An Extensive

Pre-Cretaceous Weathering Profile in

East-Central and Southwestern Minnesota

U.S. GEOLOGICAL SURVEY BULLETIN 1 ?89-H
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Chapter H

An Extensive

Pre-Cretaceous Weathering Profile in

East-Central and Southwestern Minnesota

By Dale R. Setterholm and G.B. Morey

U.S. GEOLOGICAL SURVEY BULLETIN 1989

STRATEGIC AND CRITICAL MINERALS IN THE MIDCONTINENT REGION, 

UNITED STATES

WARREN C. DAY AND DIANE E. LANE, Editors
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Published in the Central Region, Denver, Colo. 

Manuscript approved for publication May 18, 1995. 

Photocomposition by Carol A. Quesenberry.

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.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1995

For sale by

U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Setterholm , Dale R.

An extensive pre-Cretaceous weathering profile in east-central and 

southwestern Minnesota / by Dale R. Setterholm and G.B. Morey.

p. cm. (U.S. Geological Survey bulletin ; 1989) 

(Strategic and critical minerals in the midcontinent region, United 

States ; ch. H)

Includes bibliographical references.

Supt. of Docs. no. : I 19.3 : 1989-H

1. Weathering Minnesota. 2. Saprolites Minnesota. 

I. Morey, G.B. II. Title. III. Series. IV. Series : Strategic and 

critical minerals in the midcontinent region, United States ; ch. H. 

QE75.B9 no. 1989-H 

[QE570] 

557.3s dc20

[551.3'02'09776] 95-30813

CIP
CONTENTS

Abstract HI

Introduction HI

Methodology H2

Mesozoic paleogeography H3

General description of the weathering profiles

Discussion H9

Mineralogical attributes of the model H9

Slightly weathered zone H9

Saprock H9

Saprolith H10

Pisolitic lateritic clay H23 

Chemical attributes of the model H23 

Summary H 26 

Economic implications H27 

References cited H29

H6

FIGURES

HI. Index map of Minnesota showing the approximate distribution of saprolith

and associated weathering products H2 

H2. Map of the St. Cloud area, east-central Minnesota, showing the locations of

drill holes discussed in the text H2 

H3. Map of the Redwood Falls-Morgan area along the Minnesota River Valley

showing the locations of drill holes discussed in the text H3 

H4. Representative X-ray diffraction diagrams of the <2 fim clay fraction from

the St. Augusta site in east-central Minnesota H4 

H5-H12. Summary of the principal facts regarding the weathering profile at the:

H5. Cold Spring site H10

H6. St. Joseph site Hll

H7. St. Augusta site H12

H8. Redwood Falls 1 site H13

H9. Redwood Falls 2 site H14

H10. Redwood Falls 3 site HIS

Hll. Morgan 1 site HIS

HI2. Morgan 2 site H16 

H13-H15. Whole-rock chemical trends at the:

H13. St. Cloud area sites H17

HI4. Redwood Falls sites HIS

HI5. Morgan sites H19 

H16-H18. Chemical characteristics of the:

H16. St. Cloud area weathering profiles H20

H17. Redwood Falls weathering profiles H21

HIS. Morgan 1 and Morgan 2 weathering profiles H22 

HI9. Plots of modal proportions of mineral constituents in samples,

ordered by CIA values H24

Contents III
H20. Plots of relative proportions of clay-sized material versus CIA H26 

H21. Ternary diagrams in the A12O3 CaO+Na2O K2O and

A12O3 CaO+Na2O+K2O FeO+MgO fields showing chemical trends in the

weathering of granitic rocks H28 

H22. Physical stratigraphy of the in-situ and reworked weathering

products H29

TABLES

HI. Chemical analysis of saprolith and associated weathering products H6

H2. Nature of protolith at St. Cloud area sites H9

H3. Nature of protolith at Redwood Falls area sites H9

IV Contents
STRATEGIC AND CRITICAL MINERALS IN THE MIDCONTINENT REGION, UNITED STATES

An Extensive Pre-Cretaceous Weathering Profile in 

East-Central and Southwestern Minnesota

By Dale R. Setterholm1 andG.B. Morey1

Abstract

A thick mantle of residual weathering products covers 

crystalline bedrock of Archean to Early Proterozoic age in 

much of western Minnesota. Within the residuum there is a 

typical sequence of four lithologic units representing progressively more weathered material upward from the fresh bedrock 

surface. From bottom to top, they are (1) a zone of very slightly 

weathered bedrock that exhibits very few visible effects of 

weathering; (2) saprock, or weathered bedrock that is firm but 

distinctly altered; (3) saprolith that is typically so weak it can 

easily be crushed by hand but that mostly retains the structures 

and textures of the parent rock; and (4) a hard lateritic clay 

characterized by iron oxide-rich pisolites. This sequence may 

be partly eroded and (or) overlain by Cretaceous or Quaternary 

deposits. In some places the Cretaceous deposits consist of relatively pure kaolinitic shale derived from the reworking of the 

pre-Cretaceous saprolith.

Because the composition of these weathering products is, 

in part, controlled by the composition of the parent rock, heterogeneity in the parent rock typically persists as heterogeneity 

in the composition of the weathering profiles. For example, 

amphibolite rafts within a granitic gneiss result in pods of chloritic saprolith within predominantly kaolinitic saprolith. Fracture sets, joints, cleavage planes, and schistosity also exert a 

strong influence on the path and rate of chemical weathering 

and lead to anisotropic weathering patterns and complex mineral distribution patterns.

In spite of many complexities it is possible to distinguish 

an orderly sequence of chemical processes that can be related 

to the stages of weathering described above. Three main trends 

are apparent: (1) loss of CaO, Na2O, I<2O, and some SiC>2; (2) 

gain in carbon dioxide; and (3) relative gains or no change in 

Fe2C>3, MgO, TiC>2, Al2C>3, and water content. These chemical changes are consistent with the ferrallitic weathering trend 

(Chesworth, 1992) characteristic of stable landscapes in the 

humid tropics. The correlation of chemical alteration indices 

with modal mineralogy makes it apparent that the loss of 

Na2O, CaO, K2O, and possibly some silica corresponds with 

the progressive disappearance of first plagioclase, and then

'Minnesota Geological Survey, University of Minnesota, St. Paul, 

MN 55114-1057.

potassium feldspar. With continued weathering more potassium is lost as potassium feldspar continues to dissolve. Total 

iron content is more or less constant in the lower two-thirds, 

but increases appreciably in the upper third of most profiles. 

This probably reflects the breakdown of hornblende and 

biotite and the concurrent release of ferrous iron, which 

migrates toward the upper part of the profile, where oxidizing 

conditions are encountered and it is fixed as a ferric oxide. 

Diagenetic modifications of these weathering processes typically add SiC>2, CC>2, Fe2C>3, and MgO to the upper parts of 

weathering profiles, where they form oxides, carbonates, or 

clay minerals such as smectites. Potential users of kaolinite 

require a deposit that is thick, widespread, rich in kaolin, and 

relatively free of impurities that would tend to color the 

deposit. The upper part of the saprolitic interval where the 

most intense chemical weathering has occurred best meets 

these needs. However, diagenetic changes are also most likely 

to occur in this zone and the user must expect that at least 

some beneficiation will be necessary.

Natural gamma logging is a quick and inexpensive 

means of recognizing weathering products, evaluating the 

degree of weathering, and measuring the extent of the 

deposit. In weathered terranes the predominant clay mineral 

is kaolinite, and because it contains no potassium (or uranium 

or thorium), the parts of the profile richest in kaolinitic clay 

have the lowest gamma values. In general, gamma values 

increase with depth through the saprolith and saprock and 

into the protolith. The effects of uranium and thorium are typically confined to gamma peaks associated with veining in 

the protolith or bauxitic intervals.

INTRODUCTION

A thick mantle of saprolith and associated weathering products covers crystalline bedrock of Archean and 

Proterozoic age in much of central and western Minnesota 

(fig. HI). The profile is typically more weathered upward 

from fresh bedrock to an erosion surface now covered by 

strata of Late Cretaceous to postglacial age. In many 

places the profile is overlain by an interval of relatively 

pure kaolinitic clay produced by the local reworking of the 

saprolith in Late Cretaceous time.

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H1
92°

0 50 100 MILES 

H ' 

0 30 60 KILOMETERS

Figure HI. Index map of Minnesota showing the approximate distribution of saprolith and associated weathering products (modified from Parham, 1970). The areas of figures H2 

and H3 are shown as black rectangles.

Although this kaolinite-rich saprolith was first recognized in outcrops in 1872 (Winchell, 1874), and interest in 

the commercial development of this resource followed 

shortly thereafter and cyclically since (Upham, 1888; Hall, 

1899; Hall and others, 1911; Grout and Soper, 1919; Bickford and Price, 1947; Parham, 1970; Setterholm and others, 1989; Hauck and others, 1990), very little has been 

written about the attributes and geologic history of the 

weathering profile. Much of our knowledge of the processes responsible for its origin was established by S.S. 

Goldich in a 1936 University of Minnesota doctoral dissertation (Goldich, 1938) that led to the development of the 

"Goldich stability series."

This report summarizes petrographic, mineralogic, and 

geochemical properties of the weathering profile as observed 

at eight localities: three near St. Cloud in east-central Minnesota (figs. HI and H2) and five in the Redwood FallsMorgan segment of the Minnesota River Valley in southwestern Minnesota (figs. HI and H3). This work was undertaken to provide an understanding of the geologic controls 

on kaolin occurrence and grade in Minnesota. Others (Prasad 

and Reid, 1989; Hauck and others, 1990) undertook associated studies of the usefulness of these deposits and means of 

processing them for industrial use.

