Exploratory Drilling for

Evidence of

Zinc and Lead Ore in

»

Dubuque County, Iowa

By ARTHUR E. FLINT and C. ERVIN BROWN

A CONTRIBUTION TO ECONOMIC GEOLOGY

w_ - ~ ___________.^ 

GEOLOGICAL SURVEY BULLETIN 1027-K

Prepared in cooperation with 

the Iowa Geological Survey

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

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

Washington 25, D. C. - Price 20 cents (paper cover)
CONTENTS

Page

Abstract.______________________,_-___-______--___--_--____------ 471

Introduction._____________________--__--__-_-_-_-----_----___---__ 471

Purpose ______________________________________________________ 471

Summary of principal results_,_________-___---____--______-_-_ 471

History.______________--____,--__-_--_--_-----------__------- 472

Acknowledgments _____________________________________________ 473

Geology._____--_...___________________________-_---_-__----__ 473

Stratigraphy._________________________________________________ 473

Structure.-___-_-________-__-______--_-__--_---------__---_- 476

Sulfide deposits in the Decorah and Galena formations.________________ 476

Controlling structures.__-__-__--_-__.__-__-______-_--_-______._ 476

Ore minerals and associated minerals__-____-___-___----___---__ 478

Alteration of host rock______________________-________-____-_-__ 479

Exploration._ _____________________--._.-__-____--________.__----._ 479

Procedure-_-___________________-_____-____-_---_----____---_- 479

Results___-______-___-________-____-_-_-__--__-_---______-__ 480

Behnke-Krug area._________________________________________ 480

Wallis area_______________-_-____-_____----___-_____---_-_ 483

Parker area.______________________________________________ 484

Dietz-Schromen area_-____________-_____-_-__-_--_____----_ 484

Conclusions.__ ____________________________________________________ 486

Records of drill holes____________________________________________ 487

Index.---_____________________.____.____.._.__________-__.__---__ 499

ILLUSTRATIONS

Page

FIGURE 62. Index maps showing the location of the areas covered by detailed maps of this report._____________________________ 472

63. Generalized stratigraphic section of part of the Middle and 

Upper Ordovician series in the upper Mississippi Valley 

zinc-lead district_____.________________________________ 474

64. Diagrammatic section showing the characteristic forms of

crevice and "pitch-and-flat" ore deposits_______________ 477

65. Geologic map showing structure and location of drill holes at

the Behnke-Krug area_--_--_------------__-_-____-_-_- 481

66. Cross sections of drill holes at the Behnke-Krug area_.._____ 482

67. Geologic structure map and location of drill holes at the

Wallis area......._.____.__.______._________ 483

68. Geologic structure map and location of drill holes at the

Parker area__________________________________________ 485

69. Geologic structure map and location of drill holes at the

Dietz-Schromen area__-_--____--.._--__-____--____-_-- 486

ill

A CONTRIBUTION TO ECONOMICfGEOLOGY

EXPLORATORY DRILLING FOR EVIDENCE OF ZINC AND 

LEAD ORE IN DUBUQUE COUNTY, IOWA

By ARTHUR E. FLINT and C. ERVIN^BROWN

ABSTRACT

The U. S. Geological Survey, in cooperation with the Iowa Geological Survey, 

made a study of the Galena and Decorah formations in the Iowa part of the 

upper Mississippi Valley zinc-lead district, to investigate structures that appear 

favorable for the concentration of zinc and lead minerals in the Decorah formation 

and in the lower part of the Galena formation, both of Ordovician age, and to 

determine by drilling whether these structures may be delineated by mapping 

the principal outcrops, which are 50-200 feet higher in the stratigraphic section. 

Rocks of the Decorah formation and lower part of the Galena formation are the 

principal host for major zinc-lead ore bodies in the Wisconsin and Illinois parts 

of the mining district, but these strata have been explored by drilling in only a few 

places in Iowa.

A total of 2,870 feet in 13 holes was drilled in four localities. Zinc mineralized 

rock was intersected in the Decorah formation at three of the four localities, and 

drilling verified the fact that the existence of favorable structures at depth can be 

inferred from a study of maps of outcrops. Folds or small warps in the Decorah 

formation are reflected at the surface and generally coincide with structures that 

are inferred by mapping outcrops.

INTRODUCTION

PURPOSE

The twofold objective of the drilling project in the Dubuque 

subdistrict in Iowa (fig. 62) was to test drill structures delineated by 

mapping outcrops that appear favorable for the concentration of zinc 

and lead ore and to determine whether the minor downwarped structures commonly associated with ore emplacement in the Decorah 

formation and the lower part of the Galena dolomite are reflected 

upward into outcropping strata 50-200 feet higher in the stratigraphic 

section, where they may be delineated by mapping the surface.

SUMMARY OF PRINCIPAL RESULTS

Results of this strdy in the Dubuque subdistrict indicate that 

commercial zinc deposits may occur in strata of the Decorah formation 

and lower part of the Galena dolomite, and that structures favorable 

for ore concentration may be located by mapping the surface. In 

bluff areas, however, superficial structures due to mass slumpage may 

be misinterpreted as favorable for finding ore concentrations.

471
CONTRIBUTIONS TO ECONOMIC GEOLOGY

tructure contours on top of cherty 

unit of the Galena dolomite from Flint 

and Brown, MF-1955 (Datum is mean 

seo level)

FIGURE 62. Index maps snowing tne location of the upper Mississippi Valley zinc-lead district, the

Dubuque subdistrict, and the areas shown by detailed maps in this report. 

HISTORY

Mining in the Dubuque subdistrict of the upper Mississippi Valley 

zinc-lead district began about 1788, although small amounts of lead

lio-d. l>eeix <lxxg by tk.© Indians tofore tkat turrxe. Only lead ore was

mined until about 1870 when zinc ore also was recovered. From 1833

to 1854 lead production was high throughout the entire upper Mississippi Valley mining district. Statistics for the year 1852 indicate

tb.at the district produced. ST percent of tlae total domestic lead

(33,760,000 pounds), and a large part was obtained from the Dubuque 

subdistrict. In Iowa, only an occasional increase in mining activity 

interrupted the downward trend in the production of lead from 1858

to 1910; wlien tlie last of tlie important mlnoa in tiio ^ioinit;^ vf

Dubuque was shut down. Since 1010, lead production has been 

sporadic and of little consequence. Although complete production 

data are not available, Iowa zinc production, almost entirely as zinc 

carbonate, appears to have been significant from about 1890 to 1910.
DRILLING FOR ZINC AND LEAD ORE, DUBUQUE COUNTY, IOWA 473

Both the lead and zinc ore came from small, mostly shallow deposits 

in the middle and upper parts of the Galena dolomite, in contrast 

with the larger, stratigraphically lower, zinc and lead deposits that 

have been exploited in the Wisconsin and Illinois parts of the mining 

district since the late 1800's.

Detailed geologic mapping in Iowa by the U. S. Geological Survey 

in cooperation with the Iowa Geological Survey was begun in 1951 to 

determine whether major zinc and lead deposits occur in Iowa similar 

to those in the Decorah formation and the lower part of the Galena 

formation of Wisconsin and Illinois. The exploratory program is a 

part of this larger project.

ACKNOWLEDGMENTS

The authors acknowledge the fine cooperation of Martin Behnke, 

Clarence Dietz, C. H. Parker, Frank Krug, Leo Schromen, and 

Burton Wallis who granted permission to have drilling done on their

properties.

GEOLOGY

The Dubuque subdistrict of the upper Mississippi Valley zinc-lead 

district is partly in the Driftless Area, an area surrounded but not 

covered by glacial ice during Pleistocene time. The western boundary 

of the known mineralized district coincides roughly with the western 

boundary of that area. Adjacent to the Mississippi River and its large 

tributaries, maximum local relief is about 300 feet. Valley walls 

are steep to vertical, and topography is youthful. Away from these 

streams the upland is an undulating plain of moderate to low relief.

STRATIGRAPHY

Rocks exposed in the area range in age from Middle Ordovician 

to Middle Silurian. Figure 63 shows the sequence of the stratigraphic 

units pertinent to this report.

The oldest exposed beds are gray limestone of the McGregor limestone member of the Platteville formation that crops out hi only a 

few places along the Little Maquoketa and Mississippi Rivers. These 

strata are generally fine-grained and locally are sublithographic.

Where present in Dubuque County, the Quimbys Mill member of 

the same formation is a dark-brown sublithographic limestone that 

contains thin dark-brown shale partings. Some zinc and lead deposits 

occur in the upper beds of the McGregor member and in the Quimbys 

Mill member elsewhere in the mineralized district but are not known 

in the Dubuque subdistrict.

Overlying the Platteville formation are the limestone and shale of 

the Decorah formation; like the Platteville, the Decorah outcrops are 

limited to the areas of deepest dissection.
474 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Formation

Maquoketa £ shale.

