Igneous Rocks and Related 

Mineral Deposits of the 

Barker Quadrangle, 

Little Belt Mountains, 

Montana 

G E 0 L 0 G I CAL S U R V E Y P RO FE S S I 0 N A L PAP E R 7 5 2 

Igneous Rocks and Related 

Mineral Deposits of the 

Barker Quadrangle, 

Little Belt Mountains, 

Montana 

By IRVING J. WITKIND 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 752 

A laccolithic complex in central Montana is examined 

in detail with special attention given to the 

igneous rocks) the intrusions) and the related 

silver-lead-zinc deposits 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1973 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 72-600361 

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 

Price: Paper covers-$1.00, domestic postpaid; 75 cents, GPO Bookstore Stock No. 2401-00312_ 
CONTENTS 

Abstract -----------------------------------------

Introduction ------------------------------------- Previous and present work ______________________ _ 

Acknowledgments -------------------------------- Geographic and geologic setting __________________ _ 

Igneous rocks ------------------------------------

Felsic rocks ---------------------------------- Old felsic rocks _________________________ _ 

Porphyry of Clendennin Mountain _____ _ VVolf Porphyry ____________________ _ 

Young felsic rocks _______________________ _ 

Rhyolite of Granite Mountain _________ _ 

Porphyry of Galena Creek ___________ _ 

Snow Creek(?) Porphyry ____________ _ 

Chemistry of the felsic rocks _____________ _ 

Intermediate rocks ---------------------------

Quartz monzonite of Hughesville _______ _ 

Barker Porphyry ____________________ _ 

Chemistry of the intermediate rocks _______ _ 

Mafic rocks ----------------------------------

Shonkinite ------------------------------- Plagioclase shonkinite ___________________ _ 

Syenite ---------------------------------- Minette-kersantite ____________ ------------

Vogesite --------------------------------- Chemistry of the mafic rocks ______________ _ 

Composite dikes ------------------------------ Similarities of clinopyroxenes _______________ _ 

The intrusions -----------------------------------

Stock ----------------------------------------

Hughesville stock ------------------------

Laccoliths ----------------------------------- Planoconvex laccoliths ___________________ _ 

Tongue-shaped satellitic laccoliths _________ _ 

Asymmetric laccoliths __________________ _ 

Descriptions of laccoliths ____________________ _ 

Planoconvex laccoliths ___________________ _ 

Butcherknife Mountain laccolith ______ _ 

Page 

1 The intrusions-Continued 

2 Descriptions of laccoliths-Continued 

3 Planoconvex laccoliths-Continued 

3 Taylor Mountain laccolith ____________ _ 

3 Laccolith ( ? ) underlying the Limestone 

5 Butte dome ------------------------

5 Dry VVolf laccolith --------------------

5 Satellitic laccoliths ----------------------

5 Clendennin-Peterson laccolith _________ _ 

9 Clendennin fault ________________ _ 

9 Peterson fault -------------------

9 Otter laccolith ------------------------ 9 Asymmetric laccoliths ____________________ _ 

9 Barker laccolith ----------------------

11 Mixes Baldy-Anderson Peak laccolith __ 

11 Bysmalith __ --------------------------------- 11 Granite Mountain bysmalith ______________ _ 

16 Buried pluton -------------------------------

16 Indurated alluvium ---------------------------

16 Emplacement sequence of the intrusions ________ _ 

19 First intrusive episode -------------------

19 Second intrusive episode ------------------ 19 Formation of indurated alluvium __________ _ 

19 Third intrusive episode --------------------

21 Radiometric ages of the intrusions _____________ _ 

23 Mineral deposits ---------------------------------

24 Barker mining district ------------------------ 24 Fissure veins in the stock ________________ _ 

24 Fissure veins beyond the stock __________ _ 

25 Contact-replacement deposits ______________ _ 

25 Tenor -----------------------------------

27 Age of the ores --------------------------

28 Localization ------------------------------

28 San Miguel district --------------------------

28 Ore potential ---------------------------------

28 Sulfide veins ----------------------------- 28 Buried mineralized pluton ________________ _ 

28 References cited ----------------------------------

ILLUSTRATIONS 

Page 

31 

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34 

35 

35 

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41 

42 

42 

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42 

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57 

Page 

FIGURE 1. Index map of part of Montana and the study area ------------------------------------------------ 2 

2. Map showing pattern of intrusions in the Barker quadrangle ------------------------------------- 4 

3. Generalized section of sedimentary rocks exposed in the Barker quadrangle ----------------------- 8 

4. Photographs of the felsic igneous rocks ------------------------------------------------------------ 10 

5. Triangular diagram showing some chemical characteristics of old and young felsic rocks_______________ 11 

6. Geologic map of the Hughesville stock and adjacent intrusions ------------------------------------- 14 

7. Photographs of the intermediate and mafic igneous rocks------------------------------------------- 17 

8. Silica variation diagrams for intermediate rocks from intrusions in the Barker quadrangle ___________ 18 

III 
IV CONTENTS 

Page 

FIGURE 9. Triangular diagram comparing some chemical characteristics of the intermediate rocks from the 

Barker quadrangle with comparable rocks ----------------------------------------------------- 18 

10. Photomicrographs of xenoliths and xenocrysts in lamprophyres -------------------------------------- 22 

11. Triangular diagram showing some chemical characteristics of the mafic rocks _______________________ 23 

12. Map showing the Annie E dike intruding the quartz monzonite of Hughesville ________________________ 25 

13. Map showing the distribution and shape of the various intrusions as shown by structure contours 

drawn on the top of the Madison Group in the Barker quadrangle ------------------------------ 26 

14. Diagrams showing the relations between parent stock and tonguelike satellitic laccoliths _____________ 27 

15. Equal-area stereographic net plot showing joint pattern in the Hughesville stock _____________________ 27 

16. Diagrams showing three types of laccoliths ________ ------------------------------------------------ 29 

17. Diagrams showing four ways an asymmetric laccolith might develop ___________ ____________________ 30 

18. Photograph of the compound dome underlain by the Taylor Mountain laccolith and the Granite Mountain bysmalith ------------------------------------------------------------------------------ 32 

19. Sections showing one possible explanation for the structural relations between the Taylor Mountain 

laccolith and the Granite Mountain bysmalith ___________ -------------------------------------- 34 

20. Photograph of the Clendennin-Peterson anticline __________________ ---------------------------------- 36 

21. Geologic map of the proximal end of the C1endennin-Peterson laccolith showing relations between the 

Clendennin and Peterson faults and the laccolith ---------------------------------------------- 38 

22. Photograph of the Barker laccolith __________________________________ ----------------------------- 39 

23. Geologic map of the west flank of the Granite Mountain bysmalith _ --------------------------------- 40 

24. Map showing sample localities for radiometric age determinations of various intrusions in the Barker 

quadrangle ---------------------------------------------- ____ ---------------------------------- 44 

25. Map showing location of mines in and near the Barker mining district -------------------------------- 46 

26. Sketch showing the pattern and trend of major veins in the Danny T tunnel of the Liberty mine _______ 47 

27. Photographs of ore from a crustified vein --------------------------------------------------------- 48 

28. Sketch maps of the McVeda mine along the southeast flank of the Clendennin-Peterson laccolith ________ 50 

29. Idealized sketches suggesting how sulfide ores may have been localized in the Hughesville stock _________ 53 

30. Map showing location of mines and prospects in the San Miguel area -------------------------------- 54 

31. Gravity contour map of the buried mineralized pluton ---------------------------------------------- 54 

TABLES 

Page 

TABLE 1. The petrography and chemical composition of old and young felsic rocks from the Barker quadrangle 

and of a similar rock from Wolf Butte, Little Belt Mountains ------------------------------------- 6 

2. The petrography and chemical composition of intermediate rocks from the Barker and Neihart quadrangles, Little Belt Mountains, and of a similar rock from the Stanford-Hobson area ________________ 12 

3. Lamprophyre terminology ------------------------------------------------------------------------- 19 

4. The petrography and chemical composition of mafic rocks from the Barker quadrangle, Little Belt Mountains and of similar rocks from the Stanford-Hobson area ____ ----------------------------------- 20 

5. Chemical analyses of the mafic margin, transitional zone, and felsic interior of the Maytee composite 

dike ----------------------------------------------------------------------------------------- 24 

6. Tabular summary of known and inferred crosscutting relations in the Barker quadrangle _______________ 41 

7. Radiometric ages of various intrusions in the Barker quadrangle ------------------------------------- 45 

8. Production data for the Block P mine ___________________ --------------------------------------------- 51 

9. Production data for the Liberty mine --------------------------------------------------------------- 52 
IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE 

BARKER QUADRANGLE, LITTLE BELT MOUNTAINS, MONTANA 

By IRVING J. WITKIND 

ABSTRACT 

The Barker quadrangle is astride the north flank of the 

Little Belt Mountains, one of several laccolithic and volcanic 

groups that rise above the broad plains of central Montana. 

The northern third of the quadrangle includes pediments and 

sedimentary rocks which slope gently northward from the 

mountains; the remainder of the quadrangle is a mountainous 

terrain of domelike heights separated by long, narrow, sinuous valleys. 

Precambrian paragneiss and orthogneiss are exposed in the 

southwest corner of the quadrangle, and comparable rocks 

probably underlie the remainder of the quadrangle. This 

Precambrian basement is overlain unconformably by a sedimentary mantle some 4,800 feet thick. 

Both the Precambrian crystalline rocks and the sedimentary rocks have been warped, broken, intruded, and elevated 

by a host of large and small igneous masses. The igneous 

rocks which form these bodies have been subdivided, on the 

basis of their contained silica, into felsic, intermediate, and 

mafic groups. All the major plutons are formed of either 

felsic or intermediate rocks; the mafic rocks constitute only 

a small fraction of the total volume of igneous rock emplaced. 

The felsic rocks, mainly rhyolite and granite porphyries, 

have been divided into old and young groups. The intermediate rocks are chiefly quartz latite porphyries, which 

locally grade into latite porphyries or quartz rhyolite porphyries. There is also some syenite. The mafic rocks consist 

of medium- to coarse-grained shonkinite and fine-grained 

lamprophyres, which include such varied types as minette, 

kersantite, and vogesite. Several composite dikes characterized by mafic margins (kersantite) and felsic interiors 

(quartz rhyolite porphyry) imply that two magmas of 

diverse composition coexisted in the area and were emplaced 

almost synchronously. 

Eleven major plutons are recognized; these are: one stock, 

eight laccoliths, a bysmalith, and a buried ovoid pluton which 

trends northeast, extending from near Neihart, Mont., to 

near Barker. Significant deposits of silver, lead, and zinc have 

been mined from the pluton, and it seems likely that comparable deposits are still concealed in the pluton. Molybdenite, 

pyrite, and quartz fill fractures in both the exposed part of 

the pluton and the surrounding Precambrian crystalline rocks. 

The height of the range and the configuration of each 

individual mountain are the direct results of the emplacement of one or more of these intrusions. A few of the major 

intrusions are well exposed owing to the removal of their 

sedimentary cover, but elsewhere erosion has not been as 

extensive and only parts of the underlying intrusion are 

visible. In general, the structural framework of the quadrangle consists of a parent stock (the Hughesville stock) 

encircled by three laccoliths, which radiate from the stock 

much like spokes from the hub of a wheel. 

Radiometric (potassium-argon) ages that were determined 

for both mineral separates and whole rock from various of 

the intrusions indicate that the intrusions were emplaced 

during early Tertiary, most likely the Eocene. 

Silver-lead sulfide ore deposits in the quadrangle were 

mined from about 1879 to 1943. In 1968, all the mines were 

closed, and many were flooded. Two mining districts are in 

the mapped area: the Barker mining district centered about 

the Hughesville stock near the middle of the quadrangle and 

the San Miguel mining district centered about a group of 

small mines and prospects in Precambrian crystalline rocks 

exposed along the south edge. Most of the ore produced has 

come from the Barker district. Tenor of the mined ore 

probably averaged 25 ounces of silver and 30 percent lead 

per ton. 

The stock is intensely fractured. Two conjugate fracture 

systems were noted: the first fracture system consists of a · 

vertical joint set that trends N. 62° E. and a second set that 

trends N. 40° W. and dips about 80° southwestward; the 

second fracture system consists of a joint set that trends 

northerly and a second set that trends easterly. Both dikes 

and veins follow the fractures. 

Ore has been produced from fissure veins in and near the 

stock and from contact-replacement deposits along the margin 

of the stock. Although the ore deposits are considerably 

younger than the stock, they nevertheless are localized in 

and near it. Such localization may be due to a master 

conduit which, somewhat like an inverted funnel, guided the 

various magmas and ore solutions repeatedly toward the 

same site. 

The fissure veins are crustified, and three major paragenetic stages are recognizable. During the first stage, quartz, 

pyrite, and some sphalerite were deposited on the fissure 

walls. During the second stage, argentiferous galena and 

sphalerite were deposited; and during the third stage, the 

remaining voids were filled with gangue minerals such as 

barite and rhodochrosite. Although most of the ore minerals 

were deposited in an environment marked by intermediate 

(mesothermal) temperature, a few (molybdenite, scheelite, 

wurtzite) may have formed under high-temperature (hypothermal) conditions. Tenuous evidence suggests that some 

ore minerals were deposited before the formation of the 

dikes that cut the stock, whereas the major veins were 

formed after the dikes were consolidated. and fractured. 

1 
2 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

Geologic and geophysical evidence both suggest that part 

of the ovoid pluton underlies the stock. The ore potential of 

the area rests heavily on (1) the sulfide veins in the stock, 

and (2) the size, shape, and metal content of this buried 

pluton. 

INTRODUCTION 

The Little Belt Mountains .are one of several Tertiary laccolithic and volcanic mountain groups which 

Dutton 

46°30' 

0 10 

rise above the plains of central Montana (fig. 1). 

The height of the "Little Belts" and the specific 

structural features within them are directly attributable to one or more of the major intrusions. The 

composition and form of these int~usions and of 

their related mineral deposits within the Barker 

quadrangle-astride the north flank of the Little 

Belts-are the subjects of this report. 

20 

109°30' 

BLAINE 

I 

r--------------------, 

: Bearpaw Mts 

\ 

• Little Rocky Mts 

Highwood~ts , 

MISSOURI 

"- BARKER Moccasin Mts 

\ QUADR)NG~LE :t'~udith Mts 

\ Little Belt Mts ~ 

) HELENAo ._..Big Snowy Mts 

f Castle Mts tl 

\ \crazy Mts 

(,,\ M 0 N T A N A \ \ J _____________ J 

\.-/"' 

30 MILES 

FIGURE 1.-Part of central Montana showing Barker quadrangle (hachured) and the mapped part of the Neihart quadrangle. 
INTRODUCTION 3 

The geology of the Barker quadrangle is shown on 

U.S. Geological Survey Geologic Quadrangle Map 

GQ-898, issued in 1971. Readers will find the map a 

necessary adjunct to this report. 

gleven large plutons have been mapped in the 

Barker quadrangle. Of these, one is a stock, ei,ght 

are probably laccoliths, one is a bysmalith, and one 

is a buried ovoid pluton (fig. 2). These have intruded 

the Precambrian basement rocks, as well as the 

overlying sedimentary units, and have warped and 

broken them. As a result, the once nearly horizontal 

sedimentary strata have been deformed into domes 

and elongate antidines which reflect the underlying 

intrusion. Between these upwarps are oval basins 

and plunging synclines. 

The general format followed in this report is (1) 

a description of the different igneous rocks, (2) a 

discussion of the forms of the intrusions, and (3) an 

examination of the relations of the ore deposits to 

these igneous bodies. 

PREVIOUS AND PRESENT WORK 

Although the nearby Highwood and Judith Mountains have been studied intensively in recent decades, the Little Belt Mountains have been comparatively neglected since the turn of the century. Weed 

(1899a, b) furnished brief descriptions of the geology and structl;tre of the Little Belt Mountains and 

later presented a comprehensive report (1900) 

whi'ch includes detailed petrographic descriptions of 

the igneous rocks by L. V. Pirsson. 

Schafer (1935) studied the geology and ore deposits of the Neihart mining district. 

Catanzaro and Kul·p (1964) and Catanzaro (1967) 

briefly described the metamorphic rocks that crop 

out near Neihart. 

No mention will be made here of the many workers, beginning with Weed, who have contributed to 

the knowledge of the stratified rocks of the quadrangle, for these rocks are not discussed in this report. 

Previously, I have offered some preliminary views 

on the structural framework of the Little Belt 

Mountains (Witkind, 1965), on the petrographic relations suggested by the clinopyroxenes from intrusive rocks in the quadrangle (1969), on 'composite 

dikes (1970), and with M. D. Kleinkopf and W. R. 

Keefer (1970), on a buried pluton beneath the Precambrian complex. Detailed results of ground-gravity and airborne magnetometer surveys across the 

Barker and Neihart quadrangles have been published as Geophysical Investigations Map G P-837 

( Kleinkopf and others, 1972) . 

In an attempt to determine the time and sequence 

of emplacement of the intrusions, potassium-ar.gon 

ages were determined for some 32 samples from the 

Barker-Neihart area. The pertinent data and the 

conDlusions resulting from this study have been published (Marvin and others, 1973) . 

MacKnight (1892) described the prominent leadsilver mines in the Barker mining district. Robertson and Roby (1951) described the mines and mineral deposits of Judith Basin County incliuding the 

Barker mining district. 

Spiroff (1938) studied and described the nowflooded Block P mine, the major producer of lead-silver ore in the district. He ( 1939) also des·cribed 

some of the common minerals in the NeihartHughesville area. 

Taylor (1935, 1938) reported on specimens from a 

conta,ct metamorphic zone south of Neihart. 

My work began in the Barker quadrangle in 1963 

and was completed in 1966. Field compilation was on 

topographic sheets at a scale of 1: 24,000. A geologic 

map of the quadrangle at a scale of 1: 62,500 with an 

expanded ex·planation was published as U.S. Geological Survey Geologic Quadrangle Map GQ-898 (Witkind, 1971). 

ACKNOWLEDGMENTS 

I owe special thanks to Mrs. Gwenllian VaughanRhys McBride of Monarch, Mont., for many stimulating discussions and for guiding me through several mines. Mr. Roy Thorson of Barker, Mont., and 

Mr. George A. Croff of Monarch, Mont., suppli.ed 

valuable out-of-print maps and much first-hand information on the ore deposits. 

Mr. Fred Cornell and Mr. John Hook, District 

Rangers in the Lewis and Clark National Forest, 

were helpful in many ways. 

Jon P. Thorson, Benjamin L. Peterson, and 

Thomas E. Redlinger served competently as geologic 

field assistants. 

GEOGRAPHIC AND GEOLOGIC SETTING 

The Barker 15-minute quadrangle includes part of 

the north flank of the Little Belt Mountains, a 

mountain group that occupies about 1,250 square 

miles in parts of Cascade, Judith Basin, Meagher, 

and Wheatland Counties. Of the 215 .square miles 
4 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

110"45' 110"30' 47"15'.----,------------------------.-------------,-----------------------------------------------,--, 

,' 

.... ' 

,, \\ 

_ .... LIMESTONE BUTTE 

OTTER 

LACCOLITH 

\\ '''"..-, 

_~,'' ' 

-"It I II I I I\ 

DOME 

,, ,, \ ' 

"'·· 

,<' 

' 

\ 

-;.11, ~ <,' -··· .... 

"'- , .......... '. ,,, ,, --......_ ... 

/ 

) 

' . \ I I \ l.\ 0 T . : ;.,.---U -..., .·GRANITE MTN FAULT \ 

HUGHESVILLE-- ' •"''""''• STOCK '\. •• ,,'' 1 I.,,, \. 

BARKER LACCOLITH 

Pre-Belt crystalline rocks 

underlain by felsic pluton 

'--

0 

' . ,, ',,, 

,' MIXES BALDY- \( ,, ... '' 1 \~ ANDERSON PEAK \+ LACCOLITH TAYLOR MOUNTAIN 

~ LACCOLITH 

'-0)-1 ~I , ~(0 .">:-/ -, '\( y "Z-t ~~ 

::.. -:.. 

~~,;, 

BUTCHERKNIFE MOUNTAIN 

LACCOLITH 

'\ ·r' -::. - :: , .... : , '' 2 3 MILES R. 9 E. 

T. 16 N. 

T. 15 N. 

FIGURE 2.-Pattern of intrusions in the Barker quadrangle. U, upthrown side of fault; D, downthrown side. 
GEOGRAPHIC AND GEOLOGIC SETTING 5 

within the margins of the quadrangle (Witkind, 

1971), about 70 square miles is plains and pediments 

whi•ch slope gently northward from the mountains. 

The remainder of the quadrangle is a mountainous 

terrain of rounded, elongate ranges separated by 

narrow, sinuous valleys. 

The sedimentary mantle rests on a basement complex of medium- to coarse-grained metamorphic 

crystalline rocks that have been mapped as nine distinct units (Witkind, 1971). Of these, three are regarded as paragneiss and six as orthogneiss. Although exposed only over about 20 square miles in 

the southwest corner of the quadrangle, they probably underlie the entire report area. All nine units 

are more or less foliate as a result of repeated compression. Dips of the foliation are generally northward, suggesting that these units form the north 

flank of the eastward-trending anticlinorium as 

noted by Catanzaro and Kulp (1964, p. 89). 

These Precambrian crystalline rocks are the products of medium- to high-grade regional metamorphism, and they are probably best grouped in the amphibolite facies. The paragneisses have been derived 

from impure arkosic sandstone and other finegrained clastic rocks ; the orthogneisses from both 

small and large igneous intrusions. 

During the Precambrian the gneisses underwent 

at least two metamorphic episodes (Catanzaro and 

Kulp, 1964; Catanzaro, 1967) and were further altered when they were lifted and baked by the emplacement of a ,compound rhyolitic pl1uton either in 

the Late Cretaceous (Catanzaro and Kulp, 1964) or 

in the early Tertiary (Marvin and others, 1973). 

The consolidated sedimentary rocks that overHe 

the Precambrian gneisses range in age from Middle 

Cambrian (Flathead Sandstone) to Early Cretaceous (Kootenai Form.ation) and include rocks assignable to six systems (fig. 3). The sequence is broken by six unconformities, of which two (postCambrian-pre-Upper Devonian, and post-Pennsylvanian-pre-J urassitc) represent major gaps in the 

sedimentary record. 

IGNEOUS ROCKS 

The rocks that form the various intrusions belong 

to the Little Belt subprovince, one of Larsen's 

(1940) divisions of the central Montana petrographic province. In the Peacock (1931) classification, the rocks have an alkali-lime index of 51.2 and 

so are just within the alkali .... calcic group. 

In this report the igneous rocks are grouped on 

the basis of their silica (Si02) content as felsic 

( >70 percent), intermediate (60-70 percent), or 

mafic ( 45-60 percent). The intermediate rocks form 

most of the large intrusions. The felsic rocks have 

been divided into ( 1) those that were likely formed 

before most of the major intrusions were emplacedold felsic rocks, and (2) those that were formed after 

the large intrusions-young felsic rocks. The mafic 

rocks make up small lamprophyric plugs, dikes, and 

sills which are considered to be younger than the 

large intrusions and so may be correlative in age 

with the young felsic rocks. This age relation is suggested by several composite dikes which imply that 

salic and fernie magmas coexisted and were emplaced 

almost synchronously. The mafic rocks constitute 

only an infinitesimal fraction of the total volume of 

emplaced igneous rock. 

Samples of all rock types have been analyzed 

chemi,cally and the data have been processed by computer through the U.S. Geologi·cal Survey's C.I.P.W. 

Rock Norm Program to obtain a calculated mineral 

composition-the norm-of the rock. The actual 

mineral composition-the mode-has been determined for the more significant rock types by mineral 

point 'counts made on representative thin sections. 

These data are presented in various tables throughout the report. 

FELSIC ROCKS 

(More than 70 percent silica) 

In the field the felsic rocks appear as Ii.ght-gray to 

light-tan ·porphyries marked by sparse to many 

rounded quartz phenocrysts. By contrast the intermediate rocks are ·gray porphyries speckled with 

phenocrysts of tabular white feldspar and black needles of hornblende and biotite. Quartz phenocrysts 

are rare in the intermediate rocks. 