METHODOLOGY

Detailed mapping, particularly along the Minnesota 

River Valley in southwestern Minnesota, has shown that 

the crystalline bedrock in most upland areas has a weathering profile averaging 30 m in thickness, though profiles 

are locally as thick as 60 m (Parham, 1970). Weathered 

materials are considerably thinner on steep-sided slopes 

and along valleys cut into the bedrock surface.

Data for this report were acquired principally to support the possible economic development of kaolinite 

resources in the State. Therefore, emphasis was given to 

areas known to be underlain by quartzofeldspathic igneous 

and metamorphic rocks, particularly where the combined 

Cretaceous to Quaternary cover was less than 30 m thick. 

Actual drilling sites were established from local subsurface

94°00' Figure H2. Map of the St.

Cloud area, east-central Minnesota, showing the locations of 

drill holes discussed in the text. 

CS-1, Cold Spring 1; SA-1, St. 

Augusta 1; SJ-1, St. Joseph 1.

H2 Strategic and Critical Minerals, Midcontinent Region, U.S.
95°00' Figure H3. Map of the Redwood Falls-Morgan area along 

the Minnesota River Valley 

showing the locations of drill 

holes discussed in the text. 

MNE-1, Morgan 1; MNE-2, 

Morgan 2; RF-1, Redwood Falls 

1; RF-2, Redwood Falls 2; RF-3, 

Redwood Falls 3. Weathering 

products are mined at the locations indicated by the crossedpick symbol.

information, principally the written logs of water-well 

drilling contractors in the files of the Minnesota Geological Survey. Details of the entire site-selection process, as 

well as the complete data base, are given in Setterholm 

and others (1989).

In all, 291 m of weathered residuum and fresh rock 

were collected and studied. Continuous cores (HX size) 

having recoveries averaging around 90-95 percent were 

visually examined in detail, both in the field and again in 

the laboratory. Thin sections of the parent rocks were prepared and examined by standard microscopy. Descriptions 

of the cores were used to select samples 12-30 cm in 

length for subsequent petrographic, textural, X-ray diffraction, and major and minor element chemical analyses 

(table HI). Fifty-five X-ray diffraction analyses (example 

in fig. H4) were performed, including air-dried, glycolated, cation saturated, and heated samples. The clay mineral determinations from this work are qualitative. The 

relative amount of each mineral was estimated from both 

the intensity and area enclosed by the diffraction peaks. 

Because of the framework nature of this study no investigation of the crystallinity of the kaolinite was undertaken. 

Also, because many samples contained more than one clay 

type it was not always possible to determine exactly which 

clay was present at a given site within that core sample. 

The amount of clay in each core sample was roughly measured by disaggregating it in a sodium pyrophosphate 

solution and then sieving.

In addition to the analyses listed above, down-hole 

natural gamma methods were used to further characterize 

the weathering profile at each test site. The methodology 

responds principally to the amount of potassium in the 

profile. Thus, the upper part of an ideal profile where 

kaolinite is abundant is marked by low gamma values; 

the gamma response typically increases with depth

through the saprolith, saprock, weathered rock, and into 

the parent material. Lateritic clay at the top of the weathering profile is generally a good gamma-emitter because 

thorium concentrates in it as a lag during weathering (R.S. 

Lively, oral commun., 1994).

Lastly, as a means of rapidly summarizing the 

chemical attributes of various parts of the weathering profile, we have relied heavily on the use of the chemical 

index of alteration (CIA) of Nesbitt and Young (1982). 

This index, calculated from whole-rock chemical data, 

measures the ratio of A^C^ to A^C^ plus K^O plus Na2O 

plus CaO. As Goldich (1938) showed, chemical weathering predominantly involves the dissolution of feldspars 

and the concurrent removal of calcium, sodium, and potassium from the weathering profile by through-flowing solutions. As the rock weathers, alumina is concentrated in the 

remaining residue and thus is available to form kaolinite. 

Thus, CIA values increase as weathering progresses. Unaltered granitic rocks typically have CIA values between 45 

and 55; kaolinite-rich units have values approaching 100.

MESOZOIC PALEOGEOGRAPHY

The precise age of the weathering profile and rate at 

which it was produced remain unresolved. The profile is 

overlain by strata of Late Cretaceous (Cenomanian to 

Coniacian) age (Setterholm, 1994), but paleomagnetic data 

(Tyler and Bailey, 1961; and Symons, 1966) for oxidized 

and leached materials imply that weathering may have 

started on the Mesabi iron range in northern Minnesota 

(Morey, 1983) in the latter part of Late Jurassic time.

From the mid-Jurassic to the early part of the Late 

Cretaceous, much of what is now western Minnesota was 

most likely a moderately dissected upland characterized on

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H3
a regional scale by rounded hills separated by interfluves 

having a total relief of about 4CM-5 m (Parham, 1970). 

However, the front that separates weathered from fresh 

material had, at least locally, a considerably different configuration. For example, the weathering profile in the St. 

Joseph area (fig. H2) extends to a depth of more than 36 

m, but fresh dimension stone is quarried in the same rock 

type at the land surface less than 0.5 km away.

The position of the weathering front was controlled 

in large part by regional hydraulic gradients related to

paleotopography and climate. However, the permeability of 

the weathering profile itself, once it began to develop, had 

an effect on local hydraulic gradients. Where the bedrock 

is dominated by granitic rocks, both nearly vertical, 

orthogonal joints, and nearly horizontal sheeting joints 

served as the predominant channelways for ground-water 

movement. Where the bedrock is dominated by gneissic 

rocks, ground water flow also followed cleavage planes, 

mineral layering, and planes of schistosity. The anisotropic 

structure of the parent material caused ground water to

Depth= CIA= 

17.4 m (57 ft) 97.7

 = '« ig

GO'S "5

12 16

Depth= CIA= 

17.7 m (58 ft) 96.9

20

DEGREES

24

26)

28 32 36 40

N CO

12 16 20 24 28 32 36 40

Depth= CIA= 

19.2 m (63 ft) 96.6

DEGREES (

3

o

Ipm*******

4 8 12

A

16 20

DEGREES

24

(26)

28 32 36 40

Depth=

22.9 m (75 ft) 96.3 o

vw»/^+A«****

.

c ±r

s * *S =

|MM>*IM*'

12 16 20

DEGREES

24

2 6 )

28 32 36 40

Figure H4 (above and facing page). Representative X-ray diffraction diagrams of the <2 urn clay fraction from the St. Augusta site 

in east-central Minnesota. Samples air dried. CIA, chemical index of alteration (Nesbitt and Young, 1982).

H4 Strategic and Critical Minerals, Midcontinent Region, U.S.
flow faster in some directions than in others, and local 

paleohydraulic gradients rarely can be represented by 

straight flow paths. The resulting weathering profiles also 

can be expected to have a marked anisotropic configuration, particularly in the vertical dimension.

Our understanding of climatic conditions during the 

latter part of Mesozoic time in what is now Minnesota is 

rather sketchy. In the Late Jurassic, Minnesota was situated generally between lat. 30° and 40° N. (Dott and Batten, 1981). The climate most likely was arid to semi-arid

as shown by redbeds and associated evaporate deposits in 

northwestern Minnesota and adjoining parts of North 

Dakota and Manitoba (Mossier, 1978). These beds were 

apparently deposited by fluvial processes in channels that 

were graded to the west and southwest (Moore, 1979). In 

the Early Cretaceous, Minnesota was located generally 10° 

farther north between lat 40° and 50° N. in an area 

affected by seasonal monsoon rains (Dott and Batten, 

1981). Parham (1970) suggested that the region was dominated by humid subtropical or tropical conditions. Austin

Depth= CIA= 

29.0 m (95 ft) 75.2

= = N

o o t;

CO CO CO

12

Depth= CIA= 

33.2 m (109 ft) 67.4

16 20 24

DEGREES (29)

28

Chlorite,

vermiculite,

smectite

32 36 40

12 16

Depth= CIA= 

35.1 m (115 ft) 47.4

20

DEGREES

Smectite Illite

32 36 40

12

Depth= CIA= 

36.3 m (119 ft) 47.4

16 20 24

DEGREES (29)

28

Smectite £

32 36 40

1 1

4 8

i

12

i

16

i

20

DEGREES

i

24

(29)

i

28

i

32

i i

36 40

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H5
(1970) concurred with the idea that humid tropical conditions persisted through early Cenomanian time, but suggested that a significant shift from tropical to temperate 

climate took place after the weathering profiles had formed 

and prior to the advance of Late Cretaceous seas into Minnesota in late Cenomanian time. It is this climatic shift, 

combined with an increase in the height of the water table 

and the concurrent development of stagnant ground-water 

conditions, that brought to an end the period of intense 

chemical weathering in Minnesota.

GENERAL DESCRIPTION OF THE 

WEATHERING PROFILES

Approximately 70 m of saprolith and associated 

weathering materials were drilled near St. Cloud in eastcentral Minnesota (fig. H2). The profiles at St. Joseph and 

St. Augusta are developed in granite and quartz monzonite, 

respectively, whereas the profile at Cold Spring is developed in granodiorite (table H2). The profile at St. Joseph is 

complicated by alteration products derived from dikes of 

very coarse grained pegmatite and very fine grained diabasic gabbro. The granodiorite at Cold Spring includes segregations of pegmatitic potassium feldspar and coarse, 

irregularly shaped inclusions of quartz.