E

Galena dolomite. ._, 

*~i 0?

formation, Decorah ^ 

o P

Platteville formation.

Member Units of local 

usage

"Slate. "

Description

Shale, blue-green and broWn,. and 

argillaceous dolomite. Phosphatic 

fossil zone at base.

Dubuque shaly 

member.

Stewartville 

massive 

member.

Prosser cherty 

member.

"c ' 

3 '^j 

>, V

£ £ Yellow 

jr £ sandy.

0

Z j^-""'

3 0) ^ f

£""

t, oo Drab. m ^ 

x ci 

O.

Dolomite, yellow-buff, fine-grained, 

even-bedded, shaly; brown and 

gray shale partings.

Dolomite, buff, crystalline,! massive.

Dolomite, gray-brown, crystalline, 

mainly thick bedded; cherty in 

lower 118 feet.

Ion dolomite 

member.

Guttenberg limestone member.

Spechts Ferry 

shale member.

Gray.

Blue.

Oil rock.

Clay bed.

Limestone and dolomitic limestone, 

light-brown-gray, mottled, 

argillaceous;, green shale 

partings.

Limestone, medium-gray, very 

argillaceous; green shale 

partings; thins to gray-green 

shale in mineralized areas.

Limestone, light-tan, very fine 

grained; dark -brown shale 

partings; may thin to as little 

as 3. 5 feet of calcareous brown 

shale in mineralized areas.

Shale, gray and green, and gray 

fine-grained limestone; contains 

thin bentonite beds.

Quimbys Mill 

member.

McGregor limestone member.

Total exposed thickness

Glass rock.

"Trenton. "

Limestone, dark-brown, very fine 

grained; dark-brown shale 

partings.

Limestone, gray, fine-grained; 

partly dolomitic.

Thickness . 

(feet)

100 +

100+

37

34

164

235

14

6-7

 17

7

44-45

0-1

22 +

22 +

es. demoralized strattgraphic section of part of the Middle and Upper Ordovician series in the1

Dubuque subdlstrlct of the upper Mississippi Valley zinc-lead district.

The Spechts Ferry, the lowest member of the D^Qrah formation,,

is composed of shale and fine-grained gray limestone; it contains,. 

locally, sparse disseminated sphalerite and galena, but it is not known

tO 1)6 a hOSt fl)Cl[ fOr ZinO and lead ore in the mining district.

The Guttenberg limestone member of the same formation overlies 

the Spechts Ferry shale member and is a limestone in the Dubuque 

subdistrict except where it has been altered by solutions to dolomite, 

This limestone member is commonly leached and thinned, in and
DRILLING FOR ZINC AND LEAD ORE, DUBUQTJE COUNTY, IOWA 475

surrounding the mineralized areas. The unit may be thinned by 

solution from its normal thickness of 17 feet to as little as 3.5 feet. 

Carbonaceous material is dispersed throughout the Guttenberg and 

concentrated along bedding planes as brown shale partings; in its 

leached phase the Guttenberg is little more than a residual carbonaceous shale. Locally, this shale will burn and is called "oil rock" 

by the miners. The Guttenberg has been an important host rock for 

zinc and lead ore in the Wisconsin and Illinois part of the mining district but has not been appreciably explored in Iowa.

Above the Guttenberg limestone member is the Ion, the uppermost 

member of the Decorah formation. Like the Guttenberg, the Ion 

dolomite member is a limestone in the Dubuque subdistrict except 

where solutions have altered it to dolomite. The Ion, throughout 

the mining district, has been divided into two units, the "blue beds" 

below and the "gray beds" above. The subdivision is based on the 

amount of argillaceous material in the limestone; clay impurities are 

more common in the blue beds than in the gray beds. The Ion has 

been leached and thinned in and near ore bodies. The leached phase 

is a gray-green shale that is commonly not as well leached or compacted 

as the underlying member. The Ion strata are very important host 

rocks for zinc and lead ore in the district but have been tested in only 

a few places in Iowa.

The Galena dolomite, which overlies the Decorah formation, is 

composed of three dolomite members, the Prosser, Stewartville, and 

Dubuque, in ascending order.

The Prosser member is a gray-brown hard crystalline dolomite 

that contains abundant bedded chert throughout the lower 118 feet. 

The contact between the cherty and noncherty parts of this member 

is abrupt, and it is found consistently at the same stratigraphic position. Locally in the Dubuque subdistrict the lower 15 to 20 feet of 

this member may be limestone.

The Stewartville member is a buff crystalline massive noncherty 

dolomite.

The Dubuque member is a yellow-buff even-bedded fine-grained 

argillaceous dolomite. Strata of this member contain many thin 

brown and gray shale partings.

The Galena dolomite has been an important host rock for deposits 

of zinc and lead ore, but zinc deposits have been important only in 

its lower beds in the mining district. In Iowa the lower beds have 

been tested in only a few places.

Overlying the Galena dolomite is the Maquoketa shale, which is 

represented topographically by long, gentle slopes between the overlying Silurian scarp and the Galena bluffs. Although the formation 

contains some zinc and lead sulfides, it is not considered a probable

353799 56 2
476 CONTRIBUTIONS TO ECONOMIC GEOLOGY

host rock for commercial ore bodies. As much as 100 feet of-Maquoketa shale is exposed in the area.

Silurian rocks are not present in the area of this study.

STRUCTURE

The beds in the vicinity of Dubuque have an average dip southsouthwestward of 17 feet per mile. Superposed on the regional dip 

are local undulations with dips substantially more than the average. 

The structural relief of these local undulations is probably no more 

than 100 feet in the Dubuque subdistrict. Faults have not been observed in the vicinity of Dubuque, but both faults and shear zones 

occur elsewhere in the district.

STJLFIDE DEPOSITS IN THE DECOBAH AND GALENA

FORMATIONS

CONTROLLING STRUCTURES

Zinc-lead deposits in these formations can be classified on the basis 

of the structural features that were the primary control of the mineral 

emplacement. Vertical fractures have controlled ore concentration 

throughout the Galena dolomite; these fractures are locally called 

crevices.

Crevice deposits, if their geologic history is interpreted correctly, 

are in joints that resulted from lateral compressive forces and were 

developed as tension joints and shear-couple fractures in the dolomite. 

The most consistent joint trend in the Dubuque subdistrict ranges a 

few degrees from a due east direction. These joints are parallel to 

the axes of the large folds that cross the district and appear to be 

related to them. Less prominent joints trend northeastward. The 

fractures were conduits through which circulating ground water

removed the carbonate material by solution from more soluble beds, 

widening the joints and forming voids in the rock. Zinc and lead 

minerals, mainly the latter, were concentrated in the open spaces 

along the joints; and, although these deposits are nearly all sphalerite

and galena, they are small. Most of them contain about 40 to 100

tons of ore. The deposits in the joints widened by solution are confined 

to the Galena dolomite.

Small synclines or elongate basins and associated inclined fractures

in the strata appear to have controlled the localization of the ore in

the upper part of the Platteville formation, in the Decorah formation,

and locally in the lower part of the Galena dolomite. In most places 

these fractures occur on the flanks of the downwarped areas and

have offset bedding a few inches to a few feet. The fractures, where

mineralized, are known throughout the mining district as "pitches,"

and the associated ore concentrations along bedding planes intersecting them are called "flats" (fig. 64). A pitch may be an iminter-
Crevice

@

. :\:;v:Cpre'-. ground ::':'.4v20

I_

40 Feet

Approximate scale

FIGURE 64. Diagrammatic section showing the characteristic forms of crevice and "pltch-and-flat" ore

deposits.
478 CONTRIBUTIONS TO ECONOMIC GEOLOGY

rupted mineralized fracture or it may be offset horizontally at stratification to acquire a steplike appearance. These fractures and intersecting bedding planes evidently have been the channels along which 

ore solutions traveled and removed a part of the host rock, creating 

voids in which the ore minerals were deposited. The voids have 

been enlarged by differential compaction of the argillaceous residues 

from the leached carbonate rock, particularly in the Guttenberg 

limestone member, where the strata may be thinned by solution and 

compaction from their maximum thickness of 17 feet to 3.5 feet. 

Commonly, two opposing main pitches and several parallel subsidiary 

pitches are present in an ore body (fig. 64); and the area between them, 

called "core ground," is generally mineralized. The ore bodies controlled by pitches and flats are primarily zinc-bearing. In Wisconsin 

and Illinois these deposits are much larger than the ore concentrations 

in vertical joints in the Galena dolomite. Typical pitch-and-flat 

deposits are not known in the Dubuque subdistrict, but very little 

prospecting has been done for them.