OLD FELSIC ROCKS 

Two large intrusions are composed of old felsi,c 

rocks: the Clendennin-Peterson la·ccolith formed by 

the porphyry of Clendennin Mountain, and the 

Mixes Baldy-Anderson Peak laccolith formed by the 

Wolf Porphyry (fig. 2). Although both porphyries 

are similar mineralogically and chemically (table 1), 

they differ_m_arkedly in texture. 

PORPHYRY OF CLENDENNIN MOUNTAIN 

(Samples 1-5, table 1) 

Weed (1900, p. 356-358) thought that the Clendennin-Peterson anticline, 6 miles long and 31f2 

miles wide, resulted from the juxtaposition of several igneous bodies. In his opinion, the distal end, at 
TABLE 1.-The petrography and chemical composition (in percent) of old and young felsic rocks from the Barker quadrangle and of a similar rock from Wolf Butte, 

Little Belt Mountains 

[ntrusion ___ -------- ___ 

Rock name ____________ 

Rock type ________ 

Color ____________ 

Texture __________ 

:>. Phenocrysts ______ ..c:l 

A 

~ bl) 

0 

.t 

~ Groundmass ______ 

---------

Mode (percent) ___ 

I 

Laboratory No ________ _ Field No ______________ _ 

Si02--- _____ --- _------- AbOa _____ ------------ Fe20a _______ ----------- FeO ______ ------------- MgO ____________ ------

CaO _____ -------------- Na20 ___ ------ ___ ----- K20 _____ -------------- H2o- ________ -- ___ ---- H2o+ _________________ _ 

Ti02- ___ -------------- P20& _____ -------·------ MnO _____ ------ __ -----

C02- _- _---------------

Sum _____ --------

'· [All analyses by rapid-rock methods. Analysts: P. L. D. Elmore, Lowell Artis, John Glenn, James Kelsey, Samuel Botts, H. Smith, and Gillison Chloe] 

Old felsic rocks Young felsic rocks 

Clendennin-Peterson laccolith Mixes Baldy- I Wolf Granite Mtn. Dikes Dikes 

Anderson Peak Butte bysmalith laccolith I 

Porphyry of Clendennin Mountain Wolf Porphyry Rhyolite of 

Granite Mtn. Porphyry of Galena Creek Snow Creek(?) Porphyry. 

Rhyolite porphyry Granite porphyry Rhyolite Rhyolite porphyry Rhyolite porphyry. 

Light gray Light gray Light gray Light gray to light brown Light gray. 

Porphyritic Porphyritic Fine grained Porphyritic Porphyritic. 

Sparse sanidine (or anorthoclase), oligoclase (Ant6), Large, round smoky quartz, Albite (Ans), Quartz, sanidine, albite (Ans), and Quartz, sanidine, albite (Ans), locally 

hornblende, and biotite. sanidine, oligoclase (Ants), topaz. biotite. biotite. 

hornblende, and biotite. 

Sparse salite. 

Microgranitie mixture of anhedral quartz and Holocrystalline assemblage Anhedral quartz Microgranular mixture of anhedral Microgranular mixture of anhedral 

alkalic feldspar, some plagioclase microlites, and of anhedral quartz and and alkalic quartz and alkalic feldspar. quartz and alkalic feldspar; some some opaque minerals. Micropegmatite c·ommon. alkalic feldspar. feldspar. biotite. 

Alkalic feldsar, 59.6; quartz, 32.4; plagioclase Groundmass, 40.9; plagioclase Not available Not available Not available 

feldspar, 4.2; biotite, 1.5; hornblende (more or feldspar, 32.7; alkalic 

less altered to chlorite), 1.0; opaque minerals, 1.0; feldspar, 11.8; quartz, 

other, 0.3. 11.1; hornblende, 1.7; 

biotite, 0.7; others, 1.1. 

-- - -

Oxides 

: 1 1 2 1 3 L i 5 1 6 1 7 1 8 1 9 1 ;0 ~ 1 12 1 13 -~--d 14 1 15 

163683 

WL-63 

72.0 

14.2 

1.5 

.36 

1.0 

1.1 

3.1 

4.4 

.55 

.95 

.24 

.31 

.03 

.21 

99.95 

163684 

WL-64 

72.1 

13.9 

1.5 

.44 

.85 

1.2 

3.6 

4.5 

.36 

.64 

.21 

.28 

.07 

.18 

99.83 

163682 

WL-48 

72.0 

13.8 

1.4 

.44 

.42 

1.3 

3.7 

4.4 

.37 

.83 

.22 

.31 

.07 

.45 

99.71 

163686 

WL-71 

71.3 

14.2 

1.4 

.80 

.72 

1.2 

4.0 

4.4 

.34 

.76 

.23 

.25 

.07 

.21 

99.88 

163689 

WL-89 

70.8 

14.6 

1.5 

.72 

.77 

1.4 

4.1 

4.2 

.32 

.68 

.26 

.14 

.07 

.40 

99.96 

163690 

WL-101 

70.5 

15.0 

1.6 

.68 

.10 

1.4 

4.1 

4.2 

.54 

.56 

.36 

.21 

.02 

<.05 

99.32 

163685 

WL-70 

71.1 

14.6 

2.3 

.12 

.65 

.42 

3.7 

4.5 

.82 

.98 

.31 

.30 

.06 

.05 

99.91 

163691 

WL-112 

71.7 

14.5 

1.3 

.60 

.68 

1.1 

3.8 

4.4 

.66 

.56 

.28 

.14 

.02 

.06 

99.80 

163696 

WL-103 

75.4 

13.6 

.23 

.20 

.25 

. 50 

4.5 

4.2 

.14 

.20 

.02 

.00 

.10 

.08 

99.42 

163695 

WL-124 

74.6 

13.3 

.94 

.24 

1.0 

.53 

2.1 

4.3 

.94 

1.4 

.22 

.11 

.02 

.10 

99.80 

W-169695 

WL-270B 

74.1 

13.9 

2.5 

.04 

.31 

.25 

.66 

6.1 

.40 

1.4 

.14 

.04 

.06 

<.05 

99.95 

W-169699 

WL-470 

73.9 

12.8 

1.5 

.16 

.34 

1.3 

.72 

5.5 

.35 

1.7 

.17 

.06 

.07 

. 53 

99.10 

W-169697 

WL-449 

78.8 

11.4 

.20 

.04 

.06 

.10 

2.0 

5.8 

.15 

.49 

.09 

.00 

.00 

.06 

99.19 

W-169698 

WL-450 

76.9 

12.7 

.40 

.08 

.00 

.03 

4.1 

4.4 

.04 

.34 

.07 

.00 

.00 

<.05 

99.11 

W-167707 

WL-488 

76.5 

13.5 

.45 

.16 

.28 

.22 

3.2 

4.2 

.07 

.51 

.09 

.02 

.00 

<.05 

99.25 

0) 

...... 

C"l 

z 

t.%.1 

0 

c::: 

Ul 

~ 

0 

0 

?:: 

Ul 

> z 

tj 

~ 

t.%.1 

~ 

> 

~ 

t.%.1 

tj 

~ ...... 

z 

t.%.1 

~ 

> 

~ 

tj 

t.%.1 

1-d 

0 

Ul 

...... 

~ 

Ul 

0 

l'!l:j 

~ 

t:I: 

t.%.1 

t:d 

> 

~ 

?:: 

t.%.1 

~ 

.0 

c::: 

> tj 

~ 

> z 

C"l 

~ 

..t.%.1 

a= 

0 

z 

1-3 

> z 

> 
Q_ -------------------- 34.75 31.44 30.76 27.85 28.23 28.23 or _____________________ 26.01 26.64 26.34 26.14 24.83 25.00 

ab __ ------------------ 26.24 30.51 31.72 34.03 34.71 34.95 an ____________________ 2.11 2.99 6.21 5.66 3.50 5.61 

c_-.. ------------------ 3.57 2.02 .71 .80 2.03 1.68 

by{!:.~~=============== 2.49 2.12 1.06 1. 75 1.92 .25 

.00 .00 .00 .06 .00 .00 mt--- _- _ ------- _- _- _-- .56 1.04 1.44 2.04 l.RO 1.22 

ap __ ------------------ .73 .66 .02 .12 .33 ,50 

n_-------------------- .46 .40 .00 .44 .49 .69 

hm ______ -------------- 1.11 .79 .43 .00 .26 .77 

-~-

1. West flank, Clendennin-Peterson laccolith, E% sec. 29, T. 16 N., R. 9 E. 

2. West flank, Clendennin-Peterson laccolith, NWU sec. 32, T. 16 N., R. 9 E. 

3. Crest, Clendennin-Peterson laccolith, SWU sec. 32, T. 16 N., R. 9 E. 

4. East flank, Clendennin-Peterson laccolith, NEU sec. 5, T. 15 N., R. 9 E. 

5. East flank, Clendennin-Peterson laccolith, SEU sec. 32, T. 16 N., R. 9 E. 

6. East flank, Mixes Baldy-Anderson Peak laccolith, C. sec. 9, T. 15 N., R. 9 E. 

C.I.P.W. norms 

31.46 

26.62 

31.34 

.00 

3.65 

1.55 

.00 

.00 

.71 

.38 

2.30 

30.01 31.97 43.98 46.22 47.45 45.20 36.49 41.43 

26.05 24.96 25.46 36.09 32.82 34.55 26.25 25.01 

32.22 38.30 17.81 5.59 6,15 17.06 35.02 27.28 

4.17 1.99 1.28 .66 2.73 .12 .15 .65 

1.97 .93 4.73 5.98 4.72 1.80 1.15 3.48 

1. 70 .63 2.50 .77 .86 .15 .00 .70 

.00 .33 ,00 .00 .00 .00 .00 .00 

1.19 ,34 .20 .oo .02 .00 .06 .26 

.33 .00 .26 .10 .14 .00 .00 .05 

.53 .04 .42 .08 .33 .09 .13 .17 

.48 .00 .01 2.50 1.50 .20 .37 .28 

-~ -- - - ----- --------

9. Northwest flank, Granite Mountain bysmalith, N% sec. 6, T. 15 N., R. 10 E. (unsurveyed). 

10. Dike along fault, south flank, Granite Mountain bysmalith, E% sec. 7, T. 15 N., R. 10 E. 

(unsurveyed). 

11. Dike in Hughesville stock, SWU sec. 6, T. 15 N., R. 9 E. (unsurveyed). 

12. Dike in Precambrian crystalline rocks, C. sec. 2, T. 14 N., R 8 E. (unsurveyed). 

13. Dike in Precambrian crystalline rocks, C. sec. 36, T. 15 N., R. 8 E. (unsurveyed). 

7. Altered rock, northwest flank, Mixes Baldy-Anderson Peak laccolith, C. sec. 5, T. 15 N.,R. 9E. 14. Dike in Precambrian crystalline rocks, S% sec. 35, T. 15 N ., R. 8 E. (unsurveyed). 

8. Wolf Butte, S% sec. 32, T. 16 N., R. 10 E. 15. Dike in Precambrian crystalline rocks, N~ sec. 31, T. 15 N., R. 9 E. (unsurveyed). 

~ 

~ 

z 

t:t_j 

0 

c:: 

00. 

~ 

0 

a 

~ 

00. 

-::i 
8 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

Peterson Mountain (then known as Otter Mountain), was underlain by a singrle laccolith, whereas 

the ·proximal end, at Clendennin Mountain, W3JS 

formed either by several thick sills or by small laccoliths. I believe, however, that the structural feature is best explained as being the result of the emplacement of but one large single tonguelike laccolith 

SYSTEM SERIES UNIT 

Upper 

Cretaceous Lower Kootenai part 

Cretaceous Formation Basal 

sandstone UNCONFORMITY 

Morrison Formation 

Upper 

Jurassic Swift Jurassic Sandstone Ellis 

Group UNCONFORMITY Middle Piper 

Jurassic Limestone UNCONFORMITY 

Pennsylvanian Amsden Formation 

Heath 

Shale 

Upper Big Otter Snowy Mississippian Group Formation 

Kibbey 

Mississippian Sandstone UNCONFORMITY 

11 Upper I 

Mission Canyon 

Mississippian Madison Limestone 

Lower Group Lodgepole 

Mississippian Limestone UNCONFORMITY 

------ Sappington(?) 

Member 

Lower Mississippian Three Forks Trident(?) and Formation Member Upper Devonian 

Logan Gulch(?) 

Member 

Bird bear 

Devonian Member 

Upper Jefferson Middle 

Devonian Dolomite member 

Lower 

member 

Upper and Middle 

Maywood Formation Devonian 

UNCONFORMITY 

Upper Pilgrim Limestone Cambrian 

Park Shale 

Cambrian 

Middle Meagher Limestone 

Cambrian 

Wolsey Shale 

Flathead Sandstone 

UNCONFORMITY 

1 W. J. Sando, U.S. Geological Survey, (written commun., 1965). 

that extends northeastward from the Hughesville 

stock (Witkind, 1971, cross section B-B'). 

The porphyry of Clendennin Mountain is light 

gray, dense, hard, fine grained, and rhyolitirc and 

breaks with conchoidal fracture into angular boulders. In hand specimen sparse phenocrysts, mainly 

white angular feldspar laths, and black needlelike 

Approx. 

thit:kness LITHOLOGY 

(fc<lt) 

350 Light-red to red claystone and siltstone. 

Light-gray medium- to thick-bedded fine- to coarse-grained 150 "salt-and-pepper" sandstone. 

200-300 Variegated claystone, siltstone, and sandstone; some carbonaceous shale or coal at top. 

90-120 Brown conglomeratic sandstone and sandstone. 

15-30 Light-gray thin-bedded finely crystalline limestone. 

0-170(?) Red thin-bedded to platy siltstone and fine-grained sandstone. 

400± Dark-gray thin-bedded shale; interleaved limestone. 

300± Light-gray claystone, shale, and limestone. 

65-100 Pale-red siltstone and fine-grained sandstone; locally a gypsum bed, 15-25 feet thick near middle of unit. 

860 1 Gray thick-bedded to massive finely to coarsely crystalline 

limestone; brecciated in upper part. 

Gray thin-bedded, finely crystalline limestone; much black 730 1 

chert. 

25 Pale-red to light brown thin-bedded siltstone; few thin dolomite beds. 

15 Light-gray to green massive calcareous claystone. 

30 Light-gray thin-bedded to platy siltstone; few interleaved 

dolomite beds. 

60 Light-gray thin-bedded finely crystalline dolomite. 

170 Gray to dark-gray coarsely crystalline dolomite. 

100 Light-gray thin- to medium-bedded finely crystalline limestone. 

80 Red, light-brown, thin-bedded siltstone; may include some 

Upper Cambrian Dry Creek Shale at base. 

115 Light-gray thin- to medium-bedded limestone; contains many 

intraformational conglomerates. 

170-250 Gray to light-red thin-bedded to platy shale; few nodular limestone beds in upper part. 

75 Gray thin-bedded mottled limestone; dark-gray shale, about 

12 feet thick, near base. 

200 Green micaceous glauconitic shaly siltstone. 

200+ Reddish-brown thin- to thick-bedded medium- to coarsegrained sandstone and conglomeratic sandstone. 

FIGURE a.-Generalized section of sedimentary rocks exposed in the Barker quadrangle. Total thickness is 4,830 feet. 
FELSIC ROCKS 9 

grains of hornblende and biotite are scattered irregularly through the groundmass. 

WOLF PORPHYRY 

(Samples 6-8, table 1) 

This granite porphyry was named by Weed (1900, 

p. 342) after Wolf Butte, a prominent conical igneous mass (just beyond the east margin of the Barker quadrangle) about a quarter of a mile northeast 

of the Granite Mountain bysmalith (fig. 2). At Wolf 

Butte, the porphyry forms an asymmetric laocolith 

of which the butte is but a small part (Pirsson, 

1900, p. 498). In the Barker quadrangle the Wolf 

Porphyry makes up the enormous mass of the Mixes 

Baldy-Anderson Peak laccolith plus several small 

dikes and sills. 

In hand specimen the Wolf Porphyry is a li.ghtgray granite porphyry crowded with large phenocrysts of round smoky quartz, angular white feldspar, and a few needles of hornblende and flakes of 

biotite (fig. 4 A, B). 

YOUNG FELSIC ROCKS 

Various rhyolitic and quartz rhyolitic porphyries 

are here grouped as the young felsic rocks. All are 

similar; their difference is mainly in the type and 

size of the phenocrysts. Field relations suggest that 

all were emplaced after the major intrusions were 

formed. 

RHYOLITE OF GRANITE MOUNTAIN 

(Sample 9 of table 1) 

Only the west edge ·Of the Granite Mountain bysmalith is within the Barker quadrangle (fig. 2). The 

bysmalith is capped by a light-gray, dense, hard, and 

exceedingly fine grained rhyolite. This rock, here 

called the rhyolite of Granite Mountain, was classified by Pirsson (1900, p. 521-522) as a "RhyolitePorphyry (Quartz porphyry)"; he considered it 

(1900, p. 500) to be the chi.lled phase of the Wolf 

Porphyry whi•ch makes up the Wolf Butte laccolith. 

Since his work, however, several prospect pits and 

aecess .roads have uncovered a fault breccia that separates the rhyolite from the adjacent rocks (see section on "Granite Mountain Bysmalith"). 

In thin section the rhyolite 'can be seen to consist 

of an even-grained holocrystalline mixture of anhedral quartz, alkalic feldspar, and a few scattered 

grains of plagioclase, biotite, and opaque iron ore. 

Small phenocrysts, chiefly of albite (An8 ) and topaz, 

are widely scattered through the groundmass. 

PORPHYRY OF GALENA CREEK 

(Samples 10-12 of table 1) 

The Hughesville stock is cut by thin dikes of a 

distinctive quartz rhyolite porphyry whi·ch is here 

called the porphyry of Galena Creek (fig. 4C, D). 

These dikes are 10-50 feet wide, and some can be 

traced for several miles. 

The porphyry is characterized by abundant large 

round smoky quartz phenocrysts in a dense almost 

aphanitic light-brown groundmass. It resembles the 

finer grained facies of the Wolf Porphyry, but it is 

believed to be much younger. 

The thin section is dominated by the quartz phenocrysts, many of which are well rounded (fig. 4D). 

Other quartz grains, however, are euhedral, and examples of good bipyramidal crystals are common. 

Sanidine is the alkalic feldspar, and Carlsbad twins 

are plentiful. A few sparse grains of albite (Ans) 

and biotite are present. The groundmass consists of 

a holocrystalline mixture chiefly of anhedral quartz 

and alkalic feldspar. 

SNOW CREEK(?) PORPHYRY 

(Samples 13-15 of table 1) 

Quartz rhyolite porphyry dikes and plugs intrude 

the Precambrian metamorphic rocks in the southwest corner of the Barker quadrangle (Witkind, 

1971). These small intrusions are believed to be apophyses from a large buried felsi•c pluton, a small 

part of which is exposed along Carpenter and Snow 

Creeks near Neihart (fig. 31). This exposed part has 

been mapped by Johnson (1964), who considered it 

to be a compound body consisting of four very similar quartz rhyolite porphyries. In the Neihart quadrangle similar rocks have been grouped and mapped 

as the Snow Creek Porphyry by Keefer (1969). 

These dikes and plugs are marked by quartz and 

feldspar phenocrysts set in a light-gray aphanitic 

groundmass ; none of the phenocrysts are as large or 

as conspicuous as those in the porphyry of Galena 

Creek. 

In thin section the various porphyries are characterized by abundant clusters of feldspar phenocrysts 

-both alkalic (orthoclase) and plagioclase (albite, 

An8 ) phenocrysts are represented-in a microgranular groundmass of anhedral quartz and alkalic feldspar. Some of these clusters are marked by micrographi•c intergrowths of quartz. Round and euhedral 

quartz phenocrysts are common, and a few form 

clusters. Biotite is common as phenocrysts and in 

the groundmass in some of the rhyolites but is absent from others. 
10 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

A 

B 

FIGURE 4.-Felsic igneous rocks from the Barker quadrangle. 

Scale of hand specimens in centimeters (smallest divisions 

are millimeters). Photographs by R. B. Taylor, Sandra 

Brennan, and Louise Hedricks. A, B. WoU Porphyry. A, 

Hand specimen. Light-gray granite porphyry crowded with 

phenocrysts of white angular feldspar and round smoky 

quartz set in an aphanitic groundmass. B, Photomicrograph 

c 

D 

showing nature of groundmass and juxtaposition of phenocrysts. C, D. Porphyry of Galena Creek. C, Hand specimen. 

Light-brown rhyolite porphyry containing abundant round 

smoky quartz grains, sparse feldspar laths, and biotite 

flakes scattered through a fine-grained groundmass. D, 

Photomicrograph showing general nature of phenocrysts 

and microgranular texture of groundmass. 
INTERMEDIATE ROCKS 11 

CHEMISTRY OF THE FELSIC ROCKS 

The older and younger felsic :rocks differ strikingly in their silica content; the younger felsic rocks 

consistently contain more silica (.--76 percent) than 

the older ones (.--72 percent). The percentages of 

the other major oxides fail to show such a strong 

contrast. In general, the younger felsic rocks contain 

somewhat less magnesia, iron, and lime than the 

older felsic rocks, but they contain comparable 

amounts of soda and potash (fig. 5). 

INTERMEDIATE ROCKS 

( 60-70 percent silica) 

The intermediate rocks form the Hughesville 

stock, many of the laccoliths, and most minor intrusions. Details of the petrography and chemistry of 

these rocks are given in table 2. 

QUARTZ MONZONITE OF HUGHESVILLE 

(Sample 1 of table 2) 

The Hughesville stock, composed of the quartz 

monzonite of Hughesville, is a crudely circular mass 

about 1 mile in diameter which underHes parts of 

sections 6 and 7, T. 15 N., R. 9 E. (fig. 6). Virtually 

all the major ore bodies were either in the stock or 

adjacent to it, and as a result it is pitted with mines 

and innumerable prospect holes. The abandoned 

mining towns of Barker and Hughesville are within 

its confines. 

Weed (1900, p. 353) oDiginally described this rock 

under the heading "Hughesville syenite stock"; Pirsson (1900, p. 465) in the same report, referred to 

the identical rock as the "Barker syenite." The rock, 

however, is not a syenite, for it contains ~considerable plagioclase and quartz. Although Pirsson (1900, 

p. 466) ~commented that "The amount of plagioclase 

is always small in comparison with the alkali feldspar," the samples I have examined invariably contain about equal amounts of orthoclase (38 

percent) and oligoclase (37 percent). Furthermore, 

much quartz is in the groundmass. Pirsson (1900, p. 

467) noted this, and commenting on a chemical analysis of the rock stated : "The siHca is toward the 

upper limit of the syenite group, verging on the 

granites, and this explains the amount of quartz 

which is present. Since the quartz, however, is small 

and entirely microscopic, it appears best to classify 

the rock as a syenite rather than a granite." Although I have in the past (Witkind, 1970, 1971), 

follow,ing previous usage, employed the term "syenite" for this rock, I believe the term is both incorrect 

Na,O 

MgO 

0 

• 

6. 

A 

• 

CaO 

Old felsic rocks 

69 

~ _..10 

14~5 .13 

Iron 

(Total iron expressed 

as FeO) 

Old felsic rocks 

EXPLANATION 

Old felsic rocks 

Porphyry of Clendennin Mountain 

Wolf Porphyry 

Young felsic rocks 

Rhyolite of {;ranite Mountain 

Porphyry of Galena Creek 

Snow Creek(?) Porphyry 

K,O 

1~ 14 

96 

13. 

Na,O+K,O 

FIGURE 5.-Some chemical characteristics of old and young 

felsic rocks from the Barker quadrangle. See table 1 for 

locations; sample 7 of highly altered Wolf Porphyry 

omitted. 
12 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

TABLE 2.-The petrography and chemical composition (in percent) of intermediate rocks from the Barker 

[Rapid-rock analyses. Analysts: P. L. D. Elmore, Samuel Botts, 

Area ________________________ Barker quadrangle 

- Intrusion ________ -------- ____ Hughesville stock I ~I Sill northeast I Badre< I Taylor Mountain I Butcherknife Mountain I Dry Wolf I laceolith of Irene Peak laccolith laccolith laccolith laccolith 

---

Rock name ____ -------- ______ Quartz monzonite Barker porphyry of Hughesville. 