Approximately 184 m of saprolith and associated 

weathering products were drilled in the Minnesota River 

Valley. Two cores totaling 77 m of material were obtained 

from two sites north of Morgan and 107 m from three 

sites near Redwood Falls (fig. H3). The Archean bedrock 

that crops out in the valley is a complex migmatitic terrane that varies considerably from place to place. The 

migmatite is intruded at many places by small to large 

plutons of generally quartz monzonitic composition (table 

H3). Thus, the protolith at Morgan 1 is relatively homogeneous and granitic in composition, but the parent material 

at Morgan 2 only 3.35 km from Morgan 1 is a heterogeneous gneiss having amphibolite enclaves interlayered 

with hornblende-rich and hornblende-poor units of tonalitic composition. The gneiss at Redwood Falls is even 

more heterogeneous, with at least three compositionally 

distinct granitic components interlayered on a scale of several centimeters to several meters (table H3). Amphibolite 

enclaves, biotite-rich schlieren, and biotite-rich pegmatites 

are scattered throughout the gneiss, as are segregations of 

coarse-grained potassium feldspar.

The characteristics of each of the weathering profiles 

are most efficiently conveyed graphically. For each drillhole 

a composite figure displays depth-based columns showing: 

(1) the lithologic character of the parent material; (2) the 

subunits of the weathering profile; (3) the location, number, 

and CIA value of samples; (4) the gamma log; (5) the

Table HI. Chemical analysis of saprolith and associated 

weathering products.

[Results in weight percent; column numbers correspond to list at end of table showing drill hole, sample locality, and sample type; NA, not analyzed; LOI, loss on 

ignition; , below detection limit]

SiO,

A1263

CaO

MgO

Na,O

K2O

Total

Fe as

Fe203

FeO

Fe203

TiO2

MnO

P205

LOI H2O+

H2O~

CO,

SiO2

A1203

CaO

MgO

Na2O

K2O

Total

Fe as

Fe203

FeO

Fe203

TiO2

MnO

P2°5

LOI

H2O+

H2O~

CO,

SiO2

A1,O3

CaO

MgO

Na2O

K2O

Total

Fe as

Fe203

FeO

Fe?03

TiO2

MnO

P.,O5

LOI

H2O+

CO2

1

61.0

25.1

0.22

0.16

-

0.13

2.43

1.4

0.87

0.57

~

0.04

9.70

8.9

0.3

0.50

6

68.1

20.5

0.24

0.20

0.02

0.22

2.60

1.3

1.16

0.35

0.03

7.77

7.2

0.3

0.35

11

65.1

18.4

0.16

0.61

0.09

3.20

3.95

2.4

1.28

0.60

0.04

6.85

5.7

0.87

2

66.1

21.3

0.22

0.17

0.02

0.1

3.1

1.6

1.32

0.62

~

0.02

8.31

7.7

0.3

0.11

7

70.0

18.7

0.21

0.44

0.03

1.43

2.23

1.1

1.01

0.31

0.03

6.47

6.1

0.2

0.38

12

65.8

18.9

0.14

0.83

0.07

2.27

4.33

2.8

1.22

0.49

0.03

6.77

6.4

0.67

3

66.7

21.4

0.23

0.17

0.06

0.13

3.06

1.9

0.95

0.48

--

0.05

8.00

7.6

0.3

0.14

8

68.8

17.3

0.24

0.53

0.09

2.82

3.39

1.8

1.39

0.41

0.09

0.05

5.93

5

0.2

0.67

13

69.7

15.6

0.16

0.48

0.22

5.44

2.92

2.1

0.59

0.26

0.02

4.54

3.6

0.89

4

97.0

0.74

0.20

0.04

0.02

0.03

0.32

0.1

0.21

0.08

--

0.02

0.85

NA

NA

NA

9

67.9

16.9

0.68

0.90

2.45

3.38

3.45

1.5

1.78

0.50

0.03

3.77

3.5

0.5

0.02

14

74.1

13.9

0.09

0.17

0.58

7.34

0.71

0.1

0.60

0.12

_

0.02

2.54

2.1

0.1

5

62.9

21.3

0.27

0.26

0.04

0.08

4.70

3.0

1.37

0.55

0.12

0.06

9.31

7.7

0.3

1.41

10

64.3

21.8

0.20

0.20

0.03

0.26

3.36

1.8

1.36

0.57

~

0.02

8.39

7.9

-

0.40

15

74.6

13.7

1.22

0.46

3.07

4.48

1.28

0.4

0.84

0.21

0.07

0.93

0.9

0.03

H6 Strategic and Critical Minerals , Midcontinent Region, U.S.
Table HI. Chemical analysis of saprolith and associated 

weathering products Continued.

Table HI. Chemical analysis of saprolith and associated 

weathering products Continued.

SiO2

A1203

CaO

MgO

Na2O

K2O

Total

Fe as

Fe203

FeO

Fe203

TiO,

MnO

P205

LOI

H2O+

H2O~

CO2

SiO2

A1 203

CaO

MgO

Na2O

K2O

Total

Fe as

Fe203

FeO

Fe,03

TiO,

MnO

P20,

LOI

H2O+

H2O"

C07

SiO2

A1 203

CaO

MgO

NajO

K2O

Total

Fe as

Fe203

FeO

Fe203

TiO2

MnO

P,05

LOI

H2O+

16

71.0

15.0

0.99

0.71

2.41

3.59

2.48

1.4

0.92

0.15

0.12

0.03

3.08

2.6

-

0.60

21

63.5

21.1

0.20

0.22

0.30

0.23

3.79

3.0

0.46

0.42

0.05

9.16

7.6

-

1.52

26

67.7

19.6

0.20

0.27

--

0.57

2.91

1.8

0.91

0.19

0.03

7.62

6.9

17

72.4

15.0

0.75

0.53

3.32

4.79

1.33

0.4

0.89

0.08

0.02

1.85

1.0

0.2

0.09

22

69.2

20.2

0.12

0.10

0.02

0.08

1.96

0.8

1.07

0.35

0.02

7.93

7.3

-

0.29

27

71.5

17.8

0.11

0.13

0.10

3.95

0.67

0.2

0.45

0.14

..

0.02

4.85

4.7

18

73.5

14.0

1.43

0.34

3.67

4.39

1.05

0.4

0.61

0.10

0.04

0.93

0.3

0.1

0.08

23

70.3

20.6

0.13

0.07

0.03

0.08

0.77

0.2

0.55

0.21

0.02

7.77

7.4

--

0.1

28

69.5

14.5

0.28

0.46

0.99

5.90

3.39

2.0

1.17

0.22

_.

0.07

3.77

2.4

19

55.1

24.4

0.20

0.27

0.19

0.09

6.59

5.3

0.70

0.47

0.02

12.0

8.8

--

3.47

24

67.6

21.6

0.12

0.10

0.03

0.06

1.47

0.6

0.8

0.24

0.02

8.16

7.8

-

0.54

29

72.4

15.0

0.51

0.33

3.16

5.50

1.54

0.5

0.98

0.24

..

0.08

1.54

1.3

20

66.0

19.7

0.20

0.20

0.37

0.10

3.70

3.3

0.03

0.43

0.04

8.70

7.2

-

1.64

25

67.7

21.4

0.12

0.11

0.05

0.11

1.49

0.4

1.05

0.21

0.03

8.31

7.7

-

0.19

30

73.5

13.7

0.52

0.39

3.68

4.77

1.78

0.6

1.11

0.35

..

0.10

0.93

1.0 H20" 

CO, 0.98 0.06 1.26 0.32

SiO,

A1 0 63

CaO

MgO

Na,O

K2b

Total

Fe as

Fe2°.

FeO

Fe0 O3

TiO^

MnO

p?os

LOI

H0 0+

H~0'

CO,

SiO,

A1,O3

CaO

MgO

Na,O

K2O

Total

Fe as

Fe2°l

FeO

Fe-A

Tib,

MnO

PA

LOI

H,O+

H~O

CO,

SiO,

Al,63

CaO

MgO

Na,O

K2O

Total

Fe as

Fe2°i

FeO

Fe nO3

Tib,

MnO

P205

LOI

H,O+

H^O"

CO,

31

51.2

23.1

0.38

1.07

0.15

4.09

9.16

5.5

3.05

1.56

0.15

0.08

8.93

7.3

0.3

1.63

36

37.7

17.0

2.38

1.15

0.01

0.12

22.5

18.1

2.38

0.74

0.63

0.87

17.5

6.2

0.2

12.80

41

56.3

17.3

0.61

1.07

0.10

3.81

10.4

7.3

2.29

0.65

0.17

0.07

9.08

5.0

0.2

4.52

32

68.6

15.7

0.26

0.41

0.24

7.12

2.74

1.8

0.74

0.42

0.03

3.31

2.8

0.1

0.60

37

48.0

22.6

0.98

0.76

0.04

0.14

13.5

9.6

2.83

0.81

0.19

0.23

13.0

8.4

0.4

5.09

42

63.1

17.3

1.26

0.73

2.40

5.77

5.12

2.7

2.12

0.62

0.16

3.23

2.7

0.2

0.54

33

59.1

18.6

0.41

0.98

0.40

6.56

7.44

5.1

1.77

0.89

0.10

0.05

5.77

4.2

0.2

1.67

38

49.0

19.6

0.85

1.05

0.03

0.23

14.8

11.1

2.46

0.80

0.24

0.07

13.8

7.1

0.3

7.50

43

65.3

15.7

1.47

0.68

3.04

5.24

4.75

2.4

2.08

0.56

-

0.15

2.39

1.9

0.2

0.55

34

61.0

15.9

1.16

1.19

1.85

5.10

7.64

5.0

2.08

0.86

0.08

0.2

5.23

3.2

0.4

2.33

39

42.1

29.5

0.40

0.60

0.05

0.25

11.5

5.9

4.94

2.07

0.13

0.07

12.9

11.3

0.6

1.27

44

66.7

15.7

1.90

0.69

3.71

5.25

4.21

2.5

1.43

0.54

-

0.15

1.08

0.9

0.1

0.28

35

62.3

16.3

1.98

1.03

3.58

4.20

6.29

3.6

2.29

1.04

-

0.38

2.39

2.2

0.4

0.36

40

48.6

15.7

1.12

1.27

0.11

2.39

17.3

13.0

2.85

0.69

0.37

0.10

12.2

5.1

0.2

8.49

45

55.1

27.9

0.29

0.18

0.04

0.05

2.41

0.6

1.74

0.59

-

0.03

13.0

9.5

0.8

0.02

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H7
Table HI. Chemical analysis of saprolith and associated 

weathering products Continued.