ORE MINERALS AND ASSOCIATED MINERALS

The principal ore minerals are galena (lead sulfide) and sphalerite 

(zinc sulfide). Other minerals that have been mined in the upper 

Mississippi Valley zinc-lead district include smithsonite (zinc carbonate), barite (barium sulfate), chalcopyrite (copper-iron sulfide), 

chalcocite (cuprous sulfide), azurite and malachite (basic copper

carbonates), and marcasite-pyrite (iron sulfide), the latter having

been roasted to provide sulfur dioxide for the manufacture of sulfuric 

acid. None of these, except galena and sphalerite, were being recovered in 1953.

Galena, in crevice deposits, occurs mainly as veins along thin open 

joints or as vug fillings; minor amounts replace the enclosing dolomite. 

As a rule, the galena in veins or in large vugs has been released from 

its original position by postmineralization solution of the host rock}

which has permitted the galena to fall or slump into clay that is 

abundant in most crevices.

Associated with galena in crevice deposits are marcasite and pyrite

or their oxidation products, calcite, and varying amounts of sphalerite,

which has been altered, to smithsonite in the oxidized zone. Locally,

barite and gypsum are also present,

The sphalerite in pitch-and-flat deposits occurs mainly as veins in 

the pitch fractures and bedding-plane openings, and commonly is 

disseminated as small crystals, lining or filling solution vugs in the 

core ground. A minor amount replaces the enclosing carbonate rock.
DRILLING FOR ZINC AND LEAD ORE, DUBUQUE COUNTY, IOWA 479

Associated with the sphalerite in pitch-and-flat deposits are marcasite and pyrite, varying amounts of galena and calcite, and, locally, 

barite, chalcopyrite, and very rarely millerite (nickel sulfide).

ALTERATION OF HOST BOCK

Limestone into which the ore has been introduced is nearly everywhere partly or completely altered to dolomite, and both the limestone 

and dolomite host rocks are locally silicified. Evidence of dolomitization, silicification, and leaching commonly extend peripherally beyond 

the ore concentrations an important aid to prospecting.

EXPLORATION

PROCEDURE

Geologic mapping l to delineate favorable structures was the first 

stage of exploration in the program. In this phase of the investigation, outcrops that contained key stratigraphic horizons were surveyed 

with telescopic alidade and plane table. The altitudes of those key 

horizons were reduced to a common datum plane, the top of the cherty 

unit of the Galena. Available subsurface data also were used to compile the preliminary structure maps. In places, contours could be 

established for only a small part of a particular structure owing to 

sparseness of outcrops. Stage two involved the locating and drilling 

of exploratory holes. It was decided to test, with a minimum of holes, 

several favorable-appearing structures for evidence of mineralization 

rather than to concentrate the drilling on one structure. Consequently, the limited drilling on each syncline was expected to show 

no more than the presence or absence of mineralized areas. A great 

many more test holes would be required to adequately prospect the 

four structures drilled. Drill-hole locations were spaced 100 to 550 

feet apart, depending on the width and relief of the structure, and 

were alined normal to the axes of the synclines being tested. In one 

place where surface data were insufficient to define the orientation of 

the syncline, additional holes were drilled for this purpose.

Exploration was done with cable-tool solid-bit drills. At the end 

of each 5 feet (in a few places 1% feet) of drilling the tools were removed 

and the hole bailed clean, that is, all recoverable cuttings were brought 

to the surface. A representative sample from each 5-foot interval of 

drilling was studied under a binocular microscope at 10-30 power 

magnification, and the descriptive logs that are a part of this report 

were prepared from these drill cuttings. Samples from significantly 

mineralized rock were taken from the cuttings for assaying; the grade 

of other samples was estimated.

1 Flint, A. E., and Brown, C. E., 1955 Geology and zinc-lead deposits in the Durango area, Dubuque 

County, Jowa: U. S. Geol. Survey Mineral Investigations Field Studies Map MF 33.
480 CONTRIBUTIONS TO ECONOMIC GEOLOGY

RESULTS

Four different areas (fig. 62) were drilled during the investigation. 

No structure was tested with more than five holes, and some were investigated with only two. In three of the four areas, zinc-mineralized 

strata were penetrated. In addition, marked thinning by solution of 

Decorah strata, evidence of dolomitization and silicification, and 

abundant iron sulfide all considered favorable indicators of nearby 

zinc-mineralized rock were found in one or more of the synclines 

tested. The structures as mapped from outcrops in the middle and 

upper part of the Galena dolomite were found to reflect structures in 

the underlying Decorah formation. The magnitude of structural relief, however, and in one locality (see Behnke-Krug area) the orientation of the structure as well, depends on the datum plane used.

BEHNKE-KRUG AREA

Five exploratory holes were drilled in the Behnke-Krug area in 

T. 90 N., R. 1 E., 2.5 miles west of Durango, Iowa (fig. 65). The 

structure to be investigated appeared to trend westward, but because 

the beds of only the south limb of the fold crop out, its size and orientation could not be determined by surface mapping. For this reason 

the first three drill holes were located about 150 feet apart at the 

apices of a triangle to furnish a three-dimensional "view" of the bedding attitude in the favorable stratigraphic zone. Data from the 

drill holes seem to indicate a northwestward-trending downwarp at

the top of the Spechts Ferry shale member but defined also a northeasterly-trending fold at the top of the cherty unit of the Galena, 140

feet higher stratigraphically. Because zinc-mineralized Guttenberg

strata were penetrated in the drilling, the lower datum plane was 

considered to reflect the controlling structure, and hole 4 was located 

approximately in line with holes 1 and 2 to provide data across the 

lower syncline. Data from hole 4 indicates that the axis of the syncline is north of that hole. Hole 5 was drilled approximately in line 

with holes 2 and 3 for data to further clarify the structure.

Two geologic sections, constructed from the drilling information,

show the thinned and downwarped nature of the Decorah formation 

(fig. 66). The drilling data as interpreted show a syncline in the 

Decorah strata plunging westward. This small-scale structure appears to be caused mostly by thinning by solution in the carbonate 

beds of the Guttenberg and Ion members of the Decorah formation.

It cuts across northwestward-dipping strata indicated by structure

contours drawn on the top of the cherty unit of the Galena dolomite. 

The downwarp produced by the thinned and compacted Guttenberg

.and Ion members is transmitted upward through the cherty unit, as 

:shown by the inflection in the contours constructed on the top of chert 

.horizon (fig. 65).
DRILLING FOB ZINC AND LEAD ORE, DUBUQTJE COUNTY, IOWA 481

EXPLANATION

Strike and dip of beds Structure contours drawn on 

top of cherty unit of the 

Galena dolomite; based on Outcrop control point outcrop data

U.S. Geological Survey 

drill hole

Contour interval, 5 feet. Datum 

is mean sea level

_ 560 -

Structure contours drawn on 

top of Spechts Ferry shale 

member of the Decorah 

formation

Section A-A' and B-B' 

shown on fig. 66

500 I

500 Feet

I

FIOXIBB 66. Geologic map showing structure and location of drill holes at the Behnke-Krug area, 2.5 miles

west of Durango, Iowa.
482 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Vertical scale

100

Horizontal scale 400 Feel

Datum is mean sea level. Drill hole

B-2 projected *o plane of section

FIGURE 66. Cross sections of drill holes at the Behnke-Krug area 2.5 miles west of Durango, Iowa. Location of sections A-A' and B-ff shown on figure 65.

All five exploratory holes were drilled through zmc-rnineralized z6neS. 

in the Decorah formation, and hole 5 also passed through a zincmineralized zone extending from 26 to 67 feet above the base of the 

Galena. Samples from holes 2 and 4 contained the most zinc and 

ranged in grade from 1.56 to 2.2 percent zinc metal through 5 feet or

more of beds. Ore of this grade, alttiougli submargirial, is, nevei-tlie 

less, significant,

The drill samples from the Krug and Behnke holes revealed complete dolomitization of the Guttenberg and Ion members, and considerable silicification and extreme thinning by solution (from a
normal thickness of 17 feet to as little as 4 feet) of the Guttenberg 

limestone member (fig. 66).

WAL.LI8 AREA

The area termed "the Wallis area" in this report lies 1.4 miles east 

of Durango, Iowa. Across the area, as interpreted from outcrops, 

a broad, gentle, arcuate syncline trends northeastward (fig. 67). 

Mapping indicates that the syncline extends more than a mile southwestward and southward from the Wallis area, but its northeastward 

extension is not known because of scarce outcrops in the area. Three 

holes, alined normal to the trend of the structure and spaced 500 to 

550 feet apart, were drilled to investigate the syncline.

Wallis 2 was the only hole that was drilled into zinc- and leadmineralized strata. Drill samples from the Guttenberg limestone

 730 

Structure contours drawn on 

top of cherty unit of the 

Galena dolomite; based on 

outcrop data

1000 Feet

FIOUBE 67. Geologic structure map and location of drill holes at the Wallis area, 1.4 miles east of Durango,

Iowa. 

