it is supplemented by 

data on jasperoid samples studied by the author.

Ideally, a district resume includes information on 

the distribution, genesis, relationship to ore bodies, 

physical appearance, microtexture, mineralogy, and 

composition of jasperoid within the district. Unfortunately, such complete information is not available on all the major districts, but whatever 

information is available is given in the aforementioned order for each district.

Major districts are here defined as those whose 

total production is in excess of $100 million. The 

nine such districts that are characterized by the 

presence of conspicuous jasperoid bodies are discussed in order of total production as follows:

Loc. no. District 

(fig. 1)

3........Bisbee ........................

5.. ...... Leadville .................. 

6........Tintic-East Tintic.... 

7-.....Gilman (Red Cliff).. 

8... .....Aspen ........................ 

9....-..Eureka ......................

State(s)

Oklahoma, Kansas, Missouri.

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

Colorado ................................... 

Utah .........................................

Colorado ................................... 

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

Nevada .....................................

Bodies of jasperoid are present in

Production in 

excess of 

.. $2,000,000,000 

.. $1,400,000,000

.. $1,200,000,000

$800,000,000

$500,000,000 

$400,000,000

$150,000,000 

$100,000,000 

$100,000,000

some other

major districts, such as the Bingham district, Utah, 

the Santa Rita district, New Mexico, and the Upper 

Mississippi Valley district of Wisconsin and Iowa, 

but they either are not a major feature of the alteration or have not been described in the literature; 

consequently, these districts are not included in this 

list. The number in parentheses below district names 

that head the following discussions indicates the 

district number on the index map (fig. 1) and on 

the maps for the individual States or areas (figs. 

36-50).

TRI-STATE DISTRICT, OKLAHOMA, KANSAS, 

AND MISSOURI

(l,fig. 1; 2, fig. 36)

The Tri-State district covers a large region surrounding the common corner of Oklahoma, Kansas, 

and Missouri (fig. 36). In the first half of the 20th 

century it was the largest producer of lead and zinc 

ore in the United States. Most of the ore has been 

produced from two subdistricts or fields, MiamiPicher in Oklahoma and Joplin in Missouri, but the 

mineralized region also extends well into southeastern Kansas and into many smaller areas of 

western Missouri. Marine sedimentary rocks ranging in age from Ordovician to Pennsylvanian have a 

gentle northwesterly regional dip, which is modified
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 59

50

I

100 MILES

_I

FIGURE 36. Map showing the location of large jasperoid-bearing mining districts in Missouri, Oklahoma, Kansas, and Arkansas. 1, Northern Arkansas. 

2, Tri-State; A, Miami-Picher field; B, Joplin field.

by numerous warps and open folds. A few persistent 

northeast-trending faults occur in some parts of the 

district. Lead and zinc sulfide deposits are largely 

confined to the Boone Formation, a marine limestone of Mississippian age that contains many chert 

beds. Replacement ore bodies occur in long narrow 

"runs" along breccia zones in the chert beds, where 

sulfide ore forms a matrix cementing breccia fragments of chert, and in wide thin irregular mantos, 

locally termed "sheet ground," that replace limestone between two chert beds (Smith and Siebenthal, 1907).

DISTRIBUTION

The Tri-State region is characterized by many different types and ages of siliceous bodies in the 

Mississippian limestone. The oldest of these bodies 

is nodular chert, which is widely distributed in certain beds and is thought by most investigators to be 

of syngenetic or diagenetic origin. The youngest replacement silica is dark gray to black and cryptocrystalline; it commonly occupies an intermediate 

position between sulfide ore and dolomitized limestone. This variety is generally conceded to be jasperoid that is genetically related to sulfide mineralization.

Two more distinctive forms of replacement silica, 

widely distributed in the area, are intermediate in 

age between the early chert and the late jasperoid. 

One of these types is light gray, white, or buff, has a

porous appearance, and commonly contains inclusions of older chert. It has been called younger 

chert by Fowler, Lyd en, Gregory, and Agar (1935, 

p. 108) and forms irregular replacement bodies in 

the Boone Formation which are most abundant 

around the fringes of ore bodies (A. V. Heyl, written 

commun., 1967). The second type is yellow to brown, 

massive, and cryptocrystalline. It is typically represented by the Grand Falls Chert Member of the 

Boone. This variety forms distinctive stratigraphic 

marker zones near faults and ore bodies; however, 

in many unmineralized and unfaulted areas these 

same stratigraphic units consist only of limestone 

with chert nodules. Siebenthal (1915, p. 27) regarded the Grand Falls Chert Member as a jasperoid 

replacement of cherty limestone, but many other 

geologists who are familiar with the district consider it to be a true massive chert bed. Both the 

younger chert and the Grand Falls Chert Member 

may be early unfavorable varieties of jasperoid, as 

the terms are used here. However, their age, genesis, 

and relationship to mineralization, if any, are in 

dispute.

The late black jasperoid in the Tri-State district 

shows a general distribution that is closely related 

to that of the sulfide ore bodies, of which it is the 

principal gangue. It cements older chert breccia in 

the "runs," and replaces limestone or dolomite between chert beds in the underlying "sheet ground." 

Lyden (1950, p. 1256-1257) stated that the jasperoid shows a zonal distribution with respect to the 

"sheet ground" deposits in the Picher field, where it 

surrounds a core of barren hydrothermal dolomite 

and grades outward through unmineralized jasperoid into unreplaced limestone.

GENESIS

Most investigators agree that the late black TriState jasperoid was formed by metasomatic replacement of the carbonate host rock, that it was 

deposited penecontemporaneously with sphalerite, 

galena, and dolomite, and also, that most of the 

silica was transported in dispersed colloidal form; 

however, there is a considerable difference of 

opinion as to the origin and composition of the 

transporting solutions, the temperature and depth 

at which deposition of silica took place, and the 

form in which it was deposited. Smith and Siebenthal (1907, p. 14) concluded that meteoric waters 

highly charged with silica and with ore metals in 

the form of soluble sulfates moved downward along 

the flanks of the Ozark uplift and deposited both 

silica and ore in permeable zones in the limestones,
60 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

whose high organic content reduced the metal sulfates to sulfides, causing them to precipitate. Siebenthal (1915, p. 42, 179, 183) presented the theory 

that ore and jasperoid were both deposited from 

ascending alkaline saline waters and that the silica 

was deposited in colloidal form. Laney (1917, p. 

108) also concluded that most of the silica was deposited as a colloid, but he did not speculate on the 

nature of the transporting solutions.

Weidman (1932, p. 82-84) and Tarr (1933, p. 

475-478) believed that jasperoid silica was derived 

from ascending hydrothermal solutions of magmatic 

origin and that it was deposited in the temperature 

range of 100°-300°C. Tarr ascribed the origin of 

jasperoid to precipitation of silica directly as quartz 

from highly supersaturated solutions in preexisting 

solution channels and caverns in the limestone beneath the overlying impermeable Pennsylvania 

shale. He believed that precipitation was due largely 

to the escape of volatiles (C02 and H2S) from the 

transporting solutions, resulting from the sudden release of pressure when these solutions penetrated 

the open solution channels. He conceded that replacement of limestone by silica occurred, but in his 

opinion this replacement was subordinate to cavity 

filling by precipitation. Bastin (1939, p. 108-110, 

136, 142) concluded that the late black jasperoid 

was deposited as quartz rather than colloidal silica 

just before deposition of the sulfide minerals and 

that the sulfides were deposited from hydrothermal 

solutions of magmatic origin at temperatures of 

about 130°C. McKnight (in Behre and others, 1950, 

p. 58) stated "The ores are believed to have been 

deposited by hydrothermal solutions of magmatic 

origin."

RELATIONSHIP TO ORE

The jasperoid bodies are closely related to sulfide 

ore both spatially and genetically, forming the common host rock for these sulfides, with which they 

are penecontemporaneous. However, the Tri-State 

district is also characterized by the presence of 

widely distributed "chert" bodies. Fowler, Lyden, 

Gregory, and Agar (1935, p. 108) recognized two 

different ages of "chert," both younger than the 

Boone but older than the overlying Upper Mississippian (Chester) rocks. The older chert appears to be 

a true diagenetic bedded nodular chert, but the 

younger "chert" was formed by structurally controlled replacement of limestone (A. V. Heyl, written commun., 1967). The older chert is more limited 

in distribution and occurs as breccia fragments in 

the younger "chert," which is abundant in the Boone 

Formation throughout a vast region of northern

Arkansas, southwestern Missouri, and eastern Kansas and Oklahoma. If these conclusions concerning 

the age and origin of the younger "chert" are correct, then I would consider it to be early unfavorable 

jasperoid. However, both the age and mode of origin 

of this chert have been disputed (Fowler and others, 

1935, p. 151-163) ; there is general agreement only 

that it is older than the jasperoid and unrelated to 

the ore deposits.

APPEARANCE OF JASPEROID AND CHERT

The jasperoid is typically dark gray, dark brown, 

or black, dense, and finely saccharoidal textured. 

Locally, it exhibits rhythmic parallel banding in 

various shades of gray. It weathers to a light gray 

on the outcrop. In the transition zone between jasperoid and unreplaced carbonate host rock, where 

the carbonate matrix has been leached, the rest of the 

jasperoid silica is porous and spongy and crumbles 

readily into quartz sand.

The older chert is dark brown, light gray or white, 

and aphanitic with local concentric banding. It commonly contains abundant spherulitic inclusions of 

chalcedony that impart an oolitic appearance to the 

rock.

The younger "chert" (Fowler and others, 1934) 

is similar in appearance to the older, though it is 

generally lighter in color and contains less chalcedony. It fills fractures in the older chert and replaces the limestone, commonly preserving the 

original bedding structure, and in many places it 

contains abundant partly silicified fossils. It grades 

outward into limestone through a zone of soft chalky 

white material, locally called cotton rock (Fowler 

and others, 1934).

MICROTEXTURE AND MINERALOGY OF JASPEROID 

AND CHERT

The jasperoid matrix quartz consists of irregularly interlocking grains (jigsaw-puzzle texture) 

which range in diameter from about 0.03 mm to 

< 0.001 mm and which locally contain abundant 

larger quartz laths elongated parallel to the c axis. 

These grains are randomly oriented, have a lengthto-width ratio of about 3:1, and some show pyramidal terminations; locally, they impart a reticulated 

texture to the rock. Smith and Siebenthal (1907, p. 

14) noted that incipient jasperoidization of the host 

rock is marked by the presence of scattered quartz 

crystals in the carbonate matrix. The Tri-State jasperoids locally contain, in addition to quartz, penecontemporaneous inclusions of dolomite, sphalerite, 

and pyrite, and remnants of unreplaced calcite, as 

well as interstitial films of carbonaceous material
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 61

and clay. The sulfide inclusions are largely anhedral, 

but most of the dolomite is in well-developed rhombs, 

some of which contain poikilitic quartz-grain inclusions.

The older chert exhibits abundant small oval 

masses of light-brown fibrous chalcedony, and 

sponge spicules in a matrix of aphanitic irregularly 

interlocking quartz grains less than 0.02 mm in diameter. It locally contains inclusions of pyrite, 

marcasite, and tourmaline (Fowler and others, 1934, 

p. 35, 45). According to Laney (1917, p. 101), many 

of the quartz grains in the older chert show undulatory extinction that was probably induced by internal stress during crystallization from a colloidal 

gel.

The younger "chert" (Fowler and others, 1934) is 

similar in texture to the older, but chalcedony and 

sponge spicules are less abundant, and the chalcedony lacks the oval form which characterizes its 

appearance in the older chert. Furthermore, the 

younger "chert" contains numerous partly silicified 

calcareous fossils that are absent in the older chert.

COMPOSITION OF JASPEROID AND CHERT

Numerous standard rock analyses of both chert 

and jasperoid samples from the Tri-State district 

have been published (Cox and others, 1916, p. 14; 

Laney, 1917, p. 102; Fowler and others, 1934, p. 

35-36), and a few of these are reproduced in table 

7 of this report. Laney (1917, p. 103) noted that the 

average jasperoid sample contains a little less silica 

and a little more iron and aluminum than the average chert sample; also, that the jasperoid samples 

showed greater ignition losses and contained appreciable amounts of carbonaceous matter, which 

is absent in the chert samples. F. E. Gregory (in 

Fowler and others, 1934, p. 36) stated that samples 

of older chert show more A1203 , less CaC03 , and less 

loss on ignition than do samples of younger 

"chert"; also, he noted that samples of younger 

"chert" are considerably more variable in composition than samples of older chert.

A semiquantitative spectrographic analysis of a 

specimen of ore-bearing jasperoid from the Miami 

shear trough in the Picher Field of Ottawa County 

in northeastern Oklahoma showed surprisingly low 

concentrations of indicator elements for a favorable 

jasperoid; only copper and zinc were detected in 

significant amounts.

CONCLUDING REMARKS

In spite of all the work that has been done in the 

Tri-State district, the genesis and significance of 

the younger "chert" remain in dispute. The chert

may be of late diagenetic origin, it may represent 

barren silicification along old structures in prePennsylvanian time, or it may represent a very early 

barren stage of alteration related to the jasperoid 

and sulfide mineralization, and thus be early unfavorable jasperoid.

The undisputed jasperoids in the Tri-State district 

are unusual in their relative uniformity and simplicity. They exhibit only one major generation, contemporaneous with, or just preceding, the early 

stage of sulfide deposition, in contrast to the jasperoid bodies of other major districts, such as Tintic 

and Ely, which are marked by great diversity in 

color, texture, mineralogy, composition, and age of 

formation. Tri-State jasperoids also differ from most 

other favorable jasperoids in their fine-grained texture, scarcity of vugs, and in their lack of high concentrations of most of the "indicator" elements.

The fact that incipient jasperoidization is represented by disseminated quartz crystals in the carbonate host rock suggests that the first phase of 

jasperoid formation was marked by the deposition 

of silica from solution directly in the form of quartz, 

although the deposition of colloidal silica as a hydrogel from solutions more highly charged with 

silica must have followed shortly thereafter.

CLIFTON-MORENCI DISTRICT, ARIZONA

(2,%. 1; 5, fig. 38)

The Clifton-Morenci district of southeastern Arizona (Lindgren, 1905) is in an area in which Precambrian schist and granite are overlain by about 

800 feet of lower and middle Paleozoic limestone and 

shale with quartzite at the base. A few hundred feet 

of Cretaceous shale and sandstone rests unconformably on the Paleozoic sedimentary rocks. Porphyritic 

igneous rocks ranging in composition from granite 

to diorite were intruded along northeast-trending 

fissures during the Laramide orogeny to form a 

stock with associated dikes, sills, and laccoliths. 

Strong younger faults of northeasterly trend broke 

the intrusives and enclosing sedimentary rocks and 

served as conduits for hydrothermal solutions that 

deposited sulfide minerals. After a period of erosion 

that denuded the intrusive bodies and exposed the 

sulfide deposits to oxidation, the area was covered 

by a thick series of volcanic flows, breccias, and tuffs 

ranging in composition from rhyolite to basalt.

The sedimentary rocks were pyrometasomatically 

altered by the Laramide igneous intrusions, and both 

intrusives and sediments were later hydrothermally 

altered along the northeast-trending faults and fractures. In the area of most intense mineralization this 

hydrothermal alteration took the form of propylitiza-
62 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

tion and sericitization of the host rock, but jasperoid 

replaced carbonate rock farther out in peripheral 

zones.

DISTRIBUTION

The jasperoid bodies of the Clifton-Morenci 

district are not mentioned in either of the two reports that discuss the wallrock alteration of the district in detail (Lindgren, 1905; Reber, 1916). This 

discussion probably was omitted because the ore deposits are largely within the igneous rocks and contact metamorphosed sediments, where the later 

hydrothermal alteration resulted in propylitization 

and sericitization rather than silicification of the host 

rock. Jasperoid does, however, form replacement 

bodies in the Cambrian and Ordovician Longfellow 

Limestone south and southeast of the main mineralized area. Lindgren (1905, p. 62-63) recognized the 

replacement origin of these bodies, for in his description of the Longfellow Limestone he mentioned the 

presence of a bed of buff to brownish-gray cherty 

limestone, 110-200 feet thick, near the top of the 

formation. His petrographic description of this rock 

contains the following statement.

The chert occurs in irregular bands of nodules, which 

under the microscope appear as an aggregate of greatly 

varying grain. Some of it consists of irregular quartz grains, 

while other parts contain much cryptocrystalline and fibrous 

chalcedonic material. Ragged calcite grains lie embedded in 

this mass, giving distinct evidence of the metasomatic origin 

of the chert by replacement of calcite by siliceous waters.

Perhaps Lindgren did not consider this as true jasperoid because most of the rock he described does 

not exhibit the reticulated texture characteristic of 

the rock in the Aspen district of Colorado, for which 

Spurr (1898) had coined the name "jasperoid." The 

broader definition of the term "jasperoid" as used 

today was not commonly accepted until long after 

the report of Lindgren (1905).

The six jasperoid samples from this district that 

were examined during the present study all came 

from brecciated zones along faults in the Longfellow 

Limestone in the town of Morenci south and southeast of the open pit.

GENESIS

Petrographic study of the jasperoid samples suggests that the host limestone was recrystallized and 

permeated by iron-bearing solutions in a reducing 

environment, before the introduction of silica. Some 

of the iron combined with carbonate to form siderite, 

and some was precipitated as disseminated pyrite. 

The earliest silica-bearing solutions were apparently 

rather dilute, and locally permeated the recrystallized host rock and precipitated silica in the form of

disseminated quartz crystals. This stage was closely 

followed by a wave of solutions which were supersaturated with both silica and iron and which also 

contained potassium. These constituents replaced 

the host rock, probably as colloidal gels, in an oxidizing environment. Desiccation of the gels was accompanied by minor movement along fractures and by 

introduction of later silica, which formed dense 

cherty jasperoid in some places and coarse vein 

quartz in others. The youngest silica-bearing solutions formed chalcedony as coatings on open cavities. 

The available evidence suggests that much of the 

jasperoid in the Clifton-Morenci district was formed 

by replacement of favorable beds in the Longfellow 

Limestone close to fractures that served as conduits 

for the silicifying solutions, at relatively low temperature and sufficiently close to the surface to be 

within the zone of oxidation; also, that most of it 

formed subsequent to the main period of sulfide mineralization in the district. Only a more detailed study 

of these rocks can resolve the question as to whether 

silicification was induced by spent hydrothermal solution mingling with ground water or by much 

younger ground water that had leached its constituents from the siliceous and ferruginous rocks closer 

to the main center of mineralization.

APPEARANCE

The jasperoid is predominantly shades of red, yellow, and brown; it is commonly brecciated, with large 

angular breccia fragments of older jasperoid in a 

matrix of younger jasperoid heavily stained by oxides of iron and manganese. Locally, the rock contains numerous open vugs lined with quartz crystals, 

and in some places it is cut by veinlets of coarse calcite or vein quartz. The texture, however, is predominantly aphanitic.

MICROTEXTURE AND MINERALOGY

Four different textural varieties of quartz, in addition to the late chalcedony, can be distinguished. 

From oldest to youngest these are as follows:

1. Dense, relatively homogeneous quartz that has 

an average grain size of <0.005 mm, jigsawpuzzle texture, and anomalously low birefringence. Locally, it contains quartz pseudomorphs 

after original dolomite rhomb inclusions. This 

quartz forms small scattered breccia fragments 

and is probably diagenetic or syngenetic chert.

2. Dense to locally vuggy, heterogeneous quartz 

whose grain size ranges from 0.01 to 0.3 mm 

and averages about 0.03 mm. This quartz 

ranges in texture from xenomorphic to reticulated, and it commonly contains clouds of car-
CHARACTERISTICS OP JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 63

bonate particles which indicate its origin by 

replacement of the carbonate host rock. This 

variety forms the matrix in some localities and 

occurs as breccia fragments in others.

3. A generation of fine-grained heterogeneous jigsaw-puzzle-textured quartz whose grain size 

ranges from 0.003 to 0.05 mm and averages 

about 0.005 mm. It is characteristically dense, 

but vugs occur locally. This variety forms the 

matrix in which breccia fragments of older 

jasperoid and chert are locally incorporated.

4. A relatively homogeneous and coarse-grained

quartz that has a mean grain diameter of about

0.08 mm, a range of 0.04-0.3 mm, and a xenomorphic texture; it is notably clean and free of

inclusions. This youngest quartz fills veinlets

and lines vugs in the older jasperoid.

Veinlets and vug fillings of late fibrous chalcedony

are locally abundant. In one sample a vug lined with

late quartz was filled with chalcedony, which thus

seems to be the latest form of silica deposited and is

probably of supergene origin.

Other minerals that are associated with all the 

varieties of jasperoid quartz, in the samples examined, are dolomite, siderite, calcite, sericite, pyrite, 

hematite, goethite, limonite, and manganese oxides. 

Dolomite was present as disseminated rhombs in the 

chert (variety 1), but in the sample studied the 

rhombs have been replaced by quartz. Siderite and 

calcite form ragged unreplaced remnant inclusions in 

the jasperoid quartz (varieties 2 and 3), and a 

younger generation of coarse calcite also fills fractures that cut the jasperoid. Clouds of carbonate 

particles in some of the first-generation jasperoid 

(variety 2) probably are calcite, but these particles 

are too small for positive identification. Sericite appears to be contemporaneous with the first generation of jasperoid silica (variety 2); it forms small 

flakes locally disseminated through the groundmass. 

Original pyrite has been converted to limonite or 

hematite pseudomorphs in the early jasperoid (variety 2). From its petrographic relations, the pyrite 

must be either older than, or contemporaneous with, 

the enclosing silica; the quartz surrounding the 

pyrite pseudomorphs is heavily impregnated with 

contemporaneous iron oxides (hematite, goethite, 

and brown limonite), and for this reason it seems 

probable that pyrite was introduced before the silicification of the enclosing limestone. The oxides of 

iron and manganese form abundant penecontemporaneous inclusions in both older and younger jasperoid (varieties 2 and 3). These oxides also constitute 

the matrix cement for jasperoid breccia fragments 

or fill veinlets that cut the jasperoid in some places;

elsewhere, masses of iron and manganese oxides are 

cut by veinlets of late quartz (variety 4) or calcite. 

In general, hematite seems to be older than brown 

limonite, which is older than goethite and manganese 

oxide; but local departures from this sequence are 

common.

COMPOSITION

Information available on the chemical composition 

of the jasperoid of the Clifton-Morenci district is 

limited to the results of semiquantitative spectrographic analysis of the six samples in my collection. 

All these samples contain abnormally large concentrations of lead and zinc; most are rich in iron, beryllium, gallium, molybdenum, and silver; about half 

are rich in magnesium, manganese, copper, indium, 

vanadium, and nickel; and one or two samples contain abundant barium, bismuth, cobalt, and germanium. The abundance of ore metals and indicator 

elements in these jasperoids that are not closely associated with ore bodies is unusual. It seems reasonable that the silica-bearing solutions passed through 

previously formed sulfide ore bodies, leaching some 

of these elements from the ore. When the silica later 

precipitated as a colloidal gel, many of these elements 

probably were adsorbed on the surface of the gel 

particles and thus became fixed in the rock when the 

gel desiccated and crystallized.

CONCLUDING REMARKS

The jasperoid bodies in the Clifton-Morenci district and the surrounding area have not been studied 

in detail. The results of this preliminary investigation, together with the information available in the 

stratigraphic section of Lindgren's report (1905, p. 

62-63) on the district, suggest that these bodies are 

concentrated in the upper part of the Longfellow 

Limestone, that they are younger than the ore deposits, and that they were efficient accumulators of 

ore metals leached from these deposits by solutions 

moving through them along faults and fracture 

zones. Thus, the study of jasperoids in the Longfellow Limestone in the area surrounding this district 

might furnish clues to the occurrence of undetected 

blind ore bodies in the vicinity.

BISBEE (WARREN) DISTRICT, ARIZONA

(3, fig. 1;3, fig. 38)

The Bisbee district is in the south-central Mule 

Mountains near the southeast corner of Arizona. 

Here, Precarnbrian schist and granite are overlain 

by about 5,200 feet of rocks which range in age from 

Cambrian to Pennsylvanian and which consist largely of limestone above a basal quartzite. These rocks
64 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

are truncated by an erosional unconformity and are 

overlain by about 5,000 feet of Cretaceous sedimentary rocks which consist largely of conglomerate, 

sandstone, and shale and which contain a thick 

limestone bed near the top. The Paleozoic rocks were 

complexly faulted and intruded by siliceous porphyritic rocks, which resulted in the formation of numerous dikes, sills, and, at Sacramento Hill, a small 

granite porphyry stock. This stock, which lies on the 

east-trending Dividend fault, intrudes Precambrian 

schist on the north and Paleozoic limestone on the 

south. It is a focal point for much of the faulting, 

alteration, and mineralization in the district. Tectonic movement, subsequent to the igneous intrusions and major period of mineralization, produced 

thrust faults and related high-angle faults that cut 

the Cretaceous rocks. Copper ore is disseminated 

in the altered porphyry of the Sacramento stock, 

and sulfide replacement ore bodies are localized along 

faults in the limestone south of the Dividend fault.

DISTRIBUTION

Jasperoid breccia forms a nearly continuous belt in 

the limestone adjacent to the Sacramento stock eastward from the vicinity of the Gardner shaft. This 

belt, which is irregular both vertically and horizontally, grades outward into recrystallized limestone 

200-1,000 feet from the porphyry contact (Ransome, 

1904, p. 83-131, pis. I, III; Bonillas and others, 1917, 

p. 319). Irregular pods and lenses of Jasperoid breccia are also widely distributed throughout the district, especially along faults and fractures, where 

these cut favorable beds in the Paleozoic limestone. 

Some major centers of jasperoidization mentioned 

in the literature are (1) the area of the lower workings of the Lowell mine (Ransome, 1904, p. 131; 

Bonillas and others, 1917, p. 319); (2) the vicinity 

of the Czar fault where it crosses Hendricks Gulch; 

(3) in Uncle Sam Gulch above the mine and adjacent 

to a granite porphyry contact (Ransome, 1904, p. 

83; and (4) just above the contact between the 

Martin and Escabrosa Limestones in Abrigo Canyon 

(Ransome, 1904, p. 97, pis. I, III). One type of Jasperoid is commonly found in the vicinity of sulfide 

replacement deposits, and tends to occur at various 

distances above them along the plane of the controlling fault or fracture, particularly in cherty zones 

in the limestone (Trischka, 1938, p. 36). Bonillas, 

Tenney, and Feuchere (1917, p. 320) stated that Jasperoid bodies related to porphyry intrusions are 

more abundant in the Abrigo and Martin Limestones 

than in the Escabrosa Limestone. However, Trischka 

wrote that the fault- and fracture-controlled Jasperoid breccias are most abundant in the Escabrosa.

Bodies of Jasperoid breccia are found in all the 

Paleozoic formations in the district.

A distinctly younger type of Jasperoid, which 

Trischka (1928, p. 1048-1050) described and termed 

"boxworks silica," is concentrated along postCretaceous faults and fractures. It is most abundant 

in the coarse Cretaceous conglomerates resting on 

the pre-Cretaceous erosion surface, although it also 

occurs a short distance below this surface in the 

Paleozoic limestone and a short distance above it 

in the Cretaceous shale and sandstone.

GENESIS

Both types of Jasperoid in the district are considered by Trischka (1928, p. 1045-1049) to be of hypogene hydrothermal origin. According to Bonillas, 

Tenney, and Feuchere (1917, p. 319-320), the source 

of the hydrothermal solutions that silicified and 

otherwise altered the porphyry stock and the Paleozoic limestone along its southern margin was within 

or beneath the stock and genetically related to it. 

The various authors who have studied the district 

generally agree that a close genetic connection exists 

between this hydrothermal alteration and the primary ore mineralization which closely followed it, 

both within and adjacent to the stock, and outward 

from it along faults and fractures related to the intrusion. The general sequence of events appears to 

have been (1) faulting before igneous intrusion; 

(2) forceful intrusion of the stock and related dikes 

and sills, accompanied by further faulting and minor 

contact metasomatic silication of limestone adjacent 

to the stock; (3) crystallization and solidification of 

intrusive rocks; (4) further fracturing of intrusives 

and host rocks; and (5) hydrothermal alteration by 

fluids moving through these fractures, beginning 

with sericitic and chloritic alteration, progressing 

through hematitic alteration and silicification, and 

culminating with sulfide deposition.

The early "silica breccia" type of Jasperoid resulting from this process was thought by Trischka (1928, 

p. 1047-1048) to have formed in the following manner. Brittle limestone beds were dragged apart, 

fractured, brecciated, and ground during faulting, 

producing a highly permeable breccia of angular 

limestone fragments in a matrix of powdered limestone. This powdery matrix was first recrystallized 

to coarse calcite and impregnated with red hematite 

by the mineralizing solutions. Both the matrix and 

the breccia fragment inclusions were then completely 

replaced by silicia, forming a dark-red aphanitic ironsilica matrix cementing creamy-white silicified limestone breccia fragments and, locally, gray breccia 

fragments of unreplaced primary chert. The com-
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 65

pleteness of the replacement, the angularity of the 

breccia fragments, the preservation of original textures and fossils in these fragments, and the general 

absence of vugs in the matrix led Trischka (1928, 

p. 1049) to conclude that silicification was a slow 

volume-f or-volume replacement process without prior 

solution of calcium carbonate.

The late "boxworks silica" type of jasperoid originated also from hydrothermal silica-bearing solutions, according to Trischka (1928, p. 1048-1050). 

He expressed the opinion that it was formed by 

rapidly moving hydrothermal solutions, ascending 

along open fractures; these solutions partly dissolved 

and partly replaced the calcareous matrix and rock 

fragments they encountered. Later weathering and 

leaching away of the unsilicified remnants contributed to the rough vuggy texture that is characteristic of this rock. The ultimate source of these late 

siliceous emanations was not discussed, beyond the 

statement that they are later than, and unrelated 

to, the mineralizing solutions that produced the primary ore deposits.

RELATIONSHIP TO ORE

The early "silica breccia" type of jasperoid of 

Trischka (1928, p. 1047-1048) is thought by him 

to be related both genetically and spatially to sulfide 

replacement deposits in the Paleozoic limestones, 

and thus is of the favorable type. In contrast, the 

late "boxworks silica" type appears to be unrelated 

to ore, and is consequently unfavorable. Bodies of 

favorable jasperoid generally lie above the sulfide 

replacement deposits. In some places the sulfides are 

within the jasperoid, or immediately adjacent to it, 

and locally they penetrate it along small veinlets 

(Hogue and Wilson, 1950, p. 26; Mitchell, 1921, p. 

248). Elsewhere, the ore bodies are at some distance 

from the jasperoid down the feeding fissure. The 

jasperoid then serves only as an indicator of sulfide 

deposits in the general vicinity, rather than in immediate proximity (Trischka, 1928, p. 1048).

In many places within the zone of oxidation the 

primary sulfides of iron, copper, and zinc have been 

leached from jasperoid, leaving porous soft and yielding masses of silica, or, where the leached jasperoid 

has been crushed under the weight of the overlying 

rocks, pockets of coarse sand containing cerussite. 

One such mass of leached jasperoid in the Lowell 

mine was described by Ransome (1904, p. 131). Layers of chalcocite and crystals of cerussite locally 

partly fill voids in the oxidized jasperoid (Mitchell, 

1921, p. 248). Trischka (1938, p. 37) described a locality in Hendricks Gulch in which gold was sufficiently concentrated in a pocket of jasperoid sand to 

produce a minable ore body.

APPEARANCE

Bodies of jasperoid in the district form rough 

and irregular outcrops. Ransome (1904, p. 83) described them as "a rusty, cavernous siliceous rock, 

looking superficially not unlike a weathered amygdaloidal lava." According to Trischka (1928, p. 1045; 

1938, p. 34), these outcrops form continuous veinlike 

bodies as much as 40 feet wide and 30 feet high in 

some places; elsewhere, they are smaller irregular 

pods strung out discontinuously along faults and 

fractures. The silica breccia type of jasperoid is generally a dark-red aphanitic rock containing conspicuous angular inclusions of white or cream-colored 

silicified limestone and, locally, of gray chert. In 

many places this rock has been repeatedly fractured 

and recemented with later silica, forming a network 

of quartz veinlets.

The late jasperoid (boxworks silica) was described 

by Trischka (1928, p. 1045, 1049) as a pale-yellow or 

pink rock with abundant open cavities, which are 

commonly coated with small quartz crystals. This 

siliceous matrix cements rounded, corroded, and 

partly replaced pebbles and breccia fragments of 

limestone and other rocks. It forms smaller bodies 

than the older jasperoid, but they are distributed 

over a larger area.

Four jasperoid samples from the Bisbee district 

are included in my collection. Three of these samples 

are of the older jasperoid, and one is of the younger 

jasperoid.

Two of the older jasperoid specimens are definitely 

favorable, having been collected from surface exposures above known ore bodies. One of these specimens 

is derived from Martin Limestone of Devonian age 

near the Dividend fault a short distance east of its 

junction with the Czar fault; the other is derived 

from Naco Limestone of Pennsylvanian age in a 

breccia zone along the Junction fault. Both samples 

are similar in appearance, consisting of shattered 

and brecciated dense white and gray silicified limestone cemented by veinlets and interstitial masses 

of dark-red hematite and silica, with local small 

patches of green malachite.

The third sample of older jasperoid is from a replacement of Mississippian Escabrosa Limestone 

along a roadcut about a mile east of Don Luis. This 

body is not related to any known ore deposits. The 

sample differs from the other two in that it is massive, pinkish gray, is cut by veinlets of coarse-grained 

calcite, and contains little hematite. It resembles the
66 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

two favorable jasperoid samples in its aphanitic 

texture.

The sample of late unfavorable jasperoid came 

from Cambrian Abrigo Limestone along the Black 

Gap fault a short distance south of the contact between the Paleozoic rocks and the unconformably 

overlying Cretaceous rocks. It consists of partly 

rounded breccia fragments 1-3 inches in diameter of 

pale-brown slightly vuggy fine-grained silicified limestone in a matrix of fine-grained white quartz containing irregular open vugs as much as a quarter of 

an inch in diameter.

MICROTEXTURE AND MINERALOGY

The groundmass in all three samples of older jasperoid consists of dense, relatively homogeneous aphanitic quartz that has a jigsaw-puzzle texture and 

an average grain size of about 0.01 mm.

The two samples of favorable jasperoid have a 

groundmass locally impregnated with red hematite 

dust particles. This matrix is cut by veinlets and 

irregular masses of late homogeneous xenomorphic 

quartz that has an average grain diameter of 0.05 

mm. Locally, masses of this late quartz, which line 

the walls of original cavities between breccia fragments of the fine-grained matrix jasperoid, have cores 

of flamboyant fibrous chalcedony. In one sample the 

walls of fractures that cut the matrix are locally 

coated with small fibrous masses of brochantite, 

which are enveloped by late xenomorphic quartz that 

fills the fracture. These quartz stringers are cut by 

later fractures partly filled with porous red hematite, 

and these, in turn, are cut by thin veinlets of malachite. Thus, a rather complex history of supergene 

mineralization is revealed.

The aphanitic groundmass in the third sample of 

older jasperoid contains irregular remnant grains 

of calcite and also a few grains of specular hematite 

that appear to be either contemporaneous with, or 

slightly younger than, the quartz. The matrix is cut 

by veinlets of coarse calcite as much as a centimeter 

wide and by narrower younger veinlets in which calcite is mixed with opaque brown limonite. This sample 

does not contain any of the late xenomorphic quartz 

that is prevalent in the other two, older, jasperoid 

samples.

The sample of late unfavorable jasperoid from the 

Black Gap fault, east of Bisbee, differs strikingly 

in its microtexture and mineralogy from the samples 

of older jasperoid. The breccia fragments are composed of heterogeneous xenomorphic quartz grains 

whose diameter ranges from 0.005 to 0.1 mm and 

averages about 0.02 mm. Inclusions of carbonate 

particles are common, and sparsely scattered through

the groundmass are sericite flakes and larger masses 

of coarse-grained relict carbonate with high relief 

(probably ankerite or siderite). Small vugs are 

abundant, and some of these are lined with xenomorphic quartz having a mean grain diameter of about 

0.1 mm. The matrix quartz that cements the breccia 

fragments has a heterogeneous granular to xenomorphic texture and a grain diameter that ranges from 

0.015 to 0.1 mm and averages about 0.03 mm. It 

contains sparse allophane particles, but no carbonate. 

Vugs in the matrix are larger than those in the 

breccia fragments, and are lined with heterogeneous 

jigsaw-puzzle-textured quartz, which has a grain 

diameter that ranges from 0.005 to 0.05 mm and 

averages 0.02 mm, and which contains carbonate 

particles.

The appearance of this sample under the microscope clearly reveals its true identity, in contrast 

to the older jasperoid samples which closely resemble brecciated chert.

COMPOSITION

Semiquantitative spectrographic analyses were 

made on splits from each of the four samples previously described. All four samples show abnormally 

high concentrations of nickel and lead. The two favorable samples contain abundant iron, copper, vanadium, and yttrium, and one of these two is also rich 

in silver, bismuth, and ytterbium; the other contains 

unusual quantities of lanthanum. Strontium is concentrated in one favorable sample and in the unfavorable sample of older jasperoid; the latter sample 

is the only one of the four to show an abnormal 

amount of manganese. Beryllium and molybdenum 

both show slightly larger-than-normal concentrations 

in one of the favorable samples and in the sample 

of late unfavorable jasperoid. Zirconium is the only 

element present in abnormal amounts in this sample 

of younger jasperoid but not in any of the older 

jasperoid samples.

The evidence furnished by these four samples is 

insufficient to warrant any conclusions as to diagnostic indicator elements associated with favorable 

jasperoids in this district. However, it does suggest 

the possibility that one or more elements of the group 

that includes copper, silver, bismuth, lanthanum, vanadium, yttrium, and ytterbium, which were abnormally concentrated only in the favorable samples, 

might be useful for this purpose. Zirconium might 

be a useful element to distinguish the late unfavorable jasperoid.
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 67

CONCLUDING REMARKS

The jasperoids of the Bisbee district are unusual 

in that the color and texture that are generally 

indicative of unfavorable jasperoid are here associated with the favorable type, whereas the color and 

texture that would normally lead one to suspect 

favorable jasperoid are characteristic of the late unfavorable type. Nevertheless, the two types are generally distinguishable by color, texture, and mode of 

occurrence, and the use of jasperoids as a tool in the 

search for new ore bodies seems to have considerable 

promise in this area.

ELY (ROBINSON) DISTRICT, NEVADA

(4, fig. 1; 19, fig. 44)

Near the town of Ely, in the Egan Range of eastern Nevada, Paleozoic sedimentary rocks, consisting 

largely of limestone and shale, have been arched 

into a broad east-trending anticline, transverse to the 

trend of the range (Spencer, 1917). The western part 

of the axial area of this anticline is cut by low-angle 

thrust faults; near the center it is broken into alternating horsts and grabens by north-trending normal 

faults, and farther east, by minor faults along its 

flanks and across its axis. Major faulting was followed by the intrusion of a series of dikes, stocks, 

and sills of Tertiary monzonite porphyry along the 

trend of the anticlinal axis. These intrusive rocks 

together with the enclosing host rocks, were complexly shattered by renewed fault movement, hydrothermally altered, and mineralized with the disseminated porphyry-type copper deposits for which 

the district is famous; at the same time, replacement, 

vein, and breccia-type deposits of copper, lead, zinc, 

silver, and gold were formed in the Mississippian, 

Pennsylvanian, and Permian shales and limestones 

in the vicinity of the intrusives. After a long erosion 

interval, rhyolite was both intruded and extruded in 

the area, the extrusive flows partly covering the 

mineralized monzonite porphyries.

DISTRIBUTION

Irregular bodies of jasperoid are abundant in the 

western and central parts of the district (Spencer, 

1917, pis. 6,10). They range in size from small bodies 

covering a few hundred square feet to huge masses 

that can be traced for several thousand feet along 

the outcrop and are as much as 1,500 feet wide in 

places. Many of them either are at the contact of 

the monzonite porphyry with the enclosing limestone 

and shale or they cap ridges within the porphyry, 

but some form replacements in limestone at a considerable distance from the contact; the latter tend

to form elongated veinlike bodies or "reefs" along 

fault and fracture zones. Lawson (1906, p. 325) concluded that the jasperoid originally formed a discontinuous and irregular envelope along the sides and 

over the top of the monzonite porphyry stocks, separating them from the adjacent sediments. He also 

noted (p. 329) that many jasperoid bodies terminate 

abruptly "at no great depth."

GENESIS

The close spatial association between the monzonite porphyry intrusives and many of the larger jasperoid bodies in the district, noted by Lawson (1906) 

and also by Spencer (1917, p. 51), may indicate that 

much of the jasperoid in the Ely district is genetically related to these intrusives rather than to the 

subsequent hydrothermal alteration and mineralization. However, many of these large bodies locally contain chalcopyrite and pyrite; hence, they may also be 

favorable jasperoid of hydrothermal origin (A. V. 

Heyl, written commun., 1967), or they may also be 

older jasperoid that was locally mineralized by the 

ore-stage fluids. This silicification along the intrusive 

contacts must have occurred after the crystallization 

of the intrusives, because the porphyry as well as 

the host rock has locally been converted to jasperoid, and in some places jasperoid overlies remnants 

of contact metasomatic garnet rock.

Some of the jasperoid bodies are localized by faults 

and fracture zones rather than by proximity to intrusive contacts, and some contain disseminated sulfides of their oxidation products; this fact suggests 

that a considerable amount of late jasperoid silica 

was also introduced by hydrothermal solutions preceding or accompanying ore mineralization. Such a 

theory is further supported by the presence of two 

or more distinct generations of quartz in many 

samples from the district.

On the basis of studies of fluid inclusions in jasperoid quartz, Spencer (1917, p. 63) concluded that 

the Ely jasperoids formed at minimum temperatures 

between 160° and 270 °C, and that the replacement 

of limestone by silica was accomplished by cooling 

solutions, since the replacement reaction is exothermic, evolving 2,600 calories for each gram of calcite 

replaced. He (p. 64-69) also expressed the opinion 

that the early siliceous emanations, containing H2S, 

HC03 , KOH, F, Fe, and Cu, were slightly acid, that 

they became alkaline through reaction with the host 

rock as silica and sulfides were deposited, and that 

they finally were neutralized as they cooled.

RELATIONSHIP TO ORE

The early jasperoid, related to the monzonite por-
68 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

phyry intrusives, is generally unfavorable, according 

to Lawson (1906, p. 329) and Spencer (1917), although locally it has been mineralized by later hydrothermal solutions. Lawson (p. 329) reported that 

numerous outcrops of "blout" (jasperoid) in the district have been explored, and that most of them do 

not contain ore, except for small pockets and coatings of secondary copper minerals and remnants of 

disseminated pyrite. Spencer (p. 74), on the other 

hand, distinguished between a porous brecciated rubbly type of jasperoid that was associated with sulfide mineralization and a dense massive resistant 

type of jasperoid that was unrelated to ore. Most of 

the unoxidized ore-related jasperoids contain disseminated pyrite and chalcopyrite, although chalcocitebearing jasperoid is found in the Veteran and BostonEly mines. Some small fracture-controlled jasperoid 

bodies in unmetamorphosed limestone lie above pockets of chalcocite ore. Most of the favorable jasperoids 

are associated with copper ore bodies in the western 

and central parts of the district; however, outlying 

jasperoid bodies also occur in the vicinity of silverlead-zinc-, and gold-bearing galena-sphalerite replacement deposits in limestone (Spencer, 1917, p. 51, 99, 

122-123, 128).

My jasperoid samples from the Ely district display 

a great variety of colors and textures and also a wide 

range in scores for favorability. However, those at 

the low end of the favorability scale with scores of 

<5 and those at the high end with scores of >18 

are distinctive. The unfavorable samples, which probably represent Spencer's dense massive resistant 

type, are light gray or yellowish gray and have an 

aphanitic texture. The highly favorable samples, 

which probably represent his porous brecciated rubbly type, are heavily impregnated with moderatebrown to dark-brown iron oxides on the outcrop, and 

they are porous, vuggy, and coarse grained.

APPEARANCE

Lawson (1906, p. 327-329) recognized four varieties of "blout" (jasperoid) in the Ely district, which 

he classified as compact and massive, cavernous 

weathering, brecciated, and cellular, and which he 

described as follows. The compact and massive variety, the most abundant, is glassy, white or pale yellow, and it locally resembles a massive quartzite. It 

commonly has a bedded appearance, and adjacent 

layers are different in both color and texture. This 

layering is inherited from the bedding of the host 

limestone. In most places the outcrops are heavily 

stained with iron oxide. This rock weathers into 

rounded knobs or breaks down into talus of irregular 

angular blocks. The cavernous-weathering variety

weathers into very irregular forms "with rugged 

chambers and straggling channels," in the bottoms 

of which unaltered remnants of limestone occur locally. The brecciated variety consists of angular fragments ranging from minute particles to blocks 4 

inches in diameter, cemented in a matrix of quartz 

or, less commonly, of calcite. The breccia fragments 

are predominantly light colored, whereas the matrix 

characteristically consists of red or dark-yellow jasper. The cellular variety is light colored and porous, 

and it weathers to a rubble of small fragments. It 

represents silicified porphyry rather than silicified 

limestone, and it locally preserves textures of the 

porphyry and grades into unsilicified porphyry.

Spencer (1917, p. 74) emphasized two major types 

of jasperoid in the district, a massive barren variety 

and a porous friable sulfide-bearing variety. The barren type weathers to form prominent outcrops, in 

contrast to the sulfide-bearing type which breaks 

down into a rubble of small angular fragments 

stained rusty brown from oxidation of the pyrite.

My collection from the Ely district consists of 26 

samples of jasperoid, all of which were derived from 

limestone. Twenty-one of these samples are in the 

vicinity of ore deposits and were classified as favorable ; five are not associated with any known ore deposits and were classified as unfavorable. Two of the 

unfavorable samples were collected at the site of the 

old town of Ruth, one came from Verzan Canyon 

half a mile north of the east end of the Ruth ore 

body, and the remaining two from the east-trending 

ridge northeast of Weary Flat about a mile north of 

the Liberty Pit. All five are aphanitic to fine grained 

and fractured; one has been brecciated and recemented with younger silica. Their color on weathered 

surfaces ranges from pale yellow to grayish brown 

and on fresh surfaces, from light yellowish gray 

through light gray to medium gray.

Four of the favorable samples came from the area 

of the Veteran and Boston-Ely mines at the west 

end of the district, and two from small mines 1-1 y% 

miles northeast of Lane at the east end; the remainder were collected at various localities in the 

central part of the district (south of the Liberty Pit, 

in the vicinity of the Ruth ore body, and in the vicinity of the Jupiter mine). This group shows a much 

wider range in both color and texture than does the 

barren sample group. The weathered surfaces are 

predominantly brown, in various shades ranging 

from light yellowish brown through moderate brown 

and dark brown to very dark brownish gray, almost 

black; one sample is brick red, and two or three are 

predominantly light gray. On fresh fractures a few 

of the brown-weathering samples are light to mod-
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 69

erate gray or variegated brown and gray, but most 

of them show the brown color on fresh exposures as 

well as on weathered surfaces. Most of these samples 

are aphanitic to fine grained, but otherwise they are 

not consistent in texture; some are dense and massive, some are, brecciated, some are vuggy; some 

weather to relatively smooth surfaces and some to 

very rough uneven surfaces. The 10 samples from 

this suite that scored +19 or higher on the basis 

of concentration of indicator elements are more 

similar in appearance; all are vuggy, rough weathering, and heavily stained with moderate- to darkbrown limonite.

MICROTEXTURE AND MINERALOGY

Spencer (1917, p. 51, 100-101) reported that the 

typical jasperoid of the Ely district consists of finegrained quartz aggregates that locally contain abundant tiny vacuoles, some of which are partly filled 

with fluid. A few of these fluid inclusions also contain very minute crystals of halite or sylvite. Chalcedony is locally abundant; it is younger than the first 

generation of matrix quartz, but older than some of 

the late quartz. Other common accessory minerals in 

the jasperoid are fluorite, apatite, calcite, mica, and, 

locally, pyrite and chalcopyrite. Spencer (1917, p. 

117) also reported that a variety of ore-bearing jasperoid from the Veteran mine also contains rutile, 

magnetite, pyrrhotite, and chalcocite.

Most of my jasperoid samples from the Ely 

district range in grain size from 0.01 to 0.1 mm, 

although a few are as much as 1 mm in diameter. 

Fluid inclusions are present in some of the coarsegrained samples. All the common jasperoid fabric 

textures discussed on pages 11-15 of this report 

are represented in the suite of Ely samples. Xenomorphic and jigsaw-puzzle textures are most abundant, but granular, reticulated, and fibrous textures 

are also present. Most of the samples exhibit at least 

two distinct generations of jasperoid quartz, and 

some show as many as four generations. In general, 

the older generation is granular to xenomorphic in 

texture and somewhat coarser grained than the 

younger generation, which commonly exhibits a 

jigsaw-puzzle texture. These observations tend to 

support the theory of early high-temperature, diffuse, siliceous emanations, from which silica probably 

deposited directly in the form of quartz, followed by 

late denser and cooler hydrothermal silica-bearing 

solutions from which silica deposited as a colloidal 

gel, giving rise to an aphanitic jigsaw-puzzle texture 

in the resulting jasperoid. Local exceptions, in which 

the latter type is followed by coarser xenomorphic 

or reticulated jasperoid, may indicate that late-stage

hydrothermal solutions with lower silica concentration were in contact with previously silicified and 

therefore nonreactive rocks, again resulting in relatively slow deposition of Si02 as quartz. These exceptions are economically important because a late 

stage of coarse vuggy xenomorphic to locally reticulated quartz is characteristic of the most highly favorable type of samples in the Ely suite.

In thin sections cut from 25 jasperoid samples 

from the Ely district, 21 minerals, in addition to 

quartz, were identified. In order of decreasing abundance these are (1) chalcedony, hematite, and limonite (10 samples) ; (2) allophane dust and goethite 

(eight samples); (3) jarosite and calcite (six samples) ; (4) carbonate dust (five samples); (5) sericite, kaolinite, apatite, fluorite, and pyrite (three 

samples); (6) hydromica, halloysite, opal, and 

sphene (two samples) ; and (7) lussatite, zircon, siderite, and cerussite (one sample). The age relations 

of these 21 minerals to the jasperoid quartz are 

broadly indicated in table 16.

The samples were divided, on the basis of their 

indicator-element content, into three groups as follows: Highly favorable (score ^ + 19), intermediate 

(score <+19 but >+5), and unfavorable (score 

<+5). This classification resulted in 10 samples 

in the first group, 10 in the second, and five in the 

third. The seven most abundant minerals (those recognized in more than five samples) were then classiTABLE 16. Age relations of minerals in Ely district jasperoid 

to the jasperoid quartz

Mineral Older 1 Contemporaneous 2 Younger 3

Apatite ..................................

Zircon ......................................

Siderite ..................................

Sericite ..................................

Pyrite ......................................

Hydromica ............................

Sphene ....................................

Calcite (carbonate dust) ....

Allophane ..............................

Hematite ................................

Limonite ................................

Goethite ..................................

Chalecdony ............................

Kaolinite ................................

Halloysite ..............................

Fluorite ..................................

Jarosite ..................................

Cerussite ................................

Opal ........................................

Lussatite ................................

1 Older than the first generation of jasperoid quartz.

2 Formed simultaneously with a major generation of quartz or between 

two major generations.

3 Formed after the youngest major generation of jasperoid quartz, but 

not necessarily after the youngest quartz veinlets and vug linings.
70 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

fied as to the proportion of the total samples in each 

group in which they occur, as follows.

Frequency (as percent of total group)

Mineral Highly 

favorable Favorable Unfavorable

Jarosite .......................................... 50 10 0

Goethite ........................................... 30 50 0

Limonite ........................................ 60 30 20

Hematite ........................................ 40 50 20

Chalcedony .................................... 30 50 40

Allophane ...................................... 20 50 20

Calcite ............................................ 30 20 20

This limited amount of data suggests that among 

the more abundant minerals only jarosite, goethite, 

and possibly limonite are significantly more common 

in the favorable variety of Ely district jasperoid 

than in the unfavorable variety.

COMPOSITION

Spencer (1917, p. 117) reported a quantitative 

chemical analysis of a composite sample of orebearing jasperoid from the Veteran mine. This jasperoid contained rutile, magnetite, pyrrhotite, and 

chalcocite, which are not present in most jasperoids 

of the district, and therefore does not represent ordinary Ely district jasperoid. The analysis is as follows:

Element Percent Element Percent

SiO3 ................................ 79.11 H2O- .......................... 0.81

A12O3 .............................. 3.82 H2O+ .......................... 2.68

Fe2O3 .............................. .44 TiO3 ............................ .81

FeO ................................ .69 P2O5 .............................. .42

MgO .............................. 1.19 S .................................. x 3.01

CaO ................................ .62 Cu ................................ X 2.55

Na2O .............................. .31 Fe ................................ ^.64

K2O ................................ .54 Total .................. 99.64

1 In sulfide inclusions.

Semiquantitative spectrographic analyses were 

made of splits from the 25 samples studied in the 

present investigation, and in one or more of these 

samples 33 elements other than Si were detected, as 

shown in table 17. 

The actual relative abundance of these elements 

is difficult to evaluate, because many of them have 

highly irregular frequency distributions and because 

the limit of sensitivity of the analytical method 

varies widely from element to element. This evaluation difficulty is illustrated by table 18, in which the 

15 most abundant elements are listed in order of decreasing concentration according to arithmetic mean, 

median, and maximum renorted concentration. In

TABLE 17. Minor-element distribution in 26 samples of 

jasperoid from the Ely district, Nevada

[J. C. Hamilton, analyst. Leaders (......) indicate no information]

Limit of Number of 

Element detection samples Minor-element distribution (in percent)

(percent) in which - 

detected Range Mean Median Mode

Ag ............ 0.0001 12 < 0.0001 .07 0.0048 < 0.0001 < 0.0001

Al .............. .001 26 .15 - .-7 .27 .14 .15 

As ............ .1 3 <.l 1.5 ........ ........ --...

B .............. .002 4 <.002 .003 ........ ........ ........

Ba ............ .0002 26 .0007 .07 .0087 .003 .003

Ca ............ .005 26 .07 ->10.0 1.2 .12 .15

Cr .............. .0001 26 .0003- .007 .0023 .0014 .003

Fa Anna 9c rt7 "^ 1 fl 3 Q 1 ft Q

Ga ............ .0002 6 <.0002 .003 ........ ........ ........

In .............. .001 5 <.001 - .0015 ........ ........ ........

Mg ............ .0005 26 .007 - .3 .061 .021 .03

Mn ............ .0002 26 .0015 .7 .044 .0095 .015

Mo ............ .0005 17 <.0005- .007 .0015 .0007 <.0005

Nb ............ .001 1 <.001 .0015 ........ ........ ........

Ni .............. .0003 8 <.0003- .0015 .00023 ........ ........

P ................ .2 1 <.2 .7 ........ ........ ........

Pb ............ .001 17 <.001 7. .39 .003 <.001

Sn ............ .001 15 <.001 .15 .0081 <.001 <.001

Sr .............. .0002 24 <.0002- .03 .003 .0008 .0007

Ti .............. .0002 26 .007 .3 .052 .023 .07

V .............. .001 14 <.001 .015 .0027 .001 <.001

Y .............. .001 6 <.001 .0015 ........ ........ ........

Yb ............ .0001 8 <.0001 .00015 .00003 ........ ........

Zr .............. .001 22 <.001 .07 .0084 .003 .007

spite of the uncertainties regarding the true abundance of the various elements, which are inherent 

in the nature of the samples, of the analytical data, 

and of the analytical method, it is apparent that bismuth, tin, and zinc are abnormally concentrated in 

this group of samples. However, a much larger number of samples would be required to ascertain whether these elements are characteristically high in 

jasperoid bodies of the district as a whole. 

Comparison of the median concentrations of the 

various elements in the group of 10 highly favorable 

samples and the group of five unfavorable samples

TABLE 18. Relative abundance, in percent, of 15 most abundant elements in 26 samples of jasperoid from the Ely 

district, Nevada

Arithmetic mean Median Maximum reported 

concentration concentration concentration

Fe ................ 3.9 Fe ............ 1 Fe ................>10

Ca ................ 1.2 Ca ............ .15 Ca ................>10

Pb .............. .39 Al .............. .14 Pb ................ 7

Al ................ .27 Ti .............. .023 As ................ 1.5

Mg .............. .061 Mg ............ .021 Al ................ .7

Ti ................ .052 Zn .............. .015 Bi ................ .7

Zn ................ .051 Mn ............ .0095 Mn .............. .7

Mn .............. .044 Cu ............ .007 P .................. .7

Bi ................ .036 Pb ............ .003 Mg ................ .3

Cu .............. .027 Ba ............ .003 Ti ................ .3

Ba .............. .0087 Zr .............. .003 Zn ................ .3

Zr ................ .0084 Cr .............. .0014 Cu ................ .15

Sn .............. .0081 V ................ .001 Sn ................ .15

Ag .............. .0048 Sr .............. .0008 Ag .............. .07

Sr ................ .0030 Mo ............ .0007 Ba ................ .07
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 71

showed that among the common elements only iron 

exhibits a difference of an order of magnitude or 

more between the two median values (4 percent in 

the favorable group, 0.13 percent in the unfavorable 

group); similar differences were also noted in the 

ore metals, silver, bismuth, copper, lead, tin, and 

zinc, but these can be ascribed largely to the criteria 

used to establish the two groups.

CONCLUDING REMARKS

The available data suggest two major generations 

of jasperoid in the Ely district: (1) an early unfavorable generation, genetically related to the monzonitic intrusive rocks, that is dense and massive and 

has a fine-grained granular to xenomorphic texture; 

and (2) a late, locally favorable generation genetically related to hydrothermal solutions younger than 

the intrusives. This late jasperoid again may be subdivided into two types: an aphanitic variety that has 

a jigsaw-puzzle texture, which is generally unfavorable, and a coarser grained vuggy xenomorphic to reticulated variety associated with abundant iron 

oxide, which is commonly favorable. A more detailed 

study of the district would be needed to establish the 

distribution patterns, structural controls, and age 

relations of the various types of jasperoid.

LEADVILLE DISTRICT, COLORADO

(5, fig. 1; 9, fig. 40)

The Leadville district of central Colorado is on the 

western slope of the Mosquito Range near the head 

of the Arkansas River (Emmons and others, 1927). 