SiO2

A1 203

CaO

MgO

Na2O

K20

Total

Fe as

Fe203

FeO

Fe20,

TiO,

MnO

P2°5

LOI

H2O+

H2O~

CO2

SiO2

A1203

CaO

MgO

Nj^O

K2O

Total

Fe as

Fe203

FeO

Fe203

TiO2

MnO

P2°5

LOI

H2O+

H2O~

CO,

46

32.1

33.4

0.48

0.42

0.07

0.07

13.8

9.4

3.35

1.02

0.15

0.11

18.7

11.3

1.5

5.28

51

44.2

15.4

1.26

1.55

0.05

2.81

19.0

NA

19

0.68

0.72

0.33

14.2

NA

NA

10.6

47

39.6

23.7

0.38

0.50

0.07

0.03

19.7

15.7

2.25

1.08

0.12

0.04

14.1

8.5

0.6

5.03

52

61.7

20.4

0.36

1.07

0.15

5.37

4.13

1.9

2.02

0.78

-

0.22

5.93

5.0

0.3

0.18

48

54.0

19.8

0.48

0.38

0.02

0.02

10.9

8.7

1.23

0.79

0.15

0.04

12.5

7.0

0.4

5.12

53

63.0

17.3

0.61

1.44

0.85

5.43

4.84

2.3

2.28

0.71

-

0.21

4.85

3.6

0.3

0.34

49

55.5

25.7

0.33

0.39

-

0.36

6.13

2.9

2.91

1.00

0.07

10.8

8.4

0.5

0.84

54

65.4

14.6

3.57

1.14

3.3

3.93

3.17

1.5

1.5

0.57

-

0.23

4.16

1.1

0.1

2.40

50

44.5

16.4

1.18

1.47

0.02

1.16

19.0

14.8

2.55

0.72

0.20

0.17

14.9

5.1

0.2

10.2

55

63.0

15.1

3.77

2.17

3.57

3.72

4.48

2.7

1.48

0.61

0.09

0.24

3.23

1.1

-

1.90

Drill hole, sample locality, and sample type:

1. Redwood Falls 1; 92 ft below collar; saprolith.

2. Redwood Falls 1; 110 ft below collar; saprolith.

3. Redwood Falls 1; 121 ft below collar; saprolith.

4. Redwood Falls 1; 122 ft below collar; quartz vein.

5. Redwood Falls 1; 140 ft below collar; saprolith.

6. Redwood Falls 1; 153 ft below collar; saprolith.

Table H1. Chemical analysis of saprolith and associated 

weathering products Continued.

7. Redwood Falls 1; 167 ft below collar; saprolith.

8. Redwood Falls 1; 186.5 ft below collar; weathered gneiss.

9. Redwood Falls 1; 219 ft below collar; weathered gneiss.

10. Redwood Falls 2; 124 ft below collar; saprolith.

11. Redwood Falls 2; 151 ft below collar; saprolith.

12. Redwood Falls 2; 158 ft below collar; saprolith.

13. Redwood Falls 2; 189.5 ft below collar; saprock.

14. Redwood Falls 2; 229 ft below collar; granodiorite gneiss.

15. Redwood Falls 2; 261 ft below collar; granodiorite gneiss.

16. Redwood Falls 3; 155 ft below collar; saprock.

17. Redwood Falls 3; 159.5 ft below collar; saprock.

18. Redwood Falls 3; 192 ft below collar; granodiorite gneiss.

19. Morgan 2; 94.5 ft below collar; saprolith.

20. Morgan 2; 124 ft below collar; saprolith.

21. Morgan 2; 136 ft below collar; saprolith.

22. Morgan 2; 170 ft below collar; saprolith.

23. Morgan 2; 182.5 ft below collar; saprolith.

24. Morgan 2; 186 ft below collar; saprolith.

25. Morgan 2; 201.5 ft below collar; saprolith.

26. Morgan 2; 213.5 ft below collar; saprolith.

27. Morgan 2; 234 ft below collar; saprolith.

28. Morgan 1; 214 ft below collar; saprock.

29. Morgan 1; 242 ft below collar; weathered gneiss.

30. Morgan 1; 256 ft below collar; granitic gneiss.

31. Cold Spring 1; 70 ft below collar; saprolith.

32. Cold Spring 1; 79 ft below collar; saprolith.

33. Cold Spring 1; 88.5 ft below collar; saprolith.

34. Cold Spring 1; 106 ft below collar; saprolith.

35. Cold Spring 1; 111 ft below collar; weathered granodiorite

36. St. Joseph 1; 32 ft below collar; saprolith.

37. St. Joseph 1; 41 ft below collar; saprolith.

38. St. Joseph 1; 55 ft below collar; saprolith.

39. St. Joseph 1; 72 ft below collar; saprolith.

40. St. Joseph 1; 73 ft below collar; saprolith.

41. St. Joseph 1; 82 ft below collar; saprolith.

42. St. Joseph 1; 116 ft below collar; saprock.

43. St. Joseph 1; 135 ft below collar; weathered granite.

44. St. Joseph 1; 156 ft below collar; granite..

45. St. Augusta ; 57 ft below collar; bauxite.

46. St. Augusta ; 58.5 ft below collar; bauxite.

47. St. Augusta ; 63 ft below collar; saprolith.

48. St. Augusta ; 67 ft below collar; saprolith.

49. St. Augusta ; 75 ft below collar; saprolith.

50. St. Augusta 1; 82 ft below collar; saprolith.

51. St. Augusta 1; 87 ft below collar; saprolith.

52. St. Augusta 1; 95 ft below collar; saprolith. 

23. St. Augusta 1; 109 ft below collar; saprolith.

54. St. Augusta 1; 115 ft below collar; weathered quartz monzonite.

55. St. Augusta 1; 119 ft below collar; quartz monzonite.

amount of each gamma emitter; (6) the amount of clay; and 

(7) the mineralogy of the clay (figs. H5-H12). More details 

regarding the protoliths are given in tables H2 and H3.

The whole-rock chemistry of the profiles is represented in figures H13-H15. In this series of plots, apparent 

changes in bulk chemistry are plotted against a vertical depthbased scale. Where the drill holes encountered only part of 

a weathering profile (due to erosion or drilling limitations), 

we have combined the samples from sites having similar 

protoliths on a single plot. Because the samples are from 

more than one drillhole, it is not meaningful to use absolute 

depth values. The depth of any sample below the current

land surface is unimportant because it mostly reflects how 

much post-weathering erosion and glacial deposition have 

occurred. The relative spacing of samples within a weathering 

profile is important and has been maintained in these figures. 

Figures H16, H17, and HIS also illustrate chemical changes 

with depth, but variations in the amount of each constituent 

have been normalized against changes in alumina content to 

account for effects of weathering on bulk density.

The mineralogical changes associated with weathering are illustrated in figure HI9, where modal mineralogy 

is plotted against CIA, and in figure H20, where the mineralogy of the clay fraction is plotted against CIA.

H8 Strategic and Critical Minerals , Midcontinent Region, U.S.
Table H2. Nature of protolith at St. Cloud area sites, eastcentral Minnesota (Streckeisen classification, Streckeisen, 

1976).

Table H3. Nature of protolith at Redwood Falls area sites, 

southwestern Minnesota (Streckeisen classification, Streckeisen, 1976).

Site Description

St. Joseph Granite, greenish pink, coarse grained, slightly

porphyritic, massive. Microcline, 46%; plagioclase, 

37%; quartz, 10%; biotite, 2%; calcite, 2%; 

hornblende, 1%; chlorite, 1%; clay minerals, 1%; 

traces of apatite, opaque oxides, and zircon.

Cold Spring Granodiorite, slightly weathered, dark green and pink. 

Plagioclase, 40%; quartz, 28%; microcline, 12%; 

chlorite, 12%; biotite, 6%; apatite, 1%; traces of 

opaque oxides, zircon, and calcite.

St. Augusta Quartz monzonite, pink and black, equigranular, 

medium grained. Plagioclase, 44%; microcline, 

40%; quartz, 10%; chlorite (after biotite) 3%; biotite, 

1%; hornblende, 1%; traces of apatite, zircon, 

__________sphene, epidote, and calcite.

DISCUSSION

A general stratigraphic model for the pre-Cretaceous 

weathering profiles in Minnesota can be constructed from 

the data presented. A general model is possible mainly 

because the same mineral constituents quartz, plagioclase, 

potassium feldspar, hornblende, and biotite dominate all 

of the parent materials. However, the construction of a general profile is complicated by the fact that the specific properties of the profile at any given place are not a simple 

function of depth beneath the geomorphic surface. The profiles are irregularly zoned because of differences in the stabilities of the primary minerals, which are heterogeneously 

distributed, and because of differences in the duration and 

intensity of weathering between the bottom and top of the 

profile, controlled mainly by complex ground-water flow 

patterns along structurally controlled channelways. Plotting 

mineralogical changes against CIA values enables better 

correlations with weathering intensity.

From a physical perspective, the model of a fully 

developed profile consists of fresh rock, weathered rock, 

saprock, saprolith, and lateritic clay. The saprolith can in 

turn be divided into two subunits. The lower subunit, 

although composed predominantly of clay minerals, 

retains the original fabric and structure of the parent material. Chemical reactions there most likely took place 

under isovolumetric conditions. In contrast, the original 

fabric and structure in the upper subunit are typically disrupted, implying that it was formed under non-isovolumetric conditions by any number of complexly interrelated 

mechanical and chemical processes. Textural evidence 

shows that the lateritic clay also formed from interrelated 

mechanical and non-isovolumetric chemical processes.

