'/ 

I 

DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, DIRECTOR 

PROFESSIONAL P Al"'EU. 7 4 

GEOLOGY AND ORE DEPOSITS 

OF THE 

BUTTE DISTRICT, MONTANA 

BY 

\¥ALTER I-IAllVEY vVEED 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1912 

CONTENTS.· 

·Page. 

CHAPTER I.-Introduction ..................... ~ ................... , ....................... :............. 15 

Investigations. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . 15 

Ackno,vledgments ............... : .................................... ·.............................. 15 

Geography ....................................................................... , . . . . . . . . . . . . . . . . . 16 

Discovery and development ............................................ ~ ....................... ~ . . . . 18 · 

Epoch of gold mining ............................................... ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Epoch o'f silver mining ........ · ......... · ...................... .' .................... ~.............. 18 

Development of copper mining. ~ .. · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Production .................... • ................... :.................................................. 22 

Costs ............................................. .-................................................. 24 

Future of the district .................................. · .................... :. . . . . . . . . . . . . . . . . . . . . . . . 24 

CnAP'rER !I.-Geology of the region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Relations and broader features ............................. : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Igneous rocks .......................................................................... : . . . . . . . . 26 

Seditnentary rocks..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Andesite ... ~ ........................................................................ ·. . . . . . . . . . . . . . . 27 

Granite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

J.,ake beds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

Hhyolite and dacite ................................................................................ ·. 29 

Sutnmary .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . 30 

CnAP'rER IlL-Descriptive geology of the Butte district ........................ , . . . . . . . . . . .. . . . . .. . . . . . . . . 31 

Occurrence and character of the rocks ............................................................... ·. 31 

Granitic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · 31 

'l'ypes ......................................................................................... ~ 31 

Butte quartz monzonite.......................................................................... 31 

Petrographic character....................................................................... 31 

Distribution. . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

ChemiCal and mineralogical character .............. ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

Rocks of the Boulder batholith. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-

Quartz monzonite of Butte district......................................................... ·34 

Aplite.......................................................................................... 36 

Petrogmphic character ...................................... , ...................... ,......... 36 

Variations in character ..................... :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

Inclusions ................................................. , ........................ , . ~.... 38 

'\Veathering................................................................................. 38 

Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 

Origin ..................................................................................... : 40 

Porphyritic rocks .......................................... · ... ·...................................... 41 

Rhyolite porphyJ.'Y ........................ _ ......................... : ................ ·. . . . . . . . . . . 41 

Pet1·ographic character ......................... ,............................................. 41 

'\Veathering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 

Dikes....................................................................................... 42 

Rhyolite ......................................................... · .............. : . . . . . . . . . . . . . . . 42 

Distribution and character. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 

Rhyolite-dacite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

Character .............. · ............... : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

Occurrence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

Rhyolitic dikes. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

Character. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

Complex at Big Butte ............................. _. ...... · ............................... ·... 45 

Lake beds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 

Alluvium .................................................... ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

.Vein outcroppillg~ ..................................................................... · ......... : . . . 46 

3 
\ 

\ 

4 CONTENTS. 

Page. 

CHAPTER IV.-Structure of Butte district .... ; ........................................................... . 47 

Faulting ............................................ _______ .. _ . _ .................... _ ...... _ .... _ .. 47 

Mapping ........................................ __ .......... _ ............ __ .... __ ............. _ .. 47 

Continental fault ........................................................ __ ..... _ ........ _ .... _._ 47 

Physiographic changes ...................................................................... . 47. 

Evidence of the. fault ............. : ......................................................... . 47 

Evidence from Elk Park drainage ......................................................... . 47 

Evidence from the Flat ........................................................... _ ...... . 47 

Evidence from East Ridge ........................... ~ .................................. . 48 

Summary ..................................................... _ . _ ...... __ .... _____ .. _ .. 49 

Present-day faulting ...................................... _. ............ __ .. _. _ ........ ___ ...... . 50 

Structural relations of the rocks ............................... · ...................................... . 51 

General relations ............................................... ____ .......... _ . _ .. ___ .. _ ... __ .. 51 

Granite area ................. · ......... ~ .................... : ................. _ .. _ .. ______ ...... _. 52. 

General features .......................................................... ·_ .... _._ .. _ .... __ .. 52 

Jointing ........... _ ... _ .. _ ...... _ ..... _ ....... _ .. ~ . ·. _ ..... _ ..... _ ... __ .. ____ .... _____ .. __ _ 53 

Disintegration .............................................. : .. · ............................ . 53 

Decomposition .. ,· ......... , .......... .- ............. _ ..................... __ .... ___ ... __ ... . 54 

East Ridge .......... : ........................................ · ................... _ .. _ . _ ........ . 55 

Big Butte ..................... ~ ............................... .' ............................... . 56 

Summary of structural history ....................................... _ .... ___ ..... __ .. _ .......... . 57 

CHAPTER V.-The fractures .................................................... _ ... _ ..... __ .. _ .......... . 58 

~rs:~;~ ~;si'~~~ .· ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~- ~- ~ ~ ~ ~ ~ ~ : ~ ~ : : ~ : ~ ~ : ~ : : ~ ~ ~ : 

58 

59 

Classification .......................................................... _ ......... _ ...... _ ....... . 59 

Regularity of the fractures ............................................................... _ ...... . 59 

Direction ................................................. _ ..... _ . _ ............. _ .............. . 60 

Relation of fissure systems to jointing in the granite ................ _ ... _ ............ _ .... _ ....... . 60 

Spacing of fractures ............................................................................. . 61 

Degree of fracturing ............................ _ ........... _ ..... _ ......... _ .................. . 61 

Secondary fissures ........................................................................... _ ....... . 62 

Strike faults ................................................................................... . 62 

· Cross faults ............................................ : ......................................... . 63 

Relation to rhyolite porphyry dikes ............................................... _ ...... _ ........ . 63 

Relations of earlier and later fissure systems ......................................................... _. 63 

CHAPTER VI.-The ores .................................................................. _ .............. . 65 

Types ................................ -............. -...... · · · · · · · ·. · · · -· · · -.. · .... · · .. · ............ . 65 

Distribution ......................................................................................... . 65 

Vertical distribution ................................................ __ ._ ............. _ ... _ ...... . 65 

Areal distribution ..................................................... _ ..... _ ....... _._ ........ . 66 

Copper area ............................... : ... : _ ....... _ ........ __ ..... _ ..... _ . ___ .......... . 66 

Silver area ................................................... _ ... -.. _ ... ___ ....... _ ..... _ .... . 67 

Metxi.llic composition of the copper ores ................................... · ... '._ ..... _ ....... ___ ..... _ .. . 

Tenor .......................... _ . _ . _ ......... _ ......... _ . _ ..... _ .... · ... _ .... _ ................... . 

67 

67 

P~·ecious metals in the ores ....................................................................... . 67 

Gold ................................. ___ ................................. _ ....... _._ ..... _ .. . 67 

Silver ....... .- ......................... _ ....... __ .. _ ..... _~ ...................... _._ ... :._ .. . 68 

Base metals ............... ~ ................ : .............................. , ..................... . 69 

Manganese .................................................................................. . 69 

Zinc .. · ............................................................ , .... _ ............... _ .... . 70 

Lead ................................... : . .......... ~ ............................. _ ........ . 70 

Nickel. .... ~ ........................... .- ......................................... · ........... . 70 

Arsenic .... " ........................................................... _ .................... . 70 

Sulphur ............ · ........................... : . ........................ __ ............ __ ....... . 70 

Amounts of metals in the ores .................................................................... . 70 

Weight of the ores ............................... _ ........................... _ ......... _ ..... _ ...... . 

Structures of the ores ............................................................. _ ......... _ ......... · 

71 

72 

Minerals of the ores .......................................................... _._ ................ . 72 

General composition ......................................................................... . 72 

.Primary minerals .......... : ........................................ · ................ _ ........ . 73 

Pyrite ..................... · ...... · .... · ................................................... . 73 

Marcasite ............................................................................... . 74 • Bornite ................................................................................. . 74 
CONTENTS. 5 

Pngc. 

CHAPTtm VI.-The ores-Continued. 

Structures of the ores-Contimu3d: 

Minerals of the ores"'-Continued. 

Primary minerals-Continued. 

Chalcopyrite ........................... : ......... .'...................................... 75 

Chacocite ................................................................................ · 75 

Covellite .......... ·.·.................................................................... 76 

Enargite................................................................................. 77 . 

Tetrahedri te ............................................... ;·. . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 

1'ennantite ...................... ·........................................................ 78 

Sphalerite ................................................. ·............................... 78 

G·alena ............. ~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 

1Iolybden.ite .. ·........................................................................... 79 

Manganese minerals ....................................... ~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 

Gold ..................................................................... ~............... 79 

Silver ................................................ ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SO 

Pyrru·gyri te. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 

HUbnerite.............................................................................. SO 

"\V urtzi te. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SO 

Oxidized minerals .......................... :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SO 

Distribution ..................................... :........................................ SO 

Cuprite ........................................................................ ·.......... SO 

Chrysocolla ................ .' ......... : ......................................... • ..... : . . . . 81 

1Ialachito.: .............................. ' ................................... '............ 81 

Copper _pitch ........................................................................ ·.... 81 

Chalcanthite ... ·.·....................................................................... S1 

Pisanite ................... : ... :.......................... .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S1 

Goslru·ite ...... _. ................................... ,. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,S2 

Liinoni te. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S2 

Melaconi te. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 

1'enori te ................................................................. ~ . . . . . . . . . . . . . . . . 82 

Minerals of the gangue .................. · ......... ·................................................. S2 

. Quartz ..................................................... · .......................... :...... 82 

• Calcite ........................................................... :............................ S3 

Gypsun1 ...................................... · ........... ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S3 

Sericite..................................................................................... 83 

Kaolin...................................................................................... S3 

Rutile........................................................................................ 83 

Magnetite..................................................................................... 83 

Fluorite..................................................................................... S3 

Barite ........................................................... : ..................... ~..... 84 

llhodonite ................................................................... ·................ 84 

llhodochrosi te ................................... ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S4 

Paragenesis ......................................................... · ......... :. . . . . . . . . . . . . . . . . . . . S4 

CHAPTEn. VII.-Rock alteration............................................................................ 86 

Alteration of Butte quartz-monzonite ........................................ ~......................... S6 

\Veathering....................................................................................... S6 

Variations near borders of mass·(contact alteration) ................................. : ..... ·........... S7 

Metasomatic alteration ....................................................... ,................... 87 

Alteration of aplite .......... :........................................................................ 90 

Alteration of rhyolite................................................................................. 90 

Pyritization ................... · ................................................. ·. ·. . . . . . . . . . . . . . . . . . . . . 91 

Vru·iations in alteration near the veins ................ · ................... , .............. :............... 92 

CHAP'l'Ert VIII.-Genesis of the copper ores................................................................ 93 

Primary source of the copper ............................... · ................................. ·. . . . . . . . . . 93 

Concentration from the wall rocks ....................... ·........................................... 93 

Pyrite ........................ · ............................ ·.................................. 93 

Chalcopyrite in the wall rocks ................. : ....................... ·. . . . . . . . . . . . . . . . . . . . . . . 93 

Copper in basic minerals....................................................................... 94 

Sun11nation ............... ~................................................................... 94 

Vein fortuation ............................ ~ ................ ·.:.................................... 94 

Genetic relation of the rhyolite porphyry to the copper..... .. . . . . . . . . . . . . . .. . .. .. .. .. .. . . . .. . . . . . . . 95 

Genetic relation of the aplite to the copper........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

Conclusions .............. ~ ........ ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 
6 CONTENTS. 

CHA,PTER VIII.-G(mesis of the copp~r ores-Continued. 

Concentration processes .................................................. · ............................. . 

Underground water .............................................................................. . 

Amount .................. ." ............... · ...•............................................... 

Movement of underground water .............................................................. . 

Outcrops ................ : ................ _· ................................................. . 

Composition of mine waters, by W. F. Hillebrand ........... : .................................. . 

Secondary enrichment ....................................................................... . 

General process .....•..................................................................... 

Formation of chalcocite .................................. : ................................. . 

Formation of enargite ......................................................... · .. ·_ ....... . 

Formation of tetrahedrite ...................... ·.· ......................................... . 

Mine temperature .................... · ............................................................ . 

CHAPTER IX.-The veins ...................... · ...... · ..................................................... . 

Introduction . .' ........... _ ....... _. __ .......... ~._ .. _.· ........ ____ ......... _. __ ...... : ____ ......... . 

Mapping ................. _____ ......... ___ ............. _ ... _. __ .~ ....... ______ ~ .... ____ ...... __ .. · ... . 

Copper-vein systems .................... : ........................................................... . 

Classification ... · .... ~ ............................................. __ ._._ ...... ___ ...... _ ......... . 

Anaconda (east-west) system ........................ · ............................................. . 

Silverbow or High Ore system ...................... · .............................................. . 

Blue and Steward systems ....................................................................... . 

Features in common ........ · ......................... · .............. : ......................... . 

Contrasting features of Blue and Steward systems .............................................. . 

Composite copper veins ............................................ _ ........... _ ..................... . 

Vein filling ............................. ~ ................ _ ....... , ... :_._ ....... _ ................... _ 

Types ........................................................................................... . 

~:~r~~~~~ ~!1~~~~:~~~ -~~~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~: ~ ~: ~ ~ ~ ~ :·~ ~ ~ ~· ~ ~ ~ ~: ~ ~: ~: ~ ~ ~ ~ ~:: ~ ~::: ~ ~ ~::::::: ~::: 

Chad:=~:e:~~n~o:~~s~:~!~-- ·.· .· _· ~ ~: ·. ·_ ·_·_· _· ~: ~ : ~ ~ ~ ~ ~ ~ ~ ~ .: ~ ~: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~·: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ : ~ ~ : ~ : ~ ~ ~ ~ ~ ~ Changes in structure ............................................................................ . 

CHAPTER X.-Detailed description of tlw copper lodes ....... · ....... ~ ................ · ...................... . 

Method of treatment ................................................................................ . 

Subdivisions ............................................................... _ ................... . 

Nomenclature .............................................................................. ~ ... . 

Cross sections ................................. · .................................................. . 

Anaconda-Parrot belt ................................................................................ . 

.1\.naconda~Parrot lode ................................................. , ....... _ ................. . 

Anaconda lode ................................... : ................... __ ..................... . 

Anaconda vein ...................................... · ................. _ .. _ ............... . 

Ores ......................... _______ ............. _______ . __ ...................... _ .. 

Wall rock ............................................................... ___ ......... . 

Splitting of the vein ................................................ _·_ ... __ .......... . 

Summary ............ __ ................ ____ ... · ....... _ . ___ . _ ~ _ ....... _ ............. . 

Pennsylvania vein ........................................ _ ................ _____ ._. ___ ... _ 

Moonlight vein ................................................... __ ._ .... _ ............. . 

Hogan vein ............ _ ............. ____ ....................... _ .... ___ .. _._ ........... . 

Q'Neillledge ........................................... __ ........................ _ ...... . 

Mineralir.ation .............................................................. __ ..... _ ..... . 

Faulting .......... _._ .... <-_ .. _._. _____ .... _ ........ _ ... __________ ._ .................... . 

Parrot lode ......................... ~ ............................... __ .. _._._. ____ ._ .... _ .... . 

The lode as a whole ......... · ...................................... __ ._._. __ . __ ........... . 

Development and general character ... · .......................... _ ·. _ ................... . 

Splitting of the vein ............................... , ..................... _ .. __ ........ . 

Fractures ........................................................................... . 

Parrot mine ................................ _ . _ . __ . __ . ___ . ______ . ____ .. : ................ . 

Ores .... : ............................ _ .. _ .. _._ ............... _ ......... _ .... ___ .... . 

Fractures ........................................................................... . 

Faulting." ........................................................................... . 

South Parrot or Virginius vein ............... _ .... ______ ._ .. _ .......... _ ............. . 

Original mine ..... ~ ....... .- ................ _ .. _ ....... _ ... _ ... _ .... __ . _ ................. . 

. General description .................. · ... · ......................... :: ................ . 

Pa~e. 

97 

97 

97 

97 

98 

99 

101 

101 

102 

102 

103 

104 

105 

105 

105 

106 

106 

107 

107 

108· 

108 

108 

109 

110 

110 

110 

111 

111 

111 

111 

113 

113 

113 

113 

113 

114 

114 

114 

114 

114 

115 

116 

117 

117 

120 

122 

122 

122 

125 

126 

126' 

126 

128 

129 

130 

130 

130 

131 

132 

133 

133 
CONTENTS. 7 

CHAPTER X.-Detailed description of the copper lodes-Continued. Page. 

Anaconda-Parrot belt-Continued. 

Anaconda-Parrot lode-Continued. 

Parrot lode-Continued. 

Origina_l mi~e-~ontinued. , 

Ve1ns ............... ~.............................................................. 133 

Parrot vein .... ~................................................................. 133 

Rialto vein...................................................................... 133 

Steward vein ............................................. :...................... 134 

Pyrite vein. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 

Zinc vein ................. ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 

Y vein......................................................................... 134 

Gagnon mine ............................................................ ·. . . . . . . . . . . . . . . . 134 

Parrot lode.......................................................................... 135 

Steward vein .................. ·...................................................... 136 

Cross faults ...................... :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 

Summary ......................................................... ·. . . . . . . . . . . . . . . . . . . 136 

Blue vein system in the Anaconda-Parrot belt... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 

Importance ................................................................. ·................. 136 

Blue yein. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 

Judicial investigation ............................... ~.................................... 137 

Development and general character ................................................. , . . . . 138 

Intersection with Anaconda lode.......................................................... 138 

Intersection with Steward vein........................................................... 140 

Ores ....... : ........................................................................... ~ 140 

Mounta~n View fault vein.................................................................... 142 

Development and general character. . . .. . . . . .. .. . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . . . 142 

Intersection with other veins ............................... ~............................. 142 

Ores.................................................................................... 14.3 

Clear Grit vein............................................................................... 144 

Other northwest fault veins.................................................................. 145 

The Steward vein system of the Anaconda belt ................................... .'................ -145 

General charncter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 

Steward fault vein ..................................................... : .. :................. 145 

Steward mine ......................................................... ·:.:............... 147 

Veins ........................................................ : . . . . . . . . . . . . . . . . . . . . . . . . 147 

Ores ................................. : ............................. :~............... 147 

Variations in the Steward vein .................. · ................... ~:·.·............... 149 

Strike ........ · .. · ..... : .............................. :............................... 150 

Original mine ............................................................ .'. . . . . . . . . . . . . . 151 

Gagnon mine ........................................ · .................. _._................ 151 

Summary........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 

No. 6 fault vein ............................. : .................................. :............. 152 

Blue Jay fault vein ........................................................... : .. :........... 152 

Other veins of the Steward system............................................................ 154 

Intermediate copper belt .................................................................. :. . . . . . . . . 154 

Mines and veins................................................................................. 154 

Parnell mine ..................................................................... ·. . . . . . . . . . . . . . . 154 

Little Mina and Nipper mines.................................................................... 156 

Silverbow system .......................... ·.......................................................... 156 

Character and age ............................................................... : ....... · . . . . . . . . 156 

Silverbow lode.................................................................................. 156 

Char-acter and displacement .............................................. :.................... 157 

Vein filling and recent deposition............................................................. 15~ 

Bailey vein. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 

Other northwest primary veins......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 

Syndicate lode .......................................................................... .'........... 160 

Course and development........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 

Splitting of the lode.............................................................................. 161 

Thickness .. , ....................................... ~ ...................... .'. . . . . . . . . . . . . . . . . . . . . 161 

Fractures ...................................................... :................................. 161 

Wall rocks .......... ~............................................................................ 163 

Ores ........................................................... ·.................................. 164 
8 CONTENTS. 

CHAPTER X.-Detailed description of the copper lodes-Continued. 

Syndicate lode-Continued. 

Subordinate veins ..................................................... · .............•............ 

Keegan vein ................................................................................ . 

Dernier vein ............................................... · ................................. . 

Old Glory vein ........ : ............................ · ........................................ . 

Raven vein ...... ~ ......................................................................... . 

Mines ....................................... ···················································· 

Moscow mine ............................................................................... . 

Poulin, Stella, and Buffalo mines .................. · ......................................... . 

Mountain Con. mine ........................................................................ . 

Green Mountain mine ................... · ......................... · .......................... . 

\Vake-up-Jim mine .......................................................................... . 

Diamond-Bell group ................................................................................. . 

General relations .......... · ........................................................... : ........... . 

Faulting ........................................................................................ . 

East-\vest veins ................................................. · ................................ . 

High Ore group of veins ........................................................................ . 

High Ore vein ............... , .... · .................................... · ... ~ ................. . 

~fodoc vein ....................................................... :: ........ : .............. . 

Bell vein .................................... · ........ · ...................................... . 

Wild Bill vein ............................. '· ................................................ . 

Greyrock group ...... ; ... · ....................................... : .............................. . 

. General character and relations .............................................................. . 

Skyrme vein .......................................................... · ...................... . 

Covel1ite vein .............................................................................. . 

East Greyrock mine ..................................................................... . 

Corra mine ........... · ............... : .............................................. · .. 

Diamond mine .................... .' ................................. . ·: . ................ . 

Higgins (East Bell) vein .......... ~ .......................................................... . 

Mines .............. · ........................... .' ...... · .. ·.· .. · ...... ·········· .. ··········.······ 

East Greyrock mine ................................................................... · ..... . 

·General relations of V<;Jins ............................................................... . 

Sisters vein ....................... · ...................................................... . 

Demier vein ........................................................................... . 

Vale vein ....................................... ~ ........................................ . 

West Greyrock mine ............................... · .. · ....................................... . 

Snowball mine ......... · ......... · .........................•.................................. 

Corra mine ................................................................................. . 

Speculator and Adirondack .................. : ... · .......................................... . 

Miners Union ................................. : ............................................ . 

Jessie-Edith May group ....................... · ...................................................... . 

~:~~r~~~~ ·. ·. ·. ·. ~ ~ ~ ~ : ~ ~ : ~ : : : : : : : : : : : : : : : : -: : : : : : : : : ~ : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 

Edith lVIay vein ....................................... : ........................................ . 

Gem vein ................. ·.· ............................... ·.· ........ · ........................... . 

East Butte belt .................................. · .................................................. . 

General character ....... ~ ..... : ................................................................ . 

Veins ...................................................................... · .................... . 

Glengarry vein ..................... · .. : ................................. : .................. . 

Extent and development ................................................................ . 

Number Three mine ....................... ~ ............................................ . 

Glen garry mine ....................................................................... . 

Ground Squirrel mine .................................... : ............................ . 

J. I. C. mine ........................................................................ · .. . 

Geyman vein ....... · ...................................................................... . 

Belmont vein .................................................. : ..... .' .... .' ................ . 

Mines ........... : .............................................................................. . 

Otisco mine ...... : . ........................................................................ . 

Iduna mine ............................................................................... . 

Colorado mine ........................................... : .................................. . 

Lizzie mine .......... · ....... ,. ........ · ...................................................... . 

Cambers mine ........ : ................ · .................................................... . 

Anderson mine ...... · ................................................ _ ................... · ... . 

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CONTENTS. 

CliAPTER X.-Detailed description of the copper lodes-Continued. 

East Butte belt-Continued .. 

~fines-Continued .. 

Hesperus 1nine ............................................................... : ............. . 

Valley n1ine ........................................................... · ...... · .............. . 

Henry George n1ine ............... · .................. ~ ..................................... . 

Adan1s n1ine ............................................................................... . 

Preferencia, Green Copper, and Alliance mines ...... ~ ......... : . ............................ . 

Talbot & Jones claim ...................................................................... . ''r ashoe 1nine ....................... -----------------· · · · · · · · · · · · · · _. · · · · · · · · · · · · · _- · · · · · · · · · · -· 

Gold Hill n1ine ............................................................................. . 

Mountain View-Shannon-Colusa belt ................................................................. . 

~fountain View n1ine ........................................................................... . 

Location and character ................ : . ........................... · ........................ . 

Shannon vein .............................................................................. : 

General character ................................................ · ...................... . 

:Faulting ................................................ · .............................. . 

Mountain View south vein ................................................................. . 

Johnstown (North Connecting) vein .............. · ............................................ . 

Mountain View n.nd Blue Jay faults ......................................................... . 

Mountain View system veins ............................................................. · ... . 

Colusa-Leonard lode ............................................................................. . 

Extent ................................................... · ................................ . 

Colusa lode .................... ~ .......................................................... · .. 

General character ............................................................ · .......... . 

Faulting. : ............................................................................ . 

Blue vein fracture system ............................................... : ............... . 

No. 12 fault vein ........................... : ........................................ . 

Gambetta vein ..................................................................... . 

Piccolo veins ......................................... · ....... · ...................... . 

}.f:innie Healy vein .................................................................. . 

}.1inor fractures, .................................................................... . 

Blue Jay fracture system ................................................................ . 

Rarus fault .......................................................................... ~ ... . 

Leonard lode ......................................... ·.· ................................... . 

General character ....................................................................... . 

Veins ......................................... · ............................... · .......... . 

Faulting ............................................................................... . 

Ores ................................................................................... . 

Tran1,vay vein ..................................... · ........................................ . 

Mines north of Meaderville .......... ~ ............................................. · .. _. ............... . 

};fodoc 1uine ................................................................ .' ................. . 

11eins Copper Co. n1ine ............................... ~ ........................................ . 

Sunshine mine .................................................................................. . 

}.fat mine ...................... , .......................... · ...................................... . 

Alexander Scott mine ............................... : . .................. · ....................... . 

Rarus group of veins ............................................................................... . 

Development and general character ............... · .............................................. . 

Correlation of the veins ................... · ........................... · .......................... . 

Structure .. · ........... · ........................................................................ . 

Interrelations of the veins .................................................................. . 

Faulting ...................... : . .......................................................... . 

Deflection of mineralization ........ · ........................................................ . 

Veins west of the Rarus fault ..................................... · ............................... . 

North 'vest veins ............................................................................. . 

Johnstown (North Connecting)' vein ...................................................... . 

Johnsto,vn No.2 vein .................................................................. . 

Mountain View fault vein ............................................................... . 

Pennsylvania No. 8 vein ................................................................ . 

East-,vest veins ............................................................................ . 

Po,vder-Iron vein ..... : ....................................... · ......................... . 

Pennsylvania No.2 vein ................................ ·:.~ ... ~ ........................ . 

9 

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10 CONTENTS. 

CHAPTER X.-Detailed description of the copper lodes-Continued. 

Rarus group of veins-Continued. 

Veins east of the Rarus fault ................................................................... . 

Northwest veins ................ , ................... .' ....................................... . 

, Windlass vein ....... _. .................................................................. . 

South vein ••........................................................................... 

Berkeley vein ......................................................................... . 

North vein .............................................................................. . 

Snohomish vein .......•......... · ....................................................... . 

Vein No. 612 ............................... · ............................................ . 

East-west veins ............................................................................ . 

Cross vein ......................... _. , ................................................... . 

Snohomish Diagonal vein_ .............................................................. . 

Rarus fault ................................................. · ................................... . 

Importance_ .. _ .......... .' .................................................................. . 

General character .......................................................................... . 

Interfault filling ............................... · ............................................. . 

Dip and displacement ................................................. · ..................... . 

Ore bodies .......... · ...................................... __ ............ _ .................. . 

Veins of Butte Flat ................................................................................. . 

Development ... ___ ................................ : ............................................ . 

Pittsburg and Montana property ............ _ ................... , ................................. . 

Atlantic mine ....... _ .. : ............................................... ~ ...................... . 

Butte & Boston No.7 mine ..................................................................... . 

Veins of East Ridge. _ ............................ ~ .............................. · .................... . 

Character and development._ .... _ ............................................. ~ ................. . 

Rocks ........................................................................................... . 

Mines ....................... · ........................... --· · · ---· · · : · · -· · · · · · · · · · · · · · · · · · · · · · · · · 

Six o'Clock mine ......... · ......................... ~ ............. : ......................... . 

Northwestern mine ............. _ ........................................................... . 

Clinton mine .............................................................................. . 

Homestake mine ................... _ ....................................................... . 

Bullwhacker mine ..... · ........ _ ....... _ .................................................... . 

Bertha group ..................................•............................................ 

Bertha mine ........................................................................... . 

· Lillie claim ....................................... .' ................................... : . 

Sarsfield claim ..... · .................................................................... . 

Pacific claim .....•..................................... · ................................ . 

Colleen Bawn mine ...................................................................... : .. 

Exemption claim ......................... .- ............•..................................... 

Sinbad mine ............................................................................... . 

Montgomery claim ......................................................................... . 

Maggie mine ....... _ ......................................... : ......................... _ ..... . 

Altona mine ... _ ......................................................................... ~ .. . 

Ida mine ..... _ ................... _ ..................................................... _ ... . 

Schweitzer-Monitor tunnel. ................................................................. . 

Columbia Garden ....... _ . : ......................................... : ........................ . 

CHAPTER XI.-The silver lodes .......................................................................... . 

Productive status ................................................................................... . 

Area and subdivisions ... _ ........................................................................... . 

Lexington group ....................................................... · ........................ . 

Veins ................................................................. _ ......... _ ...... -... . 

Blue Wing lode .................. , .. ~ ............................................. _ ....... " .. 

Lexington mine ...................................................... · ....................... . 

Allie Brown vein ....................................................................... . 

Wappello lode .......................................................................... . 

La Plata lode ........................................... · ........ ~ ....................... . 

Cost of mining_ ................ _ ............................ · ............................... . 

Ores ....................................................................................... . 

Rainbow group ............................. _._ ....... .-................... · ......... __ .......... . 

Vein systems .......................................... _ .... ! ...•.•..•.........•.........•.. 

Valdemere system ......................................................................... . 

Northeast system ........... · ........... _ .... __ ................................ _ . __ .. __ ... _ .. . 

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CONTENTS. 11 

CHAPTER XI.-The silver lodes-Continued. Page. 

Area and subdivisions-Continued. 

Rainbow group-Continued. 

Rainbo'v lode ......................................................................... -~-... 243 

Development....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 

1\fines .................................... : ................................. :. . . . . . . . . . . . 244 

Alice mine .............................................. _. . . . . . . . . . . . . . . . . . . . . . . . . . . 244 

Magna Charta mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 

Moose mine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 246 

Belle of Butte mine .............................................................. ·.... 247 

Amy-Silversmith mine ... ~........................................................... 247 

Goldsmith mine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 

Northern mines... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 

'\Vabash n1ine................................................................................ 248 

Springfield mine............................................................................. 248 

Snowdrift-Glengarry ....................................... ·................................. 248 

Silver Lick mine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 

Missoula Gulch group .................. · ..................... ·...................................... 249 

!~~~n~~::i::.~~: .·. ·. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ -~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ::: 

Anselmo mine ...................................................................... · ........ : . 249 

Caledonia and Jasper mines ........................... · ......... _ ............ __ . . . . . . . . . . . . . . . . 250 

Silver King mine ............................. : ........... _ ......... __ ...................... 250 

Western group ........................................ _ ........ _ .... _ . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 

Nettie and Philadelphia mines ............................ _................................... 251 

Veins ...................................................... __ .......................... 251 

General character ................... _ .............. : ... _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 

Nettie vein. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 251 

Middle vein ...•..................................... _ ......................... : . . . . . 252 

Philadelphia vein ..................................... ~ ...... : ...... .'................ 252 

Fractures ...... · ......... ·................................................................. 252 

Ores .............................. : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 

Moody and Sankey, Iowa, and Kossuth mines .... .'. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 

Kit Carson mine............................................................................. 254 

Southern and eastern group .................................. : .............. : ................ .". . . . 254 

Ella mine ................................................... ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 

Ancient or Emma mine (Black Chief) ......................................................... · · 255 

Index ....... : .......................... .'............................................................... 257 
ILLUSTRATIONS. 

Page .. 

PLATE I. Geologic map of region surrounding the Butte district ..... _. ............................... In pocket .. 

II. A, General view of western part of Butte district, including The Butte; B, Sheeted granite of Boulder 

batholith near Homestake tunneL ...................................... ·_ . . . . . . . . . . . . . . . . . . . . . . 26-

III. Butte quartz monzonite, showing texture and occurrence of primary sulphides..................... 32 

IV. A, Mineralized joints in granite, excavation for foundation of a church at Butte; B, Part of Modoc 

dike, showing rhyolite porphyry surrounding bowlders of Butte quartz monzonite and filling horizontal joints in thatrock...................................................................... 32· 

V. A, Sheeted granite north of Meaderville, along Great Northern Railway line, showing weathering 

along joint planes, some of which are mineralized and form·veins; B, Disintegration bowlders, showing their relation to sheeting planes of granite and their manner of formation. . . . . . . . . . . . . . . . . . . . 54· 

VI. A, Decomposition bowlders formed by vein-making agencies in granite, north crosscut, 800-foot level 

Gagnon mine; B, Vein outcrop near Bell mine, in Great Northern Railway cut................... 54 

VII. Banded ore, Lexington mine, three-fourths natural size, with diagram showing composition........ 72 

VIII. A, Stalactites of chalcanthite (with iron sulphate), 200-foot level, Silverbow mine; B, Stalactites of 

limonite in Silverbow mine................................................................... 82· 

IX. A, Typical outcrop of silver vein, Ancient lode; B, Face of 1,600-foot drift, Parrot mine............. 84 

X. Geologic and vein map of Butte ............................................................. In pocket. 

XI. A, Fault breccia of Original mine, first floor over 1,200-foot level east; B, Anaconda vein cut off by 

:J3lue vein; sixth floor stopes over 900-foot level, Neversweat mine, west end . . . . . . . . . . . . . . . . . • . . lOS. 

XII. A, Fault cutting primary quartz-pyrite vein, Gagnon mine; B, Conglomerate ore of Steward fault 

vein, Gagnon mine; second floor of stopes above 1,600-foot level, near cro$scut to shaft........... llO· 

XIII. Ideal cross section of Anaconda vein, showing relations to porphyry and distribution of ore . . . . . . . . . . . llO· • 

XIV. A, N eversweat mine from southeast; B, Shaft of Anaconda mine ..... ·.·........................... ll4 

XV. A, Moulton mine; B, General view of Green Mountain mine..................................... 170· 

XVI. A, Quartz-pyrite vein traversed by joints filled with pyrite and glance, Mountain View mine, 1,100-

foot level, south crosscut, South(Anaconda) vein; B, Mountain View mine, sixth level,.south crosscut, shows faulting of veinlets of North vein: ......................... ;......................... 202: 

XVII. A, Fault breccia, Mountain View mine, north crosscut, eleventh level, cross slips and ore bowlders, 

breccia 45 inches wide; B, Mineralization along joints in granite, incipient vein formation, south 

crosscut, seventh level, Rarus mine, veinlets of quartz and pyrite.............................. 204 

XVIII. Diagram of elevations of levels of Butte mines .... -.- ........................................ In pocket. 

XIX-XL. Maps showing known vein structure on succgessive planes, 100 feet apart, from 3,600 feet to 5,600 feet 

above sea level... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In pocket .. 

XLI. A, Breccia~ed sulphide and quartz, L_exingt~n mine; B, Vein structure, La Plata mine, fifth .level, 

south ve1n.................................................................................. 240• 

FIGURE l. Index map showing position of Butte district.................................................... 16 

2. Variation in texture of aplite exposed near Boulder, :.Mont .. · .................... ·................... 37 

3. Small aplite intrusions along fissure lines in Butte quartz monzonite.............................. 39 

4. Vertical cross section of rhyolite porphyry dike............... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 

5. Joints in shattered granite, 500-foot level, Leonard mine........................................... 53. 

6. Relation of porphyry dike to Anaconda vein, north-south cross section through St. Lawrence shaft.. 64 

7. Diagram showing relation between copper and silver values in a drift in the Leonard mine.......... 69 

8. Pyrite vein in granite, 1,000-foot level, Leonard mine........................................... 73. 

9. Thin section of bornite ore.................................................................... 74 

10. Thin section, shoWing fragments of shattered pyrite and enargite that appear to be secondarily 

inclosed in bornite ................................................................. ~........ 74 · 

ll. Chalcopyrite in quartz in enargite veinlet, Leonard mine, 1,100-foot leveL........................ 75 

12. Chalcopyrite (glance) specimen from 1,000-foot level, Leonard mine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76: 

13. Veinlet of chalcocite (glance) and quartz ....................... :,............................... 76 

14. Vug in a quartz-pyrite vein that has been filled by covellite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 

15. Veinlet of enargite penetrated by later· covellite seam ............................. :.............. 77 

16 .. Block of ore showing relations of enargiteand pyrite in ore from the 1,100-foot level of Leonard mine. 78 

17 .. Zinc blende and galena Leonard mine ..... ·_ .... ·- ......................................... : . . . . 79· 

12 
ILLUSTHATIONS. 

J!"'roun.E 18. Wire silver and masses of silver in vugA in bornite, Parrot mine ............ · .................... . 

10. Intergrown pyrite and magnetite in fresh Butte'quartz monzonite ............................... . 

20: ~ehin section of altered quartz monzonite, showing grains of intergrown pyrite and magnetite, Mountain Con. 1nine ............................................................................ . 

21. Enargite and chalcopyrite in a quartz-pyrite vein, Leonard mine ............................... . 

22. Vein lets of chalcocite netting pyritized granite, Leonard mine ................................ · .. . 

23. Quartz veinlets in silicified granite, West Colusa mine ..... · .................................... . 

24. Successive fracturing of pyritized granite, L~onard mine ....................................... . 

25. Quartz veinlet shattered and the fissures filled by pyrite, and later broken without dislocation and 

the fissures filled by chalcocite, Leonard mine ............................................... . 

26. Blue vein cutting off Anaconda lode ......................................................... . 

27. Cut-oH .and spraying out of Dernier vein by a northwest fault ................................... . 

.28. Vertical north-south cross section through Anaconda shaft ....................................... . 

29. Diagram showing change of character and richness of vein in crossing rhyolite porphyry and aplite.· 

30. North-south section through Anaconda and Parrot veins and Blue-vein fault .................... . 

31. Section through Anaconda lode, showing splitting of vein. . .................................... . 

32. Cross section through Anaconda shaft on line through long south crosscuts ....................... . 

33. North-south cross section through Colusa-Parrot vein, showing relations of Blue .Jay fault and Moonlight vein ................................................................................. . 

34. Anaconda lode, N eversweat mine ............................................................ . 

35. Altered and mineralized granite alongside of Anaconda lode, St. Lawrence mine ................. . 

36. Section through N eversweat and Colusa-Parrot mines .......... · ............................... . 

37. Section of Hogan vein ....................................................................... . 

38. North-south section through Parrot shaft ..................... ~ ................................ . 

39. Cross section through Colusa.-Parrot shaft ...................................................... ·. 

40. Section of south ledge, Parrot mine ........................................................... . 

41. Ore bands, Parrot lode .................................................... · ................... . 

42. Plans of 80, 160, 260, and 320 foot levels, Parrot No. 6 mine .................................... . 

43. Section across Original ore body .............................................................. . 

·44. Sections on 900-foot level of Gagnon mine ..................................................... . 

45. Section through Gagnon shaft ................................................................. . 

46. West face, 1,400-foot level, Gagnon mine ..... , ................................................ . 

47. Section showing cut-off of Anaconda and Parrot veins by the Blue vein fa•ult .................... . 

·48. North-south section through Parrot, Steward, Gagnon, and No.6 veins, 75 feet west of Gagnon shaft. 

49. Not·th-south section, 210 feet west of Gagnon shaft .............................................. . 

50. North-south section, 510 feet west of Gagnon shaft ............................................... . 

.51. Faulting of Parrot vein by Steward and No.6 veins ............................................ . 

.52. North-south s~ction of veins 250 feet west of Parrot shaft ........................................ . 

53. Displacement of Rialto v~in by Clear Grit fault ......... · ........................................ . 

.54. Displacement of Rialto and Clear Grit fault vein by Steward vein .............................. . 

55. Displacement in Steward mine ...................................•........................... •. 

.56. Ore body from 700 and 800 foot levels, Steward mine ..... .' ...................................... . 

.57. Cross section through Steward and Original mines, showing Steward vein following and brecciating 

the Parrot lode ........ · ....................................... : ................ , .......... . 

. 58. Plan of 1,400-foot level of the St. Lawrence mine, showing relation ~f flat ore bodies to fault veins .. ·. 

.59. Cross section of Schweitzer vein, Parnell mine ................................................ . 

60. North-south. section through Silverbow, Rarus, and West Colusa mines .......................... . 

·61. Plan of east end of 500-foot level of Silverbow mine, sho,ving Iron vein (No. 3 vein) cut by fault .. . 

62. North-south section through Klondike crosscut, Silverbow mine ................................. . 

·63. Plan of 700-foot level (5,350 feet elevation) on the Syndicate lode .............................. . 

64. Cross section of Syndicate lode, Moscow mine ................................... · .............. . 

·65. Cross section through Stella shaft, showing the Syndicate lode and the faults that cut it .......... . 

·66. Section of Syndicate lode, 600-foot level, Mountain Con. mine .................... _. ............. . 

67. Section of Syndicate lode, 1,100-foot level, Mountain Con. mine ................................. . 

·68. Section of Syndicate lode, fourth floor above 1,000-foot level, Mountain Con. mine ............... . 

69. Plan of part of 2,100-foot level, Mountain: Con. mine, showing spraying of ore ..................... . 

'70. Section of Sytl.dicate lode, 800-foot' level west, Green Mountain mine .......... : ................. . 

'71. Section of Syndicate lode, 2,200-foot level east, Green Mountain mine ........................... . 

72. Section through Green Mountain shaft, showing S'yudicate lode ................................ . 

'73. North-south section through Diamond shaft, showing veins of Diamond mine ..................... . 

'74. North-south section through vein and faults of Diamond mine on line of Bell shaft .............. . 

'.75. Section .of High Ore vein, stopes of 2,200-foot level, High Ore mine ............................ . 

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14 ILLUSTRATIONS. 

Page. 

FIGURE 76. Plan showing cut-off and displacement of Skyrme vein by east-west Modoc fault vein, 1,600-foot 

level, High Ore mine . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 

77. Cross section through East Greyrock shaft .............. · ............................. ·. . . . . . . . . . 181 

78. East-west Speculator vein, terminating abruptly against Bell fault, High Ore mine................ 183 

79. Displacement of Jessie vein by fault of Steward system .. _ .. ~................................... 187 

80. Level on Edith May vein, showing abrupt change from high-grade ore to low-grade quartz-pyrite ore. 188 

81. Section of Gem vein, 400-foot level, fourth floor, 75 feet west of shaft. . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 

82. Section of Gem vein, 400-foot drift, east face ..................................... ·............... 189 

83. Cross section of Iduna vein, 100-foot leveL ................. , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 

84. Shannon vein cut into blocks by Blue Jay fault, No. 12 fault vein, and Rams fault................ 196 

85. Section in West Colusa mine, 323 raise, showing character of Colusa vein......................... 197 

86. Cross section through Mountain View, Rams, and Pennsylvania mines ........... :............... 198 

87. Cross section through Pennsylvania mine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 

88. Section of Mountain View south vein, showing streaks of first-class ore, 1,055 raise ............. ~... 200 

89. Truncation of Mountain View south vein by Rams fault, 2,200-foot level of High Ore mine......... 201 

90. Truncation of Mountain View ore body by Blue Jay (No. 16) fault, tenth level, Mountain View mine. 201 

91. Diagram showing relative positions of veins and faults of the Mountain View and Rarus mines..... 202 

92. North-south cross section through Leonard and Colusa mines on 5,100-foot coordinate east......... 205 

93. Loss of value in vein approaching fault vein, Leonard mine .................. · ......... ~......... 206 

94. North-south cross section through Leonard and adjacent mines, 4,800-foot coordinate.............. 207 

95. North-south cross section through Leonard and adjacent mines, 4,900-foot coordinate.............. 208 

96. Leonard ore body cut by Minnie Healy (Betty) fault vein....................................... 209 

97. Cross section· of part of Leonard lode, from 1,000-foot level upward for 77 feet..................... 210 

98. North-south cross section through Leonard mine, 4,500-foot coordinate........................... 212 

99. North-south section through Leonard mine, 4,700-foot coordinate................................ 213 

100. Ore body in south crosscut, 700-foot level, Leonard mine........................................ 214 

101. Enargite "bunch," 800-foot level, Leonard mine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 

102. West wall of Rams fault, showing projection of intersecting veins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 

103. East wall of Rarus fault, showing projection of intersecting veins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 

104. Veins of Rams area, east of Ran1s fault........................................................ 222 

105. Plan of veins on 1,100-foot level, Mountain View mine, and 1,200-foot level, Rarus mine. . . . . . . . . 223 

106. Section of Windlass vein, face of 600-foot level, Rarus mine ... ·... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 

107. Plan of workings •of Britannia mine, showing silver veins cut but not displaced by rhyolite dike... 252 

108. Verticai section through Ella mine. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 

109. Section of Ella vein......................................................................... 255 
G·EOLOGY AND ORE DEPOSITS OF TI-IE BUTTE DISTRICT, 

lVIONTANA. 

By WALTER IIARVEY WEED. 

CHAPTER I.-INTRODUCTION. 

INVESTIGATIONS. 

The fu·st geologic investigation of the Butte district was made in 1896 by S. F. Emmons, 

assisted by G. W. Tower and the writer.· The results of this work were published as a geologic 

folio in 1897'. So n1any new facts in regard to the geological conditions of the veins were afterward determined by the extensive exploration connected with the litigation that followed that 

Mr. En1mons decided to n1ake a thorough study of the district, the results to be published as a 

joint n1onographic report by hin1 and the writer. Work was begun in 1901, but after gathering data for several years :Mr. En1n1ons, because of the pressure of his duties in svpervising the 

mining investigations of the Survey and because of the severe physical labor involved, decided 

to transfer the entire investigation to the writer. The material that lu\.d already been prepared 

by hhn hn,s, however, been incorporated in this report. · 

The underground clevelopn1ent since 1896 shows that the geologic structure is far more 

c01nplex tJ1an had been ·supposed. The prin1ary veins are displaced. by great faults, and these 

later :fractures have then1selves been n1ineralized and again displaced. The working out of the 

structural relations has 'been particularly difficult because the deposits occur in a body of 

hon1ogeneous granite, which affords no clue to either the an1ount or the direction of displacement. Notwithstanding this, the correlation of displaced arens luts been satisfactorily completed, being based on. the rhyolite porphyry and aplite intrusions in the granite and on the 

structural and Inineralogic variations of individual veins. 

In the beginning of the work it was found that the complexity of the structure made 

detailed observations necessary. :Maps of each level of every mine were therefore transferred 

to 1iotebooks, and. with these in hand the writer and his assistants, while underground., carefully 

exan1ined the drifts and crosscuts and plot~ed on the maps the occurrence of each slip, vein, and. 

fault, noting the clips, strikes, and other important features. This task involved several months 

of work, as the levels alone are n1any miles in extent. Stopes and raises were noted in the same 

way, and sketches were n1ade of particular features of vein structi.n·e and ore occurrence. 

The fteld work. involved a careful examination, by the writer, of over a hundred miles of 

'these underground workings, and, owing to the magnitude of the task and the pressure of other 

investigations, it was not completed until the autumn of 1905. The work of assembling, plot-

'ting, and checking the 1nass of detail collected has been very great, henc.e the completion of this 

report has been delayed. The chief cause of the delay, however, is the litigation that has 

been in progress in the district and the assurance given that the report would not be published 

in thne to be used by either litigant. 

ACKNOWLEDGMENTS. 

The writer desires to acknowledge his great indebtedness to companies and individuals for 

courtesies extended and . for information freely given throughout the period of fteld work 

To Mr. John Gillie, general manager of the Anaconda Co., Mr. C.W. Goodale, of the Boston & . 15 
16 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

Montana Consolidated, and :Mr. A. H. Wethey, the writer owes especial thanks. The geologic 

department of the Anaconda Co. has been particularly generous. l\1r. Horace V. Winchell, 

former chief geologist of the Anaconda mine, and his successor, Mr. Reno Sales, have n1ost 

freely imparted the many important facts in regard to the niines, knowledge of which had been 

acquired by long and continuous underground study, and n1ost of the theoretical conclusions 

stated in this report accord with those advanced by them. The valuable detailed geologic notes 

of all the mine workings of the A.Inalgan1ated properties h~ve been freely placed at the disposal 

of the Survey and have been freely used in this report. 

· GEOGRAPHY. 

Like other midcontinental States, Montana embraces withirl its borders the' western part 

of the Great Plains region and the eastern part of the Rocky Mountain or Cordilleran region. 

The mountain region, comprising the western third of the State, is an assemblage of ranges whose - . . 

2. 5====~o===:::::::lzs~;;==~-s3:o===::::i75Miles 

FIGURE 1.-Inciex map showing position of Butte district. 

eastern front extends northwestward from the borders of the Yellowstone Park to the Canadian 

·line. Its southern part is traversed by well-defued ranges, with intervening valleys whose 

fertile river bottoms and bench lands are well settled and extensively cultivated. 

The Butte district lies in a well-defined mountainous tract in the center of this system of 

ranges. This tract, which lies mostly in Jefferson County, ·has long been famous for its mineral 

wealth. Helena, the capital of the State, stands on its northern flanks, and Butte, the greatest 

mineral producer of the country, on its southern foothills. The broad Deer Lodge Valley, to 

the west, separates it from the towering peaks of the Mount Powell Range. On the east it is· 

bounded by a continuous depression, formed by s-everal separate valleys~ which cuts it off: fro~ 

the higher ranges beyond. The tract thus outlined is broad and relatively low, none of its 

summits exceeding 9,000 feet in height, but it forms the main continental watershed separating 

the streams tributary to :Missouri River from those flowing into the Pacific Ocean. (See map, 

Pl. I, in pocket, and fig. 1.) 
1 I 

INTRODUCTION. 17 

Though often called the Boulder :Mountains, the tract contains no sharply outlined peaks, 

nor do its hills constitute a well-de:fi.rled range. Its central part is covered by a f<;>rest of sn1all 

pines, its lower slopes are open and grassy, and its valleys are arid; in scenery and mountain 

sculpture it presents a contrast to the more alpine type of the adjoining ranges_. Its geology 

is equally distinctive, and in this, as in its geog~·aphic relations, it constitutes a unit. 

· The city of Butte is the largest settle1uent in the State.· It is built about and over the 

copper mines which support it as well as the neighboring city, Anaconda, 20 miles dista~t, 

where the chief industry is tl~e reduction of the Butte ores. Four transcontinental railways 

run to Butte, and its traffic surpasses that of all the other cities of the State combined. 

To one approaching the city the general appearance is most desolate. Bare, brown slopes, 

burnt and forbidding, from which all vegetation was long ago driven by the fumes from the 

s:melte!~s, rise from an almost equally barren valley. The city lie~ toward the base of the slopes .. 

Within it and dotting all the hills about rise red mine buildings, which with the great heaps 

of gray waste rock fTOnl. the nlines form the. most conspicuous feature of the landscape. The 

waters· of Silverbow Creek flow through the valley toward the west, encircling the base of the 

slopes. West of the city is the sharply conical hill, Big Butte (Pl. II, A, p. 26), fron1 which the 

city takes its name. In itself, the city is not unpleasing, showing compact, well-built brick 

business blocks and many residences on hills which command magnificent mountain views. 

The area shown on the 1uap (Pl. X, in pocket) includes part of the nearly level floor of a 

broad·valley, l~cally called the Flat, traversed_by Silverbow Creek·and connecting with a wide, 

open basin to the west. The larger part of the mapped area is hilly and forms the outer flanks 

of a higher region to the north. Tlris tract, constituting the Butte nrining district, is· bounded 

by the low and almost featureless lake-bed country on the west and by the valley of Silver.bow 

Creek on the east and south. The general slope is westward, but a number of gulches transect 

the area, andtninor en1inences give a pleasing relief. The city is built upon the slopes of Mis- . 

soula Gulch, the largest of the depressions, and between it and a lesser depression to the east 

known as Dublin Gulch. The lesser settlements, known as Walkerville and Centerville, are 

built on the slopes above the city proper, and are really a part of it. The growth of the city 

northward is limited by the land owned by the n1ining companies, and the abrupt transition 

fr01n con1pactly built blocks to the bare surfaces of n1any of the mining claims is very striking. 

In the copper area the slopes are griclironed by railway tracks leading to the different 

n.unes, and great :rillne buildings, tall sn1okestacks, and steQl hoist frames mark the course of 

the greater veins. Throughout most of the silver area the monotonous aspect of the slopes is 

relieved only by occasional shaft houses, now mostly deserted, and by the almost inimmerable 

prospect pits and trenches, wlllch simulate gopher holes. The most important of these openipgs are shown on the topograplric map, but many of the shallower workings are unmarked. 

I-Ieaps of waste are everywhere prominent, attesting by their great size the extent of the 

undergrouncl workings. The n1any prospect pits and shafts pern1it a tracing of the veins, 

which otherwise would be in many places impossible. ·Yet even these are not abundant enough 

to deter.mine the boundaries of some of the rhyolite dikes, and it was only by a careful examination of the soil and in son1e places by ~ligging through the veneer of gravel-like debris covering 

the surface that the li1nits of the intrusive n1asses could be estab1ished. 

Originally na1ned the Sumtnit Valley district, a nan1e still retained in official records and significant of its situation ahnost on the divide where the waters of the Pacific and Atlantic separate, 

it is now universally known as the Butte district, the nan1e being. derived fron1 Big Butte. 

'The districtcois, as a whole, distinguished by a lack of pron1inent rock outcrops or strong 

. topographic features. The B~1tte alone is conspicuous. In the north part of the district a 

ntnnber of striking rock outcrops do occur, but throughout the mineralized area disintegration 

and decon.1position have been active agents. and good outcrops are rare. 

·The cli1nate is rigorous, owing to the altitude and midmourttain situation, but precipitation 

is not· abundant, the few strean1s are s1nall, and the water supply not plentiful. Silver bow 

Creek, the largest stream, rises in the lrigh granite region to the north, and Nlissoula Gulch has 

90<!27°-No. 74-12-2 
18 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

a small natural supply. A few springs on the otherwise bare and arid slopes afford scanty 

flows. The city has, however, an abundant water supply, derived from the high peaks to the 

south, and ditches bring water from higher levels on the eastern side of the Continental Divide 

·for the use of the concentrating plants and smelters. Vegetation is practically absent, but the 

stumps seen on Anaconda Hill attest a former forest growth and Dublin Gulch is said to have 

been once· green with verdure and trees. Though the higher country near by is green and 

wooded, the Butte district was never abundantly watered nor deeply wooded, resembling in 

this respect the foothill tracts surrounding the valley ou~sici.e the lin1its of the elistrict. 

DISCOVERY AND DEVELOPMENT. 

EPOCH OF GOLD MINING. 

The discovery of the .rich placer gold deposits of Bannock, Alder Gulch, and Last Chance 

Gulch in 1863 caused an extraordinary influx of population to the hitherto aln1ost unknown 

mountainous region of-Montana. A multitude of prospectors, trained in the gold placers of California, poured into the State and searched every valley and gulch for gold-bearing gravels. 

Gold was :first noticed in the placer gravels of the ~utte district by a passing emigrant 

early in the summer of 1864, at a point on the west side of what is now Main Street, but no 

placer mining was done in the district until late in the summer of that year. The following 

winter the Summit Valley district was organized and claims were staked out along :Missoula, 

Buffalo, Town, and Parrot gulches. Placer mining was not so remunerative here as at other 

camp's of the State, for the g.old was of low grade, worth but $11 to $14 an ounce, and occurred 

in fine particles; moreover; the gravel had to be hauled by ox. teams down to Silver bow Creek 

for washing. Several ditch lines were built, and in 1866-67 three of these carried water to 

the "diggings." One of these ditch lines is still in use. The amount of gold washed at Butte 

during the three years of placer mining has been estimated at $1,500,000. 

The quartz veins prominent on the hillsides about the placer field were promptly located by 

the early miners. The :first vein was located by W. L. Farlin, who staked the Asteroid clain1 

late in 1864 on the great black-stained quartz reef west of the city. This was called the Black 

Chief, but when afterward relocated became the Travona. During the next two years many 

lode locations were made, but at that time only free milling gold ores were sought; the black 

manganese-stained outcrops of the silver veins were not considered especially valuable until 

brought to attention by the discovery of the Comstock lode.· Claims along the Rainbow lode at 

Walkerville were located in the middle sixties; and at the Mountain Chief mine ore was taken 

out, shipped by wagon train to Fort Benton and by steamer down the Missouri, eventually 

reaching Newark, N. J. The town of Butte was laid out in the fall of 1866 and reached its 

greatest prosperity of this, its early stage, i'n 1867-68; later it was nearly deserted until 1875, 

when c'opper smelting began. After this it grew rapidly and became a city in 1879. 

EPOCH OF SILVER MINING. 

No excitement arose over silver ores until the rich ore shoot of the Travona mine was found 

in 1865. The first attempt to work silver ores was. made in a small arrastre built in 1866, just 

south of the Finlen (formerly McDermott) Hotel. The first mill, the Continental, an old 10-

stamp batte~y hauled in from Stirling, Mont., proved a financial failure. At this time some 

of the Travona ore was roasted and amalgamated and a few ounces of silver bullion produced, 

but no important development of the property was undert~ken until 1875, when Mr. Farlin 

erected the Dexter 10-stamp mill and furnace near the mine and began to treat the ore by chloridizing, roasting, and amalgamation. This mill . did not produce much. bullion until 1876, . 

when it was completed by W. A. Clark, and the first successful treatment of the silver ores of the 

district was commenced. · The price charged for treatment-$25 to $30 a ton-though not excessive for those times, led to active mill building. In 1868. a mill for treating ores by the freemilling process was built In a gulch. at the corner of Arizona Street and Broadway. It was later 

purchased by the Lexington Mining Co., a corporation formed in France, which built a 50-stamp 

mill, with roasting' furnaces, near the mine in 1881. 
INTRODUCTION. 19 

In1875 McEnery & Packard located a claim called the Acquisition, from which they shipped 

so1ne rich silver ore to Walker Bros. in Salt Lake City. The high value of this ore led Walker 

Bros. to send :Marcus Daly to the district to look over the mining prospects. l-Ie arrived in 

1876 and took a bond on the ~\.lice n1ine for $5,000. Robert Walker and Prof. John E. Clayton 

then caine to Butte, and selected the site of the present _main shaft of the Alice mine as a suitable 

place for sinkip.g. Prof. Cln,yton nanied the great lode on which the Alice, ~1agna Charta, Valdemere, and ~1oulton · clain1s are .located ·the Rainbow loae, from the broadly sweeping curve 

of its outcrop. . 

Work was started in the late summer of 1876. In 1877, the Alice shaft. having reached 

1t depth of 200 feet, an old 20-stamp mill was brought in fron1 Ophir Canyon, Utah, and was 

erected on the p~·operty. It was a dry-crushing plant (water in sufficient quantities for wet 

crushing not being available) and was designed to treat oxidi~ed or free-milling ores. This 

n1ill started in the fall of 1877. In 1878 and 1879 a White-Howell :roaster was added, thus pro~ · 

viding for the chloridizing roasting of sulphide ores, and the Washoe process was introduced. 

The 60-stamp mill of the Alice Co. was built in 1880 and was equipped with two White-I-Iowell 

roasters and revolving drier. The ~1oulton mill, compl~ted about the same time as the Alice, 

was equipped with 40 stan1ps and White-I-Iowell roasters. . 

The Silverbow ~1ining &·~1illing Co.'s null was built in the early eighties for tlu) treatment 

of ore fron1 the La Plata and other mines owned by the company. In 1884 the Bluebird mine 

was purchased by a London company, and in 1886 ~ 90-stanlp n1ill built for the property was 

co.mpleted. 

The cli1nax of whp.t 1nay be called the silver period of Butte's history was reached in 1887, 

when the Alice null was dropping 80 sta1nps, the :Moulton 40, the Lexington 50·, the Bluebird 90, 

and the Silvm:bow 30, a total of' 290 stamps. The amount of ore worked in these mills aggregated nearly 400 tons a day, to which should be added the silver ores shipped to the smelters, 

aggregating probably at least 100 tons a day. 1\.ll this ore carried considerable gold. The 

average yield was probably about $25 a ton in gold and silver. 

The period of active silver n1ining continued until1892, when, in common with other s.ilver 

producers, the Butte mines were t~thnost prostrated by the decline in the price of silver. A few 

1nines, notably the Nettie and Lexington, continued to work up to 1896-97, and others have 

worked at intervals since then,.but none has been an active producer since 1896 save the Lexing-· · 

ton, in wluch veins carrying copper are mined. . . · 

In the h,istory of Butte the 1netallurgical advance in the treatment of 'the silver ores has 

been very steady, the free-milling process giving place to chlorination and roasting, and these 

in turn to n1ore improved 1nethods, so that ores lower and lower in grade could be treated. With 

the great decline in silver in 1892-93 and the closing down of all the large silver plants in 1896, 

the nuning of silver ores became of relatively slight importance and has since been carried on 

chiefly by lessees. The present importance of Butte as a producer of silver and gold is due to the 

fn,ct that each pound of copper produced contains 0.0375 ounce of silver and $0.0025 in gold, or 

approxi1nately $0.02! in precious n1etals. According to this ratio the Butte copper mines 

yielded 8,550,090 ounces of silver in 1891. 

DEVELOPMENT OF COPPER MINING. 

I 

As most of the coppe1: ledges were destitute of vegetation and the. Parrot ledge, just north of 

the city, was strewn with copper carbonates, the copper veins were early noticed. The claims 

along the Parrot lode, mnbracing the Park, Parrot, Original, and Gagnon rriines1 were among 

the first located, the papers being filed October 14, 1864. In 1865 the Park had a 40-foot shaft, 

whicli disclosed a vein of copper ore 6 or 7 feet wide. In 1866 an unsuccessful attempt was made 

to s1nelt ·copper ores from the Parrot mine. About a year later a second smelter, built of rock 

n.nd provided with n. bellows blast, was put in the gulch of the Washoe clain1; this also proved a 

failure. ·In this period no. ore was known to exist in Anaconda I-Iill; the Anaconda-Neversweat 

dain1 was not located until1875 and the patent not applied "for until February 18, 1878. 
20 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

In 18'72 W. A. Clark turned his attention to the copper veins of the district and in 18'73 and 

187 4 began to develop the Original, Col us~, Mountain Chief, and Gambetta claims. The ore from 

these claims was hauled 400 miles in wagons to Corinne, whence it was shipped by rail to various 

buyers o~ copper ore. Among the latter was the Boston & Colorado Smelting Co., at Black 

Hawk, Colo., and in 18'78 Mr. Clark suggested to the management of tlus company the construction of a custom smelter in Butte. Henry Willian1s was sent to examine and report on the outlook. I-Iis report being favorable, the Colorado & Montana Smelting Co: was formed in 18'79, 

the present site of the Colorado smelter ·was purchased and reduction works were erected, so 

that a local market for the copper as well as for the silver ore of the district was established. The 

importance of this smelter can be judged from the fact that one shipment of 35 per cent copper 

ore from the Green Mountain claim to the works at Baltimore, l\1d., in 18'7'7, gave no profit to the 

shipper after mining, freight, and reduction costs were paid, although the ore carried about $130 

a ton in copper (then worth lSi cents per pound), and not less than $50 a ton in silver and gold. 

The smelters charged a higl:t price for treatment, owing to the presence of arsenic, which in those 

days was a troublesome element in smelting. 

The Colorado Smelting Co. leased the Fredonia, Nettie, and Selfrising mines and, using 

their manganiferous silver ores as flux,· made a copper matte, or regulus, which was shipped to 

.the Argo works in Colorado for further treatment. In 1883 the company was reorganized and 

consolidated with the Gagnon mine, which has since furnished the main sup.ply of ore for this 

smelter. This company was afterward called the Trenton. 

In 1881 Marcus Daly, representing the newly organized Anaconda Silver Mining Co., leased 

the Dexter mill and treated about 8,000 tons of oxidized silver ore from. the Anaconda ledge, 

obtaining about 30 ounces of silver to the ton. The ore contained just enough copper to make 

it unnecessary to add bluestone in raw amalgamation but yielded a very base bullion, some of 

which ran only 400 fine. A seam of copper glance a few inches wide encountered at a depth of 

100 feet, however, led to further extensive development. George Hearst, on visitmg the district, recommended deep development and selected the site of the present Anaconda shaft as 

the most suitable place for sinking. A crosscut run fron1 this shaft at a depth of 300 feet 

encountered 5 feet of copper glance, which was extracted and shipped to Swansea. Soon after 

this. the smelters of the Parrot, Montana Copper, Clark's Colusa, and Bell companies began operations, the n1atte produced being shipped to eastern markets for refining. The formation of 

the Butte Reduction, Boston & Montana, Butte & Boston, and :Montana Ore Purchasing 

companies, in the years 1884 to 1896, greatly a~ded to the production of copper of the district. 

The advent of the railroads marked the beginning of Butte's prosperity. The Utah Northern, which was finished to Butte December 21, 1881, gave access to Ogden, Salt Lake City, and 

the markets of the world over the Union Pacific lines. On July 12, 1888, the l\1ontana Central 

Railway, which for some months had been racing with the Northern Pacific to get to Butte, was 

completed and thrown open for traffic. The branch line of the Northern Pacific from Helena 

·was never completed to Butte, but a few years later that company built a line from Three Forks 

direct to Butte. The Montana Union Road from Butte through the Deer Lodge Valley to Garrison, on the Northern Pacific, built by the Union Pacific interests, was finished on September 

8, 1893. An interest in this road was purchased a few years later by the Northern Pacific, and 

it was operated jointly by both companies; it is now owned and operated by the Northern 

Pacific system. · 

··In the year 1883 the Anaconda Co. commenced the erection near Anaconda on Warm 

Spring Creek, a branch of Deer Lodge River about 27 miles w~st of Butte, of what soon became 

one of the largest copper-smelting plants of the world. The works were partly destroyed by frre 

in 1889, but were immediately rebuilt. I-Iowever, they soon proved too small and too far out of 

date to har~dle the increasing output of the mines, and in 1900 a new plant called the Washoe, 

with a daily capacity of 8,000 (now 12,500) tons of ore, was built. 

In 1886 the Butte Reduction Works were built on Silverbow Creek, just south of the city, 

and, after changing hands several times, became the property of W. A. Clark & Bro., who still 

operated them in 1906. The Great Falls Copper Smelter, completed by the Boston & l\1ontana 
.. 

· INTRODUCTION. 21 

Silver & Copper Co. in 1892, has been gradually enlarged until it now handles 4,500 tons of ore . 

a day. 