It has produced large quantities of silver, lead, and 

zinc and some gold, manganese, and copper.

Here, Precambrian granite, schist, and gneiss are 

covered by about 150 feet of Cambrian quartzite 

and shale, which, in turn is overlain by about 350 

feet of Ordovician, Devonian, and Mississippian rocks 

that consist dominantly of limestone and dolomite. 

The Mississippian and Devonian rocks are overlain 

by about 2,500 feet of Pennsylvanian continental and 

marginal marine sedimentary rocks, which are largely shale, siltstone, and arkose with a few interbedded limestones.

During Cretaceous time the sedimentary rocks 

were intruded by dikes and sills of monzonite and 

granodiorite. After these intrusions were emplaced, 

strong compressive forces folded the rocks and produced large northwest-trending thrust faults. This 

was followed by the intrusion of a small quartzmonzonite stock at Breece Hill, together with related 

dikes. Subsequent to the emplacement of this stock 

the area was again broken by numerous normal and

reverse faults. These faults served as conduits for 

hydrothermal solutions which emanated from within 

or beneath the stock and which altered and mineralized the rocks adjacent to the faults. Still later, 

northeast-trending normal faults broke and offset 

many of the ore bodies, and plugs and dikes of rhyolite were locally intruded, probably in Pliocene time. 

This complex erogenic history has complicated the 

regional distribution pattern of ore deposits and 

related types of alteration, including jasperoid.

DISTRIBUTION

The Leadville district is close to the center of a 

jasperoid province (fig. 1) that extends outward 

from the district for many miles to the northeast, 

east, and southeast. Thus, it is difficult to establish 

boundaries between jasperoid bodies of the Leadville 

district (9, fig. 40) and those of the Kokomo district 

(7, fig. 40) and Pando area (14, fig. 40) to the north, 

and the Horseshoe-Sacramento district (6, fig. 40) 

to the southeast. Within this region replacement 

bodies of jasperoid are most abundant in the upper 

part of the Mississippian Leadville Limestone, particularly in areas where this formation is capped by 

porphyry sills and has been cut by faults and fractures that provided access for mineralizing solutions. 

Jasperoid bodies are also found locally in the Devonian Dyer Dolomite Member of the Chaffee Formation and in the Ordovician Manitou Limestone 

beneath the Leadville Limestone; they are also found 

in some limestone beds in the lower part of the Pennsylvanian Minturn Formation above the Leadville 

Limestone. Igneous intrusive rocks close to centers 

of intense alteration are also strongly silicified locally.

Emmons, Irving, and Loughlin (1927, p. 172, pi. 

13) referred to many jasperoid replacement bodies 

in the Leadville Limestone on Fryer Hill and in the 

Downtown area. Additional areas that contain abundant jasperoid (Loughlin and Behre, 1934, p. 226, 

229, 234, 240) are Iron Hill, the southeastern part of 

Carbonate Hill, the head of Evans Gulch, and a small 

area west of the Mike fault opposite Empire Hill. 

Many of the most extensive jasperoid bodies are 

also associated with the Tucson Maid fault west of 

Breece Hill in the central part of the district.

The six Leadville district samples in my collection 

are all dump samples from the northwestern and 

western parts of the district. Two are from Canterbury Hill, one about 1 mile and the other l1/^ miles 

northeast of the center of Leadville. The remaining 

four samples are from mines on Fryer Hill and Stray 

Horse Ridge, i/2-1 mile east °f Leadville.
72 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

GENESIS

Much of the jasperoid in the district apparently 

was formed by hydrothermal silica-bearing solutions 

emanating from within or beneath the Breece Hill 

stock. Emmons, Irving, and Loughlin (1927, p. 218) 

concluded that the main period of jasperoidization in 

the district occurred during and after the ore stage 

of mineralization. Quartz was deposited in veins 

before the deposition of the sulfides, which partly 

replaced the vein quartz, displacing the silica outward to form jasperoid. However, Loughlin and 

Behre (1934, p. 226) pointed out that many of the 

jasperoid bodies are impregnated with sulfides and 

are cut by sulfide veins, and therefore, that some of 

the jasperoid must have formed before the ore-sulfide 

stage of mineralization.

Loughlin and Behre (1934, p. 221) classified the 

deposits of the district, on the basis of mineral 

assemblages representing successively lower temperatures of formation, into pyrometasomatic, hypothermal, high mesothermal, intermediate mesothermal, low mesothermal, and epithermal or telethermal. 

They regarded (p. 225) the jasperoids as most characteristic of the intermediate mesothermal deposits, 

which were formed outward from, and at lower temperatures than, the manganosiderite deposits that 

characterize the high mesothermal class; but they 

also mentioned the association of jasperodd with 

some deposits of the low mesothermal and epithermal 

classes.

Emmons, Irving, and Loughlin (1927, p. 218) mentioned the fact that much of the Leadville jasperoid 

is heavily impregnated with "products of oxidation." 

Indeed, most of the Leadville jasperoid samples in 

my collection are of this type, in which the jasperoid 

silica is intimately mixed with limonite and manganese oxides, suggesting a possible supergene origin.

RELATIONSHIP TO ORE

The favorable jasperoids of the district tend to 

form a floor beneath, or a casing around, massive sulfide deposits. Jasperoid impregnated with sulfide ore 

is relatively sparse. Many extensive jasperoid bodies, 

particularly those in the northwestern part of the 

district, are unfavorable (Loughlin and Behre, 1934, 

p. 228). At the Continental Chief mine, near the head 

of Evans Gulch, favorable jasperoid, which retains 

the color and texture of the carbonate host rock, 

forms a casing adjacent to the mineralized fissures, 

but prominent ledges of unfavorable jasperoid also 

crop out in the same vicinity (Loughlin and Behre, 

1934, p. 234). Favorable jasperoid is most commonly 

associated with lead-silver ore and is less abundant 

around the zinc and popper ore bodies (Ogden Tweto,

oral commun., 1965). Many of the dense dark-colored 

jasperoids impregnated with iron and manganese 

oxides have the composition of favorable jasperoid; 

however, their spatial relations to ore bodies are not 

yet known.

APPEARANCE

All the jasperoid samples from the Leadville district, in my collection, are dark gray to black, aphanitic on the outer surface, with local brown patches. 

Most of the samples are homogeneous in texture, but 

one sample, from the dump of the Annie 5 mine on 

Fryer Hill about half a mile east of Leadville, has a 

shell or rind of dense black manganiferous jasperoid 

coating a core of porous vuggy friable light-gray 

and light-brown saccharoidal jasperoid. The contact 

between shell and core of this sample is knife-edge 

sharp, suggesting leaching and thorough oxidation of 

the core before formation of the rind. The only sample of clearly hypogene jasperoid in the collection 

came from the dump of the Forepaugh mine, also on 

Fryer Hill. This sample is dark to medium gray and 

aphanitic, and it contains abundant fine-grained disseminated pyrite and a few tiny vugs that appear to 

have been formed by local leaching of the original 

pyrite.

MICROTEXTURE AND MINERALOGY

The hypogene jasperoid in the sample from the 

dump of the Forepaugh mine is fine to medium 

grained (0.005-0.1 mm) and heterogeneous, and has 

a jigsaw-puzzle texture. The extremely fine grained 

quartz is locally segregated in bands, and thin veinlets of coarser xenomorphic quartz cut the matrix. 

Abundant inclusions of pyrite and younger sphalerite 

are present. Some, if not all, of the quartz is older 

than the sulfides as shown by the presence of quartzgrain inclusions in some of the pyrite. The same 

heterogeneous jigsaw-puzzle texture is also characteristic of the quartz in the core of the sample from 

the dump of the Annie 5 mine and of rounded inclusions of older jasperoid in a matrix of younger 

iron and manganese oxides found in a sample from 

a dump on the North Fork of Little Evans Gulch.

Jasperoid of possible supergene origin forms the 

outer rim of the specimen from the dump of the 

Annie 5 mine and constitutes nearly all the remaining specimens, exclusive of the one from the Forepaugh mine dump previously described. This rock 

is characterized by small scattered inclusions of 

quartz and dolomite, in a matrix of earthy, vuggy, 

and porous iron and manganese oxides, which are 

locally crystallized into pyrolusite, goethite, and 

hematite. In some places the pores are filled with
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 73

late quartz; in others, bands of xenomorphic mediumgrained quartz alternate with bands of manganese 

oxide; and in nearly all samples veinlets of mediumgrained homogeneous xenomorphic quartz cut the 

matrix oxides. Thus, if these oxides are supergene, 

the late silica associated with them must also be 

supergene. However, this rock may not be a true 

replacement jasperoid but rather a variety of casehardened gossan. Because the samples were not 

taken in place, the field relationships of this rock 

to its host could not be ascertained; however, the 

abundant quartz and dolomite grains suggest that 

these minerals may have been original inclusions in 

limestone, of which the calcite has been replaced by 

supergene iron arid manganese oxides and silica.

COMPOSITION

Semiquantitative spectrographic analyses available 

on four of the supergene (?) samples and the single 

definitely hypogene sample showed that all five have 

a composition characteristic of favorable jasperoid. 

Of the five, the hypogene sample has the smallest 

suite of minor elements present in abnormally high 

concentrations. After the associated sulfide minerals 

had been largely removed from this sample by heavy 

liquid separation, the remaining jasperoid quartz 

showed only Ag, Ba, Mo, Pb, and Zn present in concentrations more than one order of magnitude higher 

than the median concentration for all jasperoid samples in the collection. The quartz of the remaining 

four samples was not separated before analysis, and 

the resulting data show that in them silica is subordinate to iron and manganese. The high concentrations of a number of minor elements in these samples, therefore, probably represents association with 

iron and manganese oxide rather than with quartz. 

These samples are consistently rich in Fe, Mn, Ag, 

Ba, Pb, Ni, and Zn; three of the four are also high 

in Cu and Sr; and two are high in In and Mo. High 

In is associated with high Cu, but high Mo is not.

CONCLUDING REMARKS

Although both favorable and unfavorable jasperoid samples have been reported from this district, 

only favorable samples are represented in my collection. Thus, no direct comparison between favorable and unfavorable jasperoid in the Leadville district is possible here. According to Ogden Tweto 

(oral commun., 1965), there is a marked similarity 

in appearance between the two types, such that they 

are not readily distinguishable in the field. The known 

presence of both varieties in the area, however, and 

the abnormally high concentrations of the indicator 

elements Ag, Pb, and Zn in all the available favorable

samples suggest that a detailed study of the Leadville jasperoids, coupled with adequate sampling and 

analysis for these elements, might be a fruitful adjunct of any comprehensive exploration program in 

the district.

TINTIC AND EAST TINTIC DISTRICTS, UTAH

(6, fig. 1; 21, fig. 49)

The Tintic and East Tintic mining districts in 

Utah are about 70 miles south of Great Salt Lake in 

a mineralized belt that crosses the East Tintic Mountains, whose crest forms part of the boundary between Juab County on the west and Utah County on 

the east (Lindgren and Loughlin, 1919).

A thick sequence of Paleozoic limestone, dolomite, 

and shale with a Cambrian quartzite at the base in 

this area is largely covered by Tertiary extrusive 

quartz latite, latite, and associated pyroclastics, all 

of which were later intruded by monzonite stocks and 

dikes. Before the extrusion of the Tertiary volcanic 

rocks, the sedimentary strata were folded into a 

series of north-trending asymmetrical anticlines and 

synclines, and were cut by high-angle transcurrent 

faults that were accompanied by overthrust faulting, 

particularly in the eastern part of the area. The 

major high-angle faults have predominating northeasterly and northwesterly trends; their major displacement predates the volcanics, although there has 

been some renewed postvolcanic movement on some 

of them. The intrusion of monzonite and quartz 

monzonite was accompanied and followed by hydrothermal alteration of both the volcanics and the 

underlying sedimentary rocks, culminating in ore 

deposition. The primary ore bodies consist of sulfidebearing veins and replacement deposits in the sedimentary rocks.,-Most of the production of the districts has come from the lead-zinc-silver replacement 

deposits in limestone and dolomite; but copper and 

gold, which commonly occur in fissure vein deposits 

and pipes cutting Cambrian quartzite, are also economically important locally.

DISTRIBUTION

The distribution of jasperoid bodies in the East 

Tintic district is shown by Levering (1949, pi. 4) 

and by Levering and others (1960), and in the main 

Tintic district, by Morris (1964a, pi. 1; 1964b, pi. 1).

Bodies of silicified rock occur in all of the Paleozoic 

sedimentary formations in the two districts and in 

the Tertiary volcanic rocks as well. In the East Tintic district, however, jasperoid bodies are most 

abundant in the carbonate rocks that have been altered to hydrothernial dolomite along faults (Lovering, 1949, p. 29). This structural control is very pronounced; the jasperoid bodies form envelopes around
74 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

the faults and fissures that served as conduits for 

the hydrothermal solutions. The jasperoids of the 

Tintic and East Tintic districts show no direct relationship to the monzonitic intrusive rocks; they are 

found in areas where these intrusives are lacking, 

although they are somewhat more abundant in areas 

marked by centers of intrusion.

GENESIS

The formation of jasperoid largely represents a 

late stage in a long and complex history of hydrothermal alteration in the districts, which culminated 

with the emplacement of sulfide ore bodies. Levering 

(1949, p. 16-17) recognized five distinct stages of 

alteration, each with its own characteristic mineral 

assemblage; these, in chronological order, he called 

the early barren stage, the middle barren stage, the 

late barren stage, the early productive stage, and the 

productive stage. Silicification resulting in the formation of favorable jasperoid was largely confined to 

the late barren stage (Lovering, 1949, p. 28). Locally, 

argillic alteration of the middle barren stage was 

accompanied by minor silicification (Lovering, 1949, 

p. 38).

Lindgren and Loughlin (1919, p. 156-157) concluded that the favorable variety of jasperoid formed 

as a result of the replacement of carbonate rock by 

colloidal silica. The characteristically abrupt contacts 

between jasperoid and host rock led them to express 

the opinion that the silicifying solutions moved outward in a wave from the feeding channels, converting 

all the rock behind the advancing wave front into 

silica gel. As this gel later desiccated and crystallized 

into jasperoid quartz and chalcedony it also shrank, 

causing the formation of vugs and fractures. These 

openings were later filled or coated with younger 

jasperoid, quartz crystals, barite, and sulfides. Local 

banding in the jasperoid is ascribed to penetration 

of the original gel by electrolyte-bearing solutions, 

resulting in Liesegang diffusion banding.

Lovering (1949, p. 56-58) expressed the opinion 

that the jasperoidizing solutions were highly charged 

with silica, iron, barium, carbonic acid, and sulfate; 

they were hot neutral or slightly alkaline solutions, 

partly of magmatic origin, rising along major fractures through the quartzite, from which they may 

have leached silica and iron. As these solutions rose 

into the carbonate rocks, they cooled, and the carbonates became more soluble and silica less soluble. 

The calcium and magnesium that were replaced during the silicification moved upward into the overlying volcanic rocks, resulting in calcitic and chloritic 

alteration of these rocks.

An unfavorable type of jasperoid occurs in carbonate rocks just below the base of the Tertiary rhyolite flows. This type is controlled by proximity to the 

unconformity rather than by faults and fractures. It 

appears to have formed as a result of the leaching of 

silica from these flows by water seeping downward 

through them, and subsequent precipitation of the 

silica when this water was neutralized by reaction 

with the underlying carbonate rock. Much of this 

jasperoid probably formed during the period when 

the flows were still cooling, as a result of alteration 

by hot-spring and fumerole emanations; some of it 

may be due to leaching of silica by acid waters generated by the oxidation of pyrite disseminated 

through the flows, and thus may be of comparatively 

recent origin (T. S. Lovering, oral commun., 1964). 

This type of jasperoid is, in either case, unrelated 

to the hydrothermal alteration that culminated in 

sulfide mineralization.

Bodies of possibly supergene jasperoid have been 

found in and near large oxidized ore bodies in some 

of the mines on the north slopes of Eureka Peak 

and Godiva Mountain near the town of Eureka (A. V. 

Heyl, written commun., 1967). These jasperoid 

bodies presumably formed by reaction of silicabearing ground waters with carbonate host rock 

during the oxidation of sulfide ore bodies.

RELATIONSHIP TO ORE

Howd (1957, p. 125-132) presented an excellent 

historical summary of the views of various investigators concerning the relationship between jasperoid 

and sulfide ore in the Tintic and East Tintic mining 

districts. The close association between jasperoid 

and many of the sulfide replacement deposits in carbonate rocks was recognized by the miners early in 

the development of the districts. This association 

was reported by Lindgren and Loughlin (1919, p. 

155), who concluded that the jasperoid, although 

older than the ore, was closely related to it and that 

it formed envelopes around the ore bodies. Lovering 

(1949, p. 28) recognized that jasperoid forms a broad 

envelope around the major circulation channels that 

were open during the late preore stage of alteration, 

of which it is the most characteristic product. Many 

of these same channels later served as conduits for 

ore solutions, giving rise to the association noted 

by Lindgren and Loughlin (1919, p. 155-157). However, some channels were completely sealed off by 

the early silica so that no sulfides could form in 

them; in other places, ore solutions followed new 

channels and thus resulted in ore bodies not intimately associated with jasperoid. Thus, late barrenstage jasperoid in the carbonate rocks of the district 

is not, by itself, a wholly reliable indicator of prox-
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 75

imity to ore, nor does its absence preclude the possibility of ore in an area. Furthermore, not all the 

jasperoid bodies in the districts were formed during 

the late barren stage of alteration.

Favorable jasperoid, of possibly supergene origin, 

locally forms bodies on the lower carbonate wallrock 

side of oxidized zinc ore pipes and mantos (A. V. 

Heyl, written commun., 1967). The jasperoid that is 

localized at the contact between the volcanic and 

sedimentary rocks appears to be completely unrelated 

to ore, and this unfavorable type is widely distributed, particularly in the area north of Eureka (H. T. 

Morris, written commun., 1957). The known presence 

of both favorable and unfavorable jasperoids in the 

Tintic and East Tintic districts prompted personnel 

of the Bear Creek Mining Co. to make a detailed 

study and comparison of suites of samples of the two 

types in an effort to establish criteria for the recognition of the favorable type. The results of this study 

are summarized by Howd (1957), Duke (1959), and 

Bush, Cook, Levering, and Morris (1960b, p. 1516- 

1517).

APPEARANCE

The jasperoid bodies in the Tintic and East Tintic 

districts are characterized by sharp contacts between 

completely silicified rock and completely unsilicified 

host rock. Many bodies form elongated narrow 

"reefs" along fractures, but some are highly irregular in shape. They tend to be smaller, but more widely 

distributed, than those at Ely. The largest attain a 

maximum dimension in excess of 1,000 feet, but 

most have an outcrop area of only a few hundred 

to a few thousand square feet.

Lindgren and Loughlin (1919, p. 154) described 

the typical Tintic jasperoid as a fine-grained, darkgray to bluish-gray rock, locally resembling a finegrained quartzite. According to H. T. Morris (written commun., 1957), some of the favorable hypogene 

jasperoids are locally coarse grained, many show textural as well as color banding with textures and 

structures suggestive of colloidal deposition, all are 

distinctly vuggy, and some show several periods of 

brecciation and recementation by later silica. One 

variety has a saccharoidal texture, and most of the 

favorable jasperoids contain megascopically visible 

platy crystals of barite. Although the favorable 

jasperoids range widely in color, most of them are 

lighter hued and more translucent on thin edges 

than the unfavorable jasperoids.

The unfavorable jasperoids, as a group, are dense 

and have a flinty appearance. They are predominantly 

black to brown or gray and are characterized by uniform texture and scarcity of vugs.

According to A. V. Heyl (written commun., 1967), 

the possibly supergene favorable jasperoid forms 

vuggy banded colloform casings adjacent to oxidized 

sulfide ore bodies. It contains abundant limonite and 

hemimorphite and sparse chrysocolla and malachite. 

This jasperoid is distinguishable from oxidized hypogene jasperoid by its lack of relict sulfides or of 

pits and pseudomorphs revealing their former presence.

My collection from the Tintic and East Tintic districts consists of 25 samples from 14 localities of 

which eight samples from four localities represent 

oxidized unfavorable jasperoid bodies, and the rest 

represent hypogene favorable jasperoid bodies. Six 

of the sample localities are in the vicinity of Eureka, 

four are in the southern part of the district on Mammoth Peak, one is near the center of the East Tintic 

district, one is on Pinyon Peak, one in Fremont Canyon, and one on Old Baldy Peak.

In this suite, all favorable jasperoid samples that 

are unoxidized and most that are oxidized are various 

shades of gray; several oxidized samples are white 

or moderate brown to dark brown, and a few show 

green copper stains or yellow iron sulfate stains. 

Many of the samples are mottled, banded, or 

streaked. Nearly all the favorable samples are brecciated and conspicuously vuggy, and some are porous 

and friable as well. Although a saccharoidal texture 

is evident in one or two of these samples, most are 

aphanitic; a few contain abundant randomly oriented 

blades of barite.

The few samples of unfavorable jasperoid in my 

collection are dark red, dark gray, bright yellow, or 

lavender gray, commonly variegated. All are dense, 

and one has a glassy texture and conchoidal fracture.

MICROTEXTURE AND MINERALOGY

Lindgren and Loughlin (1919, p. 155-156) described "typical" Tintic jasperoid as composed of 

quartz grains less than 0.25 mm in diameter with 

wavy extinction and commonly abrupt variations in 

grain size. They mentioned a local variety from the 

Gemeni mine which is strongly microbanded with 

alternating dark bands of cryptocrystalline quartz 

and light bands of spherulitic light-brown chalcedony, 

with minute grains of sulfides disseminated through 

both types of bands (fig. 30).

Lovering (1966) reported the presence of asymmetrically zoned quartz in much of the late barren 

stage jasperoid and made a petrofabric study of the 

preferred orientation of the asymmetry of the zonal 

overgrowths. Plots of the direction of displacement 

of the c axis showed consistent relations that were 

interpreted as indicating the dominant direction of
76 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

movement of the jasperoidizing solutions. These directions seem to coincide with the rake of the associated but later ore. The jasperoid quartz contains 

abundant minute low-index inclusions, which may 

be allophane; some of it also contains nearly isotropic 

particles, with an index of about 1.65, which may be 

barite. Chalcedony is most abundant in jasperoids 

replacing dolomite and shale away from the main 

channels of mineralization; opal is sparsely distributed and is supergene; barite is present in several 

generations, some older than jasperoid quartz and 

some younger; chlorite is younger than jasperoid 

quartz, in which it is locally abundant near mineralizing conduits; in the zone of oxidation, chlorite is 

largely altered to kaolinite; and disseminated pyritohedral pyrite is abundant in the jasperoid and is of 

about the same age as the chlorite.

The most comprehensive study yet made of the 

microtexture and mineralogy of Tintic jasperoids 

was done under the auspices of the Bear Creek Mining Co. The results of this work are summarized in 

reports by Howd (1957), Duke and Howd (1959), 

and Bush, Cook, Lovering, and Morris (1960a, b), 

and are discussed in detail by Duke (1959). A suite 

of "barren" jasperoid samples from an area north 

of Eureka was compared petrographically with a 

suite of "productive" jasperoid samples from various 

mines in the Tintic and East Tintic districts.

Seven textures were distinguished by Duke (1959) 

as follows: (1) Anhedral quartz mosaic consisting 

of relatively homogeneous aggregates of anhedral 

quartz grains ranging from 0.1 to 0.2 mm in diameter; (2) colloform texture; (3) cryptocrystalline 

texture aggregates in which all quartz grains have 

diameters less than 0.02 mm; (4) microbrecciated 

texture-angular fragments of jasperoid in a matrix 

of coarser quartz; (5) variable grain size heterogeneous mixture of minute particles and coarse 

grains; (6) veinlets; and (7) vuggy texture. The 

minerals identified are barite, calcite, chalcedony, 

clay, dolomite, galena, hematite, jarosite, limonite, 

magnetite, manganese oxides, pyrite, quartz, sericite, 

and sphalerite. Duke (1959) compared the frequency 

of occurrence of these textures and minerals in the 

two groups of samples and concluded that cryptocrystalline and anhedral quartz mosaic textures in 

the same sample, variable grain size, microbrecciation, and vugginess were significantly more common 

in the "productive" group, as were the minerals barite, galena, hematite, and sphalerite. He considered 

chalcedony, clay, and jarosite to be more abundant 

in the "barren" samples.

In a petrographic study of 17 favorable jasperoid 

samples and eight unfavorable jasperoid samples, I

distinguished 10 different textures and 21 accessory 

minerals in the combined suite of 25 samples. These 

textures I designated as (1) multiple generations 

(approximately equivalent to microbrecciated texture of Duke, 1959), (2) homogeneous coarse-grained 

(approximately equivalent to Duke's anhedral 

quartz mosaic), (3) homogeneous fine-grained (cryptocrystalline of Duke), (4) heterogeneous (variable 

grain size of Duke), (5) colloform banding, (6) 

vuggy, (7) reticulated, (8) xenomorphic, (9) granular, and (10) jigsaw puzzle. The last four of my textural classifications, referring to the shape of the 

quartz grains, have no counterpart in Duke's classification. The accessory minerals recognized, in order 

of decreasing abundance, are (1) hematite; (2) 

goethite; (3) allophane; (4) sericite; (5) limonite; 

(6) jarosite and barite; (7) pyrite; (8) chalcedony; 

(9) galena and sphalerite; (10) dolomite, siderite, 

malachite and wurtzite; (11) kaolinite, biotite, opal, 

smithsonite, and cerussite.

The frequency of occurrence of these textures and 

minerals was tabulated in each of the two groups. 

Although statistical tests of significance are difficult 

to apply to such small sample groups, a qualitative 

impression of the significance of certain textures and 

minerals, suggestive of favorable or unfavorable jasperoids, can be gained from the following tabular 

summaries, which show the differences in frequency

Common textures and minerals (observed in 20 

percent or more of all samples) suggestive of 

favorable and unfavorable jasperoid in the 

Tintic and East Tintic districts

Favorable jasperoid

Texture

Heterogeneous ...........................

Homogeneous, coarse grained 

Vuggy .........................................

Xenomorphic .............................

Multiple generations ................

Reticulated ..................................

Mineral

Jarosite ........................................

Barite ..........................................

Allophane ....................................

Pyrite .........................................

Goethite ......................................

Percent 

Difference

52

41

35

30

28

24

41

41

40

35

28

Unfavorable jasperoid

Texture

Homogeneous, fine grained . 

Jigsaw puzzle .......................

Granular .................................

Mineral

Sericite ...................................

Hematite .................................

Limonite .................................

Chalcedony .............................

(Fu-Fpi) 

70 

47 

26

58

40

38

35
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 77

of occurrence, expressed as percent of the group, between favorable and unfavorable jasperoid for the 

common textures and minerals. 

The agreement between Duke's criteria (1959) 

and mine is much closer for jasperoid-quartz microtextures than for associated minerals. This is reasonable because oxidation would have relatively little 

effect on jasperoid microtexture, but it would have 

a profound effect on the associated mineral assemblage. All of my unfavorable samples and most of 

my favorable samples were oxidized. Although the 

relative proportions of oxidized and unoxidized samples in the two groups studied by Duke were not 

specifically stated, it is improbable that the proportions of oxidized and unoxidized samples in his "productive" group were the same as in his "barren" 

group, or the same as in my favorable and unfavorable groups.

COMPOSITION

An outcrop sample of favorable jasperoid from 

near the Eureka Hill mine submitted by the author 

was analyzed by E. L. Munson. An analysis of "productive" jasperoid from the Tintic Standard mine 

was published by Levering (1949, p. 54). Analyses 

of the two samples, in percent, are as follows:

Mine 

Eureka Hill Tintic Standard

SiOj ............................................................ 95.75 90.12

A12O3 .......................................................... 1.12 4.38

Fe2O3 .......................................................... .36 .20

FeO ............................................................ .19 .36

MgO ............................................................ .01 .55

CaO ............................................................ .00 .02

Na2O .......................................................... .01 0

K2O ............................................................ .09 .87

HaO+ ........................................................ .75 2

HaO- ........................................................ .05 .45

TiOj ............................................................ .03 .31

P8O5 ............................................................ .06 .02

MnO .......................................................... .03 Trace

CO* ............................................................ .16 .08

S ................................................................ .08

BaO ............................................................ .00

Total................................................ 98.68 99.36

The agreement between these two analyses is surprisingly close, considering that they represent jasperoid replacement of different formations from different localities and that one sample is oxidized, the 

other, unoxidized. However, the variation in composition of favorable jasperoids in the district probably 

is considerably greater than is reflected by this pair 

of analyses. No quantitative chemical analyses of 

unfavorable jasperoid from the Tintic or East Tintic 

districts are available. 

Semiquantitative spectrographic analyses were 

made of splits from the 17 favorable samples and 

eio-ht unfavorable sarrmles in rnv rollprtion. ThirtvTABLE 19. Minor-element distribution in 25 samples of 

jasperoid from the Tintic and East Tintic districts, Utah

[J. C. Hamilton, analyst. Leaders (......) indicate no information. Amounts 

in parentheses are extrapolated values]

Limit of Number of 

Element detection samples Minor-element distribution (percent)

detected Range Mean Median Mode

Al .............. 0.001 25 0.07 3 0.33 0.12 0.15

Mg ............ .0005 25 .007 - .3 .039 .014 .015

Ca ............ .005 25 .015 .7 .098 .041 .07

K 7 1 <T 7 7 *C 7

Ti .............. .0002 23 <.0015 .15 .024 .009 .007

Mn ............ .0002 25 .003 -1.5 .077 .0075 .007

Ag ............ .0001 18 <. 00015- .3 .022 .001 <.00015

As ............ .15 9 <.15 3 ........ ........ <.15

Ba ............ .001 25 .0015 ->10 2.45 .013 .003

Be ............ .0001 14 <.00015- .0015 .0002 (.0001) <.00015

Cd .............. .005 4 <.007 - .03 ........ ........ <.007

Cr .............. .0001 25 .00015- .003 .0006 .0002 .00015

In .............. .002 6 <.003 .007 ........ ........ <.003

La ............ .002 2 <.003 - .003 ........ ........ <.003

Ni .............. .0005 10 <.0007 .007 ........ ........ <.0007

Pb ............ .005 19 <.007 -7 .491 .04 <.007

Sb .............. .01 8 <.015 - .7 ........ ........ <.015

Se .............. .0005 1 <.0007 .0007 ........ ........ <.0007

Sn ............ .002 4 <.0015 .15 ........ ........ <.0015

Sr .............. .0002 19 <.0007 - .7 .073 .002 <.0007

V .............. .002 12 <.0015 .007 ........ ........ <.0015

Y .............. .002 4 <.0015 - .015 ........ ........ <.0015

Yb ............ .0002 5 <. 00015 .0015 ........ ........ <.00015

Zn ............ .005 16 <.007 3 .182 (.005) <.007

Zr .............. .002 12 <.0015 - .007 ........ ........ <.0015

three elements other than silicon were detected in 

one or more of these samples. These analytical data 

are summarized in table 19, in the same way as the 

spectrographic data on the samples of jasperoid from 

the Ely district were summarized in table 17. 

The relative abundance of the 13 elements that 

were detected in more than half of the samples, as 

expressed by the mean, median, and maximum concentrations, is given in table 20. These data suggest 

that barium, lead, and silver are highly concentrated 

in this group of samples. 

Semiquantitative spectrographic analyses of suites

TABLE 20. Relative abundance, in percent, of 13 most abundant elements in 25 samples of jasperoid from the Tintic 

and East Tintic districts, Utah

Arithmetic mean Median Maximum reported 

concentration concentration concentration

Fe ................ 2.6 Fe .............. 0.43 Fe ..................>10

Ba .............. 2.45 Al .............. .12 Ba ..................>10

Pb .............. .49 Ca .............. .041 Pb .................. 7

Al ................ .33 Pb .............. .04 Al .................. 3

Zn .............. .18 Mg ............ .014 As .................. 3

Cu .............. .14 Ba ............ .013 Zn .................. 3

Ca .............. .10 Ti .............. .009 Mn ................ 1.5

Mn .............. .077 Mn ............ .007 Cu .................. 1.5

Sr ................ .073 Cu ............ .005 Ca .................. .7

Mg .............. .039 Zn .............. .005 K .................... .7

Ti ................ .024 Sr .............. .002 Bi .................. .7

Ag .............. .022 Ag ............ .001 Sb .................. .7

Cr ................ .0006 Cr .............. .0002 Sr .................. .7
78 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

of "barren" and "productive" jasperoids were made 

by the Bear Creek Mining Co. to ascertain which 

elements were characteristically concentrated in 

either type. The results of this investigation were 

summarized by Duke and Howd (1959) and Bush, 

Cook, Lovering, and Morris (1960b). Duke and Howd 

stated that Sb, Bi, Cd, Cu, Pb, Ag, Na, Th, and Zn 

are more abundant in "productive" jasperoids, whereas Ca and Mg are more abundant in "barren" jasperoids. Bush, Cook, Lovering, and Morris (1960b) 

listed Sb, Bi, Cu, Pb, Zn, Ag, Na, and Th as elements 

characteristically concentrated in "productive" jasperoid, and Ca and Mn, in "barren" jasperoids. They 

supported this conclusion with a table giving the 

average concentration of each of these elements in 

each sample group in parts per million. These averages, converted into percent for comparison with my 

data, are as follows:

Bi Ca Cu Mn Na Pb Sb Th Zn

Productive ......................

Barren ............................

........................0.0046

...........................00016

0.0093

.0040

0.41

.68

0.073

.027

0.039

.13

0.21

.14

0.42

.02

0.0055

.0045

0.0020 (i) 0.23

.13

1 Not detected.

The median values of the distributions of the commonly detected elements in my suites of favorable 

and unfavorable jasperoid samples were compared. 

Medians were used in preference to means, because 

most of the distributions are erratic and cover a 

large concentration range and therefore the mean 

values are strongly influenced by one or two high

values. The elements that showed an appreciable difference in median concentrations between the two 

groups are given in the following table, in which 

median values are given only for those elements that 

showed a greater-than-twofold difference between 

the two groups; smaller differences were considered 

unlikely to be significant.

Median values, in percent, of selected elements in 12 favorable and eight unfavorable jasperoid samples from the Tintic and

East Tintic districts, Utah

[Values in parentheses are extrapolated]

As Ba Be Bi Cu Pb Sr Ti Zn

Favorable ................

Unfavorable ............

............ 0.003

............ ( .00005)

(0.07 )

(0.001)

0.03

.007

(0.00003)

.0001

(0.0008)

( .0001)

0.025

.001

0.07

( .001)

0.0013

.0005

0.007

.03

0.02

( .001)

Some of the elements listed by Duke and Howd 

and by Bush and Cook were detected in few or none 

of my samples, and some elements in my list were 

not mentioned by these authors. Such differences 

are to be expected where different sample groups are 

analyzed independently with different analytical 

equipment.

In summary, it seems that Ba, Na, Th, and possibly Sr, in addition to the ore metals, tend to concentrate in the favorable jasperoids of the late barren alteration stage. Be, Mn, and Ti seem to be higher 

in the unfavorable jasperoid related to the unconformity at the base of the volcanic rocks.

CONCLUDING REMARKS

At Tintic, apparently two distinct major types of 

hypogene jasperoid are present. One is genetically 

related to the hydrothermal alteration that culminated in ore mineralization, and is commonly, though 

not universally, associated with ore bodies. The other 

type is not related to this alteration and is consequently unfavorable. The available evidence suggests 

that this is also true of the Ely district, Nevada. A 

more detailed study of the late barren-stage jasperoids of the Tintic district is needed to establish the 

relative favorability of various jasperoid types 

within this group, as well as the geographic patterns 

of distribution of the various minor elements in it.

OILMAN (RED CLIFF) DISTRICT, COLORADO

(7, fig. 1;5, fig. 40)

The Oilman (Red Cliff) district is in central Colorado on the east side of the Eagle River in Eagle 

County, about 25 miles north of Leadville (Crawford 

and Gibson, 1925). It is on the gently dipping southwestern limb of a northwest-plunging asymmetrical 

syncline formed in Paleozoic sedimentary rocks that 

lie between the Precambrian rocks exposed in the 

Sawatch Range just west of the district and the 

Precambrian rocks of the Gore Range about 7 miles 

to the northeast. The Precambrian granitic rocks, 

schists, and gneisses of the district are overlain by 

about 250 feet of quartzite, shale, and minor dolomite ranging in age from Cambrian to Ordovician. 

These rocks, in turn, are overlain by an approximately equal thickness of predominantly carbonate 

rocks consisting of the Devonian Dyer Dolomite 

Member of the Chaffee Formation and the dolomitized Mississippian Leadville Limestone. The Lead-
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 79

ville Limestone in this area is capped by a thin, persistent, and highly altered sill of quartz latite 

porphyry, which separates it from the nearly 5,000 

feet of Pennsylvanian shale, siltstone, arkose, and 

minor limestone that constitutes the rest of the Paleozoic section.

The ore deposits of the Gilman (Red Cliff) district 

consist of gold-silver veins in the Precambrian rocks 

and the Cambrian quartzite, auriferous manganosiderite mantos in the quartzite, large pyritic coppersilver chimney deposits in the carbonate rocks that 

underlie the upper part of the Leadville Limestone, 

and extensive lead-zinc manto deposits extending updip from the chimney deposits in the upper part of 

the Leadville Limestone. Most of the district's production has come from the deposits in the carbonate 

rocks. Faults in the main district tend to be small 

and traceable only for short distances. Sulfide distribution in the Leadville Limestone appears to have 

been largely controlled by open channels, many of 

which follow older joints and fractures. Some of 

these channels are of pre-Pennsylvanian age; others 

were formed or enlarged by early hydrothermal solutions related to mineralization.

DISTRIBUTION

There is no close spatial association between jasperoid and the major sulfide ore bodies in the Gilman (Red Cliff) district. Crawford and Gibson (1925, 

p. 57, 59) reported jasperoid outcrops in the Leadville Limestone near the junction of Turkey Creek 

and the Eagle River at the south end of the district, 

and in a large body about three-quarters of a mile 

north of Gilman, beyond the north end of the district. 

They also mentioned the occurrence of small blocks 

of jasperoid on the dumps of some of the old mines 

on Battle Mountain south of Gilman, although jasperoid does not crop out at the surface in this area. 

Large masses of jasperoid replace the Dyer Dolomite 

Member northwest of the district on the flanks of 

the Sawatch Range north of Cross Creek, and the 

overlying Leadville Limestone is locally jasperoidized, according to Lovering and Tweto (1944, p. 77). 

Very little jasperoid is present in the Pennsylvanian 

rocks east of Gilman, although there is local minor 

silicification on some of the faults. Similar bodies 

of jasperoid are also abundant in the Leadville Limestone and Dyer Dolomite Member of the Chaffee 

Formation south of Red Cliff all the way to the East 

Fork of the Eagle River near the south boundary 

of Camp Hale, but this jasperoid is too far away to 

be considered in the Gilman (Red Cliff) district and 

is discussed separately under the heading "Pando 

Area" on page 99 of this report.

GENESIS

The jasperoid bodies in the vicinity of Gilman are 

considered by Crawford and Gibson (1925, p. 56-57, 

59) to be the result of replacement of dolomite by 

silica gel, the silicifying solutions moving outward 

in a wave from major circulation channels along 

faults and fractures. They advocate the same origin 

for this rock as that suggested by Lindgren and 

Loughlin (1919, p. 156-157) for the Tintic jasperoids 

of the late barren stage. The source of the silicabearing solutions is tentatively postulated as a 

cupola on a buried monzonitic stock or batholith. 

Crawford and Gibson (1925, p. 65) further stated: 

"It is evident that both jasperoid and dolomite were 

deposited after though in part perhaps contemporaneously with the ore minerals, and it is probable 

that solutions that brought in both metallic and nonmetallic minerals had a common source." Lovering 

and Tweto (1944), on the other hand, found strong 

evidence that hydrothermal dolomitization preceded 

sulfide mineralization in the Gilman (Red Cliff) district. They found ''zebra rock" texture preserved in 

jasperoid replacing the Dyer Dolomite Member and 

concluded that jasperoidization took place after this 

phase of dolomitic alteration; however, they made 

no statement as to the relative ages of jasperoidization and sulfide mineralization. Some of the silica 

that formed the jasperoid may have been leached 

from the Cambrian quartzite by hydrothermal solutions, but this source alone is regarded as insufficient 

to account for the large volume of silica now present 

as jasperoid in the area northwest of Gilman (Lovering and Tweto, 1944, p. 77-78).

The jasperoids of the Gilman (Red Cliff) district 

seem to be relatively simple and homogeneous in 

composition. This fact suggests that there was only 

one major period of jasperoid formation, and that 

the silica-depositing solutions were different in composition from those that deposited the sulfide ore.

RELATIONSHIP TO ORE

Crawford and Gibson (1925) and Lovering and 

Tweto (1944) generally agree that jasperoids in the 

vicinity of Gilman are a product of the hydrothermal alteration that, at some stage, produced the sulfide mineralization. Crawford and Gibson (1925) regarded jasperoid as a favorable guide to ore in the 

vicinity. They pointed out that ore occurs near jasperoid in the Leadville Limestone in several small 

mines in the southern part of this district, on Battle 

Mountain, and around Red Cliff, and suggested that 

"good prospecting ground" should lie east or northeast of jasperoid bodies that occur along faults. 

Lovering and Tweto (1944) regarded jasperoid as a
80 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

fringe effect of the mineralization at Gilman because 

silicification is generally absent in the altered host 

rocks adjacent to the major ore bodies. These rocks 

have been converted to jasperoid along faults and 

fractures updip from the ore deposits to the west 

and northwest at distances ranging from a quarter 

of a mile to several miles from the major ore bodies. 

The information now available indicates that most 

of the Gilman jasperoid bodies should be classed as 

unfavorable because they show no close spatial association with ore bodies.

APPEARANCE

Crawford and Gibson (1925, p. 56-57) described 

the jasperoid of the Gilman area as being dark gray 

to medium gray and locally yellowish gray or brownish gray, varying in texture from flinty to "gritty," 

and having uneven fracture locally resembling a finegrained quartzite. Both varieties are characterized 

by abundant cavities and open fractures, and the 

dense variety commonly exhibits alternating light 

and dark streaks or bands. Some of the cavities in 

the jasperoid are lined with small quartz crystals. 

Jasperoid breccias, containing angular masses of 

material that is coarser grained and lighter colored 

than the matrix, are locally abundant along faults. 

These breccias probably resulted from the silicification of previously brecciated carbonate rock, rather 

than from brecciation and recementation of massive 

jasperoid.

The large masses of jasperoid northwest of Gilman 

consist largely of yellowish-brown, brown, and locally grayish, aphanitic to microcrystalline silicified 

Dyer Dolomite Member, which is commonly brecciated and vuggy with quartz crystals lining the 

vugs. Textures inherited from the dolomite are locally preserved in this jasperoid, including brecciation and "zebra texture," which indicates that jasperoidization of these rocks was younger than the 

early hydrothermal dolomitization.

My collection includes seven jasperoid samples 

from the vicinity of the Gilman (Red Cliff) district. 

Five of these are of jasperoid in the Dyer Dolomite 

Member 1-3 miles northwest of Gilman, one is from 

near the base of the Leadville Limestone in the same 

area, and one is a float sample from the Minturn Formation on Battle Mountain that presumably is residual from a locally silicified zone along a fault where 

it cut a limestone bed.

The samples from the Dyer Dolomite Member are 

predominantly light brown on weathered surfaces 

and light yellowish brown on fresh surfaces; one is 

medium gray, and one is moderate red with yellowishbrown patches. All are fine grained to aphanitic.

The sample from the Leadville is light gray and 

aphanitic. The float sample from the Minturn Formation is light gray and fine grained, and it contains 

abundant small irregular vugs lined with tiny crystals of quartz and calcite.

MICROTEXTURE AND MINERALOGY

Typical jasperoid, according to Crawford and Gibson (1925, p. 56-57), consists of anhedral aggregates 

segregated in some places into coarser and finer 

grained bands or masses, with locally abundant tiny 

inclusions of carbonaceous matter or limonite; these 

impurities tend to concentrate in the finer grained 

material, whereas rounded detrital quartz grains are 

more abundant in the coarser material. Sparsely 

scattered shreds of sericite are present in both types. 

Carbonate inclusions are sparse, except locally near 

the contact with the host rock; in one thin section 

transverse to such a contact, these authors reported 

that aphanitic streaky jasperoid ends abruptly in a 

wavy line against unsilicified dolomite.

Levering and Tweto (1944, p. 78) described the 

jasperoids in the Dyer Dolomite Member of the Chaffee as a mixture of cryptocrystalline quartz, brown 

limonite, and carbonaceous dust, with local vague 

wavy bands of high limonite content. Vugs locally 

contain carbonate minerals, sericite, chlorite, and 

barite.

Three of my samples of jasperoid from the Dyer 

have a xenomorphic to jigsaw-puzzle texture in the 

matrix, which is relatively homogeneous, and an 

average grain size of 0.02 mm. Rounded detrital 

quartz grains, some of which show irregular overgrowths, are sparsely scattered through this matrix; 

one sample shows a veinlet of late coarse xenomorphic quartz. Goethite and limonite are abundant 

in all samples, both as dusty inclusions in the matrix 

and as coatings on fractures cutting the matrix. The 

matrix of some samples contains, in addition to 

limonite, dust particles of allophane and carbonate.

One sample from altered Dyer along an easttrending fault zone is strikingly different from the 

others. It consists of relatively coarse ferroan dolomite (0.1-2 mm) about half replaced by disseminated 

coarse quartz (0.05-1 mm). The ferroan dolomite 

shows deformation of cleavage traces and microbrecciation along grain boundaries. Fine-grained orange 

goethite fills fractures in it. The goethite is also disseminated through the quartz, suggesting hydrothermal recrystallization of dolomite, followed by 

fracturing and oxidation along the fractures, followed by silicification.

A similar history is revealed by a sample of incipient jasperoid from the base of the dolomitized
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 81

Leadville Limestone. In this sample, fine-grained 

brown ferroan dolomite, containing abundant inclusions of orange goethite, has been brecciated and 

cemented by veinlets lined with coarse quartz and 

filled with coarse crystalline calcite. The dolomite 

fragments have been silicified in a zone about 1 mm 

wide bordering these veinlets, and the grain size of 

the replacing quartz changes progressively from 

about 0.15 mm adjacent to the vein down to about 

0.02 mm adjacent to the unreplaced dolomite core, 

where it contains abundant inclusions of orange 

goethite.

The sample of completely jasperoidized Leadville 

Limestone consists of clean aphanitic homogeneous 

quartz that has a jigsaw-puzzle texture and an average grain size of about 0.01 mm; this matrix is cut 

by sparse thin veinlets of calcite.

The sample of jasperoid float from the Minturn 

Formation has a matrix of fine-grained quartz that 

has a jigsaw-puzzle texture and a size range of 0.01- 

0.04 mm. Within this matrix are wavy concentric 

bands and small rounded masses as "ghost" textures 

that are visible with reflected light but invisible 

under crossed polars, suggesting original deposition 

of silica as a gel. The matrix is cut by many irregular masses of coarser xenomorphic quartz, which is 

most abundant around vugs and along fractures. Local concentrations of tiny equant red hematite 

grains, about 0.05 mm in diameter, and sparse flakes 

of sericite are present in the younger xenomorphic 

quartz but not in the matrix, which suggests that 

these two minerals may have formed from the same 

solutions that brought in the second-stage quartz.

COMPOSITION

A quantitative standard rock analysis of a typical 

sample of jasperoidized Dyer Dolomite Member of 

the Chaffee Formation (field No. 183A-T-41) by 

E. L. Munson gave the following results:

Element

SiOa .........................

A12O3 .......................

Fe2 03 .......................

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

MgO .......................

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

Na2O .......................

K3O .........................

H2O+ .....................

Percent

....... 96.79

....... .52

....... 1.02

....... .17

....... .16

....... .14

....... .01

OQ

....... .35

Element

H2 0- ......................

Ti02 ........................

P205 ........................

MnO ........................

C02 ..........................

S ..............................

BaO ........................

Total............

Percent

........ 0.05

........ .04

........ .01

........ .03

........ .09

........ .00

........ .00

........99.47

This sample contains somewhat more ferric iron than 

normal, as was anticipated because of abundant 

limonite in the specimen; otherwise, there appears 

to be nothing unusual in its composition.

Semiquantitative spectrographic analyses were

run by J. C. Hamilton on five of the previously described samples, including the one with the foregoing 

standard rock analysis. Only 16 elements other than 

silicon were detected in this group, and only 11 of 

these were detected in three or more of the five samples. These elements and their observed range in 

concentration follow:

Element Range (percent) Element Range (percent)

Al .................... 0.015 -0.15

Fe .................... .7 - .3

Mg .................. .015 - .15

Ca .................... .07 - .3

Ti .................... .0015- .015

Mn .................. .007 - .07

Ba .................... .0015- .03

Co

Cr ................ 0.0007 -0.0015

Cu .............. .0015 - .007

Mo .............. <.0007 - .0015

Ni ................ .0007 - .003

Pb .............. <.007 - .007

V ................ <.0015 - .003

Yb .............. <.00015-.00015

<.0007- .0007 Zn .............. <.007 - .007

The concentration ranges exhibited by these few 

elements are no greater than could be expected from 

five replicate samples taken from a single outcrop; 

yet one of these samples is from the Minturn Formation, one from the Leadville Limestone, and three 

from the Dyer Member, all taken at widely separated 

localities. Thus, it seems that the jasperoid bodies 

peripheral to the ore deposits of the Gilman district 

are unusually uniform in composition and, except for 

iron, unusually low in minor elements.

CONCLUDING REMARKS

The age relations of the Gilman jasperoids to the 

sulfide ore bodies cannot be established from the information now available. They seem to have formed 

at various, but commonly considerable, distances 

above or updip from these ore bodies, and therefore, 

if they are genetically related to the mineralization 

they formed on the outlet side from solutions that 

were poor in the ore elements. Apparently, they 

formed in an oxidizing environment, probably under 

conditions of low temperature and pressure and 

probably from a common but unknown source. These 

jasperoids seem to be of little value as direct guides 

to ore.

ASPEN DISTRICT, COLORADO

(8, fig. 1; 1, fig. 40)

The Aspen district is in Pitkin County, Colo., on 

the west side of the Sawatch Range on the Roaring 

Fork River, about 75 miles west of Leadville (Spurr, 

1898). The ore deposits of the district are confined 

to a relatively narrow, north- to northeast-trending 

belt of pre-Pennsylvanian Paleozoic sedimentary 

rocks between Precambrian schists and gneisses on 

the east and Pennsylvanian and Cretaceous sedimentary rocks on the west. A few miles south of 

Aspen this belt bifurcates around a narrow north-
82 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

plunging syncline, the trough of which is filled with 

predominantly clastic Pennsylvanian sedimentary 

rocks. The western fork of the belt is bounded by 

the large Castle Creek normal fault and terminates 

northward at the edge of the town of Aspen. The 

eastern fork swings to a northeasterly trend where 

it crosses the river just east of Aspen and continues 

in that direction for many miles, beyond the limits 

of the district. This belt has a stratigraphic thickness of about 900 feet. The lower part of it is composed largely of quartzites and shales of Cambrian 

and Ordovician age; the middle and upper parts consist dominantly of carbonate rocks of Ordovician, 

Devonian, and Mississippian age. In addition to the 

Castle Creek fault, which bounds the district on the 

west and extends far beyond it to the south and to 

the northwest, the district is cut by numerous small 

faults that form two general groups, one of which 

trends northerly, the other westerly or northwesterly. The major ore deposits of the district consist 

of silver and lead vein and replacement deposits in 

the Mississippian Leadville Limestone, which were 

localized by the intersections of cross faults with 

bedding-plane faults or with favorable beds (Spurr, 

1898; Vanderwilt, 1935). These known deposits were 

largely mined out by the end of World War I and 

there has been little mining activity in the district 

since that time.

DISTRIBUTION

The available geologic maps of the Aspen district 

do not show the distribution of the jasperoid bodies. 

According to Spurr (1898, p. 217, 220), these bodies 

formed along faults, fractures, and bedding planes in 

the limestone and dolomite, as did the ore bodies; 

however, jasperoid is more abundant and widely distributed than is the ore.

I have 12 jasperoid samples from nine localities in 

the Aspen district. These are all from the northtrending ridge formed by Aspen Mountain and Richmond Hill; the northernmost locality is on Pioneer 

Gulch about half a mile south of Aspen, and the 

southernmost locality is near the head of McFarlane 

Creek about 6 miles south of Aspen.

GENESIS

Spurr (1898, p. 217-218, 220, 229) concluded that 

the jasperoid at Aspen was introduced by hydrothermal solutions related to, but older than, those 

that deposited the primary sulfide ores of the district. These solutions probably were rich in iron, 

magnesium, and carbonate in addition to silica, because dolomite, siderite, and some pyrite are penecontemporaneous in origin with the jasperoid.

Petrographic study of my suite of oxidized jasperoid samples suggests that much of the coarsegrained reticulated type of jasperoid quartz is contemporaneous with, or younger than, the associated 

limonite, and may therefore be of supergene origin.

RELATIONSHIP TO ORE

The jasperoid bodies apparently Were localized by 

the same structures and rock units that influenced 

the deposition of the sulfide ore bodies. Spurr (1898, 

p. 220) stated that silicification always accompanies 

the ore deposition and that jasperoid quartz is an 

important gangue of the ore, although jasperoid is 

more widespread and is also found in areas where 

there has been no ore mineralization. However, 

Vanderwilt (1935, p. 238) noted that the massive 

jasperoid bodies of the district commonly are not 

found in close proximity to the ore bodies, but that 

disseminated quartz crystals in the carbonate host 

rocks, which appear to represent incipient jasperoidization, are common on old stope walls and in mineralized fractures and breccia zones.

The favorable jasperoid that forms a gangue for 

the ore may have been completely removed from the 

old stopes, and, as a result, only incipient jasperoid 

now remains in the stope walls. Samples of jasperoid 

taken from old mine dumps contain abundant ore 

minerals.

APPEARANCE

Some of the jasperoid bodies in the Aspen district 

have sharply defined contacts with the host rock; 

others grade outward through a zone marked by disseminated quartz grains or euhedral quartz crystals 

in a carbonate matrix, or by narrow anastomosing 

quartz veinlets that become visible only on weathered surfaces. The massive jasperoid is commonly 

red or yellow, and conspicuously vuggy. Its texture 

ranges from aphanitic, resembling chert, to fine 

grained, resembling quartzite. The vugs in this rock 

are commonly lined with chalcedony or small quartz 

crystals. Local leaching of the coarser grained variety 

has produced a porous, spongy mat of quartz (Spurr, 

1898, p. 217-219; Vanderwilt, 1935, p. 238).

All my jasperoid samples that were taken from 

outcrops are shades of brown, yellow, and orange. 

They range from light brown, yellowish brown, and 

yellowish orange through moderate brown to dark 

brown. Two specimens taken from mine dumps are 

gray, indicating that the outcrop colors probably are 

the result of near-surface weathering and oxidation.

MICROTEXTURE AND MINERALOGY

Spurr (1898) described and illustrated the gradual
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 83

transition from carbonate rock containing scattered 

quartz crystals and disseminated grains, through 

jasperoid containing abundant interlocking quartz 

crystals and unreplaced remnant inclusions, to jasperoid in which the inclusions have disappeared and 

the interstices of the quartz crystal net have been 

completely filled with anhedral quartz, producing a 

reticulated texture.

This texture is well illustrated in many of the 

samples. Some of them show gradations from coarse 

reticulated jasperoid to masses of coarse-grained 

relict carbonate, or carbonate replaced by limonite, 

containing abundant doubly terminated quartz crystals as much as 3 mm in length. Most of the samples 

contain abundant limonite or goethite associated with 

medium- to coarse-grained xenomorphic or reticulated quartz. The larger quartz grains in many of 

these samples exhibit poikilitic inclusions of limonite, limonite particles in their cores, or thin septa of 

limonite outlining growth stages in individual quartz 

crystals. Thus, a considerable overlap probably existed in the formation of limonite and quartz, both 

of which replaced limestone, and must have done so 

under oxidizing conditions at relatively low temperature.

An older, and less abundant, generation of jasperoid is present in one of the unoxidized mine dump 

samples and as breccia fragments in some of the 

outcrop samples. It consists of aphanitic quartz with 

xenomorphic to jigsaw-puzzle texture and sericite 

inclusions. This, quartz is older than the ore sulfides, 

and in one sample it preserves the original texture 

of the lithographic limestone it has replaced.

Accessory minerals observed in this suite of samples include t.ypogene pyrite, sphalerite, galena, 

barite, and sericite; probably supergene hematite, 

limonite, and manganese oxides; and supergene 

goethite, calcite, jarosite, cerussite, smithsonite lussatite, and an unknown apparently isotropic darkbrown mineral that forms very minute hairlike overgrowths on grains of hematite and limonite in a 

quartz matrix.

Spurr (1898, p. 218-220) referred to dolomite both 

as relict inclusions and zoned rhombohedral crystals; 

siderite and pyrite as contemporaneous inclusions in 

the jasperoid; and also to barite, hematite, and limonite as minerals that commonly accompany it.

COMPOSITION

My 12 samples of jasperoid from the Aspen district were analyzed spectrographically. All 12 are 

anomalously rich in lead and zinc, and most of them 

contain anomalous concentrations of copper and 

barium. About half of the samples contain high

values for Fe, Mn, Ag, Be, Co, and Mo, and one or 

two contain the rarely detected elements As, Cd, Ce, 

Ga, Ge, La, Nd, and Sb. Samples collected near the 

center of the sampled area, between Bell Mountain 

on the north and the head of Queens Gulch on the 

south, all show the presence of Mo, which does not 

occur in detectable concentrations in any of the other 

samples from the district.

A suite of three samples was taken from an elongated jasperoid outcrop along a small fracture about 

half a mile southwest of the nearest mines in Tourtellotte Park. One of these samples is oolitic Leadville Limestone host rock adjacent to the body, one 

is ferruginous jasperoid near the edge of the body, 

and one is highly ferruginous vuggy jasperoid from 

near the center of the body. The limestone sample 

shows a few small quartz grains and crystals, representing incipient jasperoidization, but otherwise appears fresh. It contains anomalous concentrations of 

Ba and slightly anomalous concentrations of Pb. 

