75

62

85

70

65

72

70

50

35

83

40

80

75

80

50

60

43

22

47

70

70

45

83

85

80

68

75

46

75

60

77

83

75

25

75

75

65

80

70

75

65

75

65 70 80 70

55 35

85

20

24

32

35

10

13

50

10

75

60

25 65

25

63

45 40 37

68

85

35

9

10

40

40

80

78

28

26

60

20

65

65

75

65

40

75

75

65

29 77

35

74

30

40

70

60

78

70

L

L

L L

L

L L

L

L

L

L

L

L

L

L

?

?

HARTVILLE

FAULT

McCANN PASS FAULT

Copper

Bottom

(Cu) Green Hope

(Cu)

Cu

Charter

Oak (Cu)

Crystal Palace

(P)

P

Haystack #2

(P)

Cu

Cu

Chicago

(Fe)

Central

(Fe)

Good

Fortune

(Fe)

Empire

(Cu, Zn)

Cu

Sunrise

(Fe)

Guernsey

Quarry (stone)

Green Mountain

Boy (Cu, Ag)

?

L

L

Qtu

u

Xt

Ww

Qtu Xt

Wfb Xt

Xh

Xh

Qtu

Xt Xt

Qtu Ws Xt Xh

Xp

Xt

Xp

Ws

Ws Xp

Ws

Xh

Xt

Xt

Wmc

Ww

Ww

Ws

Wr

Wmc

Wr

Xh

Ww

Wr

Xh

Wr

Ws

Xh

Ws

Ww

Xh

Ws

Xh Wmc

Ws

Ww

Ws

Wmc

Xp

Xmd

Ww

Xp

Ws

Ww

Wmc Xmd

Qtu

Xp

Ws

Wsh

Wsif

Qtu

Ww

Ws

Wsh

Ws

Wmc

Xh

Wsh

Ww

Qtu

Ws Xh

Ws

Xmd

Qtu

Ws

Ws

Xgb Xgb Ws

Ws

Xh

Ws Xh

Ws

Ws

Wmf

Ws Ws Ww

Qtu

Ww

Wwcs

Qtu

Ww

Wwcs

Ws

Qtu

Wr

u

u

u

u

Xt

u

Xh

u

Xp

u

Qtu

Ww

Qtu

Qtu

u

Xt

Ws

Xh

u

Wsif

u

u

u

Ww

u

Wmf

Ww

Xmd

u

Xmd

Xmd

Xmd

Xmd

u

Xmd

Xmd

u

Ym

Ym

Ym

Ym

Ym

Xmd

Wwp

45' 42'30" 40' 37'30" 35' 32'30" 104°30'

40'

42'30"

45'

104°47'30"

42°15'

17'30"

20'

22'30"

25'

27'30"

42°15'

17'30"

20'

22'30"

25'

27'30"

T 27 N

T 26 N

T 28 N

T 27 N

T 29 N

T 28 N

T 27 N

T 26 N

T 28 N

T 27 N

T 29 N

T 28 N

R 66 W R 65 W R 65 W R 64 W

42'30"

40'

37'30"

35'

32'30"

42°30'

42'30"

40'

37'30"

35'

32'30"

42°30'

T 30 N

T 29 N

T 31 N

T 30 N

T 32 N

T 31 N

T 30 N

T 29 N

T 31 N

T 30 N

T 32 N

T 31 N

R 64 W R 63 W 27'30" 25' 104°22'30"

p

Ws

Ws

Xpet

Ws

Xpet

Qtu

Wr

Ws

Xhg

Ww

QTu

Wr Ww

Wr

Ww

Wpt

Qtu

Ww

Xhg

Wr

Wsq

Ws

Ww

Wpt

Qtu

Wr

Ws

Wpt

Ww

Wpt

Ww Ww

Ws

Wmf

Ww

Ws

Wmf

Wwq

Ww

Qtu

Qtu

Ws

u

Wmf

Xmd

Wmf

Ww

Wpt

Wmf

Qtu

Wfb

Wfb

Wpt

Wr

Ws

Xmd

Wmf

Wr

Ww Wwc

Wmc

Xmd

Xpet

u

Qtu

Xpet

u

Ws

Xpet

Wmf

u

Xpet

Xhg

Xhg

u

Wwq

Wr

Qtu

u

u

Wr

Wr

Wr

QTu

QTu

u

Wmc

u

QTu

QTu

Wwif

Ww

Wwq

Wwq

Wwq

Wmc

u

Ww

Wsq

Ww

Wse

Ww

Abundant mafic

dikes (Xmd) in

granite (Wr)

70

78

42

67

72

45

75

72

80

82

71

68 60

80

70

77

62

78

72

67

60

82

78

55

60 47

50

58

70

52 65

52

82

62

70

67

53

52

75

76

80

35

60

10

41

45

55

57

23

27 40 72

75

48

52

36

66 82

85 80

85

65

80

22

66

86

63

62

70

80

60 72

85

80

86

75

45

55

55

75

35

58

14 25

45

63

60

60

43

45

45

65

40

47

87

78

38

52

80

40

50

30

35

52

88

76

60

87

45

83

67

?

?

?

?

?

HARTVILLE

RAWHIDE

FAULT

SILVER

SPRINGS

FAULT

45

?

P

P

P

P

U, Cu, Zn

Gold Hill

Omaha (Cu, Zn)

(Cu, Zn)

Cu m

m

m

Copper

Belt

(Cu, Zn)

Cu, Zn

Cu

Cu, Au

Cu

Cu, g

Michigan

(Cu, Fe)

Fe

Fe

Fe

Fe

Fe

54

Outline of

largely buried

intrusion (Xh)

?

MUSKRAT CANYON FAULT

LITTLE WILDCAT

CANYON FAULT

FAULT

Stone

INDEX MAP

WYOMING

Hartville

uplift

104°37'30" 104°30' 104°22'30"

104°45'

104°52'30"

42°15'

42°22'30"

42°30'

42°37'30"

42°45'

Silver

Springs

Reynolds

Spring

Rawhide

Buttes

West

Rawhide

Buttes

East

Hell

Gap

Moore

Spring

Guernsey

Reservoir

Guernsey Casebier

Hill

INDEX TO QUADRANGLES

(PROTEROZOIC Y)

EARLY PROTEROZOIC

(PROTEROZOIC X)

LATE ARCHEAN

(PROTEROZOIC W)

Hiatus

Hiatus

Hiatus

Hiatus

Hiatus

Hiatus

Hiatus

Hiatus

Xhg

Xt

Xh

Xpet

Xmd Xmd

Xgb

Wr Wr Wfb

Wmc

Ws Ws

Wmf Wmf

Wwcs

Wwif

Wwq

Wwp

Wwc

Wsh

Wsif

Wwq

Wsif

Wsq

Wpt

Ww Ww

Xp

Wse

DESCRIPTION OF MAP UNITS

CENOZOIC

Quaternary sediments and Tertiary sedimentary rocks, 

undivided—Predominantly Tertiary Arikarie Formation but includes 

Quaternary surficial deposits

PALEOZOIC

Paleozoic rocks, undivided—Includes Fremont Canyon Formation (Upper 

Devonian), Guernsey Formation (Mississippian), and Hartville 

Formation (Mississippian? and Pennsylvanian)

MIDDLE PROTEROZOIC (1,600–900 Ma)

Diabase—Dark-green, medium-grained diabase, with marginal chill zones; 

probable age, ≈1.4 Ga

EARLY PROTEROZOIC (2,500–1,600 Ma)

Pegmatite related to Haystack Range Granite—White to gray, coarsegrained, zoned to unzoned, feldspar-quartz-muscovite-tourmaline 

granitic dikes; contains accessory biotite, garnet, and beryl

Haystack Range Granite—Pink, coarse- to medium-grained, massive to 

foliated, inequigranular biotite granite. Composes a granite dome in 

the Haystack Range (Casebier Hill quadrangle) and a buried dome in 

the Reynolds Spring quadrangle; Rb-Sr whole-rock age, 1.72 Ga 

(Snyder and Peterman, 1982)

Gneissic phase of Haystack Range Granite—Strongly deformed phase 

of granite in aureole surrounding buried granite dome in Reynolds 

Spring and Rawhide Buttes East quadrangles

Twin Hills Diorite—Dark-gray, medium-grained, massive to foliated 

hornblende-biotite monzonite to mafic diorite; locally contains 

clinopyroxene and orthoclase; U-Pb discordia intercept age, 1.74 Ga 

(Snyder and Peterman, 1982)

Tourmaline-bearing granite pegmatite—White to gray, coarse-grained, 

unzoned granite pegmatite containing schorl (black iron-rich 

tourmaline); interpreted to be anatectic melt

Metadiabase—Dark-greenish-black, medium-grained hornblendeplagioclase-quartz metadiabase; granular amphibolite east of Hartville 

fault. Estimated age, ≈2.0 Ga, based on age of similar isotopically 

dated mafic dikes in the Laramie Range (Snyder, 1993; Chamberlain 

and others, 1997)

Metagabbro—Dark-grayish-green, fine- to coarse-grained, weakly layered, 

weakly to strongly foliated metagabbro containing hornblende and 

chlorite. Gabbro is older than D2 deformation. Confined to hill south 

of Graves Ranch (Guernsey quadrangle)

LATE ARCHEAN (2,900–2,500 Ma)

Rawhide Buttes Granite—Pink, red, or gray, medium- to coarse-grained, 

inequigranular granite. Locally contains abundant muscovite and 

sillimanite. Mainly foliated but locally gneissic. Rb-Sr whole-rock 

isochron age, 2.66 Ga (Day and others, 1999)

Flattop Butte Granite—Pink to red, foliated to gneissic, biotite-muscovite 

granite. U-Pb zircon age, 2.65 Ga (K.R. Chamberlain, oral commun., 

1997)

Tourmaline-bearing pegmatite—White to gray, coarse-grained, unzoned 

granite pegmatite containing schorl (black, iron-rich tourmaline); 

pegmatite interpreted to be related to Flattop Butte Granite

Whalen Group

Muskrat Canyon Metabasalt—West of Hartville fault: dark-green, finegrained, locally pillowed, actinolite-biotite-chlorite schist

Wildcat Hills Formation—West of Hartville fault: white to gray 

dolomite and marble; contains algal stromatolitic mounds near 

Hartville. East of Hartville fault: white to gray dolomitic marble, 

tremolite marble, and chondrodite marble

Calc-silicate rock unit—White to light-green lenses, commonly 

10–15 cm in diameter, compose 30–50 percent of rock, and contain 

actinolite, diopside, talc, and epidote

Banded, cherty iron-formation unit—In Muskrat Canyon

Quartzite unit—Gray to red, crossbedded

Pelite unit—Thin layer in metadolomite (Ww), east of Hartville

Quartz pebble conglomerate—Exposed 3,000 ft north of mouth of 

Muskrat Canyon

Silver Springs Formation—West of Hartville fault: dark-gray, medium- to 

fine-grained graywacke and argillite containing chlorite and, locally, 

garnet. In Hartville district, grades laterally into ferruginous 

sedimentary rocks containing lenses of banded, cherty iron-formation 

and hematitic iron ore. East of Hartville fault: gray, layered to 

massive biotite-muscovite schist containing garnet and sillimanite. In 

Silver Springs area, contains pegmatite lenses (Xpet)

Siliceous exhalite—Thin, horizontal unit within Silver Springs 

Formation

Hematitic iron ore unit—In Hartville district

Banded iron-formation and associated ferruginous sedimentary 

rocks

Quartzite—Gray to pinkish gray, medium grained, massive

Mother Featherlegs Metabasalt—Dark-greenish-gray, massive to layered, 

locally pillowed metabasalt

Ym

QTu

Xp

Xh

Xhg

Xt

Xpet

Xgb

Wr

Wfb

Wpt

Wmc

Ww

Wwcs

Wwif

Wwq

Wwp

Wwc

u

Ws

Wsh

Wse

Wsif

Wsq

Wmf

Xmd

Contact—Dashed where inferred

High-angle fault—Showing dip. Dashed where inferred; queried where 

extent uncertain. Bar and ball on downthrown side where sense of 

movement is known; opposed arrows indicate relative horizontal 

movement. L, Laramide in age

Thrust fault of Early Proterozoic age—Dashed where inferred; queried 

where extent uncertain. Sawteeth on hanging wall. Opposed arrows 

indicate relative horizontal movement

Folds—Dashed where covered

Anticline—Showing direction of plunge

Syncline—Showing direction of plunge

Overturned anticline—Showing trace of axial plane, direction of dip of 

limbs, and bearing and plunge of axis

Overturned syncline—Showing trace of axial plane, direction of dip of 

limbs, and bearing and plunge of axis

Bearing and plunge of symmetrical mesoscopic fold

Bearing and plunge of asymmetrical mesoscopic fold

Bedding

Inclined

Upright

Overturned

Vertical—Top of beds known

Vertical—Stratigraphic way-up direction not determined

Foliation

Inclined

Vertical

Primary magmatic flow

Inclined

Vertical

Bearing and plunge of lineation—May be combined with foliation or 

bedding symbol

Bearing and plunge of stretching lineation

Direction of tectonic transport

Mylonite

Thin siliceous exhalite layer—Dashed where inferred

Mineral workings—Showing commodity where known or inferred. Au, 

gold; Cu, copper; Fe, iron; g, graphite; m, marble; p, pegmatite; U, 

uranium; Zn, zinc

Mine shaft

Quarry or open-pit mine

Prospect

15 L

25 

35

40

30 

60 

80 

80 

82

82

25

60

SCALE 1: 48 000

1 1/ 2 0 1 2 3 4 MILES

1 .5 0 1 2 3 4 5 KILOMETERS

CONTOUR INTERVAL 20 FEET

NATIONAL GEODETIC VERTICAL DATUM OF 1929

GEOLOGIC MAP OF PRECAMBRIAN ROCKS OF THE

HARTVILLE UPLIFT, SOUTHEASTERN WYOMING

Compiled by

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

with a section on

Mineral deposits in the Hartville uplift by Terry Klein

1999

Base from U.S. Geological Survey

Rawhide Buttes East, Reynolds Spring, 

Silver Springs, 1974; Rawhide Buttes West, 1978.