The organization of the Amalgamated Copper Co. on April 27, 1899, was one of the 1nost 

important events in the history of Butte. As a holding corp~ration this company soon acquired 

control of the larger copper properties of the district, owning the entire capital stock of the 

Washoe Copper Co. and the Colorado :Mining & Smelting Co. (now the Trenton) and controlling 

the Parrot and Anaconda companies. In 1901 the capitalization wa.s increased from $75,000,000 

to $155,000,000, and the Butte & Boston and the Boston & :Montana Consolidated Copper & 

Silver companies were purchased. The Amalgamated therefore owns the greatest mines of the 

district and, by its affiliation with the Butte Coalition and North Butte Copper companies, 

controls all the large mines except the two owned by W .. A. Clark. 1 

About 1893 the :Montana Ore Purchasing Co. was organized by F. A. Heinze and associates 

and soon becmne an important factor in the mining industry of the district. Owning the Rarus, 

Cora, and Rock Island claims, with chief ownership in the Parnell, L. E. R., and Nipper mines, 

and with interests in the Snohon1ish and Tramway claims this con:tpany soon entered into an 

active legal can1paign to capture the great ore bodies of the mines worked by the Boston & 

:Montana and Anaconda companies. In the subsequent litigation the Heinze interests won 

in the lower courts, many mines were shut down -by injunctions, n.nd veins worked for years 

by the opposing companies were, by decree of the courts, turned over to the :Montana Ore 

Purchasi.Dg Co. The result was a great diminution in th~ output of the district. Most of 

this litigation was based on the so-called' 'law of the apex," .which gives to the owner of a mining 

cln.in1 the right to follow his vein downward in depth underneath the surface owned by other 

people. Owing to the complicated faulting and the closely spaced vein systems the experts who 

testified in the various lawsuits gave conflicting testimony, for many of those who were not specially trained in nuning geology did not understand the prevailing conditions. In the frrst great 

suit, known as the Ran1s· case, the continuity of a number of veins through and across the Rarus 

fault was alleged. In the second great case, known as the Colusa-Parrot, brought by W. A. 

Clark, at that tin1e an ally of the Heinze interests, against the Anaconda Co. for possession of 

tl1e Anaconda vein in depth, a junction of veins downward· and consequent ownership by reason 

of prior location was claimed. This claim was opposed by the Anaconda Co., which offered 

proof of the existence of a cross fault called the Blue Vein, cutting off and displacing the Anaconda ledge. The Anaconda Co.'s claim was sustained by Judge Ivww~es of the United States 

district court. 

The acquisition of the :Minnie IIealy mine by the I-Ieinze interests was followed by the starting of several suits involving the ownership of the extremely rich ore bodies mined in the Leonard 

'and other claims of the Boston & :Montana Co., and of other suits :involving the ownership of 

the rich veins in the Pennsylvania mine and the ore bodies of the Nipper mine. 

A protracted period of litigation was ended in 1906 by the sale of the I-Ieinze interests to-

:Mr. F. A. Cole, who organized the Butte Coalition Co., a holding corporation, and the Red :Metal 

Co., a n1ining corporation, formed to work the properties in contest. A satisfactory agreement. 

between the various companies was thus reached and litigation was ended. 

In 1902 the United Copper Co., a securities-holding corporation s:inlllar to the Amalgamated 

was organized and acquired control of the Montana Ore Purchasing Co. and of other com-· 

panies organized by :Mr. I-Ieinze in his legal campaign against the Amalgamated. As already 

stated, this company has been succeeded by the Butte Coalition Co~ . 

In 1904 the newly organized North Butte Copper Co. acquired control of the Speculator 

1nine for $5,000,000, and subsequently purchased a number of clauns lying in its immediate 

vicinity. Large and extremely rich ore bodies were soon uncovered in these properties and the 

c01npany became an important copper producer. Its success-led to the organization in 1905 of 

the East Butte Copper Co., which owns a number of claims in the southern part of the copper 

area. 

1 These were purchased in 1910. 
22 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The Pittsburg & Montana Co., organized in 190'2 to develop a la~ge tract lying between the 

copper area and East Ridge, explored the ground by several shafts 1,000 or more feet in depth 

and by extensive underground workings, and proved the existence of copper ores beneath the 

flat. In the years 1905, 1906, and 1907 many explqration c01npanies were organized to develop 

outlying portions of the district, in which up to that tin1e no copper ores had been found. The 

future of the district depends largely on the success of these companies. 

PRODUCTION. 

The enormous value of its metallic product n1akes the Butte district. the n1ost in1portant 

mining center in the United States and the second greatest in the world. Its annual production 

is exceeded in value only by that of tJ?.e Rand, in South Africa, which was $101,000,000 in 1905 

against about $65,000,000 for Butte. Up to the close of 1906 the total product of the. Butte 

district may be roughly estimated at $650,000,000, which is considerably in excess of that of. 

Leadville and probably about that of the Comstock lode. 

It is not possible to obtain strictly accurate data concerning the early production of the 

district, for in the pioneer days no records were made and in later years some of the larger 

companies, for business reasons, have not been willing to disclose their exact output. The 

statistics presented in various publications, however, show that up to January 1, 1906, 

971,000 ounces of gold, 194,ooo·,ooo ounces of silver, and 3,961,000,000 pounds of copper were 

mined in the district. The placer gold production of the district has been comparatively unimportant, being not only small in amount but also low in bullion value, on account of the large 

alloy of silver. At present gold forms about 3 per cent of the total value. 

Silver in the district is now mainly a by-product of copper mining, the copper ores containing about one-fourth ounce of silver to 20 pounds of copper, or, in value, about 14 per cent of 

silver to 86 per cent of copper. · 

The annual copper product in 1906 was about 283,000,000 pounds, constituting the pre-

. dominant value in the yield of the district. Its increase, both absolute and relative, in the last 

decade has been great. 

In 1888 nearly 41 per cent of the total copper product of the world came from North 

America and over 92 per cent of this was furnished by the United States. In 1895 the North 

American proportion of the world's product was 56! per cent and in 1905 it had increased to 

69 per cent. 

Previous to 1880 ·the Lake Superior region produced,. on the average, more 'than 80 per 

cent of the total copper product of the United States. In 1883 Lake Superior's proportion 

of this total product was 51.6 per cent, Butte's was 21.4 per cent, and Arizona's was 20 per cent. 

In 1887 Butte pas$ed Lake Superior, and in 1905 the relative percentages were: Montana (Butte), 

31.2 per cent; Arizona, 28.9 per cent; Lake Superior, 25.3 per cent. In 1906 Butte was furnishing about 20.6 per cent of the copper product of the world, n1ore than three-fourths of which 

was from mines controlled by the Amalgamated Coppe1~ Co. In 1907 Montana produced 

25.81 per cent of the total copper output of the United States, or 13.8 per cent of that of the 

world. · 

In early years the statistics of the Butte copper production were not carefully kept. The 

.firs.t definite statement is by the Director of the Mint in his report for .1880, in which he 

credits ·the district with a production of 9,452,800 pounds of copper. In succeeding years 

the production increased rapidly. The total output fro1n 1880 to the end of 1905 is estimated 

at 38,000,000 tons of ore, which yielded 3,960,964,935 pounds of copper. At the average 

price prevailing during the year of its production, this copper was worth $498,493,035. If to 

this sum be added the value of the gold and silver produced from the copper ores mined in the 

district the total value will. approximate $600,000,000. 

The following table was prepared by l\1r. Emmons from 1nany sources, including c01npany 

records, reports on the mineral resources west of the Rocky l\1ountains, records of the division of 

mineral resources of the United States Geological Survey, and reports on the production of 

precious metals by the Director of the Mint: 
INTRODUCTION. 23 

Production of the Butte district, by years, frorn 1882 to 1910.a 

Year. 

1882 ••........................ 

1883. •·•·•·•· ................ . 188•1. •.•...................... 1885 ••........................ 1880 ••........................ 

1887 .•... ············· ....... . 18&8 ......................... . 1880 ••........................ 1800 .•...•.................. · .. 1801 ......................... . 1802 ••........................ 1803 ••........................ 1804 ••....... : ............... . 

1895 ••. ·········· •............ 1890 .•........................ '1807 ......................... . 

Golcl.b 

Ounces. 

12,094 

14,501 

21,770 

13,838 

31,223 

48,175 

44,320 

31,052 

25,705 

20,305 

30,223 

33,808 

30,708 

41.433 

59;8w 

54,108 

Sllver.b 

Ounces. 

2,699,290 

3,480,547 

4,481,180 

5, 180,331 

5, 924,315 

G,958, 981 

8,275,950 

G,500,038 

7,500,000 

7,985,090 

8,311,130 

G,G08, 730 

7,5Gl, 124 10,051, 7GO 

11,120,732 

10,710,815 

Copper.c 

Pounds. 

9,058,284 

24,0G4,340 

43,093,054 

G7, 797,8G4 

57,Gll,G21 

78,699,()77 

97,897,908 

98,222,444 

112,980,800 

112, or..a, 320 

1()3, 200,128 

155,209,133 

183,072, 75G 

190, 172, 150 221' 918, 179 

230, 288, 141 

. Year. 

1898 ......................... . 1899 •......................... 1900 .•........................ 1901 ......................... . 1902 ......................... . 1903 •......................... 1904 ..........•............... 1905 ......................... . 1900 ......................... . 1907 ......................... . 1008 ......................... . 1909 ......................... . 1910 ......................... . 

Gold.b 

Ounces. 

55,344 

02,038 

54,552 

45,850 

40,051 

48,800 

46,974 

61,251 

00,495 

34,368 

32 005 

39,443 

37,014 

Total. .................. 1, 159, 110 

Sllver.b 

Ounces. 

8,990,555 

9,855,831 

9,454,279 

10,136,892 

10,106,884 

9,811,544 

10,530,582 

11,191,016 

10,715,721 

7,510,n59 

8,500, 729 

10,609,328 

10,400,840 

241,290,885 

Copper.c 

Pounds. 

206,173,157 

225,126,855 

270,738, 48!l 

229,870,415 

288,903,820 

272, 555, 8.'i4 

290,032,979 

304,307,893. 

289,780,050 

218,836, 627 

250, 150, 712 

311,323,050 

284, 264, 862 

5, 288,021,324 

·a Tho stntlstlcs for Butte being confidential, the production for the county is given; for gold and silver this corresponds closely to that or the 

precious metals recovered from copper ores Cor the whole State. · b Figures from rol)orts or Director or the Mint and from Mlnernl Resources; U. S. Geol. Survey. . c Figures from M: neml .Resources, U. S. Geol. Survey. 

The table shows the total production of gold and silver fr01n the Butte district for the 

years given, but does not give the silve·r produced frorn the silver-bearing veins as distinguished 

fr01n the copper-bearing. veins. The silver mines proper yielded much gold and silver fron1 

1888 to 1893, and have continued to yield lesser amounts up to the present· time, but there is no 

way of diHerentiating this product. 

In the following table the Butte production from 1881 to 1897 is separated according to comparlies, and their relativ.e importance is readily. seen. 

P1·oduction of copper in the B1.ttte district, by 1nining and s1nelting contpanies, front 1881 to 1897. 

[In pounds.) 

· Year. Anaconda. 

1882 ................................. .'....... a 33,300,000 

1881. ...... : ................................. } 

1883 •............ •···· ...................... . 1884 ........................ .' .............. :. 3,886,000 

1885 ..•............ : ...................... ·... 40,462, 000 

188G... .. . .. .. ... .. ....... .. . . .. .. .. ......... 32,858,000 

1887....................................... . . 59,242,000 

1888.. ... .. ... .... .. .. .. .. . . .. .. . .. .. .. . . . . .. G7,106,000 

1889... .. ....... .. ..... .. .. .. . . . .. .. .. .. . . . . . G1,810,000 

1890......................................... G7, 670,000 

180.1....... .. .. .. .. . .... .. . .. .. . .. .. . ... . . .. . 48,098,000 

1802......................................... 93,918,000 

189:i......................................... 81,446,000 

1894.... ... ........... ... .. .. . .. .. .. . .... .. . . 08,680,000 

1895......................................... 103,442,000 

1896......................................... 119, 700,000 

1897......................................... 128,391, 100 

Boston & 

Montana. 

Butte Colorado 

Butte & Bos- R d t• Mining & ton (now part ~V~~k~on. Smelti.ng Co. of~- & M.). (W A Cinrk) (Trenton · · " · Copper Co.). 

Parrot. 

Montana Ore· 

Purchasing 

Co. (Butte Coalition). 

· · · · 1; soo; ooo · :::::::::::::: · · · · 2; soo; ooo · · · · · i; 2oo; ooo · · · · · 9; sw; ooo · :::::::::::::: 

2,000,000 ..•..•.•..•... 1,935,846 2,000,000 10,000,000 ............. . 1,500,000 .............. 1,G49,308 1,411,000 10,000,000 ............. . 18,278,667 . . • . . . . . . . . . . . 3, 549,105 1, 440,000 10,750,000 ............. . 26,425,228 1,103,125 2,499,G48 1,774,400 9,500,000 ............. . 26,942, 298 5, 48.5, 434 3, 332,934 2, 252, 200 9, 000,000 ............. . 26,567,929 18,392,054 2,912,274 3,365,200 14,108,382 ............. . 30,386,595 10,G41,269 2,850,227 4,070.800 12,438,782 ............. . 31,800,000 20,457,928 3,078,337 6,809,000 7,791,167 8,400,000 

57,937, f>33 2,281,99a 4, 210,198 7,469,908 12,293,086 

00,746,000 3,393,920 8,004,848 7,257,000 14,861,000 

gg: ~8: ggg 'I· ... ~~~~~~~~~. 4,237,660 9,267,496 8,045,648 14,230,000 

8,645, 782 8,911,578 14,997,000 13,047,048 

a Ore sold. 

The Anaconda, the largest of the copper-producing companies, produced from June 

30~ 1884, to June ·30, 1898, a period of fourteen years, 9,.575,793 tons of ore, .which yielded 

1,068,922,000 pounds of copper. This is equivalent to 5! per eent copper, 4! ounces silver, 

and 35 cents gold per ton of ore. This output covers the period during which the bonanza 

ore bodies of the Anaconda were 1ninecl, and very large amounts of extremely high grade ore 

were extracted. 
24 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT; MONTANA. 

Production of Butte mines in May and June, 1907. 

Daily production. Production for May. Production for June. 

Companies. 

Ore. Copper Total. Ore. Copper. Ore. Copper. per ton. 

------

Tons. Pounds. Pounds. Tons. Pounds. Tons. Pounds. 

3,500 67 234,500 108,500 7,269,500 100,500 6,834,000 

4,250 61 259,250 131,750 8,036, 750 123,000 7, 380,000 600 60 36,000 18,600 1,116,000 19,500 1,209,000 400 59 23,600 12,400 731,600 10,650 628,350 350 58 20,300 10,850 629,300 11,250 630,000 380 60 22,800 11,780 706,800 12,000 708,000 

1,300 92 119,600 40,300 3, 707,600 37,500 3,003,500 

1,550 65 100,750 48,050 3,123,250 45,000 2,970,000 950 62 58,900 29,450 1,825,900 24,000 1,488,000 200 so 16,000 6,200 496,000 6, 750 52fi, 500 225 70 15,750 6,975 488,250 7,500 525,000 

Boston & Montana ................................................. . Anaconda .......................... · ................................ . Butte & Boston ......................... : .......................... . Washoe ............................................ -- .. -.. --.----- .. Parrot ................................................. -........... . Trenton ................................................ -.......... . North Butte ....................................................... . Coalition ........................................................... . Original. ................................................ -......... . East Butte ........................................................ . Pittsburg & Montana .............................................. . 200 68 13,600 6,200 421,600 } 3,000 225,000 200 75 15,000 6,200 465,000 

La France ......................................................... . Miscellaneous ...................................................... . 

Total ........................................................ . 14,105 66 936,050 437,255 29,017,550 400,650 26,161,350 

The above table, compiled from figures furnished by the Mining and Scientific Press, shows 

the relative importance of the different mines as producers and indicates plainly the low-grade 

character of the ore now being treated. The best ore is mined by the North Butte Co., which 

is extracting extremely high-grade glance and enargite ores from the Jessie and Edith May 

veins. The output of this company, 1,300 tons a day, averaging nearly 5 per cent in copper, 

. approaches that of the Anaconda mine during its bonanza days. The lowest-grade ore, carrying only 3. per cent copper, comes from the Trenton Co.'s Gagnon mine, but the Anaconda 

ore contains only 1 pound more of copper per ton and carries lower silver values. 

COSTS. 

The cost of producing a pound of copper is made up of the costs of mining, reduction, freight, 

and selling. In 1906 the cost of Butte copper ranged from 9! cents to 11 cents a pound at 

the mines. As the cost per pound. dep'ends largely on the character and richness of the1 ore, 

as well as on the cost of mining and production, no general or comprehensive statement in 

regard to it can be made. Mining cost alone, including that of ore development work, ranges 

from $2.75 to $3.50 per ton. Th~ system of working with square sets, necessitating great 

quantities of timber and the .presence of soft ground, making it. necessary to drive laterals 

parallel to the vein from which crosscuts are made, increases the cost per ton to a figure that 

is high compared with that of other districts.. The pumping expenses have been minimized 

by a system of drain tunnels which concentrate the water fron1 the entire Amalgamated properties at the I-Iigh Ore shaft. l\1oreover, there has been a decided saving in the amount of 

copper recovered fron1 the mine waters, it being generally stated that the copper so recovered 

pays the entire expense of pumping. 

The cost of mining and reducing silver ote at the Lexington mine was given at $18.58 

in 1902. (Seep. 240.) 

FUTURE OF THE DISTRICT. 

As it is the duty of the geologist to formulate, if possible, such deductions· concerning 

the future of the district as the facts appear to warrant, it seems proper to state that the evidence accumulated in this study indicates that the quartz-pyrite veins are becoming exhausted 

with depth, that the amount of glance is decreasing, but the limit of workable ore has. 

not 'yet been reached. In all the big veins of this class the amount of glance is notably less 

at the bottom levels. On the Syndicate ledge the main vein is lean on the 2,200-foot level 

except at afew places where fracturing is most severe. On the 2,400-foot level the Anaconda 

lode proper is lean, but the Middle ledge, which is a fault vein, contains a large ore body of 

high-grade glance ore. 

On the other hand, the fault fissures, which are now generally recognized throughout the 

district, hold little if any ore in the upper levels, but contain large ·and rich ore bodies at· depths 
•. 

~ 

INTRODUCTION. 25 

of 1,000 to 2,000 feet; at the -iiigh Ore mine one of these levels is sn.id to show a large high-grade 

ore body as deep aR 2,800 feet. As is stated elsewhere (p. 77), the proportion of enargite coming 

in at the deeper levels gives hope that tlus mineral may extend downward for several hundred 

feet. At any"rate it is believed that the fault veins will make up for the deficiency in the older 

ores and that the future of the district is· assured for many years. The mining, in 1906-7, 

of ores carrying 2 per cent or less was a result of the high price of copper and was due to the 

desire of the mine managers to take advantage of the opportunity to prolong the life of the mine · 

by extracting the low-grade ores wluch would not pay for mining when copper was at a lower 

price. The tables of production show that a maximum has been reached, and a knowledge of 

the n1ining conditions indicates that the output of the district will remain constant for some 

years to come and will then g.radually and slowly decline. It is believed that some nlOdification of the flotation process or newer and cheaper methods of milling, which may lead to the 

recovery of n1etal now lost in slimes, will make pay ore of what is now called waste. The 

z1nc ores of the district also promise to be of great value and to add both to the wealth of the 

district and to the length of its productive period. · 
CHAPTER !I.-GEOLOGY OF THE REGION. 

RELATIONS AND BROADER FEATURES. 

The rocks in the Butte district are of igneous origll_l, are of few types, and are closely related 

in mineral and chemical composition, though very different in appearance. To enable the reader 

to understand the origin and relation of these rocks and their bearing on the economic geology 

of the district it is necessary to present a brief sketch of the geologic features and history of the 

larger region of which the .Butte area. is a part. 

The map (Pl. I, in pocket) shows the areal distribution of the rocks in the region about 

Butte. Its area includes the gold district near flelen~, the Elkhorn silver-lead district, and a 

large number of other silver-mining districts, of which those of Wickes, Lump Gulch, Red 

Mountain or Rimi.J.ii, Lowland Creek, and Whitehall are the 1nost important. Many of these 

ate on the borders of the granite area, but others are well within it. 

IGNEOUS ROCKS. 

The quartz monzonite of the Butte area is part of a mass of granular rock, clearly of 

igneous origin, which has broken its way through and has altered earlier sedimentary and 

·igneous rocks and has itself been partly covered by later volcanic outbursts and cut by massive 

rocks. The areal extent of this granitic batholith is shown on the map (Pl. I), on which the 

general features of the geology are delineated. The area covered by this map, 60.4 miles from 

north to south and 38 miles east and west, is 2,295 square miles; it embraces parts of four of 

the quadrangles of the United States Geological Survey. It includes not only the Butte district 

but several others of the best-lmown mining districts of Montana as well. · 

Geographically this tract is in the center of the mountainous part of the State. The map, 

however, shows only part of the delimiting valleys east and west, the area mapped having been 

selected primarily to show the extent and outline of the granitic mass, often briefly referred to 

as granite. . . 

A tract 40 miles wide and 70 miles long from north to south, extending from the peaks of 

Red and Table (Highland) mountains on the south nearly to Helena on the north, and from 

the Deer Lodge Valley on the west to the Elkhorn Mountains and Bull l\1.ountain on the east, 

is underlain by granite concealed in part by other igneous rocks but constituting one connected 

mass. This gr.anite is traversed by different well-defined systems of joint planes, is extensively 

decomposed in some localities, and weathers into rugged crags, monoliths, and great bowlder 

masses, which form the picturesque scenery so frequently typical of granitic areas (Pl. II, B). 

'J;'he larger topographic features lack the ruggedness of the sedimentary ranges, for the coarsely 

granularrock weathers down into broad summits and smooth-surfaced valleys. 

SEDIMENTARY ROCKS. 

Broken and folded sedimentary rocks many thousands of feet in thickness form higher 

peaks and ranges that surround the granite and afford evidence as to its age and igneous nature. 

These sedimentary rocks are shown on the ·map (Pl. I) at six principal localities, the exposures 

not being visibly conne-cted, as later detrital deposits cover much of the lower country. The 

granite contact is irregular, and could not be shown completely without greatly .eii.largin,g 

the map. 

The sedimentary ·rocks consist of sandstone, limestone, shale, and slate. Many beds contain fossils, the series including strata ranging in age from oldest Algonkian to late Cretaceous. 

The stratigraphic section is practically that common to central Montana, and the forma-

. tions are similar in lithological character to those found in the Little Belt and Front ranges of 

the State. The lowest strata are phyllites and slates with interbedded sandstones and belong 

to the Belt series, of Algonkian age. At the southern border of the area they rest unconformably 

26 
U.S. GEOLOGICAL SURV EY PROFESSIONAL PAPER 74 PLATE II 

A . GENERAL VIEW OF WESTERN PART OF BUTTE DISTRICT, INCLUDING THE BUTTE. 

See page 17. 

B. SHEETED GRANITE OF BOULDER BATHOLITH NEAR HOMESTAKE TUNNEL. 

See page 28. 
GEOLOGY OF THE R~GION. 27 

upon crystalline schists, supposedly Archean. The next succeeding terrane contains Middle 

Cambrian fossils, the Lower and Upper Cambrian faunas being absent. The rocks embrace a 

basal quartzite, with shales, limestones, and limestone conglomerates readily distinguished from 

those of the un~erlying Belt series, and an o.verlying black limestone, the Jefferson limestone of 

Devonian age. A thi1i belt of shaly impure limestones-the Threeforks shale, also of Devonian 

age_;intervenes between the black limestone and the massive white limestone (Madison limestone) of the Carboniferous; the most conspicuous rock of the sedimentary series. The whit~ 

:Madison limestone is succeeded by white and pale-pink quartzite, also of Carboniferous age, 

known as the Quadrant quartzite. The Triassic 0) red b~ds, so conspicuous in "\IVyoming and 

Colorado scenery, are not preseu.t. Jurassic fossils occur in abundance in impure marly shales 

and limestones, which are succeeded above by rocks carrying Cretaceous fossils. The youngest 

sedimentary rocks (except only the N eocene lake beds) are the post-"Laramie" rocks, exposures 

of which occur in the extreme southeast corner of the area shown on the map (Pl. I, in pocket). 

Thes·e stratified· rocks are unaltered except near the granite borders and are conformable 

with those lying farther east. · 

The structural relations of the sedimentary rocks differ at each of tlie localities shown on 

the map. Near IIelena the strata all dip southward and form the southern flank of a broaddomed uplift whose center, now eroded away, forms the basin known as Prickly Pear Valley. 

At Elkhorn, at the eastern limit of the area mapped, the beds are conformable to those folded 

in the Crow Creek I-Iills. Near "\IVhitehall and south of Jefferson River the strata are parts· of 

the general folds formed during the mountain-making uplifts of the region. At none of these 

places do the igneous rocks markedly disturb the attitude of the beds. 

ANDESITE. 

The igt~eous rocks that rest upon and flank the granite mass are of two distinct kinds and 

represent two distinct periods of volcanic activity. The older rocks are ·andesites and diorites. 

The andesites differ in appearance from place to place but are generally dark colored and have 

a compact and dense groundmass, commonly dotted with porph)~ritic crystals of feldspar, 

augite, and other minerals. They are readily distinguished from the granites, from which they 

differ in color, texture, and character of outcrop. Though usually 1nassive and dense, porous 

Yarieties and vnrieties containing agate nmygdules also occur: Owing to their superior hardness, fragments of andesitic rock are numerous and conspicuous in the gravels of all the streams 

draining localities where bodies of andesites occur. 

The andesites are of volcanic origin and are older than the granite. In part they are 

intrusive, breaking through the sediments, and in part extrusive, forming accumulations of 

breccia, underlain by granite. They probably once covered a large part, if not all, of the granite 

t.ract, but are not now found near Butte,. though they form the high mountain summits 

east of the granite region extending from the valley of the Jefferson northward to :Missouri 

River. They also occur i- LUmerous isolated areas throughout the central. part of the mountain 

n1ass between Butte an1 '1lena. :Mineral deposits· occur in the andesites as well as in the 

.acidic granites, productive . tlins in them having been worked at the. Zosel district, a few miles 

east of Deer Lodge, at Wickes, Alta :Mountain, and elsewhere. 

The andesitic rocks are largely fragmental, in places rudely bedded, and co.ntain lava 

flows, dikes, and sills. They evidently represent the remains of old volcanic piles. The distribution of these rocks and their relations to the granite show that they once covered a large part or 

all of the region. These -rocks form the Elkhorn :Mountains. At 'rhunderbolt :Mountain, 20 

n1iles north of Butte, unaltered bedded andesitic tuffs show fragmental leaf remains and fossil 

wood, and greatly resemble the middle Tertiary beds of the fossil forests of Yellowstone Park. 

In general, however, the andesites show mdui·ation and pronounced metamorphism near the 

granitic contact, having evidently been baked and altered by the granite. :Moreover, the granite 

near Pipestone Springs includes fragments of andesite. The granite is therefore the younger 

rock, intruded both along the contact and from b~neath upward into the mass of andesite. 
28 GEOLOGY AND ORE DE~OSITS OF BUTTE DISTRICT, MONTANA. 

This is not the view formerly held, which was based on the occurrence of andesiti<? caps on 

many granite ridges, the other evidence being then unknown} 

The thickness of the andesitic rocks which once covered the granite can not be conjectured, 

as the only remnants now remaining are north and west of the town of Boulder. · 

GRA-NITE. 

The granite area is the exposed part of a great mass, a batholith, which, intruded from 

below, has taken the place of the sedimentary and pregranitic rocks which undoubtedly once 

covered this district. Similar batholiths of· granite occur elsewhere in the ~1ontana ranges 

and are all probably connected with a deep-seated parent mas~ that underlies the entire region 

between the Front Range and the Idaho plains. Thus the granite and the older andesite and 

the rhyolite make up a mountainous region, which, though it contains no commanding peaks 

and summits, forms the continental water parting that separates the Atlantic from the Pacific 

drainage. The granite is called the Boulder batholith, beeause the greater part of the area 

over which it is exposed is drained by Boulder River and its branches, and because the county 

seat, Boulder, lies at about its center. 

The rock of the batholith (Pl. II, B) is a quartz monzonite of very uniform composition 

through the entire area except at its contaet with sedimentary rocks, especially limestones, 

where it shows basic facies, and in the Butte district proper and its vicinity, where it shows an 

uimsual and significant amount of aplite. The rock prevailing about the copper mines has in 

previous publications been called Butte granite. Although it is technically a quartz monzonite 

and is called in this report the Butte quartz monzonite it will for convenience be frequently 

referred to as granite. It contains .all the ore deposits of Butte. 

· The evidence of the igneous and intrusive character of the granite mass is abundant, varied, 

and conclusive. The granite is seen in actual contact with the sedimentary series at Helena, 

at Elkhorn, and in the Highland Mountains. It cuts the stratified rocks abruptly, the contact 

crossing the ends of the folds so that the granite is seen truncating strata of different ages. The 

actual contact is even more irregular and indented than is shown upon theomap, and it is clear 

that the granite intrusion has broken across the beds and has not been influenced by the preexisting structure. Near Helena the· granite extends underneath the sediments, which can be 

seen capping it as a thin cover,· the plane of contact clipping northward at a low angle. As the 

beds preserve their normal sequence and confo:rn1 in attitude to those farther north, it is evident 

that the granite has broken off and removed the continuation of the fold. The irregularity 

of the contact and the pr~j ecting tongues and dike like masses show the true nature of the 

intrusion. 

West of the Highlan9. Mountains, at the extreme southwest corner of the area shown on the 

general map (Pl. I), several great blocks of white limes ton~ are included in and entirely surrounded by the granite. Near Elkhorn are similar blocks torn off from the sedimentary rocks. 

The alteration of the ·sedimentary rocks at the contact with the granite is intense and 

shows unmistakably the intrusive nature of the latter. The alteration is greatest at the contact 

and becomes less and less. away from it. The width of this zone of alteration differs at different 

places and with different rocks; it is commonly half a mile across, but in many places is more, 

though .conspicuous for only a small part of this distance. So far. as observed the bedded 

· rocks are nowhere metamorphosed to schist. At the contact, rocks formed of garnet, epidote, · · 

calcite, etc., represent the recrystallized condition of the impure limestones. Where the altera-

. tion was less intense coarsely crystalline marbles were formed from·limestone and dense hornstone frorn shale. All the varied products of thermal metamorphism may be observed. These 

facts indicate that the granite broke up through sedimentary beds while in a molten condition. 

The granite also shows internal evidence of its intrusive nature. The mass as a whole is an 

undoubted unit and its coarseness and evenness of grain show that its magma cooled slowly and 

under cover. The rock varies but slightly in nature throughout the greater part of the area, 

JSee Butte special folio (No. 38), Geol. Atlas U.S., U.S. Geol. Survey, 1897, p. 1. 
GEOLOGY OF THE REGION. 29 

the differences in appearance being clue to jointing and weathering or to chemical alteration. 

Near the borders of the n1ass, hO\vever, the rock changes from a light-colored typical granite to 

a clark variety appl'oaching quartz diorite or even gabbro in composition. In many places near 

the contact with the sed~n1entary rocks these changes are abrupt .and pronounced in character. 

The highest parts of the granite 1nass do not, as a rule, show the irregularities of grain and com- · 

position observable at the borders of the intrusion, but in a few places, where the andesite cover 

ren1ains, si1nilar variations 1nay be seen. 

"!''hat this great gran.ite n1ass is not Archean, but is a more recent intrusion of igneous rock, 

is conclusively proved by the exposures at several localities along the contact with the sedimentary rocks. Of the rocks actually cut and altered the youngest whos~ age is defin.itely 

recogn.izable are Cretaceous. Furthermore, 'folded coal-bearing rocks ·of "Laramie" (Cretaceous) age occur near Anaconda, and the general mountain folding of the adjacent sedimentary 

formations is known to have occurred after the "Laramie" epoch. The gran.ites are therefore 

younger than the Cretaceous rocks and not older than the post-"Laramie." 

"!''hat the gran.ite is younger than the andesitic rocks is proved by the presence in it of blocks 

of andesite near Pipestone Springs and north of Whitehall, and by the pronounced baking of 

the andesite at the contacts. The facts observed elsewhere indicate an Eocene age for the andesite, which would 1nake the granite Miocene in age. 

LAKE BEDS. 

A large part of the granite tract is now covered by volcanic rocks which have been cut through 

by the canyons of the region. Between the time of the granite intrusion and the later rhyolitic 

volcanic outbursts a prolonged period of erosion must have intervened, during which the rocks 

above the granite were largely removed and the mountain masses and intervening valleys of 

the present day carved out by the streams, the Butte distd.ct being thus developed into a 

roughly hilly surface before. the succeeding periods of ·volcanic activity began. 

The Jefferson and M:issouri valleys on the east and the Deer Lodge Valley on the west were 

at that time. deeper than and as broad as they are to-day. A long period of undisturbed 

e<tuilibrium was succeeded by a tilting of the region which reversed the drainage of the greater 

valleys, whose water accun1ulated in lakes, a phenomenon general throughout the region. The 

lake beds fonned at this tin1e may be seen about the borders of the granite tract, and in the 

Silyerbow Valley they were deposited upon the gran.ite itself. 

RHYOLITE AND DACITE. 

Rhyolite and dacite are pron1inent over a large part of the regiqn surrounding the Butte dis.:. 

trict. These rocks are light colored, present a wide variety of types, and occur both as dikes 

cutting granites and andesites nnd as extrusive lavas and fragmental rocks. They form the hills 

west of Butte and the summits of the continental divide north of the district. The fragmental 

rocks and lava flows rest upon granites and andesites whose surfaces were uneven as is that of 

the present day. The rocks are of volcanic origin and came from a number of vents. They 

represent the product of the third and latest period of igneous activity, which accompanied 

or followed the g1~eat disturbance that formed the :Miocene lakes of the region. The effects of 

this period of volcanic activity were general over this part of the Rocky :Mountain region but 

are most 1narked in the Yellowstone Parlc The age of the eruptions is of· in teres~ since the 

rocks are more recentthan the ore deposits of Butte. The lake beds of the valley are formed 

largely of rhyolitic dust which fell into the waters of the rivers and lakes and of fine volcanic ash 

and deb~·is washed frotn the surrounding slopes. In these beds vertebrate re1nains of late 

Miocene age have been found, furnishing definite evidence of the date of the rhyolitic eruptions .. 

The hot springs which occur at a number of localities in the Boulder and Butte regions are 

believed to be due to the lingering heat of this period of volcanic activity and t9 furn.ish evidence 

of its c01nparative recency. · 

l~xtensive areas of rhyolitic rocks lie northwest of Butte and cover considerable territory in 

the district proper. 
30 GEOLOGY AND ORE DEPOSITS .OF BUTTE DISTRICT, MONTANA. 

SUMMARY OF GEOLOGIC FEATURES. 

A central :rpass of granitic rock now exposed for about 64 miles in length and 12 to 16 

miles in width is surrounded by upturned and folded sedimentary rocks whose edges are 

abruptly cut off by the granite. Remnants of a former capping of dark-colored and baked 

andesites occur as patches over the northern part of the granite region, and extensive areas of 

these same rocks focm mountain masses flanking the 'g_ranite on the east, north, and west, 

concealing the sedimentary contact in these areas. These andesitic rocks are partly intrusive 

but are mainly extrusive lavas or volcanic debris. The granite itself contains_nun1erous patches 

and dikes of white aplite, in places tourmaline-bearing, that are regarded as a later siliceous 

phase of.the granite itself. All these eariier rock~, including the sedimentary limestones, etc., 

are cut by rhyolitic dikes and capped by extensive accumulations of fragmental rhyolitic rocks 

and lava flows. Mineral vein formation preceded this later volcanic period and is still in progress in some parts of the district. Over the northeastern p·art of the granite region quartz 

veins, usually barren, ~re extremely common and of unusual size, forming the crests of long 

high ridges and dominatiri.g the local topography. The deeper older valleys of the district are 

filled by alluvial and lake. beds largely composed of rhyolitic volcano dust and material washed 

down the slopes when the rhyolitic eruptions occurred. • 

From studies elsewhere it is known that over a large part of the State igneous activity 

began on a grand scale at the close of the Cretaceous period. The region between Helena and 

Butte yields no positive evidence of the age at which the andesitic rocks were formed further 

than that it was post-Cretaceous and earlier than the deposition of the Neocene lake beds. . 

Since the close of the volcanic ·epoch represented by the rhyolite no great changes have 

occurred in the geologic features of the district. The Miocene lakes have been drained by 

streams flowing northward. During later glacial time the higher summits were covered 

by local ice sheets, which formed the moraines now conspicuous in the mountains east of Elk 

Park and at other localities, though not near Butte. The grander features of topography are 

the same to-day as at the close of Miocene time, having been modified only by canyon cutting 

and valley filling, which changed only the scenic details~ 
CI-IAPTER IlL-DESCRIPTIVE GEOLOGY OF THE BUTTE DISTRICT. 

OCCURRENCE AND CHARACTER OF THE ROCKS. 

The hilly tract containing the mines of the Butte district is n1ade up entirely of igneous 

rocks. Those of earlier age than the ore deposits are mainly coarse-textured granitic rocks; 

those of later age are of volcanic origin. These later rocks are largely fragmental, resulting 

from the hardening of tuffs and breccias thrown out from a volcanic vent. Big Butte, from 

which the city takes its name, is formed of rocks typically volcanic;. it is the site of a small 

volcano, the only one yet revealed by erosion in this part of the State. :Massive volcanic rocks 

also occur, partly as dikes radiating from this vent and cutting both granite and mineral veins, 

and partly as the remains of. irregular intrusions or lava flows that were partly destroyed by 

later outbursts. In the mineralized areas the rocks of the district are more or less profoundly altered, but unweathered material is easily obtainable from underground workings and 

surface quarries. · 

Two general subdivisions of the rocks of the district can be made. The first and older 

mnbraces the granitic rocks, these rocks being older than the mineral veins. The second group 

includes the porphyritic rocks, which, with the exception of the rhyolite porphyry of Anaconda 

I-Iill, are later than the ore deposits. The rocks erupted from the Butte volcano or from some. 

neighboring c~nter of activity, those intrusive in the granite, and those that accumulated in 

the Tertiary lake basin, all belong to this second group. In the eastern part of the district a 

l.arge area which covers the old valley floor is mapped as alluvium. · 

GRANITIC ROCKS. 

TYPES. 

The oldest rocks of the district are of recognizable granitic habit, having an even and 

coarse grain and the usual appearance of a granite. They consist of two strongly contrasted 

types. One is a dark-grayish coarse-grained rock, which differs somewhat in appearance and 

mineral composition from the rock commonly prevailing throughout the surrounding region; 

as it is nearly constant in character and chemical composition and is characteristic of the district, it has· been given the distinctive name of Butte quartz monzonite. In previous reports 

it has been called Butte granite.1 · 

A second type is a white or cream-colored aplite or alaskite of variable but coarse grain 

and granitic habit, which occurs in the district in great abundance. In previous reports it 

has someti1nes been alluded to as "Bluebird granite,"· but as it is the only aplite of the region 

and is easily distinguished from the Butte quartz monzonite it will be called simply aplite in 

this report. The two Tocks are not only unlike in color and appearanee but are' readily distinguished in outcrop, the aplite forming rocky exposures standing above the surface of the more 

readily disintegrated Butte quartz monzonite. 

BUTTE QUARTZ MONZONITE. 

PETROGRAPHIC CHARACTER. 

The Butte quartz monzonite, the common and characteristic rock of the district, covers the 

eastern half, where the great producing 1nines occur, and underlies the city. Throughout the 

district it is very unifor1n in color and texture and in the kind, amount, and distribution of its 

component minerals. To the unaided eye it is a dark-colored rock, of coarsely and evenly 

granular appearance (Pl. III), but so dark and basic looking as to resemble a coarse diorite. 

Black hornblende occurs in abundant, irregular grains. Black biotite mica is but little less 

1 Notes on the geology or Butte, Mont.: Trans. Am. Inst. Min. Eng., vol. 16, 1887, pp. 49-62. 

31 
32 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

common, occurring rarely in grains with crystalline form. The light-colored constituents, 

forming about four-fifths of the bulk of the rock, consist of pink orthoclase and little less abundant gray and faintly greenish plagioclase, together with clear but not conspicuous quartz. 

Scattered black grains of magnetite, brown zircon, and apatite are recognizable, and pyrite is 

locally visible, even· in the freshest rocks. Isolated, rudely square or rectangular masses of 

pink feldspar, some of which are an inch across arid show partly crystalline forms, are a common 

feature and as they weather in relief give the rock a somewhat porphyritic appearance. 

Thin sections of the rock studied under the microscope show that the orthoclase and plagioclase feldspars are present in nearly equal amounts, so that the rock, according to precise 

petrographic nomenclature, should be called a quartz monzonite. The biotite is quite black to 

the eye but is dark brown in color und~r the microscope and shows very marked pleochroism. 

The hornblende is black, but is pleochroic in dark-green tints with large extinction angle when 

seen under the microscope. Augite is usually present in very small amount. The plagioclas·e 

is a sodic labradorite of the composition Ab1An11 and the orthoclase is also soda-bearing. The 

dark-colored constituents form a little over one-fifth of the rock. (See Pl. III.) Examination of numerous sections shows a slight variation in the relative amounts of plagioclase 

(oligoclase-albite-). The extreme variations are from a typical hornblende granite to a dioritegranite. The most basic form was found at the Poulin mine, the sodic labradorite feldspar of 

this rock slightly exceeding the orthoclase in amount. In the rock quarried east of .the Bell 

mine the plagioclase feldspar equals the orthoclase in amount. No order of arrangement of 

.such variations was found, and chemical analyses of material showing the extreme variations 

(p. 33) are nearly identical and show a remarkably uniform composition of the rock throughout 

the district. . 

Included fragments of a fine-grained and much darker colored rock occur in the granite 

in a few localities. These inclusions weather less rapidly than the rock containing them and 

project sharply above the weathered surfaces. Such fragments carry a much larger proportion 

of the dark-colored minerals and are finer grained than the granite. They resemble the basic 

contact forms of the great granitic mass and may represent portions of a partly hardened dioritic contact crust of the Butte quartz monzonite torn from deeper-seated parts of the rock 

mass and bro'ught up wl1ile the monzonite was still molten. 

DISTRIBUTION. 

The Butte quartz monzonite occurs in all parts of the district, but is in part concealed by 

later rocks. It may be t,raced northward and northeastward beyond the area shown on the 

map into the. general granite mass of the region, but elsewhere its surface is obscured by fragmental material, so that continuous exposures. are not presented and. its transition into the 

general mass of the batholith is riot apparent. · 

The copper-bearing area at Butte shows comparatively few natural exposures, being in this 

respect in marl(ed contrast to areas of the same rock in the surrounding region. In the vicinity 

of the important mines the rock is not only traversed by a multitude of large and small veins, 

but it disintegrates readily under atmospheric agencies into a coarse sand which obscures the 

underlying. decomposed and sandy rock. The transition from the surface sands to the fu·m 

and solid rock may be observed in many open cuts throughout the district. In a very few 

places rounded bowlder masses and smooth rock surfaces may be seen. 

The comparatively few rock outcrops which form a prominent feature of the ore-bearing · 

area are generally due to either vein quartz or to a silicification of the altered granite. Numerous railroad cuts show good exposures of the upper disintegrated layer of the granite. In 

excavations throughout the city the outer zone of soft disintegrated rock yields readily to the 

pick and shovel to a depth of 6 to 10 feet. In a majority of these· exposures the granite is 

seamed with a coarse network of iron-stained seams and quartz veins of varying thickness. 

, (See Pl. IV, .A_.) 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE Ill 

BUTTE QUARTZ MONZONITE, SHOWING TEXTURE AND OCCURRENCE OF PRIMARY SULPHIDES. 

White areas, q ua rt z and feld s par; dark areas, hornblende (augite) mica, magnetite, and very little pyrite. Enlarged 

one-half. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE IV 

A. MINERALIZE D JOINTS IN GRAN ITE IN AN EXCAVATION FOR THE FOUNDATION OF A 

CHURCH AT BUTTE. 

B. PART OF MODOC DIKE. 

Shows rhyolite porphyry intrusion surrounding bow lders of Butte quartz monzonite and filling horizontal joints 

in that rock. Railw ay cut near East Colusa rnine. See page 42. 
DESCRIPTIVE GEOLOGY. 33 

Much of the surface ext~nsion of the large mineralized veins consists of leached and altered 

rusty granite or more rarely of soft clayey material. The granite is, moreover, netted with a 

system of close and. small fractures, many of which seem to be merely shear or joint planes, 

along which permeating waters have concentrated the iron either as a film along the plane 

itself or as a staining of the walls of the seam, giving it a rusty ocher· color. Other veinlets 

are actual seams of quartz. 

CHEMICAL AND MINERALOGICAL CHARACTER. 

The coarse.:grained granitic rocks of the Butte district are parts of a large mass of great 

extent called the Boulder batholith, and in order to determine, if p<)ssible, why ore deposits 

occur near Butte it is necessary to ascertain in what respect, if any, the rock there differs from. 

that of other parts of the 1nass. 

ROCKS OF THE BOULDER BATHOLITH. 

A study of the field relations shows that the rocks of the batholith must be regarded not 

only as facies of the same magma but even as parts of one mass. Yet they present a wide 

variation in mineral and chemical composition. All the very basic roeks occur at the margins, 

but clearly recognizable types, which yet can not be discriminated in mapping, occur within 

the main body. This same difficulty has been experienced by geologists working in the Sierra 

Nevada, where, as stated by Turner/ a considerable variety of rock types have been mapped 

as granodiorite, "although as a rule gabbro, even when genetically related to granodiorite 

proper, has been separated." 

Where detailed mapping on a large scale is not possible, this difficulty of separating parts 

of a single intrusive body in which the rock types grade into one another can be met only by 

arbitrarily applying the name of the prevailing rock type to the entire mass, as has commonly 

been don~ heretofore, or by using a generic term like granolite 2 to embrace all coarsely granular rocks. 

In the fqllowing table are given the results of the analyses so far .made of the rocks of the 

Boulder batholith. Specimen 518 represents the prevailing type of the batholith. 

Analyses of rocks fr01n the post-Cretaceous granitic batholith of the Boulder Mountains, 1lfont.· 

[U.N. Stokes, analyst.] 

52() 525 130 . 311 ()25 989 98 518 ()40 951 

---------1---------------------------------

SIO~ .......................... 49.22 5().41 61.64 63.87 ()3.88 64.05 64.34 64.17 67.12 76.87 77.05 ·r109 ........................... 95 .68 .71 .65 .65 .Go .53 .67 .48 .u .12 Ah08 ......................... 12.02 17.62 15.63 15.39 15.84 15.38 15.72 15.25 15. oo 12.52 12.84 Fe908......................... 2. 77 1. 24 3. 39 1. 93 2.11 2. 20 1. o2 2.16 1. o2 . 67 . 56 FeO.......................... 8. 80 3. 55 2. 69 3. 08 2. 59 2. 74 2. 94 2. 98 2. 23 None. .14 MnO.......................... 'I:race. . 08 .. 04 .11 . 07 .11 .12 . 04 . 06 None. 

CuO. .. . . .. .. . .. .. .. .. .. .. .. .. 10. 5H 8. 66 4. 90 4. 30 3. 97 4. 30 4. 24 4. 24 3. 43 . 49 . 57 

~~~3:::::::::::::::::::::::::: t~& ~:~i ~:~~ ~:i~ ~J~ ~:8~ ~:6~ ~:~~ !:~~ 5:~~ Trs2 Ntl30......................... 1. 90 3. 35 2. 64 2. 76 2. 81 2. 74 2. 76 2. 62 2. 76 2. 47 2. 81 Hs0below1H) 0 ................ 27 .14 .28 .19 .22 .27 .25 .16 .09 .25 .22 :n~o above 110° ......... :. .. .. 1. G3 • 76 . 91 . 69 . 66 • 83 • 76 . 65 . 58 . 52 • 48 B110.......................... .03 .09 .08 .07 .09 .08 .06 .07 .07 None. 

SrO ....... :.. .. .. .. .. . .. .. . .. . . 03 . 08 . 04 . 02 . 04 • 03 '!'race. Trace. . . 03 None. 

P20n.......................... .43 .49 .21 .17 .21 .21 .14 .1() .15 .05 None. 

Cl............................. .08 .07 .......... .......... .......... .......... .......... Trace ............................. .. S. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 05 . . . . . . . . . . . . . . . . . . . . . 07 . .. . . . . . . . . 07 . 03 . . . . . . . . . . . . . . . . . . .. . . . . . .. . • . None. 

SOa........................... .04 None. .......... .......... .......... .......... .07 'l'race ................... .. C09........................... .......... .......... None. .15 .......... .35 .03 None. None. .......... None. 

Zr09 ....................................................................................................... : ............................... . 

~Potal. ····~············· ~~~~~~liiQ.05599.8()~-gg:gg~~-wo.ai 

~·}contact fncles of granite muss, Red Mountain. ._) \,1. 

:W~:]Diorlte, Hod.llock Creek. Intrusive in batholith. 

(i2g: Hutto quartz monzonite, Butte district. 

989. . 

98. Head of Clancey Creek, northern part of batholith. 518. Prevailing type of granite of Boulder batholith . 

~~~:}Aplite of Butte district. 

I 'l'urncr, rr. w., Grunltlc rocks or Sierra Nevada: Jour. Geology, vol. 9, 1899, p. 146. 

90427°-N o. 74-12-3 

2 Idem, p. 141. 
34 GEOLOGY AND OR~ DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The prevailing rock of the batholith is a normal hornblende granite, which is very generally 

sheeted, forming picturesque crags and bowlder groupings. It disintegrates readily into platy 

masses that shell off from the bowlders and in time crumble to a coarse sand. Over large 

tracts this disintegration has· reduced the rocks to a smoothly rolling surface, on which sca.ttered 

bowlders rise above the general level. Perfectly fresh material can therefore be obtained 

only where the rock has been quarried or exposed by mining operations. It is a medium to 

coarse grained rock, the average size of the grains being 3 to 5 mm. The grayish quartz and 

white feldspar grains are of about equal size. Black mica and dark-green hornblende are 

present in considerable quantity.· Under the microscope it shows the normal characters of a 

granite but contains an unusual amount of plagioclase. 

In the following· table only the essential elements of this rock are given, the complete 

:analysis being shown in the preceding table. Partial analyses of quartz monzonite from the 

Sierra Nevada and of Brogger's adarnellite are given for comparison. 

The first colunm gives the approximate composition of the hornblende granite of the 

Boulder batholith, the second and· third colunms the composition of quartz monzonite from 

California, and the fourth column that of adamellite. .It is evident from the analyses that the 

Boulder rock nearly corresponds to Brogger's adarnellite. 

Principal constituents of Boulder granitic batholith and allied rocks. 

Hornblende Quartz Quartz Landsberg 

granite of monzonite monzonite b. Barr, 

b!lli~8K ~e~::i~~ ~~rc~~ vi!ilr· 

Silica .......................................................................................... . 67.12 66.83 67.45 68.97 

Alumina ............. : ........................................................................ . 15.00 15.24 15.51 14.80 Lime .......................................................................................... . 3.43 3.59 3.60 3.82 Magnesia ....................................................................................... . Potash ........................................................................................ . 1. 74 1.63 1.10 1.15 4.52 4.46 3.66 4.53 Soda .......................................................................................... . 2. 76 3.10 3.47 2.40 

QUARTZ MONZONITE OF BUTTE DISTRICT. 

The exact relations of the Butte quartz n1onzonite to the granite of the general area were 

not s~tisfactorily determined, though it appears certain from the exposures that it is an integral 

part of the batholith and not a separate intrusion. At several localities a sharp gra.dation was 

observed, with narrow transition bands between the .lighter-colored granite, with its white 

feldspars, and the darker Butte typ.e. It will,· however, be seen from the analyses that the 

quartz monzonite is only a somewhat more basic phase of the granite of the region and that 

it closely resembles granodiorite; the plagioclase is more basic, being sodic labradorite . 

. The quartz monzonite nrass is remarkably uniform in character, not only megascopically 

and rnicroscopically in texture and mineral composition, but also chemically. The analyses 

confirm this statement,· which has also been noted by Washington. 1 Eutaxic and schlieric 

masses occur rarely and were avoided in taking samples for analysis. 

The following table gives partial analyses of the Butte quartz monzonite and of related 

rocks from other localities: 

Partial analyses of B'utte quartz monzonite and related rocks. 

Silica .... : ......................................................................... . Alumina ....................... · ................................................... . 

Fe20a'············································································· 

Feo~ ............................................................................. . . Lime ...................................................................... · ....... . Magnesia ............................................ , ............................. . Potash ......... ~ .................................................................. . Soda ................................................ ·: .............................. · 

Butte 

quartz monzonite. 

64.03 

15.58 

1. 96 2.83 

4. 20 2.15 

~: ~~}6. 87 

Granodiorite. 

65.48 

16.05 

1. 47 3.02 

4.88 

2.13 

2.43 

3.49 

t Washington, H. S., Prof. Paper U. S. Geol. Survey No. 14, 1903, p. 17. 

Boise 

rock. 

65.23 

16.94 

1. 60 1. 91 3.85 

1. 31 3.02 

3. 57 

Banatite 

average. 

64.39 

15.90 

5.63 

4.15 

1. 93 

~:~n7.05 

Granite of 

Boulder 

batholith. 

67.12 

15.00 

1. 62 2. 23 3.43 

1. 74 4. 52 2. 76 
DESCRIPTIVE GEOLOGY. 35 

·The first column gives the mean of the four analyses. The second column shows the 

mean of :fLve· a.nu1yses of granodiorite as given by Turner. 1 The B<)ise rock. is described b)r 

I.~indgren. 2 The banatite is a mean of five analyses quoted by Brogger.3 From the analyses 

it will be seen that the rock. closely resembles a banatite in composition, the lime and sum 

totcLl of the alku.lies being the san1e, thoug~ in the Butte quartz monzonite the potash exceeds 

the soda-in amount. It also resembles the granodiorites, but the alkalies are present in an 

inverse ratio. 

In order to furnish a basis for calculating the n1ineral composition of the Butte quartz 

n1onzonite, fresh 1naterial was crushed, and the hornblende and biotite were segregated in the 

Survey laboratory by Dr. I-I. N. Stokes by the use of Thoulet solutions, and these two minerals 

were separated from each other by sliding on paper. The resulting material was examined 

undet· the 1nicroscope and found to be very pure .. 

To the naked eye the biotite appea:r;s quite black, but under the microscope it is dark 

browti, showing very n1arked pleochroism. It is characteristic not only of the Butte quartz 

n1onzonite, but of the hornblende granite of the Boulder batholith as well. In many sections 

exmnined it appears the same in color and pleochroism, not only for the Butte quartz nlonzon.ite but for the nor1nal granite of the batholith, and it may be assumed to be the same for both. 

1'he 1nicroscopic examination of the biotite n1u.terial showed a little apatite, a very little chlorite, and very little hornblende, but these impurities form a very minute part of the whole. 

The mnphibole is also characteristic of both the Butte quartz monzonite and the norma] 

hornblende granite of the region. It is black. or very dark green when seen wi~h a hand lens, 

but pleochroic in dark-green tints with large extinction angle when seen under the microscope. 

The 1naterial tmalyzed was very pure. 

The following table shows .the result of the analyses of these minerals. Dr. Stokes was 

unable to obtain a higher sun1mation in the analyses made· of each, as the amount. of material 

available was exhausted. The· analyses published by Turner of the biotite and amphibole 

from the quartz n1onzonite of the Sierra Nevada are given for comparison. The close resemblance of the analyses of both rocks nnd minerals to those of the Butte quartz monzonite is 

noteworthy. · 

Cltem,ical cmnposit·ion of b1:otite and hornblende in the granitic rocks of Butte, :Mont., and of the Sierra Ne1 1ada; and the com- . position of the Butte quartz monzonite . 

.. 

Biotite. Hornblende. Butte quartz mon- zonite.a 

Butte.a N~~~!~~.b Bt'ltte.a N~~~!~~.b Per cent. Ratio. 

------------------------1------------------

8102··············································································· 35.79 36.75 45.93 47.49 64.03 1. 0671 

~i~:~8::::::::::::::::::::::::::::::::::::::::::::::::::::: :.:::::::::::::::::::::::::: 3. 51 3.16 1. 43 1. 21 .60 

.10 .... :ooi26 .03 .28 .06 .18 

F ................................................................................. . . 76 .17 . ............... ............... ............. 01 .................................................................................. . . 20 . .......... . ............. ............... .................... 

AI203·······················································: ..................... . :Fe~o3 ...................•.......................................................... 13.70 14.70 6. 77 7.07 15.58 .1527 

5. 22 4.65 4.94 4.88 1. 96 .0123 :J~co ............................................................................... . 13.72 14.08 10.39 10.69 2.83 .0393 ~fnO ............................................................................. . .19 . 45 .54 .51 .11 .00015 

:UnO .............................................................................. . .13 None. .07 .0005 

SrO .............................................................................. . None. .12 None. .04 .0004 

CnO ........................................................................... : .. . .05 .17 11.25 11.92 4.20 .0750 

t~~3:.: : : : : : : : : : :: :: : : : : : :: : : : :: : : : : : : : : : : :: : : :: :: : : : : : : : : : : : : : : :: :: :: : : :: : : :: :: ::: 12.13 12.37 12.32 13.06 2.15 .0537 

9.09 9.19 1. 22 .49 4.11 .0436 Nn~o ............................................................................. . .15 .32 . 77 . 75 2. 76 .0445 

l:.hO .............................................................................. . Trace. Trace. Trace. Trace. .. ............. ............... JI'~O below lto• ................................................................... . 1. 21 1. 03 . 49 . 20 n~o nbovo110° .... : .............................................................. . 3.64 3'.64 2.29 1. 86 . 73 .00405 

------------------ 'l'otnl........................................................................ 99. 59 100. 0 98. 77 100. 03 99. 87 ......... . 

Less 0 for'F+CI ............. : .................................................... ~~~~~~~ 

a Analysis by Stokes. b Analysis by Hillebrand. 

1 ~l'urnor, H. W., Rocks of tho SlmTa Nevada: :Fourteenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1894, pp. 478, 482. 

2l'ho gold and silver veins or Silver City, De Lamar, and other mining districts in Idaho: Twentieth Ann. Rept. U.S. Geol. Survey, pt. 3, 

1000, ]). 81. . . 

a Die l~ruptlonfolgo der 'L'rladlschen Eruptlvgesteino bel Predazzo, p. 62. 
.36 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The Butte analyses are incomplete, as the amount of material was too small for further 

work. The analyses of the biotite and hornblende of the Sierra Nevada rocks are those given . 

by Turner.1 

To calculate the mineral composition of the Butte quartz monzonite, one must assume that 

the phosphoric pentoxide (P 20 5) in ~he biotite and hornblende and in the rock itself is present 

as apatite and must deduct it, with an appropriate amount of lime, from the anal~es. The 

water below 110° C. is assumed to ·be accidental and is also deducted. The analyses are then 

reduced to 100 and the molecular ratios calculated. 

All the soda is calculated as albite. As the microscope shows the plagioclase to be andesine 

of about the composition of Ab1An1 (or sodic labradorite) and as albite is not seen in the section 

the orthoclase must. contain. the albite molecule. The hornblende is therefore estimated and 

an equivalent amount of lime deducted; the remainder of the lime is then calculated with the 

albite molecule to form plagioclase. The result shown in column 1 of the table gives the mineralogical composition of the rock. · 

Mineralogical composition of the Butte quartz monzonite. 

2 3 4 

-------------..------------------1------------

23.70 22.55 20.34 19.61 

19.88 17.57 19.82 23.69 

Quartz ................................ .' ............................................................... . Orthoclase ............................................................................................. . 22.98 } 42.47 41.48 { 25.23 

11.48 19.43 

13.15 4.44 5.67 a 1.36 

4.22 9. 77 8.94 b 6.94 

Albite ....................................................... : .......................................... . Anorthite ............................................................................................. . Hornblende .... , .................. , ............................. .-..................................... . Biotite ............. : .................................................................................. . 2.11 2.37 2.50 c .19 

.33 ..... i:o2· d 1. 92 

1.18 . 76 ·e. 91 

.97 ........ 04. .07 

.06 .07 .01 

~~r~:_: ~::::::::::::::::::::::::::::::::::::::::::::::::::: ~:::::::::::::::::::::::::::::::::: :·::::: 

Titanite ............................................................................................... . Pyrite ................................................................................................. . 

100. 06 100. 00 99.81 99.36 

a Diopside. b Hypersthene. c Fluorite. d Magnetite. e Ilmenite. 

1. Calculated composition of average rock. (Weed.) 

2. Measured composition of sample from Parrot mine. (Iddings and Cross.) . 3. Measured composition of sample from Walkerville. eJddings and Cross.) 

4. Theoretical composition or norm. Under 4 several of the minerals present in the first three rocks are missing, and other new ones are present, as shown by the footnotes. 

Analysis 1 gives 1.51 molecular weight against 1.50 for the bulk analysis of the rock, 

.showing a very close agreement. Analyses 2 and 3 give the percentages measured in thin sec~ 

tions by Cross, Iddings, et al., 2 for the same rock, analysis2 representing materialfrom ne~r the 

Parrot mine, and analysis 3 rock from the quarry near Walkerville. The percentage of plagioclase is greater and that of hornblende much less than in the earlier calculation made by the 

writer (analysis 1). Analysis 4 represents the normal or standard composition of the rock as 

Dalculated from the analysis. · 

The uniformity of the rock is an expression of like conditions prevailing throughout the 

mass at the time of solidification, since it is well known that a ''magma may crystallize 

with quite different mineral combinations, according to the influence of attendant conditions 

upon the union of the various chemical constituents." 3 

. ~PLITE. 

PETROGRAPHIC CHARACTER. 

The ·second variety of gr.anite found at Butte is an alaskite or aplite granite.. In previous 

reports it has sometimes been alluded to as "Bluebird granite." It is a granular, or finely 

granular, siliceous granite, consisting of alkali feldspar and quartz. At Butte it contains very 

little plagioclase feldspar and some small scattered grains of biotite and is white or cream-colored, 

medium grained, of sugary texture, and bears a superficial resemblance to sandstone. Transi1 Some rock-forming biotites and amphiboles: Am. Jour. Sci., 4th ser., vol. 7, 1899, p. 294. 

2 A quantitative classification of igneous rocks, Univ. of Chicago Press, 1903, p. 226. 

a Idem, p. 100. 
DESCRIPTIVE GEOLOGY. 

tion also occurs into the darker Butte quartz monzonite. Under the microscope it is seen to 

consist of a mosaic of orthoclase and quartz grains, locally rounded, with a sprinkling of small 

·biotite 1nica plates. When slightly decomposed the biotite is altered to chlorite, staining the 

rock pale green; further alteration changes this to iron oxide, giving the rock a rusty tinge. 

The rock varies greatly in granularity. In narrow dikes it is comrnonly quite fine grained. 

In the la1~ger masses coarser grained often alternates with finer grained rock in bands or irregular 

patches. 1'he rock grades into micropegmatite, and at times into true pegmatite, in which the 

constituent 1ninerals are easily recognizable by the eye. In one instance such pegmatites 

showed tourmaline. 

The contact between the aplite and the granite is very sharp in the small intrusions, but 

shows gradation about the larger masses. No evidence of contact chilling is ever shown by a 

denser band of n1aterial at such contacts. In places joint planes in the rock show finer-grained 

surfaces that n1ay represent shrinkage cracks. 

VARIATIONS IN CHARACTER. 

The aplite varies greatly in texture. In the Bluebird area it is :fairly constant, except at 

the edges of the intrusion. In the s1naller intrusions, 'however, it tends to become a pegmatite, 

and in places grades into such. More generally, however, the· pegmatite forms veinlike 

n1usses in the 1nain body of 

the aplite. The pegn1atite 

1nay be fine-grained .graphic 

granite or a coarse, openspn.ced aggregate of quartz 

and feldspar crystals, showing very little hornblende. 

At the n1argins of the 

ln.rger intrusive n1asses the 

rock grades into a transition 

fonn that ·rese1nbles both 

granite and aplite, and yet 

0 s Feet 

FIGURE 2.-Variation in texture of aplite e.'Cposed near Boulder, Mont. 

can scarcely be classed as either. It is too light colored and acidic to be a part of the Butte 

quartz Inonzonite, and it has too pronounced a granitic hypidiomorphic structure and contains 

too large an an10unt of dark-colored silicates to be a good aplite. It shows coarsely crystalline 

aggregates, filled in with aplitic material, and is decidedly p~gmatitic in appearance. (See fig. 2.) 

The aplite of the Butte district varies but little in mineral composition. Samples from the 

Nettie 1nine, a silver property west of Big Butte, analyzed in the Survey laboratory, show the 

following con1position: 

Analyses of aplite from Nettie mine, Butte, Mont. 

Constl t;ucn ts. 

