A Regional Structural Model for 

Gold Mineralization in the 

Southern Part of the Archean Superior 

Province, United States

U.S. GEOLOGICAL SURVEY BULLETIN 1904-M
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Chapter M

A Regional Structural Model for 

Gold Mineralization in the 

Southern Part of the Archean Superior 

Province, United States

By P.K. SIMS and W.C. DAY

U.S. GEOLOGICAL SURVEY BULLETIN 1904

CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION 

P.K. SIMS and L.M.H. CARTER, Editors
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

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: 1992

For sale by

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Library of Congress Cataloging-in-Publication Data

Sims, P.K. (Paul Kibler), 1918-

A regional structural model for gold mineralization in the southern part of 

the Archean Superior Province, United States / by P.K. Sims and W.C. Day.

p. cm. (U.S. Geological Survey bulletin ; B1904-M) (Contributions to 

precambrian geology of Lake Superior Region)

Includes bibliographical references.

Supt. of Docs, no.: I 19.3:1904

1. Gold ores Michigan Upper Peninsula. 2. Gold ores Minnesota. 

3. Greenstone belts Michigan Upper Peninsula. 4. Greenstone belts 

Minnesota. 5. Geology, stratigraphic Archaean. I. Day, Warren C. 

II. Title. III. Series. IV. Series: Contributions to precambrian geology of Lake 

Superior Region. 

QE75.B9 no. 1904-M 

[QE390.2.G65] 

557.3 s dc20

[553.4M'09774] 91-34868

CIP
CONTENTS

Abstract Ml 

Introduction Ml 

Acknowledgments M2 

Geologic framework of Superior province M2

Nature and distribution of Canadian gold deposits in Superior province M2 

Superior province in north-central United States M4 

Archean tectonic framework M4

Lamprophyre and syenite in Vermilion district, Minnesota M7 

Gold deposits, occurrences, and anomalies M9 

Ropes gold mine, northern Michigan M9 

Prospects in northern Michigan Mil 

Rainy Lake area, Minnesota M13 

Anomalies in Vermilion district, Minnesota M13 

An occurrence model for gold mineralization in the United States segment of Superior

province M14

Exploration implications in the United States M15 

Discussion M15 

References cited M17

FIGURES

1. Generalized geologic map of Superior province showing subprovinces and 

Canadian gold camps M3

2. Map showing Vermilion fault system, Vermilion district, northern 

Minnesota M5

3. Geologic map of part of Marquette I°x2° quadrangle, northern Michigan M6

4. Simplified tectonic map of Lake Superior region, showing Great Lakes tectonic 

zone and adjacent Archean terranes M8

5. Simplified geologic map of western Vermilion district, Minnesota, showing 

distribution of gold prospects and area of anomalous gold in A-horizon soils 

relative to faults, lamprophyre and syenite bodies, and buried magnetic anomaly 

at Lost Lake M9

6. Simplified geologic map of Ishpeming greenstone belt, northern Michigan, 

showing major faults and gold prospects and mines M10

7. Geologic map of Ropes mine area, Michigan Mil

8. Geologic map of 1,152-foot level, Ropes mine, Michigan M12

9. Structural map of Rainy Lake area, Minnesota and Ontario, showing relationship

of gold deposits to transcurrent faults M13

10. Simplified tectonic map of Lake Superior region, showing outline of 

subprovinces within the Archean Superior province M16

Contents III

CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION

A Regional Structural Model for

Gold Mineralization in the Southern Part of the

Archean Superior Province, United States

By P.K. Sims and W.C. Day

Abstract

The Canadian segment of the Archean Superior province 

is a major world source of lode gold. The gold deposits occur 

in or near regional transcurrent and oblique slip-shear deformation zones that comprise a conjugate set to a northwestdirected compression of the Superior province. These structures provided permeable pathways for the flow of large 

volumes of auriferous fluid derived from an external source.

Historic gold production from the United States segment 

of the Superior province is modest, but the close similarity in 

the geologic environment of the United States and Canadian 

segments suggests that large gold deposits should be present in 

the U.S.A.

An occurrence model largely based on known parameters of gold mineralization in Canada suggests that the 

greenstone-granite terranes of the Wawa and Wabigoon subprovinces in the United States are favorable for important gold 

deposits. The deposits should be hosted at a regional, district, 

and deposit scale in or adjacent to transcurrent faults, such as 

the Vermilion fault system in northeastern Minnesota and its 

smaller splays. These structures are sites of high strain that are 

commonly discordant to the boundaries of rock units on a 

regional scale and extend to great depths. The model suggests 

that gold mineralization took place during or later than the 

transcurrent faulting and that it took place contemporaneously 

with emplacement of silica-undersaturated intrusions. The 

faulting occurred late in the igneous-tectonic history of the 

Superior province, about 2,690 Ma. Extensive, intense alteration comprising carbonitization, silicification, and sulfidization accompanied the gold mineralization. The relationships 

between alteration minerals and mineralized veins suggest a 

close temporal relationship between the alteration and gold 

mineralization processes.

Manuscript approved for publication August 5, 1991.

The proposed occurrence model for gold mineralization 

and the available data suggest that two broad regions of 

greenstone in the Archean Superior province in north-central 

United States are particularly favorable for gold deposits: 

(1) the Upper Peninsula of Michigan, and (2) northeastern 

Minnesota. The Ishpeming greenstone belt of the Wawa 

subprovince in Michigan contains the important Ropes deposit 

and several other known gold occurrences, and the Vermilion 

district (Wawa subprovince) in northeastern Minnesota contains highly anomalous gold in soils and minor known bedrock occurrences. Transcurrent faults in both areas should be 

favorable sites for gold mineralization.

INTRODUCTION

A consensus obtains that the numerous gold deposits 

in the Superior province of Canada are spatially associated 

with regional transcurrent and oblique slip-shear deformation zones formed in Late Archean time (Colvine, 1989; 

Card and others, 1989; Hodgson, 1989). The deformation 

zones comprise a conjugate set to a northwest-directed 

compression of the Archean Superior province.

The United States segment of the Archean Superior 

province in northern Minnesota, northern Michigan, and 

Wisconsin lacks large known gold deposits, but it contains 

regional transcurrent structures and other geologic characteristics very similar to those in the Canadian part, where 

large deposits are known and exploited. Because of the 

similar tectonostratigraphic setting, significant gold 

deposits should exist in Archean rocks in north-central 

United States. Exploration for gold deposits in this region is 

hampered, however, by a generally thin, discontinuous 

mantle of Pleistocene glacial deposits.

Gold Mineralization, Archean Superior Province, United States Ml
ACKNOWLEDGMENTS

Development of an occurrence model for gold mineralization in the United States part of the Archean Superior 

province is possible because of the many excellent 

published geologic maps in north-central United States and 

adjacent Canada and the thoughtful syntheses of Canadian 

Archean lode gold deposits by Colvine and others (1988), 

Colvine (1989), Card and others (1989), and Roberts 

(1987). Constructive reviews by TJ. Bornhorst and G.B. 

Morey significantly improved the manuscript.