Projection and 10,000-foot grid ticks:

Wyoming coordinate system, east zone (transverse Mercator).

1,000-meter Universal Transverse Mercator grid ticks, zone 13.

Casebier Hill, 1950; Moore Spring, 1951;

Guernsey, Guernsey Reservoir, Hell Gap, 1978.

Polyconic projection. 10,000-foot grid based on

Wyoming coordinate system, east zone.

1927 North American datum 

Geology of Precambrian rocks mapped in 1993–97 

by P.K. Sims, W.C. Day, A.B. Wilson, and T.L. Klein; 

geology of Tertiary-Quaternary and Paleozoic units 

mapped in 1977–79 by G.L. Snyder.

Geology digitized by Techni Graphic Systems, Inc.

Edited by Lorna M. Carter 

Digital cartography by Alessandro J. Donatich

Manuscript approved for publication September 10, 1998

Any use of trade names in this publication is for

descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey

This map was produced on request, directly from

digital files, on an electronic plotter

For sale by U.S. Geological Survey Information Services

Box 25286, Federal Center, Denver, CO 80225

1-888-ASK-USGS

This map is also available as a PDF at http://greenwood.cr.usgs.gov
U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

GEOLOGIC MAP OF PRECAMBRIAN ROCKS OF THE

HARTVILLE UPLIFT, SOUTHEASTERN WYOMING

Compiled by

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

with a section on Mineral deposits in the Hartville uplift by Terry Klein

1999

Pamphlet to accompany

GEOLOGIC INVESTIGATIONS SERIES

I–2661
i

CONTENTS

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

Previous work .................................................................................................................................. 1

Present work ................................................................................................................................... 1

Acknowledgments ............................................................................................................................ 1

Regional tectonic setting .................................................................................................................... 1

Precambrian rock units ...................................................................................................................... 2

Mother Featherlegs Metabasalt ..................................................................................................... 2

Silver Springs Formation .............................................................................................................. 2

Wildcat Hills Formation ................................................................................................................ 3

Muskrat Canyon Metabasalt .......................................................................................................... 3

Granitoid rocks ........................................................................................................................... 3

Chemistry of metavolcanic rocks ......................................................................................................... 3

Structure ......................................................................................................................................... 4

D1 deformation .......................................................................................................................... 4

D2 deformation .......................................................................................................................... 4

D3 deformation .......................................................................................................................... 4

D4 deformation .......................................................................................................................... 5

Postdeformation events ..................................................................................................................... 5

Correlation of deformation episodes .................................................................................................... 5

Outlying areas .................................................................................................................................. 6

Sullivan Ridge ............................................................................................................................ 6

Lusk area ................................................................................................................................... 6

Lone Tree Hill ............................................................................................................................ 6

Cassa anticline ............................................................................................................................ 6

Antelope Hills ............................................................................................................................ 7

Discussion .................................................................................................................................. 7

Mineral deposits in the Hartville uplift by Terry Klein .............................................................................. 7

Introduction ............................................................................................................................... 7

Iron deposits .............................................................................................................................. 7

Copper deposits ......................................................................................................................... 8

Sediment-hosted massive sulfide deposits .................................................................................. 8

Disseminated copper sulfide deposits in shear zones 9 ...................................................................

Copper oxide and carbonate replacement deposits 10 ..................................................................
ii

CONTENTS

Mineral deposits in pegmatites .................................................................................................... 10

Uranium deposits ...................................................................................................................... 11

References cited ............................................................................................................................. 11

FIGURES

1. Geologic-tectonic map of Precambrian rocks exposed in Laramide uplifts, southeast Wyoming 14 ..............

2. Simplified geologic map of Precambrian rocks of Hartville uplift, southeastern Wyoming ...................... 16

3. Regional geologic map of the Trans-Hudson orogen ....................................................................... 17

4. Schematic diagram showing interpretation of COCORP data of crustal structure of Trans-Hudson

orogen at lat 48°30' N. ........................................................................................................... 18

5. Chondrite-normalized rare earth element plot for samples of A, Muskrat Canyon Metabasalt, and

B, Mother Featherlegs Metabasalt 19 ............................................................................................

6. La/Lu (normalized) versus SiO2 (weight percent) diagram showing relative amounts of flat REE

and enriched light REE in Muskrat Canyon Metabasalt and Mother Featherlegs Metabasalt ................. 19

7. Equal-area projections (lower hemisphere) of D2 deformation structures in Guernsey quadrangle ............ 20

8. Equal-area projections (lower hemisphere) of D3 deformation structures in a typical area in

central part of Hartville uplift ................................................................................................... 21

9. Map showing Precambrian tectonic events of Hartville uplift and outlying areas, southeastern

Wyoming ............................................................................................................................. 22

10. Schematic section showing stratigraphic position of principal mineral deposits 24 ...................................

TABLES

1. Tectonic, stratigraphic, and magmatic evolution of Hartville uplift during the Precambrian 25 ....................

2. Geochemistry of the Mother Featherlegs Metabasalt, Hartville uplift, Wyoming ................................... 26

3. Geochemistry of the Muskrat Canyon Metabasalt, Hartville uplift, Wyoming 28 .......................................

4. Approximate modes of granitoid rocks and gneiss from outlying areas 30 ...............................................
1

INTRODUCTION

The Hartville uplift, at the southeast margin of the Archean Wyoming province (fig. 1), is

a north-trending Laramide anticline containing a

Precambrian core (fig. 2) overlain by gently outward dipping Paleozoic strata and, locally, by

flat-lying Tertiary sedimentary rocks and Quaternary sediments. The core is composed of

Late Archean, moderately metamorphosed

supracrustal rocks of the Whalen Group (Smith,

1903) intruded by Late Archean granite (≈2.65

Ga) bodies (table 1). The supracrustal rocks are

also intruded by a circa 2 Ga mafic dike swarm

(Sims, 1995, pl. 1B) and by the post-tectonic

Twin Hills Diorite (1.74 Ga) and Haystack

Range Granite (1.72 Ga) (Snyder, 1993). The

basement to the Whalen Group, indicated by Nd

model ages as being in the range 2.8–3.1 Ga

(Frost, 1993; Day and others, 1999), is not exposed in the area.

The Archean rocks in the uplift were deformed during three regional compressional

events in Early Proterozoic time, which took

place in the interval from about 1.98 Ga to 1.74

Ga (table 1). Recognized compressional events

are (1) nappe formation (D1 ) in the supracrustal

rocks; (2) folding throughout the length of the

western side of the uplift on east-west axes

(D2 ); folds are open to tight, verge southward,

and plunge westward; and (3) west-vergent

folding on north-trending axes, associated thickskinned thrusting (D3 ) in the central and northern parts of the uplift (table 1), and accompanying prograde metamorphism. A fourth, local

deformation was restricted to the uplifted margins of granite domes of 1.72 Ga Haystack

Range Granite bodies.

PREVIOUS WORK

Extensive geologic studies, mainly focused

on the iron ore deposits in the vicinity of

Hartville, Wyo., have been carried out during the

past century. In an early study, Smith (1903)

formally named the Whalen Group and described

its lithologic units, but he did not name any formations. Subsequently, Ball (1907a), Lovering

(1933), and Noble and Harder (1948) described

the iron-ore bearing section. A thoughtful study

of the Good Fortune mine by Ebbett (1956)

provided for the first time significant data on the

nature and formation of the iron ores. Later

studies by Harper (1960) and Millgate (1964)

provided additional details of the stratigraphic

relations of the iron-bearing rocks. In a regional

study, Snyder (1980) compiled for the first time

a regional stratigraphy and the stratigraphic

succession (Snyder and Peterman, 1982; Snyder, 1989).

PRESENT WORK

A field trip into the Hartville uplift in 1993

led to the recognition that previous stratigraphic

interpretations were not consistent with structural observations. Accordingly, geologic mapping at a scale of 1:24,000 was undertaken by

us in 1993–1997 in selected areas for the purpose of unraveling the structure and stratigraphy and developing a coherent stratigraphy.

The southernmost quadrangles, the Guernsey

and Casebier Hill quadrangles (Sims and others,

1997) were mapped; then two rather wellexposed quadrangles, the Rawhide Buttes West

and Rawhide Buttes East in the northern part of

the uplift, were mapped (Day and others, 1999).

Unpublished mapping by T.L. Klein and W.C.

Day of the Silver Springs quadrangle provided

additional coverage of the northern part of the

uplift. To complete geologic coverage, the map

accompanying this report was compiled at

1:48,000 scale mainly utilizing Snyder’s (1980)

previous mapping to fill in areas not mapped during our current study.

ACKNOWLEDGMENTS

The present mapping was facilitated by the

earlier geologic mapping by Snyder (1980). He

located Precambrian outcrops and mapped the

younger Paleozoic and Tertiary-Quaternary materials, thus materially aiding our mapping. Previous geochronology by Zell Peterman (Snyder

and Peterman, 1982) and age determinations

concurrent with our mapping by Kevin Chamberlain and students at the University of Wyoming

(Chamberlain and others, 1997) provided a general time frame for our geologic interpretation.

REGIONAL TECTONIC SETTING

The Wyoming craton (province) is bordered on the east by the Paleoproterozoic

Trans-Hudson orogen (Hoffman, 1990; Lewry

and Collerson, 1990) and on the south and

southeast by the younger (1.78–1.76 Ga) Central Plains orogen (Sims and Peterman, 1986;

this report, fig. 1). The Hartville uplift lies near

the intersection of the Trans-Hudson and Central Plains orogens (Sims and others, 1991).

The Trans-Hudson orogen is a northtrending orogenic belt as much as 480 km wide

and more than 1,900 km long that separates

the Wyoming craton from the Archean Superior
2

craton (fig. 3). Seismic reflection profiles across

the orogen along the U.S.–Canadian border (fig.

4) are interpreted (Nelson and others, 1993;

Baird and others, 1996) to indicate that the

orogen has a symmetrical profile. The seismic

profiles also suggest westward subduction of

oceanic and arc rocks of the orogen beneath

the Wyoming craton (on the west) and eastward subduction of similar rocks beneath the

Superior craton on the east. The subducted

rocks bound an antiformal Archean(?) microcontinent whose crest is approximately in the center of the orogen. Intracrustal reflections to

the west of the zone of presumed westward

subduction suggest that the eastern margin of

the Wyoming craton was imbricated in an eastover-west sense during the Trans-Hudson

orogeny. Random drilling in North and South

Dakota (Peterman and Futa, 1988) and in adjacent Canada (Collerson and others, 1989) supports the interpretation of Archean rocks in the

seismic profile (Baird and others, 1996); Peterman and Futa (1988) concluded that Paleoproterozoic (Hudsonian) granulite facies metamorphism was imposed on a complex terrane consisting of both Archean and Paleoproterozoic

rocks in the orogen. The Black Hills uplift lies

within the Trans-Hudson orogen (Sims and

others, 1991); the Proterozoic rocks and

Archean basement in the uplift were multiply deformed during the Trans-Hudson orogeny

(Redden and others, 1990). In the Black Hills,

the dominant structural trend is north-northwest, subparallel to the structural trend of the

Trans-Hudson orogen in the southern, exposed

part of the orogen. The width of the foreland

metamorphic-deformational belt on the west side

of the Trans-Hudson orogen has not been determined at the latitude of the Hartville uplift, but

R.L. Bauer (University of Missouri, oral commun., 1997) has recognized folds 80 km west of

the uplift in the Laramie Mountains that strike

northward, subparallel to the length of the

Trans-Hudson orogen, and that are presumably

related to it.

The younger Central Plains orogen has

been traced by drilling and geophysics from the

Medicine Bow Mountains (fig. 1) eastward in the

subsurface, where it truncates the southern extent of the Trans-Hudson orogen (Sims and

others, 1991). The Central Plains orogen collided with the Wyoming craton along the

Cheyenne belt (Karlstrom and Houston, 1984)

in the interval 1.78–1.76 Ga (Premo and Van

Schmus, 1989). Chamberlain and others (1993)

have demonstrated geochronologically that the

foreland metamorphic-deformational zone extends 60–100 km northwest of the Cheyenne

belt in the Laramie Mountains, and is recorded in

the Laramie Peak shear zone (fig. 1).

PRECAMBRIAN ROCK UNITS

Supracrustal rocks of the Whalen Group

(Smith, 1903) overlie an Archean basement of

unknown composition and are intruded by Late

Archean granite (≈2.65 Ga) and younger posttectonic diorite (1.74 Ga) and granite (1.72 Ga).

Although the basement rocks are not exposed in

the uplift, Nd isotopic data on the granites indicate that they have Nd model ages in the range

2.8–3.1 Ga (Day and others, 1999), comparable

to the ages of Precambrian basement rocks in

other Laramide uplifts in Wyoming (Frost,

1993).

In previous reports (Sims and others,

1991; Day and others, 1999), an informal

(lithologic) terminology was used for rocks of

the Whalen Group. In this report, we propose a

formal terminology for four formations in the

Whalen Group, form oldest to youngest: (1)

Mother Featherlegs Metabasalt, (2) Silver

Springs Formation, (3) Wildcat Hills Formation,

and (4) Muskrat Canyon Metabasalt. Distinct

lithologic strata within the two sedimentary

formations are referred to as units, such as

quartzite units in both the Silver Springs and

Wildcat Hills Formations.