- Rock type ____ -------- __ Quartz monzonite Quartz latite phorpyry 

Color __________________ Brownish gray Light gray to gray 

Texture ____________ ---- Fine to coarse grained. 

Porphyritic 

>. Phenocrysts ____________ Locally tabular White angular feldspars and black flakes of biotite and needles of -= g. feldspar laths. 

~ 0 

"" Groundmass __ -------- __ Intergrown un- Holocrystalline mixture of quartz, alkalic feldspar, and a few grains 

~ oriented mixture 

of feldspar, hornblende, biotite. 

--------------- Mode (percent) __ ---- ___ Orthoclase, 38.3; Sanidine,46.1; oligoclase (An2a), 26.9; quartz, 17.7; hornblende, 4.9; biotite, 1.6; opaque minerals, 2.0; 

oligoclase, 36.8; 

quartz, 9.2; 

biotite, 6.0; 

salite, 4.5; 

others, 5.2. 

Oxides 

2 3 

Laboratory No_------ ____ ---- 163688 163678 W-169659 Field No _____________________ WL-79 WL-37 WL-38 

Si02-------- _---------------- 61.2 62.4 60.6 

AhOa __ --------------------- 16.4 16.1 15.8 

F1!20a _____ - ------------------ 3.2 3.4 3.0 FeO _____ --- _______ -- _____ --- 2.2 1.5 2.5 

Cao MgO ________________________ 

____________ --------- ___ 1.9 2.2 2.9 

3.0 3.0 3.9 

Na2o ______________ ---------- 4.6 4.2 3.9 K20 _______________________ -- H2o- 4.5 4.2 4.3 ________________________ .16 . 59 .24 

H2o+ ______________ ---------- .36 .81 1.2 Ti02 ________________________ .92 .47 .62 P20i- _______________________ .44 .46 . 52 MnO ____ -------- ____________ .22 .07 .12 

C02-- _----- _---------------- .15 <.05 <.05 

Sum ___________________ 99.25 99.45 99.65 

C.I.P.W. 

Q ___ ------------------------ 9.61 13.70 10.41 or ____ ---- __ ---- __ -------- __ 26.79 29.96 25.50 ab __________________________ 39.22 35.74 33.12 an_------------- __ --- _______ 10.89 11.63 12.95 

c __ ------------------------- 0 0.41 0 } M---------------------- .09 0 .89 

di fs----------------------- .01 0 .16 wo _____________ -- _______ .11 0 .14 

by fs~=:::::::::============ 4.68 5.51 6.38 

.28 0 1.16 mt ___________ ----- __________ 4.68 3.72 4.37 

ap_------------------------- 1.05 1.10 1.24 

iL ---------- __ -------------- 1. 76 .90 1.18 hm __________________________ 0 .85 0 

1 See Vine (1956). 

1. West valley wall of Galena Creek, sec. 7, T. 15 N., R. 9 E. (unsurveyed). 

2. North valley wall of McGee Coulee, sec. 28, T. 16 N., R 8 E. 

3. West valley wall of Big Otter Creek, N~ sec. 36, T. 16 N., R 8 E. 

4. Ridge at head of McKay Gulch, NWU sec. 1, T. 15 N., R. 8 E. (unsurveyed). 

5. Head of Bower Gulch, N% sec. 7, T. 15 N., R. 10 E. (unsurveyed). 

4 5 6 7 8 9 

163681 163692 163693 165857 165854 165858 

WL-44 WL-115 WL-118 WL-169 WL-148 WL-170 

66.8 67.1 67.6 68.5 63.7 64.6 

16.4 16.1 16.3 16.1 15.9 15.9 

2.1 1.1 1.1 1.0 2.0 1.3 

1.0 1.2 1.1 1.1 1.8 1.8 

1.1 1.0 1.5 1.1 2.4 2.6 

2.0 2.1 2.2 2.0 3.0 3.1 

4.5 4.1 4.6 4.7 4.5 4.5 

4.3 4.2 3. 7 4.0 3.8 3.8 

.20 .61 .29 .07 .61 .10 

.62 .89 .48 .59 1.0 1.6 

.35 .25 .24 .26 .48 .40 

.34 .27 .22 .18 .34 .23 

.06 .05 .03 .03 .07 .06 

.14 .38 .06 .11 .08 .13 

99.91 99.35 99.74 99.42 99.68 100.12 

norms 

19.60 22.69 19.47 20.42 13.79 13.82 

25.43 24.98 22.11 23.70 22.53 22.43 

38.11 34.92 39.35 39.87 38.20 38.03 

6.82 6.29 11.03 8.07 12.00 11.95 

1.85 2.53 .74 1.10 0 0 

0 0 0 0 .06 .33 

0 0 0 0 .01 .09 

0 0 0 0 .08 .46 

2.74 2.51 3.38 2.75 5.93 6.14 

0 .98 1.06 .82 .98 1.60 

2.41 1.61 1. 61 1.45 2.91 1.88 

.81 .64 0 .42 .81 .54 

.67 .48 .08 .50 .91 . 76 

.44 0 0 0 0 0 

6. Ridge between Frenchies Coulee and Bower Gulch, N~ sec. 12, T. 15 N., R. 9 

E. 

7. Near head of Butcherknife Gulch, NEU sec. 35, T. 15N., R. 9 E. 

8. One-half mile north of crest of Butcherknife Mountain, SEU sec. 27, T.15N., 

R. 9 E. (unsurveyed) 

9. East valley wall of Dry Wolf Creek, W~ sec. 6, T. 14 N., R. 10 E. 
INTERMEDIATE ROCKS 13 

and Neihart quadrangles, Little Belt Mountains, and of a similar rock from the Stanford-Hobson area 

Gillison Chloe. Lowell Artis, H. Smith, John Glenn, and James Kelsey) 

Neihart Stanford-Hobson area 1 

quadrangle 

Irene Peak Sill on Sill on Big Baldy Four-M sill 

I 

Butcherknife 

I 

Limestone Sill laccolith laccolith 

I 

Windham Dome Mtn. Butte 

Chocolate prophyry of Weed (1900). Chocolate- Barker (?) Porphyry. brown porphyry. 

Quartz latite porphyry Quartz latite prophyry. 

Grayish brown Light gray to gray. 

1------

Porphyritic Porphyritic. 

hornblende Litf~~t"~~e~?;su~~r ~~\f~~i~e~~l~. dark-gray to White angular feldspars and black flakes of biotite and needles of 

hornblende. 

of plagioclase feldspar Microgranular groundmass composed of quartz 

and alkalic feldspar. 

Holocrystalline mixture of quartz, alkalic feldspar, and a few grains of plagioclase feldspar. 

apatite, sphene, others, 0.8 Orthoclase, 47.4; oligoclase (An,.), 31.6; quartz, 

8.1; hornblende, !1.8; biotite, 1.0; salite, 0.2; 

others, 3. 7. Not available. 

Oxides--Continued 

10 11 12 13 14 15 16 17 18 19 

------ - ------ 1---- 1----· 

163680 165855 W-167706 163687 165859 165860 165856 D-112804-W D-112802-W W-169052 

WL-43 WL-165 WL-483 WL-78 WL-176 WL-177 WL-167 WL-4 WL-1 WL-496 

--------------1--------------- ------------ 67.1 65.1 68 . 1 65.7 65. 0 65 . 6 66.3 66.0 67.2 67.4 

15.3 16.5 16.2 16.3 16.2 15. 7 15. 6 16. 0 16.0 16.2 

1.7 1.3 2 . 1 1.3 1.7 1.4 1.8 1.2 1.5 3.8 

1.5 1.3 .04 1.4 .60 1.2 1.7 1.8 1.1 . 60 

1.6 1.6 .35 1.1 1.1 1. 7 1.9 2.5 2.0 1.0 

2.8 2.8 2.2 2.2 3.0 2.4 2.8 2.6 2 . 1 2.4 

4 . 5 5.0 4.1 5.2 4 . 3 4 . 3 4.5 4.6 4 . 0 8.9 

3.8 3 .6 4.5 8.8 3.6 3.5 8.9 8.8 4.3 4.4 . 18 . 55 .56 . 25 .62 1.2 .38 1.3 .40 . 87 

.49 . 95 1.1 . 75 1.2 1.4 .56 0 1.0 . 73 . 35 .33 .46 .34 .30 .31 .40 .36 .34 . 84 

.81 .22 .19 .20 .21 .21 .28 .23 .24 . 19 

.07 .05 0 .04 . 03 . 04 .05 . 05 .05 .05 

.06 .31 .15 .64 1.7 .80 . 07 <.05 < .05 . 15 

r---- 99.76 99.61 100.05 99.2~ 99 . 56 99.76 99 . 74 100 .49 100.28 101.03 

C.I.P. W. norms-Continued 

-- 18 .92 14.99 22.73 16.64 23.48 22.07 16.87 15.29 20.61 21.96 

22.51 21.36 26 . 58 22.63 21.37 20.73 23.11 22.35 25.34 25.74 

38.17 42.47 34.68 44.35 36.55 36.47 38 . 18 38.73 33.75 32 .66 10.35 10.54 8. 72 5. 61 2. 78 5.~9 10.88 11 . 03 8.51 9.62 

0 .53 1. 39 1. 61 4.24 2 .84 0 0 . 26 1. 63 1.45 

.36 0 0 0 0 0 .23 0 0 0 

.08 0 0 0 0 0 .07 0 0 0 

.49 0 0 0 0 0 . 82 0 0 0 

3 . 64 4.00 .87 2.76 2.75 4.24 4. 52 6.20 4.97 2.47 

.82 .87 0 1.02 0 . 61 1.41 1.80 .31 0 

2.47 1. 89 0 1. 90 1.17 2.34 1.89 1. 73 2.17 1.10 

.74 .52 .45 .48 .50 .50 . 66 . 54 .57 .45 

.67 .63 .08 .65 .57 .59 .76 .68 .64 .64 

0 0 2.10 0 .90 0 0 0 0 2. 51 

10. Irene Peak, W72 sec. 36, T. 16 N., R. 8 E. 15. North valley wall at head of Blankenship Gulch, E 72 sec. 21, T. 15 N., R. 9 E. 

11. Crest of Butcherknife Mountain, C. sec. 34, T. 15 N., R. 9 E. (unsurveyed). 16. Ridge at head of Snow Creek, SE~ sec. 4, T . 14 N., R. 9 E. 

12. Ridge at head of unnamed tributary to Hansens Coulee, NW ~ sec. 35, T. 17 

N., R.8E. 

13. North valley wall of Dry Fork of Belt Creek, N7\!, sec. 19, T. 15 N., R. 9 E . 

14. Mouth of Gray Creek, N72 sec. 29, T. 15 N., R. 9 E . (unsurveyed) 

4D6 - 18 9 0-73 - ~ 

17. Near head of Running Wolf Creek, NW~ sec. 5, T . 14 N., R. 11 E. 

18. East valley wall of Coyote Creek, E7\!, sec. 13, T. 16 N., R. 12 E. 

19. North valley wall of Willow Creek, NE~ sec. 19, T . 16 N., R. 13 E. 
14 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

0 

R8E R9E 

~ 

CO NTOU R I NTERVAL 80 FE ET 

DATUM IS MEAN SEA LEVEL 

2 MILES 

FIGURE 6.-The Hughesville stock and adjacent intrusions. Geology by I. J. Witkind, assisted by J. P. Thorson, 1964, B. L. 

Peterson, 1965, and T. E. Redlinger, 1966. Base from U.S. Geological Survey, Barker quadrangle, 1:62,500, 1961. Section 

and explanation on opposite page. 
INTERMEDIATE ROCKS 15 

EXPLANATION 

Surficial deposits 

UNCONFORMITY 

~ UNCONFORMITY 

8 

l~~ ~ {-Porphyry of 

6 Galena Creek 

>< 

Minette --kersantite lSEJ Vogesite 

UNCONFO RMITY ~ Syenite MWfi.i:F1 

Indurated alluvium GS:J UNCO NFORMITY Shonkinite 

Quartz monzonite 

of Hughesville 

t~~ e { Chocolate-brown - ,5 porphyry 

"' g

~ 

~ { 

Porphyry 

~ ~ of 

; Clendennin Mountain 

0 

Contact 

~ 

~ 

Barker 

Porphyry 

Syncline 

0:: 

w 

f-

~ 

:::J 

0 

~ .. ., ~·~ 

~ -~ 

Big Snowy Group 

Heath Shale, Otter Formation, 

and Kibbey Sandstone 

UNCONFORMITY 

Madison Group 

Mission Canyon and 

Lodgepole IA.mest.ones 

UNCONFORMITY 

~~ >- 1l'~ ~ 

z 

~ 

n. 

n. 

Ul 

Ul 

z 

~ 

0::<;3~ 

~ ~ ~ Three Forks 

~ 

Formation, Z 

f- ~ ._ Jefferson Dolomite, and ~ 0:: ~ ~ Maywood Formation W w ""., 0 f- :::, ;! UNCONFORMITY 

~ 

]~~ { Pilgrim Limestone, ~ Park Shale, !D ~ ~ ._ Meagher Limestone, Wolsey Shale, ::i: 

~ ~ and Flathead Sandstone ~ z ~ ~ UNCONFORMITY 0C 

Pre-Belt rocks, undivided 

65 

Strike and diP of foliation 

} !D 

::i: 

~ 

u 

w 

0:: 

n. 

Dashed where approximately located; 

short dashed where inferred Showing trace of axial plane and direction of plunge 

of axis. Dashed where approximately located 1!:1 

Vertical shaft 

X 

Prospect pit 

Sulfide ores 

u 

D 

Fault, approximately located 

Dotted where concealed 

U, upthrown side, D, downthrown sW.e 

w 

A :;:: 

0 

;>; 

'< " 

22 

-'--

Inclined 

75 

-+- -d- Ell 

Vertical Overturned Horizontal 

Strike and dip of beds --< Portal of adit 

MIXES BALDYANDERSON PEAK 

F LT 

E 

A' 
16 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

and inappropriate and here suggest that it be known 

as the "quartz monzonite of Hughesville." The rock 

is classifiable as a quartz monzonite (2- 2- 6") in the 

Johannsen (1939, p. 141-148) classification. 

The quartz monzonite of Hughesville is brownish 

gray, fine to coarse grained, dense, and hard. In most 

exposures it is equigranular, but locally it is markedly porphyritic and has large tabular feldspar 

laths. 

In thin section it can be seen to :consist of a tightly 

inter.grown unoriented mixture of orthoclase, oligoclase (An23 ), quartz, common hornblende, biotite, 

clinopyroxene (salite), opaque iron ores, and accessory minerals such as sphene and apatite. 

Several dikes and plugs of latite porphyry that 

intrude the Mixes Baldy-Anderson Peak laccolith 

resemble somewhat those igneous rocks that make 

up the east edge of the Hughesville stock. 

BARKER PORPHYRY 

(Samples 2-12 of table 2) 

Most of the floored intrusions and their related 

dikes and sills are composed of a quartz latite porphyry named the Barker Porphyry by Weed (1900, 

p. 356). Comparable rocks exposed along the valley 

walls of Dry Fork Belt Creek and called the "chocolate porphyry" (samples 13-15 of table 2) by Weed 

(1900, p. 349-351) are similar mineralogically and 

chemically to the Barker Porphyry. 

The rock invariably is some shade of gray and is 

markedly porphyritic (fig. 7). In hand specimen it is 

distinguished by abundant large white angular feldspar phenocrysts and by black flakes and needles of 

mafic minerals scattered irregularly through an 

aphanitic groundmass (fig. 7 A, B). In some exposures the phenocrysts are so large and plentiful that 

the rock looks coarse grained, but near its contact 

with sedimentary units it develops a chilled zone as 

much as 10 feet thick. Here the phenocrysts dwindle 

in size, and the rock takes on a dense fine-grained 

appearance much like that of the rhyolite porphyry 

of Clendennin Mountain. (See section on "Porphyry 

of Clendennin Mountain.") 

In thin section it can be seen that the phenocrysts 

of sanidine, oligoclase (An2s), hornblende, biotite, 

and pyroxene are set in a holocrystalline mixture of 

quartz, alkalic feldspar, and a few grains of plagioclase feldspar. Poikilitic texture is common in the 

groundmass (Pirsson, 1900, p. 505), with minute 

unoriented specks of alkalic feldspar in the quartz. 

Quartz, ·common in the groundmass, is rarely found 

as phenocrysts. Common accessory minerals are apatite, sphene, magnetite, and opaque iron ore. 

CHEMISTRY OF THE INTERMEDIATE ROCKS 

The intermediate rocks differ from the felsic rocks 

in having less silica C-·66 percent versus -7 4 percent), more magnesia, iron, and lime; but they have 

about comparable amounts of soda and potash. A 

comparison of the chemistry of the intermediate 

rocks suggests a general pattern of 

Mg0<Ca0 < Kz0<Na20. 

In figure 8 the percentages of various oxides are 

plotted on a silica variation diagram. The grouping 

indicates dearly that both large and small intrusions 

from different parts of the area were formed by the 

same magma. This close similarity is also shown on 

various triangular diagrams (fig. 9). 

Three of the intrusions-the Hughesville stock, 

the Otter laccolith, and the sill northeast of Irene 

Peak (samples 1, 2, and 3 respectively of table 2 and 

figs. 8 and 9 )-"contain significant amounts of clinopyroxene and so differ somewhat mineralogically 

from other intrusions of comparable size and shape. 

Despite this difference, the chemistry of the rocks 

from these intrusions deviates only in having less 

silica ( -61 percent versus -66 percent). I have no 

explanation for this divergence. 

In .general, there seems to be a gradational transition from the high-silica rocks (-74 percent Si02) 

which form the large felsic intrusions through highsilica intermediate rocks ( -68 percent Si02), as 

found in phases of the Barker and Butcherknife laccoliths, to other intermediate rocks that form the 

other la·ccoliths and which contain but moderate 

amounts of silica ( -65 percent). The low-silica end 

member of this sequence is the quartz monzonite 

that forms the Hughesville stock (-61 percent 

Si02). 

MAFIC ROCKS 

In striking contrast to the light-colored felsic and 

intermediate rocks are the gray to dark-gray mafic 

rocks which 'cut both sedimentary and igneous rocks. 

They form thin sills, dikes, and small plugs. These 

rocks have been divided into five groups: (1) shonkinite, composed of orthoclase, pyroxene, olivine, 

and biotite; (2) plagioclase shonkinite, similar to 

the shonkinite, but containing much sodic plagioclase; (3) syenite, composed of much alkalic feldspar and some plagioclase feldspar, and moderate 

amounts of biotite and pyroxene; ( 4) minette-ker-
MAFIC ROCKS 17 

A 

B 

FIGURE 7.-Intermediate and mafic igneous rocks from the 

Barker quadrangle. Scale of both hand specimens in centimeters. Photographs by R. B. Taylor, Sandra Brennan, and 

Louise Hedricks. A, B. Barker Porphyry. A, Hand specimen. Light-gray quartz latite porphyry characterized by 

angular white laths of feldspar and black needles of hornblende and flakes of biotite in a fine-grained groundmass. 

B, Photomicrograph showing sanidine, quartz, and a plagioc 

D 

clase grain jacketed by alkalic feldspar enclosed in a microgranular groundmass. C, D. Shonkinite. C, Hand specimen. 

Dark-gray to black mafic rock marked by medium- to 

coarse-grained texture. Large dark-gray to black partly 

rounded minerals are olivine. D, Photomi<;rograph showing 

ovoid olivine grain broken by curving fractures and encircled by biotite flakes. 
18 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

0 5 

~~ 

"' ... 4 "'+ Q) • 

... 0 3 

2~' o~ 

f- 2 

5 

4 

0 3 

biJ 

;:,. 2 

0 

5 

4 

0 3 u " 2 

b. 

b. 

J6 0 

~· 

z 

0 

0 

SPECIMEN NUMBER 

"' ~ 

..... cti ~ ~ ~ N ~ ~ 

<> <> <> 

b. b. 