The jasperoid sample from near the edge of the body 

is also high in Ba and contains considerably more 

Pb than the limestone; in addition, it contains anomalous Be, Co, Cu, Ga, Mo, and Zn. The sample from 

near the center of the body contains more of all 

these elements than the one from near the edge, and 

also contains anomalous Ag, As, B, Ge, V, Y, and Yb. 

This apparently systematic increase in both number 

and concentration of detectable minor elements toward the center of the body may be fortuitous because only one such suite of samples is available for 

study. The strong contrast between anomalous minor 

elements detected in the host rock and those in the 

jasperoid does indicate that all of them, except possibly Ba, were introduced and not inherited from 

the host rock.

The 12 jasperoid samples yield indicator-element 

scores in the range +5-+19. Seven samples, including the three samples from mine dumps, scored +15 

or higher; three samples had scores in the range 

+ 10-+ 15 and the other two scored +5 and +6. 

Thus, all but the last two fall in the definitely favorable category, and these two are in the possibly favorable category.

CONCLUDING REMARKS

The presence of anomalously large amounts of 

lead and zinc in all jasperoid samples from the Aspen district and of copper and silver in most of them, 

together with the fact that all such samples taken 

from mine dumps yield high favorability scores, 

suggests that this area should be excellent for exploration based on field geochemical analysis of jasperoid samples. The apparent contradiction between
84 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

Spurr's conclusion (1898) that jasperoid is older than 

sulfide mineralization, and the petrographic evidence 

that much of it is younger than limonitic alteration 

of the host rock, can be resolved only by a detailed 

study with emphasis on jasperoid bodies below the 

zone of oxidation. Certainly a presulfide generation 

of jasperoid is present, but examination of surface 

samples of the coarse-grained reticulated jasperoid 

described by Spurr suggests that it is not only 

younger than the sulfides but also younger than the 

oxidation of the sulfides.

EUREKA DISTRICT, NEVADA

(9, fig. 1; 20, fig. 44)

The Eureka district lies south and west of the old 

town of Eureka in eastern Eureka County, Nev., 

about 60 miles west-northwest of Ely; Nolan (1962) 

has discussed it in detail. Eureka has been one of 

the principal silver-lead districts of the Western 

United States. Paleozoic and Cretaceous sedimentary 

rocks in this district have been broken by a complicated network of faults, which locally served as 

channelways for mineralizing solutions that formed 

both fissure vein deposits and replacement deposits 

in carbonate rocks. Jasperoid in this district is not 

confined to any one stratigraphic unit, for it occurs 

in carbonate rocks of Cambrian, Ordovician, Permian, and Cretaceous age.

DISTRIBUTION

In the heavily mineralized Adams Hill area in the 

northern part of the district, the Cambrian Hamburg 

Dolomite has been extensively replaced by jasperoid 

adjacent to the overlying Cambrian Dunderberg 

Shale, although relatively little silica is associated 

with sulfide replacements in the younger Cambrian 

Windfall Formation and Cambrian and Ordovician 

Pogonip Group in the same area (Nolan, 1962, p. 63). 

This silicification of the Hamburg Dolomite is attributed to the blanketing effect of the shale.

A. V. Heyl (written commun., 1967) described 

"the Burnouts," the original discovery area of the 

Eureka district, on the upper south slope of Adams 

Hill, as follows:

At the surface, the area of "the Burnouts," the original 

discovery area of the district, consists of huge outcropping 

red and brown masses of oxidized jasperoid replacing limestone. Deep pits, small opencuts, many shafts, and several 

adits have mined the parts of the jasperoid masses containing rich yellow-brown veins and replacement masses of silverbearing plumbojarosite, anglesite and cerussite that made 

up the original rich bonanza-bodies of silver lead ore. The 

jasperoid is dense and aphanitic, but slightly sugary with 

some jigsaw-puzzle texture. The jasperoid is veined with 

limonite; cavities in the jasperoid contain white radiating 

masses of hemimorphite and small yellow areas of plumbojarosite. The large outcrops of jasperoid that still remain 

total many thousands of tons.

Nolan (1962, p. 72) mentioned prominent masses 

of jasperoid in the Cambrian Eldorado Dolomite near 

the Burning Moscow mine south of Prospect Peak. 

In lower New York Canyon, dolomite beds in the 

Ordovician Hanson Creek Formation have locally 

been brecciated and replaced by jasperoid close to 

the contact with the underlying Ordovician Eureka 

Quartzite, along steep northwest-trending faults 

(Nolan, 1962, p. 71). The Permian Carbon Ridge 

Formation, which consists of thin-bedded impure 

limestones with local chert pebble zones, contains 

no economically important ore bodies; but locally, 

particularly near its fault contact with Eureka 

Quartzite on Hoosac Mountain, it is replaced by jasperoid. In this same general area, fresh-water limestone of the Cretaceous Newark Canyon Formation 

is also locally silicified (Nolan, 1962, p. 12, 71).

Many other small jasperoid bodies are shown on 

the geologic map of the Eureka district accompanying Nolan's report.

GENESIS AND RELATIONSHIP TO ORE

Although little specific published information is 

available on the genesis and economic significance of 

jasperoid in the Eureka district, the localization of 

massive jasperoid bodies in the upper part of the 

Hamburg Dolomite, beneath the relatively impermeable Dunderberg Shale on Adams Hill (Nolan, 1962, 

p. 63), suggests a hydrothermal origin for some of 

this rock. On the other hand, Nolan's observation 

(1962, p. 43) that oxidized ore minerals in this area 

locally contain considerable quantities of fine-grained 

quartz intermixed with them indicates that supergene jasperoid is also present.

Samples of jasperoid from the Eureka district in 

my collection provide evidence that both favorable 

and unfavorable varieties are present and can be 

distinguished by the criteria discussed on page 56 

of the present report.

APPEARANCE, MICROTEXTURE, AND MINERALOGY

I have nine samples from the Eureka district; 

however, only three of these are wholly or predominantly jasperoid, four represent incipient jasperoidization of altered limestone or dolomite, and the remaining two are silicified limy siltstones. Four of 

the samples are from the heavily mineralized Adams 

Hill area west of Eureka; the other five represent 

widely separated outcrops along New York Canyon 

and Windfall Canyon south of Eureka (Nolan, 1962, 

pi. 1). The host rock for four of the samples is the 

Cambrian Hamburg Dolomite; two samples are from
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 85

the Ordovician Hanson Creek Formation, and one 

sample each was taken from the Cambrian Windfall, the Permian Carbon Ridge, and the Cretaceous 

Newark Canyon Formations.

All four samples from the Hamburg Dolomite are 

from within 200 feet of mine workings; three are 

from the Adams Hill area, and one is from an outcrop near the Catlin shaft at the head of New York 

Canyon. Samples 1 and 2, from the vicinity of the 

Helen shaft on Adams Hill, are aphanitic mediumgray jasperoids that have a heterogeneous xenomorphic to jigsaw-puzzle texture and a grain diameter that averages 0.03 mm and ranges from 0.01 to 

0.15 mm. Relict carbonate grains are locally abundant; the quartz contains abundant carbonate particles and is cut by late calcite veinlets. Both samples 

contain abnormally high concentrations of Ag, Pb, 

Zn, and Sr, and both yield scores that place them in 

the favorable category. Samples 3 and 4, one from 

near the Helen shaft and the other from near the 

Catlin shaft, consist largely of brecciated and recrystallized Hamburg Dolomite showing incipient 

jasperoidizatiort. Both samples are aphanitic and 

weather brown with a rough surface. Sample 3 is 

medium gray with dark-gray inclusions; sample 4 is 

dark yellowish brown. Sample 3 is a finely comminuted microbreccia that contains tiny fragments 

of chert and vein quartz as well as dolomite. It also 

contains abundant irregular masses of an aphanitic 

opaque mineral, creamy white by reflected light, 

which was unidentifiable in thin section but which 

is probably a supergene lead-arsenic compound. 

Sample 4 contains only dolomite fragments and 

supergene orange goethite in addition to introduced 

silica. Two generations of introduced silica are distinguishable in both samples; the older of these is 

jasperoid similar in texture to that of the two jasperoid samples first described, but slightly coarser 

in average grain size. The quartz is disseminated as 

grains and small isolated aggregates in the dolomite. 

These aggregates become more numerous and coalesce through a narrow transition zone into a jasperoid matrix heavily contaminated with carbonate 

particles and containing numerous inclusions of the 

larger dolomite grains. Both dolomite and jasperoid 

are cut by veinlets of aphanitic quartz that has a 

jigsaw-puzzle texture and an average grain diameter of about 0.01 mm. Both samples 3 and 4 are rich 

in Ag, Ba, Cu, Pb, and Zn, and sample 3 also contains 

abundant As and Sb. They scored +21 and +12, 

respectively, on their indicator element content.

One sample of partly silicified dolomitic limestone 

of the Cambrian Windfall Formation was taken from 

an isolated outcrop surrounded by valley fill a quarter of a mile southwest of the Silver Lick group of 

mines on Adams Hill, the nearest mine workings. 

This sample is dense, fine grained, and pale yellowish 

gray, weathering yellowish brown, and has a rough 

pitted surface. In thin section the texture of the jasperoid and the manner in which it replaces the limestone are similar to those in the two dolomite samples described in the preceding paragraph; however, 

no late quartz veinlets or accessory minerals are visible. In addition to the Mg, Ca, and Ce of the host 

rock, this sample is slightly high in Na, Ag, Cu, Pb, 

Sr, and V. It yields a score of + 6 on the basis of its 

indicator-element content.

Two samples of jasperoidized dolomite of the Ordovician Hanson Creek Formation were collected 

from outcrops in New York Canyon. One of these 

outcrops is near the mouth of the canyon about a 

mile from the nearest mines; the other is about halfway up the canyon and 200 yards south of the 76 

mine shaft. The first consists largely of brecciated 

yellowish-gray and light-olive-gray dolomite cut and 

cemented by medium-gray jasperoid; the second is a 

dense dark-gray fine-grained jasperoid with inclusions of dolomite fragments. Incipient jasperoid in 

the first sample differs from that in the Cambrian 

rocks previously described in that it is both coarser 

grained and more homogeneous, having an average 

grain diameter of about 0.2 mm; this probably reflects the more coarsely crystalline nature of the host 

rock. The second sample consists of heterogenous 

xenomorphic quartz that has a grain diameter that 

averages 0.1 mm and ranges from 0.02 to 0.5 mm; 

it contains inclusions of coarse-grained dolomite. In 

both samples the quartz contains abundant carbonate 

dust, and the dolomite fragments are clouded with 

opaque dark-brown or black dust particles, which are 

largely concentrated near the rims of the grains. 

Both samples are slightly high in Na, Ag, Ba, Pb, 

and Sr in addition to Ca and Mg; the second sample 

(from near the 76 mine) is also higher than normal 

in Mn and Zn. Indicator-element scores are +3 for 

the first sample, and + 7 for the second.

A sample of silicified limy siltstone of the Permian 

Carbon Ridge Formation was taken from Windfall 

Canyon near the junction of the Windfall Canyon 

road and the cutoff road to New York Canyon. This 

outcrop is in a brecciated zone along a strong fault 

that brings the Mississippian Chainman Shale in 

contact with the Carbon Ridge Formation; it is about 

a mile from the nearest mines. The rock is fine 

grained with local sparse vugs, dusky yellowish 

brown to dark gray, and weathers moderate yellowish brown. It has a matrix of aphanitic jasperoid 

quartz that has a jigsaw-puzzle texture and grain
86 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

TABLE 21. Characteristics of jasperoid

District

Tri State. 

OklahomaKansasMissouri.

Clifton-Morenci, 

Ariz.

Bisbee, Ariz ........ 

Ely, Nev ..............

Field relations of jasperoid 

(characteristics of jasperoid bodies of the district as a whole) 

Major generations 

or types

Host rocks

limestone.

Probably 2 genera- Cambrian and Ortions but not dis- dovician limetinguished. stone.

Early ........................ Paleozoic limestone.

conglomerate.

stone and shale; 

Tertiary monzonite.

Structural control

Related to fractures 

and bedding planes.

Related to faults and 

breccia zones.

Localized by strong 

faults and proximity to intrusive contacts.

Localized by unconformity at base of 

Cretaceous and by 

faults and fractures cutting it.

Localized by proximity to monzonite 

porphyry intrusives.

Relationship to intrusives

No known intrusives..

May be genetically related to felsic Laramide intrusives, but 

spatially remote from 

intrusive centers.

Genetically and in part 

spatially related to 

siliceous porphyritic 

intrusives.

Genetically and spatially related to intrusives.

Relationship to ore

Late preore, commonly 

adjacent to sulfide 

ore bodies.

Probably postore; spatially remote from 

major deposits; relationship not studied in detail.

Late preore, genetically and commonly 

spatially related to 

ore.

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

Appearance of 

jasperoid 

(characteristics of 

particular jasperoid 

bodies considered to 

be typical)

Nature of contact

Commonly gradational into host rock on 

one side and ore on 

the other.

Commonly abrupt ...... 

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

Commonly irregular, 

locally gradational.

Commonly abrupt, locally gradational 

with intrusives.

Late .do.

Leadville, Colo Not distinguished ..

Tintic, Utah ........ Early (?) ................

Late

Ordovician, Devonian, and Mississippian limestone and 

dolomite.

Paleozoic sedimentary rocks, 

largely dolomite.

.do.

Localized by faults None known 

and fractures.

Localized by faults 

and fracture zones.

Related to unconformity at base of 

Tertiary extrusive 

rocks.

Related to faults and 

fractures.

Genetically and locally Commonly abrupt 

spatially related to 

ore.

Genetically related to 

quartz monzonite 

stock, but spatially 

remote.

Largely contemporaneous to postore; some 

is spatially associated, some is not.

None apparent ............ None apparent ........

Genetically related to 

monzonitic intrusive, 

but spatially remote.

No information ..........

Commonly abrupt

Preore, genetically and ...... do

commonly spatially 

related to ore.

Gilman, Colo ........ 1 generation Devonian and 

Mississippian 

dolomite.

Related to faults ........ None apparent Possible genetic relationship; no close 

spatial relationship.

Aspen, Colo ........ Probably 2 generations, but not distinguished.

Mississippian carbonate rocks.

Related to faults and ...... do

fractures.

Preore, genetically re- Transitional, in some 

lated and locally places, abrupt in 

spatially related to others, 

ore.

Eureka, Nev ........ Not subdivided ..... Cambrian, Ordovician, Permian, 

and Cretaceous 

carbonate rocks.

do ..................... do Genetically related to ...... do

mineralization; locally spatially related to ore.
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES 87 

in major districts of the United States

Appearance of jasperoid Continued

(characteristics of particular jasperoid bodies considered

to be typical) Continued

Microtexture and composition of particular jasperoid samples

Other information

Color

Dark gray to 

black.

Red, yellow.

brown.

Dark red, grayPale yellow,

pink.

White, pale 

yellow.

Dark red, dark 

yellow, 

shades of 

brown.

Gray to black; 

locally 

brown.

Black, dark

gray, brownish red, 

yellow.

Shades of gray 

and brown.

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

Shades of yellow, brown, 

and gray.

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

Macrotexture

Dense, fine grained, 

locally banded.

Largely aphanitic;

locally brecciated 

and cemented by 

yaunger quartz.

Aphanitic, locally 

vuggy.

Vuggy, fine

grained; abundant inclusions 

of host rock.

Dense, massive, 

fine grained; locally brecciated.

Vuggy, locally porous, commonly 

brecciated.

Largely aphanitic.. 

Aphanitic. ...............

Vuggy, commonly 

banded and brecciated; aphanitic 

to fine grained.

Commonly vuggy

and brecciated; 

aphanitic to fine 

grained.

Aphanitic to medium grained, 

vuggy.

Largely aphanitic..

Other information

Weathers light gray; 

porous and friable 

in transition zone 

to host rock.

None............................

Locally weathers to 

porous friable 

masses or to 

quartz sand.

None.. ..........................

Forms prominent 

outcrops.

Weathers to a rubble of small fragments.

None... ......................... 

Commonly opaque

on thin edges.

Variable grain size, 

commonly translucent on thin 

edges.

Locally preserves

primary and older 

alteration (zebra) 

textures.

Leached; coarser 

grained varieties 

are commonly porous and spongy.

Incipient jasperoid

locally developed 

in dolomite.

Fabric texture

Largely jigsaw-puzzle texture; locally reticulated.

Older host predominantly jigsawpuzzle texture; 

younger is xenomorphic, locally 

reticulated.

Jigsaw -puzzle to locally xenomorphic 

texture.

Xenomorphic to

granular texture.

Xenomorphic to jigsaw-puzzle texture, locally granular.

Jigsaw-puzzle texture, locally 

xenomorphic or 

reticulated.

Jigsaw-puzzle to locally xenomorphic 

texture.

granular texture.

Xenomorphic to reticulated texture, 

more than 1 generation, vuggy.

Xenomorphic to

jigsaw-puzzle 

texture.

Reticulated to jigsaw-puzzle texture.

Xenomorphic to

jigsaw-puzzle 

texture.

Grain type and 

size

Generally homogeneous; 

0.001-0.03 mm.

Older, homogeneous, < 0.005 

mm; younger, 

heterogeneous, 

< 0.005-0.3 

mm.

Homogeneous; 

about 0.005 

mm.

Heterogeneous;

0.005-0.1 mm.

Relatively homogeneous; 

0.01-0.1 mm.

Heterogeneous; 

0.005-1 mm.

Heterogeneous; 

0.005-0.1 mm.

Homogeneous;

<0.01 mm.

Heterogeneous, 

commonly 

coarse grained; 

>0.1 mm.

Commonly homogeneous; 

<0.05 mm.

Reticulated type, 

coarse and 

heterogeneous, 

>0.1 mm; 

jigsaw-puzzle 

type, homogeneous, <0.05 

mm.

oome varieties

homogeneous, 

<0.05 mm; 

others heterogeneous, 

0.02-0.5 mm.

Mineralogy

Carbon, clay, dolomite, pyrite, 

sphalerite.

Dolomite, siderite,

calcite, sericite, 

pyrite, hematite, 

goethite, limonite, Mn oxides.

Hematite, chalcedony, calcite, 

brochantite, malachite, limonite.

Siderite, calcite

dust, sericite.

Chalcedony, hematite, limonite, allophane, goethite, 

jarosite, calcite, 

sericite, kaolinite, apatite, fluorite, pyrite.

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

Mn oxides, goethite, 

limonite, hematite, pyrite.

Sericite, hematite.

limonite, chalcedony.

Barite, jarosite, 

goethite, allophane, pyrite.

Limonite, goethite,

carbonaceous 

matter, sericite, 

barite.

Dolomite, siderite, 

pyrite, barite, 

hematite, limonite, Mn oxides.

Calcite, dolomite, limonite, goethite, 

chalcedony, sericite, zircon, 

tourmaline.

Elements 

concentrated

Fe, Al, C, Ni, 

Pb, Zn.

Pb, Zn, Fe,

Be, Ga, Mo, 

Ag.

Fe, Cu, Ni, Pb, 

V, Y, Yb, 

Ag, Bi.

Ni, Pb, Mo, Be,

Zr.

No information.

Bi, Sn, Zn, Fe, 

Ag, Cu, Pb.

Ag, Ba.Mo.Pb, 

Zn, Fe, Mn.

Be, Mn, Ti, Ca,

Mg.

Ba, Pb, Ag, Sb, 

Bi, Cu, Zn, 

As, Na, Th, 

Sr.

None in unusual abundance.

Fe.Mg, Mn, Ag, 

Ba, Co, Cu, 

Pb, Sr, Zn.

Ca, Mg, Na, Ag,

Ba, Cu, Pb, 

Sr, Zn.

Locally associated with 

older chert, which 

may be of replacement origin.

Many textural types

distinguishable in 

thin section suggesting more than 1 

major generation.

Jasperoid is postPennsylvanian and 

pre-Late Cretaceous 

in age.

Jasperoid is probably

Tertiary in age.

None.

None.

Some jasperoid may 

be of supergene origin.

Particularly abundant

in north part of 

Tintic district.

None. 

None.

Ore bodies commonly 

associated with incipient jasperoid 

and locally with 

coarse reticulated 

jasperoid.

None.
88 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

diameter less than 0.01 mm; it contains sparse detrital zircon and tourmaline and abundant detrital 

quartz grains with overgrowths in optical continuity 

with the grains. The matrix is cut by veinlets of late 

orange goethite and chalcedony, and chalcedony also 

lines vugs. Analysis shows this sample to be slightly 

high in Al, Fe, Mg, Ag, B, Ba, Cu, Ni, Pb, Sr, Y, Yb, 

and Zn, and abnormally high in Sb and Zr. Its indicator-element score is +11.

A sample of similar material from the Cretaceous 

Newark Canyon Formation near the head of Windfall Canyon, about a mile from the nearest mines, 

consists of dense fine-grained pale-yellowish-brown 

silicified limy siltstone or silty limestone that weathers moderate brown. The matrix is homogeneous 

aphanitic quartz that has a jigsaw-puzzle texture as 

in the specimen described in the preceding paragraph. It also contains disseminated flakes of sericite and masses of chalcedony, as well as numerous 

detrital grains of zircon and tourmaline and abundant detrital quartz. However, there are no overgrowths on the quartz grains, and the sample also 

lacks disseminated limonite particles and late orange 

goethite. Analysis shows it to be slightly high in Ca, 

Mg, Na, B, Ba, Ni, V, Y, Yb, and Zr; it yields an 

indicator-element score of 2.

CONCLUDING REMARKS

With one exception the indicator-element scores 

of specimens from the Eureka district reflect their 

location relative to known ore deposits. The four 

samples taken close to mine workings yielded scores 

in the favorable range; two samples taken within a 

quarter of a mile of mines, but more than 100 yards 

from them, yielded scores in the probably favorable 

range; two of the three samples taken about a mile 

from the nearest mines scored in the unfavorable or 

probably unfavorable category. The third such sample (from the Carbon Ridge Formation) yielded a 

score in the probably favorable category. This sample, from a breccia zone along a strong fault, may 

reflect updip leakage from a buried center of mineralization.

SUMMARY OF JASPEROID IN THE MAJOR DISTRICTS

The main characteristics of jasperoids in each of 

the major districts are summarized in table 21. It 

should be noted that the characteristics given under 

"Field relations of jasperoid" in the left part of the 

table apply to jasperoid bodies of the district as a 

whole; those given under "Appearance of jasperoid" 

are more restrictive, in general applying to particular jasperoid bodies that were examined and considered to be "typical"; and those given under "Microtexture and composition of particular jasperoid 

samples" are still more restrictive, applying only to 

those samples that were collected, studied, and ana-« 

lyzed. As a result, the confidence that can be placed 

in the stated characteristics, as representative of 

the jasperoid bodies of the district, decreases toward 

the right in the table. Thus, interdistrict comparisons based on field relations are more reliable than 

those based on appearance, and these, in turn, are 

more reliable than comparisons based on microtexture and composition.

Certain generalizations are apparent from the field 

relations. In all the major districts Paleozoic carbonate rocks are the hosts for at least one major generation of jasperoid. In the districts characterized 

by a close spatial and genetic relationship between 

intrusive bodies and jasperoid, the intrusives are 

felsic, generally monzonitic in composition, and there 

is also a younger jasperoid localized by faults and 

fractures. In most of the districts in which a major 

generation of jasperoid is associated with ore, this 

jasperoid formed during a late stage of preore alteration.

Jasperoid samples that have coarse or highly 

variable texture, abundant vugs, or a porous friable 

texture commonly are related to ore; those characterized by an aphanitic texture are commonly unfavorable. Sulfides, or the oxidation products of sulfides, and unusually high concentrations of the ore 

metals as trace elements are characteristic of favorable jasperoid samples.

CHARACTERISTICS OF JASPEROID IN OTHER

THAN THE MAJOR MINING DISTRICTS

IN THE UNITED STATES

Jasperoid has been reported from nearly 200 

mining districts or mineralized areas in the United 

States in addition to the nine major districts discussed in the preceding chapter (fig. 1). Some of 

these are large districts in which jasperoid is not 

sufficiently abundant to warrant inclusion in the 

preceding chapter; others are large districts in 

which the abundance of jasperoid is not clear and 

needs further study; most are smaller districts characterized by abundant jasperoid; a few are mineralized areas that have as yet produced no ore.

Information on these jasperoid localities has 

been derived in part from the literature and in part 

from examination and analyses of samples. This 

information ranges from detailed description with 

numerous analyses to only a brief mention of occurrence.

Summary discussions in this chapter are arranged 

alphabetically by State. The discussion of each lo-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 89

cality includes a brief summary of available information on (1) the distribution and field relations of 

jasperoid bodies, (2) genesis and relationship of 

jasperoid to ore, (3) appearance and petrography 

of jasperoid, and (4) minor-element content of jasperoid samples.

ALABAMA

No descriptions of jasperoid in specific districts 

in Alabama have been found. However, in a resume 

of cobalt-bearing manganese deposits of Alabama, 

Georgia, and Tennessee, Pierce (1944, p. 265) observed that "Cobalt-bearing manganese oxide is commonly associated with some variety of siliceous rock, 

such as sandstone, quartzite, or chert, or with a finegrained crystalline quartz which Kesler has identified as jasperoid."

In an old report on the upper gold belt of northern 

Alabama, Brewer (1896, p. 12) mentioned deposits

similar to those of Cartersville, Ga., in which ore is 

associated with "whitish flinty quartz, highly sulpheretted." Thus, it seems that Alabama is not 

devoid of jasperoid occurrences, though their 

prevalence, nature, and economic significance cannot be evaluated from the information available.

ALASKA

Siliceous replacements associated with sulfide ore 

bodies have been reported from two areas in Alaska 

(fig. 37). One of these is the southern Seward 

Peninsula area where copper, lead, and zinc deposits 

are commonly associated with jasperoid in Paleozoic 

limestone. The other is the Salmon River district, 

near the head of the Portland Canal in the southeastern part of the Alaskan panhandle. Here, Jurassic greenstones have been locally silicified near 

deposits of copper sulfide.

154-

142°

PACIFIC OCEAN

0 100 200 MILES

FIGURE 37. Map showing the location of jasperoid-bearing areas in Alaska.
90 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

SOUTHERN SEWARD PENINSULA AREA

Cathcart (1922, p. 179, 181) mentioned bleached 

and silicified limestone with copper deposits at 

Casedepaga, on Penny River in the Solomon district, 

on Mount Dixon, on Slate Creek, on Manila Creek, 

and on Iron Creek at Copper Mountain. Cathcart 

said of these jasperoids: "The quartz bodies in which 

the copper minerals occur seem to conform with the 

bedding- of the limestone. The quartz contains many 

shrinkage cavities and retains the original bedding 

planes of the replaced rock. The most noticeable feature of the rock is its banded structure." The jasperoids of the Iron Creek district he (p. 212-213) 

described as being adjacent to bleached limestone 

and consisting of shattered and strained quartz cut 

by veinlets of sericite and chlorite. Chalcopyrite is 

locally present in these bodies in layers roughly parallel to the original bedding.

SALMON RIVER DISTRICT

Bodies of greenstone, which resulted from the

metamorphism of tuff and lava, have been intensely 

silicified in mineralized areas. This rock is bleached 

and locally resembles quartzite, both in macrotexture 

and composition. Sulfide minerals were introduced 

at about the same time as the silica. In some places 

the quartz replacement bodies contain abundant calcite or sericite, and at one locality (Summit claim) 

masses of nearly pure pyrrhotite are enclosed in 

silicified greenstone (Westgate, 1922, p. 123, 133, 

137-138).

ARIZONA

Although no jasperoid provinces have been defined 

in Arizona that are comparable to those in the adjoining States of California, Nevada, Utah, Colorado, 

and New Mexico, jasperoid is present in at least 17 

mineralized areas in the State, and some information 

is available on seven of these (fig. 38). Besides the 

major districts of Clifton-Morenci (5, fig. 38) and 

Bisbee (3), previously discussed, these are the Banner district (2), the Cameron area (4), the Court36°

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EXPLANATION

 

Major district

x 

Minor district or area

 

Reported occurrence

DISTRICTS, AREAS, AND OCCURRENCES

1. Aravaipa

2. Banner

3. Bisbee

4. Cameron

5. Clifton-Morenci

6. Courtland-Gleeson

7. Fort Apache

8. Globe-Miami

9. Helvtia

10. Jerome

11. Mazatzal Mountains

12. Mule Mountains

13. Patagonia

14. Pima

15. Swisshelm

16. Tombstone

17. Winchester Mountains

FIGURE 38. Map showing the location of jasperoid-bearing areas in Arizona.
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 91

land-Gleeson district (6), the Jerome district (10), 

and the Pinia district (14). Except for Cameron and 

Jerome, all of these are in the southeast quarter of 

the State. This geographic distribution may be 

largely attributable to the tendency of such siliceous 

replacements to occur in Paleozoic limestones and 

dolomites. Mineral deposits in these rocks are largely 

restricted to the southeastern part of the State. However, jasperoid bodies have also been reported in 

Triassic siltstone near Cameron (Abdel-Gawad and 

Kerr, 1963; Barrington and Kerr, 1963) and in 

Precambrian metamorphosed tuffaceous rocks near 

Jerome (Anderson and Creasey, 1958, p. 43-44, 

109-111).

BANNER DISTRICT

(2, fig. 38)

The Banner district is in southern Gila County 

a few miles north of Hayden (Kiersch, 1951). At 

the Seventy Nine mine copper-lead-zinc-sulfide replacement deposits in faulted and fractured Pennsylvanian Naco Limestone are associated with massive 

jasperoid bodies. One of these forms a circular outcropping mass 15 feet high directly overlying a 

pyritic ore body; similar jasperoid bodies appear to 

be localized by the Keystone fault near the mine. 

Many of these form lenses parallel to the bedding 

of the Naco Limestone. Lenses and irregular masses 

of jasperoid have been penetrated by mine workings 

as deep as the seventh level.

According to Kiersch (1951, p. 78-79), the sulfide 

ore bodies are cut and replaced by stringers, veins, 

and masses of quartz, which is the youngest hypogene mineral. Although Kiersch did not directly 

stipulate the age of the jasperoid bodies relative to 

the sulfide ore, the preceding statement implies that 

he regarded them as a product of the late-stage 

hydrothermal silica-bearing solutions. Regardless of 

their genesis, many of them are closely associated 

spatially with ore bodies.

The three samples from the Seventy Nine mine in 

my collection show considerable variation in color, 

texture, and mineralogy. Two are outcrop samples, 

and these are aphanitic and dark red to reddish 

brown. Their texture is heterogeneous and largely 

xenomorphic, locally almost granular or reticulated. 

The quartz is cut by veinlets of red hematite. One 

outcrop sample contains numerous microvugs surrounded by clean xenomorphic quartz showing zonal 

overgrowths. The other outcrop sample shows no 

vugs; but the quartz contains numerous inclusions 

of chlorite, sericite, rutile, hematite pseudomorphs 

after pyrite, and a high-index carbonate which is 

probably cerussite. The third sample, from the mine

dump, is coarse grained, vuggy, and white stained 

with various shades of brown. Its texture is heterogeneous and strongly reticulated. The larger quartz 

laths contain numerous two-phase fluid inclusions, 

as well as flakes of sericite and tiny needles of rutile. 

Vugs and late fractures contain cerussite and wulfenite in addition to the ubiquitous limonite and 

goethite.

All three samples scored high in the favorable 

category on their minor-element content. All were 

high in lead; two were high in Ag, Cu, Ga, In, and 

Zn; and one was high in Bi, Mo, and V.

CAMERON AREA 

(4, fig. 38)

The town of Cameron seems to be near the center 

of a considerable area of scattered jasperoid bodies 

in the Triassic sedimentary rocks, and locally in the 

underlying Permian Kaibab Limestone (Barrington 

and Kerr, 1963, p. 1252-1253). A silicified zone 5-10 

feet thick is present at the top of the Shinarump 

Member of the Chinle Formation in two areas in 

Coconino County one on the west side of the Little 

Colorado River a few miles southeast of Cameron, 

and the other near Shadow Mountain, 11 miles north 

of Cameron (Abdel-Gawad and Kerr, 1963, p. 25- 

26). Near the junction of the Colorado and Little 

Colorado Rivers about 15 miles west of Cameron, a 

group of silicified breccia pipes, containing fragments of Shinarump and Kaibab Limestone, crops 

out in the shale and siltstone of the Moenkopi Formation (Barrington and Kerr, 1963, p. 1238). Both the 

silicified zone in the Shinarump and the silicified 

pipes in the Moenkopi are ascribed to alteration by 

siliceous hydrothermal solutions.

The jasperoid in the area southeast of Cameron 

forms anastomosing veins and lenses, locally as much 

as 7 feet thick, in sandstone and siltstone at the top 

of the Shinarump Member just below a thin gray 

shale of the Chinle. It is variegated and mottled in 

various shades of red, purple, and yellow and is 

commonly surrounded by a bleached kaolinized zone 

in the host rock. The surface is covered by an angular rubble of jasperoid surrounding the outcrops. 

Jasperoid here consists largely of dense aphanitic 

quartz and red chalcedony (Abdel-Gawad and Kerr, 

1963, p. 25-26).

The silicified pipes west of Cameron present a very 

different appearance. They are nearly vertical pipes 

filled with a rubble of silica-cemented fragments of 

quartzite, limestone, siltstone, sandstone, and clay 

derived from the underlying Kaibab Limestone and 

Shinarump. The Moenkopi sandstone and siltstone 

surrounding these pipes have been bleached in ir-
92 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

regular halos, which represent a combination of 

kaolinitic and sericitic alteration. These pipes form 

prominent conical, irregular, black-weathering outcrops. Some breccia fragments in the cores are silicified, others are not. The cryptocrystalline silica 

cement is vuggy and porous and has cavities lined 

with crystals of anhydrite. Locally, silicified breccia 

fragments are embedded in a matrix of yellow kaolinite clay. Silica is confined to the vents and does 

 not replace the wallrock. All the pipes are anomalously radioactive. The siliceous matrix is stained 

with limonite in addition to manganese oxide, and it 

locally contains malachite and azurite. Disseminated 

pyrite is present at depth in the altered wallrock 

surrounding some of the pipes (Barrington and 

Kerr, 1963, p. 1242-1246).

The silicification that produced both the zone and 

the pipes probably occurred at temperatures of about 

200°C and at moderate pressure. Silicification probably was accompanied, in the early stages, by kaolinization of the wallrock and, in the later stages, by 

the local introduction of oxides of uranium and 

manganese and sulfides of copper and iron, with 

excess sulfur resulting locally in the conversion of 

calcite to anhydrite (Abdel-Gawad and Kerr, 1963, 

p. 34, 44; Barrington and Kerr, 1963, p. 1246-1247). 

The ultimate source of the hydrothermal fluids is not 

known in this area. The jasperoid layers and lenses 

in the area southeast of Cameron are beneath, and 

near, small uranium deposits in sandstone beds of 

the Chinle Formation. No ore bodies have been developed in the area of the silica pipes, but the fact 

that the pipes show anomalous radioactivity and 

locally contain copper minerals as well as disseminated pyrite suggests that uranium and base-metal 

sulfide replacement ore bodies, if they are present 

in this area, probably are associated both spatially 

and genetically with jasperoid.

Jasperoid bodies in the Shinarump Member near 

Shadow Mountain are not described separately.

COURTLAND-GLEESON DISTRICT 

(6, fig. 38)

The Courtland-Gleeson district occupies an area 

of about 8 square miles near the southeast margin 

of the Dragoon Mountains 15 miles east of Tombstone and 20 miles north of Bisbee in Cochise County. 

Ore deposits consist of pyritic copper and lead-zincsilver replacement deposits in Carboniferous carbonate rocks. They are localized by west-dipping thrust 

faults and younger north- and east-trending normal 

faults and fractures (Wilson, 1951, p. 12, 14).

The jasperoid bodies of this district are not discussed in the literature, although Wilson (1951, p.

14-15) mentioned a prominent limonitic silicified 

breccia zone along a north-trending mineralized fault 

on the west slope of Gleeson Ridge.

Three samples from this district are included in 

my collection. One sample, from an outcrop near 

the Shannon shaft, near Gleeson, is of the favorable 

oxidized type; the other two are of unfavorable 

oxidized jasperoid one from a pit south of the 

Marine shaft near Courtland, the other from a 

breccia zone outcrop about a mile south of Browns 

Peak. The favorable sample, from a silicified breccia 

zone along a fault, consists of angular pale-orange 

and medium-gray breccia fragments of aphanitic 

jasperoid in a slightly vuggy moderate-brown siliceous matrix. The fragments have a homogeneous 

aphanitic jigsaw-puzzle texture. The matrix, which 

is similar in texture, contains abundant brown 

limonite and is cut by veinlets of orange goethite 

and younger coarse xenomorphic quartz; it also contains sparse open vugs as much as 1 mm in diameter.

The unfavorable sample from the prospect pit near 

Courtland is fine grained, light gray, and dense and 

is cut by thin veinlets of calcite. It has a heterogeneous granular to jigsaw-puzzle texture and a grain 

size of 0.005-0.15 mm. The larger grains have sutured boundaries and poikilitic inclusions of smaller 

grains. Accessory inclusions consist of fibrous 

chalcedony, calcite, and abundant large masses of 

tremolite. It also exhibits sparse elongated open vugs.

The second unfavorable sample, from south of 

Browns Peak, is fine to medium grained, grayish 

orange pink, and contains scattered vuggy areas and 

square pits. The matrix consists of homogeneous 

aphanitic jigsaw-puzzle-textured quartz, which has 

been fractured and recemented by late coarse xenomorphic quartz. The late quartz contains abundant 

allophane dust, much of which shows zonal overgrowth patterns on original euhedral crystals, and 

scattered embedded hematite pseudomorphs after 

original pyrite, which suggests that this jasperoid 

body may be of the fringe-zone favorable type rather 

than the truly unfavorable type.

The favorable sample from the Gleeson district is 

higher than normal in Fe, Ag, Bi, Cu, Ga, Mo, Pb, 

Sn, and Zn. The unfavorable sample from the pit 

near Courtland is abnormally rich only in Ba, and 

the unfavorable sample from south of Browns Peak 

is slightly high in B and Pb.

Differences in appearance, texture, mineralogy, 

and minor-element content among the three available 

samples show that several distinct types of jasperoid 

exist in this district, but their relationships to the 

ore bodies and to each other have not yet been 

determined.
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 93

JEROME DISTRICT

(10, fig. 38)

Several occurrences of jasper and silicified bodies 

in Precambrian metavolcanic and metasedimentary 

rocks in the Jerome district, Yavapai County, were 

described by Anderson and Creasey (1958).

In the vicinity of the United Verde ore body, 

tuffaceous rocks of the Grapevine Gulch Formation 

were locally replaced by fine-grained quartz adjacent 

to an intrusive gabbro contact, before the further 

replacement of this rock and the underlying quartz 

porphyry by massive pyrite. The jasperoid bodies 

thus formed are lenticular to irregular in form; they 

are most abundant in the tuffaceous sediments although some isolated masses are completely enclosed 

within the pyrite, and small jasperoid nodules are 

present in the quartz porphyry on the footwall side 

of the pyritic pipe. The largest jasperoid bodies, as 

much as 500 feet long and 150 feet wide, are localized by structural terraces in the hanging-wall 

gabbro (Anderson and Creasey, 1958, p. 109-111). 

Both the silicification and the sulfide mineralization 

in this deposit are clearly Precambrian. These are 

the only bodies of favorable jasperoid of unquestionable Precambrian age known to the author, though 

it is probable that hard massive quartz containing 

small chalcocite bodies in the upper levels of the 

United Verde extension ore body (Anderson and 

Creasey, 1958, p. 143) and pods of jasperoid in 

andesitic tuffs of the Alder Group between the 

United Verde and Copper Chief mines (Anderson 

and Creasey, 1958, p. 43-44) are also Precambrian. 

Other such bodies, remote from mineralized areas, 

in the Deception Rhyolite along shear zones and 

along the contact with the Grapevine Gulch Formation were reported by Anderson and Creasey (1958, 

p. 44), who believed them to be of Precambrian age 

but younger than the regional deformation.

The jasperoid of the United Verde deposit is fine 

grained, almost flinty, and red, black, or white with 

gradational color variations (Anderson and Creasey, 

1958, p. 111).

Jasper magnetite beds are also locally intercalated 

with dacite flows in the Grapevine Gulch Formation, 

but these beds probably represent metamorphosed 

chemical precipitates, rather than epigenetic siliceous replacements (Anderson and Creasey, 1958, p. 

19).

PIMA DISTRICT

(14, fig. 38)

At the San Xavier mine in the northern part of 

the Pima district, Pima County, about 20 miles south 

of Tucson, a few small masses of favorable jasperoid 

are associated with base-metal sulfide replacement

deposits in Permian limestone. Wilson (1950, p. 46- 

47) summarized the geology and ore deposits of this 

mine, but he did not mention jasperoid.

Two samples of favorable jasperoid from the San 

Xavier mine area are included in my collection. One 

is a dump sample; the other is from a small outcrop, 

which caps an ore body, in limestone near the service 

shaft. The distribution of the ore bodies, and apparently of the jasperoid, is largely controlled by the 

intersection of a strong northeast-trending fault zone 

with favorable limestone beds.

Both samples are porous, vuggy, and heavily 

stained with iron oxide. The quartz is coarse grained 

and heterogeneous, and it has a xenomorphic to locally reticulated texture. In both samples the quartz 

is clouded with carbonate particles, and in one of 

them, small fluid inclusions are present in some of 

the coarser grains. In one sample, abundant relict 

grains and masses of siderite form inclusions in the 

quartz; in the other sample, porous masses of brown 

limonite and orange goethite cement fragments of 

jasperoid quartz, and late fibrous chalcedony partly 

fills the voids.

Both samples are rich in Ag, Bi, Cu, Mo, Pb, and 

Zn. One sample also shows high V, and the other one, 

high Ni.

OTHER OCCURRENCES

In the Winchester silver district (17, fig. 38) in 

the northeast corner of the Dragoon quadrangle, 

Cochise County, limestone of Paleozoic age has locally been replaced by jasperoid bodies, some of 

which are as much as 100 feet wide and 1,000 feet 

long. These jasperoid bodies are host rocks for silver 

ore deposits, although the distribution of silver is 

erratic and only small parts of the bodies are minable (Cooper and Silver, 1964, p. 161).

In the Helvetia district (9, fig. 38), in the Santa 

Rita Mountains, the footwall of a copper ore body 

in the Copper World mine consists of highly silicified 

gray limestone, although the ore itself is not very 

siliceous (Schrader, 1915, p. 103). In the Patagonia 

district (13, fig. 38), at the Mowry mine, a silicified 

breccia zone as much as 250 feet wide occurs along 

a fault in limestone, according to Schrader (1915, p. 

302), who wrote, in his general description of alteration in the district, that

The quartz in limestone occurs mostly in irregular masses 

locally developed in association with the garnet along the 

contact zone and in the impure cherty zones or metamorphic 

bands in the sedimentary rocks. Here and there it replaces 

chert and the earlier metamorphic minerals, such as calcite 

and actinolite, whose crystalline forms are preserved in 

masses of relatively pure pseudomorphic silica.

Jasperoid bodies have been reported in the Penn-
94 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

sylvanian Naco Limestone in the Swisshelm district 

(15, fig. 38), Cochise County, about 30 miles north 

of Douglas (J. R. Cooper, oral commun., 1962), and 

in the Cretaceous Bisbee Group of the Mule Mountains (12, fig. 38), Cochise County, north of the 

Bisbee district (P. T. Hayes, oral commun., 1964). 

The "novaculite" in the Naco Limestone at Tombstone (16, fig. 38), Cochise County, which is associted with replacement ore deposits (Butler and 

Wilson, 1938, p. 108), also may be at least partly 

jasperoid.

At the Grand Reef mine in the Aravaipa district 

(1, fig. 38), Graham County, Ross (1925, p. 62) 

described lode deposits of lead and zinc sulfides in a 

silicified breccia of country rock, and also "irregular 

masses of white and pink glassy quartz."

In the Fort Apache iron district (7, fig. 38) in 

Navajo County, near Young, silicified chert breccias 

occur in the Precambrian Mescal Limestone. Silicification was controlled partly by proximity to an old 

erosion surface and partly by the intersection of 

joints and fractures with favorable beds. The alteration took place in Precambrian time and seems to 

have been characterized by repeated cycles of brecciation and silicification (A. F. Sliride, oral commun., 

1962). In some places these silicified zones are peripheral to, and grade into, bedded iron ore deposits. 

Silica of both the breccia fragments and the matrix 

tends to be aphanitic, and it has a jigsaw-puzzle 

texture. The rocks are variegated in color, commonly 

banded in shades of gray, red, pink, yellow, and 

brown, and locally display small vugs and open 

cavities. It is doubtful that these silicified breccias 

represent true jasperoids in the sense of bodies 

formed by heated upward-moving silica-bearing solutions; more probably their origin, like that of the 

silcretes of South Africa and the duricrusts of Australia, was due to cementation by silica-bearing 

ground and surface water at or near an erosion 

surface.

In the Mazatzal Mountains (11, fig. 38), Maricopa 

County, near some mercury deposits on Alder and 

Sycamore Creeks, conspicuous bands of red jasper 

in a pale-yellow Precambrian dolomitic limestone 

that is interbedded with schist and slate were reported by Lausen and Gardner (1927, p. 63, 65).

In the Globe-Miami district (8, fig. 38), Gila 

County, quartz monzonite and granite porphyry are 

completely replaced by quartz and pyrite along some 

major faults and breccia zones of the Copper Cities 

deposit, according to Peterson (1962, p. 92)

ARKANSAS

Jasperoid is associated with many of the small

zinc and lead deposits scattered through the Ordovician and Mississippian carbonate rocks of northern 

Arkansas, in Washington, Boone, and Marion Counties on the west, and in Lawrence and Sharp Counties about 100 miles to the east. The deposits in the 

main northern Arkansas zinc district are most concentrated in Boone and Marion Counties in the 

north-central part of the region. The deposits, although numerous, are small, and the total value of 

all the zinc and lead produced from the entire region 

is less than $10 million.

NORTHERN ARKANSAS ZINC-LEAD DISTRICT

(fig. 36)

In this district, as in the Tri-State district to the 

northwest, many of the dolomite and limestone beds 

contain large masses of preore jasperoid that resembles chert, which locally replaces the enclosing 

rocks, although McKnight (1935, p. 19-23) stated 

that it is probably only slightly younger than these 

host rocks. The deposits are very similar to, but 

smaller than, those in the Tri-State district.

Gray or brown jasperoid is closely associated both 

spatially and genetically with many of the sulfide replacement ore bodies. It selectively replaces limestone rather than dolomite in mineralized areas 

where the two rock types are present. 'McKnight 

(1935, p. 119-120, 138-150) believed that the gray 

jasperoid was deposited from hydrothermal solutions 

that resulted from the mingling of far-traveling 

magmatic emanations with ground water. He regarded it as the first stage of mineralization, immediately preceding the stage of sulfide deposition, 

and believed that the silica of which it is composed 

precipitated directly in the form of quartz, rather 

than crystallizing from a silica gel.

Incipient jasperoidization is commonly marked by 

the presence of disseminated quartz prisms in the 

carbonate host, and the massive jasperoid characteristically contains numerous relict grains of carbonate. Unreplaced dolomite rhombs occur in some 

samples of completely jasperoidized limestone. The 

jasperoid is typically a fine-grained dense dark-gray 

to black rock that has a heterogeneous reticulated 

texture (McKnight^ 1935, p. 111-112, pis. 10, 11).

CALIFORNIA

Four mining areas in California that are characterized by large bodies of jasperoid are discussed 

in the literature: the Darwin district (3, fig. 39), the 

Diadem lode in the Bidwell Bar district (1), the 

Mescal mine in the Ivanpah district (6), and the East 

Shasta district (4). The first is a base-metal sulfide 

and scheelite district in the northwestern Mojave
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 95

124

120

DISTRICTS, AREAS, AND OCCURRENCES

1. Bidwell Bar

2. Black Hawk

3. Darwin

4. East Shasta

5. Grapevine

6. Ivanpah

7. Kingston Range

8. Lee

9. Lemoigne

10. Lone Pine

11. Mayacmas and Sulphur 

Bank

12. Nopah

13. Reward

14. Russ

15. Slate Range

16. Soda Lake 

11. South Park

18. Swansea

19. Tecopa

20. Tungsten Hills

21. Ubehebe

Minor district or area

 

Reported occurrence

Jasperoid province

FIGURE 39. Map showing the location of jasperoid-bearing areas in California.
96 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

Desert near Owens Lake; the second is a gold district 

near the north end of the Mother Lode gold belt; the 

third is an antimony-silver mine in the eastern 

Mojave Desert near the Nevada State line; and the 

fourth is a copper-zinc district in Shasta County. 

Jasperoid is known to be present in many other areas 

in California (fig. 39), but the literature on mining 

districts in the State contains little information 

about it.

DARWIN DISTRICT 

(3, %. 39)

The Darwin district is in hills that lie between the 

south end of the Inyo Mountains and the north end 

of the Argus Range, about 20 miles east of the south 

end of Owens Lake in Inyo County (Hall and MacKevett, 1962). The Panamint Springs, Zinc Hill, and 

Modoc mining districts a few miles west of Darwin 

in the Argus Range also contain abundant jasperoid 

(A. V. Heyl, written commun., 1967).

A series of upper Paleozoic carbonate rocks in 

the area has been metasomatically altered to calcsilicate rocks in broad zones surrounding Mesozoic 

felsic intrusive stocks and batholiths. Most of the 

ore bodies are in fissure veins and bedded replacements within this zone of contact metamorphism.

Knopf (1915, p. 16-18) noted the occurrence of 

"iron-bearing jasper" gangue at the Lane, Columbia, 

and Wonder mines in this district. Hall and MacKevett (1958, p. 17-18; 1962, p. 63, 68, 76) listed 

"jasper" as an important gangue for some of the ore 

bodies formed in major fault zones and stated that 

it is particularly abundant at the Santa Rosa mine. 

"Jasper" in this district apparently is confined to 

the fault zones and does not appreciably replace the 

host rock. However, this rock replaces breccia within 

the fault zones and thus is true jasperoid (A. V. 

Heyl, written commun., 1967).

B1DWELL BAR DISTRICT

(1, %. 39)

Turner (1899, p. 389-390) described a replacement of Carboniferous limestone and dolomite on 

the Diadem lode in the Bid well Bar district, Plumas 

County, Calif., near the north end of the Mother 

Lode gold belt. This body is localized by a strong 

fault zone, and attains a maximum width of 60 feet. 

Silicified foramanifera are present in this rock, 

which consists largely of iron- and manganesestained quartz and chalcedony and, locally, of finegrained silicified shale beds. The jasperoid contains 

selenides of Au, Ag, Pb, and Cu in addition to free 

gold. Ore mineralization is regarded as penecontemporaneous with silicification.

IVANPAH DISTRICT 

(6, fig. 39)

The Mescal mine is in the Ivanpah district, on the 

northeast slope of the Mescal Range about a mile 

south of U.S. Highway 91 in eastern San Bernardino 

County, close to the Nevada State line. Hewett 

(1956, p. 132) has summarized the geology and ore 

deposit at this mine.

The host rock is lower Paleozoic Goodsprings 

Dolomite, which at this locality is a thin-bedded 

dark-gray dolomite intruded by a rhyolite sill. The 

ore zone is along a minor thrust fault in the dolomite, 

nearly parallel to the bedding. Stibnite, pyrite, and 

other sulfides are disseminated through a jasperoid 

body replacing the dolomite along this fault. According to Hewett, "these sulfides fill the pores of 

the spongelike mass of quartz that replaced the 

dolomite." A. V. Heyl (written commun., 1967) reported that jasperoid is abundant at many other 

silver and base-metal mines in this district.

EAST SHASTA DISTRICT

(4, fig. 39)

The East Shasta district is on Shasta Lake in 

central Shasta County, about 20 miles northeast of 

Redding. Massive base-metal sulfide deposits form 

lenses along shear zones and faults in Triassic rhyolite. The geology of the district is complex, and rocks 

ranging in age from Devonian to late Tertiary or 

early Quaternary are exposed within it. These are 

predominantly extrusive rocks and pyroclastics of 

many different ages, with subordinate interbedded 

shales and mudstones and a few limestone beds; a 

small stock of felsic plutonic rocks was emplaced in 

Late Jurassic or Early Cretaceous time.

Albers and Robertson (1961, p. 51, 52, 73, 97) 

mentioned silicification of rocks of many kinds, including Mississippian and Permian limestone, in the 

district; however, the rhyolitic host rock for the ore 

deposits is the most conspicuously silicified rock unit, 

and it is this silicification of the rhyolite that they 

discussed, as summarized in the following paragraph.

In its more intensely silicified phases both the 

groundmass and the feldspar phenocrysts of this 

rock have been replaced by anhedral microcrystalline 

quartz, and only the relict quartz phenocrysts remain. Silica, liberated during the replacement of 

rhyolite by sulfates and sulfides, probably moved outward to replace feldspar in the rhyolite at the Rising 

Star mine, where sulfide lenses are largely enclosed 

by intensely silicified rhyolite. A dense reddish-brown 

flintlike jasperoid containing disseminated sulfides 

in the Bully Hill mine appears to be a siliceous
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 97

replacement of metadiabase, and Albers and Robertson (1961, p. 97) stated that "its presence near 

prominent ore shoots seems to be an important indicator of mineralization within the metadiabase."

Jasperoids of the favorable type are thus abundant 

in parts of the East Shasta district, though they are 

somewhat unusual in that they replace igneous rocks

rather than sedimentary carbonate rocks. IOTHER OCCURRENCES

oerpentine in the vicinity of mercury deposits in 

the Mayacmas and Sulphur Bank districts (11, fig. 

39), Sonoma County, was reported by Ross (1940, 

p. 333, 340) to have been hydrothermally altered to 

a fine-grained rock composed of quartz, chalcedony, 

opal, and carbonates. In the Tungsten Hills (20, fig. 

39), Inyo County, 10 miles west of Bishop at the 

east base of the Sierra Nevada, roof pendants of 

metamorphosed sedimentary rocks are enclosed in 

granite and form the host rocks for scheelite deposits. Lemmon (1941, p. 502) wrote that "The 

calcareous rocks, limestone, shaly limestone, and 

calcareous shale show the most varied alteration. 

Some beds are silicified and on casual inspection resemble quartzite."

A. V. Heyl (written commun., 1967) reported that 

jasperoid is common or abundant in the following 

lead and zinc mining districts in Inyo, San Bernardino, and Kern Counties in eastern California: 

Tecopa (19, fig. 39), Black Hawk (2), Lemoigne 

(9), Grapevine (5), Kingston Range (7), Nopah 

(12), Reward (13), Slate Range (15), Russ (14), 

Ubehebe (21), and Panamint Springs (hypogene 

jasperoid) ; Zinc Hill, Modoc, and Swansea (18) 

(both hypogene and supergene jasperoid) ; Lee (8), 

Clark Mountain, Soda Lake (16), Lone Pine (10), 

and South Park (17) (supergene jasperoid). The 

host rock of the jasperoid in most of these districts 

is limestone or dolomite; however, jasperoid replaces 

andesite and tuff in the Grapevine district.

COLORADO

Most of the small jasperoid-bearing mining districts of Colorado are within the central Colorado 

jasperoid province (fig. 1), which covers parts of 

Eagle, Summit, Lake, Park, Pitkin, Chaffee, Saguache, and Gunnison Counties, and includes the major 

districts of Leadville (9, fig. 40), Gilman (5), and 

Aspen (1), previously described. These smaller districts within the province include the HorseshoeSacramento district (6) in the Mosquito Range 

southeast of Leadville, the Kokomo district (7) in 

the Gore Range a few miles north of Climax, the 

Pando area (14) in the upper Eagle River Valley

between Tennessee Pass and Red Cliff, the Sedalia 

district (18) near Salida, the Monarch-Tomichi 

(12), Quartz Creek (15), Tincup (22), and Sugar 

Loaf and St. Kevin (21) districts in the Sawatch 

Range, the Lenado (10) and Snowmass Mountain

(19) districts near Aspen, the Spring Creek district

(20) north of Gunnison, and the Bonanza district 

(2) in the northeastern Saguache County. Isolated 

occurrences of jasperoid have also been reported 

from the Uncompahgre (23) and Red Mountain (16) 

districts near Ouray in the northern San Juan Mountains, in the Rico (17) and La Plata (8) districts 

in the southwestern San Juan Mountains, the 

Massadona-Youghall district (11) in Moffat County, 

and the Carbonate district (4) in eastern Garfield 

County outside the jasperoid province (fig. 40). The 

host rocks for nearly all these Jasperoids are limestone and dolomites ranging in age from Devonian 

to Pennsylvania.

HORSESHOE-SACRAMENTO DISTRICT

(6, fig. 40)

The Horseshoe-Sacramento district is south of 

Alma and southeast of Leadville on the east slope of 

the Mosquito Range in Park County. The nature and 

genesis of its jasperoid bodies were discussed in 

detail by Butler and Singewald (1940), from which 

the following information is abstracted.

The ore deposits consist of lead-zinc-silver sulfide 

vein and replacement deposits in Devonian Dyer 

Dolomite Member of the Chaffee Formation and the 

overlying Mississippian Leadville Limestone on the 

steep west limb of a northwest-trending anticline, 

which is cut off by the major north-northwesttrending London fault on the west. This fault brings 

barren Pennsylvanian shale, arkose, and siltstone in 

contact with the ore-bearing carbonate rocks.

Silicification of the carbonate rocks was preceded 

by the formation of vein quartz that fills faults and 

small fractures. Several distinct types and ages of 

jasperoid were distinguished in the area, and they 

exhibit both abrupt and transitional contacts with 

their host rocks (Butler and Singewald, 1940, p. 

820-828). The jasperoid forms lenticular bodies 

parallel to the bedding and silicified breccia zones 

along major faults, which locally act as "feeder 

dikes" to the lenticular bodies. Butler and Singewald 

recognized four types of jasperoid, which they designated as coarse euhedral, coarse granular, fine 

granular, and nodular. These types grade transitionally into each other and exhibit a crude regional 

zonation outward from a core of coarse euhedral 

jasperoid to a peripheral zone of nodular jasperoid. 

They (p. 828-831, 835-836) believed that this tex-
98 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

102° EXPLANATION

40°

M 0 F 

11

/X8

L...