Silica............................................. 76.87 

'l'ltlllllc acid.. . . .. . .. . .. . .. .. .. .. .. .. .. .. .. .. .. .. . .11 Alumina......................................... 12.52 J~crrlc oxide...................................... . 67 ]?crrous oxide.................................... None. 

~~~~:;~~~ :~:: :::. ·.:::::::::::::::::::::::::::::::::: ...... :49. 1\fn~ncsla......................................... . 09 

Potash. . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . 5. 78 Soda ............................... ·.............. 2.47 

Water below 110° C............................... .25 

l. Analysis by Hillebrand. 

77.05 . 12 

12.84 . 56 

. 14 

None. • 57 '!'race. 5.52 

2.81 

.22 

Constituents. 2 

Water above ll0° C............................... . 52 . 48 

Baryta........................................... . . . . . . . . . . None . Strontia.......................................... . . . . . . . . . . None. 

Phosphoric acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 05 None . Chlorine ............................................................. . Sulphur.......................................... . . . . . . . . . . None. 

SOa .... , ............................................................. . Carbon dtoxlde .............. : .. .......... :.. .. .. . .. .. .. . .. . None. 

99. 82 100. 31 

2. Analysis by Stokes. 

The nlineral c01nposition of the aplite represented in analysis 1 has been calculated. A 

little biotite, found in the fresh aplite, is similar to that in the gran,i.te and is supposed to have 

the san1e COinposition; to it all the magnesia is ascribed. This leaves an excess of 0.09 per 

cent of titanic oxide, which is calculated as titanite. 
38 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

M.ineral composition of aplitesfrom the Butte district and from the Sierra Ne1mda. 

Constituents. 

Quartz .•...... : ...... , ........... · ............... . Potash feldspar .................................. . 

2 

39.45 

29.43 

23.03 

Constituents. 

0.40 

.05 

.18 ~~~ f~~~~~r·_·:·.· _-:::::::::::::::::::::::::::::::: Biotite .......................................... . 

. 37.70 

33.90 

23.81 

2.45 

. 72 6.56 

.90 100. 00 100. 00 

1. Aplite from Nettie mine, Butte, Mont. '' 

2. Granodiorite mass of the Sierra Nevada (Turner, The granitic rocks of the .Sierra Nevada: Jour. Geology, vol. 7, 1899, p. 160). 

INCLUSIONS. 

A few inclusions of Butte quartz monzonite are found in the aplite. Some of these show 

fracturing, the related pieces lying near together, showing that the granite was solid and not 

viscous when the aplite was injected. Small aplite intrusions in the Butte quartz p:wnzonite 

show, however, that the granite was not cold at the time of intrusion, as no change whatever 

of grain is visible up to the actual contact. This is clearly shown in specimens from the I-Iyde 

Park claim. In the south wall of the BtJ.tte, Anaconda & Pacific Railroad cut, below the road 

from the· Nettie, the aplite intrusions follow two. well-defined fissure systems and are slightly 

coarser grained and of more open texture on both contacts than in th~ center. Near the Bluebird mill an exposed wall shows rounded detached masses of aplite and irregular 'stringy injec-

·tions that look like inclusions torn off and carried up while both rocks were still viscous. In 

the railroad cutting below the Philadelphi~ the aplite is brecciated and altered, showing palelavender, cream, pink, and green tints. Some of the fragments are well rounded and are up 

to 6 or 8 inches in greatest dimension; they are held in a paste of aplite, sand, and clay. This 

seems to be a fault .breccia. 

WEATHERING. 

In the larger intrusions the aplite weathers to rounded surfaces and gentle slopes resembling, at first sight, those of the adjacent granite areas. The smaller intrusions resist· weathering 

better than the granite and form conspicuous exposures. Whatever may be the amount of 

disintegration or alteration to which the two rocks have been subjected, the aplite is always 

readily distinguishable from the coarser and darker granite by its light color and characteristic 

grain. 

The slopes about Burlington and the Bluebird mine show that the aplite weathers into slabs 

which either scale off or rest upon and cover the surface. This weathered crust, though appearing perfectly fresh, is loosely granular and friable and is easily reduced to coarse sand. It is, 

however, quite unlike the loose-textured material of the disintegrated granite, for it forms 

smooth rock surfaces checked. by a rudely hexagonal network of cracks. Even where . the 

slopes· are steepest no conspicuous outcrops occur when the rock is all aplite. It is only. where · 

it is ·contrasted with the granite that this difference of weathering emphasizes the aplite in the 

topography. The rock does not weather.into bowlders or rounded monoliths, such as characterize certain parts of tlie granite area. 

Quarries show that the aplite possesses a rudely platy parting and breaks into square-edged 

cubical blocks, which greatly facilitates quarrying. Where it has suffered decomposition, 

especially by the waters of mineral veins, the feldspars are reduced to a clayey n1aterial, through 

which the quartz· grains are scattered. This is, however, seldom observable on surface 

outcroppings. 

The aplite has suffered from the same forces which have sheeted and fissured the Butte 

quartz ·n1onzonite, but the result is not so apparent in surface exposures. · 

DISTRIBUTION. 

The aplite occurs intrusively in the Butte quartz monzonite in a great variety of fonns. It 

is most commonly seen in dikes and in irregular sheets of widely varying size and form. Where 

possible both dikes. and sheets are shown on the geologic map, but many intrusions in the 
DESCRIPTIVE GEOLOGY. 39 

vicinity of the copper mines are too small to represent. Many dikes spread out into sheets, 

the forn1 of the intrusion depending on the position of the fracture plane of the granit~. Some 

of the intrusions are remarkable fo1· their size; the largest extends 1! miles from the west base 

of Big Butte to the broad open valley at the western limit of the district, and has an equal 

breadth. Branches of ·this intrusion penetrate the borders of the quartz monzonite, and its 

n1ass contains included frag1nents of granite; it is, however, relatively shallow, being underlain 

by granite at a depth of only a few hundred feet. 

Besides the large 1nasses the aplite occurs in dikes ranging front a few inches to a few feet 

in width. As the rock c01nposing these is fine grained jt closely resmnbles vein quartz where it 

occurs on weathered surfaces or in railway cuttings. These sn1all dikes are not very numerous 

and are not shown on the geologic n1ap (Pl. X). No definite relation between them and the 

fissuring of the granite was estaplished. Son1e of then1 connect with horizontal expansions of 

the smne n1aterial. Where good natural exposures of the Butte quartz monzonite occur these 

aplite dikQlets are seen weathered in i·elief. . 

'I'he contact between the aplite and the quartz monzonite is commonly a sharp one in the 

dikes and smaller intrusions, but is indefinite about the borders of the larger masses. In the 

dikes the welding of the two ro'cks is perfect; the rock fractures as one mass, but the dividing 

line is very sharp. 

·~ ~ 

~ [I] 

Aplite Granite Vein quartz. 

o.__ __ _._s __ _._1o __ _,_._,1s Feet 

FIGURE 3.-Small aplite intrusions along fissure lines in Butte quartz monzonite. 

Special occurrences worthy of note are seen near the :Mountain Boy 1nine, where inclined 

dikelike 1nasses of the aplite have. been exposed in quarrying. Flat lenticular masses are also 

seen on the hills to the east. Commonly the aplite intrusions are rather thin sheets of small 

e~tent, soon passed through in mining (fig. 3); their prominence in surface exposures is due to 

their not crmnbling to sand as readily as the surrounding quartz monzonite. 

ORIGIN OF THE APLITE. 

The conunonly accepted theory of the origin of aplite is that it represents the acidic remainder in a granite or quartz diorite magma after the n1ore basic elen1ents have crystallized. The 

aplite is forced up fr01n below and fills previously forn1ed cracks, \vhich are perhaps the result 

of. cooling, in the 1nain 1nass of the granitoid rock. On tllis hypothesis aplite is genetically 

related to the n1ore basic granites with which, in the Sierra Nevada, it is most directly associated.1 . 

So far as known. to the writer, the aplite of the Butte district is the most extensive ·body of 

that rock yet discovered. In other occurrences observed by the writer and in those con1monly 

described, aplite occurs in. dikes generally narrow, though in many places of considerable length. 

A study of the aplites of the Butte district shows that though dikes of this material may ·be 

explainable by the generally accepted theory, yet son1e of the irregular lenslike or miniscoidshaped n1asses are local bodies unconnected with any feeder. The inference derived from a 

caref1.il examination of 1nany exposures is that the n1aterial is due to son1e process of segregation such as that suggested by Turner-a squeezing out fr01n the crystallizing granite and a 

1 Turner, H. W., Geology of Sierra Nevada, 1894, p. 722. 
40 GEO.LOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

collection into ~hrinkage cracks. · In the description of the remarkable differentiation zone of 

Square Butte 1 the basic outer part of the intrusions, itself a product of differentiation, contains 

a thin band of white syenite due to further separation or differentiation of the feldspathic 

constituents in the crystallizing mass. 

This hypothesis, belief in which has been strengthened by further observations of other 

laccoliths in the same region, seems to explain the manner of occurrence of the aplite in the 

Butte quartz monzonite. It is believed (see p. 47) that the Butte district lies on the downthrown side of a fault, and that its granitic rocks represent the upper part of the batholithic 

intrusion. In. this uppermost part of the intrusion partial differentiation is believed to have 

taken place, the normal granite splitting up into the basic phase represented by the Butte 

quartz monzonite and the addic phase represented by the aplite. As the monzonite is but 

slightly more basic than the prevailing form, this hypothesis demands that the proportion of 

aplite should be small. The field observations show a quantitative relation which, as far as it 

can be estimated, confirms the view. 

The hypothesis implies a gathering of the iron, magnesia, and lime mol~cules out of the 

general magma and their concentration in the Butte quartz monzonite, followed by a segregation of the aplitic material, richer in alumina, alkalies, and silica, not as an inner kernel (as in 

laccolithic differentiations), but as local masses in the basic granite. This hypothesis has been 

advanced by Cross in the discussion of evidence ·of differentiation at Rosita, Colo. 2 

If the Butte quartz monzonite is a border qr upper-contact facies of the batholith,' this 

segregation may have been ind~ced by contact cooling. Observations of many of the smaller 

intrusive stocks of the :Montana mountains and of the contacts of the larger batholiths show 

more or less mixing of basic and siliceous materials, as if they had been stirred together while 

pasty. The rocks grade into one another and show no sharp contacts. 

In the large aplite intrusions no transition zone exists. The grain is the same in both rocks, 

but at a certain line a change takes place in the relative ·proportions of the minerals. In the 

smaller bodies and little dikelets the grain of the aplite is finer, though it shows no contact band 

nor evidence of chilling. In the Butte area this is common. True, the contact between quartz 

monzonite and 11plite is sharp, but the latter shows transition forms and even masses of quartz 

monzonite that are clearly not included fragments but are integral parts of the mass. Yet the 

sepa:r;ation of the two rocks is commonly definite and it is certain that no mixing of the two 

materials due to convection or movement before consolidation has taken place. 

In most aplite bodies the grain varies considerably from place to place; in some the rock 

becomes a micropegmatite, · rarely a coarse pegmatite, and in some shows banding of fine and 

coarse grained material. 

PORPHYRITIC ROCKS. 

RHYOLI',rE PORPHYRY. 

PETROGRAPHIC CHARACTER. 

The. rhyolite porphyry, which in other publications has been called the :Modoc porphyry 

and is locally known by that name, occurs in dikes and wedge-shaped masses intruded in the 

quartz monzonite forming Anaconda Hill. It is extensively altered at the surface, and fairly fresh 

material is obtainable only from railroad cuttings and underground mine workings. The 

least-altered material has a pale-green or gray-green color· and is thickly dotted with small 

white or cream-tinted crystals of opaque feldspar, larger but less abundant grains of quartz, 

and much larger pale-pink or white phenocrysts of orthoclase. Biotite grains and foils are 

scattered sparingly through the very dense green groundmass and in a few of the big orthoclase 

crystals. The large orthoclase crystals vary from half an inch to an inch in length, are mostly 

tabular in ~a bit, and are more or less altered, some of them sho\ving a vitreous center surrounded 

1 Weed, W. H:, and Pirsson, L. V., Highwood Mountains of Montana: Bull. Geol. Soc. America, vol. 6, 1895, p. 406. 

2 Geology of Silver Cliff and Rosita Hills, Colo.: Seventeenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1896, p. 329. 
DESCRIPTIVE GEOLOGY. 41 

by a shell of opaque and altered material. More commonly they are dull and show a wellInarked poikilitic structure. The smaller white phenocrysts are of feldspar and are commonly 

dull, opaque, and altered. Quartz is very prominent and on weathered surfaces is the only 

recognizable mineral. It is gray, transparent, with greasy luster, no cleavage, and splintery 

fracture, due to a crackled condition of the grains. The grains are mostly corroded~ some of them 

to irregular or rounded forms, though they commonly preserve the doubly'terminated pyramidal 

crystalline shape; All the biotite is much. altered and is recognizable only in the freshest material. Epidote and pyrite are common in the material from underground workings. The 

groundmass is very dense and felsitic looking. In the material from the railway cuttings 

rectangular masses an inch or two across consist of a granular nlLxture of feldspar, quartz, and 

biotite. They apparently represent poikilitic intergrowths of quartz and feldspar, with biotite 

leaves, the whole resembling aplite and having the crystal form of orthoclase. 

Under the microscope the rock is seen to be a rhyolite porphyry; by some it might be 

classed as a granite porphyry, as the groundmass is nlicrocrystalline. It is of very uniform character in. all its occurrences and is everywhere decomposed. The smaller feldspar phenocrysts 

are seen to be plagioclase and orthoclase, the former predominating. The groundmass consists 

of alkali feldspar and quartz; both feldspar and groundmass are altered, the former showing. 

patches of sericite, especially along cleavages, and the biotite being largely altered to chlorite 

and iron ore. The plagioclase appears to have suffered less alteration than the orthoclase, a 

condition contrary to that observed in the granite. A specimen of the freshest rock obtained 

was analyzed by Dr. H. N. Stokes in. the Survey laboratory, with the following result: 

Analysis of rhyolite porphyry from Butte distn:ct. 

Silica (Si02) •••••••••••••••••••• - - •• - - - - - - - - • - - • • • 

'l'itanic acid (Ti02) ••••••••••••••••••••••••••••••• 

Alumina (A120 3) ••••••••••• - •• ·- • • • - • • • • • • • • • • • • • • 

Zirconium (Zr02) •••••••••••••••••••••••••••••••• 

Iron sesquioxide (Fe20 3) ••••••••••••••••••••••••• 

Iron monoxide (FeO) ........................... . 

:Manganese oxide (MnO) .......................... . 

Lime .(CaO) .................................... . 

. Magnesia (MgO) ................ .' ............... . 

Potash (K20) ................................... · 

Soda (Na20) ..................................... . 

69. 95 

. 24 

15. 14 

. 02 

. 38 

. 83 

. 08 

1. 45 

. 56 

6.36 

2. 70 

Moisture at 110° (H20).... .... .. . .. . . . . . . . . . . . . . . . 0. 40 

Moisture above 110° (H20)....................... . 91 

Baryta (BaO) ............... : . . . . . . . . . . . . . . . . . . . . . 13 

Strontia (SrO) ... ·................................ . 02 

Phosphoric acid (P 20 5). • • • • • • • • • • • • • • • • • • • • • • • • • • • 10 

Sulphide of iron (FeS2)....... • • • • • • • • • • • • • • • • • • • • • 39 

Carbon. dioxide (C02). • • • • • • • • • • • • • • • • • • • • • • • • • • • • 37 

Copper (Cu). .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . 03 

100.06 

The ·analysis confirms the microscopic examination and shows the rock to be a rhyolite 

porphyry, son1ewhat low in silica. Compared with the other rocks of the district the percentage 

of potash is rather large, being the saine as that of the aplites; the percentage of soda is that 

common to most of the rocks of the district. · 

WEATHERING. 

The rhyolite porphyry is well jointed and has a prevailingly smooth fracture, breaking into 

angular fragments, which in many places cover the ground and obscure the outcrop. Good 

surface exposures are, therefore, uncommon. The exposed surface is frequently brightly 

stained by iron oxides or is a rich umber brown. The resemblance to altere.d silicified granite 

is very great, bu~ close inspection always shows the crystals of quartz which protrude above 

the weathered surface. The rock on long exposed surfaces is pitted by small rectangular centers, due to the complete ren1oval of the smaller feldspar crystals and the biotite. · In railway 

cuttings the rock is seen in solid masses, whose hardness is in marked contrast to the loose sandy 

texture of the disintegrated granite that forms the walls. 

DIKES. 

Rhyolite porphyry is found only in the copper area, where it. forms dikes cutting the 

quartz monzonite of Anaconda I-Iill. These dikes are irregular, parallel or nearly so, have a 

general west-northwest direction, in many places coin~ident in course with the veins. 
42 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

Three large intrusions of the rock are known-the Modoc, Rarus-Anaconda, and Pennsylvania dikes. The largest, the Modoc dike, is well exposed on the surface. The RarusAnaconda dike has not cut through ·to the surface in the regular way, but is recognizable in 

de.tached outcrops along a definite line a mile in length extending from the M. 0. P. smelter 

to about west of the Anaconda shaft house. The Pennsylvania dike is recognizable on the 

surface by scattered debris only. All three dikes are well exposed in underground workings. 

The Modoc dike is. exposed both on the surface and in several railway cuttings. It is 

traceable from the foot slopes back of Meaderville westward to the railway line above the 

Modoc shaft, a distance. of 3,200 feet with a vertical rise of 430 feet. The dike shows a maximum width of 210 feet in the railway cut below the Modo.c mine and is 117 feet wide on the 

1 ,000-foot level of the Modoc. The outcrop thins out westward and is about 27 feet across in 

the lowest exposure. Figure 4 shows a vertical section of the Modoc dike. 

In the west wall of the rock cut along the main track of the Great Northern Railway the 

dike shows as a single intrusion 45. feet across, but in the east wall it is split into two forks, 

5 and 8 feet wide, respectively, separated by lOt feet of altered granite. This cut shows 

clearly that the intrusion took place in the solid granite after it had been fractured by a 

system of joints corresponding to those seen to-day-a system probably emphasized by later 

earth movements. An exposure on the East Colusa railroad cut (Pl. IV, B, p. 32) shows. clearly 

Rhyolite porphyry· 

FIGURE 4.-Vertical cross section of rhyolite porphyry dike. 

that the porphyry followed preexisting cracks. In a general way the contacts follow the joint 

fissures, but tend to widen upward, as if resistance had been less. The main body of the dike 

followed nearly vertical fissures, but injected stringers along planes and cross fractures. That 

the dike is older than the copper veins and is cut bY. them can be seen in the lowest. railway 

cuttings, where a 6-inch seam of quartz, with a 3-foot decomposed zone on either side, cuts the 

dike, and the dike has been sheeted by the same forces that intensified the earliest fissures a:r;J.d 

was the direct cause of the vein-fracture system. (See also pp. 58-62.) 

The porphyry breccia on the 1,200-foot level of the West Colusa mine on the south side 

line of the Modoc Extension is cut by a fault vein near the center of the Balaklava claim. 

This porphyry occurs not in a solid mass, but in bowlder-like and angular fragments in solid 

granite, which would seem to indicate that it was solid when the granite was injected. 

The Modoc is the only dike having a well-defined, conspicuous outcrop. Its superior 

hardness causes it to weather in relief above the softer disintegrated granite, and to form the 

crest of a lateral spur of the Anaconda Hill on which the Modoc shaft is built. 

RHYOLITE. 

DISTRIBUTION AND CHARACTER. 

About one-fifth of the surface of the Butte district is covered by rhyolitic rock. It is the 

most variable rock of the district, occurring in many colors and forms, representing the different phases which were produced from one molten rock magma under different conditions of 
DESCRIPTIVE GEOLOGY. . 43 

consolidation. Two distinct varieties, distinguished by their manner of o·ccurrence, have been 

n1apped: (1) Intrusive rhyolite, forming the dikes and filling volcanic necks or conduits, and 

(2) rhyolite-dacite, an extrusive or surface type, forming lava flows and surface breccias and 

other products of explosive volcanic action. The boundaries are indefinite and are not always 

recognizn,ble where the fragmental rocks overlap the intrusive form. Both forms are of 

economic interest, since the dikes intercep.t and cut off the ore deposits, and the surface rocks 

cover and conceal them. 

The rhyolitic rocks are porphyritic, showing phenocrysts in a dense groundmass. The 

porphyritic crystals vary in abundance; in some rocks they are small and few, but commonly 

they are 1nany and in places are so closely crowded as to give the rock a granular aspect. White 

feldspar is universally present, and· biotite peppers the groundmass or appears in minute flakes, 

characteristic of the rocks. Quartz grains and sanicline are found in n~arly all of the rocks. 

Studied under the microscope the rocks are chiefly rhyolitic, but some dacites and transition fonns between dacite a~d rhyolite are found. Though presenting strongly marked regional 

similarity, the rocks possess considerable diversity in groundmass, varying from microcrystalline to glassy textures, this being clue to differences. of origin and occurrence. Over a large 

part of the district they are extrusive, in part lava flows, in part the finer products of violently 

explosive volcanic outbursts. In other places they are intrusive dikes, resulting from injections of viscous 1nagmas along fissures. At Big Butte both types occur in a complex of rocks 

·filling the volcanic channel or neck of the small vent or piled up about it. 

RHYOLITE-DACITE. 

CHAH.ACTER. 

Extrusive rocks, consisting of rhyolitic breccias and flows, cover the northwestern part of 

the district, where they fonn the border of the great rhyolite area extending for many n1iles north 

and west of Butte. Within the Butte area they are not so varied as farther north, but are 

rocks of rather uniforn1 type and appearance. They vary from massive to clearly fragmental 

fonns of gray, p'ink, or yellowish color. Many of the massive forms include fragments whose 

differing tint and texture 1nake them prominent on weathered surfaces. The rocks vary from 

dense to lithoidal forms, from those of small and scattered phenocrysts to those in which the 

porphyritical qrystals are clos.ely packed. The m9st common type shows an abundance of 

glassy, crackled, gray quartz grains, uniformly about 2 millimeters in diameter, together with 

sanidine and andesine phenocrysts, a f~w chlqritic spots, and a dusting of biotite flakes. The 

phenocrysts are cracked and arranged in line showing 'flowage of viscous magma. The 

phenocrysts and crystal fragments are held in a groundmass of brown glass. In part at least 

the n1assive rocks represent lava flows in which the congealed. surface portions, cracked by 

continued flow of the lava and mixed or kneaded in the pasty mass, make a flow breccia. The 

tu.ffnceous forms show fragments held in a well-indurated, very dense cement of similar but 

s1naller :frag1nents. In many places ready weathering of the fragrnents gives a pitted appearance to exposed surfaces of the rock. OCCUH.RENCE. 

The rhyolite-dacites cover large areas, ·but vary in thickness. Near the Nettie and 

other mines of the western part of the district they are locally but a few feet thick-a mere 

veneer upon the granite surface. In the Oro Fino IIills they are several hundred feet thick, 

but they'rest upon a very uneven, hilly surface of granite and vary in thickness accordingly. 

Pron1inent outcrops are scarce, as the rock breaks into irregularly platy or angular fragments, 

few of which are a foot across, and generally forms well-rounded slopes tufted with grass. 

Exposures near the Nettie n1ine are. typical; the rocks are a light rusty red and form low, 

rough n1asses not unlike debris piles. A few buttresses outcrop on the slopes north of Oro 

Fino Gulch. 

The breccia shows a general increase in the size of the component particles toward the northwest, showing that the 1naterial was derived not fro1n the Butte but from son1e unknown vent 

northwest of Butte. 
44 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

RHYOLITIC DIKES. 

CHARACTER. 

The n1assive rock of rhyolite dikes is in few places well exposed· on the surface, but the 

denser contact forms form many low inconspicuous reefs traceable as outcrops or debris over 

the smooth slopes. The main body of the dikes is similar in all the intrusions. It is white, 

pale cream, or pink, has a minutely rough fracture, and shows numerous phenocrysts of sanidine 

and plagioclase feldspar, quartz grains, and a .liberal peppering of black biotite leaves. The 

sanidine is the most abundant, appearing as the customary square cross sections of tabular 

crystals; commonly these measure not over one-sixteenth inch across, though a few individuals 

up to one-eighth inch across, showing included biotite, occur. The gray or pale an1ethystine 

quartz occurs in rounded, corroded grains, usually slightly smaller than the sanidine. In thin 

section the plagioclase feldspar is seen to be andesine and the rock a typical rhyolite porphyry. 

The contact forms· vary in color and texture. The groundmass is most dense at the contact and less and less so away from it. Platy parting is prominent, and the biotite leaves are 

arranged parallel to the planes of fissility. Locally the rock is banded, dense fonns, showing 

marked flow structure, alternating with more lithoidal varieties. Miarolitic cavities studded 

with sanidine, biotite, and quartz crystals appear in the rock fron1 the south end of the· east 

branch of the Travona dike. In general the groundmass contains fewer and srnaller porphyritic crystals than the main rock of the dike. In son1e instances quartz appears to be 

entirely wanting· in the contact forms, and the andesine feldspar and sanidine are present in 

nearly equal amount. 

The following analysis of the massive rock from the Hyde Park dike was n1ade by Dr. H. N. 

Stokes~ of tlie Survey laboratory: 

Analysis of rhyolite from Hyde Park dike, south of Silverbow Creek, Butte, lJfont. 

Silica ......................................... . 

Titanic acid ................. , .................. . 

74.34 

. 18 

Soda .................. · ........................ . 

Water at 110° C ................................ . 

Alumina................................. . . . . . . . 12. 97 Barium ............................ ~ .......... . 

2.49 

1.11 

. 07 

Ferric oxide ................................... . . 75 Strontium ...................................... Trace. 

Ferrous oxid~ ................................... . . 54 Phosphoric acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 07 

Manganese. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trace. Zirconium .......... ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 05 

Lime .. :........................................ . 85 

Magnesia........................................ . 86 100.03 

Potash ................. ;......................... 4. 72 

This analysis shows the rock to be a normal rhyolite. 

OCCURRENCE. 

The dike rock breaks 'readily into small,, generally platy debris, and it is only the denser 

cont~ct form of the dike walls that offers enough resistance to weathering agencies to appear in 

outcrops above the general surface of the ground. 

·In general all the rhyolite dikes exposed have an approximately north-south trend. A 

few of them are directly traceable to Big Butte as a center of eruptive activity, and all of thern 

are believed to be offshoots from this vent. 

The longest dike is seen near the Nettie mine .and. is encountered in the mine workings. 

Its outcrop is obscure, but is traceable by the fine debris or in a few places by the platy contact 

band. The surface exposures range in width from 20 to 100 feet and extend from the rhyolite 

area on the north to the detrital sands and clays south of the railway track near the mine. 

The Germania dike trends nearly north and south just west of the Germania mine. At the. 

south end it is· about 25 to 30 feet wide; near the north end it splits and one of its branches 

extends nearly to the mine shaft. It is traceable by a few obscure outci·ops and by debris for 

nearly 4,000 feet until lost in the detrital sands of the valley. 

The Soudan dike, which cuts off the vein of the Soudan nline, is the widest of the intrusions. 

Dikes of rhyolite, mostly decomposed to white clay, are exposed by the placer workings 

west of Miss~ula Gulch. The Travona dike, near the Travona mine, on the east side of Mis-
DESCRIPTIVE GEOLOGY. 45 

soula Gulch, has an average width of 100 feet and a general north-south direction. Southward 

it extends to the alluvial deposits of Silverbow Creek: and northward it terminates before 

reaching the Ancient vein. It is said to be cut in the Travona workings, where it has a width 

of 140 feet. In good exposures in the railway cuts and in prospect pits near by it has vertical 

walls and varies in width fr01n 25 to 85 feet. 

The Brewery dike is an irregular intrusion, with four finger-like br~nches running south 

frmn the Blain Blass exposed near the Butte brewery. In the railway cut the two easternnlost 

branches are 30 feet in width, and the granite between then1 is altered to clay.~ These branches 

tenninate abruptly, for although 30 feet wide in one wall of the cut they do not appear on the 

opposite side. West of the westernmost of the two a fissure vein of brecciated material consists 

rnainly of aplite fragn1ents cen1ented together by rhyolite. The viscous rhyolite magma appears 

to have brought up the fragrnents broken fron1 the walls. Their presence indicates that the 

original upper part of the dike still rernains, and has been little eroded ~ince its formation. 

COMPLEX AT BIG BUTTE. 

Big Butte is cornposed of a complex of rhyolite rocks showing a great variety of colors and 

textures. On the southern flank, where erosion has revealed what is very plainly a volcanic 

vent, the rocks are of rnany kinds. Pumiceous, glassy, and n1assive rhyolite fragn1ents occur 

in a fumly indurated 1natrix: of fine par~ticles of the san1e material. Much granitic debris is also 

. present, the fragrne:nts varying fr01n sn1all grains to bowlders several feet in diameter. Big· 

Butte is forrned of rnassive rhyolite and ejected n1aterial. Both the fragn1ental rocks and the 

rnassive rhyolite forming the platforn1 to the south and underlying the butte are prevailingly 

dacitic in habit. To the eye they show numerous feldspar phenocrysts, abundant biotite mica, 

and smne quartz. Thin sections show the feldspar to be mainly andesine, with a little sanidine. 

A little hornblende of the ordinary gray variety is accessory. The phenocrysts are cracked 

or broken into chips and lie crowded together in lines of flowage. The rock grades fron1 rhyolite 

through rhyolite-dacite to dacite, and varies fr01n brown and gray banded glasses and black 

})itchstone porphyries to lithoidal forrns. The breccias containing granite and aplite fragrnents 

are the products of explosive showers; those with a glassy n1atri.~ are flow breccias. The black 

pitchstone is supposed to be typical of the rnagrna, as it holds no inclusions. The following 

analysis of a carefully selected sample of the rock was nuide by Dr. H. N. Stokes in the Survey 

laboratory: 

Analys1:s of porphyritic dacitic pitchstone (lassenose) from B1:g Butte. · 

Silica ........................................... 67. 55 

Titanic acid...................................... . 34 

Alumina ......................................... 15. 68 

Ferric oxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 

Ferrous oxide ........................... ·. . . . . . . . . . l. 02 

:Manganese oxide .................................. Trace. 

Litne............................................ 2. 51 

Magnesia..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l. 11 

Potash.......................................... 2. 86 

Soda............................................ 4.15 

Moisture below 110° C............................. 0. 38 

Moisture above 110° C............................. 2. 76 . - Zirconia ........................................ . 

Carbon dioxide .. : . ..................... ~ ....... . 

Baryta........................................... .11 

Strontla..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 03 

Phosphoric oxide................................. .12 

Chlorine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 05 

99.65 

Un'-l.er the 1nicroscope the rock is seen to be a colorless glass· thickly crowded with broken 

phenocrysts and s1naller chips of quartz, andesine, sanidine, and biotite, with a little accessory 

hornblende. The andesine exceec~s the sanidine in amount, thus agreeing with the analysis. 

In son1e specin1ens the sanidine sho·ws indications of alkali variations by zonal· structure, and 

the quartz phenocrysts are surrounded by coronm of oriented quartz in the groundmass. 

LAKE BEDS. 

Deposits of sediment which accun1ulated on lake bottoms are found only in the extreme 

western part of the district·. They consist of con1pact but generally unconsolidated sands, 

gravels, tuffs, and stony clays. The beds are horizontal, but show local cross-bedding and vary 
46 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

from place to place both in general character and in the nature of the material composing them. 

The gravel is composed of granite and aplite. The stony clays show no bedding or only such 

as is too rude to be recognizable in prospect shafts. The tuff beds are formed of fine rhyolitic 

ash, which enters also into the composition of some of the sand beds. Under the microscope 

this ash is seen to be a volcanic dust, the product of a volcanic explosion. It is composed of 

minute angular particles and threads of glass filled with tiny microlites of quartz, biotite, and 

feldspar, the latter arranged in keranoids. A partial chemical analysis. shows 1.06 per cent lime, 

14.84 per cent potash, 1.52 per cent soda, and 67.33 per cent of Si02 ; the rock is therefore rhyolitic in nature. 

Lake-bed deposits form the level benches and almost flat slopes west of the district, only a 

small part of them occurring within its limits. Topographically the area differs markedly from 

the rest of the district, being the typical valley bench land so common in the State, devoid of 

timber, but covered by sagebrush 1 and from a distance looking like a burnt stubble field: Natural 

outcrops are poor and are seen only in the cut banks of dry channels. The material weathers 

clown and often is recognizable only by the bare light-colored spots seen on the slopes. Near 

·the hills the deposits form benches resting on the steep ·slopes. Prospect shafts sunk in· these 

benches to depths of over 60 feet show only stony clays. The slopes of the benches show horizontally stratified gravels and sands. The gravels are generally rounded, not flat like beach 

shingle. The pebbles show a slightly altered surface,. and some of them are lime incrusted. 

Locally the beds ·have been cemented by percolating waters carrying iron, lime, or silica in 

solution. . 

· These deposits represent the material washed into a· lake which covered the Silverbow 

Valley west of Rocker, extending south acro!3s what is now the Continental Divide. Only the 

extreme eastern margin and shore of this lake were within the district described, but the deposits 

were continuous westward and southward to places where vertebrate bones have been found. 

These fossils were of upper Miocene. types. The evidence is of importance, as the lake beds were 

contemporaneous .with the rhyolite eruptions, and these latter took place after the period of 

ore deposition, so that the age of the ores must be pre-Miocene. 

ALLUVIUM. 

The areas shown on the map (Pl. X, in pocket) as covered by alluvium include those parts 

of the district where the rock bed is concealed by a mantle of recent detritus. This includes, 

therefore, the alluvium of stream bottoms, the sands which cover the valley flat, whether 

wind blown or water laid, and the unassorted angular debris from the mountain slopes often 

significantly called "wash." Areas covered by tailings and other debris from the smelters are 

also included. These deposits are wholly detrital, are unconsolidated, and conceal the nature of 

the underlying rock. They vary greatly in thickness, but in general simply fill the valley 

bottom, as is indicated in the cross sections. In the valley east of Meaderville alluvium 

fills an old drainage channel to a depth of 400 feet-about 350 feet below the present channel 

of Silverbow Creek. The placer grounds of Missoula Gulch arid South Butte have not been 

mapped as all1:1vium because the gravels are nowhere more than a few feet deep, and the workings 

afford numerous exposures of the underlying rocks. 

VEIN OUTCROPPINGS. 

Large quartz veins form a number of abrupt ridges and narrow crests rising above the general slope, and smaller veins form broken-down walls or reefs. The outcrops are composed 

in part of true vein quartz and· in part of an altered granite indurated by secondary silica in 

minute veinlets and disseminated through the substance of the rocks. They are generally 

black with manganese oxides or rusty with iron. Such veins, though long and of great width, 

have not been great mineral producers. The Ancient and Czarina are the best-known and largest, 

forming steep ridges rising 60 to 100 feet above the general surface. (See Pl. XLI, B, p. 240.) 
CHAPTER TV.-STRUCTURE OF BUTTE DISTRICT. • 0 

FAULTING. 

MAPPING. 

. The faults shown on the geologic map (Pl. X) emorace only those whose existence is 

detenninable froni surface o~tcropping or from underground workings of the veins, since, 

owing to their occurrence in a single rock type, their presence can only be detected by such 

means. The vein fissures and sheeting planes of the rocks are in fact true fault planes, though 

the throw is small, often so minute as to be measured in fractions of an inch, and is determinable only when dikes of the dense white aplite afford means of measurement. The faults 

mapped are, however, those having a throw of many feet. They displace both copper and silver 

v.eins have a general north and south direction. Their occurrence is described later (pp. 58-64). 

CONTINENTAL FAULT. 

PHYSIOGRAPHIC CHANGES. 

The chief mineral-producing area, . embracing the hills and slopes of the Butte district 

proper, is bounded on the east by a depression 1 .to 3 miles wide-an arm of the open and nearly 

level basin lying south of Butte known as the Flat. Beyond rises the precipitous granite 

wall of East Ridge (Rampart Mountain), sharply delimiting the Butte area from the general 

lllOUntain tract of which it is geologically but not topographically a part. Mountain wall and 

depression are equally noteworthy, for both are believed to have originated from the great 

Continental fault and other fractures, which not only determined the dominant features of the 

present topography but perhaps had also a profound influence on the economy of the ore deposits. 

It is believed that the drainage of Elk Park, which lies east of East Ridge, was formerly 

westward into the present course of Silverbow Creek, the present Flat being a valley in which 

several tributary streams gathered, the combined drainage flowing through a canyon to the 

Silver bow Valley. This siJl!ple system of drainage, with the appropriate topography developed 

by it, was completely changed by post-Tertiary faulting which dev~loped along a line that now 

marks the base of East Ridge, producing parallel and closely spaced fractures. This faulting 

uplifted and tilted. the area on the east, and depressed that on the west to a thousand or more 

feet below its former level, leaving the scarp of th~ mountain wall to mark the line of fracture. 

The drainage of Elk Park and vicinity was reversed so as to flow north and east to Boulder 

River; and the Flat, deprived of the Elk Park drainage and so depressed that its streams had 

little carrying power, was filled up and leveled off with the waste from the surrounding slopes 

and fTonl East Ridge. 

EVIDENCE OF THE li'.AULT. 

The evidence supporting this hypothesis is triple, being derived (1) from the Elk Park 

drainage; (2) fTom the condition of the Flat; and (3) from the mountain. 

EVIDENCE FROM ELK PARK DRAINAGE. 

Elk Park is a mountain valley filled with waste. It shows by the arrangement of its tributary 

stteatns and their gorges, as well as by its own slope, that its drainage has been reversed and now 

drains to the.north instead of to tl;le south. The general map (Pl. I) shows.this very clearly. 

EVIDENCE FROl\1 THE ~'LAT. 

The Flat, south of Butte, can not have originated from any normal drainage development. 

Its present drainage. is not only insignificant, but it's watershed is too small to account for the erosi~n of its basin even were the rainfall augmented a hundredfold, and its slope is too gentle to 

47 
48 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

afford a run-off or to give carrying power to the streams. The general arrangement of the drainage courses (Pl. I) shows that Silverbow Creek is a trunk stream beheaded of its branches, like 

a tree whose bushy top has been broken off, leaving only the trunk and a few lower branches. 

The natural exposures on" the Flat and the conditions revealed in well sinking show that the 

valley is filled to an unknown depth with gravelly waste from the surrounding granite areas. 

This material is not ·of lacustrine origin, and there is no evidence of a permanent body of water 

having been retained in the basin; it is of the nature of "wash" and was evidently derived from 

the waste of adjacent slopes, a process still actively going on to-day. That the absence of 

rock in place is actual was proved by a careful examination of every place on the Flat where 

strea.m cutting or low valley bluffs showed exposures. In each case the material seen was not 

of rock disintegrated in place, but sand (of granitic disintegration) partly brought and arranged 

by stream action but being mostly flood or rain wash. The slopes immediately above the 

valley show rock· in places beneath a few inches of sandy debris. With every rain the small 

gulches from the ridges bring down large quantities of this sandy material and spread it out 

along the base of the slopes in great flat cones,_ which ultimately coalesce and make a uniform 

valley sheet. · 

The unusual and abnormal depth of wash immediately west of the supposed fault line is 

itself valid evidence of the faulting movement. 

The extension of the Flat northward, west of East Ridge, has been extensively prospected 

by tunnels, cuts, and shafts. Between the rocky slopes of East Ridge and the granite gorge of 

Silver bow Creek above Meaderville a depression filled with "wash" or waste has been found, 

which may be either a filled valley or a brecciated mass making a part of the fault zone. 

EVIDENCE FROM EAST RIDGE. 

The condition of the East Ridge wall itself shows that it owes its origin to faulting and that 

such movement has been repeated at relatively recent times. As the rocks are granitic, and as 

the supposed faulting involves a displacement of 1,000 feet or more, the observed facts will be 

given in considerable detail. 

The long bold wall of the Continental Divide, which forms the eastern boundary of the 

Flat, is scored by sharply incised gulches that lie between and define numerous sharp buttress 

ridges or lateral spurs. These gulches, though scarcely large enough to be shown on the map, 

necessitate many high trestles along the Northern Pacific track. The steep lateral spurs between 

them are all notched in profile, markedly so between Par~ and Horse canyons. The notching, 

which abruptly cuts gentle depressions into steeply westward facing ridges, can not be accounted 

for hydrographically. The streams which cut back into the mountain are small and relatively 

insignificant, and in any event stream cutting alone could not form these features. 

The most prominent notch, known as ·the White Notch, is about 6 miles from Butte. It 

is a broad white gash or scar that is very prominent upon the darker wooded mountain side. 

It is certainly not due to normal erosion and is not a wind gap, for no drainage could form this 

notch and the knob seen in front of it. The adjacent gulch is no wider than the others spanned 

by the trestles of the Northern Pacific track, but it is filled by a large stream of clear cold water 

that dashes through a rocky channel, among angular blocks of rock that all but conceal it. 

The bases. of the slopes show disintegrated granite, the hollows being sand filled. Above a milk 

ranch that is situated conveniently near the stream is a small ridge covered with great bowlders, 

the largest 8 feet in diameter, of light-gray granite in place. This is the normal granite of the 

region. The rock blasted out in building the trestle is, in contrast to this, a light-gray rock, 

decidedly more acidic in character, resembling the semiaplitic forms of Butte. Above the 

trestle this rock, which extends as far as the summit of White Notch, shows gray streaks and 

smears. It contains a large amount, about 33 per cent, of white aplite grading into pegmatite. 

Up the gulch the rocks are marked by pronounced parallel sheeting of the granite. The 

fissures are not close enough together to make the rock platy and are sufficiently far apart to 

form great blocks, which where overturned make immense monoliths. The direction of the 
STRUCTURE. 49 

fissure planes appears to be nearly parallel to the ridge. The crushed rock in the fissures here 

is the source of the water that issues in ·copious springs from the lower part of the ·notch. 

White Notch itself lies transverse to the gulch and to the normal drainage. Its lower slope 

is step like and ,consists entirely of debris, not rock altered in place, for it is most unlike the great 

pla~es of granite that rise in walls on the west and almost as abruptly on the east. Its upper 

slope is gentle, showing much sand and a crumbly ~sintegrated gray granite near the top. At 

the top the depression in the ridge is less prominent when examined closely than it is from a 

distance, and its surface can not be more than 100 feet below the top of the knob to the west. 

A second parallel fault slope appears liigher up the mountain. 

The most pertinent feature observed from this notch is. the persistent, similar, though somewhat less striking, notching of each of the large buttresses between it and Horse Canyon. 

If, as is believed, this notching is due to faults, it is apparent that the. mountain wall is 

not formed by one fault, for the lines traceable by the notches are many, parallel, and overlapping, but is the result of a steplike succession of short parallel faults, to which the sheeting 

of the granite conforms. · 

The flat-topped ridge north of Columbia Garden shows a dike of rhyolite porphyry, cut by 

numerous faults whose displacement can be measured and whose attitude makes apparent the 

step-fault . character of the displacement which separates the copper area of Butte from the 

vein area of East Ridge. The dike, which is traceable for about 3,000 feet, trends N. 45° E. on 

the west side of the ridge and N. 80° E. on the east side. It is faulted at least seven times, four 

ti1nes to the north and three times to the south. The displacement varies from 20 to 400 feet 

and the distance between faults from 500 to 600 feet. 

Another large dike of the rhyolite porphyry, 75 to 120 feet wide, outcrops in East Ridge 

about 700 feet west of the portal of the Great Northern tunnel. It runs N. 75° E. to the sumInit of the 1nountain, corresponding to the dike seen in tl;le railroad cut on the Continental 

Divide (Pl. I); but the latter is faulted and the two dikes do not line up. ·The dike in the 

railroad cut is 60 feet wide and trends N. 80° E.; its displacement is due to the great northsouth fault which runs along the west side of Elk Park. 

· The fault, which is recognizable in the vVhite Notch and which forms the saddles back of the 

foothill knobs, has a general north-south course and is the cause of the abrupt separation. 

between the flat and the mountain. At the Bertha and Bullwhacker mines this fault, or a 

sympathetic fracture ·parallel to it, is from 50 to 100 feet wide an4 is mineralized by chrysocolla 

and other oxidized ores which are mined on the claims mentioned. The workings at these 

clnims and on the :Montgon1ery claim show that this fault is itself displaced by east-west 

fissures, so that this continental fault systen1 is not the latest phase in the faulting of the region. 

SUMMARY. 

The facts 1nay be stimtned up as follows: (1.) The chain of detached knobs along the west 

slope of the East Ridge are not of ordinary erosion types. The White Notch is only explainable 

by faulting; (2) brecciation with slickensides has been noticed at several localities along the fault 

zones; (3) the reversed watercourses of the Elk Park Valley show a tilting of the region toward 

the north. The drainages have not been stolen by Boulder drainage, for the eastward-flowing 

streath, Bishop Creek, is relatively sluggish and n1eandering and does not begin actively to 

cut its channeltn1til the north end of Elk Park is reached. 

The faulting of the East Ridge with actual as well as relative uplifting seems the only reasonable explanation. The Butte area is actually as well as relatively thrown down and the 

flat is produced by the debris filling up the valley. The fault is not single, but is a succession of 

parallel faults, with overlapping ends, which probably split and branch out. This arrangement 

carries one of the fault lines directly to Meaderville and may have an important bearing upon 

the relationship of the veins and the vein faulting. · 

The evidence thus outlined seems to indicate the con1paratively recent faulting of the region 

and 1nay account for the absence of any rock in place in the surface of the Flat. 

90427°-No. 74-12--4 
50 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT~ MONTANA. 

PRESENT-DAY FAULTING. 

That faulting is taking place at the present time has been conclusively proved by comparisons 

of bench marks and lines of precise leveling. For many years there have been breaks in. the 

water and gas pipes in certain sections of Butte, cracking in the walls of houses, and occasionally the formation of gaping fissures in the streets. As such displacements 'are frequent and 

troublesome in the vicinity of mine workings, little was at first thought of these occurrences. 

Later, however, it was rmnarked that there were no workiJ?-gS under the place where repeated 

breaks in the water pipes had occurred. Attention was alsc5 drawn to the peculiar and apparently 

recent fault scar or notch on East Ridge (p. 48). These facts led to the investigation: 

Study at the Boulder Hot Springs showed that slight faulting and reopening of the veins 

formed and forming by these springs had taken place, so that it is probable that crustal adjustment is taking place throughout the region and is not confined to Butte. 

To determine the amount of change taking place in the levels of different portions of the 

Butte district, as a result of faulting movements now in progress, a series of carefully determined bench marks were established in Butte and in the neighboring mountains. Bench 

marks had already been est~blished throughout the district as a result of the top.ographical 

survey made in 1895 and 1896, but there having been considerable change in the levels, spirit 

leveling was undertaken again in October, 1904, by R. I-I. Chapman, United States topographer, 

every precaution being taken to make the work as accurate as possible. This work resulted 

in the establishment of many bench marks, which will make it possible· in the future to determine, by means of releve~ing, the amount of surface 1novement in and about the city of Butte. 1 

Sixteen standard oench marks were left in the city of Butte and seven additional ones in 

adjacent regions. Most of the lines were run two or three times; a large circuit of about 12 

miles was run and checked and was tied to the bench marks of the work of 1896 at Elk Park 

Pass (W ood~ille Summit). In the first week of the work an old Gurley 22-inch level was used, 

. but owing to the difficulty in keeping this instrument in adjustment, a new Berger level was 

substituted and used till the end of the work. The rod used was of theN ew York type, and was 

found to be without appreciable error when tested by the Bureau of Standards. The levels 

showed considerable change in the bench mark at the city courthouse, and as this bench mark 

was the standard for all reference in 1896, all the elevations of the other bench marks were 

reestablished. 

Bench marks were established from the Flat south of Silverbow Creek, at a point near the 

foot of Timber Butte, to one on the Walkerville Ridge, thus crossing the undermined area from . 

south to north. A second line was run from Meaderville toward the Big Butte, which gave an 

east and west control. · 

In 1906 the Coast and Geodetic Survey brought a line of precise levels from the southwest 

(Pocatello, Idaho), and tied to nine of the benches of 1904 .. · Though .this work is not finally 

adjusted it is improbable that any changes will be made which will affect the relative elevations of the Butte benches. If the bench mark at the Butte Reduction Works be taken as a 

datum, the relative changes northward are as follows: 

Relative changes in elevations of bench marks north from Butte Reduction Works. 

Foot. 

1. Butte Reduction Works ................................. .' ............................. 0. 000 

2. Webster SchooL ....................................... ·................................ . 017 

3. Colorado State school. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 051 

4. Owsley Block ..................................... ·.................................... . 436 

5. Courthouse............................................................................. . 737' 

6. Government building ................................. ,................................ . 888 

1 In this work the following precautions were observed: First, the instruments were ·examined for all adjustments every morning; second, 

equal length of foresights and backsights was, with very few exceptions, always used; third, the instrument was shaded from the'sun and the 

bubble was under the constant scrutiny of a bubble tender; fourth, the rod used was kept in position by a level to insure verticality; fifth, the 

· turning points were usually on steel pins, but when running on paved streets 20-penny nails were drivtln between paving blocks. When run'ning 

on railroad tracks two turning pins were used,. one of determined elevation being always in the ground. 
STRUCTURE. 51 

This shows an increasing subsidence as -the benches approach extensive underground 

workings. 

A comparison in a northeasterly direction from the same datum s~ows: 

Relative changes in elevations of bench 1narks northeast from B'tttte Reduction 1-Vorks. 

Foot. 

1. ·Butte !~eduction Works .......................... · ...................................... 0. 000 

2. South Butte .. ' .......... ·.............................................................. . 051 

3. :Braund House........................................................................ . 130 

4. Florence Hotel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791 

5. Government building ............................................... :.................. . 888 

These figures show subsidence in the two years fron1 1904 to 1906, as follows: 

S~tbsidence in Buttefrom 1904 to 1906. 

Actual subsidence: Foot. 

Owsley Block ...................... , ................................... 0. 218 per annum. 

Courthouse............................................................... . 368 

Government building.................................................... . 444 

Differential subsidence: 

Owsley Block and courthouse .................. ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 

Courthouse and Government building...................................... . 076 

Owsley Block and Government building................................... . 226 

In 1naking c01nparisons betwe~n the levels of 1896 and 1899 and those of 1904 the results 

can not be accepted so confidently as the later figures, but it is found that between 1896 and 

1904 the courthouse sank 0.895 foot, or 0.112 foot a y~ar, more than the Owsley Block, though 

the latter n1ltst have sunk appreciably during that time. The actual subsidence of the courthouse between 1896. and 1906 was undoubtedly as much as 1.632 feet, or o:163 feet per year. 

Probably this is tnade up of a constant slow sinking and of spasmodic greater movements. 

In 1904 a circuit was run which. crossed the great structural fault of the mountains east of 

Butte, and a bench mark was established in Elk·Pa·rk Pass, which is probably east of this fault 

line. By c01nbining the work of 1896-1899 and con1paring it with that of 1906 it appears that 

the difference in elevation between the bench n1arks at the Owsley Block and Elk Park Pass 

was 663.161 feet in 1896 and 663.839 feet in 1904, showing in eight years a change of 0.678 foot, 

which is 1nostly accounted for by. the sinking or' the Owsley Block. By indirect' comparison of 

the Owsley Block with a point to the west of it through a· combination of the work of 1896 and 

1899 and the application of a subsidence correction it is found that the Owsley Block has sunk 

0.551 foot; the difrerence between this and the 0.678 foot obtained by comparison with the 

Elk Park bench is 0.127 foot, which may be assigned to possible movement on the fault plane in 

eight years. This figure, however, is of very doubtful value and can not be accepted except in 

a preli1ninary way. 1-Iowever, it indicates possible changes of such magnitude as to renew 

interest and afrords a basis for In ore c01nplete comparisons. in the future. 

STRUCTURAL RELATIONS OF THE ROCKS .. 

GENERAL RELATIONS. 

l'he ·relation$ of the rocks to each other are of much econ01nic importance. The oldest 

rock, the Butte quartz 1nonzonite, is cut by dikes and overlain by or interleaved with lenses 

and broad though shallow masses of. aplite .. Tllis latter phase of the aplite, however, appears 

to be a tnere local segregation out of the mass of Butte quartz monzonite. . 

These relations are shown in the structure sections. The presence of ·much aplite in the 

deep underground workings, as, for example, on the 2,100-foot level of the I-Iigh Ore mine, 

shows that the rock is not of superficial origin and is not confined to the outer borders of the 

1nass. In fact, it was found impossible to 1nap all the aplite found in the East Ridge region, 

owing to the transition of one rock into another. This is less marked underground than at 

the surface. 
GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT,· MONT AN A. 

·The. rhyolite porphyry, so far as seen, is everywhere intrusive and later than the granitic 

rocks. Ball-like masses of this rock in the granite have been. repor~ed, but in the light of the 

relations shown in Plate II, B (p. 26), their occurrence seems hard to explain. The rock occurs 

both in the productive area and in the East Ridge as dikes cutting cleanly through granite, 

, older than the vein, and dislocated by cross faults. 

Nothing is known of the downward extension of the granite. It is probably very great, 

as the rock is an integral part of the great intrusive Boulder batholith. 

The extrusive rhyolites blanket a large part of the silver area. A few veins worked on the 

border of the rhyolite have been followed beneath it by underground workings, but in general 

this part of the district is unexplored. Rich secondary ores, if present there, must be older than 

the rhyolite, which now prevents the access of oxidizing waters to the veins. The rhyolite 

dikes and the intrusive rock of Big Butte cut through the granites and mineral veins alike, but 

do not displace them. They appear to be the filling of fissures suddenly opened and filled and 

hav~ no bearing upon .the ore deposits save to interrupt their continuity. 

The lake beds mantle all the older rocks and fill the depressions west of Butte to varying 

depths. The veins have not been unfavorably affected by their presence, and it is possible 

that future exploration may develop extensive mineral deposits in this· area. 

The alluvium and wash which cover the Flat are simply the filling of an old valley. The 

depth variesfrom place to place, reaching 400 feet at several points. The underlying rocks are 

decomposed granite carrying mineral veins in which rich copper ores occur (at the Pittsmont 

mines). 

The evidences of recent hot-spring action in the Butte district are confined to the Oro Fino 

area, but the study of the Boulder Hot Springs, where quartz veins are now forming and the 

thermal waters are altering the rocks precisely as they are altered about the copper veins of 

Butte, indicates that the vein formation may in part be the result of hot-spring action. At 

Crystal Springs, 7 miles west of Butte, warm waters are still flowing. These springs and those 

of Boulder are deficient in hot-spring sinters, so that when dead the only evidence that they 

once existed lies in the rock alteration. 

GRANITE AREA. 

GENERAL FEATURES. 

In a general view of the district from the east the abrupt slopes above :Meaderville and the 

featureless floor of the Flat are strongly contrasted. 

The granite area is an uneven plateau, presenting steep slopes to the south and east. Above 

Walkerville the plateau character is very marked, forming the highest part of the cllstrict and 

being preserved in the flat-topped spur whic~ terminates in Anaconda I-Iill. West ward the 

surface is less regular, being scored by Oro Fino Gulch and its branches. A corresponding, 

somewhat lower, plateau lies south of Silverbow Creek. Throughout the district the granite is 

constant in character and composition (pp. 31-36). The surface is, ·however, varied in aspect, 

for the colors of the altered rock and the peculiarities of weathering are very unlike in dif-

. ferent parts of the district. In the tract northeast of Walkerville the surface is covered by 

immense bowlders, monoliths, and castellated outcrops, due to the fissuring of the granite. In 

the Oro Fino Gulch area reefs or ridges formed by quartz veins are the only outcrops, but brilliantly colored debris, which looks very unlike the al~ered granite, is common in the many 

prospect pits .that dot the slopes. In most of the granite areas about the producing mines a 

few bowlder outcrops occur, but the surface is mostly rounded and covered by the angular sand 

of disintegrated granite. 

The differing features of the granite area are due to (1) jointing, (2) disintegration, and (3) 

decomposition; and as the effects of t~1ese agencies are most marked in the granitic rocks and 

produce the characteristic features of this district, they may be appropriately discussed here. 
STRUCTURE. 53 

JOINTING. 

The 1nnss:ive rocks nll show fissuring, which is, however, n1ost prominent in the. granitic 

.rocks. In the n1ore intensely nrineralized nreas the joints are close together, but, owing to the 

general disintegration and alteration, they are prmninent only on the exposed walls of artificial 

excavations, being especially so where they are occupied by quartz veinlets or stained with iron 

rust. In areas where the joints are less numerous, as above Walkerville and north of Meaderville, in the. northeastern part of the district, the develop1nent of well-n1arked fissure systen1s 

splits the Butte quartz monzonite into very rugged and picturesque clusters of .bowlders and 

n1onoliths. The jointing is pronrinent over a considerable area, but is not unifqrm, differing 

greatly in spacing and nu1uber of the fissures. (See fig. 5.) 

The vertical joints belong to two sets running at right angles to each other, but one set, that 

corresponding in direction to the prevailing vein systen1, is best developed. The fissures may 

be seen in the railway cuttings, where they give the rock a sheeted appearance. In natural 

exposures they fonn great blocks whose surfaces are frequently as smooth as if sawn across . 

. Pln.te V, A, shows fissured rocks, in part weathered to rounded bowlders, along the line of the 

Great Northern Railway near :Meaderville. 

Locally the nearly vertical joints are marked by slickensides, much of their surface showing 

an indurated crust or filn~ and some of it a thin clayey coating. Some of them· ar~ clearly fault 

0 5 10 IS Feet 

Granite 'Seams orfissures Veins 

FIGURE 5.-Joints in shattered granite, 500-foot level of Leonard mlne. 

fissures, but the throw of these faults is slight and is ,measurable only where the Butte quartz 

monzonite is traversed by dikelets of the white aplite.1 Where noted the throw was less than a 

foot, the downthrow being to the south. 

Becker 2 has shown that such fissure systems may result from simple, horizontal thrust. It 

is believed that the later fissuring was not confined to movement or renewed fracturing along 

preexisting lines, for the rhyolite porphyry is sheeted and the veins, which in part coincide in 

direction with th,e dikes of this rock, cross the dikes. · 

DISINTEGRATION. 

Disintegration of the quartz monzonite, as shown elsewhere (p. 86) by analyses, is accompanied by almost no chemical change. It consists of a physical change in the rock due to heating, chilling, and the action of the wind, and results in a loosening of the grains, a so-called 

"rotting" of the solid rock into n1aterial which· may be easily crumbled between the fingers. 

On rocky outcrops the surface scales off and t~e detached plates crumble to loose angular sand, 

which if? blown away by he~Vy winds. Where the rock is netted with small fissures, as i.t is over 

1 Decker, G. l!"., Structure or tho Sierra Nevada: Bull. Geol. Soc. America, vol. 2, p. 53. sop. cit. 

• 
54 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

much of the district, disintegration is hastened and the granite is changed, in places to a depth of 

20 feet or more, to a soft material easily excavated with pick and shovel. . 

Exposures in railway cuttings &nd in excavations for buildings show why rock outcrops 

and the bowlder masses are absent over so much of the Butte district. Commonly the granite 

is intersected by a network of fissures. Sheeting, as observed in the area north of Meaderville, 

is apparent in all the more prominent fissures, and the space between is netted with smaller cross 

fractures, which separate the rock into polyhedral fragments. These lesser fractures are com-

·monly marked by iron rust, a few by minute stringers of quartz, and it is apparent. that they 

have been planes along which percolating waters have altered the rocks. This relatively 

minute fissuring having facilitated disintegration as well as true rock decay, the rock is commonly rather loose and crumbly and yields readily to frost and wind and rain. The condition 

of the rock seems to result from close sheeting and from the development of the fissures n·oted in 

the less mineralized area with short connecting cross fractures. Typical reticulating of the 

;granite by rusty veinlets and seamings is shown in a wall exposed in digging the foundation for 

a church at Butte (Pl. IV, A, p. 32). In some places, especially on Anaconda Hill, the granite 

appears shattered by these fractures. Where the upper parts of the big veins are exposed they 

show no mineralization, but are zones of decomposed claylike material and partly altered 

pyrite-holding granite. 

The rate of the degradation of the granite surface is largely dependent upon the fissuring 

<>f the rocks. When the fissures are close together, disintegration is rapid, the blocks, being 

small, are rapidly worn away and the surface becomes smooth, with scattered bowlders. Where 

fissuring is less close, the rocks weather into great blocks. As disintegration proceeds the out-

·Crop becomes a mass of isolated or partly detached blocks, and the area of exposed surface 

.being thus increased, these are soon reduced to spherical masses. 

DECOMPOSITION. 

· Where the disintegrated material is not removed q,s rapidly as formed, a condition prevail-' 

ing over a large part of the Butte district, where the work of wind and rain can not keep pace 

with the secular disintegration, the rock is changed in place to a more or less coherent material 

·Containing spherical nuclei of the unaltered rock surrounded by shells of progressively more 

:and more loosened material. This action may be seen along the Northern Pacific Railway 

line south of the city; for instance, in a rock cut near· the Homestake tunnel. (See Pl. V, B.) 

At the top o~ the cut, platy masses and bowlders of granite-harder residual masses left 

in relief by the removal of the loosened granite about them-rise above a gently sloping grassy 

surface. ' Lower down the bowlders are surrounded by concentric shells and the loose sandy disintegrated granite. The kernels of the bowlders are hard and resistant, the shells are more or 

less crumbly; and the interspace is so soft as to be easily removed with pick and shovel. These 

bowlders are undoubtedly a result of fissuring and not a ball or spherical structure of the rock. 

Underground, rock alteration, the result of vein waters, forms similar bowlders out from 

the fissured granite. Plate VI, A, shows the granite of the north crosscut on the 800-foot level 

Gagnon mine closely netted by fissures, along which the polyhedral masses have been altered to 

rounded bowlder forms. The zonal character of the decomposition, which the iron oxide makes 

so prominent, shows that the bowlders are due to alteration proceeding from the fissures. 

The prevalence of extensive disintegration accounts also for the lack of outcrops. In the 

absence of protecting vegetation erosion of the loose rock is rapid, and the drainage channels 

are choked with sand. The porous crust of the granite absorb~ water readily. and assists in the 

further disintegration of the rocks. 

Throughout the productive area the rocks show few outcrops, the surface being either 

smooth and rounded, covered by granitic sand, or near the veins strewn with rusty silicified rock 

in fragment~ 1 to 4 inches across. Anaconda Hill shows neither granitic bowlders nor prominent 

vein outcrops. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE V 

A. SHEETED GRANITE NORTH OF MEADERVILLE, ALONG GREAT NORTHERN RAILWAY. 

Shows weat he rin g a long joint p lanes, so me of which are minera li zed and form veins. See page 53. 

B. DISINTEGRATION BOWLDERS, IN PLACE, SURROUNDED BY SOFT SANDY DISINTEGRATED 

GRANITE. 

Shows manner of form ati on of th e bowlders and th e ir re lati on t o s heeting planes of th e g ran ite. Rai lway cut 

at west porta l t o Homestake tunnel , east of Butt e, on Northern Pac ific Rail way. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE VI 

A. DECOMPOSITION BOWLDERS FORMED BY VEIN-MAKING AGENCIES IN GRANITE. 

North c rosscut , 800-foot le ve l, Gagnon mine. 

B. VEIN OUTCROP NEAR BELL MINE IN GREAT NORTHERN RAILWAY CUT. 

Sh ows c lay s lip cutting through g rani t e a ltered by network of j oint planes. Th e clay slip is faulted by a second 

fissure, see~ on th e left-han d side. See page 61 . 
STRUCTURE. 55 

EAST RIDGE. 

The East Ridge area, though often spoken of as part of the Butte district, is distinct topographically and geologically, and though it contains copper-bearing silver veins they differ 

fr01n those of the productive area of Butte. Topographically the locality consists of the long 

and steep mountain ridge which forms the Continental Divide, broken by the pass to Elk Park, 

but otherwise continuous, separated from the Butte district proper by the broad, nearly level 

expanse called the Flat. 

Geologica1ly this area consists of granitic rocks sin1ilar to those at Butte, but they are 

traversed by the so-called continental fault and other fractures, the tern1 being popularly used 

to include a group of faults which combined have caused a difference in elevation of about 1,200 

feet between the floor of Elk Park and that of the Flat. The rocks are similar on both sides of 

the fault, but they show local and important peculiarities and the veins are dissimilar. Two 

dikes of the rhyolite porphyry give in places conClusive evidence of the character and extent of 

the faulting, but unfortunately they can not be traced continuously. Clear evidence of this 

faulting is also shown by the topography, the foothill knobs and saddles, such as the flat-topped 

bench on which the ball grounds are located back of Columbia Garden, and the peculiarly 

isolated hillocks whose slopes make the portal of the gulch in which the gardens are. situated. 

In general the rocks of the East Ridge show an unusual develop:ment of aplite, with transitions to pegmatite on one hand and to Butte quartz monzonite on the other. This is so marked 

that the atten1pt to map the areas of aplite separately from the Butte quartz n1onzonite was 

abandoned after niuch ti1ne had been spent ·on the work. The surface in the vicinity. of the 

Altona and :Montg01nery mines shows much quartz, which has led to much useless prospecting 

but which mining developn1ent proves to be local and due to pa_tches of aplitic material passing 

into quartz and not to quartz veins. It is the "blout" of Lawson.1 A£3 shown by underground 

work, this quartz is not confmed to the surface but occurs at depths of 200 to 300 feet; moreover, 

the present surface is elevated by faulting and represents a depth of 1,000 feet or more below 

what was the fanner stn·face. Study of the exposures,. surfn.ce and underground, shows that 

the quartz is itn extren1e differentiation of the Butte quartz monzonite. 

·Another interesting feature of this part of the district is the rather basic character of the 

granite found associated with the quartz, aplite, and quartz monzonite just mentioned, at the 

:Montgomery, Altona, A1nazon, and vicinity. The granite when freshest contains an unusual 

mnount of ferr01nagnesian 1ninerals and a considerable amount of chalcopyrite, so" much, in fact, 

th11t the rock often holds 0.75 to 1 per cent copper. The associated acidic rock is more or less 

sericitized and impregnated wi~h scales and veinlets of molybdenite. The basic form is neither 

unaltered nor decomposed, but the basic ininerals are still fairly fresh. The pyritization which 

prevails so genen1lly throughout the copper district is wanting. The chalcoi)yrite has weathered, 

and oxidized copper ores are comn1on in the zone of weathered rock, but there is no chalcocite 

zone and no glance except where veins are cut. 

The veins of the foothills region include quartz-fliled fissures with a general east-west 

course, and north-south fault fissures cutting and displacing the quartz veins. 

The v:eins on the higher slopes of the mountain, east of the continental fault, are typical 

quartz-filled fissure veins carrying the usual ore and gangue minerals characteristic of the 

Butte silver veins, and in some cases notable quantities of copper glance. The quartz is usually 

gl11ssy, coarsely crystalline or camby, and the veins show frequent vugs and long, narrow 

crysto.l-lined spaces in the n1iddle. The rocks show sericitization, but in much smaller areas 

than across the Flat. 

The flat benches lying behind what have been termed the foothill knobs, and the intervening ground along the line connecting these saddles, show no exposures; and frequent prospect pits show that they are underlain, not by solid rock but only by a mass of fine rock fragments. The bencJ:es evidently overlie a "crush" zone. To the north, near the limit of the 

1 Lawson, A. C., Copper deposits of tho Robinson mining district, Nevada: Bull. 'Dept. Geology Univ. California, vol. 4, 1906, p. 324. 
56 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

area shown on the map, a cut excavated in the lower slopes by a steam shovel shows only 

crushed rock· and sand, although the bowlders and quartz veins of the mountain slope lie 

immediately alongside. 

BIG BUTTE. 

The. most prominent single topographic feature of the district is a sharply conical hill that 

rises abruptly from the rather gently rounded slopes west of the city. This hill (Pl. II, A, 

p. 26), which has given the name to the city and district, is known as Big Butte. 

Big Butte is of complex structure, which the simple representation on the geologic map 

does not express. In the structure sections an attempt to show its nature has been made, but 

it is impossible to do this fully on any single plane. Instead of a single mass of rhyolite cutting up through the granite or spreading over it as a flow, there are a number of bodies of massive rhyolites associated with predominating rhyolite tuffs, with brecciated (autoclastic) rhyolites, and with agglomerates. These relationships are far too complicated for expression on 

the map (Pl. ;x), and the narrow exposures do not afford sufficient data for the purpose. 

The rocks of this hill are extremely variable in nature and in their relations to one another. 

In part they probably represent the filling of a typical volcanic vent and in part the remains 

of a volcanic cone, consisting of both breccias and massive intrusive forms. (See also p. 45.) 

Both surface and intrusive forms of the same rocks therefore occur in intimate association and 

in great variety of colors and texture. 

The light-gray rock capping the butte resembles. a lava flow, having a rough, irregular 

fracture with pale-buff streakings, emphasized by a ribbed surface where weathered. 

The intrusives are very like the dike rocks; they are generally gray·and like the fragments 

in the breccia described below. 

The breccias are two-those found in the vent and those found outside of it. The vent 

breccias, as they may be called in contradistinction to the extrusive forms, are well shown 'in 

the gully scoring the south side of Big Butte, and exposing the granite walls of the old vent. 

In places the fragments are so large, some of them measuring 3 feet in greatest dimension, that 

the material might be called an agglomerate. They include granite and aplite, besides a great 

vari~ty of rhyolitic rocks. The most prominent is a dark-colored glassy rock, itself a breccia 

of black glass cemented by a steely or brownish gray matrix. 

On the east flank of the butte near the granite contact the rock, which has been opened 

by a quarry, is a breccia which for an area of 30 yards in diameter is bright green in color. Assay 

shows. that no copper is present, and the color is probably clue to the decomposition products 

of the ferromagnesian minerals of the rock. The breccia contains many fragments of gray 

granite and a few of aplite, as· was also the case in the exposures of the south face of the butte. 

The distribution of the two kinds of breccia forming Big Butte can not be shown on the 

map, and it is in places difficult to distinguish them in the field. The commoner forms, probably rea.lly extrusive, cover veins in aplite rocks which outcrop and have been prospected on 

the sou therJ:!. flanks of the butte. 

The contacts of the granite with the massive intrusive rock and the intrusive breccias are 

very irregular, the granite itself b~ing in part a fault breecia, though showing no recent alteration. The most interesting natural section of this mass is in the gully on the south slopes of 

the butte, where the contact is exposed about 300 feet from the road above the old shaft whose 

clump now partly fills the gulch. The porphyry is rep}aced by a dark orange brown, crumbly 

sand that is unquestionably decomposed granite in place. The exposure of this is not over 100 

feet long and is seen only in the drain channel, as the adjacent slopes are of porphyry. The 

upper contact of the porphyry is a contact breccia of aplite fragments and bowlders in granite 

sand, the breccia forming a zone iu few places more than 4 feet wide, and showing abundant 

rounded pebbles of aplite up to 8 inches in diameter. Careful search in this breccia failed to 

show a:ny pebbles of porphyry, so that it is believed that the breccia has npt been formed since 

the intrusion of the rhyolite. A dike 4 feet wide, of which but 15 inches is hard and glassy 

porphyry, cuts the decomposed granite not far from the contact. 
STRUCTURE. 57 

:Massive rhyolite, whose red color has frequently tempted prospectors to more or less 

extensive excavation, occurs in several places about the flanks of Big· Butte; it weathers 

readily to a soft, clayey 1naterial which Irides all eontacts. · 

Sheeting, wlrich is very prominent in exposures near the School of Mines, is due to recent 

·fissuring; it shows evidence of movement along the fissure planes. Lamination of the rock, 

believed to be of different origin, is apparent in bands of denser material along the fractures; 

the evidence seems to indicate that the fissures represent shrinkage planes in the rock as it 

cooled 'from a molten state. 

The contact between the granite and intruded rhyolite is well exposed in the railway cutting north of the Soudan mine. The granite bloel\: between the Soudan dike and the main 

n1ass of the intrusion to the east tapers to two thin wedges, one 30 feet and the other only 8 

feet wide. The wider wedge, of pale rusty brown altered granite, is separated from the narrower ~eclge, of darker granite, by 7~ feet of white clay whose origin is uncertain and from the 

Soudan dike by 10 feet white clay that is certainly altered and leached rhyolite, since it shows 

rmnnants of a vei·y dense form of that rock at· the granite conta.ct. Between the 8-foot granite 

wedge and the main body of the rhyolite to the east, a zone of breccia 30 feet across is composed 

of subangular rounded bowlders of clacitic and rhyolitic porphyry, with granite fragments near 

the. contact. The rhyolite rocks are very dense and evidently represent a contact form of the 

intrusion; they are Inuch decomposed and lie in a cement of similar but much finer fragmental 

Inaterial. The breccia is evidently a contact one. 

SUMMARY OF STRUCTURAL ·HISTORY. 

Granite forms the bedrock of the district and underlies its entire extent. It is of two 

kinds, which when fresh are unlike in color and composition, but when highly altered can 

be distinguished only with difficulty. The light-colored aplite is intrusive in, and hence later 

than, the clark Butte quartz monzonite, though both were formed from the same molten 

magma and in the same geologic periqd. 

After the consolidation of the granite it was fissured by horizontal pressure due to movements of the earth's crust and was injected by dikes of the rhyolite porphyry. Another period 

of rock f~~acturing formed the fissures which mineralizing waters changed to ore veins. After 

the consolidation of the granites erosion removed the overlying rocks, whose nature is unknown, 

and eroded theregion into a rugged topography of greater relief than that of to-day. A period 

of volcanic activity followed that of vein formation; the rhyolitic rocks were thrown' out by 

explosive volcanic outbursts and fissures were open·ed which filled with molten matter that 

fonned dikes. Big Butte is a small volcanic center. 

The dynanric forces that caused the volcanic outbursts. also warped the land, damming 

up the rivers and forn1ing lakes in many of the valleys. Silverbow Valley was the site of a 

Neocene lake in whose waters ash showers from volcanic eruptions mingled with the waste of 

the land to form lake beds. :More recent earth movements drained the lake and formed fissures which faulted the veins and raised the abrupt mountain wall east of Butte. Recent 

erosion filled and leveled up the valley floor, producing the hills and ridges that ·forn1 the recent 

irregularities of the surface· but not -essentially n1odifying the larger topographic features. 
CHAPTER V.-THE FRACTURES. 

AGE. 

As the Butte district lies wholly within an area of igneous rocks with no sedimentary 

formation save Neocene lake beds in the immediate neighborhood, it is impossible to determine 

definitely the ages of the different movements that have produced its multiple and complicated 

fissure systems. 

One can indeed trace their actual or probable connection with the successive eruptions of 

igneous rock and thus determine their relative ages; but in a region of such complicated fracturing 

even this is more or less tentative. · That there have been several periods of fracturing and 

fissuring is very evident, and though the relative ages of the different fissure systems have been 

satisfactorily determined by the mining operations of recent years, yet in many individual cases 

it is difficult if not impossible to determine positively whether the fracture-now occupied by 

a lode-is the result of one or several movements. 

In a general way the fractures may be separated into two classes; the first, formed before 

the rhyolitic eruptions, trend either (a) east and west or (b).northwest and $Outheast; the second, 

accompanying or following the rhyolite intrusions, trend in the same directions as the first, 

but are most marked in a (c) northwest or (d) northeast direction. Still later, after ore deposition, northeast fracturing occurred. 

The earliest fracturing recognized is that which is assumed to have taken place in the 

partly consolidated mass of Butte quartz monzop.ite, causing openings which were fille~ by 

the analogous but more acidic magma that cooled as aplite. The larger bodies of this rock, 

most of which are stocks of irregular form, are shown on the geologic map (Pl. X), but many 

small sheetlike bodies or dikes of it in the granite area ~re too small to be represented, and 

many other dikes of it are found in the deep underground workings. Where the rocks have 

been much altered it is, moreover, not easy to distinguish the small dikes. Most of them, 

however, trend east and west, showing that in this earliest system the tendency was' similar to 

the later one that fonned the mineral-bearing fissures. (See fig. 3, p. 39.) 

The rhyolite porphyry intrusion, which probably took place after both the Butte quartz 

monzonite and the aplite had been consolidated, formed irregular dikelike bodies, ·often difficult 

to trace on the surface because of the difficulty in differentiating the altered and weathered 

forn1s from those of altered granite or aplite. These rhyolite porphyry dikes, some of which 

are of considerable size and extent, have mostly, so far as observed, a general northwest trend, 

though the one in the Anaconda mine runs east and west. At the best exposures, in the several 

railway cuts at the east point of the ~1odoc mine ridge, apophyses or small offshoots from the 

main body fill small joints and cracks which lead off into the granite in different directions, 

some of them almost horizontal (Pl. IV, B, p. 32). It is evident, therefore, that dynamic 

movement must have fissured and jointed the granite previous to or at the time of the intrusion 

of this rhyolite porphyry. Further evidence of some such early dynamic movement is found 

in certain seams of fine-grained breccia or fault material of distinctly earlier age than any 

mineral or ore deposit, which have been observed at a few points in the mines. 

The most important fracturing-that which formed the fissures that admitted the original 

mineral-bearing solutions-occurred subsequent to both aplite and rhyolite porphyry intrusions. 

This is shown by the mineral-bearing veins cutting indifferently through both of these rocks 

as .well as through the granite.· 

Subsequent to the 9riginal deposition of mineral along the vein fissures several later dynamic 

movements took place, each producing fracturing whic)l affected the mineral deposits. These 

later movements have heretofore been designated secondary or postmineral movements, but 

58 
THE FRACTURES. 59 

inas1nuch as these later fissures are also mineralized the term postmineral is really inappropriate. 

These later movements have formed cross fissures faulting the earlier veins and strike fissures 

coincident with or parallel to and reopening earlier veins. 

The volcanic outbr~ak which caused the rhyolite intrusion occurred subsequent to the earlier 

vein fissuring, as is shown by the fact that the silver veins are cut off, in places even cut in two, 

by the intrusive dikes of rhyolite. The relation of these rhyolite dikes to the different periods 

of late fracturing is, however, not positively known. More than one postmineral movement 

certainly took place, for the rhyolite dikes have been markedly sheete.d and somewhat fractured 

since their intrusion. The rhyolite intrusion itself, however, was probably accompanied by a 

certain amount of fracturing of the adjoining rocks. It is, therefore,. not improbable that the 

secondary fracturing, which as will appear later has had an important bearing on the enrichment 

of the copper veins, was genetically connected ~vith the intrusion of the rhyolite. 

FISSURE SYSTEMS. 

CLASSIFICATION. 

The following fissure systems are recognizable throughout the district, both in joint planes 

in the rocks and in veins underground: 

(a) Parrot system, N. 80° E., and its complement (b) Anaconda system, N. 80° W., . 

occupied by the principal east and west veins of the district. 

(c) Silverbow system, N. 60° to 65° W. . 

(d) Blue Vein or Nipper system, N. 40° to 45° W.; includes the Covellite, the Skyrme, 

Jessie, Edith :.May, and Blue veins, the Mountai.ri View, and many other prominent faults . 

. (e) The Steward system, N. 64° E.; includes the Middle or Blue Jay fault, which becomes 

No. 16 in the RartlS ground, the Steward fault, whose vein is worked in the Gagnon, Original, 

and Steward Inines, the No.6 fault of the Parrot workings, and a number of faults having the 

salne general course in the Bell and Diamond mines. 

(j) Raru·s system, N. 45° E.; faults wl).ich carry ore torn off from earlier veins. 

The veins now· occupying the first two systems of fractures are workable in the aggregate 

for several thousand feet; they include the great east and west lodes of the camp, the Anaconda, 

Parrot, and Sy·ndicate, all of which follow intersecting fissures having these two directions. 

The first systen1 approximates and in places coincides in direction with the secondary fissures 

(seep. 62), to which the existence of its great ore bodiesis due. The first two systems are the 

oldest in the district; the third syste1n is also old, but it has generally been reopened by later 

fracturing, and the value of its veins lies in their secondary ore bodies. 1 

REGULARITY OF THE FRACTURES. 

The fractures of the Butte district are remarkably regular. Not only do individual fissures 

maintain a definite average course for considerable distances, but practically all the fissures 

belong to definite systems, in which the individual fractures are parallel. T~s regularity of 

the older fissures is 'disturbed by faulting,· so that the persistency of the older veins is broken, 

as shown on the maps. 

Tlris regularity is due to the remarkable homogeneity of the rocks. The .Butte quartz 

mo~zonite is uniform not only chemically and mineralogically but physically, and other rocks 

forn1 but very subordinate parts of the mass. The conditions are therefore favorable for. the 

development of coordinate fractures and the complementary fissures which result when a block 

of homogeneous material is submitted to pressure and the force is resolved into two components. The Butte veins do not show the conjugate fissures with identical strike but opposed 

dip, which often result from su~h force, but they do show a regular cracking or fissuring with 

deftnite opposed systems and simultaneous origin. 

1 'eho directions o.re dotonniued In tho long drifts run on tho principal veins. The compass readings on fractures observed in crosscuts show 

an apparently greater variation ln tho strike of the first two systems than is given above, but owing to the difficulty of observing direction in short 

exposures and to local. variations ln tho veins, the directions on crosscuts are less reliable than those taken directly from the mi.Iie maps. 
60 GEOLOGY AND OR.E DEPOSITS OF BUTTE DISTRICT, MONTANA. 

DIRECTION. 

The most striking feature in the vein fissure !;Systems of Butte, as shown in the map (Pl. X, 

in pocket) is the presence of three first definite directions of fissuring noted above. The great 

veins worked for many years, including the Anaconda and Steward o systems, are comprised 

in the quadrant of the circle between northeast and southeast. The Blue vein system, which 

in recent years has played so important a part in both ore production and litigation, is a later 

and independent system running northwest and southeast. 

In most systems of rock fracture one major direction of fracture planes and one or more 

minor directions are observable, the fissures of the latter being usually cross fractures connecting two or more master fracture fissures. In the copper area, although in individual mines · 

or groups of veins it is generally possible to· distinguish two prevailing directions of strike, the 

one north of east and the other south of east, it is not possible to say that in all cases the fissuring in one of these directions is so much stronger than that in the other as to be ·called the 

major direction. The rule seems rather to be-if indeed there is a sufficient uniformity in 

such matters to constitute a rule-that the strongest and· most .persistent lodes are those which 

appear to be a resultant of these two directions. In a general way, it may be observed that 

the fractures (or the veins occupying them) in each lode group tend to strike north of ·east 

at their west ends and to diverge southward at their eastern extremities. Furthermore, that 

the divergence to the south is more common and greater in degree. The average divergence 

between the two directions may be taken at 30° and the maximum in one and the same vein 

system or lode at 45°. The veins named below show the following generalized courses: 

Trend of the mineral-bearing fractures. 

Neversweat-Anaconda ........................ : ..................................... N. 87° W. 

Silverbow ........................................................................ N. 67° W. 

Johnstown (North Connecting) ........................................... : ......... N. 60° W. 

Windlass ....... ·............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. 63° .W. · 

L. E. R ............................................ ~ ............................. N. 40° W. 

High Ore .......................................................................... N. 60° W. 

Blue Jay (Middle) fault ............................................................. N. 70° E. 

Steward fault ..................................................................... N. 62°-64°W. 

Covellite ..... : ................................................................... N. 35° W. 

Clear Grit .......................................................................... N. 40°-51 °vV. 

Caledonia ............................................. · ............. · ................ N. 70°-73° E. 

Zinc (Original mine) .............................................................. N. 76° E. 

South Parrot or Virginius ............... : .......................................... N. 70° E. 

Original fault ..................................................................... N. 80° W. 

Syndicate ........................................................................ N. 80° E. 

Shannon-Colusa ......................................................... · .......... N. 70° E. 

Blue ............... · ............................................................... N. 40° "Vil. 

Mountain View fault ............................................ : ................. N. 45° W. 

The fissuring in places produces a rhombohedral parting of the granite, which is well illustrated in the workings of the Parrot vein. It is not clearly shown on the level maps, but is well 

brought out by the stope sheets, which show an angle of 25° to 26° between the two sets of fractures along which the vein has been formed. These fractures run practically N. 76°-80° E. and 

N. 80° W. In a general way, the Steward veiri corresponds to one of these fractures, as its 

course is N. 64° E., and the Neversweat-Anaconda vein, which has a course of N. 87° vV., to 

the other. As a whole, however, the Anaconda ledge runs east and west, but this may be 

the resultant of vein formation along the two systems of fractures just noted-that is, N. 80° 

E. and N. 80° W. 

RELATION OF FISSURE SYSTEMS TO ·JOINTING IN THE GRANITE. 

In general, the fissures correspond to the jointing planes of the granite. This is well 

shown in the northern part of the district, where well-defined veins are seen to follow the direction of the main or master joints. It accords also with observations underground, which show 
THE FRACTURES. 61 

that the earlier veins are replacements of sheeted granite. Outside of the producing copper 

area-as, for example, near the Bhtek Rock and Niagara claims-the hard blocky granite is 

sheeted, and son1e of the sheeting planes have become veins. (See Pl. VI, B, p. 54.) Throughout the productive copper area the rocks are so altered that this relationship between joints 

and veins is obscured, but it is evident from surface cuts that the rocks are netted .by many closely 

spaced fissures and that the veins are merely unusually well mineralized fissures. Plate IV, A. 

(p. 32), shows a network of rusty fissure~? exposed in excavating for a church at Butte. 

To determine whether the jointing planes in the granitic rocks agreed with the fissure 

systems, a careful observation was made of the joints in the·granite area. This work showed 

two principal joint systems, one striking N. 10° E. with a dip of 70° to 80° W. or E., more 

rarely of 40° to 64°, and a second striking N. 80° E., with a dip of 75° to 85° S. and with conjugate fissures dipping at the same angle to the north. Somewhat rarely, flatter fissures were 

also observed, having the sam~ strike but dipping 35°, 55°, and 60° S. 

In the silver area the clip of the fissures is more uniform than their stril{e. The veins 

north of the Alice n1ine, including the north vein of the Rainbow lode, stand either vertical 

or clip 80° to 85° N. South of the Alice, both silver and copper veins, with but one or two 

exceptions, dip south, but at not more than 55°, except in the region west of Big Butte. The 

angle between the two directions of dip, then, is about 25° on an average with a m~Um.um of 35°. 

These are the average clips of the fissures as a whole; in detail the profile or cross section of a 

vein is generally a wavy line. (See s.ection of Anaconda vein, fig. 4, p. 42, showing at different 

points varying angles of dip, whose ma..'-imum divergence may equal the above.) When a vein 

sends off spurs-that is, sn1aller veins branching off at an appreciable and fairly constant ·angle 

fron1 the 1nain vein and not returning to it, sin1ilar divergences of 25° to 30° may in many 

places be noted between the dip of the spur and the average dip of the main lode. 

The dip of a given fissure generally comprises two or n1ore distinct directions, one nearly 

vertical, the other 60° to 70° S. S01ne subordinate planes of fracture have very shallow dips 

approaching the horizontal, whose inclination is prevailingly to the south. 

SPACING OF FRACTURES. 

In the spacing of the fissures ~ sort of rhythmic tendency is observable-closely spaced 

alternating with n1ore widely spaced fissures. Comparatively few widely spaced fissures contain 

large or rich ore-bearing veins, the great productive vein fissures being closely spaced. The 

rich vein systmns are n1ade up of nun1erous veins, occupying fissures which follow two or more 

principal directions or strikes, the strike of the whole system not being exactly coincident with 

that of either .of the constituent fissures. Thus the :Moulton-Alice silver-vein system, which has 

a general dil~ection of about N. 75° E., is n1ade up of fissures running N. 80° W. to N. 75° E. 

and N. 65° E. The Rainbow lode, as this vein group is son1etilnes called, consists· of parallel 

fissures which in general have a course sin1ilar to that of the ·whole group but which vary in 

direction in different parts of it, in places assuming more nearly one, and other places another 

of the constituent strikes. 

The copper-bearing area comprises two great vein belts with a comparatively barren zone 

between. The northern belt consists of the Syndicate and Greyrock-Bell lodes and ends in 

the :Modoc vein to the east. The southern belt includes the Gagnon-Parrot lode, the AnacondaSt. Lawrence lode, with the Blue J ay-Nioonlight to the south, ending eastward in three diverging lodes, the Pennsylvania and Silverbow lodes, the Windlass, and. the :Mountain View and 

Colusa lode. In detail the 1nain directions of the constituent fissures which make up the lodes 

of these two vein systems are N. 85° E., N. 55° W., and subordinately about N. 65° W. 

DEGREE OF FRACTURING. 

~!~he evidence-though it must be achnitted that in a rock of the nature .of granite this 

evidence is rather unsatisfactory-shows that the original fracturing that resulted in the nlineralbearing veins was not accompanied by any considerable movement or displacement· on the 
62 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT J MONT AN A. 

:fissure planes. Slickensides and friction breccias are generally wanting in the primary fissures. 

In the copper-bearing veins little or. no evidence is seen of original open spaces along the earlier 

fissure planes, such as would have been left had there been any considerable n1oven1ent of one 

wall upon the other. It is probable, therefore, that although there was enough n1ovement 

on the fracture. planes to break the continuity of the adjoining walls so as to adn:iit water 

freely and in some parts to leave small open spaces that have since been filled with vein n1aterial, 

the amount of this movement was very slight as compared with that connected with the secondary fracturing. In addition to the absence of striation and the s1nall amount of brecciation, 

the absence of microscopic fracturing in the structure of the rock and the character of n1uch of 

the vein filling indicates that the displacement on the earlier fissure was slight. 

It is noticeable, moreover, that the fissuring and sheeting of the granite, though intense, 

extends over a comparatively small area and becomes gradually less as distance frmn the center 

of mineralization increases. This center of mineralization corresponds to a line running eastward from Big Butte through the middle of the copper-bearing area; that is, along this zone 

mineralizing action has been most vigorous and abundant. A tendency in the veins to wrap 

around this copper-bearing area or center of n1ineralization n1ay also be observed. 

The movement that produced the fissuring, it m~y therefore be assumed, was not an 

orogenic movement, a general warping and deformation of the earth's crust, which would be 

very widespread in its effects, but was rather a local and sudden one, like that accon1panying 

an earthquake or an eruption of igneous rocks. 

SECONDARY FISSURES. 

Two principal kinds of secondary fractures, which fault the ore bodies and have apparently 

had important influence on their enrichment, have· been recognized. These are (1) strike 

faults, or those which are for the most part parallel to, and in places are for considerable distances actually coincident with, the vein fissures; '(2), dip or cross faults, which are more nearly 

at· right angles to the vein fissures. 

STRIKE FAULTS. 

Strike faults are generally secondary fissures or zones filled with ground-up material and . 

containing well-rounded fragme_nts of ·country rock (quartz n1onzonite) and vein rnaterial 

(quartz and pyrite for the most part). They vary in width from a few inches up to many feet. 

Few of them conform exactly in course with the primary veins, but cross then1 at low angles in 

strike and dip. 

Many of them contain so much moisture, especially in the upper levels of the mines, that 

their filling becomes a soft white pebbly mud which runs· when they are opened by a drift·. 

Many, too, are accompanied by clay seams or selvages; indeed, all the clay seap:ts observed 

appear to belong to the periods of secondary fissuring, for all contain comminuted fragments 

of vein material. It is possible, however, that some of them were formed by original fissuring, 

and that during the· secondary fissuring renewed movement along them brought in the finely 

ground-up vein material. 

Strike faults are very widespread, especially in the copper-bearing area, having been noted 

at some point, generally near foot or hanging wall, of every well-explored vein. Most of them 

have the same or nearly the same average dip as the vein, but a few depart fron1 it, at distinct 

angles. In the Lexington mine a series of such secondary fractures has produced 1narked 

step faulting in one of the veins. In the Gagnon mine a secondary fissure in the footwall 

country but near the vein (see Footwall or Steward vein, p. 136) is generally straighter than 

the vein itself and in places comes into actual contact with its. footwall,· which then carries a 

certain amol!-nt of secondary material. 

Where a secondary fissure crosses the vein at a low azimuth angle, as in the west end of 

the Parrot mine, a slight displacement of the latter is noticeable. Else\vhere movement is 

indicated oil the wall of the fissure by striation lines, which generally stand at an angle of about 

45°; but there is no means of determining the amount of distplacement, which is presumably 

slight. · 

'. 
THE FRACTURES. 63 

In many places the secondary fiSsuring has produced a zone of broken and crushed material 

25 or 50 feet wide, consisting of country rock when not in a mineral-bearing fissure and containing more and more vein material as it approaches ore. Such an instance occurs in the 

lower levels of the.Original mine, where a breccia.zone or wide fissure for some distance showed 

no sign of ore; then ore, at fu·st only detected by assay, then in visible fragments, appeared 

mixed with the granite fragments; fmally the breccia zone merged into a vein of solid rich ore. 

That these secondary fissures are often coextensive in depth with the original fissures is very 

probable; it is known that they extend downward in connection with the veins to the lowest 

levels opened in the larger mines (2,200 to 2,800 feet below the surface). 

CROSS FAULTS. 

Cross fau1ting, so far as observed, is fu1ly as extensive as the strike faulting and is 

usually more readily detected because its displacement is in many places across the strike of 

the veins. vVhether the two or more systems of cross faults were practicaliy contemporaneous 

with the strike faulting or were slightly late.r has not yet been definitely determined, but the 

writer inclines to the latter view. Their strike in some places is nearly normal to the direction 

of the veins, and their dip is generally very shallow, 65° to 4.5° or even·less. In many places, 

however, the dip, which can be observed only in the underground workings, can not be detected, 

the presence of the fault being indicated only by the displacement of the vein. 

'rhese cross faults commonly throw the vein from a few feet to in places a hundred 

or more feet, beyond which, however, the vein is readily found again. Less commonly the 

fault cuts off the vein, which can not be found with certainty beyond. In still other places 

what may be called zones o(disturbance. are bounded on the east and west, respectively, by a 

series of cross faults, which are not strictly parallel to each other either in strike or dip; in the 

intern1ediate zone both vein and country rock seem to have been subjected to a sort of violent 

side thrust, which has not only broken the continuity of the veins but has pushed them, at 

certain depths, several hundred feet to one side and in places has shattered the whole rock mass 

within the zone, as shown in the Leonard mine (fig. 5, p~ 53). Such zones, within the copperbearing area, have received secondary enrichment by rich copper minerals. One has been 

traced in a direction about N. 30° E., through the Pennsylvania, Rarus, and Colusa mines. 

Another passes through the Colusa-Parrot and Neversweat min_es. 

RELATION TO RHYOLITE PORPHYRY DIKES. 

In the eastern part of the copper area s'ome secondary fissures follow or parallel dikes of 

the rhyolite porphyry for considerable distances (fig. 6). The earlier system of fractures, in 

which the dikes were intruded, has been evidently a line of weakness. 

No positive genetic association of the ore and the rhyolite porphyry can be established 

further than the fracturing just noted, but it is believed by some observers that such association exists. If so it is possible that the rhyolite porphyry,.which was part of a larger deeperseated mass, supplied magmatic vapors which altered the granite and formed the veins. 

ll.ELATIONS OF EARLIER AND LATER FISSURE SYSTEMS. 

Fr01n the intersection of so many fissures it is evident that the whole district is netted and 

that there has possibly been a mutual displacement by intersecting fissures of the same age,· 

though such has not been observed in the great fault fissures, which are filled by crushed rock 

and ore balls. The difficulty is to reconcile the movements along similar systems at different 

periods. Thus, it is evident that the Northwest or Blue system of fissures, which is typically 

observed in the Blue, l\1ountn,in, and Skyrme,· is later than and has displaced the quartz-pyrite 

veins of the east-west fissures. On the other hand, it is found that the B1ue vein is itself 

faulted by a N. 70° E. fissure belonging to the Steward system. (Numerous other fissures 

having this same direction are observed, as, for example, the Bell fault fissure, which cuts and 

displaces all the veins in the Bell-Diamond workings.) . This appears simple·until it is observed 

that the Clear Grit silver vein fissure, a Northwest fissure greatly resembling the Blue and 

parallel to it, has cut and displaced the Steward vein and with it all the earlier veins: This, of 
64 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

course, means, for the evidence seems indisputable, that there were two periods of northwest 

LEGEND 

Fault 

WIJJI 

Pqrphyry and vein 

1 nterm 1ngled 

0 100 

400-FT. L£V£L 

..!gf]E;,{.I..J-:.f.Xf!=.:.-: .. :=.=.===-=-========--== 

FIGURE 6.-Relation of porphyry dike to Anaconda vein. North-south cross section through St. 

Lawrence shaft. 

fracturing and faulting, the 

earlier of which resulted in 

the formation of the Blue 

vein fault and the later in 

that of the Clear Grit fault. 

Observations iri the neighboring mines show, however, that the Windlass and 

Johnstown (North Connecting) veins, and probably a 

number of others in the 

·same neighborhood, were 

formed previous to the 

Blue Jay fault and are old 

quartz-pyrite veins carrying enargi te and are pro bably later in age than the 

Anaconda vein. The argument, then, carried to its 

logical conclusion, proves 

three periods of northwest 

fracturing, which accords 

with the evidence that the 

Covellite, Skyrme, Jessie .. 

and others of this northwest series carry remnants 

of the quartz-pyrite filling 

of fissures produced by the 

earlier and primary faulting. The second faulting, 

which shattered this filling, 

was follo,ved by ore deposition, presumably from below, by which the rich ore 

bodies characteristic of these 

fault veins were formed 

at depths of 1,000 feet or 

more. The third opening 

along northwest fissures 

may have been a general or 

orogenic phenomenon clue 

to the displacement of the 

block along the East Ridge 

fault line, and a consequent 

settling in which the earlier 

fractures formed planes of 

weakness. At any rate, 

the Clear Grit fissure and 

others of this type show 

that silver- bearing solutions followed this period 

of fracturing and formed. typical silver veins and silver minerals in many of the fault fissures. 
CHAPTER VI.-THE ORES. 

TYPES. 

The m·etalliferous ores of the Butte district are of two distinct classes, copper and siliceous 

silver. The copper ores contain a little silver; the silver ores rarely contain copper; both copper 

and silver ores contain a little gold, and the high-grade silver ores contain it. in important 

amounts. 

The typical ores of the two classes are distinctive and are characterized by well-marked 

n1ineral association, but other ores. occur which are not typical but are a 1nixture of both kinds. 

Some of the copper veins were originally worked for the residual-silver values in the oxidized 

material from which the copper had been leached, but the ores from such veins differ both in 

character and occurrence from the typical ores of the silver 'veins. So1ne of the silver veins 

on the border of the copper area contain bodies of copper ore, but gene~ally in mineral composition and association differing from that of the typical copper ores of the district. The variation 

in the silver content of the copp~r ores is discussed later (p. 68) 0 

DISTRIBUTION. 

The ores of the Butte district occur only in the older rocks, the productive deposits being 

practically confined to the Butte quartz n1onzonite. A few silver veins have been productive 

in the aplite, and several o'f the largest copper veins cut through both the rhyolite porphyry 

and the aplite, but where the veins traverse the aplite they are lean. The association of porphyry and ore is certainly one of fracture, possibly of genesis by nlagmatic vap,ors. The porphyi:Y occurs only in the copper n.rea. The rhyolite dikes are younger than the silver veins 

and are found only in the silver area. · 

VERTICAL DISTRIBUTION. 

The distribution of the payable copper ores is well defined and sharply limited. At pre 

sent (1906) nothing. indicates that either the silver area proper or. the area in which the ores 

are essentially zinciferous silver ores is underlain by copper· ores. No evidence exists of a 

so-called iron zone, ai1d the copper veins, fron1 the Poulin 1nine of the Syndicate ledge on the 

north. to the Blue Jay 1nine on .the south (except in the Gagnon 1nine, whose copper ores extend 

exceptionally far west), grade rapidly westward into low-grade zincky, pyritic, silver-bearing 

. ores. Recent development work in the fault ve~ns has shown the existence of silver-bearing 

ore bodies which do not cmne within 700 or 800 feet of the surface. 

The vertical distribution of the .ores has not been definitely determined. Thus far (1906) 

the silver veins have been generally unprofitable at depths exceeding 900 feet beneath their 

outcrop. The Alice and Lexington n1ines have been opened to depths of 1,500 and 1,450 feet, 

l'espectively. The l\1oulton.is 800 feet deep, the Bluebird 600, and theN ettie 650 feet, but none 

of the deep levels of these mines have been worked for years. According to current report the 

silver ores decrease in value with depth, but this could not be verified, nor is evidence obtainable to prove that the silver ores change into copper ores with depth. The Lexington, the Si~'­

ters, and a few other veins contain bodies of chalcopyrite ore, but chalcopyrite is aln1ost foreign 

to the typical copper veins. However, as son1e copper veins have been broken and reopened 

and traversed by silver-bearing waters, composite ores occur in places. 

The copper ores seldmn extend upward to the outcrop. Their upper limit is extremely 

variable. In the Anaconda and other great east-west lodes, it lies at from 60 feet to 400 feet 

below the surface. In so1ne of the n1ore recently explored northwest veins, which cut and displace the others, few payable ore bodies are found in the first 1,000 feet. The downward limit . 

90427°-No. 74-12-5 65 
66 GEOLOGY AND ' ·oRE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

of payable ore has not yet been determined for the copper veins. In some parts of the district 

the ore bodies be~ome lean in depth and are composed of almost barren pyrite. On the other 

hand, the middle vein of the Anaconda mine contains large bodies of rich glance ore at 2,400 feet, 

and the saine is true of the High Ore shaft at 2,850 feet. In general, however, many mines 

show a decrease in richness below 1,200 feet beneath the surface. This impoverishment does 

not begin at any definite horizon or ·elevation above sea level; it depends on the locality and the 

extent of the fracturing of the vein and the inclosing rock. " 

The lowest workings of the principal copper lodes are 3,700 feet to 4,000 feet above sea 

level, but several large mines have not yet reached this horizon. 

AREAL DISTRIBUTION. 

The areal distribution of the copper-bearing and silver-bearing veins is shown on the 

geologic map. (P~. X, in . pocket). The copper veins are confined to a relatively small area 

lying north of Sil~erbow Creek, extending from Meaderville westward to the slopes of Missoula Gulch and northward to the high ground east of Walkerville. The most important 

silver veins lie northwest of this. In general, there is a remarkably sharp distinction betwe.en 

the copper and silver· ~reas, but the silver area overlaps the coppe~ ore somewhat, and the 

outline of the copper a:r:ea is not regular: Roughly, it is 2 miles long by 1! miles wide. A 

few productive silver veins occur in the copper area and at the western border the veins 

interlock. 

COPPER AREA. 

The copper veins are known to extend eastward beneath the alluvium filling the valley 

and to occur in the foot slopes of the mountain ridge to the east. This ea~tern extension of the 

copper area, however·, is as yet more of prospective than of known value. East of the Continental fault in East Ridge· the veins, though copper and silver bearing, . appear to be of wholly 

different character. · · · 

In the western part of the copper area the copper veins separate into two belts, with an 

intermediate area carrying mostly lean veins, changing to silver veins west of. Main Street. 

The northern belt embrac~s the great Syndicate lode, worked in the Moscow, Poulin, Stella, 

Buffalo, Mountain Con., Green Mountain, and Wake-up-Jim mines, with a few other properties on neighboring allied veins. Eastward the belt is continued in wholly different clusters 

of veins in the Corra, Greyrock, Diamond, Bell, Speculator, and High Ore mines. The Modoc 

vein appears to be at the eastward end of this belt. 

The. southern belt commences on the west with the Gagnon-Original lodes and extends 

through the Parrot, N eversweat, Anaconda, and St. Lawrence workings, eastward to the Pennsylvania, Mountain View, and Rarus ground, with a branch to the Silverbow. South of thi~ 

lies the Blue J ay-l\1oonlight belt and numerous other veins. Mining work has proved the breaking and cl.isplacement of all the great e~st-west lodes of these belts by cross veins, and it is not 

possible to trace a single vern continuously the entire extent of these belts. (See further, pp. 

106 ·et seq.) · 

The Edith May, Jessie, Gem, Poser, and Elm Orlu lodes were formerly regarded as silver 

veins but are now ( 1906) copper producers, thus greatly extending the supposed northern 

limit of the copper area. Extensive prospecting wo1;k, in progress ( 1906-7) north of the area 

mapped, will determine whether or not the mostly barren-looking, supposedly silver veins of 

these areas are copper bearing. Silver ores carrying copper (usually as chalcopyrite) have 

· been found locally in bunches in veins along the northern borders of the copper area, notably 

in the south veins of the Lexington and :Magna Charta, in the Old Glory, Flag, Sisters, J\IIoose, 

West Greyrock, and a few other mines. The Gem, Tuolumne, Mat, and neighboring veins 

are composite, containing a mixture of pyritic ores representing two periods of 1nineralization. 

Chalcopyrite occurs as a normal but not as a generally abundant constituent of silver ores, 

and reports of discoveries of bunches of copper ore are not rare. The large northwest fault 

veins carry valuable shoots of copper ore, with large silver values. 
THE ORES. 67 

SILVER AREA. 

The 1nost ilnportant silver deposits have been developed immediately north of the west 

end of the copper area. The Alice, :Moulton, and Lexington have been the largest mines. 

Very rich silver ores have also been o btainecl from the n1ines along the east bank of ·:Missoula 

Gulch, especially in the intermediate belt included between the western wings of the copper 

belt; o:f. these the Late Acquisition and Clear Grit lodes are the most in1portant. Several 

rich -veins have been 'vorked directly south of Big Butte, and the systen1 of veins running 

through the Nettie, Bluebird, and Independence grounds, in the aplite area west of Big Butte, 

have been in1portant silver producers. In the northern tier of viens, north of the line of the 

Rainbow lode: the nu1nber of silver-bearing lodes is very large. Of the :rnines, all now abandoned, which flourished on these lodes in earlier clays, many are said to have yielded large 

mnounts of silver, individual producers running up into the hundred thousands of ounces. 

MErl'ALLIC COMPOSITION OF THE COPPER ORES. 

TENOR OF THE ORES. 

Copper, silver, gold, and arsenic are the only elen1ents extracted from the Butte ores~ 

The sn1all an1ounts of other 1netals present, though recoverable in the process of electrolytic 

refining, are of no econon1ic in1portance. The average amount of copper per ton in the Anaconda ores lnined fronl 1884 to 1898 was 111 pounc1s, or 5! per cent, with 4! ounces silver 

and 35 cents in gold per ton. In 1906 it was about 65 pounds of copper per ton of ore or 3iper cent for the entire district, with about 5 cents worth of the ·precious metals. lligh-grade 

o~·es are still produced, but in small amount; possibly 6 per cent of the ore carries as high as 

6 per cent copper; the balance is concentrating ore. The tenor of the ore in the vein has not 

decreased as rapidly as is indicated by the above figures, but decreased costs and increased 

prices for copper have made· it possible to treat lower-grade material, and th~ reduction works 

have been correspondingly enlarged. 

The following analyses are representative of the ores mined about 1896 in the Rarus and 

Pennsylvania n1ines, where the veins carry n1ore or less enargite: 

Partial analyses of ore samples from Rarus mine, Butte, Mont. 

Locality. Ag Cu Au Fe s As I Total determined 

-------------------1-----------------------· --

A. Nortt. Connecting vein .................................. . B. Soutl:. vein ............................................... . C. 77 rainc. Middle ore streak above 451) feet, Snohomish .... . D. Sotcc·:cd oro ....................................... · ....... . l~. Southwest face ..... : ..................................... . F. Smal. oro stopcs .......................................... . G. No.1 raise .............................................. .. 

A·rerago ............................................... . 

Ounces 

per ton. 

3. 35 

5.81i 

1. 30 2. 50 3.10 

27.10 

4. 40 

6. 00 

Per cent. 

37.87 

25.87 

9.34 

23.78 

6.80 

42.17 

36.21 

23.05 

.Ounces 

per ton. 

0.015 

. 03 '!'race. . 01 

.015 

.045 Trace. 

. Q13 

Per cent. 

11.6 

22.6 

32.5 

19.6 

38.8 

5. 5 13.3 

23.37 

PRECIOUS METALS IN THE ORES. 

GOLD. 

Per cent. 

0.8 

8.1 

13.0 

22.4 

7.6 

6. 3 

1G. 0 

9. 92 

Per cent. 

35.4 

36.5 

42.5 

31.0 

46.5 

32.2 

30.5 

37.90 

Per cent. 

5. 55 

4. 43 1. 88 3.99 

.Hi 

4. 45 

3.02 

2.85 

Per cent. 

91.37 

96.53 

99.22 

100.78 

99.875 

90.66 

99.03 

97.103 

Gold is universally distributed througho~1t the ores, but in such small quantities that 

it is not usually detern1inable in commercial assays. In the mines along the east bank of 

upp€1r :Missoula Gulch it has proved an in1portant part of the value. The gold in the placer 

depc,sits was probably derived nlainly fronl these veins since both native silver and copper 

havo been ·found in company with it. In the silver mines the proportion of gold to silver by 

wei~;ht has run as high as 1 to 40 in n1ill lots. An average of five n1onths' run in the Alice 

mill yielded 0.06 ounce gold to 21 ounces silver pei' ton treate~. 

In the Leonard n1ine the gold values have been exceptional; they are somewhat spotty 

and appear to depend on the occurrence of a peculiar bronze-colored tetrahedrite, a very rare 
68 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

mineral in B~tte mines. A 200-ton shipment from the 1,200-foot stopes, which are 150 feet 

wide, yielded $5 in gold per ton, the highest yield being about $6. The gold values in the 

average ores appear not to shade off from the Leonard to the Colusa, or from the Leonard to 

the Pennsylvania mine. An average of 10,000 tons treated in the Great Falls smelter gave 

the following gold values per ton of ore: 

Gold values in copper ores of Butte district. 

Mountain West 

View. Colusa. Grade of ore. 

-----------~------------------1------------

Cents. 

First-class. .. .. . . .. .. . . • .. . .. . .. . . .. .. . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . .. . . . . .. . .. . .. . . . . .. . . .. .. . . .. .. .. . 70 

Second-class... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . 30 

Cents. 

30 

GO 

Cents. 25 

15 

Cents. 50 

(jQ 

The higher gold values in some second-class copper ores indicates that the first-class ores 

may have come from a single ledge, and as the tetrahedrite occurs in streaks scattered through 

the second-class ore of the Leonard stopes, the relatively high value of the second-class ore is 

explainable. 

The figures given above are more reliable than those based on a comparison of local details, 

but as they represent ore from different veins, they show the distribution of values in a general 

way only. 

SILVER. 

The average silver content o£ the ores extracted in 1905-6 from the Anaconda lode, extending from the Gagnon eastward, is 1! ounces to each per cent of copper in the Gagnon ores; . 

1 ounce to each- per cent of copper in the ores of the Original mine; three-fourths ounce to. 

1 per cent copper in the Parrot and Anaconda ores; one-half ounce to 1 per cent of copper 

in _the Mountain View ores; and one-fourth to three-eighths ounce to 1 per cent of copper in 

the ores of. the Leonard mine. These ratios, however, hold good only for the ores w<;>rked in 

1905-6, for in the upper levels of the Gagnon mine the ore carried 3 ounces of silver to 1 per 

cent in copper. ' • 

On the 900-foot level of the Leonard mine the following variations in the amount of silver 

were noted: 

Silver and copper per ton of ore, 900-joot level, Leonard mine. 

Silver. Copper. 

Ounces. Per cent. 

Y2 2' 

:Ji 27!! 

Y2 47!! 

1U 3 

17!! 1:Ji 

These figures represent the averages of a large number of assays on sets of samples collected 

from .different points, each set consisting of ore in one vein. The maximum results shown in the 

different assays on each vein were as follows: 

Maximum assays of s~lver and copper per ton of ore, 900-joot level, Leonard mine. 

Silver. Copper. 

Ounces. Per cent. 3:Ji 87!! 

47!! 9:Ji 

1:Ji 37!! 

17!! GY2 

The following table· was furnished by Mr. John Gillie, general manager of the Amalgamated 

properties. It shows the amount of gold and silver to each per cent of copper in the ore extracted 

from the principal mines of the Butte district. The figures are .based on the smelter determina-

. tions for 1904. 
THE. ORES. 69 

Am,ownt of silver and gold to each per cent: of copper in different B·utte rnines. 

[Ounces per ton.] 

Mine. Silver. Gold. Mine. Silver. Gold. 

----------·-------------------l------1------ll---------------------------------------

Anaconda ........................................ . Neverswcat ...................................... . St. Lawrence .................................... . Motmtain Con ................................... . l3cll. ............................................. . 

{~~~:ll?~;~i:::::: :::::::::::::::::::::::::::::::::: 

Parrot ........................................... . 

~l~~~~)jc),'V.'.': ::::::::.:::::::::::::::::::::::::::: 

0.503 

. iG5 

. 351 1. 004 

. i93 

.455 

2.000 

.884 

1. 6iu 

. 421 

0.003 

. 004 

• 002 

. 003 

. 002 

. 004 

.004 

. 004 

.004 

. 002 

East Greyrock ................................... . Leonard .......................................... . l.lli o. 003 .484 .004 \Vest Colusa •..................................... . 313 . 003 East Colusa ...................................... . .444 . 001 Pennsylvania .................................... . ~fountain View .................................. . .400 . 002 .414 . 002 

==== Average for Anaconda mine ................. . Average for Butte & Montana .............. .. Average for all mines of table ............... . 

. 323 .003 .411 .0024 . i55 .003 

During the Colusa-Parrot trial before the United States court at Butte, 1\iont., ·expert 

testimony was introduced to show the actual value of the ore extracted. From this it appeared 

that on tha 1,200-foot level of the Parrot mine a breast of ore 25 feet wide, carefully sampled 

and assay€,d, carried 25.4 per cent copper and 17.16 ounces silver per ton. Another breast on 

the same level, at the west face of. the stope, 23 feet wide, yielded 9.3 per cent copper and 8.24 

ounces silYer per ton. On the 1,300-foot level a breast 10 feet wide yielded 7.1 per cent copper 

~ Veins 

9 

25 50 75 100 125 150 175 

!/\ Feet 10% 

1\c' 

I~ 8 

......... I \ 

'!.~ \ 1/ \ 1/ \ /I\ Vi'- II\ --r--~\ \I/ 1\ )/ \If 'V \1/ \ 

6 

5 

4 

!'......- VI\ \ /\ ;I/ !\'I \V \v j\,1 \1\ / \I \ 3 

/I\ V"-r-.,/ ~--~ -..It0 

FIGURE 7.-Diagrmn showing relation between copper and silver values in a drift in the Leonard mine. 

and 5.12 ounces silver per ton. These figures, representing the rich ore of the mine, show considerah.e variation in the ratio of silver and copper, and it is therefore certain that no rule for 

the ra6o of gold and silver can be based on the assays of a few samples only. (See fig. 7.) On 

the otl:.er hand, the general samples from the whole mine represent such a variety of veins 

that the returns can not be used to deduce the relative ages ?f the veiris. · 

BASE ~ETALS. 

1\IANGANESE. 

Manganese is widespread in the silver veins, but is wanting in all the copper veins except 

those i~hat form a transition phase between copper and silver .veins. In amount it varies from 

1 up t:> 20 or 30 per cent of the metal. It,is esp~cially abundant.in the aplite area west of Big 

Butte1 where the outcrops of the veins were prima:dly worked for the manganese oxides, which 

were 11seful as flux in smelting. 
70 GEOLOGY AND OR.E DEPOSITS OF BUTTE DISTRICT, MONTAN:A. 

ZINC. 

Zinc is also very widespread and is generally more abundant in the silver than in the copper 

ores. In the latter, except in certain veins south of ~he central area and in those at the western 

ends of the two belts, it is not usually distinguished in the ore. In some second-class ores it 

averages 2 per cent, and in an average of analys~s of matte from a certain group of mines, extending over several months' production, it ran about 2! per cent to 60 per cent of copper. In the 

silver veins it may be in considerable amount, many smelters' assays showing fron1 2 to 40 per 

cent. Its distribution is by no means uniform. 1 

LEAD. 

Lead is relatively small in amount and is not usually taken account of by ore purchasers, 

nor is it generally visible in the ores. In the average copper matte above n1entioned its proportion was about one-quarter that of zinc, with which metal it is generally associated. It is 

said that considerable amounts of galena were found in the Humboldt, in the Blue vein in the 

Little 1\1ina claim, and in the Clear Grit. 

'NICKEL. 

Nickel is present in minute traces. It was first detected in the copper sulphate crystals 

from the electrolyte and its presence was later confirmed by direct analysis. 

ARSENIC. 

Owing to the large and increasing amount of eriargite in the Butte ores the amount of arsenic 

mined is large. Increasing litigation over the alleged poisonous effects of the smelter fumes 

condensed on vegetation and eaten by animals has led to the erection of extensive dust chambers, 

in which the arsenic is condensed and from which it is collected. From 3.3 to 5.5 p'er cent of the 

mineral is recovered from about 22,000 pounds of dust, the finest portion of the 60 to ~0 tons 

collected daily at the Washoe works. The plant yields from 11 to 18 tons of arsenic a month. 

SULPHUR. 

As all the ores treated are sulphides the amount of sulphur in the great tonnage extracted 

daily is enormous.· The Washoe plant at Anaconda, treating 7,000 tons of ore per clay (in 1905), 

yielcled42,200 pounds of gases (693,000 cubic feet per minute) containing 1.5 per cent of sulphur, 

equal to 3 per cent 802 or 1.37 per cent sulphur by volume. This is equivalent to 494 tons of 

sulph'Qr per 24 hours. Over half of this amount comes from the roasting furnaces. 

AMOUNTS OF METALS IN THE ORE. 

To determine the amount of each metal present in the ore, where such metals are present 

in traces only, it is necessary to use the percentages shown in the analyses of the electrolytic 

slimes, many metals not being otherwise detectable. With these percentages and a knowledge 

of the tonnage of ore treated, the amount of each can be fairly approximated. Due allowance 

must be made for losses in roasting, smelting, bessemerizing, and calcining. Ina copper matte 

carrying 50 per cent copper, the lead, bismuth, antimony, arsenic, tellurium, and selenium will 

be largely eliminated in the bessemerizing process. According to Mr. E. Keller, 2 the average 

percentages eliminated in bessemerizing are lead, 96; bismuth, 91; arsenic, 78; antimony, 67; 

tellurium and selenium, 95. 

The loss in calcining the matte, the process followed when these figures were obtained, 

amounts to 1 per cent copper, 1.8 per cent lead, 1.6 per cent bisnl.uth, 8.15 per cent antimony, 

27.16 per cent arsenic, and 2.8 per cent tel1urium and selenium. 

--------------------------------- 1 Great bodies of it exist in the Butte Superior and Elm Orlu properties. 

2 The figures given in this and the next four paragraphs were furnished to the Survey by Mr. Keller. 
THE ORES. 

Tho following table shows further losses: 

Percentage loss by smelting calcined matte and by slagging. 

r._~gs~~:::: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 

Bismuth ......................................... . 

1. 00 

.13 

2.08 

Metal. 

1. 00 Antimony ....................................... . 7. 58 Arsenic .......................................... . 1. 06 Selenium and tellurium ... : ........... ·.· ......... . 

1. Loss In nne dust by smelting calcined matte. 2. Loss by stagging. 

1. 27 2.99 

2. 70 

71 

5.02 

1. 74 

None. 

'i\Then, as in the practice frorn 1896 to 1900, a 60 per cent copper rnatte is derived fron1 the 

6 per cent c:o.ncentru.ting ore, the percentage of gold and silver in the ore rnay be safely regarded 

as one-tenth of tl1at in the 1natte. As to bisml.1th, sele.niun1, and telluriun1, one gets sitnilarly 

reliable 1nininuun figures. For arsenic and antimony the problen1 is cotnplex; ·as to antirrwny, 

probably 50 per cent is elin1inated in the reverberatory process;_ and as to arsenic, it is impossible to drMv definite conclusions as the excess of pyrite greatly facilitates its volatilization. 

The following table represents an estimate which is a close approxin1ation to the truth: 

.A.1;erage comJ)OS'ition of matte and of the copper ore front which it ·was derived, based upon or.es mined in 1897. 

Metal. Matte. Ore. Metal. 

Per cent. Per cent. Copper ........................................... . Bismuth ......................................... . 60.00 6.00 

.04 .004 

Antimony ....................................... . .10 .02 

n 60 ounces per ton. · b 6 ounces per ton. c 0.3 ounce per ton. · d 0.03 ounce per ton. 

Ore .. 

Per cent. 

0.001 

b .0206 

d .0001 

As stA.ted on page 69, the ores now worked do not yield such high values in silver and gold. 

The 1natte produced in 1897 by the Butte sn1elters and shipped cast for treattnent contained the following constituents: 

Matte shippedfrmn Butte smelters in 1897. 

I 

1 I Metal. 3· 

-------------------------J-P-e-rc-e--nt. -P-e-rc-e-nt-. -P_e_r_c-en-t.-ii------------------~-----i-P-e_r_c_cn--t. _P_cr_c_e-nt-. _P_e_r-ce-nt-. 

Col> per .................................• 

1 

60. 76 ~9. 34 61. 42 Bismuth ....................... ,........ 0. 042 0. 0337 0. 0049 

l\[etal. 

Su phur ..... ,.......................... 23. 25 . . . . . . . . . . . . . . . . . . . . Antimony.............................. . Oi9 . 101 .133 

Iron ............................... ,.... 11.43 .......... .......... Arsenic ........................ ·......... .045 .0484 .128 

]i'et03 •••••••••••••••••••••••••••••••••• • 1.13 .................... Selcniumandtelluriuma ................ 015 .0021 .0042 

t~~~~l:.:::::: :::::::::::::::::::::::::: :i 2. 8t ::::: ~~~~:::: :: ::~~~ ~J!i~:~~~~:: :::::: ~: ::::::::::::::::::: ~~ce ... i4jf~ .... is:~~d~ 

n 'l'he ratio cr tellurium and selenium is from 1:1 to 1:!. ,b 61.2 ounces per ton. c 0.29 ounce per ton. d Ounces per ton. 

1. Jtcvcrbcrat>ry matte from the Anaconda works. 

2. Revcrbemtory matte from the Boston & Montana Great Falls plant. 3. Blast furnaqc matte from the Boston & Montana plant. 

The nu.ttes produced at present (1905) are n1uch lower in grnde, 40 per cent being usual 

and as low {LS 30 per cent being made. 

'VEIGHT OF THE ORES. 

The weight of the ores frotn the difrerent rr1ines varies son1ewhat. Generally, however,· 

about 9 cubic feet weigh a ton. Actual rneasurements. show that the loose or shipped from 

the Leonard mine varies from 15.9 to 16.5 cubic feet per ton, and that from the Pennsylvania 

n1ine from 14.9 to 16.9 cubic feet per ton. Tests on the West Colusa ore showed tl.1at the ore 

carried froin 3! to 5 per cent copper and ran 16.8 cubic feet per ton. Broken ore carrying 8 

per cent copper ran 16.04 cubic feet per ton, and broken ore carrying 20.4 per cent copper 

15.37 cubic feet per ton. 
72 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

STRUCTURES OF THE ORES. 

The ores show several distinct structures, which may be roughly classed as follows: 

1. Orustijied.---'-Symmetrical crusts deposited in definite order as banded vein filling m 

silver lodes. (See Pl. VII.) 

2. Massive.-Quartz-pyrite veins showing massive quartz and pyrite, with accessory 

sphalerite in irregularly distributed and patehy masses. Definite evidence of crustification is 

lacking, but here and there rude bandingeorresponds to the replacement of plates of granite 

along the zone of shearing. · 

3. Ribbon.-Plating due to sheeting of ·the vein filling by shearing stresses, resulting in 

drawn-out streaks of pyrite, the crushing of the quartz being recognizable only in thin sections; 

may be recognized by the branching veinlets and shattering of the pyrite ... Throughout the 

entire district not only have these earlier quartz-pyrite veins been generally fractured and 

dislocated by cross fissures but they have also suffered from movement along the plane of the 

vein; and as this movement has' been intermittent from the time of the vein formation to the 

present it is very difficult to decide at what particular period the ribbon structure ·was formed. 

4 .. Banded.-NeVITer material superimposed on massive vein filling by the. reopening of the 

faul t.ed vein. 

5. Disseminated.-Ore in which grains and films of glance and pyrite or of enargite occur 

scattered through the altered granite, either as a replacement of the pyrite, itself formed by the 

alteration of biotite and hornblende, or as a filling of a network of minute cracks which shattered the rock. · 

The normal quartz of the pyritic veins has a very characteristic granular hypidiomorphic 

structure, whieh is independent of the size of the vein. The quartz differs n1egascopically 

from that associated with either the glance or enargite ore. Drusy cavities occur in which 

crystals have developed, but in the ore proper the pyrite and sphalerite almost universally lack 

crystal form. Fluid inclusions are common in the quartz, but ·are small, of irregular form, and 

occur in lines apparently independent of crystal outline, though in places eonforming to the 

boundaries of the sulphide minerals. These inclusions have not been tested chemically. 

:MINERALS OF THE ORES. 

GENERAL COMPOSITION. 

The minerals in the Butte ores are neither rare nor of great variety. 

Chalcocite, bornite, and enargite are the most common copper minerals. Covellite occurs 

in large amounts in one mine and in small quantities in others. Chalcopyrite is present in 

workable quantities in a few properties but is an insignificant part of the total copper output. Tetrahedrite is found as a rarity in the deep workings of a few mines. Chalcanthite, 

or native bluestone, is common in the old workings. Pyrite is the most common sulphide. 

It is estimated that since the beginning of mining about 75 per cent of the copper production 

has come from glance, 20 per cent from enargite, 4'per eent from bornite, ! per cent from covellite, and ! per cent from chalcopyrite. The proportions in 1906 were different, being estimated 

at 49 per cent from glance, 49 per cent from enargite, and 2 per cent from other minerals, mainly 

bornite. 

Silver occurs native in the copper ores, especially those from the upper levels. Ruby 

silver and indeterminable black sulphantimonites and arsenides occur in the siliceous silver 

ores. Free gold is rare, but occurs in some silver ores, and has been seen in specimens from 

the Leonard mine, where it is parasitic on glance. 

The ores consist of ore minerals mixed with earthy and mostly worthless gangue. In 

the Butte silver ores the gangue minerals are abundant and decomposed granite is comparatively scanty. In the copper ores the gangue minerals are few, quartz predominating. The 

following notes on1it technical descriptions, being confined to n1atters of general interest and 

to local peculiarities of character or occurrence. 
U. S. GEOLOGICAL SURV EY PROFESSIONAL PAPER 74 PLATE VI I 

Second growth of quartz. crystals with 

pyramidal pciinti n~ toward interior cavity of vein 

J1 ~c ,,J' 

V halcopyriteV o<' ..r~<> '<.:<>'~ c,d~ 

F1 rst g,rovvtn of a,ua'"l:-1-

BANDED ORE SPECIMEN, LEXI NGTON MINE. 

Three.fourths natural size. Diagram show s co mposition. 

0'" 
THE ORES. 73 

PRIMARY MINERALS.· 

PYRITE. 

Pyrite is the n1ost common n1etallic n1ineral of the district. It occurs as a primary constituent of the Butte quartz monzonite and in pegmatitic facies of the aplite. It is, next to 

quartz, the most abw1dn.nt constituent of the copper veins and is abnndant in the altered 

grnnite adjacent to the veins. It for1ns, with quartz, the great quartz-pyrite veins, whose 

enrichment by copper glance is directly due to the pyrite. It also occurs intermi.~ed with all 

the other metallic sulphides of the district. (8ee fig. 8.) 

Pyri1.e also forn1s nearly pure n1assive vei1~lets of different ages. The pyrite carries some 

copper ar.d is supposed to be the mother copper n1ineral of the district. ·Numerous qualitative 

:FIGURE 8.-Pyrite vein in granite, 1,000-foot level, Leonard mine. 

and a few quantitative tests were made ·on pyrite from different parts of the district to deternline th~ copper content and to ascertain whether it contained arsenic and antimony. The 

quantita.tive results follow: 

Copper, arsenic, and antimony content of pyrite from Butte copper mines. 

Locality. Depth. 

Feet. 

1. :Fiat scan1. :Mountain View... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 

~: ~~-u~1ia~~~~vy~~ ~~1I.\~~·~~~~--::::::::::::::::::::::::::::::::::::: :'::::::::::::::::::::::::::::: 1

• ~gg 4. St. LawrEnce................................................................................ 1,400 

5. Mountain Con •••..................................................................... :...... 1, 800 . 

~: -~~i:f.l~~l\~~~:: :::::::::::::::::::: :~ ::::::::::::::::::::::::::::::::::::::::::::::::::::: ..... -~;~~~- !). Orccn :Mountain ...... :...................................................................... 2,000 

Copper. 

Per cent. 

0.10 

2. 76 None. 

None. 

None. • 5 

. 2 

. 7 

. 86 

Arsenic. Antimony. 

Per cent. Per cent. 

· .. · · i'~a<i(i." · · · · · · · · i: oo 

None. None. 

None. None. 

None. None. 

None. None . Trace. Trace . None. None . .005 None • 

Nos. 1 io 7 were examined by A. B. Rombauer, Butte, Mont.; Nos. 8 and 9 were examined by Dr. W. :F. Hilh~brand, in the Survey laboratory. 
\ 

74 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

The samples were generally taken from pyrite seams or from perfectly pure material free 

fr01n other minerals. Most of the seams were in granite and were not parts of the main lodes, 

except as noted. Samples were also assayed for gold and silver; generally they gave negative 

results, but an apparently pure pyrite from Cambers mine, 200 level, gave 0.70 ounce silver 

_per ton, and 0.01 ounce gold per ton. MARCASITE. 

:Marcasite (white iron pyrite) is common in the Butte mines. 1 It differs from pyrite in 

crystallization, lowet· specific gravity, and color. It tarnishes and decomposes more readily 

than pyrite, and hence may be .important in promoting secondary enrichment. It is found 

: adn1ixed with pyrite and also in aggregates of imperfect crystals lining vugs and generally 

associated with kaolin. Though no detailed studies have been made it is assumed that much 

of the material decomposing so readily on the 'clumps of the different mines is marcasite. 

BORNITE. 

Bornite (peacock copper, FeCuS2) is a common. ore mineral in several lodes, especially the 

Parrot, Original, Gagnon, Jessie, and Edith May mines. It also occurs sparingly in a few of 

FIGURE 9.-Thin section of bornite ore: 1, White quartz; 2, 

massive pyrite with quartz; cracks and interspaces where 

quartz grains and crystals join filled with bornite, which 

also replaces part of the pyrite; enargite fills minute cracks 

in the pyrite; 3, bornite. 

FIGURE 10.-Thin section showing fragments of (2) shattered 

pyrite and (3) enargite that appear to be secondarily inclosed in (1) bornite. 

the silver veins. It is always· massive, :with a recognizable crystalline structure. _on fresh 

fracture it has a silvery luster that tarnishes quickly to copper red, and this in turn to indigo 

blue .. :Much of the Parrot ore contains large amoy.nts of this mineral; in it small cavities onesixteenth to one-fourth inch across containing wires of native silver are often seen. (See fig. 

18, p. 80.) 

Bornite occurs both as a primary and as a secondary mineral, hence its presence does not 

necessarily mean secondary enrichment. It appears in rounded masses or cobbles in the 

fault breccias of the Original, Gen1, Jessie, and other fault veins, and in these veins is of earlier 

formation than the chalcopyrite and· other minerals typical of the silver period. :Microscopic 

studies show a close association between it and chalcopyrit~, and also that it occurs as a secondary :filling in altered and fractured enargite. It occurs mostly above the 1,000-foot level. (See 

figs. 9 a.nd 10.) 

t Winchell, A. N., Econ. Geology, vol. 2, 1907, p. 292. 
• 

THE OHES. 75 

CHALCOPYRITE. 

Contrary to common belief, chalcopyrite is not common in the Butte copper ores. , It l1as 

been supposed to occur mixecl with pyrite in the big veins of the district, but study. of the ores 

under the 1nicroscope discredits this idea. Xt does occur in quantity in a few of the northwest 

fault veins, where it is indigenous, notably in the Blue vein at the Little ~Iina n1ine, at the Clear 

Grit 1nine, and in the Gen1 vein. The mineral is clearly related to the pyrite of the silver veins, 

and occurs 1nainly in a pasty, clayey vein filling in the copper ores of faUlt veins. In the silver 

veins it occurs together with quartz in isolated ore bodies. It is especially abundant in the 

Lexingtonn1ine above the 800-foot level, and in the neighboring properties. 

Chalcopyrite is a primary 1nineral in the Butte quartz 1nonzonite, a study of thin sections 

and of polished specimens showing that it is intergrown with the rock 1ninerals -in the perfectly 

fresh rock. It was fust noticed in a specin1en kindly 

forwarded to the writer by :Mr. I-I. V. Winchell fron1 

a quarry near Elk Park, but has since been noted 

in other speciluens and is particularly abundant near 

the Altona 1nine. Primary chalcopyrite is also found 

LEGEND 

11~1 Enargite 

. 

- Quartz 

I~ ~~I Pyrite 

Chalcopyrite 

in small crystals 

'in abundance in an aplite granite band 60 feet wide 

between the 1nain body of granite and the bordering 

secl.Unentary rocks near Anaconda. At the Altona 

1uine and vicinity the granite fTon1 the 200 and 400 

foot levels is clark, fairly fresh, and full of what appears to be original chalcopyrite .. the sulphide being 

associated with biotite and hornblende and also 

intergrown with feldspar. In the fault fissures chalo copyrite occurs in dendritic bunches of intergro,vn Z.lnches ~------~------~ 

crystals lining VUgS and as lOOSe aggregateS aSSOCiated FIGUREll.-Chalcopyritc in quartz in enargitc veinlet,· Leon· 

ard mine, l,lOD-foot level. . · with tetra.heclrite in the fault clays of the Gem n1ine. 

The 1nineral is believed to occur in recently formed veins; in the deep levels of the Leonard 

n1ine it is found under conditions which indicate very recent deposition, forming brilliant and 

readily detern1inable coatings on fractures anclin fissures in the covellite. (See fig. 11.) 

CHALCOCITE. 

Chalcocite (copper glance, 79.8 per cent copper) is the n1ost abundant and characteristic 

copper 1nineral of the district. It is lacking in the strictly silver-bearing veins but is typical 

of the copper area and also in large amounts in fault veins of composite character. In the 

exceptional veins of the Clinton and Homes take n1ines east of Butte it occurs as a recent mineral, 

filling the spaces about and upon the large quartz crysbtls which line tlie veins. 

In the great ore bodies of the Butte n1ines chalcocite forms steely-gray masses having a 

pronoullCecl conchoidal fracture. . In the upper 600 feet of the Anaconda and Syndicate lodes 

it has a leaden color and fracture. At lower levels clown to 2,400 feet it shows a massively 

crystalline structure and is clotted with included crystals and masses of pyrite. It occurs 

filling crevices and cen1enting a breccia co1nposecl of fragments of enargite and of earlier quartzpyrite veins. It envelops and incloses well-formed and large quartz crystals; it cuts pyrite 

grains and also fills fractures in pyrite and in bornite, and therefore is certainly the latest ore 

1nineral fonned and is in large.part a replace1nent of pyrite. (Seep. 102.) It forms most readily 

as a replacement of pyrite but is also pseudon1orphic after sphalerite. A specin1e~ of banded 

ore from the Colusa uline, submitted to technical tmalysis, gave 79.2 per cent copper and 20.8 

per cent sulphur. . 

Son1e inter~sting specimens of very coarsely crystallized and peculiarly banded chalcocite 

frcnn the deep levels of the Leonard nune possess unusually brilliant luster and have much 

n1ore perfect cleavage than any othei· mineral from the district. The fractured surfaces show 
I 

-76 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

that the chalcocite includes bornite crystals. The surfaces of the chalcocite crystals are etched 

and corroded by nonoxidizing solutions. 

The bulk of the ore mined at Butte consists of altered gr:a.nite carrying disseminated. 

DQUARTZ 

~ GRANITE. , 

~~CLAY 

.ENARGITE 

