NEBRASKA

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PRECAMBRIAN

The Midcontinent Strategic and Critical Minerals Project 

Summary and Background Information to Accompany 

^olio of Maps of the Northern Midcontinent Area, 

latitude 36°-46° N. and Longitude 88°-100° W.

U.S. GEOLOGICAL SURVEY CIRCULAR 1124

^repared in cooperation with the geological surveys of 

Arkansas, Illinois, Iowa, Kansas, Kentucky, Minnesota, Missouri, 

7 Tebraska, Oklahoma, South Dakota, Tennessee, and Wisconsin
Cover. A portion of map MF-1835-G, Lithologic cross sections, showing part of 

section along long 98° W. (reduced approximately 50 percent). From Mugel, D.N., 

and Pratt, W.P., 1991, compilers., Lithologic cross sections of Phanerozoic rocks in the 

northern Midcontinent, U.S.A.: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-1835-G, scale 1:1,000,000.
The Midcontinent Strategic and Critical Minerals ProjectSummary and Background Information to Accompany 

Folio of Maps of the Northern Midcontinent Area, 

Latitude 36°-46° N. and Longitude 88°-100° W.

By Walden P. Pratt

U.S. GEOLOGICAL SURVEY CIRCULAR 1124

Prepared in cooperation with the geological surveys of Arkansas, 

Illinois, Iowa, Kansas, Kentucky, Minnesota, Missouri, Nebraska, 

Oklahoma, South Dakota, Tennessee, and Wisconsin

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For sale by U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government

Library of Congress Cataloging-in-Publication Data

Pratt, Walden P.

The Midcontinent strategic and critical minerals project: Summary and background 

information to accompany folio of maps of the northern Midcontinent area, latitude 

30°-46° N. and longitude 88°-100° W. / by Walden P. Pratt.

p. cm. (U.S. Geological Survey circular ; 1124) 

Includes bibliographical references.

1. Mines and mineral resources Middle West. I. Title. II. Series. 

TN23.4.P73 1995

553' .0977 dc20 95-31576

CIP
CONTENTS

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

Miscellaneous Field Studies Maps (MF Series)............................................................. 3

MF-1835-A: Drill-Hole Map ............................................................................... 3

MF-1835-B: Equivalent Freshwater Head and Dissolved-Solids 

Concentration of Water in Rocks of Cambrian, Ordovician, and 

Mississippian Age............................................................................................... 3

MF-1835-C: Radiometric Ages of Basement Rocks............................................ 3

MF-1835-D: Sauk Sequence Isopach and Lithofacies Map................................. 7

MF-1835-E: Phanerozoic Structural Features...................................................... 7

MF-1835-F: Alkaline Igneous Rocks, Carbonatites, and Peridotites................... 7

MF-1835-G: Lithologic Cross Sections of Phanerozoic Rocks........................... 7

MF-1835-H: Areal Extent of Selected Paleozoic Shales..................................... 12

MF-1835-1: Thickness and Limestone-Dolostone Ratios of Selected

Paleozoic Carbonate Units.................................................................................. 12

Miscellaneous Investigations Series Maps (I Series)..................................................... 16

I-1853-A: Precambrian Basement Map of the Northern Midcontinent............... 16

1-2214: Precambrian Basement Map of the Trans-Hudson Orogen and

Adjacent Terranes............................................................................................... 16

References Cited............................................................................................................. 18

FIGURES

1. Midcontinent Strategic and Critical Minerals Project area of initial inventory, showing major

	mining districts........................................................................................................................................................... 1

2. Portion of map MF-1835-A, selected deep drill holes............................................................................................. 4

3. Portion of map MF-1835-B, equivalent freshwater head and dissolved-solids concentration................................. 5

4. Portion of map MF-1835-C, radiometric ages of basement rocks ........................................................................... 6

5. Portion of map MF-1835-D, isopach and lithofacies map of the Sauk sequence .................................................... 8

6. Portion of map MF-1835-E, Phanerozoic structural features................................................................................... 9

7. Portion of map MF-1835-F, alkaline igneous rocks................................................................................................. 10

8. Portion of map MF-1835-G, lithologic cross sections (section along lat 36° N.).................................................... 11

9. Portion of map MF-1835-H, selected Paleozoic shales............................................................................................ 13

10. Stratigraphic relationship of selected shale units and principal carbonate units in the northern

	Midcontinent region and their relation to sandstone aquifers.................................................................................... 14

11. Portion of map I-1853-A, Precambrian basement map............................................................................................ 15

12. Portion of map 1-2214, Precambrian basement map of the Trans-Hudson orogen................................................... 17

III
r"HE MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECTSUMMARY AND BACKGROUND INFORMATION TO ACCOMPANY 

FOLIO OF MAPS OF THE NORTHERN MIDCONTINENT AREA, 

LATITUDE 36°-46° N. AND LONGITUDE 88°-100° W.

By Walden P. Pratt

INTRODUCTION

The Midcontinent Strategic and Critical Minerals 

Project was a cooperative effort between the U.S. Geological 

Survey and the geological surveys of Arkansas, Illinois, 

Iowa, Kansas, Kentucky, Minnesota, Missouri, Nebraska, 

Oklahoma, South Dakota, Tennessee, and Wisconsin. The 

project was begun in 1984 as a broad investigation into the 

mineral resource potential of the northern Midcontinent 

region of the United States. The purpose of this report is to 

summarize briefly the history of the project and the general 

content of the 11 map publications that make up the northern 

Midcontinent folio, and to give a visual sense of the scope 

and content of the folio through page-size samples of each of 

the map products.

The premise of the Midcontinent Strategic and Critical 

Minerals (SCM) Project was that the subsurface of the Midcontinent region is one of the last great frontiers for mineral 

exploration in the United States. Four world-class basemetal mining districts occur within this region: the Upper 

Mississippi Valley lead-zinc district, the Illinois-Kentucky 

fluorspar (-lead-barite) district, the Southeast Missouri leadzinc (-silver-copper-nickel-cobalt) district, and the Tri-State 

(Missouri-Kansas-Oklahoma) lead-zinc district (fig. 1). Significantly, all four districts lie outside the areas of glacial 

cover (the Upper Mississippi Valley district is dominantly 

inside the perimeter of the "driftless area" of southern Wisconsin), and the original discoveries of all four districts were 

made at the surface. All four districts are hosted by Paleozoic platform carbonate rocks, and the same sedimentary 

succession continues north and northwest in the subsurface 

all the way through Canada, where the succession hosts the 

Pine Point lead-zinc district, and on through Alaska to the 

Arctic Ocean.