GEOLOGIC FRAMEWORK OF 

SUPERIOR PROVINCE

The Superior province is the world's largest relatively 

undisturbed Archean craton; it has been tectonically stable 

since 2.5 Ga. It comprises the core of the Canadian Shield 

and extends southward into north-central United States. The 

south half of the province consists dominantly of alternating 

belts of volcano-plutonic (greenstone-granite) terranes and 

metasedimentary rock terranes that have been designated as 

subprovinces (fig. 1). The Superior province is surrounded 

by Proterozoic orogenic belts, which marginally affect the 

Archean craton, and is covered to the west and north by 

Phanerozoic rocks. The geology of the Superior province 

has been described elegantly by Card (1990) and Hoffman 

(1989).

The subprovinces of the Superior province have 

contrasting lithologic assemblages, metamorphic and structural styles, geophysical characteristics, and ages, and are 

largely fault bounded. They are comparable to Phanerozoic 

tectonostratigraphic (or suspect) terranes in the North American cordillera (Jones and others, 1977). The greenstonegranite terranes, which host the gold deposits known in 

Canada and are the most favorable hosts for deposits in the 

United States, are characterized by dominantly greenschistfacies volcano-sedimentary sequences that are mainly 2.75 

Ga to 2.70 Ga. Volcanism was accompanied by mafic to 

trondhjemitic plutonism. Late Archean orogenesis, accompanied and followed by calc-alkalic to alkalic plutons, 

occurred in the interval 2.70-2.68 Ga in the southern part 

(Wawa and Quetico subprovinces) of the Superior province. 

The deformation resulted from general north-south compression and dextral transpression (Poulsen, 1986; Hudleston and others, 1988), which was caused in part at least by 

oblique collision of the southern Archean gneiss terrane (in 

part 3.5 Ga) with the Superior province along the Great 

Lakes tectonic zone (Sims, 1991).

NATURE AND DISTRIBUTION OF 

CANADIAN GOLD DEPOSITS IN 

SUPERIOR PROVINCE

The Superior province of the Canadian Shield has 

yielded more than 4,5001 (metric tons) of gold more than 

any other Archean craton in the Western Hemisphere. One 

hundred twenty deposits exceed 3,000 kg (kilograms) of 

production each, plus reserves. About 60 percent of the 

production has come from the Abitibi subprovince, in 

eastern Ontario and western Quebec (fig. 1); substantial 

production has also come from the Uchi and Wabigoon 

subprovinces. More than 80 percent of the gold has been 

recovered from about 30 lode gold deposits, each with a 

production of more than 30 t (Card and others, 1989; 

Colvine, 1989).

Card and others (1989) have distinguished two types 

of gold deposits in the Superior province of Canada: 

(1) sulfide schist deposits, and (2) epigenetic vein deposits. 

The sulfide schist deposits are paraconcordant and consist 

dominantly of disseminated and vein pyrite and (or) pyrrhotite in sericitic schist; quartz veins are subordinate. The wall 

rocks are altered to aluminous mineral assemblages, including combinations of aluminosilicate species, chloritoid, 

staurolite, and garnet. This deposit type, which many 

believe is that of the large Hemlo, Ontario, deposit (Muir 

and Elliot, 1987; Corfu and Muir, 1988), is sited in wide 

zones of ductile transcurrent shear. Sulfide schist deposits 

are less common and less productive than epigenetic vein 

deposits.

Epigenetic vein deposits comprise veins, disseminations, and replacements in steeply dipping reverse to 

reverse-oblique, ductile to brittle shear zones, with subordinate veins in extensional fractures and stockworks. The 

gold deposits are spatially associated with major fault or 

shear zones tens to hundreds of kilometers long within or 

along the margins of greenstone belts. The mineralized 

structures transect all rock types. Lode gold deposits occur 

in every rock type within greenstone belts (or greenstonegranite terranes) but are spatially and temporally associated 

with small, late-tectonic to post-tectonic intermediate to 

felsic intrusions, including syenite and lamprophyre (Colvine and others, 1984; Wyman and Kerrich, 1988). The 

veins contain quartz and carbonate minerals with subordinate pyrite, arsenopyrite, tourmaline, chlorite, and scheelite. They are surrounded by zoned alteration envelopes 

dominated by carbonate, including ferroan dolomite and 

ankerite, and are a few meters to a few tens of meters thick; 

hydrothermal minerals overprint metamorphic minerals, 

and a correlation exists between alteration mineralogy and 

regional metamorphic grade, presumably because alteration 

within the shear zones was approximately synchronous with 

subprovince-wide regional metamorphism (Colvine, 1989, 

table 1). The alteration is characterized overall by carbonitization, potassium metasomatism (generally sericite), and

M2 Precambrian Geology of Lake Superior Region
EXPLANATION

 Phanerozoic, Proterozoic rocks 

Subprovince boundary

ARCHEAN SUBPROVINCE TYPE 

Plutonic

Volcano-plutonic 

Metasedimentary

^i^^^^^^Kf PJJSKASING! " V-«^ 

 ^ SuCT^o^ W-\^f^ Vji^ll^7

^ -' r * < "> ; " 5^» r < li^i *; Jt-i-r-zTpoN

MIDCONTINENT 

RIFT SYSTEM

Figure 1 . Generalized geology of Superior province showing subprovinces and Canadian gold camps. Modified from Card 

and Ciesielski (1986). Gneiss in Minnesota River Valley and in northern Michigan is not part of Superior province. Dot, major 

gold camp.

sulfidization of adjacent wall rocks and is accompanied by 

the addition of CO2, K, S, and H2O, as well as Au, As, Bi, 

and W (Roberts, 1987; Kerrich, 1983).

The fundamental regional control on gold deposits in 

the Superior province is transcurrent and oblique slip-shear 

deformation zones that formed in Late Archean time

(Colvine and others, 1988, Colvine, 1989; Card and others, 

1989; Roberts, 1987; Hodgson, 1989). The deformation 

zones form a conjugate set to a northwest-directed 

compression. The major structures are east-trending, dextral 

transcurrent shear zones, many of which are subprovince 

boundaries, and northeast-trending, sinistral faults that

Gold Mineralization, Archean Superior Province, United States M3
branch from and occur between the dextral shears. The 

known distribution of gold deposits can be seen to be 

controlled by the complex structures, but it is also 

influenced by and closely associated spatially and 

temporally with late tectonic syenite and lamprophyre dikes 

(Wyman and Kerrich, 1988), which were emplaced preferentially along the regional shear zones. Wyman and 

Kerrich (1988) contended that volatile-rich lamprophyre 

magmas from deep sources were emplaced along major 

deep-seated structures that also hosted gold mineralization. 

They did not suggest, however, that gold mineralization in 

the Superior province is directly related to lamprophyre 

emplacement; they suggested instead that both gold mineralization and lamprophyre genesis are related to a common tectonic environment; both were emplaced under 

localized tensional conditions along structures that extend to 

the mantle, but each is derived from a different source 

region. In a far-reaching study, Rock and others (1989) 

further emphasized the close space-time association 

between gold deposits and calc-alkaline (shoshonitic) lamprophyres. They also demonstrated that many lamprophyric 

rocks are enriched in gold relative to other igneous rocks, 

and suggested that lamprophyres may contribute at least 

some gold directly to gold-bearing systems.