<> ~ 

<> 

~~~ o~, 0 

~ 

60 62 64 

SiO,, IN PERCEJ'IT 

EXPLANATION 

0 Hughesville stock 

<> Laccoliths 

b. Sills 

l 

l 

70 

FIGURE 8.-Silica variation diagrams for intermediate rocks from both large and small intrusions 

scattered through the Barker quadrangle. The 

grouping indicates that the intrusions came 

from the same magma. Specimen numbers are 

identified in table 2. 

santite, composed of biotite, orthoclase, and plagioclase; and ( 5) vogesite, similar to the minette-kersantite, but including much pyroxene or hornblende 

(table 3). Petrographic details and modal and chemical analyses of these rocks are given in table 4. 

The mafic rocks do not seem to be distributed at 

random. Most of the shonkinite, plagioclase shonkinite, and syenite crops out in the northwestern part 

of the Barker quadrangle (closer to the shonkiniterich Highwood Mountains) ; most of the minetteNa,O 

MgO 

CaO 

3 8 914 0 

11 -EJ !0~2 6) 16 

15 17 19 

1Pfo&s\12 7 4 18 

Iron 

EXPLANATION 

0 Barker quadrangle 

.&. Neihart quadrangle 

b. Stanford-Hobson area 

K,O 

(Tota l iron expressed 

as FeO) 

Na,O+ K,O 

FIGURE 9.-Comparison of some chemical characteristics of 

the intermediate rocks from the Barker quadrangle with 

comparable rocks from the Neihart quadrangle and from 

the Stanford-Hobson area. See table 2 for sample locations, and Vine (1956, p. 454-455) for location of samples 

from the Stanford-Hobson area. 
MAFIC ROCKS 19 

TABLE 3.-Lamprophyre terminology 

Dominant feldspar 

Orthoclase Plagioclase 

~ C,) :;:; c= 0 Minette Kersantite 

"' iii s 

~ 

.:: 

Vogesite Spessartite 

"' .$ .:: 

'§ Q)o 

0 ~:a ~ ~1=1. 

~= »= p., 

0 "" 

kersantite and vogesite is in the southern half. I am 

uncertain whether this pattern has more than local 

significance, inasmuch as shonkinite is also exposed 

to the south at Yogo Peak (Weed, 1900, p. 397) 

SHONKINITE 

(Sample 1 of table 4) 

The largest shonkinite intrusion, a blunt plug 

about 1,600 feet wide at its base and some 400 feet 

high, bows up and alters Paleozoic (Big Snowy 

Group) and Mesozoic (Ellis Group and Morrison 

Formation) sedimentary rocks exposed along Little 

Otter Creek in the SEl)t sec. 18, T. 17 N., R. 8 E. 

(Witkind, 1971). In this general area shonkinite 

sills, some as much as 160 feet thick, are ~commonespecially in the Heath Shale of the Big Snowy 

Group. 

The shonkinite is dark gray and even grained, 

ranging from medium to coarse ,grained with the 

coarser types much more common (fig. 7C, D). 

Hand specimens show discrete grains of biotite, pyroxene, and olivine enclosed in a matrix of feldspar. 

In thin section the rock is seen to consist of a 

heterogeneous crystalline mixture of olivine, clinopyroxene, biotite, and some plagioclase (albite, 

An5-7) that is tightly cemented by orthoclase. Many 

of the orthoclase grains are poikilitic, enclosing 

grains of pyroxene and biotite. Orthoclase dominates 

the assemblage and is wrapped around all other 

grains. Accessory minerals include apatite, sphene, 

ilmenite, magnetite, and the zeolites analcime and 

thomsonite. 

The shonkinites grade from those in which there 

is but little plagioclase feldspar to others in which 

plagioclase feldspar is a major constituent. 

PLAGIOCLASE SHONKINITE 

(Sample 2 of table 4) 

Several minor plagioclase shonkinite intrusions 

around Barker Mountain .are indistinguishable in 

hand specimen from the shonkinites ; their greater 

plagioclase content is apparent only in thin section. 

The plagioclase feldspar is albite (An5_ 7 ), and it 

dominates the mineral assemblage. It forms elongate 

laths that are enveloped by alkalic feldspar. 

Many of the olivine grains have been altered to a 

fibrous mesh of alteration products, which (because 

they probably include both antigorite and chrysotile) are here grouped as serpentine. 

SYENITE 

(Samples 3-5 of table 4) 

A few thin syenite sills are interlayered in the 

sedimentary units of the Big Snowy Group exposed 

along the valley walls of both Little and Big Otter 

Creeks. And several more are exposed in the steeply 

tilted beds that form part of the nose of the Clendennin-Peterson anticline (sec. 20, T. 16 N., R. 9 E.) 

(Witkind, 1971). 

In hand specimen, the syenite is light gray to 

gray, holocrystalline, and medium to ,coarse grained 

and is distinguished by abundant biotite flakes and 

long thin needles of pyroxene scattered through a 

light-gray .groundmass of feldspar. 

In thin section the .rock is seen to be a crystalline, 

equigranular mixture of orthoclase, oligoclase 

(An2a), biotite, augite, and sparse hornblende. The 

orthoclase predominates over the oligoclase and commonly jackets it. Some of the plagioclase grains are 

altered to analcime. Apatite, sphene, magnetite, and 

ilmenite are common accessories. 

MINETTE-KERSANTITE 

(Samples 6 and 7 of table 4) 

The minette-kersantite is composed of biotite, orthoclase, and plagioclase, and minor amounts of 

hornblende or pyroxene. In a few rocks, the plagioclase content increases somewhat, and these grade 

toward the kersantites. In others, the hornblende 

becomes more abundant, and they are like the vogesites. I have selected the combined term "minette-kersantite" to reflect the approximately equal amounts 

of alkalic and 'Plagioclase feldspar. Those lamprophyres that contain much clinopyroxene or hornblende have been called vogesite, although some contain :considerable plagioclase feldspar and so are like 

spessari te. 
20 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

TABLE 4.-The petrography and chemical composition (in percent) of mafic rocks from the Barker quadrangle, 

Little Belt Mountains, and of similar rocks from the Stanford-Hobson area 

[Rapid-rock analyses. Analysts: P. L. D. Elmore, Samuel Botts, Gillison Chloe, Lowell Artis, H. Smith, John Glenn, and James Kelsey] 

Area ________________ Barker quadrangle 

I 

Stanford-Hobson area t 

Rock type ______ Shonkinite Plagioclase Syenite Minette-kersanti te Vogesite Vogesite Shonkinite. 

shonkinite. 

Color __________ Dark gray Dark gray Light gray to gray Gray Gray to dark gray Gray to Dark gray. dark gray. 

Texture ________ Medium to Medium to Medium to coarse grained Fine to medium Very fine grained Very fine Medium to coarse coarse grained. grained. coarse grained. grained. grained. 

Phenocrysts _____ Biotite, Biotite, Biotite and pyroxene None Biotite and pyroxene Biotite and Biotite, pyroxene, pyroxene, pyroxene. pyrox£'ne, 

ol!vine. olivine. olivine. 

---------

Xenocrysts _____ None None None Quartz, feldspar, Quartz, sanidine, plagioclase, Quartz, None. mafics(?). feldspar (oligoclase (Ann) feldspar. >. to labradorite (An&o)). ..c:: 

~ ------------------ <II 

th Groundmass _____ Mixture of Mixture of Equigranular mixture of Holocrystalline, Holocrystalline mixture of Mixture of Mixture of e biotite, biotite, orthoclase, oligoclase (An2a), anhedral grains pyroxene (augite, salite), pyroxene, biotite, ~ olivine, olivine, biotite, augite, hornblende, of orthoclase, biotite, orthoclase, and biotite, olivine, ll; pyroxene pyroxene and zeolites. Orthoclase plagioclase plagioclase microlites. and feld- pyroxene, cemented cemented jackets plagioclase. microlites, Some apatite, sphene, spar. cemented 

by ortho- by plagi- Sodalite(?). biotite, and opaque minerals. by orthoclase. oclaseplus hornblende. clase. 

ortho- Some pyroxene. clase. 

Mode (percent)_ Orthoclase, Albite Orthoclase, 51.0; oligoclase Alkalic and plagio- Alkalic and plagioclase feld- Not avail- Not avail39.2; (An3-7)- (An2a), 32.4; biottte, 8.6; clase feldspar, spar, 56.7; clinopyroxene, able. able. 

olivine, 38.1; augite, 5.7; opaque min- 59.3; biotite, 26.0; biotite, 6.4; opaque 24.6; biotite, erals, 2.2; others (analcite, 22.7; clinopyrox- minerals, 7.0; others pyroxene, 22.2; or- heulandtte, thomsonite), ene, 7.7; opaque (including xenocrysts), 9.9. 

15.7; thoclase, 0.1. minerals, 3.4; 

biotite, 17.6; others (including 14.4; salite, xenocrysts), 6.9. 

albite, 10.7; 

2.2; serpen- others, tine, 9.6; 

4.0. others, 

1.8. 

I 

Oxides 

1 2 3 4 5 6 7 8 9 10 11 12 

Laboratory No _______ 163677 163679 D-112806 W-169661 W-169662 D-112805 W-169663 163694 W-167705 W-169696 D-112803 W-169051 Field No _____________ WL-31 WL-42 WL-15 WL-32 WL-35 WL-11 WL-108 WL-120 WL-286 WL-417 WL-3 WL-495 

Si02--- ________ ------ 48.3 56.3 51.1 55.0 54.5 50.0 52.2 49.2 53.7 56.9 50.7 50.1 

AbOa ---------------- 10.4 14.1 16.9 18.3 18.8 13.2 13.3 12.9 15.2 17.2 14.4 13.0 

Fe20a _______ - -------- 2.0 2.3 3.7 2.9 2.6 4.2 4.1 3.9 2.3 6. 5 3.2 4.0 FeO _________________ 7.7 3.3 3.8 2.8 3.4 2.9 3.3 3.1 3.8 .02 4.8 3.6 

Cao MgO_ --------------- 16.0 7.6 3.1 2.2 2.0 6.8 5.6 6.9 3.4 1.0 5.7 9.8 _________________ Na2o 6.8 5.4 5.6 3.3 3.9 8.9 6. 7 9.4 5.4 5.0 7.2 7.1 ________________ 1.4 5.0 4.6 3.6 4.4 2.4 3.6 2.1 3.4 3.9 2.5 2.8 K20 _____________ ---- 3.6 3.2 6. 6 8.2 6.0 4.9 3.2 4.6 3.3 3.7 4.1 4.7 H2o-______________ -- H2o+ .31 .38 .30 0 .18 1.3 .93 1.6 .94 1.3 2.6 1.2 ________________ 1.7 1.0 2.4 2.1 2.6 2.2 2.2 1.4 2.3 1.4 2.0 1.7 

Ti02----------------- .75 .45 .96 .51 .62 1.4 .73 1.3 1.1 .86 .78 .69 

P20&----------------- .65 .57 .77 .45 .40 1.3 .52 1.6 .56 .60 .65 .65 MnO __ ---- __________ .16 .13 .12 .12 .14 .08 .12 .10 .42 .13 .10 .14 C02- ___________ - ____ .08 .09 .37 .36 .06 .43 3.4 1.3 4.2 1.5 1.6 .35 

Sum ___________ -· 99.85 99.82 100.32 99.84 99.60 100.01 99.90 99.40 100.02 100.01 100. 33 99.83 
MAFIC ROCKS 21 

TABLE 4.-The petrography and chemical composition (in percent) of mafic rocks from the Barker quadrangle, Little Belt 

Mountains, and of similar rocks from the Stanford-Hobson area-Continued 

I 1 2 3 4 6 6 7 8 9 10 11 12 

- --- --- ----· - -- Laboratory No _______ 163677 163679 D-112806 W-169661 W-169662 D-112805 W-169663 163694 W-167705 W-169696 D-112803 W-169051 Field No _____________ WL-31 WL-42 WL-15 WL-32 WL-35 WL-11 WL-108 WL- 120 WL- 286 WL- 417 WL- 3 WL-495 

C.I.P.W. norms 

Q_- ----------------- 0 0 0 0 0 or_- _______________ -_ 21.27 18 . 91 38.88 48.53 35.60 ab ___ ______ _________ 11.84 42.30 14.73 21.57 30.60 an _______ __ ----- ____ 11.46 6. !;9 5.95 9.57 13 .88 

c_------------------ 0 0 0 0 0 ne ___ ________ ______ - _ 0 0 13. 04 4.84 3 . 67 en ________ ______ 5.18 5.00 4.15 .45 . 61 di fa ______ __ __ ___ -_ 1. 50 .97 1.38 .17 .41 wo __ _______ _____ 7.31 6. 64 6.01 .67 1. 06 hy en __ ------------ 3. 35 1.47 0 0 0 fs __________ _____ .97 .28 0 0 0 ol fo ________ _______ 22.03 8.80 2.49 3.53 3.08 fa ______ _________ 7.03 1.87 .91 1. 51 2.27 

mt_----------------- 2.90 3.33 5.35 4.21 3. 79 

ap- -------- - -------- 1. 54 1.35 1.82 1.07 . 95 iL _ _________________ 1.42 .86 1.82 .97 1.18 hm ______ ___ ______ ___ 0 0 0 0 0 

1 See Vine, (1956, p. 454- 455). 

1. Plug along Little Otter Creek, SE ~ sec. 18, T. 17 N., R. 8 E. 

2. Sill at Irene Peak, W!-1 sec. 36, T. 16 N., R. 8 E . 

3. Sill along northwest flank, Clendennin- Otter anticline, sec. 20 T. 16 N., R. 

9 E. 

4. Sill at Hansen's Coulee, sees. 28 and 33, T, 17 N., R. 8 E. 

5. Sill along west valley wall Big Otter Creek, sec. 18, T. 16 N ., R . 9 E . 

6. Sill along northeast flank, Clendennin- Otter anticline, C. sec. 24, T. 16 N., 

R. 9 E. 

Scattered sills and small plutons of minette-kersantite intrude Cambrian shales and limestones exposed along Dry Fork Belt Creek between Barker 

and Servoss Mountains (center T. 15 N., R. 8 E.) 

(fig. 6). They range in thickness from a few feet to 

as much as 100 feet; most can be traced for several 

miles. One sill contains much hornblende; and it is 

this sill, 4 miles west of Barker, that Weed (1900, p. 

352) described as a vogesite sheet. The Pilgrim 

Limestone seems to be the favored host rock, although a few sills are in the Park Shale. 

One minette-kersantite siU that contains considerable pyroxene is interleaved in Big Snowy strata 

along the northeast flank of Peterson Mountain 

(center sec. 24, T. 16 N., R. 9 E.); dikes of similar 

rock are along the fault that encircles the Granite 

Mountain bysmalith (fig. 23). 

VOGESITE 

(Samples 8-10 of table 4) 

. \ few sills and dikes of vogesite crop out in the 

south half of the quadrangle. One sill in theE% sec. 

24, T. 15 N., R. 8 E. follows the unconformity between the Flathead Sandstone and the Precambrian 

crystalline rocks; and another, following the same 

unconformity, is exposed in the E% sec. 31, T. 15 

406~ 188 0 . 73. 1 

0 1.28 0.22 5. 95 13.66 1. 60 0 28.95 19.58 27.18 20.47 2l.R9 24.15 27.82 20.31 31.54 17.76 30.20 33.04 21.08 18.66 10.77 11.06 12.19 17.29 11.42 15.91 9.04 0 0 0 0 2.60 0 0 0 0 0 0 0 0 2. 75 8.00 6.49 5. 56 1. 01 0 1. 53 6. 63 0 .75 .17 .67 0 .55 .66 9.26 8.17 6. 58 1. 76 0 2 .26 8.26 1.29 7. 95 11.62 7.88 2.50 12.62 0 0 .92 .35 5. 29 0 4.50 0 5. 36 0 4.82 0 0 0 12.48 0 0 .76 0 0 0 1.37 5. 55 6.15 5. 66 3. 50 0 4 . 62 5.81 3 . 08 1.28 3 . 79 1.39 1.42 1. 53 1. 54 2.66 1. 53 2.47 . 22 .04 1. 48 1.31 .37 0 0 0 6. 51 0 0 

7. Sill(?) along northwest flank, Granite Mountain, S!-1 sec. 31, T. 16 N., R. 

10 E. 

8. Dike, Frenchies Coulee, NW}i sec. 18, T. 15 N., R. 9 E. 

9. St. Louis mine, S!-1 sec. 7, T . 15 N., R. 9 E . (unsurveyed). 

10. Dike (altered ), Gold Run Creek, C. sec. 18, T. 15 N., R. 9 E. 

11. Sill, Skull Butte, NE}i sec. 1, T. 15 N., R. 11 E . 

12. Dike, Skull Butte, S!-1 sec. 35, T. 16 N., R. 11 E . 

N., R. 9 E. (unsurveyed) (Witkind, 1971). A vogesite dike, exposed in Frenchies Coulee, cuts the Taylor Mountain laccolith (NW1,4 sec. 12, T. 15 N., R. 9 

E.) ; another intrudes an old indurated alluvium (p. 

41) exposed in the valley of Gold Run Creek 

(center sec. 18, T. 15 N., R. 9 E.). Still a third dike 

was intersected by the workings of the St. Louis 

mine (fig. 25; S1;2 sec. 7, T. 15 N., R. 9 E., unsurveyed), as shown by vogesite fragments found in the 

mine tailings. 

In hand specimen the vogesite is a .gray to darkgray, very fine grained rock speckled with phenocrysts of brownish-black biotite. Locally near contacts, it contains xenoliths and xenocrysts of country 

rock. In thin section those vogesites that are more or 

less free of inclusions consist of phenocrysts of clinopyroxene (augite and salite) and biotite in a bolocrystalline groundmass of the same minerals, and 

abundant orthoclase and plagioclase microlites. 

' Accessory minerals are apatite, sphene, and magnetite . 

All the vogesites examined contain xenocrysts 

chiefly of quartz, sanidine, and plagioclase feldspar. 

An assortment ·Of different plagioclase feldspars extending from oligoclase (An17 ) to labradorite 

(Anso ) is included. Each xenocryst is rounded, corroded, and encircled by a distinctive reBJction rim 
22 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

Quartz xenocryst 

•• 

A 

Plagioclase 

feldspar ·• • 

·-· ... .. 

c 

B 

D 
MAFIC ROCKS 23 

(probably of clinopyroxene) which varies in thickness from mineral to mineral (fig. 10). In general, it 

is thickest around the plagioclase feldspars and thinnest around the sanidines. 

The source of the xenocrysts is uncertain; most 

apparently are relics of country rocks, inasmuch as 

xenoliths of both metamorphic and sedimentary rock 

have been found in the vogesites. So, some xenocrysts are obviously derived from the pulling apart 

of the xenoliths; others, however, may represent 

transferred phenocrysts-relics of blebs of salic 

magma picked up as fingers of fernie magma 

breached and moved up through a salic one (Witkind, 1970, p. C87). 

The vogesite dike that cuts the indurated alluvium 

has been thoroughly weathered to a light tan, and 

the included xenocrysts of quartz and feldspar give 

it a superficial appearance strikingly like that of the 

porphyry of Galena Creek. Its texture and composition (sample 10 of table 4), however, show that it is 

a lamprophyre. 

CHEMISTRY OF THE MAFIC ROCKS 

Compared to the intermediate rocks, the mafic 

rocks contain less .silica, soda, and potash, and more 

iron, lime, and magnesia. A comparison of the rocks 

within the mafi·c group indicates that a close relation 

exists between the vogesites and the minette-kersantites-both are characterized by high iron, magnesia, and lime, and low soda and potash (fi.g. 11). 

(Sample 10 .of table 4, a weathered vogesite, is disregarded in this comparison.) 

Possibly most of these lamprophyres are a result 

of the differentiation of a parental fernie magma 

that has the composition of shonkinite. As a result 

of crystal fractionation-mainly settling of the 

heavier olivine and pyroxene-the parental magma 

differentiated into two contrasting magmas: a 

lighter fraction represented by the syenite, the plagioclase shonkinite, and some of the pyroxene-poor 

and hornblende-poor minette-kersantite; and a heavier fraction represented by the pyroxene-rich vogesite. 

This differentiation pattern is reflected by the 

chemical analyses; the syenite, plagioclase shonkinFIGURE 10.-Xenoliths and xenocrysts in lamprophyres. All 

photomicrographs by R. B. Taylor and Sandra Brennan. 

A, Corona of clinopyroxene (?) grains about a rounded 

quartz xenocryst. B, Corona of clinopyroxene (?) grains 

about a corroded quartz xenocryst. C, Reaction rim about 

plagioclase feldspar xenocryst. D, Xenoliths and xenocrysts 

derived from Precambrian crystalline fragments enclosed 

in vogesite. 

Na,O 

MgO 

01 12 6 

CaO 

A 

11 

~7 8 .. 6 

_,2 

B 

Iron 

(Total iron expressed 

as FeO) 

10 

• .9 ()3 ()5 

()4 

EXPLANATION 

Barker quadrangle 

0 Shonkinite 

_, Plagioclase-shonkinite 

() Syenite 

ct Minette-kersantite 

• Vogesite 

Stanford-Hobson area 

6 Shonkinite 

.a. Vogesite 

Na,O+K,O 

FIGURE 11.-Some chemical characteristics of the mafic rocks. 

A, CaO-Na20-KzO ratios. B, FeO-MgO-Alk ratios (FeO 

=Total iron expressed as FeO; Alk = Na20+K20). See 

table 4 for sample locations, and Vine (1956, p. 454-455) 

for location • of samples from the Stanford-Hobson area. 
24 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

ite, and the minette-kersantite-the lighter fraction 

of the differentiated magma-contain, in general, 

more alkalies and less iron, magnesia, and lime than 

the vogesite (fig. 11). 

COMPOSITE DIKES 

At least two composite dikes-characterized by 

mafic margins that •contain quartz xenocrysts and by 

felsic interiors that contain quartz phenocrystshave been recognized in the Barker quadrangle, and 

at least one more is known in the Neihart (Witkind, 

1970). It is highly likely that many more are in the 

TABLE 5.-Chemical analyses, in percentage, of the mafic 

margin, transitional zone, and felsic interior of the Maytee 

composite dike, sees. 6 and l, T. 15 N., R. 9 E. (unsurveyed), Judith Basin County, Montana 

[Rapid rock analyses. Analysts: P. L. D. Elmore, Gillison Chloe, James 

Kelsey, S. D. Botts, H. Smith, Lowell Artis, and John Glenn] 

Mafic Transitional 

margin zone 

Rock Kersantite Kersantite (?) name 

Lab No. W-170181 W-171084 

Field No. WL-270-c WL-552-a 

Oxides 

Si02 -------------------- 57.5 68.6 

Al20a ------------------ 16.0 15.7 

Fe20a ------------------ 2.4 1.4 

FeO -------------------- 2.8 .92 

MgO ------------------- 3.1 .88 

CaO ------------------- 3.9 1.0 

Na20 ------------------ 3.3 2.9 

K20 ------------------- 4.0 4.6 

H2o- ------------------- .22 .69 

H20+ ------------------- .78 2.1 

Ti02 ------------------ .89 .77 

P205 ------------------- .42 .33 

MnO ------------------- .16 .03 

C02 -------------------- 3.9 < .05 

Sum ------------- 99.37 99.97 

C.I.P.W. norms 

Q --------------------- or ____________________ _ 

ab ____________________ _ 

an ____________________ _ 

c ----------------------

hy { ~~ ================ mt ____________________ _ 

ap ---------------------

il --------------------- hm ___________________ _ 

19.33 

23.79 

28.10 

0 

6.28 

4.85 

2.00 

3.50 

1.00 

1.70 

0 

31.74 

27.18 

24.54 

2.49 

5.04 

2.19 

0 

.83 

.78 

1.46 

.83 

Felsic 

interior 

Porphyry of 

Galena Creek 

W-171083 

WL-551-a 

75.9 

13.0 

.74 

.60 

.29 

.11 

.53 

6.3 

.51 

1.7 

.15 

.02 

.00 

< .05 

99.90 

48.12 

37.23 

4.49 

.10 

5.27 

.72 

.24 

1.07 

.05 

.29 

0 

Little Belt Mountains, either concealed under the 

thick foliage or unrecognized. The darker margins, 

marked by conspicuous large round quartz grains, 

have been interpreted as chilled borders of felsic 

dikes. Their mineralogy and chemistry, however, 

differ completely from the mineralogy and chemistry 

of their felsic cores (table 5). Moreover, the field 

relations of these bodies indicate that they are composite dikes, the products of :coexisting salic and 

fernie magmas. 

The two composite dikes recognized in this quadrangle intrude the quartz monzonite of Hughesville. 

One, called the Maytee dike, is well exposed on an 

old mine road near the Maytee tunnel of the Block P 

mine (SW1,4 sec. 6, T. 15 N., R. 9 E., unsurveyed) 

(fig. 6). The other, the Annie E dike, has been cut 

through by the Annie E tunnel of the Liberty mine 

(fig. 12) (center sec. 7, T. 15 N., R. 9 E., unsurveyed; see fig. 25 for mine locations). 

SIMILARITIES OF CLINOPYROXENES 

More than half a century ago Pirsson (1905, p. 

38) noted that clinopyroxenes from igneous bodies 

scattered through central Montana are similar regardless of rock type. A study of clinopyroxenes concentrated from the diverse rocks exposed in this 

quadrangle has confirmed Pirsson's observation. Pyroxenes from f.elsic rocks such as granite porphyry 

are remarkably like those from mafic rocks such as 

shonkinite in optical and chemical properties and in 

unit cell dimensions. 

It was concluded that this close similarity of pyroxenes from widely disparate rock types implies a 

genetic relationship of the parent magmas. 

Detailed results of this study have been reported 

elsewhere (Witkind, 1969). 

THE INTRUSIONS 

The •configuration of the mountains and valleys 

reflects the distribution and :shape of the various 

intrusions (Weed, 1900, p. 384-400). Each upwarp, 

anticline or dome, is more or less ~shaped by the 

subjacent intrusion; the intervening ~synclines or 

basins are formed of sedimentary strata squeezed 

between adjacent intrusions (fig. 13). 

The 11larger mapped plutons have been emplaced 

or are exposed at various stratigraphie levels. The 

single stock intrudes strata of the Madison Group. 

Three, and probably four laccoliths, are emplaced 

along the Cambrian-Precambrian unconformity and 

so are roofed by the Flathead Sandstone or younger 
THE INTRUSIONS 25 

EXPLANATION 

Fe

~ 

~ 

lsic interior 

(porphyry of Galena Creek) 

D Ill 

0 

a. 

E 

0 

u 

D 

Quart z monzonite of Hughesville 

Vein 

Da•hed where approximately located 

~ 

Composite dike 

I· \ v v v \· \ 

\ ' \ vv vvvvvv \ ; \ 

~ •\ v v v v v \ • \ 

Vein 3 to 4 inches thick in face 

Mafic margin 

(kersantite) \•\v : ~ v\:\ ~ 

r vvv. ' / _j :. ~ vv ::, v v \' ·\ / 

\ ' \\v"v "v" \\.\\ Orechute ,,//-----:__;,../ 

---'--·- ' \ v v v "\'·\ ?' '--.._ ~~------ \ •,v v v v • 

--- - --- /

Portal Wmze[ 

- -=-=-1 ~ \' \ v v v "v \ i:l vv ':, v ~\.' \ 

N 2<\ It ___.-\ 

Ve 1n poorly exposed 1n roof of dnft. pos1t1on and r--- Vein thins abruptly to about !-foot thickness 

thickness uncertain ; local ly 2 to 3 feet wide where it cuts across dike 

0 20 40 FEET 

FIGURE 12.-The Annie E dike intrudes the quartz monzonite of Hughesville, as revealed in the Annie E tunnel of the 

Liberty mine. Mapped June 26, 1967 hy I. J. Witkind, assisted by Mrs. Gwenllian Vaughan-Rhys McBride. 

Cambrian rocks. Two laccoliths are higher in the 

section, possibly resting on Devonian strata and 

roofed by limestone beds of the Madison Group. One 

laccolith is in fault contad with comparable beds of 

the Madison, and another laccolith rests chiefly on 

the Heath Shale, the uppermost unit of the Big 

Snowy Group. The lone 'bysmalith is in fault contact 

with the Park Shale of Cambrian age. A buried pluton intrudes and domes the Precambrian crystalline 

rocks and likely extends northeastward beyond the 

exposed Precambrian rocks (fig. 31). 

Near the •Center of the quadrangle three laccoliths 

form a radial pattern about the circular stock. This 

stock-laccolith .grouping, interpreted as denoting a 

genetic relationship (fig. 13), has been noted elsewhere, especially on the Colorado Plateau. There, 

for example, ea:ch of the mountain groups that together constitute the Henry Mountains consists of a 

parent stock and its surrounding tongue-shaped satellitic laccoliths (Hunt, 1946, 1953). The laccoliths 

radiate from the parent stock much like spokes from 

the hub of a wheel. Hunt's illustration showing the 

ground plan of the intrusions around the Mount 

Ellen stock in the Henry Mountains is reprinted as 

fi.gure 14A of this report. A similar pattern between 

parent stock and satellitic .laccoliths was found in 

the Abajo Mountains by Witkind (1964); and another was reported by C. E. Erdmann (oral 

commun., 1964) in the Sweetgra:ss Hills of northcentral Montana. 

On the Colorado Plateau, sulfide mineralization is 

concentrated in and near the stocks; the laccoliths 

are barren. Consequently, the stocks are considered 

to be far more significant than the encirding laccoliths. In the Barker quadrangle the main sulfide ore 

deposits are in and near the HughesviUe stock. 

Hence this stock also is believed to be of special 

significance. 

STOCK 

HUGHESVILLE STOCK 

The Hughesville stock is bounded on the north, 

west, and south by variably altered limestone beds 

of the Madison Group and on the east by various 

intrusions (fig. 6). On the north boundary, the limestone beds directly adjacent to the stock dip steeply 

toward the stock; on the west and south, they dip 

steeply away from it. On the northeast the exact 

relations between the stock and the Clendennin-Peterson laccolith are concealed beneath the al,luvial fill 

of Green Creek. Locally, there appears to be an intrusive cont31ct between the two, but elsewhere the 

two are separated by a narrow tight syncline of 

Madison beds. On the east the stock intrudes the 

west flank of the Mixes Baldy-Anderson Peak laccolith. Fingers of the stock extend into the laccolith, 

and other dikes and plugs of a latite porphyry similar to that which forms the east margin of the stock 

(p. 16) intrude the laccolith. 

The stock, in turn, is intruded by felsic, mafic, and 
26 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

110'45' 47"15' 

0 2 

------- --~-

3 MILES 

110'30' 

. 17 N. 

16 N. 

RANITE MOUNTAIN 

BYSMALITH 

GRANITE MTN 

FAULT 

. 15 N . 

. 14 N. 

FIGURE 13.-Distribution and shape of the various intrusions as shown by structure contours which are drawn on or 

projected to the top of the Madison Group. Shaded areas are exposures of various igneous and metamorphic 

rocks. Projected fault planes are hachured. Contour interval 200 feet; datum is mean sea level. 
STOCK 27 

a few composite dikes, all of which follow fra!Ctures 

that break the stock. Locally, veins of sulfide minerals follow the contact between the dikes and the 

stock ( p. 45). None of the dikes and veins extend 

beyond the margins of the stock. 

The stock is intensely jointed. Many of the joints 

are isolated curved fractures which are either vertical or steeply dipping. Others, however, are very 

closely spaced and form zones 2- 6 inches wide. All 