MOTHER FEATHERLEGS METABASALT

Mother Featherlegs Metabasalt is named

from the Mother Featherlegs cemetery alongside the Silver Springs road in the southern part

of the Silver Springs quadrangle (sec. 27, T. 31

N., R. 64 W.), in Niobrara County. The

metabasalt is exposed sporadically in a belt

trending through most of T. 31 N. It is about

900 m wide and 8 km long; this belt is designated as the type area. The metabasalt also is

exposed on the hill north-northeast of

Guernsey. It is predominantly a dark-greenishgray rock that ranges from medium-grained amphibolite to a fine-grained actinolite-biotitechlorite schist. Some parts are layered, and

pillows are present locally. Metabasalt near

Guernsey has an estimated thickness of 150–

180 m; that northeast of the cemetery is

perhaps as much as 1,500 m thick.

SILVER SPRINGS FORMATION

The Silver Springs Formation is named

from outcrops of subgraywacke and metashale

in the vicinity of Silver Springs (SW1/4 sec. 11,

T. 31 N., R. 64 W.), which is the type area.
3

The outcrops compose a north-trending belt as

much as 900 m wide and 10 km long immediately

east of the belt of Mother Featherlegs

Metabasalt. The Mother Featherlegs

Metabasalt is interpreted to be overridden by the

metagraywacke along the Silver Springs thrust

fault. Another large exposed area of the formation is in the vicinity of Haystack Range, in the

western part of the Casebier quadrangle; the

graywacke in this area is intruded by the 1.72

Ga Haystack Range Granite. In the vicinity of

Hartville (Guernsey quadrangle), a ferruginous

schist unit that hosts the hematite ore bodies in

the Hartville district is interpreted (Sims and

others, 1997) as being laterally equivalent to

graywacke as exposed on the hill southwest of

the Graves Ranch. The iron-bearing unit is

considered as being part of the Silver Springs

Formation. The Silver Springs Formation is absent in the central part of the Hartville uplift.

The predominant rock type varies from gray,

medium-grained, granular biotite-quartzplagioclase schist and quartz granular

metagraywacke to biotite-muscovite-garnetsillimanite schist. The formation is estimated to

range in thickness from 0 to 1,500 m.

WILDCAT HILLS FORMATION

The Wildcat Hills Formation is a metacarbonate unit named from outcrops on the east

slope of Wildcat Hills. Outcrops form a narrow

band extending south from Wildcat Hills to

Hartville, where the rock is folded on easttrending axes. Another band of dolomite extends north from Muskrat Canyon to the vicinity of Rawhide Creek, west of the Hartville fault.

A third area of outcrop is on the west flank of

Rawhide Buttes. The type area is the HartvilleSunrise area. In the type area, the formation

contains abundant concentrically layered algal

stromatolitic mounds, which have been used to

determine stratigraphic way-up. The rock is

predominantly gray, buff, pink, and white,

medium-grained dolomite and siliceous dolomite,

and locally limestone. In northern outcrops east

of the Hartville fault, tremolite dolomite and

chondrodite dolomite are common. Thicknesses

range from 0 to about 1,500 m.

MUSKRAT CANYON METABASALT

The Muskrat Canyon Metabasalt is named

from excellent exposures of metabasalt in

Muskrat Canyon, which is the type area. The

metabasalt extends continuously from Muskrat

Canyon southward for a distance of 10 km on

the east slope of Wildcat Hills. The rock is

predominantly dark-green actinolite-biotite-chlorite schist. The metabasalt is locally pillowed;

excellent pillows are exposed on the south bank

of the stream in Muskrat Canyon. Thicknesses

are estimated to range from 0 to about 1,500 m.

GRANITOID ROCKS

Rocks of the Whalen Group are intruded,

from oldest to youngest, by the Rawhide Buttes

Granite (2.66 Ga), Flattop Butte Granite (2.65

Ga), Twin Hills Diorite (1.74 Ga), and Haystack

Range Granite (1.72 Ga) (Sims and others,

1997; Day and others, 1999). Compositionally,

the three granites indicate successive origins

through partial melting of crustal material. This

observation is consistent with the Sm-Nd model

ages (crustal-residence ages), which are considerably older than zircon and Rb-Sr crystallization ages.

The granite bodies have been described in

the two previously published maps of the area

(Sims and others, 1997; Day and others, 1999).

A note of explanation for our interpretation of

the northernmost granite body is warranted.

We interpret this body as a buried, domal pluton

of 1.72 Ga Haystack Range Granite because of

(1) its geophysical expression (circular shape)

and resemblance to the granite pluton exposed

in the Haystack Range, to the south, and (2)

the presence of 1.72 Ga granite gneiss (K.R.

Chamberlain, oral commun., 1996) on the south

(deformed) margin of the granite dome. This

granite gneiss is interpreted by us to have been

deformed during emplacement of the granite

dome. An outcrop of granite within the outline

of the buried body (see map) is a large Archean

granite inclusion; an Archean age is indicated by

the presence of mafic dikes in the granite body.

CHEMISTRY OF METAVOLCANIC ROCKS

The mafic metavolcanic rocks can be divided into two stratigraphic and geochemically

distinct units: the Muskrat Canyon Metabasalt

and the Mother Featherlegs Metabasalt. Rocks

in both units occur as metamorphosed pillow

lavas, as massive flows, and as gabbro sills and

dikes. The major and trace element geochemistry for samples from the Mother Featherlegs

Metabasalt is listed in table 2 and that for the

Muskrat Canyon Metabasalt is given in table 3.

The Mother Featherlegs Metabasalt is

distinguished from the Muskrat Canyon

Metabasalt mainly on the basis of trace element

geochemistry. Whereas both metabasalt units

have similar major element geochemistry (tables

2 and 3), the Muskrat Canyon Metabasalt is
4

enriched in light-rare earth elements (LREE), as

shown in figure 5A. The Mother Featherlegs

Metabasalt has a relatively flat REE pattern (fig.

5B). The relative enrichment of the Muskrat

Canyon Metabasalt in the LREE abundance is

also shown in figure 6. Both units show a similar range in SiO2 content. However, the La/Lu

normalized ratio for the Muskrat Canyon

Metabasalt is greater than 2 (and as high as

about 15) as compared with the Mother

Featherlegs Metabasalt, for which the ratio

remains less than 2 even for rocks of similar

SiO2 content.

STRUCTURE

The three compressional deformations

(D1 –D3 ) recognized in the Hartville uplift have

been distinguished mainly by field relationships,

particularly mesoscopic structures (foliations and

lineations). Only one event, D2 deformation,

has been dated geochronologically (Day and

others, 1999). The deformational episodes took

place during the time span ≈2.0 Ga to 1.74 Ga

and were followed by local doming related to

post-tectonic (1.72 Ga) Haystack Range Granite bodies (table 1). The compressional deformations represent discrete orogenies; evidence for

strain continuums is lacking.

D1 DEFORMATION

Following deposition of the Whalen

Group, fold nappes of regional extent produced

widespread overturned beds. Inverted stromatolitic structures in metadolomite in the southern part of the uplift, near Hartville, suggest that

these beds and possibly all of the section south

of Hartville are upside down; the Sunrise syncline is a downward-facing syncline (Sims and

others, 1997). Also, overturned quartzite

crossbeds indicate inverted beds in the western

part of Muskrat Canyon. Neither fold hinges

nor an S1 cleavage has been identified for the

nappes, suggesting that the nappes could have

formed by soft-sediment deformation, as suggested by Hudleston (1976) for similar folds in

Archean graywacke in northern Minnesota.

The strata east of the Hartville fault generally

lack “way-up” sedimentary structures because of

the amphibolite-grade metamorphism and internal shearing.

D2 DEFORMATION

Following nappe formation and the emplacement of Late Archean granite plutons and

≈2.0 Ga mafic dikes (table 1), D2 deformation

folded the supracrustal rocks, the granite bodies,

and probably the basement. F2 folds trend eastwest, are generally tight to moderately open

and overturned to the south, and have northdipping axial surfaces and an accompanying axialplanar cleavage (fig. 7A). S0 –S2 intersection

lineations (L2 ) and related F2 fold axes plunge

moderately to gently westward (fig. 7B). The

D2 flexures are similar-type folds, and accordingly it is probable that the compressional axis

for folding was approximately north-south.

D2 folds are exposed in the Hartville area

and areas to the south, where D3 and younger

structures are absent in outcrop (Sims and others, 1997). In a transitional zone about 3 km

wide parallel to the trend of uplift, extending

northward beyond the Chicago mine (fig. 2), D3

structures are variably superposed on D2 structures. Notably, the fold axis of the Sunrise

syncline is bent from its original east-west trend

to a northeast strike; also, intersections of D3

structures with older, largely obscured F2 folds

plunge either to the south or north, depending

upon which limb of the original D2 fold is involved. A pre-D3 prominent west-northwesttrending foliation, and more rarely a lineation,

are present on the western side of the uplift

northward from the transition zone to the

northern limit of the Hartville uplift; we interpret

these pre-D3 structures as S2 and L2 , respectively. S2 structures have been reoriented, generally to a northeast trend, whereas L2 generally plunges east-southeast.

Because D2 deformation was of regional

scope, we propose the name “Oregon Trail

orogeny” for this deformation. The type area

for the D2 deformation is that between

Guernsey and Hartville (Sims and others, 1997).

D3 DEFORMATION

D3 deformation was the major compressive event in the Hartville uplift. It produced a

north-trending foreland fold-and-thrust belt that

parallels the axis of the uplift and spans the

length of it. Of the several D3 thrust faults, the

principal one is the Hartville fault, which juxtaposes middle amphibolite facies rocks on the east

with upper greenschist facies rocks on the west.

Based on the petrology and mineralogy, the

eastern block is estimated to have been uplifted

about 5 km relative to the western block (K.R.

Chamberlain, University of Wyoming, oral

commun., 1993). Where exposed in the Hell

Gap quadrangle (location A, fig. 2), the Hartville

fault is a nearly vertical, 100-m-wide mylonite

zone that has a steep stretching lineation and a
5

late component of sinistral strike-slip offset. D3

folds are present throughout the uplift north of

the Chicago mine (fig. 2). The folds are upright

to recumbent, west-vergent structures that fold

an older (D2) foliation (fig. 7A); S3 is poorly developed in many areas (see for example, fig. 8A).

The folds plunge both to the south and north,

but mainly plunge north (fig. 8B).

At places within mylonitic zones in the

northern part of the Hartville uplift, a moderately

plunging stretching lineation bearing about N.

45° W. is present. These areas are shown by

heavy arrows on the map. The stretching lineation is interpreted as local high strain areas in

the D3 deformation. It represents the X-axis of

the strain ellipsoid (maximum extension) and thus

indicates the direction of tectonic transport

during D3 deformation.

D4 DEFORMATION

Local deformation related to doming

around two subcircular Haystack Range Granite

bodies interrupts the trends established by the

older regional compressional events. Both

granite bodies are in the hanging (east) wall of

the Hartville fault. The southern body is moderately well exposed about 6 km east of Hartville

(Sims and others, 1997). The body has a weak

internal foliation, interpreted as a primary flow

structure, that is accentuated at the margins.

Steeply dipping foliation in the biotite-quartzplagioclase schist host rock wraps around the

northern and western margins of the granite

body (Sims and others, 1997). A second dome

lies in the northern part of the uplift, about 4 km

north of Rawhide Buttes. The northern granite

body is not exposed, but can be outlined on the

basis of (1) its having greater magnetic susceptibility than surrounding country rocks and (2)

the dome-shaped conformable foliation in surrounding rocks. On the south side of the dome,

in section 31, T. 31 N., R. 63 W., and on Bald

Butte, to the south, tongues of Haystack

Range Granite, now granite gneiss (unit Xhg),

are infolded with the metamorphosed Whalen

Group rocks. A sample of the granite gneiss

has been dated by the U-Pb zircon method at

≈1.73 Ga (K.R. Chamberlain, University of

Wyoming, written commun., 1997), indicating

that it is a metamorphosed equivalent of the

Haystack Range Granite. The granite gneiss

has a pronounced steep stretching lineation

caused by upward, plastic transport of the dome

during granite emplacement. Also, doming at

this locality rotated older D3 structures from a

northeast to a northwest trend, as can be seen

on the geologic map.

At Bald Butte (sec. 31, T. 31 N., R. 63

W.), large-scale mullions that plunge steeply

southwest—parallel to the stretching lineation—

are exposed in quarry walls. The mullion structures warp older northwest-trending foliation interpreted as S2 .

POSTDEFORMATION EVENTS

Following development of the granite

domes (D4 deformation; table 1), two unrelated

events are recorded in the uplift. Krugh and

others (1993) obtained a monazite age of 1.66

Ga from a phase of the Rawhide Buttes Granite,

which has a zircon crystallization age of circa

2.4 Ga. Krugh and others (1993) interpreted

the monazite age as marking a prograde metamorphic event possibly related to the tectonism

within the Central Plains orogen. Lacking

structural evidence for a late event, we interpret

the age as a cryptic thermal event of unknown

cause. Scattered mafic dikes (Ym) in the southern part of the uplift are presumed to be related

to emplacement of the 1.4 Ga Laramie

anorthosite complex and the Sherman batholith.

CORRELATION OF DEFORMATION

EPISODES

The compressional deformations in the

Hartville uplift, D1 through D3 , represent distinct, separate tectonic events. The sequence

of events has been determined by geologic observations, mainly superposition of older mesoscopic structures by younger ones. The deformation events took place in the interval 2.6–

1.74 Ga, but only D2 has been dated isotopically. The 2.65 Ga Flattop Butte Granite has a

Rb-Sr whole-rock age of 1.98 Ga where deformed by D2; this age is interpreted as a metamorphic (D2 ) age (Zell Peterman, in Day and

others, 1999).