106° 104°

3a

-5._ LD 0

1 M A S

50 100 MILES

FIGURE 40. Map showing the location of jasperoid-bearing areas in Colorado.

Major district

x 

Minor district or area

 

Reported occurrence

j 

Jasperoid province

DISTRICTS, AREAS, AND 

OCCURRENCES

1. Aspen

2. Bonanza

3. Breckenridge

4. Carbonate

5. Oilman (Red Cliff)

6. Horseshoe-Sacramento

7. Kokomo

8. La Plata

9. Leadville

10. Lenado

11. Massadona-Youghall

12. Monarch-Tomichi

13. Mosquito Range

14. Pando

15. Quartz Creek

16. Red Mountain

17. Rico

18. Sedalia

19. Snowmass Mountain

20. Spring Creek

21. Sugar Loaf and St. Kevin

22. Tincup

23. Uncompahgre

tural gradation reflected a change from relatively 

dilute and relatively low temperature silica-bearing 

solutions precipitating quartz to form coarse 

euhedral jasperoid, through successively hotter and 

more concentrated silica solutions to a hot, highly 

supersaturated solution, which precipitated silica 

gel that later crystallized to form the aphanitic 

nodular type of jasperoid.

The coarse euhedral jasperoids are restricted to a 

small area at the southeast end of the larger 

jasperoid-bearing area. This rock resembles finegrained quartzite and is transitional into the 

recrystallized dolomite host rock through a zone 

characterized by skeletal quartz crystals or disseminated quartz prisms in the dolomite gangue. In thin 

section it shows a coarse reticulated texture with 

carbonate particles in the laths, which are cemented 

by, and locally overgrown with, clear quartz. Late 

clear coarse quartz also forms veinlets and drusy 

coatings of cavities and vugs. Relict inclusions of 

dolomite and grains of barite partly replaced by 

jasperoid are common. Flakes of sericite are locally 

abundant, and late ferruginous carbonate replaces 

some of the jasperoid. This type of jasperoid is 

closely associated with, and grades into, baritic sulfide ore consisting largely of galena, sphalerite, and

pyrite in a gangue of barite, dolomite, and jasperoid 

(Butler and Singewald, 1940, p. 808, 821-823).

Euhedral jasperoid grades into coarse granular 

jasperoid consisting of sparse, poorly terminated 

quartz laths embedded in a groundmass of relatively 

coarse anhedral quartz grains. This type also contains relict inclusions of carbonate host, but it lacks 

the carbonate particles that characterize the euhedral 

variety. The coarse granular jasperoid grades outward into fine granular jasperoid with the disappearance of quartz laths and gradual diminution in 

grain size. This type could have formed either by 

the crystallization of colloidal silica or by the rapid 

precipitation of quartz from solution at abundant 

centers of nucleation. Both barite and the early 

quartz laths show strain, brecciation, and corrosion 

by the granular matrix quartz (Butler and Singewald, 1940, p. 826-827, 831).

The fine granular jasperoid is transitional outward into nodular jasperoid that consists of nodules 

of fine-grained jasperoid quartz in a matrix of 

aphanitic cherty-looking quartz whose average grain 

size is a few thousandths of a millimeter. The nodules 

lack spherulitic or chalcedonic banding, but they 

commonly contain carbonate particles that are segregated in the cores of some nodules and concentrated in the rims of others. Both nodules and matrix
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 99

are cut by veinlets of late coarse clear quartz. This 

nodular jasperoid, which is most abundant on the 

outer fringes of the jasperoid area, characteristically 

exhibits sharp contacts with the host rock and is 

thought to represent the recrystallization of a silica 

gel deposited by-hot solutions highly supersaturated 

with silica (Butler and Singewald, 1940, p. 824-825). 

Ore bodies associated with this type of jasperoid 

apparently consist of pyrite, sphalerite, and galena 

and subordinate tennantite, argentite, and chalcopyrite, although this relationship is merely inferred 

and not directly stated by Butler and Singewald. 

They did state that this assemblage of ore minerals 

is characteristic of the nonbaritic ores and that 

barite is abundant in the euhedral jasperoid and not 

in the nodular jasperoid.

KOKOMO DISTRICT

(7, fig. 40)

The Kokomo district is a few miles north of 

Climax, near the south end of the Gore Range in 

Summit County. The White Quail Limestone Member, one of several limestones in a thick section of 

siltstone, shale, and arkose in the Pennsylvanian 

Minturn Formation, is the host rock for lead-zinc 

sulfide replacement deposits along northeast-trending 

faults and fractures. Masses of jasperoid are closely 

associated with some of these ore bodies, and, in 

places, jasperoid quartz forms the matrix for siliceous ore.

The ore zone was argillized before it was silicified, 

and silicification preceded deposition of the sulfides. 

Limestone beds above and below the ore zone show 

no visible alteration, suggesting that the mineralizing solutions moved updip from their feeding channels for some distance in the ore zone before reacting 

to form the ore bodies and their associated alteration (A. H. Koschmann, oral commun., 1959).

Kokomo jasperoid, where unoxidized, is typically 

medium to dark gray, coarse grained, vuggy, and 

heavily impregnated with pyrite, which ranges from 

tiny disseminated grains to masses an inch or more 

in diameter, and locally forms a network of veinlets 

cutting the quartz. Much of the pyrite is euhedral, 

with striated cube faces predominating, although 

these are locally modified by octahedral and pyritohedral faces. Breccia fragments of light-gray soft 

friable argillized wallrock are commonly incorporated in the jasperoid. Masses of coarse-grained calcite cement the jasperoid fragments in places, and 

most vugs in the jasperoid are encrusted with 

prismatic quartz crystals associated with pyrite and 

younger dark sphalerite.

In thin section the jasperoid quartz is coarse

grained, and it has a heterogeneous texture that 

grades from reticulated to xenomorphic. Many 

quartz grains contain carbonate particles, and some 

of the larger quartz grains have zone inclusions of 

allophane. Flakes of sericite, penecontemporaneous 

with the matrix quartz, are abundant. Pyrite, galena, 

and sphalerite inclusions are all younger than jasperoid quartz and seem to have formed in approximately the order in which they are listed. Veinlets 

of calcite and of quartz cut both the sulfides and the 

jasperoid.

Spectrographic analyses of two jasperoid samples 

from Kokomo show abnormally high concentrations 

of Fe, Mn, Ag, Bi, Ge, Pb, and Zn, and thus confirm 

that it is a favorable jasperoid.

LA PLATA DISTRICT

(8, fig. 40)

The La Plata district is in western La Plata 

County, about 20 miles northwest of Durango. Complex gold and silver ore has been mined, largely from 

vein deposits in sedimentary rocks that range in age 

from Pennsylvanian to Cretaceous, in an area cut by 

many dikes and sills of Tertiary felsic igneous rocks. 

The sedimentary rocks, which consist largely of siltstone, shale, and sandstone, are commonly silicified 

adjacent to the veins in zones as much as 3 feet thick. 

This silicification ranges in intensity from cementation to nearly complete replacement (Eckel, 1949, 

P. 77).

The Jurassic Pony Express Limestone Member of 

the Wanakah Formation has been largely replaced 

by sugary quartz and pyrite on Jackson Ridge, particularly on the slope south of Rush Basin (Eckel, 

1949, p. 111). Hydrothermal alteration and subsequent mineralization in the district closely followed 

intrusion of the Tertiary igneous rocks and are 

probably genetically related to the intrusives.

PANDO AREA

(14, fig. 40)

The Pando area of central Colorado is west of 

Kokomo, north of Tennessee Pass, and south of Red 

Cliff. It comprises about 50 square miles bounded 

approximately by the valleys of the Eagle River and 

Homestake Creek on the west, the east fork of the 

Eagle River on the south, the crest of the Gore Range 

on the east, and the divide south of Turkey Creek 

on the north. It is in Eagle County and includes the 

Camp Hale Military Reservation. A few small mines 

and prospects in pre-Pennsylvanian rocks in the 

western part of the area produced some oxidized 

lead, silver, and gold ore before 1900; but these
100 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

mines and prospects are now idle, and there is no 

mining activity in the area at present.

The Devonian Dyer Dolomite Member of the 

Chaffee Formation and the hydrothermally dolomitized Mississippian Leadville Limestone overlying it 

have been extensively replaced by jasperoid at many 

places along the valley of the Eagle River from its 

confluence with the East Fork of the Eagle River 

northward to the north boundary of the Pando area. 

Scattered bodies of jasperoid are also found in carbonate beds in the thick pile of dominantly clastic 

sedimentary rocks of the Pennsylvanian Minturn 

Formation overlying the Leadville Limestone to the 

northeast.

The jasperoid bodies of this area, together with 

those of the adjoining Oilman district (5, fig. 40), 

were first described by Crawford and Gibson (1925, 

p. 56-59), and their observations have been summarized in my section on the Oilman district (p. 

78). Tweto (1953), in a more recent study of these 

rocks, pointed out the association of jasperoid with 

previously hydrothermally dolomitized and brecciated rock, particularly in the permeable Oilman 

Sandstone Member of the Leadville Limestone and 

the adjacent dolomite beds of the Dyer below and the 

Leadville above. This zone and local channels in the 

old karst erosion surface at the top of the Leadville 

served as major conduits for the silicifying solutions.

Carbonate beds in the Pennsylvanian Minturn 

Formation are also strongly jasperoidized along 

faults near the heads of Cataract and Pearl Creeks 

and on North Sheep Mountain.

Silicification that resulted in the formation of 

jasperoid seems to represent a late barren stage in a 

long period of hydrothermal alteration that began 

with pervasive conversion of the Leadville Limestone into fine-grained dolomite, with subsequent recrystallization of the dolomite into "zebra rock," 

sanding of the dolomite along channels, and brecciation preceding silicification. Local fracturing and 

brecciation continued during silicification, which was 

followed by weak local sulfide mineralization. Tweto 

regarded this sequence as probable manifestations of 

fringe zone mineralization leaking updip from a 

major center of mineralization that lies buried beneath the thick section of Pennsylvanian rocks, to 

the northeast of Camp Hale. The scattered areas of 

alteration in the Pennsylvanian carbonate rocks may 

also represent leakage upward, along strong faults, 

from this same source.

Many varieties of jasperoid are present in the 

area, and some of the larger bodies exhibit several 

distinctive types and generations. Most of these 

varieties seem to be unfavorable; but small grains of

pyrite, cerussite, and cerargyrite occur locally, and 

barite is common (Tweto, 1953).

My samples from the Pando area exhibit wide 

variations in appearance. Some are mottled, some 

show thin alternating color bands like varves, some 

are silicified breccias that contain angular fragments 

of chert and older jasperoid, and some are megascopically homogeneous. The samples are white 

mixed with various shades of gray, brown, brick 

red, yellow, or orange. Most samples have aphanitic 

textures, but some are vuggy and have a saccharoidal 

texture like fine-grained quartzite.

Many of the Pando samples have a homogeneous 

aphanitic jigsaw-puzzle texture, which in some samples characterizes an older generation that is cut by 

veinlets and masses of coarser xenomorphic quartz. 

Wavy colloform banding is characteristic of some 

samples. Heterogeneous textures with abrupt variations in grain size characterize a few samples, and 

one of these has a strongly reticulated texture suggestive of favorable jasperoid. Common accessory 

minerals include hematite, pyrite, barite, chalcedony, 

and late orange goethite; flakes of sericite are 

scattered through the matrix in a few samples, and 

much of the aphanitic jasperoid quartz is clouded 

with abundant dust-sized inclusions of allophane, 

carbonaceous particles, or carbonate.

Spectroscopic analyses were obtained on three 

samples from the Pando area. One of these 

samples is from Dyer Dolomite Member near a small 

adit in the Eagle River Canyon near the north 

boundary of the area; the second is from an unmineralized body in the lower dolomitized part of the 

Leadville Limestone in the Eagle River Canyon a 

little farther south; and the third is from a body 

replacing a dolomite bed in the Pennsylvanian Minturn Formation on a ridge south of Pearl Creek in 

the east-central part of the area. The first of these 

is high in Ba, Be, Na, Sr, and Ti; the second is high 

in Ba, Be, Sr, Yb, and Zr; and the third shows no 

abnormally high concentrations of minor elements 

but is deficient in Fe, Ti, and Cr. Although none of 

these samples contain high concentrations of the 

indicator elements for productive jasperoid, it is 

highly probable that-some of the jasperoid bodies in 

the lower Paleozoic carbonate rocks along the Eagle 

River valley do contain them, and a detailed study of 

these bodies might outline favorable areas for exploration.

RICO DISTRICT 

(17, fig. 40)

The Rico mining district is in eastern Dolores 

County, in the western part of the San Juan Moun-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 101

tains, about 35 miles north-northwest of Durango 

and 30 miles southwest of Ouray. It lies about 20 

miles northward from the La Plata district (8, fig. 

40) in the same part of the San Juan Mountains.

According to Cross and Ransome (1905, p. 14-15, 

20), the major ore deposits of the district are blanket 

replacements of limestone and shale of the Pennsylvanian Hermosa Formation by silver-bearing galena 

associated with sphalerite and abundant pyrite. The 

sedimentary rocks in the district were intruded by 

sills of monzonite porphyry in late Tertiary time at 

the beginning of a domal uplift that culminated with 

profound faulting. Bedding-plane faults and northeast-trending normal faults, formed at this time, 

served as conduits for later mineralizing solutions 

that silicified the wallrocks and deposited the ores. 

Black shale, limestone, and monzonite porphyry sill 

rocks have locally been replaced by jasperoid.

Ransome (in Cross and Ransome, 1905, p. 14-15) 

stated:

In the form of jasperoid (a cryptocrystalline aggregate commonly associated with replacement deposits) quartz occurs in 

the Blackhawk mine and in the blanket of the Sambo mine. 

In the former mine, also, are found spongy, cavernous 

masses of rusty quartz, apparently due to the removal of 

limestone, by solution, from a network of quartz stringers. 

Quartz is abundant in some of the blanket breccias as a replacement of breccia material.

In a further description of the Blackhawk mine, 

Ransome (p. 19) stated that massive sulfide ore 

bodies have selectively replaced a limestone bed and 

that the limestone next to the ore is commonly 

changed to jasperoid.

UNCOMPAHGRE DISTRICT

(23, fig. 40)

The Uncompahgre mining district is in the northern San Juan Mountains near Ouray, the county seat 

of Ouray County. This district, like the Leadville 

district (9, fig. 40), is characterized by fissure vein 

deposits of copper, lead, zinc, gold, and silver. The 

deposits show a zonal arrangement around a center 

of mineralization that developed at the intersection 

of major northeasterly and northwesterly structural 

trends. High-temperature pyritic gold ore was deposited in the core area, which is surrounded by an 

intermediate zone of base-metal sulfides; this, in 

turn, is surrounded by a silver belt that forms the 

outer zone of commercial mineralization. Jasperoid 

bodies are largely confined to this outer zone (Burbank, 1940).

Jasperoid formed during a preore stage of hydrothermal alteration that was preceded or accompanied 

by leaching of carbonate rocks, which opened up

solution channels. This stage was followed by the 

formation of ankerite, sericite, pyrite, and barite 

immediately preceding the ore stage of mineralization. During the ore stage, pyrite, sphalerite, chalcopyrite, galena, tetrahedrite, pearceite, pyrargyrite, 

rhodochrosite, and manganocalcite were deposited. 

This was followed by the emplacement of late calcite, 

quartz, and barite (Burbank, 1940, p. 207).

At the Mineral Farm mine, about a mile south of 

Ouray, silicification and subsequent mineralization 

were localized by an unconformity between the Leadville Limestone and the overlying shales and siltstones of the Mississippian and Pennsylvanian Molas 

Formation. Small fractures in the top of the Leadville were opened up by hydrothermal leaching, and 

the overlying red shale of the Molas was silicified. 

The larger ore bodies formed in these open channels 

in the Leadville beneath the competent and impermeable caprock of silicified shale. The mineralized 

upper part of the Leadville is coarsely clastic and 

contains interbedded porous sandstone layers, indications that it was highly permeable during mineralization (Burbank, 1940, p. 209-210). I have three 

samples of partly oxidized jasperoid from the Mineral Farm mine, taken from the walls of a sulfide 

deposit that formed in one of these channels at the 

top of the Leadville Limestone. They range in color 

from light gray through light olive gray and from 

grayish orange to pale yellowish brown, have a distinctly saccharoidal texture, small sparse vugs, and 

visible disseminated grains of pyrite and galena. 

One sample contains angular breccia fragments of 

white, light-gray, and dark-gray aphanitic silica and 

coarse-grained white vein quartz with disseminated 

pyrite. This latter inclusion suggests that some pyrite 

must be older than the matrix jasperoid.

Thin sections reveal that the sample with the most 

abundant sulfides has a coarse heterogeneous reticulated texture, characteristic of favorable jasperoid; 

pyrite and galena in this sample show incipient 

alteration to limonite and cerussite, respectively, and 

the matrix quartz contains local concentrations of 

allophane and carbonate particles. The other two 

samples consist largely of rounded detrital-looking 

quartz grains cemented by aphanitic quartz that has 

a jigsaw-puzzle texture. These probably represent a 

silicified sandstone bed in the limestone.

The favorable jasperoid sample is rich in Ag, Cd, 

Co, Cu, Mo, Ni, Pb, Te, Zn, and Zr. The two samples 

of silicified sandstone contain abnormally high concentrations of Ti, Ag, Cu, Nb, Pb, Te, Zn, and Zr, but 

they do not yield as high a score on indicator elements as the favorable jasperoid sample.
102 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

OTHER OCCURRENCES

White sulfide-bearing jasperoid in the Pennsylvanian Hermosa Formation at the Black Queen mine, 

on the south slope of Sheep Mountain in northern 

Gunnison County, was reported by Vanderwilt 

(1937, p. 106, 116). He also mentioned a bed of 

barren white jasperoid in Pennsylvanian sedimentary rocks near the head of Yule Creek in the same 

area. Intensely silicified Cretaceous shale in the 

Wellington mine at Breckenridge (3, fig. 40), Summit County, was described by Levering (1934, p. 56), 

who stated that "Much of the limy shale has been 

strongly silicified near the veins and is converted into 

black jasperoid, locally called jasper." In the Sugar 

Loaf and St. Kevin districts (21, fig. 40), Eagle 

County, in the northern part of the Sawatch Range, 

the widespread occurrence of "chert" dikes, zones, 

and veins cutting Precambrian igneous and metamorphic rocks was reported by Singewald (1955, p. 

260). The larger "chert" zones are as much as 350 

feet wide, and Singewald ascribed their origin to 

replacement of the country rock along strong faults.

Burbank (1932, p. 72) described the replacement 

of Tertiary volcanic rocks by silica adjacent to faults 

in the Bonanza district (2, fig. 40), Saguache County, 

and (1941, p. 203) similar silicification forming 

"casings" around ore channels in quartz latite of the 

Red Mountain district (16, fig. 40), San Juan 

County.

Replacement of limestone by silica, adjacent to 

sulfide replacement deposits in limestone, in the 

Quartz Creek (15, fig. 40), Tincup (22), and 

Monarch-Tomichi (12) districts, Gunnison and Chaffee Counties, was noted by Dings and Robinson 

(1957, p. 60, 63-64, 69). Behre (1953, p. 99, 100) 

mentioned jasperoid in densely packed anhedral 

grains replacing the groundmass of porphyry near 

some ore bodies and also replacing carbonate rocks, 

particularly the Leadville Limestone, on the west 

slope of the Mosquito Range (13, fig. 40), Lake 

County, east and southeast of the Leadville district.

Jasperoid is also mentioned by Heyl (1964, p. C25) 

as a gangue mineral in oxidized zinc veins of the 

Massadona-Youghall deposit (11, fig. 40) in central 

Moffat County near the Yampa River. Brecciated 

upper Paleozoic limestone is both replaced and cemented by large masses of jasperoid that form the 

principal gangue of an oxidized zinc-lead replacement ore body at the Doctor mine in the Spring 

Creek district (20, fig. 40) north of Gunnison in 

Gunnison County (Heyl, 1964, p. C25, C28, C29). 

Heyl (written commun., 1967) also reported the 

presence of abundant jasperoid associated with oxidized zinc and lead deposits in the Lenado district

(10, fig. 40), Pitkin County, north of Aspen, the 

Sedalia district (18, fig. 40), Chaffee County, on the 

Arkansas River north of Salida, and the Carbonate 

district (4, fig. 40) on the White River Plateau in 

eastern Garfield County.

GEORGIA

CARTERSVILLE DISTRICT 

(1, fig- 41)

An economically important mining district in 

Georgia that contains large bodies of jasperoid is 

the Cartersville iron and manganese district about 

40 miles northwest of Atlanta in Bartow County in 

the southern Appalachian Mountains. The Cartersville district is largely underlain by folded and 

slightly metamorphosed shale, limestone, and dolomite of Cambrian age. The rocks were apparently 

folded in Carboniferous time; folding was closely 

followed by high-angle faulting and fracturing. 

These faults and fractures later served as conduits 

for hydrothermal solutions that formed fissure vein 

and replacement deposits of jasperoid, hematite, 

barite, siderite, pyrite, and base-metal sulfides. Deep 

weathering accompanied by supergene alteration and 

enrichment, during the Tertiary Period, produced 

commercial deposits of manganese oxide and brown 

iron ore (Kesler, 1950, p. 1-2).

Jasperoid bodies are not restricted to any one 

stratigraphic zone, although they are confined to 

carbonate rocks or to residual clay underlain by 

carbonate rocks in the vicinity of faults and fractures. They decrease in size and abundance from east 

to west across the district. Residual clays derived 

from weathering of carbonate rock contain irregularly distributed bodies of jasperoid ranging from 

small nodules to masses 20 feet in diameter.

Jasperoidization is related to deposition of primary ore and gangue minerals. Local preservation of 

original carbonate bedding textures and fossils in 

jasperoid gives clear indication of its replacement 

origin. Angular inclusions of barite and sulfidebearing vein quartz in jasperoid matrix show that 

some silicification took place subsequent to sulfide 

mineralization. However, similar inclusions of dense 

fine-grained jasperoid in a matrix of coarse-grained 

jasperoid also show that there was more than one 

period of silicification. Primary ore and gangue 

minerals consisting of sulfides, barite, vein quartz, 

and carbonate were introduced by hydrothermal solutions moving upward along faults and fractures. 

The deposition of these minerals preceded renewed 

faulting and brecciation, which was followed by 

silicification in the form of jasperoid of both vein
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 103

50

I

100 MILES

1. Cartersville

2. Gold Hill

3. Howie and Whitney

4. Brewer

EXPLANATION

Area of large mining district 

x

Minor district or area

Reported occurrence

LIST OF DISTRICTS, AREAS, AND OCCURRENCES

5. Haile 8. Eastern Tennessee

6. Bumpass Cove 9. Sweetwater

7. Central Tennessee 10. Austinville

FIGURE 41. Map showing location of jasperoid-bearing areas in Georgia, North Carolina, South Carolina, Tennessee,

and southwest Virginia.

carbonate and wallrock carbonate (Kesler, 1950, p. 

49-50).

Some jasperoids of the Cartersville district are 

thinly bedded and aphanitic, but most are massive 

and have a saccharoidal texture. The fresh rock is 

light to dark gray; but in the zone of alteration, and 

particularly in the residual clay, it is commonly 

heavily stained and colored by oxides of iron and 

manganese. Much of this weathered jasperoid consists of porous friable masses of ocherous quartz, 

coated with minute euhedral supergene quartz crystals; unweathered jasperoid does not contain these 

crystals. Coarse-grained massive jasperoid commonly 

contains angular breccia fragments of aphanitic 

jasperoid, and locally it also contains disseminated 

grains of pyrite, chalcopyrite, and tennantite. 

Coarser textured jasperoid replaced coarse vein 

carbonate; aphanitic jasperoid replaced carbonate 

host rock. Near the close of jasperoid deposition a 

late generation of crystalline barite, pyrite, and

hematite was locally deposited as crystals lining vugs 

in the jasperoid.

In thin section, jasperoid typically consists of 

minute anhedral interlocking grains of quartz, 

though locally the coarser textured variety faithfully 

preserves the form and even the cleavage of the 

coarse vein carbonate it replaced (Kesler, 1950, p. 

48, pi. 13D).

OTHER OCCURRENCES

Pardee and Park (1948, p. 131-140) described 

some lode gold deposits in Precambrian schists and 

associated felsic intrusive rocks in Lumpkin County 

in northern Georgia, in which the gold occurs in irregular veins and lenticular masses in silicified wallrock. Both the schists and associated intrusives are 

locally replaced by, as well as impregnated with, 

silica; however, most of the quartz lodes appear to 

be fracture fillings rather than replacement bodies.
104 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

46'

44'

112°

x5 i

HAMTTE |

'--

; B i N G H

50 

I

100 MILES 

_I

EXPLANATION

x 

Minor district or area

 

Reported occurrence

FIGURE 42. Map showing location of jasperoidbearing areas in Idaho and Montana. 1, Bayhorse; 2, Challis; 3, Lemhi; 4, Skull Canyon; 

5, Phillipsburg.

IDAHO

A search of the literature has failed to reveal any 

description of replacement bodies of jasperoid in the 

mining districts of Idaho, although the existence of 

such bodies in Paleozoic carbonate rocks of Custer 

County may be inferred from references in various 

reports. Umpleby (1917, p. 80) stated that the copper veins in Skull Canyon (4, fig. 42) near Mackay, 

are composed of heavily iron stained jaspery material enclosing irregular lenses and slabs of limestone 

and large bunches of hematite. Ross (1937, p. 101) 

wrote of the lead-silver replacement deposits in 

Custer County in the Bayhorse Dolomite near the 

town of Bayhorse (1, fig. 42): "Commonly the rock 

in and near the ore is more or less completely silicified, silicification being evidently one of the earliest 

and volumetrically one of the greatest effects of the 

mineralizing solutions." In a report on fluorspar 

deposits in this same formation in Custer County 

near Challis (2, fig. 42), Anderson (1954, p. 11)

mentioned, but did not describe, silicified ledges of 

dolomite.

It seems logical that jasperoid should also occur 

with the lead and zinc replacement deposits in 

Paleozoic carbonate rocks in Lemhi County; however, the only "jasperoid" mentioned in association 

with ore deposits in Lemhi County (3, fig. 42) is in 

Precambrian quartzite of the Belt Supergroup. Sharp 

and Cavender (1962, p. 21, 22, 25, 40) discussed 

copper-gold-thorium vein and replacement deposits 

in micaceous quartzite associated with "dense brown 

jasperoid" formed by the silicification of hydrous 

iron oxide gangue.

ILLINOIS, IOWA, KENTUCKY, AND WISCONSIN

Three districts in which base-metal sulfide ore 

deposits are locally associated with jasperoid have 

been reported in the region that comprises Illinois, 

Iowa, Kentucky, and Wisconsin. (1) The upper 

Mississippi Valley zinc-lead district (3, fig. 43) in 

southwestern Wisconsin and northwestern Iowa, 

where zones of thin veins, breccias, and replacement 

deposits of sphalerite, galena, pyrite, and barite are 

found in carbonate rocks of Ordovician age. (2) The 

Kentucky-Illinois district (2, fig. 43), in northwestern Kentucky and adjacent parts of southeastern 

Illinois, in which many fissure veins and a few replacement deposits of fluorite are associated with 

sphalerite, barite, galena, and jasperoid in Mississippian carbonate rocks. (3) The central Kentucky mineral district (1, fig. 43), where barite, fluorite, and 

base-metal sulfide veins cut Ordovician limestone, 

and where breccia fragments of limestone in some 

of these veins are locally replaced by jasperoid.

UPPER MISSISSIPPI VALLEY DISTRICT

(3, fig. 43)

Siliceous replacement of carbonate rocks in this 

district is confined to the sulfide ore bodies and the 

wallrock adjacent to them. Jasperoid is most 

abundant in dolomite of the Lower Ordovician 

Prairie du Chien Group. The overlying Ordovician 

St. Peter Sandstone has been locally silicified along 

major faults and fracture zones; the carbonate rocks 

of the Ordovician Platteville and Decorah Formations and the Galena Dolomite, above the St. Peter 

Sandstone, have been replaced by jasperoid to a much 

smaller degree than those of the Prairie du Chien 

Group, geiierally within, and adjacent to, the larger 

sphalerite ore bodies. Jasperoid is most prevalent 

along faults, shears, and shatter zones, extending 

outward from these channels along selected beds for 

short distances. In the Galena Dolomite, dark-gray 

pyritic jasperoid locally forms overgrowths on older
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 105

50 

I

100 MILES

FIGURE 43. Map showing location of large jasperoid-bearing mining districts in Illinois, Iowa, Kentucky, Wisconsin, and southeastern Missouri. 1, Central Kentucky; 2, Kentucky-Illinois; 3, Upper Mississippi Valley; 

4, Southeastern Missouri.

sedimentary chert nodules in intensely mineralized 

areas. Silicified zones in the Platteville and Decorah 

Formations are notably more abundant in the southern part of the district than in the northern part. 

Where the larger reverse faults flatten along bedding 

planes, the wallrock is commonly replaced by jasperoid in ore bodies. In such areas, as in the TriState district, all the lithologic units that are cut by 

the faults are replaced by gray or brown jasperoid

or by white "cotton rock," but, unlike the Tri-State 

district, jasperoid is very abundant in only a few 

deposits.

Jasperoid is massive, dense, locally banded, brown 

or gray, and, because it commonly preserves both the 

color and texture of the host rock so faithfully, it 

can be distinguished from unaltered rock only by its 

superior hardness. At one locality (the Hoskins 

mine), jasperoid preserves the original appearance
106 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

not only of the carbonate rocks but of interbedded 

carbonaceous shale as well. Thin sections of jasperoid 

show a grain-for-grain equal volume replacement of 

the host rock (Heyl, and others, 1959, p. 101-105).

KENTUCKY-ILLINOIS DISTRICT 

(2, fig. 43)

Jasperoid in western Kentucky was first reported 

by Smith (1905, p. 128, 139-140). He noted its replacement of limestone adjacent to fissure veins and 

of breccia fragments within the veins and concluded 

(p. 139): "This silicification of limestone by quartz 

is believed to be related to the process of fissure 

filling, and not to be a common characteristic of the 

limestones of the district."

According to Fohs (1910, p. 382, 384), fluorite, 

barite, zinc, and lead veins and a few replacement 

deposits in Mississippian limestone are irregularly 

distributed through an area about 80 miles long, east 

and west, by about 50 miles wide, north and south. 

Most of the production from this district has come 

from mines in Caldwell, Crittenden, and Livingston 

Counties in Kentucky and in Hardin, Pope, and 

Saline Counties in Illinois. Jasperoid and fluorspar 

are associated both genetically and spatially with 

many of these deposits. The jasperoid and fluorspar 

probably were deposited penecontemporaneously, at 

least in part. In some localities, laminated limestone 

is replaced by alternating bands of jasperoid (or 

quartz) and fluorspar.

Hardin (1955, p. 24) estimated that 5-20 percent 

of the limestone within 10 feet of many of the veins 

had been replaced by cryptocrystalline quartz. He 

believed that this silicification largely preceded the 

deposition of fluorite.

The paragenesis of ore and gangue minerals from 

this district and the composition of their primary 

fluid inclusions have been studied by Hall and Friedman (1963). They believed that several recognizable 

generations of fluorite preceded the deposition of 

vein quartz and sulfides, which was followed by 

deposition of late fluorite, calcite, barite, and witherite. They concluded (p. 902) that the fluids trapped 

in the early fluorite are mainly connate brines, that 

a water of different and possibly magmatic origin 

was introduced during the quartz-sulfide stage, and 

that the composition of the fluid returned to that of 

a normal brine during formation of the late gangue 

minerals.

Silicified breccia pipes and dikelike bodies are 

present near the center of Hicks dome, a broad structural dome in western Hardin County, 111. The host 

rock of these breccia bodies is cherty Devonian limestone, and in drill-core samples below the zone of

oxidation, the bodies consist largely of angular 

breccia fragments of chert and partly silicified host 

rock in a matrix of fine-grained iron-stained microcrystalline quartz, with accessory fluorite and apatite 

and minor sulfides. Locally, this breccia is slightly 

radioactive, although no uranium-minerals have been 

recognized in it. The breccias are considered to be 

explosion breccias formed by the explosive venting 

of steam and hot gases possibly related to deeply 

buried igneous intrusive rocks (Brown and others, 

1954; Bradbury and others, 1955, p. 1-8).

CENTRAL KENTUCKY DISTRICT 

(1, fig. 43)

This district covers an area of about 3,600 square 

miles extending from Owen and Henry Counties on 

the north to Lincoln County on the south and from 

Bourbon and Clark Counties on the east to Anderson 

and Mercer Counties on the west. This large area 

roughly follows the trend of the Cincinnati arch and 

is best developed near the Lexington dome.

Ore deposits within the district consist largely of 

fracture fillings in veins or of breccia-zone replacements along numerous faults and fractures. These 

deposits show a zonal arrangement outward from a 

central zone characterized by fluorite, calcite, and 

black sphalerite through a transition zone of fluorite, 

barite, calcite, and both light and dark sphalerite, to 

a broad peripheral zone of barite, galena, and lightcolored sphalerite with little fluorite (Jolly and Heyl, 

1964, p. 597, 605, 615). The host rocks for these 

deposits are of Ordovician age and consist largely of 

limestone.

Jasperoid is not abundant in the Central Kentucky 

district, but it does occur in a few of the breccia 

zones in the veins. Jolly and Heyl (1964) stated that 

gray jasperoid replaces breccia fragments of limestone and older ore and gangue minerals, and that 

this jasperoid is probably younger than most of the 

fluorite, barite, and sulfide minerals. They ascribed 

the origin of these deposits to hydrothermal solutions, mainly heated connate brines and a lesser magmatic solution fraction, ascending along faults from 

a deep-seated magmatic source centered beneath the 

Lexington dome.

MICHIGAN

The word "jasperoid" was originally coined by 

Spurr (1898) because of the resemblance of this rock 

to the Precambrian jasper of the iron formations in 

Michigan and Minnesota. Although the jasper beds 

of the iron formation are now considered by Huber 

(1959, p. 111-113) to be of syngenetic origin, some 

Precambrian dolomites in the Michigan iron ranges
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 107

have been extensively silicified in places, subsequent 

to their lithification. Leith (1925, p. 515-516) 

described silicified chert breccias in the upper part 

of the Randville Dolomite on the Menominee Range 

and in the upper part of the Kona Dolomite in the 

Marquette district of Marquette County in the Upper 

Peninsula (fig. 1). These siliceous replacements he 

ascribed to the action of silica-bearing ground water 

on residual chert rubble accumulating on an old 

erosion surface. However, Gair, Thaden, and Jones 

(1961, p. C79-C80), after a detailed study of silicification in the Kona Dolomite, concluded that the 

silicification was more probably caused by silicabearing solutions migrating laterally or upward 

along faults and fractures.

MISSOURI

Jasperoid is abundantly associated with bedded 

sulfide replacement deposits in the vicinity of Joplin, 

in southwestern Missouri. These deposits are within 

the big Tri-State district or province (2, fig. 36), 

which has been discussed previously in the present 

report. Copper, lead, and zinc sulfide deposits are 

also concentrated in southeastern Missouri, in St. 

Francois and Washington Counties; most of these 

are vein deposits in carbonate rocks of Cambrian and 

Ordovician age.

SOUTHEASTERN MISSOURI DISTRICT 

(4, fig. 43)

The genesis of much of the silica in the carbonate 

host rocks for the sulfide deposits in this area is 

controversial. Buckley (1909, p. 51-52, 59-60) mentioned the association of lead deposits with pipelike, 

sheetlike, and lenticular chert bodies in dolomite beds 

of the Potosi, Bonneterre, and Gasconade Dolomites. 

These "chert" bodies in the Potosi he described as 

irregular crosscutting bodies of honeycombed chert 

with drusy quartz nodules. In describing the deposits 

of the Gasconade Dolomite, he (p. 60) wrote: "The 

horizons at which occur lens-like masses or pockets 

of chert have associated with them galena, blende, 

and barite." Buckley (p. 225-226) concluded that 

both silicification and later sulfide deposition in the 

Potosi resulted from ground-water circulation in 

Pennsylvanian or pre-Pennsylvanian time. However, 

he (p. 225-233) attributed similar deposits in the 

Bonneterre Dolomite to metasomatic replacement of 

dolomite (by downward percolating solutions) in 

post-Pennsylvanian time.

Spurr (1926, p. 974) stated that these deposits in 

general are characterized by the lack of major 

gangue minerals or wallrock alteration, and he attributed their origin to the injection of a fluid sulfide

ore magma. However, he (p. 975) also stated that 

"silicification of wall rocks took place during the 

deposition of the original sulphides."

Ohle and Brown (1954, p. 219-221), in a paper 

on the lead deposits of the main Southeast Missouri 

district, ascribed the origin of the ore to aqueous 

fluids that rose from a deep source and migrated 

laterally along favorable structures. However, they 

did not mention silicification in their discussion of 

wallrock alteration. Brown (1958, p. 6-7) proposed 

that hot mineralizing fluids rose from an igneous 

basement along favorable structures and spread 

laterally; then, as these fluids cooled and mingled 

with ground water, they changed to downwardmoving mineralizing solutions that deposited the ore. 

Heyl, Delevaux, Zartman, and Brock (1966, p. 952) 

mentioned a marked similarity in isotopic composition of lead derived from two galena samples in this 

area, one from an alkalic peridotite dike and the 

other from a bedded replacement ore body in dolomite.

The Cornwall copper mines, in Madison County 

near the east edge of this district, have been described by Rust (1935). They are mostly copperiron-zinc sulfide deposits in pockets and lenses along 

favorable stratigraphic zones in massive Ordovician 

dolomites. Solution of the dolomite preceded ore 

deposition. The remaining pillars between these solution cavities locally collapsed forming "crush breccias"; the dolomite in these breccias was then 

replaced by silica to form a dense aphanitic rock 

containing abundant angular breccia fragments of 

primary chert. The sulfides were then deposited in 

the remaining open cavities as colloids by fartraveling hydrothermal solutions contaminated with 

ground water.

Although there is considerable argument as to the 

origin of the base-metal sulfide and barite deposits 

of southeastern Missouri, there seems to be general 

agreement that bodies of silica replacing carbonate 

rocks are associated, both spatially and genetically, 

with many of them.

MONTANA

I know of only one mining district in Montana that 

is characterized by the development of jasperoid; 

this is on the west flank of the Flint Creek Range 

near Philipsburg in Granite County, about 50 miles 

northwest of Butte. The Philipsburg (or Flint 

Creek) mining district and several smaller districts 

are in this area. There probably are other jasperoidbearing areas in the State, but they are not described 

in the literature. Much of the following data on the
108 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

Philipsburg district is from W. C. Prinz (written 

commun., 1967; 1967, p. 2-10).

PHILIPSBURG DISTRICT

(5, fig. 42)

The Philipsburg district has yielded $70 million in 

base and precious metals from steeply dipping quartz 

veins in Tertiary granodiorite and intruded Precambrian rocks and Paleozoic limestone, shale, and 

quartzite and from quartz-rich bedding veins in 

Paleozoic limestone. In addition, the district has 

produced substantial amounts of manganese oxide 

ore that was derived from the weathering of primary manganese carbonate replacement deposits in 

Paleozoic limestone and marble.

Two types of favorable jasperoid are recognized 

in the district, but nowhere is jasperoid abundant. 

One type is associated with primary manganese and 

vein deposits and is most abundant in the manganese 

deposits, where it consists of light- to medium-gray 

or greenish-gray silicified limestone that is commonly brecciated and cemented by rhodochrosite and 

manganoan dolomite. In a few places jasperoid also 

occurs along the borders of steeply dipping quartz 

veins where they cut carbonate rocks. Some of this 

jasperoid is brown, probably owing to admixed very 

fine grained sphalerite.

The second type of jasperoid in the Philipsburg 

district is associated with the oxidized manganese 

deposits. Medium- to dark-gray silicified limestone 

occurs locally along the borders of these deposits 

and in remnants, veinlets, or cavity fillings within 

the deposits. That some jasperoid fills cavities in 

manganese oxides shows that it is, at least in'part, 

supergene in origin.

Emmons and Calkins (1913, p. 68-69) also referred to the prevalence of abundant irregular 

masses of "chert" in the upper part of the Madison 

Limestone along Flint Creek 6 miles south of Philipsburg and to one large mass of this "chert" nearly 100 

feet thick along a fault that forms the contact between Madison Limestone and Precambrian rocks, 

near the mouth of Boulder Creek 8 miles north of 

Philipsburg. The mass along Boulder Creek, they 

said, is probably the result of silicification along the 

fault zone. The irregular masses of "chert" in the 

upper part of the Madison they described as consisting chiefly of fine-grained cryptocrystalline quartz 

in allotriomorphic grains, mixed with some carbonate. From these descriptions it seems probable that 

much of the "chert" in the Madison is really unfavorable jasperoid.

NEVADA

Information is available on jasperoid bodies in at 

least 33 mining districts in Nevada besides the Ely 

(Robinson) (19, fig. 44) and Eureka (20) districts, 

which are previously described in this report. Silicified rocks that are probably jasperoid also have been 

noted, but not described, in another 20 districts (fig. 

44). These districts are scattered throughout most of 

the State east of long 118° W. and north of lat 

37°30' N., but they seem to be most concentrated in 

two provinces. One province comprises most of 

Eureka and White Pine Counties as well as parts of 

Elko, Lander, and Lincoln Counties in eastern and 

north-central Nevada, and it extends eastward into 

Utah. A second province comprises Esmeralda 

County and the eastern part of Mineral County in 

southwestern Nevada, and it extends southward into 

California.

In most of these districts, jasperoid is associated 

with either silver-bearing or non-silver-bearing basemetal replacement deposits in Paleozoic carbonate 

rocks and in felsic volcanic rocks. The jasperoid in 

these districts generally is localized by faults or fracture zones that also served as conduits for the orestage mineralizing solutions, and in many districts 

it also seems to be related to intrusive siliceous dikes 

and stocks. The Atlanta (2, fig. 44), Delmar (14), 

and Getchell (23) districts are mainly gold producers; Boyer (5) is a nickel-cobalt district; in the 

Cortez district (12) antimony, silver, and gold are 

abundant; the Manhattan district (34) produced 

gold, arsenic, and antimony; and the Taylor district 

(47) produced antimony, lead, and silver.

ATLANTA DISTRICT

(2, fig. 44)

The Atlanta mining district lies close to the Utah 

border in northeastern Lincoln County about 40 

miles northeast of Pioche. Silicified pipes, faults, and 

fracture zones in Ordovician limestone and dolomite 

were mined for gold and silver in the early part of 

the 20th century, and small silicified pods containing 

uranium were developed during the 1950's (Hill, 

1916; Sharp and Myerson, 1956).

Hill (1916, p. 116-117) mentioned prominent 

bodies of jasperoid along a north-trending fault zone 

in the vicinity of the Atlanta mine, and argentiferous 

red jasper bodies in quartzite at the Bradshaw mine 

about a mile south of Atlanta. According to Sharp 

and Myerson (1956, p. 10), breccia pipes and fault 

zones in dolomite overlying the quartzite are extensively silicified into drusy quartz and jasperoid in 

the area of mineralization, and some of the silicified 

pipes contain gold, silver, and uranium minerals
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 109

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1. Antelope

2. Atlanta

3. Bald Mountain

4. Belmont

5. Boyer

6. Candelaria

7. Cedar Mountain

8. Chief (Caliente)

9. Cherry Creek

10. Columbia

11. Contact

12. Cortez

13. Delano 

14. Delmar

LIST OP DISTRICTS, AREAS, AND OCCURRENCES

15. Diamond

16. Dolly Varden

17. Duck Creek

18. Dyer

19. Ely (Robinson)

20. Eureka

21. Ferguson

22. Fireball

23. Getchell (Potosi)

24. Gilbert

25. Gold Banks

26. Goodsprings

27. Groom

28. Kern

29. Kingston

30. Klondike

31. Lewis

32. Lida

33. Lone Mountain

34. Manhattan

35. Mill Canyon

36. Mineral Hill

37. Mount Hope

38. Mud Springs

39. Nevada

40. Patterson

41. Santa Fe

42. Sheba-De Soto

43. Silverhorn

44. Silver Peak

45. Spruce Mountain

46. Success

47. Taylor

48. Tecoma

49. Ward

50. West Ward

51. White Pine (Hamilton)

52. Willow Creek

53. Wyndypah

54. Yerington

FIGURE 44. Map showing location of jasperoid-bearing areas in Nevada.
110 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

disseminated in the jasperoid. At the Atlanta mine, 

breccia fragments of limestone, quartzite, rhyolite, 

and jasper are cemented by quartz containing gold 

and silver minerals, manganese oxides, limonite, and 

barite'. Northeast-trending reefs of red jasperoid east 

of the Atlanta mine contain some low-grade gold ore 

(Hill, 1916, p. 117).

BALD MOUNTAIN DISTRICT

(3, fig. 44)

The Bald Mountain district is in the northwest 

corner of White Pine County, near the south end of 

the Ruby Range and about 60 miles northwest of Ely. 

Ordovician limestone is here intruded by a quartz 

monzonite stock. Sulfide deposits form replacement 

ore bodies in the limestone and vein ore bodies in the 

stock and its aureole of lime-silicate rock. Some of 

the ore bodies in the limestone consist of pockets of 

copper carbonate in jasperoid (Hill, 1916, p. 159- 

160).

Four jasperoid samples from this district are included in my collection; one of these is from a shaft 

dump, the other three are from outcrops a few 

hundred feet, a quarter of a mile, and half a mile 

from the nearest mine workings. The dump sample 

consists of medium-gray aphanitic jasperoid which 

is cut by veinlets of brown limonite and which contains sparse small vugs filled with white clay. The 

other three samples are jasperoid breccias in which 

both breccia fragments and matrix are dense and 

aphanitic. The fragments are shades of gray, and the 

matrix is yellowish brown, moderate brown, or reddish brown, locally banded and streaked.

In thin section the sample from the mine dump 

consists of heterogeneous xenomorphic quartz that 

has an average grain diameter of about 0.03 mm. It 

contains locally abundant carbonate particles and 

sparse scattered grains of pyrite and zircon. Two 

of the outcrop samples, taken from breccia zones, 

contain fragments of jasperoid similar to those in the 

dump sample, as well as aphanitic cherty fragments, 

and masses of feathery-textured jasperoid (apparently derived from chalcedony). The matrix has 

texture and grain size similar to those of the older 

jasperoid fragments. It is heavily loaded with dustsized particles of brown limonite and carbonate, and 

also contains abundant inclusions of a pale-yellowish 

mineral with low anomalous birefringence, which is 

probably one of the chlorite group. The matrix is cut 

locally by jarosite veinlets. The remaining outcrop 

sample consists of dense cherty-looking quartz containing abundant tiny particles of brown limonite, 

goethite, and sericite. This matrix has been shattered, 

and the fractures have been filled with a mixture

of limonite, goethite, cryptocrystalline apatite, and 

kaolinitic clay in various proportions.

All four samples are slightly richer than average 

in copper, nickel, and zirconium. One of the outcrop 

samples from a breccia zone contains detectable 

amounts of the rare-earth elements cerium, 

lanthanum, yytrium, and ytterbium as well as 

arsenic, molybdenum, and vanadium. The sample last 

described above, which is the farthest from mine 

workings, contains abundant phosphorus and 

strontium as well as detectable amounts of gallium, 

scandium, vanadium, yttrium, and ytterbium. None 

of the samples scored higher than +10 on their 

indicator elements, and the dump sample scored 

only +5.

BOYER DISTRICT

(5, fig. 44)

The Boyer district is in northeastern Churchill 

County, about 30 miles southeast of Lovelock. Nickel 

and cobalt ore occurs here in small veinlets cutting 

quartzite and silicified limestone near an intrusive 

body of diorite (Ferguson, 1939, p. 8, 12). Within the 

partly silicified limestone are conspicuous bodies of 

dense white silica that may be either bleached chert 

or jasperoid. Silicification of the limestone in and 

around the Nickel mine in Cottonwood Canyon was 

specifically mentioned by Ferguson (p. 17, 20), but, 

unfortunately, no description or analysis of this 

jasperoid was included in his report.

CANDELARIA DISTRICT

(6, fig. 44)

Candelaria is about 50 miles west of Tonopah in 

southeastern Mineral County. Deposits of gold, silver, lead, and zinc are present here in veins cutting 

highly altered Ordovician, Permian, and Triassic 

rocks, which originally consisted predominantly of 

shale and a few thin beds of carbonate rocks and 

sandstone. Within the mineralized area the shale 

has been intensely silicified, sericitized, argillized, 

carbonatized (Page, 1959, p. 21, 44-46), and stained 

gray and black by manganese. The most extensive 

alteration in the area is carbonatization, which has 

converted large volumes'of argillite and associated 

fine-grained metadolorite intrusive rock to a dense 

fine-grained grayish-white hydrothermal dolomite. 

Bodies of jasperoid resembling fine-grained quartzite 

nearly everywhere form prominent outcrops associated with the hydrothermal dolomite. These jasperoid bodies are particularly conspicuous near the 

Lucky Hill mine.
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 111

CEDAR MOUNTAIN DISTRICT

(7, fig. 44)

Cedar Mountain is in eastern Mineral County 

about 20 miles northeast of Mina. Triassic limestones and interbedded quartz keratophyres have 

been intruded by granodiorite, which is cut by dikes 

of aplite, lamprophyre, alaskite porphyry, and diorite porphyry. Replacement deposits of argentiferous 

galena and sphalerite are encased in a dark-gray 

fine-grained jasperoid replacing limestone adjacent 

to dikes and fractures. These latter have been cut 

and offset in places by postmineral faults (Knopf, 

1922, p. 370-373).

CHERRY CREEK DISTRICT

(9, fig. 44)

Cherry Creek is in northern White Pine County, 

about 30 miles east of the Bald Mountain district 

(3) and 40 miles north of Ely, at the south end of 

the Cherry Creek Range. The ore deposits of the 

district consist largely of fissure veins of lead, zinc, 

and silver in lower Paleozoic quartzite and shale and 

in small bodies of quartz monzonite that locally 

intrude these rocks. Contact-metamorphic bodies of 

scheelite were mined in the 1950's. A few manto-type 

replacement deposits of base and precious metals 

have also been developed in the northern part of the 

district in a massive lower Paleozoic limestone overlying the shale, and it is with these deposits that 

jasperoid is associated. The geology and ore deposits 

of the Cherry Creek district have been summarized 

by Hill (1916, p. 161-172) ; however, most of the 

ore deposits in limestone have been developed since 

that report was written. The only mine of this type 

described by Hill is the Biscuit mine, of which he 

(p. 166) stated that lenslike bodies of white quartz 

occur in limestone, and these lenses locally contain 

disseminated particles of a soft black metallic silver 

mineral.

I have five jasperoid samples from the Cherry 

Creek district, taken from localities in the limestone north and west of the mines described by Hill 

(1916). Three are from outcrops adjacent to mine 

workings, one is from the dump of a prospect pit, 

and one is from a breccia zone along a gently dipping 

fault near a small quartz monzonite dike, about half 

a mile from the nearest mine workings. All five 

jasperoid bodies sampled appear to have been localized by breccia zones along faults in the limestone.

Three distinct ages and types of quartz are distinguishable in jasperoids from this district. The 

oldest of these is dark gray and dense, and has a 

homogeneous xenomorphic texture, an average grain

size of about 0.02 mm, and abundant tiny inclusions 

of sericite and hematite. This type is cut by, and 

locally forms inclusions in, a light- to medium-gray 

compact coarse-grained jasperoid that has a heterogeneous, strongly reticulated texture and a grain 

diameter that averages about 0.1 mm and ranges 

from 0.01 to 1 mm; it contains abundant carbonate 

particles locally concentrated in the cores of the 

larger grains. This type commonly contains relict 

inclusions of coarse crystalline calcite. The youngest 

generation of quartz has a coarse xenomorphic texture, an average grain diameter of about 0.2 mm, 

and sparse local concentrations of allophane dust. It 

fills veinlets cutting the older jasperoid and commonly lines sparse small vugs.

The two types of jasperoid were not analyzed 

separately, and therefore, no comparison of their 

chemical composition is possible. Analyses of the 

five whole-rock samples show that most are anomalously high in Ag, Pb, and Zn, as well as Ca, Mg, and 

Sr. The high concentration of Ca, Mg, and Sr reflects 

the abundance of calcite in the samples. Silver (lead, 

and zinc) may be useful indicator elements in jasperoids of the Cherry Creek district; all four samples 

taken in the vicinity of mine workings are anomalously high in silver, which was not detected in the 

sample taken half a mile from the nearest mine.

CONTACT DISTRICT 

(11, fig- 44)

The Contact district is in northeastern Elko 

County about 15 miles south of the Idaho State line 

and 40 miles west of the Utah State line. The ore 

deposits consist of copper oxides and carbonates 

in replacement deposits and veins cutting Paleozoic 

limestone close to the contact with a small granodiorite stock. Limestone adjacent to the intrusive contact is metasomatized to a lime-silicate skarn, but 

beyond this contact zone, jasperoid is abundant. 

Schrader (1912, p. 118, 121, 130, 137) spoke of 

conspicuous bodies of silicified limestone in the Blue 

Bird, Brooklyn, Queen of the Hills, Ivy Wilson, and 

War Eagle mines. Some of this jasperoid he described as light colored and fine grained, resembling 

quartzite, and some as blue and chloritic. Both 

silicification and ore mineralization in the district 

seem to be genetically related to the intrusion of 

the stock.

CORTEZ AND MILL CANYON DISTRICTS

(12 and 35, fig. 44)

The old mining districts of Cortez (12) and Mill 

Canyon (35) straddle the county line between Eureka and Lander Counties, a few miles north of the
112 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

40th parallel and about 40 miles south-southeast of 

Battle Mountain. The Cortez district is just south 

of Mount Tenabo, a prominent peak at the south 

end of the Cortez Range; the Mill Canyon district 

is on the northern flanks of Mount Tenabo.

The geology and ore deposits of these two districts 

have been summarized by Emmons (1910, p. 100- 

108), and the general geology of the area is discussed 

in more detail by Gilluly and Masursky (1965). 

Emmons reported that the ore bodies of the Cortez 

district consist of irregular bedded replacement deposits in Paleozoic limestone. These deposits are 

localized by northeast-trending fractures, and consist 

of galena, sphalerite, stibnite, stromeyerite, tetrahedrite, and other arsenic antimony sulfosalts, associated with pyrite and calcite, in a siliceous 

(jasperoid) matrix. A number of small silver deposits in jasperoid were mentioned "on the trail 

between Cortez and Mill Canyon." In the Mill Canyon 

district argentiferous base-metal sulfide deposits in 

a siliceous gangue are localized by the intersection 

of fractures with favorable beds in limestone close 

to its contact with an intrusive granodiorite stock.

A few miles west of the Mill Canyon district, the 

Roberts Mountain thrust fault brings Ordovician 

siliceous shale and chert in the upper plate over 

Silurian shale and Devonian limestone in the lower 

plate. Both upper and lower plates are broken by 

high-angle normal faults and are intruded by small 

dikes and lenticular masses of Tertiary felsic plutonic rocks. Geochemical mapping of altered rocks 

close to these faults and intrusive masses in both 

upper and lower plate rocks has defined pronounced 

copper, lead-zinc-silver, arsenic, bismuth, and manganese anomalies in the siliceous rocks of the upper 

plate close to the trace of the thrust fault and gold, 

arsenic, antimony, and tungsten anomalies in the 

carbonate rocks of the lower plate adjacent to a 

strong northeast-trending normal fault (Erickson 

and others, 1961, 1964b).

Thirteen samples of jasperoid are included in the 

suite from the lower plate rocks collected and analyzed by Erickson and his colleagues (1964a). Most 

of these samples contain anomalously high concentrations of As, Ba, Sb, and Zr, and many of them 

are also high in B, Be, V, and W. Only five of the 

13 samples score as possibly or probably favorable 

on the basis of their indicator-element concentrations. Only two of these samples were described as 

conspicuously vuggy, and these two yielded the highest scores, +12 and +9, respectively. Four of the 

five jasperoid samples scoring +5 or higher came 

from close to the strong northeast-trending fault in 

the area with the strongest geochemical anomaly

(Erickson and others, 1964b, p. B93). Although no 

gold assays are reported on these samples, the recent discovery of a large low-grade gold ore body in 

the area suggests that gold is also present.

DELMAR DISTRICT 

(14, fig. 44)'

The Delmar district is in south-central Lincoln 

County about 40 miles southwest of Pioche. Most 

of the production from the district has been of gold 

ore from veins and breccia zones in the Lower 

Cambrian Prospect Mountain Quartzite; however, 

evidence of mineralization is also found in Middle 

Cambrian shale and limestone above this quartzite 

(Callaghan, 1937, p. 33, 40, 45-49).

The quartzite breccia fragments are commonly 

cemented and partly replaced by fine-grained vuggy 

ore-bearing silica, and some limestone beds in the 

thick shale units have been completely replaced by 

jasperoid in places. The thick Middle and Upper 

Cambrian Highland Peak Formation has locally been 

converted to aphanitic dark-gray jasperoid along 

faults and breccia zones in the southern part of the 

district, particularly near the wash northeast of Big 

Lime Mountain (Callaghan, 1937, p. 45). A small 

body of rhyolite on the Jumbo claim has been completely replaced by silica with preservation of the 

original quartz phenocrysts.

DOLLY VARDEN DISTRICT 

(16, fig. 44)

The Dolly Varden district is in southeastern Elko 

County in a small group of mountains at the south 

end of Goshute Valley about 35 miles southwest of 

Wendover. The general geology and ore deposits of 

the area were summarized by Hill (1916, p. 76-88).

A small quartz monzonite stock in the northern 

part of the district is in intrusive contact with 

Carboniferous shale and limestone near the center of 

the district. These sedimentary rocks form the bedrock in the rest of the district, south and east of Dolly 

Varden Pass. Close to the edge of the intrusive these 

rocks have locally been contact metasomatized to 

skarn, hornfels, and white marble. In the southeastern part of the district, around Castle Peak, the 

unmetamorphosed sedimentary rocks consist of a 

thick section of medium-bedded limestone overlain 

by calcareous and cherty shale and argillite. Oxidized 

copper ore bodies are associated with lime-silicate 

rocks near the intrusive, and bedded replacement 

lead deposits occur in limestone in the southeastern 

part of the district.