are stained by limonite, and locally the adjacent rock 

is sericitzed ( p. 49). Because of thick foliage, neiEXPLANATION 

0 

A 

B 

Copper R1d ge 

laccolith 

2 Miles 

FIGURE 14.-Tonguelike satellitic laccoliths. A, " Ground 

plan of intrusions around the Mount Ellen stock in Henry 

Mountains, illustrating radial distribution of the laccoliths." From Hunt (1956, fig. 30). B , "The laccoliths * * * are tongue-shaped and are bulged linearly and radially 

from the stocks." From Hunt (1956, fig. 1A). 

ther individual joints nor joint zones are traceable 

for more than a few hundred feet. 

The fracture pattern was not studied in detail, but 

the attitudes of many conspicuous joints were measured. The poles of perpendiculars to these joints 

have been plotted and then contoured on an equalarea stereo.graphk net (fig. 15). This plot shows that 

all the joints are very steep with the great majority 

being vertical or nearly so. Two conjugate fracture 

systems are postulated. One system consists of a 

joint set that trends about N. 60 ° E. and that is 

vertical; at almost right angles to this set is another 

set that trends N. 40° W., and dips about 80° SW. 

The second fracture system, locally the more dominant of the two, consists of a set of almost vertical 

joints, which trend in a general northerly direction 

(ranging from N. 15° E. toN. 15° W.), and a second 

set, at right angles to the other set, which trends 

easterly. These two fracture systems seem to be 

dominant in the stock; most of the other joints appear to be diversely oriented. 

LACCOLITHS 

Most of the large intrusions in the Barker quadrangle are here classed as laccoliths, although only 

three are demonstrably floored. It ·Could be argued, 

therefore, much as Goddard (1950) has done for 

comparable intrusions in the nearby Judith MounN 

w E 

s 

FIGURE 15.- Joints in the Hughesville stock. Lower hemisphere plot; 127 poles. Contoured in percent. 
28 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

tains, that those masses without visible floors are 

not laccoliths but rather are deep-seated plugs. But I 

prefer to think of them as laccoliths, as did Weed 

(1900), because they are similar in both structure 

and petrography to the floored bodies, and because 

the overall character of this intrusive complex is so 

much like that of demonstrable laccolithic complexes 

elsewhere, such as in the Henry Mountains (Hunt, 

1953) and the Abajo Mountains (Witkind, 1964) in 

Utah. 

Moreover, the alkalic feldspar in all but one of the 

laccoliths is marked by low to moderate opti•c angles 

(,....,30 ° to ,....,50 °) that imply sanidine, rather than by 

high optic angles (75°) that imply orthoclase. The 

presence of orthoclase suggests slow cooling and 

gradual crystallization, whereas the occurrence of 

sanidine implies high temperatures quickly 

quenched. Conditions favoring sanidine would prevail during the formation of a laccolith. Being isolated somewhat from the main heat source, laccoliths should crystallize before their sanidine could 

transform to orthoclase. Stocks, on the other hand, 

are connected at depth with a continuous source of 

heat, and the transformation is likely to occur as it 

did in the Hughesville stock. 

The previous work done on laccolithic complexes 

has demonstrated that laccoliths assume at least 

three different shapes: (1) a planoconvex (mushroomlike) type (fig. 16A, B), (2) a tonguelike satellitioc type atta•ched to a parent stock (C, D), and (3) 

an asymmetric (half a mushroom type (E, F). It 

seems likely that all three types are in this quadrangle. 

PLANOCONVEX LACCOLITHS 

Gilbert's (1880, p. 19) original work in the Henry 

Mountains gave rise to the classic concept of a laccolith-a lenticular planoconvex (mushroomlike) 

body presumably fed by a nearly vertical dike or 

pipe (fig. 16A, B). 

This type of laccolith probably underlies Taylor 

and Butcherknife Mountains and possibly the Limestone Butte dome (fig. 13). 

TONGUE-SHAPED SATELLITiC LACCOLITHS 

These include those linear laccoliths (Hunt, 1946, 

1953) that are attached to a parent stock. They are 

tongue.:shaped masses, thick where they are attached 

to the stock and thin at their distal ends (fig. 16C, 

D, and fig. 14B). As the individuallacocoliths may be 

emplaced in different stratigraphic units, some laccoliths can be either wholly or in part above or beneath others. 

In the Barker quadrangle this stock-laccolith relation is suggested by the three intrusions that seem to 

radiate from the HughesviUe stock (figs. 2 and 13): 

the Barker laccolith, the Clendennin-Peterson laccolith, and the Mixes Baldy-Anderson Peak laccolith. 

Of the three intrusions, however, only the Clendennin-Peterson laccolith appears, on the basis of its 

deformed sedimentary cover, to have the requisite 

tonguelike shape of a satellitic laccolith. 

ASYMMETRIC LACCOLITHS 

Asymmetric laccoliths resemble half a planoconvex (mushroomlike) laccolith; one flank is blunt and 

the other flanks taper to thin edges (fig. 16E, F). 

These igneous bodies have been given various 

names: Hunt (1946, 1953, and 1956, fig. 31B) referred to them as "bysmaliths"; Pratt and Jones 

(1961, p. C164) called them "trap-door laccoliths," 

and Cross (1894, p. 237), Weed (1899c, p. 25), Pirsson (1898, p. 581) and Harker (1909, p. 66-67), 

among others, called them "asymmetric laccoliths." 

This latter name is used here. 

How they formed is uncertain; there are several 

possibilities. One explanation, advanced by Hunt 

( 1956, fig. 31B), involves the di.lation of the distal 

end of a tonguelike laccolith (fig. 17A). A second 

explanation, offered by Cross (1894, p. 237) and by 

others involves either a vertical or an inclined feeder 

beneath the laccolithic floor (fig. 17B, C). I would 

add a third alternative: The laccolith developed adjacent to and along a preexisting fracture which 

served as a channel for the ascending magma (fig. 17 

D). 

Of the laccoliths in the Barker quadrangle, only 

the Barker laccolith is asymmetric. Weed (1900, p. 

355, fig. 43) considered the north flank to be the 

blunt end, whereas I think the east flank near the 

stock is the blunt side (fig. 6, cross section A-A', 

and fig. 13). 

DESCRIPTIONS OF LACCOLITHS 

PLANOCONVEX LACCOLITHS 

BUTCHERKNIFE MOUNTAIN LACCOLITH 

An intensely dissected dome known as Butcherknife Mountain occupies the southeast corner of the 

quadrangle (fig. 2). The dome, astride Tps. 14 and 

15 N., R. 9 E., is almost 41;2 miles across and rises 

about 2,200 feet above the floor of Dry Wolf Creek. 

It is underlain by the Butcherknife Mountain laccolith, from which much of the sedimentary cover has 

been stripped. 
LACCOLITHS 

A B 

~tor i Shattered zone .. 

D 

II I 

.. 

. . . 

c D 

E F 

EXPLANATION 

u 

D -.-+--

Fault 

U, upthrown side; D, 

downth1·own side 

Syncline 

Showing troughline and 

directi,Qn of plunge 

Strike and direction 

of dip of beds 

FIGURE 16.- Three types of laccoliths. Dark arrows 

and dashed lines indicate direction and general 

sequence of magma emplacement. A, Cross section 

of the simple planoconvex (mushroomlike) laccolith (from Gilbert, 1880, fig. 8) . B, Diagrammatic map of the planoconvex laccolith assuming 

erosion has reached line B-B' on section A. Line 

A-A' represents plane of cross section shown in 

A. C, Cross section of tonguelike satellitic laccolith 

attached to the parent stock (from Hunt, 1953, fig. 

70). D, Diagrammatic map of satellitic laccolith 

assuming erosion has reached line D-D' on section 

C. Line C-C' represents plane of cross section 

shown in C. E, Cross section of an asymmetric 

laccolith developed adjacent to and along a preexisting fracture. F, Diagrammatic map of" asymmetric laccolith assuming erosion has reached line 

F-F' on section E. Line E-E' represents plane of 

cross section shown in E. 

29 
30 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

Inasmuch as only the roof is exposed, the shape 

and size of the laccolith can only be surmised. Likely 

it is planoconvex. I estimate it to be about 3 miles in 

diameter and a maximum of about 3,000 feet thick. 

The laccolith and its related sills are 'composed of 

the Barker Porphyry (samples 7 and 8 of table 2). 

A 

c 

FIGURE 17.-Four ways in which an asymmetric 

laccolith might develop. In the first three (A, 

B, and C), the magma (arrow) moves generally 

toward the fracture; in the fourth (D), it 

moves away from the fracture. A, Magma intruded along a near-horizontal bedding plane 

moves laterally to form first a sheet and then 

a tonguelike satellitic laccolith. As the distal 

edge of the laccolith dilates, the overlying 

strata are raised, folded back, and finally 

broken. Fault does not extend below laccolithic 

floor. From Hunt (1956, fig. 31B). B, Magma 

rises in a nearly vertical conduit which crosscuts host rocks. When upward progress of 

magma is halted, it moves laterally to form 

first a sheet and subsequently an asymmetric 

Most of the laccolith underlies the Flathead Sandstone, but locally it cuts across the sandstone to 

younger Cambrian strata. The youngest rocks deformed by the laccolith belong to the Big Snowy 

Group, and remnants of these are preserved in a 

triangular trough north of Butcherknife Mountain. 

B 

D 

laccolith. Here also the fault does not extend 

below laccolithic floor. From Cross (1894, fig. 

30). C, Magma rises in an inclined conduit 

which crosscuts host rocks. The greatest thickness of the laccolith develops opposite the 

mouth of the inclined conduit owing to the 

intrusive force of the magma. Fault does not 

extend below laccolithic floor. From Howe 

(1901, p. 299) . D, Magma rises in a preexisting 

fracture. Where the upward progress of the 

magma is halted-possibly because the fracture 

closes-the magma moves laterally along a 

bedding plane. Dilation of the laccolith causes 

the overlying beds to break; consequently these 

are offset more than those beneath the laccolith. 
LACCOLITHS 31 

TAYLOR MOUNTAIN LACCOLITH 

Taylor and Granite Mountains together form a 

•compound dome which dominates the east edge of 

the quadrangle. The dome, astride the junction of 

four townships (Tps. 15 and 16 N., Rs. 9 and 10 E.), 

is underlain in its southern half by the Taylor 

Mountain laccolith and in its northern half by the 

Granite Mountain bysmalith (fig. 18). Field relations indicate that after the laccolith was emplaced, 

it was bowed upward and likely broken in two by 

the developing bysmalith (fig. 19). The northern 

half of the laccolith has since been eroded away, 

leaving the southern half tilted to the southwest (fig. 

19 D and Witkind, 1971 cross section D-D'). 

The dome is about 5 miles in diameter and rises 

some 2,200 feet above the floor of Lone Tree Park; 

only the western two-thirds is within the Barker 

quadrangle. Originally the laccolith may have been a 

somewhat linear body that trended about N. 55° E. I 

estimate it to have been some 4 miles long and about 

2% miles wide. It probably had a maximum thickness of about 1,800 feet. 

The laccolith rests on the Jefferson Dolomite and 

directly underlies the Madison. In theN% sec. 12, T. 

15 N., R. 9 E., (unsurveyed) a thin sliver of Madison is preserved along the laccolithk ·crest (fig. 19 D 

and Witkind, 1971 cross section D-D'). 

The laccolith is composed of the Barker Porphyry 

(samples 5 and 6 of table 2) but contains orthoclase 

rather than sanidine as in the other laccoliths. This 

laccolith is the only floored intrusion that contains 

orthoclase; possibly it is connected at depth with a 

part of the stock. 

To determine whether any significant variation or 

differtmtiation occurred as the la·ccolith dilated, one 

sample was collected from the floor of the laccolith 

(sample 5) and another from the roof (sample 6). 

The rocks are alike mineralogically and chemically, 

implying that the magma was emplaced rapidly 

enough to preclude any differentiation. 

LACCOLITH ( ?) UNDERLYING THE LIMESTONE BUTTE DOME 

Limestone Butte dome, in the northwest corner of 

the quadrangle (NE1,4, T. 16 N., R. 8 E.), is about 4 

miles ·in diameter and almost perfectly circular. Its 

top rises smoothly and evenly some 1,000 feet above 

the adjacent stream floors. Softer strata have been 

stripped, leaving a surface held up by the more durable limestone beds of the Madison Group. The 

flanks of the dome are outlined by moderately dipping strata of the Big Snowy Group (Witkind, 

1971). 

I believe that the dome is underlain by a planoconvex laccolith whose general composition is suggested 

by a plug and sill which intrude the strata along the 

north flank. The igneous rock (sample 12 of table 2) 

is like the Barker Porphyry. 

The dome was tested unsuccessfully for oil in 1957 

by the Oien Oil Co. The test, known as the J. W. 

Bodner 1, was collared on the crest of the dome at 

an altitude of 5,761 feet in the SW% sec. 2, T. 16 N., 

R. 8 E. It was abandoned as a dry hole in the Jefferson Dolomite at a total depth of 1,887 feet. Inasmuch as the test did not penetrate any igneous rock, 

the laccolith must have formed at greater depth, possibly along the unconformity between the Precambrian basement •complex and the overlying Middle Cambrian strata (Witkind, 1971 cross section 

A-A'). 

DRY WOLF LACCOLITH 

A small part of the north flank of the Dry Wolf 

laccolith is exposed in the southeast corner of the 

quadrangle; this exposure occupies most of sec. 6, T. 

14 N., R. 9 E. (fig. 2). Practically all the sedimentary ·cover has been stripped from the laccolith; and 

the la·ccolithic floor, sloping gently northward, is exposed along the east valley wall of Dry Wolf Creek. 

The floor truncates limestone beds (which here dip 

about 10° NE) of the Madison Group. A few limestone beds of the Madison Group are still preserved 

on the laccolith's flank; the implication is that the 

laccolith was emplaced wholly in the Madison 

Group. 

The laccolith is composed of the Barker Porphyry 

(sample 9 of table 2). 

SATELLITIC LACCOLITHS 

CLENDENNIN-PETERSON LACCOLITH 

The north flank of the mountains is dominated by 

the nose of an elongate northeast-trending anticline 

whose general shape, length, and width are believed 

to result from the emplacement of the ClendenninPeterson laccolith (fig. 20). The anticline, which 

trends northeast from the Hughesvil.le stock (fig. 2), 

is about 6 miles long and 3 miles wide; it rises 

about 2,500 feet above the adjacent valleys. Parts of 

the laccolith are exposed in various streams ; all exposures are believed to be parts of the laocolithic 

roof. The laccolithic floor is not exposed. 

On the basis of exposures and the general configuration of the anticline, I suggest that the underlying 

lacc~lith is about 5 miles long, about 2 miles wide, 
32 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

Crest of Wolf Butte 

FIGURE 18.-Panoramic view of the compound dome underlain by both the Taylor Mountain laccolith and the 

and possibly as much as 3,500 feet thick near the 

stock (Witkind, 1971, cross sections B-B' and C-C'). 

The oldest sedimentary unit that is domed by the 

laccolith is the Flathead Sandstone. The laccolith 

cuts younger beds, possibly because of faults, so that 

beds as young as the Jefferson Dolomite rest on its 

roof. Commonly, however, the Wolsey Shale directly 

overlies the laccolith. In sharp contrast to most of 

the other laccoliths, those beds that overlie the crest 

and upper flanks of the thick end of the laccolith 

have been intensely metamorphosed. 

Two major faults cut the laccolithic flanks. The 

northwest flank is broken by the Clendennin fault, 

and the southeast flank by the Peterson fault (fig. 

21). The field relations imply that the faults may 

have formed during dilation of the laccolith (Witkind, 1965). 

CLEN DEN NIN FAU LT 

The Clendennin fault is normal. It dips valleyward (northwestward) at a high angle-at least 60° 

locally-and the beds southeast of the fault have 

been raised. The fault can be traced northeastward 

for about 2 miles from near Lost Creek (fig. 21, and 

Witkind, 1971). Originally it may have extended for 

a distance of 4 miles, for southwestward from Lost 

Creek a thin dike of the porphyry of Clendennin 

Mountain follows the fault trace for about 1 mile 

before the dike passes into the main mass of the 

laccolith. Southwestward beyond this point the linearity of this flank of the laccolith implies that it 

developed against a preexisting fault. I interpret 

these relations to mean that even as the sedimentary 

strata were arched and broken by the dilating laccolith, magma from the laccolith invaded and obliterated part of the fault traee. 

The stratigraphic throw along the fault increases 

toward the Hughesville stock. So, at the northeast 

end of the fault, Madison strata are juxtaposed; and 

near the midpoint of the fault trace, Madison beds 

are in fault contact with the Jefferson Dolomite. 

PETERSON FAULT 

The Peterson fault (along the southeast flank of 

the anticline, like the Clendennin fault is normal and 

dips valleyward (southeastward) at a high angle 

(fig. 21). The beds on the northwest side of the fault 

have been raised. The fault can be traced southwest 

for about 2112 miles where it ends against the southeast flank of the la•ccolith. Here also, the straightness of the laccolithic flank implies that the southeast flank, like the northwest flank, is fault controlled. If so, this fault too may have been as much 

as 4 miles long. 

The stratigraphic throw, as along the Clendennin 

fault, increases toward the stock. So, at the north-
LACCOLITHS 33 

Granite Mountain bysmalith 

I Taylor Mountain 

Granite Mountain bysmalith. View is northeastward across Lone Tree Park from the east flank of Mixes Baldy. 

east end of the fault Madison strata are juxtaposed; 

near the midpoint Cambrian and Devonian beds are 

in fault contact with the Madison; and near the 

southwest end the Madison rests against the Flathead Sandstone. 

Both faults, thus, increase differentially in stratigraphi•c throw toward the stock. This increase is 

attributed to the pattern of dilation followed by the 

la;ccolith. The magma was probably fed northeastward from the parent stock. As the laccolith dilated, 

it first raised the overlying sedimentary strata, then 

arched them until they finally broke to form the two 

faults. 

OTTER LACCOLITH 

The otter laccolith, here tentatively classed as a 

satellitic laccolith, occupies the center ofT. 16 N., R. 

8 E. (fig. 2). I believe it is closely related to the 

thickened sill northeast of Irene Peak some 2 miles 

to the southeast in the NE1,4 sec. 36, T. 16 N., R. 8 

E. (Witkind, 1971). Probably both features were 

once joined to form an elongate thin igneous mass 

which encircled the north flank of Barker Mountain. 

The laccolith is •completely stripped of sedimentary cover and now appears as a pile of igneous rock 

resting on various units of the Big Snowy Group, 

chiefly the Heath Shale. Its floor conforms to the 

under.lying strata and slopes gently northward. It is 

about 2 miles in diameter and some 700 feet thick. 

Its original size and shape are unknown. 

It is ·composed of a rock similar to the Barker 

Porphyry (sample 2 of table 2) but has more clinopyroxene than other samples of the porphyry. Much 

the same is true of the porphyry that forms the 

thkkened sill northeast of Irene Peak (sample 3 of 

table2). 

The laccolith was probably fed from the parent 

stock through the thickened sill. 

ASYMMETRIC LACCOLITHS 

BARKER LACCOLITH 

Due west of the Hughesville stock is Barker 

Mountain, a circular dissected dome about 3 miles in 

diameter which rises about 3,000 feet above the floor 

of Dry Fork Belt Creek (fig. 22). The mountain is 

underlain by the Barker laccolith (Witkind, 1971, 

cross sections A-A', D-D'). Extensive dissection has 

stripped the sedimentary cover from the laccolith's 

crest and upper flanks, and the remaining sedimentary beds are now preserved chiefly along the lower 

flanks (fig. 6). 

Inasmuch as the floor is nowhere exposed, only a 

general estimate can be made as to the size of the 

laccolith. It is •crudely drcular, 3-31;2 miles in diameter, and possibly as much as 4,000 feet thick. 

On the north, west, south, and southeast the lac-
34 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

9000' 

8ooo·-L------------

7000' Mm 

5ooo·-L~~~-~~~ +- + + + + + ~~+ "" -~~~ Tba + + + ++++++ +-+ +++t-+++ 

5000' + + + Du + TAY LOR MOUNTAIN LACCOLITH+ + + + + + + + + + + + + + + + + + + + + + 

4000' 

12,000' 

11.000' 

10,000' 

9000' 

8000' 

7000' 

6000' 

13,000' 

12,000' 

11,000' 

10,000' 

sw 7800' 

7000' 

6200' 

£u 

A 

c 

GRAN ITE MOUNTAIN 

D GRANITE MOUNTA I N 

BYSMALITH 

0 2000 4000 FEET 

NE 

FIGURE 19.-Four sections offering one possible explanation 

for the structural relations between the Taylor Mountain 

laccolith and the Granite Mountain bysmalith. p£r, Precambrian crystalline metamorphic rocks; £ u, Cambrian 

units; Du, Devonian units; Mm, Madison Group; Tba, 

Barker Porphyry; Tgm, rhyolite of Granite Mountain. A, 

Taylor Mountain laccolith develops as a planoconvex body. 

colith is ovedain by Cambrian strata. On the northeast it is in sharp linear contact with the Madison 

Group, and its edge may conform to a preexisting 

fault. If so, the northeast flank is steep, whereas all 

other flanks thin laterally and pinch out beneath the 

sedimentary •cover. 

The laccolith is semiconcordant, transgressing to 

younger beds. Thus, the northwest flank of the laccolith underlies the Flathead Sandstone; farther 

south the laccolith underlies the Wolsey; and still 

farther south the laccolith has cut across the 

Meagher Limestone and Park Shale and underlies 

the Pilgrim Limestone. These relations imply that 

the floor of the laccolith, particularly its north half 

(Witkind, 1971, cross sections A-A' and D-D'), 

rests on Precambrian ·crystallines, whereas its south 

half rests on one or more Middle Cambrian units. 

The Barker laocolith, formed by the Barker Porphyry (sample 4 of table 2), is classed as an asymmetric laccolith chiefly because I' think it was 

formed by magma that moved up a preexisting fracture, possibly one related to the Irene Peak fault. I 

suspect that the position of the laccolith-radial to 

the parent stock-was determined by an old high-angle fracture which trended about N. 30° W. from the 

west flank of the Hughesville stock (fig. 6). The 

former trace of the fracture is now followed by the 

.linear northeast flank of the laccolith. 

Probably the magma that fed the Barker laccolith 

rose in the same master conduit (now oocupied by 

the Hughesville stock) responsible for the Clendennin-Peterson and Mixes Baldy-Anderson Peak laccoliths. During its upward progress it was probably 

diverted westward into the high-angle fracture that 

intersected the conduit. The magma rose in the fault 

until its upward progress was slowed or stopped, 

then it migrated laterally along the Cambrian-Precambrian contaJCt and slowly raised and arched the 

beds. With the gradual addition of magma, those 

beds closest to the former fracture, which served as 

a feeder conduit, were raised the most. 

MIXES BALDY- ANDERSON PEAK LACCOLITH 

Southeast of the Hughesville stock is the Mixes 

Baldy-Anderson Peak laccolith, an igneous mass alB, The rhyolite of Granite Mountain invades the area and 

differentially tilts both the sedimentary rocks and the 

enclosed laccolith. C, With continued uplift, the sedimentary rocks and the laccolith finally break along part of the 

high-angle circumferential Granite Mountain fault. D, Erosion strips some of the sedimentary cover from the laccolith and the bysmalith. 
BYSMALITH 35 

most completely encivcled by a high-angle fault (fig. 

2). The laccolith is about 21/2 miles in diameter and 

rises some 2,000 feet above the floor of Dry Fork 

Belt Creek. Its thickness is unknown ; on cross section A-A' of figure 6 I have shown it as underlain by 

a younger pluton. 

Virtually the entire sedimentary cover has been 

stripped from the laccolith exposing the coarsely 

phenocrystk Wolf Porphyry (samples 6 and 7 of 

table 1). Only a very thin layer of steeply dipping 

Cambrian and Devonian beds is preserved around 

the north and northeast flanks. The laccolith, thus, is 

even more denuded than the Barker laccolith and is 

far better exposed than the Clendennin-Peterson laccolith. 

Locally, the evidence for the circumferential fault 

is tenuous. On the north and northeast the evidence 

is incontrovertible-the Cambrian and Devonian 

beds wrapped around the laccolith have been raised 

and are in fault contact with the Mississippian Madison Group. On the south and southeast, however, 

the Wolf Porphyry is juxtaposed with Madison 

strata. In that area the limestone beds adjacent to 

the porphyry are unbleached and unbaked, and the 

texture of the porphyry in contact with the Madison 

is as coarse as its texture distant from the contact, 

suggesting a fault relation. On the southwest the 

relations between the laccolith and adjacent strata 

are concealed beneath a pediment deposit, and on the 

west the laccolith is intruded by the Hughesville 

stock (fig. 6). Possibly the laccolith crystallized at 

depth and then was punched upward by a younger 

pluton; if so, it formed much like the trapdoor lac-

•coliths in the Little Rocky Mountains (Knechtel, 

1944). According to this interpretation the southeastern edge was raised the most, and the hinge was 

along the west edge (fig. 6, cross section A-A'). 

The general size, shape, and extent of such a pluton is uncertain. Presumably if a younger pluton did 

raise this laccolith, the resultant heat should have 

converted the sanidine of the laccolith to orthoclase. 

One possible explanation for the lack of such an 

inversion is that this younger pluton may have been 

relatively thin- possibly it was a sill some 600-1,000 

feet thick. (This thickness is implied by the stratigraphic displacement along the Mixes BaldyAnderson Peak fault; fig. 6, cross section A- A'.) 

The •Causative magma could have risen in a nearly 

vertical fracture and then spread ,laterally beneath 

the laccolithic floor. A second alternative is that this 

younger pluton may be ·part of a much larger subjacent body of magma and that it, in fact, did heat the 

floor of the laccolith and did modify the alkalic feldspar. If so, erosion has not as yet cut deeply enough 

to expose this basal part .of the laccolith. I favor this 

second alternative. 

A gravity map of the Barker-Neihart area suggests that the north edge of an elongate northeasttrending buried pluton does, in fact, underlie the 

Mixes Baldy- Anderson Peak laccolith (fig. 31). 

BYSMALITH 

The term "bysmalith," coined by Iddings (1898), 

has been used to describe wholly different igneous 

bodies. In •common usage (Am. Geol. Inst., 1960, p. 

41; Billings, 1942, p. 273), it describes a more or less 

vertical cylindrical body of igneous rock that has 

pushed the overlying strata up along one or more 

circumferential faults. Hunt (1956, fig. 31B), however, has applied the term to the kind of intrusions 

here called asymmetric laccoliths, but I use the term 

