Zinc-Lead-Copper 

Resources and 

. General ,qeology. ·of 

The U pp.er. Mississippi I 

Valley District 

ll. -1" 

GkOLOGICAL SURVEY BULLETIN 1015-G 

Prepared in cooperation with the 

Wisconsin Geological and Natural 

His tory Survey, the Illinois State 

I Geological Survej~, and the 

Iowa Geological Survey 

\ 

I 
Zinc-Lead-Copper 

Resources and 

. General Geology of 

The Upper Mississippi 

·Valley District 

By ALLEN V. HEYL, ERWIN J. LYONS, ALLEN F. AGNEW, and CHARLES H. BEHRE, Jr 

Information on Illinois furnished by H. B. WILLMAN and R. R. REYNOLDS 

A CONTRIBUTION TO ECONOMIC GEOLOGY 

GEOLOGICAL SURVEY BULLETIN 1015-G 

Prepared in cooperation with the 

Wisconsin Geological and Natural 

History Survey, the Illinois State 

Geological Survey, and the 

Iowa Geological Survey .. 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

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

·Washinatoa 25, .D. C. - Price 70 cents (paper cover) 
CONTENTS 

Page 

Abstract__________________________________________________________ 227 

Introduction______________________________________________________ 227 

Geology__________________________________________________________ 229 

Stratigraphy__________________________________________________ 229 

Structure-----------------------------~-------------~--------- 231 

Oredepo~ts------------------------------------------------------ 232 

History and production_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 232 

Ore minerals and types of deposits_______________________________ 233 

Pitch-and-flat deposits ________________ -,...--_________________ 234 

Gash-vein deposits _____________________ ---------___________ 236 

Relations between ore deposition and major geologic features_______ 236 

Distribution of ore deposits at the district boundaries__________ 237 

Distribution of ore deposits within the district_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 239 

Ore deposits and the main lithologic units____________________ 241 

Ore deposits and the major folds ____ ------------------------ 242 

Selected bibliography_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 242 

Index____________________________________________________________ 245 

ILLUSTRATIONS 

[Plates in pocket] 

PLATE 25. Map of the Upper Mississippi Valley zinc-lead district. 

26. Structure map of area east of Hazel Green, Wis. 

FIGURE 33. Generalized stratigraphic section of the Upper Mississippi 

Valley zinc-lead district_ _______ ..:. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 230 

34. Diagrammatic plans and sections illustrating typical patte-rns 

of gash-vein lead deposits and underlying pitch-and-flat 

zinc deposits_________________________________________ 234 

TABLE 

Tonnage and value of zinc and lead metal produced in Wisconsin and 

northern Tilinois from 1925-50, and in Iowa from 1917-53____________ 233 

Ill 

A CONTRIBUTION TO ECONOMIC GEOLOGY 

ZINC-LEAD-COPPER RESOURCES AND GENERAL GEOLOGY OF THE UPPER MISSISSIPPI VALLEY DISTRICT 

By ALLEN V. HEYL, ERWIN J. LYoNs, ALLEN F. AGNEW, and 

CHARLES. H. BEHRE, JR. 

ABSTRACT 

The Upper Mississippi Valley zinc-lead district in southwestern Wisconsin, 

northwestern Illinois, and northeastern Iowa contains thousand.s of small lead 

mines, about 400 zinc mines, and a few small copper mines. The ores are chiefly 

in the Galena dolomit•e and in the limestones and dolomites of the Decorah formation and upper part of the Platteville formation, all of Middle Ordovician age. 

Locally, minable deposits have been found in the Prairie du Chien group of 

Early Ordovician age, and small deposits of lead and iron sulfides have been 

found iii the formations of Cambrian and Silurian age. The area has been gently 

flexed, and folds of three orders of magnitude are recognized. 

Zinc ore deposits are commonly linear or elliptical in plan. The ore is in the 

form of veins, replacements, and impregnations, and it occurs along shears, small 

reverse faults, and bedding-plane faults related to the intermediate and small 

folds. Gash-vein deposits, most of which are restricted to the Galena dolomite. 

occur as replacement veins along Yertical joints. The main primary minerals are 

quartz, dolomite, pyrite, marcasite, sphalerite, galena, c"P.alcopyrite, barite, and 

calcite. 

The east, south, and west boundaries of mineralization are hidden either by 

overlying Silurian rocks or Pleistocene glacial .deposits. The north boundary of 

the area of known deposits lies at the eroded edge of the southward-dipping 

Ordovician strata that were most favorable for ore deposition, but its original 

position may have been farther north. In a few places, where the ore deposits 

are small, lean, and widely spaceq, the actual limit of the district can probably 

be defined. Calcite and small quantities of galena, marcasite, and pyrite are the 

main minerals of these marginal deposits. In many parts of the district, mines 

are closely spaced, but between these parts only a few deposits are known. 

Lack of ore deposition, local erosion of the favorable/ beds, patches· of overlying 

rocks that hide the favorable beds, and. lack of prospecting determip.e the size 

and location of the mining centers. 

INTRODUCTION 

This report discusses the general geology of the Upper Mississippi 

Valley zinc-lead district, the distribution of ore deposits, and some re227 
228 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

lations of the ore deposits to the major geologic features. The district includes an area of about 3,000 square miles in southwestern Wisconsin, northwestern Illinois, and a narrow fringe of northeastern 

Iowa (pl. 25) drained by the Mississippi River and its tributaries. 

The central part is a rolling plain dissected by the major streams to 

a depth of about 300 feet; the 1narginal areas are relatively hilly. 

Within the district are thousands of· small lead mines, about 400 

.zinc mines, and a few small copper mines. For convenience in numbering, these mines were arbitrarily grouped. The distribution of 

these groups and of the mining areas is shown in plate 25. In another 

report 1 the mines are listed and individually located. The deposits 

in the Prairie du Chien group are differentiated from those in the 

Platteville, Decorah and Galena formations and those in the Lower 

Silurian dolomite in plate 25. The boundary of the Silurian escarpment is shown, but because of the numerous mine workings the boundary between the Middle and Lower Ordovician beds could not be represented. Grant and Burchard ( 1907) have delineated this contact 

in the central part of the district at the same scale as plate 25. ~1any 

of the reports in the selected bibliography give further details on the 

geology of the district and on individual mines. 

In 1942 the TJ. S. Geological Survey began ·a · detailed restudy of 

the geology and ore deposits of this district. Since 1945 the work 

in Wisconsin has been done in cooperation with the Wisconsin Geological and Natural History Survey. Although the geologic studies 

are being continued ( 1955), this report and related reports 2 that are 

now in preparation are based on work that was completed in July 

1950. In 1943 the Illinois State Geological Survey started a geologic 

study of the Illinois part of the district, and this investigation is also 

being continued (1954) .. 