Figure 1. Midcontinent Strategic and Critical Minerals 

Project area of initial inventory, showing major mining districts. 

1, Upper Mississippi Valley district; 2, Tri-State district; 3, Southeast Missouri district; 4, Illinois-Kentucky fluorspar district.

Similarly, Precambrian basement rocks occur throughout the region, but with the orientation of exposed terranes 

reversed. The famous iron ores of the Lake Superior district, 

potentially valuable copper-nickel deposits in the LN iluth 

Complex, and zinc-copper massive sulfide deposits in metamorphosed volcanic rocks in northern Wisconsin are all in 

Precambrian terranes that are known at least partly from outcrops in the shield area and that appear to extend southward 

beneath the Phanerozoic sedimentary cover. Dilling 

throughout the Midcontinent has shown that the basement 

also contains many other Precambrian terranes, some of 

which have potential as host rocks for other kinds of mineral 

deposits.

In summary, the subsurface terranes of the Mid"ontinent region are believed to have some potential for und: ^covered mineral deposits of the following types:
2 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

Precambrian Rocks

Sedimentary iron ores of Lake Superior type

Layered gabbros and ultramafic rocks with chromium, 

copper-nickel sulfides, platinum-group metals, and 

gold

Massive sulfide deposits of base and precious metals

Olympic Dam-type deposits iron oxide with associated 

copper, cobalt, molybdenum, gold, silver, and 

uranium

Algoma-type volcanogenic iron-ore deposits

Conglomeratic quartzites with potential for gold and

uranium_________________________ 

___ ____ Phanerozoic Rocks ____ ____

Mississippi Valley-type (stratabound, carbonate-hosted) 

lead-zinc ores with silver, copper, nickel, and cobalt

Zambian-type (stratabound, sandstone-hosted) coppersilver ores

Black shales containing a variety of metals (silver, 

vanadium, zinc, chromium, nickel, and molybdenum)

Sedimentary manganese ores

Diatremes of alkalic-ultramafic intrusive rocks with rareearths, fluorspar, base metals, and possibly diamonds

The Midcontinent SCM Project was a major integrated 

effort to more clearly define this varied mineral potential, 

with the following objectives.

1. To prepare an inventory of geologic data on the "core" 

area of the Midcontinent a rectangle bounded by lat 

36°-46° N. and long 88°-100° W. (fig. 1). This area 

was selected as representative of the Midcontinent 

geologic terrane. To the north, it "anchors" onto the 

exposed Precambrian Shield, and to the south it 

includes several contiguous I°x2° quadrangles for 

which substantial databases were accumulated 

through the Conterminous United States Mineral 

Assessment Program (CUSMAP). The product of 

this first-stage inventory is a folio of 1:1,000,000- 

scale maps and cross sections, published in the U.S. 

Geological Survey Miscellaneous Field Studies (MF) 

and Miscellaneous Investigations (I) map series, giving a grossly accurate three-dimensional picture of 

the major geologic and hydrologic terranes and 

known mineral systems in the region.

2. To develop and refine mineral-occurrence models for 

the types of mineral deposits likely to be associated 

with these terranes.

3. To define and pursue both regional and topical problems pertinent to the mineral-occurrence models.

4. On the basis of this research, to prepare 1:1,000,000 

maps indicating mineral favorability of basement and 

sedimentary terranes in the region.

The Midcontinent SCM Project was formally begun as 

a multi-State cooperative effort in January 1584. One of the 

first tasks undertaken in the project was to compile an inventory of selected aspects of subsurface geology of the core 

area of the project the area delimited by lat 36°-46° N. and 

long 88°-100° W. The U.S. Geological Survey (USGS) contracted with the various State geological surveys for input, 

which consisted of 1:500,000- or 1:1,000,010-scale maps 

compiled by geologists in each State from drill-hole logs 

available in the respective State files. The UJTGS then combined the State maps for each product onto a common 

1:1,000,000-scale base for publication and we in studies of 

resource potential. Eleven such maps have b^en published, 

and these products together constitute the folio of the northern Midcontinent. The remainder of this report contains 

descriptions of each of these 11 map publications, accompanied by representative portions of each map, reduced to page 

size (approximately 1:2,000,000).

Progress reports on many aspects of the Midcontinent 

project were presented at a public symposium held in St. 

Louis, Mo., in April 1989 (Pratt and Goldhrber, 1990). In 

addition, reports on the following topical studies resulting 

from the project have been published: Geolcriy and metallogeny of Archean and Proterozoic basement terranes (Sims 

and others, 1987); Stratigraphy and geochemistry of the Cretaceous rocks of southwestern Minnesota (Setterholm and 

others, 1987); Does the Midcontinent contain permissive terranes for an Olympic Dam-type deposit? (P'att and Sims, 

1990); Geology and mineral paragenesis of the Pea Ridge 

iron ore mine, Missouri (Nuelle and others, 1992); Mineralogical and geochemical aspects of Middle and Upper Pennsylvanian marine black shales (Desborough and others, 

1992); Mineralogical and geochemical analyst of the metaland organic-rich Grassy Creek Shale in Hardin County, Illinois (Desborough, 1992); Paleohydrology of the Central 

United States (Jorgensen, 1992); Precambrian clastic sedimentary rocks associated with the Midcontinent rift system 

(Berendsen and Barczuk, 1993); Feldspar diagenesis in 

Cambrian clastic rocks of the southern Ozark Mountains and 

Reelfoot rift Implications for Mississippi Valley-type ore 

genesis (Diehl and Goldhaber, in press); and Regional potential of selected Paleozoic carbonate units for undiscovered 

Mississippi Valley-type lead-zinc deposits (Fratt, in press). 