D1 deformation (nappe formation) followed

an unknown period of time after deposition of

the Whalen Group rocks; deposition preceded

2.65 Ga, the age of the Flattop Butte Granite,

which intruded the Whalen Group rocks. The

absence of an associated axial-planar fabric suggests that the nappes could have formed by

soft-sediment deformation.

Following nappe formation and emplacement of the Late Archean granite bodies, D2 deformation was developed throughout the

Hartville uplift. F2 folds are preserved as the

youngest exposed structures in the area south

of Sunrise. (See map, and recall discussion of

D2 folds, p. 4.) North of Sunrise, the F2 folds
6

are overprinted by D3 structures, and in the

northern part of the uplift D2 is represented by a

prominent pre-D3 foliation, and more locally, a

lineation. Possibly D2 is correlative with northvergent thrusting on the Reservoir Lake fault

(Houston and Karlstrom, 1992) in the Medicine

Bow Mountains. In the Medicine Bow Mountains, Karlstrom and others (1981) assigned deformation of rocks north of the Reservoir Lake

fault to their D2 ; this deformation preceded intrusion of gabbroic sills in the Deep Lake Group,

whose intrusive age is 2,092±4 Ma (Houston

and Karlstrom, 1992, p. 39). The Reservoir

Lake fault and adjacent rocks were folded later

by their D3 , caused by collision along the 1.78–

1.76 Ga Cheyenne belt.

D3 deformation is attributed to the TransHudson orogeny inasmuch as D3 structural

trends are northerly, subparallel to the trend of

the western margin of the Trans-Hudson orogen (Sims and others, 1991; this report, fig. 3).

The direction of tectonic transport during D3

deformation was mainly N. 45° W., which is

compatible with the Trans-Hudson orogeny. Its

age is intermediate between 1.98 Ga and 1.74

Ga, which is consistent with the age of the

culmination of metamorphism (circa 1.81 Ga) in

the orogen in northern Saskatchewan (Lewry

and others, 1996). The location of the Hartville

uplift relative to the Trans-Hudson orogen is

analogous to the Wollaston domain of the Cree

Lake mobile belt in northern Saskatchewan

(Annesley and others, 1992).

Although deformation related to the

Cheyenne belt (1.78–1.76 Ga) has been recognized in the adjacent Laramie Mountains by isotopic data (Chamberlain and others, 1993;

Resor and others, 1996), this deformation has

not been definitely recognized in the Hartville

uplift. The above authors have shown that the

Laramie Peak shear zone, which is in the

Laramie Mountains about 65 km north-northeast of the Cheyenne belt, was deformed at

1.76 Ga, concurrent with movement on the

Cheyenne belt. We considered the stretching

lineations indicated by the heavy arrows in the

northern part of the map area as possibly being

related to Cheyenne belt deformation, but lacking definitive age data on the mylonite we now

interpret these stretching lineations as late

stage D3 deformation structures.

Laramide deformation had minimal effect

on the Precambrian rocks in the Hartville uplift.

During this deformation, the Precambrian rocks

were gently uplifted, as indicated by nearly horizontally bedded Paleozoic rocks in the core of

the uplift and gently outward dipping Paleozoic

rocks on each flank. An exception occurs in the

valley of Whalen Canyon in the northern part of

the uplift (Niobrara County and adjacent Goshen

County to the south). In this area the Paleozoic rocks have a homoclinal dip to the west of

about 45° as a consequence of Laramide(?)

normal faulting (Day and others, 1999).

OUTLYING AREAS

Precambrian rocks are exposed at five localities outside of but near the Hartville uplift,

from north to south, (1) Sullivan Ridge, 10 km

north of Lusk; (2) Lusk; (3) Lone Tree Hill, in

Niobrara County; (4) Cassa anticline, in Platte

County; and (5) Antelope Hills, in Platte County

(fig. 9). Approximate modes of selected granitoid

rocks are given in table 4.

SULLIVAN RIDGE

Metagraywacke (biotite-muscovite schist)

is exposed sporadically on Sullivan Ridge, in Niobrara County. The unit presumably belongs to

the Silver Springs Formation. Foliations strike

about north and dip steeply. This structure is

interpreted as deformation D3.

LUSK AREA

Metagraywacke (biotite-muscovite schist),

presumably a part of the Silver Springs Formation, is exposed locally in the western part of

Lusk, on both sides of the Niobrara River. The

schist has a strong foliation (N. 2°–5° E.) that

dips 60°–85° E. and a stretching lineation that

plunges about 72° S. 80° E. This structure is interpreted as deformation D3.

LONE TREE HILL

Medium- to coarse-grained augen granite

gneiss and biotite granite are exposed sparsely

on Lone Tree Hill. The granite is inferred to be

equivalent to the Rawhide Buttes Granite. The

gneiss has a foliation of N. 70° W. (dip 55° N.)

and a west-plunging lineation, indicating deformation by D2 .

CASSA ANTICLINE

Biotite-quartz-plagioclase augen gneiss,

muscovite schist, and crosscutting foliated granodiorite are exposed along the axis of the

Cassa anticline. Possibly the granodiorite is

correlative with the 2.66 Ga Rawhide Buttes

Granite, and if so, the layered gneiss represents

Archean basement. Rb/Sr model ages on the

gneiss range from 2.85 to 3.3 Ga, which
7

supports an affinity with the basement

(Peterman and others, in Day and others,

1999). A U-Pb zircon age of 2.36 Ga is

anomalously young (the zircons are metamict).

Foliations in the rocks trend about N. 40° E.,

but have been reoriented by the Laramide deformation. We interpret the deformation as D2.

ANTELOPE HILLS

Biotite-quartz-plagioclase-microcline gneiss

(table 2), amphibolite, marble, and quartzite are

exposed sparsely in the Antelope Hills, 13 km

south of Guernsey, on the south side of Grayrocks Reservoir. These rocks are intruded by

bedding-parallel tourmaline-bearing pegmatite.

The pegmatite and supracrustal rocks are highly

deformed (deformation D2 ). The foliation is

folded into a Z-fold that lacks an axial-planar

cleavage; possibly the folding is Cheyenne belt

deformation.

DISCUSSION

Areas adjacent to the Hartville uplift, as

defined here, provide additional insights into the

Precambrian geology of the region. Outcrops of

metagraywacke at Lusk and Sullivan Ridge and

supracrustal rocks in the Antelope Hills area extend the strike length of Whalen Group rocks to

a total distance of at least 85 km, supporting interpretation of these rocks as largely composing

a north-trending continental Archean margin

assemblage.

To the west of the exposed metasedimentary and metavolcanic rocks, granite and gneiss

are exposed locally in faulted Laramide anticlines

of small scale. At Lone Tree Hill, foliated biotite

granite (HU-18, table 4) cuts granodioritic

gneiss, suggesting that the gneiss is basement,

possibly older than 2.9–3.0 Ga. Similarly, foliated granodiorite cuts a granitic gneiss, which

also is possible basement of the Wyoming

province.

At the Lone Tree Hill and Cassa anticline

localities, the Precambrian rocks were deformed

by D2 deformation (fig. 9). Similarly at the

Antelope Hills locality, the rocks were deformed

by D2 , then subsequently folded, possibly by the

Cheyenne belt (1.78 Ga) deformation. At Lusk

and Sullivan Ridge, the graywacke was folded by

D3 deformation; this deformation folded a foliation presumably of D2 origin.

MINERAL DEPOSITS IN THE

HARTVILLE UPLIFT

By

Terry L. Klein

INTRODUCTION

Mineral production began in the Hartville

uplift as early as 1880, with the production of

copper in the Hartville district. Shortly after

copper production ceased, mining of hematitic

iron deposits associated with these copper deposits began in 1898 and continued for more

than 80 years. Volumetrically, the major mineral

commodity produced from the uplift has been

iron. Currently, the only commodity being produced is crushed stone from metadolomite near

Guernsey, Wyo. In addition to iron, copper, and

crushed stone, minor amounts of muscovite,

gold, silver, uranium, and ornamental stone have

been produced from the uplift. Most of the mineral production has come from metasedimentary

units of the Whalen Group. Of the eight commodities produced in the uplift, this report covers

only deposits of iron, copper, uranium, and pegmatite-related minerals.

IRON DEPOSITS

Iron was first produced from the Sunrise

mine in the Hartville district in 1898, after the

site was initially developed in the early 1880’s

for copper. The district is located in the southern part of the map area (secs. 5, 7, and 8, T.

27 N., R. 65 W.) near the town of Hartville. It

includes the Sunrise mine and three other

nearby mines, the Chicago, Central, and Good

Fortune, which were developed on the same

iron-rich ore zone, as well as several copper deposits (for example, the Empire and Green

Mountain Boy). These iron mines produced

direct-shipping hematite ore for the Colorado

Fuel and Iron Corporation open-hearth furnaces

in Pueblo, Colo. At the time mining ceased at

the Sunrise mine in 1980, the district had

produced about 41 million t (metric tons) of iron

ore (Hausel, 1989).

Two distinct types of iron deposits occur

in the Hartville uplift: (1) structurally controlled

pods of soft, earthy, massive hematite ore that

grades downward to a vuggy to massive, blue-
8

gray, specularite ore (for example, deposits of

the Hartville district), and (2) layers of Lake

Superior-type hematite-quartz iron-formation

(for example, Michigan mine). Both types are

associated with iron-rich schist (Sims and others, 1997), immediately below the contact with

overlying metadolomite in the Whalen Group.

The iron-rich layer along which the iron

deposits in the Hartville district are distributed is

folded by east-trending folds related to deformation D2 . All the large mines in this district are

located in the same stratigraphic position within

iron-rich biotite schist, which was probably derived from a pelite protolith, immediately below

the contact with metadolomite (fig. 10). The

Sunrise ore body is located in a steeply easterly

plunging fold that is S-shaped in map view

(Osterwald and others, 1966) and extends to a

depth of at least 300 m (Ball, 1907a). Oxidation

resulting in soft, earthy hematite ore extends to

about 60 m below the present-day surface

(Osterwald and others, 1966). The origin of the

deposits is problematic. Much of the soft,

earthy hematite ore in the upper parts of the deposits was the product of ground-water oxidation of the gray specularite ore; this oxidation

occurred after the deposition of the Mississippian Guernsey Formation. Ball (1907a) described earthy hematite pseudomorphs after

rounded specularite pebbles and cobbles in the

basal conglomerate of the Guernsey Formation,

indicating that the oxidation of specularite took

place after the deposition of the Guernsey Formation. In addition, oxidation must have taken

place along the pre-Mississippian unconformity.

A zone rich in earthy hematite replacing, in part,

massive specularite ore in Precambrian rocks

parallels the unconformity generally to a depth

of 10–20 m (Chance, 1897). Earthy hematite is

also concentrated along fractures extending

downward from the unconformity into the

specularite ore below the level of general oxidation, indicating that oxidizing fluids migrated

downward. The distribution of the vuggy, massive, and (or) brecciated specularite ore follows

an iron-rich sedimentary protolith layer that was

folded by D2. Alteration of the sedimentary protolith by fluids to form specularite probably took

place after D2 folding, as suggested by the lack

of penetrative fabric in the specularite ore.

However, the character of the iron-rich protolith and the source and physical character of

the altering fluids are not known.

In the area of the Michigan mine (sec. 24,

T. 30 N., R. 65 W.) in Muskrat Canyon (in the

central part of the uplift) three layers of

hematitic iron-formation lie in moderately east

dipping slates that are interbedded with a thinto thick-bedded quartzite unit of the Whalen

Group. The western contact of the thickest

(westernmost) iron-formation with metadolomite

is a northwest-trending, steeply east dipping

normal fault. A small amount of iron was produced from this mine. Iron ore reserves at the

mine were estimated to be about 105 million t

averaging about 25 percent iron. Several grab

samples were reported to contain about 1 percent copper (Hausel, 1989).

COPPER DEPOSITS

Copper was the first commodity mined in

the Hartville uplift. During the period 1880–

1887, several mines in the area now covered by

the Sunrise mine produced more than 630 t of

copper and more than 70 kg of silver (Hausel,

1989) from oxide and carbonate deposits lying

above the hematitic iron ore near the Paleozoic

unconformity. In addition, about 100 t of copper was produced from hematitic iron-formation

at the Michigan mine (Knight, 1893), about 185

t of copper and 8.5 kg silver from a replacement

deposit at the Green Mountain Boy mine (sec.

36, T. 27 N., R. 66 W.), and about 85 t of copper from the Greenhope mine (sec. 26, T. 29 N.,

R. 65 W.).

Three types of copper deposits are present in the uplift: (1) copper sulfides in sedimenthosted massive sulfide deposits—for example,

Omaha mine (sec. 2, T. 30 N., R. 64 W.), Empire

mine (sec. 12, T. 27 N., R. 66 W.), and Charter

Oak prospect (sec. 26, T. 27 N., R. 65 W.); (2)

disseminated copper sulfide deposits in shear

zones—for example, prospects in Muskrat

Canyon (sec. 19, T. 30 N., R. 64 W.) and the

Copper Bottom prospect (sec. 23, T. 29 N., R.

65 W.); (3) copper oxide and carbonate replacement deposits associated in the basal Guernsey

Formation—for example, Green Mountain Boy

and the Greenhope mines, or immediately below

the Paleozoic/Precambrian unconformity in ironrich rocks—for example, copper in the Sunrise

and Michigan mines. Both gold and silver are

associated with shear zone-hosted copper deposits, sediment-hosted massive sulfide deposits,

and copper deposits in iron-formation.