~~~2·~t>l PYRITE 

~ ~GLANCE 

0 2 3 Inches 

FIGURE 12.-Chalcocite (glance) specimen from 1,000-foot level, Leonard mine; natural scale. Shows pyritized granite alongside of quartz vein,. 

with pyrite grains. Stringers of glance cut through quartz, granite, and the fault clay between them. (Sketched by Bard.) · 

grains and veinlets of chalcocite (copper glance), intergrown with pyrite or replacing that. 

mineral partly or completely. The chalcocite is seldom found as distinct crystals, but in a. 

few vugs well-formed crystals have been found coated with quartz and etched by later solutions. 

/' I 

From the studies made of thin sections it is believed that the min-· 

eral is almost universally secondary but that it also occurs as a. 

primary mineral in some veins. It is undoubtedly in process of 

formation by descending waters at the present time, but as the. 

great ore bodies found at deep levels are far below the. present'level. 

of ground water, they can not have been produced by the reac-· 

tions commonly offered in explanation. (See figs. 12 and 13.) 

The replacement of .zinc blende by chalcocite has also been noticecl 

at Morenci, Ariz., by Lindgren. 

COVELLITE. 

Covellite (indigo copper, CuS), a beautiful and brilliant indigo· 

minerai, is abundant in the Covellite vein and occurs locally in some 

other copper veins. It is rather rare outside of Butte, which 0 linch. makes its presence there the more interesting. In the Butte ores. 

FIGURE 1

a.-Veinletofchalcocite(glance). it is always massive and shows a perfect cleavage, with a platy and quartz. The (1) chalcocite fills 

the central·cavity of an open fissure structure. It occurs as a secondary ore, either derived· from chal-· 

orvuglined with comb quartz. Crys- · · • talsof(a) quartzand(Z)pyriteoccur, coc1te or deposited under exceptional conditions in the crushed and 

isolated, in the chalcocite. Leonard clayey matter of fault veins. (See figs. 14 and 15.) The mineral 

mine, 1,ooO-foot level. After Bard. has not been found in the attrition breccias of the fault veins, but. 

some of it is undoubtedly the result of decomposition of masses of glance broken and dragged 

by fault movements. An analysis made in the Survey laboratory by Dr. W. F. Hillebrand gave 

the following results: · 
THE ORES •. 77 

Analysis of covellite from Butte, },font. 