353799 56 3
484 , CONTRIBUTIONS TO ECONOMIC GEOLOGY

member of the Decorah formation were estimated to contain a trace 

to 1 percent of combined zinc and lead. In all three holes, however, 

the Guttenberg contains iron sulfide, is substantially thinned, and, in 

two of the three holes, is partly or completely dolomitized. The 

common occurrence of calcite-filled vugs and small fractures in the 

Decorah strata is also considered favorable. The sphalerite in the 

Guttenberg samples is in the form of very dark small crystals that 

probably lined vugs in the rock.

Data from the drilling in general verified the structure as interpreted by surface mapping.

PARKER AREA

A syncline trending N. 75° E, across the ''Parker area," 1.2 miles 

southwest of Durango, (fig, 68) was mapped from nearby bluff 

exposures; the area is almost entirely in the flood plain of the South 

Fork of the Little Maquoketa River. Drilling here was intended, 

first, to test for evidence of zinc and lead mineralization; second, to 

determine if favorable beds had been removed by stream erosion 

below the valley fill; and third, to determine if mapped surface 

structures are due to undetected large-block slumpage in the nearly 

vertical bluff outcrops. Three drill holes wer,e spaced about 300 feet 

apart in a line nearly normal to the trend of mapped structure.-. The 

upper half of the Ion dolonSite member is dolomitized, and thinning 

in the Guttenberg: limestone jnember is not notable, although Mbhe 

latter was reduced in thickness by ES milch as 3 feet. Traces of sphalerite are present in the Guttenberg strata in Parker hole 3, and minor 

amounts of marcasite occur in cuttings of the'Guttenberg from 

Parker holes 1 and 3. >

Figure 68 shows the adjustment in structure contours required by 

the subsurface data. The orienta.tion of the syncline was slightly 

changed; its structural relief was reduced. The latter is regarded as 

evidence of subsidence of large blocks in the nearly vertical bluff 

walls, owing probably to undercutting by stream action.

DIETZ-SCHROMEN AREA

In the Dietz-Schromen area, 2.4 miles southwest of Durango, two 

exploratory holes (fig. 69) were located in a line normal to the axis 

of a northeasterly-trending syncline to explore the southeast limb. 

Neither hole revealed significant evidence of zinc mineralization. 

Moreover, the Guttenberg and Ion members of the Decorah formation 

SnOW little Solution effect, are limestone rather than dolomite, and are 

not silicified. Considerable amOUDtS Of iron sulfide occur in the 

Galena dolomite penetrated in both holes, and the cherty unit Of tllG 

Galena dolomite appears to be thinned from 118 feet to 88 feet.
DRILLING FOR ZINC AND'LEAD ORE, DUBTJQUEHGOttNTY, IOWA 485

R..IE. R.2E.

EXPLANATION : ',:., . ;-.] .< -^ !< ;'njj;- ' -720 :'*""'

 ' ; '"'if - Structure contours drawn*on 

A ' .... ---'top Oj Cherty unit of the 

Galena dolomite; revised

.- ' f . . "by drilling data.-Contours 

4 dashed wnere inferred

Outcrop control point

U.S.Geological Survey 

drilfhole

Contour interval. 10 feet. Datum 

 < ' is mean sea level Structure"contours drawn on 

top of cherty unit of the 

Galena dolomite; based on 

outcrop data

500 500 *" Feet

FIOUBK 68. Geologic structure map and location of drill holes at Parker area, 1.2 miles southwest of

Durango, Iowa. ' '
; CONTRIBUTIONS TO ECONOMIC GEOLOGY

R. IE.

700 

Structure contours drawn on 

top of cherry unit of the 

Galena dolomite

1000 Feet

FIGURE 69. Geologic structure map and location of drill holes at the Dietz-Schromen area, 2.4 miles

southwest of Durango. Iowa.

The syncline as mapped from outcrops was verified by the drilling,

with only slight modifications.

CONCLUSIONS

Based on data from surface mapping and from the limited investigation of the Decorah formation and the lower part of the Galena

dolomite by churn-drilling, ft total of thirteen holes in lOUr ftrfiftS, it is

concluded that:

1. Tire several favorafole lines of evidence of mineralization, in tnese

strata indicate a reasonable possibility that zinc ore bodies occur in

these stratigraphic units in the Dubuque subdistrict, in Iowa.

2. Structures favorable for ore concentration can generally be

delineated by mapping outcrops from 50 to 200 feet higher in the

stratigraphic section than the principal ore zone.

3. Because of mass slumpage along bluff outcrops, fayorableappearing structures may be mapped that are not reflected below in
DRILLING FOR ZINC AND LEAD ORE, DUBUQUE COUNTY, IOWA 487

the principal ore zone, and for this reason a syncline interpreted from 

this type of data should be verified before drilling, if possible, by 

outcrops or subsurface information in areas away from the bluff 

outcrops.

RECORDS OF DRILL HOLES.

Behnke-Krug area, drill hole 1

Location: 730 feet north and 10 feet east of the southwest corner of the SEJ4 sec. 34, T. 90 N., R. 1 E., Iowa.

Driller: H. Landgraf (0-190 ft) 10/29/52-11/6/52; E. Dietz (190-300 ft) 1/5/53-1/7/53.

Collar elevation--.......-.-----....----....----.-.-.---.-..-.....-...--.-........--......-..... 847.7 ft

Total depth--__.-----------.--------------.........__.-.-...__--...._............_-,......... 300ft

Depth to water.-.--..-....----....-----.....--.-.......-........---................-__..__ 95 ft

Sample study and logging: C. E. Brown.

Depth 

(feet)

Surficial: Soil, loess, brown shale residuum________-_-______-__-__-____ 0-24

Maquoketa shale ("slate"): Shale, dolomitic, dark-brown; abundant 

depauperate fossils lower 2 feet--_____-______-_____-_-_-_-_____._ 24-32

Galena dolomite:

Noncherty unit (yellow-sandy):

Dolomite, gray and buff, medium-grained, argillaceous.-------- 32-35

Dolomite, yellow-buff, argillaceous__--_-------_--__-----__-_- 35-70

Dolomite, buff, medium crystalline, partly limonite stained. ___ 70-125 

Dolomite, drab and tan, medium crystalline, vuggy; speckled

with minute pyrite crystals.___.-_____-_-_-_-_-_-_-__-__ 125-147

Cherty unit (drab):

Dolomite, light-brown, slightly disintegrated; leached-white,

gray, and drab chert is common.________________________ 147-155

Dolomite, tan, medium crystalline, moderately hard; drab to 

gray chert partly decomposed; disseminated pyrite in the 

chert..___-_---__--------.__-___-.---_-_---.-__....- 155-160

Dolomite, medium crystalline, tan; mottled drab, gray, and

white chert with very fine disseminated crystals of pyrite.-_ 160-185 

Dolomite, light-gray, recrystallized, speckled with pyrite; whitegray chert is sparse.___________________________________ 185-200

Dolomite, gray to tan; trace of green-blue shale partings; gray

chert is common.._____________________________________ 200-215

Dolomite, tan, medium crystalline; leached-white, gray, and

drab chert is common._________________________________ 215-260

Dolomite as above; chert is sparse.________________________ 260-263

Decorah formation:

Ion dolomite member (gray beds and blue beds):

Dolomite, medium crystalline, vuggy, argillaceous with dark-gray

specks; green shale common in lower 5 ft _________________ 263-274

Limestone, dolomitic, gray-blue, medium-grained, argillaceous;

calcite is common--.-__--___________-_-_-____-__-_.__-__ 274-284

Guttenberg limestone member (oil rock): Limestone, dolomitic, gray 

to flesh-colored, medium-grained, silicified in part; much drab to 

tan argillaceous residuum.___-_.--__-___-______.________-___ 284-288

Spechts Ferry shale member (clay bed): Shale, blue-green, fossiliferous, and dense gray limestone; phosphatic nodules------.-. 288-295

Platteville formation:- McGregor limestone member ("Trenton") Limestone, mottled gray, sugary, fine-grained, fossiliferous._--___-__---__ 295-300
488 . CONTRIBUTIONS . TO ECONOMIC GEOLOGY 

Estimated zinc, lead, and iron content in percent

Depth Zinc Lead Iron

185-190 . - 

190-215-. .

275-280-...... . .. ......... ...... ..... .......... 2

280-282J___._._ i _- Trace ---------------- . ___.. 3

285-290..... -.- . . Trace.--------------- - Trace.---------------- 2

295-300...... .

Behnke-Krug area, drill hole %

Location: 20 feet east and 580 feet north of the southwest corner of the SEH sec. 34, T. 90 N., R. 1 E., Iowa.

Driller: H. Landgraf, 11/7/52-11/24/52.