Sediment-hosted massive sulfide deposits

Several prominent gossans overlie massive

sulfide lenses in a muscovite schist unit in the

Whalen Group in the Silver Springs quadrangle

(for example, in sec. 23, T. 31 N., R. 64 W.) and

in the Omaha mine area, south of Flattop Butte.

The zones are typically associated with layers of

graphitic metapelites and cherty exhalites within
9

muscovite schist; some zones are also associated with thin carbonate layers in the schist.

Throughout the map area most of these zones

are at or near the transition between metapelite

and metadolomite. A schematic stratigraphic

section for the Hartville uplift (fig. 10) illustrates

that not only are cherty exhalites and massive

sulfides interpreted to be associated with this

transition, but also the Sunrise-type hematite

ore. At the Omaha mine, a thin layer of mineralized schist and a cherty exhalite layer lying between two thick metadolomite layers were exploited. At the Gold Hill mine, which is located

about 150 m N. 30° E. of the Omaha mine along

the same cherty exhalite layer, ore samples assayed 6 percent copper and 6.9 g/t gold

(recalculated from Ball, 1907b). The deposits in

this area contain copper carbonates and silicates

at the surface; below the weathering zone, chalcopyrite is the dominant copper mineral, and

barite is reported to be a common gangue mineral in these deposits (Ball, 1907b). The adjacent Copper Belt mine (sec. 11, T. 30 N., R. 64

W.) was developed to a depth of about 90 m and

included more than 1,000 m of underground

workings (Osterwald and others, 1966). This

deposit is along and adjacent to a D3 thrust that

is characterized by some left-lateral displacement. The deposit consists of two ore lenses

that range from 0.3 to 1 m thick and which assayed from 2 to 8 percent copper, 1.7 to 20 g/t

gold, and 69 to 170 g/t silver (Ball, 1907b).

These lenses are hosted by biotite schist

(metapelite) immediately below a 1-m-thick metadolomite layer. All these deposits show some

remobilization of sulfide minerals from massive

sulfide/cherty exhalite layer into discordant

veins. These veins may have developed during

D3 folding. Two laterally extensive exhalite

units are recognized in this area, the most continuous of which can be traced for at least 1 km;

they outline a large F3 fold southwest of the

Omaha mine. The Empire mine, about 1 km

southwest of the Sunrise mine, is a metadolomite-hosted exhalite-associated copper deposit similar to the Omaha and Gold Hill mines.

In the McCann Pass area, located in the

southeastern part of the map area, several

strata-bound sulfide-rich lenses are exposed as

gossans along the west-northwest-striking

McCann Pass fault and north of the fault where

the lenses are conformable to bedding (S0 ) in

schist. These gossans are associated with a

thick graphite-rich metapelite (Ball, 1907b) which

contains fine-grained quartz-rich rocks that are

probably metamorphosed siliceous exhalites.

The Charter Oak prospect is the most significant in this area. Copper minerals in this

prospect include malachite, chrysocolla, and

chalcocite which are found in a zone about 1 m

wide. Assays of as much as 33 g/t gold and

150 g/t silver were reported by Ball (1907b).

These gossans are composed of siliceous breccia

clasts in an earthy hematitic matrix and were

derived by weathering of the primary sulfide minerals, pyrrhotite, pyrite, and chalcopyrite. This

sulfide mineral assemblage was encountered

during exploration drilling in the 1970’s

(Zahoney, 1976). Chemical analyses of surface

samples from the McCann Pass gossan lens,

which is about 1 km long and 100 m thick, yield

values of 20–300 ppm copper, 200–900 ppm

zinc, as much as 7,000 ppm arsenic, and 30–

3,000 ppm boron (Zahoney, 1976). In the

northern part of the Hartville uplift, gossans occur in several places (for example in the western

part of sec. 23, T. 31 N., R. 64 E.), and are similar to those described at McCann Pass. These

deposits share many characteristics with

Besshi-type massive sulfide deposits, including

host-rock lithology (pelitic sedimentary rocks),

associated rock lithology (mafic volcanic rocks),

tectonic setting (continental margin), and principal sulfide mineral assemblage (pyrrhotite, pyrite,

chalcopyrite) (Slack, 1993). Metal ratios of the

deposits in the Hartville uplift (Cu/Zn, Zn/Pb) are

not known because of the lack of samples from

unoxidized sulfide-bearing rock units.

Disseminated copper sulfide deposits in

shear zones

Several prospects in Muskrat Canyon and

along the Hartville fault, near Hell Gap (secs. 2

and 10, T. 29 N., R. 65 W.), contain disseminated secondary copper minerals associated

with quartz-calcite veins in graphite-rich rocks.

Locally abundant graphite is associated with alteration in metadolomite and probably formed

from leaching of carbonate rocks by hydrothermal fluids focused along the shear zones. This

leaching caused a residual enrichment of insoluble carbon from the metadolomite to form

graphite. The prospect in Muskrat Canyon is

located in metadolomite of the highly deformed

footwall along the Muskrat Canyon fault. Malachite and chrysocolla, associated with iron oxide

lenses in quartz veins or as fracture coatings on

graphitic rocks or metadolomite, are locally

abundant. Quartz and calcite stringers and pods

are exposed in the prospect where they are enclosed in an intensely deformed graphite-rich

zone that ranges from 0.1 to 0.3 m wide. Locally, thin crossfiber tremolite veins are generally conformable to the trend of the graphitic

vein but formed later than minor folds in
10

surrounding graphite; these veins indicate that

high-temperature hydrothermal activity took

place after deformation. Regionally, exploration

drilling along these graphitic zones has encountered zinc and gold concentrations in disseminated sulfide minerals of as much as 1.2 percent

and 2.4 g/t, respectively (Woodfill, 1987).

In a prospect near the southwest corner

of sec. 10, T. 30 N., R. 64 W., a large quartz

vein containing copper minerals (azurite, malachite, and chalcopyrite) was emplaced in

Archean granite along the Little Wildcat fault, a

D3 structure. The quartz vein is sheared parallel

to the tectonic foliation associated with the fault

as are ore minerals within the vein. This vein is

as much as 10 m thick and is continuous for at

least 150 m. Farther north along the Little

Wildcat Canyon fault in SE 1/4 sec. 5, T. 30 N.,

R. 64 W., low-level gold enrichment (0.1 ppm

Au) accompanies copper minerals in a large,

strongly deformed quartz vein at the faulted

contact of gneissic Rawhide Buttes Granite and

metadolomite (T.L. Klein and W.C. Day, unpub.

data, 1997). Silicic and propylitic alteration is

common in the footwall along the exposed

length of the Little Wildcat Canyon fault.

The structures (D3 ) that control these

copper and precious-metal deposits in the

Hartville uplift are similar to those controlling

low-sulfide quartz-Au deposits in metamorphic

terranes throughout the world (that is, reverse/tranpressive regional faults). Faults or

shear zones with a reverse sense of movement

are typically the principal controlling structures

for epigenetic precious-metal mineralization, at

both regional and local scales (see Hodgson,

1989; Poulsen and Robert, 1989). These faults

and shear zones also typically have a component of lateral movement. Within these compressive domains, precious metals are generally

localized in tensional environments (dilational

zones) produced during deformation and (or) in

related secondary structures. Deposition also

preferentially occurs in lithologies and (or) environments where rocks in the shear zones behaved in a brittle or brittle-ductile manner during

deformation.

Copper oxide and carbonate replacement

deposits

Much of the early copper production from

the Hartville area was from copper oxide and

carbonate replacement deposits located near the

Paleozoic unconformity in the basal Guernsey

Formation. The deposits occur in both carbonate rocks and the coarse basal conglomerate of

the Guernsey Formation and below the

Paleozoic/Precambrian unconformity iron-rich

Precambrian rocks. One of the largest deposits

in the Guernsey Formation, the Green Mountain Boy mine, is located near the site of the

present-day dolomite quarry east of Guernsey,

Wyo. It consisted of a thick, keel-shaped chalcocite replacement body in the Guernsey Formation (Ball, 1907a). As much as 500 t of highgrade copper ore (37 percent copper and as

much as 17 g/t silver) was produced from this

deposit (Ball, 1907a). At the Greenhope mine,

north of Hell Gap, secondary copper minerals

occur in the basal Guernsey Formation along

the Paleozoic/Precambrian unconformity. The

underlying metadolomite of the Whalen Group is

characterized by the development of small-scale

karst features (Ball, 1907a).

Copper deposits in iron-formation and

other iron-rich rocks were economically important in the early history of mining in the uplift.

All the ore that was exploited consisted of secondary copper minerals. The Village Belle mine

produced significant amounts of copper from the

Precambrian hematite-rich rocks in the area of

the later Sunrise iron mine. The copper was

primarily enriched in permeable zones related to

fractures in the iron-rich rocks (Ball, 1907a).

This mine site was destroyed during development of the Sunrise mine. Most of the development on the iron-formation at the Michigan

mine was for copper in the early 1880’s. Copper carbonate and silicate minerals are disseminated in the iron-formation in the hanging wall

of the northwest-trending normal fault that

forms the western contact of the iron-formation

and in both iron-formation and basal Guernsey

Formation along the Paleozoic/Precambrian unconformity. The copper at both of these deposits appears to be supergene in origin, probably related to low-temperature meteoric water

migrating along the base of the Paleozoic sedimentary rocks. A hypogene source of copper

has not been identified for these two deposits.

MINERAL DEPOSITS IN PEGMATITES

Small amounts of muscovite were produced between 1881 and 1900 from pegmatites

associated with the Haystack Range Granite

near the south end of the Hartville uplift (T. 27

and 28 N., R. 65 W.). These bodies are the

youngest phases of the Haystack Range Granite (1.72 Ga). In the northern part of the uplift

near Silver Springs (T. 31 and 32 N., R. 64 W.),

pegmatite bodies were prospected for beryl

(Osterwald and others, 1966). All the pegmatite

bodies in the Hartville uplift are relatively small

and from poorly zoned to well zoned; most
11

contain minor amounts of tourmaline and beryl

(Ball, 1907c). The pegmatites associated with

the Haystack Range Granite are discontinuous

bodies ranging from 10 to 100 m in length.

They intruded along the principal schistosity related to D4 , which forms a domal pattern

(Hanley and others, 1950; Sims and others,

1997), but they do not exhibit a penetrative fabric. Pegmatite bodies in the northern part of the

Hartville uplift are as much as 350 m long and 60

m wide, roughly parallel to S2 , and deformed by

D3 folds. Pegmatites throughout the uplift generally occur within muscovite-rich (metapelitic)

schists in the Whalen Group.

URANIUM DEPOSITS

Uranium has been produced in the Hartville

uplift from the Silver Cliff mine, located approximately 1 km north of the map area at Lusk,

Wyo., and from several prospects in the map

area. Uranium, as well as silver and copper, at

the Silver Cliff mine is enriched in a carbonaterich, brittle, northeast-trending reverse fault

that is probably Laramide in age. This fault produced a gouge zone as much as 1 m thick in

basal Paleozoic rocks (Wilmarth and Johnson,

1954); it is coincident with a portion of a Precambrian shear zone that controlled primary

copper and low-grade gold mineralization. Production of six carloads of uranium ore containing

3 percent U3 O8 was recorded from 1918 to

1922 (Osterwald, 1950).

Anomalous radioactivity has been recorded

in many prospects throughout the Hartville uplift; several prospects have produced a few tons

of low-grade uranium ore (for example, the gossan in sec. 23, T. 31 N., R. 64 W.). Several are

associated with the earthy hematite in gossans

that developed from weathering of the sedimenthosted massive sulfide deposits or graphite-rich

zones in metasediments of the Whalen Group.

These deposits were probably formed by the reduction of dissolved uranium by graphite or sulfide minerals in rocks of the Whalen Group.

Uranium may have been transported along

Laramide(?) fault or fracture zones by oxygenated low-temperature meteoric water and

then precipitated at or below the Precambrian/Paleozoic unconformity by reductants

along the unconformity and in the Precambrian

rocks. Uranium at the Silver Cliff mine is primarily concentrated in sandstone and conglomerate

at the base of the Guernsey Formation. Here,

uraniferous ground water was concentrated

along a Laramide structure and was precipitated

in subsidiary fractures in the locally carbonate

rich Paleozoic clastic rocks in the footwall of the

Laramide fault (Wilmarth and Johnson, 1954).

REFERENCES CITED

Annesley, I.R., Madore, Catherine, and Krogh,

T.E., 1992, U-Pb zircon, titanite, and

monazite ages from the Wollaston Domain—A summary, in Summary of Investigations 1992: Saskatchewan Geological

Survey Miscellaneous Report 92–4, p. 61–

65.

Baird, D.J., Nelson, K.D., and three others,

1996, Crustal structure and evolution of

the Trans-Hudson orogen—Results from

seismic reflection profiling: Tectonics, v.

15, no. 2, p. 416–426.

Ball, S.H., 1907a, Hartville iron ore range,

Wyoming: U.S. Geological Survey Contributions to Economic Geology, Pt. I, p.

190–205.

———1907b, Copper deposits in the Hartville

uplift, Wyoming: U.S. Geological Survey

Contributions to Economic Geology, Pt. I,

p. 93–107.

———1907c, Mica deposits in the Hartville uplift, Wyoming: U.S. Geological Survey

Contributions to Economic Geology, Pt. I,

p. 423–425.

Chamberlain, K.R., Cox, Dave, Krugh, K.A., and

Harper, K.M., 1997, Widespread ca. 2.0

Ga rifting in southeastern Wyoming—Evidence from U-Pb crystallization ages, uplift

ages, hydrothermal zircon growth, and

reset Rb-Sr and U-Pb systematics: Geological Society of America Abstracts with

Programs, v. 29, no. 6, p. A–467.