Copper ..................................................................... . 66.06 

Iron .............................................................. : ......... . . 14=0.30 pyrite. 

Sulphur ....................... · ............................................. . 33.87 

Insoluble ............................................................ -...... . .11 

100. 18 

Sp~cific gravity at 16° C. (uncorrected for PY!ite and for insoluble material) .......•..••..... 4~ 76 

'l'he nut.terial tested contained a very little pyrite 

:and was as pure as could be obtained. It came from 

the covellite stopes of the East Greyrock mine on the 

:800-foot level. · 

J!'J.omu~ 15.-Vclnlct of 

0) cnurgltc pcuctmtcd by (3) Iuter 

covcllltc scam. (2) 

Quartz. Natural 

size. J.conard mine, 

1,100-foot level 

Shows sccondury 

clmmctcr or the covel· 

lltc. 

BNARGITJ<~. 

Enargite is, next to glance, the 

most abundant copper mineral, 

greatly exceeding bornite in quantity. It occurs in veins which differ 

in many ways from the quartzpyrite veins carrying great masses 

of chalcocite. It does, however, 

occur ·in the latter veins,· . particularly in the deepest levels, and it is o 21nches· 

abundant in the fault veins. It is FIGURE 14.-Vug in a quartz-pyrite vein that has been 

a primary mineral, and in sqme filled by covellite. (1) Enargite occurs In sac-shaped 

veins, as in tlle Gambetta and nei2'11- replacements in the (2) quartz. (3) Chalcocite is seen ..., in center or ( 4) covellite mass. (5) Pyrite. Natuml 

boring veins of the Leonard group, scale. Leonard mine, 1,100-foot level, Butte, Mont. 

After Bard. it extends upward to the base of the • 

oxidized ground son1e 20 feet beneath the surface; in general it becomes 

increasingly abundan.t with depth. :Many small veins of this ore, formerly 

unrecognized or regarded as zinc blende and left untouched, are now 

diligently sought for and mined. 

In general, enargite is massively crystalline, with well-developed cleavage, 

but without crystal outline. Well-formed crystals have, however, been 

found in vugs in ·a number of veins, and it is notable that the terminal 

face (basal pinacoid) has a clean, mirror-like surface and the prismatic faces 

a mossy coating of copper glance. The mineral completely fills many 

fissures in altered granite, generally separated from the granite by a narrow 

band of comby quartz. A breccia of enargite, cemented by glance, .has 

been mined in considerable quantity in the Cplusa property. In the old 

quartz-pyrite veins the Inin.eral generally occurs at a depth of 2,000 feet or 

ll10l'e. 

A san1ple of enargite from the Rarus nline, analyzed by Dr. W. F. Hillebrand in the Survey 

.laboratory, showed the following composition: 

Analysis of e~wrgite from the Rants ?nine. 

Copper ..................................................................... · ........... . 

Iron ................................................................................... . 

Zinc •................................................................................... 

Arsenic ................................................................................ . 

Antimony ............................................... · ............... : ............... . 

Sulphur ............................................................. ·.· ................ . 

Insoluble ......................... · .................... : ... · .. -.. · .... --- ... -.-- ... ----·---

48. 67 

. 33 

.10 

17.91 

1. 76 

31.44 

. ;n 

100. 32 
78 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

Enargite is an original miner~l in the veins of the eastern patt of the district. It is su bsequent to pyrite, but earlier than glance. . (See figs. 15 and 16.) 

Enargite pseudomorphs after hiibnerite have been observed in the Leonard mine. Specimens received from· :Mr. R. H. Sales show prisms of enargite surrounded by radial quartz, the 

basal pinacoids of the prisms being clear and mirrorlike, and the remainder of the crystal coated 

with mossy glance. The white quartz penetrates the inassive enargite and both the quartz 

and the included enargite fill spaces between fragments of the earlier quartz-pyrite vein filling. 

The difference between the two forms of quartz is marked, as the mineral of earlier formation 

has a dull, greasy luster and lacks the coarse crystallization and glassy look of the later one. 

Enargite occurs ab'undantly in scarf-like masses in the fault clays and breccias of the 

Original, Leonard, and other veins, under conditions where bornite and the earlier quartzpyrite vein filling are invariably crushed and broken. Enargite 

also forms solid veins, sometimes as much as 3 or 4 feet thick, 

in which the mineral carries included particles of pyrite and a 

very little quartz, but is practically free from gangue matter. 

Study of thin sections shows that the enargite is later in formation than the pyrite, and that it is associated with fluorite, 

barite, rhodonite, and other minerals commonly due to thermal 

waters. The great abundance of the minerals in the fault veins 

of the St. Lawrence and Leonard mines is particularly noticeable. It must, however, be noted that in the Johnstown vein the 

~..___,___--L.... ___ __.~21 nches mineral is of earlier formation, .s.o that two periods of enargite 

deposition appear to have existed. 

TETRAHEDRITE. 

Tetrahedrite (gray copper) occurs in the northeast silver 

FIGURE 16.-Blockofore showing relations 

of enargite and pyrite in ore from the 

l,lDO-foot level of Leonard mine. Natural size. The two minerals (2) quartz 

and (1) pyrite, appear to be broken and 

the fragments cemented together by (3) 

enargite. After Bard. 0 

belt and in the fault veins, particularly on the upper levels of 

the Jessie, Gem, andsimilarveins on the northeast border of the copper area. It is an original mineral which corresponds to enargite in its position in the ~equence of vein minerals. 

In the deeper levels of the_Leonard mine the mineral is relatively abundant as a bronze or 

brown variety carrying low values in silver and appearing to be of comparatively recent formation, more recent in fact than the enargite and other copper minerals. It is everywhere 

massive, but occurs intergrow:ri. With other minerals. On the 1,200-foot level of the Leonard 

it is found as a streak about 3 feet wide near the west end line of the claim. A carload lot 

containing much gangue yielded 4 per cent of copper, 2 ounces per ton in silver, and $13 per 

ton in gold. A little tellurium is present and it is believed that the tet~ahedrite holds inclusions of some gold-silver telluride, whose decomposition may have supplied the native 

gold found in mossy aggregates, parasitic upon glance. Similar ores occur in the deep levels 

of the mines at Cripple Creek, Colo. Tetrahedrite also occurs in the silver veins east of Butte, 

particularly in the Clinto.n; Homestake, and other mines adjacent to Columbia Garden. 

TENN ANTITE. 

Tennantite occurs sparingly and only in the copper veins, where it appears to be a product 

of the decomposition of enargite, with which, so far. as known, it is always associated. 

SPHALERITE. 

The sulphide of zinc (sphalerite) is common in the veins, both in the copper and silver 

areas. Commonly it is associated with pyrite (fig. 17), but veinlets of solid blende also occur in 

the wall rock of the Syndicate lode. The blende of the quartz-pyrite veins i~ a primary m~eral, 

deposited simultaneously with the sulphide of iron. In some veins it is very abundant, both 

near the surface and in depth, but is absent in the enriched copper glance ores. A specimen 
THE. ORES. 79 

kindly given the writer by Mr. I-I. V. Winchell shows the different stages of replacement by 

glance. As blende is replaced before pyrite, it is propable that some of the glance seen in the 

Butte mines is a replacement of this mineral. This is also indicated by the abundance of zinc 

sulphate in the ·mine waters. This replacement has been observed by Lindgren at :Morenci, 

Ariz. 

Zinc blende is also common throughout the silver area and is so abundant in the ores of the 

Alice and :Moulton 1nines that a zinc extraction plant was erected for its recovery. South of 

the copper area proper the veins carry large amounts of zinc blende and the ores are penalized 

when sent to the smelter. Veins southwest of the Emma mine and those. of the silver belt 

generally contain ores high in zinc, which has proved a serious detriJnent in their treatme.nt. The current belief that the fault veins 

northeast of the copper area carry galena and zinc near the surface, 

and that beneath ~his zone of worthless sulphides bodies of commercial copper ore will be found, has not yet (1906) been substantiated, though observations by lVIr. E. Waller, of the Tasmanian 

Govenunent Survey, show that the zinc and galena bearing veins of 

N or~h Dundas, Tasmania, change in depth to copper-bearing ores. 

GALENA. FIGURE 17.-Zinc blende (3) and 

galena (I) on quartz crystals(2) 

attached to pyritized granite 

Sulphide of lead (galena) occurs sparingly in the silver veins and (4) south of Colusa vein, 500-

in considerable amount in some of the fault veins of the copper area, foot level of Leonard mine. 

notably in the Blue vein, from which many carloads of lead ore were extracted within the limit 

of the Little Mina claim. It seems not to be present in the old copper veins but. to be confined 

to the later fault veins. MOLYBDENITE. 

:Molybdenite, a disulphide of molybdenum, is found in a number of places east of the Flat 

and in the Gagnon mine. The mineral, which resembles graphite, occurs in small .black shiny 

scales having a bright metallic luster and lying in fracture planes and veinlets in both fresh and 

altered granite. It is abundant alongside the veins on the Montgomery, Altona, and neighboring claims. MANGANESE MINERALS • 

. Manganese minerals are characteristic of n1ost of the silver veins and occur in th~ copper 

veins where these have been broken and mineralized by later fraqtures. Rhodochrosite and 

rhodonite appear to be the chief sources of the manganese; but oxidized ores, which are clearly 

the result of a normal decomposition of the silicate and carbonate of manganese, are abundant 

in the outcrops of all the silver veins. Pyrolusite, too, is common in these outcrops, and its 

sooty black stains many of the. great quartz reefs seen throughout the district. vVad, which is 

the commonest of the oxides, is usually disseminated through the vein quartz, mostly as an · 

extremely fmely divided powder arranged in curly, grotesque forms around crystals and along 

cracks. The other oxides of manganese are in· some places crystalline, but they usually occur 

in botryoidal, reniform, and massive forms, in which it is hard to distinguish the separate 

1ninerals. GOLD .. 

The constant presence of gold, together with telluriu'm and selenium, in the blister copper 

produced by the smelters, suggests the probable presence of minute quantities of some goldsilver telluride. Native gold has, moreover, been found by :Mr. Reno Sales as distinct and fairly 

good-sized particles on the surface of glance crystals from the 1,000-foot level of the Leonard 

m1ne. 
80 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

SILVER. 

Native silver is common ~ the silver veins and also in the oxidized portions of the copper 

veins. It has been observed in mossy aggregates. and co~tings, in fractur~ planes in glance 

ores, and in bornite. Wire silver and fibrous silver also occur in cavities in bo.r:nite and glance, 

particularly in the upper levels of the Parrot mine (fig. 18). 

PYRARG YRITE. 

Pyrargyrite has been observed in the ore from the Springfield mine, where its crystals line 

fractures in the altered granite of the vein walls. Elsewhere in the district it has not been 

positively identified, although there is reason to 

suspect its widespread occurrence, as indicated 

by the red streakwhen many of the massive silver ores are scratched. 

HUBNERITE. 

Hubnerite (tungstate of manganese) has 

o ' Inch . been found in both the Gagnon and Leonard 

mines, forming many perfect but deeply altered FIGURE 18.-Wire silver (2) and masses of silver in vugs (4) in bor_ 

nite (1) from 600-foot level, Parrot mine; (3) quartz crystal. mouoclinic crystals of considerable size associated 

The conditions closely agree with those noted by Vogt in the with sphalerite, copper minerals, and quartz. On . Norway silver deposits. the 300-foot ~evel of the Gagnon mine it formed 

an ore shoot of argentiferous material and passed over into cupriferous massive wurtzite. 

Hubnerite is regarded as an original vein mineral, which occurs in bands of quartz inclosed 

by sphalerite and copper sulphides. WURTZITE. 

, · Specimens ofwurtzite have also been obt·ainecl from the 1,600-foot crosscut of the Gagnon, 

where it formed about 1.29 per cent of the ore mined. The following analysis was made: 

Analysis of wurtzite ore from 1, 600joot crosscut of Gagnon mine. 

Copper ....................................................................... per cent. . 6. 18 

Zinc ........ · ..................................................................... do. . . . 19. 10 

Gold ................................................... · ................ ounces per ton. . . 05 

Silver ............................................................................. do .... 11.60 

OXIDIZED MINERALS. 

DISTRIBUTION. 

In general the veins of the district lack the abundance of oxidized surface ores seen in so 

many copper camps. Such minerals occur, but they have never furnished even a small percentage of the ore mined. In the area east of Butte they are more common, having been mined for 

a few months at the Bullwhacker and Bertha claims. In these mines seams of the reel oxide are 

common both in the veins and in the country rock adjacent to the veins; the chief ore, however, 

is a green chrysocolla, which occurs in great abundance in the north and south fault vein, which 

crosses the Bertha, Bullwhacker, and Maggie Fraction claims. In the early history of the camp 

the ·outcrop of the Parrot ledge is described by Raymond as being marked by an abundance of 

bright-colored carbonate ores. CUPRITE. 

Cuprite (Cu 20, 88.8 per cent copper), the dark-red oxide of copper, occurs sparingly in the 

upper portions of many of the veins lying along the foothills of East Ridge but is not important 

commercially and has not contributed materially to the copper output of the region. 
THE ORES, 81 

CHRYSOCOLLA. 

Clu·ysocolla ·(hydrated silicate, 36.05 per cent copper), is found in small ~mounts in many 

veins, but forms commercial ore only in the claims east of Butte along the foothills of East Ridge. 

The n1ammillary crusts common in other districts are rare at Butte, the mineral occurring as a 

light, extremely porous, corklike material of a bright-green color that was mined in considerable 

quantity in 1907-8. MALACHITE. 

Both green and blue carbonates of copper occur sparingly along the copper .outcrops, and 

are particularly noticeable in the East Ridge claims. The ores have not, however, been important, and are of Inore mineralogic than economic interest. 

COPPER PITCH." 

Material which appears to correspond to the copper-pitch ore, observed in Arizona, has been 

found on the :Montgomery, Ida, Amazon, and other eastern claims, where it occurs as a lustrous 

coal-black or dark-brown crust, associated with other copper ores. No analysis has been made, 

and it is uncertain whether the material corresponds exactly to that collected in Arizona. 

CHALCANTIDTE. 

Chalcanthite (bluestone or copper sulphate) is by far the most abundant recent mineral of 

the oxide zone. It occurs in old mine workings, forming crusts or crystalline tufts on mine 

ti1nbers and wall rocks. lt coats rock fragments in old stopes, in some mines so abundantly 

that it has been found profitable to collect these from time to time. Chalcanthite occurs in the 

mine waters, from which many tons of metallic copper have been precipitated by contact with 

metallic iron. In the old drifts of the Mountain View mine it forms clear blue stalactites of 

considerable beauty, which appear to be perfectly pure, different in this respect from stalactites 

found in other 1nines. · A specimen of an aluminous copper sulphate forming stalactites on 

the 600-foot level of the Anaconda mine was analyzed by Dr. W. F. Hillebrand, who reports its 

composition as follows: 

Analyms of cupro-alum stalactite, Anaconda mine, Butte, Mont. 

Copper oxide .................... ·........................................................ 9. 32 

li'errous oxide... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Al20 3 •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• ; • • • • • • • • • • • .. • • • • • • • • 10. 67 

MgO.......... ........................................................................ .. .08 

Alkalies ................................................................. · ................. Trace. 

803 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• •••••••••••••• 35.05 

Phosphoric acid ............................................................. ·. . . . . . . . . . . . 1. 13 

Arsenious oxide.......................................................................... . 07 

'\Vater ................................................................................... 43.44 

99.94 

As the material is wholly soluble in cold water it is readily carried off, but as the acids in 

the a~ove analysis are far in excess of the amount required for a normal salt, the material is · 

probably a mixture of acid salts and free sulphuric acid, with a little phosphoric and arsenic 

acid. · 

In the Silverbow mine pure chalcanthite is so abundant as to almost fill some of the old 

drifts. Pli~te VIli, A, shows the stalactites extending from roof to floor on the 200-foot level. 

In the 1naterial from the Mountain View mine only copper sulphate was found, but most of the 

material gathered elsewhere contained admixed iron and zinc sulphate. 

90427°-No. 74..:_12-6 
82 GEOLOGY' AND OR.E DEPOSITS OF BUTTE DISTRICT, MONTANA. 

PISANITE. 

Pisanite, commonly regarded as a mixture of copper and iron sulphates, is common in many 

of the unworked drifts of the mines where seepage waters come down through old stopes and carry 

both copper and iron sulphides in solution. It usually occurs in stalactites in deserted drifts. 

GOSLARITE. 

Goslarite (zinc sulphate, ZnS04 + 7H20) is extremely common in old mine workings, where 

it forms an efflorescent coating of long and delicate hairlike needles on walls, air pipes, and 

other exposed surfaces. It occurs somewhat rarely in seams in the dry stopes and drifts of the 

upper. levels ~f the Rarus and other mines. 

LIMONITE. 

Limonite is extremely abundant throughout the district, but is rarely found in quantity at 

any particular place. In the mines it is· deposited by the mine waters and coats the walls of 

both crosscuts· and drifts or forms stalactites (Pl. VIII, B) which in some places extend from 

roof to floor. It is the most common oxidation product of the mine waters, which deposit 

limonite wherever they emerge into the open air. It is also common in small quantity in the 

vein outcrops and throughout the zone of oxidation generally. The great limonite outcrops of 

other localities are, however, wanting at Butte. On the slopes near Park Canyon it occurs as 

a surface coating, capping the veins and extending down the slope below the vein outcrop, but in 

Butte it is notable for its absence rather than its abundance. · 

A sample of a limonite stalactite from the 900-foot level of the Silver bow mine (Pl. VIII, B) 

was sul;>mitted to Dr. W. F. Hillebrand and analyzed by him in the Survey laboratory. 

Analysis of limonite stalactite from Silverbow mine, Butte, Mont. 

SHica ................... · ....... · .................................. .' . . . . . . . . . . . . . . . . . . . . . 2. 55 

Ferric oxide ............................................................................ 68. 53 

Zinc oxide ........................... "................................................. . 40 

Lime oxide............................................................................. . 28 

Magnesia .................................................................. ·_ .............. Trace. 

Alkalies .................... : ..................................................... : ...... Trace. 

Phosphoric pentoxide................................................................... 4. 06 

Arsenic pentoxide .......................................... , ........................... Trace. 

Sulphur trioxide........................................................................ 3. 24 

Water ................................................................................... 20.01 

99.58 

MELACONITE. 

Melaconite, the solid. black oxide of copper, occurs in several of the East Ridge claims, 

notably the Bullwhacker, Montgomery, Amazon, and others near by. The mineral ·forms 

seams and small bunches in the altered surface rock. It is jet black, has a glistening conchoidal 

fracture resembling coal, · and lacks crystalline form or texture. It occurs associated with 

cuprite, generally in seams or fracture planes or as coatings about nodules. 

TENORITE. 

Tenorite, the earthy black oxide of copper, occurs sparingly at a number of localities 

throughout the copper district proper. 

MINERALS OF THE GANGUE. 

QUARTZ. 

Quartz is the common gangue mineral of the veins, being abundant in both copper and silver 

veins. In the copper veins it is a replacement material and has a dull greasy look, even when 

crystalline. In ~he silver veins it is commonly massively but coarsely crystalline and shows a 

comby structure, in many places with lines of vugs runn~ng through the center of the vein. It 
U.S. GEOLOGICAL SURVEY 

A. STALACTITES OF CHALCANTHITE WITH SOME ADMIXED FERROUS 

SULPHATE, SILVERBOW M!NE. 

200.foot leve l. See page 81 . 

PROFESSIONAL PAPER 74 PLATE VIII 

B . STALACTITES OF LIMONITE IN SILVERBOW MINE. 
THE. ORES. 83 

also occurs in well-defmed c(ystals embedded in glance and as a coat~g about enargite veins. 

It is clearly a mineral of several generations, being one of the earliest and possibly also the latest. 

of all the 1ninerals of the district. In the western part it occurs in great reefs which forn1 ridges 

and hills. One of these, the outcrop of the Ancient vein, is shown in Plate L~, A. In the silver 

veins the quartz is commonly stained black by n1anganese oxides when subjected to oxidizinginfhiences. Below the water level, however, it occurs mixed with rhodonite and rhodochrosite, 

fro1n which it is distinguishable with difficulty .. Silica also occurs in opaline and chalcedonic: 

n1asses in the so-called silicified granite found about 1nany of the vein outcrops. I-Iere, however,. 

it is due to the fonnation of mnorphous silica as a result of kaoliniza~ion. 

CALCiTE. 

Calcite is not n.bundant in the Butte 1nines. It occurs somewl1at rarely in the silver veins,: 

and n1ore often in the fault veins, notably the Blue, Clear Grit, and other northwest veins. Good 

crystals of dog-tooth spar deposited upon chalcopyrite and intergrown with that 1nineral were 

fpund in the vugs of the Blue vein, where opened by the Little Mina workings. Calcite is one of 

the Inost recent 1ninerals formed; it is still heing gathered by rock waters in little veinlets in granite reJnote fron1 the 1nineral veins; for instance, in north crosscuts driven from the Original n1ine. 

The charn.cter of. this alteration is noted elsewhere (p. 89),.but it is significant, as the calcite is 

i'eadily repln.ced. b)r quartz in a later period of 1nineralization. 

OYPSUl\I. 

Gypsmn hits been noted in n1any places as incrustatiol).s in old n1ine workings and on n1ine 

chunps. It is believed to result frmn the decompositi9n of lime-bearing feldspars and of pyrite~ 

being due to the act~on of the sulphuric acid on the feldspars in the presence of oxygen and water. 

SEIUCI'l'E. 

Sericite, the finely felted form of n1uscovite, is the most abundant mineral of the alterecl 

rocks, not only in the vein walls but also in the gangue of the enargite veins. The bulk of the. 

concentrating ore se.ot to the n1ills is· a decomposed sericitized granite, speckled with minute 

grains of pyrite, either partly or wholly r.eplaced by glance. This sericite, when acted on by 

acidic watet·s cmning fron1 the oxidation of pyrite, alters readily to kaolin. 

KAOLIN, 

This 1nineral is common in the weathered zone of the altered rocks of Butte. It occurs also 

in the veins and as a constant associate of glance, particularly in crystals lining vug~ in the veins. 

Its fonnation is clue to the same processes which have oxidized the gfance ores near the surface 

and carried the n1aterial downward to be deposited as an enrichment at greater depths. · 

RU'l'ILE. 

N eeclles and prisn1s of dark-brown rutile are common in the sericitized Butte quartz monzonite. They are n1ost frequent where biotite is decomposing, 'but .probably result from the altera-

. tion of titaniferous n1agnetite. 

1\IAGNETI'l'E. 

:Magnetite .is a con1mon constituent of the Butte quartz monzonite, occurring in irregular 

grains and poorly formed crystals, in many places intergrown with the ferromagnesian minerals 

but alsq standing alone. It has been observed interlocked with pyrite, the two together forming 

an irregular crystal (figs. 19 ancl20). It has not been observed in the veins. 

Ji'LUORI'l'E. 

Fluorite hiLS been found by the writer in both the Original and Gagnon workings, where it is 

associn.teci ·with enargite in the fault clays. It is a result of a late mineralization, which has 

' 

--I 
84 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

deposited rhodonite and other minerals characteristic of the silver veins. It has also been noted 

in the Leonard mine and the Gem mine, where it is associated with barite and tetrahedrit.e. (See . . fig. 21.) 

DARITE. 

Barite (barium sulphate) occurs only in the fault veins. It has been noted in fine crystals of 

a clear yellowish-brown color and tabular form lining vugs in the Blue vein .and cavities in the 

veins of the Leonard mine. It occurs incrusting all the other minerals characteristic of the vein 

and seems extremely recent. Its occurrence is limited to 

vugs and water channels. 

RHODONITE. 

X40 

Rhodonite, the silicate of manganese, is, next to quartz, 

the most common gangue mineral of the silver veins. It 

occurs in crusts and bands alter:q.ating witli quartz, the layers being made up of microscopic rhombs. It also occurs 

disseminated through the quartz, so that it is clearly of the 

same age as the quartz, and some of it is·younger than the 

FrauRE 19.-Intergrown pyrite and magnetite in fresh 

. metallic minerals. Rhodonite is found only in the silver 

veins and in the fault veins of the copper area. In the 

latter it forms concretionary masses and rather loose aggreButte quartz monzonite. b, Biotite; q, quartz; p, gates filling little seams in the fault clays. It has been 

pyrite; h, hornblende; pl, plagioclase; m, mag- . observed in the Original, Gem, Clear Grit, and other fault 

netite. X 80. veins of the copper area. 

RHODOCHROSITE. 

Rhodochrosite is less abundant and less widely distributed than rhodonite. In places its 

relations indicate its formation from rhodonite, of which it appears to be a decomposition product. 

In many -veins it forms a cementing material, filling fractures in the ore and binding together 

fragments of country rock. It is typical of the silver veins and of 

the reopened, faulted copper veins. It has been observed in the fault 

veins of the Gagnon mine, associated with bornite and other copper 

minerals .. PARAGENESIS. 

The relations of the ore minerals to each other are well shown in 

the Leonard and Gagnon mines. In the Gagnon, bornite cements 

crystals of quartz in the middle of the ore body and fractured quartzpyrite ore in vein walls. It is the last mineral formed in vugs. With 

depth it becomes more abundant and carries an increasing amount of 

silver. It is particularly plentiful in the 400 to 800 foot levels of the 

Gagnon and in the middle vein on the. 800-foot level. In all the veins 

blende. is abundant, but appears to be somewhat less so' in depth. 

Enargite comes in with depth and in the westward workings. It carries a large amount of silver and is distinctly associated with the fault 

veins. Glance is _not characteristic of the Gagnon workings, although 

FIGURE 20.-Thin section of. altered 

quartz monzonite, showing grains 

of intergrown pyrite (2) and magnetite (1); 1, 900-foot level Mountain Con. mine. Plagioclase completely, orthoclase partly, and 

biotite about half scricitized; 

hornblende wholly gone over to 

chlorite; magnetite, pyrite, and 

liematite as accessories. 

found in much of the ore. In the fault veins pyrite is argentiferous, carrying an average of 300 

ounces of silver per ton; in the normal quartz-pyrite veins it cardes no silver. 

The ore from the Greyrock vein ( 1 ,600-foot level of the Dianwnd) shows radiate Clusters 

of quartz crystals in a high-grade ore con1posed of a dense mixture of gl~.nce and borriite 

intergrown with pyrite. The bornite _is _not crystalline but. occurs in scattered grains whose 

surfn,ce indicates etching. The pyrite fron1 tlus vein shows evident shearing; the breaks are 

cemented by numerous parallel barlike n1asses of intergrown and later-deposited quartz, spotted 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE IX 

A. OUTCROP OF ANCIENT LODE, A SILVER QUARTZ VEIN, BUTTE, MONT. 

See page 83. 

B. PARROT MINE, FACE OF 1,600-FOOT DRIFT EAST . 

Shows so lid quart z- pyrite ore. See page 107. 
THE ORES. 85 

with glance. On the same level the first station north of the shaft shows a vein composed of 

bornite and pyrite replacing granite, with little or no quartz. 

'"!"'he following conclusions concerning the paragenesis of the different minerrt1s is.based on 

all the observations so far made in the Butte district: · 

Chalcocite is genern11y secondary, but in places primary. 

Enargite is generally primary, but in places in part secondary. 

Bornite is partly prirnary, but largely secondary. Chalcocite altered to bornite is very 

COUlmOn. 

Chalcopyrite is largely secondary, but is also primary in veins and is certainly primary in· 

granite. 

Tetrn.hedrite is primary, but is found 

only under conditions indicating· mineralization by later wn.ters. Fractures in it are filled 

by enargite_, glatice, and quartz, so that it 

must be_ older than these minerals. It occurs 

in the 1,600-foot level of the St. Lawrence 

mine and in lower levels. It is also found in 

the 1,000-foot and 1,200-foot levels of the 

Leonard and the Mountain View. 

fiubner.ite and wurtzite are found in the 

Leonard and West Colusa and in the Shannon 

mines, as well as· in the Gagnon. Everywhere they are associated with fault veins. 

They occur only in the deeper levels, the· 

highest occurrence being in the 600-foot level 

of the Leonard; mostly they are found from 

900 feet clown. . 

Wulfenite is found in the Anaconda vein 

in little seams in the 1,200-foot and 1,400-

foot Pennsylvania workings east of the :Mountain View fu.ul t. :FIGURE 21.-Enargite (2) and chalcopyrite (1) in a quartz-pyrite vein; 

Chalcopyrite pseuclomorphic after glance granite (3), zinc blendc (4), cmshed rock and clay (5), fluorite (6); 

OCCUrS fi,S a change fron1 glance to bornite 1,100-foot level of Leonard mine, Butte, :Mont. Natural scale. After 

Bard. ·and bornite to chalcopyrite. 

Specimens show enargite crystals entirely inclosed in a blanket layer of chalcocite and 

mossy glance; some cracks in this enargite are filled by gypsum crystals. 

Some crystals of copper glance an inch in cliame~er occur, especially in the deep levels of 

the Leonard. mine. These are commonly cracked and altered, and the cracks sometimes contain chn.lcopyrite. It is believed that these large crystals are now decon1posing as a result of 

saturrttion by mine waters and that chalcopyrite is being deposited in these cracks by descending 

ferruginous waters. 
CHAPTER VII.-ROCK ALTERATION. 

Throughout much of the district the rocks are altered both on the surface and jn the underground workings. The areas of altered rocks are more fissured and the rocks in them nlo.re" 

.shattered than those of the less altered or fresh rocks, but the later fault veins cross all of them 

.indifferently. Generally the surface rocks, both granite and rhyolite porphyry, are thoroughly 

decomposed and nett~d with irregular qu~rtz seams. In general, it may be said that the alteration is not confined to the immediate vicinity of the lodes, that it ~s not uniform, and that, 

.although it extends over a large part of the district, it is n1ost intense in the productive areas; 

fr~sh normal granite, however, is found in places between the highly altered·r~cks. 

ALTERATION OF BUTTE QUARTZ MONZONITE. 

WEATHERING. 

To determine what changes, if any, are accon1plished in the ordinary weathering of the 

Butte quartz monzonite, an analysis of a coherent but quite friable rock has been made. The 

material, which is typical of that comnwnly seen in natural exposures, is rather lighter in.color 

than the perfectly fresh rock and has a clayey odor when moist. The greenish plagioclase and 

pinkish feldspar hav.e been bleached to a dull white or w~xy tint. In the still more altered rock 

.and in the saJ;!ds formed by its crumbling the white minerals are stained by iron rust. In the 

rock analyzed the biotite is partly fresh and unaltered, but many of the. grains are dull and 

lusterless and others are altered to green chlorite; more rar~ly the· cleavages are coated· with· 

iron rust. The hornblende shows most alteration. Some of the grains are fresh, but most of 

them show masses of o(~her and are penetrated by films of it along cleavages, and the grains all 

show 1nore or less chlorite as the first stage of alteration. These changes all indicate sin1ple 

hydration and oxidation of. the rock and should accordingly be revealed in the analysis. 

The following tables show ( 1) the average composition of the fresh Butte quartz n1onzonite, 

(2) the composition of the disintegrated material, ( 3) the percentage of each constituent lost, 

:and ( 4) the percentage of each gained. 

Analyses showing effects of alteration of Butte quartz monzonite by weathering. 

Constituents. 1. Fresh 2. Altered 3. Loss(-) Constituents. 1. Fresh 2. Altered 3. Loss(-) 

rock. rock. orgain(+). rock. rock. or gain(+). 

Silica ............................ 64.03 65.14 +1.11 Potash ........................... 4.11 4.29 +0.18 

Titanic dioxide ................... .60 .59 - . 01 Soda ............................. 2. 76 2.63 - .13 

Alumina ......................... 15.58 15.63 + .05 Moisture combiuled ............... :~n-96 . 75 + .02 

Ferric oxide ...................... 1. 96 2.37 + . 41 Moisture below 110° .......... · ..... .37 + .14 Ferrous oxide .................... 2. 83 2.13 - . 70 Baryta ........................... .07 .10 + .03 

Manganese oxide ................. .11 Trace. - .11 Strontia .......................... . 04 Trace • - .04 

Lime ............................ 4.20 3.62 - .58 Phosphoric pentoxide ............ .18 .16 - .02 

Magnesia ......................... 2.15 1. 85 - .30 

99.58 99.63 ~ .... -........ -... 

The fresh rock contained a little chJorine (0.17 per cent); the disintegrated rock has none .. 

The fresh rock held 0.06 per cent sulphur (as pyrite), the altered rock 0.05 per cent 803• 

The changes in the character of the rock are largely physical, and its disintegration is due 

to the rapid expansion and contraction to which it is subjected by the extremes of temperature 

·characteristic of the climate and to the few chemical changes that result from the penetration by 

moisture of the minute cracks formed by this expansion and contraction. Yet the chemical 

-changes themselves, slight as they appear to be, aiel this disintegration, as there is an increase 

<>f volume when the molecules become oxidized and hydrated. 

86 
ROCK ALTERATION. 87 

The analysis shows remarkably small chemical alteration. It is evident also that the 

process is not the normal one of weathering, since silica is not lost. The presence of sulphides 

in the rock itself, the proximity of mineral veins, and the almost constant presence of sulphurous 

acid forn1ed in the atmosphere, which would of course acidulat~ the rainfall, probably account for 

this abnormal nature of the weathering. Under such circumstances none of the constituents 

of the rock are constant, since they could all partJy go into solution. As, however, an increase 

of silica could not take place, this substance must either decrease or remain constant, .and the 

analysis can be best con1pared by assuming it to remain constant. 

VARIATIONS NEAR BORDERS OF MASS (CONTACT ALTERATION). 

The first two analyses of the table (p. 33), the principal constituents of which are given 

below, represent the compositions of two lamprophyric contact facies of the batholith. The 

rocks grade into the granite, though the transition is rapid. More often such rocks occur as 

intrusions in the altered sediments about the border of the batholith. The rock ·of the first 

analysis might be called a diorite: It consists mainly of stringy green hornblende which appears 

to be derived from augite, of small zonally built basic plagioclase feldspars, and of a very little 

quartz. It is a nearly black, coarsely crystalline rock and is of an unusual type. It is 

intrusive in phyllites and schi:3ts on the summit of Red Mountain, 16 miles south of. Butte. 

The rock of the second analysis is fairly typical of that at the batholith contact in many 

localities. It is dark gray and granular and is rather fmer grained than the granite, into which, 

in some places, it insensibly grades. In composition it is a very. basic diorite, approaching a 

hornblende gabbro. The hornblende. is stringy and ura~itic, its pale green passing into deeper 

green and into colorless forms. Brown biotite is rare. Orthoclase is present in ~mall amount 

and only in interstices between more idiomorphic plagioclase. The latter, which shows an · 

extremely fine zonal structure, varies between labradorite and albite, and perhaps generally 

has an average c01nposition corresponding to andesine. A very little quartz is also present. 

Apatite and iron ore are present as accessories . 

. ~The rock grades into one consisting of zonally built basic plagioclase, in small idiomorphic 

cryst~ls equal in an1ount to that of the combined dark-colored constituents, and con~aining son1e 

brown pleochroic biotite and hornblende derived frorn light-colored pyroxene, remnants of 

which still rernain. 

Silica ........................... . Alu1nina ........................ . ]!~erric oxide .................... . ]!~errous oxide ................... . Mngnesia ........................ . 

Analyses of basic border ]Jhases of the Butte quartz monzonite mass. 

?!fontana .. 

49.22 

12.02 

2. 77 8.80 

9.20 

56.41 

17.62 

1. 24 3.55 

3.97 

Basic 

quartz 

diorite of 

• N~i;~fa. 

Montana. 

2 

Basic 

quartz 

diorite or Sierra 

Nevada. 

57. 00 Lime.. .. .. .. .. .. .. .. .. .. .. .. .. .. . 10. 56 8. 66 6. 24 17.46 Soda............................. 1. 90 3. 25 2. !l4 1. 12 Potash ....... : .. .. .. .. .. .. .. .. .. . 1. 70 2. 61 2. 02 5.08 1----1----1·~--

4. 06 9(i.l7 97.31 95.92 

1. Basic diorite from Hed Mountain, 16 miles south of Butte. 

2. Dioritlc rock, Hed Mountain, 16 miles south of Butte. 

3. Hock described by 'l'urner. 

METASOMATIC ALTERATION. 

The metasomatic altei:ation of the rock, called. sericitization by Lindgren, 1 consists in a more 

or less complete transformation of the hard dark-colored rock into s.ericite, the microscopically 

fine-felted variety of muscovite, which forms a softer, bleached, dull-white or gray cl~ylike or 

talcy n1ass. In this process the biotite and hornblende are the first minerals attacked; chlorite 

1 Lindgren, Waldemar, Metasomatic processes in fissure veins: Trans. Am. Inst. Min. Eng., vol. 30, 1901, p. 578. 
88 GEOLOGY AND OR,E DEPOSITS OF BUTTE DISTRICT, MONTANA. 

is formed, which also alters to sericite; the feldspars become clouded, the plagioclase suffering 

before the orthoclase, and both finally alter to a mass of sericite fibers; the iron of the magnetite 

combines with biotite and hornblende to form pyrite; and the titanite alters to rutile. Much of 

the altered rock seen at the surface is silicified, but this is a later phase, rare in depth. The 

minerals are usually attacked along cleavage planes and cracks, all stages of alteration being 

seen in the less-altered rocks. The development of kaolin is a different and later process, probably due to surface waters, and ·it is accompanied by chalcocitization. 

Under the microscope the altered Butte quartz monzonite is a mass of sericite and qunrtz. 

In intermediate stages the outline of- the feldspar crystals is still recognizable~ nlthough the feldspar itself is completely changed to sericite and the ferromagnesian minerals are indicated by 

pyrite grains clustered about remnants of chlorite. The original quartz is partly etched and 

replaced by sericite, but in all cases a large proportion of the original material is still present. 

The hornblende and biotite have altered to sericite and limonite. The rock as a whole is peppered 

with pyrite, either arranged in chains around nucleal relnnt:tnts of the altered ferromagnesian 

minerals or scattered without order through the quartz-sericite, mass. In some specimens secondary quartz is seen in threads artd saclike masses scattered through the sericite. The sericite 

itself varies in structure from fine to coarsely fibrous forms and as a whole has a mottled and 

patchy appearance. Plagioclase alters more readily than orthoclase, apatite and zircon are 

unchanged, ilmenite alters to rutile, and fluorite is introduced in a few cases. The ferromagnesian minerals, though completely altered, have left traces of their former presence by a slight 

green tinge presumably due to chlorite, by the occasional presence of limonite, and by the 

coarseness of the sericite formed as the final product of decomposition. In the change of hornblende to sericite, epidote and chlorite form as a transition product. The same is true of biotite 

and of the earlier stages of the alteration of pyroxene. In the advance.d stages of decomposition 

the rock is merely a mass of coarse and fi?e sericite fibers, laced together with abundant interstitial 

quartz. In such rocks no trace remains of the former iron-bearing minerals, but pyrite is 

abundant; apatite, zircon, and rutile are accessory. 

Analyses of the altered Butte rock illustrate the variations in the process of alteration. All 

the rocks, even the most altered, retain a clearly recognizable structure, so that there is no 

doubt concerning their derivation. The analyses were made by W. F. Hillebrand and E. A. 

Allen in the Survey laboratory. 

Analyses of fresh and altered rocks from the copper mines of Butte, Mont. 

2 3 4 6 

-------------------------!1------------------

Silica (Si02)....................................................................... 64.03 64.81 56.80 62.09 66.90 54.30 

Titanic dioxide (Ti02)............................................................. . 60 . 73 . 60 . 51 . 68 • 61 

Alumina (AbOa)...... .................................. ........................... 15.58 19.44 21.02 15.49 15.83 13.63 

Ferric oxide (Fe20a)............................................................... 1. 96 1. 82 3. 06 } 8_ 52 { 4. 37 1. 89 

Ferrous oxide (FeO ).. .. . . .. . .. . . . .. . . . . . .. . . . . . . . . . .. . . . . . . .. . . . .. . .. .. . . . . .. .. . .. 2. 83 .16 . 90 (Fe) 2. 22 

Lime(CaO)....................................................................... 4.20 .18 .35 .20 .05 7.36 

~~f~~it:J~61~!::~:::::::::::::::::~:::::::::::::::::::::·::::::::::::::::::::::::: ~J~ 5J5 !:~~ 4:~~ Tr~~3 ~:!~ 

~~fe~~~~J iio"::::::::::::::::·:::::::::::::::::::::::::::::::::::::::::::::::::: :~ 1:~~ 2:~ 1jb :~ 2:tg Waterabove110° .................................................................... 73 5.25 7.68 3.01 3.88 4.09 Man~anese oxide (MnO)........................................................... .11 Trace. Trace. Trace? None. . 71 · 

~~~g~yJJ~g~~~~~~:r::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::: ::::::: ~~: ... ~~~~~ .... ~~~~~ .... ~~~~~ ..... No~:~ Phosphonc pentoxide (P2 05) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 .10 . 05 .13 . 20 

Baryta and strontia (BaO,SrO).................................................... .11 .10 (Ba.). 05 Trace. . .. .. .. .. . Trace. 

Copper (Cu)....................................................................... . . .. . .. . . . . . . . . . .. . . .10 . 25 Present. .. ....... . Carbon dioxide (C02).............................................................. .15 None. None. None. None. 5. 50 

------------------

. 99. 93 100. 01 100. 15 102. 00 . 98. 15 100. 01 

Less 0 ...................... ,........................................................ .......... .......... .06 2.05 .................. .. 

100.09 99.95 ........ · ........... . 

1. Fresh unaltered Butte quartz monzonite. The figures given represent the average of four analyses. 2. Altered Butte quartz monzonite. Specimen from the railway cut near Wake-up-Jim mine. 

3. Altered ~anite from 3DO-foot level of Colusa mine. 

4. Sericitized granite, Parrot mine, 1,300-foot level, forms the footwall of vein; specimen 6 inches from vein wall. 

5. Altered granite, 1,000-foot level, Leonard mine, forms wall of enargite-bearing vein. 

6. Altered granite, north crosscut from 700-foot level of Original mine. 
• 

ROCK ALTJ!}RATION. 89 

The analysis of the altered rock (No.2) shows a slight increase in silica, a large increase in 

alumina, potash, and water, and a loss of almost all the ferrous iron, lime, magnesia,· and soda. 

The aln1ost total extraction of soda is a condition characteristic of the alteration of rocks by 

vein waters and in accord with the abundance of this element in hot spring waters generally. 

These analyses represent practically every important phase of the· altered granite of the 

district. The principal results effected by the alteration consist in a reduction of the rock to 

a n1i..xture of sericite, pyrite, and quartz. Kaolin occurs in only two of the a:qalyses, Nos. 3 

and 5. Calcite occurs in the specimen from the Original mine in a rock in which calcite veinlets 

are now forming. The silica. content shows considerable variation. Compared with the 

normal granite it shows no change in the kaolinized rock, is increased in the rock of the Leonard 

nune, and is decreased in all the other rocks analyzed. ·Alumina has increased ·in analyses 2 

and 3, is const~nt in analyses 4 and 5, and has decreased in No. 6. Titanium, zircoillum, and 

phosphoric acid are supposedly constant, but the presence of phosphoric acid in the mine waters 

and in the material deposited by them shows that these elements are attacked during the 

process of oxidation. Li1ne and soda have been practically eliminated from the sericitized 

rocks, and potash either remains constant or shows a marked addition. 

The alteration of the rock . from the Original mine shows that the waters have been rich 

in carbon dioxide. The alteration of the other rocks indicates waters deficient in alkaline 

carbonates, but rich in silica and iron. The evidence indicates that the alteration is similar 

to that observed in the Morenci copper deposits by Lindgren, whose study showed that the alteration at that place was due to' thermal waters. In the present instance the probable source of 

the deep-seated waters appears to be the rhyolite porphyry. Thin sections of these rocks 

examined under the microscope show that the alteration of most of the specimens has been 

normal, and that sericite, quartz, and 'pyrite make up the rock, with some specimens showing 

accessory rutile. Analysis No.6 indicates an entirely different character of alteration, and one 

which is in operation at the present time. 

Study of several hundred thin sections collected from the surface downward to the deepest 

levels showed no difference either in the character or in the intensity of the alteration. An 

attempt to outline the areas of decomposed and pyritized granite, as disclosed by the crosscuts 

from the :High Ore, Diamond, Bell, Green ~1ountain, Mountain Con., and Buffalo shafts, as well as 

by the great drainage tunnels driven across country, showed in a general way that alteration has 

been effected in broad zones of somewhat.irregular outline not conforming to the course of the 

veins. This irregularity is observed both in vertical and in horizontal sections. In studying 

this feature all changes in the granite were marked on the mine maps, and specimens were taken 

at 50-foot intervals, or nearer, where ehanges in the rock occurred. Plotting these observations, 

it is found that the min01;alizing waters have spread out through cross fissures from the main 

trunl\:: channels; thus, on the 1,600-foo't level the crosscut between the High Ore shaft and the 

Bell 1nine shows almost no normal granite. The altered rock extends for 500 feet west of the 

Bell shaft and then gradually lessens, and the rock between the Green ~1ountain and Mountain 

Con. is a fresh normal granite, with intrusions of aplitic material. As many of the zones of 

decon1posed rock are entirely lacking in veins, it is evident that the alteration has been far 

more extensive than it would have been had it been confined to the veins themselves. 

The altered rock when exposed about the surface weathers readily and crumbles. It has 

been asstnned that this is due to a change of volume, inasmuch as calculations indicate a reduction of 13 per cent in volume in the alteration of orthoclase to sericite and quartz. The formation of pyrite in veins will offset this loss of volume, but it will not be an important faqtor in the 

decomposition of the Butte quartz monzonite. · 

As sericite has not the same specific gravity as muscovite, and as the calculations are based 

on determinations of the muscovite, it is possible that the rock has visibly increased in volume, 

owing to porosity clue to the leaves and foils of sericite; and hence that the actual bulk of the 

sericitic rock is equal to that of the sericite plus its accompanying spaces and is therefore greater 

than that of the unaltered normal granite. 
• 

90 GEOLOGY AND ORE DEPOSITS ,OF BUTTE DISTRICT, MONTANA. 

Analysis No. 2 represents a rock that has been sericitized and subsequently altered by 

surface waters acidified by the oxidation of the pyrite. When collected, the rock was soft 

and coherent, sh_9wed a normal granite texture, in which th~ outlines of the original grains 

were stiH recognizable, but the dark minerals were altered to a very pale-brown lusterless mica, 

and the feldspar to quartz and an opaque white material soft enough to cut with a knife. Seen 

in thin sections under the microscope the quartz grains are slightly corroded, crackled, and dull, 

and the rock is highly altered and 9palized, with strings and patches of opaline silica replacing 

the other minerals. This is in accord with observations at other localities in which the seri-

. citized rock has been changed to kaolin by changes incident to the weathering and degrndation 

of the veins. 

ALTERATION OF APLITE. 

The alteration. of the aplite is entirely similar in nature to that observed in the quartz 

monzonite, but owing to the different composition of the rock the resulting material is somewhat 

different in appearance. So far as observed, the process of decomposition has never been carried 

far enough to prevent the recognition of the prevailing character, the greater proportion of 

quartz and its peculiar texture being quite sufficient to distinguish .it from the bleached and 

altered forms of the Butte quartz monzonite. · 

ALTERATION OF RHYOLITE. 

The rhyolitic rocks alter readily to decomposition products similar to those of the granite. 

The dike rocks are found to be largely changed to a white clayey material in which no trace 

of the original structure remains, and of which origin. can be determined only by careful study 

of the field relations. This alteration has most frequently taken place. along planes parallel 

to the walls of the dike, from which the alteration has extended outward to a degree varying 

with the density and texture of the rock. In the decomposition of rhyolite, biotite is the first 

mineral to disappear, and its alteratio~ is a·ccompanied by devitrification of the groundn1ass. 

Biotite changes to green chlorite, which in turn alters to limonite; the feldspars change to 

sericite, and eventually the entire rock is reduced to a claylike, structureless, white mass of 

sericite and opaline silica. This silica shows a tendency to gather and form irregular n1asses 

colored red and yellow by iron oxide .. 

The rhyolite porphyry has also been sericitized by the vein-forming waters. Analyses of 

the fresh and altered rock of the Anaconda dike on the 1,800-foot'level of the Anaconda 1i1ine 

. are given below: 

Analyses of fresh and altered rhyolite porphyry (toscanose) of Butte, .Mont. 

Silica .......................... . 69.95 71.01 +1. 06 P205............................. 0.10 ....................... . Alumina ........................ . 15.14 14.37 - . 77 8 ................................................................... . .38 .18. - .20 .83 .26 - .57 .56 .58 + .02 1.45 . 10 -1.35 2. 70 1. 56 -1.14 6. 36 4. 53 -1.73 

.40 ············ ..... ······· .91 ....................... . . 24 . 24 Const. ·.02 ...................... .. .37 I· ...................... . I I 

[~~--;-:: :.: :::••:- -···~ ~~d~- ••• (•;>:37•• ;• ~a;9s SrO .. ........................... .021 ....................... . 

~~~~:_.~-~~:: :·::::::::: ::::::::::::: 1'ra~g~ :: ::ij~~~~:t~: :::::::::::: 100.061 97.20 ........... . 

Ferric oxide ..................... . Ferrous oxide ................... . Magnesia ........................ . Li.nle ........................... . Soda ..•.......................... Potash .......................... . Water at 110° .................. . 'Vater above 110° ............. .. 

Ti02····························· ZnO ............................ . C02 ............................. . 

Analysis 1 represents the composition of the normal rhyolite porphyry. Tlus rock (toscanose) is not absolutely fresh, as the feldspars are crowded together, and in some places 

·show a little sericite, but the biotite is still fresh and the sample represents the least-altered . 

material of the dike. Analysis 2 represents the composition of the altered rock, whose chief 

constituents are sericite, quartz, and pyrite. The third, column represents the additions and 

losses of material incurred during the decomposition of the rock. The nnalyses were made in 

the Survey laboratory by Dr. W. F. Hillebrand. ·Examined in .thin section under the micro-
ROCK ALTERATION. 91 

scope the nltered rock (No. 2) shows sharply defined phenocrysts of quartz in a groundmass of· 

sericite. The latter nut'terial is patchy, sho.\ving faintly the outlines of fonner crystals of orthoclase. Elsewhere the sericite is fme and the fibers have no defmite order. Pyrite is abl:Jndant, 

occurring in crystals that are often surrounded by a ri1n of quartz or by a halo of fine sericite. 

Pyrite occurs 1nixecl with sericite in linear arrangement, as if derived from a prismatic crystal 

of son1e iron n1anganese 1nineral. Zircon, apatite, and kaolin are present as accessories. From 

thin sections and from analyses it is apparent that there is a positive increase in pyrite and· a 

great decrease· in lime, soda, and potash. Lime has been practically extracted; magnesia 

has gone to fonn chlorite; iron has united with sulphur to forn1 pyrite and much more has 

been added; alumina, generally assun1ed to be constant in the alteration of rocks, shows a 

loss of three-fourths per cent; the remainder is all in the form of sericite. 

Fron1 the an~lyses and from the study of the rocks it is noticed that the normal sericitizecl 

rock shows practically no opaline silica; nev.ertheless, it is well known that when carbonated 

waters attack the feldspars of an igneous rock, with the production of sericite, silica is freed. 

If open spaces exist, silica will migrate and be deposited in the open fissures. If, however, no 

opportunity ofrers for n1igration, the silica will remain and form a finely granular quartz, in 

places n1i.'.:ecl with opal and chalcedony. The silicified rocks found on the surface of the copperbearing n.rea are, however, n1ainly clue to a secondary change or alteration of the sericitizecl 

rock. In this forn1 silicn. has not been added, but has been freed from its combination with 

alun1ina and other ele1nents. 

PYRITIZATION. 

An itnportant feature of the ·alteration of the Butte rocks is the formation of pyrite. As 

already shown, the nonnal fresh rock contaii1s a very small amount of primary pyrite, estimated 

at 0.04 to 0.07 per· cent. The altered· rock, on the contrary, contains fro1n 4 to 6 per cent 

of pyrite, derived partly fron11nagnetite and partly fron1 the alteration of the ferromagnesian 

tna.terials. '!''he importance of the formation of pyrite from magnetite is believed not to have 

been previously understood. The nonnal rock, when fresh and unaltered, contains froni 0. 7'5 to 

1.25 per cent of magnetite, and this 1s the first mineral to change. to pyrite. Tiny veinlets 

fron1 one one-thousandth to one thirty-second inch in width may be seen ii1 rock which is but 

slightly altered. Under the 1nicroscope the ~Iteration is seen to extend outward fron1 these 

veinlets along 1ninute fractures. The particles of magnetite lying in the one-half to threefourths inch zone on each side of the veinlet are next entirely changed to pyrite, while 

farther away, outside of this zone, the 1nagnetite re1nains unchanged. A comparison of 

the thin se.ctions of the fresh and altered rock frmn · the san1e specin1en indicates ·that the 

pyrite replaces the 1nagnetite and also runs out into ~he rockitself in thin fihns and threads, 

marking 1nicroscopic fractures. Such filn1s of pyrite are seen both in the plagioclase n.nd 

crossi11g aggregates of biotite ·and hornblende, and the microscopic fractures are only recognizable when pyrite shows their presence. The veinlets appear to be filled not with quartz 

but with a recetnented crushed 1naterial containing. zinc blencle. As the 111agnetite of the 

originn.l rock is ahnost entirely inclosed by ferrmnagnesian minerals, the sa~ne fissure which 

afrorded access to the 1nagnetite a11d caused its pyritization would also serve for the replacement of the dark-colored1nineral. 

The amount of pyrite which could be obtained by the replacement of bioti.te, hornblende, 

pyroxene, and 1nagnetite of the unaltered rock·may be esti1nated quantitatively. The 1nineral 

cmnposition of the Butte quartz n1onzonite as detern1ined from thin sections obtained fr01n 

a surface excavntion 20 feet frmn the Parrot vein is~ as follows: 

Mineral composition of Butte ·q·uartz monzonite: . 

Per cent. Per cent. 

Quartz .......................................... 23. 17 Hornblende. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. 78 

Orthoclase ........................... : . . . . . . . . . . 18. 62 Pyroxene ...... · .............................. ·. . . l. 97 

Plagioclase.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43. 10 Magnetite.......................................... . 40 

Biotite ........ ···~--~--......................... 8. 87 Pyrite........................................... . 04 
92 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

Dividing each of these by the specific gravity of the mineral and recalculating to 100 we 

have the following volumes: 

Composition, by volume, of Butte quartz monzonite. 

Per cent. Per cent. 

Quartz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22. 55 

Orthoclase ............................. · .... , .... 17.57 

Hornblende..................................... 4. 44 

Pyroxene....................................... 2. 37 

Plagioclase ...................................... 42. 47 

Biotite ....................................... .- 9. 77 ~;t::~i-t~ ... · ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ .~ ~ ~ ~ ~ ~ ~ ~ ~ ~ : ~~ 

From these figures it can be calculated that if all the dark-colored minerals were replaced 

by pyrite, and no other pyrite introduced, the pyrite would amount to 15.36 per cent of the 

total volume. This assumption is evidently not correct, because the biotite, hornblende, 

an~ pyroxene only yield the iron to form pyrite, their remaining constituents forming other 

minerals. 

VARIATIONS IN ALTERATION NEAR THE VEINS. 

In general the country rock is less altered along the hanging wall of the veins than along 

the footwall side. At the Green Mountain mine the alteration is intense for about 25 feet from 

the hanging wall; on the foot wall side it extends for a very much greater distance, 50 feet or 

more at the mine mentioned. The country rock forming the horse betweep the two streaks of 

the Syndicate lode shows much more intense alteration than that of the vein walls. 

The character of the claylike material in. the fault slips, presumably a wet rock powder 

due to grinding of the walls· of the slip, has been determined -by analyses, which follow: 

Chemical .cornposition of vein and fault clays. 

_· ----1~-----4 ____ s 

Silica ..................................... 1 . . . . . . . .. . . . . . . • • . . 51. G 45. 46 51. 7 51. 3 58. 5 46. 96 66. 9 71. 01 

Alumina ............ ,........................................ 26.6 39.01 a 31.4 . . . . . . . . . . a 26.4 a 27.86 15.83 14.37 

~~~~~~~·:.·.·. ~::::: ::::::::::::::::::::::::::::::::::::::::::: Undi.~ Tr~cf" 1. 7 . .. . .. . . . . .. . .. . . . . . Tr~e9 Tr~5.5 : fg Soda.......................................................... . 2 Trace. · · .... · :i · · "i'~ace·: · · · .. · · :i · :8 . 08 1. 56 

Potash....................................................... 5. 1 'l'race. 8. 2 2. 34 4. 5 3. 67 . 03 4. 53 

H20-........................................................ 1. 4 .S ····b·6·._·4·· c9". s8 6 26". 92 ··b·1·2.·9·5·· "87 H20+ ................................................ :....... 9.6 b 13.98 - 3.88 

a Includes a little iron and possibly P205 and Ti02. b Ignition. c Includes sulphur from sulphides. 

1. Clay from fault slip in main vein, Original mine. 

2. Clay fifth floor above 1,400-foot level· east; hanging-wall side of horse and foot wall of vein; Anaconda mine. 

3. White clay from glance ore, Middle ledge, Anaconda mine, 1,600-foot level. 

4. White clay from vug, 1,200-foot level, Pennsylval}ia mine. 

5. Clay 1,800-foot level; Anaconda mine, O'Neill ledge fault; finest float analyzed. · 6. Clay 1,400-foot level, Anaconda mine, O'Neill ledge fault; finest float analyzed; contains 4.37 pyrite and 0.18 Fe20a+0.26 FeO. 

7. Altered granite of an enargite vein, Leonard ore body. 8. Altered rhyolite porphyry, 1,800-foot level, Anaconda mine. 
... 

. CHAPTER VIII.-GENESIS OF THE COPPER ORES. 

Study of the Butte ore deposits naturally involves speculation concerning the genesis of 

the ores and particularly concerning the ultimate source fron1 which the copper has been derived. 

It is therefore advisable to review the evidence afforded by the n1ines and to see what conclusions may be drawn from the facts. 

PRIMARY SOURCE OF THE COPPER. 

CONCENTRATION FROM THE WALL ROCKS. 

The wall rocks of the veins contain copper. Chemical analyses of fresh unaltered material 

show that· the Butte quartz monzonite holds copper, though in less amount than the altered 

rock. 

PYRITE. 

Ahnost all specin1ens of the fresh Butte quartz monzonite show a little pyrite, which, by 

3tudy of polished surfaces and of thin sections under the microscope, is shown to be primary 

and an original constituent of the rock. Studies by Cross, Iddings, Pirsson, and Washington 1 

show thn.t pyrite is a constant constituent of the Butte rocks to an extent of 0.6 to 1 per cent. 

Quantitative tests show that this pyrite contains copper. 

· CHALCOPYRITE IN THE WALL ROCKS. 

The presence of primary chalcopyrite in the Butte quartz monzonite was first brought to 

the writer's attention by H. V. Winchell, who forwarded to him a polished specimen of the rock 

fron1 the Elk Park quarries, a few miles fron1 But.te. Chemical tests showed this specimen to 

contain chalcopyrite intergrown with primary rock minerals, and a thin section, examined under 

the 1nicroscope, showed the rock to be fresh and unaltered and the copper mineral to be indigenous. Reexamination of the rocks in the vicinity of the mines resulted in the finding of 

nun1erous specin1ens, which had been previously 1nistaken for pyrite. On the whole, however, 

chalcopyrite is present in few places and in scanty amount: 

To tllis general staten1ent one notable exception n1ust be made. The Butte quartz InonzOilite along the base of East Ridge in the vicinity of Colun1bia Garden shows a tendency to 

shade into aplite, with corresponding basic n1odi:fications of the magn1a. In the basic rock 

pyrite is absent or nearly so 1 but chalcopyrite is abundant. This is best seen in the material 

. fr01n the deep workings of the Altona, l\1ontgomery, and Bullwhacker nrines. So abundant .is 

the nrineral that n1uch of the rock contains between 0.5 and 1 per cent of copper: It is notable 

that in this section of the district copper oxides and carbonates are found in the altered surface 

rocks, but that chalcocite is a minor constituent, if present ·at all. The chalcopyrite is largely,. 

if not wholly, prirnary and shows a marked and constant association \vith the augite and hornblende as well as intergrowths with n1agnetite, this last being characteristic of the pyrite. 

This occurrence of chalcopyrite as a primary rock constituent is not unique, as it has been 

previously observed by Lindgren in the rocks of the Grass Valley district, California, 2 and has. 

been reported by Boutwell as probably present in the rocks of Bingham, Utah. In n1ost places, 

however, where present, it has been assun1ed or prove'd to be a secondary result of agencies 

altering the rocks. 

t Qnnutltatlve cll\Sslficatlou of igneous rocks. 

D rl'ho gold quartz veins of Nevada City and Grl\Ss Valley districts, Cal.: Seventeenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1896, pp. 36, 94. 

93 
94 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT J MONT AN A. 

COPPER IN BASIC MINERALS. 

To determine whether the rocks contain any copper other than that belonging to the 

sulphides just :rioted, a san1ple of the fresh and perfectly unaltered rock, free fr01n sulphides, 

from the Walkerville quarry was examined in detail. Rock weighing 136.6 grains was crushed, 

passed through a 100-mesh sieve, and separated as follows by Dr. E. T. Allen in the Survey 

laboratory: First part, magnetic portion, 2.7 grams; second part, mica, hornblende, etc., 9.9 

grams; third part, quartz and feldspar, 124 grams. The nlica and hornblende were separated 

from the quartz and feldspar by Thoulet solution and the magnetic portion by the use of a 

horseshoe magnet. These samples when carefully tested showed that the rock,. as a whole, 

was 0.006 per cent copper, portion No. 1 was 0.009 per cent copper, and portion No. 2 was 

0.047 per cent copper. In other words, the percentage of copper in the basic minerals was 

nearly eight times as great as the percentage in the whole rock. · Expressed quantitatively, 

the first or magnetic portion contained 0.0243 gram copper and the second or basic portion 

0.4653 gram, leaving the remainder (0.33 gran1) to be contained in sulphides in the quartz 

and feldspar. l'he basic minerals, or 6.5 per cent of the rock, contained over one-half the copper 

in the sample. · 

It is therefore believed that the Butte quartz monzonite carries copper, present both as 

chalcopyrite and associated with or in the ferromagnesian silicate. 

SUMMATION. 

Although it is known that the unaltered Butte monzonite contains copper it is not probable 

that the veins derived their metallic contents from the leaching of the adjacent wall rocks, for 

if this were true the altered rocks must carry less copper than the fresh ones. I-Iundreds of assays 

of wall rock and intervein rock made by expert chemists for use in the various lawsuits over 

mining rights have as a rule shown the presence of a greater amount of copper than is present 

in the fresh rock. This argues that the hydrothermal alteration of the rocks not only formed 

the veins by metasomatic replacement but also mineralized the wall rocks to a slight degree. 

VEIN FORMATION. 

All the evidence seems to point to rock alteration as an early phase of vein formation. 

Mining operations have shown that the alteration is similar in character at all depths yet 

attained throughout the copper area, and that it has been carried further quantitatively in 

the ·upper levels; that is, intervein rocks that are merely altered at lower levels are converted 

to ore in the upper levels of some properties. · 

· This alteration is solfataric and is attended by the absorption of potash and sulphur from 

the vein solutions and the formation of pyrite from the magnetite and iron of the ferromagnesian minerals. Sodium and some silica was lost and, as already shown (p. 87), the granite 

of the district became a mass of quartz and sericite peppered throughout with pyrite cubes 

and particles. The fault movements which broke and displaced the earlier veins also strained 

the country rock and, with the shifting of the fault blocks, produced numerous fractures and a 

netted jointing, in which circulatmg waters were able to extend downward to depths of 1,000 

feet or more. "As a result surface waters are not entirely confined to the veins but, deriving 

their mineral contents from the oxidation of the upper portion of the veins, pass outward along 

the fractures into the country rock, where their copper content is reduced by the pyrite of the 

rock. This condition has led to much controversy in mining litigation, as it is possible in ·the 

upper levels of many of the mines to obtain high assay values from the altered rock between 

the veins, ariel these values when platted have been used in an attempt to prove an extension 

of the veins, although no vein structure proper might be recognizable. In tile Gagnon mine 

altered rock between the Steward (or Gagnon) fault vein and the main ledge was carefully 

sampled and was found to contain not only copper glance, but quartz, pyrite, and sphalerite. 

The samples showed from 0.4 to 1. 7 per cent copper, from a trace to 10 ounces per ton in silver, 
GENESIS OF THE COPPER ORES. 95 

and from 8.6 to 31.6 per cent zinc. , Such rock is properly designated ledge matter, and together 

with the bounding veins constitutes a lode. 

The earliest copper veins of the Butte district are the east-west quartz-pyrite veins that have 

been formed along lines of fracture by replacement of the country rock. In the eastern part of 

the district the transition from vein to wall rock is inclis.tinct, the mineralization fading gradually 

into the wall. In the western part the evidence is complicated by the presence of fault slips 

and clay selvages. The observed facts show that the primary ores. were formed by hot ascending solutions, which not only attacked the rocks and replaced them by quartz and pyrite (see 

fig. 22), but also formed the broad zones of decomposition or sericitization of the granite that 

constitute the most pronounced feature of the mineralized area. In the region about the 

Rarus mine, where mineralization has been intense and the veins are close together, the entire 

country rock is altered, pyritized, and more or less impregnated with copper (fig. 23); practically 

no fresh unaltered granite rem runs. Farther north the belts 

of decomposition are separated 

by narrow strips of unaltered 

granite, which becomes ·increasingly abundant northward until 

ill the vicinity of the Black 

Rock and Niagara claims the 

rock shows well-marked jointing, 

the dominant fissures running 

parallel to the veins and sheeting the rock. In this locality the 

mineral veins are merely mineralized joint planes and the interveningrockis butslightly altered. 

As already stated (p. 87), 

this solfataric decomposition 

antedated the fault fissures. It 

is true that the latter have been 

accompanied by more or less rock 

decomposition, but it was neither 

as in tense nor as widespread as 

that of the earlier period. The 

earlier quartz-pyrite lodes carried 

comparatively little copper in the 

primary vein filling. In fact, 

9 I I I I 2,51nc.hes 

FIGURE 22.-Veinlets of chalcocite (copper glance) (2)netting p'yritized granite (l),on 1,000-

foot level of Leonard mine; one-tenth natural scale. Only the l~rger veinlets are shown, 

the small ones being too numerous for representation. (Sketch by Bard.) 

many of these veins were unfractured and consequently not enriched; the vein filling. is unworkable, consisting of a mass of pyrite and quartz, carrying less than 1 per cent of copper. The 

evidence indicates, however, that the gradu81 weathering and degradation of these great masses 

of extremely low-grade material has furnished the copper for the dow:Q.-seeping waters which 

have formed the ore bodies that have made these verns the greatest copper producers of the 

en tire world. 

GENETIC RELATION OF THE RHYOLITE PORPHYRY TO THE COPPER. · 

Several observers who have investigated the Bu~te copper mines, particularly those who 

know the1n best, believe a genetic relation to exist 'between the rhyolite porphyry and the ore 

deposits. It is, however, difficult to adduce convincmg grounds for this belief, though the fact 

that the porphyry occurs in dikes whose course corresponds in general to that of the principal 

veins, gives some basis for assuming that it was the ore-bringer. The rhyolite porphyry, however, is found only in the eastern portion of the copper area, where it is younger than the granitic 

rocks and older than the veins, since even the oldest veins cut through it. It has been altered 
96 GEOLOGY AND ORE DEPOSITS OF BUTTE· DISTRICT, MONTANA. 

by sericitization, but less profoundly so than the granite. Moreover, where the veins cut 

through the porphyry, they are lean and narrow; and the big ore bodies of the Parrot, Gagnon, 

Steward, and Syndicate mines are not very near any known bodies of it. The porphyry may 

possibly have supplied the mineralizing vapors which altered the rocks and which caused vein 

formation, but no such evidence has yet peen found as that observed by Lindgren in the Morenci 

(Ariz.) deposits, where the quartz phenocrysts of the porphyry contain fluid inclusions similar to 

those in the vein quartz. 

GENETIC RELATION OF THE APLITE TO THE COPPER. 

Careful observations throughout the mine workings have failed to establish any relationship between the occurrence of aplite and ore or to show that the aplite has played any partFIGURE 23.-Quartz veinlets in silicified granite; 1,000-foot level, West Colusa mine; natural scale. The sacllke terminations of the velnlets are 

typical of replacement. Pyrite appears later than quartz, and chalcocite fills minute vugs in veins. (Sketch by Bard.) 

whatever in the mineralization of the district except to act as an uncongenial country rock 

which fractures with difficulty and in a different manner from the granite, and, not being easily 

replaceable, always serves to impoverish the veins. In the northern tier of veins the aplite 

appears to be much more abundant in the, deeper levels than on the surface, but its relationship 

is the same and no conclusions can be based on its presence. The mere fact, hQwever, that the 

aplite is abundant 2,000 feet or more beneath the surface is conclusive evidence that the aplite 

bears no definite reiation to the former cover of the granitic mass, and that consequently the 

theory advanced by Lawson for the Ely (Nev.) deposits, is not applicable here. 
GENESIS OF THE COPPER ORES. 97 

CONCLUSIONS. 

The question as to tne source of the copper in the lodes is ·complex, as the amount of copper 

present in the altered rocks is in excess of that in the fresh rock and there is no body of leached 

rock from which this excess of copper could have come. The evidence seems to indicate that 

the alteration of the rock and its impregnation with copper are due to a common cause, and that 

copper has been added to the rock, together with silica and iron, the two other constituents 

JVhich are so abundant in the altered granite. 

Though the evidence is not conclusive, it is believed to indicate that the copper and other 

metals of the quartz-pyrite veins are derived from magmatic emanations coming from a deepseated mass of igneous magma. The rhyolite porphyry intrusion appears the most probable. _ 

A second and later mineralization occurred at the time of the rhyolitie eruption, forming the 

silver veins u.nd the orcs of the Blue vein and other fault vein. series. 

CONCENTRATION PROCESSES. 

UNDERGROUND WATER. 

AMOUNT. 

The annuu.l precipitation in the district is meager, averaging less than 20 inches, and the 

run-off is great, owing to the bare and steep slopes, so that much of the local rainfall and snowfall 

either runs off or is evaporated before sinking 1nto the ground. The disintegrated granite and 

the sandy debris, however, form an extremely porous receptacle, catching and holding much of 

the rainfall. :Moreover, the district is depressed compared to its former altitude above sea 

level, so that the old valley that held the trunk drainage is now filled to! a depth of several 

hundred feet with debris, making a vast natural reservoir. These facts account both for the 

water encountered at the shallow depths in all the mines first opened n.nd for the large amounts 

of water pun1ped fTom the deep levels, inasmuch its the fault fissures form open channels by 

which the deep-seated waters have access to the mine workings. 

MOVEMENT OF UNDERGROUND W ATE H.. 

Practically itll the mine waters .are actually descending (fig. 24). In a few places rising' water 

was encountered at the deep levels, tor instance, on the 2,200-foot level of the :Mountain Con. 

mine and on the 1,600-foot crosscut of the Anaconda (where uprising waters were encountered 

some 2,000 feet fTom other workings), but the outflow diminished in a few weeks and finally 

all but ceased, indicating that the area from which the water came was probably drained. The 

long crosscuts driven to connect various mines all indicate descending water. In opening new 

ground along. a vein the workings, no matter how wet at first, gradually dry out, and the minerals indicate arrested deposition of material. These facts' all show that the underground 

waters are descending. Their distribution, however, is not as uniform as would be natural if 

the ground were uniformly or equally fissured. The long crosscuts north from the Speculator. 

mine cross a belt of ·dry granite before encountering the second wet belt, in which the Jessie 

vein occurs. 

In the Green :Mountain and :Mountain Con. veins the mine waters are all descending. In 

opening up new ground the a1nount of water always seems to be proportionate to the block of 

ground opened up-thn.t is, the ground between the new level and the old working above. If 

tlie waters were ascending the deepest level would always be wet, whereas, in fact, it becomes 

quite dry ·soon after being opened; water comes into it only at the he}tding where new ground 

is being opened. In the 2,000-foot level of th~ :Mountain Con. the vein nt the "face" and 

near-by shows by its very distinct watercourses, its· loose and open texture, its content of 

skeleton crystals in vugs, etc., that it has been but recently the seat of descending currents of 

water which have both dissolved out mineral matter and deposited mineral matter. The 

quartz is the latest-formed mineral, but bunches of glance occur with it. The ore body shows 

90427°---~o. 74---12------7 · 
98 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

skeleton-like residuals (~) of rich mine~al and nests of newly deposited mineral. As the face 

dries the quartz loses Hs vitreous character and assumes a frosted, somewhat opaque appearance resembling g~ound glass, similar to the siliceous h~t-spring deposits. of the Yellowstone, 

notably the sinter deposits. of the Coral Spring at the Norris Geyser Basin. This hot-spring 

deposit when removed from the water is a pellucid glassy substance, but on exposure to the 

air for a few week~ becomes dull and opaque and ge~erally cracked, through changes incident 

to the loss of water. An attempt was made to sketch the face of the 2,000-foot l\1ountain · 

~~~I 

Pyrite 

~ 

~ 

Quartz• 

Glance 

~ 

r-::::-::1 

~ 

Clay 

[2J 

Fissure 

0 2 3 Feet 

FIGURE 24.-Successive fracturing of pyritized granite, 1,000-foot level of 

Leonard mine. The earliest fractures are filled with pyrite and quartz; 

these are broken by later fissures now filled by glance, and these in 

turn cut and dislocated by joint or movement planes carrying water. 