in its •customary sense. 

GRANITE MOUNTAIN BYSMALITH 

Granite Mountain, along the east edge of the 

quadrangle, consists of a plug of igneous rock encircled by a high-angle fault- the Granite Mountain 

fault. I have called this plug the Granite Mountain 

bysmalith; only its west flank is within the quadrangle (fig. 2, and Witkind, 1971). 

The plug is composed of the extremely fine 

grained rhyolite of Granite Mountain (sample 9 of 

table 1) which is in fault contact with steeply upturned Cambrian and Devonian beds (fig. 23). 

For most of its extent the circumferential Granite 

Mountain fault is ·concealed, but it is well exposed in 

a roadcut along the south flank of the mountain 

(Nlf2 sec. 7, T. 15 N., R. 10 E.). There, the fault 

.gouge is about 15 feet thick and consists of angular 

fragments of rhyolite and Park Shale firmly held in 

a finely comminuted matrix chiefly of the rhyolite 

and of .intermixed smaller amounts of shale. The 

fault dips valleyward at ang.les between 60 ° and 80°, 

but locally it is vertical. 

In several places dikes of felsic and mafic rocks 

follow the fault. As an example, a dike of the porphyry of Galena Creek follows the south flank of the 

bysmalith (east of quadrangle boundary), and 

nearby is a dike of minette-kersantite (fig. 23). 

How the bysmalith developed is uncertain. One 

possibility involves the gradual dilation of a laccolith until its roof, partly congealed, is punched upward by rising magma. Another interpretation is 

that large .segments of other ·previously emplaced 
36 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

FIGURE 20.-View from the crest of Granite Mountain looking westward across Lone Tree Park toward the southeast flank of the elongate anticline underlain by the Clendennin-Peterson laccolith. The configuration of the anticline is believed to reflect the laccolith, part of which is exposed at Clendennin Mountain. The nose of the anticline 

and congealed intmsions were punched upward by 

younger subja•cent masses of magma. Some of the 

dikes that follow the fault may be apophyses of this 

younger magma. 

BURIED PLUTON 

A very large ·compound pluton has intruded and 

raised the Precambrian crystaMine rocks that form 

the core of the Little Belt Mountains. In this quadrangle the pluton is completely concealed, and only 

here and there do small dikes and plugs of felsic 

rock give some idea of its lithology, Its northern 

flank is reflected by steeply tilted Cambrian strata 

whkh wrap around the Precambrian complex. 

Wherever exposed, these beds dip at high angles 

away from the comp.lex; dips average 70 °, but locally the beds are vertical or nearly so (•Witkind, 

1971). To the south, however, in the Neihart quadrangle, a cupola of the pluton is exposed along Carpenter and Snow Creeks (fig. 31). In those areas it 

is a compound mass that consists of at least four 

bodies of quartz rhyolite porphyry, all strikingly 

similar (Johnson, 1964), which have been mapped as 

the Snow Creek Porphyry (Keefer, 1969). The 

thickness of the pluton is unknown, but the presence 

of orthoclase in various of the quartz porphyries 

that form it implies that it is floorless. 

What is very likely the same pluton is exposed 

beneath a ·cover of metamorphk rocks in the nearby 

open 'Pit of the Silver Dyke mine. Here, Precambrian 

xenoliths in the porphyry, dikes of one or more porphyries in the Precambrian cover, and brecciated 

porphyry indicate that many :intrusive pulses 

formed the pluton. 

Extending northeastward from this point into the 

southwest corner of the Barker quadrangle is a zone 

of felsic dikes and plugs which intl'!ude the Precambrian rocks (fig. 31, and samples 13-15 of table 

1). These minor intr,usions , singularly like various 

of the rhyolite porphyries that ·constitute the Snow 

Creek Porphyry, form a zone about 1 mile wide and 

3% miles long that trends N. 50° E. through the 

SE1;4 T. 1'5 N., R. 8 E. (unsurveyed) (Witkind, 

1971). I interpret them as apophyses from the crest 

of the central part of the pluton. 

Stioll farther to the northeast in the San Miguel 

area (N% sec. 31, T. 15 N., R. 9 E., unsurveyed) of 

the Barker quadrangle, the hornblende-biotite gneiss 
BURIED PLUTON 37 

Peterson Mountain 

I 

Is formed by limestone beds of the Madison Group. The crest of the Barker laccolith shows along the skyline 

through the low pass-underlain by faulted Paleozoic rocks-between Mixes Baldy and Clendennin Mountain. 

country rock has been severely deformed and altered. There the rocks are intensely sheared and 

thoroughly impregnated with chlorite. No faults 

were detected in the San Miguel area, and this catadasis is attributed to localized deformation during 

empla·cement of the pluton. 

The geologic evidence, thus, suggests that the pluton is an oval body elongate to the northeast. Some 

recent geophysical work involving both ground gravity and aeromagnetic surveys confirms this interpretation (fig. 31) (Witkind and others, 1970). 

Where exposed, the pluton is mineralized and contains in different localities, molybdenum, galena, and 

sphalerite. In the past, significant amounts of silver, 

lead, and zinc have been mined from the pluton, and 

it seems likely that comparable amounts are still 

concealed elsewhere in the pluton (see section on 

"Buried Mineralized Pluton"). 

INDURATED ALLUVIUM 

Of the surficial deposits in the quadrangle, one 

unit-the indurated alluvium- is here considered in 

detail because it offers evidence on the relative ages 

of several igneous rock types. 

The indurated alluvium consists of a heterogeneous mixture of sedimentary, igneous, and metamorphic rocks which crop out in scattered deposits 

along the sides of Galena, Daisy, and Gold Run 

Creeks (fig. 6). These deposits, part of a fill that was 

once continuous across the valleys of these streams, 

either were not deposited or are not preserved downstream from the mouth of Gold Run Creek. 

In the upper reaches of Daisy and Galena Creeks, 

the indurated alluvium is preserved as thin discontinuous layers 2-3 feet thick. Southward along Galena Creek the deposit is thicker and finer grained. 

There, the base of the alluvium extends below the 

stream floor. 

Inasmuch as the base of the indurated alluvium is 

nowhere cleavly exposed, its total thickness is uncertain. None is preserved downstream from the mouth 

of Gold Run Creek, and its absence must be due to 

erosion by modern Galena Creek. At the mouth of 

Gold Run Creek, the bottom of the indurated alluvium-as indicated by truncated bedrock exposures-must have been at or near an altitiude of 

about 5,500 feet. Upstream and along the walls of 

Gold Run Creek, the top of the old alluvium, truncated by pediment deposits, is at a maximum altitude 
38 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

CONTOUR INTERVAL 400 FEET 

00 

..,. EXPLANATION 

'iii £{ "

v 

'; Porphyry of 

§ Galena Creek 

0 

>-< 

00 

1{ '6 G . ~ Quartz monzomte 

1;) of Hughesville +0 

"' H 

Wolf Porphyry 

Porphyry of 

Clendennin Mountain 

00 ..,. 

" 0 

" 

.~ 

..... 

~ 

~ 

I Tv~ ~ Vogesite 

G 

Syenite 

Barker Porphyry 

>-

0:: 

<( 

i= 

0:: 

w 

IFIGURE 21.-Map of the proximal end of the ClendenninPeterson laccolith showing relations between the Clendennin and Peterson faults and the laccolith. Paragon and 

Cape Nome mines probably followed veins localized along 

the northwest flank of the laccolith (which likely developed against the Clendennin fault). The Tiger mine 

UNCONFORMITY 

Mississippian units 

UNCONFORMITY 

Devonian units 

UNCONFORMITY 

Cambrian units 

UNCONFORMITY 

Precambrian units 

Contact, approximately located 

D 

u Fault, approximately located 

U, upthrown side; D, down thrown side 

Anticline 

Showing trace of axial plane and direction 

of plunge of axis 

Syncline 

Showing trace of axial plane and direction 

of plunge of axis 

50 

---'---

Inclined Horizontal 

Strike and dip of beds 

probably followed a vein localized along the southeast 

flank of the laccolith (which likely developed against the 

Peterson fault). The Harrison and Moulton mines are 

believed to have mined veins localized along the southwestward extension of the Mixes Baldy-Anderson Peak 

fault. All mines contained sulfide ores and are inactive. 
INDURATED ALLUVIUM 39 

FIGURE 22.-View looking westward from Mixes Baldy at 

the north and east flanks of Barker laccolith. The northeast flank of the laccolith is in intrusive contact-possibly 

as a result of a preexisting fault-with MadisQn strata, 

whereas all other flanks pass below Cambrian strata, 

of about 5,750 feet. Here the indurated alluvium extends down to and passes beneath the valley floor; 

the altitude of its base is unknown. If, however, the 

gradient of modern Gold Run Creek, 100 feet to the 

mile, is accepted as the gradient of its ancestor, then 

the altitude of the base of the indurated alluvium in 

this locality can be calculated to be about 5,600 feet. 

The 150-foot difference between exposed top and 

calculated base is probably an average thickness for 

the indurated alluvium. It seems doubtful that the 

alluvium exceeds 200 feet in thickness. 

Commonly, the indurated alluvium stands as a 

steep or nearly vertical wall, and is veined by manganese-stained fractures. Locally, steeply tilted 

blocks of the alluvium, 50-100 feet across, are enclosed in the main mass and invariably dip toward 

the embankment. These features suggest that they 

are slide blocks. 

In most exposures the indurated alluvium is a 

light-brown to grayish-brown, firm, well-cemented 

jumble of angular to well-rounded rock fragments 

which range in size from a quarter of an inch to 1 

foot; most, however, are about half an inch long. A 

few beds are composed of moderately well sorted 

sand and pebbles; crossbedding is common; and here 

and there cobbles of the indurated alluvium, as much 

Contact between laccolith (left) 

and Madison strata (right) 

chiefly the Pilgrim Limestone. Heavily wooded area in 

left foreground is part of the west edge of Hughesville 

stock. Rockslides in right foreground are part of the denuded southwest end of the Clendennin-Peterson laccolith. 

Irene Peak is the upturned edge of a resistant sill. 

as 6 inches in size and rather well rounded, are 

incorporated in other masses of indurated alluvium. 

The deposits were clearly laid down by streams. 

The indurated alluvium includes poorly sorted angular to subrounded cobbles of Wolf Porphyry, of 

the porphyry of Olendennin Mountain, and of the 

quartz monzonite of Hughesville. In these cobbles, 

many of the feldspars have been intensely altered to 

white clay. Grains and seams of pyrite and chalcopyrite are in fragments of both the quartz monzonite of Hughesville and the Wolf Porphyry. 

The matrix invariably is brown and consists of a 

motley of fine to coarse particles more or less 

cemented by silica and limonite. Much of it consists 

of minerals derived from the disintegration of the 

Wolf Porphyry, of the quartz monzonite of Hughesvine, and of various metamorphic rocks. As a result, 

round and angular quartz grains (from the Wolf(?) 

Porphyry), as well as altered alkalic and plagioclase 

feldspars (from the quartz monzonite.), are 

common. Small amounts of garnet (from the metamorphic rocks) are present. Small specks of pyrite 

are also scattered irregularly through the matrix. 

Mafi·c minerals are rare, presumably because most 

have been weathered and removed. 
40 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

0 1 MILE 

CONTOUR INTERVAL 200 FEET 

~~ L___j_ _ _j__J___-='~_j_---,1 

0:: 

0 

z 

EXPLANATION 

Minette-kersantite 

Barker Porphyry 

UNCONFORMITY 

~ z 

<( 

" 0.. "' ... ·s. 0.. 

"' 0. Lower part of Madison Group :s-·oo (j) 

0 "' ~·;; (j) UNCONFORMI TY 

"' 

~ (j) 

(j) 

~ 

" Three Forks Formation 

·.: "' 

0 z 0 :> <( 

~ "' 

... z 

"' 0. 0 0. Jefferson Dolomite > ;::J w 

0 .:: 

"' "' ;:a '2 

"" 0 

·- :> ~0 Maywood Formation 

UNCONFORMITY 

;::J"' 0. 

~] 

... 

u 

" 

s 

"' J l 

Pilgrim 

~ Limestone 

z 

B <( 

§ 0:: 

·.: Ill .0 ~ s Park Shale 

"' <( u u 

"' 'il 

"" 

~ j Older Cambrian units 

Contact, approximately located 

u 

D 

Fault, approximately located 

U, upthrown side; D, downthrown side 

/4 ___]__ 

Strike and dip of beds 

FIGURE 23.-The west flank of the Granite Mountain bysmalith. Base from U.S. Geological Survey, Mixes Baldy quadrangle, 

1 :24,000, 1961. 
EMPLACEMENT SEQUENCE OF THE INTRUSIONS 41 

The sedimentary rock fragments are mainly 

dark...,gray Paleozoic shale, but include some bluishgray limestone from the Madison Group. A few 

fragments of a coarse-grained sandstone, likely from 

the Flathead Sandstone, were also found. 

Ina:smuch as neither the Flathead Sandstone nor 

the metamorphic rocks are exposed in the headwaters of any stream now flowing into Barker basin, 

the presence of these fragments imply that the ancestral drainage pattern was somewhat different 

than it is now. The Flathead Sandstone and a broad 

variety of metamorphk rocks, however, are exposed 

south of Barker basin where they form part of the 

north flank of the upland that is domed by the buried pluton (Witkind, 1971). I suggest that the ancestral streams rising in this highland flowed northward into Barker basin and added their detritus to 

that of those other streams confined within the 

basin. This drainage pattern was disrupted as the 

Mixes Baldy-Anderson Peak laccolith was punched 

up. This laccolith effectively blocked access to the 

basin from the south, and the northward-flowing 

streams were for,ced into a new outlet through Dry 

Fork Belt Creek. 

Dikes of both felsic and mafic rock cut the indurated alluvium. For example, along both Galena and 

Gold Run Creeks, dikes of the rhyolite of Galena 

Creek, as much as 25 feet wide, intr:ude the alluvium. And a dike of vogesite, about 5 feet wide, cuts 

the alluvium along the north wall of Gold Run Creek 

(center sec. 18, T. 15 N., R. 9 E.). 

The presence of fragments of the Wolf Porphyry 

(from the Mixes Baldy-Anderson Peak laccolith), of 

the quartz monzonite of Hughesville (from the 

Hughesville stock), and of the porphyry of Clendennin Mountain (from the Clendennin-Peterson laccolith) indicates that these igneous bodies had been 

partly denuded before emplacement of the dikes. 

The ,gross pattern of intrusion suggested by the 

indurated alluvium and the dikes that cut it, therefore, is: emplacement of the old felsic and intermediate rocks, then their partial destruction to form 

the indurated alluvium, followed by the intrus~ion of 

the felsic and mafi,c dikes. The validity of this sequence is examined in the following section. 

EMPLACEMENT SEQUENCE OF THE JNTRUSIONS 

Although the relations between the indurated alluvium and the dikes that cut it suggest a general 

sequence of emplacement, there is still much uncertainty as to the exact sequence of emplacement of 

the individual intrusions. The available geologi'c evidence is fragmentary, and for some rock types inconclusive. Only here and there do crosscutting relations, chilled zones, or xenoliths demonstrate that 

one igneous rock is older than another (table 6). 

TABLE 6.-Tabular summary of known and inferred crosscutting relations in the Barker quadrangle 

[U =unsurveyed] 

Relative age of the intrusions 

Oldest Intermediate Youngest Field locality 

Intrusion Lithology Intrusion Lithology Intrusion Lithology rll 

= --- .2 Mixes Baldy- intruded Fingers of Intermediate Sees. 6 and 7, T. 

~ Anderson Peak by Hughesville (quartz monzo- 15 N., R. 9 E. ... laccolith stock nite of (U). bD Old felsic (Wolf Hughesville) = Porphyry) I Mixes Baldy- intruded Dikes and plugs Intermediate Sees. 7, 8, 17, 18, 

Anderson Peak by (quartz monzo- T. 15 N., R. 9 E ~ laccolith nite of (U). 0 Hughesville) ... 

c,) 

~ Hughesville stock Intermediate intruded Dikes Young felsic Sees. 6 and 7, T. 1 0 (quartz monzo- by (rhyolite of N., R. 9 E. (U). 

~ 

= nite of Galena Creek) 

Hughesville) 

Hughesville stock Intermediate intruded Dikes Mafic (vogesite, Sec. 6, T. 15 N., R (quartz monzo- by kersantite) 9 E. (U). 

5 

nite of 

Hughesville) 

Taylor Mountain Intermediate intruded Dike Mafic (vogesite) Sees. 11 and 12, T. 

laccolith (Barker by 15 N., R. 9 E. 

Porphyry) 

bD Mixes Baldy- Old felsic (Wolf intruded Dikes (1) Young felsic E~ sec. 18, T. 15 "C.S 

Q)..., Anderson Peak Porphyry) by (rhyolite of N., R. 9 E. 

:::= laccolith Galena Creek) · J;:CJ 

=:! 

~0 (2) Mafic S~ sec. 7, T. 15 

tl (vogesite) N., R. 9 E. (U). 
42 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

The geologic evidence suggests that there have 

been three intrusive episodes; two marked by the 

emplacement of mainly felsic rocks (old felsic (see 

section on "Old Felsic Rocks") and young felsic 

rocks (see ·section on "Young Felsic Rocks")) separated by one during which intermediate rocks (see 

section on "Intermediate Rocks") were emplaced. 

Many, if not all, of the mafic intrusions (see section 

on "Mafic Rocks") seem to have been emplaced after 

the intermediate intrusions, likely during the third 

intrusive episode. The potassium-argon data (fig. 

24) suggest that a localized resurgence of igneous 

activity occurred near the Hughesville stock, lowering the radiometric age of the stock and of several 

of the adja•cent intrusions (Marvin and others, 

1973). 

FIRST INTRUSIVE EPISODE 

During the first episode, it is likely that the Clendennin-Peterson and Mixes Baldy-Anderson Peak 

laccoliths were emplaced. This sequence began when 

a highly siliceous magma moved up a master conduit 

(now occupied by the Hughesville stock) (fig. 29) 

and started to form the Clendennin-Peterson laccolith. At the time-as indicated by the porphyry of 

Clendennin Mountain that forms the laccolith-only 

a few phenocrysts of mafic minerals and feldspar 

had crystallized. 

As the laccolith grew, a time came when increased 

resistance to the addition of magma forced the 

magma to seek new conduits. One conduit was found 

to the southeast, and a new pulse of magma from the 

same chamber moved laterally into the available 

space and be~an to form the Mixes Baldy-Anderson 

Peak laCJcolith. By this time many more phenocrysts 

had formed, and most of them had become large. 

This magma solidified to become the Wolf Porphyry, 

mineralogicaJ,ly and chemically like the porphyry of 

Clendennin Mountain, but much coarser. 

SECOND INTRUSIVE EPISODE 

After the development of the Mixes BaldyAnderson Peak laccolith, a magma of intermediate 

composition, now represented by the Barker Porphyry, used the same master conduit as the previous 

felsic magma to form the Barker laccolith. In time 

other channels were used to form such large intrusions as the Butcherknife Mountain, Taylor Mountain, and Dry Wolf laccoliths, as well as in the inferred ·laCJcolith that underlies the Limestone Butte 

dome. 

Subsequently, a somewhat less siliceous phase of 

the magma-similar in composition to the quartz 

monzonite that now forms the Hughesville stockmoved through the master conduit and formed various floored intrusions. Among these are the Otter 

laccolith, the expanded sill northeast of Irene Peak, 

and the various latite porphyry plugs and dikes that 

cmt the Mixes Baldy-Anderson Peak laccolith. 

The final stage in this episode was the ·crystallization of the magma in the master conduit, exposed 

now as the HughesviUe stock. 

FORMATION OF INDURATED ALLUVIUM 

After these intrusions were emplaced, part of 

their sedimentary cover was removed and the igneous rock exposed. The resultant sedimentary and 

igneous debris was deposited in a partly enclosed 

basin to form the indurated alluvium (p. 41). 

THIRD INTRUSIVE EPISODE 

A highly siliceous magma-whose composition is 

represented by the young felsic rocks-gave rise to a 

compound pluton which further deformed the rocks 

in the area. The southern edge of the magma elevated the Precambrian complex in the southwest 

corner of the quadrangle. The northern edge of the 

magma, em·placed below the floor of the Mixes Baldy-Anderson Peak laccolith, punched up the solid 

igneous laccolithic plug, even as it sent dikes cutting 

through the Hughesville stock and the indurated alluvium. And another apophysis from the northern 

edge may have formed the Granite Mountain bysmalith. Finally the small lamprophyric intrusions 

were emplaced, the earliest of them overlapping the 

young felsic rocks in time and the composite dikes in 

space. 

RADIOMETRIC AGES OF THE INTRUSIONS 

In an attempt to fix both the time and sequence of 

emplacement of the various intrusions, 16 samples 

of igneous rock were submitted for radiometric age 

determinations. Details of the study have been reported on elsewhere (Marvin and others, 1973). The 

location of the 16 samples analyzed and the pertinent data derived from their analyses are given in 

figure 24 and table 7. 

It was concluded that the great majority of the 

intrusions were formed during the Tertiary, most 

likely the Eocene, in the time span from 54 to 48 

m.y. ago. The time sequence of the three intrusive 

episodes (see section on "Emplacement Sequence of 
MINERAL DEPOSITS 43 

the Intrusions") recognized in the field could not be 

resolved with the potassium-argon ages available. 

Local resurgence of igneous activitJ occurred near 

the Hughesville stock about 42 m.y. ago resulting in 

lower ages for these intrusions. 

MINERAL DEPOSITS 

Mining began in this region with the discovery of 

placer gold in Yogo Creek in 1865.1 Hostile Indians 

drove off the first prospectors, and active prospecting was not resumed until 1879. In October of that 

year Buck Barker and Patrick W. Hughes, grubstaked for a trapping expedition by U.S. Senator 

Thomas C. Powers, came upon an outcrop of what 

they thought was tin where the Block P vein crosses 

Galena Creek. Their "tin" was quickly recognized as 

galena, and the Barker and Gold Eagle claims were 

staked on this discovery. The news of the strike 

spread quickly, and the Barker area boomed. Prospects were staked and mines opened along promising 

veins. The ore, reportedly of high quality, was 

hauled by wagon across the Kibbey Divide (fig. 1) to 

Fort Benton on the Missouri where it was loaded 

onto steamers, ferried down the river, and eventually shipped to smelters ov·erseas. 

To reduce haulage costs two small smelters were 

constructed, one at Hughesville and the other at 

Clendennin-now known as Barker. Neither was 

used extensively, and by 1883 both were dismantled. 

Mining declined slowly untirl 1891 when a railroad 

spur was constructed to Barker from Monarch. In 

response to this stimulus several of the larger mines 

increased production. The silver panic of 1893 

forced most of the mines to close, and shortly there- ' 

after the railroad spur from Monarch was disman-· 

tied. The smaller mines 'continued to operate until 

the financial depression of 1897 ended all mining 

activity. The community turned to logging operations to survive. In 1902, Senator Powers formed the 

Block P Mining Co., named after the flag design of 

his Missouri River steamboats. 

The Block P and several other mines in the Barker area were operated intermittently on a small 

scale until 1927 when the St. Joseph Lead Co. purchased the Block P Mining Co. The new owners rebuilt the railroad spur and constructed a new 400-

ton selective flotation 'Plant just ~south of Barker at 

the junction of Galena Creek and the Dry Fork Belt 

Creek (fig. 6). To connect the Block P mine with the 

1 The cited historical data come from various sources, mainly Robertson 

and Roby's (1951) Bureau of Mines report on the mines of Judith Basin 

County. 

plant, a 10,250-foot aerial tramway was constructed. 

Mining and milrling continued until1930 when unfavorable market conditions forced the suspension of 

mining wctivity. Mining was resumed in 1941 but 

was finally ended in 1943 by :government order, 

mainly because the mine was considered to be a marginal producer and lead was no longer a critical 

metal (Woodward and Luff, 1945, p. 400-401). In 

1944, the mill was dismantled, the railroad tracks 

removed, and the railroad right-of-way abandoned. 

In that year the Thorson Brothers and Brazee purchased part of the holdings of the St. Joseph Lead 

Co. and produced a smaH amount of ore. 

In 1946, the Block P properties passed into the 

hands of the American Smelting and Refining Co. 

The Thorson Brothers and Brazee continued mining 

the upper workings under a lease agreement until 

1952. 

The amount of ore produced since then has been 

small; most of it has come from the reopening of 

former mine drifts by various miners, who continue 

to live in and near the area in hope that a new strike 

will revitalize the district. 

BARKER MINING DISTRICT 

About $6 million worth of metals, chiefly silver, 

lead, and zinc, has been recovered from mines in the 

Barker quadrangle. Most of this ore ~came from 

those mines in and near the HughesvHle stock-the 

lllnor.ganized Barker (Hughesville) mining district 

(fig. 25). Several other mines in the quadrangle are 

~Jome 31;2 miles south of the Barker district and are 

grouped as the San Miguel mining district. Very 

little ore has been produced from these mines. 

My attention will go largely to the geologic relations of the ore deposits in the Barker mining district. 

Geologically, the heart of the district is the 

Hughesville stock (see section on "Stock"). All the 

mines that have produced significant tonnages of 

sulfide ore are either within the stock or along and 

near its mar.gins. The major veins are near its 

center; these dwindle in tenor and size toward the 

margins. Beyond the stock the ore deposits are 

small; several are alined along the laccolithic flanks 

of the Clendennin-Peterson and Mixes BaldyAnderson Peak laccoliths, seemingly localized in the 

various faults that limit these laccoliths (see section 

on "Clendennin-Peterson Laccolith" and fig. 21). 

For purposes of discussion the ore deposits have 

been grouped as those formed ( 1) in fissure veins in 
44 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

110°45' 110°30' 47°15',----,------------------------,-------------,-----------------------------------------------r--. 

,' 

,, \\ ,' 

-' LIMESTONE BUTTE 

DOME 

EXPLANATION 

u ------ D 

Fault 

U, upthrown s·ide; D, 

downthrown side 

/ 

/ 

) 

N. 

T. 16 N. 

47"00' 

\\\' 

\ ,, ' 

,,~ 

OTTER 

LACCOLITH ,II II_.. 

\\ - :''' ' 

-.-,,II I I II\ 

BARKER LACCOLITH 

\ 

l~o !::. /.' 't ,,,' -···-......_··· 

// 1,,\ D T . ~ ;,.--U-.., •'GRANITE MTN FAULT \ 11 ' ,,,\\''"''''''''' . \ r··· __ ,,,,,'' ,, ~~\ 1 ' MIXES BALDY- \ .- ',, ''' '\~ ANDERSON PEAK ', 

"''Qt \S LACCOLITH TAYLOR MOUNTAIN 

DU 

'\..P LACCOLITH 

~<o •3 EJ 

e14 "'?, 4 <::j - ~~13 ' • /'> /1 ,~ 

/I \' 

111 I I I I I I 11/11 I I I 1 \

1 

~ Fork 

1'''''''''''''''''''1'''''1'''1 fett ,1,11 ,,, 

\I II I 

1 I'.-

\I\ I I ~ 

R. 

Pre-Belt crystalline rocks 

underlain by felsic pluton 

8 E. 0 

'--. ·-r' 

: 

~11 t~ ~R~_J, /~ \\ 

:. 

-:::. 

::: 

2 

.7 'II IJJ IIIII I Ill\ II I I\ I 

... ( .. ?1!!:!:!!:~. 

111111\1111,, .. 1,,,, ·~ , ~~~ . I ). ,,,,,, ... ,' I/ 