Hill (1916) mentioned a prominent iron-stained 

siliceous outcrop containing copper carbonate on the
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 113

Hidden Treasure claim in limestone south of Watson 

Spring. He also mentioned a jasperoid body on the 

Victoria claim in Watson Canyon west of Watson 

Spring, of which he (p. 86) wrote: "The croppings, 

iron-stained cellular quartz and jasper, with some 

copper carbonates, stand about 10 feet above the 

surrounding country and cover an area about 100 

feet long north and south by 75 feet wide." The ore 

on this property consists of secondary copper minerals in iron-stained silicified limestone containing 

abundant tremolite.

Three samples of jasperoid from the Dolly Varden 

district are included in my collection. One of these 

samples is from an outcrop close to the Victoria mine 

shaft, probably the same one described by Hill 

(1916) ; the other two are from outcrops adjacent 

to old mine workings in the lead-bearing southeastern part of the district on both sides of Spring Canyon north of Castle Peak.

The sample from the outcrop near the Victoria 

mine shaft looks barren in the hand specimen. It is 

aphanitic and dark red to reddish brown on fresh 

surfaces and weathers almost black. It consists of 

heterogeneous matrix quartz that has xenomorphic 

to jigsaw-puzzle texture and a grain diameter that 

ranges from 0.01 to 0.15 mm and averages 0.03 mm, 

and it contains abundant disseminated grains and 

interstitial masses of red hematite. The brown areas 

consist of irregular ragged quartz particles disseminated through a mixture of hematite and orange 

goethite. Spectrographic analysis of this sample, 

however, belies its unpromising appearance. It contains abundant copper (0.15 percent) and is also 

anomalously high in Fe, Bi, In, Mo, Ni, and V. The 

concentrations of indicator elements in the sample 

yield a score of +15, which places it in the highly 

favorable category.

One of the two remaining samples, from the dump 

of a prospect pit, appears to be a silicified siltstone; 

the other is from a jasperoid outcrop in limestone 

close to the collars of two adjacent inclined shafts. 

These samples are similar in appearance but are 

strikingly different from the sample previously 

described. They are light gray, yellowish gray, 

brownish gray, and aphanitic, and they contain local 

porous areas honeycombed with microvugs. Both are 

fractured though not brecciated, and the fractures 

are coated with brown limonite and, locally, with 

green copper stains.

The dump sample has a matrix of rounded quartz 

grains and sparse accessory tourmaline, zircon, 

sphene, and hematite. This matrix is cut by veinlets 

rimmed with fibrous chalcedony and commonly filled 

with coarse jigsaw-puzzle-textured quartz. Thin

veinlets of orange goethite cut the chalcedony quartz 

veinlets, and goethite is also disseminated through 

the matrix in scattered equant grains that look to 

be pseudomorphous after pyrite.

The outcrop sample has a granular to xenomorphic 

heterogeneous matrix whose grain diameter ranges 

from <0.01 to 0.1 mm and averages 0.03 mm. Small 

barite crystals and an unidentified aphanitic yellow 

mineral with low birefringence and indices of refraction greater than quartz but less than those for barite 

form abundant inclusions in the matrix, which also 

contains sparse hematite and goethite pseudomorphs 

after original pyrite. Small irregular open vugs are 

moderately abundant in the finer grained matrix 

quartz.

The dump sample of silicified siltstone is high in 

B and moderately high in Fe, Na, Be, Cr, Mo, Pb, Sc, 

Sr, V, and Zr. The outcrop sample of jasperoid is 

high in Ag and moderately high in B, Bi, Pb, and Sr. 

Both samples yielded a score of +9 for their indicator elements.

The indicator elements present in these favorable 

jasperoid samples faithfully reflect the nature of 

the ores with which they are associated. The sample 

from the copper mine in the central part of the district is high in copper and its associated minor 

elements indium, molybdenum, and nickel but low in 

lead and silver; whereas the samples from the southeastern part of the district are high in lead and silver 

but low in copper, indium, molybdenum, and nickel. 

All samples are moderately high in bismuth.

DYER DISTRICT 

(18, fig. 44)

The Dyer district is in western Esmeralda County 

close to the California State line and about 45 miles 

west of Goldfield. Little information has been published about the geology and ore deposits of this 

small district, which has long been abandoned. Spurr 

(1906b, p. 84-85) mentioned the occurrence here of 

replacement deposits of siliceous black argentiferous 

copper sulfide ore along bedding-plane faults in 

lower Paleozoic limestone; he also referred to small 

irregular pods of jasperoid scattered abundantly 

through this limestone.

FERGUSON DISTRICT 

(21, fig. 44)

A group of small abandoned mines and prospects, 

just west of U.S. 50 Alternate Highway at Ferguson 

Springs, Elko County, Nev., about 25 miles south of 

Wendover, and 7 miles west of the Utah State line, 

constitutes the Ferguson district. In a brief summary 

of this district, Hill (1916, p. 97-98) stated that
114 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

mineralization is concentrated in Paleozoic limestone along an east-trending fracture zone. The ore 

consists of irregular replacement deposits of barite 

and limonite, locally stained with copper carbonate. 

He mentioned the occurrence of large bodies of dark 

chert in the limestone but said nothing about silicification related to the mineralization.

Three samples collected from this district consist 

of aphanitic gray slightly vuggy jasperoid or jasperoid breccia fragments in a yellowish-brown siliceous matrix with similar texture; the rock weathers 

yellowish brown or dark brown. Both the older 

jasperoid quartz and the younger matrix quartz have 

a slightly heterogeneous xenomorphic texture and an 

average grain diameter of about 0.02 mm. The older 

jasperoid contains sparse detrital grains of tourmaline and sphene and local concentrations of carbonate 

particles. The matrix quartz is heavily clouded with 

yellow limonite dust, and it contains abundant shreds 

of sericite. Vugs in both older jasperoid and matrix 

are largely open, though a few are lined with calcite, 

which also fills late fractures cutting the matrix. 

These samples are all slightly high in Ba, Sr, and Zr, 

and one sample, taken at a prospect pit, also is 

slightly high in B, Ga, Ni, and V. All three samples 

yielded indicator-element scores of 1.

GETCHELL MINE AREA (POTOSI DISTRICT)

(23, fig. 44)

The Getchell mine is at the northeast end of the 

Potosi district on the northeast flank of the Osgood 

Mountains, in Humboldt County, about 30 miles 

northeast of Winnemucca. In this area Cambrian 

shale and argillite with some interbedded limestone 

have been intruded by a granodiorite stock of Cretaceous age. A strong steeply eastward-dipping fault 

zone strikes northerly along the east base of the 

range in the sedimentary rocks. Gold deposits of the 

Getchell mine are largely concentrated along sheeted 

zones in black shale within this fault zone. Much 

arsenic and some mercury are associated with the 

gold ore (Erickson, Marranzino, Oda, and Janes, 

1964, p. A2-A4). Tungsten has been mined in the 

mountains west of the fault, in tactite zones adjacent 

to the granodiorite stock (Hobbs and Clabaugh, 

1946).

Jasperoid bodies are exposed in Paleozoic rocks on 

the east side of the fault. One such occurrence is in 

limestone of Permian and Pennsylvanian age about 

a quarter of a mile east of the northern workings 

of the Getchell mine, and another is in interbedded 

argillite and limestone of Ordovician age about 2 

miles south of the southern workings of the mine.

The jasperoid replaces the country rock along

small shears and fractures. It is commonly brecciated 

and heavily stained on the outcrop in various shades 

of yellow, brown, and red. Analyses of four samples 

of jasperoid from the northern area and 11 from the 

southern area (by Erickson and others, 1964, tables 

2, 4, 5) show that most of the jasperoid samples 

from the northern area are anomalously high in As, 

Ba, Pb, and Zn, and that most of the samples from 

the southern area are anomalously high in As, B, 

Ba, Sr, and W. All samples from the northern area 

yield favorable scores. Four from the southern area 

would be classified as favorable, four as possibly 

favorable, and three as barren.

GILBERT DISTRICT

(24, fig. 44)

The Gilbert district is in northern Esmeralda 

County, about 20 miles northwest of Tonopah, at the 

east end of the Monte Cristo Mountains. Tertiary 

volcanic rocks cover most of the district, but older 

rocks are exposed in the vicinity of the Carrie mine 

in the northwestern part of the district. These older 

rocks consist of massive crystalline limestone, of 

probable Ordovician age, interbedded with a little 

dark shale and tuff and intruded by dikes of quartz 

monzonite. The limestone has been silicified near the 

dikes to form prominent jasperoid "ledges" cut by 

abundant quartz veins (Ferguson, 1928, p. 130,138).

At the Carrie mine silver-bearing base-metal sulfide deposits formed in these quartz veins. Ferguson 

(1928) noted that the jasperoid contains sericite and 

epidote, and that the ratio of epidote to quartz increases with distance from the dikes. In his description of the Carrie mine, Ferguson (p. 139) stated:

The silicified wall rock is texturally the equivalent of the 

jasperoid ledges which occur in the district. The vein locally 

includes a considerable proportion of this jasperoid in relations that suggest a gradation between the replaced limestone 

cut by later veinlets of crystalline quartz and the massive 

quartz veins themselves.

The jasperoid and its associated quartz veins are 

older than the Tertiary volcanic rocks.

GOODSPRINGS DISTRICT

(26, fig. 44)

Jasperoid has been reported in the Goodsprings 

district by Albritton, Richards, Brokaw, and Reinemund (1954, p. 25-26), and was described under 

other names by Hewett (1931). This district is in 

southwestern Clark County, close to the California 

line and about 35 miles southwest of Las Vegas. 

Mississippian limestone in the district has been cut 

by numerous faults and fractures that controlled 

the mineralizing solutions that formed base-metal
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 115

sulfide deposits as both replacements and veins. Jasperoid is not abundant in this district. Hill (1914) 

did not mention it, and, in fact, he (p. 246) stated 

that most of the limestone replacement deposits in 

the district are characterized by absence of gangue 

minerals. Hewett (1931, p. 57) noted that, although 

silicification is not a conspicuous feature of the district, "ferruginous chert" is abundant in some mines, 

and that Yellow Pine, Double Up, Boss, and John 

mines contain appreciable silica related to ore deposition. Although Hewett did not refer to either of these 

rocks as jasperoid, his description clearly indicates 

that the ferruginous chert corresponds to supergene 

jasperoid and that the silica related to ore deposition 

corresponds to hypogene favorable jasperoid.

Hewett (1931, p. 83) described a dense, opaque, 

yellowish-brown to dark-brown ferruginous chert, 

associated with limonite and jarosite, which is locally 

abundant at and near the surface and grades downward into cream-colored chert containing scattered 

quartz grains. This variety forms veinlike masses 

replacing shale or dolomite, and is absent at depths 

of 100-250 feet below the surface. The origin of this 

"chert" is ascribed to the action of circulating surface water.

Hewett also referred to masses of cavernous gray 

quartz, exposed in some copper and silver mines, 

that is composed of interlocking grains that are 

0.05-0.2 mm in diameter and that contain minute 

inclusions of octahedrite and rutile, and of cavities 

filled with a white powder consisting of tiny doubly 

terminated quartz crystals. He described hypogene 

silicification of dolomitic wallrock at the Double Up 

and Pilgrim mines resulting in veinlets and poorly 

defined areas of quartz that in part replace and in 

part fill cavities in the dolomite. A broad fracture 

zone at the Double Up mine contains lenses of dark 

fine-grained quartz as much as 35 feet long, 20 feet 

wide, and 5 feet thick bordered by a porous limonitic 

zone. A similar mass forms a lenticular pipe which 

is the main ore body at the Boss mine. This pipe 

consists of dark coherent cellular masses composed 

of interlocking quartz grains that are 0.03-0.1 mm 

in diameter, interspersed with white crystalline 

quartz powder, surrounded by an envelope of limonite that grades outward into dolomite impregnated 

with copper carbonates. Assays of the dark cellular 

quartz in the core of this pipe yielded as much as 12 

oz Au, 11 oz Ag, 7 oz Pt, and 4.5 oz Pd per ton 

(Hewett, 1931, p. 82, 109, 115-116).

Albritton and his colleagues (1954, p. 25-26) reported jasperoid near the Yellow Pine and Prairie 

Flower mines. These two mines are on the east slope 

of Shenandoah Peak in the Spring Mountains near

the center of the district. In this area the limestone 

has been intruded by irregular dikes and sills of 

quartz monzonite porphyry and extensively altered 

by hydrothermal solutions. The limestone is dolomitized and silicified. Silicified zones are generally 

parallel to the bedding and range from a fraction of a 

foot to 25 feet in thickness. Within these zones the 

jasperoid in part preserves the original color and 

texture of the limestone, and in part consists of 

irregular gray, black, and brown cherty lentils and 

pods. Veins of brown "chert" follow many fractures 

and faults (Albritton and others, 1954, p. 25-26).

GROOM DISTRICT

(27, fig. 44)

The Groom district is in southwestern Lincoln 

County, about 75 miles west-southwest of Caliente 

and 35 miles west of Alamo. The district is in a 

downfaulted block of Cambrian shale and limestone; 

the internal structure of this block is complex. Replacement deposits, which consist largely on argentiferous galena, occur both along fractures and as 

mantos in the limestone (Humphrey, 1945, p. 9, 17, 

32). This limestone is commonly silicified along 

faults and fractures in the vicinity of the ore bodies.

KERN DISTRICT

(28, fig. 44)

Hill (1916, p. 207) mentioned the occurrence of 

jasperoid in Water Canyon about 12 miles southeast 

of Tippett, near the south end of the Kern Mountains 

in northeastern White Pine County. Dark-blue 

Paleozoic limestone has been replaced by lenticular 

masses of quartz, parallel to the bedding near the 

contact of the limestone with an intrusive granitic 

stock. The jasperoid quartz locally contains hematite, 

and some of it is coated with yellow cerussite along 

fractures.

LEWIS DISTRICT 

(31, fig. 44)

The Lewis district is near the north end of the 

Shoshone Range in northeastern Lander County, 

about 12 miles southeast of Battle Mountain. Paleozoic quartzite and limestone in this area have been 

intruded by granodiorite porphyry of Laramide age. 

The ore deposits consist of pyritic gold-quartz veins 

in the intrusive rocks and quartzite and of base-metal 

sulfide replacement bodies in the limestone. One of 

these replacement deposits, at the Starr Grove mine, 

contains disseminated sulfides in a siliceous baritic 

gangue. Emmons (1910, p. 126) stated that the main 

ore body is a large tabular-bedded replacement body 

in dark-gray limestone overlain by massive quartzite.
116 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

This body consists of barite and quartz with disseminated pyrite, galena, and sphalerite. The barite is 

older than both quartz and sulfides, as shown by the 

fact that breccia fragments of barite occur in a 

matrix of quartz with disseminated sulfides. From 

Emmons' brief description, it cannot be ascertained 

whether the quartz gangue in this deposit is a true 

replacement jasperoid or whether it consists only of 

vein quartz filling fractures and cavities in an older 

barite body.

MANHATTAN DISTRICT

(34, fig. 44)

The Manhattan district is in the southern part of 

the Toquima Range in northwestern Nye County, 

about 35 miles north of Tonopah. Fissure veins and 

replacement deposits in Cambrian limestone have 

been mined for gold, arsenic, and antimony. The 

following description is taken from Ferguson's report (1921) on the geology and ore deposits of this 

district.

The ore-bearing limestone beds are concentrated 

near the bottom and near the top of a thick section 

composed mostly of micaceous schist with some interbedded lenticular sandstones and quartzites. These 

Cambrian rocks are overlain by about 400 feet of 

Ordovician schists, and these schists, in turn, by a 

similar thickness of dark-gray thin-bedded barren 

limestone containing abundant black to dark-gray 

jasperoid. The main ore bed, known locally as the 

"White Caps limestone," is cut by a number of closely 

spaced preore normal faults, some of which show 

postore movement. These faults were the conduits 

for mineralizing solutions that formed replacement 

ore bodies in the limestone.

The earliest gangue mineral is coarse white calcite, which was followed by dark-gray fine-grained 

jasperoid that replaced both the early calcite and the 

limestone host rock in the immediate vicinity of the 

ore bodies. Muscovite and fine-grained auriferous 

pyrite and arsenopyrite formed penecontemporaneously with this jasperoid and are disseminated 

through it. Younger stibnite and realgar replace 

coarse calcite and, to a lesser extent, the jasperoid.

Numerous lenticular vugs, elongated parallel to 

the bedding of the host rock, are present in the 

jasperoid, and many of these are encrusted with one 

or more of the following minerals: quartz, calcite, 

dolomite, fluorite, stibnite, pyrite, orpiment, and 

realgar. The dark-gray to black color, characteristic 

of the jasperoid in this district, is caused by abundant carbonaceous particles disseminated through it. 

In some places, jasperoid has been brecciated by 

postore movement on the faults. The deposits of this

district were considered by Ferguson (1921, p. 34) 

to be of probable Tertiary age and to have formed at 

shallow depth.

MINERAL HILL DISTRICT

(36, fig. 44)

The Mineral Hill district is on the west side of the 

Pinyon Range in east-central Eureka County, about 

50 miles south-southwest of Elko. According to Emmons (1910, p. 95-99), argentiferous base-metal 

sulfides form replacement deposits in gray crystalline 

Paleozoic limestone along a north-trending silicified 

fracture zone. These deposits are all shallow, and 

were chiefly mined for silver. The ore bodies are 

irregular, highly silicified bodies that are localized 

by fractures transgressing the bedding of the host 

rock. In some places, quartz and sulfides have replaced the host rock; in others, they merely cement 

breccia fragments in a fracture zone. Iron-stained 

jasperoid forms prominent outcrops over many of 

the ore bodies. Near the surface the sulfides have 

oxidized to cerargyrite, malachite, azurite, pyromorphite, cerussite, limonite, and manganese oxides. 

Primary ore and gangue minerals of the deposits are 

sparse sulfides (pyrite, galena, sphalerite, tetrahedrite, and argentite) and quartz, barite, and calcite.

PATTERSON DISTRICT

(40, fig. 44)

The Patterson district is in northwestern Lincoln 

County, about 45 miles north-northwest of Pioche, 

and 50 miles south of Ely, near the south end of the 

Schell Creek Range. According to Schrader (1931a, 

p. 7, 11, 15), the country rock in the district is 

Cambrian shale, quartzite, and limestone. Ore deposits consist of siliceous copper-lead-silver minerals 

in quartz-carbonate replacement veins in limestone 

that is commonly silicified to a jasperoid. In his 

description of ore deposits on the Streater claims, 

Schrader (p. 15) wrote that

The ores occur mostly as replacement deposits in silicified 

limestone in a gangue of quartz, barite, and altered rock. The 

chief ore mineral is argentiferous galena * * *. Some of the 

ore consists chiefly of silicified limestone, stained by yellowishbrown iron oxide and by lead and copper carbonates. It is 

crudely ribbed or banded with stringers of replacement quartz 

as much as two-tenths of an inch wide * * *.

SANTA FE DISTRICT

(41, fig. 44)

The Santa Fe district is in eastern Mineral County, 

near Luning, in the Pilot Mountains. White and gray 

crystalline limestone of probable Triassic age has 

been intruded by quartz monzonite and quartz diorite
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 117

and metasomatized to garnet rock adjacent to the 

intrusive contacts (Hill, 1915, p. 159-160).

In addition to the typical contact skarns, which 

are host rocks for copper and lead sulfide ores, partly 

metasomatized limestone has been locally silicified to 

form jasperoid bodies with calc-silicate inclusions. 

Hill (1915, p.'168-170) described the Giroux Ledge 

as a dark-gray, brown-weathering jasperoid containing angular breccia fragments of white cellular 

quartz; at the Mayflower property the top of a hill 

is altered to greenish-white jasperoid containing 

garnet and epidote; and at the Wall Street mine 

supergene copper minerals form thin films and irregular masses in reddish-brown jasperoidal limestone.

SILVERHORN DISTRICT

(43, fig. 44)

The Silverhorn district, in northern Lincoln 

County, is about 20 miles northwest of Pioche and 

4 miles north of Bristol Pass. Westgate and Knopf 

(1932, p. 51) described huge outcrops of jasperoid, 

as much as several hundred yards long and several 

hundred feet wide, in the Mississippian Bristol Pass 

Limestone in this district. It is apparent that this 

jasperoid is structurally controlled and that it locally 

formed the host rock for oxidized silver deposits. An 

adit in the district cuts an 80-foot-thick jasperoid 

body 200 feet below the outcrop. This body replaces 

limestone along its fault contact with shale and, 

according to Westgate and Knopf (1932, p. 51), ''is 

the normal fine-grained siliceous rock that is formed 

as a result of the replacement of limestone by 

minutely crystalline quartz."

SILVER PEAK DISTRICT

(44, fig. 44)

The Silver Peak district is about 25 miles west of 

Goldfield in central Esmeralda County. Most of the 

production from this district has come from mines 

on Mineral Ridge, 4 miles northwest of the town 

of Silver Peak. The ore bodies are bedded replacements in Cambrian and Ordovician limestone and 

dolomite associated with intrusive dikes and sills of 

alaskite. The ore consists of a black copper-silver 

sulfide locally disseminated through white jasperoid, 

according to Spurr (1906b, p. 73-74). He described 

the jasperoid as a mesh of interlocking quartz crystals with the interstices filled by finer grained anhedral quartz (reticulated texture) ; the jasperoid is 

coarser grained in the vicinity of the sulfides than 

elsewhere. It is approximately contemporaneous with 

the sulfides, and it has gradational contacts with the 

enclosing carbonate rock.

I have one sample from this area, taken from the 

north end of Mineral Ridge, about 6 miles north of 

the town of Silver Peak and more than 1 mile from 

the mines. This sample is light gray and aphanitic 

with local porous areas, it has dark-yellowish-orange 

fracture coatings, and it weathers grayish brown. 

In thin section it does not exhibit the reticulated 

texture described by Spurr, but it has a heterogeneous xenomorphic texture and an average grain size 

of 0.04 mm. It contains abundant disseminated 

grains of microcline approximately contemporaneous 

with the quartz. It also contains numerous red hematite inclusions pseudomorphic after pyrite, shreds of 

sericite, and irregular masses of opaque dark-brown 

limonite. The matrix is cut by veinlets of coarse 

calcite.

Spectrographic analysis shows this sample to be 

slightly high in Fe, Na, K, Ti, Ba, Co, Cr, Ga, Sc, 

Sr, V, Y, Yb, Zn, and Zr. It yields a score of +4 on 

the indicator elements. The absence of reticulated 

texture and of high Cu and Ag suggests that this 

sample probably does not represent the ore-bearing 

jasperoid described by Spurr.

TAYLOR DISTRICT

(47, fig. 44)

The Taylor district is near the south end of the 

Schell Creek Range in White Pine County, about 

15 miles southeast of Ely. The geology and ore deposits of this district have been briefly described 

by Hill (1916, p. 200-201) and, more recently, by 

Drewes (1962, 1967).

According to Hill, the ore deposits at the Argus 

mine are in a massive brownish-gray bed of limestone, 70 feet thick, which is cut by north-trending 

block faults. The limestone is brecciated near the 

faults, and it has been selectively silicified in two 

bands, one about 15 feet above the base and the 

other about 15 feet below the top of the bed. These 

silicified bands contain most of the ore. They are 

heavily stained with carbonates of lead and copper 

and contain a disseminated dark-gray metallic sulfosalt with Fe, Cu, and minor As, Ag, and Pb. Both 

mineralization and silicification extend outward irregularly into the limestone from these high-grade 

bands. The silicified rock is cut by veinlets of late 

calcite.

According to Drewes (1962), most of the ore in 

the district is concentrated in two stratigraphic 

units, the upper member of the Devonian Guilmette 

Formation and the upper part of the Mississippian 

Joana Limestone. Both of these units are thin-bedded 

limestones that are overlain by black shale. Most of 

the production from the district has come from mines
118 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

in the Guilmette Formation, which was the unit 

described by Hill. Mineralization is largely restricted 

to silicified zones in limestone, and these zones, in 

turn, are controlled structurally by proximity to 

faults and stratigraphically by thick shale cappings 

over the limestone host rock. Many thick short rhyolitic dikes are present in the district, and these dikes 

may be related to mineralization (Drewes, 1962).

Although the ore in the district has been mined 

mostly for its silver content, it also contains gold, 

copper, lead, zinc, and antimony in various places. 

A number of grab samples of jasperoid taken by 

Drewes from abandoned mine workings in the central part of the district were analyzed spectrographically. Seven of these samples were abnormally 

high in Ag, Cu, Pb, and Zn and slightly high in B. 

Most of the samples were also high in Ba, Cd, Sb, 

and Zr. Their indicator-element scores range from 

+ 18 to + 26, placing them high in the favorable 

category (Harald Drewes, written commun., 1965).

Seven samples from the Taylor district and its 

vicinity are included in my collection. Three of these 

samples were collected about 2 miles north of Taylor 

close to the road leading to Taylor Springs; the 

stratigraphic unit represented by these samples is 

probably Guilmette Formation. One sample of jasperoid from the Joana Limestone was collected from 

the dump of an adit along a strong fault on the North 

Star claim half a mile north of the main workings 

of the district. The remaining three samples are of 

jasperoid from the upper member of the Guilmette 

Formation near the center of the district and close 

to the old Monitor and Argus mines. These three 

samples are from a large brecciated zone not far 

from major faults; all the other samples are from 

silicified fault zones. The first three samples, from 

the ridgecrest above the Silver Queen shaft and the 

small saddle just west of it, close to the road, are all 

more than a mile from mine workings and hence, 

presumably are unfavorable; however, they vary 

considerably in both appearance and other characteristics.

One of these samples consists 01 light-gray breccia 

fragments in a dark-gray slightly vuggy matrix. 

In thin section two types of breccia fragments can 

be distinguished: aphanitic pale-brown cherty-looking fragments and fine-grained heterogeneous reticulated jasperoid fragments that have an average grain 

diameter of about 0.03 mm. These fragments are 

embedded in quartz that has a xenomorphic to reticulated texture and a grain diameter that averages 

0.02 mm and ranges from <0.01 to 0.1 mm. Calcite 

is present as ragged relict grains in jasperoid breccia 

fragments, as carbonate particles in both breccia

fragments and matrix, and as filling in late veinlets 

cutting the matrix. The sample showed anomalously 

high values for Na, As, B, Mo, Pb, Sb, Sr, Zn, and 

Zr, and it yielded an indicator-element score of +9 

(probably favorable). Thus, this sample may indicate leakage along the fault from ore deposits at 

depth.

A second sample of this group appears to represent 

the same jasperoid that formed the breccia fragments in the first one. It has a similar appearance 

and microtexture, but it contains tiny red hematite 

grains and interstitial yellow limonite in addition to 

the carbonate particles. B, Ba, Pb, Sr, and Zn are 

slightly high, and the indicator-element score is +5.

The third sample of this group is dense, dark-red, 

streaked with light brown, xenomorphic jasperoid 

quartz whose grain diameter averages 0.03 mm and 

ranges from 0.01 to 0.2 mm. The quartz contains 

abundant carbonate particles, and it is cut Jby a 

mesh of red hematite veinlets, many of which are 

filled with a microbreccia of jasperoid particles. The 

trace-element suite associated with it consists of Fe, 

B, Ba, Ni, Sb, Sr, V, Y, Yb, and Zr. Its indicatorelement score is 1; this jasperoid, therefore, is 

classified as unfavorable.

The single sample of jasperoid from the Joana 

Limestone, from the adit dump on the North Star 

claim, is unusual in that it contains antimony as a 

major constituent. It is light olive gray and dark 

yellowish brown, fine grained, and compact, and it 

is cut by veinlets of relatively coarse white quartz. 

The matrix jasperoid is xenomorphic, and its grain 

diameter averages 0.02 mm and ranges from 0.01 to 

0.1 mm. The late white quartz is also xenomorphic, 

and its grain diameter averages 0.1 mm and ranges 

from 0.03 to 0.5 mm; it contains sparse irregular 

open vugs. The antimony mineral, which forms 

abundant irregular inclusions in the matrix, is 

aphanitic and yellowish brown, and it has a high 

index of refraction. It probably is a supergene alteration product of stibnite and may be the basic antimony sulfate klebelsbergite. In addition to Sb, this 

sample is highly enriched in Ag and slightly enriched 

in As, B, Ba, Pb, Ni, Sr, Y, Yb, and Zn. It yields a 

score of +14.

The three samples of jasperoid from the central 

part of the district are light gray to yellowish brown, 

fine grained, and locally vuggy with abundant limonite stains and fracture coatings. They exhibit a 

reticulated to xenomorphic texture, and their grain 

diameter averages about 0.05 mm and ranges from 

0.01 to 0.1 mm. The samples are locally cut by veinlets of slightly coarser xenomorphic quartz. The 

matrix contains abundant carbonate particles; limo-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 119

nite, jarosite, and hematite are locally abundant as 

supergene inclusions and fracture fillings. Minorelement content varies considerably among the three 

samples, but there is general enrichment in Ag, B, 

Cu, Pb, Sb, Sr, Yb, Zn, and Zr. Presumably, these 

samples are similar to those collected by Drewes 

from the same locality, though they do not yield as 

high scores; the maximum score obtained from my 

group is +13.

Ore deposits of this district appear to be closely 

associated both spatially and genetically with jasperoid bodies, and jasperoid in the immediate 

vicinity of such deposits commonly exhibits favorable characteristics; thus, these jasperoids should 

provide a useful tool for any future exploration in 

the area.

TECOMA DISTRICT

(48, fig. 44)

The Tecoma district is in northeastern Elko 

County, about 4 miles west of the Utah State line 

and 35 miles south of the Idaho State line in the 

southwestern part of the Goose Creek Range. The 

ore deposits in the district are largely oxidized lead 

and zinc sulfide vein deposits in complexly faulted 

Paleozoic sedimentary rocks, consisting predominantly of limestone and dolomite.

Near the Jackson mine coarse-grained quartzite 

is in fault contact with Devonian blue-gray limestone and dolomite. These carbonate rocks are cut 

by several north-trending faults that locally have 

served as conduits for silicifying solutions producing 

large jasperoid bodies. One such body, about 500 feet 

long and 40 feet wide, is the host rock for the ore 

bodies in the mine. These bodies consist of silverbearing cerussite, a little smithsonite, and a few 

residual pods of galena in a gangue of oxidized rusty 

jasperoid; limonite, calcite, clay, and barite occupy 

fracture zones in the jasperoid. A larger, but apparently unmineralized jasperoid body, crops out 

1,000 feet northeast of the mine; it is about 200 feet 

wide and extends northward for several thousand 

feet. Contacts between jasperoid and host rock are 

commonly brecciated (Granger and others, 1957, p. 

149-150).

WARD DISTRICT AND WEST WARD AREA

(49 and 50, fig. 44)

The Ward district (49) is in White Pine County 

about 10 miles south of Ely, on the east side of the 

Egan Range. A second mineralized area, centered 

about 21/2 miles west of the Ward district on the 

opposite side of the Egan Range, is characterized by 

magnetic and geochemical anomalies and by locally

abundant jasperoid (Brokaw and others, 1962). This 

area I refer to as the West Ward area (50).

The geology and ore deposits of the Ward district 

have been summarized by Hill (1916, p. 180-186). 

Paleozoic limestone beds, which make up a thick 

section and which have gentle easterly dips throughout most of the district, are locally intruded by 

north-trending quartz monzonite dikes. Both dikes 

and limestones are cut by younger faults and have 

been hydrothermally altered by mineralizing solutions. The ore deposits are closely associated with 

the dikes, and they generally occur close to the contacts as bedded replacements in the limestone and as 

veins in both the limestone and the dikes. Within 

the zone of oxidation the ore consists largely of 

argentiferous cerussite, hemimorphite, smithsonite, 

and copper oxidation products in a siliceous limonite 

gangue. Primary sulfides below the zone of the oxidation are galena, sphalerite, pyrite, and a little 

chalcopyrite. Limestone is locally silicified near the 

dikes, and in some places the ore bodies are in this 

silicified zone. The Defiance ore body, 500 feet below 

its outcrop, is a silicified zone 300 feet wide impregnated with pyrite and galena adjacent to a strong 

northeast-trending fault (Hill, 1916, p. 183-184). 

Silicified limestone adjacent to porphyry dikes is also 

present in the lower Paymaster tunnel and the Welcome Stranger Tunnel (Hill, 1916, p. 185-186).

I have three jasperoid samples from the Ward district. The host rock for all three samples is Mississippian, Pennsylvanian, and Permian Ely Limestone. 

One sample is from a silicified zone along a northeast-trending fault about a mile south of the district. 

Another sample is from a zone adjacent to a quartz 

monzonite dike a few hundred feet south of the 

strong east-west fault that marks the south boundary 

of the district and about a quarter of a mile southwest of the 280 Tunnel. The third sample is siliceous 

gossan from the outcrop of a vein in a fault zone 

adjacent to a large quartz monzonite dike; it was 

taken within a few feet of mine workings about half 

a mile west of the 280 Tunnel.

The first sample is grayish red and aphanitic, and 

it contains sparse irregular vugs, of which some are 

open and some are filled with coarse white calcite. 

Its microtexture is xenomorphic, and its grain diameter averages 0.02 mm and ranges from 0.01 to 0.1 

mm. The larger grains have carbonate particles, and 

some show zonal overgrowths. Red hematite is 

abundant both as disseminated particles and as irregular inclusions. The sample is slightly high in Ag 

and Sr and yields a score of +2.

The second sample is dark gray and dense and is 

cut by sparse veinlets of white calcite. The matrix
120 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

has a homogeneous granular texture, and an average 

grain diameter of 0.06 mm. It contains partly assimilated breccia fragments of feathery chalcedony mixed 

with jigsaw-puzzle textured quartz having an average grain diameter of 0.05 mm, and also of similar, 

but more heterogeneous, quartz without the chalcedony. Ragged relict grains of calcite are abundant 

in both matrix and inclusions. Small flecks of brown 

limonite are scattered through the matrix, and some 

of these surround tiny grains of pyrite. In addition 

to abundant Ca and Mg, the sample is slightly high in 

Al, Cr, Ni, Pb, Sr, Y, Yb, and Zr.

The third sample is moderate brown, brownishblack weathering, aphanitic, and porous. The matrix 

is vuggy orange goethite cementing isolated grains 

and small breccia fragments of coarse reticulated 

jasperoid quartz that has a grain diameter that 

averages 0.1 mm and ranges from 0.03 to 0.8 mm. 

Carbonate particles are moderately abundant in the 

quartz. This sample is unusually rich in minor elements; Fe, Ag, As, and Pb are enriched by more 

than two orders of magnitude above the norm, and 

Ca, Mg, Ti, Bi, Cr, Cu, In, Mo, Ni, Sn, Sr, V, Zn, 

and Zr are enriched by more than one order of 

magnitude. The indicator-element score is +31 (very 

favorable).

The geology of the West Ward area and the results of a geochemical exploration program in the 

area were summarized by Brokaw, Gott, Mabey, McCarthy, and Oda (1962, p. 7). On the geologic map 

accompanying their report, jasperoid in the Mississippian Joana Limestone is shown in a stippled 

pattern. The West Ward area is underlain by a 

thick section of middle Paleozoic marine sedimentary 

rocks consisting largely of limestone, dolomite, ancl 

shale. This section is broken by both low-angle thrust 

faults and high-angle normal faults.

Spectrographic analyses of 27 jasperoid samples 

from the Joana (Mississippian) and Arcturus 

(Permian) Limestones in the West Ward area, given 

to me by J. H. McCarthy, show that the modal concentrations of Ti, Ag, Ba, Cr, Ni, and V are appreciably higher than in my reference groups of 200 

samples from various localities. Geochemical anomaly 

maps for various elements, based on analyses of both 

jasperoid and limonite samples, are illustrated by 

Brokaw, Gott, Mabey, McCarthy, and Oda (1962, 

p. 5-6).

Five additional samples of jasperoid from the 

Joana Limestone in the West Ward area are in my 

collection. These samples have been analyzed both 

petrographically and spectrographically. Three samples are from the vicinity of a small prospect about 

a quarter of a mile north of the abandoned Old

Quake mine. The exact sample localities for the other 

two samples are not known, but they represent bodies 

not associated with any known ore.

One sample, from the group of three, consists of 

angular and irregular crudely stratified inclusions 

of aphanitic dark-reddish-brown and dark-brown 

jasperoid in a matrix of coarse white quartz. Three 

distinct generations of quartz are in the sample. The 

oldest generation consists of homogeneous xenomorphic quartz having an average grain diameter of 

0.015 mm, sparse carbonate dust, and abundant interstitial yellow limonite. This generation forms 

inclusions in a cleaner and coarser heterogeneous 

xenomorphic matrix that has a grain diameter that 

averages 0.03 mm and ranges from 0.01 to 0.12 mm. 

The matrix is cut by the coarse vein quartz whose 

grains are as much as 3 mm in diameter. In spite 

of its complex nature, this sample has a very ordinary composition, exhibiting a minor anomaly only 

for Ba, and yielding an index element score of 1 

(unfavorable).

The second sample from this group of three samples is dark gray and dense; it is cut by vuggy white 

quartz veinlets, and it weathers olive gray to pale 

yellowish brown. The matrix has a jigsaw-puzzle 

texture and a grain diameter that averages 0.01 mm 

and ranges from <0.01 to 0.06 mm. It contains 

sparse carbonate and hematite particles and is cut 

by veinlets of xenomorphic quartz that has a grain 

diameter that averages 0.07 mm and ranges from 

0.01 to 0.2 mm. Most vugs in this late quartz are 

open, but a few are partly filled with jarosite. The 

sample contains anomalous concentrations of Ag and 

Ba and slightly anomalous concentrations of Cr, Cu, 

Sb, Sr, V, Y, Yb, and Zr, yielding an indicatorelement score of +6 (probably favorable).

The last sample in this group is similar in appearance to the second, but it lacks the late quartz veinlets and weathers dark gray. It consists of homogeneous quartz particles that have an average grain 

diameter of 0.02 mm in a matrix of dark-brownishgray to black amorphous opaque material, presumably organic, that contains abundant shreds of 

sericite and grains of goethite as well as sparse irregular masses of nontronite. The matrix is cut by 

sparse lenticular masses of younger quartz that has 

a jigsaw-puzzle texture and a grain diameter that 

averages 0.02 mm and ranges from <0.01 to 0.15 

mm. Some of the larger grains of this younger quartz 

contain sparse carbonate particles and small fluid 

inclusions. This sample contains highly anomalous 

concentrations of Ag, Ba, Cr, Ni, Sr, and Zr, as well 

as slightly anomalous concentrations of Na, K, Ti, B,
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 121

Cu, La, Pb, Sb, V, Y, Yb, and Zn; it gives an indicator-element score of +15 (favorable).

One of the two remaining samples in my collection 

is dark gray, dense, brecciated, and cemented by 

coarse white calcite. It has a homogeneous jigsawpuzzle texture and an average grain diameter of 

<0.01 mm; it contains carbonate particles and is cut 

by veinlets of coarser xenomorphic quartz as well 

as coarse calcite; and it grades transitionally through 

a zone about 2 mm wide into lithographic limestone 

that contains scattered grains and irregular masses 

of coarse-grained epigenetic calcite. Tiny subhedral 

grains of hematite, which appear to be pseudomorphous after pyrite, are sparsely disseminated in both 

jasperoid and limestone. This jasperoid sample is 

slightly high in Na, Ag, Ce, Cu, and Ga, and it yields 

a score of +4. Comparison of spectrographic analyses of the jasperoid and the adjacent Joana Limestone host rock shows the jasperoid to be significantly 

enriched in Si, Fe, Ag, Cr, Cu, Ga, and Ni relative 

to the limestone.

The other remaining sample is a breccia composed 

of angular fragments of dark-gray aphanitic jasperoid in a matrix of fine-grained, locally vuggy, 

dark-yellowish-orange to moderate-brown jasperoid. 

In thin section several different types of breccia 

fragments can be distinguished. One type consists of 

clean coarse homogeneous xenomorphic quartz that 

has an average grain diameter of 0.4 mm. Another 

type has a xenomorphic to jigsaw-puzzle texture and 

average grain diameter of 0.2 mm; it is locally vuggy 

and it contains abundant carbonate particles. A 

third type has a jigsaw-puzzle texture gradational to 

fibrous chalcedony and an average grain diameter 

of 0.03 mm; it contains sparse carbonate particles. 

The last type of inclusion is similar to the matrix 

jasperoid in the specimen discussed in the preceding 

paragraph. The cementing matrix for all these fragments is a vuggy limonitic microbreccia of smaller 

jasperoid particles. This sample is very high in As, 

Sb, and Ti and slightly high in Al, Fe, Na, Ba, Cr, 

Cu, Ga, Mo, Ni, and Y, and it yields a score of +8 

(probably favorable).

WHITE PINE (HAMILTON) DISTRICT 

(51, fig. 44)

The White Pine district is in western White Pine 

County, about 30 miles west of Ely in the White Pine 

Mountains. The sedimentary section in the main 

mineralized area consists predominantly of Devonian 

and Mississippian limestone and shale, broken by 

strong north-trending faults and smaller subsidiary 

faults and fractures. About 5 miles west of this area 

the Paleozoic sedimentary rocks have been intruded

and locally metasomatized by a small stock of quartz 

monzonite. The stock rock is strongly brecciated and 

silicified, but neither the stock nor the altered sediments surrounding it have thus far yielded any 

economically important ore deposits.

Bonanza silver deposits of cerargyrite and silvermanganese-bearing calcite were mined in the early 

days on Treasure Hill. In recent years most of the 

ore in the district has come from argentiferous basemetal sulfide replacement deposits, oxidized near the 

surface, in the Devonian Nevada Limestone westsouthwest of Treasure Hill. This host rock is overlain, as in the Taylor district (47), successively by 

the Pilot Shale of Devonian and Mississippian age 

and by the Joana Limestone and the Chainman Shale, 

both of Mississippian age. Jasperoid bodies are 

largely confined to the upper part of the Joana Limestone near its contact with the Chainman Shale and 

close to faults and fracture zones. The Joana Limestone, however, is largely barren of ore (Humphrey, 

1960, p. 32, 46-47, 88). Jasperoid in the Joana 

Limestone typically is brecciated, dark reddish 

brown, and fine grained, and it resembles quartzite. 

Jasperoid bodies similar in appearance to those in 

the Joana Limestone, except that they are not conspicuously brecciated, are present locally in limestone beds above the Chainman Shale (Humphrey, 

1960, p. 35). I have 13 jasperoid samples from within 

or near the White Pine district. Most of them were 

taken from the Treasure Hill area of the main silver 

district; but two samples of supposedly barren jasperoid in the Joana Limestone were collected l*/^ 

and 5 miles southwest of this area, and three more, 

from the same stratigraphic zone, were collected 5 

miles north and about 10 miles northeast of it. Five 

of the eight samples from within the Treasure Hill 

area of the district are of jasperoid from the Joana 

Limestone; the other three are of silicified Pilot 

Shale in breccia zones along the contact with Nevada 

Limestone.

All five of these jasperoid samples from the Joana 

Limestone show two distinct generations of silica. 

The older is predominantly light gray to moderate 

gray and aphanitic. It has jigsaw-puzzle texture and 

contains abundant inclusions of chalcedony; locally, 

it contains microvugs, some of which have been filled 

with coarse xenomorphic quartz, and in places it is 

clouded with dusty particles of limonite or carbonate. 

The younger silica forms a matrix surrounding inclusions of the older silica. It is various shades of 

yellow, orange, brown, and red, and it has a heterogeneous jigsaw-puzzle texture and an average grain 

size markedly coarser than that of the older silica; 

it also contains larger and more abundant vugs. It
122 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

commonly contains abundant particles of hematite, 

limonite, jarosite, or carbonate as well as larger 

masses of jarosite and barite. These minerals, together with coarse xenomorphic quartz, also fill 

fractures and vugs. All five of these samples are 

anomalously high in Fe and Ba, and some are also 

high in Na, Cr, Ni, Pb, Sr, V, and Zn. Their indicatorelement scores range from +1 to +19 and average 

about +9.

The three remaining samples from the mineralized 

area are of silicified Pilot Shale in breccia zones close 

to the Nevada Limestone contact. These, too, contain 

gray and brown angular chert inclusions in a slightly 

coarser, gray, red, yellow, or brown locally vuggy 

matrix, which, in two of the samples, is itself brecciated and cemented by coarse white vein quartz. 

The matrix is heavily clouded with dust-sized particles of carbon, limonite, and hematite, and it contains 

abundant shreds of sericite. These breccia-zone samples, which contain several different kinds of fragments and which are from mineralized zones, display 

more elements in anomalously high concentration 

than do the samples of jasperoid from the Joana 

Limestone. Ba, Pb, and Sr are high in all three samples; Al, Mg, Na, P, Ag, B, Cu, La, Ni, Y, Yb, Zn, 

and Zr are high in two of them. Their indicatorelement scores are +6, +12, and +16.

Five samples of barren jasperoid from the Joana 

Limestone represent four localities, two of which 

are several miles south and southwest of the district, 

and two of which are several miles north and northeast of the district. These five samples are pastel 

shades of red, yellow, brown, pink, and orange. Some 

of them contain chert fragments; the matrix jasperoid has a fine-grained jigsaw-puzzle texture and 

a grain diameter that averages about 0.01 mm and 

ranges from < 0.005 to about 0.03 mm. The microtexture of jasperoid samples from this stratigraphic 

zone is remarkably consistent in all 10 samples 

collected at intervals over a distance of about 30 

miles. These unfavorable samples also contain hematite, limonite, and, locally, jarosite inclusions both 

as small discrete grains and as dust-sized particles. 

They differ most notably from the samples in the 

mineralized area in that they contain fewer minor 

elements in higher than normal concentration. Most 

of them are high in Ba and Sr; those from the 

southwest are high in B and Ni, and those from the 

northeast are high in Na. The indicator-element 

scores of these samples range from 1 to 3.

WILLOW CREEK DISTRICT

(52, fig. 44)

The Willow Creek district in Nye County is about

12 miles north of lat 38° N. and 15 miles east of long 

116° W. on the northwest side of the Quinn Canyon 

Mountains and near the south end of Railroad 

Valley. Oxidized argentiferous base-metal deposits 

are found here in veins cutting shaly siliceous 

Ordovician limestone near a small intrusive stock of 

quartz monzonite.

At the Queen of the Hills mine, 3 miles southeast 

of Mormon Well, limonitic jasperoid replaces a 

massive limestone bed just above its contact with a 

shaly limestone. This jasperoid contains copper carbonates and a little silver (Hill, 1916, p. 144-145, 

150).

WYNDYPAH DISTRICT

(53, fig. 44)

The Wyndypah district is in south-central Esmeralda County on the northeast flank of the south end 

of the Silver Peak Range, about 15 miles southwest 

of Silver Peak. Argentiferous copper deposits occur 

here in veins close to the contact of a small intrusive 

granitic stock with lower Paleozoic calcareous sedimentary rocks.

At the Chloride mine a vein containing breccia 

fragments of brown jasperoid and partly silicified 

limestone in a quartz gangue follows the contact 

between an alaskite porphyry dike and altered limestone a few hundred feet from the granite contact. 

This vein contains some disseminated black silvercopper sulfide ore. A similar vein, in altered limestone near the granite contact about a mile south 

of the Chloride mine, has also been explored (Spurr, 

1906b, p. 90-91).

OTHER OCCURRENCES

Silicified limestone containing barite is the host 

rock for small oxidized zinc and argentiferous lead 

replacement ore bodies along bedding planes adjacent to basalt dikes in the Antelope district (1, 

fig. 44) southwest of Eureka, Nev. Nearly all the 

ore is oxidized and consists of cerussite, smithsonite, 

hemimorphite, manganese oxides, and jasperoid. In 

the Diamond district (15), also, the prevailing formation is silicified limestone cut by veins containing 

argentiferous galena, cerussite, and stibnite in a 

quartz and calcite gangue (Vanderburg, 1938, p. 17, 

28-29). Both of these districts are in Eureka County.

In the Belmont district (4, fig. 44), a few miles 

east of Manhattan, in Nye County, cerargyrite pods 

are found in quartz veins and lenses in metasomatized slate and limestone close to an intrusive granite 

stock. Slate is altered to mica schist, and limestone 

to jasperoid near this contact (Krai, 1951, p. 20). 

Emmons (1910, p. 73) mentioned "decomposed silici-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 123

fied limestone" gangue enclosing base-metal sulfides 

in the Jack Pot mine, Columbia district (10), in 

Elko County.

Ore bodies of the Delano district (13, fig. 44), 

also in northern Elko County, occur in two parallel 

beds in Paleozoic carbonate rocks adjacent to a 

quartzitic sandstone. These ore beds consist of cerussite, residual galena, anglesite, and copper carbonates in a brecciated gangue of amorphous silica. 

The beds are separated by a partly silicified dolomite 

bed 6-8 feet thick (Granger and others, 1957, p. 

45-46).

The small, isolated Fireball district (22, fig. 44) 

in northwestern Churchill County contains gold- and 

silver-bearing quartz veins in silicified limestone that 

is cut by rhyolite and andesite dikes (Vanderburg, 

1940, p. 30). Gold- and silver-bearing quartz veins 

are also reported along shear zones that cut highly 

silicified Tertiary rhyolite in the Gold Banks district 

(25), Pershing County. Dreyer (1940, p. 15) described this rock as having a conchoidal fracture 

and closely resembling chert, and wrote: "The feldspar is in part replaced by a chalcedonic silica which 

in some places is in contrast with the more coarsely 

silicified groundmass, and thereby preserves the 

feldspar outlines."

At the Victorine mine, Kingston district (29, fig. 

44), Lander County, pockets of base-metal sulfide in 

a quartz gangue are irregularly scattered through a 

25-foot-thick bed of silicified Paleozoic limestone, 

interbedded with black shale and slate (Hill, 1915, 

p. 128).

Spurr (1906a, p. 376) reported silver-bearing 

quartz and jasperoid veins cutting Cambrian and 

Silurian limestone in the southern Klondike district 

(30, fig. 44), about 10 miles south of Tonopah in 

Esmeralda County. These limestones are intruded 

by granitic rocks and are surrounded by Tertiary 

rhyolitic extrusive rocks.

The Nevada district (39, fig. 44), in White Pine 

County, about 10 miles southeast of Ely, contains 

pods and pipes of manganese oxides in Devonian 

limestone. The host rocks for these ore bodies are 

"irregular jaspery quartz lodes that replace the 

limestone along fractures, joints, and bedding 

planes" (Lincoln, 1923, p. 252).

Cameron (1939, p. 582, 593, 621), in discussing 

the geology and ore deposits of the northeastern 

Humboldt Range, Pershing County, stated that chert 

bands and nodules are locally conspicuous in limestone of the Triassic Star Peak Group, and that 

several limestone specimens "show partial replacement by quartz of the jasperoid variety." However, 

he also noted that silicification of calcareous wallrocks adjacent to ore deposits had been observed in 

only a few places, principally at the Sheba-De Soto 

mine (42, fig. 44), where bands of aphanitic cherty 

silica in the lower limestone beds are tentatively 

ascribed to hydrothermal silicification. This mine 

produced silver from argentiferous sulfides and 

sulfosalts in veins and stockworks that cut the limestone.

The Yerington district (54, fig. 44), in central 

Lyon County, contains economically important contact-metasomatic copper deposits in calc-silicate 

rocks resulting from the intense metamorphism of 

Triassic limestone by intrusions of granodiorite and 

quartz monzonite (Knopf, 1918, p. 7). Although 

contact metamorphism within the mineralized area 

was evidently too intense for the development of 

jasperoid, I have two samples of dense light-gray 

jasperoid taken from unmetasomatized limestone at 

localities about 3 miles south of the district. Both 

of these are unfavorable.

In the Lone Mountain district (33, fig. 44), at the 

Alpine mine about 15 miles west of Tonopah fc in 

Esmeralda County, replacement ore bodies of galena 

and cerussite surrounded by jasperoid zones in white 

dolomitic limestone near an intrusive granitic stock 

were described by Spurr (1906b, p. 81). He (p. 12) 

also referred to bedded replacement "veins" of gold 

and silver in a siliceous gangue in Paleozoic limestone and dolomite in this district.

In the Chief (Caliente) district (8, fig. 44), near 

Caliente in Lincoln County, the presence of jasperoid 

associated with oxidized gold-silver-lead ore in veins 

cutting limestone was mentioned by Callaghan (1936, 

p. 16, 17, 28). A. V. Heyl (written commun., 1967) 

also reported abundant jasperoid in this district.

The Spruce Mountain district (45, fig. 44), at the 

south end of the Goshute Range in southeastern Elko 

County, contains prominent masses of jasperoid near 

the Spruce Standard mine (Schrader, 1931b, p. 9, 

24). These jasperoid "blowouts" consist of masses of 

iron-stained quartz breccia as much as 500 feet in 

diameter.

A. V. Heyl (written commun., 1967) further reported that jasperoid is also common to abundant in 

the lead and zinc deposits of the Duck Creek (17, fig. 

44) and Success (46) districts in White Pine County, 

the Mount Hope district (37) in Eureka County, the 

Mud Springs district (38) in southern Elko County, 

and the Lida district (32) in southern Esmeralda 

County.

NEW MEXICO

Information is available on jasperoids from 16 

mining districts in New Mexico (fig. 45), and jas-
124 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

108' 106" EXPLANATION

x 

Minor district or area

 

Reported occurrence

Jasperoid province

DISTKICTS, AREAS, AND 

OCCURRENCES

1. Bishop Cap

2. Carpenter

3. Cooks Peak

4. Cuchillo Negro

5. Georgetown

6. Goodfortune Creek

7. Hadley (Graphic)

8. Hansonburg

9. Hermosa (Sierra 

Caballos)

10. Hillsboro

11. Hot Springs

12. Kingston

13. Lake Valley

14. Magdalena

15. Mockingbird Gap

16. Organ

17. Santa Rita

18. Steeple Rock

19. Tierra Blanca

20. Tres Hermanas

21. Velarde

22. Victorio

23. Victorio prospect

24. Water Canyon

FIGURE 45. Map showing location of jasperoid-bearing districts and prospects in New Mexico.

peroid is known to be present in eight other districts. 

All these localities are in the southwestern part of 

the State in Dona Ana, Grant, Luna, Sierra, and 

Socorro Counties; most of them are concentrated in 

an irregular belt or province extending south-southwest from the Magdalena district in Socorro County 

at least as far as the Mexican border.

Most of these jasperoid-bearing districts contain 

oxidized, locally argentiferous base-metal sulfide vein 

and replacement deposits in silicified Paleozoic limestone and dolomite. In the Hadley (7, fig. 45) and 

Steeple Rock (18) districts, base-metal sulfide vein 

deposits are in silicified Tertiary volcanic rocks. Replacement deposits in jasperoidized Paleozoic limestone in the Bishop Cap (1) district and at the Hot 

Springs (11), Velarde (21), and Victorio (22) 

prospects consist of fluorspar rather than base 

metals. The Lake Valley (13) and the Georgetown 

(5) districts have produced high-grade oxidized silver ore associated with manganese oxides.

BISHOP CAP DISTRICT

(1, ng. 45)

The Bishop Cap district is 11 miles southeast of 

Las Cruces at the south end of the Organ Mountains 

in Dona Ana County.

Limestones and interbedded shales of the Pennsylvanian Magdalena Formation are cut by three distinct sets of faults in the mineralized area. The oldest 

faults strike north and contain the principal 

fluorspar deposits; a younger set of barren faults 

strikes northeast. The third, and youngest set, strikes 

nearly east and occupies an intensely silicified zone. 

Within this zone, fluorite and jasperoid quartz are 

largely concentrated along the footwall; in contrast, 

calcite and barite are abundant along the hanging 

wall. The jasperoid quartz is white, largely massive, 

and aphanitic, and it contains local vugs and fractures coated by drusy quartz deposited by descending 

surface water. The mineralization is of probable 

Tertiary age and genetically related to intrusion of
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 125

the Organ Mountains batholith (Rothrock and 

others, 1946, p. 62).

CARPENTER DISTRICT

(2, fig. 45)

The Carpenter district is in Grant County, about 

6 miles southwest of Kingston on the west slope of 

the Black Range.

Base-metal sulfide deposits are concentrated along 

shear zones in the Ordovician Montoya Dolomite. 

Locally, this limestone has been replaced by jasperoid 

containing small bunches and veinlets of sulfide ore. 

At the Grand Central mine such a shear zone about 

25 feet wide strikes northerly, dips steeply to the 

east, and has ore-bearing jasperoid on the footwall 

side (Harley, 1934, p. 110-111).

COOKS PEAK DISTRICT 

(3, fig. 45)

The Cooks Peak mining district is about 2 miles 

north of Cooks Peak, a conspicuous landmark about 

18 miles north-northeast of Deming, in Luna County. 

Silver and base metals were produced from oxidized 

replacement and fissure vein ore bodies in the 

Silurian Fusselman Dolomite close to its contact with 

the overlying Devonian Percha Shale.

Both the upper part of the Fusselman Dolomite 

and the lower part of the Percha Sale are intensively 

silicified in the mineralized area. According to Jicha 

(1954, p. 62), this jasperoid layer has been brecciated and recemented at different times by successive generations of silica as shown by the presence 

of several different colors and types of jasperoid. 

Some of these types contain conspicuous vugs lined 

with small quartz crystals. Silieification extended 

over a considerable period of time. Some jasperoid 

is postore, but some may also be preore. Most of the 

ore bodies are encased in jasperoid, and the intensity 

of silicification tends to diminish away from them.

Three jasperoid samples from the Fusselman 

Dolomite in this district are included in my collection. Two samples were collected near the east end 

of the east-trending mineralized Othello fault, and 

the third, from the same area about 500 feet north 

of the fault; all three samples were taken about a 

quarter of a mile from the nearest mine workings.

Both samples from the fault zone are gray on 

fresh surface, shades of brown on the weathered 

surface, fine grained, and vuggy, and they have a 

reticulated microtexture. One has hematite pseudomorphs after pyrite and breccia fragments of dense 

aphanitic cherty jasperoid. These two samples have 

slightly anomalous concentrations of Ba, Be, Ga, Pb,

and Zn, yielding indicator-element scores of +6 and 

+ 2.

The single sample from the locality north of the 

fault zone is similar in color but has an aphanitic 

jigsaw-puzzle texture and fewer vugs, and it contains 

detrital-looking quartz grains. This sample is slightly 

high in Na, Ti, Ba, Be, Ga, and Ni, yielding a score 

of -2.