The data used in this report, including the distribution of ore deposits shown in plate 25, were obtained largely by field mapping, by 

compilations from aerial photographs, and, where other information 

was lacking, from maps and .geologic reports. The mapping in Wisconsin and Iowa was done by the w·riters, assisted by M. L. Heyl, A. 

E. Flint, J. J. Theiler, C. W. Tandy, J.P. Moor, H. G. Hershey, and 

Carl Spradling. The lead mine areas and fold axes in Illinois were 

mapped py H. B. \Villman snd R. R. Reynolds of the Illinois State 

Geological Survey. Information concerning the location and geologic occurrence of zinc and lead deposits was compiled at a scale of 

1 mile per inch by the writers, and prints were .made available in open 

1 Heyl, A. V., Agnew, A. F., Lyons, E. J., and Behre, C. H., Jr., Geology of the zinc and 

lead deposits of the Upper Mississippi Valley district. In preparation as a Geological 

Survey report. 2 Heyl, A. V ., and others op. cit. 

Agnew, A. F., Heyl, A. V., Bebre, C. H., Jr., and Lyons, E.. J., Stratigraphy of the Upp,er 

Mississippi Valley district. In preparation as a Geological Survey report. 
ZINC-LEAD-COPPER, UPPER MISSISSIPPl VALLEY DISTRICT 229 

file in 1951. In order to present and emphasiz-e -the major-features of 

the district, plate 25 was compiled; this was done mainly by Reta E. 

Linebaugh. 

Many individuals, mining companies, and the State geological surveys o:f Wisconsin, Illinois, and Iowa gave valuable information. 

Because contributors are so numerous, it is impossible to ac~nowledge 

each one; however, we wish to thank them as a group :for their help. 

GEOLOGY 

The Uppe~ Mississippi Valley mining district is about 100 miles 

south o:f the main area o:f outcrop o:f rocks of the pre-Cambrian shield 

in 'Visconsin (Bean, 1944). The lead, zinc, and copper ore deposits 

are in the northern fringe of gently flexed Paleozoic sedimentary rocks 

that overlap the shield area. Most of the known lead, zinc, and 

copper deposits are restricted to the dolomites, limestones, and shales 

of :Middle Ordovician age (fig. 33) , but deposits are found in all other 

Paleozoic rocks exposed in the district. 

Most of the district lies within the Driftless Area (Grant and Burchard, 1907, p. 2-3; Shaw and Trowbridge, 1916, p. 1-2, 7), qut glaciers 

of pre-vVisconsin age have crossed the eastern and western boundaries 

and part of the southern boundary (pl. 25). The nearest glacial deposits of vVisconsin age are :found in the immediate vicinity of Madison, Wis. The glacial deposits o:f pre-Wisconsin age thin gradually 

toward the boundary of the Driftless Area and are represented by only 

small remnants of drift. Pleistocene bench and terrace gravels, sands, 

and clays are common in the valleys of the principal rivers that flow 

across the Driftle~s ~rea from the surrounding country. D~posits 

of interglacial loess of pre-Wisconsin age that are as much as ~0. :feet 

thick cap the bluffs along both sides of the Mississippi River and extend several m~les away from the river. . 

STRATIGRAPHY 

The rocks exposed in the district are Cambrian, Ordovician, and 

Silurian in age (fig. 33). Rocks of the pre-Cambrian basement have 

been :found only in wells at depths of 1,500 to 2,000 feet. The oldest 

rocks exposed-the Franconia and Trempealeau formations of Late 

Cambrian age-crop out only along the Wisconsin River and near 

~ladison, Wis. The Prairie du Chien group of Early Ordovician 

age is exposed in some o:f the deep valleys and along the north and 

east margins of the district (Grant and Burchard, 1907) . Most of 

the outcrops in the district are Galena dolomite, but exposures o:f 

the Platteville formation and St .. Peter sandstone are common, particularly in the valleys. Maquoketa shale of. Late Ordovician age 

(Grant and Burchard, 1907; Shaw and Trowbridge, 1916) covers 
230 , CONTRlBUTIONS TO ECONOMIC GEOLOGY 

z 

<( 

;;: 

::> 

g 

z 

<( 

0 

> 

8 

0:: 

0 

z 

:s 

0:: 

~ <( 

u 

/ / 

0:: Dolomite, buff, cherty Q / , 0/ r..:l 

~ Do lom ite 0/C> 190 1 

0 V o// 0 ..J Dolomite, light- g ray, sha1y 

0:: 

r..:l f:f:====-==== 

Maquoketa shale Shale, blue-green, w ith thin limestone 0.. r=::-::=-__:-=::_--::=- 130'! 0.. lay ers. Phosphatic fossil zone at base ::> r-- Dubuque shaly m embe r 33' Dolom ite, yellow, thin-bedded, shaly 

/ / Gal Dolomite, buff, thick-bedded. ena Stewartville massive membe r "/-. "%. 80' dolmite z z Rec eptaculites in lower part 

- Pi) Prosser cherty member oc co 0 110' Dolomite, gray -buff, cher ty . 

..J 0 0 

Receptaulites near base 

0 Decorah Ion dolomite membe r ,\ o 

/ 40'! 

Do lom ite, gray, argillaceous. Limestone, 

8 forma- Guttenberg limestone member_'\ 0 0 0 pink, and c a r bonac eous shale "o il rock". ::;; tion Spec hts Ferry shale member Shale, light green 

Platte- Quimby s Mill membe r Lim e stone , p ink, and carbonaceous shaleville McGregor limestone member "g lass rock. 11 Lim e stone, gray, thinforma- P e catonic a dolomite member 60°! bedde d. Dolom ite, gray -buff, thicktion Glenwood shale member ..... . :.':"·.· . :. ' "-. bedded. Shale, light-gre en, sandy 

St . P eter sandstone .:::·. 70' ! Sandst one, white to brown 

Shakopee dolomite :./ )'.;/ 7 50-75' Dolomite, gray , locally cherty / -=> / o/ 

New Richmond sandstone )/0' 0 -25' Sandstone, white lenses 

0:: P rairie 

r..:l Du ~ Chien 0 Dolom ite, gray , locally ..J group Oneota dolomit e 185'! c he r ty, shaly and sandy 

Jordan sandstone member :')..:··;g ·.'::-'. 30'! Sandstone Trempealeau .:··:·,:.-·:·:: 

0:: for ma- r..:l St. Lawrence member 125' Sandstone and dolomite p.. tion 

I j p.. 

::> 

Franconia sandstone i::\:- . 115 1 Sandstone 

FIGURE 33.-Generalized stratigraphic section of the Upper Missdssippi Valley 

zinc-lead district. 

some of the high hills and underlies the long slopes that rise to higher 

hills capped with Lower Silurian dolomite. Most outcrops of the 

youngest strata-dolomite of Early Silurian age-occur along .a partly' 

incised escarpment along the southern and western boundaries of the 

district; these strata also form a few isolated erosional outliers within 

the district (pl. 25) . 