The time of gold mineralization in the southern part 

of the Superior province has been approximately determined by precise isotopic analyses of zircon, titanite, and 

rutile from the Rainy Lake area, Ontario (Davis and others, 

1989), which lies astride the Quetico-Wabigoon subprovince boundary (figs. 1 and 9). The major ductile deformation took place between 2,696 Ma and 2,692 Ma; this 

deformation was followed shortly by transcurrent (wrench) 

faulting and simultaneous deposition of conglomerate and 

arenite of Timiskaming type (Thurston and Olivers, 1990), 

which can be constrained in the interval 2,692-2,686 Ma. 

Late (Algoman) granitic plutons were emplaced about 

2,686 Ma. Gold was deposited at about 2,690 Ma in 

structures related to transcurrent faulting. In the Shebandowan belt of the Wawa subprovince, west of Lake 

Superior, in Canada (fig. 1), transcurrent faulting occurred 

between 2,689+3/-2 Ma and 2,684+6/-3 Ma (Corfu and 

Stott, 1986), thus approximately dating the gold mineralization in this area. In the Abitibi subprovince, gold deposits 

in the Timmins and Matheson areas are somewhat younger, 

having formed in the interval 2,678-2,673 Ma; deposits in 

the Detour Lake mine are 2,722+3/-2 Ma (Marmont and 

Corfu, 1989).

SUPERIOR PROVINCE IN NORTH-CENTRAL 

UNITED STATES

The United States segment of the Archean Superior 

province, in northern Minnesota, northern Michigan, and 

northwestern Wisconsin, contains regional transcurrent

structures and other geologic characteristics similar to those 

in the southern part of the Superior province in Canada. 

Although major known gold deposits currently are lacking, 

the transcurrent structures should be favorable for the 

occurrence of such deposits.

Archean Tectonic Framework

Three subprovinces of the southern part of the 

Superior province extend from Canada into the United 

States (fig. 1). From north to south, these are the Wabigoon, 

Quetico, and Wawa subprovinces. The Wawa subprovince 

is the southwestern extension of the Abitibi subprovince, 

on the west side of the Kapuskasing structure, which is a 

discontinuous, partly fault bounded, north-northeasttrending zone of high-grade gneiss that cuts across the 

east-west trends of the lower grade, supracrustal rocks of the 

central Superior province (Percival and Card, 1983). The 

Wawa subprovince comprises volcano-plutonic rocks typical of greenstone-granite terranes in the Superior province, 

such as that exposed in the Vermilion district of northeastern Minnesota (Sims, 1976) and the Ishpeming greenstone belt in northern Michigan (Johnson and Bornhorst, 

1991). The Vermilion district consists mainly of a central 

belt of metavolcanic and metasedimentary rocks that is 

bounded on the south by the Giants Range batholith. It is 

separated from the Quetico metasedimentary-granitoid subprovince to the north by the Haley and Burntside Lake 

normal faults and locally by the Vermilion dextral transcurrent fault (fig. 2). The dominant structures in the region 

compose the Vermilion fault system, which consists of 

several east-trending anastomosing fault strands, each of 

which shows dextral movement; the aggregate horizontal 

displacement on the fault system within the area of figure 2 

is 17-19 km (Sims, 1976). Subsidiary complementary faults 

having sinistral movement trend northeast and show lateral 

offsets of as much as 7 km (Waasa fault, fig. 2). Details of 

the conjugate fault system are shown on the geologic maps 

of the Vermilion district (Sims and Southwick, 1985; Sims, 

1985).

The Ishpeming greenstone belt consists dominantly of 

mafic metavolcanic rocks (Johnson and Bornhorst, 1991) 

but includes felsic metavolcanic and metasedimentary 

rocks. These rocks are bounded by gneissic plutons of 

tonalite-granite (Archean) and are locally overlain by 

sedimentary rocks of the Early Proterozoic Marquette 

Range Supergroup (fig. 3). Several dextral transcurrent 

faults or shear zones, the largest of which are assigned 

names in figure 3, cut the Archean rocks.

In the Vermilion district, Minnesota, the deformed 

and metamorphosed volcanic and sedimentary rocks compose an east-trending belt between more competent rocks of 

the Late Archean Vermilion Granitic Complex (Southwick 

and Sims, 1980) (Quetico subprovince) and the Giants 

Range batholith to the south (fig. 2). Hudleston and others

M4 Precambrian Geology of Lake Superior Region
92°30' 92°00' 91°30'

4B°00'

47°45' ^

 - ;*«*T * r * #\* * * * ^ ^. * *»» »;. * ** */ * * * *. * *»*-. ***'_

0 4 8 12 16 KILOMETERS

I I I I I

EXPLANATION 

ARCHEAN (>2,500 Ma)

Vermilion Granitic Complex of Quetico subprovince 

Greenstone-granite terrane of Wawa subprovince 

Greenstone 

Granitoid rocks of Giants Range batholith

Contact

Normal fault Bar and ball on downthrown side

Transcurrent (strike-slip) fault Barbs show 

relative horizontal displacement

High-angle fault

MAP AREA

Figure 2. The Vermilion fault system of dextral transcurrent faults and complementary sinistral faults, Vermilion district, northern 

Minnesota. The faults comprise a conjugate system. Modified from Sims and others (1987).

(1988) attributed the measured strain, a steep cleavage, 

upright folds, and a mineral lineation in this belt to the 

"main" phase of deformation (D2) that followed an early 

nappe-forming event (Dj) (Bauer, 1985). The nappes in the 

Vermilion district show little evidence of a penetrative 

fabric (Hudleston, 1976). Hudleston and others (1988) 

attributed the D2 deformation to a regional dextral 

transpression, as the strain pattern requires a northeastsouthwest component of shortening in addition to shear. 

They concluded that major dextral faults, such as the 

Vermilion fault (fig. 2), are later more brittle expressions of 

this shear regime. They postulated that the D2 transpressive 

deformation resulted from oblique compression of the 

greenstone between the two more rigid crustal blocks to the 

north (Quetico subprovince) and south (Giants Range 

batholith). A similar tectonic regime has been recognized in

Gold Mineralization, Archean Superior Province, United States MS
87°45' 87°30'

5 

. I

10 

I

15 KILOMETERS

Ishpeming

greenstone

belt

EXPLANATION 

MIDDLE PROTEROZOIC -t-^

Jacobsville Sandstone i

EARLY PROTEROZOIC H 

Alkali granite (Age 1,733±25 Ma) 5 

Marquette Range Supergroup

Thrust fault Sawteeth on overthrust block

Inclined foliation

Vertical foliation 

15 Bearing and plunge of lineation

Bearing and plunge of minor fold 

^ » ~ Mylonite 

CRSZ Carp River shear zone 

CRFSZ Carp River Falls shear zone 

DRSZ Dead River shear zone 

GLTZ Great Lakes tectonic zone

ARCHEAN

Greenstone-granite terrane

Reany Creek Formation 

Gneissic tonalitc-granitc 

Metavolcanic rocks

Ultramafic rocks 

Gneiss terrane 

Granite near Tilden (Hammond, 1978)

Gneiss, migmatite, and amphibolite

Contact 

High-angle fault

Transcurrent fault Barbs show relative 

horizontal displacement

Figure 3. Geology of part of Marquette 1 °x2° quadrangle, northern Michigan. Compiled by P.K. Sims, 

1990.