Two other reports are in review: Petrology cf an extensive 

pre-Cretaceous weathering profile in east-cen*ral and southwestern Minnesota, by G.B. Morey and D.R. Setterholm, 

and geologic maps and cross sections of min~ levels of the 

Pea Ridge iron mine, Washington County, Missouri, by 

C.M. Seeger and others.
MISCELLANEOUS FIELD STUDIES MAPS (MF SERIES)

MISCELLANEOUS FIELD STUDIES 

MAPS (MF SERIES)

MF-1835-A: DRILL-HOLE MAP

Map compiled by Douglas N. Mugel

The Midcontinent drill-hole map (fig. 2) shows the 

location and other data for more than 3,000 drill holes in the 

"initial inventory" area. Most of the drill holes shown are oil 

or mineral tests or water wells. The information shown for 

each hole consists of hole location, State drill-hole log number, bottom-hole elevation, age of rock at total depth, and 

types of samples, if any, that are available. The map is 

intended to show the availability of data and samples for representative deep drill holes in the northern Midcontinent 

region. It was compiled from maps prepared by each of the 

State geological surveys to meet the following specifications: (1) basement penetration, or (2) other holes that in the 

judgment of the State contributor are deep enough to provide 

data and (or) samples for a significant part of the sedimentary section. Data obtained from these holes constitute an 

important database for the project; many of the holes have 

been utilized in the cross sections and some of the maps of 

this folio. The map is also intended as a database for other 

investigators involved in research into mineral potential in 

the Midcontinent area.

Of the more than 3,000 drill holes shown on this map, 

most penetrate at least as deep as the Ordovician rocks, and 

about one-half penetrate the Precambrian basement. Drillhole samples exist for approximately 2,000 of the drill holes, 

of which approximately 200 are core samples.

The maps indicate that each of the two aquifers corfains 

three major regional ground-water flow systems and that the 

regional extent and dissolved-solids concentration (salinity) 

of the three systems are similar in both aquifers. The flow 

systems in each aquifer in the Ozark area in southwestern 

Missouri and northwestern Arkansas make a pair, each containing fresh water with less than 1,000 milligrams per liter 

(mg/L) dissolved solids. A similar pair of flow system? is in 

northeastern Oklahoma and southeastern Kansas and contains water with a salinity ranging from about 20,000 to more 

than 200,000 mg/L. In each aquifer, these two flow systems 

merge in a narrow zone of mixed waters about 40 km wide, 

which trends southward through southeast Kansas and rortheast Oklahoma.

The third pair of major flow systems is generally similar in areal extent but less so in the patterns of salinity. Water 

in the aquifer in Cambrian and Ordovician rocks flows 

southeastward (or locally to the Mississippi River) from 

recharge areas in northeastern Nebraska, northwestern Iowa, 

southeastern Minnesota, and southern Wisconsin, and the 

salinity ranges from less than 500 mg/L in eastern Iowa to 

more than 1,000 mg/L in western Iowa. This concentration 

gradient implies that water has flowed from east to west 

under different geologic and hydrologic conditions than at 

present. In particular the concentration gradient is beloved 

to reflect the paleoflow direction from east to west during the 

Pleistocene. Water in the aquifer in Mississippian rocks in 

this third system flows southeast from east-central Nebraska 

and west-central Iowa, and salinity decreases from 5,000 

mg/L in western Iowa to less than 500 mg/L in central Iowa. 

This distribution of dissolved solids may result from rrixing 

of meteoric water with formation water.

MF-1835-B: EQUIVALENT FRESHWATER

HEAD AND DISSOLVED-SOLIDS

CONCENTRATION OF WATER IN ROCKS

OF CAMBRIAN, ORDOVICIAN, AND

MISSISSIPPIAN AGE

Map compiled by D.G. Jorgensen, J.O. Helgesen, 

R.B. Leonard, and D.C. Signer

These two l:l,000,000-scale maps (part of one of 

which is shown in fig. 3) show preliminary interpretations of 

pre-development hydrogeologic conditions of water in the 

two aquifer systems named, and can be used in a manner 

described by Signer and others (1980) to develop conceptual 

and predictive models of hydrologic and geochemical 

aspects of regional flow systems.

MF-1835-C: RADIOMETRIC AGES OF 

BASEMENT ROCKS

Map compiled by R.F. Marvin

This product consists of two maps (part of one of which 

is shown in fig. 4) showing age ranges of available radiometric dates for basement rocks throughout the Midcont: nent, 

and accompanying tables listing pertinent data for the pitted 

samples. Map A shows sample localities for 111 samples 

giving 410 U-Pb zircon ages. These ages indicate that basement rocks in the northern reaches of the region are Archean, 

whereas those in the remainder of the region are Proterozoic, 

probably dominantly Middle Proterozoic; in general, the 

ages of basement rocks become younger from north to south. 

Map B, which shows sample localities for 560 sample^ giving 139 K-Ar and more than 400 Rb-Sr dates, indicates the
4 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

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Figure 2. Portion of map MF-1835-A, selected deep drill holes.
MISCELLANEOUS FIELD STUDIES MAPS (MF SERIES)

Figure 3. Portion of map MF-1835-B, equivalent freshwater head and dissolved-solids concentration. Original map has shades of gray 

and pink.
6 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

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Figure 4. Portion of map MF-1835-C, radiometric ages of basement rocks (map B).
MISCELLANEOUS HELD STUDIES MAPS (MF SERIES)

same general trend but with a much wider age span from oldest to youngest dates. Moreover, Proterozoic thermotectonic events in Wisconsin, Michigan, and probably the 

eastern Dakotas have affected the K-Ar and Rb-Sr isotopic 

systems to such an extent that Archean rocks generally have 

secondary (reset) Proterozoic ages. Much of the buried basement has not yet been dated radiometrically owing to the 

absence of samples.

Accompanying tables list locations (county, latitude, 

and longitude), rock types, stratigraphic or plutonic names 

(if known), minerals or material dated, radiometric ages, and 

references.

MF-1835-D: SAUK SEQUENCE ISOPACH 

AND LITHOFACIES MAP

Map compiled by Walden P. Pratt

This map (fig. 5) was compiled from l:l,000,000-scale 

isopach and lithofacies maps contributed by the States in the 

hope of defining a regional limestone-dolostone interface to 

be used as a prospecting guide for Mississippi Valley-type 

lead-zinc sulfide deposits (see below under map 

MF-1835-1). It shows that Cambrian and Lower Ordovician 

sedimentary rocks of the Midcontinent pinch out across Kansas, Nebraska, and Minnesota, and thicken south and east 

from the pinchout. Excluding the basal elastics, the rocks are 

overwhelmingly dolomite. Thicknesses of limestone that are 

locally significant within certain formations, such as the 

Bonneterre Formation in southeast Missouri, are for the most 

part obscured by the preponderance of dolomite when the 

Sauk sequence is considered in its entirety.

trends of multiple Phanerozoic structures that may define 

major buried Precambrian structures.