CUCHILLO NEGRO DISTRICT

(4, fig. 45)

The Cuchillo Negro district is in northwestern 

Sierra County in the Cuchillo Mountains, about 5 

miles east of the small town of Fairview. In this 

area Pennsylvanian limestones of the Magdalena 

Group have been intruded by a large sill of Tertiary 

quartz monzonite porphyry, which intrusion has 

caused local contact metasomatism of the limestone. 

Small oxidized base-metal sulfide replacement deposits are in the limestone close to the intrusive contact. Limestone on the Black Knife property has been 

converted to jasperoid along the intrusive contact 

and along small fractures extending upward from 

this contact, above the ore bodies. A 10-foot-wide 

north-northwest-trending silicified shear zone cuts 

the limestone a few hundred feet east of the Black 

Knife claims. This silicified zone with jasperoid contains fluorite and calcite, and it is slightly mineralized at its contact with the porphyry a quarter of a 

mile to the south (Harley, 1934, p. 113-122).

HADLEY (GRAPHIC) DISTRICT 

(7, fig. 45)

The Hadley (Graphic) district is in northern 

Luna County, about 16 miles north of Deming and 

5 miles east of Cooks Peak. Lead and zinc ores have 

been mined here from fissure veins cutting Tertiary 

andesite. According to Jicha (1954, p. 67-68), silicification of the country rock is conspicuous along veins 

and faults near the mines, but the richest ore occurs in the less intensely silicified areas. Extensive 

silicification preceded ore mineralization, and more 

localized silicification accompanied or followed it.

Two jasperoid samples taken from an outcrop 

near the southwestern end of this district are included in my collection. This body of jasperoid is 

massive and grayish brown, and is partly surrounded by a zone of bleached kaolinized andesite.

Both samples are dense and massive. One is grayish orange to pinkish gray and consists of homogeneous medium-grained quartz that has a jigsawpuzzle texture and contains local concentrations of 

fibrous chalcedony. The other is white to pale orange 

with local dusky-brown spots of Hmonite; it has an
126 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

aphanitic cherty texture and contains disseminated 

clay as well as limonite. Both samples are slightly 

high in Mg, Ti, Ba, and Pb; one also contains a 

little Ag, and the other shows anomalous concentrations of Ga, Mo, and Sr. One sample yields an indicator-element score of +9, the other, + 2.

HERMOSA (SIERRA CABALLOS) DISTRICT 

(9, fig. 45)

The Hermosa silver-lead district is on the east 

slope of the Black Range in Sierra County; it extends 

from Monument Creek southward to Seco Creek, 

about 25 miles west of T-ruth or Consequences.

Pennsylvanian limestone has been extensively silicified near the north-trending Pelican fault north 

of Palomas Creek. The Pelican shaft, on the west 

side of this fault, passed through jasperoid cut by 

galena-bearing quartz veinlets above a black shale 

bed; below the shale it entered unsilicified limestone 

cut by veinlets of high-grade lead-silver ore (Harley, 

1934, p. 96).

HILLSBORO DISTRICT

(10, %. 45)

The Hillsboro district is in southwestern Sierra 

County along Percha Creek in the western foothills 

of the Black Range. Most of the mineral production 

from this district has come from gold, silver, and 

base-metal-bearing quartz veins cutting Tertiary 

andesitic rocks.

A belt of jasperoidized Silurian Fusselman Dolomite forms a prominent escarpment on the east side 

of a strong north-trending fault about a mile east of 

Hillsboro on the north side of Percha Creek. This 

rock is red to brown and strongly brecciated and is 

cut by numerous veinlets of white quartz. The jasperoid is locally vuggy and weathers to a rubble of large 

iron-stained boulders. The base of the Devonian 

Percha Shale above the Fusselman Dolomite has also 

been altered locally to a dense red jasperoid. No 

mines have been developed in this large jasperoid 

body, and Harley (1934, p. 125-126, 130) regarded 

it as barren.

I have six samples of the Fusselman jasperoid from 

the top of the escarpment about midway between the 

north end of the ridge and Percha Creek, These 

samples range in color from light gray through yellowish brown, yellowish orange, and grayish red to 

moderate red. Most of their* are brecciated, vuggy, 

and aphanitic.

The samples consist of an older generation of 

cherty jasperoid that has a jigsaw-puzzle texture and 

a younger generation of medium- to coarse-grained 

heterogeneous xenomorphic quartz that fills vugs

and fractures in the older jasperoid and locally forms 

the matrix in which angular breccia fragments of 

older jasperoid are embedded.

The older jasperoid contains abundant red hematite as both disseminated particles and red stain; it 

also contains carbonate particles locally. The younger 

quartz is associated with penecontemporaneous 

yellow to brown limonite and fibrous chalcedony.

Most of the five samples that were analyzed are 

anomalously high in Fe, Ba, Be, Pb, and Zn, and one 

sample is also high in Mn, Cu, and Ga. The suite of 

samples yields indicator-element scores of +3, +3, 

+ 8, +9, and +10. The presence of jasperoid with 

probably favorable characteristics in this body suggests that ore may exist downdip in the Fusselman 

Dolomite.

KINGSTON DISTRICT 

(12, fig. 45)

The Kingston base-metal district in Sierra County 

extends from the crest of the Black Range eastward 

between the North and South Forks of Percha Creek 

about 11/2 miles beyond the town of Kingston.

Fusselman Dolomite has been silicified in an irregular zone at its contact with Percha Shale adjacent 

to a small stock of quartz monzonite porphyry. In 

this zone the replacement jasperoid is a fine-grained 

white to pink breccia partly cemented by white 

crystalline quartz. Elsewhere in the district, Percha 

Shale has been converted to dense red jasperoid, 

which contains disseminated pyrite, adjacent to its 

contact with unaltered Fusselman Dolomite.

Silicifying solutions, considered by Harley (1934, 

p. 98-102) to be genetically related to the quartz 

monzonite intrusive, rose along fractures and shear 

zones in the dolomite and spread out along the contact with the overlying shale, locally converting the 

adjacent rock to jasperoid; this jasperoid apparently 

formed an impermeable seal that trapped later ore 

solutions rising along the same conduits. Locally, the 

jasperoid is slightly auriferous; the younger sulfide 

ore bodies are vein and replacement deposits of 

galena, sphalerite, chalcopyrite, and pyrite in a 

gangue of quartz, rhodochrosite, and manganiferous 

calcite.

LAKE VALLEY DISTRICT

(13, fig. 45)

The Lake Valley district is in southwestern Sierra 

County, about 15 miles south of Hillsboro and 18 

miles west of the Rio Grande.

Manto deposits of silver and manganese ores were 

formed here in Mississippian Lake Valley Limestone 

that is now exposed in a fault block of Paleozoic sedi-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 127

mentary rocks, largely surrounded by Tertiary volcanic rocks.

A thin persistent layer of "chert" or jasperoid at 

the contact between the Alamogordo Member (blue 

limestone) and the Nunn Member (crinoidal limestone) of the Lake Valley Limestone forms the footwall of many silver and manganese ore mantos in 

the central part of the district. Near the major fault 

that bounds the district on the southwest, this layer 

has been brecciated and recemented with younger 

ferruginous, manganiferous, and argentiferous 

jasperoid that displays a variety of colors (Harley, 

1934, p. 176-177).

Silurian Fusselman Dolomite has also been extensively replaced by jasperoid beneath the Percha 

Shale west of the mined area in the district. Younger 

quartz has recemented breccia blocks of silicified 

limestone in large irregular masses with rough 

craggy outcrops that weather to a rubble of talus 

blocks (fig. 2A). The older jasperoid in the breccia 

fragments is milky and granular, and, in some places, 

it resembles quartzite; elsewhere, it is stained red 

with abundant hematite. The younger cementing 

quartz is slightly coarser and has abundant vugs 

lined with quartz crystals (Harley, 1934, p. 173). 

No known ore deposits are associated with the 

jasperoid bodies in the Fusselman Dolomite, although 

the texture, mineralogy, and chemical composition 

of some of them furnish criteria that place them in 

the favorable category (Young and Lovering, 1966).

Many jasperoid samples collected from this district have been described in detail (Young and Lovering, 1966); therefore, these descriptions will not be 

repeated here.

According to Harley (1934, p. 177), early mineralizing solutions, preceding the primary ore stage in 

the district, were rich in silica, but those that emplaced the primary ore minerals were rich in calcium 

carbonate and relatively poor in silica. This conclusion, together with the occurrence of favorable jasperoid in the Fusselman Dolomite close to the south 

boundary fault and the known occurrence of sulfide 

ore bodies in this stratigraphic zone at Kingston and 

Cooks Peak, led Young and Lovering (1966, p. D24- 

D26) to the opinion that similar ore bodies may exist 

in the Lake Valley district at the top of the Fusselman Dolomite close to the south boundary fault.

MAGDALEN A DISTRICT

(14, fig. 45)

The Magdalena district in Socorro County, about 

20 miles west of Socorro, at the north end of the 

Black Range, has been one of the major lead, zinc, 

and copper producers in the State. Most of the ore

deposits are concentrated in a zone of contactmetasomatized upper Paleozoic sedimentary rocks 

surrounding quartz monzonite stocks and smaller intrusive bodies of Laramide age.

The same siliceous emanations that formed limesilicate rock adjacent to the intrusives also rose along 

fractures in the Mississippian Kelly Limestone and 

spread out beneath overlying shale at the base of the 

Pennsylvanian Sandia Formation, forming jasperoid 

in the southern part of the district, farther from 

their source (Loughlin and Koschmann, 1942, p. 53).

The jasperoid is light gray and various shades of 

brown, and it contains abundant drusy vugs that are 

lined with quartz crystals and are elongated parallel 

to the bedding of the limestone host rock. In some 

places, the jasperoid has been brecciated and recemented by white vein quartz containing vugs that 

are locally lined with crystals of quartz, barite, and 

sulfides. Boundaries between jasperoid and host rock 

appear to be sharp, but petrographic study of thin 

sections cut across the contact reveals the presence 

of euhedral quartz crystals disseminated in the limestone. The primary jasperoid is preore, but the white 

vein quartz that cuts and cements it belongs to the 

ore stage of mineralization. The relationships of 

jasperoid to contact-metasomatic skarn and ore deposits at Magdalena are suggestive of those at Yerington, Nev.

ORGAN DISTRICT

(16, fig. 45)

The Organ district is in Dona Ana County, 15 miles 

northeast of Las Cruces at the west base of San 

Augustine Pass between the Organ Mountains and 

the San Andres Mountains. In this district, basemetal sulfides were deposited in veins and as replacements in limestones of the Magdalena Group along 

a strong north-trending fault and fracture zone.

Bodies of white fine-grained locally vuggy jasperoid crop out within this zone in the vicinity of the 

ore bodies. The jasperoid commonly preserves the 

primary textures of limestone and dolomite breccia 

fragments it has replaced. Sparse vugs within it are 

locally lined with crystals of quartz, aragonite, and 

dolomite. An unusual feature of these jasperoid 

bodies is that they are present only near the surface 

and die out abruptly at depths of less than 200 feet 

into a rubble of breccia fragments of unaltered carbonate rock (Dunham, 1935, p. 126-129, 160).

A sample of this jasperoid from a brecciated outcrop near the center of the district is light yellowish 

gray, fine grained, and vuggy. In thin section it has 

a heterogeneous xenomorphic to locally reticulated 

texture with small vugs. It contains sparse dissemi-
128 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

nated grains of apatite and of hematite pseudomorphs after pyrite, also disseminated dust-sized 

particles and local aggregates of a yellowish-orange 

clay mineral, probably nontronite. Spectrographic 

analysis shows slightly high concentrations of Mn, 

Ba, and Cu, yielding an indicator-element score of 

+ 3.

SANTA RITA DISTRICT

(17, fig. 45)

The Santa Rita mining district in Grant County 

is the foremost producer of copper, lead, and zinc in 

the State. Because of its commercial importance, this 

district would have been discussed under the major 

mining districts but for the fact that jasperoid bodies 

are not abundant.

Of three samples taken from small masses of jasperoid in and near the district, two are from exposures in the town of Santa Rita, one about a 

quarter of a mile northeast and the other about the 

same distance north-northeast of the old north pit of 

the Chino copper mine; the third is from an outcrop 

close to the Georgetown Road, about 2 miles northeast of Santa Rita in an unmineralized area. All three 

samples are of silicified limestones in the Magdalena 

Group.

Both samples from Santa Rita are brecciated and 

vuggy, and they weather brown on the outcrop. Their 

breccia fragments are aphanitic and light brown. The 

matrix of one sample consists largely of hematite and 

orange goethite, which contains numerous veinlets 

and drusy vugs of coarse vein quartz; the matrix 

of the other sample is fine-grained medium-gray 

quartz with lenticular vugs, parallel to the bedding, 

that are coated and locally filled with brown limonite. 

The breccia fragments have a homogeneous aphanitic jigsaw-puzzle texture and are heavily impregnated with yellowish-brown limonite particles. Matrix 

quartz in the second specimen is medium grained 

and heterogeneous; it has a xenomorphic to locally 

reticulated texture and contains inclusions of jarosite, goethite, specular hematite, and a little sericite.

The sample of aphanitic jasperoid from the unmineralized area 2 miles northeast of Santa Rita is 

aphanitic and pale red to moderate red. It has a finegrained heterogeneous xenomorphic to jigsaw-puzzle 

texture. Some of the numerous original microvugs 

have been filled with somewhat coarser xenomorphic 

quartz. This matrix contains a few granules of 

chalcedony and breccia fragments of silicified grayish-brown coquina in which the original shell textures are well preserved.

Although both samples from Santa Rita are high 

in Fe, Hg, Ni, Y, and Zn, they show a marked difference in the accompanying suites of other minor elements. The sample with the iron oxide matrix is 

slightly high in Be, Co, Ga, In, Mo, Sn, and V. The 

sample with the quartz matrix is slightly high in Ag, 

Bi, Cu, Pb, and Te. This difference in minor-element 

content may be caused, in part, by the difference in 

iron oxide content; colloidal iron oxide may selectively retain a different suite of minor elements 

than does colloidal silica. The third sample, from 

northeast of Santa Rita, shows traces of Ag and Hg, 

but otherwise it contains no unusual concentrations 

of minor elements. The indicator-element scores of 

these three samples are +15, +16, and +2.

Although bodies of jasperoid are not numerous in 

the Santa Rita area, those that are present seem to 

conform to the criteria for the recognition of favorable and unfavorable jasperoids.

STEEPLE ROCK DISTRICT

(18, fig. 45)

The Steeple Rock district is in the northwest 

corner of Grant County about 50 miles northwest of 

Silver City. Base-metal sulfide ore deposits in the district are localized by a strong fault in Tertiary 

andesitic rocks.

The country rock has been strongly brecciated, and 

locally replaced by silica adjacent to the fault, in the 

vicinity of the ore bodies. These ore bodies consist 

of fissure-vein and replacement deposits of sphalerite, galena, and chalcopyrite in a gangue of vein 

quartz or jasperoidized andesite. The ore occurs both 

as coarse-grained masses relatively free of gangue 

and as fine-grained disseminations in vein quartz and 

jasperoid (Russell, 1947, p. 5, 6).

TIERRA BLANCA DISTRICT 

(19, fig. 45)

The Tierra Blanca district is in Sierra County on 

the east slope of the Black Range near the head of 

Tierra Blanca Creek, about 6 miles south of Kingston. Lower Paleozoic sedimentary rocks in the area 

have been intruded by a small stock and numerous 

dikes of Tertiary quartz monzonite. Silver-lead replacement deposits occur in the Lake Valley Limestone along north-trending faults. The Fusselman 

Dolomite, at its contact with the overlying Percha 

Shale, has been extensively replaced by a finegrained pink and white jasperoid. This jasperoid 

is commonly brecciated, and the breccia fragments 

are cemented by coarser grained vuggy quartz. The 

jasperoid contains a little gold and is similar to the 

jasperoid in the Fusselman Limestone at Kingston 

(12) (Harley, 1934, p. 108-110).
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 129

TRES HERMANAS DISTRICT

(20, fig. 45)

The Tres Hermanas district is in southern Luna 

County, about 30 miles south-southwest of Deming 

and 5 miles north of the Mexican border. It has produced small quantities of base-metal sulfide and oxidized ores from replacement deposits in contactmetasomatized Paleozoic sedimentary rocks close to 

a quartz monzonite stock. A large xenolith of Mississippian Escabrosa Limestone in the northern part of 

the district has locally been replaced by nodules and 

larger irregular masses of massive fine-grained gray 

to white jasperoid. Silicified fault zones in the limestone have been prospected without result. This 

jasperoid is thought to be genetically related to the 

quartz monzonite intrusion, but it appears to be older 

than, and unrelated to, the ore mineralization (Griswold, 1961, p. 50-53).

In spite of Griswold's conclusion that jasperoid is 

not related to ore in the district, some jasperoid 

bodies are, at least spatially, related to sulfide ore. 

A sample of jasperoidized Escabrosa Limestone 

from the Mahoney mine in the northern part of the 

district contains fine-grained galena and is taken 

from a body adjacent to ore. This jasperoid is dense, 

fine grained, and light gray. It has a homogeneous 

granular texture and an average grain diameter of 

0.05 mm. The rock is cut by veinlets of coarse white 

calcite, but the quartz matrix is unusually clean and 

free of inclusions. In spite of its unpromising appearance, the rock is high in several indicator elements. It is rich in Ag, Ce, Cu, Pb, and Zn, and yields 

a score of + 23, and thus it is markedly favorable.

VICTORIO DISTRICT

(22, fig. 45)

The Victorio district is in the southeast corner of 

the panhandle of Grant County. It is about 60 miles 

south of Silver City and 25 miles west of Tres 

Hermanas.

Griswold (1961, p. 79) reported several large irregular masses of jasperoid in Fusselman Dolomite 

on Mine Hill, near the center of this base-metal sulfide district. These masses he regarded as having 

formed contemporaneously with barren quartz veins 

that commonly fill preore fault zones. He stated that 

most of the jasperoid bodies are barren, but that a 

little galena, chalcocite, and tetrahedrite are present 

in one of them.

A sample of jasperoid from the Victorio district, 

taken from a large boulder near the portal of the 

Chance mine adit, presumably represents this body 

of ore-bearing jasperoid referred to by Griswold. It 

consists of coarse-grained vuggy light-yellowish-gray

jasperoid resembling quartzite in texture and color; 

it contains coarse inclusions of galena as much as an 

inch in diameter. The vugs are lined with clear 

quartz crystals.

In thin section the sample appears to be a breccia 

of coarse-grained, relatively homogeneous jasperoid 

fragments that have a reticulated texture and a 

grain diameter that averages 0.1 mm, in a matrix of 

even coarser grained heterogeneous xenomorphic to 

reticulated quartz that ranges in grain diameter 

from 0.2 to 3 mm. The older jasperoid contains rutile 

needles and some fluid inclusions in negative quartz 

crystals. Both generations contain local inclusions of 

diopside and small pyritohedral pseudomorphs of 

hematite after pyrite, as well as abundant dust-sized 

particles of allophane and an unidentified yellowishgray opaque mineral with high relief.

The sample is unusually high in Ag, Ba, Cu, Pb, 

Sb, Sn, and Zn and yields an indicator-element score 

of +22 and thus is very favorable.

OTHER OCCURRENCES

At the old Georgetown district (5, fig. 45) in 

Grant County, about 5 miles northeast of Santa 

Rita, high-grade silver ore was mined from replacement deposits in silicified Fusselman Dolomite beneath the Percha Shale. Silicification of the limestone and deposition of the primary ore probably 

were caused by solutions genetically related to the 

intrusion of Tertiary latite porphyry dikes in the 

area (Paige, 1916, p. 14).

In the Hansonburg district (8, fig. 45), along the 

west front of the Sierra Oscura in eastern Socorro 

County, Lasky (1932, p. 67-69) reported jasperoid 

that locally replaced limestone of the Magdalena 

Group. This jasperoid is locdly cut by veins containing galena and chalcopyrite. Lasky (p. 79, 81) also 

mentioned silicified breccia zones along faults in 

Paleozoic limestone in the Goodfortune Creek (6) 

and Mockingbird Gap (15) districts near the north 

end of the San Andres Mountains.

In the Water Canyon district (24, fig. 45), which 

adjoins the Magdalena district on the southeast, 

base-metal sulfide vein and bedded replacement deposits have formed at the intersections of faults and 

fractures in the Lake Valley Limestone, which has 

been locally silicified (Lasky, 1932, p. 48-53), but 

it is not clear whether this is jasperoid or a coarser 

form of quartz.

Sheridan (1947, p. 4-5) reported a small fluorspar 

deposit with minor galena along fault zones in partly 

jasperoidized Paleozoic limestone in Sierra County 

just across the Rio Grande from Hot Springs (11, 

fig. 45), now known as Truth or Consequences.
130 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

At the Velarde prospect (21, fig. 45), 6 miles 

northeast of Garfield in the southern Caballos Mountains, southeastern Sierra County, fluorite fills cavities in a bed of jasperoidized limestone in the 

Magdalena Group (Rothrock and others, 1946, p. 

156). The Victorio prospect (23) in the Sierra 

Cuchillo Range; 2 miles east of Chise in northwestern 

Sierra County, explores a fluorite-quartz vein cutting 

jasperoidized Paleozoic limestone (Rothrock and 

others, 1946, p. 169).

NORTH CAROLINA AND SOUTH CAROLINA

The only reference I have found in the literature 

to rock that could be considered jasperoid in these 

States is contained in Pardee and Park's discussion 

(1948, p. 35, 42-44, 50) of rock alteration at the 

Howie (3, fig. 41), Whitney (3), and Gold Hill (2) 

mines in North Carolina, and the Haile (5) and 

Brewer (4) mines in South Carolina, and Sundelius 

and Bell's report (1964, p. 212-214) on the Heglar 

prospect in the Gold Hill district (2), North Carolina.

The gold-mining region in which these mines are 

located is in the Piedmont belt east of the Blue Ridge 

Mountains just east of the Catawba River where it 

crosses the border between North Carolina and South 

Carolina, from about 20 to about 50 miles south 

of Charlotte, N.C. These deposits are in metamorphosed Paleozoic volcanic rocks.

Pyritic gold ore is disseminated through intensely 

silicified zones. The ore bodies grade transitionally 

outward into barren quartz. The quartz is dense, 

fine grained, and light gray to dark bluish gray, 

commonly preserving primary textures of the metamorphosed volcanic rocks it replaces. Silicification 

preceded mineralization but followed regional metamorphism. It probably occurred in late Paleozoic or 

Triassic time.

The Heglar prospect in the Gold Hill district (2, 

fig. 41) of North Carolina, is in a belt of lower 

Paleozoic amphibolite, which is intruded by granitic 

rocks. The prospect is in a deeply weathered contactmetamorphic zone consisting largely of pyrite and 

garnet in a siliceous gangue, and of subordinate 

epidote, allanite, apatite, chalcopyrite, magnetite, 

and barite. Allanite, or its alteration products, is 

largely responsible for both the rare-earth elements 

and the radioactivity. Silica, in the form of opal, 

chalcedony, and aphanitic quartz, was introduced late 

in the paragenetic sequence, and has replaced garnet, 

sulfides, allanite, and other gangue minerals 

(Sundelius and Bell, 1964, p. 214-215).

PENNSYLVANIA AND NEW JERSEY

Jasperoid is associated with zinc deposits in lower

'VA

50

I

100 MILES

EXPLANATION

Area of large mining district

X 

Minor district or area

 

Reported occurrence

FIGURE 46. Map showing location of jasperoid-bearing areas 

in parts of Pennsylvania, New Jersey, northern Virginia, 

and West Virginia. 1, Bamford; 2, Calif on (German Valley) ; 3, Friedensville; 4, New Galena; 5, Howell; 6, Rappahanock; 7, Timberville.

Paleozoic carbonate rocks in southeastern Pennsylvania. Miller (1924, p. 62; 1941, p. 337, 340) mentioned silicified Ordovician Beekmantown Limestone 

associated with zinc ore in the Friedensville district 

(3, fig. 46) near Bethlehem in eastern Lehigh 

County. He noted a similar occurrence in the same 

approximate stratigraphic zone in the Bamford district (1) near Lancaster, and in the Calif on (German 

Valley) district (2) in northwestern New Jersey. 

Argentiferous base-metal sulfide ores are associated 

with jasperoid replacing Triassic shale at New 

Galena (4) in Bucks County. Miller (1941, p. 260) 

also referred to "jasperoid quartzite" associated with 

iron ores in Lehigh County; however, these rocks 

are metaquartzites formed by silica cementation of 

Cambrian sandstone, and hence are not jasperoids 

in the sense used here. However, A. V. Heyl (written 

commun., 1967) reported the presence of large bodies 

of true jasperoid at the contact of this quartzite or 

sandstone with the overlying Cambrian limestone at
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 131

Allentown, Topton, Macungi, and Zionsville, all in 

the vicinity of Friedensville.

FRIEDENSVILLE DISTRICT

(3, fig. 46)

Sphalerite in the Friedensville district forms both 

vein and replacement ore bodies in the Ordovician 

Beekmantown Limestone associated with pyrite and 

vein quartz. No galena is found in these deposits, 

and the sphalerite is so low in iron that it is light 

bluish gray, resembling dolomitic limestone. Miller 

(1941, p. 340) stated:

Quartz is especially abundant and occurs as a compact 

quartzite produced by metasomatic replacement of limestone, 

as thin veins cutting the limestones in all directions, and as 

small crystals lining cavities in the somewhat porous altered 

limestones.

The jasperoid at Friedensville is older than the 

sulfides, but it appears to be closely related to them 

both spatially and genetically. I have two samples of 

this rock, which is slightly darker gray than the 

dolomitized aphanitic limestone it replaces, but which 

resembles it closely in texture. Indeed, this jasperoid 

is so dense and so fine grained that, except for its 

field relations, it could easily be mistaken for common chert. The contact between jasperoid and host 

dolomite is megascopically sharp; however, a thin 

section shows abundant tiny relict grains and rhombs 

of dolomite in the jasperoid and incipient silicification of dolomite along grain boundaries close to the 

contact. Both dolomite and jasperoid are cut by veinlets of coarse calcite that contains vugs lined with 

sphalerite and pyrite and filled with late vein quartz. 

This rock is remarkably deficient in associated minor 

elements for an ore-bearing jasperoid. It contains, 

in addition to Ca, Mg, Fe, and Zn (which are present 

in visible inclusions of dolomite, pyrite, and sphalerite) , slightly abnormal concentrations of Na, Ce, Ga, 

and Mo.

Jasperoid is also present in large bodies in Cambrian limestone and quartzite at Allentown, Topton, 

Macungi, and Zionsville, all within a few miles of 

Friedensville and included in the Friedensville district as shown in figure 46. This jasperoid is red or 

brown from abundant iron oxide, and it differs 

strikingly in appearance from the dark-gray jasperoid that is characteristic of the main Friedensville 

district (A. V. Heyl, written commun., 1967).

OTHER OCCURRENCES

Jasperoid at Bamford (1, fig. 46), in Lancaster 

County, is light gray and is closely associated with 

galena and sphalerite. At New Galena (4), in Bucks 

County, dark-gray jasperoid replaces black Triassic

shale in a mineralized fault zone. It is associated 

with galena, sphalerite, and white vein quartz (A. V. 

Heyl, written commun., 1967).

At Calif on (German Valley), in Warren County, 

N.J., jasperoid replaces Beekmantown Dolomite, and 

is closely associated with oxidized lead and zinc ore 

and iron deposits.

SOUTH DAKOTA

In South Dakota, jasperoid-bearing mining districts are concentrated in a roughly triangular area, 

about 5 miles on a side, in Lawrence County in the 

northwestern Black Hills. The apices of this triangle 

are formed by the West Lead district (3, fig. 47) 

about 3 miles west of Lead, on the southeast, the 

Ragged Top Mountain district (2) just east of 

Spearfish Creek on the southwest, and the Carbonate 

district (1) north of Squaw Creek near its junction 

with Spearfish Creek on the north.

The West Lead district contains gold-bearing 

jasperoid that replaces thin dolomite beds in the 

Cambrian and Ordovician Deadwood Formation. In 

the Ragged Top Mountain district, jasperoid bodies 

in Carboniferous limestone have been mined for 

gold and silver. In the Carbonate district, jasperoid

108° 104°

42'

CARBON

 o

 -3 i

00 t,_ _

50 

J_

100 MILES

FIGURE 47. Map showing location of minor jasperoid-bearing 

districts or areas in South Dakota and Wyoming. 1, Carbonate; 2, Ragged Top Mountain; 3, West Lead; 4, Miller 

Hill.
132 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

in the same limestone forms the gangue of argentiferous galena ore bodies.

WEST LEAD DISTRICT 

(3, fig. 47)

According to Irving (1904, p. 112), auriferous 

jasperoid replacement deposits in the Deadwood 

Formation have been developed at West Lead and 

Bald Mountain, and also in the neighboring mining 

camps of Yellow Creek, Garden, and Squaw Creek 

a few miles northwest of Lead. The nature of the 

occurrence of ore and jasperoid is similar in all these 

places, and these deposits have been described as a 

group by Irving under the heading "Refractory 

Siliceous Ores." The deposits are in blankets very 

similar to those in the Mississippi Valley.

These jasperoid bodies are flat-banded masses of 

channellike form, following fracture zones in thin 

beds of impure dolomite that alternate with beds 

of shale and siltstone. The banding in the jasperoid 

preserves original bedding texture in the host dolomite (fig. 2). Where this rock is fresh, it is dense, 

gray, hard, and brittle, and contains pyrite, fluorite, 

and other minor accessory minerals. At and near the 

outcrop, however, it has been oxidized to various 

shades of red and brown and has local porous layers 

that contain abundant small vugs. Individual bodies 

commonly terminate abruptly against impervious 

shale beds. They exhibit a complete gradation from 

narrow stringers closely confined to the feeding 

fractures to broad mantolike conformable masses 

whose widths are many times their thicknesses 

(Irving, 1904, p. 124).

In thin section the unoxidized ore consists of irregularly bounded quartz and chalcedony with finely 

divided disseminated pyrite. The proportions, of 

chalcedony to quartz vary, but quartz is commonly 

more abundant. Detrital quartz grains and residual 

masses of glauconite, as well as fluorite, calcite, 

barite, and sufide minerals, are locally abundant 

(Irving, 1904, p. 137).

I have suites of jasperoid samples from the Deadwood Formation at two localities. One is the dump 

of the Clinton portal of the Bald Mountain mine 

about a mile northwest of the summit of Bald Mountain ; the other is the dump of the Annie Creek mine 

near the head of Annie Creek about 2 miles west of 

Bald Mountain.

Six of the seven samples from the Bald Mountain 

mine show conspicuous banding or layering parallel 

to the original bedding; the seventh sample is a silicacemented breccia of various types of rock. The rock 

is extremely variable in color, showing variegated 

bands of black, dusky red, and various shades of

brown; many of the thinner bands are porous and 

friable, and as a result, the rock tends to break along 

these zones of weakness into flat slabs. Some layers 

are poorly sorted ferruginous siltstone, and these 

alternate with layers of impure silty dolomite. Both 

siltstone and dolomite have been replaced by silica, 

but replacement is more extensive and complete in 

the dolomite.

In thin section the jasperoid samples show detrital 

grains of quartz, microcline, dolomite, tourmaline, 

chert, muscovite, glauconite, clay, and zircon. The 

replacing silica contains penecontemporaneous 

pyrite, sericite, and fluorite; the samples are heavily 

stained and are cut by anastomosing veinlets of 

supergene hematite, limonite, goethite, and jarosite. 

Matrix quartz in different layers ranges in texture 

from aphanitic homogeneous with jigsaw-puzzle 

texture to medium-grained moderately heterogeneous 

with xenomorphic texture. Many of the apparently 

detrital quartz grains contain hematite pseudomorphs after pyrite; some exhibit peculiar braided 

microveinlets of goethite, with a strong preferred 

orientation, which terminate at the grain boundaries.

The suite of samples from the Annie Creek mine 

area is similar in appearance to the one from the 

Bald Mountain mine. These rocks are also variegated 

in color and are banded or laminated with local thin 

porous vuggy layers. Most of the samples under the 

microscope are revealed as silicified impure siltstones 

with a supergene liesegang banding caused by alternating bands of fibrous chalcedony and iron oxides 

(limonite, goethite, and hematite). The iron oxiderich bands commonly are conspicuously vuggy, and 

many of the original vugs have been filled or lined 

with opal. In one sample, vugs in limonite are lined 

with lussatite rather than ordinary opal.

One sample consists of breccia fragments of dense 

medium-gray jasperoid cemented by fine-grained 

medium- to light-gray silica, which is locally porous 

and vuggy. The jasperoid has a heterogeneous 

jigsaw-puzzle texture and a grain diameter that 

averages 0.01 mm and ranges from 0.005 to 0.05 mm; 

it contains numerous microvugs. Sparse rounded 

detrital grains of tourmaline form inclusions, and 

fine-grained pyrite and barite are heavily disseminated through the matrix; some of the vugs have 

been filled with opal. The silica cement consists of 

xenomorphic quartz that has an average grain diameter of 0.04 mm.

The samples from both the Bald Mountain and 

Annie Creek mines contain an unusually large number of minor elements present in greater-thannormal abundance. Many of these elements can be 

attributed to the abundant and varied detrital min-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 133

eral inclusions in these rocks, but some appear to 

have been introduced by the hydrothermal silicifying 

solutions. The following elements are abnormally 

high in most of the samples from both localities: Al, 

Fe, Na, K, Ag, As, Ba, Be, Ga, Ni, Pb, Sr, V, Y, 

and Yb. One or more samples also contain higherthan-normal concentrations of Mn, Co, Cu, In, Nb, 

Nd, Sc, Tl, Zn, and Zr.

Indicator-element scores on eight samples analyzed 

ranged from +23 to +4. Three of these samples 

yielded scores of > + 15, three yielded scores between + 10 and +15, and two yielded scores of + 4.

RAGGED TOP MOUNTAIN DISTRICT

(2, fig. 47)

At Ragged Top Mountain a laccolith of phonolite 

has been intruded at the base of massive Carboniferous limestone. Locally, this limestone has been replaced by jasperoid, which contains gold and silver 

telluride ore along fracture zones north, south, and 

west of the intrusion.

On the Dacy claims just north of the mountain, 

locally brecciated limestone in a northeast-trending 

fracture zone has been replaced by fine-grained 

dense gold-bearing jasperoid that preserves both the 

texture and the color of the host rock, yet has a sharp 

contact with this rock. In the zone of oxidation near 

the surface the jasperoid consists of irregular 

boulders and masses of iron-stained silicified limestone breccia fragments cemented by coarser quartz 

which contains many sharp angular cavities lined 

with quartz crystals (Irving, 1911, p. 646; 1904, p. 

172-176).

At the Ulster mine on the south side of Ragged 

Top Mountain, according to Irving (1904, p. 176),

The ore occurs as irregular masses of silicified limestone 

with which are associated quantities of brilliant purple 

fluorite. These masses are generally in the limestone at the 

contact of that rock with irregular bodies of porphyry * * *. 

The portion containing fluorite is usually lower in gold than 

other parts of the rock, and the highest values are contained

in the dark-colored silicified limestone. 

******

The general character of the ores is such that they may 

readily be seen to be replacements of limestone by silica and 

fluorite with small quantities of gold, silver, and tellurium.

Five samples of jasperoid taken from blocks that 

were excavated from opencuts of a mine between 

Johnson Gulch and Calamity Gulch about a mile west 

of the summit of Ragged Top Mountain consist 

largely of angular dense jasperoid breccia fragments. 

They are light gray, medium gray, pinkish gray, and 

grayish orange, and have an aphanitic, locally vuggy, 

quartz matrix that is heavily impregnated with iron 

oxides, which impart to it various shades of brown 

and red.

The breccia fragments are homogeneous to slightly 

heterogeneous quartz that has a jigsaw-puzzle texture and a grain diameter that averages about 0.01 

mm and ranges from 0.005 to 0.05 mm. The fragments contain sparse microvugs, allophane particles, 

local concentrations of tiny black opaque particles, 

and tiny hematite cubes pseudomorphous after 

pyrite. Some of them contain aggregates of coarser 

(0.01-0.15 mm) xenomorphic to subhedral quartz 

grains with abundant carbonate particles in their 

cores.

The matrix quartz is vuggy and has a heterogeneous xenomorphic texture that is coarser than that 

of the breccia fragments; its grain diameter averages about 0.05 mm and ranges from <0.01 to 0.3 

mm. It contains abundant goethite, brown and 

orange limonite, hematite, and irregular masses of 

fluorite.

Irving (1904, p. 174-175) mentioned the occurrence of a pinkish-brown pigment uniformly distributed as a thin coating on quartz grains of 

jasperoid ore from the Dacy claims. This material 

was thought to be an oxidation product of sylvanite.

Standard oxide analyses of two samples of this 

ore (Irving, 1904, p. 174) are given, in percent, in 

the following table. It is noteworthy, though possibly 

fortuitous, that the sample that showed the higher 

silica content also showed more Ag and Au. (In the 

table, "N.d." indicates not detected.)

Sample Sample

SiOz ............

AbOa ..........

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

MgO ..........

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

BaO ...........

NaaO ..........

K20 ............

Li2O ..........

1

.......... 90.990

.......... 2.970

1 1 <?8

.......... N.d.

.......... N.d.

N.d.

.......... N.d.

2

96.27

.26

19

3 19

1.16

.06

.05

.11

HaO- 105° 1

Hi;O+ 105° J

C02 ...................

s .......................

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

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

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

1

..... .802

...... N.d.

...... .003

...... .091

.....99.181

2

0.03

.42

.96

.05

.06

.02

.03

100.12

Most of the five samples from the mine west of 

Ragged Top Mountain are high in Fe, Ba, Be, Mo, 

Ni, Pb, and V, as shown by spectrographic analyses. 

The richest sample also contains abnormally high 

concentrations of As, In, Sb, and Zn. Indicatorelement scores on the five samples are +20, +12, 

+ 7, +3, and +3. Although fewer minor elements 

are included in this list than in the one for samples 

from the West Lead district, all these samples contain detectable amounts of molybdenum (0.15 percent in one sample), whereas this element was not 

detected in most of the samples from the West Lead 

district.
134 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

CARBONATE DISTRICT

(1, fig. 47)

In the Carbonate district, on the north side of 

Squaw Creek, Carboniferous limestone is intruded 

by sills, dikes, and irregular masses of porphyry. 

Locally, replacement deposits of argentiferous 

galena, oxidized near the surface to cerussite, are 

present in silicified limestone adjacent to these intrusives. At the Iron Hill mine, the largest in the 

district, an ore body of this type was developed to 

a depth of 300 feet on the east side of a thick dike 

of fine-grained white porphyry. In the Seabury mine 

a fracture filled with pinkish-red auriferous gouge 

is encased in ferruginous jasperoid that replaces the 

limestone for as much as 3 feet from the fracture. 

This jasperoid locally contains galena, cerussite, and 

cerargyrite in amounts sufficient to be profitably 

worked (Irving, 1904, p. 177-178).

TENNESSEE

In Tennessee, bodies of jasperoid are known in the 

mining districts of Bumpass Cove (6, fig. 41), Eastern Tennessee (8), Central Tennessee (7), and 

Sweetwater (9). In the Bumpass Cove area large 

masses of jasperoid are associated with iron and 

manganese deposits in a residual clay overlying 

Lower Cambrian Shady Dolomite and with the oxidized base-metal sufide deposits in this dolomite.

The Eastern Tennessee district is characterized by 

extensive zinc sulfide replacement deposits in dolomitized limestone of the Ordovician Kingsport Formation ; in some places the host rock has been replaced 

by jasperoid adjacent to these ore bodies. The Central Tennessee district covers a large area south and 

east of Nashville in which small fissure vein deposits 

of sphalerite, galena, barite, and fluorite cut Ordovician limestone and dolomite; breccia fragments of 

carbonate host rock in some of these veins have 

been replaced by buff to gray jasperoid, but silicification of the host rock outward from the veins is not 

abundant. It is more abundant in the Hoover and 

Knight zinc veins than in some of the others.

BUMPASS COVE DISTRICT

(6, fig. 41)

Bumpass Cove is near the east end of Tennessee 

in Washington and Unicoi Counties a few miles 

north of the North Carolina State line. Masses of 

ferruginous, manganiferous, and zinciferous jasperoids are locally abundant in this area in residual 

clay overlying the Shady Dolomite, although, commonly, the fresh dolomite beneath the clay contains 

little jasperoid. Similar jasperoids are also present 

south of Mountain City at the northeast tip of Tennessee. Here, the jasperoid is locally jointed and 

brecciated and is most abundant where the underlying dolomite has been cut by faults. In the Bumpass 

Cove district, however, most of the jasperoid is 

apparently unrelated to faults, although it is concentrated in areas where the dolomite shows considerable deformation (King and others, 1944, p. 22-23).

This jasperoid forms irregular, but approximately, 

equidimensional bodies ranging in size from small 

nodules to masses 20 feet in diameter. Generally, it 

is yellowish brown, but, locally, it is white, gray, 

black, red, or dark brown. In some places it forms 

open boxworks lined with light-colored drusy saccharoidal quartz or mammillary cryptocrystalline 

silica. Silicified oolites and molds of dolomite rhombs 

in this jasperoid provide evidence that it formed by 

replacement of dolomite. The jasperoid is commonly 

associated with deposits of iron, manganese, and zinc 

oxides, which have replaced the matrix clay and, in 

some places, the jasperoid (Rodgers, 1948, p. 15-16).

Silica in the dolomite beneath the clay is largely 

limited to light-colored friable quartz, which coats 

fractures and open cavities but which does not replace the dolomite. It is similar in appearance and 

mode of occurrence to the late quartz found in voids 

in the jasperoid.

The clay in which the jasperoid is found is largely 

confined to high dissected terraces and is overlain 

in most places with old terrace gravels. Jasperoid is 

thought to have formed by silicification of dolomite 

contemporaneous with its weathering during an 

ancient, more humid climatic cycle (King and others, 

1944, p. 24; Rodgers, 1948, p. 17).

EASTERN TENNESSEE ZINC DISTRICT

(8, fig. 41)

Large replacement deposits of sphalerite in the 

Ordovician Kingsport Formation in the Eastern Tennessee district, north and northeast of Knoxville, are 

associated with extensive preore dolomitization of 

limestone beds and brecciation of the dolomite. Locally, replacement of the carbonate host rock by early 

gray and black jasperoid has occurred adjacent to 

the ore bodies. This jasperoid, which generally extends only a few feet from the ore bodies, contains 

disseminated sphalerite, with which it is considered 

to be penecontemporaneous (Hoagland and others, 

1965, p. 708).

Two samples of this jasperoid are aphanitic in 

hand specimen and have a greasy luster and irregular 

color bands of light gray, olive gray, greenish gray, 

and moderate brown; locally, they contain small 

irregular masses of white calcite.

In thin section the matrix is seen to consist largely
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 135

of homogeneous aphanitic jigsaw-puzzle-textured 

quartz, which contains scattered relict grains and 

small masses of dolomite. Chalcedony is abundant, 

both as small spherical or ellipsoidal masses with 

concentric colloform bands and as coarser grained 

feathery masses filling former vugs. Some former 

vugs have been filled with medium-grained xenomorphic quartz: A rounded mass of white coarsely 

crystalline calcite surrounded by matrix jasperoid 

in one of the samples is probably an inclusion, but it 

could also be a late vug filling. This calcite mass 

contains abundant disseminated euhedral quartz 

crystals which, in turn, contain dust-sized carbonate 

particles. Thin veinlets of late calcite and pale-yellow 

opal cut the matrix in places. The contact between 

the dense jasperoid and equally dense dolomitic host 

rock is sharp in some places, though generally it is 

marked by a transition zone about 0.1 mm wide that 

consists of slightly coarser recrystallized dolomite 

with intergranular veinlets and scattered disseminated masses of jasperoid quartz.

Spectrographic analyses of these samples show 

that they contain only Na, Ba, and Sr in greaterthan-average abundance. The absence of indicator 

elements from this list is unusual in view of the 

close association of the jasperoid with sphalerite ore, 

both spatially and genetically. The cherty appearance 

of this jasperoid and the abundance of colloform 

textures and chalcedony suggest that it was 

originally deposited as a silica gel.

CENTRAL TENNESSEE DISTRICT 

(7, fig. 41)

The Central Tennessee district is within the Nashville Dome south of Nashville. Middle Ordovician 

limestone and dolomite exposed in this broad upwarp 

have been cut by many faults and small fractures. 

These locally are filled by base-metal sulfide, barite, 

and fluorite veins. Breccia fragments of host rock in 

these fissures locally have been completely silicified, 

and in a few places the vein walls also have been 

converted to jasperoid for a distance of 1-2 feet 

outward from the vein (A. V. Heyl, written commun., 1965).

Two jasperoid samples from the Hoover mine, 

south of Milton in the Central Tennessee district, 

are replacements of limestone breccia fragments 

one from the vein and the other from the vein wall. 

Both samples are dense, fine grained, and dark gray, 

and the one from the vein also contains abundant 

disseminated dark-yellowish-orange sphalerite. The 

matrix quartz is fine grained and somewhat heterogeneous ; it has a reticulated to xenomorphic texture, 

a mean grain diameter of about 0.02 mm, and a size

range of 0.005-0.15 mm. Relict carbonate grains and 

dust-sized carbonate particles are abundant in the 

quartz. Narrow veinlets of white calcite cut the 

matrix. Sphalerite grains locally surround matrix 

quartz grains. The sample from the vein wall shows 

a well-marked transition zone about 1 cm wide between jasperoid and limestone host rock. This zone 

is marked by a gradual change from fine-grained 

quartz with sparse interstitial calcite to fine-grained 

calcite with sparse interstitial quartz. These specimens and those of typical black jasperoid from the 

Blue Goose mine in the Joplin area of the Tri-State 

district are strikingly similar in appearance.

The sphalerite-bearing jasperoid sample from the 

breccia fragment in the vein is abnormally high in 

Cu, Ga, Pb, and Zn, and yields an indicator-element 

score of +15. The sample from the vein wall shows 

high Nb, Sr, and Zn and yields an indicator-element 

score of +3.

OTHER OCCURRENCES

Jasperoid, which contains barite and fluorite but 

which otherwise is similar to that of the East Tennessee district, is present in the Sweetwater district 

(9, fig. 41) in northwestern Polk County, about 50 

miles southwest of Knoxville (A. V. Heyl, written 

commun., 1967).

TEXAS

Jasperoid has been reported from two mining districts in western Texas, close to the Rio Grande. One 

is the Shafter silver-lead-zinc district (3, fig. 48) in 

south-central Presidio County, about 200 miles southeast of El Paso, where structurally controlled sulfide 

replacement deposits occur in Permian limestone. 

The other district, the Eagle Mountains (1), is a 

fluorspar district near Eagle Peak in southern 

Hudspeth County, about 100 miles southeast of El 

Paso, where the ore deposits are replacement bodies 

in Cretaceous limestone and vein fillings in Tertiary 

rhyolite.

SHAFTER DISTRICT

(3, fig. 48)

A massive section of Permian limestone 1,000 feet 

thick contains most of the ore in the Shafter district. 

This limestone is overlain unconformably by about 

1,500 feet of Lower Cretaceous rocks that also consist largely of limestone. The ore is principally in the 

form of mantos, controlled by high-angle normal 

faults and, to a lesser extent, by low-angle thrust 

faults and related shear zones in the Permian limestone. There has also been some mineralization of 

the overlying Cretaceous rocks, but it has not re-
136 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

32

104°

30°

CULBERSON /

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v^

x

.. , ^.,. . 1 ,

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t- - J, y_-_.

X AS/7 '\

\ / P E C O S

Avis X

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0 50 100 MILES

I .... I_________|

EXPLANATION

x 

Minor district or area

 

Reported occurrence

FIGURE 48. Map showing location of jasperoid-bearing 

areas in Texas. 1, Eagle Mountains; 2, Sanderson; 

3, Shafter.

suited in minable ore deposits. Hydrothermal alteration and mineralization in the district apparently 

occurred in the following sequence: (1) Dolomitization of limestone, (2) siliceous replacement of limestone and dolomite, (3) deposition of calcite and ore 

sulfides, and (4) supergene alteration of sulfide ore 

(Ross, 1943, p. 45). Hypogene ore and gangue minerals include dolomite, calcite, quartz, pyrite, 

sphalerite, galena, and argentite and minor chalcopyrite and tetrahedrite. Extensive supergene alteration 

of the ore bodies has largely converted the primary 

sulfide minerals into a variety of minerals, including 

iron and manganese oxides, plumbojarosite, cerargyrite, native silver, cerussite, anglesite, descloizite, 

covellite, and chrysocolla.

The ore bodies contain abundant fine-grained 

jasperoid, and the limestone host rock adjacent to 

the ore bodies has locally been replaced by silica, 

partly as disseminated quartz grains in the host rock 

and partly as massive jasperoid in irregular masses 

and layers along bedding planes. Ross (1943, p. 104) 

stated that "In much of the better ore, silicification 

appears to have been nearly complete." Although 

quartz veins are not found in the ore zone, much of 

the ore has been brecciated and recemented by silica, 

after the original jasperoidization of the limestone.

Andesite and basalt dikes in the area are partly 

silicified, and beds of the Lower Cretaceous Presidio 

Formation have been locally silicified along fractures 

(Ross, 1943, p. 104-105).

EAGLE MOUNTAINS DISTRICT

(1, fig. 48)

The Eagle Mountains district consists of several 

small fluorspar deposits that are concentrated in the 

vicinity of a Tertiary syenite stock at Eagle Peak, in 

southern Hudspeth County. These deposits consist 

of replacement mantos in Lower Cretaceous limestone and also of fillings and breccia cement in veins 

and faults cutting the limestone and the overlying 

Tertiary rhyolite (Gillerman, 1953, p. 1, 91).

Quartz occurs in the limestone manto deposits both 

as detrital sand grains and as recrystallized quartz 

intimately associated with fluorite. Locally, the host 

limestone adjacent to such replacement deposits has 

also been extensively silicified. In Spar Valley and in 

deposits at Rocky Ridge, fluorspar veins in limestone 

are encased in conspicuous masses of fine-grained 

dense brown or bluish-gray jasperoid. Gillerman 

(1953, p. 85) wrote of the deposits at Rocky Ridge:

The effects of recrystallization and silicification are present throughout the limestone sequence, and it is generally 

difficult to determine the original nature of the rock. Complete silicification of the limestone resulted in 'a brown or 

blue-gray hard quartzitic-appearing rock that breaks with a 

conchoidal fracture and a smooth surface. Gradations from 

pure unaltered limestone to these quartzitic-appearing rocks 

can be observed in the same boulder or outcrop. The recrystallization and silicification of the limestone is due primarily to 

mineralizing solutions travelling along many faults and other 

fractures in the area.

OTHER OCCURRENCES

Near Sanderson (2, fig. 48) in Terrell County, 

high terrace gravels presumed to be of Pleistocene 

age contain abundant rounded pebbles which consist 

of light-gray aphanitic silica shells surrounding irregular cores of altered Cretaceous limestone (V. L. 

Freeman, oral commun., 1965). Examination of a 

thin section cut through one of these pebbles shows 

that the outer part of the limestone core is weathered 

and porous with numerous large irregular vugs in 

the contact zone. The shell consists of vuggy heterogeneous medium-grained quartz that has a jigsawpuzzle texture, masses of flamboyant chalcedony, and 

abundant carbonate particles in the quartz. This 

suggests that the limestone core fragment was partly 

weathered before the silica shell was formed, that 

silica was precipitated as a colloidal gel, and that it 

partly replaced limestone in the contact zone.
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 137

UTAH

Jasperoids in the major districts (21, fig. 49) of 

Utah, the Tintic and East Tintic, have been discussed 

previously in this report. Fifteen other districts in 

the State also contain abundant jasperoid, and nine 

additional localities are known in which siliceous 

replacement bodies have been noted (fig. 49).

Most of the jasperoid-bearing districts of Utah 

are scattered through the Great Basin province, 

which occupies approximately the western third of 

the State; however, jasperoid is also present in the 

San Rafael Swell, west of Moab, in eastern Utah. 

Most Utah mining districts that are distinguished by 

jasperoid bodies are argentiferous base-metal sulfide 

producers in which both jasperoid and ore formed as 

structurally controlled replacements in Paleozoic 

carbonate rocks. The Bull Valley district (3, fig. 49) 

produced gold from veins that cut Pennsylvanian 

limestone. In the uranium mines of the San Rafael 

Swell area (18) and the silver mines at Silver Reef 

(20), silica has replaced Triassic siltstone or shale 

below the ore zone.

114° 112

BINGHAM DISTRICT

(2, fig. 49)

In the Bingham mining district in Salt Lake 

County, north-central Utah, a thick Pennsylvanian 

quartzite, containing interbedded limestone, has 

been folded into an open syncline that plunges northwest; it is intruded by quartz monzonite porphyry 

stocks and several dikes and sills. Both the sedimentary and the intrusive rocks are cut by numerous northwest- and northeast-trending faults. One 

of the quartz monzonite porphyry stocks contains a 

large low-grade disseminated "porphyry copper ore 

body"; numerous smaller, higher grade copper, lead, 

and silver deposits replace the limestone beds south 

and west of the stock. The ores show a zonal distribution in which copper predominates in and close 

to the stock, and lead and silver predominate farther 

out. Mineralization was preceded and accompanied 

by marmarization and jasperoidization of the carbonate beds (Boutwell, 1905; Cook, 1961).

Although Bingham is the largest mining district 

in Utah, the abundance and significance of jasperoid

EXPLANATION

Area of large mining district

 

Major district

x 

Minor district or area

 

Reported occurrence

Jasperoid province

DISTRICTS, AREAS, AND OCCURRENCES

1. Argentia 13. Mount Nebo

2. Bingham 14. North Tintic

3. Bull Valley (Goldstrike) 15. Park City

4. Castle Creek

5. Clifton

6. Drum Mountains 

. (Detroit)

7. Dugway

8. Fish Springs

9. Gold Hill

10. Lakeside

11. Lucin

12. Mercur and Ophir

16. Rush Valley (Stockton)

17. San Francisco and 

vicinity

18. San Rafael Swell

19. Silver Islet

20. Silver Reef

21. Tintic and East Tintic

22. Tutsagubet

23. Vernon

24. West Tintic

FlGURK 49. Map showing location of jasperoid-bearing areas in Utah.
138 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

in it are uncertain. Boutwell (1905, p. 67-68, 118, 

133, 189-192, 202) discussed at length the jasperoid 

at Bingham; however, Hunt (1924, p. 879) stated 

that much of the presumed "jasperoid" is only altered quartzite and that suites of samples from 

highly mineralized limestone show very little silicification. According to Winchell (1924, p. 898), much 

silica was deposited with the replacement ore bodies 

in the limestone, but very little silica was deposited 

elsewhere. A more recent comprehensive report 

(Cook, 1961) on the Bingham district and surrounding area does not mention jasperoid.

Jasperoid is present in many limestone beds in 

the mineralized area but is most abundant in limestone of the Oquirrh Group. Large, siliceous bodies 

are present on the east flank of Clipper Peak, others 

are scattered irregularly through a belt about a mile 

wide between the stock and the ridge running easterly from West Mountain to the head of Bear Gulch, 

and a large mass caps the northeast-trending ridge 

at the head of Yosemite Gulch, east of the Bingham 

stock.

Mineralization was accompanied, or immediately 

preceded, by jasperoidization that was localized 

along fractures. This silicification started with small 

isolated masses of fine-grained quartz, followed by 

coarse crystalline quartz with contemporaneous 

pyrite and chalcopyrite; it resulted in selective replacement of favorable carbonate beds outward from 

northeast-trending fractures (Boutwell, 1905, p. 

189-192, 199).

The jasperoids are closely related both spatially 

and genetically to some of the sulfide replacement 

deposits in limestone, and pockets of barren'altered 

material within the ore bodies commonly consist 

.largely of jasperoid quartz.

According to Boutwell (1905, p. 38, 118, 133, 

202), the jasperoids of the Bingham district vary 

widely in physical appearance. Some bodies retain 

the texture and color of the- original host rock, 

which they resemble so closely as to be indistinguishable, except for their superior hardness; others are 

dense, white, and coarse grained with a saccharoidal 

texture. Locally, beds of white marble alternate with 

beds of dense cherty jasperoid that are white, black, 

bluish gray, and various shades of yellow, brown, 

and red. Limestone in mineralized areas is commonly replaced by porous spongy masses of quartz.

Incipient jasperoidization of the carbonate rocks 

is marked, in some areas, by thin, anastomosing 

veinlets of quartz and chalcedony following joint 

planes and fractures. In other places it takes the 

form of tiny disseminated quartz particles in recrystallized limestone. In the Commercial mine thin 

veinlets of green and brown opal cut brown recrystallized limestone (Boutwell, 1905, p. 68).

I have only four jasperoid samples from the 

Bingham district. One is from a small outlying jasperoid body on the divide about li/fc miles east of 

West Mountain. The other three are from a larger 

jasperoid body near the quartz monzonite contact a 

few hundred feet north of a saddle on the divide, 

which is about two-tenths of a mile east of Copperfield.

The sample from the ridge east of West Mountain 

has a dense, heterogeneous, largely xenomorphic 

groundmass with a few scattered elongated laths. 

The grain size of the quartz particles ranges from 

0.01 to 0.3 mm, and the large grains are locally 

segregated in irregular masses. Many of the larger 

grains show zoning of allophane inclusions around 

cores. The matrix contains abundant disseminated 

grains of red hematite, a few of which have small 

residual pyrite cores. The jasperoid is cut by veinlets and irregular masses of earthy yellow to orange 

limonite and also by narrow veinlets of jasperoid 

microbreccia particles in a clay matrix (probably 

kaolinite and halloysite).

The three samples from the ridge above Copperfield consist of angular breccia fragments of jasperoid in a matrix of orange-brown limonite and, locally, of jarosite. The larger fragments contain 

abundant irregular open vugs. In texture the matrix quartz ranges from medium-grained homogeneous xenomorphic to heterogeneous xenomorphic. 

The diameter of the quartz particles ranges from 

0.02 to 0.4 mm; local masses and bands of finer 

grained quartz average 0.01 mm. The quartz contains interstitial brown limonite with local concentrations of carbonate dust particles and scattered 

flakes of sericite.