Some of the details of the stratigraphy are illustrated by the generalized stratigraphic section (fig. 33). The rocks of the Prairie du 

Chien group, the Platteville, Decorah, and Galena formations, and 

Lower Silurian rocks in the district are composed mostly of dolomite, 

although they include some limestone, shale, and a sma11 amount of 

sandstone. Between these carbonate rocks are the predominately 

clastic St. Peter sandstone and Maquoketa shale. The Franconia, 

Trempealeau, and St. Peter formations are permeable sandstones that 

are widespread aquifers. 

Most of the zinc deposits are in the lower part of the Galena dolomite, the Decorah formation, and the upper two-thirds of the Platteville formation. The principal lead deposits are restricted to Galena 
ZINC-LEAD-COPPER, UPPER MISSISSIPPI VALLEY DISTRICT 231. 

dolomite. Small lead, zinc, and copper deposits are :found locally in 

the northern part of the district in the Prairie du Chien group (Heyl, 

Lyons, and Agnew, 1951, p. 1-12) and the Trempealeau and Franconia. 

formations. In places, the St. Peter sandstone is pyritized; it is most 

heavily pyritized where it directly underlies zinc deposits. 

STRUCTURE 

The mining district lies about 100 miles south of the north edge of 

the Paleozoic sedimentary rocks that overlap the North American 

pre-Cambrian shield. The Wisconsin arch (pl. 25), a broad northward-trending anticlinal structure, lies on the east side of the mining 

district. The Illinois basin lies south of the district, and the Forest 

City basin lies to the west and southwest in Iowa. 

The regional strike of the sedimentary :formations is N. 85° W. 

throughout most of the district, but in the western part the strike 

swings to N. 45° W. The regional dip is about 17 :feet to the mile 

towards the south-southwest. The rocks o£ the district have been 

folded into low, broad undulations that differ greatly in magnitude. 

The limbs of the :folds rarely have dips greater than 15 degrees. 

The largest :folds range from 20 to 30 miles in length, 3 to 6 miles 

in width, and 100 to 200 :feet in amplitude. The axes o£ the largest 

folds that have been mapped are shown in plate 25. These :folds trend 

northeastward, eastward, and north westward, the trends changing 

sharply :from place to place across the district. Many o£ these :folds 

are traceable as continuous structures :for miles. The anticlines are 

commonly asymmetrical with the steeper limbs on the north. The 

folds of intermediate magnitude and those of small magnitude trend 

either eastward to northeastward or northwestward (pl. 26). These 

folds occur throughout the area and :form an unusual rhombic pattern .. 

Most o£ the :faults in the district are small reverse, bedding-plane, 

normal, and shear :faults, having displacements of 1 :foot to 10 :feet. 

Some thrust :faults on the steep north limbs o£ the large anticlines 

have displacements o£ 25 to 50 :feet. A :few shear :faults that have 

displacements of 25 to possibly 1,000 :feet have been located. 

All the rock :formations in the district contain vertical and inclined 

joints (Heyl, Lyons, and Theiler, 1952), the :former being particularly 

well developed in the Galena dolomite. Single vertical joints are 

traceable :for more than 1 mile and cut as mueh as 300 :feet of beds. 

Most of the vertical joints :fall into three general strike groupsN. 77° W., N. 12° W., and ,N. 25.

0 E. The joints of the N. 77° W. 

group are generally more open than those o£ the other two groups. 

The inclined joints are commonly tight and in many places are in sets 

·of ciosely spa~ed par~llel :fractures. . Many of them are probably 

incipient reverse :faults. 

327275-55-2 
232 CONTR1BUTIONS TO ECONOMIC GEOLOGY 

Most of the geologic structures observed in the district were formed 

during a period of diastrophism that was preceded by minor regional 

deformation and followed by some uplift and tilting. 

ORE DEPOSITS 

HISTORY AND PRODUCTION 

The lead deposits were discovered by the French in the latter part 

of the 17th century. The French taught the Indians primitive mining 

methods, and for 150 years small-scale mining operations were carried 

on by the Indians and French (Thwaites, 1895, p. 271-292). The 

first American settlers arrived in 1821. .· The district quickly boomed, 

and by 1840 most of the mineralized areas had been discovered. During the 1840's this was the principal lead-producing district in the 

United States, but production afterwards declined, and now lead is 

recovered only as a byproduct of zinc mining. Most of the lead ore 

was produced from the gash-vein deposits, and many of the lead mining areas shown in plate 25 are groups of such deposits. 

Zinc production began in 1860 and reached a peak during World 

War I. A revival in zinc mining by small companies occurred in 

about 1938 and continued until shortly after World War II. Since 

then a few large companies have developed ample reserves and are 

mining on .a major scale. By 1952 the district had again taken one 

of the leading positions in production. The known reserves of ore 

have been increased from about 1,000,000 short tons in 1942 to nearly 

10,000,000 short tons in 1950. 

Zinc production from 1860 to 1951 was about 1,200,000 short tons of 

metal from about 43,000,000 tons of ore. The value of the metal on 

the basis of 15 cents per pound metallic zinc is $363,000,000. Nearly 

85 percent of the zinc was mined in 'Visconsin, 15 percent in Illinois, 

and a small amount in Iowa. In recent years, however, Illinois and 

'\Visconsin have produced nearly equal quantities of zinc. 

The total recorded lead production from 1795 to 1951 was 821,000 

short tons of metallic lead valued at $248,000,000 on the basis of 15 

cents per pound. Slightly more than 50 percent of the lead was mined 

in Wisconsin and the rest was produced in northern Illinois and Iowa. 

Copper was mined in Wisconsin in the 19th century, and as much as 

10,000 short tons of 15- to 20-percent copper ore may have been produced. Barite was mined in Wisconsin between 1919 and 1930, but 

data on the total quantity produced and its value are not available. 