Collar elevation ..................... ............... ... ..................... 837.5ft

Total depth.. .................. ...... .. ............. ......... 288ft

Depth to water..___..___.___..__..._______.____.____.______ 90ft 

Sample study and logging: C. E. Brown.

Depth 

(feet)

Surficial: Soil, loess, and residuum___________________________________ 0-20

Galena dolomite:

Noncherty unit (yellow-sandy):

Dolomite, buff, fine-grained, argillaceous___________________ 20-38

Dolomite, yellow-buff, fine-grained, argillaceous; lower 5 ft

medium crystalline-__--____-_-_-_---___---____-_____-___ 38-55

Dolomite, medium crystalline, buff with limonite-staining_____ 55-65

Dolomite, buff, medium crystalline_______-_--___-_-______-__ 65-80

Dolomite, buff, hard, finely crystalline; slight limonite-staining

in lower 15 ft______-_-_____--_____-__________________ 80-115

Dolomite, drab; minute crystals of disseminated pyrite are common. ____.____-____-_-___----_---_----------_-------- 115-134

Cherty unit (drab):

Dolomite, drab, hard; white to tan chert is sparse,__________ 134 140

Dolomite as above; white to tan chert is common_________ 140-170

Dolomite, tan to drab, hard; light-gray chert is common; disseminated pyrite in chert _ . _ 170-180

Dolomite, light-gray, hard; light-gray chert is SparSG-________ 180 1QO

Dolomite, tan, hard; gray to white chert is sparse.__________ 190-225

Dolomite as above; drab to gray chert is common. __________ 225 24O

Dolomite, light-brown; white chert is abundant.____________ 240-250

Dolomite, buff, medium crystalline; chert is sparse___________ 250-256

Decorah formation:

Ion dolomite member (gray beds and blue beds):

Dolomite, gray-drab, argillaceous, medium-grained; green shale

partings..._____.-_. 256-205 

Dolomite, gray-blue, argillaceous, medium-grained; blue-green

shale is common______--_--_-----_--------_------------ 268-275

Guttenberg limestone member (oil rock) : Dolomite, tan, fine-grained,

siliceous; drab clay is abundant._-._-_ _. 275-282 

Spechts Ferry shale member (clay bed): Shale, blue-green and dense

gray limestone___________-___-_---_-_----------------_---- 282 287

Platteville formation: McGregor limestone member ("Trenton"): Limestone, gray, argillaceous._--___ >_____._____._.___.---.--. 287-288
DRILLING FOR ZINC AND LEAD ORE, DUBUQUE COUNTY, IOWA 489 

Zinc and iron content

Depth

Estimated percent

Zinc Iron

Assayed percent

Zinc Iron

140-180 

180-190.-.-------- ------ _ . - .......... 1-2

195-205 2

205-210 3

210-225 . 1

225-235-.. - ----- . 3

235-265 

265-270 - - 3

270-275 5

275-280. -- - -- 1-2 5 2.20 5.60

280-285 # 3

286-288 'Trace-*. 2

1 Caved?

Behnke-Krug area, drill hole 3

Location: 620 feet north and 135 feet east of the southwest corner of the SEH sec. 34, T. 90 N., R. 1 E., Iowa.

Driller: E. Dietz, 1/8/53-1/15/53.

Collar elevation ... ... ......................... 853.1ft

Totaldepth.... ...... ..... 302ft

Depth to water . . ____ 67 ft 

Sample study and logging: A. E. Flint.

Depth 

(feet)

Surficial: Soil and loess _________ ___________________________ 0-13

Maquoketa shale ("slate"): Shale, mainly dark brown and gray, slightly 

calcareous siltstone._----________--__-__--______-._-_____________ 13-32

Galena dolomite:

Noncherty unit (yellow-sandy) :

Dolomite, buff and gray, mainly fine grained, partly argillaceous;

limonite is sparse.___----______--__._-___________________ 32-55

Dolomite, buff, fine-grained and crystalline; crevice clay is

sparse__---_-__-___--_-_--_-_-_-----____-.____________ 55-60

Crevice clay, red-brown; much limonite staining, no indurated

rock___________________________________________________ 60-70

Dolomite sand, buff, limonite-stained; no indurated rock.______ 70-80

Dolomite, buff, fine- to medium-grained, leached and soft, with

sparse limonite staining._________________________________ 80-95

Dolomite, buff, finely to medium crystalline, hard.___________ 95-128

Dolomite, drab, finely to medium crystalline, slightly leached. _ 128-149

Cherty unit (drab):

Dolomite as above; gray and brown glassy chert is common to 

abundant; marked leaching at 185-190 ft; iron sulfide disseminated in both chert and dolomite at 185-215 ft._______ 149-215

Dolomite as above; chert is generally sparse, but very common at

225-230 ft-_ ____ .___ _--------___-_-__--...- 215-245

Dolomite as above; gray chert is common to abundant_._____ 245-260

Dolomite, drab and buff, finely to medium crystalline; chert is 

sparse_----_-----_-----_-_.___---_-_________._______ 260-267
490 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Depth 

(feet)

Decorah formation:

Ion dolomite member (gray beds and blue beds):

Dolomite, gray, mottled, soft----------------------------- 267-276

Dolomite, dark-gray, mottled; gray shale is abundant-____.-_ 276-283

Guttenberg limestone member (oil rock): Dolomite, brown, fine- to

medium-grained, partly silicified_-___________________________ 283-285)

Spechts Ferry shale member (clay bed): Shale, gray, and gray

dolomite and dolomitic limestone---_---------_--_--------_-- 289-296'

Platteville formation: McGregor limestone member ("Trenton"): Dolomite, gray, fine-grained_____-__--_-_-------_-_------------------ 296-302

Estimated zinc, lead, and iron content, in percent

Depth

30-40. 

40-45.. . 

1 9^ 1*^^

165-185 

185-200 -

200-235 

235-240.. 

240-250. 

250-270 

270-275. - 

97c*}j3c

ac<^-_9Qn

OQ £_QfiA

300-302.. 

Zinc

Trace

1J*

Yi

Trace plus

Lead

Trace

Iron

1

Trace plus

H

A1

Trace plus

H

6

8-

6

4

2

2

Behnke-Krug area, drill hole 4

Location: 35 feet east and 470 feot north of the southwest corner of the SE54 sec. 34, T. 90 N., R. 1 E., Iowa. 

Driller: E. Dietz, 1/16/53-1/21/53.

Collarelevation . . - - - -- - - 829.3ft

Total depth.... ... . . _ 273ft

Depth of water. _. - -- -- 

Sample study and logging: A. E. Flint.

65 ft

Depth 

Surficial: (feet)

Soil and loess.________________________________________________ Q-10

Residual brown shale and buff dolomite....__.__.._...._______.__ 10-15

Galena dolomite:

Noncherty unit (yellow-sa^av-) .- Dolomite, buff and gray, fine-grained, argillaceous. ____________ 15-45

DolOmite, buff, mainly finely to medium crystalline----------- 45-115

Dolomite, drab, finely to medium crystalline________-______- 115-120

Cherty unit (drab):

Dolomite as above; gray and brown chert is sparse. _________ 120-125

Dolomite as above but chert is abundant-_______-_--------- 125-165

Dolomite as above; chert is sparse to common; disseminated iron

suifide in dolomite at 165-175 ft._______________________ 165-185

Dolomite as above; Chert is abundant at 185-190 ft, sparse to

common at 190-220 ft_ ------------------------------ 185-220

Dolomite as above; chert is common to abundant ______-- 220-23.-> Dolomite, drab ftr,a s^y-b^, «"-^ ^9 mcaium crystalline; chert 

is sparse----...--------------------------------------- 235-24.2
DRILLING FOR ZINC AND LEAD ORE, DUBUQUE COUNTY, IOWA 491

Depth 

(feet)

Decorah formation:

Ion dolomite member (gray beds and blue beds):

Dolomite, gray, mottled, finely to medium crystalline._______ 242-257

Dolomite, dark-gray, very argillaceous, soft; gray clay is common. 257-261 

Guttenberg limestone member (oil rock): Limestone and dolomitic

limestone, tan, mainly fine grained, soft; brown shale is common. _ 261-268 

Spechts Ferry shale member (clay bed): Shale, green and gray, and

gray fine-grained limestone.____________________________ 268-273

Zinc and iron content

Depth

Estimated percent

Zinc Iron

Assayed

percent

zinc

75-90...-----------.-----.----..------------------------------------- --.---...--- Trace

100-165---.------.---------.-.----------,-------------------------- ------------ Trace

165-175 -------------- ..... *_

176-220. --------.-.. Trace

220-225 }_ .

225-252*......-.-.-- . Trace plus

262*_-257H---- Trace 1

257*_-260 - Trace plus 5

260-262*...... 1 12

262*_-265. 2-3 5 1.56

265-267*.... _. . 1-2 4 0.78

267*_-270 M. 2

270-273.............................................................. 54 2

Behnke-Krug area, drill hole 5

Location: 80 feet west and 440 feet north of the southwest corner of the SEJ4 sec. 34, T. 90 N., R. 1 E., Iowa.