Site Description

Redwood Three major rock types are present. One is a granitic 

Falls 1 gneiss, greenish gray and white, medium grained, 

composed of potassium feldspar, 30%; quartz, 25%; 

hornblende and biotite, 25%; and plagioclase, 20%. 

Another is a pegmatitic phase of pink quartz and 

orthoclase. The third is an inequigranular hybrid 

gneiss containing coarse, pink, orthoclase 

porphyroclasts and an increased granitic component.

Redwood Three types of protolith exist. One is a granitic gneiss, 

Falls 2 medium grained, greenish gray and white to pink, 

composed of potassium feldspar, 30-35%; quartz, 

25%; plagioclase, 20%; hornblende, 20%; and 

biotite, 5%. Another is a well-foliated granodiorite, 

medium to coarse grained, and composed of feldspar, 

50%; biotite, 40%; and quartz, 10%. The third is 

segregations of granitic pegmatite composed of 

potassium feldspar, 50%; plagioclase, 25%; and 

quartz, 25%.

Redwood The complex protolith includes (1) tonalite, well 

Falls 3 foliated, pink and green, containing large

porphyroblasts of pink potassium feldspar, and 

variable amounts of mafic minerals from 15 to 75%; 

(2) granite, weakly foliated, pink, equigranular, 

medium to coarse grained; (3) a mafic phase, dark 

greenish-black with fine white mottling and possible 

microdiabasic texture; and (4) amphibolitic enclaves, 

dark greenish-black and very rich in foliated, altered 

biotite.

Morgan 1 Granitic gneiss, coarse-grained, weakly porphyritic. 

Microcline, 39%; plagioclase, 32%; quartz, 27%; 

biotite, 2%; trace of apatite and zircon.

Morgan 2 No protolith recovered._________________

Mineralogical Attributes 

of the Model

Slightly Weathered Zone

The lowest zone in the weathering profile involves 

slightly weathered rock that is typically 2-30 cm thick. 

Mineral alteration is confined to fracture faces and to 

where the ferrous iron component of mafic minerals has 

been oxidized to the ferric state to produce iron staining 

and plagioclase grains have been etched locally along 

cleavage planes. No clay minerals were detected by X -ray 

diffraction in this slightly weathered rock.

Saprock

Saprock is transitional between weathered rock 

below and saprolith above. Though it contains appreciable 

clay minerals, saprock is fairly rigid. Rigidity is maintained by grain-to-grain bonds inherited from original 

magmatic crystallization or subsequent metamorphic

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H9
recrystallization. The lowermost few centimeters of the 

saprock are characterized by grains of white and chalky 

plagioclase and by hornblende partly replaced by green 

clay, mostly a mixture of chlorite and smectite. Other minerals such as quartz, potassium feldspar, and biotite seem 

unaffected. Toward the top of the saprock, nearly all of 

the hornblende is altered to chlorite and much of the green 

clay is a mixture of illite and kaolinite. Plagioclase is 

replaced by a white clay, which is mostly a mixture of 

kaolinite and illite, and biotite is replaced by vermiculite. 

Quartz and potassium feldspar remain relatively unaffected. A textural correlation between plagioclase, hornblende, and associated clays implies that the saprock was 

formed by isovolumetric weathering processes.

Saprolith

Much of the saprolith, like the underlying saprock, has 

textural attributes that mimic those of the protolith. Although 

there is a transitional interval of 1 m or so between them, 

the saprolith is marked by the complete dissolution of hornblende and nearly complete dissolution of plagioclase. 

Therefore, saprolith is considerably less indurated than 

saprock. The modal proportions of biotite and potassium 

feldspar also decrease, whereas kaolinite increases stratigraphically upward in the saprolith. The level where nearly 

all of the biotite and much of the potassium feldspar disappear generally corresponds to the level where primary igneous or metamorphic texture disappears. Above that level, the 

saprolith is dominated by kaolinite, a minor amount of 

quartz, and a trace amount of potassium feldspar.

Ideally, the development of saprolith is dependent 

upon a mixture of primary minerals that alter at different 

rates. Different dissolution rates selectively remove the 

more reactive mineral species such as the amphiboles 

and plagioclase. The remaining, more resistant minerals such as potassium feldspar and quartz provide the 

supporting structural framework that is essential to maintain isovolumetric weathering conditions.

In the upper part of the saprolith, however, dissolution 

of even the most resistant minerals leads to a breakdown in 

textural integrity. This, in turn, leads to a physical environment where non-isovolumetric chemical processes can prevail. Chemical changes in this zone may reflect absolute 

losses, but absolute gains also can take place because of the 

physical translocation of particulate mineral constituents.

The relative instabilities of silicate minerals, as 

inferred from the generalized weathering profile described 

above, are very similar to those first documented by Goldich 

(1938). However, we observed that amphiboles alter first, 

followed by biotite, and that both dissolve more readily than 

the feldspars, which dissolve more readily than quartz. Of 

the feldspars, plagioclase is much more reactive than potassium feldspar. Quartz persists as a discrete primary phase in 

all but the most intensely weathered saprolith.

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H10 Strategic and Critical Minerals , Midcontinent Region, U.S.
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CIA value

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Protolith Weathering 

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Th ppm

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Figure H6. Summary of the principal facts regarding the weathering profile at the St. Joseph site, east-central Minnesota. CIA, chem

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Weathering 

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0 

Clay c

(per

Figure H7. Summary of the principal facts regarding the weathering profile at the St. Augusta site, east-central Minnesota. CIA, chem

Young, 1982).
n

JO

"5 

o

_o

CD

o. 

o 

Q

m ft

30-

35-

40-

45-

50-

55-

60-

65-

-100

-110

-120

-130

-140

-150

-160

-170

-180

-190

-200

-210

-220

Sample No.; 

CIA value

L/\/\/VVV\/\/\/\/\/\j

,r

Ct3t±)

V

««2;97

^3;97

-«4;63

 «5;97

Protolith Weathering 

profile

o

Q. 

CO

D) 

*

K20%

U ppm

/Th ppm

150 250 350 0 .1

Gamma log Gamma

(API units) emitters

Miiii imi """i

10 1000 0 

Clay c

(perc

Figure H8. Summary of the principal facts regarding the weathering profile at the Redwood Falls 1 site, southwestern Minnesota

(Nesbitt and Young, 1982).
m ft

Sample No.; 

CIA value

Q.

n

"

1

0 

.Q

Q. 

<D 

O

40-

45-

50-

55-

60-

65-

70-

75-

80-

-120 

130

-140

-150

-160

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-^1;97

' + + + + I +

+ + + + !- I f t +

+ + + + f + +

+ + + +»+ + +

+ + -f j r + + +

+ + + T + + + +

Protolith Weathering 

profile

O 

Q. 

(C

.2w"O'g) 

O C

go>

\\

'U ppm

Th ppm

20 100 200 300

Gamma log 

(API units)

0 1

Gamma 

emitters

10 100 0 

Clay c

(per

Figure H9. Summary of the principal facts regarding the weathering profile at the Redwood Falls 2 site, southwestern Minnesota

(Nesbitt and Young, 1982).
n

m

50-

Js"o

0 

^ 55-

O 

0)

_<- 60- 

Q.

Q 

65-

ft

-160

-170 

-180

-190 

-200 

-210 

-220

Sample No.; 

CIA value

y\7v/Y\^/yvyN^>

^'SS/Ss +

<-;/.<'>< 

:*:::*::>

 ,',*,' ,'^s ,'.'

Protolith

:w.vx

+ + + ' * f* r +

Weathering 

profile

<«2;56

c<

\ 

/

0)

re

0

t

\

3

a 

n

i

U)

«

c

)0)

(

Jr

^'"^^

?

k i i i

D 50 100 150 200

Gamma log 

(API units)

A

t

t

^

L 1

U F

1 ! 

<20% Th ppm 

)pm

i i i i i i i i i i i i i 

D 5 10 15 C

Gamma 

emitters

n

i i i i 

) 

Clay c

(perc

QTQ 

 D 

O

n

Figure H10. Summary of the principal facts regarding the weathering profile at the Redwood Falls 3 site, southwestern Minnesot

(Nesbitt and Young, 1982).

Sample No.; 

CIA value

1;63

S'5 

2 c

Protolith Weathering 

profile

U ppm

\

K20%

Th ppm

150 200 250.1 10 100

Gamma log 

(API units)

Gamma 

emitters

0 

Clay c

(per

Figure H11. Summary of the principal facts regarding the weathering profile at the Morgan 1 site, southwestern Minnesota. CIA, 

and Young, 1982).
&)

Q.

n

m

30-

35-

40-

^ 45-

"o

O

O 50-

0)

n

a. 55-

0) 

Q

60-

65-

70-

ft

-90

-100

-110

-120

-130

-140

-150

-160

-170

-180 

190

-200

-210 

220

-230

-240

'/VVV\/VVV'VVVV|

< .7 L

\ ' V ,. > '" 7

^Diabase dikes

Sample No.; 

CIA value

/\y\/\/\/vAy\/\/\/\/\

Protolith

<«2;95 

<3;95

««4;98

<«5;98 

««6;98

<«8;95

<«9;79

Weathering 

profile

0 100 200

Gamma log 

(API units)

K20%

Th ppm

0 .1 1 10 100 0 

Gamma Clay c

emitters (perc

Figure H12. Summary of the principal facts regarding the weathering profile at the Morgan 2 site, southwestern Minnesota. CIA, chem

Young, 1982).
30 40 50 60 70

Si02%

10 20 30

AI2O3%

0 1 2

TiO2%

Q_ 

0)

T3 H

O)

_c

CO - 

CD

O

c

I I I I I

234

CaO%

01234

Na2O%

02468

K2O%

8 16

FeO%

024

Fe2O3%

0 0.4 0.8

P2 05%

Figure H13. Whole-rock chemical trends at the St. Cloud area sites, east-central Minnesota. The data from all three sites are 

arranged on a single plot and positioned according to the degree of weathering in each profile. The outside ticks on the vertical 

axis are 50-ft increments, and the inside ticks are 20-m increments. Dot, St. Joseph; triangle, St. Augusta; square, Cold Spring.