~~~ ~ 

.::: 

:. 

-

-

BUTCHERKN I FE MOUNTAIN 

LACCOLITH 

\ , .... ,, 

3 MILES R. 9 

:: 

\ ,, ,, ,, 

T. 15 N. 

FIGURE 24.-Sample localities for radiometric age determinations of various intrusions in the Barker 

quadrangle. Ages are given in table 7 on facing page. 
No. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

Labo- Field 

ratory No. 

No. D- WL1032 210 

1922 575 

1030 208 

1924 579 

1589 404 

1959 582 

1925 580 

1031 209 

1029 31 

1911 103 

BARKER MINING DISTRICT 

TABLE 7.-Radiometric ages of various intrusions in the Barker quadrangle 

[Analysts: R. F. Marvin, H . H. Mehnert, Violet Merritt, and Wayne Mountjoy] 

Decay constants: K" :>., = 0. 584 Xl0-10 per year M ~ 4. 72 XlO-to per year Atomic abundance: K•'= 1. 19 XlO-• 

K,O% 

Intrusion Rock name Material analyzed (avg.) 

Clendennin-Peterson Porphyry of Clendennin { Biotite _________ ____ _ 8.66{ laccolith Mountain. Sanidine _____________ 4.80 ___ _ do ________ _______ ____ do ________ _______ Biotite __ ____ ________ 8.54 

Mixes Baldy- Anderson Wolf P"phm--- ____ ~ Biotite ____ _______ ___ 8.75 

Peak laccolith. Sanidine ________ __ ___ 6.59 ____ do _______________ ___ _ do _______________ Biotite ______ ___ ____ _ 7.58 

Hornblende 2 _ _ ___ _ _ _ 0.904 

Barker laccolith _____ __ Barker Porphyry______ Biotite ___ ___________ 8.18 Sanidine ___ __ ________ 9.94 ____ do _____ ____ __ ____ ____ do__ ___ __ __ ______ Biotite _____ ______ ___ 7.90 SilL __________ _____ __ ____ do ________ _______ Biotite ______ _____ ___ 7.20 

Hughesville stock __ ____ Quartz monzonite of i Biotite_- ---------- - - 9.05 

Hughesville. Orthoclase ___ ________ 8.81 

Biotit•--------------~ 8.06 

8.10 Plug __________ _______ Shonkinite ____ _______ -1 Orthoclase _______ _ - __ 8.74 

8.42 

Barium orthoclase(?) _ 7.68 

Granite Mountain Rhyolite of Granite Whole rock _____ ___ __ 4.10 

bysmalith. Mountain. 

Radiogenic argon 

(moles/ 

gm.) 

< xlO-"l 

7.218 

7.116 

3.705 

6.438 

6.054 

4.420 

5.353 

0.6248 

5.907 

7.247 

5.875 

5.706 

6.075 

5.931 

6.719 

5.876 

8.257 

8.336 

5.215 

2.991 

Percent 

radiogenic argon 

92 

92 

92 

85 

86 

87 

91 

86 

80 

89 

80 

94 

81 

86 

82 

83 

93 

92 

94 

84 

1927 589 ___ _ do ____ ____ _______ ____ do ___ ______ __ ____ Whole rock (Rb / Sr) ____________ _______ _______ 

1923 576 Composite dike ____ ___ Kersantite ______ __ ____ Biotite________ ___ ___ 8. 84 5. 802 87 

1960 583 SilL ___________ __ __ __ 

1590 417 Dike ___ ____ __________ 

1591 450 Plug __ ___ __________ __ 

1926 581 Dike _____________ ____ 

' Standard deviation. • Potassium determined by isotope dilution. a Z. E. Peterman, written commun., 1970. 

Vogesite____________ __ Hornblende 2 _____ _ _ __ 

W .,thmd vog.,ite ___ ~ Biotite_----- -------- Sanidine ________ _____ 

Snow Creek(?) Biotite ________ ___ ___ Porphyry. Orthoclase _______ ____ __ __ do_ __________ ____ Whole rock __ ______ __ 

Sample No. Rb (ppm) 

WL-589-2 529 

WL-589-4 523 

Srn (ppm) 

8. 51 

8.91 

Rb" Sr" 

179.9 

169.8 

Sr 87/ Sr 86 

0. 8341 

0.8269 

0.674 0.5841 72 

8.56 5.430 93 

11.02 6.807 94 

7.16 5.451 82 

6.16 4.566 87 

4.36 3.453 92 

45 

Calculated age (millions of 

years) 

±2otl 

55.6±2.3 

54.9±2 .3 

51.6±1.8 

50.4±1.9 

46.4±1. 6 

44 9±1.5 

47.3±1.8 

46.3±1. 7 

48.3±1. 6 

48.8±1.7 

49.7±2.3 

53.0±2.0 

44. 9±1. 5 

45.1±1. 5 

51.3±1. 5 

48.5±1.5 

61.0±1.8 

65.9±2.0 

45. 4±1.4 

48.8±2.0 

3 50.0±5.0 

44. 0±1. 7 

57. 8±2.2 

42. 5±1.3 

41.4±1.2 

50. 9±1. 7 

49.6±1.7 

52. 9±2. 0 

the stock, (2) in contact-repla·cement deposits along 

the stock's margin, and (3) along contacts between 

the laccoliths and the intruded sedimentary rocks. 

The fissure veins in the stock have provided, by far, 

the most ore. 

the northeast set and the Transverse vein follows a 

northwest-trending fracture (fig. 26). Most of the 

mines west of Galena Creek followed veins that 

trend northwestward, whereas most of the mines 

east of Galena Creek followed veins that trend 

northeastward. 

FISSURE VEINS IN THE STOCK 

Many of the fissure veins in the stock formed in 

fractures of the two systems that have been discussed. One system of joint sets trends N. 60° E., 

and N. 40 ° W.; the other, a northerly set and its 

companion set, trends easterly. In the Block P mine, 

for example, the major vein is concave to the north 

(Spiroff, 1938, fig. 3); this fact indicates that the 

ore minerals were deposited in the northwest-northeast system. Other veins in the Block P mine follow 

the northwest-trending fractures (Spiroff, 1938, p. 

559). In the Liberty mine both the northeast- and 

northwest-trending fractures are also followed by 

major veins-the Liberty and Angela veins follow 

96 ~18 9 0- 73 - 2 

In .general, all joint sets are followed by both 

dikes and veins, and locally the dikes have one or 

more veins along their flanks (Weed, 1900, p. 353; 

Spiroff, 1938, p. 559; G. VR. McBride, written 

commun., 1967). Some dikes are also •cut by veins 

(fig. 12). 

Further, the veins are broken by a postmineralization fracture set which trends N. 10 ° W. (Spiroff, 

1938, p. 560; G. VR. McBride, written commun., 

1968). The stock, thus, appears to have been broken 

repeatedly: one or more times before the dikes were 

empl3iced, again after the dikes solidified, and again 

after the veins formed. Each of these minor deformational episodes may have been caused by the re-
46 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

47'05' 

' /I 

\ '·-

I 

ti ! ~ i / 

:0 Appr,bx imat!i' margin 

· Hugh~Svolle stock 

I i 

i 

i 

/ 

'· 

.. / ··· _)! I 

i . I /1 '·· ) ·'·;: 

\ 

i 

i 

I 

i 

Vein 

Dotted where projected 

CONTOUR INTERVAL 200 FEET 

'...__, ......... .......__. __ 

FIGURE 25.-Mines in and near the Barker mmmg district. Almost all were inactive as of August 1968. Base from U.S. 

Geological Survey, Barker and Mixes Baldy quadrangles, 1: 24,000, 1961. Key to lettered symbols given on opposite 

page. 
BARKER MINING DISTRICT 

Symbols used in figure 25 

A. "A" tunnel of Block P. L. Liberty tunnel of Liberty. 

AE. Annie E tunnel of Liberty. LC. Last Chance tunnel of Liberty. 

A2. August No. 2 tunnel of Liberty. 

B. "B" tunnel of Block P. 

BC. Barker crosscut of Block P. 

BF. Bon Ton- Fairplay. 

BS. Barker shaft of Block P. 

C. Chesapeake tunnel. 

LS. Lucky Strike. 

M. Mayflower tunnel. 

MA. Maytee tunnel of Block P. 

MC. McKinley. 

ME. May and Edna. 

MG. Magnolia. 

CA. Carter. 

CN. Cape Nome. 

MM. Middle tunnel of May and Edna. 

MN. Myrtle-Navy. 

CT. Cape Nome tunnel. 

CS. Carter shaft. 

DK. Dockter Kalloch. 

MO. Moulton . 

MT. Main tunnel of Liberty. 

MV. McVeda. 

DT. Danny T tunnel of Liberty. 

E. Equator tunnel of Block P. 

F. Frances tunnel of Liberty. 

Ml. Marcelline tunnel No. 1 of Liberty. 

M2. Marcelline tunnel No. 2 of Liberty. 

0. Oasis. 

FF. Double Eff. P. Paragon. 

H. Harrison. PH. Philharmonic. 

peated emplacement of magma (see sedion on "Localization" and fig. 29). 

The fissure veins are sinuous tabular bodies as 

much as 6 feet thick which dip steeply. Commonly, 

they pinch and swell, and in places dwindle to mere 

leads a few inches thick. Here and there they split 

for short distances and then -coalesce to enclose a 

wedge of country rock. 

Locally, they show excellent nearly symmetrical 

crustifi:cation that indicates at least three paragenetic stages (fig. 27 A) . During the first stage (I) , 

quartz and pyrite and small amounts of .sphalerite 

were deposited on the fradure walls. In the second 

stage (II), the dominant ore minerals of the district, 

argentiferous galena and sphalerite, formed; and 

during the third stage (III), various gangue minerals, mainly barite and rhodochrosite, filled the remaining voids. Sparse ore minerals were also deposited during this stage. Pyrite apparently was deposited during all three stages. 

Subsequently, these veins were fractured and 

were displaced a few millimeters; and veinlets of 

rhodochrosite, barite, and pyrite former1 in these minute fractures (fig. 27B, C). 

Many of the veins are filled, but in places their 

centers contain small vugs lined with well-developed 

•crystals of pyrite, .galena, and sphalerite. 

\ 

\ 

\ 

\-Fault? 

\ 

\ 

PR. Plymouth Rock. 

PT. Paragon tunnel. 

PW. Pride of the West. 

PX. Phoenix. 

QH. Queen of the Hills. 

S. Sinclair. 

SB. Silver Bell. 

SC. St. Charles. 

SD. Snow Drift tunnel. 

SL. St. Louis. 

SM. Shaft of May and Edna. 

SP. St. Patrick. 

ST. Spruce tunnel. 

T. Thorson tunnel of Block P . 

TI. Tiger. 

TW. TW. 

47 

WS. Wright and Edwards shaft of Block 

P. 

200. 200-foot level, Wright and Edwards 

shaft of Block P. 

of Liberty vein 

N 

0 100 200 FEET 

Most of the ore minerals are hypogene; very few 

supergene minerals are present. Argentiferous galFIGURE 26.-The pattern and trend of major veins in the 

Danny T tunnel of the Liberty mine. Modified from sketch 

supplied by G. VR. McBride (written commun., 1967) . 
48 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

(/) Ill :J c:: c. Q) 

N Ill 

i~ 00 

~ "0 :J'- c:: c:: cr~ Ill 

'iii "011) Q) (/) c::.r:. .... 

K II) c. ·;;:: (/) 

Q)Q) ~ 

Ill 

tii ~E .r:. >-o c. ~ 0..1/l (/) 

I 

I II 

I 

I 

I 

I 

20 mm 

B 

Ill (/) 

c:: :J 

Q) 0. 

I Ill N !!2 00 

.... 

Ill Q) "0 i.~ c:: :J .... Q)..., Ill cr~ .!: 'iii Eo "011) Q) Q) ........ .... c::.r:. Q) J: .i: ·;;:: II) c. :J (,) Ill Q) (/) 

ooo.c Ill Q)Q) 

c::"O-o .r:. ~E Ill 0 c:: c. >-o 

CJflll (/) 0..1/l 

III II 

FIGURE 27.-Explanation on opposite page. 

~ c:: 

(/) 

(/) 

E 

= Ill 

~ 

I 

I 

I 

Fracture filled with 

rhodochrosite 

Area enlarged in B 

c 
BARKER MINING DISTRICT 49 

ena, sphalerite, and pyrite are the principal ore minerals. Others that have been found by me or reported by other geologists (Spiroff, 1938; G. VR. 

McBride, oral commun., 1967; J. J. Wallace, Jr., 

written commun., 1968; H. D. Hess, written 

commun., 1953) follow: 

Common 

Barite 

Chalcopyrite 

Marmatite 

Rhodochrosite 

Rare 

Anglesite 

Arsenopyrite 

Azurite 

Bornite(?) 

Cerrusite 

Covellite 

Gold 

Malachite 

Marcasite 

Molybdenite 

Scheelite 

Siderite 

Tetrahedrite 

Wurtzite 

Most of the ore minerals were deposited under 

mesothermal (intermediate-temperature) conditions, 

but three of them, molybdenite, scheelite, and wurtzite, imply hypothermal (high-temperature) conditions. In the Lucky Strike mine (LS of fig. 25), a 

small veinlet of molybdenite and quartz ~cuts the 

stock. Blebs and streaks of molybdenite disseminated in shattered and brecciated quartz rhyolite are 

found as fragments in the mine tailings. Molybdenite has also been reported from the Frances tunnel 

( F of ftg. 25) of the Liberty mine. From the Frances 

tunnel, 2 tons of molybdenite-bearing rock was 

mined, but not shipped, from a 3- to 4-inch-thick 

eastward-trending vein (G. VR. McBride, oral 

commun., 1966). 

A few grains of s·cheelite have been identified in 

samples collected at the 10- to 20-foot depth from a 

newly opened prospect on the St. Patrick-Double Eff 

properties (J. J. Wallace, Montana Bur. Mines and 

Geology, written commun., 1968). And wurtzite has 

been identified by Bureau of Mines personnel in 

samples collected from the Transverse vein of the 

FIGURE 27.-Crustified vein, Barker mining district. Photographs by R. B. Taylor. A, Crustified fissure vein from the 

Liberty mine showing three paragenetic stages. I. Pyrite, 

quartz, and a little sphalerite deposited. II. Argentiferous 

galena and sphalerite formed. III. Remaining voids filled by 

rhodochrosite and barite. B, C, Vein broken and slightly 

offset by a minor fracture which is now filled with rhodochrosite. G, galena; S, sphalerite; P, pyrite; Q, quartz; R, 

rhodochrosite. 

Liberty mine (H. D. Hess, U.S. Bur. Mines, written 

~commun., 1953). 

Zones of intensely altered rock flank the sulfide 

veins. On the surface the altered zones appear as 

bands 10-20 feet wide compos.ed of strongly sericitized rock much stained by limonite. Alteration has 

been severe, for both the stock and dike rocks are 

converted chiefly to quartz, seritCite, and pyrite. Virtually all the normal rock-forming minerals, except 

quartz, have been changed. Both the alkalic and the 

plagioclase feldspars have been converted almost 

completely to a fine-grained mixture of quartz and 

sericite. In places the alteration has been so complete that the original texture of the feldspars has 

been wholly obliterated. 

It is difficult to estimate how much of the stock 

has been altered; a conservative estimate is that between 20 and 30 percent of the rock shows significant effects of hydrothermal alteration. Locally, the 

intensely altered rocks and the related sulfied veins 

are cut by small veinlets of mosaic quartz indicating 

a late-stage episode of silicification. Whether the 

quartz-molybdenite veinlets are similarly cut is unknown. 