0 40 KILOMETERS ^Edfle of

, : Paleozoic >;'°<*s

M6 Precambrian Geology of Lake Superior Region
the Rainy Lake area, astride the International border 

(Poulsen and others, 1980; Day and Sims, 1984; Day and 

others, 1990; Day, 1990), where early recumbent folding 

was followed by upright folding and dextral strike-slip 

faulting. The same general tectonic regime has been recognized in the Ishpeming greenstone belt in northern 

Michigan, north of the Marquette trough (fig. 3) (Johnson 

and Bornhorst, 1991). In this region, early recumbent folds 

(Fj) are deformed by upright, predominantly Z-shaped folds 

and by younger dextral faults.

Sims (1991) has proposed that the transcurrent 

faulting and earlier upright folding (D2) in the Wawa 

subprovince, and possibly also the Wabigoon subprovince, 

in north-central United States, resulted mainly from oblique 

collision along the Great Lakes tectonic zone (GLTZ), 

which is the paleosuture between Superior province rocks 

(Wawa subprovince) and the Archean gneiss terrane to the 

south (fig. 4). Based on data from the Marquette, Mich., 

area, the collision resulted in dextral thrust shear along the 

GLTZ and northward vergence and probable overriding of 

the south margin of the Superior province by the Archean 

gneiss terrane (Sims, 1991). This implies southward subduction of the Superior province rocks beneath the gneiss 

terrane, or northward obduction of the gneiss terrane over 

the Wawa subprovince. Age dating in the Rainy Lake area 

(Davis and others, 1989) indicates that the collision along 

the GLTZ occurred about 2,690 Ma, approximately 

concurrent with gold mineralization.

In east-central Minnesota, the nature of the GLTZ and 

its vergence is controversial. Shallowly dipping seismic 

reflectors throughout the upper 30-35 km of greenstonegranite crust have been interpreted as indicating faults, 

probably thrusts, that dominantly dip gently (-30°) northward (Gibbs and others, 1984). A particularly conspicuous 

zone of reflectors of this attitude projects to the surface 

about 45 km north of the position of the GLTZ as delineated 

previously from discontinuities in gravity and magnetic 

anomalies (Morey and Sims, 1976, fig. 8), and this zone has 

been interpreted by Gibbs and others (1984) as the GLTZ. 

Other shallow-dipping reflectors both above and below the 

zone interpreted as the GLTZ presumably represent imbricate thrust structures related to the GLTZ. With this 

interpretation, the northward dip implies southward vergence and southward overriding of the gneiss terrane by the 

greenstone-granite terrane. However, by analogy with seismic reflection profiles in the greenstone-granite terrane of 

the Abitibi subprovince (Jackson and others, 1990), along 

strike to the northwest in Ontario and Quebec, we propose 

an alternative interpretation of the Minnesota seismic data. 

In the Abitibi belt, relatively flat seismic reflectors characterize the upper 12 km of greenstone crust. These reflectors resemble those in the greenstone crust of Minnesota in 

being discontinuous and having variable shallow dips. 

These reflectors are truncated and in part offset by regional, 

steeply dipping, ductile-brittle shear zones, such as the

Dexter-Porcupine and Cadillac-Larder Lake fault zones, 

which are transparent in seismic profiles. The shallowdipping reflectors in the Abitibi subprovince are interpreted 

by Jackson and others (1990) as layering and (or) tectonic 

high-strain zones, perhaps low-angle faults that produced an 

"out of sequence" stratigraphy revealed by U-Pb geochronology (Corfu and others, 1989). We propose that the 

shallow-dipping seismic reflectors in the greenstone crust of 

central Minnesota represent recumbent folds and perhaps 

related faults, rather than structures related to the GLTZ. 

Such recumbent folds have been demonstrated in outcropping areas in northern Minnesota (Hudleston and 

others, 1988) as preceding upright folding and transpressive 

dextral shear (D2).

We also propose that the steep southeast-dipping fault 

shown by Gibbs and others (1984) near station 500 on line

3 is the GLTZ. This structure, locally called the Morris fault 

(Gibbs and others, 1984, fig. 2), is 5 km south of Alexandria, in Douglas County, Minn. This position (locality A) is 

shown along the trace of the GLTZ in Minnesota in figure

4 of this report. The Morris fault has been determined from 

surface-wave focal-plane determinations of a recent earthquake near Morris to have a steep southerly dip (=70°) 

(Herrmann, 1979). A steep southerly dip for the GLTZ in 

Minnesota would be consistent with structural observations 

in the tectonic zone near Marquette, Mich. (Sims, 1991), as 

well as with northward vergence on the structure. Also, the 

apparent narrowness of the tectonic zone in Minnesota is 

consistent with the 2.4-km-wide mylonite zone in the GLTZ 

exposed in Michigan.

Lamprophyre and Syenite in Vermilion 

District, Minnesota

Lamprophyre and syenite bodies of Late Archean age 

are common in the Vermilion district (Wawa subprovince) 

and adjacent parts of the Vermilion Granitic Complex 

(Quetico subprovince) (fig. 5). They are concentrated along 

and near the boundary of the Wawa subprovince and the 

Vermilion transcurrent fault, but are not confined to this 

zone, and are late- to post-tectonic, having been emplaced 

after the main regional deformation (D2) (Hudleston and 

others, 1988).

The lamprophyre bodies are dominantly metaspessartite that contains euhedral ferromagnesian phenocrysts in a 

microgranular groundmass (Sims and Mudrey, 1972; 

Geldon, 1972). Hornblende and clinopyroxene are the 

dominant phenocrysts; plagioclase and potassium feldspar, 

in varying proportions and amounts, and ferromagnesian 

minerals occur in the groundmass. The intrusions are silicaundersaturated and volatile rich; they have high Fe2O3:FeO 

ratios and relatively high lime and total alkali contents. 

Lamprophyres within the Vermilion Granitic Complex 

(Quetico subprovince) are associated with and locally cut 

by appinites and hornblende diorites, their plutonic

Cold Mineralization, Archean Superior Province, United States M7
97

I

J- CANADA- 4 ... |- .......... I

 UNITElTsTATF*1:!: ' L'.WABIGOON SUBPRDVINCE

ftainy Lake area. ............... CANADA

FAULT

SUBPROVINCE:

nvi^vr.:::::::: :Thunder Bay 

; i

t ...... VERMILION

DISTRICT :>;

LAKE SUPERIOR

IAGARA**FAULT* 

.. ii »»"*»* ^ . *

WISCONSIN MAGMATICTERRANES

47'

46

50

i I

100 KILOMETERS 

_I

EXPLANATION

MIDDLE PROTEROZOIC 

Rocks of Midcontinent rift system (age.=r 1,100 Ma) 

EARLY PROTEROZOIC

Turbidites overlying shelf deposits 

Plutonic and volcanic rocks

Complex continental-margin sequences 

ARCHEAN

Rocks of greenstone-granite terrane Rocks of gneiss terrane

t

A

Contact 

High-angle fault

Transcurrent fault Barbs show relative 

horizontal displacement

Thrust fault Sawteeth on 

overthrust block

Trace of Great Lakes tectonic zone (GLTZ)Trend of foliation

Direction of tectonic transport

Locality mentioned in text
Figure 4 (facing page). Simplified tectonic map of Lake 

Superior region, showing Great Lakes tectonic zone and 

adjacent Archean terranes. Fault pattern is simplified from 

figure 2. Modified from Sims (1991). Terminology of Early 

Proterozoic rocks modified from Southwick and Morey (1991).

equivalents. McCall and others (1990) have shown that 

these lamprophyres range from olivine-normative to quartznormative and are associated with cumulate hornblenditic 

rocks and pyroxenites. Values for eNd indicate derivation 

from a depleted mantle source. Lamprophyres along or 

adjacent to faults are foliated and metamorphosed, suggesting emplacement during the faulting. The lamprophyres 

and associated syenitic rocks in the western Vermilion 

district are clustered about a magnetic anomaly that

presumably indicates a buried, cogenetic magnetite series 

(Ishihara, 1981) pluton (fig. 5). This interpretation is based 

on outcrops of syenite and lamprophyre along the margins 

of the buried anomaly.