A preliminary examination of the map suggests that 

many of the major Precambrian structural features, as interpreted by Sims (1990), Sims and Peterman (1986), Anderson 

and Ludvigson (1986), and others, are reflected in the trends 

of some of the mapped Phanerozoic structures. Other Phanerozoic structural trends do not appear to relate to any known 

Precambrian features.

MF-1835-F: ALKALINE IGNEOUS ROCKS, 

CARBONATITES, AND PERIDOTITES

Map compiled by FA. Hills, R.W. Scott, Jr., 

T.J. Armbrustmacher, and Pieter Berendsen

This map (fig. 7), prepared by the U.S. Geological Survey from all available data, shows the locations of alkaline 

and ultramafic igneous rocks, including carbonatites and 

kimberlites, and of structural domes and diatremes known or 

thought to be associated with similar igneous rocks. Also 

shown are other structures and geophysical anomalies of 

uncertain origin that may be related to buried igneous intrusions. These include cryptoexplosion structures, some of 

which have been interpreted as astroblemes, and gravity and 

magnetic anomalies that have been interpreted as indicating 

buried mafic plutons. A pamphlet accompanying the map 

includes (1) tables summarizing what is known of the 

petrography, age, and structural setting of each occurrence;

(2) a list of the principal references for each occurrence; and

(3) larger scale maps of areas in which occurrences of igneous rocks and related features such as diatremes are too 

dense to show clearly at 1:1,000,000 scale.

MF-1835-E: PHANEROZOIC 

STRUCTURAL FEATURES

Map compiled by R.R. Anderson

Because Precambrian structural features may provide 

controls for undiscovered mineral deposits hosted by Phanerozoic sedimentary rocks, this map (fig. 6) was prepared to 

evaluate the possibility of locating Precambrian structural 

features by their expression in the structures of overlying 

Phanerozoic rocks. The map includes most known Phanerozoic structural features in the region areas of Phanerozoic 

uplift or depression and Phanerozoic paleotopographic 

highs, as well as known and inferred Phanerozoic faults, synclines, and anticlines. Because many areas have been subjected to multiple tectonic episodes, many of these structures 

overlap. Different shades of pink and gray are used on the 

map to differentiate between these overlapping structures. 

The goal of this map compilation is to show the combined

MF-1835-G: LITHOLOGIC CROSS SECTIONS 

OF PHANEROZOIC ROCKS

Compiled by Douglas N. Mugel and Walden P. Pratt

Thirteen cross sections of the study area along evennumbered lines of latitude and longitude were compiled 

from cross sections at 1:500,000 horizontal scale prepared 

by the State geological surveys. With a vertical scale of 1 

inch = 1,000 ft (vertical exaggeration 83x), the sections 

show major lithologies and the stratigraphic-tectonic 

sequences and subsequences of Sloss (1982) for the entire 

Phanerozoic (fig. 8). Major lithologies are limestone, dolomite, evaporite, sandstone and related elastics, shale, and 

organic shale. The sections also include important structural 

features, such as major faults, and the topography of the buried Precambrian surface.

The objective of these cross sections is to show, at a 

usable scale, the general stratigraphy and major structural
8 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

36

Figure 5. Portion of map MF-1835-D, isopach and lithofacies map of the Sauk sequence.
MISCELLANEOUS FIELD STUDIES MAPS (MF SERIES)

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Figure 6. Portion of map MF-1835-E, Phanerozoic structural features. Original map shows shades of gray and pink.
10 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

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O" R E G O N

L.

N !

HARP [ ~V,

36°

50 MILES

Figure 7. Portion of map MF-1835-F, alkaline igneous rocks.
MISCELLANEOUS FIELD STUDIES MAPS (MF SERIES) 11

WEST

100° 99" 98*

OKLAHOMA

97°

CONTROLWELL __» | 

LOCATIONS^ | 

(Total depth, in feet) §

3,000 FT-.

2,000 FT1,000 FTSEA LEVEL

NEMAHA 

UPLIFT

Figure 8. Portion of map MF-1835-G, lithologic cross sections (section along lat 36° N.).
12 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

features of the Midcontinent region. When used in conjunction with some of the maps compiled for this project, they 

will help to evaluate the potential of the region for sedimenthosted ore deposits.

to Desmoinesian) Cherokee Group, and in Arkansas, the 

Cane Hill Member of the Hale Formation (Morrowan). Age 

assignments of all these formations reflect the usage of Adler 

(1986) and the participating State geological surveys.

MF-1835-H: AREAL EXTENT OF 

SELECTED PALEOZOIC SHALES

Map compiled by Walden P. Pratt

These maps (part of one of which is shown in fig. 9) and 

the carbonate maps in the following set (MF-1835-1) were 

prepared as an aid to regional appraisal and prospecting for 

Mississippi Valley-type (MVT) lead-zinc sulfide deposits. 

MVT deposits in the Midcontinent are predominantly 

galena-sphalerite stratabound deposits in shallow-water platform carbonate host rocks. The currently favored model for 

their genesis invokes upward movement of metal-bearing 

brines from an underlying aquifer to a site in the carbonate 

section where the metals are precipitated as sulfides (Leach 

and Rowan, 1986; Palmer and Hayes, 1989). Implicit in this 

model, as factors that control the site of mineralization, are 

(1) windows through any regional shale underlying the host 

unit, and for many workers, (2) a shale caprock overlying the 

host unit. The seven maps in this report (MF-1835-H) show 

the areal extent of eight principal groups of Paleozoic shales 

whose thicknesses are 5 ft or more; 5 ft was selected by consensus as the minimum thickness of shale necessary to form 

an effective aquitard. The stratigraphic positions of these 

eight groups of shales are shown in figure 10. The formations 

containing shale units, and the respective maps, are as follows, from the base up. Map A shows the Upper Cambrian 

Davis Formation and equivalents, including the Lone Rock 

Formation in Iowa and the Franconia Formation in Minnesota. Map B, the Middle Ordovician (Champlainian) Glenwood Shale and equivalents, shows a shaly facies of the St. 

Peter Sandstone in Nebraska. Map C, the Middle Ordovician 

(Champlainian) Decorah Formation and equivalents, shows 

in part the composite Simpson Group in Oklahoma and Kansas; in Iowa and Illinois the unit mapped is the Spechts Ferry 

Shale Member of the Decorah Formation. Map D shows the 

Upper Ordovician (Cincinnatian) Maquoketa Shale and 

partly equivalent Sylvan Shale in Oklahoma. Map E, the 

Upper Devonian and Lower Mississippian Chattanooga 

Shale and partial equivalents, shows the Maple Mill Shale 

(Upper Devonian) in Iowa and Nebraska, the Boice Shale 

(Lower Mississippian) in Nebraska, and the New Albany 

Shale (Middle Devonian to Lower Mississippian) in Illinois. 