Neither kaolinite nor clay minerals have been 

found in the altered rocks of the Hughesville stock; 

likely their absence is due to the temperature· of the 

hydrothermal solutions. Experimental evidence suggests, among other possible factors, that at a depth 

in the earth's crust of about 10,000 feet, kaolinite is 

not stable above 400 o C, whereas the quartz-sericite 

couple remains more or less unchanged to 640°C 

(Creasey, 1966, p. 55). This absence of kaolinite is 

explicable, then, if the temperature of the hydrothermal solutions fell somewhere between these two 

values. 

To the south in the Neihart area, there is much 

evidence of potassic alteration (Johnson, 1964, p. 

60). Orthoclase has been added to the Precambrian 

crystalline rocks as well as to the Tertiary intrusions. Comparable feldspathization has not been 

found in the Barker area. 

FISSURE VEINS BEYOND THE STOCK 

Little is known about fissure veins outside the 

stock. The Paragon and Cape Nome mines along the 

northwest flank of the Clendennin-Peterson laccolith 

and the Tiger mine along its southeast flank are 

believed to have followed veins localized along the 

Clendennin and Peterson faults respectively (fig. 

21). In like fashion the Harrison and Moulton 
50 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

mines, along the northwest flank of the Mixes 

Baldy-Anderson Peak lac,colith, probably mined 

veins that followed the circumferential Mixes 

Baldy-Anderson Peak fault. It seems likely that the 

ore solutions moved up through the stock and then 

migrated along the preexisting faults using them as 

channel ways. 

CONTACT -REPLACEMENT DEPOSITS 

Contact-replacement deposits have formed along 

the contact between the Hughesville stock and the 

limestone beds of the Madison Group. These were 

tapped by the May and Edna mine and the M~cKinley 

mine (ME and MC of fig. 25). The major ore extracted from these deposits was massive galena 

whi,ch, in contrast to that in the fissure veins, carried very low si,lver values (6-8 ounces versus 20-40 

ounces per ton) (G. VR. McBride, written commun., 

1968). 

Elsewhere in the Little Belt Mountains, blanket 

like replacement deposits of iron and manganese loA 

0 50 

cally follow contacts between laccolithic flanks and 

overlying sedimentary beds. These appear to be tabular bodies which more or less conform to the intrusion. So, the McVeda mine (fig. 28) on the southeast 

flank of the Clendennin-Peterson laccolith taps such 

a deposit. A similar deposit is exposed in the open 

pit of the Whittaker mine east of the Barker quadrangle (sec. 7, T. 14 N., R. 11 E., Judith Basin 

County) (Westgate, 1920). 

TENOR 

Exactly how much ore has been produced from 

the Barker mining district will never be known, for 

early records are few and notoriously inacCJurate. 

During the period 1921-48, however, about 416,000 

short tons was extracted, mainly from the Block P 

mine. From this were recovered approximately 4,000 

ounces of gold, 2, 700,000 ounces of silver, 850,000 

pounds of copper, 46 million pounds of lead, and 18 

million pounds of zinc (Robertson and Roby, 1951, 

p. 7). 

B 

100 FEET 

EXPLANATION 

Porphyry of 

Clendennin Mountain 

Blanket deposit of 

iron and manganese; 

many clay seams and 

some altered igneous 

sills 

Madison ~ Group Contact --+-t-+-t-+- -+- + + ~ Narrow-gage track Attitude of beds Dashed where subsurface 

FIGURE 28.-Mc Veda mine along southeast flank of the Clendennin-Peterson laccolith. A, Geologic relations in and near 

the mine. Much of the area is covered by boulder fields weathered from the laccolith. B, Inferred geologic relations. 

A blanketlike deposit of iron and manganese is adjacent to a sill in limestone mantling the southeast flank of the 

laccolith. 
BARKER MINING DISTRICT 51 

The dominant metal is lead; and galena, its source 

mineral, probably contains most_ of the silver although some may be carried by sphalerite and pyrite. Silver minerals are rare in the district. Polished 

sections of ore show no silver minerals ; this lac}{ 

implies silver either is very finely admixed or is 

•carried in solid solution by the other ore minerals. 

Minor amounts of gold have been produced. No 

gold minerals were found in the polished sections, 

and here too, I suspect that the gold is carried by 

other minerals, possibly the pyrite. 

Any estimate concerning the tenor of the ores produced from the fissure veins in the stock is based on 

the production records of the two major mines in 

the area: the Block P and the Liberty. It is regrettable that the information is contradictory. As an example, MacKnight (1892) reported that in the early 

1890's the Block P produced ore that contained values of 40-65 ounces of si·lver and 40-48 percent lead 

per ton. The production data for the mine for the 

period 1915-48 (table 8), however~ indkate a much 

lower tenor. Of the 406,000 tons of ore produced, the 

weighted average values recovered were close to 61;2 

ounces of silver and 5 percent lead per ton. 

There s·eems to have been some drastic variations 

in metals produced from time to time (table 8). Although in several periods, the recovered values wer.e 

as high as 31 ounces of silver and 29 percent lead 

·per ton, during other periods the values dipped to as 

low as 5 ounces silver and 4 percent lead per ton. 

This wide variation in tenor suggests to me a major 

change in mining operations rather than a change in 

the veins that were mined. The higher values probably represent careful selective mining of the veins, 

whereas the lower values may indicate dilution of 

vein material with wall rock. If this is true, this 

implies that the metal content of the veins alone is 

probably closer to the higher values. This higher 

value, which is supported by the production data 

available for the Liberty mine, indicates that for the 

period 1900-64 the produced ore contained a 

weighted average of 24 ounces of silver and 30 percent lead per ton (table 9). These v3ilues, I believe, 

more closely approximate the tenor of veins in the 

district. 

AGE OF THE ORES 

It seems likely that there have been at least two 

episodes of sulfide ore mineralization: one older than 

the young felsic dikes, and a second younger than 

the dikes. This is suggested by field ·relations: a dike 

of the porphyry of Galena Creek, exposed near the 

Sinclair mine (S of fig. 25), contains fragments of 

galena (as well as :xenoliths of the stock). The implication is that some .galena was in existence prior to 

the time the young felsic dikes were emplaced. But 

other veins are younger than these dikes, inasmuch 

as several dikes are cut by the veins. The sulfide vein 

that cuts the Annie E composite dike is an example 

of this group (fig. 12) . 

I believe that most of the ores were formed during 

this younger episode of mineralization, likely from 

mineralizing solutions expelled during the crystallization of the salic magma responsible for the felsi•c 

dikes. The time of emplacement of the high-temperature minerals is uncertain. 

Some evidence indicates that parts of the stock 

were broken after the veins were formed. For example, in the Block P mine a vein of steel galena is 

adj3icent to a felsic dike (G. VR. McBride, written 

commun., 1968). I interpret this relation to mean 

that a vein of massive galena crystallized alongside 

the previously formed dike. Then, as the stock was 

jostled-possibly during a local resurgence of igneous activity-the galena was mylonitized and recrystallized to steel galena. Inasmuch as not all veins 

contain steel galena, the movement in the stock 

TABLE B.-Production data for the Block P mine 

[Modified from data supplied by Robertson and Roby (1951, p. 18)] 

Period Ore 

(tons) 

Gold Silver 

Ounces 

Copper Lead Zinc 

Pounds 

Recovered Ounces Recovered Ounces Recovered Percent- Recovered Percent- Recovered Percent- per ton per ton age age age 

-------------r------l--------l------l--------l------l--------l------l---------------------1------

1915-20_------------- 1921-30_ ------------- 1942-45_------------- 1947-48_ -------------

1,560 

316,054 

87,963 

275 

66.11 

2,877.02 

378.00 

11.00 

TotaL ___ ------ 405,852 3,332.13 

Metal content; 

0.04 

.009 

.004 

.04 

weighted average ____ ---------- ------------ 0.008 

49,247 

2,090,173 

430,569 

8,235 

2,578,224 

31.0 

6.6 

4.9 

29.9 

6.4 

6,469 

550,911 

216,315 

• 1,417 

775,112 

0.21 904,733 . 09 34,964.584 

.12 6,689,323 

.26 191,777 

42,750,417 

0.10 

29.0 - 5.5 14,579,545 

3. 8 3,209,200 

34.9 59,653 

17,848,398 

5.3 

2.3 

1.8 

10.8 

2.2 
52 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

TABLE 9.-Production data for the Liberty mine 

[Modified from data supplied by Mrs. G. VR. McBride, Faith Mining Co.] 

Gold I Silver Copper I Lead I Zinc 

Ore - (dry weight) 

Vein P~oductive years Ounces Pounds 

Pounds Tons Re- Ounces 

covered per ton 

Liberty ___________ 1900, 1916, 1917, 192L _________ 1,151,553 575.8 24.60 0.04 Emerald ___________ 1921, 1924, 1927-- 812,254 406.2 8.96 .02 August No.2 ______ 1921-1924, 1926, 

1933, 1935 __ - -- 558,719 279.2 10.44 .04 

Danny T ---------- 1923, 1936-1947, 

1950, 1951, 1953, 1958 _____ 496,261 248.3 5.90 .02 Marcelline _________ 1939, 1941, 1963, 1964 __________ 359,831 179.9 3.80 .02 

Queen of the Hills __ 1916.----------- 88,349 44.2 .40 .01 

TotaL _______________________ 3,466,967 1,733.6 54.1 ----------

Metal content; weighted average ______ ----------- --------- -------- 0.03 

1 Based on incomplete data. 

probably was differential because some parts were 

more severely affected than others. 

LOCALIZATION 

The Hughesville stock has been the center of repeated igneous and hydrothermal activity. At least 

three intrusive episodes, each more intense than the 

preceding one, can be recognized on the basis of 

geologic evidence, and a fourth is implied by the 

radiometric data (p. 43). This has led me to propose that a master conduit-now occupied by the 

Hughesville stock-has acted much like an inverted 

funnel (fig. 29). Successive diverse magmas as well 

as mineralizing fluids from crystallizing magmas at 

depth have been repeatedly channeled into the conduit and so ,localized in the stock. 

During the first intrusive episode, salk magma 

rose in the conduit to form first the Clendennin-Peterson laccolith and then the Mixes Baldy-Ander,son 

Peak laccolith (p. 42). 

Subsequently, magma of intermediate composition, using the same conduit, flushed out the salic 

magma as it formed the Barker laccolith (p. 42). A 

more bask phase of this magma, again using the 

Same conduit, formed the Otter laccolith, the sill 

northeast of Irene Peak ; and when it finally crystal-

,lized in the conduit, it formed the Hughesville stock 

(p. 42). Minor amounts of mineralizing fluids possibly accompanied this activity (fig. 29A). 

The third intrusive episode is represented in and 

near the Hughesville stock by felsie, mafic, and composite dikes (fig. 29B). The major sulfide veins 

probably represent mineralizing fluids expelled during the final stages in the crystallization of the felsic 

Re- Ounces Re- Per- Recovered Per- Re- Per- covered per ton covered centage 1 centage covered centage 

---

15,859 27.5 2,824 0.3 295,239 25.6 108,952 9.5 

10,128 24.9 884 .1 296,260 36.5 61,952 7.6 

6,444 23.1 346 -------- 231,482 41.4 23,278 4.2 

4,331 17.4 353 -------- 91,550 18.5 49,527 10.0 

3,522 19.6 377 -------- 104,415 29.0 27,220 7.6 

1,648 37.3 -------- -------- 22,355 25.3 17,432 19.7 --- ------- 41,932 -------- 4,784 -------- 1,041,301 -------- 288,361 -- -------- --------- 24.2 -------- -------- ----------- 30.0 --------- 8.3 

magma of this episode. T:here is some geologic and 

geophysical evidence that the felsi•c pluton which 

was formed at this tim.e extends as an ovoid mass 

beneath the Precambrian crysta;llines from near 

Neihart to near Barker (see section on "Buried Pluton" and fig. 31). 

Evidence for the fourth intrusive epi'sode is 

largely radiometric and has been presented elsewhere (Marvin and others, 1973). In brief, the potassium-argon data imply that another young felsic 

pluton is concealed beneath the stock. Clear geologic 

evidence of such a pluton is lacking. 

SAN MIGUEL DISTRICT 

The San Miguel district is centered on a group 

of abandoned mines in the N1f2 sec. 31, T. 15 N., R. 9 

E. (unsurveyed). The district; about 31f2 miles south 

of Barker, is along the west valley wal,l of the Dry 

Fork Belt Creek and is accessible by way of mountain roads (fig. 30). 

The ore deposits in the district were discovered 

about 1881 (Robertson and Rohy, 19'51, p. 39). At 

that time considerable exploratory work was do~e, 

but it is unknown whether any ore was shipped. 

MacKnight, writing in 1892 (p. 108), commented on 

the activity in the Dry Fork Mining Co.'s mines and 

claims 3 miles south of Barker. It seems likely that 

these are the properties here grouped in the San 

Miguel district. 

It is certain that mining was ructive in the district 

during the late 1920's because at least one carload of 

silver-lead ore was produced and shipped in 1927 

(Gerry, 1930, p. 769). And in 19,29, "about 2,000 feet 

of tunnel work was done at the San Miguel property 
SAN MIGUEL DISTRICT 53 

c 

Brecciated and altered 

contact zone 

FIGURE 29.-How a master conduit may have repeatedly 

guided diverse magmas and ore solutions into the Hughesville stock. 

The magmas and their related ore solutions were 

channeled into an old master conduit which acted somewhat like an inverted funnel. Presumably the radial pattern of laccoliths about the stock (fig. 2) is the result of 

ascending magma repeatedly using the same parent 

conduit. A, At the conclusion of the second intrusive 

episode, intermediate magma congeals in the throat of 

the conduit. This plug, now known as the Hughesville 

stock, has solidified and been broken by fractures. B, 

EXPLANATION 

1/ ~+i /,I b__'_;_J 

Inferred pluton 

1

~ 

~ 

7Tgc .I 

Porphyry of 

Galena Creek 

~i:J Quartz monzonite 

of Hughesville 

; 

B 

Minette- kersantitevogesite 

~ 

I Tba+l + 

Barker 

Porphyry 

Mesozoic and Paleozoic rocks 

tp£rj 

Precambrian rocks 

During the third episode, young salic and fernie magmas, 

guided into the master conduit, invade fractures in the 

stock to form felsic, mafic, and composite dikes. Upon 

cooling, the salic pluton expels mineralizing solutions. 

These solutions rise in available fractures to higher and 

cooler parts of the stock and form veins which locally 

are adjacent to the dikes but elsewhere cut across them. 

C, During a renewed surge of localized intense igneous 

activity, another pluton is again guided into the master 

conduit. It jostles the stock and reactivates some fractures. 
54 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

* * *" (Gerry and Miller, 1932, p. 859). Work 

stopped shortly thereafter, and since then only 

minor amounts of assessment work, chiefly the bulldozing of exploration pits, have been carried on by 

the owners, the Faith Mining Co. of Helena, Mont. 

During the summer of 1968, a small prospect pit dug 

in the Montgomery property along the nose of a 

knoll in the NE 14 sec. 31 exposed small discrete 

pods, seams, and lenses of sulfide minerals, mainly 

galena. 

The distri;ct is near the east edge of the uplifted 

Precambrian complex of crystalline rocks, and the 

intensely fractured and altered rocks are believed to 

reflect the east flank of a buried pluton (see section 

on "Buried Pluton" and fig. 31). The host rock for 

the ore deposits is chlorite s•chist, the alteration 

product of hornblende-biotite gneiss. 

Very little is known about the veins in the district. A mineralized seam that is exposed in the 

prospect pit which was dug on the Montgomery 

0 lf2 1 MILE 

CONTOUR INTERVAL 200 FEET 

EXPLANATION 

0 

Abandoned cabin 

-< Mine tunnel 

Showing direction 

X 

Prospect 

Road 

FIGURE 30.-Mines and prospects in the San Miguel area. 

Base from U.S. Geological Survey, Barker and Mixes 

Baldy quadrangles, 1:24,000, 1961. 

property strikes about N. 5° W. According to G. VR. 

McBride (oral commun., 1968), most veins strike 

almost due north. Robertson and Roby (1951, p. 40) 

reported a N. 5° E. trend for a narrow stringer 

containing galena that is exposed at the San Marcos 

ad it. 

The thickness and tenor of the veins are also uncertain. A sample of ore from the Montgomery property contained about 0.10 ounce gold, 19 ounces silver, and about 78 percent lead per ton, according to 

G. VR. McBride (oral commun., 1968). The carload 

of silver-lead ore that was shipped in 1927 was reported to contain 0. 70 ounce gold, 18 ounces of silver, about 51 percent lead, and 3.0 percent zinc per 

ton (Robertson and Roby, 1951, p. 40). 

Galena, sphalerite, and pyrite occur as small pods, 

stringers, and disseminations in the schist. Other ore 

minerals found in rock fragments in the mine dumps 

include chalcopyrite, azurite, malachite, and 

bornite(?). 

ORE POTENTIAL 

The ore potential of the Barker quadrangle lies in 

two types of deposits: first, the sulfide veins in the 

stock, and second, disseminated ore minerals that 

may be in part of a deeply buried pluton beneath the 

Hughesville stock. Geologic and geophysical evidence 

both indicate that a large Tertiary pluton underlies 

the southwest •corner of this quadrangle and the 

northwest corner of the Neihart quadrangle (see 

section on "Buried Pluton" and fig. 31). It is the 

northwest flank of this pluton that may extend beneath the stock. 

SULFIDE VEINS 

Inasmuch as most of the mines were caved or 

flooded in 1968, it was not possible to determine the 

thickness and nature of those veins exposed in the 

workings. Many of the mines have been closed for 

more than half a century, presumably because the 

veins are s·o thin that mining them is uneconomic, 

but other undiscovered veins may still contain sizable deposits of ore minerals. One of the last large 

mines to close was the Block P which ceased operations in 1943. At that time the vein being worked 

FIGURE 31.-The trend, size, and shape of the buried mineralized pluton. Gravity contoured by M. D. Kleinkopf; contour 

interval is 2 milligals. Geology north of lat 47°00' by I. J. 

Witkind in 1967; south of it by W. R. Keefer in 1965. Base 

from U.S. Geological Survey, Barker and Neihart quadrangles, 1 :24.000, 1961. Tsc, Snow Creek Porphyry, Th, 

quartz monzonite of Hughesville; Tgc, porphyry of Galena 

Creek (all units of Tertiary age). All mines shown are 

abandoned. 
SAN MIGUEL DISTRICT 

110.35' 

BARKER 

47 00,~-------------++-~~L-~--~--~----~~~~L-~--~~F-~~----~~~Q~U~A~D~R~A~N~G~LE~ NEIHART 

0 2 MILES 

QUADRANGLE 

• Gravity station 

• 

• 

55 
56 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA 

reportedly contained "good ore" and was about 3 

feet wide (Roy Thorson, miner, Barker, Mont., oral 

commun~, 1966). Apparently there was considerable 

difficulty in bringing sufficient ore to the surface 

through the one available shaft. As a result the government concluded that the mine was a marginal 

producer and ordered it closed (Woodward and Luff, 

1945, p. 401). 

Since then, intermittent mining in the Block P 

and Liberty mines has resulted in the production of 

minor amounts of ore. 

Under current economi'c conditions the sulfide 

veins do not seem to offer much chance of succes·sful 

exploitation ·exeept by small-scale low-overhead operations. 

BURIED MINERALIZED PLUTON 

The general size and shape of the buried pluton is 

expressed by a large northeast-trending gravity 

anomaly whkh extends from N ei.hart to near Barker 

(fig. 31). A part of the ~south flank of the pluton is 

exposed beneath Precambrian rocks in the Carpenter Creek-Snow Creek area near Neihart. Farther to 

the northeast the axis of the pluton is fol,lowed by a 

zone of quartz rhyolite porphyry dikes (Snow Creek 

Porphyry) which intrude the Precambrian crystallines. I interpret these dikes to be offshoots from the 

crest of the buried pluton. And in the Barker area 

the small fel·sic dikes (porphyry of Galena Creek) 

that cut the stock are interpreted to be apophyses 

from the northwestern flank of the pluton. The collinearity between these intrusions and the gravity 

anomaly can hardly be fortuitous. I believe that 

these relations indicate that the pluton is a northeast-trending ovoid body at least 11 miJes long and 

some 4 miles wide. 

All offshoots or exposures of the pluton are composed of felsic rock. The general composition of the 

pluton is probably well represented by the outcrops 

along Carpenter Creek. In that area, the deroofed 

part of the pluton is a compound mass ·composed of 

four quartz rhyolite porphyries similar in mineralogy and chemkal composition (Johnson, 1964). 

These units have been mapped as the Snow Creek 

Porphyry (Keefer, 1969, 197~). 

Mineralized exposures are along the axis of the 

pluton. At its southwest end near Neihart, veins of 

argentiferous galena and sphalerite have been 

mined. About 2 miles to the northeast in the Carpenter Creek-Snow Creek area, molybdenite and pyrite 

fill fractures in the Snow Creek Porphyry as well as 

in the Precambrian crystalline rocks. Still farther to 

the northeast the pluton is exposed in the open pit of 

the Silv_er Dyke mine, a once famous producer of 

silver, lead, and zinc. In the pit parts of the pluton 

are seen to be a breccia tightly cemented by sulfides. 

Northeast of the Silver Dyke mine and along the 

trend of the buried pluton, small stringers of galena 

and pyrite cut the Precambrian rocks. And still farther to the northeast, also along the axis of the buried pluton, is the San Miguel district (see section on 

"San Miguel District") in which stringers and lenses 

of galena are in the Precambrian crystalline rocks. 

At its inferred northeast end is the Hughesville 

stock. 

Several factors suggest that the pluton merits investigation. (1) The potassium-argon data (fig. 24) 

indicate that the intrusions, and by implication the 

related mineral deposits, were emplaced in the early 

Tertiary, a time during which many of the large ore 

deposits in the western United States were formed. 

(2) The ore deposits in both quadrangles are spatially related to felsic rocks, quartz rhyolite porphyries and quartz monzonite. These are quartzose host 

rocks that have been repeatedly •cited as being favorable for the deposition of ore. (3) Sulfide mineralization of varying degrees of intensity is scattered 

erratically along the length of the pluton from N eihart to Barker. 

Although certain segments of the pluton are more 

promising than others, it seems to me that the area 

most worthy of test by deep drilling is the Hughesville stock. This conclusion is suggested by the following factors: (1) In other laccolithic complexes in 

the western United States, the ore deposits are spatially related to stocks. (2) The known major ore 

deposits in this quadrangle are localized in the 

Hughesville stock; other likely as-yet-undiscovered 

ore deposits may be similarly localized. (3). The 

quartz-molybdenite veinlets and the few scheelite 

blebs imply geochemical leakage from more extensive deposits at depth. In the past, minor amounts of 

molybdenum in the ,surface rocks have indicated 

richer deposits of copper and molybdenum at depth 

(Kinney and others, 1968). (4) Major volumes of 

mineralizing fluids are implied by the amount 

(20-30 percent) of rock that has been hydrothermally altered. Such extensive alteration implies a 

large source of heat and mineralizing solutions at 

depth. (5) A favorable structure is suggested by the 

large volumes of mineralizing solutions which have 

been channeled through the stock. 
REFERENCES CITED 57 

REFERENCES CITED 

American Geological Institute [Howell, J. V., chm.], 1960, 

Glossary of geology and related sciences with supplement [2d ed.]: Natl. Acad. Sci.-Natl. Research Council 

Pub. 501, 325 p. 

Billings, M. P., 1942, Structural geology: New York, PrenticeHall Inc., 473 p. 

Catanzaro, E. J., 1967, Correlation of some Precambrian 

rocks and metamorphic events in parts of Wyoming and 

Montana: Mountain Geologist, v. 4, no. 1, p. 9-21. 

Catanzaro, E. J., and Kulp, J. L., 1964, Discordant zircons 

from the Little Belt (Montana), Beartooth (Montana), 

and Santa Catalina (Arizona) Mountains: Geochim. et 

Cosmochim. Acta, v. 28, no. 1, p. 87-124. 

Creasey, S. C., 1966, Hydrothermal alteration, in Titley, S. R., 

and Hicks, C. L., eds., Geology of the porphyry copper 

deposits, southwestern North America: Tucson, Ariz., 

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U.S. GOVERNMENT PRINTING OFFICE: 1973 0-496-189