Gold Deposits, Occurrences, and Anomalies

Ropes Gold Mine, Northern Michigan

The Ropes gold mine, in northern Michigan (location, 

fig. 6), has been the only substantial gold producer in the 

United States segment of the Archean Superior province. 

From 1882 to 1897 it produced 1,250 kg of gold and 6,200 

kg of silver (Broderick, 1945), and from 1985 to closing in 

1989 it produced 5,219 kg of gold (R.A. Brozdowski, 

written commun., 1990).

48°00' 92°45' 92°30' 92°15' 92°00'

47°45'

10 KILOMETERS

EXPLANATION

ARCHEAN INTRUSIVE ROCKS 

Lamprophyre 

Syenite

Quetico subprovince 

Wau/a subprovince 

Contact

High-angle transcurrent fault Barbs 

show relative horizontal displacement; 

dashed where concealed

High-angle normal fault Bar and ball 

on downthrown side; dashed where 

concealed

Outline of buried magnetic anomaly

Outline of gold (>3 parts per billion)

anomaly in A-horizon soils; western 

limit of geochemical survey is 

long 92°22'30" W.

Gold prospect

MAP AREA

Figure 5. Simplified geology of western Vermilion district, Minnesota, showing distribution of gold prospects and area of 

anomalous gold in A-horizon soils relative to faults, lamprophyre and syenite bodies, and buried magnetic anomaly at Lost Lake. 

Sinistral faults are highly generalized. Modified from Sims and Mudrey (1972), with additions from Sims and Southwick (1985).

Gold Mineralization, Archean Superior Province, United States M9
The Ropes deposit contains 2.8 million t (metric tons) 

of ore assaying 3.24 g Au/t and minor silver (R.A. 

Brozdowski, written commun., 1989). It occurs in quartzsericite-chlorite rock within serpentinized peridotite (fig. 7). 

The protolith of the quartz-sericite-chlorite rock is altered 

dacite tuff, tuff breccia, and flows. The quartz in the altered

rock shows undulose extinction and subgrain textures 

indicative of grain size reduction (Hanmer, 1982) during 

ductile deformation. The deposit has been described by 

Bornhorst and others (1986), Brozdowski and others (1986), 

and Brozdowski (1988; 1989); and earlier by Broderick 

(1945).

B7°45' 87°30'

46°42' -

46°30'

R 28 W R 27 W R 26 W R 25 W

EXPLANATION

Sedimentary rocks (Early Proterozoic) and 

granitoid rocks (Archean), undivided

Greenstone (Archean)

Contact

Transcurrent (strike-slip) fault 

CRSZ Carp River shear zone 

CRFSZ Carp River Falls shear zone 

DRSZ Dead River shear zone 

WCSZ Willow Creek shear zone INDEX MAP 

A Gold prospect or mine 

R Ropes mine

Figure 6. Simplified geology of Ishpeming greenstone belt, northern Michigan, showing major faults and gold prospects and 

mines. Geology modified from Brozdowski (1989) and Johnson and Bornhorst 0991). A, B, and C mark concentrations of gold 

occurrences (Brozdowski, 1989, fig. 8).

M10 Precambrian Geology of Lake Superior Region
. 

, Wb*

' ' Wtb"

EXPLANATION 

EARLY PROTEROZOIC (2,500-1,600 Ma)

Graywacke

Quartzite 

ARCHEAN (2,500 Ma AND OLDER)

Tonalite and granodiorite

Serpentinized peridotite

Metagabbro

Banded iron-formation

Metabasalt

Tuff and tuff-breccia

Volcanic conglomerate and tuff

Contact Dashed where concealed

Transcurrent fault Barbs show relative 

horizontal displacement; dashed 

where inferred

High-angle fault

CRSZ Carp River shear zone

CRFSZ Carp River Falls shear zone

X Ropes mine shaft

Figure 7. Geology of Ropes mine area, Michigan. Modified from Brozdowski (1989).

The ore is of two types: (1) finely disseminated gold 

with disseminated pyrite in quartz-sericite-chlorite rock 

(altered dacite), which comprises about 75 percent of the 

ore, and (2) gold-bearing quartz-tetrahedrite veins. The 

main ore zone trends N. 80° E., subparallel to the foliation, 

dips steeply, and has a strike length of about 335 m, an 

average width of 12 m, and a down-dip extent of more than 

600 m (Brozdowski, 1989).

Ore shoots within the N. 80° E.-trending main ore 

zone strike N. 55°-65° E. and form en-echelon sigmoidal 

zones of gold and dispersed pyrite (fig. 8). Brozdowski 

(1989) determined that the sigmoidal zones of gold concentration follow an S fabric (Lister and Snoke, 1984), 

interpreted as a largely compressive, ductile feature. The 

orientation of the S fabric relative to the C direction (fig. 8) 

indicates a dextral component of shear when viewed in the 

horizontal plane.

The auriferous quartz veins occur on the south margin 

of the deposit as en-echelon ore shoots that strike N. 55°- 

65° E. within the N. 80° E. trend of the host rock, plunge 

steeply west, and occur progressively farther east in 

successively deeper mine levels. As in the main ore zone, 

the quartz has undulatory extinction, subgrain development, 

and mortar texture along grain boundaries. The maximum 

stretch direction (X axis of strain ellipse) determined by 

connecting the midpoints of these extension veins is 

oriented at an angle of about 45° S. 45° E. These ore shoots 

plunge subparallel to the stretch lineation in the GLTZ 

(Sims, 1991).

Prospects in Northern Michigan

Gold occurrences are widely distributed in the Ishpeming greenstone belt but are concentrated in three main

Gold Mineralization, Archean Superior Province, United States M11
a 

S

!

60 METERS

EXPLANATION 

ARCHEAN

Serpentinized peridotite

Carbonate-talc rock

Layered to massive carbonate-quartz-chlorite rock

Quartz-sericite-chlorite rock

Ore body containing >2g Au/ton

Contact Dashed where inferred

Figure 8. Geology of 1,152-foot level, Ropes mine, Michigan. Modified from Brozdowski (1988). Sketch at right shows S-C fabric with dextral sense
areas (Brozdowski, 1989, fig. 8), designated A, B, and C in 

figure 6. In area A, several small deposits and prospects 

occur within a kilometer-wide belt trending southwestward 

from the Ropes mine. The deposits strike in diverse 

directions and lack a common structural control. In area B, 

known as the Silver Creek area (Brozdowski, 1989), several 

small occurrences occur in a chlorite-rich altered rock in 

and adjacent to the Dead River shear zone. In area C, gold 

occurrences are along sheared rhyolite sills that strike 

subparallel to the Dead River shear zone.