(Sketch by Bard.) 

Con. level, but it was abandoned owing to 

the excessive amount of detail and the impossibility of showing it for the entire vein. 

Its ap:p_earance was exactly that of a satura.,teabody fron1 which the water had suddenly drained away. 

The few records of "first water" for the 

older mines appear to locate it at about the 

upper limit of the sulphide ores. This upper,. 

limit varies greatly, ranging from about 20 

feet to 400 feet, being in part independent 

of the surface level but varying with the 

degree of fracture. 

In the granite, the network of lesser 

fractures, and the veins and faults are 

apparently all filled With water and serve 

as a vast reservoir. That this water has a 

natural level not far below that of the 

neighboring valleys is evident, and that it 

is moving slowly downward can not be 

doubted, though it can not be readily 

proved. The conditions of mineralization 

afford some evidence; and in the East Ridge 

region, where higher collecting ground exists, 

the springs became dry when the Altona 

mine was pumped out to a depth of some 

200 feet, proving a connection between the 

mine waters and surface drainage. The 

drying out of the upper workings of some 

of the mines 'when the surface seepage is eliminated shows that in these mines the waters 

come from above. In short, all the evidence shows that the waters are surface waters seeping 

downward. They come, however, from a broad area, and not from the surface of the Butte 

mines alone. 

OUTCROPS. 

Surfac.e waters decomposing the abundant pyrite of the Butte quartz monzonite, with the 

form.ation of sulphuri~ acid and fe:rrous sulphate, have produced most in1port~1.nt results not 

only in the. country rock itself but also in the mineral veins. Oxidation processes in the sericitized granite produce n1ainly kaolin and free silica, but in the veins and in the mineralized 

rock adjacent to them they attack the unoxidized pyrite and any other sulphides that are 

present. At the same time the ferrous sulphate oxidizes to ferric sulphate, which also attacks 

the pyrite and other sulphides, and the series of chemical changes thus initiated usually results 

in the formation of limonite. 

At Butte iron caps are wanting in the copper area, but it is probable that. they were formed 

during the ear~ier stages of alteration and removed by subsequent erosion. ·At one point on 
GENESIS OF THE COPPER ORES. 99 

the East Colusa vein there is a gossan outcrop, but in general the copper veins have inconspicuous or ill-defined outcrops. The recognizable outcrops show but. little limonite or other 

iron ore, and in n1ost cases but little copper staining. The Parrot and Original claims showed 

an absence of vegetation, and scattered fragments of copper carbonates were pron1inent along 

its course. The Syndicate lode has a scanty scattering of carbonates and oxides. The other 

great veins of the camp on Anaconda I-Iill show no indication of the copper below, their upper 

portions consisting of more or less crackled or broken, somewhat rusty quartz, rather solid, 

though often showing pitting due to the oxidation of pyri'te. This indicates that the waters 

seeping downwn,rd soon lost their oxygen and tha.t subsequent changes were due to ferrous 

sulphate n,nd dilute sulphuric acid. Such waters attack other sulphides, an.d the oxidation of 

blende, ·glance .. chalcopyrite, etc., is a small but far fron1 negligible factor in the chn,nges that 

result. 

Th~ absence of an iron gossan on the outcrop of the veins, or between the surface and the 

sulphide zone, shows that the upper part of the vein now seen is not the residual material of 

a leanfpyritic ore. It is.therefore probable that the conditions here are similar to those observed 

at ~Iorenci and ~o some extent at Bingham, and that gradual erosion worked down and removed 

the true gossan, thus exposing a secondarily enriched part of the vein to oxidizing waters, the 

copper going into solution and seeping downward; the iron having already been removed by 

replacement no limonite was left to mark the change. 

At Rio Tinto in Spain the ore body, which consists of solid pyrite devoid of silica, carries 

films and specks of glance in the pyrite. In this ore the copper is readily leached out by water 

alone, and in fact water is now used for the extraction of copper.1 The reactions involved are 

simple; ferrous sulphate, cupric sulphate, and sulphuric acid are forn;:t.ed by oxidation, and 

the abundant pyrite keeps the iron in a ferrous state, so that no gossan is formed. It is evident 

that si1nilar conditions prevail in the enriched portion of the Butte veins. At any rate the 

vein outcrops can not always be definitely located at present. The quartz-pyrite veins 

are often distinct, though not conspicuous, but the glance-enargite veins in· altered granite 

can rarely be detern1ined in outcrop; where uprtm.ses have been driven to find their apex, it 

is found to consist merely of kaolinized granite cemented by stringers of quartz. Indeed, one 

may infm~ fron1 the absence of limonite that the barren quartz found between the surface and 

the big ore bodies is the result of oxidation of chalcocite and pyrite only. 

.. The descending waters became charged with ferrous, cupric, and zinc sulphates and have 

an acidic reaction. All three of these salts are easily soluble in water and all three are carried 

by the n1oisture of the air circulating in the mine workings. Such air· deposits its n1oisture by 

chilling, and as n. result n1any of the old mine workings are coated by efflorescent deposits of 

zinc, iron, and copper sulphates. · 

It is in1portant that the exact nature of the mine waters be understood, as it is evident 

fron1 the field relations that the rich ores, the bonanzas· of copper glance which have made 

the district so famous, are the result of descending waters either wholly or in part. 

COl\I.POSITION OF l\IINE WATERS. 

By W. :F. HILLEBRAND. 

In the following table the analyses represent practically every type of· water found in the 

underground workings. The waters represent a wide variety in derivation and in composition and the analyses n.re therefore of more than ordinary interest. The waters analyzed were 

collected by G. W. Tower, then of the Geological Survey, but not all at the same time. Samples 

A to E were collected and analyzed in 1897 and I and Fin the winter of 1901-2. Samples I 

and ir were filtered in the n1in.e into clean glass-stoppered bottles and promptly sealed. It is 

not known whether the others were :filtered or no.t, but the analyst's notes. show that the 

I JO:ilCS, c. n., Trans. Am. Inst. Min. Eng., vol. 35, 1905, p. 3. 
100 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

bottle containing A was closed by a cork stopper, and the inference is plain that the bottles containing B, C, D, and ~ were similarly closed. 

In Washington it was found that sediment varying in color and amount had formed in 

each sample. The solution and sediments were analyzed separately except as to the free sulphur 

deposit from sample A, but the data thus ·obtained are combined in the analytical tables, since 

the sedimentary matter was originally in solution. The analyst has considered in his calculations the iron to be in a ferrous stat~, except in E, where it was found to be ferric. Where the 

bicarbonate radicle· appears the amounts have ·been calculated to meet the requirements. 

Samples E and F ar~ acid waters and naturally carry no carbonates. Samples I and D showed 

by analysis enough carbon dioxide to form bicarbonates with all of the available metals and 

to leave.an excess of free carbon dioxide. A trace of bicarbonate with much free carbon dioxide 

is indicated in ·A, but in this case there was considerable reduction of sulphates after bottling. 

Samples B and C contain both carbonates .and bicarbonates and as it was impossible to fix the 

relative amounts neither the normal nor the bicarbonate radicle is entered in the analytical 

summation. Where total carbon dioxide is represented in excess of. that required for bicarbonates. the excess is assumed to be free: Because of evident decomposition in sample A, as 

evidenced by the character of th~ deposit formed after bottling, no great importance is to be 

attached to the calculated values for the bicarbonate and sulphate radicles. 

. ;No better illustrations can be offered of the futility of making detailed analyses of waters 

that have not been collected hi an experienced chemist, who alone can be depended on· to 

observe all necessary precautions. The use of a cork stopper, for instance, makes impossible 

any conclusion as to 'the cause of the chemical changes in sample A. The origin of much of the 

deposit in F is likewis~ put in doubt by the fact that common gray filter paper was used for 

filtering the water in the mine. 

Sample I, from the 2,200-foot level of the Green Mountain mine, was taken to represent as 

near as practicable the composition of the water of the, deep levels of the district. It is from 

a fissure in normal granite remote from any known veins and far from any old mine workings, 

coming frorp. a fissure tapped by a newly opened crosscut the day before the sample was taken. 

It is a very weak water carrying sulphates and some carbonates of calcium and magnesium, 

sodium and potassium, stated in their relative order of abundance. Its specific gravity at 

15° C was 1.00105 and its reaction faintly alkaline. The water is unlike river water in that 

it contai~s calcium sulphate in large amount. Sample A ~arne from the 220-foot south crosscut of the Glengarry mine and represents water from the upper part of the earth's crust in the 

vicinity of the workable· ore deposits. The water deposited som(3 ferrous sulphides and sulphur. 

Sample B came from the 800-foot level west of th~ Anaconda mine. It is faintly alkaline and 

may be fairly assumed to represent the water descending through that great vein at a point beyond 

the reach of oxidizing influences. Sample C, taken from the Gagnon, on the 1,800-foot level 

1,125 feet south of the shaft, is also a rock water. and not a vein water in the ordinary sense. 

SampleD from the Nettie mine, taken from th~ 300-foot level at the end of the crosscut north, 

represents the composition of the waters found in the silver mines. Sample E, from the 1,200-

foot level of the crosscut of the St. Lawrence mine 90 feet fron1 the shaft, js faintly acid and repre-

.sents the waters descending along the quartz-pyrite veiri. Sample F from the Mountain View 

mine, second level, is exceptional; it is perfectly clear, deep blue in color, and comes from surface waters seeping dow:ri from old stopes. The water has formed stalactites and stalagmites of 

perfectly clear and transparent chalcanthite, showing that it is probably a saturated solution. 

In comparing the analyses taken from these different points .and representing such very unlike 

conditions; there is a wide variation observable in all the ~onstituents, particularly in the amount 

·of zinc, alumina, and iron. S9dium chloride is present in small amount. Aluminum is absent 

from five of the samples.· Iron. manganese, and 7-inc occur in these five in small amounts. 
GENESIS OF THE COPPER ORES. 

Analyses of ttnderground waters from the mines of Butte, ·Mont. 

[Parts per million. Analyst, W. F. Hillebrand.) 

I. A, B. c. 

101 

D. E. F. 

----------~--------------·1---- ------------------------ 8109.... .... • .. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 23.2 27.2 36.1 29.5 55.8 47.7 67.4 

'1:109 ••••••••••••••••••••••••••• ·•••• ••••••••••••••• •• ••••• ••••••••••••• ••••• ••••• •••••••••• •••••••••• ••••• ••••• •••••••••• None. Trace. 