The lead and the cqpper ores and some of the zinc ores were smelted 

locally in the 19th century. In recent years, however, most of the 

zinc and lead ores have been concentrated in gravity and flotation 

mills at the mines or custom mills in the district, and the concentrates 

shipped to central and southern Illinois and to ~1:issouri for smelting. 
ZINC-LEAD-COPPER, UPPER MISSISSIPPI VALLEY DISTRICT 233 

Tonnage and value of zinc and lead metcil produced in Wisconsin and northern 

Illinois fr·om 1925-50, and in Iowa from 191"1-53 

[Data from U. S. Bureau of Mines] 

Zinc Lead 

Years 

. Short tons I Value Short tons I Value 

Wisconsin 

1925-29_----------------------------------------- ------- 1930-34_------------------------------------------------ 1935-39_------------------------------------------------ 194()-44 ___ ---------------------------------------------- 1945-49 __ ----------------------------------------------- 1950.---------------------------------------------------

114,914 

47,775 

31,964 

51,370 

55,220 

5, 722 

---- TotaL __ ~ ____ ------------------------------------ 306,965 

' Illinois 

1925-29_--- --------------------------------------------- 5, 503 193(}-34 __ ----------------------------------------------- 9 1935-39_ ------------------------------------------------ 0 194()-44_ ------------------------------------------------ 6, 269 1945-49_ -------- 0 --------------------------------------- 31,308 1950.----------------------------- ---------------------- 21, 071 

TotaL __ ----------------------------------------- 64, 160 

Iowa 

$15, 787, 634 8, 726 3, 922,158 4,173 

3,312, 788 2,989 

10,068,720 4, 780 13,425,566 6, 240 1, 625,098 532 --------- 48,141,914 27,438 

817,666 813 844 0 0 0 1, 209,492 438 7, 762,914 3, 556 5, 984, 164 1, 269 

15,775,080 6,094 

1917---------------------------------------------------- 18 3, 672 34 1918-52 ___ ---------------------- ----c------------------- . 0 0 0 1953---------------------------------------------------- 0 0 1 

$1,225,156 

336,064 

300,618 

692,400 

1; 566,702 

143,640 -----

4, 264,580 

136,852 0 

0 59,782 

1,043,346 

342,630 

1, 582, 610 

5,848 0 

266 ---------------1·----

TotaL ___ ---------------------------- ---- -------- 18 . 3, 672 35 6,114 

ORE MINERALS AND TYPES OF DEPOSITS 

The main primary minerals have been deposited in the following 

paragenetic sequence: quartz (chert and other forms of cryptocrystalline . silica), dolomite, pyrite, marcasite, sphalerite, galena, barite, 

chalcopyrite, and calcite. The principal secondary minerals are 

smithsonite, limonite, and cerussite. 

The ore bodies can be classified into three types: "pitch-and-flat" 3 

deposits (fig. · 34), "gash-vein" 4 deposits (fig. 34), and placer and 

residual deposits. 

Zinc ores are mined principally from the pitch-and-flat deposits, 

and lead ores from the g~sh-vein and placer types of deposits. Copper 

minerals and barite are found locally in the first two types. 

3 A pitch is a mineralized reverse fault; a fiat is a mineralized bedding-plane fault or a 

vein in an opened bedd·ing plane. 4 The ~erm "gash-vein" for a joint-controlled lead deposit was proposed by Whitney (1854, 

p. 48), Hall and Whitney (1858, p. 437-438), and later used by Winslow (1894, p, 14Q) 

and Chamberlin (1882, p, 453-454·). Whitney (Hall and Whitney, 1858) states that "the 

term 'crevice,' as generally applied, in the lead-region • * * deslgnat~s the vein~like fissures, or gash:.veins as they may be termed, in which the ore is found • . • * ." Winslow 

notes, "To these 'openings [vertical ore-bearing joints]! the name of 'gash-vei:li' so generally given to the deposits of. this region [Wisconsin.] more particularly applias.l' .. 
234 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

400 

SECTION 

.!! 

.L ...L. / I:!:YA 7 7 " 7 u 7 ·e Lead ore ·· ::~:m:;~ ~ 

Joints..--:::--7 17 

/ 

7 

/77 I z, ~ -.; 

(!) 

I 7 

7 

7 

/ 

GASH -VEIN DEPOSITS 

SECTION Gash-vein deposits 

:o~,~ c·e{ --··· shovm ·· ·n·.· ···pla~) ..... . ··.··•···· ·. · •.• B' ~E Ore (!)0 

-a/ .( \ & : 

Decorah formation 

(limestone and dolomite) 

PITCH-AND-FLAT DEPOSITS 

0 800 Feet 

FIGURE 34.-Diagrammatic plans and· sections illustrating typical patterns of gash-vein 

lead depos•its, unde rlying pitch-andt-flat zinc depo&its of the arcuate and linear types, and 

their stratigraphic positions relative to one auother. 

Most zinc ore bodies range in size between 100,000 and 500,000 short 

tons of ore, but a few contain more than 2,000,000 tons. Most of the 

ores mined in recent years range from 4 to 8 percent zinc and from 

0.5 to 1 percent lead. 

Recently mined gash-vein deposits have produced less than 100 short 

tons of 80 percent lead concentrate. Formerly, individual gash-vein 

deposits produced as much as 5,000 tons of 80 percent lead concentrate. 

Present-day operators consider that the gash-vein lead deposits are not 

generally amenable to large-scale production methods, although one 

deposit, the Rodham (pl. 25), was mined in this way. 

Production from individual placer and residual deposits has never 

been large, and mining has always been on a very small scale. 

PITCH-AND-FLAT DEPOSITS 

Most of the ore that has been mined since 1900 has been from the 

pitch-and-fiat deposits. Sphalerite is the main ore mineral, but locally 

galena or pyrite and marcasite or barite has been produced from these 

· deposits.· In 1943 chalcopyrite was discovered in possible commercial 

quantities in drill-hole samples from a pitch-and-fiat zinc ore body on 
ZINC-LEAD-COPPER, UPPER MISSISSIPPI VALLEY DISTRICT 235 

the Mcilhon property in the copper area east o:f Mineral Point, Wis. 

(pl. 25). 

Folds of small and intermediate size that trend northwestward and 

east to northeastward controlled the localization of the pitch-and~flat 

zinc ore bodies (pl. 26). These folds occur throughout the district 

(Agnew, Hey l, Behre, and Lyons, 1948), and the trends of their axes 

form a marked rhomboidal pattern. Both arcuate and linear ore 

bodies occur along the flanks and axial areas of some of the synclines 

and anticlines of intermediate size (fig. 34 and pl. 26). The linear ore 

bodies occu:r at fairly regular intervals and are elongate in directions 

parallel to the :folds. The arcuate ore bodies are in echelon, and they 

a.re most numerous along the northeastward-trending folds o:f intermediate size. Localization of some ore bodies also has been controlled by folds of small size not associated with the intermediate folds. 

Pitch-and-flat ore bodies occur along reverse and bedding-plane 

faults (pitches and flats, respectively) that have small displacements. 

Bedding-phne faults occur in the incompetent uppermost Platteville 

and lower :)ecorah strata. The reverse faults curve upward at low 

angles from these bedding-plane faults, steepening to about 45 degrees in the overlying beds (fig. 34). The faults occur commonly in 

parallel groups that lie on the flanks of folds, the reverse faults usually 

dipping toward the anticlinal area. Many such fault zones follow 

the outline~ of a fold to form an arcuate or linear pattern (fig. 34) 

and are more commonly associated with synclines than with anticlines (Agnew and Heyl, 1944). Most of the fault zones in the southern part of 1;he district are larger and have greater displacements than 

those in the northern part. 