Rainy Lake Area, Minnesota

Scattered occurrences of gold were discovered in 

northern Minnesota during the latter part of the 19th 

century, but these deposits have yielded negligible amounts 

of gold (Sims, 1972, and references therein). The Little 

American mine, on Little American Island, near the south 

shore of Rainy Lake (fig. 9; Day, 1990) yielded a small 

amount of gold in 1894 and 1895. The gold was extracted 

from a 4- to 6-ft composite quartz vein zone in sheared 

chloritic and biotitic schist. The deposit lies within the 

Rainy Lake-Seine River fault zone, a major dextral transcurrent fault (Day, 1990) that in this area separates the 

Quetico subprovince from the Wabigoon subprovince to the 

north (figs. 1 and 9). The gold-bearing quartz vein or veins

have associated arsenopyrite and pyrite and ankerite 

alteration. The veins form concordant and locally discordant 

pods, boudins, and stringers within the host schist, indicating that mineralization was during or slightly later than 

shearing associated with the Rainy Lake-Seine River fault. 

Other prospects were opened intermittently along the eastnortheast extension of the vein zone in the Little American 

mine and in the Vermilion district, to the south.

Poulsen (1983) has reported that the numerous small 

gold-quartz veins in the Mine Centre-Fort Frances area, 

between the Rainy Lake-Seine River fault and the Quetico 

fault to the north (fig. 9), occur in ductile shear zones and 

associated dilation zones. The shears between the two major 

dextral transcurrent faults that host the gold deposits are 

mainly secondary sinistral faults, which are conjugate to 

the longer east-trending major dextral faults. Stott and 

Schnieders (1983) reported a similar structural control for 

Archean lode gold occurrences in the Shebandowan belt 

(Wawa subprovince) in Canada.

Anomalies in Vermilion District, Minnesota

High-angle faults and shear zones form the subprovince boundary between the migmatitic and granitic 

Vermilion Granitic Complex (Quetico subprovince) to the 

north and the greenstone-granite terrane of the Vermilion

B 10 20 KILOMETERS 

i< t i;

4B°30'

EXPLANATION

Wabigoon subprovince 

Quetico subprovince

High-angle fault

Transcurrent fault Barbs show relative 

horizontal displacement

Gold mine or prospect

Figure 9. Structure of Rainy Lake area, Minnesota and Ontario, showing relationship of gold deposits to transcurrent faults 

(modified from Klein, 1989).

Gold Mineralization, Archean Superior Province, United States M13
district (Wawa subprovince) to the south (fig. 5). The 

subprovince boundary is delimited in the Vermilion district 

by the Vermilion, Haley, and Burntside Lake faults. As in 

the Rainy Lake area, several gold prospects occur within a 

2-km-wide belt in adjacent shear zones associated with the 

subprovince bounding fault zones (fig. 5). The gold-bearing 

shear zones are typically chlorite schists or phyllonitic 

schists with notable carbonate and quartz alteration and 

variable amounts of talc, fuchsite, and tourmaline (A. 

Koyner, written commun., 1989).

A-horizon soils in the west-central Vermilion district, 

northern Minnesota, contain anomalous amounts of gold 

as well as base metals (Alminas and others, 1992). The 

principal anomalous area, centered on Lake Vermilion 

(fig. 5), comprises about 90 km2. In this area, the gold 

contents of the soils are as high as 1.1 ppm (parts per 

million); the gold is associated with Ag, Cu, Pb, Zn, Ti, Cr, 

Co, Ni, La, V, and Y. The original mineralization was 

nearly restricted to areas underlain by Late Archean 

volcaniclastic rocks of greenschist facies (Sims, 1985), and 

took place within an area coincident with a pronounced 

positive aeromagnetic anomaly that represents a buried 

pluton probably having affinities with syenite and lamprophyre (fig. 5).

The second anomalous gold area, about 77 km2 in 

areal extent, lies about 30 km east-northeast of the east end 

of Lake Vermilion, and is east of the area of figure 5. Here, 

the gold is associated with Cu, Ti, Mn, Ag, Co, Mo, Ni, Sc, 

Zn, and V. The mineralization took place in areas underlain 

by metavolcanic rocks and metagraywacke bedrock of 

greenschist facies (Sims, 1985). Lamprophyre and syenite 

bodies are present in the core of the anomalous area. 

Alminas and others (1992) have stated that a pronounced 

positive aeromagnetic anomaly is virtually coextensive with 

the gold anomaly.

The two areas of anomalous gold and base metals in 

A-horizon soils are within bedrock, in greenschist-facies 

volcanic-related rocks that are intensely faulted (Sims, 

1985). The east-trending Vermilion and related dextral 

transcurrent faults and abundant northeast-trending sinistral 

faults transect the area. Also, as noted previously, epizonal 

lamprophyre and syenite bodies are uncommonly abundant. 

Alminas and others (1992) suggested that the gold and 

base-metal mineralization was spatially related to these 

magmatic intrusions.

AN OCCURRENCE MODEL FOR GOLD 

MINERALIZATION IN THE UNITED STATES 

SEGMENT OF SUPERIOR PROVINCE

The voluminous literature on Archean lode gold 

deposits in the Canadian segment of the Superior province 

and the definitive syntheses of Colvine and others (1988), 

Colvine (1989), and Card and others (1989), together with

numerous detailed geologic maps, provide a firm basis for 

formulating an occurrence model for gold mineralization in 

the United States part of the Superior province, inasmuch as 

the geologic setting of the two regions is remarkably 

similar.

The widely held consensus that Archean lode gold 

deposits in the Superior province in Canada resulted from 

the flow of large volumes of fluid, derived from an external 

source, through structurally formed permeable zones (Colvine and others, 1984; Colvine, 1989; Card and others, 

1989) points up the important role of structure in localizing 

those Archean gold deposits. On a regional scale the 

deposits are within or near major transcurrent faults or shear 

zones that are sites of high strain and which form a 

conjugate system: (1) east-trending dextral faults, some of 

which are of subcontinental length, and (2) northeasttrending sinistral faults. These faults cover a wide range in 

style of deformation, from ductile shear zones through 

brittle-ductile zones to brittle shear zones and faults (Ramsay, 1980; Hodgson, 1989). The faults are a late phase of the 

regional deformation (D2). The conjugate systems require 

compression oriented northwest-southeast. This tectonic 

environment is similar to that in the Golden Mile area of the 

Kalgoorlie mining district, Western Australia (Mueller and 

Harris, 1987; Mueller and others, 1988, and references 

therein); in Australia, gold deposits are localized in 

structures subsidiary to large-scale transcurrent shear zones; 

they postdate regional folding and metamorphism.

Structures related to the regional transcurrent conjugate fault system in the Superior province (figs. 2 and 4) 

provide the plumbing system for the fluids that deposited 

the gold. At a deposit scale, enhanced permeability in 

dilational areas is the main locus of mineralization, relative 

to the compressional segments of a transcurrent shear 

system (Sibson, 1987; Hodgson, 1989).

Deformation zones are commonly discordant to the 

boundaries of rock units on a regional scale. Therefore, they 

contain the deformed equivalents of many rock types that 

characterize Superior province greenstone-granite terrenes. 