Map F shows the Mississippian (Kinderhookian) Northview 

Shale in Kansas and southwestern Missouri, and the Mississippian (Meramecian) Warsaw Shale in northern Missouri 

and Iowa, together with the Mississippian (Meramecian and 

Osagean) Borden Siltstone and (Osagean) Springville Shale 

in Illinois. Map G shows the Middle Pennsylvanian (Atokan

MF-1835-I: THICKNESS AND

LIMESTONE-DOLOSTONE RATIOS

OF SELECTED PALEOZOIC

CARBONATE UNITS

Map compiled by Walden P. Pratt and Craig J. Wandrey

The preceding map in this folio (MF-1835-H) shows the 

extent of eight principal Paleozoic shale units in the project 

area. These three maps (MF-1835-1) show the other main part 

of the MVT depositional model mentioned previously specifically, the areal extent, thickness, and carbonate lithofacies 

of the region's three principal carbonate units that have proven 

potential as host rocks. As shown in figure 10, from the base 

up these are (1) the Upper Cambrian carbon?te units (Bonneterre and Eau Claire Formations and equivalents), which are 

the principal host rocks of MVT deposits in the Southeast Missouri district (Snyder and Gerdemann, 1968); (2) the Middle 

and Upper Ordovician carbonate units, (Galena Dolomite-Viola Limestone-Kimmswick Limestone and equivalents), host rocks in the Upper Mississippi Valley district 

(Heyl, 1968); and (3) the Lower Mississippian (Kinderhookian-Osagean-Meramecian) carbonate units (ChouteauBurlington-Keokuk and Ste. Genevieve Limestones and 

equivalents), host rocks in the Tri-State (Kansas-MissouriOklahoma) district (Brockie and others, 1968) and in the Illinois-Kentucky fluorspar district (Grogan <nd Bradbury, 

1968). At this writing, map MF-1835-1 is still in press and 

therefore cannot be reproduced here. The three printed maps 

that make up this publication will show carbonate isopachs 

in black and limestone-dolostone isopleths in red, in values 

of 1/4, 1/2, 1,2, and 4.

Map MF-1835-D in this series, described above, 

attempted to define permissive lithologies for MVT deposits 

by showing the carbonate-to-clastic and limestone-to-dolostone ratios of the Sauk sequence rocks of Cambrian and 

Early Ordovician age. That attempt failed as a regional prospecting guide because of the great preponderance of dolostone over limestone when the Sauk sequence is considered in 

its entirety. However, it was that failure that led us to the 

approach of mapping the limestone-dolostone ratio for thinner stratigraphic units the three units shown on the present 

set of maps.

The limestone-to-dolostone ratio is shown on these 

maps because of the apparent importance of the limestonedolostone interface (defined as the 1:1 ratio) as one of the 

most important controls of ore deposition in many Midcontinent MVT districts (Snyder, 1968, p. 278); therefore, it is 

important as a first-cut prospecting tool, especially if
MISCELLANEOUS FIELD STUDIES MAPS (MF SERIES)

94° 93° 92°

13

 -- - _ _ Mankato

I WATONWAN '

--r-.i -__._L_^__

V 

 jUKVf." .

AYEJTE7 P. 

 F ____J_____V

h 4- 

CALHOUN! WEBSTER] HAM.LTON

GREl^NE X. | STORY 

. ./ ' ^OONE I >

--

. JOHffSON I CEDAR

 ' © I

Iowa City i__ _ 

M*USCA

/ 1 

-fN^AHASKA I* v.X

L_

. ^ I L.__-J-

^ .1 /

4 £ *l f

 , x. i * * *

|>MADI30N | W^REN | \

 - - -.--i ^-

42

Figure 9. Portion of map MF-1835-H, selected Paleozoic shales (map B).
14 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

SYSTEM

'ENNSYLVANIAN 

(PART)

FISSIPPIAN 

CO 

CO

5

1

DEVON

SILURIAN

z

o

ORDOVI

<r

Is.

SERIES

I

_j

v_ 

CX

ex

D

1

Desmoinesian

Atokan

Morrowan 

Chesterian

Meramecian

Osagean

Kinderhookian

Upper

Middle

Lower

Upper

Middle

Lower

8. 

ex

0)

r

o5 

I

Cincinnatian

Champlainian

Canadian

Trempealeauan

Franconian

Dresbachian

LITHOLOGY

i i i i i i i i i i

i i i i i i i i i i

i i i i i i i i i i

i i i i i i i i i i

'I'l'i'i'i'i'i'i'i'i

i i i i i i i i ii

/ / / / /i i i i i

/ / / / / i i i i i

/ / / / /i i i i i

/ / / / / i i i i i

i i i i i i i i i i

i i i i i i i i i i

! I 1 III .!._! L._Q_

I 1 l' t' i' /' /' l' /' /' l'

//////////

NAME

Cherokee Group

Cane Hill Member of 

NJHale Formation

Ste. Genevieve, St. Louis, 

Salem, and Ullin Limestones

Warsaw Formation

Keokuk and Burlington 

Limestones

 yJMorthview Formation Choutoau 

\ Group

Chattanooga Shale

Maquoketa Shale or Group

Galena Group or 

Viola and Kimmswick 

Limestones

->^Decorah Formation

Platteville and Plattin 

^Limestones

\Glenwood Shale

\St. Peter Sandstone

^Davis Formation 

/^Bonneterre or

Eau Claire Formation

^Lamotte or

Mount Simon Sandstone

Figure 10. Stratigraphic relationship of selected shale units and principal carbonate units in the northern Midcontinent region and their relation to sandstone aquifers. Blank sections are formations not pertinent to this report. Names 

and series assignments are in current usage by participating State geological surveys. Modified from Adler (1986).
95°

MISCELLANEOUS FIELD STUDIES MAPS (MF SERIES)

94° 93°

15

92°

43

Figure 11. Portion of map I-1853-A, Precambrian basement map. Original map is multicolor.
16 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

combined with other potential ore controls such as faults, 

folds, or regional distribution of shales as underlying windows or overlying caprocks. The reason for control by the 

limestone-dolostone interface is not known, but such control 

does seem to be empirically valid (Pratt and others, 1984).