Chamberlain, K.R., Patel, S.C., Frost, B.R., and

Snyder, G.L., 1993, Thick-skinned deformation of the Archean Wyoming province

during Proterozoic arc-continent collision:

Geology, v. 21, p. 995–998.

Chance, H.M., 1897, The iron mines of

Hartville, Wyoming: Transactions of the

American Institute of Mining Engineers, v.

30, p. 987–1003.

Collerson, K.D., Lewry, J.F., Van Schmus,

W.R., and Bickford, M.E., 1989, Sm-Nd

isotopic restraints on the age of buried

Precambrian basement in central and

southern Saskatchewan—Implications for

diamond exploration: Saskatchewan Geological Survey Miscellaneous Report 89–4,

p. 168–171.

Day, W.C., Sims, P.K., Snyder, G.L., Wilson,

A.B., and Klein, T.L., 1999, Geologic map

of Precambrian rocks, Rawhide Buttes

West quadrangle and part of Rawhide
12

Buttes East quadrangle, Hartville uplift,

Goshen and Niobrara Counties,

Wyoming, with a section on Geochronology by Z.E. Peterman, Kiyoto Futa, and

R.E. Zartman: U.S. Geological Survey

Geologic Investigations Series I–2635,

scale 1:24,000.

Ebbett, B.E., Jr., 1956, Structure and petrology

of the metasedimentary rocks of the Good

Fortune mining area, Platte County,

Wyo.: Laramie, Wyo., University of

Wyoming M.A. thesis, 151 p.

Frost, C.D., 1993, Nd isotopic evidence for the

antiquity of the Wyoming province: Geology, v. 21, p. 351–354.

Hanley, J.B., Heinrich, E.W., and Page, L.R.,

1950, Pegmatite investigations in Colorado, Wyoming, and Utah: U.S. Geological Survey Professional Paper 227, 125 p.

Harper, J.L., 1960, The geology of the southern Hartville Uplift area, Platte and

Goshen Counties, Wyoming: Lincoln,

Nebr., University of Nebraska M.S. thesis,

123 p.

Hausel, W.D., 1989, The geology of

Wyoming’s precious metal lode and placer

deposits: Geological Survey of Wyoming

Bulletin 68, 248 p.

Hodgson, C.J., 1989, Patterns of mineralization, in Bursnall, J.T., ed., Mineralization

and shear zones: Geological Association

of Canada Short Course Notes, v. 6, p.

51–88.

Hoffman, P.F., 1990, Subdivision of the

Churchill Province and extent of the

Trans-Hudson orogen, in Lewry, J.F., and

Stauffer, M.R., The Early Proterozoic

Trans-Hudson orogen of North America:

Geological Association of Canada Special

Paper 37, 505 p.

Houston, R.S., and Karlstrom, K.E., 1992, Geologic map of Precambrian metasedimentary

rocks of the Medicine Bow Mountains, Albany and Carbon Counties, Wyoming:

U.S. Geological Survey Miscellaneous Investigations Series Map I–2280, scale

1:50,000.

Hudleston, P.J., 1976, Early deformational history of Archean rocks in the Vermillion

district, northeastern Minnesota: Canadian Journal of Earth Sciences, v. 13, p.

579–592.

Karlstrom, K.E., and Houston, R.S., 1984, The

Cheyenne Belt—Analysis of a Proterozoic

suture in southern Wyoming: Precambrian Research, v. 25, p. 415–446.

Karlstrom, K.E., Houston, R.S., Flurkey, A.J.,

Coolidge, C.M., Kratochvil, A.L., and

Sever, A.K., 1981, A summary of the

geology and uranium potential of Precambrian conglomerates in southeastern

Wyoming: Bendix Field Engineering Corporation Report DJBX–139–81, 541 p.

Knight, W.C., 1893, Notes on the mineral resources of the State: University of

Wyoming Experiment Station Bulletin 14,

p. 103–212.

Krugh, K.A., Chamberlain, K.R., and Snyder,

G.L., 1993, U-Pb evidence for ca. 1.66 Ga

metamorphism and deformation in the

Hartville uplift, southeastern Wyoming:

Geological Society of America Abstracts

with Programs, v. 25, no. 5, p. 64–65.

Lewry, J.F., and Collerson, K.D., 1990, The

Trans-Hudson Orogen—Extent, subdivision, and problems, in Lewry, J.F., and

Stauffer, M.R., eds., The Early Proterozoic Trans-Hudson orogen of North

America: Geological Association of

Canada Special Paper 37, p. 1–14.

Lewry, J.F., and four others, 1996, Tectonic

assembly and orogenic closure in the

Trans-Hudson orogen: Geological Association of Canada—Mineralogical Association of Canada, Program with Abstracts,

v. 21, p. A56.

Lovering, T.S., 1933, Precambrian ore deposits

of Colorado and southern Wyoming, in

Ore deposits of the western states, Lindgren volume: American Institute of Mining

and Metallurgical Engineering, New York,

p. 272–277.

Millgate, M.L., 1964, Geology of the Haystack

Range, Goshen and Platte Counties,

Wyoming: Salt Lake City, Utah, University of Utah M.S. thesis, 96 p.

Nelson, K.D., Baird, D.J., Walters, J.J., Hauck,

M., Brown, L.D., and Oliver, J.E., 1993,

Trans-Hudson orogen and Williston basin

in Montana and North Dakota—New

COCORP deep profiling results: Geology,

v. 21, p. 447–450.

Noble, J.A., and Harder, J.O., 1948, Stratigraphy and metamorphism in a part of the

northern Black Hills and the Homestake

mine, Lead, South Dakota: Geological

Society of America Bulletin, v. 59, p. 941–

976.

Osterwald, F.W. 1950, Notes on the geology at

the Silver Cliff mine, Lusk, Wyoming:

Geological Survey of Wyoming Report

50–4, 8 p.

Osterwald, F.W., Osterwald, D.B., Long, J.S.,

Jr., and Wilson, W.H., 1966, Mineral resources of Wyoming: Geological Survey

of Wyoming Bulletin 50, 287 p.
13

Peterman, Z.E., and Futa, Kiyoto, 1988,

Contrasts in Nd crustal residence ages between the Superior and Wyoming cratons: Geological Society of America Abstracts with Programs, v. 20, no. 7, p.

A137.

Poulsen, K.H., and Robert, Francois, 1989,

Shear zones and gold; practical examples

from the southern Canadian Shield, in

Bursnall, J.T., ed., Mineralization and

shear zones: Geological Association of

Canada Short Course Notes, v. 6, p.

239–266.

Premo, W.R., and Van Schmus, W.R., 1989,

Zircon geochronology of Precambrian

rocks in southeastern Wyoming and

northern Colorado: Geological Society of

America Special Paper 235, p. 13–32.

Redden, J.A., Peterman, Z.E., Zartman, R.E.,

and DeWitt, E.H., 1990, U-Th-Pb

geochronology and preliminary interpretation of Precambrian tectonic events in

the Black Hills, South Dakota, in Lewry,

J.F., and Stauffer, M.R., The Early Proterozoic Trans-Hudson orogen of North

America: Geological Association of

Canada Special Paper 37, p. 229–252.

Resor, P.G., Chamberlain, K.R., Frost, C.D.,

Snoke, A.W., and Frost, B.R., 1996, Direct dating of deformation—U-Pb age of

syndeformational sphene growth in the

Proterozoic Laramie Peak shear zone:

Geology, v. 24, p. 623–626.

Sims, P.K., 1995, Archean and Early Proterozoic tectonic framework of north-central

United States and adjacent Canada: U.S.

Geological Survey Bulletin 1904–T, 12 p.

Sims, P.K., Day, W.C., Snyder, G.L., and Wilson, A.B., 1997, Geologic map of Precambrian rocks along part of the Hartville uplift, Guernsey and Casebier Hill quadrangles, Platte and Goshen Counties,

Wyoming, with a section on Geochronology of post-tectonic intrusive rocks by

Z.E. Peterman: U.S. Geological Survey

Miscellaneous Investigation Series Map I–

2567, scale 1:24,000; 18 p. pamphlet.

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

Proterozoic Central Plains orogen—A

major buried structure in the north-central

United States: Geology, v. 14, p. 488–

491.

Sims, P.K., Peterman, Z.E., Hildenbrand, T.G.,

and Mahan, Shannon, 1991, Precambrian

basement map of the Trans-Hudson orogen and adjacent terranes, northern Great

Plains, U.S.A.: U.S. Geological Survey

Miscellaneous Investigations Series Map I–

2214, scale 1:1,000,000.

Slack, J.F., 1993, Descriptive and grade-tonnage models for Besshi-type massive sulphide deposits, in Kirkham, R.V., and others, eds., Mineral deposit modeling: Geological Association of Canada Special Paper 40, p. 343–371.

Smith, W.S.T., 1903, Hartville Folio: U.S. Geological Survey Folio 91.

Snyder, G.L., 1980, Map of Precambrian and

adjacent Phanerozoic rocks of the

Hartville uplift, Goshen, Niobrara, and

Platte Counties, Wyoming: U.S. Geological Survey Open-File Report 80–779, scale

1:48,000.

———1989, Hartville uplift geologic summary,

in Snyder, G.L., Hausel, W.D., Klein, T.L.,

Houston, R.S., and Graff, P.J., Precambrian rocks and mineralization, southern

Wyoming province: 28th International

Geologic Congress, Field Trip Guidebook

T 332, p. 4–12.

———1993, Hartville uplift, in Houston, R.S.,

and others, eds., The Wyoming province,

in Reed, J.C., and others, eds., Precambrian—Conterminous U.S.: Boulder,

Colo., Geological Society of America, The

Geology of North America, v. C–2, p.

147–149.

Snyder, G.L., and Peterman, Z.E., 1982, Precambrian geology and geochronology of

the Hartville uplift, Wyoming: 1982

Archean geochemistry field conference, p.

64–94.

Wilmarth, V.R., and Johnson, D.H., 1954, Uranophane at Silver Cliff mine, Lusk,

Wyoming: U.S. Geological Survey Bulletin 1009–A, 12 p.

Woodfill, R.D., 1987, Hartville uplift, southeastern Wyoming: Geological Survey of

Wyoming Mineral Files (unpublished), 20 p.

Zahoney, S., 1976, Report on McCann Pass,

Wyoming (Cu-Zn-Ag): Mine Finders Inc.

Report, Geological Survey of Wyoming

files (unpublished), 5 p.
JOHNSON CAMPBELL WESTON

WASHAKIE

NATRONA CONVERSE NIOBRARA

GOSHEN PLATTE

CARBON ALBANY

LARAMIE

WYOMING

COLORADO

NEBRASKA SOUTH DAKOTA

WYOMING

PROVINCE

COLORADO

PROVINCE

HARTVILLE FAULT

BLACK

HILLS

DOMAIN OF

TRANSHUDSON

OROGEN

Laramie

Mountains

HARTVILLE

UPLIFT

Possible

suture

CHEYENNE BELT

Richeau

Hills

LARAMIE PEAK

SHEAR ZONE

CENTRAL PLAINS OROGEN

Medicine Bow

Mountains

CHEYENNE BELT

RAMBLER SHEAR ZONE

MULLEN CREEK–NASH FORK

SHEAR ZONE

Sierra Madre

107° 106° 105° 104° 44°

43°

42°

41°

14

Base from U.S. Geological Survey

Wyoming State base map, 1:500,000, 1964

Revised 1980

Xsp

Agn Wvs

Wvs

Agn

Agn

Agn

Agn

Agn

Wvs

Wvs

Wvs

Xsp

Xvg

Agn

Xsp

Xsp

Xvg

Xsp

Xm

Xm

Ys Ys

Xm

Xvg

Ys

Ys

Ys

Xvg

Yan

Ys

Wvs

Agn

Agn

Xvg

Agn

Agn

Yls

Wg

Wg

Xgb

Xgb

Wvs

Xgb Xgb

Xgb

Xgb

Wvs

Wvs

Agn

Wg

Xgb

Xgb

Xgb Xgb

Xgb

Wvs

Wvs

Wg

Agn

Agn

Agn

Agn

Ws

Ws

Ws

Xd

Xg

Xg

Xgb

Wg

Xgb

Ws

0 25 50 100 KILOMETERS
EXPLANATION

MIDDLE PROTEROZOIC

Syenite of Laramie Mountains (1.43 Ga)

Anorthosite of Laramie Mountains (1.43 Ga)

Sherman Granite

EARLY PROTEROZOIC

Haystack Range Granite, Hartville uplift (1.72 Ga)

Twin Hills Diorite, Hartville uplift (1.74 Ga)

Metamorphosed volcanic and sedimentary rocks and mafic to felsic 

intrusive rocks of Colorado province (Central Plains orogen) 

(1.8–1.63 Ga)

Mylonite and granite in Cheyenne belt, Medicine Bow Mountains

Metamorphosed mafic dike (≈2.0 Ga)

Metasedimentary rocks of Snowy Pass Supergroup, Sierra Madre 

and Medicine Bow Mountains

ARCHEAN

Granite of Laramie Mountains and Hartville uplift (Late Archean)

Ferruginous schist, including iron-formation, metadolomite, and 

metabasalt (Whalen Group) of Hartville uplift (Late Archean)

Metavolcanic and metasedimentary rocks (Late Archean)

Paragneiss and orthogneiss

Contact

Fault—Bar and ball on downthrown side

Thrust fault—Dashed where inferred. Sawteeth on upper plate

15

Figure 1 (above and facing page). Geologic-tectonic map of Precambrian rocks 

exposed in Laramide uplifts, southeast Wyoming. Modified from Sims (1995).