The ore (ICCUrs in the fault zones as vein fillings and replacement 

veins along fractures and bedding planes; as cavity fillings in solution and tectonic breccias; and as disseminations formed by replacement and impregnation of favorable beds by poikilitic crystals of 

sulfides, pa1ticularly the shaly residuum of altered limestone strata. 

The ore solutions have altered the host limestones and, to a lesser extent, the dolomites within and in the immediate vicinity of the de.-

posits. Thi~:; has been done by three main processes: silicification; dolomitization ; and solution of the carbonate rocks, particularly the 

limestones. Solution of the carbonate rocks has considerably thinned 

some of the favorable beds in many ore bodies. The thinning has 

caused the :~ractures in the rock to open, thus providing spaces for 

deposition of the ore. In places the rock has been so altered by solu-

. tion that the overlying Dock has collapsed to form tumbled breccia. 

Dolomitic rocks within and near the ore bodies have locally · been 

"sanded" (Lovering, and others, 1949, p. 27), that is, changed to a 

friable or incoherent ·mass of dolomite crystals by the ore-bearing 
236 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

solutions. The cementing bond between the large dolomite crystals 

was weakened by intergranular solution, and many of the fine dolomite gra.ins were dissolved by the ore-bearing solutions. 

GASH-VEIN DEPOSITS 

Most of the ore produced before 1900 was mined from the jointcontrolled gash-vein deposits (fig. 34). Lead ores are the main product of these deposits, but in a few places zinc or copper ores hav~ been 

mined. The joint-controlled ore bodies are confined to _the Galena 

dolomite except for a few deposits in the Lower Silurian dolomite 

and the Prairie du Chien group. Ore is deposited as narrow gash 

veins that fill vertical joints and expand into podlike masses in favorable beds along these joints. In the podlike masses, locally known 

as openings, the ore. has replaced the rock, and it fills previously 

formed solution cavities in sanded dolomite along the joints. The 

podlike masses ma.y lie one above the other in different favorable beds 

along the same joint. Single mineralized joints are traceable for 

more than 1 mile; they have nearly constant strikes, N. 70° W. being 

most common (Heyl, Lyons, and Theiler, 1952). 

The gash-vein deposits contain the same mineral constituents as 

the pitch-and-flat deposits, but galena rather than sphalerite is the 

most abundant ore mineral. Before oxidation and leaching, pyrite, 

marcasite, and perhaps calcite were also abundant. Sphalerite, or its 

oxidation product, smithsonite, is locally common. In a few 

places, particularly east of Mineral Point, Wis., chalcopyrite is 

abundant and galena is absent. Barite, vein dolomite, and jasperoid 

are rare. Galena is the only abundant sulfide remaining in most gashvein deposits in the oxidized zone above the water table. It is accompanied by limonite and cerussite, and less commonly by smithsonite, 

calcite, chalcocite, azurite, and malachite. Sanded dolomite is 

abundant in many of the gash-vein deposits. 

RELATIONS BETWEEN ORE DEPOSITION AND MAJOR 

GEOLOGIC FEATURES 

Plate 25 shows. the location of the zinc, lead, and copper mines and 

most of the old lead and copper mining areas; it does not include the 

outermost fringe deposits of the district. Most of the fringe mineral 

deposits and ore bodies are composed of lead, copper, and iron (hematite and limonite) ore bodies that were worked many years ago. Although nearly all of these deposits are small, at least one lead mine 

and one hematite 1nine produced considerable quantities of ore. Zinc 

ore has been found in the fringe areas but not in large enough quantities to be mined commercially. The size of the mineralized district, 

which includes all of these outlying districts, is about 3;300 square 
ZINC-LEAD-COPPER, UPPER MISSISSIPPI VALLEY DISTRICT 237 

miles; however, the part that was being mined in 1950 comprises 

a central area. of only about 650 square miles. 

DISTRIBUTION OF ORE DEPOSITS AT THE DISTRICT BOUNDARIES 

The niain part of the district is bounded on the south and southwest by a deeply incised cuesta (pl. 25) (Grant and Burchard, 1907; 

Shaw and Trowbridge, 1916) of Maquoketa shale and Silurian dolomite. These rocks cap the Galena, Decorah, and Platteville strata, 

which are the most favorable host rocks for lead and zinc deposits. 

Several mineralized areas have been exposed by erosion in the deep 

valleys south and west of the northward-facing cuesta, examples 

being the lead deposits in the Apple River valley near Elizabeth, 

Apple River, and vVarren, Ill.; and other deposits (pl. 25) in Illinois 

and Iowa. The limit of mineralization is probably many miles south 

and southwest of the edge of the covered area, as is indicated by the 

following: 

1. The outlying mineralized areas in erosional windows. 

2. The abundance of mineralized areas along the main cuesta face, 

such as at Scales Mound and Galena, Ill., and from Dubuque to Rickardsville, Iowa. 

3. Small deposits of lead in the Silurian rocks in Iowa near. Lytle 

Creek, Jackson County, and south of Dyersville, Dubuque County, 

and still farther south near Clinton, Clinton County ( Bain, 1906, p. 

66), and Anamosa, Jones County (Calvin, 1895, p. 110). 

4. Known deposits that extend beneath the cap rocks-for example, 

the ore body of the Bautsch mine of the Bautsch mine group (pl. 25) 

south of Galena, Ill., and the ore bodies of the (New) Blackstone and 

Calumet mines south of Shullsburg, vVis., which lie beneath a thick 

cover of Maquoketa shale from which most of the beds of Silurian 

dolomite have been eroded. 

The known southeastern boundary, in Illinois, is determined by 

large areas of Maquoketa shale and Silurian dolomite that conceal the 

favorable host rocks, and the overlapping glacial drift that marks the 

east edge of the Driftless Area. The limit of mineralization may extend many miles to the southeast beyond the present boundary of the 

main part of the district at Apple River and Warren, Ill.; if so, the 

deposits probably decrease in size and abundance in that direction. 

The possibility that undiscovered deposits lie beyond the present defined boundaries of the district is suggested by a number of nearly 

forgotten deposits near Morseville, Stockton, Elroy, Freeport, and 

Oneco (pl. 25), and farther south at Mount Carroll, Ill. These deposits undoubtedly were discovered only because erosion had locally 

exposed the favorable host rocks. Other deposits probably exist in 

places where the host rocks have not been exposed by erosion. 
238 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

In Wisconsin the known district boundary on the east is determined 

by the overlap of the glacial drift marking the east edge of the Driftless Area, and the erosion of the ore-bearing Galena, Pl~tteville, and 

Decorah formations. Erosion of the ore-bearing formations has been. 

progressively · more complete as the formations rise toward the Wisconsin arch, until only a few erosional outliers remain in the least 

dissected interstream areas. The number and size of the ore deposits 

also decrease toward the east in some of the remaining outliers of 

favorable beds, suggesting that the limit of lead deposition may not 

be far east of the 1nargin of the Driftless Area. The- widely spaced 

deposits south of Mount Horeb, northeast of Monticello, and east and 

south of l\Ionroe may represent the east limit of mineralization. On 

the other hand, this limit may be many miles farther east, as suggested by small quantities of sulfides found near Broadhead, and on 

the east side of the Wisconsin arch near Appleton, Milwaukee, Cambria, and Rio. 