Driller: E. Dietz, 1/22/53-1/26/53.

Collar elevation---.-..--...--.----.--.-----------------------.------------------------- 818.5ft

Total depth. ............... ... .. .. . ... ....... 262.5ft

Depth to water.---...---..---...---..---.-....----------.----..----..-----------------.--- 50 to 60 ft

Sample study and logging: 0. E. Brown.

Depth 

(feet)

Surficial: Soil, loess, and highly decomposed dolomite residuum.________ 0-20

Galena dolomite:

Noncherty unit (yellow-sandy):

Dolomite, buff, argillaceous, fine-grained; partly light gray____ 20-25

Dolomite, buff, argillaceous, moderately soft__________________ 25-40

Dolomite, buff, medium crystalline, partly recrystallized._____ 40-100

Dolomite, drab, medium to coarsely crystalline, vuggy; disseminated pyrite specks-______--_--_--_-___________________ 100-121

Cherty unit (drab) :

Dolomite, drab to gray, recrystallized, vuggy; gray chert is 

sparse______________________________________________ 121-125

Dolomite, drab to buff, moderately soft, vuggy; gray-white to

drab chert is common.________________--_-___-__--___-_ 125-150

Dolomite, drab to gray, medium crystalline, partly vuggy; gray

chert is abundant____________________________________ 150-165

Dolomite as above, very vuggy; chert is sparse________--____ 165-170

Dolomite, drab to buff, medium crystalline, moderately hard;

leached white chert is common__-_______________________ 170-185

Dolomite, tan to buff, medium crystalline, moderately hard; drab 

to buff and leached white chert is common, chert is sparse from 

195-205 ft ------_-_-----_-- - 185-220

Dolomite as above; drab and leached white chert is common.. 220-230 

Dolomite as above; chert is sparse-------------------.--..- 230-237
492 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Decorah formation:

Ion dolomite member (gray beds and blue beds):

Dolomite, light-gray, calcitic, argillaceous with dark-gray flecks,

medium crystalline-.-.--.----------------------------- 237-250

Dolomite, medium-gray, mottled, very argillaceous; quartz grains 

are sparse_-__----_-__________________________________ 250-25$

Guttenberg limestone member (oil rock): Dolomite, flesh-colored, 

medium crystalline, very vuggy; siliceous fossil fragments abundant; 

brown shale abundant in lower 4 ft.__--_---_-_-___-__--_---- 256-262

Spechts Ferry shale member (clay bed): Shale, blue-green, fossiliferous, and dense gray limestone_____-_-___--__-_-_-____-._.- 262-262|4

Zinc, lead, and iron content

Depth

125-140--- __ .. _ .................. .....

165-170... ___ .. _ ............. _____

170-195-.........-....-..... ...........

195-200-. ............................. .....

200-205-.... ... ...-...- .. _._...

205-210... _______ .. ___ ----- ........

210-235............. .-_.._--__ ..._...

235-250...................................

M-286....................................

255-257^....... ..._........ ......

257^-260. ....... .... ........

260-262^.......... ........ ................

Estimated percent

Zinc,

Trace-^ 

J4 

Trace- %

rn ^

Trace

Trace

H

(9 

0)

Lead

Trace 

Trace 

Trace

Iron

M-i

Trace- V£ 

Trace 

Trace 

Trace 

Trace 

V4-1 

10

6 

(0 

2

Assayed percent

Zinc

1.15

.77

.72 

.92

Iron

6.08.

i Samples were studied after these assays were made; therefore, estimates were made by referring to assayed 

samples.

Wallis area, drill hole 1

Location; 1,350 feet west and 200 feet soutb of tne nortneast corner of sec. 5, T. 89 N., E. 2 E., iowa.

Driller: H. Landgraf, 12/1/52-12/11/62.

Collar elevation; ------__.---- _-______......__.-___--________--_ -- 801.6 ft

Total depth..._..--..... -....,...........__..__.__.......... .. .......... 210 ft

Depth to water____-____.__________________________________..._- 195ft

Sample Study and logging: C. E. Brown.

Depth 

(feet)

Surficial: Soil, loess, and residmun......_...-_._______________________ 0-15

Galena dolomite:

Noncherty unit (yellow-sandy):

Dolomite, yellow-buff, crystalline-_-_-_________-_-___--__---- 15 4i>

Dolomite, buff, medium crystalline__________________________ 45-61

Cherty unit (drab):

Dolomite as above; tan chert with red iron-oxide specks is sparse- 61 6&

Dolomite as above; drab to tan chert is abundant..----------- 65-80>

Dolomite as above; slight limonite staining; leached white chert

is common________________________-___-_-_------_------- SO 85-

Dolomite, yellow-brown; chert is sparse...- - ------ 85-90'

Dolomite, buff; white chert common; clear calcite is sparse. _ _ - 90-10S

Dolomite as above; leached white chert is sparse ------------ 105-150

«.__; ril«^ ,,__te et__e; whtte c^_a_s_rr 150-170

........ 170-175

abundant; clear calcite is common.... -

Dolomite, coarsely crystalline; calcite .is common.
DRILLING FOR ZINC AND LEAD ORE, DUBUQUE COUNTY, IOWA 493

Decorah formation:

Ion dolomite member (gray beds and blue beds) : (feet) 

Dolomite, buff, crystalline, vuggy; green shale partings are common; clear calcite is common _ _________________________ 175-188

Dolomite, blue-gray, mottled, argillaceous; blue-green shale is 

common; clear calcite is abundant. ______________________ 188-195

Guttenberg limestone member (oil rock) : Dolomite, medium-grained

light-brown; brown shale is common; disseminated iron-sulfide__ 195-204 

Spechts Ferry shale member (clay bed) : Shale, blue-green, fossiliferous; dense fossiliferous gray limestone is abundant; clear 

calcite is common ; pyrite is sparse. __________________________ 204-210

Estimated iron content in percent

Depth Iron 

190-1Q5. ................................................... J_

195-200. ___________________________________________________ 3

205-210.. ....................................... .........^. #

Wallis area, drill hole 2

Location: 570 feet south and 425 feet west of the northeast corner sec. 6, T. 89 N., B. 2 B., Iowa.

Driller: H. Landgraf, 12/13/52-12/24/52.

Collar elevation................................................................................. 759.6 ft

Total depth..................................................................................... 165ft

Depth to water... ............ _ ............................................................... 130ft

Sample study and logging: 0. E. Brown.

Galena dolomite:

Noncherty unit (yellow-sandy) : (/«<) 

Dolomite, buff, medium crystalline, limonite-stained. __________ 0-10

Dolomite, buff, hard, recrystallized, limonite-stained- ______..__ 10-17

Cherty unit (drab) :

Dolomite, yellow-brown, hard, crystalline; light-tan chert is

sparse _ ___-__-____-_-_-__-_____-__-__--.--_.__-__-___- 1 7-23 

Dolomite, light-brown, medium crystalline, partly limonite

stained; white and drab chert, common __ _________________ 23-55

Dolomite as above ; white chert is sparse _ .________._-___-___ 55-60

Dolomite, buff, fine- to medium-grained; drab chert is common. _ 60-70 

Dolomite, buff, crystalline, partly decomposed; chert fragments

are sparse. -_-____-__--___-___-___________-___-_--_--_-_ 70-85

Dolomite, buff, limonite-stained; white chert fragments common;

clear calcite common.. _ __________________________________ 85-95

Dolomite, buff, recrystallized, limonite-stained; chert is sparse. 95-110 

Dolomite, calcitic, buff, limonite-stained; white and drab chert

is abundant__________-_______-________-______._-_____ 110-125

Dolomite, calcitic, light-brown, medium crystalline; chert is

sparse.. __ --_.__- _ _ _ __ _____ _ _______ ___ 125-134

Decorah formation :

Ion dolomite member (gray beds and blue beds):

Limestone, dolomitic, argillaceous, buff with black specks; green

shale partings are common___. ___________________________ 134-147

Limestone, dark- and lightrgray, mottled, argillaceous. _______ 147-156
494 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Decorah formation Continued

Guttenberg limestone member (oil rock): Limestone, light-brown,

very fine grained, fossiliferous; brown shale is abundant______-_ 156-164

Spechts Ferry shale member (clay bed): Shale, blue-green, fossiliferous, and dense gray limestone-_________________________ 164-165

Estimated zinc, lead, and iron content, in percent

Depth Zinc Lead Iron

155-160 } $-!

160-164....... ... £_-! Trace-H 1

164-165-.... . -..- ..- .. . - --- ............ .. ...- J.-1

Wallis area, drill hole 3

Location: 420 feet south and 880 feet west of the northeast corner sec. 5, T. 89 N., K. 2 E., Iowa.