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H17
60 65 70 75

SiO2%

12 14 16 18 20 22 24 26

AI2O3%

0 0.2 0.4 0.6

TiO2%

Q. 

CD 

T3

O)

'co C

CO

CD

O

JC

4

0.5 1

CaO%

1.5 01234

Na2O%

02468

K2O%

1 2

FeO%

0.4 0.8 ,1.2 1.6

Fe2O3%

0.01 0.03 0.05 0.07

P2 05%

Figure H14. Whole-rock chemical trends at the Redwood Falls sites, southwestern Minnesota. The data from all three sites are 

arranged on a single plot and positioned according to the degree of weathering in each profile. The outside ticks on the vertical 

axis are 50-ft increments, and the inside ticks are 20-m increments. Square, Redwood Falls 1; triangle, Redwood Falls 2; dot, 

Redwood Falls 3.

H18 Strategic and Critical Minerals , Midcontinent Region, U.S.
55 60 65 70 75

SiO2%

12 14 16 18 20 22 24 26

AI203%

0.1 0.2 0.3 0.4 0.5

TiO2%

Q_ 

CD 

T3

O)

'coC

03 

0)

O

JC

I

0.1 0.3 0.5

CaO%

01234

Na2O%

FeO %

0.4 0.8

Fe2O3%

1.2 0.12

Figure H15. Whole-rock chemical trends at the Morgan sites, southwestern Minnesota. The data from both sites are arranged on 

a single plot and positioned according to the degree of weathering in each profile. The outside ticks on the vertical axis are 50-ft 

increments, and the inside ticks are 20-m increments. Triangle, Morgan 1; square, Morgan 2.

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H19
-3-2-1 0 1 23

Relative concentration 

(log value) SiC>2

Relative concentration 

(log value) CO2

-3-2-1 0 1 23

Relative concentration 

(log value)

Q. 

o -o

O)

c 'w

CO 

CD

O

_c

4

-3-2-1 0 1 23

Relative concentration 

(log value) CaO

-3-2-10123

Relative concentration 

(log value)

-3-2-1^0 1 2 3

Relative concentration 

(log value) K

-3-2-1 01 23

Relative concentration 

(log value) FeO

-3-2-1 01 23

Relative concentration 

(log value)

-3-2-1 01 23

Relative concentration 

(log value) MgO

Figure H16. Chemical characteristics of the St. Cloud area weathering profiles, east-central Minnesota. Based on the methods of 

Prasad and Roscoe (1991), where AI 2 C>3 is assumed to be an inert constituent and where Mva | ue/samp | e = Log 

[(M02 samP |e/M02 Parent)/ (Al 2 03 sam P |e/Al 2 03 Parent)]. The outside ticks on the vertical axis are 50-ft increments, and the inside ticks 

are 20-m increments. Dot, St. Joseph; triangle, St. Augusta; square, Cold Spring.

H20 Strategic and Critical Minerals , Midcontinent Region, U.S.
-3-2-1 0 1 23

Relative concentration 

(log value) SiO2

-3 -2 -1 -3 -2-101

Relative concentration 

(log value) C02

Relative concentration 

(log value) TiO2

.c

Q. .

CD

O)

'coC

03

CD

O

_c

4

t

A

i

k

>

\

r \

' 1

i

-3-2-1 01 23

Relative concentration 

(log value) CaO

\

-3-2-10123

Relative concentration 

(log value) Na2O

-3 -1

Relative concentration 

(log value) K2O

-3 -2 -1 -3 -2 -1 -3 -2 -1

Relative concentration 

(log value) FeO

Relative concentration 

(log value) Fe203

Relative concentration 

(log value) MgO

Figure H17. Chemical characteristics of the Redwood Falls weathering profiles, southwestern Minnesota. Based on the methods 

of Prasad and Roscoe (1991), where A^C^ is assumed to be an inert constituent and where Mva | ue/samp| e = Log 

[(MO2sam P|e/MO2 Parent)/ (Al 2O3sam P |e/Al2O3 Parent)]. The outside ticks on the vertical axis are 50-ft increments, and the inside ticks 

are 20-m increments. Square, Redwood Falls 1; triangle, Redwood Falls 2; dot, Redwood Falls 3.

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H21
-3-2-1 0 1 23

Relative concentration 

(log value) SiO2

-3-2-1 0 1 23

Relative concentration 

(log value) C02

.c 1 

Q. 

CD o

O)

_C

CO

0)

o

c

1

1

1

1

\

F 1 i

-3-2-1 01 23

Relative concentration 

(log value) CaO

-3 -2-1 0 1

Relative concentration 

(log value) Na2O

-3-2-10123

Relative concentration 

(log value) FeO

-3-2-1 01 23

Relative concentration 

(log value) Fe20s

-3 -2-101

Relative concentration 

(log value) TiO2

-3 -2 -1

Relative concentration 

(log value) K2O

-3-2-1 01 23

Relative concentration 

(log value) MgO

Figure H18. Chemical characteristics of the Morgan 1 and Morgan 2 weathering profiles, southwestern Minnesota. Based on the 

methods of Prasad and Roscoe (1991), where AI 2O3 is assumed to be an inert constituent and where Mva| ue/samp | e = Log 

[(MO2 sam Ple/MO2 Parent)/(Al 2O3sam Ple/Al2O3 Parent)]. The outside ticks on the vertical axis are 50-ft increments, and the inside ticks 

are 20-m increments. Triangle, Morgan 1; square, Morgan 2.

H22 Strategic and Critical Minerals , Midcontinent Region, U.S.
Pisolitic Lateritic Clay

In his regional study, Parham (1970) suggested that 

an interval of undisturbed pisolitic lateritic clay marks the 

top of the weathering profile at many places in southwestern Minnesota. However, we intersected lateritic clay only 

at the St. Augusta site in east-central Minnesota where it 

is about 1.5 m thick. The pisolites are hollow or are partly 

filled with pyrite; pyrite in turn is partly replaced by goethite. Goethite also rims many of the pisolites. A chalky, 

light-brownish-gray, or light-gray to white, clay-rich 

groundmass consists mostly of kaolinite and halloysite, 

and lesser amounts of quartz, gibbsite, and goethite. Siderite occurs as disseminated euhedral grains, and calcite fills 

many microfractures. The light-colored clay gives way 

downward to a green, clay-rich interval composed of 

kaolinite, chlorite, quartz, and lesser amounts of gibbsite 

and goethite. Kaolinite-rich pisolites are scattered throughout both the light-colored and green clay intervals.

Chemical Attributes of the Model

Because feldspars are a major component of the parent rocks and CIA values represent their distribution, these 

values are useful in correlating major chemical trends in 

the weathering profiles with their physical stratigraphy. 

Fresh rock has CIA values that vary from 47 to 53. 

Although contacts are gradational, slightly weathered rock 

has CIA values that range from 50 to 55, whereas saprock 

typically has values in the range of 55 to 65 or 70. The 

lower part of the saprolith has CIA values of 67 to 82, 

whereas the values in the upper part approach 95. Two 

samples of lateritic clay, which occurs only at the St. 

Augusta site, have CIA values of 97 and 98. These CIA 

changes represent the progressive loss of plagioclase and 

potassium feldspar, constituents that comprise half to twothirds of the modal volume of the parent materials. The 

dissolution of the feldspars and the concurrent loss of 

CaO, Na2O, and K^O from the weathering profile are well 

illustrated in figures H13-H15. Silica is also lost, whereas 

alumina, titanium, and iron content increase or remain 

constant.

In assessing the chemical behavior of constituents as 

weathering progresses, analysis must take into account 

changes in the bulk densities of the samples. Several 

schemes have been proposed to compare weight-percent 

chemical data from samples of different densities by normalizing the mobile constituents against some generally 

inert component. One procedure, developed by Reiche 

(1943), involves measuring progressive gains or losses of 

various constituents relative to the amount of alumina

present in the parent material or, where that is unknown, 

in the least altered part of the profile (see also Prasad and 

Roscoe, 1991). Though unlikely to be totally immobile, 

alumina is one of the least mobile of the major rock-forming oxides (Goldich, 1938). Therefore, if nothing else, the 

procedure eliminates scatter caused by inhomogeneities in 

the original crystalline parents.

The chemical profiles in figures H19-H21 illustrate 

three principal upward trends: (1) the expected loss of 

CaO, Na2O, K2O, and some SiO2; (2) gain of carbon 

dioxide; and (3) relative gains or consistency of Fe2O3, 

MgO, and TKK The first trend, involving the loss of plagioclase and some loss of potassium feldspar and the concurrent loss of CaO, Na2O, K2O, and possibly some SiO2, 

has been discussed. However the data in figures HI6, 

HI7, and HI8 show that sodium is lost from the system 

much earlier than calcium. Thus, the loss of sodium must 

be the rate-controlling step in the dissolution of plagioclase. The data also show that at least some calcium 

remains in the system, where it becomes available to combine with carbon dioxide to form calcite, typically in the 

upper part of the weathering profiles. Potassium is lost 

from the system at a stratigraphic level somewhat above 

the level at which calcium and sodium are lost. This is 

consistent with the relatively greater stability of potassium 

feldspar, and with the development of illite as an intermediate weathering product. Potassium, like sodium, is generally lost at the top of the saprolith. Some potassium is 

apparently gained at the very top of the profile at the St. 