Yls

Yan

Ys

Xg

Xd

Xvg

Xm

Xgb

Xsp

Wg

Ws

Wvs

Agn
Haystack Range Granite, 1.72 Ga

Twin Hills Diorite, 1.74 Ga

Phanerozoic cover rocks

Flattop Butte Granite, 2.65 Ga

Rawhide Buttes Granite, 2.66 Ga

Whalen Group

Contact

Thrust fault—Sawteeth on upper plate. 

Opposed arrows show transcurrent 

movement

EXPLANATION

104°45' 104°30'

42°30'

42°15'

0 5 10 15 KILOMETERS

Haystack

Range

Hartville

Guernsey

WYOMING

Study area

I–2567

HARTVILLE FAULT

I–2635

Casebier

quadrangle

Guernsey

quadrangle

Rawhide

Buttes

Figure 2. Simplified geology of Precambrian rocks of Hartville uplift, southeastern 

Wyoming. Location of published geologic maps shown for reference. A, Hartville 

fault exposed near Hell Gap.

A

Muskrat

Canyon

× Chicago

mine

RAWHIDE

FAULT

Lusk

6.4 km

16
ALBERTA

SASKATCHWAN

MANITOBA

NORTH DAKOTA

SOUTH

MONTANA DAKOTA

WYOMING

NEBRASKA

MINNESOTA

ONTARIO

UNITED STATES

CANADA

112° 108° 104° 100° 96°

56°

52°

48°

44°

XAm

YXs

Thompson

belt

Wollaston domain 

of Cree Lake

mobile belt

RAE AND

HEARNE

PROVINCES

WYOMING

PROVINCE

SUPERIOR

PROVINCE

XAi

YXs

Xp

BH

HU

LM

MB Xcp

GLTZ

GFTZ

MIDDLE AND EARLY PROTEROZOIC

Athabasca Sandstone and Sioux Quartzite

EARLY PROTEROZOIC (2.5–1.6 Ga)

Central Plains orogen (1.78–1.64 Ga)

Penokean orogen (2.2–1.84 Ga)

EARLY PROTEROZOIC AND ARCHEAN 

TRANS-HUDSON OROGEN

Juvenile terranes

Miogeoclinal belt

ARCHEAN (2.5 Ga and older)

Rae and Hearne provinces

Wyoming province

Superior province

Cheyenne belt

Great Falls tectonic zone

Great Lakes tectonic zone

Laramide uplifts

Black Hills uplift

Hartville uplift

Laramie Mountains

Medicine Bow Mountains

Thrust fault—Sawteeth on upper plate. Dashed 

where approximately located

Fault—Dashed where approximately located

Boundary between exposed geologic domains

Boundary between domains in the subsurface

Edge of exposed Precambrian rocks—Hachures 

point toward exposed area

Figure 3.MMRegional geology of the Trans-Hudson orogen. It separates the Wyoming and Superior cratons, and is 

truncated to the south by the Central Plains orogen.

Xcp

Xp

XAi

XAm

XAm

TRANS-HUDSON

OROGEN

EXPLANATION

17

CB

0 200 400 KILOMETERS

CB

GFTZ

GLTZ

BH

HU

LM

MB

YXs
Figure 4. Schematic diagram showing interpretation of COCORP data of crustal structure of Trans-Hudson orogen at 

lat 48°30' N. Figure is at crustal velocity of 6 km/s. Modified from Nelson and others (1993).

Wyoming

province

Batholith

Moho

Trans-Hudson orogen

Superior

province

0 50 100 KILOMETERS

18

EXPLANATION

Trans-Hudson orogen

North American Central Plains conductivity anomaly

Archean Wyoming province

Archean Superior province

Archean microcontinent

Lower crustal layering

Contact—Location uncertain
SiO2, IN WEIGHT PERCENT

40 45 50 55 60

La/Lu (NORMALIZED)

0

5

10

15

20

25

Mother Featherlegs Metabasalt

Muskrat Canyon Metabasalt

Enriched LREE

Flat REE

19

Figure 6. La/Lu (normalized) versus SiO2 (weight percent) diagram showing 

relative amounts of flat REE and enriched light REE in Muskrat Canyon 

Metabasalt and Mother Featherlegs Metabasalt.

EXPLANATION

100

10

1

100

10

1

Sample/Chondrite Sample/Chondrite

La Ce Pr Nd Sm Eu Tb Gd Dy Ho Er Tm Yb Lu

A

B

Figure 5. Chondrite-normalized rare earth element plot for 

samples of A, Muskrat Canyon Metabasalt, and B, 

Mother Featherlegs Metabasalt.
20

1.0

1.0

1.0

5.0

5.0

10.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

5.0

5.0

5.0

5.0

10.0 10.0

N

N

n=77

n=67

A

B

Figure 7. Equal-area projections (lower hemisphere) of D2 deformation 

structures in Guernsey quadrangle. A, poles to S2; B, azimuth and 

plunge of F2 fold axes and L2 (S0/S2 intersection).

5.0

5.0

5.0

5.0

5.0

5.0

10.0

10.0

10.0

10.0 10.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0
21

Figure 8. Equal-area projections (lower hemisphere) of D3 deformation 

structures in a typical area in central part of Hartville uplift. A, poles to 

S3; B, azimuth and plunge of F3 fold axes and L3 lineatons.

B n=33

A n=52

N

N

1.0

1.0

1.0

1.0

5.0

5.0

5.0

5.0

10.0

10.0

10.0

10.0

10.0

10.0

10.0

5.0

5.0

5.0

5.0

1.0

1.0

1.0

1.0

1.0

5.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

10.0

10.0

20.0

20.0
Lusk

Manville

Lone Tree Hill

Outline of

Precambrian core

Tectonic front

D3 deformation

104°45' 104°30'

EXPLANATION

Proterozoic granite, age 1.72 

Ga—Composes structural domes

Twin Hills Diorite, age 1.74 

Ga—Inferred to compose a structural 

dome. Diorite is cut by numerous 

irregularly oriented cataclastic shears; 

age and origin of shears not known

Areas of D4 deformation and 

1.72–1.74 Ga metamorphic 

aureole—Boundary approximately 

oriented

Areas of D3 deformation—Trans-Hudson 

orogeny, but possibly includes 

Cheyenne belt deformation

Areas of D2 deformation, age 1.98 Ga 

(Oregon Trail orogeny)

Outlying outcrop area

Thrust fault—Sawteeth on upper plate

HARTVILLE FAULT
North Platte River

Fort

Laramie

Antelope Hills Projected position of 1.78-Ga Cheyenne belt (after Sims and others, 1991)

Guernsey

Hartville

TICLINE

Tectonic front

D3 deformation

Outline of

Precambrian core

ecambrian tectonic events of Hartville uplift and outlying areas, southeastern Wyoming. Sullivan Ridge is 10 km north of Lusk.

1 23 4

2 3 4 5 6 7 KILOMETERS

5 MILES

HARTVILLE FAULT

McCANN PASS

FAULT
SW NE Empire mine Good Fortune mine Michigan mine Section 23 prospect Charter Oak prospect (McCann Pass) Omaha/Gold Hill/ Copper Belt mines Sunrise/Chicago mines

(Not exposed)

Fault

24

Muskrat Canyon Metabasalt Silver Springs Formation

Mother Featherlegs Metabasalt

Wildcat Hills Formation

Siliceous exhalite/

massive sulfide

Quartzite

Metadolomite

Iron-formation

Metapelite

Siliceous exhalite/

massive sulfide Iron-formation

Metagraywacke

Iron-rich schist Hematite ore

Jasper

EXPLANATION

Stromatolites Mine Prospect

Figure 10. Schematic section showing stratigraphic position of principal mineral deposits.

Ironformation
25

Table 1. Tectonic, stratigraphic, and magmatic evolution of Hartville uplift

during the Precambrian

Age, in Ga Event

circa 1.4 Emplacement of mafic dikes; undeformed

circa 1.66 Cryptic thermal event, indicated by apatite and monazite ages (Krugh and others, 1993).

1.72 Emplacement of granite domes (D4 deformation)

circa 1.8* D3 deformation; fold-and-thrust belt developed along length of uplift (TransHudson orogen).

circa 1.98 D2 deformation; folding on east-west axes and accompanying metamorphism

circa 2.0 Mafic dike swarm

2.66–2.65 Emplacement of Rawhide Buttes and Flattop Butte Granites

2.8–2.65 Deposition of Whalen Group in miogeoclinal environment, followed by nappe

development (D1 deformation).

3.1–2.8 Crystalline basement, indicated by Nd model ages

*Isotopic age indications for 1.78–1.76 Ga Cheyenne belt deformation (Central Plains orogeny)

are lacking for the Hartville uplift.
Table 2. Geochemistry of the Mother Featherlegs Metabasalt, Hartville uplift, Wyoming

G , Guernsey; RBE, Rawhide Buttes East; RBW, Rawhide Buttes West; RS, Reynolds Spring; SS, Silver Springs. LOI, loss on ignition. n.a., not available]

129 147 148 195 665 666 714 2539 2593

metabasalt amphibolite metabasalt metabasalt amphibolite metabasalt amphibolite amphibolite amphibolite

pillowed dike in marble pillowed xenolith dike dike dike

42.29468139 42.27914444 42.28818944 42.63881806 42.63385111 42.63881806 42.56342806 42.57559722 42.611975

104.715715 104.721747 104.718463 104.520078 104.464434 104.520078 104.499397 104.501719 104.462836

G G G SS RS SS RBE RBW RBE

Major element oxides by X-ray fluorescence analysis (weight percent)

50.21 49.74 52.68 48.64 52.11 51.09 49.36 49.7 49.915.23 13.25 13.95 14.25 11.02 13.77 14.57 14.4 13

12.57 15.59 10.68 12.43 19.94 12.78 11.44 12.6 14.5

7.80 9.30 n.a. n.a. 11.20 7.40 5.80 8.80 7.787.52 5.85 6.00 7.10 2.94 8.11 8.29 7.45 6.35

9.81 9.53 10.15 15.35 8.53 9.20 11.22 1.70 7.71

2.27 2.16 2.28 1.00 1.55 3.11 2.94 2.38 0.82

0.18 0.18 0.18 0.14 0.99 0.10 0.83 0.78 5.78

0.97 1.43 0.94 0.96 2.67 0.97 0.65 0.76 1.320.08 0.12 0.10 0.08 0.20 0.08 0.05 0.05 0.11

0.15 0.2 0.14 0.18 0.24 0.18 0.19 0.21 0.2

1.29 1.05 1.11 0.78 <0.01 0.6 0.69 0.49 1.31

100.3 99.12 98.21 100.9 100.19 99.99 100.23 99.54 100.14

Trace element analysis by X-ray fluorescence analysis (parts per million)

2 4 3 3 7 <2 <2 n.a. n.a.

58 83 56 61 137 66 39 n.a. n.a.

21 27 22 20 45 20 19 13 2896 139 106 69 61 42 110 n.a. n.a.

3 3 3 6 20 4 8 n.a. n.a.

101 112 81 72 110 90 68 n.a. n.a.

62 61 38 55 789 85 14 n.a. n.a.

Trace element analysis by instrumental neutron activation analysis (parts per million)

51.8 54.1 44.3 56.9 42.4 49.6 50.1 49.1 49.4

121 88.8 182 103 5.3 113 155 141 59.3

1.5 2.2 1.4 1.4 3.4 1.5 0.9 1.11 2.3

130 <50 130 <50 <50 105 82 n.a. n.a.

46.8 41.6 44.2 35.7 38.2 38.1 45.4 51.4 49.1

<0.3 <0.3 <0.3 0.5 0.5 <0.3 <0.3 0.101 0.49

0.2 0.5 0.3 0.4 1.9 0.4 0.2 0.281 0.865

<0.1 <0.1 <0.1 <0.1 1.3 <0.1 <0.1 0.082 0.708

1.6 4.3 2 3.8 8.1 4.1 2.3 2.69 7.386 14 7 11 26 12 6 5.3 214 9 4 8 18 7 4 4 13.8

1.4 2.74 1.48 1.97 4.97 2.19 1.47 1.81 4.16

0.63 1.05 0.67 0.84 1.69 0.81 0.62 0.725 1.22

n.a. n.a. n.a. n.a. n.a. n.a. n.a. 2.5 4.89

0.4 0.7 0.4 0.5 1.2 0.5 0.4 0.44 0.795

n.a. n.a. n.a. n.a. n.a. n.a. n.a. 3.1 5.35n.a. n.a. n.a. n.a. n.a. n.a. n.a. 0.33 0.525

2.1 2.87 2.05 1.78 4.19 1.98 1.88 2.27 3.22

0.32 0.43 0.3 0.27 0.59 0.27 0.26 0.358 0.499
Table 2. Geochemistry of the Mother Featherlegs Metabasalt, Hartville uplift, Wyoming—Continued

2624 2688 0709C 0835A HU-010 HU-022 TKHU 044 TKHU 090 TKHU 117 2507

amphibolite metabasalt amphibolite amphibolite metabasalt amphibolite metagabbro metabasalt metabasalt metabasalt

dike dike pillowed dike

42.61777778 42.59976111 42.57490417 42.614765 42.638875 42.59640278 42.67207639 42.69668917 42.70146222 42.28846944

104.566333 104.497217 104.48847 104.454859 104.520089 104.478036 104.520741 104.522882 104.517681 104.718131

RBW RBE RBW RBE SS RBE SS SS SS G

Major element oxides by X-ray fluorescence analysis (weight percent)

50.9 48.5 49.02 49.53 49.1 49.7 49.64 49.92 49.13 53.913.2 14.3 15.35 13.88 14.7 13.5 16.13 14.48 15.06 14.4

14.9 14 11.76 14.49 11.5 16.2 8.73 13.24 16.29 8.7

8.94 10.80 6.10 n.a. 9.11 11.46 5.40 8.00 9.60 7.83

6.19 8.20 8.06 6.44 6.26 5.79 8.91 7.77 4.41 7.07

10.10 9.60 11.68 9.57 17.60 9.75 14.10 11.76 8.37 8.99

1.61 2.30 2.27 2.72 0.67 2.62 1.30 1.21 3.75 2.43

1.01 0.12 0.99 0.81 0.07 0.64 0.13 0.14 0.49 0.13

1.30 1.30 0.73 1.28 0.95 1.67 0.54 0.84 2.22 0.930.12 0.10 0.06 0.06 0.07 0.08 0.07 0.07 0.18 0.08

0.22 0.22 0.17 0.2 0.19 0.23 0.15 0.2 0.24 0.14

1.24 n.a. 0.6 0.47 0.46 0.39 1.1 0.95 0.33 n.a.