The four whole-rock samples previously discussed 

were ground and submitted to semiquantitative 

spectrographic analysis. The three samples from the 

vicinity of Copperfield contained an appreciable 

quantity of matrix limonite in addition to jasperoid 

quartz, and the abnormally high concentrations of 

some of the elements detected in these samples may 

reflect this contamination.

All four samples showed greater-than-average 

concentrations of lead and zirconium. Zinc was detected in the single outlying sample but not in any 

of the three close to the stock. Copper is an order 

of magnitude higher in these three samples than in 

the outlying sample. Silver is distributed erratically; 

in the outlying sample it shows 3 ppm, and in other
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 139

samples it shows 3 ppm, 30 ppm, and below the limit 

of detection. None of the remaining elements detected in the single sample from the ridge east of 

West Mountain are present in greater-than-average 

abundance. The group of samples from near Copperfield on the edge of the Bingham pit contains abnormally high concentrations of Fe, Na, As, Ba, Bi, 

Mo, Ni, and Sn in addition to the elements previously discussed.

The scores of these four samples suggest that the 

single sample from the ridge east of West Mountain 

is in the probably favorable category, probably near 

the fringe of the zone of sulfide mineralization; the 

other three samples from the edge of the pit, above 

Copperfield, all fall in the favorable category.

BULL VALLEY (GOLDSTRIKE) DISTRICT 

(3, fig. 49)

The Bull Valley mining district is in western 

Washington County near the north end of the Beaver Dam Mountains, about 50 miles west-southwest 

of Cedar City and about 10 miles from the Nevada 

State line. In this area Pennsylvanian limestone has 

been highly silicified locally along fractures, forming conspicuous outcrops of jasperoid that is stained 

yellow and brown by iron oxides. This rock contains 

free gold disseminated in the gangue of quartz, calcite, jarosite, and limonite (Butler and others, 1920, 

p. 598).

CLIFTON DISTRICT 

(5, fig. 49)

The Clifton district is in western Tooele County 

at the north end of the Deep Creek Range, a few 

miles north of Gold Hill and about 12 miles east of 

the Nevada State line. Here, a thick Mississippian 

limestone has been intruded by a small stock of 

Tertiary quartz monzonite. Sulfide ore bodies formed 

in fissure veins that cut the stock; they are also in 

the zone of contact metasomatic alteration surrounding it. Beyond this zone of high-temperature alteration the limestone has been replaced by large bodies 

of cherty fine-grained jasperoid associated with 

some limonite. These bodies form conspicuous outcrops near the Gold Hill-Clifton road about li/2 

miles south of Clifton. A small amount of prospecting on these "reefs" has failed to locate any ore 

bodies (Butler and others, 1920, p. 479).

DRUM MOUNTAINS (DETROIT) DISTRICT 

(6, fig. 49)

The Drum Mountains, or Detroit, district straddles the line between Juab and Millard Counties 

about 30 miles northwest of Delta. The small desert

range in which the district lies is situated between 

the Sevier Desert on the east and Whirlwind Valley 

on the west. This range is a westward-tilted block, 

composed of a thick series of Precambrian and 

Cambrian quartzite overlain by Cambrian limestone 

and dolomite. In the mineralized area these rocks 

are cut by numerous east- to northeast-trending 

faults that have displacements ranging from a few 

feet to a few thousand feet.

The district was originally worked for gold and 

copper, mostly during 1895-1918, but more recently 

it has produced manganese ores. The ore bodies are 

localized by the intersection of fractures with favorable carbonate beds. Although the manganese and 

gold-copper ores are related genetically, they are 

separate and distinct in occurrence and composition. 

Manganese ore bodies contain only traces of gold 

and copper, and gold-copper ore bodies contain little 

manganese (Crittenden and others, 1961, p. 507).

Many of the stronger faults served as conduits 

for silica-bearing hydrothermal solutions that silicified adjacent limestone and dolomite locally and 

formed conspicuous yellowish-brown jasperoid 

reefs. These reefs contain disseminated pyrite or 

limonite after pyrite, chalcopyrite and its oxidation 

products, and small amounts of other sulfides in and 

near gold-copper ore bodies (Butler and others, 

1920, p. 464). Crittenden, Straczek, and Roberts 

(1961, p. 515) believed that jasperoid may be closely related genetically to manganese, as well as to copper and gold, and recommended the exploration of 

jasperoid bodies where they intersect the basal 

carbonate beds near the Martha mine.

Ten samples of jasperoid from the Drum Mountains district were collected by Lovering (in Lovering and others, 1963, p. Bl) in the course of an 

investigation of hydrothermal dolomite in the area. 

All these samples were taken from bodies along 

faults and strong fractures; three are from mine 

prospects, and seven are from bodies that have not 

been prospected.

The jasperoid samples appear to represent two 

distinct types of rock. Most of the samples, including the three from prospected bodies, are crystalline, vuggy, and heavily iron stained in various 

shades of yellow, brown, and red. They have a relatively coarse-grained heterogeneous and distinctly 

reticulated texture and distinct zonal overgrowths 

on some of the larger quartz crystals. The quartz 

crystals are locally disseminated through coarsegrained patches of calcite. The jasperoid samples 

also contain abundant hematite, goethite, and brown 

limonite; sparse patches of malachite are visible in
140 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

one sample from a mine adit, and chalcedony locally 

lines vugs in the quartz.

The other type of jasperoid is represented by 

three samples from faults and fracture zones near 

the abandoned townsite of Joy, northwest of the 

main mining district. These samples consist of lightgray, yellowish-gray, and brownish-gray chertylooking quartz which locally is stained brown by 

iron oxides and which in some places contains large 

irregular open vugs. The quartz is fine grained and 

homogeneous and has a xenomorphic to jigsawpuzzle texture. Yellow limonite and fine-grained calcite are abundant, and chalcedony locally lines vugs.

Most jasperoid samples of both types contain 

anomalously high concentrations of Ag, Au, Bi, Cu, 

Pb, and Sb. The coarser grained jasperoid with reticulated texture generally shows more minor elements with abnormally high concentrations than 

does the aphanitic variety. In addition to the elements listed above, most samples in this group also 

show abundant Ba, Ni, and Zn; one or two of them 

are also high in As, Co, Ga, Sn, and V. All but two 

of the samples contain >0.02 ppm of Au, and one 

sample contains 26 ppm Au.

Indicator-element scores for the group range from 

+2 to +22. The sample that yielded the highest 

score contains > 1 percent Cu, 0.05 percent Ag, 0.05 

percent Zn, and 1.7 ppm Au.

The association of Ag, Bi, Cu, and Pb in this 

group of samples is noteworthy because it also characterizes jasperoids of the Bingham (2, fig. 49) and 

Ely (19, fig. 44) districts. This similarity and the 

high gold content of the jasperoid suggest that the 

Drum Mountains district may contain considerably 

more ore than has thus far been mined.

DUGWAY DISTRICT

(7, fig. 49)

The Dugway district is in south-central Tooele 

County, near the north end of the Granite Range, 

about 55 miles southwest of Tooele. Faults and fractures cutting Mississippian limestone in this district 

have localized replacement ore bodies of argentiferous galena and sphalerite, all partly oxidized. In the 

northern part of the district, in the vicinity of the 

Four Metals mine, the limestone has been highly 

fractured and replaced with jasperoid near the 

oxidized ore bodies (Butler and others, 1920, p. 

463).

GOLD HILL DISTRICT 

(9, fig. 49)

The Gold Hill district is in southwestern Tooele 

County in Tps. 7 and 8 S., R. 18 W., at Gold Hill,

a few miles south of the Clifton district and about 

15 miles east of the Nevada State line. Paleozoic 

shales and carbonate rocks in this area have been 

broken by both low-angle thrust faults and highangle faults and intruded by a Tertiary quartz 

monzonite stock and several smaller igneous bodies. 

Mining activity in the district centered at Gold Hill, 

a small northwest-trending ridge, about l}/2 miles 

west of Gold Hill townsite, and at the U.S. mine 

about half a mile south of the townsite. Large replacement ore bodies of arsenopyrite and base-metal 

sulfides associated with jasperoid were developed 

here in Carboniferous and Permian limestone. Many 

other jasperoid bodies are present in various parts 

of the district in the Mississippian Ochre Mountain 

Limestone and in carbonate beds of the Mississippian to Permian Oquirrh Formation. These jasperoids are thoroughly discussed by Nolan (1935) and 

are also shown on the geologic map of the district 

that accompanies his report.

Nolan (1935, p. 93) stated that jasperoid bodies 

tend to be concentrated close to the quartz monzonite 

contact or along faults in the Ochre Mountain Limestone and the Oquirrh Formation that predate the 

quartz monzonite, and that large jasperoid bodies 

are exposed on Gold Hill, near the mouth of Barney 

Reevey Gulch, and at the U.S. mine south of Gold 

Hill townsite. The district map that accompanies 

Nolan's report also shows a mass of jasperoid that 

is more than 1 mile long and as much as 1,000 feet 

wide in places along an east-trending fault about 

li/2 miles south of the summit of Ochre Mountain, 

outside the main mining area in the district.

Nolan (1935, p. 152-153) described these outcrops as consisting of jagged reddish-brownweathering jasperoid that has been brecciated and 

recemented by several generations of quartz exhibiting different textures and colors. This jasperoid 

is commonly vuggy, with breccia fragments of unreplaced limestone and, locally, visible plates of 

barite, oxidized copper minerals, and masses of 

green chalcedony. The jasperoid outcrop on Gold 

Hill is more than 100 feet wide and has been cut by 

mine workings at a depth of 700 feet, where it has 

a sharp contact with unreplaced limestone.

The older jasperoid quartz matrix is fine grained, 

crystalline, and free of fluid inclusions; it shows 

features that may be desication cracks which partly 

controlled the location of younger veinlets of coarser 

quartz. These veinlets commonly exhibit vague outlines of crystals which are normal to the walls and 

which are now recrystallized to aggregates of anhedral quartz grains; contacts of veinlets with ma-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 141

trix quartz are gradational. Where associated with 

ore the jasperoid commonly contains pyrite, arsenopyrite, galena, sphalerite, and tetrahedrite or their 

oxidation products. Elsewhere, barite, chlorite, chalcedony, opal, calcite, and sericite are common accessory minerals! Contacts between sulfide ore bodies 

and jasperoid tend to be gradational in contrast to 

the characteristically abrupt contacts between jasperoid and host rock.

Nolan (1935, p. 94) expressed the opinion that the 

silica that formed the original jasperoid was deposited as a gel and that the younger quartz veinlets 

in it may have formed by the expulsion of silicabearing fluid into shrinkage cracks during the 

crystallization of this gel.

The jasperoid of the Gold Hill district is younger 

than the contact metasomatism and recrystallization 

of carbonate rocks that accompanied intrusion of the 

quartz monzonite. In the major arsenic replacement 

ore bodies of the U.S. mine, quartz is continuous and 

contemporaneous with jasperoid replacing the limestone host rock. At the Gold Hill mine, jasperoid is 

closely related to tetrahedrite-bearing quartz veins 

in the limestone, and limestone adjacent to ore 

bodies is locally replaced by fine-grained pale-gray 

jasperoid. Within these ore bodies, in some places 

arsenopyrite ore has been brecciated and recemented 

by fine-grained quartz resembling jasperoid; however, it seems that sphalerite is nearly contemporaneous with the silica, and that galena, jamesonite, 

and stibnite are somewhat younger.

Of nine samples from the vicinity of Gold Hill, 

two are from outcrops about 5 miles northwest of 

the townsite, one is from the townsite, and six are 

from exposures on the south side of Ochre Mountain, 

5-6 miles southwest of the townsite. Unfortunately, 

I have no samples of the jasperoid described by 

Nolan as being associated with the ore bodies on 

Gold Hill or at the U.S. mine.

The two samples from the area northwest of Gold 

Hill may represent the bodies of barren jasperoid 

mentioned by Butler, Loughlin, Heikes, and others 

(1920, p. 479) in their description of the Clifton 

district (5, fig. 49). These two samples were taken 

from conspicuous outcrops close to the road about 

midway between the two districts. Both samples 

represent brecciated and silicified fault zones in 

Paleozoic limestone. Both consist of gray breccia 

fragments enclosed in a dense grayish-orange to 

moderate-brown matrix. Breccia fragments consist 

of dense dark-gray material that looks like chert 

and of medium-gray heterogeneous quartz that has 

a xenomorphic to jigsaw-puzzle texture and an average grain diameter of about 0.02 mm, cemented in a 

matrix whose appearance is so similar to that of the 

fragments that, commonly, the boundaries between 

fragments and matrix are clearly visible only by reflected light. The matrix contains irregular masses 

of yellow to brown limonite, and locally shows disseminated grains of hematite that may be pseudomorphs of original pyrite. Small vugs in the matrix, 

and fractures cutting it, are commonly lined with 

coarse xenomorphic quartz, some of which show 

crystal faces and zonal overgrowths; these fractures 

and vugs are locally filled with coarse late calcite. 

Both samples are slightly higher than normal in Ba, 

Ni, and Pb, but not sufficiently so to place them in 

the favorable category.

The single sample from Gold Hill townsite was 

taken from a prominent knob adjacent to an old 

millsite about 100 yards west of some abandoned 

buildings. It is not a true jasperoid, but rather a 

fault breccia composed of comminuted chert and 

limestone fragments, cemented by indurated calcite 

microbreccia that shows incipient replacement by 

quartz that has a coarse jigsaw-puzzle texture and 

wavy extinction. Opaque orange limonite forms irregular veinlets cutting the carbonate. The sample 

shows slightly anomalous concentrations of Na, Ba, 

Cr, Pb, Sr, V, and Zr, but it yields an indicatorelement score of only +2.

The six samples from outcrops on the south side 

of Ochre Mountain, well beyond the limits of the 

main productive area, are mostly breccias that consist of chert or jasperoid fragments in a matrix of 

younger jasperoid. The matrix is commonly light 

olive gray to pale yellowish brown on fresh exposures, grayish orange to yellowish orange on 

weathered surfaces; breccia fragments are commonly dark yellowish brown to dark gray, darker 

than the matrix. The breccia fragments are uniformly aphanitic and dense; the matrix is also 

aphanitic but is locally porous and vuggy. In thin 

section, both matrix and inclusions have a relatively 

homogeneous jigsaw-puzzle to locally xenomorphic 

texture and an average grain size of 0.01 mm; both 

commonly contain relict dolomite rhombs and carbonate particles. The inclusions are dense, and some 

are full of opaque carbon particles; whereas the matrix is free of carbon and locally contains abundant 

open microvugs. Veinlets of calcite, brown limonite, 

and coarser grained xenomorphic quartz cut the 

matrix. Two samples taken about 100 yards from a 

small abandoned shaft contained disseminated pyrite 

that is largely altered to hematite, and one of these 

samples also exhibits late veinlets filled with goethite 

and jarosite. All six samples are higher than average
142 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

in Ba, and most of them are also high in Ni and 

Sr. The two samples that contain disseminated 

pyrite also show traces of Pb. One of them contains 

a little Ag and Zn, and the other, detectable As and 

Bi; their indicator-element scores are +8 and + 4, 

respectively. The other four samples yielded scores 

ranging from 2 to +3.

LUCIN DISTRICT 

(11, fig. 49)

The Lucin district is in Box Elder County in T. 6 

N., R. 19 W., about 10 miles southwest of Lucin. 

The district overlaps the Utah-Nevada State line, 

but most of it is in Utah. Ore deposits consist of copper and lead-zinc-silver fissure replacement ore 

bodies in Pennsylvanian limestone, which has been 

intruded by a small stock of Tertiary quartz monzonite with local contact metasomatic alteration. The 

Copper Mountain mine developed copper replacement ore in jasperoid in, and adjacent to, a strong 

north-trending fault. At the south end of the deposit, massive copper-bearing limonite grades into 

barren iron-stained jasperoid along this fault (Butler and others, 1920, p. 493).

A jasperoid sample from this district taken from 

near the head of a gulch about 3 miles north of Bald 

Eagle Mountain and 1 mile east of the Nevada line, 

about half a mile from the nearest mine workings, 

consists of sparse dense dark-gray breccia fragments 

cemented by a porous fine-grained dark-yellowishorange matrix. A thin section shows heterogeneous 

matrix quartz that has a xenomorphic texture and a 

size range of 0.01 to 0.06 mm; it contains numerous 

small rounded inclusions of older quartz, minor 

sericite, carbonate particles, and allophane. Orangebrown limonite is abundant in short veinlets, irregular masses, and as a coating on quartz grains. 

The sample is slightly high in Ba, Be, Cu, Li, Mo, 

and Sr, yielding an indicator-element score of +5.

MERCUR AND OPHIR DISTRICTS 

(12, fig. 49)

These two districts are about 4 miles apart in 

eastern Tooele County on the western flank of the 

Oquirrh Mountains, 15-20 miles south-southeast of 

Tooele. In both districts the ore deposits are largely 

localized by intersections of faults and fractures 

with favorable carbonate beds of Mississippian age. 

Mercur, the southern district, was a famous gold 

camp early in the 20th century, and it also produced 

some silver. The Ophir district produced silver, lead, 

zinc, and copper, but relatively little gold.

According to Gilluly (1932, p. 97), jasperoid is 

abundant between Mercur and Lion Hill, near West

Mercur, near the mouth of Silverado Canyon, in Dry 

Canyon, and in the hills between Dry Canyon and 

Ophir. Although most jasperoid bodies in the two 

districts are in Mississippian rocks of either the 

Great Blue Limestone or the Humbug Formation, 

their distribution is erratic and discontinuous. 

Structural control of the distribution of jasperoid 

bodies is shown by their tendency to transgress 

bedding and by their local association with fracture 

zones. The outcrops typically are conspicuous, 

jagged, rusty brown, and thoroughly brecciated, 

and they contain angular blocks of unreplaced limestone. Contacts between jasperoid and host rock are 

sharp with no visible transition zone. Coarse-grained 

white vein quartz commonly cements jasperoid 

breccia and lines vugs in the jasperoid. Many of 

these vugs are filled with white calcite. Fresh j asperiod is light gray to black and aphanitic to fine 

grained.

Two common varieties of jasperoid are readily 

distinguished under the microscope. One consists of 

cryptocrystalline anhedral interlocking quartz 

grains <0.03 mm in diameter and accessory chalcedony, tourmaline, sericite, calcite, epidote, apatite, 

and zircon. The other variety consists of interlocking 

euhedral to subhedral quartz crystals averaging 

about 0.2 mm in diameter (reticulated texture) and 

carbon and carbonate dust particles in addition to 

the accessory minerals that characterize the first 

variety. The aphanitic variety commonly contains 

streaks and lenses of coarser quartz with wavy extinction, which is associated with barite and, locally, 

with stibnite. Younger flamboyant vein quartz with 

barite cuts both varieties of jasperoid and, locally, 

this vein quartz is cut, in turn, by still younger 

brown-stained veinlets of cryptocrystalline quartz 

and accessory tourmaline, apatite, calcite, and 

zircon.

Gilluly (1932, p. 100) concluded that the first 

stage in the formation of jasperoid at Mercur was 

the replacement of carbonate rock by colloidal silica 

gel. Rapid crystallization of this gel led to the formation of aphanitic cherty jasperoid, whereas more 

gradual crystallization produced the coarser grained 

(reticulated) variety. Crystallization of the gel was 

accompanied by shrinkage. Coarser grained vein 

quartz associated with barite and, locally, stibnite 

and chalcopyrite then filled the shrinkage cracks. 

Brecciation and fracturing of this mass was followed by introduction of the late-stage cryptocrystalline brown quartz; local replacement was marked by 

blended contacts. The association of tourmaline with 

early jasperoid was cited by Gilluly (p. 101) as 

evidence favoring a relatively high temperature of
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 143

replacement of limestone by silica. He pointed out 

that barite and stibnite are not present in the oldest 

jasperoid, and that calcite is abundant only in the 

youngest.

The genetic and spatial relationships between the 

various types of jasperoid and the primary ore deposits were not stressed by Gilluly (1932, p. 135), 

although he noted that in certain parts of the districts (near Mercur and in the hills between Ophir 

and Dry Canyon) ore deposits are commonly localized within or beneath jasperoid bodies. His detailed 

description of the various types and ages of jasperoid and the minerals commonly associated with 

each suggests that the original replacement of limestone by silica gel preceded ore-stage mineralization, 

but that the later silica, which cements jasperoid 

breccia and forms quartz veinlets cutting jasperoid, 

was approximately contemporaneous with it.

Sixteen samples of jasperoid from the MercurOphir area are in my collection; eight are from the 

main mineralized area close to the old town of Mercur, three are from outcrops in the relatively unmineralized area between the two districts, and five 

are from the Ophir district.

The samples from Mercur were taken in the vicinity of the Franklin Lease mine west of the townsite 

and the Sacramento mine south of the townsite. They 

contain examples of the two types of older gray 

jasperoid and of the younger brown jasperoid described by Gilluly (1932). The aphanitic variety 

with jigsaw-puzzle texture is largely free of inclusions, but it contains sparse carbonate and allophane 

dust particles. The coarser grained reticulated 

variety contains pyrite, or its oxidation products, 

and barite in addition to sericite, and carbonate particles. The brown jasperoid contains all these minerals plus abundant limonite particles and, locally, 

tourmaline.

The three specimens from outside the main mining districts were collected from near the top of 

Rover Hill, near the mouth of Silverado Canyon, and 

about half a mile up Silverado Canyon. The sample 

from Rover Hill is of the coarser grained reticulated 

older jasperoid and contains sericite, carbonate particles, and sparsely disseminated pseudomorphs of 

jarosite after pyrite. Both samples from Silverado 

Canyon are of the aphanitic older jasperoid and contain only sparsely disseminated sericite, allophane, 

and carbonate particles.

Of the five samples from the Ophir district, two 

are from the vicinity of the Chloride Point mine 

about a mile south-southeast of Ophir, two are from 

the outskirts of the townsite of Ophir, and one is 

from an outcrop near the Lakes of Killarney mine

about 2 miles west of Ophir. Four of these samples 

show the coarse-grained reticulated jasperoid, but 

the fifth one, which was collected close to a porphyry 

contact, has a coarse-grained heterogeneous xenomorphic texture. The sample from near the Lakes 

of Killarney mine is from a fault zone and is the 

only one in the suite that shows well-defined examples of both the older jasperoid types described 

by Gilluly (1932). In this specimen, breccia fragments of aphanitic jasperoid are cemented by a 

matrix of coarser reticulated jasperoid that is cut 

by veinlets of still coarser xenomorphic quartz; the 

whole mass was then rebrecciated and cemented by 

coarse calcite. Accessory minerals in these jasperoids are the same as in their counterparts from the 

Mercur district: carbonate particles, sericite, pyrite, 

or its oxidation products, and, locally, barite.

There appears to be some difference between the 

suites of minor elements present in abnormally high 

concentrations in the jasperoid samples from the 

two districts. Nearly all the Mercur samples are high 

in Ba and Hg, and most of them are high in Ag, Sr, 

and Te. Nearly all the Ophir samples are high in 

Sr, Ag, Cu, Pb, and Zn, and most of them are high 

in Ba, Hg, Ni, Sb, Te, and Zr. Two of the Mercur 

samples contain detectable amounts of As and Mo, 

elements not found in any of the Ophir samples. 

Two samples from Ophir, however, contain Bi, Nb, 

and Sc, elements not found in the Mercur samples.

Only three of the eight samples from the Mercur 

district yield indicator-element scores greater than 

+ 5, and the highest was +11. Four of the five samples from the Ophir district yield scores greater than 

+10. The highest score for this group was +18, and 

the lowest, +1. All three of the samples taken between the two districts gave scores of 1.

MOUNT NEBO DISTRICT

(13, fig. 49)

The Mount Nebo district is in the northeast corner 

of Juab County in the Wasatch Range, about 10 

miles northeast of Nephi. Sulfide ore deposits in the 

district form replacement bodies along faults and 

fractures in Paleozoic carbonate rocks.

At the Santaquin Chief mine a pipelike ore body 

of galena in a gangue of quartz and calcite has been 

developed at the intersection of north- and easttrending fractures in jasperoidized Mississippian 

limestone. This jasperoid contains sericite, chlorite, 

titanite, fluorite, limonite after pyrite, and galena 

as both disseminated grains and narrow streaks and 

lenses. Vugs in the jasperoid are lined with crystalline quartz and calcite (Butler and others, 1920, 

p. 332).
144 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

NORTH TINTIC DISTRICT

(14, fig. 49)

The North Tintic district is on the line between 

Utah and Tooele Counties, about 5 miles north of 

Eureka in the northern East Tintic Mountains. It 

lies just north of the Tintic and East Tintic districts 

(21, fig. 49), which were previously discussed in 

the present report. Oxidized lead and zinc deposits, 

lean in silver, were mined in the district. Paleozoic 

sedimentary rocks in the area, consisting largely of 

limestones and dolomites, have been folded into a 

north-trending asymmetrical anticline and syncline; 

these folds are cut by several north-trending, westdipping thrust faults that- were, in turn, cut by 

north- and northeast-trending high-angle faults before early Tertiary volcanism that blanketed the 

area with flows and pyroclastics (Proctor, 1964, p. 

1565-1567).

Dikelike and bedded replacement bodies of jasperoid are abundant in and near Chiulos Canyon, 

largely in the Deseret and Humbug Formations, but, 

locally, in the Great Blue Limestone above the Humbug. These dark-brown to reddish-brown bodies are 

as much as 100 feet thick and several hundred feet 

long and form conspicuous outcrops. North and 

northeast of this area of intense jasperoidization is 

a zone in which smaller bodies of fine-grained gray 

jasperoid occur as replacement masses in brecciated 

fault zones. Intensity of jasperoidization is greatest 

in the southwestern part of the area closest to the 

Tintic and East Tintic mining districts.

The jasperoid consists of fine-grained quartz that 

has an average grain diameter of <0.1 mm. Vugs 

are abundant locally, and they are commonly lined 

with euhedral quartz crystals. Brecciation of jasperoid and recementation by later quartz are conspicuous in some places. Red iron oxide commonly 

accompanies this late quartz, a few hematite pseudomorphs after pyrite have been noted in thin sections, 

and late calcite also fills some fractures in jasperoid 

(Proctor, 1964, p. 1575).

In this area, as in the Tintic and East Tintic districts (21, fig. 49) to the south, hydrothermal 

dolomitization preceded jasperoidization which, in 

turn, preceded sulfide mineralization.

RUSH VALLEY (STOCKTON) DISTRICT 

(16, fig. 49)

The Rush Valley district is in eastern Tooele 

County, about 8 miles south of Tooele and 10 miles 

northwest of the Ophir district.

In this district replacement base-metal sulfide deposits have been formed close to the axis of a northward-plunging anticline in favorable beds of Carboniferous limestone and quartzite, where fractures 

and small faults, parallel to the anticline, cut these 

rocks. Highly altered felsic dikes fill some of these 

fissures. Jasperoid replacing limestone adjacent to 

the fractures is locally abundant, as it is in the 

Ophir district.

At the Muscatine mine, near the SW cor. T. 4 S., 

R. 4 W., abundant jasperoid and hornfels are associated with pyrite, sphalerite, and galena replacement bodies in limestone (Gilluly, 1932, p. 163).

SAN FRANCISCO DISTRICT AND VICINITY 

(17, fig. 49)

The San Francisco mining district is at the south 

end of the San Francisco Mountains in Beaver 

County, about 15 miles west-northwest of Milford. 

A much larger area, which extends from the Escalante Valley on the east to the Wah Wah Mountains 

on the west and from the Iron County line on the 

south to the Millard County line on the north, contains many widely scattered small silver, lead, zinc, 

and copper mines and areas of hydrothermally silicified rocks. This larger area is considered here, for 

convenience, with the San Francisco district.

At the Horn Silver mine, in the main San Francisco district, volcanic rocks on the hanging-wall side 

of a strong mineralized fault zone have been extensively leached of all their principal constituents, 

except iron and silica, yielding a rock composed 

chiefly of fine-grained quartz with disseminated pyrite and some barite. Limestone on the footwall side 

of this zone is much less altered, although it has been 

generally recrystallized and locally silicified along 

fissures (Butler, 1913, p. 168).

At the Harrington-Hickory mine in the Star district on the east side of the Star Range, 5 miles from 

Milford, Triassic limestone, interbedded with siliceous shale and quartzite, has been replaced by 

argentiferous galena and sphalerite ore bodies along 

small fractures, and has been converted to jasperoid 

for as much as 30 feet outward from the fractures, 

although the associated shale and quartzite are only 

slightly altered. The jasperiod quartz contains accessory galena, pyrite, orthoclase, apatite, titanite, 

garnet, and magnetite (Butler, 1913, p. 195).

Of 10 samples from the San Francisco district and 

surrounding area in my collection, three are from 

the south end of the main district along State Highway 21, close to Squaw Spring; three are from a 

prominent jasperoid ridge surrounded by altered 

Tertiary volcanic rocks about 10 miles south of 

Squaw Spring; and the remaining four were collected in T. 30 S., R. 14 W., at intervals along a dirt 

road running from Milford around the south end of
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 145

the Wah Wah Mountains far south of the old Wah 

Wah lead-zinc district. Two of this last group are 

jasperoid samples, and the other two are dolomite 

showing incipient silicification.

The samples from near Squaw Spring weather 

yellowish brown to reddish brown; one of these is 

light brownish gray on fresh surfaces, and the other 

two are pale red. They were collected from an easttrending breccia zone in Cambrian limestone, about 

a mile from the nearest large mines. The rocks are 

microbreccias of small angular jasperoid and limestone fragments cemented by aphanitic quartz that 

has a jigsaw-puzzle texture. Some of the jasperoid 

fragments are coarser grained and have a heterogeneous, locally xenomorphic texture, and contain 

abundant carbonate dust particles. The matrix is cut 

by veinlets of xenomorphic quartz that has an average grain diameter of about 0.1 mm. Hematite is 

locally abundant in irregular masses and anastamosing veinlets that cut the matrix, but it shows no 

evidence of derivation from original pyrite. Sparse 

irregular inclusions of barite as much as 1 mm in 

diameter were observed in one sample. All three 

samples are slightly high in Pb and Sr, one is 

slightly enriched in Ba, and another in Hg. The indicator-element scores for the three are + 2, 2, 

and 3, respectively.

The three samples from the locality 10 miles south 

of Squaw Spring were collected from the north end, 

center, and south end of a strongly jasperoidized 

limestone ridge about a quarter of a mile long, surrounded by argillized and pyritized Tertiary volcanic 

rocks. The nearest known ore deposits are in the 

Star Range 5 miles to the northeast. All three samples are aphanitic, dark gray on fresh exposures and 

yellowish brown on weathered surfaces; the sample 

from the north end of the ridge contains aphanitic 

olive-gray breccia fragments, and the one from the 

south end is cut by small veinlets of yellowish-gray 

fine-grained quartz with sparse tiny vugs. Petrographic study reveals three generations of silica. 

The oldest of these is aphanitic with jigsaw-puzzle 

texture, is pale brown by transmitted light, and 

contains rounded detrital quartz grain inclusions. 

The intermediate generation has a heterogeneous 

xenomorphic to reticulated texture and an average 

quartz grain diameter of 0.02 mm; carbonate particles are abundant in the grains, and opaque amorphous brownish-black carbonaceous material is 

concentrated along the grain boundaries. In one 

specimen the quartz of this generation contains disseminated jarosite and hydromica. The youngest 

generation of quartz fills veinlets. It is coarser 

grained, has a xenomorphic texture, and is free of

inclusions. All three samples contain traces of Ag, Y, 

and Yb and slightly anomalous Zr. Two of the three 

also show higher-than-normal Ba, La, Ni, and Sr. 

The indicator-element scores are all low ( 1, 1, 

and +2).

The four samples from near the south end of the 

Wah Wah Mountains represent bodies located many 

miles from the nearest known mineral deposits. 

These bodies are localized by fracture zones in 

Paleozoic limestone and dolomite, and many of them 

exhibit a well-marked transition zone characterized 

by an interlacing network of quartz veinlets in the 

host rock. Two samples are from these transition 

zones, and the other two are from the main jasperoid bodies. Both of the jasperoid samples have a 

moderate-gray medium-grained locally vuggy matrix, cut by coarser grained quartz veinlets. The matrix consists of heterogeneous xenomorphic to locally 

reticulated quartz that has an average grain diameter of about 0.05 mm; it contains abundant 

carbonate particles, small ragged masses of relict 

calcite, and numerous open vugs. The veinlets have 

a xenomorphic texture and an average grain diameter of about 0.2 mm, and they are free of inclusions. 

Although the texture of these samples is promising, 

the scarcity of accessory minerals in them is reflected in the chemical analyses, which show only Ba, 

Sr, and Zr in slightly abnormal concentrations. Both 

samples yield scores of 1.

The samples from the transition zones are carbonate breccias consisting of angular fragments of 

coarse-grained recrystallized dolomite in a matrix 

of intimately mixed fine-grained carbonate and 

quartz in various proportions. The quartz in this 

matrix has a heterogeneous texture and contains 

abundant carbonate particles. Numerous veinlets of 

clear homogeneous xenomorphic quartz cut the matrix; although these contain local inclusions of 

coarse-grained calcite, the vein quartz is free of 

carbonate particles. The rock was thoroughly brecciated before silica was introduced; however, it is 

not clear from examination of these samples whether 

the brecciated host rock was first cut by the coarser 

quartz veinlets and then replaced by the finer 

grained matrix jasperoid, or whether replacement 

was followed by vein filling.

SAN RAFAEL SWELL AREA 

(18, fig. 49)

The San Rafael Swell is a broad anticlinal flexure 

in southwestern Emery County between the San 

Rafael River on the north and the Muddy River on 

the south. Uranium deposits in continental mudstones, sandstones, and conglomerates of Triassic
146 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

age have been mined in this area since early in the 

20th century, but mining was most active in the late 

1940's and early 1950's. Most of these deposits are 

in the lower part of the Chinle Formation near the 

erosional unconformity that separates it from the 

underlying Moenkopi Formation.

At several localities in this area, basal siltstones, 

mudstones, and shales of the Chinle Formation have 

been silicified, dolomitized, and argillized beneath, 

and adjacent to, uranium deposits. The following 

information has been abstracted from a report by 

Abdel-Gawad and Kerr (1963, p. 27-33).

At the Magor mine, 11 miles southwest of Temple 

Mountain, a silicified green clay about 2 feet thick 

underlies uranium-bearing sandstone. Reddish-tan 

and light-tan silica layers and lenses with abundant 

chalcedony are prevalent in this clay. Coalified logs 

in the ore zone have been partly replaced by darkbrown to black silica, a jasperoid that is cut by 

veinlets of white quartz and calcite. Ore minerals 

consist of galena, sphalerite, pyrite, uraninite, chalcopyrite, bornite, covellite, and their oxidation products. Silicification disappears within a few hundred 

feet of the ore. At the Green Dragon 3 mine, uranium ore occurs at the base of a sandstone channel 

scoured into the siltstone, in a silicified zone surrounded by a halo of argillic alteration.

At the Dirty Devil 6 mine a layer of altered 

greenish-gray siltstone contains abundant layers, 

lenses, and veins of reddish-tan cherty jasperoid. 

Rounded quartz pebbles are sparsely distributed 

through this bed, and in its silicified parts, chalcedony locally cements these pebbles as well as sand 

and clay. Pyrite-, marcasite-, sphalerite-, and coffinite-bearing asphaltite are disseminated through 

the silicified zones in close association with the 

younger chalcedony veinlets that cut the jasperoid. 

Cavities in this silica are rimmed with chalcedony 

and filled with cockscomb quartz.

At the Lucky Strike mine, two types of jasperoid 

are distinguishable in siltstone. One forms thinly 

banded brick-red layers and lenses a few inches thick. 

The other is more crudely banded, brownish to bluish 

gray, and contains urano-organic material filling 

fractures and cavities. The silicified zone is surrounded by a bleached argillized halo.

At the Conrad mine, layers of jasperoid are associated with dolomite in green clay in the basal siltstone of the Chinle Formation. Radioactive asphaltite fills fractures and cavities in these silicified 

layers.

These jasperoid zones consist largely of chalcedony and microcrystalline quartz with local late 

coarse quartz filling cavities. Much of the original

silica probably precipitated in colloidal form from 

hydrothermal solutions supersaturated with silica. 

This process probably was accompanied by a drop 

in temperature and an increase in pH from slightly 

acid to slightly alkaline. Temperature of silica deposition probably was slightly above 100°C. Silicification was accompanied by argillic alteration and 

closely followed by deposition of carbonates and 

sulfides; this deposition, in turn, was followed by 

urano-organic mineralization (Abdel-Gawad and 

Kerr, 1963, p. 34, 44).

SILVER ISLET DISTRICT 

(19, fig. 49)

The Silver Islet district is in northwestern Tooele 

County, just south of the Box Elder County line, 

and about 15 miles northeast of Wendover, near the 

north end of the Desert Range.

In this area Ordovician limestone has been cut 

by north-northeast-trending faults and fractures 

and by northwest-trending dikes of diorite porphyry. 

The limestone adjacent to one such dike on the west 

side of the range has been recrystallized near its 

junction with a north-trending vein. Outward from 

the recrystallized zone for a distance of 10-12 feet 

the limestone is replaced by red jasperoid containing 

abundant hematite, calcite, and muscovite. The vein 

contains argentiferous lead and copper carbonates 

and limonite in a quartz gangue (Butler and others, 

1920, p. 488).

TUTSAGUBET DISTRICT

(22, fig. 49)

The Tutsagubet district is in southwestern Washington County in the Beaver Dam Mountains, about 

15 miles west of St. George. At the Dixie mine in 

this district, an irregular, chimney-shaped replacement deposit of oxidized ore cuts Pennsylvanian 

limestone. This limestone has locally been replaced 

by brown and yellow jasperoid adjacent to the pipe, 

which contains carbonates and sulfates of iron, lead, 

and copper associated with limonite.

OTHER OCCURRENCES

Abdel-Gawad and Kerr (1963, p. 33) mentioned 

Silicification of the lower part of the Chinle Formation 11 miles northeast of Moab, Grand County, near 

the junction of Castle Creek and the Colorado River 

(4, fig. 49). No ore deposits are known in the immediate vicinity of this occurrence.

At Silver Reef (20, fig. 49) about 34 miles southwest of Cedar City, in Washington County, red 

"jasper" replaces a green shale in the Chinle Formation a few feet beneath the silver-, copper-, vana-
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 147

dium-, and uranium-bearing "Silver Reef sandstone," a local economic term. The "jasper" replaces 

shale, as an aggregate of very fine grained red 

quartz, over a large area (Proctor, 1953, p. 120). 

From Proctor's description, this material apparently 

is very much like the red cherty jasperoid in the 

Chinle Formation in the San Rafael Swell, as described by Abdel-Gawad and Kerr.

I have a specimen of jasperoid from Paleozoic 

limestone just east,of Vernon (23, fig. 49) in southeastern Tooele County. This locality is only about 

12 miles northwest of the Tintic district (21), but 

there are no known ore deposits in the vicinity. The 

sample is grayish red, has a heterogeneous xenomorphic to reticulated texture, and contains abundant carbonate particles and hematite; some of the 

hematite is pseudomorphous after pyrite. In spite of 

its favorable texture and mineralogy, the sample is 

slightly high only in Ga, Sr, and Zr, and has a trace 

of Zn.

Butler, Loughlin, Heikes, and others (1920, p. 

441) mentioned the occurrence of a bed or vein of 

jasperoid in Paleozoic limestone at the "88" mine 

in the West Tintic district (24, fig. 49), about 15 

miles southwest of the Tintic district, in Juab 

County. However, H. T. Morris (oral commun., 

1965) reported very little jasperoid from this district.

Abundant masses of hypogene jasperoid are associated with lead-zinc replacement deposits in the 

Argentia district (1, fig. 49) in Morgan County, the 

Fish Springs district (8) in western Juab County, 

and the Lakeside district (10) in northeastern 

Tooele County (Heyl, 1963, p. B44, B57, B79). 

Hypogene jasperoid is also present in small amounts, 

in a few of the lead-zinc ore bodies of the important 

Park City district (15) in southwestern Summit 

County (C. S. Bromfield, written commun., 1967).

VIRGINIA AND WEST VIRGINIA

Jasperoid bodies have been recognized in three 

areas in these two States: the Austinville district 

(10, fig. 41) in Wythe County in southwestern 

Virginia, the Timberville district (7, fig. 46) in 

Rockingham County in western Virginia, and the 

Howell property (5, fig. 46) in Jefferson County at 

the eastern tip of West Virginia. In all three places 

gray and grayish-black jasperoid is associated with 

sphalerite and galena breccia and replacement deposits in lower Paleozoic limestone or dolomite. In 

addition to these areas, the north end of the piedmont gold belt (6, fig. 46) in Fauquier County, Va., 

on both sides of the Rappahannock River, contains 

disseminated gold deposits in massive quartz along

shear zones in schist; field evidence indicates partial 

replacement of the host rock by silica before mineralization.

AUSTINVILLE DISTRICT 

(10, fig. 41)

At Austinville, in southern Wythe County, Va., 

large replacement deposits of sphalerite have been 

localized by breccia zones in the Lower Cambrian 

Shady Dolomite. In the main mine cherty quartz of 

two types has been noted: One is dense "black chert" 

that appears to be older than both recrystallization 

of dolomite and sulfide mineralization. The other 

variety is also dense, but it is nearly white arid is 

much younger than the first type; it may be younger 

than the sulfide mineralization (Currier, 1935, p. 

79). Although the silica at Austinville strongly resembles chert in appearance, the bodies are structurally controlled, giving evidence of their epigenetic 

replacement origin (A. V. Heyl, written commun., 

1964).

HOWELL MINE AREA 

(5, fig. 46)

A small zinc deposit in Jefferson County, W. Va., 

known as the Howell mine, has been developed along 

a breccia zone in the Cambrian Tomstown Formation. In this zone a core of coarse white dolomite is 

surrounded by sphalerite ore which, in turn, is enveloped by a marginal zone of jasperoid (Ludlum, 

1955, p. 860; A. V. Heyl, written commun., 1964).

TIMBERVILLE DISTRICT 

(7, fig. 46)

Small replacement deposits of sphalerite are present in the Ordovician Beekmantown Dolomite in an 

area about 50 miles long and 25 miles wide in western 

Virginia, centered near the town of Timberville, in 

Rockingham County. These deposits probably were 

formed from low-temperature hydrothermal solutions, according to Herbert and Young (1956, p. 

1-3). Although they did not mention silica associated 

with these deposits, dense black cherty-looking jasperoid that cemented dolomite breccia at an early 

stage during the general period of sulfide deposition 

is common at the Tri-State Zinc Co.'s BowersCampbell mine (A. V. Heyl, written commun., 1964).

OTHER OCCURRENCES

On both sides of the Rappahannock River (6, fig. 

46) in Fauquier County in northeastern Virginia, a 

belt of Precambrian schist has been cut by shear 

zones that locally are strongly silicified. This silicification has resulted in large coarse-grained quartz
148 JASPEROID IN THE UNITED STATES ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE

bodies which replace the schist but locally preserve 

its texture, and which contain disseminated gold 

deposits at the Vauclause, Mellville, and Franklin 

mines (Pardee and Park, 1948, p. 35, 47).

WASHINGTON

Abundant masses of jasperoid are closely associated with replacement deposits of sphalerite and 

galena in the Cambrian Metaline Limestone in the 

Metaline district (2, fig. 50), Pend Oreille County, 

near the northeast corner of Washington. A similar, 

but much smaller, deposit, known as the Anderson 

prospect (1, fig. 50), is also in Metaline Limestone 

in northeastern Stevens County, a few miles west of 

the Metaline district.

METALINE DISTRICT 

(2, fig. 50)

The close association between jasperoid and leadzinc replacement ore bodies in breccia zones in the 

upper part of the thick Metaline Limestone in the 

Metaline district has been described and discussed 

by Park (1938), Park and Cannon (1943), and 

Dings and Whitebread (1965).

Park (1938, p. 723) described typical Metaline 

jasperoid as a dense dark-gray to black rock that

122° 120° 118°

W H A T c O M 'x

 . . --(

48'

46°

SNOHOMIS

\. C H E L A N

'WASHINGTON

K 1 T T 1 T A S

Y A K 1 M A

N O G A N 1

GRANT

0

I_,

I B e N T O N \

Ui--' ~"

50

i I______

 1

100 MILES

EXPLANATION

x 

Minor district or area

» 

Reported occurrence

FIGURE 50. Map showing location of jasperoid-bearing 

areas in Washington. 1, Anderson; 2, Metaline.

commonly preserves the texture of the carbonate 

host rock it replaces and shows gradational contacts 

with it, merging outward through a zone of anastomosing quartz veinlets and disseminated quartz 

crystals into unreplaced dolomite or limestone. Small 

vugs in this jasperoid are commonly lined with 

quartz crystals.

Park and Cannon (1943, p. 44-46) reported that, 

although jasperoid is widespread throughout the 

district, it is particularly abundant at the Lead Hill 

and Pend Oreille mines, where it commonly forms 

the gangue of the sulfide ore. Both jasperoid and ore 

appear to have formed from the same, presumably 

hydrothermal, solutions, but the ore for the most 

part is younger than the jasperoid. Nodules and 

small masses of light-gray chert are locally abundant 

in the upper part of the Metaline Limestone.

Dings and Whitebread (1965, p. 18) reported that 

this chert is composed of fine- to medium-grained, 

locally recrystallized quartz. Some chert nodules are 

surrounded by a rim of coarse-grained calcite. The 

chert is most abundant in the upper 200 feet of the 

Metaline Limestone on Lead Hill and Lead King Hill. 

In some places near ore bodies this chert grades 

transitionally into dark-gray jasperoid.

The jasperoid is most abundant in breccia zones 

30-200 feet beneath the contact of the Metaline 

Limestone with the overlying Ordovician Ledbetter 

Slate. The jasperoid commonly occurs as irregular 

bodies as much as 200 feet across, replacing limestone and dolomite breccia fragments and the more 

coarsely crystalline dolomite that forms the matrix 

for these fragments. Most of the sphalerite and 

galena occurs either within the jasperoid or adjacent 

to it; however, some jasperoid bodies are barren of 

sulfides, and some sulfide deposits are not associated 

with jasperoid. The coarsely crystalline white dolomite that forms the original matrix in the breccia 

zones is presumed to be largely of hydrothermal 

origin, and this dolomite is the preferred host material for the jasperoid and sulfides. Dolomitization, 

silicification, and mineralization are thought to have 

resulted from hydrothermal fluids that originated in 

the deep-seated magma chamber of a large body of 

plutonic rock related to the Jurassic Kaniksu batholith (Dings and Whitebread, 1965, p. 54, 62-64, 68).

A sample of dark-gray sphalerite-bearing jasperoid from the Metaline district in my collection is 

relatively coarse grained and has a very heterogeneous xenomorphic to locally reticulated texture. The 

quartz grains range in diameter from about 0.02 

to about 1.5 mm, and the smaller grains commonly 

form inclusions in the larger ones. Ragged remnants 

of coarse crystalline dolomite are scattered through
REFERENCES CITED 149

the quartz, and carbonate dust particles are abundant 

in the larger quartz grains. Irregular masses of 

light-gray sphalerite cut the jasperoid quartz and 

locally contain quartz grain inclusions. Spectrographic analysis of the sample showed slightly high 

Cd, Ga, Ge, Mo, and Sr, as well as very high Zn. 

The indicator-element score is +11.

OTHER OCCURRENCES

The Anderson prospect (1, fig. 50) in northeastern 

Stevens County, a few miles west of the Metaline 

district, consists of galena, sphalerite, and minor 

pyrite disseminated through jasperoid gangue in the 

Metaline Limestone. The ore-bearing bed is about 

100 feet thick; the silicified ore zone is about 50 feet 

wide and follows the general course of a lamprophyre 

dike (Lorain and Gammell, 1947, p. 4).

WYOMING

A jasperoid occurrence in Wyoming is reported 

from the Miller Hill area (4, fig. 47), about 25 miles 

south of Rawlins in Carbon County (Vine and 

Prichard, 1959). At this locality small amounts of 

uranium are concentrated in silicified fresh-water 

limestone in Tertiary rocks that have been tentatively 

correlated with the North Park Formation.

MILLER HILL AREA

(4, fig. 47)

The North Park(?) Formation in this area is 

about 800 feet thick and consists largely of porous 

tuffaceous sandstone with some interbedded freshwater limestone. These limestone beds are 3-10 feet 

thick, and have locally been brecciated and replaced 

by chalcedonic jasperoid, which locally contains concentrations of uranium ore. Silica and uranium are 

thought to have been leached by ground water from 

the porous tuffaceous sandstone and precipitated 

from the ground water by reaction with the limestone (Vine and Prichard, 1959, p. 210, 215-217, 

225).

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INDEX

[Italic page numbers indicate major references]

Page

Abrigo Canyon, Ariz 64 

Abrigo Limestone 64, 66 

Accessory minerals, classification by age.. 15 

Accessory minerals, use in categorizing

jasperoid 54 

Acid, solubility of silica in 39 

Acid solutions, solubility of silica in 40 

Acknowledgments -- 3 

Adams Hill area, Eureka district,

Nevada ____________-_____ 84, 85 

Alabama, jasperoid bodies 89 

Alamo, Nevada 115 

Alamogordo Member of the Lake Valley

Limestone __ 127

Alaska, jasperoid bodies 89

Albers, J. P., and Robertson, J. F.,

quoted ______ 97 

Alder Creek, Ariz__ . 94 

Alder Group ________ ______ 93 

Alkaline solutions, solubility of silica in 39,

41

Allentown, Pa______ ______ 131 

AHophane 18 

Alma, Colo______ 97 

Alpine mine, Nevada- 123 

Alteration. See Hydrothermal alteration. 

Ames, L. L., Jr., quoted 47 

Analyses, jasperoid samples 55, 66, 70,

73, 77, 81, 83, 91, 93, 96, 99, 100, 101. 110,

111, 112, 113, 114, 117, 118, 120, 122, 125,

126, 128, 129, 131, 133, 135, 138, 141, 142,

143, 144, 147, 149

Analysis, thermal differential SO, 55 

Anderson County, Ky 106 

Anderson prospect, Washington___ 148, 149 

Ankerite ___- - 18 

Annie Creek mine, South Dakota 132 

Annie 5 mine, Colorado 72 

Antelope district, Nevada ______ 122 

Antimony deposits, California 96 

Nevada ______-_________ 108, 116 

Apache Group 36 

Appalachian Mountains, Ga _ . 102 

Aravaipa district, Arizona _ - 94- 

Arcturus Limestone 120 

Argentia district, Utah 147 

Argus mine, Nevada 117, 118 

Argus Range, Calif . - 96 

Arizona, jasperoid bodies - - . 90, 93 

Arkansas, jasperoid bodies 94 

Arkansas Novaculite - 26 

Arkansas River, Colo 71, 102 

Arkansas zinc district .__ 94 

Arsenic deposits, Nevada _ .108, 116 

Aspen, Colo - 3, 46 

Aspen district, Colorado ______ 81, 97 

Aspen Mountain, Colo 82 

Atlanta district, Nevada 108 

Atlanta mine, Nevada _________ 108, 110 

Austinville district, Virginia _____ H7 

Australia, duricrusts 36

Page

B

Bald Eagle Mountain, Utah -______ 142 

Bald Mountain, S. Dak__________ 132 

Bald Mountain district, Nevada 110, 111 

Bald Mountain mine, South Dakota 132 

Bamford, Pa_________ ______ 131 

Bamford district, Pennsylvania ___ 130 

Banner district, Arizona 29, 90, 91 

Barite _______________-______ 18 

Barney Reevey Gulch, Utah -~____- 140 

Bartow County, Ga____ __-. _ 102 

Base-metal deposits, Central Kentucky 

district ____________________ 104 

Georgia ______ ___- 102

Iowa ____________--______ 104 

Kentucky-Illinois district _- 104 

Mississippi Valley district ______ 104 

Montana 108 

Utah _ . __--_.__ 137, 140 

Wisconsin 104

Battle Mountain, Colo___________ 79, 80 

Battle Mountain, Nev__________ 112, 115 

Bayhorse, Idaho 104 

Bayhorse Dolomite -- _.__ ______ 104 

Bear Creek Mining Co - __ 75, 76, 78 

Bear Gulch, Utah __._._______ 138 

Beaver County, Utah __. -______ 144 

Beaver Dam Mountains, Utah ____ 139, 146 

Beekmantown Limestone 130, 131, 147 

Beidellite ____________________ 18 

Bell Mountain, Colo ____ 83 

Belmont district, Nevada _- ______ 122 

Belt Supergroup - 104 

Bethlehem, Pa_________________ 130 

Bibliography 149 

Bidwell Bar district, California __ 94, 96 

Big Lime Mountain, Nevada 112 

Bingham district, Utah ..... 9, 58, 137

Biotite _____________ -______ 19 

Bisbee, Ariz____-___________ 9, 66, 92 

Bisbee Group _____.._ _.__._ _ 94

Bisbee (Warren) district, Arizona 19,

63, 90, 94

Biscuit mine, Nevada - 111 

Bishop, Calif__________________ 97 

Bishop Cap district, New Mexico 1S4 

Black Gap fault, Arizona ________ 66 

Black Hawk district, California ___ 97 

Black Hills, S. Dak_._.__ 3, 24, 47, 131 

Black Knife property, New Mexico 125 

Black Queen mine, Colorado ____ 102 

Black Range, N. Mex __ 125, 126, 127, 128 

Blackhawk mine, Colorado ..._____ 101 

Blue Bird mine, Nevada 111 

Blue Goose mine 135 

Blue Ridge Mountains __._. ______ 130 

Bonanza district, Colorado 97, 102 

Bonneterre Dolomite 107 

Boone County, Ark __ 94 

Boone Formation ... ..._ .____ 59, 60

Boss mine, Nevada 115 

Boston-Ely mine, Arizona 68 

Boulder Creek, Mont____________ 108 

Bourbon County, Ky____________ 106 

Bowers-Campbell mine, Virginia 147

Page

Box Elder County, Utah ____ 142, 146 

Boyer district, Nevada ____ 108, 110 

Bradshaw mine, Nevada 108 

Breckenridge, Colo__ ______ 102 

Breece Hill, Colo___.__________ 71 

Brewer, W. M., quoted _______ 89 

Brewer mine, South Carolina _____. 130 

Bristol Pass, Nev______________ 117 

Bristol Pass Limestone __________ 117 

Brochantite ____.. 19 

Brooklyn mine, Nevada __ ____. Ill 

Browns Peak, Ariz._______.._____ 92 

Buckley, E. R., quoted __________ 107 

Bucks County, Pa_____________ 130, 131 

Bull Valley (Goldstrike) district,

Utah . . _ ____ 137, 139 

Bully Hill mine, California _______ 96 

Bumpass Cove district, Tennessee ___ 134 

Burning Moscow mine, Nevada 84

Caballos Mountains, N. Mex_-______ 130 

Calamity Gulch, S. Dak_________ 133 

Calcite _____________________ 19 

Caldwell County, Ky ______ 106 

Caliente, Nev____ - ____ 115, 123 

Caliente district, Nevada _________ 123 

Califon (German Valley) district,

New Jersey - 130, 131 

California, jasperoid bodies 94 

Cameron, Ariz .___ 91 

Cameron area, Arizona - ._______ 90, 91 

Camp Hale, Colo______________ 79, 100 

Candelaria district, Nevada .. . 110 

Canterbury Hill, Colo____________ 71 

Carbon ________.____________ SO 

Carbon County, Wyo - ______ 149 

Carbon Ridge Formation _____ 84, 85, 88 

Carbonate district, Colorado ______ 97, 102

South Dakota ____________ 131, 134 

Carbonate Hill, Colo_____________ 71 

Carbonate rocks, replacement of 48, 49

See also Host rocks.

Carpenter district, New Mexico ____ 1S5 

Carrie mine, Nevada . _ ______ 114 

Cartersville district, Georgia 10S 

Casedepaga, Alaska 90 

Castle Creek, Utah ____ ______ 146 

Castle Creek fault, Colorado ______ 82 

Castle Peak, Nev___ _.__._ 112 

Cataract Creek, Colo 100 

Catawba River 130 

Cathcart, S. H., quoted . 90 

Catlin shaft, Nevada _ - 85 

Cave-in-Rock fiuorite district, Illinois _. 42 

Cedar City, Utah _____ ____ 139, 146 

Cedar Mountain district, Nevada 111 

Central Kentucky district 106 

Central Tennessee district, Tennessee 134,

135

Cerussite .. SO 

Chaffee County, Colo___________ 97, 102 

Chaffee Formation _ 71, 78, 79, 81, 97, 100 

Chainman Shale 85, 121 

Chalcedony __ SO, 46

157
158 INDEX

Page

Chalcopyrite. SI 

Challis, Idaho _ __ __- 104

Chance mine, New Mexico 129 

Charlotte, N.C _ -_ 130

Chemical analyses. See Analyses. 

Chemical composition. See Composition of 

jasperoid.

Cherry Creek district, Nevada _ 111 

Cherry Creek Range, Nev 111 

Chert, Philipsburg district, Montana _ 107 

Tri-State district ________ 59, 60, 61 

Chi-square test 56 

Chief (Caliente) district, Nevada _ 123 

Chinle Formation ____ 7, 91, 92, 146, 147 

Chino copper mine, New Mexico - _ 128 

Chise, N. Mex-___________-_ 130 

Chiulos Canyon, Utah 144 

Chlorapatite __ SI 

Chloride mine, Nev_____________ 122 

Chloride Point mine, Utah -__ 143 

Chlorite - -______-______-__ SI 

Chochise County, Ariz 93 

Churchill County, Nev_________ 110, 123 

Cincinnati arch ___-~_____ - 106 

Clark County, Ky______________ 106 

Clark County, Nev______________ 114 

Clark Mountain district, California 97 

Clifton district, Utah _______-_ 139, 140 

Clifton-Morenci district, Arizona -- 50, 61, 90 

Climax, Colo_________________ 97, 99 

Clipper Peak, Utah _______ __ 138 

Cobalt deposits, Alabama . 89 

Nevada ________________ 108, 110 

Cochise County, Ariz___._._____ 92, 94 

Coconino County, Ariz 91 

Colorado, jasperoid bodies 97 

Colorado Plateau __ _______ 7

Colorado River ______________ 91, 146 

Colors, characteristic, jasperoid 7 

use of in categorizing jasperoid

samples 53 

Columbia district, Nevada 123 

Columbia mine, California 96 

Commercial mine, Utah -- 138 

Composition, silica-bearing solutions 41 

Composition of jasperoid, Aspen district.