Deformation zones commonly consist of several separate 

shears that anastomose and bifurcate in both horizontal and 

vertical dimensions. Planar fabrics in the shear zones, which 

may be superposed on one another, include S-C structures, 

extensional crenulation cleavages, stretch lineations, and 

lineations caused by the intersection of C and S fabrics 

(Hodgson, 1989). Grain-size reduction, resulting from syntectonic recrystallization associated with ductile strain or 

crystal-plastic processes (Wise and others, 1984), and grain 

fracturing are characteristic of deformation zones. The 

resulting rocks are mylonite or cataclasite. Colvine and 

others (1988) have shown that gold-bearing vein systems 

show systematic vertical and lateral changes in mineralization style: breccia-bearing veins occur mainly within 

zones of brittle deformation and replacement veins typify

M14 Precambrian Geology of Lake Superior Region
ductile deformation zones. Extensive, intense wallrock 

alteration is associated with most of the lode gold deposits 

in both mineralizing environments (Roberts, 1987).

With few exceptions, the Canadian gold deposits are 

restricted to the greenstone belts and immediately adjacent 

areas. Thus, in the United States, the greenstone-granite 

terranes of the Wawa and Wabigoon subprovinces should 

be most favorable areas for the occurrence of gold deposits. 

Rocks of the Wabigoon subprovince are exposed in extreme 

northern Minnesota (fig. 10), in the vicinity of International 

Falls and areas to the west (Day, 1990; Day and others, 

1990). Rocks of the other favorable greenstone-granite 

terrane, the Wawa subprovince (fig. 10) are exposed in 

northeastern Minnesota, as exemplified by the Vermilion 

district (Sims and South wick, 1985; Sims, 1985), and in the 

Upper Peninsula of Michigan, within the Ishpeming greenstone belt (figs. 3 and 6) (Johnson and Bornhorst, 1991). 

Potentially favorable host rocks would include ultramafic, 

mafic, and felsic metavolcanic rocks; clastic metasedimentary rocks, generally of volcanogenic affinity; ironformation; and mafic to felsic plutons. The most favorable 

metamorphic grade of the supracrustal host rocks is greenschist facies.

A close spatial and temporal association of silicaundersaturated plutons with gold deposits (Colvine and 

others, 1988) is observed in many gold-bearing areas, but 

the role of this suite of alkalic intrusions in gold mineralization is uncertain. Commonly, these intrusions were 

emplaced within or near the deformation zones with which 

the gold-mineralized material is associated. As suggested by 

Wyman and Kerrich (1988), both the gold and the intrusions 

were emplaced under tensional conditions along structures 

that extend to mantle depths, but each could have been 

derived from separate source regions. Alternatively, the 

mineralization and magmatic activity could be genetically 

related, as suggested by Rock and others (1989) for at least 

some deposits; this possible relationship deserves further 

study.

The nature of the ore-forming fluid is known moderately well for Canadian deposits, as determined from 

several mining districts in the Abitibi, Wawa, and Wabigoon subprovinces (Colvine and others, 1988, and references therein; Foster, 1990). In brief, the Archean 

auriferous fluids appear to be characterized by high fluid 

pressure, low salinity, moderate temperature, and the 

presence of CO2 . From the striking similarities between data 

from Canadian and Australian Archean gold deposits, 

Colvine and others (1989) have suggested that a compositionally uniform fluid of either magmatic or metamorphic 

derivation was involved in the gold-related alteration and 

gold precipitation event in both regions. The fluid was 

derived from a large reservoir, which was external to the 

immediate depositional environment.

EXPLORATION IMPLICATIONS IN THE 

UNITED STATES

The occurrence model described previously suggests 

that two regions in north-central United States are 

particularly favorable for gold mineralization: (1) northern 

Michigan and (2) northeastern Minnesota. Both areas 

contain moderately good bedrock outcrops and have a 

generally thin cover of Pleistocene glacial deposits and 

colluvium.

Archean rocks in the Ishpeming greenstone belt in 

northern Michigan are favorable host rocks for potential 

gold deposits because of the known valuable deposit at the 

Ropes mine, minor gold occurrences elsewhere (Bodwell, 

1972; Brozdowski, 1989), and the existence of several 

major dextral transcurrent faults (figs. 3 and 6). Exploration 

in this region is difficult, however, because of extremely 

complex folding, including large Z-shaped folds, that 

preceded development of the dextral transcurrent faults 

(Johnson and Bornhorst, 1991).

Northern Minnesota has been explored sporadically 

for gold (Morey, 1989), mainly using a fault model. It 

deserves further exploration because of the known gold 

occurrences, the exceptionally anomalous soils in the Lake 

Vermilion area and vicinity, the numerous lamprophyre and 

syenite plutons, and the abundant transcurrent faults (figs. 2 

and 9). The anomalous gold values in soils in the two areas 

in the west-central Vermilion district (Alminas and others, 

1992) particularly deserve attention, as does the possible 

relationship between gold mineralization and the late alkalic 

intrusions.

DISCUSSION

The major transcurrent faults that host gold mineralization in the Superior province of north-central United 

States and adjacent Canada resulted at least in part from 

convergent tectonics along the GLTZ. Sims (1991) has 

shown that the major dextral transcurrent faults in northern 

Minnesota and Michigan can be accounted for by oblique 

collision along the GLTZ. This collision caused dextral 

transpression, resulting in a northwest-southeast component 

of shortening in addition to shear, followed by dextral 

faulting, a more brittle expression of the shear regime. A 

conjugate, northeast-trending sinistral fault system formed 

essentially concurrently with dextral shear. The northern 

extent of this shear regime is equivocal, however, because 

structures resulting from dextral transpression characterize 

the whole of the Superior province (Card and others, 1989, 

fig. 6). The shearing provided permeable zones extending at 

least to the crust-mantle boundary into which lamprophyre 

and related late- to post-tectonic syenitic rocks were 

emplaced. Gold deposits are localized in these zones.

Cold Mineralization, Archean Superior Province, United States M15
WISCONSIN8 MAGMATICTERRANES

100 KILOMETERS

_J

EXPLANATION

Rocks of Midcontinent rift system (age, ~ 1,100 Ma)

Early Proterozoic continental margin assemblage 

(2,100-1,820 Ma)

Early Proterozoic island-arc plutonic and 

volcanic rocks (1,892-1,760 Ma)

ARCHEAN GREENSTONE-GRANITE TERRANES (2,750-2.650 Ma)

Wabigoon subprovince

Quetico subprovince

Wawa subprovince 

ARCHEAN GNEISS TERRANE (3,600-2.640 Ma)

Gneiss and supracrustal rocks

	Contact

 ^ : Transcurrent fault Barbs show relative horizontal displacement

 j High-angle normal fault Bar and ball on downthrown side

"U 7~ Early Proterozoic thrust fault Sawteeth on overthrust block

T T- Late Archean thrust fault Sawteeth on overthrust block

GLTZ Great Lakes tectonic zone

R L-S R F Rainy Lake-Seine River fault

Figure 10. Simplified tectonic map of Lake Superior region, showing outline of subprovinces within the Archean Superior 

province.

M16 Precambrian Geology of Lake Superior Region
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portions of St. Louis, Lake, and Cook Counties, northeastern Minnesota: U.S. Geological Survey Bulletin 1984, 

37 p.