It is widely agreed that the Midcontinent MVT deposits 

are of hydrothermal origin, and a more direct indicator of 

hydrothermal activity in some places is coarsely crystalline, 

sparry dolomite not the same as the regional, diagenetic 

dolostone discussed in the previous paragraphs. Occurrences 

of sparry dolomite reported on drill logs are indicated on the 

Cambrian and Ordovician maps.

MISCELLANEOUS INVESTIGATIONS 

SERIES MAPS (I SERIES)

I-1853-A: PRECAMBRIAN BASEMENT MAP 

OF THE NORTHERN MIDCONTINENT

Map compiled by Paul K. Sims

This map (fig. 11) was compiled from 1:500,000-scale 

maps contributed by the respective State geological surveys 

showing basement drill holes, lithotypes or geologic map 

units, and basement topography, contoured at 200-ft intervals (500- and 1,000-ft intervals in the Illinois Basin). In 

compiling the map, available aeromagnetic and gravity 

anomaly maps were used to help define the trend, extent, and 

boundaries of individual rock bodies. The completed map 

shows basement topography, structure, and principal lithologic terranes comprising more than 50 individual units. The 

principal geologic contribution resulting from this compilation is the recognition and delineation of a major, buried, 

northwest-trending Early Proterozoic orogen, named the 

Central Plains orogen (Sims and Peterman, 1986). It extends 

from Nebraska through Kansas into Missouri, where it is 

overlapped by Middle Proterozoic rhyolite-granite terranes, 

and it sharply truncates Archean rocks and an older Proterozoic erogenic (Penokean) belt in the inner part of the craton.

The 1-1853 series consists of map I-1853-A only.

1-2214: PRECAMBRIAN BASEMENT MAP

OF THE TRANS-HUDSON OROGEN AND

ADJACENT TERRANES

Map compiled by P.K. Sims, Zell E. Peterman, 

T.G. Hildenbrand, and Shannon Mahan

The Trans-Hudson orogen (Hoffman, 1981) is a 

deformed, generally north-trending erogenic belt of Early 

Proterozoic age that extends from outcrop areas in the Canadian Shield southward beneath Phanerozoic strata into the 

subsurface of the Northern Great Plains of the United States.

It consists of Early Proterozoic, mainly arc-related rocks 

(Lewry and others, 1985; Green and others, 1985) and 

Archean rocks. The orogen separates two major Archean 

cratons, the Superior on the east and the Wyoming on the 

west, and represents a major constructional phase in the 

assembly of Laurentia (Hoffman, 1988), the North American 

craton. It terminates against the younger Early Proterozoic 

Central Plains orogen in southern South Dakota (Sims and 

Peterman, 1986; Bickford and others, 1986).

This Precambriari basement map of the area enclosed 

by lat 42°-49° N. and long 96°-106° W. (fig. 12) was prepared as a companion to the basement map of the northern 

Midcontinent region, described above (Sims, 1990), in order 

to provide a better geologic framework of the Precambrian 

basement in the North-Central United States. It was compiled from drill-hole data and magnetic and gravity data. The 

States submitted l:l,000,000-scale maps or other records 

showing basement drill holes and lithotypes; in addition, the 

Nebraska and North Dakota Geological Surveys submitted 

l:l,000,000-scale maps showing basement topography, contoured at 200-ft intervals. J.S. Klasner submitted a map and 

report on the basement rocks of North Dakota and South 

Dakota, prepared under an earlier Federal-State contract. In 

addition, the geologic map of that part of eastern South 

Dakota and Nebraska between lat 42° N. and lat 46° N. and 

east of long 100° W. was revised because of the availability 

of some new drill-hole data and new gravity and aeromagnetic data. This area, together with a narrow strip of Minnesota and Iowa, was included in the earlier basement map of 

the northern Midcontinent (Sims, 1990). A report by Faircloth (1988) provided petrologic and geochemical data on 

several basement drill-core samples in North Dakota, South 

Dakota, and Minnesota.

One of the authors (TGH) compiled digital aeromagnetic and gravity maps of the Northern Great Plains at the 

compilation scale; Lindrith Cordell compiled a magnetic 

potential terrace map (Cordell and McCafferty, 1989) at a 

scale of 1:2,000,000 for use in the geologic interpretation. 

These geophysical maps were used to define, insofar as possible, the trend, extent, and boundaries of gross geologic 

rock units.

Six major tectono-stratigraphic terranes were delineated 

for the first time in the map area, from oldest to youngest:

1. Archean gneiss terrane of Superior craton (3,600- 

2,600 Ma);

2. Archean gneiss terrane of Wyoming craton (3,400- 

2,500 Ma);

3. Archean greenstone-granite terrane of Superior craton 

(2,750-2,600 Ma);

4. Wisconsin magmatic terranes of Penokean orogen 

(1,890-1,840 Ma);

5. Trans-Hudson orogen (1,910-1,800 Ma) (exclusive of 

older continental-margin rocks; and

6. Central Plains orogen (1,800-1,630 Ma).
MISCELLANEOUS INVESTIGATIONS SERIES MAPS (I SERIES) 17

101°

45'

r ~ Vv- ZL.-A/ j. -

M jWf XWoTSDrini^r,- .^7 ~~^~~,

i&vvmtx. '\$\>\W*vs&

a\^?*m*

^ ^s&afrr^&ZX&X

Figure 12. Portion of map 1-2214, Precambrian basement map of the Trans-Hudson orogen. Original map is multicolor.
18 MIDCONTINENT STRATEGIC AND CRITICAL MINERALS PROJECT SUMMARY, BACKGROUND INFORMATION

In addition, the Sioux Quartzite forms a coherent, platform sedimentary body unconformably overlying Early Proterozoic and Archean rocks in eastern South Dakota and a 

small adjacent part of Nebraska and Iowa.

A 53-page pamphlet accompanying this map includes 

selected published and unpublished age data, well records 

used in constructing the maps (except for Minnesota and 

Iowa), and a brief discussion of mineral resource potential in 

the Trans-Hudson orogen.

REFERENCES CITED

Adler, F.J., 1986, Correlation of stratigraphic units of North America (COSUNA) project Mid-Continent region: American 

Association of Petroleum Geologists, 1 sheet.