Colorado ______________-___ 83 

Bisbee (Warren) district, Arizona _ 66 

chemical ______ __.__ SO 

Clifton-Morenci district, Arizona _ 63 

comparison of __________ __ 55

Ely district, Arizona 70 

Oilman district, Colorado 81 

Leadville district, Colorado 73 

statistical summary . 34 

Tintic and East Tintic districts, 

Utah _____ ___________ 77

Tri-State district _____ 61

Conrad mine, Utah 146

Constituents of jasperoid, major 30

minor _______________ 34

Contact district, Nevada 111

Continental Chief mine, Colorado 72

Cooks Peak, N. M________-__ 125

Cooks Peak district, New Mexico -- 125, 127

Copper Chief mine, Arizona 93

Copper Cities deposit, Ariz. 94

Copper deposits, Alaska ____ 89, 90

Arizona ____ _____ _ 93

California ________________ 96

Colorado __________________ 101

Idaho ___.....__._______ 104

Missouri .... 107

Nevada _....._ 112, 113, 115, 117, 123

New Mexico .__ _____ . 127, 128

Utah ____.__..._____ 137, 142, 144

Copper Mountain, Alaska . 90

Copper Mountain Mine, Utah _-___ 142

Copper World mine, Arizona _ 93

Page

Copperfield, Utah ____________ 138, 139 

Cornwall copper mines, Missouri ... 107 

Cortez district, Nevada 108, 111 

Cortez Range, Nev_____ 112 

Cottonwood Canyon, Nev._. 110 

Courtland, Ariz____________-_ 92 

Courtland-Gleeson district, Arizona 90, 92 

Crittenden County, Ky. 106 

Crystobalite _ 45 

Cuba, jasperoid occurrences . ___ 7 

Cuchillo Mountains, N. Mex 125 

Cuchillo Negro district, New Mexico 1S5 

Custer County, Idaho - 104 

Czar fault, Arizona 64, 65

D

Dacy claims, South Dakota 133 

Darwin district, California 94, 96 

Data analysis, methods of - . 51 

Deadwood Formation _______ 24, 131, 132 

Deception Rhyolite _______.. _ 93

Decorah Formation .____ 104, 105 

Deep Creek Range, Utah - 139 

Defiance ore body, Nevada 119 

Definition, favorable jasperoid 50 

unfavorable jasperoid 50 

Definition of jasperoid -__ . . S 

Delano district, Nevada _ .____. 123 

Delmar district, Nevada ._ 108, 112 

Delores County, Colo_____________ 100 

Delta, Utah __-_-_..___-____ 139 

Deming, N. Mex____.._______ 125, 129 

Density, use of in categorizing

jasperiod samples 56 

Density of jasperoid S9 

Deposition of silica 43 

Description of jasperoid, Aspen district,

Colorado __________________ 82 

Atlanta district, Nevada . . -_ 108 

Austinville district, Virginia ____ 147 

Bald Mountain district, Nevada ... 110 

Banner district, Arizona _____ . 91

Bidwell Bar district, California 96 

Bingham district, Utah - 137 

Bisbee (Warren) district, Arizona . 65 

Bishop Cap district, New Mexico _ 124 

Bull Valley (Goldstrike) district, 

Utah __.__._..._________ 139 

Bumpass Cove district, Tennessee 134 

Cameron area, Arizona 91 

Candelaria district, Nevada ._ ._ 110 

Carbonate district. South Dakota _. 134 

Cartersville district, Georgia ___ 102 

Cedar Mountain district, Nevada _ 111 

Central Kentucky district 106 

Central Tennessee district ...____ 135 

Cherry Creek district, Nevada __ 111 

Clifton district, Utah ________ 139 

Clifton-Morenci district, Arizona _ 62 

Contact district, Nevada -______ 111 

Cooks Peak district. New Mexico _. 125 

Courtland-Gleeson district, Arizona. 92 

Cuchillo Negro district, 

New Mexico . ______. ___ 125 

Darwin district, California __.___ 96 

Delmar District, Nevada 112 

Dolly Varden district, Nevada 113 

Drum Mountains (Detroit) district, 

Utah __.......__._ .____ 139

Eagle Mountains district, Texas __ 136 

East Shasta district, California . 96 

Eastern Tennessee zinc district ._ 134 

Eureka district, Nevada 84 

Ferguson district, Nevada 114 

Fort Apache iron district, Arizona- 94 

Friedensville district, Pennsylvania 131 

Getchell mine area, Nevada .. __ 114 

Gilman district, Colorado 80

Description of jasperoid Continued

Gold Hill district, Utah _ __._ . 

Goodsprings district, Nevada 

Hadley (Graphic) district. 

New Mexico _________________________

Hillsboro district. New Mexico _____

Horseshoe-Sacramento district, 

Colorado __ __ 

Ivanpah district, California _______

Jerome district, Arizona ___________

Kentucky-Illinois district ___________

Kern district, Nevada _ 

Kingston district, New Mexico ____

Kokomo district, Colorado __________

La Plata district, Colorado _______

Lake Valley district, New Mexico 

Leadville district, Colorado ._ 

Lucin district, Utah 

Magdalena district, New Mexico .. 

Manhattan district, Nevada __ ____

Mercur district, Utah _______

Metaline district, Washington 

Mount Nebo district, Utah ________

North Carolina __ ________.________

North Tintic district, Utah _ __. 

northern Arkansas zinc-lead 

district _ ______

Organ district, New Mexico _. 

Pando area, Colorado ________ 

Philipsburg district, Montana ______

Pima district, Arizona _____..

Ragged Top Mountain district, 

South Dakota 

Rico district, Colorado _______ ___

San Francisco district, Utah _ 

San Rafael Swell area, Utah _____

Sanderson, Tex 

Santa Fe district, Nevada ... ... 

Santa Rita district, New Mexico ___ 

Silver Islet district, Utah _ 

Silver Peak district, Nevada __ 

Silverhorn district, Nevada ________

South Carolina 

Southeastern Missouri district ______

Taylor district, Nevada ____________

Tierra Blanca district.

New Mexico ___ _____ ____

Tintic and East Tintic district, 

Utah _ __ .-__ . _____ ____

Tres Hermanas District, 

New Mexico 

Tri-State district _ _ __ 

Tutsagubet district, Utah -_ 

Uncompahgre district, Colorado _ 

Upper Mississippi Valley district 

Victorio district, New Mexico _____

Ward district, Nevada ______. _

West Lead district, South Dakota 

West Ward district, Nevada .. ___

White Pine (Hamilton) district,

Nevada ___ __ ______. _...

Deseret Formation _ ______ ___

Desert Range, Utah _- _______

Diadem lode, California .____ 

Diamond district, Nevada ..___ _ 

Dickite _.. . __._.__ _ ____._.___

Differential thermal analysis _.._______

Dirty Devil 6 mine, Utah .._________

Distribution of jasperoid, Aspen district, 

Colorado 

Bisbee district, Arizona __- __ 

Clifton-Morenci district, Arizona ._ 

Ely district, Nevada ____ _..._. _

Eureka district, Nevada _..._ ._. 

Gilman district, Colorado _____ 

Leadville district, Colorado _ . 

Tintic and East Tintic districts. 

Utah _ _. _____ _ 

Tri-State district - _ -

Page

140

115

125

126

97

106 

 115

126

99

99

127 

72 

142 

127 

116 

142 

148 

14E 

130 

144

94

127

100

108

93

133

101

144

146

136

117

128

146

117

117

130

107

118

128

75

129

60

146

101

104

129

119

132

120

121 

144 

146

94, 96

122

SI

30, 55 

146

82

64

61

67

84

79

71

73

59
INDEX 159

Page

Dividend fault, Arizona 64, 65 

Dixie mine, Utah ___ _______ 146 

Doctor mine, Colorado . __-____- 102 

Dolly Varden district, Nevada ___ - 112 

Dolly Varden Pass, Nev.________ 112 

Dolomite ______ _________ SI 

Don Luis, Ariz _ _ 65 

Dona Ana County, N. Mex______ 124, 127 

Double Up mine, Nevada _________ 115 

Douglas, Ariz _ 94 

Downtown area, Colorado ..__ 71 

Dragoon Mountains, Ariz_________ 92 

Dreyer, R. M., quoted _____ 123 

Drum Mountains (Detroit) district,

Utah _____________________ 139 

Dry Canyon, Utah _____________ 142 

Duck Creek district, Nevada ______ 123 

Dugway district, Utah -~_________ HO 

Dunderberg Shale ___________ 84 

Durango, Colo_______________ 99, 101 

Duricrusts, Australia __ ______. 36 

Dyer district, Nevada _-__________ 113 

Dyer Dolomite Member, Chaffee 

Formation ____71, 78, 79, 80, 81, 97, 100

E

Eagle County, Colorado 78, 97, 99, 102 

Eagle Mountains district, Texas __ 135, 136 

Eagle Peak, Tex_______________ 136 

Eagle River ___ _ 78, 79, 99, 100 

Eagle River Canyon, Colo_________ 100 

Eagle River Valley, Colo_________ 97 

East Shasta district, California ___ 94, 96 

East Tintic district, Utah ___ 7$, 137, 144 

East Tintic Mountains, Utah ____ 73, 144 

Eastern Tennessee district, Tennessee 134 

Egan Range, Nev_____________ 67, 119 

"88" mine, Utah _______________ 147 

Eldorado Dolomite _ 84 

Elko, Nev____________________ 116 

Elko County, Nev. 108, 111, 112, 113, 119, 123 

Ely, Nev__ 3, 75, 84, 111, 116, 117, 119, 123 

Ely Limestone _______________ 24, 119 

Ely (Robinson) district, Nevada 21, 

24, 67, 77, 78, 108, 140

Emery County, Utah . ____ 145 

Empire Hill, Colo____________. 71 

Epidote -- ____ ________ SI 

Escabrosa Limestone __ __ 64, 65, 129 

Escalante Valley, Utah __________ 144 

Esmeralda County, Nev.-____ 108, 113, 114,

117, 122, 123

Eureka, Nev_________74, 75, 84, 122, 144 

Eureka County, Nev__ 84, 108, 111, 116, 125 

Eureka district, Nevada _- 84, 108 

Eureka Hill mine, Utah ____,_____ 77 

Eureka Peak, Utah _ . __.. 74 

Eureka Quartzite -.__ -~- 84 

Evans Gulch, Colo_____________ 71, 72 

Evaporation, effects on deposition of 

silica - ____ ______ 43

Fairview, N. Mex 125

Fauquier County, Va_. ____. 147

Favorable jasperoid, definition of __ 50

Ferguson, H. G., quoted --________ 114

Ferguson district, Nevada _______ 113

Ferguson Springs, Nev. .. __ 113

Fireball district, Nevada _________ 123

Fish Springs district, Utah ______. 147

Flint Creek Range, Mont_________ 107

Fluorite ____________________ SI

Fluorspar deposits, Idaho ... 104 

Texas ______ ____.___ 135, 136

Forepaugh mine, Colorado .___ __ 72 

Fort Apache district, Arizona 7, 94

Page

Fossils ___________ 36, 46, 65, 96, 102 

Four Metals mine, Utah _____ _-- 140 

Franklin Lease mine, Utah 143 

Franklin mine, Virginia -- 148 

Friedensville, Pa_________________ 131 

Friedensville district, Pennsylvania ..130, 1S1 

Fryer Hill, Colo__________.___ 71, 72 

Fusselman Dolomite 125, 126, 127, 128, 129

Galena _ - SI

Galena Dolomite . 104

Garden mine, South Dakota 132

Gardner shaft, Arizona 64

Garfield, N. Mex ___ .. ___ _ ____ . 130

Garfield County, Colo __________ - 97, 102

Gasconade Dolomite . _ . __ - 107

Gemeni mine, Utah 75

Genesis of jasperoid, Alabama 89

Aspen district, Colorado 82

Austinville district, Virginia _ 147

Banner district, Arizona 91

Bisbee district, Arizona 64

Bishop Cap district, New Mexico 124

Bumpas Cove district, Tennessee 134

Cameron area, Arizona - 91

Cartersville district, Georgia 102

Central Kentucky district 106

Clifton-Morenci district, Arizona -- 62

Cooks Peak district, New Mexico _ 125

Courtland-Gleeson district, Arizona - 92

Darwin district, California 96

Eagle Mountains district, Texas 136

East Shasta district, California ____ 96

Eastern Tennessee zinc district _ - 135

Ely district, Nevada 67

Eureka district, Nevada 84

Fort Apache iron district, Arizona- 94

Gilbert district, Nevada 114

Gilman district, Colorado 79

Gold Hill district, Utah _______ 141 

Horseshoe-Sacramento district,

Colorado _______ _. . . 97

Ivanpah district, California . 96

Jerome district, Arizona 93

Kentucky-Illinois district 106

Kingston district, New Mexico 126

Kokomo district, Colorado - - 99

La Plata district, Colorado 99

Lake Valley district, New Mexico -. 127

Leadville district, Colorado 72

Magdalena district, New Mexico 127

Mercur district, Utah 142

Metaline district, Washington 148

Michigan ________ _ ___ - - 107

Miller Hill area, Wyoming _.- 149

North Carolina __

North Tintic district, Utah

Pando area, Colorado _ 

	130

 144

 100

Rico district, Colorado 101

San Rafael Swell area, Utah __ 146

Sanderson, Tex..---. 136

Shafter district, Texas --- __ -- 135

South Carolina ____________ -- 130

Southeastern Missouri district 107

Timberville district, Virginia 147 

Tintic and East Tintic districts,

Utah __ _______ . _ - ___ 74

Tri-State district __________ 59

Uncompahgre district, Colorado -- 101 

Geology, Anderson prospect,

Washington _______________ 149

Aspen district, Colorado 81

Atlanta district, Nevada 108

Austinville district, Virginia - _ -- 147

Bald Mountain district, Nevada 110

Banner district, Arizona 91

Bidwell Bar district, California - 96

Page

Geology Continued

Bingham district, Utah _____ 137

Bisbee (Warren) district, Arizona - 63

Bishop Cap district, New Mexico _ 124

Boyer district, Nevada 110 

Bull Valley (Goldstrike) district,

Utah ____________________ 139

Bumpass Cove district, Tennessee -- 134

Cameron area, Arizona _..____ 91

Candelaria district, Nevada 110

Cartersville district, Georgia _ 102

Cedar Mountain district, Nevada 111

Central Kentucky district ______ 106

Central Tennessee district 135

Cherry Creek district, Nevada _ 111

Clifton district, Utah _________ 139

Clifton-Morenci district, Arizona -- 61

Contact district, Nevada -~_____. Ill

Cooks Peak district, New Mexico _ 125

Cortez district, Nevada 112 

Courtland-Gleeson district,

Arizona -___- ____-- 92 

Cuchillo Negro district,

New Mexico 125

Darwin district, California .__.. 96

Delmar district, Nevada _______ 112

Dolly Varden district, Nevada __ 112 

Drum Mountains (Detroit) district,

Utah ______.____._______ 139

Dugway district, Utah _______ 140

Eagle Mountains district, Texas -_ 136

East Shasta district, California _ 96

East Tintic district, Utah ______ 73

Eastern Tennessee zinc district 134

Ely district, Nevada ______ 67

Eureka district, Nevada __-- 84

Fort Apache district, Arizona ._ 94

Getchell mine area, Nevada ___ 114

Gilbert district, Nevada -~_____ 114

Gilman district, Colorado ______ 78

Gold Hill district, Utah _.____ 149

Goodsprings district, Nevada __ 114

Groom district, Nevada ______ 115 

Hadley (Graphic) district,

New Mexico __. 125 

Hermosa (Sierra Caballos) district,

New Mexico ______________ 126

Hillsboro district, New Mexico 126 

Horseshoe-Sacramento district,

Colorado ___________________ 97

Howell mine, West Virginia 147

Ivanpah district, California . - 96

Jerome district, Ariz_ ______ 93

Kentucky-Illinois district 106

Kokomo district, Colorado 99

La Plata district, Colorado ____ 99

Lake Valley district, New Mexico 127

Lewis district, Nevada 115

Lucin district, Utah _________ 142

Magdalena district, New Mexico _ 127

Manhattan district, Nevada _____ 116

Mercur district, Utah 142

Metaline district, Washington __ 148

Mill Canyon district, Nevada -___ 112

Miller Hill area, Wyoming .___. 149

Mineral Hill district, Nevada ___.. 116

Mount Nebo district, Utah ____ 143

North Tintic district, Utah ___ 144 

Northern Arkansas zinc-lead

district ____-__ 94

Organ district, New Mexico 127

Pando area, Colorado 100

Patterson district, Nevada 116 

Ragged Top Mountain district,

South Dakota -__ - 133

Rico distri-t, Colorado ______-- 101 

Rush Valley (Stockton) district,

Utah _._________-__-__ 144

San Francisco district, Utah 144
160 INDEX

Page

Geology Continued

San Rafael area, Utah 146 

Santa Fe district, Nevada __ 116 

Shafter district, Texas __-____ 135 

Silver Islet district, Utah . 146 

Silver Peak district, Nevada _ 117 

Silverhorn district, Nevada -~_-- 117 

Southeastern Missouri district 107 

Steeple Rock district, New Mexico - 128 

Taylor district, Nevada 117 

Tecoma district, Nevada 119 

Tintic district, Utah _________ 73 

Tres Hermanas district, 

New Mexico _______ ._._- 129 

Tri-State district __ _ 58 

Tutsagubet district, Utah . 146 

Uncompahgre district, Colorado 101 

Upper Mississippi Valley district -- 104 

Ward district, Nevada 119 

West Lead district, South Dakota 132 

West Ward area, Nevada - __ - 120 

White Pines (Hamilton) district, 

Nevada 121

Willow Creek district, Nevada __ 122 

Wyndypah district, Nevada 122 

Georgetown district, New Mexico .. 124, 129 

Georgia, jasperoid bodies __ 10$ 

Getchell district, Nevada . - 108 

Getchell mine area (Potosi district),

Nevada 114 

Geysers, silica content 41 

Gila County, Ariz______________ 91, 94 

Gila River, silica content 42 

Gilbert district, Nevada __ 114 

Gillerman, Elliot, quoted _________ 136 

Oilman (Red Cliff) district,

Colorado __________ 36, 50, 78, 97, 100 

Oilman Sandstone Member, Leadville

Limestone 100

Giroux Ledge, Nev 117

Glauconite _ SI

Gleeson, Ariz _______-...____ 92

Gleeson Ridge, Ariz__.. _.__ 92

Globe-Miami district, Arizona 94

Godiva Mountain, Utah _ 74

Goethite _____________________ 21

Gold Banks district, Nevada _______ 123

Gold deposits, Alabama 89

Arizona 65

California ________________ 96

Colorado ______________ 79, 99, 101

Georgia __ - 89

Montana ____________-____ 108

Nevada . 108, 110, 112, 114, 115, 116, 123

New Mexico _______________ 126

North Carolina ____________ 130

South Carolina _____________ 130

South Dakota ___________. 131, 133

Utah ._ _______.______ 142

Virginia -_______- -_____ 148

Gold Hill, Utah ___ . _ .-_ -_- 139, 140

Gold Hill district, North Carolina __ 130

Gold Hill mine, North Carolina ____ 130

Goldfield, Nev.____._._______ 113, 117

Goldstrike district, Utah __.____ 137, 139

Goodfortune Creek district,

New Mexico .._______________ 129 

Goodsprings district, Nevada ____ 114 

Goodsprings Dolomite 96 

Goose Creek Range, Nev ____ 119 

Gore Range, Colo___________ 78, 97, 99 

Goshute Valley, Nev____.______ 112, 123 

Gossans, silicified ____._ ___.. 36 

Graham County, Ariz_____ ____ 94 

Grain size, jasperoid 9 

Grand Central mine. New Mexico 125 

Grand County, Utah 146 

Grand Falls Chert Member, Boone 

Formation 59

Page

Grand Reef mine, Arizona 94 

Granite County, Mont 107 

Granite Range, Utah __ __ 140 

Grand County, N. Mex__ 124, 125, 128, 129 

Grapevine district, California 97 

Grapevine Gulch Formation 93 

Graphic district, New Mexico. See Hadley

(Graphic) district, New Mexico. 

Great Basin province 137 

Great Blue Limestone 142, 144 

Great Salt Lake, Utah _____ 73 

Green Dragon 3 mine, Utah 146 

Groom district, Nevada - - 115 

Ground water, formation of

jasperoid ________--_ 36, 149

silica-bearing _ __ 74, 94, 107

Guilmette Formation 117, 118

Gunnison, Colo__ 97

Gunnison County, Colo 97, 102

H

Hadley (Graphic) district,

New Mexico _____-______ 124, 1S5 

Haile mine, South Carolina -___ 130 

Haiti, jasperoid occurrences 7 

Halloysite ____ _ SS 

Hamburg Dolomite 84, 85 

Hamilton district, Nevada. See White

Pine (Hamilton) district, Nevada. 

Hanson Creek Formation 84, 85 

Hansonburg district, New Mexico 129 

Hardin County, 111______________ 106 

Harrington-Hickory mine, Utah 144 

Hayden, Ariz..---- 91 

Heglar prospect, North Carolina 130 

Helen shaft, Nevada 85 

Helvetia district, Arizona ____ 93 

Hematite ____________________ SS 

Hendricks Gulch, Ariz ____ 64, 65 

Henry County, Ky______________ 106 

Hermosa Formation __________ 101, 102 

Hermosa (Sierra Caballos) district,

New Mexico 186 

Hewett, D. F., quoted ___________ 96 

Heyl, A. V., quoted _______- 84 

Hidden Treasure claim, Nevada 113 

Highland Peak Formation ___ 112 

Hillsboro, N. Mex______________ 126 

Hillsboro district, New Mexico _ 186 

Homestake Creek, Colo __ 99 

Hoosac Mountain, Nev - 84 

Hoover mine, Tennessee _____- 134, 135 

Horn Silver mine, Utah 144 

Horseshoe-Sacramento district,

Colorado ____ __... 71, 97 

Hoskins mine, Wisconsin 105 

Host rocks, jasperoid _-_ - 6 

replacement, by silica 46 

theory 49 

Hot Springs, N. Mex____________ 129 

Hot springs, silica content 41 

Hot Springs prospect, New Mexico __ 124 

Howell mine, West Virginia 147 

Howie mine, North Carolina 130 

Hudspeth County, Tex__________ 136 

Humboldt County, Nev__________ 114 

Humboldt Range, Nev .. 123 

Humbug Formation 142, 144 

Hydromica .____-- __- SS 

Hydrothermal alteration __.. 61, 64, 67, 74,

79, 84, 91, 99, 100, 101, 102, 106, 136, 144, 

146, 147, 148

Hydrothermal solutions 60, 64, 67, 79, 92, 94 

Hypogene jasperoid 97

Iceland 41

Page

Idaho, jasperoid bodies 104

Illinois, jasperoid bodies 104

Inyo County, Calif______ ___- 97

Inyo Mountains, Calif. 96

Iowa, jasperoid bodies - 104

Iron County, Utah __ 144

Iron Creek, Alaska . 90

Iron Creek district, Alaska 90

Iron Hill, Colo _ 71

Iron Hill mine. South Dakota - 134

Iron ore deposits, Arizona 94

Colorado 102

Georgia __ - 102

Pennsylvania -__ 130

Tennessee 134

Ironwood Iron-Formation 3

Irving, J. D., quoted 133

Ivanpah district, California . 94, 96

Ivy Wilson mine, Nevada - - 111

Jack Pot mine, Nevada ___- 123

Jackson mine, Nevada 119

Jackson Ridge, Colo_- 99

Jarosite S3

Jasper, Lake Superior region 3

Jasperoid, age dating of 6

as guide to ore 50

characteristics, megascopic 7, 53

microscopic _ 9, 54

colors 7

composition SO

constituents, major SO

minor 34

criteria for use as ore indicator 56

definition $

density __ 29

distribution, geographic 3

geologic 6

favorable 50

genesis of -~___-. _ __ 35

See also Genesis of jasperoid.

geologic age __ ..__ 6

host rock types -- _ 6, 46

hypogene 97

in major mining districts 57, 88

in minor mining districts 88

minerals associated with _ _ 9

porosity 29

texture 7

unfavorable ... 50

use as ore indicator 50-56

Jasperoid-bearing mining districts,

foreign 6 

Jasperoid bodies, structural control 6 

Jasperoid provinces - 3, 4 

Jefferson County, W. Va 147 

Jerome district, Arizona - 7, 91, 93 

Joana Limestone ______ 117, 118, 120, 121 

John mine, Nevada . 115 

Johnson Gulch, S. Dak 133 

Joplin, Mo 135 

Joplin district, Missouri-Kansas 3 

Joplin field, Missouri 58 

Juab County, Utah _____ 73, 139, 143, 147 

Jumbo claim, Nevada 112 

Junction fault, Arizona 65 

Jupiter mine, Arizona _ ___ 68

K

Kaibab Limestone _....... __ 91

Kaolinite - S3

Kelly Limestone __ 127

Kentucky, jasperoid bodies 106

minor jasperoid bodies 104

Kentucky-Illinois district __ __ 104, 106

Kentucky mineral district 104
INDEX 161

Page

Kern County, Calif ____ ___ 97 

Kern district, Nevada 115 

Kern Mountains, Nev 115 

Keystone fault, Arizona ___ ___ 91 

Kingsport Formation __ 134 

Kingston, N, Mex______ 125, 126, 127, 128 

Kingston district, Nevada 123 

New Mexico 126 

Kingston Range mining district,

California -_____ ___ __ 97 

Klondike district, Nevada __ ____ 123 

Knight zinc veins, Tennessee 134 

Knoxville, Tenn____ ____ ____ 135 

Kokomo district, Colorado ____ 71, 97, 99 

Kolmogorov-Smirnov two-sample test 51,

54, 55

Kona Dolomite _______________ 107 

Kostajnika, Yugoslavia *.......... 27

La Plata district, Colorado _ 97, 99. 101

Lake County, Colo____________ 97, 102

Lake Superior region _. 3

Lake Valley district, New Mex__ 8, 124, 126

Lake Valley Limestone __ 126, 127, 128, 129

Lake water, silica content -- _ 41

Lakes of Killarney mine, Utah ____ 143

Lakeside district, Utah .__ __ 147

Lancaster, Pa ___ __________ 130

Lancaster County, Pa___________ 131

Lander County, Nev.____ 108, 111, 115, 123

Lane mine, California _ __ 96

Laramide orogeny ... __ ___ 61

Las Cruces. N. Mex__________ 124, 127

Lawrence County, Ark _ 94

S. Dak___________________ 131

Lead, S. Dak_________________ 131

Lead deposits, Alaska ___ ____ 89

Arizona 94

Arkansas -- __ ___ 94

Colorado ___________ 82, 99, 101, 102

Idaho ____________________ 104

Missouri __ __ ___ 107

Nevada ... 84, 110. 112, 116, 117, 119, 123

New Mexico _________ 125, 127, 128

South Dakota ______________ 132

Utah ___________.__ 142, 144, 147

Washington . _ _ 148

Lead district, South Dakota ________ 24

Lead Hill, Wash___________.___ 148

Lead Hill mine, Washington 148

Lead King Hill, Wash____________ 148

Leadville, Colo____________ 3, 71, 78, 81

Leadville district, Colorado _. 71, 97, 102

Leadville Limestone 71, 78, 79, 80, 81, 82,

83. 97, 100, 101, 102

Ledbetter Slate ____________.__ 148 

Lee district, California - 97 

Lehigh County, Pa______________ 130 

Lemhi County, Idaho 104 

Lemmon, D. M., quoted _ 97 

Lemoigne district, California 97 

Lenado district, Colorado ____-__ 97, 102 

Lewis district, Nevada .__. -__. 115 

Lexington dome 106 

Liberty Pit, Ariz___ __ ___ 68 

Lida district, Nevada _ 123 

Limonite ._ 23 

Lincoln, F. C., quoted __________ 123 

Lincoln County, Ky - _ 106 

Nev________108, 112, 115, 116, 117, 123 

Lindgren, Waldemar, quoted . 2, 47 

Lion Hill, Utah _______________ 142 

Little Colorado River. Ariz . 91 

Little Evans Gulch, Colo. .. 72 

Livingston County, Ky . 106 

London fault, Colorado 97 

Lone Mountain district, Nevada .. 123

Page

Lone Pine district, California 97 

Longfellow Limestone _ __ 62, 63 

Lovelock, Nev_________________ 110 

Lowell mine, Arizona ________ 9, 64, 65 

Lucin, Utah ______.__________ 142 

Lucin district, Utah 142 

Lucky Hill mine, Nevada 110 

Lucky Strike mine, Utah _________ 146 

Lumpkin County, Ga____________ 103 

Luna County, N. Mex______ 124, 125, 129 

Luning, Nev...._________ ____ 116 

Lussatite ._ __...___ __ 2S 

Lyon County, Nev_____________ 123

M

Mackay, Idaho -___ __. . 104

Macrotexture, use of in categorizing

jasperoid samples . _ -- 53 

Macungi, Pa_-__________ ____ 131 

Madison County, Mo_______ ____ 107 

Madison Limestone _ ____ ___ 108 

Magdalena, New Mex_ 3 

Magdalena district, New Mexico 124,

127, 129

Magdalena Formation 124

Magdalena Group _. 125, 127, 128, 129, 130

Magma, source of silica solutions 36

Magnetite 24

Magor mine, Utah _ ___ 146

Mahoney mine, New Mexico 129

Malachite ..._____ ____ __ 24

Mammoth Peak, Utah ____________ 75

Manganese deposits, Alabama 89

Georgia -_____-_____ ___ 102

Montana _________________ 108

New Mexico __ - 126

Tennessee . -. 134

Utah __________._____.._ 139

"Manganese oxides" 25

Manhattan, Nev _______________ 122

Manhattan district, Nevada ., 108, 116

Manila Creek, Alaska 90

Manitou Limestone 71

Manto deposits, Colorado ____ __ 79

New Mexico ____.__.__-__ 126, 127

Texas ____.__._________ 135, 136

Maricopa County, Ariz- ____ ... 94

Marion County, Ark 94

Marquette County, Mich____ _-- 107

Marquette district, Michigan 107

Martha mine, Utah _ 139

Martin Limestone 64, 65

Massadona-Youghall district.

Colorado __________________ 97, 102 

Mayacmas district, California - 97 

Mayflower property, Nevada _ . 117 

Mazatzal Mountains, Ariz 94 

Megascopic characteristics, use of 53 

Mellville mine, Virginia -~___....... 148

Menominee Range, Mich 107 

Mercer County, Ky_______-____ 106 

Mercur, Utah _-_______ _ 142 

Mercur district, Utah -____ 7, 27, H2 

Mercury deposits, Arizona ~ 94 

Mescal Limestone 94 

Mescal mine, California 94, 96 

Mescal Range, Calif_._____. .. 96 

Metaline district, Washington 148, 149 

Metaline Limestone 148, 149 

Metasomatical alteration 96, 107

See also Replacement.

Miami-Picher field, Oklahoma 58 

Michigan, jasperoid bodies 106 

Microline 25 

Microscopic characteristics, in

categorizing jasperoid 54 

Microscopic features, accessory 

minerals 15

Page

Microscopic features Continued

fabric texture 11 

grain size _ . __ 9 

jasperoid -____ -___________ 9 

Microtexture, use of in categorizing

jasperoid samples _- __._ ___ 54

Microtexture of jasperoid, Aspen

district, Colorado _ _ ___ 82

Bisbee (Warren) district, Arizona . 66

Clifton-Morenci district, Arizona ._ 62

Ely district, Arizona ._ __ 69

Eureka district, Nevada _______ 84

Gilman district, Colorado 80

Leadville district, Colorado _ 72

Tintic and East Tintic districts,

Utah ____________________ 75

Tri-State district __-____ 60

Mike fault, Colorado . _ 71

Milford. Utah ______-__....____ 144

Mill Canyon district, Nevada 111 

Millard County, Utah _________ 139, 144 

Miller, B. L., quoted ____._______ 131 

Miller Hill area, Wyoming __ ___ H9 

Milton, Tenn__________________ 135 

Mina, Nev____________________ 111 

Mine Hill, N. Mex 129

Mineral County. Nev____ 108, 110, 111, 116 

Mineral Farm mine, Colorado 101 

Mineral Hill district, Nevada __ 116 

Mineral Ridge, Nev 117 

Mineralization, hypogene, source of silica

solutions _ __ -_ 36

Mineralizing solutions . _ __ 84

Mineralogy of jasperoid, Aspen

district, Colorado . 82

Banner district, Arizona 91

Bisbee (Warren) district, Arizona - 66

Clifton-Morenci district, Arizona 62

Courtland-Gleeson district,

Arizona _ 92

Ely district, Arizona 69

Eureka district, Nevada 84

Gilman district, Colorado 80

Leadville district, Colorado 72

Northern Arkansas district 94

Tintic and East Tintic districts,

Utah ____.____.._________ 75

Tri-State district ___________ 60

Mining districts, major, jasperoid in 57

minor, jasperoid in 88

Minor-element contents. See Analyses,

jasperoid samples.

Minturn Formation .. 71, 80, 81, 99, 100 

Mississippi Valley 132 

Mississippi Valley district __ 36, 58, 104 

Missouri, jasperoid bodies 107 

Moab, Utah ___________-____ 137, 146 

Mockingbird Gap district, New Mexico 129 

Modoc mining district, California 96, 97 

Moenkope Formation. 91, 146 

Moffat County, Calif_.____-___ 97, 102 

Mojave Desert, Calif 94 

Molas Formation 101 

Monarch-Tomichi district, Colorado 97, 102 

Monitor mine 118 

Montana, jasperoid bodies 107 

Monte Cristo Mountains, Nev 114 

Montmorillonite 25 

Montoya Dolomite 125 

Monument Creek, N. Mex .. 126 

Morgan County, Utah 147 

Mormon Well, Nev . 122 

Morrison Formation 7 

Mosquito Range, Colo - 71, 97, 102 

Mother Lode gold district, California .. 96 

Mount Dixon, Alaska 90 

Mount Hope district, Nevada 123 

Mount Nebo district, Utah US 

Mount Tenabo, Nev 112
162 INDEX

Page

Mountain City, Tenn _ 134

Mowry mine, Arizona 93

Mud Springs district, Nevada ~-_ 123

Muddy River, Utah . 145 

Mule Mountains, Ariz 63, 94

Muscatine mine, Utah __- - 144

Muscovite -____ ___- --____ 25

N

Naco Limestone ___-____ _ 65, 91, 94 

Nashville, Tenn___ ___ - 134 

Nashville Dome _______________ 135 

Navajo County, Ariz____.____ __.__ 94 

Nephi, Utah .. _--_ -__ ._._- 143 

Neutralization of solutions, as cause of

silica deposition 43 

Nevada, jasperoid bodies - 108 

Nevada district, Nevada ___ __-- 123 

Nevada Limestone ____ __ 121, 122 

New Galena, Pa__._______-__ 130, 131 

New Jersey, jasperoid bodies ISO 

New Mexico, jasperoid bodies - - 123 

New York Canyon, Nev__________84, 85 

Newark Canyon Formation 84, 85, 88 

Nickel deposits, Nevada _______ 108, 110 

Nickel mine, Nevada -___ 110 

Nontronite __ __-~__- 25 

Nopah lead and zinc mining district.

California ____________ ____ 97 

Norris Basin, Yellowstone National

Park ____________________ 46 

North Carolina, jasperoid bodies - 130 

North Fork, Little Evans Gulch __... 72 

North Park(?) Formation ________ 149 

North Sheep Mountain, Colo 100 

North Star claim, Nevada _ 118 

North Tintic district, Utah __ 144 

Northern Arkansas zinc-lead district _-- 94 

Nunn Member, Lake Valley Limestone - 127 

Nye County, Nev_.___________ 116, 122

O

Ochre Mountain, Utah _ __ 140, 141 

Ochre Mountains Limestone _~. - 140 

Old Baldy Peak, Utah .._________ 75 

Old Quake mine, Nevada __ __- 120 

Opal ________________ 25, 37, 43, 45, 46 

Ophir district, Utah ______ . 7, 142, 144 

Oquirrh Formation -________- - - 140

Oquirrh Group 138

Oquirrh Mountains, Utah 142

Ore, jasperoid as a guide to _ .__ 50

relationship to jasperoid, Alabama 89

Anderson prospect,

Washington __________ 149 

Aspen district, Colorado ___- 82 

Atlanta district, Nevada 108 

Austinville district, Virginia -- 147 

Bidwell Bar district, 

California ______________ 96 

Bingham district, Texas . 138 

Bisbee (Warren) district, 

Arizona _-- __..~ _ _._ 65 

Bishop Cap district, 

New Mexico -_________ 124

Carbonate district, South

Dakota __ ____ ____- 134

Cartersville district, Georgia 102

Central Kentucky district 106

Central Tennessee district 135

Clifton district, Utah ____-- 139

Contact district, Nevada 111

Cooks Peak district, New

Mexico _ ___ __ _-_- 125

Cortez district, Nevada 112

Cuchillo Negro district,

New Mexico 125

Page

Ore Continued

relationship to jasperoid Continued

Darwin district, California 96

Drum Mountains (Detroit)

district, Utah __ 140

Dugway district, Utah 140

Eagle Mountains district,

Texas ________ _ 136

East Shasta district, California. 96

Eastern Tennessee zinc

district ______ 134

Ely district, Nevada ____ 67

Eureka district, Nevada - 84

Friedensville district,

Pennsylvania - . 131

Getchell mine area, Nevada 114

Gilbert district, Nevada __ 114

Gilman district, Colorado . . 79

Gold Hill district, Utah ___ 140

Goodsprings district, Nevada .. 115

Groom district, Nevada _ _ 115

Hadley (Graphic) district,

New Mexico . -. 125

Hillsboro district, New Mexico_ 126 

Horseshoe-Sacramento district, 

Colorado ____________ - 98 

Ivanpah district, California _ 96 

Jerome district, Arizona 93 

Kentucky-Illinois district _ _ 106 

Kern district, Nevada _- -_ 115 

Kingston district. New Mexico.. 126 

Kokomo district, Colorado 99 

La Plata district, Colorado __ 99 

Lake Valley district, New 

Mexico _______________ 127 

Leadville district, Colorado 72 

Lewis district, Nevada 115 

Lucin district, Utah 142 

Magdalena district.

New Mexico __________ . 127 

Manhattan district, Nevada - - 116 

Mercur district, Utah - 143 

Metaline district, Washington ._ 148 

Mill Canyon district, Nevada 112 

Miller Hill area, Wyoming 149 

Mount Nebo district, Utah . .. 144 

North Carolina _ 130 

North Tintic district, Utah .... 144

Northern

Arkansas zinc-lead district _ 94 

Organ district, New Mexico _ 127 

Pando area, Colorado 100 

Patterson district, Nevada .... 116

Rico district, Colorado 101 

Rush Valley (Stockton) 

district, Utah _________ . 144 

San Francisco district, Utah _ 144 

San Rafael Swell area, Utah 146 

Santa Fe district, Nevada ___ 117 

Shafter district, Texas ____ 136 

Silver Islet district, Utah ___ 146 

Silver Peak district, Nevada _. 117 

Silverhorn district, Nevada 117 

South Carolina __ 130 

Southeastern Missouri district 107 

Steeple Rock district. 

New Mexico 128 

Taylor district, Nevada 118 

Tecoma district, Nevada 119 

Tennessee .._ 134

Tintic and East Tintic districts, 

Utah .-..-. - 74

Tres Hermanas district, 

New Mexico 129 

Tri-State district . 60 

Uncompahgre district, Colorado- 101 

Utah 137

Victorio district. New Mexico . 129 

West Lead district,

Page

0 re Continued

relationship to jasperoid Continued

South Dakota __^.. ____ 132

Organ district. New Mexico . ___ 127

Organ Mountains, N. Mex.. 124, 125, 127

Origin of jasperoid. See Genesis of jasperoid.

Orthoclase ...____ _ __.. 25

Osgood Mountains, Nev_________ 114

Othello fault. New Mexico _ ___. 125

Ouray, Colo________._________ 97, 101

Owen County, Ky_______________ 106

Owens Lake, Calif . .. 96

Oxidized deposits, Colorado 102

Montana _________________ 108

New Mexico _________ 124, 125, 129

Tennessee 134

Utah .._____.______._____ 144

Pahasapa Limestone 24 

Palomas Creek, N. Mex__________ 126 

Panamint Springs district, California _ 96, 97 

Pando area, Colorado .._____ 71, 79, 97, 99 

Park City district, Utah ____-____ 147 

Park County, Colo______________ 97 

Patagonia district, Arizona 93 

Patterson district, Nevada . 116 

Paymaster Tunnel, Nev.____ ....... 119

Pearl Creek, Colo.. __ ____ 100 

Pelican fault, New Mexico ________ 126 

Pelican shaft, New Mexico .__-___- 126 

Pend Oreille County, Wash__ ___. 148 

Pend Oreille mine, Washington ____ 148 

Pennsylvania, jasperoid bodies ISO 

Penny River, Alaska 90 

Percha Creek, N. Mex____________ 126 

Percha Shale __ 125, 126, 127, 128, 129 

Pershing County, Nev____ ____ 123 

Petrography. See Geology. 

Petrology. See Description of jasperoid. 

Philipsburg district, Montana __107, 108 

Physical properties, jasperoid __ . 7 

"Picher Field," Okla____________ 3 

Pierce, W. G., quoted____________ 89 

Pilgrim mine, Nevada_._ -.____ 115 

Pilot Mountains, Nev . . 116 

Pilot Shale __-___... ...____121, 122 

Pima district, Arizona .__ ____ 91, 93 

Pinyon Peak, Utah _ 75 

Pinyon Range, Nev . __ 116 

Pioche, Nev ___ ._.___108, 116, 117 

Pioneer Gulch, Colo ____________ 82 

Pitkin County, Golo ______ ..81, 97, 102 

Plagioclase _-._._._..-____. -_.__. . 25 

Platte River, silica content_ __ 42 

Platteville Formation ._____ __104, 105 

Plumas County, Calif. __________ 96 

Pogonip Group __ ... ~~~ _ 84 

Polk County, Tenn _____________ 135 

Pony Express Limestone Member,

Wanakah Formation 99 

Pope County, 111 __ __ __ 106 

Porosity ____________________ 29, 54 

Portland Canal, Alaska __________ 89 

Potosi District, Nevada. See Getchell

mine area, Nevada.

Potosi Dolomite _ _ . 107 

Prairie du Chien Group 104 

Prairie Flower mine, Nevada. 115 

Precipitation of silica, See Deposition

of silica.

Presidio County, Tex __________ 135 

Presidio Formation 136 

Pressure, effects on solubility of silica.. 37, 40 

Prospect Mountain Quartzite 112 

Prospect Peak, Nev 84 

Pyrite . 85
INDEX 163

Page

Q

Quartz, accessory mineral _. _ 26

conversion of silica gel 45

in jasperoid .______-___..___ 45

solubility _________ - 37

Quartz Creek district, Colorado_____97, 102

Queen of the Hills mine, Nevada __111, 122

Queens Gulch, Colo ______ 83

Quinn Canyon Mountains, Nev 122

R

Ragged Top Mountain District,

South Dakota _____________ 131, 133 

Railroad Valley, Nev 122 

Randville Dolomite _____________ 107 

Ransome, F. L., quoted __ 101 

Rappahannock River, Va 147 

Rawlins, Wyo _________ _____ 149 

Red Cliff, Colo ___________._.. 79, 97, 99 

Red Mountain district, Colorado 97, 102 

Redding, Calif _________ --____ 96 

Replacement, chemical factors _ 48 

host rocks 46 

physical factors 46 

theory ___________,.______ 49 

Reward district, California 97 

Richmond Hill, Colo _____ ____ 82 

Rico district, Colorado __________ 97, 100 

Rio Grande _____________ 126, 129, 135 

River water, silica content 41 

Roaring Fork River 81 

Roberts Mountain thrust fault, Nevada. 112, 

Rock-Color Chart, use of- - __--_ 53 

Rockingham County, Va 147 

Rocky Ridge, Tex ______ 136 

Ross, C. P., quoted ____________ 104, 136 

Rover Hill, Utah _-____.____- 143 

Ruby Range, Nev _____________ 110 

Rush Basin, Colo ______________ 99 

Rush Valley (Stockton) district, Utah 144 

Russ district, California __ . _ 97 

Ruth, Ariz _______ __ 68

Sacramento mine, Utah . _______ 143

Sacramento stock, Arizona 64

Saguache County. Colo _________ 97, 102

St. Francois County, Mo. __ 107

St. George, Utah _______________ 146

St. Kevin district, Colorado - - 97, 102

St. Peter Sandstone _____- .__ 104

Salida, Colo _.__ _._ 97, 102

Saline County, 111 ______________ 106 

Salmon River district, Alaska 89, 90

Salt Lake County, Utah _________ 137

Sambo mine, Colorado ...___ ___ 101

San Andres Mountains, N. Mex. __ 127, 129

San Augustine Pass, N. Mex _ 127 

San Bernardino County, Calif _____ 96, 97

San Francisco district, Utah 144

San Francisco Mountains, Utah 144

San Juan County, Colo __ 102

San Juan Mountains, Colo _______ 97, 100

San Rafael River, Utah __________ 145

San Rafael Swell area, Utah 137, US, 147

San Xavier mine, Arizona ___ ... 93

Sanderson, Tex _______ _ 136

Sandia Formation 127

Santa Fe district, Nevada __ ____ 116

Santa Rita, N. Mex __-__ 128, 129

Santa Rita district, New Mexico ___ 58, 128

Santa Rita Mountains, Ariz . _ 93

Santaquin Chief mine, Utah ______ 143

Sawatch Range, Colo ___ 78, 79, 81, 97, 102

Scheelite deposits, California 94

Nevada 111

Page

Schell Creek Range, Nev _______ 116, 117 

Schrader, F. C., quoted __________ 93, 116 

Seabury mine, South Dakota 134 

Seco Creek, N. Mex _____________ 126 

Sedadlia district, Colorado _______ 97, 102 

Sericite ________________ Z7 

Seventy Nine mine, Arizona _____29, 91 

Sevier Desert, Utah _____________ 139 

Seward Peninsula area, Alaska .____ 89, 90 

Shadow Mountain, Ariz __ ._____ 91 

Shady Dolomite ______________ 134, 147 

Shafter district, Texas ___________ 135 

Shannon shaft, Arizona __ ______ 92 

Sharp County, Ark _____________ 94 

Shasta County, Calif ____________ 96 

Shasta Lake, Calif _____________ 96 

Sheba-de Soto mine, Nevada __.._.___. 123 

Sheep Mountain, Colo ___________ 102 

Shenandoah Peak, Nev __________ 115 

Shinarump Member of the Chinle

Formation _________________ 7, 91 

Shirley Basin, Wyo ______ ___ 21 

Shoshone Range, Nev ____ 115 

Siderite _____________________ 27 

Sierra Caballos district, New Mexico. 

See Hermosa (Sierra Caballos) district. New Mexico.

Sierra Cuchillo Range, N. Mex ____ 130

Sierra County, N.M 124, 125, 126, 128, 129, 130

Sierra Nevada, Calif ____________ 97

Sierra Oscura, N. Mex __________ 129

Silcretes, South Africa ___ _____ 36

Silica, deposition of _ __ __ 43

replacement theory ___ _. 46

solubility _________________ 37

sources of _________________ 35

transportation _ _______ __ 36

types in jasperoid ____ 45

Silica-bearing solutions ___41, 62, 65, 79, 91,

94, 98, 107

Silica gel, conversion to quartz 45 

deposition __________..._____ 81 

Siliceous replacement, Alaska __ 89 

Silicifled rocks, Tanganyika 36 

Silver City, N. Mex ___...._____ 128, 129

Silver deposits, Arizona ______ 92, 93 

California ________________ 96 

Colorado ___ ..... 79, 82, 99, 101

Idaho ___________________ 104 

Montana _________________ 108 

Nevada 84, 108, 110, 112, 114, 115, 116, 

117, 121, 123 

New Mexico _____.... 124, 125, 126, 129

South Dakota ____________ 131, 133 

Utah ___..____._____ 137, 142, 144 

Silver Islet district, Utah ________ 146 

Silver Lick mines, Nevada 85 

Silver Peak, Nev _. .__ 117, 122 

Silver Peak district, Nevada 117

Silver Peak Range, Nev __________ 122 

Silver Queen shaft, Nevada .- ___- 118 

Silver Reef, Utah .............__._ 137, 146

"Silver Reef sandstone" ._______.. 147

Silverado Canyon, Utah __ 142, 43 

Silverhorn district, Nevada 117 

Skull Canyon, Idaho ____________ 104 

Slate Creek, Alaska _____________ 90 

Slate Range district, California ____ 97 

Smith, W. S. T., quoted _._-___-_ 106 

Smithsonite ___________ _____ 27 

Snowmass Mountain, Colorado _ _--_._ 97 

Socorro County, N. Mex ____ 124, 127, 129 

Soda Lake lead and zinc mining

district, California _____ 97 

Solomon district, Seward Peninsula,

Alaska ____________________ 90 

Sols, mixing of, effects on deposition 44 

Soluble salts, as a cause of deposition 

of silica _________ 44

Page

Solution of silica 36 

Solutions, hydrothermal 60, 64, 67, 79, 92, 94 

Sonoma County, Calif 97 

South Africa, silcretes 36 

South Carolina, jasperoid bodies .__ 130 

South Dakota, jasperoid bodies ____. 131 

South Park district, California _ 97 

Southeastern Missouri district 107 

Spar Valley, Tex ______________ 136 

Spearflsh Creek, S. Dak __ _ 131 

Spectrographic analyses. See Analyses,

jasperoid samples.

Sphalerite ___________________ 27 

Sphene ........____ _ 27

Spring Canyon, Nev . 113 

Spring Creek district, Colorado ____ 97, 102 

Spring Mountains, Nev __. ._ 115 

Spruce Mountain district, Nevada 123 

Spruce Standard mine, Nevada 123 

Spurr, J. E., quoted _____________ 2, 107 

Squaw Creek, S. Dak _ . 131, 134 

Squaw Creek mine, South Dakota 132 

Squaw Spring, Utah . _ 144 

Standard rock analyses __ -____ 81 

Star district, Utah ._. 144 

Star Peak Group _______ -___ 123 

Star Range, Utah _____________ 144 

Starr Grove mine, Nevada 115 

Statistics, use of, for evaluation of 

japeroid samples _____ _ 51

Steamboat Springs, Nev 45, 46

Steeple Rock district, New Mexico 124, 128

Stevens County, Wash ____ __,. 149

Stibiconite __________________ 27

Stray Horse Ridge, Colo _________ 71

Streater claims, Nevada 116

Success district, Nevada 123

Sugar Loaf district, Colorado ____ 97, 102

Sulflde deposits, Alaska __ __ 89

Arizona ____________ 65, 91, 93, 94

California _________ 96

Colorado .._._______ 79, 99, 101, 102

Kentucky __________________ 106

Missouri __________ ____ 107

Nevada 84, 110, 111, 112, 113, 115, 116,

117, 119, 121

New Mexico -___... 124, 125, 126, 129 

Pennsylvania 130 

Tennessee ___________-__ 134, 135 

Texas ___________________ 135 

Tri-State district ____________ 60 

Utah ....._______... 74, 137, 141, 143

Washington 148 

Sulphur Bank district, California 97 

Summit claim, Salmon River district,

Alaska ____________________ 90 

Summit County, Colo ____ 97, 99, 102, 147 

Supergene jasperoid _ 84, 97, 115 

Surface water, silica-bearing ~ 94 

Swansea district, California 97 

Sweetwater district, Tennessee 134, 135 

Swisshelm district, Arizona .__ 94

Sycamore Creek, Ariz__ 94

Tanganyika, silicified rocks 36 

Taylor, Nev____ __ .. 118 

Taylor district, Nev________ 27, 108, 117 

Taylor Springs, Nev- 118 

Tecoma district, Nevada 119 

Tecopa district, California 97 

Telluride ore, South Dakota . _ 133 

Temperature, effects on solubility of

silica ___________________ 37, 40, 43 

Temple Mountain, Utah _________ 146 

Tennessee, jasperoid bodies 134 

Tennessee Pass, Colo _ 97, 99 

Terrell County, Tex 136
164 INDEX

Page

Texas, jasperoid bodies 1S5

Texture, categorizing jasperoid 53

fabric _- ._ _ _ 11

in jasperoid 7

Texture of jasperoid. See Microtexture

of jasperoid.

"The Burnouts," Nevada 84 

Thermal analysis, differential SO, 55 

Thermal springs, silica content 41 

Tierra Blanca Creek. N. Mex_.... 128 

Tierra Blanca district, New Mexico 128 

Timberville, Va____.___________ 147 

Timberville district, Virginia 147 

Tincup district, Colorado ________ 97, 102 

Tintic district, Utah 21, 61, 73, 137, 144,

147

Tippett, Nev __-___ ___ _ 115 

Tombstone, Ariz_______________ 92, 94 

Tomstown Formation 147 

Tonopah, Nev_______ 3, 110, 114, 116, 123 

Tooele, Utah ____-__ __ 144 

Tooele County, Utah ______ 139, 140, 142,

144, 146, 147

Topton, Pa_______________-__- 131 

Toquima Range, Nev__ __ ____ 116 

Tourmaline _ ___-______- ._ 27 

Tourtellotte Park, Colo- 83 

Transportation of silica solutions 36 

Treasure Hill, Nev___ __ __ 121 

Tremolite ___________________ 27 

Tres Hermanas, N. Mex- - 129 

Tres Hermanas district. New Mexico 129 

Tri-State district ____ 3, 6, 47, 58, 94, 105,

107, 135

Truth or Consequences, N. Mex__ 126, 129 

Tucson Maid fault, Colorado __ 71 

Tungsten deposits, Nevada 114 

Tungsten Hills, Calif 97 

Turkey Creek, Colo________-___ 79, 99 

Tutsagubet district, Utah US 

280 Tunnel, Nev______________- 119

U

Ubehebe district, California 97

Ulster mine, South Dakota ._ . 133

Uncle Sam Gulch, Ariz__________- 64

Uncompahgre district, Colorado 97, 101

Unfavorable jasperoid, definition __ 50

Unicoi County, Tenn 134

U.S. mine, Utah _-__________ 140, 141

United Verde mine, Arizona _____ 93

Upper Mississippi Valley district 36, 58, 104

Upper Peninsula, Mich- _ . 107

Page

Uranium deposits, Arizona 92 

Nevada ______ 108 

Utah ____________________ 145 

Wyoming ______ _ 149 

Utah, jasperoid bodies 137, 146 

Utah County, Utah _________ 73, 144 

Vauclause Mine, Virginia - 147 

Velarde prospect, New Mexico 124, 130 

Vernon, Utah ______ - 147 

Verzan Canyon, Ariz 68 

Veteran mine, Arizona 68, 69 

Victoria mine, Nevada _____ - 113 

Victorine mine, Nevada 123 

Victorio district, New Mexico 129 

Victorio prospect, New Mexico 124, 130 

Virginia, jasperoid bodies 147 

Volcanism, relation to silica-bearing

water 41 

Vugs, abundance 7

W

Wah Wah district, Utah __ - 144 

Wah Wah Mountains, Utah ____ 144 

Wall Street mine, Nevada 117 

Wanakah Formation 99 

War Eagle mine, Nevada 111 

Ward district, Nevada --_ - 119 

Warren County, N.J 131 

Wasatch Range, Utah 143 

Washington, jasperoid bodies 148 

Washington County, Ark 94 

Mo 107

Tenn _- _ _ -_ 134

Utah 139, 146

Water, hot springs, silica content 41

silica-bearing __ 94

solubility of silica in 37-39

See also Ground water.

Water Canyon, Nev 115

Water Canyon district, New Mexico 129 

Watson Canyon, Nev 113 

Watson Spring, Nev-- - 113 

Weary Flat, Ariz_______ _ 68 

Weathering, source of silica solutions 36 

Welcome Stranger Tunnel, Nev 119 

Wellington mine, Colorado 102 

Wendover, Nev-- 113, 146 

West Lead, S. Dak_____ - 132 

West Lead district, South Dakota 131, 132 

West Mercur, Utah 142 

West Mountain, Utah ___ - 138, 139 

West Tintic district, Utah 147

Page

West Virginia, jasperoid bodies 147 

West Ward district, Nevada ______ 119 

Whirlwind Valley, Utah ___.__ _ 139 

"White Caps limestone" . . 116 

White Pine, Nev_____._________ 115 

White Pine County, Nev- 108, 110, 111, 117,

119, 121, 123 

White Pine (Hamilton) district,

Nevada _______ 121

White Pine Mountains, Nev_______ 121 

White Quail Limestone Member, Minturn

Formation . 99 

White River Plateau, Colo . __ 102 

Whitney mine, North Carolina 130 

Willow Creek district, Nevada _____ 122 

Winchester district, Arizona 93 

Windfall Canyon, Nev__________ 84, 88 

Windfall Formation 84 

Winnemucca, Nev 114 

Wisconsin, jasperoid bodies 104 

Wonder mine, California 96 

Wulfenite ___ _ .__ _____ .___ 29 

Wyndypah district, Nevada 122 

Wyoming, jasperoid bodies 149 

Wythe County, Va - 147

Y, Z

Yampa River, Colo____ ___ 102 

Yavapai County, Ariz._ _ _ 93 

Yellow Creek mine, South Dakota 132 

Yellow Pine mine, Nevada 115 

Yellowstone Basin 7 

Yellowstone National Park __ ___ 41, 46 

Yerington, Nev__ __ . 127 

Yerington district, Nev -_ ___ 123 

Yosemite Gulch, Utah _ _ _ 138 

Young, Ariz 94 

Yule Creek, Colo ... ______.___ _ _ 102

Zinc deposits, Alaska 89 

Arizona 94 

Arkansas 94 

California .___ . . 96 

Colorado _____________ 99, 101, 102 

Idaho _______________-___ 104 

Missouri _______ __ ___ 107 

Nevada 110, 119

New Mexico __________ 125, 127, 128

Pennsylvania - 130

Tennessee 134

Utah __.___________ 142, 144, 147

Virginia __ - - 147

Washington ___.. 148

Zinc Hill mining district, California .__ 96, 97

Zionsville, Pa_________-__ 131

Zircon 29

U.S. GOVERNMENT PRINTING OFFICE: 1972 O 442-66O