99.8 99 100.67 99.45 100.56 99.3 100.79 100.58 100.48 98.82

Trace element analysis by X-ray fluorescence analysis (parts per million)

n.a. n.a. <2 3 n.a. n.a. 2 2 3 5

n.a. n.a. 44 46 n.a. n.a. 41 50 109 42

28 5.6 18 17 13 20 16 18 38 15

n.a. n.a. 133 136 n.a. n.a. 124 124 296 113n.a. n.a. 15 15 n.a. n.a. 3 5 11 n.a.n.a. 140 76 93 n.a. n.a. 49 83 124 143n.a. 160 73 99 n.a. n.a. 80 105 32 70

Trace element analysis by instrumental neutron activation analysis (parts per million)

51.9 44.4 49.2 52.9 48.4 58.1 39 53.6 41.9 40.4

54.8 302 303 123 132 97.6 567 131 15.6 195

2.1 1.76 1.1 1.2 1.63 2.11 0.9 1 2.8 1.25

n.a. n.a. <50 95 n.a. n.a. 164 83 <50 87

47.4 39.6 43.7 37.3 40.9 43.9 38.1 43.1 42.4 46.9

0.249 0.204 <0.3 0.3 0.193 0.291 <0.3 <0.3 0.5 0.132

1.6 0.315 0.3 0.3 0.4 0.185 <0.1 0.2 1 0.313

0.428 0.432 <0.1 0.1 0.1 0.83 <0.1 <0.1 0.4 0.3

6.56 4.19 2.5 3.9 3.95 3.06 2 2.7 6.5 2.73

16.8 12 8 10 12.5 12.2 6 9 20 7.76

9.98 9 6 7 n.a. 9.28 5 5 13 6.1

3.1 2.72 1.63 1.85 2.5 3.3 1.26 1.78 3.7 1.97

1.06 0.911 0.63 0.75 0.901 0.883 0.52 0.68 1.36 2.7

3.36 3.18 n.a. n.a. n.a. 4.2 n.a. n.a. n.a. 0.692

n.a. 0.55 0.4 0.4 0.54 0.6 0.4 0.5 0.9 0.5

4.01 3.61 n.a. n.a. 3.6 3.78 n.a. n.a. n.a. 3.27

0.433 0.33 n.a. n.a. 0.33 n.a. n.a. n.a. n.a. 0.34

2.97 2.03 1.78 1.78 1.95 2.39 1.44 1.94 3.83 2.2

0.486 0.302 0.26 0.27 0.275 0.382 0.21 0.29 0.57 0.329
Table 3. Geochemistry of the Muskrat Canyon Metabasalt, Hartville uplift, Wyoming

mes: CH, Casebier Hill; G , Guernsey; HG, Hell Gap; MS, Moore Spring; RBE, Rawhide Buttes East; RBW, Rawhide Buttes West; SS, Silver Springs.

LOI, loss on ignition. n.a., not available]

257 275 307 314 332 506 510 829 930 2343 2703

metabasalt gabbro sill metabasalt metabasalt metabasalt metabasalt metagabbro metagabbro amphibolite metagabbro metabasalt

pillowed in graywacke pillowed layered dike pillowed

42.32716806 42.30998556 42.37389917 42.368285 42.376585 42.31084139 42.31120833 42.69777667 42.62679944 42.03718333 42.56415

04.7239464 104.7118364 104.6569775 104.661005 104.6637161 104.71028 104.7072353 104.5211506 104.5002417 104.6179889 104.5848167

G G G G HG G G SS SS CH RBW

Major element oxides by X-ray fluorescence analysis (weight percent)

48.22 49.75 49.13 53.67 47.01 47.8 47.72 49.56 48.08 48.5 51.3

16.24 14.19 14.56 16.30 15.45 13.87 14.88 14.96 11.05 16.90 12.10

13.82 14.48 12.72 10.23 13.02 15.34 13.29 11.53 13.21 11.30 11.13

n.a. 7.90 6.70 n.a. 6.50 n.a. n.a. n.a. 8.00 8.66 8.40

5.71 5.75 6.73 4.53 5.41 6.55 6.71 8.10 11.66 8.11 9.90

10.33 8.64 8.50 5.92 9.84 11.27 9.99 10.59 10.02 9.70 9.60

2.94 3.33 3.40 5.83 3.14 2.37 2.90 2.42 1.25 2.62 3.40

0.38 0.19 0.65 0.35 0.26 0.22 0.24 0.32 0.62 0.52 0.23

1.74 1.45 1.69 1.86 1.71 1.69 1.37 0.75 0.91 1.46 0.960.17 0.13 0.19 0.17 0.17 0.13 0.12 0.06 0.08 0.16 0.170.15 0.23 0.16 0.11 0.16 0.25 0.21 0.18 0.19 0.17 0.21

0.90 2.71 2.53 1.98 3.12 1.09 1.49 0.83 1.44 1.34 1.30

100.6 100.84 100.27 100.95 99.29 100.58 98.93 99.3 98.51 99..82 101

Trace element analysis by X-ray fluorescence analysis (parts per million)

6 9 8 8 5 10 11 3 3 6 n.a.

147 90 140 159 138 96 97 47 71 154 n.a.

25 19 24 28 23 21 22 20 17 19 21

593 147 420 279 576 172 230 144 136 312 n.a.

4 2 9 3 4 5 5 8 12 26.3 n.a.

109 100 110 83 117 102 88 97 90 154 140

56 <5 <5 <5 86 86 78 54 19 n.a. 75

Trace element analysis by instrumental neutron activation analysis (parts per million)

68.9 57.8 51.3 38.4 56.7 54 50 44 62.5 42.9 39.4

60.5 10.3 120 43.5 56.9 21 50.7 236 1830 203 573

4.1 1.4 3 3.3 3.3 2.2 1.9 0.9 1.8 2.8 1.94

120 <50 112 86 117 <50 <50 158 395 n.a. n.a.

23.1 40.9 22.1 20.5 22.6 45.5 39.3 38.5 27.6 29.6 25.2

0.9 0.8 0.7 0.6 0.6 0.4 <0.3 0.3 0.4 0.414 0.27

1.5 0.8 1.4 1.6 1.4 0.9 1 0.6 1.1 1.2 2.58

0.5 <0.1 0.2 <0.1 0.4 <0.1 0.4 0.2 0.5 0.3 0.646

16.1 8.1 14.5 14 16.4 9.1 13.2 13.8 8.3 11.2 8.61

41 21 33 38 38 23 31 26 20 25.6 18.9

22 13 18 20 21 13 16 15 11 12.7 9.96

4.72 2.89 4.1 4.28 5.04 3.22 3.59 3.21 2.54 3.89 2.77

1.75 1.03 1.48 1.7 1.7 1.19 1.24 1.08 0.89 1.3 0.931

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. 4.02 n.a.

0.8 0.7 0.7 0.9 0.8 0.7 0.6 0.5 0.5 0.518

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. 3.9 3.35n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. 0.375 0.26

1.98 1.72 1.7 1.89 1.95 1.89 1.71 1.57 1.55 2.18 1.54

0.3 0.23 0.23 0.26 0.29 0.26 0.26 0.23 0.23 0.346 0.235
Table 3. Geochemistry of the Muskrat Canyon Metabasalt, Hartville uplift, Wyoming—Continued

0016b 0019-MSC-1 0022-MSC-1 0307-3 0319A 0510r 0738R B CU#3-378 HU-028 HU-035 TKHU 017A

amphibolite metabasalt metabasalt metabasalt metabasalt metagabbro amphibolite metabasalt metabasalt metagabbro metabasalt

mottled dike layered dike

42.58098639 42.47810556 42.47810556 42.37563694 42.37692361 42.31120833 42.61618944 42.49005 42.56415 42.28031389 42.65166111

104.502737 104.587367 104.587367 104.66029 104.656234 104.707235 104.458265 104.616492 104.584817 104.72538 104.520011

RBW MS MS HG HG G RBE MS RBW G SS

Major element oxides by X-ray fluorescence analysis (weight percent)

52.34 50.2 56.3 47.12 48.16 47.62 50.8 53.8 50.6 48.3 44.81

12.37 12.30 13.30 16.09 15.19 15.07 13.14 14.40 11.90 16.40 17.33

16.34 13.60 10.50 13.46 13.87 11.84 15.01 13.60 8.40 12.80 15.61

n.a. 10.90 8.67 6.00 n.a. 7.70 n.a. 8.06 7.56 8.66 9.80

4.37 8.96 6.23 5.78 5.89 7.31 6.57 13.60 7.89 6.73 10.156.88 10.60 7.99 11.05 8.73 9.06 8.99 4.07 10.90 9.47 7.49

1.85 1.73 3.22 2.24 2.56 3.20 2.10 <0.15 3.87 2.55 0.93

0.64 0.50 0.33 0.26 0.90 0.21 0.62 4.43 0.25 0.74 0.142.10 1.40 1.41 1.84 1.76 1.46 1.57 1.43 0.98 0.84 1.340.28 0.15 0.16 0.18 0.19 0.11 0.16 0.08 0.14 0.25 0.120.26 0.20 0.14 0.14 0.16 0.29 0.20 0.11 0.18 0.18 0.18

0.53 0.64 0.51 2.69 2.64 1.98 0.74 1.01 n.a. 1.32 2.15

97.96 99.11 99.39 100.83 100.05 98.14 99.9 97.9 98.49 98.62 100.24

Trace element analysis by X-ray fluorescence analysis (parts per million)

10 n.a. n.a. 6 7 11 9 n.a. 6 5 7

149 n.a. n.a. 140 157 89 99 n.a. 67 74 77

51 21 11 23 25 22 33 14 15 18 19

199 n.a. n.a. 587 686 268 188 n.a. 156 524 82

34 n.a. n.a. 6 17 3 13 n.a. 3 15.8 6

138 n.a. n.a. 112 129 106 100 n.a. 124 74 117

63 n.a. n.a. 54 43 157 70 n.a. 50 n.a. <5

Trace element analysis by instrumental neutron activation analysis (parts per million)

45.2 48.3 36.1 54.2 61.7 67 47.9 37.9 39.4 48.6 61.7

17.6 556 316 54 49.6 77 75.9 98.6 665 143 159

3.8 2.86 2.74 3.3 3.9 2 2.6 2.71 2.09 1.85 1.7

<50 n.a. n.a. 176 <50 <35 <50 n.a. n.a. n.a. <50

39.5 31.9 30.3 21.5 23.8 47 46.3 17.5 26.3 28.5 50.8

0.5 0.47 0.418 0.6 <0.3 <0.5 <0.3 0.415 0.291 0.234 0.3

3.6 3.4 3.18 1.3 1.6 36 1.2 1.21 2.61 3.7 0.3

1.4 0.698 0.921 0.5 <0.1 <0.5 0.4 0.355 0.625 1.03 <0.1

26.3 16.9 12.3 15.1 18.6 8.7 10 7.11 7.62 39.3 4.6

53 37.4 28.9 36 42 15 25 25.3 17.3 83.4 1329 17.8 16.5 21 26 5 16 16 10.3 32.7 8

6.65 4.75 3.9 4.67 5.53 2.3 4.06 4.32 2.73 5.49 2.39

2.3 1.36 1.2 1.73 1.86 0.7 1.38 1.38 3.08 1.46 0.71

n.a. 4.95 4.1 n.a. n.a. n.a. n.a. 4.5 0.9333 4.13 n.a.

1.3 0.811 0.623 0.9 0.8 <0.5 0.9 0.7 0.5 0.601 0.5

n.a. 4.55 3.9 n.a. n.a. n.a. n.a. 4.23 3.15 3.7

n.a. 0.33 0.28 n.a. n.a. n.a. n.a. 0.33 0.266 0.341

4.51 1.94 1.67 1.8 2.21 1.6 3.41 1.95 1.6 2.03 1.57

0.68 0.297 0.244 0.25 0.32 0.21 0.51 0.269 0.241 0.283 0.22
30

Table 4. Approximate modes of granitoid rocks and gneiss from outlying areas

(percent by volume)

[Tr, trace]

Sample No. HU 18 HU 17 HU 15 HU 16 HU 34

Plagioclase 23 45 42 42 46.5

Quartz 37 38 23 18.5 26

Potassium 33 10.5 24 33 19

 feldspar.

Biotite 6 3.5 11 5 7.5

Muscovite 1 3 Tr 1.5 1

Accessory Tr Tr Tr Tr Tr

 minerals.

SAMPLE DESCRIPTIONS

HU 18 Lone Tree Hill; foliated medium- to coarse-grained biotite granite. Some

biotite altered to chlorite.

HU 17 Lone Tree Hill; medium-grained granodiorite gneiss. Some biotite altered

to chlorite.

HU 15 Foliated fine-grained granodiorite. Cuts gneiss (HU 16).

HU 16 Granite gneiss.

HU 34 Granodiorite gneiss; associated with amphibolite.