Anderson, R.R., compiler, 1988, Phanerozoic structural features in 

the northern Midcontinent, U.S.A.: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1835-E, scale 

1:1,000,000.

Anderson, R.R., and Ludvigson, G.A., 1986, Baraboo interval 

quartzite in Washington County, Iowa, in Greenberg, J.K., and 

Brown, B.A., eds., Proterozoic Baraboo Interval in Wisconsin: 

Geoscience Wisconsin, v. 10, p. 15-27.

Berendsen, Pieter, and Barczuk, Andrzej, 1993, Petrography and 

correlation of Precambrian clastic sedimentary rocks associated with the Midcontinent rift system, in Day, W.C., and Lane, 

D.E., eds., Strategic and Critical Minerals in the Midcontinent 

Region, United States: U.S. Geological Survey Bulletin 

1989-E, 20 p.

Bickford, M.E., Van Schmus, W.R., andZietz, Isidore, 1986, Proterozoic history of the Midcontinent Region of North America: 

Geology, v. 14, p. 492-496.

Brockie, D.C., Hare, E.H., Jr., and Dingess, P.R., 1968, The geology and ore deposits of the Tri-State district of Missouri, Kansas, and Oklahoma, in Ridge, J.D., ed., Ore Deposits of the 

United States, 1933-1967 (Graton-Sales Volume): New York, 

American Institute of Mining, Metallurgical, and Petroleum 

Engineers, v. 1, p. 400^430.

Cordell, Lindrith, and McCafferty, A.E., 1989, A terracing operator 

for physical property mapping with potential field data: Geophysics, v. 54, p. 621-634.

Desborough, G.A., 1992, Mineralogical and geochemical analysis 

of the metal- and organic-rich Grassy Creek Shale of the New 

Albany Group (Upper Devonian and Lower Mississippian) in 

Hardin County, southern Illinois, in Day, W.C., and Lane, 

D.E., eds., Strategic and Critical Minerals in the Midcontinent 

Region, United States: U.S. Geological Survey Bulletin 

1989-C, 9 p.

Desborough, G.A., Hatch, J.R., and Leventhal, J.S., 1992, Some 

mineralogical and geochemical aspects of Middle and Upper 

Pennsylvanian marine black shales in part of the Midcontinent 

region, in Day, W.C., and Lane, D.E., eds., Strategic and Critical Minerals in the Midcontinent Region, United States: U.S. 

Geological Survey Bulletin 1989-B, 21 p.

Diehl, S.F., and Goldhaber, M.B., in press, Feldspar diagenesis in 

Cambrian clastic rocks of the southern Ozark Mountains and 

Reelfoot rift, southeastern Missouri and northeastern

Arkansas Implications for Mississippi Valley-type ore genesis, in Day, W.C., and Lane, D.E., eds., Strategic and Critical 

Minerals in the Midcontinent Region, United States: U.S. 

Geological Survey Bulletin 1989-F.

Faircloth, S.L., 1988, Precambrian basement rock from North 

Dakota, South Dakota, and western Minnesota A petrologic 

and geochemical analysis of 51 drill core samples: Rapid City, 

South Dakota School of Mines and Technology M.S. thesis, 

part II, 49 p.

Green, A.G., Weber, W., and Hajnal, Z., 1985, Evolution of Proterozoic terrains beneath the Williston Basin: Geology, v. 13, p. 

624-628.

Grogan, R.M., and Bradbury, J.C., 1968, Fluorite-zinc-lead deposits of the Illinois-Kentucky mining district, in Ridge, J.D., ed., 

Ore Deposits of the United States, 1933-1967 (Graton-Sales 

Volume): New York, American Institute of Mining, Metallurgical, and Petroleum Engineers, v. 1, p. 370-399.

Heyl, A.V., 1968, The Upper Mississippi Valley base-metal district, in Ridge, J.D., ed., Ore Deposits of the United States, 

1933-1967 (Graton-Sales Volume): New York, American 

Institute of Mining, Metallurgical, and Petroleum Engineers, v. 

1, p. 431-459.

Hills, F.A., Scott, R.W., Jr., Armbrustmacher, T.J., and Berendsen, 

Pieter, 1991, Map showing distribution of alkaline igneous 

rocks and associated carbonatites and peridotites in the northern Midcontinent, U.S.A.: U.S. Geological Survey Miscellaneous Field Studies MapMF-1835-F, scale 1:1,000,000.

Hoffman, P.P., 1981, Autopsy of Athapuscow Aulacogen A 

failed arm affected by three collisions, in Campbell, F.H.A., 

ed., Proterozoic Basins of Canada: Geological Survey of Canada Paper 81-10, p. 97-102.

 1988, United plates of America, the birth of a craton Early 

Proterozoic assembly and growth of Laurentia: Annual 

Reviews Earth and Planetary Sciences, v. 16, p. 543-603.

Jorgensen, D.G., 1992, Paleohydrology of the Central United 

States, in Day, W.C., and Lane, D.E., eds., Strategic and Critical Minerals in the Midcontinent Region, United States: U.S. 

Geological Survey Bulletin 1989-D, 32 p.

Jorgensen, D.G., Helgesen, J.O., Leonard, R.B., and Signer, D.C., 

1986, Equivalent freshwater head and dissolved-solids concentration of water in rocks of Cambrian, Ordovician, and Mississippian age in the northern Midcontinent, U.S.A.: U.S. 

Geological Survey Miscellaneous Field Studies Map 

MF-1835-B, scale 1:1,000,000.

Leach, D.L., and Rowan, E.L., 1986, Genetic link between Ouachita foldbelt tectonism and the Mississippi Valley-type lead-zinc 

deposits of the Ozarks: Geology, v. 14, p. 931-935.

Lewry, J.F., Sibbald, T.I., and Schledewitz, D.C.P., 1985, Variation 

in the character of Archean rocks in the western Churchill 

Province and its significance, in Ayres, L.D., Thurston, P.C., 

Card, K.D., and Weber, W., eds., Evolution of Archean 

Supracrustal Sequences: Geological Association of Canada 

Special Paper 28, p. 239-261.

Marvin, R.F., compiler, 1988, Radiometric ages of basement rocks 

in the northern Midcontinent, U.S.A.: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1835-C, scale 

1:1,000,000.

Mugel, D.N., compiler, 1986, Map showing availability of data for 

selected deep drill holes in the northern Midcontinent, U.S.A.:
REFERENCES CITED 19

U.S. Geological Survey Miscellaneous Field Studies Map 

MF-1835-A, scale 1:1,000,000.