Ca...................................................................... 151. 2 92. 7 49. o 512. 1 39.1 132. 5 307. 7 

~~~: ·. ·. ·. ·.::::: ~:::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 2~: i ~~: ~ lg: ~ 1~~: ~ ~: ~ ~~: ~ 14~: ~ Na...................................................................... 16.2 176.9 11.1 82.8 30.1 39.6 41.7 

Ll ............... : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trace. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trace. 

7.n ............ :......................................................... . 3 1. 8 1. 9 None. Trace? 852.0 411.2 

Cd .............................................................. ~....... . . . . . . . . . . . . . . . . . . . . . .• . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.1 ......... . AI...................................................................... None. . .................... ~........ .......... 83.5 85.2 J~o". . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . .. .. . . . . . . . . .. .. .. . . .. . . . . . . . . . . . . .. . 1. 8 1. 4 . . 9 . 4 • 4 . .. . . . . . . . 49. 8 

l•'o"' .............. ,..................................................... . . . . . . . . . . . . . . . . .. .. . .. . .. . .. . .. . .. .. .. . .. . .. .. .. . 159. 8 ........ .. 1\fn...................................................................... .5 Trace. 2.5 1.4 .8 12.0 13.2 

Co........................................................................................................................ .5 4.6 

Nl...................................................................... .......... .......... .......... .......... .......... .......... 3.5 

Cu . .. .. .. .. . .. .. . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . .. .. .. Trace. • 4 Trace. '!'race. None. 59. 1 45, 633. 2 

Sn ....................... : .............................................................................. ·····'···· .......... 17.0 ......... . Ph .................................................................. :... . . . . . . . . . . Trace. '!'race? None. None? .................. . AsO............. ... ..... ... ...... ........ .................... ..... ...... Faint. '!'race? '!'race. None. None. · 'l'race. 

vo...................................................................... Trace. Trace. 'l'raco. ·Trace. '!'race. '!'race. 1. 5 

SO...................................................................... 40G. 5 544.7 90.6 593.4 67.2 2, 672.0 71, 05.1. 3 

Cl...................................... ..... .. .. .. . .. .. .. .. .. .. .. .. .. .. .. G. 8 118.5 11.8 842.8 15. o 13.0 17.7 

Organic 1natter .................... ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Consid. Little. None. Trace. Considerable. 

HCOs ......... _........................................................... G~::: ~~r~:~·o ~:~.7 2,~:6.4 ::~:: .. ~:~~~:~-~-~~;:~~~:~ 

~J'otal C02 ................................................ :.. .. .. .. 7G. 5 167.2 a 59.9 a 73.3 102.0 23.7 9. 0 

a Calculation shows lnsnfficlont carbon dioxide In tho bicarbonate state to satisfy the bases, hence both normal and bicarbonates arc to bo 

nssumcd us prosont and the summation mlscd to correspond. 

I. (lrcon Mountain mlno, 2,200.foot crosscut south; from normal granite not nmu vein. Specific gravity at 15° C., 1.00105. Reaction faintly nllmllno. 

A. Glengarry mine, 220-foot crosscut south; temperature 70° F. when collected. Very. slightly alkaline. mack deposit containing FcS, 

much free S, and perhaps 7.nS, since practically all tho Zn found was in tho sediment. Sediment black and slimy stopping the filter pores and turnln~ brown by oxidation before the filtration was complete. 'I~ho frco sulphur was presumably duo to tho decomposition of sulphatcs by organic matter. Whether this organic matter came from tho cork stopper or was already present the analyst was unable to determine. 

or tl~~· t~~~~~n~~·~llll~l~\i 83?o tr;;n~\'OSt. Very faintly alkaline. Deposit dark brown, probably !rom manganese, of which it contained one-fourth' 

C. Oa~non mlno, 1,125 foot from shaft. Very faintly alkaline. Nearly all tho iron but no manganese deposited. D. Nottlo mlno, 30:>-foot crosscut north. Very faintly alkaline. 

g, St. Lawronco mlno, 1,20Q.foot crosscut south; 90 feet from shaft. Very faintly acid. Iron all in the ferric state; over one-half of It (but no man~anoso) In a coplons reddish-brown deposit found in tho bottle. Titanium, antimony, arsenic, lead, and bismuth cc,uld not bo detected. 

'l'ho source of tho cadmium anti tin is a mystery. ~I:ho tin was all found in the deposit in a condition readily soluble in hydrochloric acid. Over 

hair tho Iron was found in the deposit, where it oxistod as a basic sulphate. 'l'he excess of basic over acid radicles may be accounted for, In 

part at least. Possibly, however, tho value given for zinc is somewhat high. F. Mountain View mino, second love!; slow drip, forming chalcanthito. Specific gravity atl5° C., 1.1317. Deposit reddish and very flocculent. On treating It with l1ydrochlorlc acid a voluminous network of fibers was left which suggested fiber from the coarse filter paper that had 

boon used in collecting tho water in tho mine. Bowovcr, after standing In the glass flask in the laboratory for a few weeks tho freshly filtered wator began to deposit a whitish flocculontscdhncnt which gradually becrune reddish from iron. Except for the iron it was found to be of organic nature and of fibrous structure as If an organized growth. 

The analyses give no proof of the presence of cuprous sulphate. Winchell has, however, 

found it in testing the mine waters, and his artificial production of glance depends on its presence. 

The chlorine content varies widely in the different waters. In analyses I, B, D, E, F, it is 

no greater than in many surface waters. In analysis A it is high-for a surface water, but not 

abnormal. In annlysis C we have a water in which chlorine and sulphuric acid are very high fi:nd 

wholly unlike surface water, there being large amounts of sulphates of calcium, magnesium, 

sodium, and potassium. . 

Analyses E and F are the only ones showing appreciable amounts of copper, the latter 

being a saturated solution of copper sulphate. Analysis E is abnormal. Zinc sulphate is the 

most abtindant salt present, with calcium, magnesinm, and alkaline sulphates in lesser quantity. 

The amounts of tin and cadmium suggest that the waters have attacked some pumping machinery 

before collection. Iron, aluminum, and manganese sulphates are present. I • 

SECONDARY ENRICHMENT. 

GENERAL PROCESS. 

The most important work of the sulphate waters is the formation of copper glance by the 

action of cupric sulphate upon pyrite and to a limited extent on zinc blende. This ·process, 

now generally known as secondary enrichment, 1 depends on the reduction of the metals from. 

sulphate sqlutions by pyrite. The order of the affinity for the common metals for sulphur is 

I Wood, W. H., Bull. Gool. Soc. America, vol. 11, 1900, p. 179. Emmons, S. F., Trans. Am. lust .. Min. Eng., vol. 30,1901, p. 177. 
102 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

as follows: Mercury, silver, copper, anti:J;Ilony, lead, zinc, iron, arsenic, and manganese; the 

salt of any metal in this series will be decomposed by the sulphide of any succeeding metal 

and the first metal precipitated as sulphide. In complex solutions the secondary sulphides 

should be deposited in the following order: Argentite, chalcocite, bornite, chalcopyrite, galena, 

zinc blende, with pyrite at. the bottom .. In some silver veins an approximation to this exists, 

resulting in a vertical distribution of the ores in depth. In the Butte copper n1ines the silver 

has probably formed argentite, which has altered to native silver, as frequently seen in the 

upper levels of chalcocite ore bodies. The relative amount of silver is small, and iron, copper, 

zinc, and arsenic are abundant. The limit of secondary deposition depends on the fracturing 

and circulation, and this is not uniform, therefore the simplicity of the operation, as outlined 

above, does not prevail in the underground workings. 

FORMATION OF CHA:T,COCITE. 

Of the secondarily fonned minerals copper glance is the n1ost important (fig. 25), it being· 

· e~tin1ated that up to 1906 

three-fourths of the copper 

production of the district 

came from this n1ineral; at 

present it furnishes about 

one-half. The glance is 

not necessarily secondary, 

but in the Butte 1nines it 

is believed to be partly so 

and to have replaced pyrite 

as a result of the action of 

copper sulphate upon pyrite. It has been found, 

however, that glance alters 

under the action of oxygen 

to cupric sulphide; and 

FIGURE 25.-Quartz vcinlet (1) shattered and tlle fissures filled by pyritP- (2), and later broken 

without dislocation, and the fissures filled by chalcocite (glance) (3). Natural scale. Leonard 

mine, 1,000-foot level. both glance and covellite 

can easily be produced by the action of cupric sulphate on unaltered primary sulphides. (See 

p. 76.) 

· The following reactions illustrate the change of glance under the influence of oxygenated 

waters: 

2Cu2S · + 0 = 2CuS + Cu20 

CuS + 40 = CuS04 

CuS + H2S04 = H2S + CuS04 

H2S + 40 = H 2S04 • 

FORMATION OF ENARGITE. 

The enargite (sulpharsenate of copper) found in the fault veins is generally primary in the 

sense that it is indigenous and is not introduced by descending later waters, as is the case with 

the glance often found cementing fractured enargite. It might be formed secondarily from 

surface waters if these contained arsenic. But as only traces of the latter metal exist in the 

waters, and only traces in the pyrite veins of the district, it is impossible to explain the formation 

of enargite by descending waters whose metallic contents are ·aerived from the weathering of 

the veins. As surface solutions, however, become more and more basic, a~d hence reducing 

and not oxidizing in their action, as they get deeper into the ground, they tend first to deposit 

glance and deeper down to form enargite. This hypothesis agrees well with chemical facts,. 

but does not agree with the observations n1ade in the district. Thus, for example, the Johns..: 

town (North Connecting) vein of the :Mountain View mine shows 6 feet or n1ore of glance ore 

on the tenth level; higher in the v.ein, however, enargite appears in greater and greater abundance until on the third level the vein contains practically no glance,. its copper being in the 

form of enargite, which continues up to the oxidized zone. Ip. general, however, the reverse 
GENESIS OF THE COPPER ORES. 103 

conditions obtain, and greater quantities of enargite may be expected in depth, and have 

actually been found in the deep levels of the Green Mountain and Anaconda mines. 

The general mode of occurrence of enargite throughout the world indicates secondary 

deposition, for np Platter how abundant in the upper levels, immediately beneath the oxidized 

zone it plays out at a few hundred feet in depth and is replaced by less complex sulphides, 

mainly pyrite. , Such occurrence is noted in Chile, Argentina, Japan, and the Philippines, the 

other localities where enargite is abundant. . 

A good examp~e of an old vein enriched by· enargi'te is seen in the Gambetta South vein, 

where exposed on the 400-foot level of the West Colusa mine. The stopes show a narrow vein 

of lean, white, dense quartz-pyrite transversecl by a strike fault, the mashed granite alongside 

being impregnated and its cracks filled by solid black enargite, with little or no accompanyingquartz or pyrite, and with no apparent alteration of the granite: Between the 400 and 500 

· foot level the vein shows 2 to 3 feet of solid enargite. A 3-foot streak of glance mi..xed with 

crumbly pyrite occurs on the west side. The· Gambetta vein itself consists of white quartz 

with pyrite and nests of enargite, with druses about nuclei. Glance occurs in cracks and films. 

The an1ount of enargite present varies from place to place. The vein is cut off by the Piccolo. 

Where the east and west veins of the district are faulted by clay seams the location of the 

rich ores ~hows clearly whether the solutions come from above, or fr01n below, or from the immediate vein itself. Thus, if they came from above the enrichment would be alo1;1g the upper side 

of the clay wall, a condition seen at the Rarus and at the Ramsclell-Parrot. If from below, 

the enriching solutions would meet the impervious clay wall, would spread out and impregnate 

the tuashecl granite alongside of the wall and form ore bodies beneath the fault. The facts 

observed in the workings along the Blue vein show that the solutions followed the east and 

west veins downward to the Blue vein and spread out in it. It also appears that the descending 

solutions spread out over the clay walls of other faults and formed ore bodies. Attention is 

also called to the difference between the wall rock on the hanging-wall and footwall sides of 

the ·east-west veins. . The footwall granite shows threads and stringers of glance running off 

from the vein and clown into the rock. The hanging-wall rock does not show such stringers, 

hence it is inferred that they are clue to seepage into the footwall. In a few of the mines the 

character of the ore show's decided change in passing downward on the same vein. Thus, the 

Johnstown vein at th.e :Mountain· View mine contains glance changing gradually to enargite 

fTon1 the tenth up to the third level, at which last practically no glance remains. 

The ore on the·2,000-foot1evel of the :Mountain Con. contained both glance and enargite and 

what appeared to be sphalerite, although no tests were made. Neither limonite nor copper sulphate was ·seen. The face was only a week old. at the time seen. The vein showed in its 

eastward extension a very nearly solid mass of quartz and pyrite, or rather of solid pyrite with 

very little quartz. vYherever the recent white quartz occurs, the vein carries the leached sulphides and is pay ore. In the solid quartz-pyrite vein, however, the values are too low to pay 

and the ore can not be concentrated, so that in general the pyrite bodies are left unworked. 

This lack of pay ore in the pyrite, though apparently opposed to the theory of enrichment by 

descending ·waters, is in reality evidently clue. to physical causes-the pytite vein being solid 

has not been attacked by waters and its copper leached out and concentrated. Thus, in places 

where the pyrite vein has been shattered by later movement, but not brecciated, films and stringers of glance will be found in it, generally associated with little threads of quartz, and locally the 

joint fractures will be coated with an iridescent film of copper glance. 

If the rich ores are to be credited to descending waters leaching this great mass of low-grade 

pyrite the problen1 is, What becomes of the iron sulphate~ Only part of it ·can be accounted 

for by the newly fonned pyrite, and the concentration n1ust be accounted for quantitatively 

as well as qualitatively. Thus the pyrite vein, which is perhaps 10 to 40 feet across in the 

Green Mountain, is ~o low in copper as to be unworkable, carrying about 2 per cent. 

FORMATION 0~' TETRAHEDRITE. 

So far as kllown, tett·ahedrite is rare in the Butte district. It is found in the veins of East 

Ridge and in the fault veins of the eastern section of Butte, notably at the Gem 1nine on the 

northerly ?r northeasterly border of the copper belt and at the Leonard n1ine. In other dis-
104 GEOLOGY AND ORE DEPOSITS OF 'BUTTE DISTRICT, MONT AN A. 

tricts it does not generally extend more than 700 feet below the surface, the best-known exception being Cripple Creek, Colo. Its composition makes it quite reasonable to suppose that it 

is of secondary origin, but thus far no data confirming this opinion have been obtained. In the 

Gem mine it occurs associated with considerable quantities of fluorite. In the East Gem mine 

a shoot of tetrahedrite ore is apparently the downward extension of ore in the West Gem mine, 

where it is unmistakably associated with later fracturing and with an east-west strike fault. 

This strike fault has so broken up the original vein that it is recognizable only in the rounded 

quartz and pyrite bowlders which occur in the clay. As no bowlders or balls of tetrahedrite 

occur, and as this mineral does occur in little veinlets and streaks in the clay; it must be inferred 

that it is of recent origin. The chalcopyrite with it is shattered and undoubtedly represents 

the original ore, about which the richer mineral was precipitated, cementing the fragments. 

A marked feature· of all these and the veins of this vicinity is the great, amount of zinc which 

they show near the surface and for 200 or 300 feet down. As dept}]. is gained bunches of· 

galena appear, and this in turn disappears when the tetrahedrite comes in. As these are perhaps 

on the borders of the copper belt their relation to the silver mines is unsettled; evidence. thus 

far accumulated, however, does not contradict the assumptions, based on the mineral character 

of the Blue vein and of the different strike faults, that the silver-lead-zinc solutions are more 

recent than the copper veins, and that they were introduced after a period of fracturing, and that 

this period of fracturing was probably coincident with the rhyolite eruptions of the ·district. 

MINE TEMPERATURE. 

No chemical determination has been made of the mine gases. In general the air in the 

mines gives no evidence of emanations from the rocks, but in many u dead ends" it is so 

bad th:at a candle will not burn, though an acetylene lamp still gives light and a n1an can live. 

It is probable, however, that this is due not to carbon dioxide but to the combination of the 

oxygen of the air with the pyrite, leaving the air unfit for respiration. A loss of 5 per cent of 

oxygen is regarded as dangerous. 1 

When the mine workings have been on fire the air is bad; even where solid conci·ete dams 

have been built to exclude all air from t~em gas leakages occur and render the vicinity extreiD:ely 

dangerous to many of the men, who differ greatly in their susceptibility to the gases. 

The small amount of moisture present in ordinary air is sufficient to take up a.nd carry 

metallic salts, principally sulphates of zinc, copper, and iron. Walls of dry a.nd long-deserted 

passages traversed by air currents have become thickly coated with tufts and incrusta.tions of 

goslarite, chalcanthite, and melariterite. As these e:ffiorescences form on iron, stone, a.nd other 

solid materials, as well as on the rock walls, they can not be e:ffiorescences due to the moisture 

ofthe walls themselves, but must be deposits formed by chilling of the moisture below the dew 

point. · 

The deep workings of the Butte mines are all warm, even where ventilation is good, the 

temperature averaging from 75° to 86° at a depth of 2,000 feet, a.nd being largely independent 

of the surface temperature. The following observations made in the St. Lawrence mine, under 

the supervision of H. V. Winchell, have been kindly furnished by him. 

Temperatures in the Butte mines. 

Level. Elevation. Tempera- ture. 

Feet. Feet. oF. 200 5,877 45.77 

400 5,673 49.55 600 5,471 51.40 

800 5,271 69.80 

1,000 5,081 62.00 

1,600 4,477 74.30 

The observations were made with carefully adjusted self-registering thermometers inserted 

in holes driven in the wall rock a.nd sealed in the hole for 24 hours before reading. The 

temperature at the 800-foot level is too high, being raised by local gases above the normal. 

1 Kohler, G., Lehrbuch der Bergbaukunde, Leipzig, 1900, p. 674. 
CHAPTER IX.-THE VEINS. 

INTRODUCTION. 

The entire Butte district north of Silverbow Creek, from the low ground near Rocker 

to the crest of the mou:ntain ridge forming the Continental Divide on the east, is probably 

traversed by veins. Later rock~, rhyolites, and alluvial sands and gravels cover and conceal 

these veins over a considerable portion of the district, but in parts of the area the veins are 

conspicuous features of the landscape. They are not, however, uniformly mineralized, the 

pi·ocluctive properties being clustered in a comparatively small area. 

In considering these lodes t~1e- two ·economically most important features to be treated 

are their structure and their 1nineralization. As mineralization follows and is dependent on 

structure, the structural relations of the veins are as important scientifically as they are from 

the standpoint of the mine superint~nclent. 

In 1896, when the district was first examined, the broader structural relations of the veins 

were but partly understood. To-clay, how~ver, as a result of the developn1ent necessitated by 

lawsuits, and of the remarkable and detailed work done by the geologic staffs of the mining 

c01npanies, it is possible to predict ahnost precisely where veins will be found even in the most 

intricately fn,ultecl blocks. The laws governing the occurrence ... of workable ore in the veins 

n,re, however; a·s yet but imperfectly known, and the presence of ore bodies in unexplored 

ground can only be predicted, not assured, from the facts 

MAPPING. 

On the n1ap (Pl. X, in pocket) the outcrops of the mineral-bearing veins have been platted 

with great care by the aid of a plane table. This map, which was made by Emmons, Tower, 

and the writer for the Butte folio, 1 is reprinted with minor corrections. It is, however, deficient 

in some respects and should be checked by comparison with the maps showing the veins and 

geologic features developed by n1ining and reduced to a definite horizontal datum plane (Pis. 

XIX to XL). Plate XVIII (in pocket) shows the elevations of levels in the. Butte mines. 

The prominence of an outcrop is by no means necessarily indicative of the economic 

importance of the vein in depth; many veins that carry large and rich bodies of ore do not 

reach the surface at all. Where, as is not infrequently the case, the surface is so obscured by 

debris or buildings that outcrops of well-known veins can not be traced it has been necessary 

to deter1nine their proba:ble position by projecting upward from the nearest known underground 

workings. Underground workings, however, as a rule follow only the payable part of the 

vein, and a vein is often continuous geologically even where it does not carry payable ore. 

Veins which appear disconnected on the map, but which, from their position and direqtion, 

appear to be parts of the same vein, might possibly have been demonstrated to be continuous 

had the necessary underground drifts been driven or had those that exist been accessible. 

It has not been possible, owing to the smal~ scale of the geologic map, to indicate the 

relative importance of the different veins as ore carriers. :Many of the veins represented are 

not now and may never prove productive. This is especially true of those at a considerable 

distance from the center of production or on the outer limit .of the district. 

The map (Pl. X) indicates the position of the outcrops on the present surface and hence 

fails in some degree to represent the true relationships of the veins. In crossing a hill.the line 

of outcrop is thrown backward and in crossing a valley forward in the direction of the dip, 

the variation being greatest where the dip is flattest. As the largest veins clip steeply, the 

1 Butte special folio (No. 38), Goo!. Atlas U.S., U.S. Geol. Survey, 1897. 

105 
106 GEO~.OGY AND .ORE DEPOSITS OF. BUTTE DISTRICT, MONTANA. 

distortion produced by inequalities of the surface is generally very slight. At Emmons's 

suggestion, an attempt has been made to represent the intersection of the veins by horizontal 

planes. Plates XIX to XL show these intersections, so far as obtainable, on the planes of 

successive 100-foot contours ranging from 3,600 to 5,600 feet above sea level throughout the 

area of the copper lodes which have been inost extensively and n1ost recently developed by 

underground working, and about which, therefore, i~ has been possible to obtain the most 

complet~ information. Even here the data are not complete; the n1aps of son1e n1ines were 

not obtainable; some of the veins have not been developed; and some of the stopes have 

become inaccessible. The outlines of some few of the ore bodies have therefore been somewhat 

generalized. 

COPPER-VEIN SYSTEMS. 

CLASSIFICATION. 

The copper veins 1 may be grouped in several well-defined classes which in the main correspond to the principal fi$sure systen1s. As shown on the geologic map (Pl. X) and in the 

series of maps (Pis. XIX to XL) showing the veins projected on the horizontal planes of 

fixed elevations above sea level, they fall into four recognizable systems; the big n1ines of the 

western part of the district, including the Anaconda, Syndicate, and other great producers, 

derive their main ore supply from large east-and-west lodes; the chief n1ines of the northern 

and eastern parts of the district obtain their ores from northwest veins; a number of large 

and productive mines are situated on northeast veins; some other mines are on veins whose 

course is N. 65° W. "' · 

More in detail the four groups, based on distinctive structural, mineralogical, and physical 

features, are as follows: 

1. The Anaconda (east-west or quartz-pyrite) system, embracing the lode of that name and its displaced portions 

worked by the Parrot, Original, Gagnon~ and Mountain View mines; the Syndicate, including the Mountain Con. 

and its various spurs;- the Colusa-Shannon, Diamond-Bell, Speculator, Modoc, Mat, North Wild Bill, Moonlight, 

Pennsylvania or South Ledge and its continuation, Penn. No. 3, O'Neill, Enargite, Snohomish, Berkeley, and the 

veins numbered 4, 14, 17, and 19 of the Rarus mine. The course of the system is practically east and west. 

2. The Silverbow or High Ore system, embracing the Silverbow, High Ore, Windlass, Johnstown (North 

Connecting), and Wild Bill veins, with a course of N. 65° W. This system antedates the Blue Vein system (No. 3) 

and is characterized by enargite in some of the veins. 

3. The Blu~. Vein or northwest system, including the Blu.e, Mountain View fault and its extensions, Nos. 7, 10, 

and 11 of the Pennsylvania mine, Clear Grit, Greyrock, Covellite, Bell or North Greyrock, Jessie, Edith May, and 

Skyrme veins. The system consists of ore-producing fault veins of a second period of copper-ore formation. It cuts 

and displaces the veins of the earlier periods (Nos. 1 and 2). , 

4. The Steward system, including the Steward fault, Caledonia, No. 6 of the Parrot mine, Bell fault, Blue Jay 

fault and its continuations, Middle fault and No. 16 of the Rarus mine, Tramway, Modoc fault, La Plata vein, and 

severallesse'r veins not yet named. The system consists of ore-producing fault veins of a' third period of copper-ore 

formation. The veins have an east to northeast course: 

Besides the vein systems there are two fracture systems, not mineralized, but of much 

econo.mic an.d scientific importance, namely: · 

1. The Mountain View system, a series of north-south fissures that are clean cut and persist~nt, nearly vertical, 

and contain as their characteristic filling a mass of rounded pebbles from the wall roc~, held in a paste of comminuted 

rock. As the fissures show little or no appreciable faulting they are regarded as the result of shrinkage or contraction 

or perhaps of settling and adjustment of the fault blocks with very little movement but with considerable grinding of 

the walls. 

2. Rarus fault system, a great fault zone running N. 45° E., accompanied by many sympathetic fractures, which 

displace all the veins cut by it. · 

3. Post-Rarus fault fractures. 

tIn the present work, as in the Butte folio (No. 38), the term vein is confined as far as possible to a single mineralized fissure or to the ore body 

formed along a single fissure, whereas the term lode is applied to an assemblage of ore-bearing fissures so closely spaced that the ore that has formed 

along and between t:hem may in places be considered to form a single ore body. The principal fissures making up a lode are nearly parallel to 

. each other, but there are also smaller cross fissures connecting them, through which the intermediate rock becomes impregnated with ore until 

it may constitute vein material. A lode may be only 10 feet wide, or it may b~ 100 feet or more; and within it are included zones of more or less 

alterecl country rock, in places carrying enough values to pay for mining, in other places too barren to pay, in which case they are generally called 

"horsos." An assemblage of veins too widely spaced to form a single lode and yet to a certain extent coordinated into one system is designated a 

vein system. 
·THE VEINS. 107 

The veins of the Anaconda and Silver bow systems are quartz-pyrite veins; thpse of the 

Blue apd St~ward systmns are tnineralized fault veins: Many of the most productive lodes 

of the district are c01npouncl or composite veins, due to a combination or superposition of the 

two types in one vein -that is, a reopening of an old vein with deposition of new material. 

As tnany of the older veins have been reopened in this way they have the characters of both the 

quartz-pyrite and fault veiil.S. · 

The sequence of the vein systems is considered to' be as follows: (1) East-west or Anaconda 

systen1 (oldest); (2) Silverbow systen1; (3) ·Blue Vein system; (4) silver veins; (5) Steward 

systmn; (6) Mountain View fractures; (7). Rarus fault zone. The enargite veins are of different ages, but. are all younger than the. Anaconda system. 

The four systen1s en1brace practically all 'the productive veins of the district. It is not 

certain, however, that all the veins having a sitnilar direction are of the same age. It is known 

that the district has been an area of n10vement and fracture ever since the time of the granite 

intrusion, and has continued so to the present clay. The early fractures, though cemented by 

mineral matter, have been lines of weakness and have been reopened either by direct fracture 

or during the straining of the rock n1ass by the faulting of blocks by other crossing fractures. 

Grouped according to their mineral content, the veins may be classed as pyrite, quartzpyrite, chalcocite, enargite, sphalerite, silver-quartz, and fault breccia yeins. 

ANACONDA (EAST-WEST) SYSTEM. 

The tnmnbers 'of the east-west or Anaconda system, of which the Anaconda and Syndicate 

lodes are the best exan1ples, are the most v.ridely-lrnown veins ·of the district, and for many 

years in the earlier history of Butte furnished almost the entire copper output .. 

These veins are of rmnarkable width and tni.neralogic unifonnity. The larger ones, which 

have been stop eel for thousands of feet along their ·courses show local variations in richness 

but no well-:fonnecl ore shoots. (S~e Pl. XI, A.) They present abundant evidence of their 

fonnation by replacetnent along shear zones, but their fracturing was not accompanied by 

displacmnent, and it is quite probable that their continuity and uniformity of size and character is clue to the fact that the vein fissures permitted general circulation throughout the fracture zone, with gradual replacement, u.rihampered by clay seams, slips~ or friction breccia. 

The ftlling is preclonunantly a dull white or vitreous quartz, carrying abundant pyrite, 

s01ne sphalerite, and abundant chalcocite, in many places showing rude banding in the arrangement of the sulphides. The ore grades into the wall rock. The lodes are wider. in the upper 

than in the lower levels, as the rock between the constituent veins is replaced by ore in the 

upper zone. (See Pl. IX, B, p. 84.) 

The ores are notable for copper glance, which is their most abundant copper mineral, and 

which, with bornite, enargite, and tetrahedrite, only occurs where the vein has been fractured. 

The veins lose their secondary glance with depth, even where the fracturing is strong; on this 

point the Syndicate lode is particularly convincing, for in it good strong streaks of glance are 

seen to pinch out until fmally the glance occurs only as a coating or ftlm on the pyrite. In the 

large fracture~l quartz-pyrite veins enargite comes in at 2,000 feet or more below the surface 

but is not seen at higher levels. It may be clue to uprising mineral waters. 

The enargite-bearing veins are quite different ~rom the quartz-pyrite veins. Typically 

they have well-defmed walls of granite, but though in many of them a crust of comby quartz 

intervenes between the enargite and the wall rock, the vein ftlling is practically devoid of 

that 1nineral, the gal}gue, if any, being altered granite. The enargite runs upward to the 

oxidized zone, or n.hnost to surface in some veins. It decomposes to a brownish sooty n1aterial, 

and the veins do not show enriclunent. 

SILVERBOW OR HIGH ORE SYSTEM. 

The veins of the Silverbow or I:Iigh Ore system have a course of about N. 65° W., in 

places varying to parallelisn1 with the Blue Vein system. rhough the veins which name the 

series are quartz-pyrite veins, in most respects similar to those of the Anaconda system, other 
108 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

members of the series, notably the Johnstown (or North Connecting) and the Windlass veins, 

differ in character, containing enargite as a primary vein mineral, with little quartz-pyrite ore. 

Further exploration may result in the inclusion of the Silverbow and High Ore with the 

Anaconda veins, despite their wholly different strike. An analogous case is that of .the ColusaShannon lode, whose course is that of the Steward fault vein system. As already stated in 

discussing fissure formation (p. 60), the mineralization wl}.ich formed the Anaconda system acted 

upon several fissure systems, producing quartz-pyrite veins, but the action was most intense 

along an east-west direction, making the immense Anaconda and Syndicate lodes. 

BLUE AND STEWARD'S.YSTEMS. 

FEATURES IN COMMON. 

The fault veins of the Blue and Steward systems differ markedly fron1 those of the Anaconda system. They cut and displace the older veins and have the characters typical of veins 

filling faults. The fissure is clean cut and is filled by crushed quartz monzonite, aplite, and 

porphyry, softened and altered, containing· more or less disseminated pyrite and quartz, in scarflike masses, resulting from the crushing of pyrite veinlets. (See Pl. XI, B.) The·fissure varies 

in width from a few inch~s to 20 feet or n1ore, but showing well-defined planes of n1ovement, 

with striations and slickensides on the walls and bands of tough clark-colored or black clay 

varying from a fraction of an inch to a ·foot in thickness. 

These fault vei:qs either cu.t across country or reopen and follow older vein fissures. Characteristically they are fissures filled by friction 1naterial, with ore shoots at intervals along 

their course. 

Some of the veins are opened for a mile or more and 1nost of them show ore shoots whose 

occurrence appears to be entirely independent of any law. 

In their characteristic development _the ore shoots are lenticular, with a n1aximum thick· 

ness of 2t> to 30 feet, tapering to nothing at either encl. ·Beyond the feather edges some of 

the veins contain lenticules of ore,· wP.ich may be pure glance, for 100 feet or more; finally 

these disappear. 

The distance between shoots is variable, but ·is often hundreds of feet, the vein. showing 

not a trace of ore in this distance, even when the walls are 5 or 10 feet apart. The ore shoot 

may fill. the entire width of .the fissure or only part of it. The ore is usually quartz and iron 

pyrite, with smaller amounts of chalcocite, enargite, bornite, and zinc blencle. Covellite and 

chalcopyrite also occur. The ore body itself shows little or no evidence that it occurs in a 

fault fissure, the ore entirely rep~acing the crushed country rock, though usually showing a 

clay selvage. The shoots vary in size from little lenticules or bunches up to immense bodies 

over 1,000 feet long, 1,500 feet high, and as much as 30 feet thick. 

Transverse fractures across the ore bodies are found in most of the veins. They seem to 

indicate extensive movement and crushing subsequent to the formation of the ore bodies, 

with consequent rearrangement of the vein filling, and the removal of many solid blocks of rich 

ore, to positions against low-grade ore or barren masses of crushed granite. The ore shoots 

frequently show banding, and where thickest often contain slabs and wedges o'f waste rock. 

The ore composing the shoot is not uniform in richness but has local gatherings of richer 

material, also enrichments due to later deposition on cross fractures. (See fig. 26.) 

The fault veins as a whole have been open and free trunk channels for circulating waters, 

which have altered the crushed rock filling th~ fissure throughout its entire course, but this 

alteration has penetrated the wall rock but slightly if at all. In many cases the barren part of 

the vein is dry and the ore shoot wet, the location of the latter marking the position of a pipe 

or channel of readiest circulation, determined by the presence of clay walls developed across 

the vein. 

In general the fault veins carry minerals typical of silver veins and contain more silver 

than the quartz-pyrite ores. The Blue vein, extensively worked in the Little Mina and Nipper 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE XI 

A . FAULT BRECCIA OF ORIGINAL MINE. 

First fl oo r ove r 1,200-foot ie ve l east. See page 107. 

B. ANACONDA VEIN CUT OFF BY BLUE VEIN . 

Neversweat mine, 900-foot leve l, sixt h floor stapes, west en d, looking southeast. Not e cu rved pl ane of 

fa ult wa ll . 
· .. THE VEINS. 109 

mines, and the Clear Grit vein were both forme:rly mined for silver. The Nipper ore is, in 

fact, intertnediate in character bet-ween the silver and copper ores. 

The vein filling is usually zincky near the surface, this being the case in the Nipf:.'-'~r, Gem, 

Jessie, and Clear Grit. At a few hundred feet depth the zinc becomes less. The veins contain some pyritic ore, evidently from an. older filling that is shattered, but not chalcocitized. 

The stopes show a cross netting with lenses of ore. The following minerals are fomid in the 

fault veins: Spho.lerite, tetrahedrite, rhodochrosite, fluorite, galena, pyrite, chalcopyrite, bornite, 

enargite. 

CONTRASTING FEATURES OF BLUE AND, STEWARD SYSTEMS .. 

The foregoing description applies especially to the veins of the Blue Vein system, for most 

of.these are "cross" veins, whereas many. of those of the Steward system are strike fault veins 

along older veins. 

The result is a marked difference in the structural features of the two systems in general. 

The Blue vein and its congeners contain definite shoots of newly formed ore, separated by 

intervening stretches of barr~n fault material devoid of · 

even a trace of ore (Pl. XII, B) other than what may 

have been dragg~d in where they cut and displace older 

veins. On the other hand, the fault veins of the Steward system are remarkable for their shoots of conglomerate ore, composed of a typical friction breccia of an 

older vein filling (Pl. XII, B), with which newly deposited 

ore .is associated. A few· Blue veins, however, follow 

older quartz-pyrite or enargite veins with a northwest 

course, and a few veins of the later Steward system are 

productive away frmn other veins. · 

So f11r as the 1nineralogic evidence is concerned, no 

:fL'\:ed distinction is possible.. In a gener11l way .the Steward systetn c11rries n1ore enargite 11nd has accessory miner~.tls of the silver vein series. IIowever, the Jessie and 

other veins of the Blue Vein system h~.tve been reopened 

and in p11rt crushed by strike faults, with the introduction of tetr~.thedrite, rhodochrosite, and other minerals 

forn1ed during the period of silver-vein forn111.tion. The 

discovery of the rich ore bodies of the Jessie 11nd Edith 

May veins, belonging to this systen1, showed that the 

view held by Winchell was correct, and that these f~.tult 

veins should be developed, not nlet·ely by a crosscut 

or by drifts upon them 200 or ~00 feet apart, but by 

system11tic drifting along then1 for long distances, on 

levels cmnpi.tr~.ttively close together. Work of this kind 

oL-----.,_..J~s Feet 

FIGURE. 26.-Blue vein cutting off Anaconda lode (2) 

showing so-called spraying out of ore. (1) New endogenous ore formed along wall of fault at cut-off. 

(3) Fault matter of Blue vein, containing ore 

bowlders. 

led to the discovery of extensive ore bodies on the Mountain View fault and Skyrme veins. 

COMPOSITE COPPER VEINS. 

The f~.tct· thi.tt m~.tny of the richest bodies of copper ore are of composite character and 

derive their n1et11llic content in part fron1 each one of the three distinct periods of minerali.zation 

necessit11tes careful study to discritninate the evidence and results of each period .. As already 

st11ted (p. 107), the earliest or quartz-pyrite. veins can be differentiated from the enargite veins; 

in composite veins original ore matter Gan be distinguished from that brought in by a later 

period of deep-se11ted n1ine.rn.l waters;· and all the foregoing ores can be distinguished from 

the so-called secondary ore formed of transposed and redeposited material of the vein itself. 
110 GEOLOGY. AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The rich ore bodies which have made the d~strict famous have been largely of this last-named 

character. The original ores of the quartz-pyrite veins were generally of too low a grade to work, 

and most of the glance and enargite ores are of later age. 

The term "conglomerate" is locally used in the Original and Gagnon mines to indicate a 

vein filling consisting of more or less rounded fragments of an older ore and of country rock 

lying in a paste of clay and ground""up rock and vein matter. The walls are usually defined 

by seams of tough dark-gray clay, a ground-up mixture of altered rock, and vein filling of 

variable composition. Where the vein is formed. of massive quartz and pyrite, the term "vein 

filling" is appropriate, even if the vein be due to replacement, but in general the term is ambiguous, as It may be used to designate any material filling the.fissure, whether it ·carries ore or not. 

The copper veins are in large partreplacen1ents or are masses of crushed and n1ashed rock 

impregnated with copper minerals. This complex recurrent faulting, with sympathetic fractures accompanying the greater faults, the crushing of large masses being cmnmon, has produced a very complex composite vein. The lesser cross fractures, which cross the great lodes of 

the camp (notably various portions of the Anaconda and the Syndicate lode) have determined 

the extent of .the impregnation with glance. The great ore bodies of glance have in some places 

been slightly displaced by such fractures, but more commonly have been simply cracked and the 

fracture filled by new material; the fissure, running out into the wall rock, is also filled for v_ariable but not great distances from the vein. These lesser fractures are naturally best shown in 

the deeper levels, where they are extremely important factors in determining the location of 

bodies of rich secondary ore, for it is here that the process is caught in the act, as it were; higher 

up its effect is obscured by the greater amount of mineral and by.olcJ. mine workings. Near the 

surface few of the fault veins show ore. For the most part they are indistinct breaks or fissures 

filled by crushed rock and clay and devoid of any mineral matter, not only at the outcrop, but 

for many hundred feet down. 

VEIN FILLING. 

·TYPES. 

The vein filling differs in the different classes of veins. (1) In the oldest n1ineralized fissures, the pyrite seams, the filling is massive nearly pure pyrite. 

(2) In the quartz-pyrite veins the primary filling consists of an intimate mixture of pyrite 

and quartz, in 'places rudely banded parallel to the vein walls, but more commonly the pyrite is 

patchily and irregularly distributed in the quartz. This latter is the normal form of the vein 

and is clue to replacement, in part, of the smaller rock fragments that filled the original fractures, 

but in greater part to the replacement of the granite between the fractures. 

(3) Where a primary quartz-pyrite vein has been opened by a strike fault or, as is often the 

case, has been cracked and crackled as the ground was adjusted as a result of cross faulting, the 

effect has been to permit the descent of water down the vein, with accompanying replacement of 

the pyrite. 

Plate XII, A, shows the primary quartz-pyrite of the Parrot-Gagnon vein, cut by a strike 

fault, the Steward vein, in the west face of the 1,600-foot drift of the Gagnon mine. 

(4) The filling may be a mass of crushed and ground-up rock fragments fron1 the fissure 

walls, or it may be material introduced or deposited in this fault breccia. Very commonly both 

are, present. Replacement veins are not fissure fiJlings. 

INFLUENCE OF COUNTRY ROCK. 

The variations in the veins in the three varieties of rock, the Butte quartz monzonite 

(either normal or altered), the aplite, and the rhyolite porphyry, are very marked, both in the 

character of fissuring and in the richness of the vein·filling. In the granite the quartz-pyrite 

veins are wide and generous; in the aplite they maintain their identity and course, but ilre lean; 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE XII 

A. GAGNON MINE, WEST FACE 1 ,600-FOOT DRIFT. 

Shows the Parrot-Gagnon vein of Anaconda system, with banded quartz-pyrite o re, cut by 

the Steward fault vein, fil led with o re bowlders and granitic cobbles-a tr ue fau lt 

breccia. 

B. CONGLOMERATE ORE OF STEWARD FAULT VEIN , GAGNON MINE. 

Second floo r of st apes above 1,600-foot leve l, near crosscut to shaft. Shows fragments 

of earlier ore and of granite torn from old quartz-pyrite vein and rounded by 

movement al::>ng fault vein. See page 109. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE X III 

IDEAL CROSS SECTION OF ANACONDA VEIN. 

Shows relations to porphyry and distribution of ore. (Afte r H . V. Winchell.) 
THE VEINS. 111 

and in the r~1yolite porphyry they are narrow and split up and carry relatively leaner or unpayable vein filling; this is believed to be clue to the litek of readily replaceable minerals. (See 

Pl. XIII.) 

INTRA VEIN RELATIONS. 

The change of vein filling .at intersections, offsets, spurs, etc., is very marked and merits 

full and detailed description, which is given in later chapters. In general it may be said that 

the occwTt:mce of workabie ores is dependent on the fracturing and faulting of a prin1ary lean 

vein. The earlier veins n.re pyritic, the later ones carry enargite, and both, when fractured, 

carry glm~ce ore. 

CHANGES IN VEINS 'VITH DEPTH. 

CHANGES IN COMPOSITION. 

Each class of veins shows certain changes, clue to depth. The quartz-pyrite veins now seen 

are probn.bly the lower parts of the veins. That the district has suffered much erosion since 

these earlier veins were formed is beyond dispute, but the amount is not determinable. In the 

Colusa-Parrot grotmd the Blue Fault vein has dropped the grou.lld 510 feet on the west side. 

Tho oro bodies seen in that mine belong, therefore, to a hori~on 510 feet higher than those at a 

corresponding elevation in the N eversweat, which lies east of the fault. The vein in the ColusaParrot ground might be called a ''granite" vein down to the 800-foot level, where it gradually 

passes into a normal quartz-pyrite vein. In the upper levels the ore is an impregnated mineralized granite, in which several veinlets have mineralized granite between____:a feature seen in the 

Leonard-Colusa ground, where, however, the mineralization is not exactly the same. These 

branches represent a bifurcation of the vein not seen in the Anaconda ledge to the east, as the 

portion corresponding to this has been re1noved by erosion. The north branch of the ColusaParrot bec01nes the Parrot ledge going west. 

The Pennsylvania or Anaconda South vein shows material changes in character with depth. 

The upper levels, 200 to 400, show a· vein composed of granite netted with rather ·sparse films of 

pyrite and a very little quartz. It is what is locally called a granite vein, meniing ore composed 

of craclded granite with films and specks of glance replacing pyrite. (See fig. 22, p. 95.) Lower 

down the vein contains an increasing amount of quartz, and below the 400-foot level it becomes 

a norn1al quartz-pyrite replacement vein without definite walls, carrying a large amount of 

pyrite. Glance occurs in fracture planes and as speeks in the rock adjacent to the quartzpyrite vein. 

Another and1nore significant change in the quartz-pyrite veins in depth is their tendency to 

split up or disappear. Great wide ledges finger out i!1to individual quartz-pyrite veins, and 

then into less mineralized fissures, and lastly into a mere closely fissured 1nass of altered granite. 

This condition represents the first stage of the vein forn1ation. 

The Covellite (or Dernier) vein, where cut on· the 2,200-foot level of the Diamond mine, 

shows a remarkable exan1ple of the bifurcation of a vein with depth. On the upper levels it is 

a single well-defined fissure of notable persistence, though cut by cross fissures with a northwest course and slight displacement. On the 2,200-foot level west of the crosscut it is a very 

lean vein, consisting mainly of a fault breccia composed of mashed granite with ~valls of more 

or less solid rock. Eastward the vein splits into branches and is cut square off by cross faults, 

and does not continue as a recognizable vein, the streak observed being .composecl.of pyrite in 

a fault of different character. On the 2,100-foot level enargite is first seen. This seems to be 

in line with observations that enargite is at Butte a n1ineral formed at great depths, though 

directly opposed to the known occurrence of the 1nineral in Chile and J apa:n. 

CHANGES IN STRUCTURE. 

In. general, broad and thick lodes change downward, passing into a n.et,~wrk of small veins, 

with silicified but unreplaced granite between. This condition probably results from sheeted 
112 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

(or less regularly fissured) granite being attacked by mineral solutions; in the upper part of the 

lode !'eplacement and mineralization,of ·rock between fissures was complete, but lower down 

only. the rock adjacent to fissures wa~ replaced. This condition is see:I?- to be more ·and more 

common as deeper and deeper parts of veins are opened. 

The veins are less regular in depth,· and the ore bodies irregular, and, though in places 

large, are not continuous. (See Pl. XXXI.) . 

The tendeilcy of the veins is to split up with depth. For instance, the Covellite vein of 

the Diamond west of the 2,200 crosscut is very lean, consisting mainly of a breccia of mashed 

w 

granite. Eastward it splits into branches 

and is cut square off by a cross fault and 

does not show again as a recognizable vein, 

/J~~~~~~:::::::I::::::t::::I:J~~~n~~ E the streaks found being of pyrite in a fault 

-r of different character. · 

In general, the faults and cross slips 

appear to affect the vein more on the deep 

levels than above. This apparent differFIGuRE 27.-Cut-off and spraying out of Deroier vein by a northwest fault. ence, however, is believed to be largely due 

to the action of secondary glance-forniing 

waters, which thoroughly mineralized the shattered ground lying between the fractures on the 

upper levels, but did not penetrate to nor mineralize. the lower fractures, though these are 

more easily ·recognizable, nor the intervening granite, even though this was shattered. The 

effect of cross fractures on ore deposition, even where there is no clay streak to deflect enriching 

solutions, is well shown in the spr~ying out of the Dernier vein of the 2,100-foo.t level of the 

Mountain Con. mine. (See fig. 27.) · 
CHAPTER X.-DETAILED DESCRIPTIONS OF THE COPPER LODES. 

METHOD OF TREATMENT. 

SUBDIVISIONS. 

In this chapter an attempt is made to describe the copper lodes in some detail-a description by lodes rather than by individual mines seeming to be the most generally satisfactory 

method of treatment. As n1any lodes extend through several mines no method can be devised 

that will give all the related facts, either of individ':lal lodes or of particular areas, in an altogether satisfactory n1anner. For this reason a geographic division by belts and clust~rs has 

been adopted, with modifications to suit each case. The most important subdivisions adopted 

are· (1) the southern or Anaconda-Parrot belt, which embraces all the contiguous lodes north 

and south of the lodes from which the name is taken; (2) the Intermediate belt, which lies 

between the Anaconda-Parrot and Syndicate b.elts; (3) the Silverbow system; (4) the northern 

or Syndicate belt, which comprises the mines of the extreme northwest part of the copper 

district; (5) the Bell-Diamond group, which includes the Greyrock and Speculator mines; (6) 

the Jessie-Edith :May copper-silver veins of the Blue system; (7) the East Butte group, lying 

along the southeastern. bor.ders of the di~trict; (8) the Mountain View-Shannon-Colusa belt to 

the east; (9) mines north of Meaderville ;. (10) the Rarus-Pennsylvania group; (11) the Butte 

Flat group; and (12) the East Ridge group. These names are all sufficiently distinctive to be 

understood, and it has been found most conv~nient to discuss the various veins· under them, 

despite the fact that this method brings together veins of different ages and characters. 

Each of the larger lodes is separately described, but local details of structure, together 

with descriptions of the lesser lodes of the mines, if given at all, are more conveniently grouped 

under the name of the mine. The complex tangle of lodes in the Rarus mine and in the Bell 

and Diamond mines, and the stockwork of veins in the Leonard are also described und.er the 

name of those mines, as it seems neither wise nor feasible to attempt to.segregate the veins and 

describe them under the systems to which they genetically b~long. 

NOMENCLATURE.· 

As far as practicable the :names already in use at Butte are u~ed in this report. Where 

several names are applied to a vein, an endeavol," has been made to select the best known or 

most appropriate; where the same name has been given to different veins, it is dropped for all 

but one of them; A few of the veins have been given personal names for convenience. 

Many of the smaller but workabie veins are unnamed. In such cases local custom is followed, and they are designated by the number of a drift or raise on the vein, as for example 

No. 27 raise vein of the Rarus mine. In many cases it has been deemed unwise to give the 

name of a claim to a vein, as this might imply that it is the discovery vein, or the most important 

vein of the claim of that.name. North and south as prefixes are convenient and are frequently 

used, but may be misleading.if development should disclose other veins to which the adjectives 

could be more properly applied. Such terms are, therefore, discarded where possible. 

CROSS SECTIONS. 

In gener.al, the cross-sectional drawings are constructed from data gathered along the 

actual plane of the section, but lack of data has necessitated in many the use of projections for. 

as far as 100 feet on either side. In making such projections care was taken to avoid the comnlon error of projecting a vein at 90° to the plane of the section, where, as a matter of fact, the 

strike of the vein would carry it to the plane at a wholly different point, giving a hypothetical 

section very different fron1 the true one. 

90427°-No. 74-12--8 113 
114 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, M.ONTANA. 

Some of the sections have been made directly from inine maps, verified at critical points 

by underground observation; generally, however, owing to the necessity of determining whether 

the fault fissures which intersect the east and west veins cross the latter or are deflected and 

follow them, forming strike fissures, it has been necessary to check up each section by actual 

inspection of workings from the surface downward. · 

In constructing the horizontal sections it has been necessary to ascertain whether the mine 

workings· actually followed veins or were laterals in the country rock. Observations, too, 

have been made as to any changes in the mineralogic character of the ore, and these have been 

duly recorded for.the same vein from one end to the other. 

ANACONDA-PARROT BELT. 

The Anaconda-Parrot belt stretches nearly due east, with a width of not more than onefourth mile, from Missoula Gulch almost to ~Ieadervil1e. It traverses Anaconda Hil1, crosses 

Dublin Gulch, and follows along the high ground back of the compactly built city proper. It 

contains six great mines, the Gagnon, Original, Parrot (with Colusa-Parrot), Neversweat, 

Anaconda, St. Lawrence, and Steward, all but the last deriving their main ore supply from. 

the Anaconda lode. (See Pl. XIV.) Other east-west veins and members of the two systems 

of fault veins also occur in the area of the belt and h~ve not only directly contributed to the 

output of ore but have also been important factors in the formation of the ore bodies of the 

older veins of the Anaconda system. · · 

ANACONDA-PARROT LODE. 

The Anaconda and Parrot, the most important lodes not only of this belt but of the whole 

. district, are portions of one continuous vein, which has been severed by ·the Blue Vein fault, 

and displaced and brought into its present position by movement along the walls of that fault. 

The Anaconda-Parrot lode has been worked for a horizontal distance of over 7,200 feet, to 

a depth of 2,400 feet; it has a minable width varying from 5 to 90 feet, averaging 40 feet in the 

Anaconda workings and 25 feet in the mines west of that property. The western segment, 

worked in the Parrot, Original, and Gagnon mines, is the Parrot lode; and the eastern segment, 

mined in the Neversweat, Anaconda, and St. Lawrence claims, is the Anaconda lode proper. 

Farther east, beyond the :Mountain View fault, the Anaconda lode is continued in the South 

ledge of the Mountain View mine. 

ANACONDA LODE . 

..In the Anaconda mine proper, comprising the N eversweat, Anaconda, and St. Lawrence 

mines, four large veins are worked. Of these, the Anaconda vein is by far the most important. 

Next south of it is the Moonlight (Middle ledge), still farther south the Pennsylvania (South 

ledge), and still farther south the O'Neill-the last probably the Pennsylvania vein beneath 

the ·Rarus fault (p. 228). North of the Anaconda lode is the Hogan vein (p. 122), known and 

worked only in deeper levels. The relation of this vein to the Anaconda is shown in the cross 

section (fig. 28). The general east'-west course of the lode is the mean of two directions-N. 80° 

W. and N. 80° E.-which prevail in different parts. 

ANACONDA VEIN. 

ORES. 

The Anaconda vein has been enormously productive from the 200-foot level downward. 

It is a typical replacement vein, composed of quartz and pyrite with streaks and masses of 

. cha~cocite. The entire vein is as a rule workable, but it also contains large masses of rich chalcocite ore, constituting true bonanzas. The chalcocite replaces the primary ore and fills fissures 

and cavities in it. It is recognizably secondary in most places, though it is found from the upper 

limit of the sulphide ore to the deepest level (2,400 feet)_ of the mines. Chalcocite is associated 

with secondary fracturing and faulting and not only occurs in the vein but also extends in places 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE XIV 

A. NEVERSWEAT MINE FROM SOUTHEAST. 

B . SHAFT OF ANACONDA MINE. 
ANACONDA-PARROT BELT. 115 

ns stringers and veinlets into the hanging-watll rock. The ore ranges 'from 15 to 100 feet in 

width. 

The primary vein filling is a very dense and massive mixture of quartz and pyrite, with 

more or less accessory sphalerite in places. The quartz is finely crystallme, shows neither 

marked banding nor crustification, and is a characteristic replacement product. Most of the 

pyrite shows lack of arrangement, but on a broad scale plating or rude banding parallel to the. 

vein walls can be distinguished. The vein filling is so massive and solid that it stands well 

without timber. The altered granite lying between the veins is in some places impregnated 

FIGURE 28.-Vertlcal north-south cross section through Anaconda shaft. Figures on left are feet above sea level; those in center are levels of 

4 Anaconda mine. 

with enough copper to be workable. The plating of granite, the gradual .replacement of that 

rock observed on a broad scale in the underground workings, and the detailed replacement seen 

in thin sections of the rock studied under the microscope,. all show that the lode results from 

the gradual replacement of the country rock along a line of fissuring or sheeting. 

WALL ROCK. 

The un:fractured primary vein filling seldon1 shows any traces of the original sheeting planes 

of the granite, but consists of a thick and solid mass of quartz and pyrite that ·lacks symmetrical 

banding or comb structure. Definition is in many places lacking, not merely between the ore 
116 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

and the altered granite horse that separates the two streaks of the Anaconda vein, but also ·, 

between the ore and the wall rock proper. In general, however, the vein shows fairly distinct ; 

boundaries, especially on the footwall side, where a slip or gouge has resulted from later frac..: t.. ~~ 

turing. The wall rock is impregnated with secondary quartz, thoroughly sericitized and dotted :· 

with pyrite, but· this alteration, intense near the vein, fades gradually out ·away from the walls~; : 

The prevailing rock cut by the vein is the Butte quartz monzonite. The more siliceou~{. ~ 

aplite is abundant on the 300-foot level of the N eversweat mine, but elsewhere is neither more"~; 

nor less abundant than on the surface. ' 

In its eastern half the Anaconda shows a general parallelism to a dike of the rhyolite· 

porphyry, which for a considerable distance forms its footwall. The Anaconda, however/ 

crosses the dike in the St. Lawrence and :Mountain View mines, and, as shown in the verticai 

cross sedtion (fig. 28), in general lies south of the dike and at a varying distance from it. ~ .. 

Where the Anaconda cuts the rhyolite porphyry and also where it traverses aplite it gener+ · · 

ally consists of lean or unworkable ore. On the other hand, ·the uncongenial character of thes~ : 

two rocks, preventing replacement and ore depositi<?n, has made them retain the original cha#~~· 

acteristic fissuring, and has revealed the fact that the veins are replacements irn parallel and 

netted· fractures. (See fig. 29.) · 

Granite 

~ 

~ Quartz. 

FIGURE 29.-Diagram showing change in character and richness of vein in crossing rhyolite porphyry and aplite. 

... ' ; ~. 

Where. the Anaconda crosses the porphyry dike the latter shows no displacement. This 

is ·also true where it crosses aplite. These facts prove that the. vein fissuring was without any 

appreciable faulting or displacement, and confirm the theory that the Anaconda is a result of a 

replacement of fissured rock and not the filling of an open fracture. 

SPLITTING OF THE VEIN. 

In the upper levels the Anaconda is one big vein, with a few horses ·of ,granite, but in depth 

its structure is dual, consisting of two nearl'y parallel veins 25 to 50 feet apart (fig. 30). From 

the surface down to the 700-foot level local splits occur, showing the tendency of the lode to 

divide downward. In the Anaconda mine the hanging-wall portion separates at a depth of 700 

'feet, and thereafter continues (see fig. 31)- a's two ledges, known as the "hanging-wall" and 

the "footwall," and are very persistent .throughout the Anaconda mines. Westward on the 

Parrot lode the south or hanging-wall ledge diverges, both in strike and dip, forming the south 

or Virginius ledge of the Parrot mine. (Seep. 132.) Farther west in the Parrot and Original 

mines a footwall fault vein appears and in the Gagnon the dual character is resumed. 

The lode has a general dip of 72° to·80° S., but as the walls roll, the dip varies to the extent 

of 10° or s·o. In the Neve~sweat mine its upper 200 feet is nearly vertical. . 

The two ledges composing the Anaconda are alike in character, but the north or footwall 

ledge is the thicker and more persistent. This ledge varies considerably in_ width, but in the 
ANACONDA-PARROT BELT. 117 

Anaconda mine 1naintains an average thickness of 25 feet to the 2,400-foot level (the lowest 

depth attained in 1907), whereas the hanging-wall ledge is thin and unrecognizable ·below 1,800 

feet. SUl\11\:IARY •. 

The Anaconda vein, which is typical of the series, is an east-west lode, formed of a hard, 

compact DlL'\::ture of pyrite and quartz, lacking crusts but having rude banding. This quartz 

differs frOin that formed in cavities and shows all the characters of replacement material. The 

vein has been in part sheeted and is 

crossed by numerous northwest fractures, three of which are mineralized 

and of considerable size. The vein is 

also fTactured by east-northeast faults 

(N. 70° E.). Both classes of faults 

have shattered the vein and permitted 

extensive secondary enrichment, making the rich ore bodies of glance for 

which the n1ine is famous. 

The vein is· in large part double, 

consisting of two streaks, united in the 

upper levels ~though horses occur here), 

but distinct below, the interval widening. The rock between is netted with 

fractures and is pyritized but not 

crushed. The north branch of the 

vein has an average width of 40 fee't in 

the St. Lawr~nce and Anaconda 

ground and of 25 feet in the ground 

westward. It is developed to a depth 

of 2,400 feet and a length of 2,700 feet . 

It w.as once continuous with the Parrot and the Mountain Yiew lodes, 

which are di$placed parts of the same 

vein, but is now cut off from them by 

the Blue vein fault, and again by the 

:Mountain View fault. Farther to the 

east it is again cut by the Rarus fault, 

beyonci which it has not been positively identified, the st1ggested correlation with the Windlass lacking substantiation. 

PENNSYLVANIA VEIN. 

.300-FT.LEVEL Q 

1400-F'T. LEVEL 

.SOO-FT. LEVEL 

500-FT.LEVEL 

LEGEND 

Anaconda 

~ 

~ vein 

" 

+-

Parrot vein 

. ·ra 

Fault 

c::."C 

800-FT. LEVEL 

1100-FT. LEVEL 

0 .. 100 • 200 300 FEET 

Themostin1portantlocleof the belt FIGURE 30.-North-south section through Anaconda and Parrot veins and Blue 

next to the Anaconda is the Pennsyl- vein fault. 

vania. This large and in1portant n1ember of the Anaconda system, 'vhich has long been the 

chief ore producer of the Pen~sylvania mine, has also been extensively worked in the Anaconda mines (fig. 32), where it is called the South ledge. As the identity of the South ledge 

and Pennsylvania veins is well established, it seems best to use the latter name. It has been 

continuously developed fron1 the Blue vein eastward thro1,1gh the Anaconda, St. Lawrence, and 

Pennsylvania mines a distance of 2,600 feet. In the ·Pennsylvania n1ine it is known as the 

Pe1msylvania No.2 vein eastward to the Rarus fault and as No. 3 vein east of that fault. It is 
118 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

not positively identified west of the Blue vein, but is· probably continued eastward • beyond the 

Mountain View fault in the Enargite vein. . 

The vein has a course nearly or quite parallel to the Anaconda, and, like that lode, shows 

mineralization alternately along N. 80° E. and N. 80° W. fracture planes. It has a thickness 

of 6 to 20 feet, averaging 8 feet in the Pennsylvania and 12 feet in the Anaconda properties. 

The dip averages 65° in the Anaconda, but varies both horizontally and vertically, being 80° 

in the lower levels of the Pennsylvania mine. The character of the upper vein is well seen· in 

600-FT. LEVEL 

900-FT. LEVEL 

1000-FT. LEVEL 

1300-FT. LEVEL 

1400-FT. LEVEL 

LEGEND 

~ Vein 

~ Fault 

the fourth, fifth, and sixth levels of the 

Anaconda mine, where it has been extensively worked. In these levels the 

vein is double, and has the same granite gangue seen in the Parrot lode, as 

exposed in the uppermost levels of the 

Colusa-Parrot mine. The vein filling 

consists of altered granite netted by 

quartz and pyrite films, with more or 

less complete replacement of the pyrite 

by chalcocite. 

In these workings the ledge has 

evidently been shattered during the 

downward movement of the block by 

faulting, and the crackled vein matter, 

being readily permeable to descending 

waters, has been enriched by the deposit of chalcocite in the fractures. 

With increasing depth more and more 

quartz appears until the vein has a 

normal quartz-pyrite filling. The oxide ore extends downward to the fourth 

level of the Anaconda workings with 

soft and friable sulphides between" this 

and the solid sulphide ore. Lower 

down chalcocite is found in films and 

specks in the included rock and replacing the pyrite. 

In the Pennsylvania mine the vein 

has been productive from the surface 

downward. In the upper levels it has 

been cut· and deflected by the Rarus 

fault, but, as described in the account 

of 'that fault, the vein has not suffered 

0 100 200 3oo FEET abrupt and great displacement, but· is 

1600-FT. LEVEL broken by distributed faulting, with 

numerous slight shifts which have not FIGURE 31.-Section through Anaconda lode, showing splitting of vein. . interfered with development along the 

-vein. In t)lis mine the general eastward course of the· vein which prevails in the upper levels 

11lters to N. 70° E. at a depth of 900 feet beneath the surface, the dip steepening to 80° in the 

1,000-foot level and below. This is also the dip in the faulted part of the vein called Pennsylvania No.3. · · 

The width of the vein in the Pennsylvania workings varies from 6 feet to 16 feet~ In the 

deeper levels there is commonly a clay or breccia. streak a few inches to a foot thick on the 

hanging wall, with about 3 feet of first-class ore between this and t_he crushed granite footwall. 

In part it follows the quartz porphyry contact. · 
DR7i/N TUNNEL 

o 100 200 300 400 !:;100 feet 

FIGURE 32.-Cross section through Anaconda shaft on line through long south cr.osscuts. 

• 

> z 

> 0 

0 

z 

t::! 

~ > 

~ 

~ 

0 

1-3 

t:d 

t;j 

~ 

....... 

....... 

~ 
• 

120 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRr"CT, MONTANA. 

Mineralogically the Pennsylvania vein shows the s~me general composition and variations 

seen in the Anaconda. In the uppermost level of the Pennsylvania mine it has an average 

thickness of 8 feet and is inclosed by walls of softened altered granite. In the 200-foot level 

of the mine the vein showed a streak of enargite 6 inches to a foot thick, clue to secondary 

mineralization along postvein faulting. 

The vein appears to join the.Silverbow vein for a short distance, separating again westward. 

On the projection of the veins of the district on the 5,600-foot plane the vein is traced from the 

Pennsylvania workings westward through the St. Lawrence, Anaconda, and Ramsdell-Parrot 

m1nes. 

Down to the 1,000-foot level the Pennsylvania vein carries more or less glance and enargite, 

but lower clown it become$ leaner and has less secondary quartz or pyrite, though evidences of 

crushing and stdke fault movements are plainer than above. · · 

On the 1 ,000-foot level of the Pennsylvania mine the vein is 7 to 10 feet thick, and shows an 

upper or hanging-wall streak of mashed grani.te and day above a 3-foot band of solid but lean 

pyrite and quartz devoid of secondary minerals. The· center of the vein is a 3-foot band of 

broken quartz carrying streaks ·of glanc.e and secoJ}dary milky quartz holding a litt~e pyrite and 

· some clay. An enargite streak 6 to 10 inches thick separates the last b~nd from the foot-wall 

layer 3.2 feet thick, carrying clay with friction breccia and pebbles, and running parallel to the 

clay streaks and slips in the ore body proper. The vein carries 2 to 3 feet of first-class or smelting ore in the 1 ,000-foot stope. Where it crosses the porphyry dike, as for example on the 900-

foot level; it is lean. · · 

Numerous southeast slips run out from the hanging wall of the vein and many of them 

carry gla11ce for a few feet from the wall. Even when not recognizable in the mines these slips 

show an offset of the vein, as indicated on the level maps. The· vein walls are smooth but rolling, showing varying dips of 60° to 80°. Clay slips are common, but are not uniformly present 

except near cross faults; 

In the deeper levels the vein consists of a·mixture of quartz and pyrite, ·the latter in many 

places predominating, but showing drusy streaks of white recently formed quartz. This white 

quartz also cements together the crushed vein where it is· fractured by fault seams. This secondary quartz often carries chalcocite, but the amount varies from place to place and is. sometimes nil. .· 

At 1,200 to 1,400 feet below the surface the vein is very irony, hard, and lean; it still shows 

its composite character, having the original solid quartz-pyrite vein along the ha:r;Iging wall 

with crackled and in places crushed ore in the center, and showing many clay cross slips and 

· rounded masses of white quartz carrying druses of quartz and pyrite. The recementation of 

the ·crushed older vein by new quartz and ore is not complete. The ore is dry and shows no 

glance above a heavy clay slip, above which the streaks dip north into the vein. The vein 

varies from 8 to 16 feet in thickness in these lower levels of this mine. 

The Pennsylvania vein is correlated with the O'N eillledge, but there is some doubt as to 

the identity of these two. (See p. 122.) · 

MOONLIGHT VEIN. 

The Moonlight is the first large vein south of the Anaconda lode and has a course parallel 

to it. It is worked in the Blue Jay, Bellona, and Moonlight mines, being developed to a depth 

of 1,300 feet and for a length of about 2,000 feet. It is an east-west quartz-pyrite lode, cut 

and displaced by the Blue Vein fault, the eastern part forming the Middle ledge of the Anaconda 

mine east of that fault. It is also intersected and enriched by the Blue Jay fault vein of the 

Steward system (fig. 33). The Moonlight vein belongs to the Anaconda system, and shows the 

usual characters of the older quartz-pyrite lodes. Its dip averages 68° S. The ve.i.n filling consists of hard and generally solid. quartz and pyrite, 5 to 50 feet wide, with ill~de:fi.ned walJs, the 

ore fading into the hanging-wall rock except where strike faults have formed clay selvages. 

The vein is not uniforn1ly mineni1ized, the richer ore occurring in shoots; the largest of these, 

worked in the Bellona mine continuously from the oxidized zone down to a depth of 1,300 feet, 
ANACONDA-PARROT BELT. 121 

shows 50 feet of stoping ore. The ore shoots consist of shattered primary ore, enriched by 

intersecting northwest fault veins, the intersection determining the location of the shoots. 

These richer ores contain enargite, sphalerite, and chalcocite, the first named in irregular streaks 

and masses embedded in a clay matrix, or in·altered granite, while the glance is later and forms 

a cement binding fr~gn1ents of rock and earlier ore together or filling fractures .. In the stopes, 

fragments 5 feet across are common. 

On the 7 50-foot level of the :Moonlight mine the Bricker ore body is 50 feet or· more wide, 

narrowing westward to the Blue Jay fault vein. The· ore shoot is defined by soft fault matter 

on the hanging wall, with. soft, decomposed, blocky granite on the outside of it for 115 feet. 

This is incased in black granite netted with joints, along which the rock is altered and is soft and 

slacks· readily. The footN wall of the ore body is irregular, showing a 5-fo.ot band 

of 3 per cent ore between the 

wall and the vein proper. 

The vein beyond the Bricker 

ore body is now proved eastward on the 7 50-foot level to 

the shaft, the ore pinching 

and passing into the wall of 

the level near the raise to the 

600-foot level, the drift following a n1ere clay seam. 

North of the vein the granite 

is norma]. On the 500, 

750, 1,.000, and 1,100 foot 

levels of the :Moonlight mine 

the lode has been worked 

for over 1,000 feet horizontally. The vein in these 

workings shows the usual 

netted fissuring of the east 

and west veins. 

A north and south section through the Bellona 

· shaft shows the vein to lie 

wholly above both the Blue 

and the Blue Jay fault veins, 

' ' ' ' 

~' "~\ L\ 

~-\ 

? ' \ 

\ 

s 

--200 

--300 

' --400 

-.-500 

--600 

--700 

Faults Ore 

and i_t appears prObable FIGURE 33.-North-south cross section through Colusa-Parrot vein, showing relations of Blue Jay 

fault and Moonlight vein. · that the east-west quartzpyrite vein east of the Blue vein is the extension of the :Moonlight, displaced by the Blue and 

subsequently broken along its strike by the Blue Jay fault vein.· As. the ore shoots result from 

the cutting of the vein by faults, a knowledge of their occurrence is of prime importance. 

Tl1!e Blue Jay fault cuts off the vein both downward on its dip and westward, so that the 

vein is seen west of the fault in the Blue Jay mine workings. It becomes zincky and lean westward. The eastern displaced portion of the vein, seen east of the Blue vein, is so shattered by 

the Blue Jay that a c01nposite vein.is formed, and the vein is not known beyond the point where 

the Blue Jay leaves it. The structural features of interest are those also common to the Middle 

ledge. It is to be noted tl~at the v~in has been first faulted by the Blue vein, and then along its 

strike by the Blue Jay, which after leaving the :Moonlight crosses the Blue and becomes a strike 

fault on the eastern part of the vein. 

The 1,000 and 1,100 foot levels of the :Moonlight :rp.ine show the vein of this name extensively worked both in drifts and stopes. On lihe 1,000-foot level the vein lies on the south side 

0 
122 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

of the Blue Jay fault, but between the 1,000 and the 1,100 foot levels the Blue Jay passes through 

the Moonlight with almost no shifting of the ledge, so that on the lower level the vein lies on the 

northwest side of the Blue Jay fault and follows along a displaced easterly section of the Moonlight, which probably fades out eastward, as it does not show in ·the mine workings. That it 

corresponds to the Middle ledge of the Anaconda mine is plain if one matches the opposed ends 

of the vein on each side of the Blue vein, allowing for approximately the same displacement 

observed between the Anaconda ledge arid Parrot. 

HOGAN VEIN. 

The Hogan (or Hogans Alley) vein is a quartz-pyrite contact vein, belonging to the Anaconda system., that is cut on the deep levels of the Anaconda properties. Its outcrop has not 

been recognized. The vein is best developed on the 1,200 to 1,600 foot levels of the Anaconda, 

where it occurs underneath the porphyry dike that lies either on or near the foot wall of the 

Anaconda ledge. .The Hogan vein thus lies between porphyry and granite, being overlain by 

the former, but departing from the contact and running off into the granite as it is followed 

upward. The vein is from 5 to 15 feet wide and shows an average of 8 feet of stoping ore, but 

is not everywhere workable. It carries much water, and its ore contains both crystalline and 

sooty glance. (See fig. 37, p. 126.) 

The vein is well developed on the fifteenth level of the Anaconda mine, where it lies on the 

foot wall of a 30-foot dike of the rhyolite porphyry. The course is S. 80° W. magnetic, ·and 

the dip 65° S. The vein shows a thickness of 3 to 4 feet of pyrite and quartz ore carrying perhaps 3 per cent' copper. On the 1,800-foot level this vein is too lean to warrant working. The 

lode is cut off to the west by a nor.thwest fault fissure 4 feet wide, running N. 40° W. and dipping 

75° s. 

O'NEILL LEDGE. 

The O'N~ill ledge is a faulted block of the Pennsylvania vein beneath the Rarus fault. 

(See fig. 32.) The lode shows in the south crosscut from the Anaconda mine, and is ·worked in 

the Belmont, but, being cut off by a northwest fault, its continuation west of the Anaconda 

crosscut is unknown. The lode is 15 to 20 feet wide, consisting of shattered quartz-pyrite ore, 

with well-defined walls marked by clay seams. The clip is southerly and rather flat. The vein 

is continuously developed· east of the Rarus fault on the Pennsylvania 1,000-foot, Anaconda 

(South) 1,400-foot, and the _Belmont 900-foot levels. In the Belmont mine it has been· opened 

up on the eighth and ninth levels, and the identity of the ledge worked on these levels with the 

O'Neill ledge drifteq on in the Anaconda 1,200-foot (which would be equivalent to the Belmont 

700-foot if such existed) seems beyond question. But as the Blue vein passes through this 

ground it is possible that the correlation with the Pennsylvania vein is incorrect. 

MINERALIZATION. 

The enormous copper production of the Anaconda lode is clue .to the great q~antities of 

copper glance which it contains. The upper levels held masses of nearly solid chalcocite 2q 

or more feet wide, several hundred feet in both length and depth. Besides these masses of 

solid· glance, the intervening granite was netted by veinlets and impregnated· with scattered 

grains of copper glance, formirig the concentrating ore which furnished the bulk of the production. Chalcocite is most abundant where the vein has been shattered or faulted, and the 

larger ore bodies of rich ore show a marked dependence upon the presence of cross :fissures. 

Plate XIII (p. 110, after H. V. vVinchell), which represents an ideal cross section of the lode, 

shows the relation of the lode to the quartz porphyry dike and to fault fissures. 

· In general it may be said that chalcocite is less abundant with increasing depth and that 

the thick bodies of solid chalcocite found throughout the vein from 500 to 1,200 feet in depth 

gradually narrow downward and end in threads or films of glance pen(3trating the primary 

vein filling. The presence of this 1nineral appears to be wholly dependent on the depth of 

the fracturing and the readiness with which waters penetrated downward. Where the primary 

quartz-pyrite vein filling is solid and unbroken it carries little or no glance and is usually too 

• 
ANACONDA-PARROT BELT. 123 

~ean to work. In the upper levels the large masses of chalcocite formerly mined resulted 

fron1 a con1plete replacen1ent of the primary pyrite ore by reaction between descending waters 

·carrying copper sulphate and the· primary pyrite or other sulphides. Glance is most often, 

l10wever, found in areas of crushed and faulted material, where it largely results from the filling 

of open spaces, as shown by the occurrence of large included crystals of quartz in the chalcocite 

{fig. 34). 

The outcrop of the Anaconda is not conspicuous and throughout most of its course must 

be searched for, as it is broken down and its quartz greatly resembles the silicified granite 

-of the adjacent rocks. For 20 to 150 feet below the surface it consists of quartz, generally 

:shattered and stained a rusty brown by limonite, but rather massive, and lacking either the 

porous structure or the great amount of limonite usually characteristic of the gossan of quartz-

·pyrite veins. At a d~pth varying from 20 to 100 feet tlus quartz, which is devoid of copper 

but carries a residual silver content, gives way to a mass of black friable material consisting 

-of pyrite and copper glance. 

'This layer of so-called "sooty 

:sulpludes," which ranges from 

2 to 6 feet thick in the Parrot 

urine to the west, is tlrin or ab-

.sent altogether along the Ana-

·conda lode proper. It is un-

,derlain by solid glance and pyxite ore, the upper surface of 

the 'glance showing the effects 

.of the oxidizing waters. 

As already indicated, the 

·cross fractures, wluch are later 

than the primary lode filling, 

.are most in1portant, as they 

govern the occurrence of the 

.high-grade ore. These frac- o 4 e 12 IG Feet 

tures va1~y from mere joints, FIGURE 34.-Anaconda lode, third floor west on the 1,.600-foot level of Neversweat mine. 1 

only recognizable by fihns of Solid quartz hanging-wall band, 8 feet; 2, crushed white quartz peppered with pyrite, 2 

·glance in freshly exposed sur-. feet; 3, clean glance, 4 inches; 4, brecciated white quartz, () feet, inclosing fragments (5) of 

quartz-pyrite ore. 

faces, to well-marked "spur . 

·veins" carrying glance ores. Where ore-bearing these cross fractures have evidently derived 

their copper fron1 the san1e source as the secondary ores of the lode, and their copper content 

.fades out as the distance from the lode increases. 

The two main faults of the district, the Blue Vein and the :Mountain View,· have produced 

great cJ.isplacements, and are, for convenience, used ·as limits defining the sections of t~e lode . 

. All the numerous minor cross fractures whose general course is noi·thwest cause slight displacements, but are not shown on the maps, as they are far too numerous to plot on the 'scale 

used. 

Besides the copper glance, enargite and bornite appear in the·lode. The enargite is found 

·Only in connection with faulting and is the result of mineralization later than the vein. Bor-

.. nite appears to be both pri1nary and secondary, but as it is inclosed by the enargite it is known 

.to be the older. Much bornite is found in the Parrot mine and in the workings westward, 

but it occurs in comparat.ively small amount in the. Anaconda properties and in the Mountain 

·view mine. · 

In the lower levels of the mines which work this lode cross fracturing has resulted in a 

.shattering of the grmute, due to an adjustment of the displaced blocks, and this shattered 

granite has been enriched by the deposition of copper glance, so that considerable masses of 

•Ore outside of the vein proper have been 1nined at various points. 
124 GEOLOGY AND OHE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

Figure 35 shows the rock traversed by a series of slips and seams, running from N. 20° to 

N. 30° W., arid dipping southwest at varying steep· angles. ·The granite is thoroughly sericitized and bleached. Besides the fault slips shown, a network of joints runs at every angle and 

in every direction. These joints are filled by glance and pyrite and the intervening rock 

is impregnated. 

In general the vein filling in the vicinity of fault fissures has been found to contain rich ore 

in the deeper levels, but to be poor at such places in the upper parts of the lode. 

In the Colusa-Parrot mine (Parrot lode) the upper portion is unlike the normal quartzpyrite vein below. It consists· of narrow quartz-pyrite veins, with the intervening granite 

impregnated with grains of pyrite replaced or coated by glance. As it is known that the 

displacement of the Blue vein caused a downthrow (of the Colusa-Parrot) of at least 510 feet 

the Parrot workings represent the highest portion of the Anaconda lode preserved at the present 

time. (See fig. 36.) It is not known how much erosion thi~ portion of the lode has suffered; 

but inasmuch as the adjacent Neversweat workings east of the fault show enriched ore at much 

greater depths than those of the Parrot it is assumed that tlus enrichment is due to a concentration within a zone 2,000 feet deep of the copper leached from a former vertical extent of 

the lode above the present surface much greater than that which contributed to the enrichment of the Parrot ground. 

·In the Anaconda lode, as well as in other lodes throughout the district, the workable ore 

sprays out above the cross faults, showing that the deposition of glance has been by descending 

waters. · Owing to the greater abundance of gfance in the 

upper levels, this feature is not so marked as it is in levels 

1,000 feet or more beneath the surface. 

Besides the northwest fissures, whose effects have been 

noted above, fissures having a general course of N. 60° to 

70° E. intersect the lode at a comparatively small angle. 

These intersecting fault veins have been extremely important factors in the production of large ore bodies; but 

inasmuch as they have brought about a separate miner-

. alization, arid as the earlier ore found in the~ is broken 

FIGURE 35.-Altered and mineralized granite along· and comes from the.· primary veins, their discussion is 

side of Anaconda lode (south) on third floor above postponed. 

the 500-foot level of the St. Lawrence mine. 

Faults 

'G 

Minor faults 

m· 

Veins 

The footwall of the vei:t;_l is commonly marked by breccia and clay; forming a porous layer that is everywhere a source of water. The abundance of 

water is regarded as a favorable sign, as where the ledge is dry and tight it is .generally too low 

grade to be workable. This clay slip separates the altered rock from the normal biotite granite 

to the north. The Blue Jay fault or Middle ledge, where cut on the 1,800-foot Anaconda 

level, admitted water which .gushed to a height of several feet, but gradually subsided in the 

course of a few weeks. 

Thc:s rock between the two ledges of the Anaconda vein is always more or less jointed, though 

seldom crushed. It is pyritized and shows extreme alteration along the joints. 

Although normally devoid of banding, the vein, where crushed or crackled, shows new 

quartz and secondary ore minerals arranged in bands and vugs. 

The general character of the Anaconda is well shown in the 2,000-foot level of the Neversweat (east), where the vein is 40 to 50 feet wide, and is generally solid (and lean); if cracks 

occur they carry recently deposited pinkish quartz; where the vein is. vuggy, glance appears. 

Enargite also appears at this depth, occurring mainly in patches and in veinlets, but also in 

streaks in the granite walls. . 

The cross fractures that cut through the Anaconda lode are not shown on all the vein maps .. 

All of them were not recognizable on all the levels when the notes were made and no attempt 

was made .to proj~ct them. Their distribution is evidently important, determining the ·exist-

. ence of rich ore bodies, but the vein is so large that they are easily overlooked in working. Such 
ANACONDA-PARROT BELT. 125 

· fractures and "sp~rs" were seen in many freshly opened stopes~ but they are hard to recognize 

in the levels; even a 3-foot shift in the wall of a vein 60 feet wide could scarcely be noticed. 

The Anaconda vein in the Neversweat mine west of the main crosscut is cut by a dozen strong 

clay slips running N. 35° to 65° W. and dipping 60° to 80° SW. In places th~se slips can be seen 

to cross the vein, but more generally they can not be recognized except on perfectly clean faces. 

The map (Pl. XXXVI) showing the vein structure on the 5, 700-foot plane (300-foot level 

Anaconda. and 100-foot level St. Lawrence) shows the full development of the Anaconda vein . 

. The vein passes through a dike of the . 

rhyolite porphyry at the eastern 

end, and is lean, .carrying pyrite, 

but no glance, in this rock. The 

· oxidized "free-milling" ore extends too-Fr. LEVEL a 

down to this level in some places. 

FAULTING. 200-FT. LEVEL ::· 

.300-FT. LEVEL 

400-FT. LEVEL 

500-FT. LEVEL 

_600-FT. LEVEL 

700-FT. LEVEL 

800-FT. LEVEL . 

900-FT. LEVEL 

/000-FT. LEVEL 

1100-FT. LEVEL 

LEGEND 

Anaconda 

-

vein 

Parrot vein 

Blue 

~ vein 

0 100 200 300 FEET L.....----'----'-----1 

The n1ost interesting structural 

feature of the eastern part of the 

Anaconda lode is its cutting and 

dislocation by three cross faults, 

known as the Blue Jay (l\fiddle or 

No. 16), the :Mountain View, and 

the (later) Rarus. The two last 

na1necl intersect on the 1,400 and 

1,500 foot levels of the St. Lawrence 

mine. At the east end of this Inine. 

the Rarus fault splits up into four 

or five strong fiSsures, with crushed 

and altm~ed granite between, and 

this crushed and altered ground 

contains flat ore bodies which have 

yielded large amounts of rich enargite.ore quite different from that 

found elsewhere in the mine. These 

ore bodies have an inclination of 

about 30°, are not over 15 or 20 

feet thick, and appear to be displaced and enriched podions of the. 

main vein. The strong fault fissures 

of the Rarus are very apparent, cutting off the ore abruptly on the west; 

beyond them the Anaconda lode is 

solid, but is a lean mi.."Cture of quartz 

and pyrite. Between the fissures · 

the ore is a crushed granite, filled 

with streaks and fault slips running FIGURE 36.-Section through Neversweat and Colusa-Parrot mines. 

in every direction and thoroughly in1pregnatecl with pyrite and enargite. The interfault matter, 

. where composed of rhyolite porphyry, is lean and is not enriched, unlike the broken ground in the 

granite area proper. The diagram (fig. 58, p. 153). represents conditions on the 1,400-foot level 

of the St. Lawrence mine, where the ore body worked on the 1,300-foot level has been followed 

downward and has been' extensively developed. On the underlying 1,500-foot level the intersection of the Mountain View fault vein is well shown. The vein, whichis 3 sets wide, is cut by 

north and south fracture's passing through the solid quartz. The vein has apparently been 

twisted, as shown by the fractures observable on fre~h surfaces. The vein quartz is mostly 

white and very lean, but in places carries pyrite, with specks of glance. Between the faults, 
126 GEOLOGY AND OR.E DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

marked by strong cla.y seams arid gouge, the ore· consists of mashed granite impregc.ated with 

pyrite and enargite. 

The Hogan vein is seen east of the Rarus fault in the south crosscut fron1 the 1,500-foot 

level (fig. 37), but it is lean and not workable. ' 

The 1.,400-foot level (St. Lawrence) shows the typical structural features of the main lode. 

It here ];las a general east-west course, and lies parallel to a quartz porphyry dike, which is 

about 30 to 50 feet back in the footwall. This dike shows very plainly that northwest faults 

lying between the Blue and Mountain View faults have broken and thrown both the dike and 

lode, and have been channels for enriching waters. A fault of the Steward system crosses the 

ledge, but gives slight displacement. East of the St. Lawrence shaft the lode is lean and, on 

account of. the still persisting mine fire, has not been stopecl. The lode is thrown eastward by 

the Mountain View fault, a northeast.fissure filled with hardened clay and friction pebbles. The 

oxidized quartz has been mined for converter linings and to recover its silver content on the 

150-foot (5,872 feet) and 200-foot (5,821 feet) levels of No. 2 St. Lawrence shaft. 

The Rarus fault cuts across the Anaconda 

~;:___,..--.---6 --;;------_,s. ledge in the workings of the St. Lawrence mine, 

6 

showing well on the 1,800-foot and 2,000-foot 

levels. On the 2,000-foot level, south of the 

Rarus fault, the Anaconda workings show drifts 

on three veins of the Anaconda lode. The n1ain 

one is a fault vein, worked through to the St. 

Lawrence; it is flat (clipping 35° S.) and is lean at 

the west end, showing but 12 inches of quartz, 

running 2-! per cent copper and 3! ounces per ton 

of silver. The second vein is 6 feet wide and carries 1 to 3 per cent copper, with 1.8 ounces of 

silver per ton. The third vein is also 5. to 6 feet 

thick, with ore of the sanle general tenor. 

On the Anaconda 2,200-foot level the vein 

FIGU!lE 37.-Section of Hogan vein. 1, Quartz monzonite; 2, has a strike of N. 65° E. and a dip of 65° S.; it 

5 10 Feet 

crushed quartz monzonite witb clay streaks; 3, clay; 4, quartz-· carries 3 feet of quartz containing 5 to 6 per cent. 

pyrite vein; 5, porphyry with clay streaks;. 6, porphyry. 

copper and 2 ounces per ton of silver. The vein 

is cut and displaced eastward by a northwest fault and by several northeast slips, and the rich 

ore occurs along these fracturas. The inain ledge, where cut by the St. Lawrence main crosscut, 

is 30 feet wide, and farther west where crossed by the fault slips is 45 feet wide and runs 7 to 

11 per cent copper. 

The southwestern extension of the· Rarus fault is disclosed in the twentieth level of the 

Anaconda, showing in the south crosscut. The interfault material holds large blocks of ore 

and porphyry turned partly around. The Rarus fault is 300 feet wide at this place. 

PARROT LODE. 

THE LODE AS A WHOLE. 

DEVELOPMENT AND GENERAL CHARACTER. 

The Parrot was, the first copper vein discovered and. the first one worked in the Butte 

district. It has been traced almost contmuously from Missoula Gulch eastward to the Blue 

fault vein, near the Anaconda mine, a distance of·3,750 feet, all of which has been.actually developed by underground workings. The deepest levels driven on the lode are 1,800 to 2,200 feet 

beneath the surface, corresponding to an absolute elevation of 3,400 to 3,800 feet above the 

sea. So far as shown by present mine development the lode forms the southern limit of the 

productive copper belt west of the Blue Jay mine. 

The general course of. the Parrot lode is nearly east and west, with divergence of about 

5° S. at the west end. The vein dips south, generally at 75° to 85°. (See fig. 38.) 
ANACONDA-PARROT BELT. 127 

The. outcrop is readily traceable and in early days is said to have been marked by an 

abundance of green carbonate and silicate of copper and by an entire absence of vegetation. 

Atpresent it is seen as a distinct band, differing in color a.nd character of debris from the adjacent granite, though rising but slightly if at all above the general level of the weathered rock. 

5 

--------------

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

0 250 500 Feet 

FIGURE 38.-North-south section through Parrot shaft. 

N 

~:~NipperApex drift 

FEET 

5800' 

5600 

5400 

5200 

5000 

4800 

4600 

4400 

4200 

4000 

The Parrot lode shows the same general characters as the Anaconda, but differs in·minor 

features. As already stated, the vein consists of quartz and pyrite, cracked by secondary 

fractures and enriched by secondary mineralization. It bears bornite and carries enargite in 

increasing amounts toward the west, glance becoming of secondary importance. Its structural 

features also change, and its silver ratio increases westward toward the silver belt. 
128 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

SPLITTING OF THE VEIN. 

At the east end the Parrot lode shows the two ledges which compose the Anaconda lode; 

the hanging-wall ledge diverges from the main vein both downward and westward (see fig. 39) 

and west of the Parrot shaft can not be regarded as part of the lode; it is known as the South 

Parrot or Virginius vein. 

Toward the western end of the Parrot mine another·vein is observed on the footwall side. 

This, known as the Original fault vein, is nearly parallel to the. main Parrot vein, both vertically 

LEGEND 

Fault 

100 200 300 

1400-FT. LEVEL 

FIGURE 39.-Cross section through Colusa-Parrot shaft. 

and along its course, from No. 6 shaft westward to the Gagnon, being recognizable to depths 

of 500 feet or more, but being lost when the entire lode is crushed and broken by the intersection 

of the Steward fault vein. 

The Parrot vein maintains its identity intact, despite ·numerous cross fissures and veins, 

from the Colusa-Parrot mine to the Gagnon. ·This is true, however, only in the upper levels, 

for in the lower levels (fig. 40) west of the Parrot mine the lode is cut and crushed by faults, the 

largest of which follows along the strike and forms a composite vein. The Parrot vein proper 

is regular in course and dip from the surface downward to a depth of 800 to 900 feet~ below this 
ANACONDA-PARROT BELT. 129 

· it shows fracturing and many minor displacements, with corresponding irregularity in mineralization. The general course is east-west, the qrifts running either N: 80° W. or N. 80° E. and the 

stopes showing the course of the vein to be first along one and then along the other of these 

directions. 

In the Original mine the Parrot maintains its character as a solid quartz-pyrite vem, 

cracked by slight faulting, with seams and films of glance filling the cracks. 

Near the surface the Parrot lode consists of the 

0 2 3 4 Feet 

footwall vein (No. 6 vein) and the Parrot vein proper. 

The latter is itself double from No. 6 shaft westward. 

The P.arrot No. 6 vein consists of two ledges, each 2 

feet thick, of hard, lean, quartz-pyrite ore, carrying 

less than 1 per cent copper, with 6 to 7-ounces of silver; 

the veins are separated by 25 feet of altered granite. In 

the 200 and 300 foot levels of the Original mine these 

veins are thicker, the southern· one being 3 to 5 feet 

and the main ledge from 10 to 15 feet wide. The intervening granite is 12 to 25 feet thick. The veins show 

ba~cling, the streaks clippiri.g 65° to 70° S. with the vein. 

The ore is solid, but lean, there being no secondary fracturinbcr and enrichment. FIGURE 40.-Section of south ledge, 1,400-foot level of 