Driller: H. Landgraf, 1/11/53-1/29/53

Collar elevation.... ... .. .................................. ............ 794.9ft

Total depth. .....__.-_-__..............__...................__........... .... 195ft

Depth to water_._...._____... . .-- - - - _-______ - _- No water

Sample study and logging: C. E. Brown.

Galena dolomite: D th 

Noncherty unit (yellow-sandy): (feet) 

Dolomite, buff, medium crystalline; partly decomposed.._______ 0-10

Dolomite, buff, moderatley soft, medium crystalline____________ 10-53

Cherty unit (drab):

Dolomite, buff, medium crystalliner normally hard; white to 

pink chert is sparse_______--___-_-______________-_-_-_-_- 53-60

Dolomite, buff, medium crystalline; pink chert is common._____ 60-65 _,

Dolomite, buff, moderately soft, partly limonite stained; white to

cream-colored chert is common___________________________ 65 90 i

Dolomite, buff, slight limonite stains, fine- to medium-grained;

chert is sparse_________________________________________ 90-95

Dolomite as above; pink to white chert is common_________ 95-115

Dolomite as above; white chert is common to abundant._____ 115-140

Dolomite as above; white chert is common to abundant._____ 140-160

Dolomite, buff, recrystallized, vuggy; chert is very sparse. _ 160-168 ^~ 

Decorah formation:

Ion dolomite member (gray beds and blue beds):

Dolomite, calcitic, buff, gray-specked; greenish-buff argillaceous ^

partings... -____-____.-_-_______________________ 168-181

Limestone, blue-gray, very argillaceous, medium-grained; calcite

and pyrite specks.---.---------------- -------- isi-iss

Guttenberg limestone member (oil rock): Limestone, dolomitic, '' 

flesh-colored, fine-grained; brown carbonaceous shale; brown chert

is sparse .. . ---- - 188-193

Spechts Ferry shale member (clay bed): Skale, blUG-gFeen, fOSSilif" w 

erous, and dense gray limestone__-_____------_-------------- 193-195

Estimated iron content, in percent 

Depth ' Irm (.

190-195 __ _ _--_ - i-2
Parker area, drill hole 1

Location: 375 feet west and 25 feet south of the northeast corner sec. 12, T. 89 N., R. 1 E., Iowa.

Driller: E. Dietz, 12/12/52-12/16/52.

Collarelevation................................ ... ...-............ ... ...... ...... 713.0ft

Total depth................................... ..................... ..... . .... 148ft

Depth to water..-.-.._......_.-.--.-... .- .... ...... 70ft

Sample study and logging: A. E. Flint.

Depth 

Surficial: (feet)

Soil..._.__._._._..__.... _______ _______________________________ 0-5

Loess. ___________________________________________ 5-27

Residual dolomite, sand, and chert_____________________________ 27-31

Dolomite, buff, fine- to medium-grained, partly decomposed, probably 

talus_.____._____________________________ 31-55

Galena dolomite:

Cherty unit (drab):

Dolomite, buff, finely to medium crystalline, soft; buff clay

common________________________________________________ 55-60

Dolomite and clay as above, slight ocher staining; gray-white 

chert common; angular quartz sand grains and other glacial 

material is sparse______--_-_-_-_--_-_-__-__--__-___--_-_- 60-70

Dolomite and chert as above-____--_-__---___-_-__-_---__-__ 70-85

Dolomite as above but very soft; light-gray and white leached 

chert is common; slight ocher staining; crevice clay at 85-105 

ft_-___--__---__-_--_---_----------__--_----____-____._ 85-108

Decorah formation:

Ion dolomite member (gray beds and blue beds) :

Dolomite and dolomitic limestone, gray, mottled; very argillaceous.... __________..-_____________________________ 108-125

Limestone, gray, mottled, very argillaceous; blue-green shale,

common; disseminated iron sulfide in limestone, common.__ 125-131 

Guttenberg limestone member (oil rock): Limestone, light-tan, mainly

fine grained; sparse disseminated iron sulfide; calcite is sparse.__ 131-145 

Spechts Ferry shale member (clay bed): Shale, gray and green, and 

gray mainly fine-grained limestone with disseminated iron sulfide 

common in both shale and limestone________-_--_--__-_______ 145-148

Estimated iron content, in percent 

Depth Iron

125-130. ___.__-__-_______----__------__-_-____-.-_________ J_

130-148-._____________________________ Trace plus

Parker area, drill hole 2

Location: 300 feet west and 350 feet south of the northeast corner, sec. 12, T. 89 N., R. 1 E., Iowa.

Driller E. Dietz, 12/16/52-12/22/52.

Collarelevation...__.___________.. .._.__._.........__.___.__._ 659.2ft

Total depth... ..._. _._._ __..__... .... ..................... 110ft

Depth to water.....__.____________________.________________ 10 ft 

Sample study and logging: A. E. Flint.

Depth 

Surficial: (feet)

Soil..______________________________________________________ 0-4

Stream deposit, mainly glacial sand and pebbles.______-__-___-__-_ 4-50

Residual Galena dolomite, glacial sand, and abundant chert______ 50-60
496 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Decorah formation: D h 

Ion dolomite member (gray beds and blue beds): Limestone, gray, (feet) 

mottled, partly dolomitic, very argillaceous. ____________________ 60-78

Guttenberg limestone member (oil rock): Limestone, light-tan, finegrained, fossiliferous; sparse brown shale __ ____________________ 78-94

Spechts Ferry shale member (clay bed): Shale, green and tan-gray, 

and gray fine-grained limestone; phosphatic nodules and disseminated iron sulfide common___________________________________ 94-102

Platteville formation: McGregor limestone member ("Trenton"): Limestone, gray, fine-grained, dolomitic __ ___________________________ 102-110

Parker area, drill hole S

Location: 205 feet west and 700 feet south of the northeast corner sec. 12, T. 89 N., R. 1 E., Iowa.

DrilJer; E. Dietz, 12/22/52-1/3/53.

Collar elevation.. ..... .... ..- . 660.5ft

Total depth....... .. . ... .. ... - 95ft.

Depth to water ________________________ .- ___ 10 ft 

Sample study and logging, A. E. Flint.

Depth 

Surficial: (/«<*)

Soil 0-6

Stream deposits of chert, glacial sand, and pebbles __ ______ _ _______ 6-55

Stream deposits of glacial sand and decomposed buff dolomite,--- - 55-65 

Decorah formation:

Ion dolomite member (gray beds and blue beds) :

Dolomite, mottled gray, finely to medium crystalline, argillaceous. 62-70 

Limestone, dark-gray, mottled, finely to medium crystalline;

gray and green shale, common_____ _______________________ 70-78

Guttenberg limestone member (oil rock) : Limestone, tan, fine-grained,

fossiliferous, and sparse brown shale. _ -------_-------------- 78-92

Spechta Perry shale member (day bed) :

Limestone, gray, fine-grained, and green shale. ________________ 92-95

zinc and iron content, in percent

Depth ZiM I 

__________ Trace ___ _ _ Traceplus

70-75 . . Traceplus------ 1

75-8o.._______________ __ ___ Traceplus __ ... K

Dietz-Schromen area, drill hole 1

Location: 630 feet west ana sso foet nOTth Of the southeast corner S6C. 11, T. 89 N., R. 1 E., Iowa.

Drlller:E. Burg, 11/3/52-11/14/52.

Collar elevation _____________ ________________ so*.7ft Total d$ft.--------""----"-----""-"-::^

Depthofwater ... . .. """"""""""""""""""""" " 65ft 

Sample study and logging: O. E. Brown. TWh 1/vfJt/" 

(feet) 

Surfifiiftl.1 DarK-brOWn SOU, loess, and residuum....^. _________________ 0-10

Galena dolomite:

Noncherty unit (yellow-sandy) :

Dolomite, Hght-gray, fine-grained, argillaceous; calcite common- _ 10-20 

Dolomite, gl*ay flne-gr»i»ed; ««Bm»oeoua. partly crystalline;

clear calcite, sparse ____ - - '" '" 2°~»« 

Dolomite, buff, crystalline, soft, slight limonite stains. --------- 38-7U
DRILLING FOR ZINC AND LEAD ORE, DUBUQUE COUNTY, IOWA 497

Galena dolomite Continued ,, .. JJeptn

Noncherty unit Continued (feet) 

Dolomite, gray-buff, medium crystalline, partly vuggy, hard.--- 70-110 

Dolomite, tan, medium crystalline, vuggy; limonite stains lower 

5 ft----------___----_-_--_____..__._................. 110-120

Cherty unit (drab):

Dolomite as above; sparse, white, leached chert--_--_-_____-_ 120-125

Dolomite, tan, crystalline grains of sand, very soft; chert common, selectively limonite stained, also as gray grains with disseminated pyrite------_--_-----_--_-__--_--_--_.______ 125-130