The north boundary of the main part of the district lies between 

the \Visconsin River and Military Ridge, the crest of which is followed by the Chicago and North Western Railroad between Madison 

and Fennimore, Wis. (pl. 25). Along this boundary the Galena, 

Decorah, and Platteville beds form a northward-facing cuesta (Grant 

and Burchard, 1907), north of which they have been partly eroded 

a way. Probably the boundary at one time was many miles north of 

its present position between Blue Mounds and Highland, because, for 

about 30 miles to the north, widely scattered lead, copper, and iron 

(oxidized iron sulfides) deposits are in the partly eroded Lower Ordovician and Cambrian rocks. Examples of such deposits are those near 

Black Earth, northwest of Ridgeway, along Otter Creek (pl. 25), 

and ·north of the Wisconsin River near Orion and Ironton. Similar 

deposits ·lie far to the northwest at Mount Sterling, Wis., Lansing 

and vVaukon, Iowa, and Dresbach, Minn.', and form a part of the 

widespread fringe deposits of the district. 

Within the main · district south of Military Ridge the St. Peter 

sandstone and Prairie du Chien group crop out in wide belts along 

the large streams. The principal outcrop areas of these rocks have 

been mapped by Grant and Burchard (1907) and lie west and south 

of Mineral Point and near Hollandale, Iowa County, Wis., and north 

and east of Lancaster, Grant County, 'Vis. Only a very few ore de-. 

posits are known in these outcrop areas. 

From Fennimore, Wis., the north boundary of the n1ain district 

turns toward the southwest, extends through Glenhaven; Wis., and 

across the Mississippi River into Iowa northwest of Guttenberg, 

Clayton County. Here is the small Guttenberg mining area. · From 

this point the 'west boundary extends southward to the Turkey River 

west of 1\tlillville, Iowa, and theri southeastward to the Cuesta of 
ZINC-LEAD-COPPER, UPPER MISSISSIPPI VAt.LEY DISTRICT 239 

Silurian rocks to join the previously described southwest boundary. 

Between Fennimore and the Silurian cuesta, the boundary appears to 

coincide with the limits of mineralization beyond which practically 

no ore was deposited in the favorable Galena, Decorah, and Platteville beds. 

The fringe area between the boundaries of the main part of the 

district and the limit of mineralization is characterized by .small, 

widely spaced lead deposits without zinc. Only one large center of 

abundant ore deposits, the Beetown area, lies near the limit, and even 

this area is 6 to 10 miles from the nearest centers of ·abundant deposits 

at Cassville and Potosi, vVis. -

The deposits at Guttenberg suggest by their mineralogy and other 

features a very weak type of ore deposition. The mineralogy of the 

ores is very simple, consisting of thin coatings of pyrite and marcasite on the wall rocks, small galena crystals perched at intervals 

on the iron sulfide coatings, and a little barite. The rest of the space 

in the many fractures and cavities in the ore bodies is filled with 

calcite. Probably the minerals were deposited from weak, low-temperature solutions far from their source, as might be expected of 

deposits near the limit of mineralization. 

DISTRIBUTION OF ORE DEPOSITS WITHIN THE DISTRICT 

Within the district are many groups of closely spaced lead and zinc 

deposits (pl. 25). Two of the groups are designated as subdistricts. 

The larger subdistrict comprises about 280 square miles and is roughly 

triangular in shape with Platteville, 'Vis., its northern point, Shullsburg, Wis., its eastern corner, and Galena, Ill., its southern point. 

Mines within this area are most numerous between Hazel Green and 

Shullsburg and near Platteville. Most of the zinc production of the 

district and a considerable part of the lead production has come from 

this area. 

Northeast ot this triangular area is the second large mining subdistrict, which comprises about 215 square miles extending from the 

southwest corner of Iowa County, "\Vis., northeastward to Ridgeway, 

Wis. Here the most important mining areas ·are Miffiin (mainly 

zinc), Linden (lead and zinc), Mineral Point (lead, zinc, and copper), and Dodgeville (lead and zinc). Some copper was produced 

near Mineral Point, Linden, and possibly Highland, 'Vis. 

The boundaries of the two subdistricts are defined chiefly by a 

decrease in the quantity of ore deposited, but also by erosion of the 

favorable beds, lack of prospecting, and by beds of ~1:aquoketa shale 

and Silurian dolomite that cap the principal host rocks. Erosion of 

the favorahle beds cuts off the northern subdistrict northeast of · 

Dodgeville and Highland. . There has · been little prospecting for 

either lead or zinc between the northern subdistrict and the small 
240 CONTRIBUTIONS TO ECONOMIO GEOLOGY 

mining area at Montfort. Possibly the southern and northern sub-

-districts are connected by undiscovered deposits beneath widespread 

cap pings of Maquoketa shale (Grant and Burchard, 1907) and small 

remnants of Silurian dolomite in the vicinity of Platte Mounds 

(marked by the patches of Silurian dolomite northeast of Platteville 

in plate 25). The Potosi mining area west of Platteville may be a 

westward prong of the southern subdistrict but separated from it by 

a belt of less abundant deposits and iby deep erosion along the Platte 

River. Prospecting has shown that in places the southern subdistrict 

extends for miles beneath the Maquoketa and Silurian escarpments 

to the south and southeast; the Elizabeth and Apple River areas, 

Illinois, may actually be connected to the subdistrict, at least by lead 

deposits. 

The Guttenberg, Beetown, Sinsinawa, and other small mining areas 

are probably centers of mineralization surrounded by lands in which 

there are few or no deposits. However, those at Elizabeth, Warren, 

and Morseville, Ill., are probably parts of larger mineralized areas 

exposed in erosional windows in the capping rocks. A few mining 

areas are situated in erosional outliers of the most favorable strata, as 

at Highland; Wis., and the Sugar River mine group northeast of Monticello, Green County, Wis. Before erosion of the Galena, Decorah, 

and Platteville strata, mineralized areas may have connected these deposits with those in adjacent parts of the main district. 

The underlying Prairie du Chien rocks are exposed in the deep valleys in the western part of the Highland area (Agnew, Flint, and 

Allingham, 1953, pl. 3). Here, at the Ohler king group of mines, the 

Prairie du Chien is mineralized with lead and iron sulfides (pl. 25, 

mine no. 55) and forms what may be a mineralized "root" beneath the 

rich zinc deposits in the partly eroded Galena, Decorah, and Platteville formations. The Demby-Weist mine group (pl. 25, group no. 57) 

may represent a similar "root" in the Prairie du Chien and Trempealeau strata from which a former overlying mineralized center has 

now been nearly completely eroded except for one small lead deposit 

in the Decorah formation west of the main group of mines. Such 

"root" deposits may mark the location of the channels through which 

the ore-bearing solutions rose into the overlying rocks. 