Joseph site, in the St. Cloud area.

Iron and magnesium behave somewhat differently in 

the profiles. In general, ferrous iron is more or less constant in the lower half, but increases slightly in the upper 

half of several profiles. This trend corresponds to the dissolution of hornblende and biotite and the concurrent 

release of ferrous iron, which migrates upward to a level 

where oxidizing conditions fix it as either goethite or 

hematite. Several profiles also show a slight decrease in 

ferric iron in their uppermost parts. Solutions moving 

downward in the vadose zone may dissolve small amounts 

of ferric iron and reprecipitate it in the phreatic zone. 

Magnesium shows a much more erratic distribution. In 

several profiles, it systematically declines from bottom to 

top, whereas in others it remains more or less constant 

through the lower half and declines abruptly in the upper 

half of the saprolithic interval. That abrupt decline generally corresponds to the level where biotite disappears.

Techniques developed by Nesbitt and Young (1984, 

1989) further demonstrate the chemical changes that occur 

during weathering. They have shown that chemical trends 

in modern weathering profiles developed on granitic rocks 

mimic those predicted from kinetic leaching data for alkali

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H23
CD

£

cc

100

90

80

70

60

50

40

30

20

10

50 60

Green Clay

Quartz

70 80

CIA Value

90 100

40

c

50 60 70 80

CIA Value

100

100

70 80

CIA Value

100 70 80

CIA Value

90 100

Figure H19 (above and facing page). Plots of modal proportions of mineral constituents in samples, ordered by CIA (chemical 

index of alteration; Nesbitt and Young, 1982) values. Each vertical series of dots represents a sample aligned on its CIA value. The 

width of each field along that vertical line corresponds to the proportion of the constituent named in the field. Modal proportions 

determined from thin sections and visual estimation from core. A, Cold Spring; B, St. Joseph; C, St. Augusta; D, Morgan 1 and 

Morgan 2; E, Redwood Falls 2 and Redwood Falls 3; F, Redwood Falls 1. For each sample, total proportion of mineral constituents 

equals 100.

H24 Strategic and Critical Minerals , Midcontinent Region, U.S.
100

90

80

70 

<D

60

50

O 40

2

30

20

10

Quartz

50 60 70 80

CIA Value

90 100

0)

100

90

80

70

60

CO

O 40

30

20

10

Hornblende

Plagioclase 

Quartz

i

50

F

60 70 80

CIA Value

90 100

and calcium from feldspars. Ternary diagrams in the field 

A12O3 CaO+Na2O K2O (A CN K) show that the 

progressive dissolution of plagioclase moves the bulk composition of the residue toward the A K join (fig. H21). 

Residues located near that join are poor in calcium- or 

sodium-bearing phases, and the predominant remaining 

minerals include aluminous phases, such as kaolinite, and 

potassic phases, such as potassium feldspar and illite. As 

weathering proceeds, the trend is abruptly redirected 

toward the alumina apex, reflecting the dissolution of the 

potassic phases and the concurrent increase in the profile of

residues enriched in the aluminum-bearing phases. Similarly, on an A12O3 CaO+NaCT+KoO FeO+MgO 

(A CNK FM) diagram, the initial trend during early 

weathering moves the residual compositions in a direction 

sub-parallel to the A CNK join. As the A FM join is 

approached during advanced weathering, there is again an 

abrupt change in the compositional trend toward the alumina apex. This relationship implies that iron and magnesium are leached from the residual products more rapidly 

than is alumina. Nesbitt and Young (1984) suggest that 

these trends can be used as templates to which the chemical history of geologically old profiles can be compared. 

Deviations from the templates generally are caused by 

heterogeneity in the protolith composition, or post-weathering diagenetic modifications. For example, four trends 

are apparent in the St. Joseph data (fig. H215). The first, 

involving samples 9, 8, 7, and 6, defines compositional 

changes associated with the weathering of granite. The 

second, apparent on the A CN K diagram, shows that 

the upper part of the saprolith is enriched in the CN component. The third shows that the uppermost part of the 

saprolith is also enriched in the FM component. The second and third trends are most likely the result of diagenetic processes that added or concentrated constituents 

such as calcium and iron to the upper part of the profile. 

The fourth trend, involving samples 4 and 5, is associated 

with the weathering of a diabasic protolith.

Similar bulk compositional changes are seen at the 

St. Augusta site. In the A CN K diagram of figure 

H21C, materials derived from a granitic protolith (samples 

11-8 and 5) define a weathering trend in which the saprolith is enriched in alumina at the expense of alkalies and 

calcium. Samples 3, 2, and 1 are lateritic clays that cluster 

at the alumina apex. A trend involving enrichment in alumina at the expense of iron and magnesium is also well 

illustrated on the A CNK FM diagram, which shows 

that samples 3-1 follow a trend parallel to the A FM 

join. Materials of diabasic affinity (samples 7, 6, and 4) 

define a second weathering trend.

In another example (fig. H21E1 ), the partial profiles 

at Morgan 1 and Morgan 2 together define a similar trend 

showing the progressive loss of calcium at Morgan 1 and 

the progressive loss of potassium at Morgan 2. However, 

the upper part of the Morgan 2 profile is unique in that it 

is apparently enriched in sodium or calcium such that 

compositional changes follow the A CN join toward the 

CN apex. That part of the profile also shows appreciable 

iron enrichment on an A CNK FM plot. It is therefore 

likely that the upper part of the profile at Morgan 2 was 

affected by post-weathering diagenetic processes.

At Redwood Falls 2 (fig. H21F) samples 6, 4, 3, 2, 

and 1 define an ordinary weathering sequence in both the 

A CN K and A CNK FM diagrams. Sample 5, a pegmatitic segregation, falls off that trend in both diagrams.

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H25
SUMMARY

In parts of western Minnesota a weathering profile, 

as much as 90 m thick, was developed on a variety of prePhanerozoic igneous and metamorphic rocks (Parham, 

1970). In the areas described here, evidence of weathering 

extends in places to a depth of at least 60 m beneath the

paleogeomorphic land surface. The generalized weathering 

profile and landform model illustrated in figure H22 shows 

that weathering occurred along fractures and joints as 

shown by isolated corestones separated by considerably 

altered material. In general, some quartz and at least trace 

amounts of potassium feldspar persist throughout most of 

the profiles. Plagioclase is rapidly weathered with the

100

90

80

§75 70

oe

0.0, 50

a-* N

30

20

10

50

Kaolinite

Quartz

_L

60 70 80

CIA Value

90 100

100

90

80

0« 70

§.« 6°

o E

Q. m 50

40

Kaolinite

50

Quartz

60 70 80

CIA Value

90 100

100

90

80

.21 7° 

SS 60

Q. CO

0-0) 50 

.> '« 40

(^ o 30 

20 

10

50

Quartz

100

90

80

It -2 CO

50

30

20

10

60

a

70 80

CIA Value

90 100 50 60 70 80

Q CIA Value

90 100

Figure H20 (above and facing page). Plots of relative proportions of clay-sized material versus CIA (chemical index of alteration; 

Nesbitt and Young, 1982). Each vertical series of dots represents a sample aligned on its CIA value. The width of each field along 

that vertical line corresponds to the proportion of the constituent named in the field. Relative proportions determined by X-ray 

diffraction of clay-sized material. A, Cold Spring; B, St. Joseph; C, St. Augusta; D, Morgan 1 and Morgan 2; E, Redwood Falls 2 

and Redwood Falls 3; F, Redwood Falls 1.

H26 Strategic and Critical Minerals , Midcontinent Region, U.S.
100i 

90 

80

I 70

2 E

0-0) 50 

0) N

£'540

20

10

50

Q. (0

2 E

100

90

80

' 60 

50

 

£030

20- 

10

50

Kaolinite

Quartz

60 70 80

CIA Value

90 100

Kaolinite

Quartz

J_______I

60 70 80

CIA Value

90 100

concurrent and pronounced loss of calcium and sodium. 

Large amounts of kaolinite are ultimately produced at the 

expense of the plagioclase. As weathering proceeds, illite 

forms as a common alteration product of potassium feldspar, which dissolves much more slowly than plagioclase. 

However, with continued weathering and the concurrent 

loss of potassium, the illite is transformed into kaolinite. 

Hornblende and biotite alter to chlorite, vermiculite, iron 

oxides, and other clay minerals such as the smectites, and 

at the same time aggressive solutions reacting with these 

phases produce alumina-rich phases such as kaolinite and, 

less commonly, gibbsite.

The extremely weathered upper parts of well-developed profiles, which contain abundant kaolinite, have been 

the focus of the exploration community. Other factors, 

however, tend to complicate that simple relationship. In 

many places the weathering profiles have been modified 

by diagenetic processes involving the remobilization of 

iron, calcium, and carbon dioxide to produce very late 

forming phases such as siderite, calcite, hematite or goethite, and pyrite. Unlike the in-situ weathering products 

formed by through-flowing ground-water solution, these 

minerals likely accumulated at some later time in poorly 

drained areas under stagnant conditions, and their presence 

may be a useful indicator of the changing position of the 

water table in pre-Late Cretaceous time. From petrographic and X-ray diffraction data it is not possible to distinguish mineral phases that formed by in-situ weathering 

or diagenetic processes from those that formed much later 

by metasomatic processes involving the introduction of 

chemical constituents from outside the weathering system. 

For example, the lateritic clay interval at St. Augusta and 

the upper part of the saprolithic intervals at Redwood Falls 

1 and Morgan 2 are apparently enriched in sodium, a component which is relatively mobile under ordinary weathering conditions. However such situations are not unique, 

and Nesbitt and Young (1989) suggest that sodium metasomatism can occur, mainly by reactions involving the 

weathering profile and marine water having a large ratio 

of sodium to potassium. If so, the weathering profile in 

western Minnesota records the incursion of a marine sedimentary system during Late Cretaceous time.