Bauer, R.L., 1985, Correlation of early recumbent and younger 

upright folding across the boundary between an Archean 

gneiss belt and greenstone terrane, northeastern Minnesota: 

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Bodwell, W.A., 1972, Geologic compilation and nonferrous metal 

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Brozdowski, R.A., 1988, Geology of the Ropes gold mine, in 

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___ 1989, Geology of the Ropes gold deposit, in Precambrian 

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Smith, P.M., and Troop, D.G., 1988, Archean lode gold 

deposits in Ontario: Ontario Geological Survey Miscellaneous Paper 139, 136 p.

Corfu, F., Krogh, T.E., Kwok, Y.Y., Marmont, S., and Jensen, 

L.S., 1989, U-Pb zircon geochronology in the south-western 

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Corfu, F., and Stott, G.M., 1986, U-Pb ages for late magmatism 

and regional deformation in the Shebandowan belt, Superior 

province, Canada: Canadian Journal of Earth Sciences, 

v. 23, p. 1075-1082.

Davis, D.W., Poulsen, K.H., and Kamb, S.L., 1989, New insights 

into Archean crustal development from geochronology in 

the Rainy Lake area, Superior Province, Canada: Journal of 

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Day, W.C., 1990, Bedrock geologic map of the Rainy Lake area, 

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Day, W.C., and Sims, P.K., 1984, Tectonic evolution of the Rainy 

Lake area, northern Minnesota: Geological Association of 

Canada, the Mineralogical Association of Canada, London, 

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Day, W.C., Southwick, D.L., Schulz, K.J., and Klein, T.L., 1990, 

Bedrock geologic map of the International Falls I°x2° 

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Foster, R.P., 1990, Gold mineralization Recent advances in 

predictive metallogeny: Terra Nova, v. 2, p. 215-225.

Geldon, A.L., 1972, Petrology of the lamprophyre pluton near 

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Gibbs, A.K., Payne, B., Setzer, T., Brown, L.D., Oliver, J.E., and 

Kaufman, S., 1984, Seismic-reflection study of the Precambrian crust of central Minnesota: Geological Society of 

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Hammond, R.D., 1978, Geochronology and origin of Archean 

rocks in Marquette County, Upper Michigan: Lawrence, 

Kans., University of Kansas M.S. thesis, 108 p.

Hanmer, S.K., 1982, Microstructure and geochemistry of plagioclase and microcline in naturally deformed granite: Journal 

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Herrmann, R.B., 1979, Surface wave focal mechanisms for eastern 

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Hodgson, C.J., 1989, The structure of shear-related, vein-type gold 

deposits A review: Ore Geology Reviews, v. 4, p. 231- 

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Hoffman, P.P., 1989, Precambrian geology and tectonic history of 

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rocks in the Vermilion district, northeastern Minnesota: 

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Hudleston, P.J., Schultz-Ela, D., and Southwick, D.L., 1988, 

Transpression in an Archean greenstone belt, northern 

Minnesota: Canadian Journal of Earth Sciences, v. 25, 

p. 1060-1068.

Ishihara, Shunso, 1981, The granitoid series and mineralization, in 

Sims, P.K., and Skinner, B.J., eds., Seventy-fifth Anniversary Volume, 1905-1980: Economic Geology, 

p. 458-484.

Jackson, S.L., and eight others, 1990, Southern Abitibi greenstone 

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profiles: Geology, v. 18, p. 1086-1090.

Johnson, R.C., and Bornhorst, T.J., 1991, Archean geology of the 

northern block of the Ishpeming greenstone belt, Marquette 

County, Michigan: U.S. Geological Survey Bulletin 

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Jones, D.L., Silberling, N.J., and Hillhouse, J.W., 1977, Wrangellia A displaced terrane in northwestern North America: 

Canadian Journal of Earth Sciences, v. 14, p. 2565-2577.

Kerrich, Robert, 1983, Geochemistry of gold deposits in the 

Abitibi greenstone belt: Canadian Institute of Mining and 

Metallurgy, Special Volume 27, 75 p.

Klein, T.L., 1989, Mineral occurrence and drill-hole location map 

of the International Falls 1 °x2° quadrangle, Minnesota and 

Ontario: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-2082, scale 1:250,000.

Lister, G.S., and Snoke, A.W., 1984, S-C mylonites: Journal of 

Structural Geology, v. 6, p. 617-638.

Marmont, Soussan, and Corfu, F., 1989, Timing of gold 

introduction in the Late Archean tectonic framework of the 

Canadian Shield Evidence from U-Pb zircon geochronology of the Abitibi subprovince, in Keays, R.R., and 

Skinner, B.J., eds., The geology of gold deposits The 

perspective in 1988: Economic Geology Monograph 6, 

p. 101-111.

McCall, G.W., Nabelek, P.I., Bauer, R.L., and Glascock, M.D., 

1990, Petrogenesis of Archean lamprophyres in the southern 

Vermilion Granitic Complex, northeastern Minnesota, with 

implications for the nature of their mantle source: 

Contributions to Mineralogy and Petrology, v. 104, 

p. 439-452.

Morey, G.B., 1989, Application of mineral deposit models to 

Minnesota, in Morey, G.B., ed., Workshop on the 

applicability of gold and platinum-group-element models in 

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Morey, G.B., and Sims, P.K., 1976, Boundary between two 

Precambrian W terranes in Minnesota and its geologic 

significance: Geological Society of America Bulletin, v. 87, 

p. 141-152.

Mueller, A.G., and Harris, L.B., 1987, An application of wrench 

tectonic models to mineralized structures in the Golden 

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and Groves, D.I., eds., Recent advances in understanding 

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Mueller, A.G., Harris, L.B., and Lungan, A., 1988, Structural 

control of greenstone-hosted gold mineralization by transcurrent shearing A new interpretation of the Kalgoorlie 

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v. 3, p. 359-387.

Muir, T.L., and Elliot, C.G., 1987, Hemlo tectono-stratigraphic 

study, district of Thunder Bay: Ontario Geological Survey 

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Percival, J.A., and Card, K.D., 1983, Archean crust as revealed in 

the Kapuskasing uplift, Superior Province, Canada: Geology, v. 11, p. 323-326.

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mineralization in the Mine Center-Fort Francis area 

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___ 1986, Rainy Lake wrench zone An example of an 

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deWit, M.J., and Ashwal, L.D., eds., Tectonic evolution of 

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in hydrothermal systems: Geology, v. 15, p. 701-704.

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and metallogeny of Archean and Proterozoic basement 

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Ml 8 Precambrian Geology of Lake Superior Region
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foredeep development in the Penokean orogen, east-central 

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and the results of test-drilling: U.S. Geological Survey 

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the Shebandowan belt and its relation to regional deformation patterns, in Colvine, A.C., ed., The geology of gold 

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major structures, and gold deposits Implications for greenstone belt gold metallogeny: Economic Geology, v. 83, 

p. 454-461.

Published in the Central Region, Denver, Colorado 

Type composed by Marie F. Melone 

Graphics by W.E. Sowers 

Edited by Lorna Carter

6U.S. GOVERNMENT PRINTING OFFICE: 1992-673-049/46057 Gold Mineralization, Archean Superior Province, United States M19

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