In the central part of the district the general areas of greatest lead 

and greatest zinc concentration are nearly identical, although individual gash-vein lead deposits may lie to one side of the pitch-andflat zinc deposits (fig. 34). Probably this relationship continues 

nearly to the limits of mineralization. ·In the western, southern, and 

eastern parts of the district .many areas of gash-vein lead deposits 

have not been adequately prospected to determine if they are associated with pitch-and-flat zinc deposits. However, in the western part 

several important pitch-and-flat zinc deposits have been discovered 
ZINC-LEAD-COPPER, UPPER MISSISSIPPI VAL~EY DISTRICT 241 

by prospecting in recent years at Tennyson, Wis. (Potosi area in 

pl. 25), and small deposits are know:p.Iiear Beetown (.Hey~, ~yons, and . 

Theiler, 1952); in the eastern part small deposits occur between Waldwick and Blanchardviire, Wis. Probably most · pitch-and-flat deposits that will be :found near the limits of mineralization of the district will be.smaller, leaner, and more widely spaced than those i~ the 

central part. Copper deposits are restricted to small areas that are 

scattered from localities near Gratiot, Wis., ·northwestward through 

Mineral Point, Linden, and Highland, to Wauzeka ·and M;ount Sterling, north of the Wisconsin River. Many of these are isolated from 

both the lead and zinc deposits, but near l\1ineral Point and Highland 

they are closely associated, and some intermingling of the lead,' zinc, 

and copper ores occurs. 

-ORE DEPOSITS AND THE MAIN -LITHOLOGIC UNITS 

Deposits of lead, zinc, copper, and iron sulfides have been found in 

all the strata of Cambrian, Ordovician, and Silurian age that are 

exposed in the district. However, all the deposits of lead, zinc, and 

copper of commercial size occur -only in the Prairie du Chien group 

and the Platteville, Decora,h, and Galena formations of Ordovician 

age. Considerable limonite and hematite, formed by the oxidation of 

iron sulfides, have been produced from deposits in the sandstones of 

Cambrian age (Strong, 1882, p. 49-56; Chamberlin, 1882, p. 518-520). 

-Most of the known deposits in rocks of Cambrian and Early Ordovician age are :found in the main outcrop areas o:£ these rocks in the 

northern :fringe of the district. Recent exploratory drilling by the 

U.S. Geological Survey within the main district has located lean deposits of zinc and iron sulfides in these rocks (Heyl, Lyons, and Agnew, 

1951). 

The St. Peter sandstone of Middle Ordovician age is locally impregnated with pyrite and traces of galena and ·sphalerite. None o:fthe 

deposits is of commercial value. Many known deposits in the St. 

Peter sandstone are directly below large sulfide deposits in the overlying formations. 

Nearly all n1ineral deposits in the main part of the district are in the 

Galena, Decorah, and Platteville fbrmations of Middle Ordovician 

age. The ores are deposited over the same stratigraphic range in these 

:forn1ations both in the northern part of the district where the :formations are largely eroded, and in the southern part where the beds are 

buried beneath the Maquoketa shale and Silurian dolomite. 

The l\1aquoketa shale is only locally mineralized. Small quantities 

of galena, sphalerate, and barite were found at the Glanville prospect 

(pl. 25, no. 5) near Scales Mound, Ill. 

The few localities where the Silurian rocks are known to contain 

small deposits of lead or iron sulfid~s are in Iowa, far to the southwest 
242 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

of the main part of the district. Only a very few tons of ore were produced from any of these deposits. 

ORE DEPOSITS AND THE MAJOR FOLDS 

The locations of the ore deposits appear to be controlled in a general 

way by the major folds of the district (pl. 25), particularly in the 

northern half. Parts of the highly mineralized areas of the district 

are within, and trend parallel to, the axes of the large synclines. For 

example, the Crow Branch deposit (pl. 25, no. 50), soutnwest of 

Livingston, Wis., is near and parallel to the axis of a large syncline. 

Also along this syncline are the Coker mine group (pl. 25, no. 45), 

the Linden area (pl. 25, no. 48), and the Dodgeville area (pl. 25, no. 

53), all highly minei·alized. Similarly, several deposits are in the 

large syncline that extends from Potosi, Wis., eastward through Platteville and Calamine. The relationship between mineralized areas and 

major synclines is particularly apparent from Beetown to Lancaster, 

Wis. Few of the large and important ore deposits are near the crests 

of the principal anticlines. 

In the southern part of the dist:r:ict most of the principal mining 

areas lie on the gently d-ipping south limb of the large anticline extending eastward from Sherrill, Iowa, through Jamestown and Cuba. 

City, Wis. The mines near Dubuque, Iowa, Sinsinawa, Wis., and 

between Hazel Green and Shullsburg, Wis., are on this structure 

(Agnew, Heyl, Behre, and Lyons, 1948). The Hazel Green-Shullsburg area, the most concentrated mining center in the district, lies 

south of and is partly enclosed by a marked northward bow of the 

axis of the large anticline. An extension of this area to the southwest 

into Iowa along the Tete des Morts River follows, in part, a southwestward-trending syncline which passes through Galena, Ill. (Willman and Reynolds, 1947). 

SELECTED BIBLIOGRAPHY 

Agnew, A. F., and Heyl, A. V., Jr., 1944, Zinc deposits of the Mifflin-Cokerville 

area of the Wisconsin lead-zinc district; U. S. Geol. Survey Strategic Min. 

Inv. Prelim. Rept. 3-134. 

Agnew, A. F., Heyl, A. V., Jr., Behre, C. H., Jr., and Lyons, E. J., 1948, Zinc-lead 

deposits of the Hazel Green-Shullsburg area, Lafayette and Grant Counties. 

Wis.: U. S. Geol. Survey Strategic Min. Inv. Prelim. Rept. 3-216. 

Agnew, A. F., Fl~nt , A. E., and Allingham, J. W., 1953, Exploratory drilling 

program of the U. S. Geological Survey for evidences of zinc-lead mineralization in Iowa and Wisconsin, 1950-51: U. S. Geol. Survey Circ. 231, pl. 3. 

Bain, H. F., 1906, Zinc and lead deposits of the Upper Mississippi Valley: U. S. 

Geol. Survey Bull. 294. 

Bean, E. F., 1944, Geologic map of Wisconsin: Wis . . Geol. and · Nat. History 

Survey ; seale, 1 : 1,000,000. 

Calvin, Samuel, 1895, The geology of Jones County, Iowa: Iowa Geol. Survey 

Ann. Rept., v. 5, p.llo. 
ZINC-LEAD-COPPER, UPPER MISSISSIPPI VALLEY DISTRICT 243 

Chamberlin, T. 0., 1882, The ore deposits of southwestern 'Visconsin. [Wisconsin 

Geol. Survey] Geology of Wisconsin, v. 4, p. 432-468. 