ECONOMIC IMPLICATIONS

Potential users of the in-situ kaolinite resource in 

Minnesota require a thick, widespread kaolinite-rich product, free of impurities that would tend to degrade the quality. Ideally, the uppermost part of the weathering profile, 

where intense chemical weathering has reduced the saprolith to a mixture of kaolinite and quartz, would best satisfy 

a user's needs. However, a breakdown in the mechanical 

integrity of that part of the weathering profile has led to 

an environment particularly susceptible to the introduction 

of diagenetic and metasomatic constituents that will contaminate the deposits. Thus, it seems likely that if the 

saprolith is to be fully utilized as a kaolinite resource, at 

least some beneficiation will be necessary. This problem, 

which has plagued the exploration community for almost 

as long as the resource has been recognized, has been 

examined in considerable detail by Wayland (1964), and 

more recently by Prasad and Reid (1989).

Although problems persist, contemporary mineral 

exploration in Minnesota is tackling increasingly more 

difficult areas lacking significant outcrop. This is in part

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H27
CN K CNK FM CN K CNK FM

e

CN K CNK FM CN K CNK FM

CN K CNK FM CN K CNK FM

Figure H21. Ternary diagrams in the AI2O3 CaO+Na2O K2O and AI 2O3 CaO+Na2O+K2O FeO+MgO fields showing 

chemical trends in the weathering of granitic rocks. A, Cold Spring; B, St. Joseph; C, St. Augusta; D, Redwood Falls 1 and Redwood Falls 3 (triangle); E, Morgan 1 (triangle) and Morgan 2; Ft Redwood Falls 2. The numbers are those used in figures H5-H12 

to indicate sample locations in the drill core. The samples were numbered consecutively from the top of the core to the bottom.

for the obvious reason that many areas having reasonable 

outcrop have already received exploration attention, even 

by several generations of activity. Another reason is that it 

has been shown that the non-outcropping areas contain 

depositional regimes characterized by widespread kaolinite-rich sediments reworked from saprolith and redeposited 

as parts of a fluvial system that existed prior to the incursion of marine water in Late Cretaceous time (Hauck and 

Heine, 1991). Some sedimentary kaolinitic deposits are at 

least 14 m thick in some channels or valleys. Although 

they thin rapidly away from the valleys, they probably 

remain relatively uniform in thickness for some distance 

along the strike of the channels. Clearly, these reworked 

deposits are inviting exploration targets, but it will be necessary to establish a better understanding of weathering

profile and landform relationships in western Minnesota to 

find and delineate them.

Lastly, this study has emphasized weathering processes that affect rocks of quartzofeldspathic composition. 

However, much of the area where saprolith is developed 

in western Minnesota is also underlain by mafic volcanic 

rocks of Archean age. As judged from numerous mines 

just across the International Boundary, in Ontario, these 

so-called "greenstone belts" have potential for lode-gold 

and base-metal (zinc and copper) deposits. Exploration in 

the greenstone belts has focused on finding a primary 

deposit, but it is interesting to speculate about the size and 

grade of a world-class Archean deposit that was modified 

by supergene processes related to an episode of intense 

weathering before the arrival of Late Cretaceous seas.

H28 Strategic and Critical Minerals , Midcontinent Region, U.S.
Quaternary materials

*,' Upper Cretaceous I 

rocks |

J

pisolitic lateritic 

clay

Figure H22. Physical stratigraphy of the in-situ and reworked 

weathering products. The patterns (as in figs. H5-H12) in the 

lower block diagram represent fresh rock, saprock, saprolith, 

pisolitic lateritic clay, and fluvial deposits of kaolinitic shale. 

Upper Cretaceous and (or) Quaternary deposits (upper block) 

cover this profile in most places.

REFERENCES CITED

Austin, G.S., 1970, Weathering of the Sioux Quartzite near New 

Ulm, Minnesota, as related to Cretaceous climates: Journal of 

Sedimentary Petrology, v. 40, no. 1, p. 184-193.

Bickford, K.F., and Price, D., 1947, Report on work done on clays 

in summer 1947: Unpublished Minnesota Geological Survey 

file report, 20 p.

Chesworth, W., 1992, Weathering systems, Ch. 2 in Martini, I.P., 

and Chesworth, W., eds., Weathering, soils, and paleosols: 

New York, Elsevier, p. 19^0.

Dott, R.H., Jr., and Batten, R.L., 1981, Evolution of the Earth (3d 

ed.): New York, McGraw-Hill, 573 p.

Goldich, S.S., 1938, A study in rock weathering: Journal of Geology, v. 46, p. 17-58.

Grout, F.F., and Soper, E.K., 1919, Clays and shales of Minnesota: 

U.S. Geological Survey Bulletin 678, 259 p.

Hall, C.W., 1899, The gneisses, gabbro schists, and associated 

rocks of southwestern Minnesota: U.S. Geological Survey 

Bulletin 157, 160 p., includes maps.

Hall, C.W., Meinzer, O.E., and Fuller, M.L., 1911, Geology and 

underground waters of southern Minnesota: U.S. Geological 

Survey Water Supply Paper 256, p. 34-35.

Hauck, S.A., and Heine, J.J., 1991, Regional and local geologic, 

mineralogic, and geochemical controls of industrial clay 

grades in the Minnesota River Valley and the Meridian 

aggregates quarry, St. Cloud, Minnesota: University of Minnesota, Natural Resources Research Center Technical Report 

NRRIATR-91/15.

Hauck, S., Heine, J.J., Zanko, L., Power, B., Geerts, S., Oreskovich, J., and Reichoff, J., 1990, LCMR clay project; NRRI 

summary report: University of Minnesota, Natural 

Resources Research Institute Technical Report 

NRRI/GMIN-TR-89-12A, 201 p., 7 pis.

Moore, W.L., 1979, A preliminary report on the Red River Valley 

drilling project, eastern North Dakota and north-western 

Minnesota: U.S. Department of Energy Open-File Report 

GJBX-3(79), 292 p.

Morey, G.B., 1983, Animikie basin, Lake Superior region, U.S.A., 

in Trendall, A.F., and Morris, R.C., eds., Iron-formation facts 

and problems: Amsterdam, Elsevier, p. 13-67.

Mossier, J.H., 1978, Results of subsurface investigations in northwestern Minnesota, 1972: Minnesota Geological Survey 

Report of Investigations 19, 18 p.

Nesbitt, H.W., and Young, G.M., 1982, Early Proterozoic climates 

and plate motions inferred from major element chemistry of 

lutites: Nature, v. 299, p. 715-717.

 1984, Prediction of some weathering trends of plutonic and 

volcanic rocks based on thermodynamic and kinetic considerations: Geochimica et Cosmochimica Acta, v. 48, p. 

1523-1534. 

-1989, Formation and diagenesis of weathering profiles:

Journal of Geology, v. 97, p. 129-147.

Parham, W.E., 1970, Clay mineralogy and geology of Minnesota's 

kaolin clays: Minnesota Geological Survey Special Publication Series SP-10, 142 p.

Prasad, M.S., and Reid, K.J., 1989, Process options and testing procedures for Minnesota clays: Mineral Resources Research 

Center Technical Report MRRC/LCMR-TR-89-08.

Prasad, M.S., and Roscoe, S.M., 1991, Profiles of altered zones at 

ca 2.45 Ga unconformities beneath Huronian strata, Elliot 

Lake, Ontario: Evidence for early Aphebian weathering 

under anoxic conditions, in Current research, pt C: Geological Survey of Canada Paper 91-1C, p. 43-54.

Reiche, P., 1943, Graphic representation of chemical weathering: 

Journal of Sedimentary Petrology, v. 13, p. 58-68.

Setterholm, D. R., 1994, The Cretaceous rocks of southwestern 

Minnesota A marine to nonmarine transition along the 

eastern margin of the Western Interior Seaway, in Shurr, 

G.W., and Hammond, R.H., eds., Geology of the eastern 

margin of the Western Interior Seaway: Geological Society 

of America Special Paper 287, p. 97-110.

Setterholm, D.R., Morey, G.B., Boerboom, T.J., and Lamons, R.C., 

1989, Minnesota kaolin clay deposits A subsurface study 

in selected areas of southwestern and east-central Minnesota: 

Minnesota Geological Survey Information Circular 27, 99 p.

Streckeisen, A., 1976, To each plutonic rock its proper name: Earth 

Science Reviews, v. 12, p. 1-35.

Symons, D.T.A., 1966, A paleomagnetic study on the Gunflint, 

Mesabi, and Cuyuna iron ranges in the Lake Superior region: 

Economic Geology, v. 61, no. 8, p. 1336-1361.

Tyler, S.A., and Bailey, S.W., 1961, Secondary glauconite in the 

Biwabic iron-formation of Minnesota: Economic Geology, 

v. 56, no. 6, p. 1033-1044.

Upham, W., 1888, The geology of Renville County: Minnesota 

Geological Survey Final Report, v. 2, p. 190-204.

Wayland, T.E., 1964, The Redwood Falls kaolin deposit, Redwood 

Falls, Minnesota: Unpublished report of the International 

Minerals and Chemical Corporation, Industrial Minerals 

Division, Geology Department, 14 p. text; various unnumbered tables and appendices; 4 pis.

Winchell, N.H., 1874, The geology of the Minnesota valley: Minnesota Geological and Natural History Survey Annual 

Report, 2nd, for the year 1873, p. 127-212.

An Extensive Pre-Cretaceous Weathering Profile in East-Central and Southwestern Minnesota H29

U.S. GOVERNMENT PRINTING OFFICE: 1996 - 774-045 / 20016 REGION NO. 8



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