Mugel, D.N., and Pratt, W.P., 1991, compilers., Lithologic cross 

sections of Phanerozoic rocks in the northern Midcontinent, 

U.S.A.: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-1835-G, scale 1:1,000,000.

Nuelle, L.M., Day, W.C., Sidder, G.B., and Seeger, C.M., 1992, 

Geology and mineral paragenesis of the Pea Ridge iron ore 

mine, Washington County, Missouri, in Day, W.C., and Lane, 

D.E., eds., Strategic and Critical Minerals in the Midcontinent 

Region, United States: U.S. Geological Survey Bulletin 

1989-A, lip.

Palmer, J.R., and Hayes, T.S., 1989, Late Cambrian lithofacies and 

their control on the Mississippi Valley-type mineralizing system in the Ozark region [abs.], in Schindler, K.S., ed., U.S. 

Geological Survey Research on Mineral Resources, 1989, Fifth 

Annual V.E. McKelvey Forum on Mineral and Energy 

Resources: U.S. Geological Survey Circular 1035, p. 51-54.

Pratt, W.P., compiler, 1987, Isopach and lithofacies map of the 

Sauk sequence (excluding basal elastics) in the northern Midcontinent, U.S.A.: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-1835-D, scale 1:1,000,000.

 compiler, 1992, Maps showing areal extent of selected Paleozoic shales in the northern Midcontinent, U.S.A.: U.S. Geological Survey Miscellaneous Field Studies Map MF-1835-H, 

scale 1:1,000,000.

 in press, Regional potential of selected Paleozoic carbonate 

units in the northern Midcontinent for undiscovered Mississippi Valley-type deposits, in Day, W.C., and Lane, D.E., eds., 

Strategic and Critical Minerals in the Midcontinent Region, 

United States: U.S. Geological Survey Bulletin 1989-G.

Pratt, W.P., Erickson, R.L., Kisvarsanyi, E.B., and Wharton, H.M., 

1984, Maps showing areas of significant metallic mineralresource potential in the Rolla I°x2° quadrangle, Missouri: 

U.S. Geological Survey Miscellaneous Field Studies Map 

MF-1005-A, scale 1:250,000.

Pratt, W.P., and Goldhaber, M.B., eds., 1990, U.S. Geological Survey Missouri Geological Survey Symposium, MineralResource Potential of the Midcontinent, St. Louis, Missouri, 

April 11-12, 1989, Program and Abstracts: U.S. Geological 

Survey Circular 1043, 42 p.

Pratt, W.P., and Sims, P.K., eds., 1990, The Midcontinent of the 

United States Permissive terrane for an Olympic Dam-type 

deposit?: U.S. Geological Survey Bulletin 1932, 81 p.

Pratt, W.P., and Wandrey, C.J., compilers, in press, Isopach and 

carbonate-ratio maps of selected Paleozoic carbonate units in 

the northern Midcontinent, U.S.A.: U.S. Geological Purvey 

Miscellaneous Field Studies Map MF-1835-1, scale 

1:1,000,000.

Setterholm, D.R., Morey, G.B., and Southwick, D.L., 1987, Stratigraphy and geochemistry of the Cretaceous rocks of southwestern Minnesota: Minnesota Geological Survey, Open-File 

Report, March 19,1987, 85 p. plus 5 maps and 2 cross sections, 

scale 1:250,000.

Signor, D.C., Kontis, A.L., Jorgensen, D.G., and Mandle, R.L., 

1980, Ground-water flow regimes based on preliminary data: 

Eos, v. 61, no. 46, p. 952.

Sims, P.K., compiler, 1990, Precambrian basement map of the 

northern Midcontinent, U.S.A.: U.S. Geological Survey Miscellaneous Investigations Series Map I-1853-A, scale 

1:1,000,000.

Sims, P.K., Kisvarsanyi, E.B., and Morey, G.B., 1987, Geology and 

metallogeny of Archean and Proterozoic basement terra nes in 

the northern Midcontinent, U.S.A. An overview: U.S. Geological Survey Bulletin 1815, 51 p.

Sims, P.K., and Peterman, Z.E., 1986, Early Proterozoic Central 

Plains orogen a major buried structure in the North-Central 

United States: Geology, v. 14, p. 488-491.

Sims, P.K., Peterman, Z.E., Hildenbrand, T.G., and Mahan, Shannon, 1991, Precambrian basement map of the Trans-Hndson 

orogen and adjacent terranes, northern Great Plains, U.S.A.: 

U.S. Geological Survey Miscellaneous Investigations Series 

Map 1-2214, scale 1:1,000,000.

Sloss, L.L., 1982, The Midcontinent Province United Stages, in 

Palmer, A.R., ed., Perspective in Regional Geological Synthesis Planning for "The Geology of North America:" Geological Society of America, DNAG Special Publication 1, p. 

27-39.

Snyder, F.G., 1968, Geology and mineral deposits, Midcortinent 

United States, in Ridge, J.D., ed., Ore Deposits of the United 

States, 1933-1967 (Graton-Sales Volume): New York, American Institute of Mining, Metallurgical, and Petroleum Engineers, v. 1, p. 257-286.

Snyder, F.G., and Gerdemann, P.E., 1968, Geology of the Southeast Missouri lead district, in Ridge, J.D., ed., Ore Deports of 

the United States, 1933-1967 (Graton-Sales Volume): New 

York, American Institute of Mining, Metallurgical, and 

Petroleum Engineers, v. 1, p. 326-358.

Published in the Central Region, Denver Colorado 

Manuscript approved for publication April 3, 1995 

Edited by Richard W. Scott, Jr. 

Graphics prepared by Wayne Hawkins 

Photocomposition by Mari L. Kauffmann

.S. GOVERNMENT PRINTING OFFICE: 1995-673-046/86121
OKLAHOMA KANSAS

SOUTH

CONTROL-^

WELL

LOCATIONS

36° 37° 38° 39°

otal depth, in Feet)

2.OOO FT1.OOO FTSEA LEVEL-

-1,O OOF T-

- 2,OOO FT

-3.OOOFT-

-4.OOO FT-

-5.OOOFT

-6,OOOFT-t

-7.OOO F T-

-8,OOO FT-

- 9,OOO FT-

-1QOOO FT-

-11,OOO FT

I I I II I I I I

SEDGWICK 8 3 

BASIN ~ °

TEJAS nr