Grant, U. S., and Burchard, E. F., 1907, Description of the Lancaster and 

Mineral Point quadrangles: U. S. Geol. Survey Geol. Atlas, folio 145. 

Hall, James, and 'Vhitney, J. D., 1858, Report on the geological survey of the 

State of Iowa: Iowa Geol. Survey, v. 1, pt. 1, p. 437-438. 

Heyl, A. V., Jr., Lyons, E. J., and Agnew, A. F., 1951, Exploratory drilling in the 

Prairie du Chien group of the Wisconsin zinc-lead district by the U. S. 

Geological Survey in 1949-50: U. S. Geol. Survey Circ. 131. 

Heyl, A. V., Jr., Lyons, E. J., and Theiler, J. J., 1952, Geologic structure map of 

the Beetown lead-zinc area, Grant County, Wis.: U. S. Geol. Survey Mineral 

Invs. Field Studies Map MF-3. 

Lovering, T. S., and others, 1949, Rock alteration as a- guide to ore--East Tintic 

district, Utah; E'con. Geology Mon. 1, p. 27. 

Shaw, E. W., and Trowbridge, A. C., 1916, Description of the Galena and Elizabeth quadrangles: U. S. Geol. Survey Geol. Atlas, folio 200. 

Strong, Moses, 1882, Geology of the Mississippi region north of the Wisconsin 

River: [Wisconsin Geol. Survey] Geology of Wisconsin, v. 4, p. 49-56. 

Tester, Allen 0., 1937, Geologic map of Iowa : Iowa Geological Survey; scale 

1:500,000. 

Thwaites, R. G., 1895, NotJs on early lead mining on the Fever (or Galena) River 

region: Wisconsin Hist. Coli., v. 13, p. 271-292. 

Weller, J. Marvin, and others, 1945, Geologic map of Illinois: Ill. Geological 

Survey ; scale, 1 : 500,000. 

Whitney, J.D., 1854, The metallic wealth of the United States: p. 48, Pbila. 

Willman, H. B., and Reynolds, R. R., 1947, Geological structure of the zinc-lead 

district of northwest~rn Illinois: Ill. Geol. Survey Rept. Inv., no. 124. 

Willman, H. B., Reynolds, R. R., and Herbert, Paul, Jr., 1946, Geological aspects 

of prospecting and ar~as for prospecting in the zinc-lead district of northwestern Illinois: Ill. Geol. Survey Rept. Inv., no. 116. 

Winslow, Arthur, 1894, Lead and zinc deposits: Mo. Geol. Survey, v. 6. p. 140. 

INDEX 

Page Page 

Acknowledgement__ ____ _______________ ------- 229 Mineralization, limits oL __________________ 237-:-238 

Ages of exposed rocks ________________________ _ 

Azurite ..• ___________ ----------- __ ---_--------

229 Minerals, deposits in fringe areas_---------- 236,239 

236 primary __ -------------------------------- 233 

secondary________________________________ 233 

Barite _______________ _______________ 233, 236,"239, 241 

Ore, deposition oL___ ___ __ _____ _ _ _ _ _ __ __ _ __ _ _ 235 

Calcite ___ ---------------------------- __ 233,236,239 Ore deposits, distribution at district boundCerussite. _____________ --· __________ , __ _____ 233, 236 aries ___________________________ ___ ________ 237-239 

Chalcocite __________________ ________ ··---__ ___ _ 236 distribution within district_ ___ ____ _____ 239-241 

Chalcopyrite. _________________________ _ 233, 234, 236 erosion oL __ __ __ _____ _ _ ____ _ __ __ _ __ _ _ __ __ 238 

Copper deposits, distribution of. ___ ._________ 241 exposure of by erosion _____ --------------- 237 

production from ________________ ._______ __ 232 relation to faults__________________________ 235 

relation to lithologic units __________ 23Q-231, 241 relation to folds ______ ----------------- __ 235,241 

relation to lithologic units________________ 229 

Decorah formation___________________________ 230 types_____________________________________ 233 

erosion of ____________________________ --.--- 238 

Dip, regionaL ___________________________ >; ____ 231 "Pitch-and-flat" deposits ___________ 233-236, 24Q-241 

Dolomite _______________________ 228, 230, 233, 235-236 Placer deposits. ____________________________ 233, 234 

Driftless Area __ ------------------------ 229,237,238 Platteville formation, composition oL _ _ ______ 230 

erosion of_________________________________ 238 

Faults, features of._________________ ____ ______ 231 Prairie du Chien group __________ ___ 229,230,238,240 

relation to ore bodies. __ _______________ ___ 235 Prospecting ___ ------------------------- ____ 239-240 

Folds,features of._________________________ ___ 231 Pyrite __________________________ 233,234,236,239,241 

relation to ore bodies. ______ -------------- 235 Pyritization _________________________ --------- 231 

Franconia formation ________________________ 229,230 

Quartz __ ---------____ __ ______________________ 233 

Galena_------------------------ 233, 234,236,239,241 

Galena formation, composition oL______ ___ __ 230 Residual deposits ___________________________ 233,234 

erosion of.____________ ___ _________________ 238 

"Gash-vein" deposits _______ ________ 233,234,236,240 Smithsonite_ ---------- ______ -------- _______ 233, 236 

Geologic data, source of_______________________ 228 Sphalerite __________________________ 233,234,236,241 

Glacial deposits. __ --------------------------- 229 St. Peter sandstone _________________ 229,230,231,238 

Strike, regionaL______________________________ 231 

Hematite _____________ ---------------------- 236,241 

History of the area _____ ---------------------- 232 Topography---------------------------------- 228 Trempealeau formation ____________________ _ 229; 230 

Jasperoid ____________________________________ _ 236 

Joints _______ -------------------------- ______ _ 231 Upper Mississippi Valley district, features of._ 228, 

Lead deposits, distribution oL_______________ 240 

production from __ ____ __ ________________ . 232,233 

relation to main lithologic units _____ 230-231, 241 

Limonite. ________________ ______________ 233, 236, 241 

Loess_____________________ ___ ___________ __ ____ 229 

Malachite. ____________________________ -··--___ 236 

Maquoketa shale____________ _________________ 230 

Marcasite ________________ __ ________ 233, 234,236,239 

229,231 

stratigraphic section oL__________________ 230 

Wisconsin arch _______ _________ __________ ----_ 231 

Zinc, distribution of deposits ______ . ______ -_ 24Q-241 

production._--------------------------- 232,233 

relation of deposits to lithologic units____ 230-231 

241 

size of deposits ____ _____________ ______ ____ _ 234 

245 

U. 5. GOVERNMENT PRINT ING OFFICE: 1955