Dolomite as above; chert as above very abundant----_--_-._ 130-140

Dolomite, buff to tan, harder than above; light-gray and white

chert, partly limonite stained, very abundant.____-_-__-__ 140-145

Dolomite, buff to light-brown, soft, crystalline; light-gray and

dark-gray chert with very abundant disseminated pyrite... 145-170 

Dolomite, tan to buff, hard, specked with disseminated pyrite,

slight limonite staining; very abundant chert as above...-. 170-200 

Dolomite, light-gray to buff, vuggy, medium crystalline; abundant chert as above..._-_-_-_.-_--_---_-__--__--___-_-_ 200-208 

Decorah formation:

Ion dolomite member (gray beds and blue beds): Limestone, lightgray to buff, argillaceous, hard; sparse green shale; calcite common. _.____.__---._____-_____-__-.._-.-_____ 208-220

Limestone, gray with dark-gray patches, medium-grained, argillaceous,

moderately soft; green shales, common_______________________ 220-227

Guttenberg limestone member (oil rock): Limestone, whitish-tan, 

partly fine grained, earthy, argillaceous; brown shale common in 

lower 7 ft.__-----------_..-_-__----_---..-._-.---.-.._._ 227-243

Spechts Ferry shale member (clay bed): Shale, blue-green, fossiliferous; dense gray limestone.-.----------------------------- 243-251

Platteville formation: McGregor limestone member ("Trenton"): Limestone, gray, granular, argillaceous-..---------------.---------.-- 251-255

Estimated zinc and iron content, in percent 

Depth Zinc Iron Depth Zinc Iron

10-25.-..--..-.... Trace 175-186-- - - - 1-2

25-40..................... Trace.... Trace 185-1'JO..................... .............. Yt-\

40-145.................................... Trace 190-205-- 1-2

145-150................... ................ 2 205-215.- ^-1

150-170................... ............._ 4 215-220..................... .............. Trace

170-175 3

Dietz-Schromen area, drill hole 2

Location: 740 feet west and 430 feet north of the southeast corner sec. 11, T. 89 N., B. 1 E., Iowa.

Driller: E. Burg, 11/15/52-12/5/52.

Collar elevation..._______.__.........._........................................... 818.7ft

Total depth................... ............................................................ 267ft

Depth to water_. _______.__.__________. __________._. ____. 70ft 

Sample study and logging: C. E. Brown.

Depth 

(feet)

Surficial: Soil, loess, and residuum._____-_____-_---__--_--__-_--__ 0-20 

Maquoketa shale ("slate"): Shale, dark-brown, carbonaceous; depauperate 

fossils common in lower 3 ft; calcite common__-__-_-_--_-__.-_____ 20-26
498 CONTRIBUTIONS TO ECONOMIC GEOLOGY

_ .. Depth

(feet)

Galena dolomite:

Noncherty unit (yellow-sandy):

Dolomite, gray-buff, fine-grained, argillaceous; calcite common.. 26-50 

Dolomite, gray and buff, partly crystalline, argillaceous; slight

limonite straining lower 5 ft-___--_---__-----------____-___ 50-65

Dolomite, buff, finely to medium crystalline.---.- _____________ 65-90

Dolomite, buff and drab, crystalline __-.__-_______-_-_______ 90-100

Dolomite, tan and drab, finely to medium crystalline ---_-_--__ 100-140 

Cherty unit (drab) :

Dolomite, buff to tan, slight limonite staining; sparse gray chert

with disseminated pyrite. ______________________________ 140-145

Dolomite, buff to tan; white chert common. ________________ 145-155

Dolomite, drab, slight limonite staining; dark-gray and leached

white chert abundant; disseminated pyrite common.. _____ 155-175

Dolomite, drab, hard; abundant chert as above __ __________ 175-185

Dolomite, tan to drab, hard; chert as above _ ______________ 185-205

Dolomite, gray-drab, hard ; sparse chert ..___._____._____ _ 205-220

Dolomite, tan; abundant white chert __ ___________________ 220-228

Decorah formation:

Ion dolomite member (gray beds and blue beds) :

Limestone, light-gray, medium crystalline, dark-brown argillaceous partings.. __--_-____--__________._____._-________ 228-242'

Limestone, gray, mottled with dark specks, argillaceous; green 

shale partings. _ _______________________________________ 242-250

Guttenberg limestone member (oil rock) : Limestone, light-tan, fossiliferous, fine-grained, hard; brown shale common _______________ 250-265

Spechts Ferry shale member (clay bed) : Shale, blue-green; gray, dense

limestone-... _ ______ _ ____________ _ _________________ 265-267"

Estimated zinc and iron content, in percent

Depth

25-30 

30-35 .

110-120 

120-125 

125-130 

130-135 

135-140 

Zinc

vs

Trace

Iron

3

1

1

2-3

3

1-2

Depth

145-150... .

150-155... 

155-175.. 

185-220.-.- - - .

230-235... .

235-240 

Zinc Iron

0

3

Trace-1

1

2'

i
INDEX

Page

Abstract...---------.--.-.-------.--------- 471

Acknowledgments ----------- .--..-.- 473

Alteration of hostrock... . . 479

Behnke-Krug area, records of drill holes in.. 487-492 

results of drilling in....-.---..........-. 480-483

Cherty unit.---..-----------------------..--- 474

See also Eecords of drill holes.

Conclusions..--------------------------.--. 486-487

Crevice deposits..___--__-___--_ 476-477

Decorah formation, description..-.___... 473-475 

records of drill holes in ____-_.-_--_.___. 487-498 

zinc and lead deposits in......._...... 476-478

Dietz-Schromen area, records of drill holes

in....--.-....---..----..-..... 496-498 

r.esults of drillingin....-.-.--..--.--- 484-486

Drilling, results of 480-486

toolsfor.. _ - 479

Drill holes, records of ___.____ 487-498

Dubuque member of Galena dolomite..-.-. 474,475 

See also Records of drill holes.

Exploration, methods.. . __ 479

Galena. 476,478,479

Galena dolomite, crevice deposits in.......... 476

description of. ...--. . ...-. 474,475 

pitch and flat deposits.-- ------------- 477

records of drill holes in. __ _ 487-498

zinc and lead deposits in._ --- --- 476

Geologic mapping.. ... .-. 479

Geology...------.--------------.------.--.- 473-476

Glass rock. See Qulmbys Mill member of

Platteville formation. 

Guttenberg limestone member of Decorah

formation....--.... .. 474-475

See also Records of drill holes.

History of mining. 472-473

Introduction-__ _ ... _ _. 471

Ion dolomite member of Decorah formation. 474,475

See also Records of drill holes. 

Iron, estimate of content of, in drill hole. 488, 

489,490,491,492,493,494,495,496, 497, 498

Krug. See Behnke-Krug area.

Lead, estimate of content of, in drill hole....- 488,

490,492,494

Page

Location of the area...__...-_...__... 472

McGregor limestone of Platteville forma*

Hon.. .... 473,474

See also Records of drill holes. 

Maquoketashale. .... 474,475-476,487,489,497

Minerals, accessory_...................._ 478-479

Minerals, ore..__._______._____ 478-479

Noncherty unit..__.__._________ 474 

See also Records of drill holes.

Oil rock. See Guttenberg limestone member 

of Decorah formation.

Parker area, records of drill holes in........ 495-496

results of drilling in_...----..--........ 484

Pitch and flat ore deposits.. - - _.__.-_. __ 476-478

Platteville formation description........ 473,474

records of drill holes in..---.._....... 487-498

zinc and lead deposits in.._....-_... 476-478

Prosser member of Galena dolomite.--- -- 474,475 

See also Records of drill holes.

Purpose of the project.__...__..... .._ 471

Quimbys Mill member of Platteville formation. . _..... 473,474 

Set also Records of drill holes. 

Records of drill holes. ...._... 487-498 

Results of the drilling, summary of.-__. 471

Schromen. See Dietz-Schromen area.

Slate. See Maquoketa shale.

Spechts Ferry shale member of Decorah

formation.-..-..--... -. .._. 475

See also Records of drill holes. 

Sphalerite.----.----.----.--.--.-.--.... 476,478 

Stewartvillc member of Galena dolomite... 474,475

See also Records of drill holes. 

Stratigraphy.. 473-476 

Structure, control of mineral emplacement-. 476-478

regional dip... - .. ....... ... 476

Trenton limestone. See McGregor limestone 

member of Platteville formation.

Wallis area, records of drill holes in. . 492-494 

results of drilling hi ..... ...... 483-484

Zinc, estimate of content of.---- _...... 488,

489,490,491,492,494, 496, 497, 498

499

U. S. GOVERNMENT PRINTING OFFICE. 1986