Parrot mine. 

Farther east, near the Parrot shaft, the lode is single , 

down to a depth of 1,000 feet, splitting below this into two veins separated by 50 feet of altered 

granite. On the Parrot· 1,200-foot level the footwall vein .is the lesser, varying from 5 to 12 

feet across. It is a very hard pyritic quartz vein with a thick clay and breccia sean1 on ·the 

footwall and a foot or n1ore of nearly pure bornite lying between the· clay and the quartzpyrite vein (fig. 41). The main ledge or hanging-wall vein is 8 to 25.feet thick, but rolls and 

pinches, b'Oth vertically and horizontally. It is cut by N. 10° to 40° E. fractures with a clip 

of 80° to 90° W.; in s01ne places these fractures are· so close together as to brecciate the vein. 

0 SFeet 

They vary from mere cracks to clay seams 2 feet 

thick and. delimit the rich ore on the hanging-wall 

side. In some places streaks of glance run out 

along the cross fissures for several feet fron1 the lode. 

The Parrot vein is continuously worked from 

the Blue vein westward through .the Parrot and 

Original nunes to the extren1e limits of the Gagnon (on the 200-foot level of the latter property, 

corresponding to an elevation of 5,600 feet). This 

continuity does not· obtain in the deeper levels, 

for, below the 800-foot level, the Parrot vein, as 

developed in the nune of that name, has a flattish 

southward clip, and the main ore supply of the 

deep levels, 1,100-foot to 1,800-foot, of the Original 

and Gagnon mines comes from a compound or 

composite vein formed by the· union of this and the FIOURI~ 41.-0re bauds, Parrot lode, 1,400-foot IC\"'.ll. 1, Quartz; Steward fault. vein. It appears probable that a ' 

2, pyrite; 3, soft sand. 

spur of the Parrot vein runs into and forn1s this 

vein. The Pa1;rot vein is certainly continuous through the entire length of the Parrot mine on 

the 700-foot level westward into the Steward and Original workings. 

FRACTURES. 

The Panot lode is not so wide as the Anaconda, averaging perhaps 20 feet. Cross fractures are often strongly developed in the upper levels, particularly near what is known as No. 

6 shaft, hut 1nore conup.onl}r the northwest cross fractures are scarcely recognizable in. the 

90427°-No. 74-12-9 
130 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

levels from 500 to 1,000 feet, whereas from the 1,000 to the 2,000 foot levels they are 1nnrked, 

delimiting the rich ore and.causing 'much troubl~ in mining. 

From east to west there is a gradual change in mineralization shown in the larger an1ount 

of bornite, in the in·creasing abundance of enargite where fnulting has .occurred, and in the 

increased proportion of silver carried in the ·ore. 

The Clear Grit vein, a prominent northwest fracture parallel to the Blue vein, cro'Sses the 

Parrot lode without much displacement of the latter, and many of the lesser fault fractures shift 

the veinfrom a few inches to several yards. 

Westward the Parrot lode is intersected by the Steward fault vein, with which it forms the 

great composite lode that has yielded richly in the deep levels of the Original and Gagnon mines. 

In these mines the lode above the intersection is lean, or where pay ore is 'found it is limited to 

small ore shoots, but below the intersection large ore bodies, rich in enargite, are encountered. 

At its east end, on the lower levels of the Colusa-Parrot claims, the lode closely resembles, 

in its structure and characteristics, the faulted end of the Anaconda ledge lying east of the 

Blue vein. The lode, however, to a depth of 700 to 800 feet, consists of mineralized and altered 

granite rather than of quartz-pyrite veins. The significance of this has already been n1entioned 

in discussing the faulting of the district (pp. 58, 125), the inference being that the Parrot represents the faulted downthro\vn block in which the upper granite part of the vein has been preserved while erosion has removed it from the Anaconda to the east. This means a time interval 

since the Blue vein was formed sufficient for the differential erosion of 510 feet of vein and rock 

from the surface of A-naconda Hill. PARROT MINE. 

ORES. 

In the Parrot mine the rich bornite ore which isS<? abundant in the upper levels gradually 

decreases in amount with increasing depth, until at 1,000 feet the ore is relatively lean. This 

character prevails westward until the big Steward fault is encountered in the Original mine. 

There is little doubt that in the Parrot mine the lode does not carry rich ore to as great depth 

as the Anaconda; the physical, as well as the mineralogic, character of the ore indicate incomplete replacement in the· deeper levels, as compared with those above. 

FRACTURES. 

The character and influence of the lesser cross fissures is difficult to estimate. West ward 

they certainly appear to continually shift the vein to the north and to have a marked influence 

on the richness of the vein, as shown by comparison of the ore mined on the upper and lower 

sides of the cross fault. Most of these faults have so slight displacement that it is difficult to 

find them in the level workings, but they can not be found at all in the old stopes of the upper 

levels as these are all filled and closed up; those at the deeper levels are therefore more apt to 

appenr on the mine map than are those nearer the surface. Figure 41 shows the fracturing oh 

the 1,400-foot level. 

The west stopes of the 1,300-foot level of the Parrot mine show a vein having an 18-inch 

foot-wall streak of crushed granite and clay, which at times passes into breccia. This adjoins 

4 feet of quartz and pyrite formed as a replacement along a network of fractures in a shattered 

granite, the rock showing no recognizable sheeting or plating. The hanging-wall portion shows 

2 feet of .shattered quartz and granite. This portion of the vein shows very plainly that it 

is cut by cross fractures, which cut off the ore and destroy the continuity of the ore shoots. In 

general they strike 90° to the vein, and dip 80° E. This may indicate a greater number of 

such cross fractures in the lower workings than in the levels above 1,000 feet, but the excess is 

believed to be only apparent and probably due to the fact that in the upper workings no fresh 

faces are obser-Vable. However, there is a strong- probability that the mineralizing process is 

not complete in the lower levels and that the workings are approaching a zone of leaner ore 

(or rather of ore· streaks separated by barren places) and that for this reason the deflection of 

the enriching currents by the cross fractures is much more evident in the lower than in the 

upper levels. 
ANACONDA-PARROT BELT. 131 

The second floor of the 1,300-foot stope shows 15 feet of good ore, which consists mostly 

of pyrite, with enargite and bornite, the latter occurring in spots and along vugs. The bornite 

here seems partly primary and partly secondary; attention should be called to the elongated 

vesicles, which indicate gas inclusions, found both in the bornite and glance of these lower 

levels. The hanging-witH side of the solid ore has been crackled and shows 2 inches to 6 inches 

of crushed quartz on tl~e wall, with 6 inches to 10 inches of quartz-pyrite ore and one-sixteenth 

inch of glance. 

The character of the lode in the deeper levels of the Parrot mine is well shown in the 1,400-

foot level. The main ledge consists of somewhat crackled quartz, with a chalky texture, owing 

to the fact that the mine waters have been drawn off by the deeper N eversweat openings. 

The quartz contains much pyrite with threads and small scattered particles of bornite. In general.the main ledge at this level is a solid quartz-pyrite vein, in which enrichments occur where 

the ledge is shattered. Considerable reel quartz appears and is considered to be the result of the 

precipitation of glance by reaction with carbonates. The south drift shows dark altered 

granite with disseminated pyrite, netted by films and streaks of quartz carrying pyrite, and by 

veinlets of pure white n1ilky quartz.. The pay streak is 18 inches to 20 inches wide and shows 

disseminated bornite in the quartz-pyrite vein, in which the pyrite occurs in irregularly defined 

patches. The vein has a workable width of 15 feet. 

Away fron1 the immediate fissures of the Blue vein the vein is very solid. Moreover, the 

lode shows n1uch secondary quartz and glance, especially in the south streak of the main 

ledge on the 1,400-foot level, where ore and quartz make against the footwH,ll gouge and where 

frosty quartz is forming against the clay selvage. The .footwall streak is composed in part 

of curly quartz, with interlocked sulphides, and the main ore streak is a banded but so1id mass 

of pyrite and sphalerite, traversed by flat fissures and joints having a dip of 20° N. and a strike 

parallel to the vein. These fissures often show thin sheets of ore along the joint planes. 

In the Parrot ledge rich sulphides extend westward to cross fractures, which appear to 

stop the mineralization. The vein keeps on without disturbance but is lean; <;>re shoots at 

the intersection, which are of considerable· size and of fair value, were stoped on the upper 

levels. The same fissures probably extend downward but they are not recognizable; their 

intersection is not 1narked by ore in the deeper levels noi· do they apparently interrupt or 

displace the Pal'rot vein. · FAULTING. 

The PaiTot_ is cut by numerous fault veins of different systems and different ages. The 

principal northwest faults are the Blue and Clear Grit; the Washoe is of less importance, and 

nunor fractures are very numerous. 

As already stated (p. 129), it. is impossible positively to correlate the Parrot ledge developed 

continuously throughout the Parrot mine with the east· and west composite vein (Gold vein) 

found below the 900-foot level of the Original mine, for the latter appear~ to lie north of and 

pn.rallel to the Parrot, at a distance of about 100 feet, extending westward until cut by the 

Steward fault vein. · 

The Pennsylvania (South) vein is not definitely recognizable west of the Blue vein. 

I~ mn.y correspond to the Zinc vein of the Original mine, which is a fault vein itself, and has. 

a course nearly parallel to that of the Steward fault vein. 

'fhe character of the Parrot lode near the surface indicates the correctness of the conclusions derived from a study of the Blue vein faulting (p. 136), that the Parrot mine stiU preserves 

the 11pper part of the vein. The character of the lode in the 50, 150, and 200 foot levels of the 

Originn.l mine and in the Benham workings indicates a wholly different phase from that observed 

below, and shows that the top of the vein is near .. 

Both in the Parrot and Gagnon mines small faults, which differ materially from any of the 

fault veins previously mentioned, may be observed. One of these cuts off all the veins exposed 

on the 1, 700-foot level of the Gagnon. Its course is N. 65° E. and its dip 65° N., the fault 

showing 1 to 3 inches of clay, with quartz and pyrite associated with it on the footwall side.· 
132 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

On the 1,800-foot level the vein is also cut by a N. 35° W. vein, dipping 65° W. The main 

drift on this level of the Gagnon is on the Steward fault vein, which has here left the Gagnon 

ledge (Parrot), going off into the footwall. The vein shows rhodochrosite in the center, 

associated with a streak of crushed granite, with lenses of ore, and is inclosed between two 

well-defined walls. The main ledge on this 1,800-foot level is also crushed, consisting of fragmentary ore with an 8-foot band of lean ore and an 8-foot band of high-grade ore; it gradually 

recovers its values as it approaches another cross fracture. / 

Throughout the Parrot workings the vein shows many peculiarities of structure which govern 

the richness and character of .the mineralization. Generally, the lesser fissures crossing the vein 

have not only had a· structural influence on it, but have materially altered its original filling, 

producing enrichments and apparent depletions of the copper contents. The influence of these 

cross fissures. bears no relation to· the amount of faulting, but seems to depend rather on the 

amount of the descending waters and the influence which the. clay fissure exerts in deflecting 

them. A similar fissure on the 1,600-foot level of the Anaconda mine passed through the 

·porphyry and displaced it and yet does not show at all in the Anaconda vein, the mineralization 

being thorough enough to obscure and heal up. Another example is seen in the Neversweat 400-

foot level, where a northwest fault lying east of the shaft cuts off the ore of a south stringer of the 

;vein but does not show in the Anaconda vein proper. This same peculiarity is very strikingly· 

shown in the Virginius shaft and in the No.6 shaft of the Parrot lode (fig. 42) in both of which the 

workings show a deflection of mineralization along the cross fissure and the formation of ore 

N 

LEGEND 

~ §!8 ~ [Ei3 

80-ft. level 160-ft. level 260-ft .level 320-ft. level 

FIGURE 42.-Plans of 80, 160, 260, and 320 foot levels, Parrot No. 6 mine . 

. consisting of fragments of quartz, pyrite, and bornite, inclosed in a cementing material of well- -

altered granite. A third vein on this level, lying to the south, shows 2 feet of sphalerite on the 

foot wall of a fault vein composed of clay, quartz, and pyrite with mineralized granite, the vein 

getting less bowldery to the west. In ·drifting westward on the vein several perpl~xing cut-offs 

were encountered, but fortunately the shifting is not extensive. On the 1,500-foot level one 

such cut-off is due to two fault fissures, one having a course ofN. 55° W. and a dip of 60° SW., 

and the other running north and south, vertical, and terminating the ore, the stopes between 

t~ese two faults being filled by crushed granite and clay. (See Pl. IX, B, p. 84.) 

SOUTH PARROT OR VIRGINIUS VEIN. 

The South Parrot vein, whose relation to the Parrot has already been alJuded· to (p. 128), 

is well developed on the Parrot 100, 200, 300,400, 500, and 600-foot leve1s, and in .the 300-foot 

drift of the Virginius mine. It has been drifted on for 1,200 feet, from the walls of the Blue vein 

westward to the Virginius shaft and on the Virginius workings for 250 feet farther. These workings show that the South Parrot diverges to the south from the course of the Parrot ledge as it 

goes west, and as its dip is flatter than that of the Parrot it rapidly separates from it, both 

westward and downward. Like the Parrot it is cut and shifted by newer· northeast faults. It is 

cut in the south crosscut of the Original, but is worthless westward and in the deeper levels of the· 

PaiTot mine. 
ANACONDA-PARROT BELT. 133 

ORIGI.NAL MINE. 

GENERAL DESCRIPTION. 

The Original mine lies west of the Parrot, between it and the Gagnon. It is in the heart 

of the city, north of the courthouse and but a short distance west of':Main Street. The mine is 

owned by l-Ion. W. A. Clark 1 and is worked in conjunction with the Steward. The Original 

claim is only 200 feet wide and 1,000 feet long. 

The Parrot lode passes through the Original claim, but proved disappointing in the upper 

levels, as the pay ore occurred only in shoots neither very rich nor large. For 600 feet the ore 

extracted hardly paid expenses, though in recent years these old levels were reopened and 

furnished considerable anwunts of low-grade ore. Below 700 feet the drifts. on the Parrot ledge 

showed good ore (fig. 43), cut off westward .bY the St_eward; a northeast fault vein, which at 

greater depths held great bodies of high-grade ore. 

VE.INS. 

Fro-':11 the surface clown to 900 feet the Parrot vein was the chief producer; below that level 

the Steward fn.ult vein furnished nwst of the ore, ·as it does in the deeper levels of the Gagnon on 

the west and the Steward n1ine 

. on the northeast. Besides 

these two veins the Original 

includes an east-west vein (the 

Rialto), a prestnnably dislocated section of the Bailey or 

Old Steward, running parallel 

to the Parrot and north of it, 

and several lesser veins-the 

northwest Pyrite vein, the 

Zinc vein, the No.6 fault vein 

and others. All of these, cut in 

the deeper levels,have contributed sn1all tunounts of ore and, 

by their intersection, have 

permitted the formation of the 

great ore bodies of the mine, 

where the ground was most extensively crushed and opened. 

2 3 4 5 6 7 8 9 10 II 12 13 814 

FIGURE 43.-Section across Original ore body. 1, Fault breccia; 2, ore; 3, altered granite; 4, firstclass ore; '5, crushed quartz and bornite; 6, fault clay; 7, solid pyrite and bornite; 8, crushed 

quartz and pyrite; 9, solid enargite ore with bornite; 10, banded white quartz and bornite; 11, 

white quartz, G inches; 12; solid bornite; 13, solid pyrite with bornite and quartz blotches; 14, 

bornite; 15, granite. 

Parrot vein.-In the Original1nine the Parrot vein yields but a small part in the ore supply . · 

of the mine, and is, indeed, of minor importance. It is worked westward to the intersection by 

the Steward fault vein clown to the 900-foot level and is developed for 200 feet lower, but its ore 

is lean and zincky. The main ore supply of the mine comes from the Steward fault and from the 

east-west Rialto vein. 

The Parrot vein is commonly distinguished by considerable bornite. On tlie 1,200-fo~t 

level of th~ n1ine the vein is 15 to 20 feet wide, consisting of solid quartz, banded in alternating 

dark and light streaks, with lines and patches of pyrite, though in smaller amount than is usual 

in this vein. Threads ·and streaks of bornite occur in the ore, and also patches of enargite, 

though the latter n1ineral is n1ore characteristic of th~ fault veins. The walls are commonly 

marked by postinineral clay slips, but where these are absent the ore grades rapidly into pyritized 

silicified granite. 

Rialto vein.-The Rialto, which is about 100 feet north of the Parrot lode and which runs 

parallel. to it, is a solid v_ein of quartz and pyrite, with films and nests of bornite and of enargite, 

and is the source of the ore bowlders of the ore body found in the fault vein. It is from 15 to 20 

feet thick on the 1,200-foot level, with clay slips on each wall, incasing unbroken quartz banded 

with enargite and pyrite containing Vligs lined with enargite. In part the qua~·tz is milky; 

• It was purchased in 1910 by the Anaconda Co. 
134 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, lVIONTAN A. 

in part it is dark and banded with pyrite; but in general it has very little pyrite. Threads and 

streaks of bornite and patches of enargite occur through it. Recent cracks in the ore are rust 

colored, showing a replacement of pyrite, without access of oxygen-bearing waters. The vein 

carries 10 feet of rich enargite ore, and is marked by fluorite on the footwall side. This vein has 

been fractured and the enargite crushed,_ clay seams crossing the enargite ore. Fluorite appears 

to be more recent than the enargite and of the same age as the galena sometimes seen in the footwall fault breccia. The Rialto is considered a quart~7"pyrite vein later than the. Anaconda 

system, but of eccentr:ic character. 

Stewa,rd vein.-That the Steward. is a fault vein cutting off the older veins and carrying drag 

ore torn from them, is particularly well shown on the 1,100-foot level of the Original mine. The 

east-west Rialto vein here splits into two branches. The south branch shows 6 to 10 feet of lean 

banded· quartz-pyrite ore with granite streaks near the footwall, ca1~rying bornite and enargite 

in films and patches, even where not crushed. The south split is 5 to 10 feet wide, 1nostly low 

grade and zincky, but where crossed by minor fractures, enriched and workable. It ·has hard 

walls of but little altered granite. 

Sixteen feet below the 1,000-foot level the Steward ledge, here 15 feet wide, is sepq,rated 

from the east-west quartz-pyrite vein by 8 to 10 feet of pyrltized granite. The latter, however, 

shows 2 to 3 feet of fault matter on the hanging wall, showing that the faulting opened a fracture 

along the vein wall. So far as known this did not affect the Parrot vein on this level. 

3 2 4 2 

A 

·,o Feet 

6 

8 

5 

FIGURE 44.-:-Sectionson 900-foot level of Gagnon mine:· A,Westface; B, 3i5 feet west of raise. I, Quartz monzonita; 2, crushed quartz monzonite; 

• 3, banded bornite ore in white quartz; 4, enargite; 5, quartz breccia; G, quartz porphyry. 

Pyrite vein.-The Pyrite vein is a northwest fault, which has been drifted on from the 300,400, 

and 500 foot levels of the Original mine; below 500 feet it passes into the Gagnon. It is a cross 

·vein having a course of N. 45° W. and a dip of 63° S. It carries but little ore, shatters but does 

not displace the primary veins, and is probably itself displaced by the Steward fault vein. Like 

th.e Clear Grit it is due to fracturing and is probably eoincident in age with the Steward and 

No.6 veins.· 

Zinc vein.-The Zinc vein, aN. 70° E. veiri, with 75° to 80° dip, is developed by drifts and 

stopes on the 700 and 800 foot· levels, with a raise on the vein between the two drifts. It is a 

banded quartz-pyrite vein, carrying an unusual amount of zinc and a lo'v percentage of copper, 

partly a replacement of sphalerite by glance. It is probably the sam~ vein on which the south 

1,000-foot drifts on the Gagnon are driven. The vein shows fault clays along the footwall. 

Two other veins running N. 70° to 75° W., with steep southerly dip, are cut by the south 

crosscuts of the 800-foot level. They are narrow quartz-pyrite veins carrying much sphalerite. 

Yvein.-The Y vein, developed on the 700 to 1,000-foot levels of the "Original, is aN. 60° 

W. fault vein, dipping 80° W., that has shattered but has not shifted the oth~r veins. 

GAGNON MINE •. 

The veins worked in the Gagnon mine include the western end of the Parrot lode and two 

intersecting fault veins. The fault vein lying to the north is the Steward (or Conglon1erate) 
ANACONDA-PARROT BELT.: 135 

vein; the one to the south is the Caledonia or No. 6. Both these vmns Intersect the Parrqt, the 

Caledonia cuttinO' throuO'h the lode and continuing downward as an independent ledge, and the 

Steward vein ap1~·oa~~1i;g the main lode and following it westward both on strike and dip (fig. 44). 

PARROT LODE. 

T.he Parrot lode shows in the Gagnon workings the usual structure observed in other parts 

of its course. It has two ore streaks, consisting of quartz and pyrite, which in this mine are 

usually zincky, the proportion of sphalerite being very much 

larger in the Gagnon ground than it is in any other portion of 

the lode. The zinc content apparently gradually decreases 

both eastward and downward along the ledge, the ores· in the 

Original ground being les~ zincky than in the Gagnon, and the 

upper levels Containing lllOre zinc than the ·lower ones; the 

apparent decrease with depth, however, is thought to be chiefly 

due to the fact that the ore taken out from the depths of 600 

to 2,000 feet is from a composite vein and not from the priInary quartz-pyrite ledge. Where the Parrot vein is solid and 

unbroken it is 40 to 50 feet wide, but it is generally separated 

by 10 to 20 feet of altered granite showing quartz-pyrite veinlets from an·underlying footwall vein 10 feet wide. Compared 

with the sa1ne ledge eastward it luis maintained both its size 

and regularity· to an unusual degree, but has changed in the 

character of its vein filling, this having become extremely 

zincky. The bulk of the lode filling, when unfractured, consists 

of milky white quartz carrying an abundance of pyrite and 

showing rude banding in places. The lode presents the usual 

structural features of two parallel veins, which approach and 

diverge along the strike, and are separated by horses of more 

or less 1nineralized granite (fig. 45). 

The GabO'non mine yields ores which are notably higher in FIGURE 45.-Section 'through Gagnon shaft. 

silver than those of any other copper mine of the district. The 

ore is not only zincky, but it contains minerals characteristic of both copper and silver lodes. 

This is because it comes both from the fault veins and from the :Parrot ledge; the ores of each 

vein have their proper characte1:. As the main ore supply comes from the composite veins and 

as the great ore stopes are at the intersections of the Steward fault vein with the Parrot, it is 

. easy to understand why a 

0 

FIGuRg 40.-Wost face, 1,400-foot level, Gagnon mine. 1, Qnartz monzonite; 2, clay; 3, crushed quartz 

monzonite; 4, glrmco; 5, ore; U, first-class oro; 7, enargite; 8, quartz; 9, cmshed quartz; 10, pyrite; 11, 

porphyry. 

the ores differ from those 

of other mines. The 

n1ain drifts and stopes 

are all on the big Steward vein, either alone or 

where it is merged with 

the Parrot; but in the 

western workings the 

hanging wall or south 

vein of the.Parrot lode is 

followed by the drifts, 

which shows that it has 

regained its individuality. · (See fig. 46.) 

The Parrot lode proper show~ tl~e two veins observed elsewhere, but the footwall ledge 

is relatively unimportant in the upper levels; in the lower levels the veins n1erge near the 

shaft but separate westward, having 10 feet of altered granite between them. In the extreme 

western workings the identity of the hanging-wall ledge is lost, owing to faulting. 
136 GEOLOGY AND ORE DEPOSITS OF BUTTE) DISTRICT, MONTANA. 

STEWARD VEIN. 

In the lower levels of the Gagnon mine the· ore comes chiefly from the Conglomerate vein 

formed by the intersection of the western end of the Parrot vein with the Steward fault vein. 

On the 1,800-foot level a drift has been driven on this fault vein where it has branched off and 

left the main lode, going off into the footwall. The Steward fault vein here shows a c.entral 

streak of rhodochrosite in the crushed granite of the lode filling. Lenses of enargite occur all 

through the vein; the main ledge, or Parrot vein, which on this level is.somewliat crushed and · 

in places well brecciated, carries 8 feet of lean ore, alongside of 8 feet of rich fault ore made up 

of fragments of quartz, broken pyrite, and bornite, lying in a cement of granite and clay. In 

places a 2-foot streak of sphalerite shows on the footwall, and streaks of clay, pyrite, quartz, and · 

mineralized granite occur. In general, it may be said that the vein contains fewer bowlders 

toward the west. On the level above-the 1,600-foot-the same vein is well defined, having 

clean-cut walls, clay selvages, and a filling of highly altered and mineralized granite, with streaks · 

of copper glance. 

The granite alongside the veins is sheeted by many parallel fractures, following in a general 

way the course of the veins, and many of these fractures contain blende or quartz. In the mine 

workings it has been observed that this sheeted granite is frequently decomposed and altered, 

forming decomposition bowlders in which ·nucleal masses of fresh granite are surrounded by 

crusts or shells of altered material. Plate VI, A, which shows the first west crosscut on the 

800-foot level of the Gagnon mine, illustrates this. This altered material has contributed 

htrgely to the formation of the fault Clays which are so comn1on in the fault veins. 

CROSS FAULTS. 

The veins_ c.ut in the Gagnon aFe intersected by numerous cross faults, mostly with a northwest course, and slight displacement. One observable on the 300-foot level, about 300 feet west 

of the shaft, has a northwest course and a dip of 60° SvV., and displaces the main ledge 8 feet 

to the north. The N. 70° E. system, to which the big faults belong, also shows in minor fractures with throws of 6 to 8 feet. · SUMMARY. 

The Gagnon is the most westerly of all the ·copper mines; its ores are high in silver and 

zinc and have been supposed to represent a transition between the silver and copper types. 

They are, however, due to crushing and faulting, followed by impregnation of copper ores by 

silver-bearing solutions. The mine shows three distinct veins, which, where intersections occur, 

form large shoots. The composite Steward-Parrot lode consists of a mass of crushed granite 

and ore, in .which fragments rounded by attrition are conspicuous. 

BLUE VEIN SYSTEM IN THE ANACONDA-PARROT BELT. 

IMPORTANCE. 

Veins of the Blue Vein system were worked for .many years. in the Greyrock and Bell 

mines 'and the Blue vein itself was extensively developed in the Little :Mina and Nipper mines 

· before the true character. and relations of the veins were understood. It was not until 1898, 

when the Colusa-Parrot case was prepared for trial, that new development work in the disputed 

territory revealed the relation of the Blue and Anaconda veins. · 

The discovery that the Blue vein represented a fault cutting off and dislocating the Anaconda led to the recognition of other cross faults and displacements, solving many of the most 

perplexing problems -of vein structure, and led at once to an intelligent planning out of ne\v 

development work in many of the mines. With the discovery of the rich ore shoots of the Jessie 

and Eqith May mines the impor~ance and value . of the Blue Vein system became generally 

appreciated. The importance of these discoveries rested not alone on the fact that the veins 

themselves constituted a great addition to the wealtli and production of Butte and considerably extended the limits of the productive area, but also iri the demonstration of the fact that 
ANACONDA-PARROT BELT. 137 

fault veins carried lenses of high-grade ore, worthy of careful systematic develo.pment. It may 

be truly said that the recognition of these conditions has prolonged the life and prosperity of 

:Su tte by many years. · 

The general character of the Blue Vein systern has already been described (p. 108), but 

individually the veins pr~sent many in.teresting feat~res worthy of detailed description. The 

southerly 1nernbers of the Blue Vein system and the three great cross fat~lts of the district and 

their lesser c01npanions are described below; those of the northern and northeastern part of 

the copper area, including t~1e veins of the 

North Butte Co.'s property and of the High 

Ore, Bell, Diamond, Greyrock, and Cm:ra 

mines, are treated separately in connection 

with the Bell-Diamond area (p. 171). 

BLUE VEIN. 

JUDICIAL INVESTIGATION. 

In the search for evidence in the ColusaParrot lawsuit the relation of the Blue vein 

to the Parrot and Anaconda veins was the 

subject of det~iled study by a number of 

fan1ous mining experts. It is doubtful if 

any other 1nining suit ever brought together 

such an array of mninent engineers and 

geologists as those who took part as expert 

witnesses in this case; Clarence King, R. W. 

Hayn1ond, W. S. Keyes, Louis Janin, N; S. 

Shaler, and D. W. Brunton were but a few 

of those engaged in the work. Under the 

direction of I-I. V. Winchell for the Anaconda and of F. L. Sizer for the opposing 

side, thousands of feet of crosscutting and 

drifting were driven for the purpose of establishing the relation of the veins and fault 

slips. 

The suit was nominally an action 

brought by the Colusa-Parrot Co. against . 

the Anaconda Co. for trespass, a suit based 

· on the so-called "law df the apex," the 

first-nan1ed company alleging a union of the 

Anaconda and Colusa-Parrot veins in depth 

and an ownership below the l.1nio11 by reason of priority of location and patent of the 

clai1n. The Anaconda reply held (1) that. 

0 100 

Parrot vein 

Anaconda 

~ 

~ 

vein 

0 

Fault 

200 3oo Feet 

both the strike and the dip of the Colusa- FIGURE47.-Sectionshowingcut-offofA.nncondaandParrotvelnsbythe 

Blue vein fault. 

Parrot and Anaconda veins being parallel, 

they could not unite in depth, especially as the Anaconda becan{e steeper in the 1,600-foot and 

deeper levels; and (2) that the Blue vein, a diagonal cross vein, cut off the Anaconda on the 

west and t~1e Parrot vein qn the east, thus preventing any such union even if the dips could 

bring it about. (See fig. 47.) 

Though the legal question involved was one of apex rights, the real issue was whether or not 

the Parrot and Anaconda veins are cut off and terminated by the. Blue vein. The decision 

by the court held that the evid~nce established such a cut-off; that the Anaconda and Parrot 

veins were once one, but that tllis vein had been cut and the ends displaced by the Blue fault • I 
138 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

vern. Tlfis deci~ion gave the Anaconda Co. the right to follow the vein beneath the subfault 

apex, and limited downward working on the Parrot (by the Colusa-Parrot Co.) by the walls 

of the Blue fault vein. 

Underground development since this suit fully confirms the decision and shows conclus~vely that the Blue vein not only cuts and displaces the great Anaconda lode, but also the 

ne~ghboring east and west lodes from the sou.th side of the Syndicate iedge on the north to the 

vicinity of the Glengarry mine to the southwest. It shows, further, that besides faulting and 

. displacing the east and west veins and containing drag ore broken off from these earlier fissures, 

the Blu~ vein holds endogenous ore deposited within the fissure, and forming ore bodies differing 

in mineral character and occurrence from those of the earlier veins. 

DEVELOPMENT AND GENERAL CHARACTER. 

The Blue vein is justly regarded as the most in1portant fault vein of the district. Its outcrop 

has been carefully developed by pits and trenches from the streets of Centerville to the vicinity 

of the Moonlight shaft.. Underground it has been continuously developed from the Little 

Mina on the northwest, through the Nipper, across the Anaconda belt far to the southeast 

of the Neversweat mine, and if it be correctly identified in the extreme southerly workings of 

the Anaconda properties it has a total known length of over 1! miles. It has been explored 

fr01n the surface downward for 1,600 feet and is cut in isolated places to depths 600 feet greater. 

In the Little Mirra mine the Blue vein contains a l~rge ore body which has been worked 

continuously from the 150-foot to the 1,000-foot levels. In the Nipper mine it has yielded large 

amounts of ore, and in the 1,000-foot level of the Parrot mine it contains a large ore shoot. 

To the southeast the vein .is found in deep workings from the Anaconda shaft, and it is probably 

present in the vicinity of the Glengarry mine, though owing to its intersection and displacement 

by the Rarus fault and to the extremely broken character of the adjacent ground, it can not b3 

positively identified. 

Through its entire course the Blue vein maintains a very constant strike of N. 40° to 50° W. 

and a dip of 64° S. It splits in the Little Mina property into two streaks, both carrying ore, 

as well shown on the 800-foot level of that mine. In crossing the great Anaconda lode the 

fracture is accompanied by displacement. The breaking of this great lode 1nust have caused 

considerable disturbance in the neighboring granite, and the workings show that the force was 

sufficient to actually ,bend the lode before rupture occurred. Quartz outcrops on the Little 

Mina claim show a well-defined quartz vein running the entire length of. the claim parallel to 

the outcrop of the Blue vein. This quartz outcrop is not developed in depth, so that its relationship is not positively known, but it is believed to represent a fault fracture similar to the 

Blue. 

The width or the Blue vein varies greatly from point to point. It' is naturally widest where 

the rocks fracture n1ost readily, the bounding walls in son1e such places being as much as 50 

feet apart. On the other hand, in its northwest extension it is narrow in places; where cut and 

displaced by the Steward vein it has a width of only 5 or 6 feet: In the vicinity of the Neversweat mine its width is 50 feetoon the 900 to 1,300 foot levels and its least width 20 to 25 feet. 

INTERSECTION WITH ANACONDA LODE. 

The Blue vein was systematically explored where it cuts the Anaconda lode, and as this 

development extends from the sud ace to the 1 ,800-foot level, full details of the cut,..o:ff are 

known. The cross sections shown in figures 30, 31, 36, 38, 39, and 47, c.onstructed from the 

detailed measurements made of stopes, raises, and levels during the litigation, show'the proved 

relationship at this point. 

A notable feature in connection with the Blue vein, which is also observed in the other 

.fault veins, is the ilnpoverishment of the Anaconda lode at and near the actual contact. Where 

· the east and west lodes are cut off abruptly and the ore is solid or but little shattered, an undinlinished copper content would naturally be expected up to the. actual point of cut-off. As a 
ANACONDA-PARROT BELT • 139 

. matter of fact a deci·ease in values near the fault vein is in many places observed, as if descending 

solutions penetrating the east and west veins had leached out the copper fron1 the portion of the 

vein near the fault and had carried the material into the fault fissure to be redeposited as fresh 

ore. That this hypothesis can not account for'the ore shoots in the fault veins is, however, 

apparent when the mineral character of the ore is considered. The. Anaconda lode is essentially 

a glance vein, enargite first appearing at the 2,200-foot level and then only in connection with 

strike faulting. 1\1oreover, galena is scarce, being present only iri minute amounts in and near 

broken .or faulted parts of the Anaconda ledge. Chalcopyrite is practically never found in the 

latter, and sphalerite occurs intergrown with pyrite. On the other hand, in the ore found in the 

Blue lode galena is locally abundant, chalcopyrite is present in large amounts, enargite is 

abundant, and sphalerite occurs in crystalline aggregates. These facts and the presence of 

· well-defined ore bodies lying against clay walls seem to prove conclusively that the ore has not 

been derived directly or indirectly from east and west veins, but is due to uprising solutions 

.introduced as a result of the Blue vein fault. 

Southeast of the Anaconda ledge the Blue vein narrows and in places is only a foot or two 

in width. The vein cuts the :Moonlight, another east and west vein in the Ramsdell-Parrot 

.ground, and the stope sheets show a progressive rising of the cut-off to the. east, conforming to 

the dip of the Blue vein. It is true in a general way that the east-west veins ·show hnpoverishment at the general contact with the faults, but it is also true that the largest ore bodies and· 

Tichest ore found in these east-west veins occur where they are crossed either by the Blue vein 

·or by other parallel fault fissures. This 1s believed to be due to the open character of the ground, 

resulting fr01n the fault, by. which down-seeping waters find ready access to the ground and 

deposit their burden of c9pper. Barite and calcite are minerals characteristic of the Blue, 

·Steward, and other fault veins of the district, but barite is lacking entirely in the east-west veins. 

The displacement of the Anaconda vein varies from 500 to 520 feet vertical, as shown by 

n1atching the curves of the broken-off ends of the Anaconda and Colusa-Parrot veins. This 

n1atching can, of course, be best done by projecting the veins on the plane of the fault, and this 

.gives a very close adjustment. This is not entirely satisfactory since the Colusa-PaiTot down 

to the .800-foot level is a granite vein (not a quartz vein) until that level is reached, and below 

the 900 it is quite like the Anaconda-that is, is quartzy and contains 52 per cent Si02 by volume. Thus a n1atching of 510 feet would bring a wide quartzose vein against a narrow granite 

vein. One n1ay therefore suppose a very n1uch greater throw. :Moreover, the glance cha1~acter 

of the Anaconda vein does not extend to the cut-off on the 1,300 foot level, but fades out. On 

the other hand the original unfaulted ·Anaconda is essentially a trunl\: vein. In the Neversweat ground it branches westward, and in the Colusa-Parrot, as the branches diverge, the intervmring space instead of being quartz is a mineralized granite, changing gradually to barren 

.grmrite farther west. It is true that the South Parrot (or Virginius) vein diverges in depth 

and is not seen in the Colusa-Parrot workings below the 400 level, but it is cut on the Parrot 

down to the 600-foot level and ~t the 1,000-foot level south, where it is 150 feet south of the Parrot vein. The South Parrot vein is also seen in the Dave Bricker crosscut to the :Moonlight,· 

where it is 30 feet wide and very irony. The other forks diverge and re1nain so westward all the 

way to the Original nrine. It n1ay therefore be inferred that the Blue vein cut the Anaconda 

vein just where the trunl\: vein bifurcates; hence the Colusa-Parrot does show granite betweefl: 

veins and the Anaconda does not show it, except as big horse between the foot and hanging 

wall ore bodies. The northern vein becomes the main Parrot going west, and the others diverge 

and thin out. · 

Recent development has shown that in the upper levels the Parrot vein does not extend 

in a perfectly straight line eastward to the fault, but bends ·north. This evidence modifies 

conclusions as to the an1ount of throw, wlrich were based. on a correlation of the 'faulted ends of 

the vein, and son1e observers question \vhether the fault is not a thrust instead of a normal 

fault . 

. In smne places the cut-off of the Anaconda vein by the Blue vein is acco1npa1ried by the 

presence of ore bodies lying along the wall of the Blue vein and apparently clue to descending 
140 G~OLOGY AND ORE DEPOSITS OF BUTTE J?ISTRICT, MONTANA. 

solutions coming from the Anaconda vein and ponded back by the clay walls of the. Blue vein. 

In one case ore bodies approximately 6 to 8 feet thick and 50 to 100 feet long were formed on 

SOO-FT. LeVEL 

1000-FT. LeVeL 

:o-_-.= :;:; ~ ~==== 

1100-FT. LEVEL 

1200-FT. L.EVEL 

/300-FT. LEVeL 

LE.GEND 

~ 1400-FT:LEVeL 

Porphyry 

\ 

Quartz pyrite ore 1500- FT. LEVEL 

Crushed ~ material (fault ore) 

[ZJ 

Fault 

each wall of the Blue vein. This has been called a 

spraying out of the vein at the cut-off, but as it is 

clearly due to a later enrichn1ent, it is not properly to· 

be attributed to the fault itself. 

The Nipper mine has been developed mainly on 

the Blue vein, the workings on the lode connecting 

northwest with .those of the Little Mina and southeast 

with those of the N eversweat. Two other prominent 

fissures, which also show in the Syndicate ledge, trend 

N. 70° E. and N. 70° W. and clip 65° to 70° S.; they 

are barren or nearly so. The mine is traversed by a. 

rather regular dike of rhyolite porphyry 15 feet wide, 

the rock being dense, hard white porphyry, sheeted 

parallel to the planes seen in the granite. 

INTERSECTION WITH STEWARD VEIN. 

That the Blue vein is cut and displaced by the 

Steward fault vein is well shown on the 1 ,000-foot. 

level north crosscut from the Parrot vein, where the 

displacen1ent is 116 feet. The Blue vein is here a. 

· mass of fault breccia and clay, with a streak of solid, 

and banded pyrite and quartz. The Steward vein at 

this point is from 5 to 10 feet wide. The vein is wet, 

the water forming limonite where it enters the drift, 

and the vein consists mainly of fault breccia, the ore 

streak having given out at tlus point. The eastward 

extension of the Steward vein has not been drifted 

upon, but is cut in the Nipper workings, where, how-· 

ever,.its true relations were not recognized when the 

Nipper was studied, and can not now be studied, as the 

latter mine has been under water for some years past 

as the result of litigation. That the Blue vein is actually cut off and displaced is established beyond doubt 

by these workings, and it is . drifted on 250 feet or 

more north of the Steward vein. (See figs. 48 and49.) 

ORES. 

The endogenous ore of the Blue vein consists of 

pyrite, glance, sphalerite, chalcopyrite, and enargite in 

quartz, with accessory. galena and hiibnerite. The silver content is large. The new ore occurs as streaks 

(seldom persistent for more than a few yards) of 

quartz with enargite, bornite, glance, and zinc sulphide. In the 600-foot N eversweat workings the new 

ore of the Blue vein is very zincky and contains 

much galena, with newly formed pyrite, the ore containing high silver values. Where most abundant it 

FIGURE 48.-North-south section through Parrot, Steward, formed wedges a few inches to 2 feet thick and 8 to 10 

Gagnon, and No. (j veins, 75 feet west of Gagnon shaft. feet long, limited by clay slips. This ore was solid 

and uncrushecl and was continuous from the 800 to the 900 foot levels. In general, however, 

the new ore has· been crushed and brecciated by the settling and adjustment of the \vhole 
·district that is still going ot1 

(p. 50). 

The ore in the Little ~lina 

.1nine shows 1nany vugs lined 

with pyrite crusted by quartz 

and chalcopyrite; these in turn 

are covered with needles of comb 

quartz; with flat-lying crystals 

of dogtooth spar an inch or more 

in length, parasitic upon earlier 

minerals but thus inclosing copper glance. :Many specimens 

. ·frOin these vugs show a final 

coating of the quartz with galena 

and chalcopyrite~ The vein was 

·forinerly considered a silver lode, 

and was worked as such to a 

depth of 600 feet, where a good 

·shoot ·of copper ore was found 

and worked out down ~o a depth 

·Of 800 feet. The ore frolll this 

shoot consists of dark-colored 

·quartz with copper sulphides 

and sphalerite. Bunches of 

chalcopyrite are conunon and 

with dogtooth spar (cu1cite), are 

parasitic on it. Galena is COinInon. 

In April, 1900, the stopes in 

the Little ~1ina mine yielded ore 

carrying 40 per cent lead and 

·27 5 ounces of silver per ton. 

·This cmne from the stopes below 

the 600-foot level, below the 

raise on the Blue vein. The 

Anaconda vein shows 1nore zinc 

but has no lead nor n1anganese. 

The vein is well exposed at · 

the point where it cuts off the 

Anaconda vein four sets· (28 feet) 

below the 600-foot level of the 

N eversweat 1nine. At tlll.s place 

it shows the smooth wall of the 

Anaconda lode cut off by the 

'Blue vein, whose new ore carries 

,galena and other n1inerals that 

are extremely scarce in the Anaconda. The ore body is itself 

cut by clay slips, which are not 

mineralized. The walls of the 

Blue vein consist of very fresh 

gran!te on the north, while the 

ANACONDA-PARROT BELT. 141 

LEGEND 

·~ 

Crushed ore and fault 

~ Solid ore 

[ZJ 

Fault 

1600·(T. LEVEL 

FIGURE 49.-North-south section 210 feet west or Gagnon shaft. 
142 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRJCT,. MON'l'ANA. 

rock on the south shows fractures with a rusty stain, though the granite is not crushed or 

mashed. The quartz streak of the Blue vein is only 2 inches wide at this place and dips 30° S. 

The country adjacent to the Blue vein has been 1nined in many places where parallel sympathetic fractures come in, and in such cases it is hard to distinguish between the BJue vein 

proper and the entire lode. 

MOUNTAIN VIEW FAULT VEIN. 

DEVELOPMENT AND GENERAL CHARACTER. 

The :Mountain View fault vein is one of the largest and most persistent fault veins of the 

Blue vein system in the entii·e district, being cut in the Parnell mine and being almost continuously traceable from t]J.e Mountain View workings south, through its displacement by the 

Rarus fault and through the Pennsylvania ground, to the vicinity of the Silverbow mine. It 

has been positively identified on both sides of the Rarus fault, being known as the Orange vein 

in the testimony given during the Rarus case. 

The .Mountain View fault vein varies in width from a few feet to 20 or 30 feet or more. 

Its outcrop is scarcely recognizable and is usually but a few feet wide, but it is extensively 

developed underground, the averag~ strike being N. 40° W. and the dip ~0° to 80° SW. 

To a depth of 500 or 600 feet it generally carries only fault material and no pay ore. In deeper 

levels it carries isolated shoots of ore, and in the ground beneath the Rarus fault it has ore 

bodies of considerable value. On the 500-foot level of the Mountain View, where it is developed by drifting for 600 feet, it varies in width from 3 to 4 feet and has a filling of fault 

breccia and clay, with 2 feet of barren pyrite on the hanging-wall side. The extreme northwest development of the vein is on this level (5,289feet elevation). 

The Mountain View fault cuts sharply through quartz Inonzonite, aplite, and porphyry, and 

clean across all preexisting veins; on the Ana.conda lode it sh9ws a horizontal displacement of 

about 300 feet. It is therefore comparable with the Blue vein in its size and extent. Through- . 

out its course .the vein is marked by fault clays or selvages, which vary from a few inches 

· to 1! feet in width. The granite walls are in many places striated and in some places polished,. 

the strire indicating diagonal movement. A tendency toward splits or branch fractures appea.rs 

in the hanging-wall side. In the deep levels the vein carries good ore, an average of 7 feet, 

with· a 15-inch band of nearly pure bornite, being observed on the 1,200-foot level. 

Though parallel to the North Connecting vein this fracture differs materially from that· 

lode. So far as known it contains no traces of an earlier vein filling but is a fault fissure traversing country rock, whereas the N ort~ Connecting vein is a much older fissure filled by quartz 

and pyrite-a replacement vein later enriched by enargite. 

INTERSECTION WITH OTHER VEINS. 

The ~Io~ntain View fault vein appears to be cut and displaced by the Blue Jay fault vein, 

a feature analogous to the displacement of. the Blue vein by the Steward fault vein. In the 

Mountain View mine the vein has been extensively developed on the 200-foot level, where it 

shows 6 to 18 feet of clay with hard granite walls and well-n1arked slickensides: To the southwest the granite alongside is crushed; to the northeast it is hard. The foot-wail streak is a 

solid band 3 to 5 feet wide of hard quartz-pyrite ore, with a southerly dip of 77° S. On the 

level below the character is similfl:r, but the clay and fault matter is 5 feet thick. On the 

fifth (500-foot) level the vein is 7 feet wide and shows a foot-wall band 2 feet thick of crushed 

granite and clay containing pebbles 2 to 4 inches in clian1eter, then a 15-inch band of solid 

pyrite and bornite ore with crushed granite and ore above it. The cut-off ends of the veins 

seeri along the fault resemble spur veins. Farther east the vein narrows to 5 feet with 2 feet 

of pyritic ore in the foot wall and a .course of N. 40° W. 

South of the Anaconda the Mountain View fault vein is known as the Orange vein. It 

cuts and displaces at least two east-west veins, whose segments ar~ known as the Iron and 

Cross veins to the west and as the Cross and the Powder veins to the east. 
ANACONDA-PARROT BELT. 143 

The Mountain View fault vein is itself cut and displaced by the Rarus fault, but reappears 

to the east in three branches, Nos. 7, 11, and 10 of the Pennsylvania mine, the last named 

being the main fissure. At t~1is point it has cut and displaced the Pennsylvania vein (now 

called No. 3), the part east of it forming the Enargite vein. 

Westward the Mountain View fault probably extends into the complex of veins of the 

Bell and Diamond workings. In the Parnell mine a fault vein whose course and dip correlate 

it with the :Mountain View fault ~s cut on the 500-foot level. 

In the I-Iigh Ore 1nine the deeper levels along the veins show a decreasing amount of 

water, and up to the end of 1906 the lowest li1nit of this water had not been reached. In the 

Speculator 1nine, on the other hand, the ·deeper levels on the fault veins of this series show a 

perfectly dry vein;. further, the Ran1s fault, where cut on the 2,200-foot level of the I-Iigh 

Ore n1ine, was dry and dusty, indicating that this, the most recent .faulting of the district, 

which produced great fractures whose open porous character has favored descending waters·, 

has not yet been saturated by descending solutions at tllis depth. 

Although the :Mountain View fault is .one of the largest and strongest fault veins of the 

district, it has not been. well explored, and there is reason to believe that at depths below 

1,000 feet it 'is worthy of careful prospecting. Its relation to the veins on either side is well 

shown by a glass model constructed by the Anaconda Co.; the fault is seen to be nearly vertical 

and to displace the .Anaconda lode, whose eastern segment forms the :Mountain View South 

or n1ain Anaconda vein. To the south the fault is convex to the east. 

ORES. 

The ~fountain View fault vein itself is not well mineralized west of the Rarus, or at least 

carries but small bunches of ore. In the :Mountain View n1ine it is a well-defined fault fissure 

with clear-cut walls, a filling of friction breccia, .clay, and crushed or mashed granite, and 

some drag ore. No great bodies of either drag or endogenous ore were seen in the workings. 

In the Pennsylvania mine the vein is cut on the fifth, sixth, and ninth levels. It has also 

been extensively stoped in the Rarus mine, where it shows 1 to 3 feet of good ore, generally a 

solid mass of hard quartz and pyrite with 2 to 10 feet of clay and fault matter on both• sides 

of ore, though most abundant on the footwall side. The dip is 75° S. · 

Where the crushed matter is replaced by quartz, pyrite, and enargite, as it is in vein 

No. 10 of the Pennsylvania, the vein does not resemble a fault vein. On the 1,000-foot level 

of the Pennsylvania 1nine the middle branch is but slightly mineralized, the northern one not 

at all. The turning about of the faulted blocks of the Enargite vein shows a strong horizontal 

southeast shift of the hanging wall of all three forks, though the ends of No. 3 or the Enargite 

vein are not twisted fLt all. 

The Mountain View fault vein, between the walls of the Rarus fault, shows a large ore 

body of crushed and crackled pyrite and enargite. The· ore contains numerous vugs itlong 

fracture plitnes. Considerable glfLnce occurs in persistent streaks in the enargite; it is solid 

and not shattered and is therefore regarded as of more recent formation. In its structure it 

shows incipient cleavfLge or sheeting, indicating very slight movement since deposition. The 

enargite does not form persistent strefLks, but occurs in bunches. and lenses, accompanied by 

small·Inasses of white. quartz. Inclusions of altered granite occur in the vein, and these are 

usually crackled a.nd permeated by seams and fllms of enargite. This portion of the vein also 

shows the sa.me peculiar breccia seams shown in the :Mountain View system. The material 

consists of well-ro'l;lnded pebbles, with a cement of arkose, generally rather dry, filling sharply 

cut fissures, whose walls are solid and lack the mashed granite characteristic of many other 

veins. These fractures are later than the veins, and they contain neither pyrite nor ore exc~pt 

where they cross existing veins and have brecciated them. The nearest approach to this 

charact9r is seen in the Tramway vein, which is essentially a glance vein and sho~vs a breccifLted structure similar to that of these fractures. A peculiarity of the breccia of the :Mountain 

View sean1s is the unevenness of the fractures and the fact that they jump from one joint 

plane .to n.nother. They give no evidence of any measurable movement. 
144 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

CLEAR .GRIT VEIN. 

The Clear Grit -is the third important northwest fault vein of the district. It outcrops 

about 700 feet southwest of the Blue vein and is parallel to the latter, the course averaging 

N. 51° W. and the dip 58° to 65° ·sw. The .importance of the vein lies both in its mineral contents and in its dislocation of east and west veins. It is developed both in the Clear Grit shaft 

and the workings from it, and in the underground workings of the Steward and Original mines. 

In the Clear Grit shaft the vein, which was worked for its silver ores in the early days, is 

developed by drifts of 100 to 200 feet· at depths of ·100, 200, 300, and 400 feet, the collar of the 

shaft being 57970 feet above sea level. Throughout this part of its development the vein shows 

lenses of solid ore composed of quartz, pyrite, and sphalerite, with high values in silver. It . 

varies frorri 5 to 12 feet in thickness and has a clay gouge which varies from a few inches in 

the northwest workings to a thickness of 3 or 4 feet at the southeast end of the mine drifts. The 

vein is well developed both in the workings from the Clear Grit shaft and in- those of the Steward 

min·e·. 

On the 700-foot level of the Steward mine the Clear Grit vein cuts off, and seemingly faults 

the Steward ore body, producing a throw of 60 feet south along the hanging wall. It intersects 

the much-broken ground of the 800-foot level of the Steward and possibly appears in the 500 and 

600 foot levels of the Parrot mine, as indicated by exposures noted in the stopes. In this southern extension of its course it ·appears to shift the Parrot vein, but the displacement is slight and 

scarcely recognizable in the mine levels. 

The evidence in the Steward mine shows that the Clear Grit vein cuts and displaces the 

north branch or north vein of the Steward mine, which is regarded .as the old vein, but is itself 

cut off by the Steward fault vein. These relations are well shown on the 1,100-foot level of the 

Steward vein. In the earlier workings of the Clear Grit veiri a shaft was sunk to a depth of 500 

feet and two veins were developed, one generally kriown as the Silver vein and the other the 

Copper vein; they come together in depth. The copper ore consisted of bornite in a darkgrayish, extremely fine grained quartz resembling that of the Parnell mine. In recent years 

these old workings have been reopened and the vein thoroughly explored, its continuity being 

proved as far as its intersection with the Steward vein. . 

The Clear Grit vein is characterized by distinct fault breccia of granite, drag ore, and older 

vein matter, together with streaks of newly deposited endogenous ore, the latter occurring in 

well-defined bands and as· layers along clay slips in the fault matter. The mineral character of 

this endogenous ore differs from that of the earlier vein fillings, resembling that of the Blue vein 

and containing galena, an abundance of sphalerite in bunches, bornite, chalcopyrite, calcite, 

and some copper glance. The ore carries high values in silver, and in depth intersects a silver 

vein cut in the upper workings of the rriine. 

·On the 500 and 600 foot levels of the Clear Grit mine the vein is extensively developed, the 

drifts being several hundred feet in length. These workings show a vein containing from 3 to 

5 feet of solid quartz, carrying pyrite and sphalerite, and separated from the granite by clay 

walls. The granite is nearly fresh, and shows very little, if any, effect from the vein-forming 

waters. To the east this solid vein changes to a fault fissure filled by breccia and clay, the 

quartz streak thinning to 2 feet. On the 600-foot level (5,413 feet· elevation), 240 feet to the 

northwest of the shaft, the vein is thrust about 25 feet south by a northeast cross fissure. Beyond 

this cross fissure the vein consists only of fault matter and shows no quartz. 

In the West Steward mine the vein is extensively developed from the 700 to the 1,300 foot 

levels. Its most remarkable feature here is the square cut-off of the Steward ore body by the 

Clear Grit. The relationship of the Steward, Original, Parrot, and Clear Grit veins is all well 

shown on the 1,100-foot levels of the Original (4,816 feet), Steward (4,819 feet), and Old Steward 

(4,821 feet), in which the Clear Grit vein is ·seen to cut off the east and west Rialto vein (figs. 

54 and 55, pp. 149 and 150) and to be itself faulted by the Steward fault vein as it leaves the· 

east-west vein developed in the Original mine. The workings in the Original mine do not 

develop the Virginius or South Parrot vein, which lies off to the south and whose westward 

extension is a worthless zincky vein which is not drifted upon. 
ANACONDA-PARROT BELT. 145 

OTHER NORTHWEST FAULT VEINS. 

Several other northwest fractures lie parallel to the Blue vein. One of the~e is 400 feet 

southwest of the Blue vein, approximately n1idway between the Clear Grit and the Blue. This 

vein is cutin the East Steward workings at the 160 and 300 foot levels. It has a northwest course 

and has yielded some ore, but the ore shoots play out in depth. 

Another northwest vein lies 325 feet southwest of the Clear Grit. This ledge is cut in the 

Virginius workings, an old shaft lying near the Washoe al\d Parrot, and is also ·seen in the 

workings of the No. 6 Original shaft on the 160-foot level, where its intersection with an eastwest.vein 1nakes the large ore body stoped out in that property. 

These parallel sympathetic fractures and many others which show in the stopes along the 

course of the Parrot ledge displace the veins slightly, but are not in1portant features in the mining operations. They do not show on the surface, and have not been traced far enough to determine whether' or not they are persistent in length. They are regarded as due to settling of the 

fault blocks, ap.d not to direct fissuring. · The apparently contradic.tory evidence of the relative 

age of the Clear Grit. and Blue veins and the Steward and other northeast faults, supplied by 

displaceinfmt of the Blue by the Steward, of the Clear Grit by the Steward, and of the latter by 

northeast fissures (on the 600-foot level), .. is best explained· by rupture with simultaneous displaceinent in two dire?tions. 

THE STEWARD VEIN SYSTEM OF THE ANACONDA BELT. 

GENERAL CHARACTER. 

The Steward vein system consists of fault veins, the result of the latest period of fracturing 

and primary copper-ore formation. It has a general course of N. 65° to 70° E., but many of 

its veins are deflected by the quartz-pyrite veins of the Anaconda system, forming strike faults 

and following these older veins for considerable distances both in strike and depth. They also 

break and dislocate the veins of the Blue Vein system, and are themselves fractured and shifted 

by small northwest fissures and by the Rarus fault. 

The principal men1bers of the system are the Steward and No. 6 veins, opened and mined 

in the Gagnon, Original, Steward, and Parrot mines; the Blue Jay fault vein and its eastern 

continuation, the l\fidclle vein, called No. 16 beyond the Rarus fault, and the Bell fault vein of 

the Greyrock-Diamond Bell group of mines. The Bell fault vein is described in connection 

with the Bell-Diamond area (p. 171). 

The veins, which represent a third and important period of copper-ore formation, furnish the 

main ore supply of the westernmost mines of the Anaconda belt. The ores are relatively high in 

silver, are characterized by enargite, and. contain fluorite and rhodonite, mine,rals typical of 

silver veins and not found in the ores of the Anaconda lode. Secondary enrichment, or glance 

forn1ation, by descending waters is a minor feature. .As in the Blue Vein system the ores occur 

in shoots, separated by barren stretches of fault matter, and the veins show swells and pinches 

with striated and irregularly warped walls. The dip is always to the so~th, and varies from 50° 

to 80°. 

That the veins are younger than those of the Blue Vein system is shown by the dislocation 

of the Blue vein by the Steward, and by the shifting of the various northwest fault veins of the 

Bell-Dian1ond and Greyrock n1ines by the Bell (l\fiddle) fault. One vein of the system is, 

however, dislocated by the .Rarus fault. 

The ore shoots show fracturing, with cross seams, clay streaks and other evidences of movement, but the fractures, in large part at least, are confined to the vein itself, and are probably 

due to adjustments during or immediately succeeding the period of ore deposition. As the 

largest ore shoots occur n1ainly where the fissures follow veins of . the Ana·conda system, the 

veins now worked are composite; they have both old and new ore and are correspondingly 

modified in character. Although the Steward fault vein, from which the system is named, is 

90427°--~0. 74--12----10 
146 

COLLAR NATIONAL SHAf"T 

LEGEND 

[JIJ 

Quart~ pyrite ore 

Cru>hed ~ material (fault ore) 

1~1 fault 

GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

,, 

,, 

,, '<,, \\ 

SOO-F\'tfVEL 

,, 

,, 

,, 

I' 

,, 

,, 

1\ 600-FT. LEVEL ,, 

,, 

,, 

,, 

\\ 

,, 

,, 700-FT.LEV~L 1 

' 'S.LEOGE 

1300-FT. LEVEL 

1500-FT. LEVEL 

1700-FT. LEVEL 

the largest and most productive vein of the group, 

the No. 16 vein of the Rarus mine shows the best 

examples of displacement and of ore deposition 

that is clearly later and endogenous; in the Bell 

fault ore deposition has not thus far been demonstrated. 

In the western part of the copper area three 

veins of this system occur; the most northerly 

is the Steward (often called the Conglomerate) 

vein; 235 feet south of it is the No. 6 fault vein, 

which has been identified throughout the extent 

of the Gagnon, Original, and Parrot mines; farther south is the Blue Jay fault vein. 

The Steward is worked continuously from 

the west end of the Gagnon mine eastward 

through the Original and Steward mines, supplying the great ore bodies of these n1ines. 

In· the Steward mine the Steward vein shifts 

the northern displaeed portion of the Blue Vein 

110 feet west, but in the Gagnon it is itself cut 

by numerous flat-clipping northeast fissures, 

whose course of N. 43° to 5.1 o E. corresponds 

with the Rarus fault,- though they have an opposed dip of 54 ° to 70° SW. In the Bell and Dianlond mines the Bell fault cuts and displaces the 

Covel_lite, Skyrme, and other northwest veins; 

and in the middle and eastern parts of the .Anaconda belt, the long and wide fracture called the 

Blue Jay or Middle fault has been an important 

factor in the formation of the ore bodies. 

The slight angle which many of the veins 

make with those of the .Anaconda system, and 

the fact that in many places they join the latter, makes their discrimination difficult. 

STEWARD FAULT VEIN. 

The Steward lode is developed from the west 

end of the Gagnon mine eastward almost to the 

Nipper property, a distance of 5~100 feet on its 

strike, to a depth of 1,100 to 2,000 feet in the 

Steward, Gagnon, and Original mines. 

FIGURE 50.-North-south section 510 feet west of Gagnon shaft. 

On the 1 ,500-foot levels of both the Steward and Original mines, the Steward vein has a 

broad and continuous ore body some 20 to 30 

feet '~ide, that has been worked the entire length 

of the Original mine, a distance of over 1,400 feet, 

and through the length of the Gagnon mine a 

distance of 2, 700 feet. In the latter property it 

consists mostly of a breccia carrying fragn1en ts 

and bowlders of earlier ore, but in the Steward 

and Original workings much of the or.e is solid 

and was undoubtedly formed in place. 
ANACONDA-PARROT BELT. 147 

STEWARD .MINE. 

The Steward mine is situated in the western part of the district, the claim of that name. 

being north of the Original and Parrot mines and extending east from the main working shaft. 

near Woolman arid :Main streets (across from the Gagnon and Original shaft houses) almost t(} 

the Nipper mine. The mine is an old one, formerly worked froin an inclined shaft near the. 

Nipper, but the large ore bodies which have been found in the lower levels were later discovered 

as a result of exploration work following the sinking of the West Steward, now the main working: 

shaft of the mine, which has a depth of 1,800 feet ·(fig. 50) . 

. VEINS. 

The older workings at tne eastern end of the property have developed a lean quartz-pyrite 

vein (here called the Bailey) that hn,s a general northwest course and is probably a member of the 

Silverbow group of the Anaconda system. (Seep. 156.) The Bailey vein was explored I 50 to 200 

feet west of the shaft to a depth of 250 feet. A second incline shaft was then started; it e:p.coun-· 

tered another older vein between 300 and 400 feet, and followed it 

down to the 800-foot level at a vertical depth of 750 feet (5,158 

feet above sea level) .. On the 400-foot level (5,537 feet) the Steward fault vein intersects and cuts off the Bailey vein. 

Below this another vein, here called the Acquisition, Wi_ts encountered and a large ore body stoped out on the 600, 700, and 

800 foot levels. This vein, in which all the criteria of a fault fissure are now seen, is a former member of the Anaconda system, 

an old qua1;tz-pyrite vein, reopened and crushed by' the Steward 

strike fault. Parts of the old vein filling still remain in places 

and the ore is in large part fragn1entary, c01nposed of balls and 

angular fragments of the old quartz-pyrite ore, mixed with newly 

deposited sulphides. The Acquisition is developed from the 600. 

to the 1,000 foot levels, but the Steward departs from it, and its 

ore is cut off .to the west by a cross fault, the Clear Grit. The 

·"Steward fault vein was followed westward, and a new vertical 

shoJt (the West Steward) sunk to develop it. In this shaft the 

Steward fault vein Wits found to be wide, strong, and generally 

ore bearing and to pass into and intersect the ore bodies of the 

Gagnon and Originaln1ines in depth. (See figs. 51 and 52.) 

The Acquisition vein runs N. 85° E. and dips 70° S. On the 

700-foot level of the Steward mine it is dry and composed of 

solid unbroken quartz and pyrite, with irregular streaks and ' /..~ 

bunches of good ore, in which bornite in specks and spots has FIGURE 51.-Faulting or Parrot vein lly 

enriched the lean primary vein filling. Its width is about 15 Steward and No.6 veins. 

feet. The richness of the ore varies somewhat from point to point through the stopes, a~d the 

vein itself is in places \y-ell banded by streaks of nearly solid pyrite a foot or more thick. In 

general the footwall streaks or bands are vuggy and show bunches of b01~nite 2 to 6 inches 

thick. :Much of the quartz is milky, ns if recently deposited, and now drying out. Where 

cut by the Steward fault the composit~ vein has a rolling and irregular hanging wall of hard 

normal granite that shows slickenside surfaces. The footwall is straighter and has a more 

uniform dip, which averages 70°, and is marked by strire and slickensides dipping 20° E. 

The vein narrows eastward in the mine workings from 20 feet to 5 feet, showing at the end 

some 2 feet of fault breccia and clay of the Steward fault. The most persistent feature of 

the· vein is the abundance of zinc, generally in streaks, 1 to 4 inches thick, containing some 

associated galena and ce1nenting fragments of altered granite for 6 to 18 inches from the 

footwnJl. This zinc and galena ore is endogenous and is not crushed like the older ore. 
148 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

, In the vicinity of the East Steward shaft the composite Acquisition vein is nearly vertical 

from the 700-foot to the 1,000-foot level, but westward it has a pronounced southerly dip. Much 

of the fault material is barren, and varies from a breccia or conglomerate, formed of granite and 

ore, to an arkose sandstone. The primary vein is solid on the east drifts of the 900-foot level 

and comprises slabs of ore on the east 700 and 800 foot drifts. These conditions result from the 

faulting and displacement of the Acquisition vein by the Clear Grit (see fig. 53) in the same 

a· 

LEGEND 

n 

Ore 

Clay 

-

Fault vein 

0 100 zoo .300 400 FEET 

FIGURE 52.-North-south section of veins 250 feet west of Parrot shaft. 

manner that , the Blue Vein 

has cut the Anaconda. The 

Steward vein has cut and 

shifted both the Clear Grit 

and the displaced part of the 

Rialto. (See fig. 54.) On 

the 800, 900, and 1,000 foot 

levels the situation is complicated by the presence of 

a subsidiary northwarddipping fork of the Steward, 

and b~ a parallel sympathetic fracture to the south, 

so that the conditions approximate, if they do not 

exactly correspond to, those 

shown in figure 55. 

In the East Steward 

. mine the vein has a general 

course of N. 70° E. and a clip 

of 60° S. Where it follows 

the older veins the course is 

N. 85° E. and the dip 85° S. 

It varies greatly in thickness 

both vertically and horizontally, its average 'vicl th being 

about 2 feet and its maximum about 50 feet. In the 

Steward mine the vein's 

most peculiar feature is the 

presence, between the 700 

and 900 foot levels, of an 

arkose or sandstone, where 

the strike fault has produced 

open fissures filled by material washed down from 

above and deposited in approximately horizontal·layers, the material forming a friable sand rock. This material consists partly of quartz ·fragments but mainly of crushed granite. In the 800~foot level this 

arkose gradually giv~s ·place to a fine breccia or conglomerate. 

ORES. 

In general it may be said that the ore shoots now mined consist of the filling of the older 

quartz-pyrite vein, shattered and displaced by the Steward strike fault and carrying sulphides 

deposited not from above but by the mineralizing waters introduced along the strike fault. In 
ANACONDA-PAR-ROT BELT. 149 

places the old vein is but slightly broken, and the stopes show an average width of 7 feet of 

massive quartz-pyrite vein filling, with an abundance of zinc blende, the fault showing only as 

a black cln.y seam running 

through the center. Where, 

however, the fault has crushed 

and breccin.ted the older vein 

fllling the stopes show 8 to 10. 

feet of ore, consisting of clay 

carrying ore balls, crushed 

rock, with son1e · secondary 

chalcopyrite, and bornite. 

Bornite increases and enargite 

appears in quantity a.t 900 

feet in depth and below. 

A 

II\ 

B 

FIGURE 53.-Displacementof Rialto vein by Clear Grit fault. a-c, b-d, Segments of Rialto vein; 

A-B, Clear Grit fault; D-G. Steward vein fracture before faulting. 

VARIATIONS IN THE STEWARD VEIN • 

. Where the Clear Grit vein n1eets the Steward the relations of the two veins are distinguished 

with difficulty, owing to the abundance of. soft, clayey material, and the fact t.ha.t the materia] 

ralls so easily that close timbering is necessary. At this intersection fractures in the ore body. 

A 

B 

FIGUR!i.: 54.-D!splacement of Rialto and Clear Grit fault vein by Steward vein. a-c, b-d, Segments of Rialto vein; A-B, broken Clear Grit 

vein; D-C~ Steward vein. • 

show bunches of crackled calcite and glance, with pale cream-yellow barite. , Galena is found 

in the vein in scattered spots and streaks 1 to 4 inches thick. Zinc blencle aJso occurs, both. 

FIGURE 55.-Displacement in Steward mine; 800, 900, and 1,000 foot levels. 

Jninerali~ed and cmnenting fragments of altered granite, so that the material is evidently 

endogenous and is not crushed like the older ore. 
150 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

Eastward toward the Nipper mine the Steward vein is progressively ]ower in grade. In . 

general, the values in the upper levels come from such portions of the older vein as have been 

100·FT LeVEL 

torn off and lie within the fault filling. Near the shaft the vein is 

nearly vertical from the 700-foot level to the 1 ,000-foot level, but 

westward it has a strong south dip. 

The cross section of the vein varies greatly in detail from point 

to point. Aside from the primary ore of the older vein it holds 

bun<?hes and streaks of later bornite· and enargite, with masses of 

altered granite (shot through by a network of films of glance, which 

make it a good concentrating ore), fading out in the hanging wall into 

barren granite; these are evidently due to descending solutions. 

The diagram (fig. 56) was sketched underground to show the conditions in a raise from the 800 to the 700 foot level. The exposure~:! 

show a formerly solid quartz-pyrite vein, consisting chiefly of dense, 

:fine-grained, dark-colored quartz, mixed with shattered and crushed 

FwuRE56.-0rebodyfrom 700and pyrite, partly cemented by later white comb quartz. Many cracks 

800 foot levels, Steward mine. 

and cavities in the pyrite ore show blue-gray friction clay. Two distinct seams, separated by a horse of mashed granite, are visible. The fault breccia and conglom-

-erate is much wider than the ore streak. 

In the western part of the St.eward mine, beyond the Clear Grit fault vein,. the Steward 

vein follows a displaced part of the older quartz-pyrite vein; its course is N. 85° E. and its dip 

straightens to 85° S., cutting the older vein at a sharp angle (see fig. 57). The composite lode 

shows its typical development on the sixth floor above the 800-foot level, where it has a width 

of 15 feet. At this point it shows a footwall fissure filled with sand washed do·wn fron1 the upper 

levels and having rude horizontal banding. Next to this there is 7 feet of solid quartz-pyrite ore. 

The hanging wall consists of decomposed granite carrying the 

usual amount of pyrite. Along the 800-foot level the vein narrows to 5 feet, arid the sandstone is replaced by a fault muck, 

composed of ground-up granite and clay carrying balls of rock 

and of ore. The vein soon widens to 10 to 15 feet, of which 6 

feet is solid quartz:-pyrite ore. The fracture being uneve~, the 

:filling varies greatly in thickness. 

A typical cross section of the Steward fault vein, exposed 

on the east face of the 800-foot level, shows 2 feet of soft clay 

on the footwall, with 1 foot of banded quartz and pyrite above 

it, overlain by 3 feet of breccia with numerous clay seams, and 

this in turn by 6 inches of quartz and pyrite, covered by 2 

feet of. mashed granite and clay, overlain by hard clay gouge 

forming 'the hanging wall. This portion of the vein carries no 

pay ore and, as indicated by the section just given, is a typical 

fault vein. The width varies greatly, but is generally least at 

the eastern end of the property.. On the 1,100-foot level it is 37 

feet wide, and from this level downward it has an average 

workable width of perhaps 25 feet; between limiting fractures 

·it is 50 to 75 feet wide. · STRIKE. FIGURE 57.-Cross section through Steward 

and Original mines. showing Steward vein 

The Steward shows a marked change in strike between the following and brecciating the Parrot lode. 

900 and 1,300 foot levels, its course being northwest on the 900-foot level, east-west on the 1,100-

foot level, and N. 75°E. on the 1,300-foot level; west of the Clear Grit fault its course is more 

uniform. It shows the same swerving in dip that it does in strike, and in certain places 

shows marked flattening, which can not be correlated with any intersecting faults as yet 

recognized. 
ANACONDA-:-PARROT BELT. 151 

The directions just given correspond to those distinguished in the east-west veins of the 

district, IHtn1ely, N. 70° to 80° E. and N. 70° to 80° W. It seen1s probable, therefore, that the 

fault fissure chose a direction of easy fracturing along the earlier fissure systems, that the faulting 

of the Clear Grit is to be ascribed to a period of fracture not later than that of the Blue vein, 

and that the Steward and Clear Grit faults were due to simultaneous fissure formation in two 

opposite directions. 

ORIGINAL MINE. 

The Steward fault vein shows in the deeper levels of the Original mine, where it coalesces 

with the Parrot (Gagnon) quartz-pyrite vein, forming the Conglomerate vein, which yielded 

the great ore bodies of the Original and Gagnon mines (p. 136). if it cuts through and passes 

southward of these ore bodies, it does so at a level deeper than any yet developed. The 

occurrence of the Steward vein in the Original mine has already been described (p. 133). 

GAGNON MINE. 

In the Gagnon n1ine the outcrop of the Steward fault vein has not been located. The 

Steward comes from the north and intersects the Parrot at a small angle in the n1iddle of the . 

Gagnon workings. The vein has a dip of about 60° in the Original min~, and intersects the 

Parrot ledge at the 1,000-foot level. To the southwest the intersection is somewhat higher. 

In the lower levels the two veins unite (see figs. 49 and 50), the fault vein shattering the older, 

n1aking n. n1ass of friction breccia and c~mglon1erate, so that the composite vein is often called 

the Conglon1erate vein; in places it forms a footwall streak underlying a slightly broken but 

continuous portion of the pri.Inary vein that now forrns the hanging wall. 

In the eastern par:t of the Gagnon mi.I1e the hanging-wall ledge of the Parrot is a distinct 

vein parallel to and 30 feet distant from this cornposite or conglornerate vein. West ward the 

. con1pound vein shows fatilt n1atte; on the footwall, and the workings indicate that the Steward 

fault crosses the vei.I1 ii1 depth. The 1,600-foot east level displays a solid vein of shattered 

rni1~eralizecl granite with stringers and two distinct streaks of ore on the footwall side, n.nd 

the conglomerate vein lies on the east or hanging-wall side and has a north dip. 

In the Gagnon n1ine a segment of the rnain Parrot vein is cut off by the Caledonia (No. 6) 

vein above, and is cut by and n1erges with the Steward vein below. In the eastern part of .the 

n1ine the hanging-wall ledge of the Parrot vein rnaintains its identity, running parallel to and at 

son1e distn.nce from theN o. 6 fault; in the western part, however, it n1erges into this fault, or at 

least it 1naintains identity as a hanging-wall layer only in depth (800 to 1,300 feet) at 1,100 feet 

'vest of the shaft. · 

The Steward as exposed in the Gagnon n1ine is essentially a fault vein, characterized by 

friction breccias, clays, Q.nd bowlders of' granite, bornite, and quartz-pyrite ore, ·with scarf-like 

rnasses of dragged and crushed ore lying in the fault n1aterial. It contains a little galena and 

still less n1anganese and fluorite. In other w01;ds, it has the same 1nineral characteristics as the 

Blue vein, has a high silver content, n.nd may be consider~d as a pyrite-bearing silver vein. · 

SUMMARY. 

Briefly summarized, the Steward fault ~uts across prin1ary quartz-pyrite veins, reopening 

and shattering then1 along their str~ke. In this reopening the fissure was not straight, and the 

resultant fracture varies in width. In places it shows parts of the still unbroken pri.Inary vein 

either attached to the footw~ll or inclosed within the fault 1naterial. More frequently the 

earlier vein is broken up into a breccia, n1any of whose fragments are rounded. In places the 

older vein is only cracked and is enriched along such cracks by glance and bornite. The workable ore shoots consist largely of fault m~tter, with ore balls. They do not extend to the surface, 

but lie approxi.Inately 800 feet beneath the outcrop. The most notable feature of the pri.Inary 

ore is its zincky character eastward. The most notable feature of the fault fissure is the presence 

of open spaces, now n1o1:e or less filled by sandstone, and the occurrence of endogenous enargite 

and bornite. The vein shows a slight deflection by cross fissures, northwest and southeast 
J52 GEOLOGY AND ORE DEPOSITS OF BUTTE p!STRICT, MONTANA. 

fissures producmg a· displacement of 10 feet and 5 feet, respectively, op. the Steward 800-foot 

level west. The Clear Grit vein produces a doubling and displ~cement of the older Rialto vein 

analogous to the shifting of the Blue vein by the Steward. · 

The upper levels of all the fault veins carry little copper. The faulted and crushed Gagnon 

vein above the 300-foot level w~s originally worked for the rich silver ores which formed a 4 to 

6 foot footwall streak, but in recent years, when a 2 per cent ore became payable, 50 to 75 feet 

in width was removed, the copper occurring in the ore as a dense, black, powdery chalcocite. 

The footwall of the combined vein showed on the 300-foot level a very constant but irregu~ar 

and small streak of sphalerite, chalcopyrite, pyrite,· and galena, but the streak was too small 

and low grade to be worked. The best and widest stopes occur at intersections. 

NO·. 6 FAULT OR CALEDONIA VEIN. 

The No. 6 fault vein, another member of the Steward system, is seen in the upper levels of 

. the Original mine, extending westward and forming the footwall fault vein in the Gagnon working's from the 300 to the 500 foot level. It unites with the Parrot lode above the 400-foot 

level, follqwing and brecciating it and making a composite vein. About 500 feet below the 

surface it passes through the Parrot ledge southward into the hanging wall with an average 

dip of 50°. · 

TheN o. 6 vein is workable above and for 50 to· 60 feet below its union with the Parrot vein. 

This fact hnplies that the pay ore is in part original in the vein and is not due to fragments of 

the older lode, but to mineralizing waters which have perhaps derived their copper from the older 

vein. The cross section (fig. 48) shows a hanging-wall stringer of the main ledge, which may 

have caused local enrichment and may account for the pay ore below the main intersection. 

As a whole the vein is zincky and low grade. It shows 3 ~o 4 feet of clay and a pay strea;k 

averaging 3 feet wide of low-grade quartz-pyrite ore relatively high in silver.· The hanging 

wall is of hard granite; the footwall of shattered granite seamed with quartz for 5 or 6 feet 

from the vein. 

Drifts have been run on this lode, and it has been worked on the 300 and 1,000 foot levels 

of the Gagnon and the 500 and 600 foot levels of the Original. It is also encountered. 

eastward in the deep levels of the Parrot mine, where it is well exposed on the 1,3oo· and 1,500 

foot levels, and in the Neversweat 1,800-foot level it dips about 76° S. It faults ·both the 

Blue and the Parrot veins. (See figs. 50 and 52.) 

BLUE JAY FAULT VEIN. 

The Blue Jay vein is the second largest member of the Steward system. This occupies 

one of the largest and most persistent fault fissures of the district, extending eastward from 

the west end of the Blue Jay n1ine, through the Moonlight and Anaconda mines, to the West 

Colusa mine. It is known by different nan1es in different parts of its course, being called 

the Blue Jay fault vein in the Blue Jay mine, the Middle vein in the workings of the Anaconda mines, and the No. 16 vein east of the Rarus fault. (See fig. 105, p. 223.) 

The in1portance of the vein lies not only in the ore, which is extensively mined in the deep 

levels of the mines east of the Rarus fault, but also in the influence it has had on earlier ore 

shoots·. It has materially affected the mineralization as well as the displacement of the veins of 

the Anaconda, :Mountain View, Rarus, and Leonard mines, not only cutting and displacing the 

Anaconda vein, but also introducing mineralization into the shattered ground adjacent to the 

displacements. In the St. Lawrence and Colusa mines its course differs only some 15° or 20° 

fron1 that of the Ran1s fault, running about N. 55° to 60° E., but its clip is opposite. Its strike 

is also parallel to ·that of the Tramway vein, but the latter dips north and the Blue Jay south. 

The throw is to the southeast. Southwestward it splits, one fork passing behind the Anaconda 

vein near the shaft, and the other crossing and faulting the Anaconda vein. Both the Mountain 

View fault and the Blue veins are probably displaced by the Blue Jay. The fault breccia con- , 

tains stringers and lenses of endogenous ·enargite ore, and many large ore bodies occur where it 

crosses the east-west veins. 
ANACONDA-PARROT BELT. 153 

The Blue Jay fault vein is developed in the :Mountain View mine from the second level 

down to the deepest workings. It cuts through the Anaconda (Mountain View South vein) 

with many subordinate syn1pathetic fractures, which h'ave been filled by glance. It cuts and 

displaces the Anaconda, North Connecting, and other veins, as 'n1ay be seen on the 200, 300, 

400, 800, and 000 foot levels of the :Mountain View n1ine. The displacement of the east-west 

veins· is particularly apparent on the 800 and 900 foot levels. 

The identity of the :Blue Jay fault vein with the :Middle fault vein of the Anaconda ground, 

and this with a vein in the :Mountain View and with the No. 16 Ran1s, has only recently been 

recognized by I-I. V. vVinchell. It makes only a small angle with the Rarus fault fissure, but 

has a steep opposing dip; that is, it dips to the southeast. It is easily recognizable in the Mount~tin View 200-foot, 300-foot., etc., levels, where it cuts off and displaces theN orth Connecting 

vein and the :Mountain View South ledge. Its dip is very regular. Under the Sullivan claim it 

swerves southwest and flattens a few degrees on the lower levels under the Johnstown surface. 

It is cut off by the Rarus fault on the 1 ,100-foot Mountain View workings, under the Sullivan 

claim. 

The vein is not recognizable in the \vorkings of the St. Lawrence 1,200-foot level but appears 

at this level east of the Ran1s and has been definitely identified in the St. Lawrence 1,30() and 

LEGEND 

~ • . 

Oro Ore mixed with 

. 

fault· 

~ 

~ ~ matter 

~o roo 

Porphyry 

zoo 

Faults , 

300 FEET 

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

FIGURE 58.-Plan of 1,400·foot level of the St. Lawrence mine, showing relation of flat ore bodies to fault veins. 

1,200 foot levels, where it (the l\1idclle fault vein) n1akes an angle of 25° with the east wall of the 

Ran1s (11s seen in the 1,200-foot level of the St. Lawrence). 

The fault is also WQll exposed on the 1 ,200-foot level of the Pennsylvania mine, where a. 

long nqrth crosscut successively encounters the :Mountain View fault, the Blue Jay fault, and 

the Rarus fault. Its occurrence in the Rarus area is described on page 223. 

The Blue J 11y fault vein has been n1ined for 300 feet in the Ran1s n1ine, where it is encountered underneath the Rarus fault. It carries fron1 8 to 10 feet of ore, and in places on the 1,200-

foot level of the Rarus has as n1uch as 20 feet of good ore, the chief production of this level 

coining frmn this Blue Jay, which here faults northwest veins Nos. 14 and 17, whose correlations 

are not known. 

. The correlation of the Blue Jay fault with the No. 16 vein o.f the Rarus is based on its 

position and character. As there is son1e uncertainty as to the exact point at which it is cut 

off by the west fissure of the Ran1s fault, this correlation is not perfectly satisfactory. However, its n1ineral character and structural features seem to indicate plainly .that the Blue Jay 

corresponds to the No. 16·beneath the Ran1s fault. 

In the St. Lawrence 1nine the vein takes an in1portant part in the shattering and crushing 

of the rocks now hea,;ily in1pregnatecl with enargite and chalcocite forming the great flat ore 

bodies of the 1,200, 1,300, and 1,.400 foot levels of this mine (fig. 58). 
154 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

On the 1,200-foot level the vein shows a quartz-pyrite streak, carrying secondary glance, 

in the crushed and altered granite and clay that fills the fault fissures. The 1,600-foot stopes 

show a lode 26 feet wide, containing 6 feet of ore, half of which is high-grade enargite ore. 

The 2,200-foot level of the Anaconda has a good ore body on the Middle or Blue Jay vein. 

It shows 50 feet of fairly good ore, with 10 feet more of solid glance ore. The Anaconda vein 

at this level is very lean, lying just under the Rarus fault. The Rarus fault on the 2,400-foot 

level is but 40 feet wide, whereas on ·the 2,200 it is 80 feet wide. Veins Nos. 4 and 5 are hangingwall splits to the south. 

OTHER VEINS OF THE STEWARD SYSTEM. 

As already stated, the Bell fault belongs to the Steward system, but its description is given. 

with. that of the other veins of the Bell-Diamond area. Several other fault veins of the system 

occur in different parts of the district, especially near the Syndicate lode and south of the Ana-

~onda belt in the Belmont and Colorado mines. These faults have shown little or no ore and 

are, so far as known, of no commercial importance. 

INTERMEDIATE COPPER BELT. 

MINES AND VEINS. 

The broad tract of ground lying between the Anaconda and the Syndicate 1~des .is for 

convenience called the I:ttermediate belt. It contains few and relatively unimj:>artant mines, 

although it is traversed by a nun1ber of wide and persistent veins of the Anaconda system, as 

well as by the three great fault veins of the district. The greatest production is from the 

Blue vein, which is worked in the Little Mina, Nipper, and Oden mines, diagonally across the 

entire width of the belt. The Parnell mine has opened up the central part of the area. 

With these exceptions the mines are not worthy of especial mention. The North crosscut from 

the 1,000-foot level of the Anaconda to the Bell mine passes entirely through the belt and cuts 

some 21 veins, a few of which are workable, though of low grade. Five diamond-drill holes 

driven.hoTizontally across the belt at elevations between 5,000 ·and 4,000 feet above sea-level, 

and at distances about 600 feet apart, have cut the same veins as the Anaconda crosscut. South 

of the Green Mountain mine one of these holes shows the existence of SL"\: veins aggregating 59 

feet of quartz in a width of 149 feet and, farther north, of three veins in a width of 400 feet. 

The Clear Grit, Ste"\vard, Skyrme, and other fault veins with numerous lesser fissures, cross 

the belt, but are only locally mineralized, if at all, and are seldom traceable for more than 

short distances. It is a noticeable fact that some of the strongest quartz outcrops cover veins 

that are inconspicuous and carry little or no ore. The Parnell mine develops ore in the Parnell, 

Schweitzer, and L. E. R. claims. · 

PARNELL MINE. 

The Parnell mine contains several veins, three of which have been productive during the 

short period of the 1nine's activity. The veins are comparatively narrow and tight, and the 

ores. are peculiar in that they n1ore closely resemble silver than copper ores. Those produced 

have been high in silver and rather low in copper. Much of the ·quartz is extremely dense ancl 

fine grained; the sulphides, bornite, chalcocite,. and pyrite, occur in minute particles disseminated through it and so interlocked with it as to be difficult to separate by concentration. 

The veins are thinner and less promising than those in the eastern continuation of the belt in 

the Mountain View or northwestward in the Syndicate mines. . 

The \vorkings extend to a depth of 760 feet. The shaft is 650 feet deep, with long crosscuts to the south on the 550 and 650 levels, and one to the northeast at a depth of 450 feet. 

A number of veins of the Blue and Anaconda systems have been cut and three of them have 

been worked, yielding ores unlike those of either the copper or the silver mines of the district, 

though less unlike the silver ores. Two other veins, opened by drifts; contributed to the 

output of the mine dining the short period it was worked, before it was closed by injunction, 

pending decision regarding its ownership. 

. . 
INTERMEDIATE COPPER. BELT. 155 

The northernmost of the developed veins, seen only in a drift 118 feet north of the shaft 

·On the 650-foot level, is not identifiable with any surface outcrop. It is an east-west quartzpyrite vein, with steep (73°) southerly dip, reopened by strike faulting, with crushing of the 

vein filling and the fault clay sea~ns. The vein varies in width,. averaging about 32 inches. 

Where cut it is 3 feet thick, but lean and unworkable. Generally, it shows 2 feet of barren 

-quartz, separated by sev~ral inches of fault clay from a footwall streak of crushed, mashed, 

and altered granite, carrying streaks of black copper ore. 

The Coquette vein, also an east-west quartz-pyrite vein, outcrops north of the shaft and 

has been developed and worked on the 250, 350, and 450 foot levels, with an ore body ~toped 

both above and below the 350 level. The vein has an average width of 21- feet. of dense fme-

_grained quartz-carrying bornite. In the fourth l~vel the ore is crushed by fractures accompanying a fault vein of the Steward system, which has cut and dislocated the vein in the west 

drift about 15 feet from the crosscut. The vein is not developed below the 400-foot level. The 

.Steward system vein runs N. 80° E.; like the Coquette vein it dips 72° S. 

The L. E. H. vein has been the most productive of the mine. It is a niember of the Blue 

vein systmn and has been often correlated with the Mountain View fault vein, ,,r].th which it 

corresponds in character and composition. Its course is northwest and its dip 56° to 64° S. It 

.has SI~ooth, sharply cut walls averaging about 5 feet apart, with fault brec~ia and clay, save 

where. a shoot of hard blackish quartz fills the vein from wall ·to wall. In the ore shoot the 

·quartz carries covellite as well as pyrite, with enargite and bornite in the fault clays, the extreme 

width seen being 16 feet. The rich ore occurs in a band about 16 inches across, carrying about 

5 per cent of copper and 5 ounces of silver per ton. Drifts explore the vein for about 300 feet 

·On the 550 and 650 levels, with a winze on the ore shoot down to the 700 level. The fault 

clays carry rock and ore fragments, and show son1e rhodonite, a mineral peculiar to the silver 

veins. The vein is opened by short drifts on the 450-foot level, where it is cut by a cross fault 

running N. 50° E. and clipping 60° SE. and is shifted about 6 feet to the south. This san1e 

·cut-off appears in the 550 and 650-foot levels, but here no displacement was seen. 

The L. E. H. vein is developed for a distance of 650 feet on the 5,200-foot plane, and for a 

·depth of 400 feet vertically, being worked in the 650 to 800 foot levels of the Parnell mine, and 

·eut in the Anaconda north 1,000-foot crosscut, about 1,030 feet north of the shaft·. At this 

point the vein is 13 feet wide and carries a 6-inch streak of good ore .. It is a northwest vein 

whose course projected·intersects the Anaconda lode in the St. Lawrence n1ine, ·where, however, 

no cross vein is recognizable on the 700-foot level, though the crosscuts and laterals of the 

600-foot level (5,300 feet) do show a small cross vein. 

The Parnell vein is 200 feet south of the L. E. H., being recognized in both the 550 and 

650 crosscuts, and opened by a west drift from the lower of the two. ·It is an east-west qu~rtzpyrite vein clipping south, and carrying streaks of low-grade pyrit.e ore along each wall. The 

vein averages 8 feet across, \\rith a foo_t of fault breccia along the ·hanging wall. 

The Schweitzer, the n1ost southerly vein developed in the n1ine, has been worked by a 

drift running west fl'Ol11 the 650-foot crosscut, with a winze going down to a short drift 160 

feet below. It is a northwest fault vein, vertical, or with very steep (86°) southerly dip. The 

vein is about 8 feet wide in. the stopes, consisting of fault matter a few inches to a couple of 

feet \\ride, \\ri.th lenses of quartz OI;e, carrying streaks and bunches of bornite in barren quartz. 

(See fig. 59.) 

Two other veins are seen in the sixth level crosscut north of the Schweitzer. The east-

. west vein, 10 feet fron1 the Schweitzer, is opened by a short west drift, showing about 2 feet 

·of lean quartz and pyrite with an 8-inch band of pyrite. The second vein runs northwest and 

·dips at 50° N. This vein also carries quartz, the width varying between 2 and 5 feet, being 

thickest in the raise. 

A third vein at the elbow in the crosscut shows a course of N. 78° W. and a dip of 50° S.; 

·it displays 6 inches of clay and quartz but no workable ore. 0 . 

Three other undeveloped veins are seen in the 600-foot crosscut between the Schweitzer 

.and L. E~ H. veins. One, 25 feet south of the L. E. R., runs S. 85° E. and has a southerly 
156 GEOLOGY AND ORE DEPOSITS OF BUTTE DJSTRICT, MONTANA. 

dip of 60°; a second, 160 feet south, runs N. 78° W. and dips 50° S.; the third is 200 feet fron1 

the L. E. R. drift. All three are thin and carry no ore in the crosscut. The northernmost of 

these same veins is seen in the 500 crosscut, but is small and not workable. They are mostly 

east-west veins. 

A big fault vein cut on the 400-foot level 10 feet south of the shaft shows 6 feet ·of fault 

breccia and clay, with ore fragments. It has a dip of 45° S. a:n.P, an east-west course. It is 

24"black quartz and ore 

22"rich ore rn white quartz 

FIGURE 59.-Cross section of Schweitzer vein, Parnell mine. 

nearly 15 fe~t wide on the 550· and 6 feet 

wide on the 650 foot crosscut. 

The veins of the Parnell can not be 

positively correlated with those of either 

the Bell or l\1ountain View mines, though 

their position and course are similar. 

LITTLE MINA AND NIPPER MINES. 

The Little Mina and Nipper mines 

have already been discussed (pp. 136 to 

145) in connection with the Blue vein 

system in the Anaconda belt. 

SILVERBOW SYSTEM. 

CHARACTER AND AGE. 

The Silverbow system of enargite 

veins was not recognized for many years, 

because these veins have been so generally reopened and faulted by later fractures. (This later faulting, as so often 

·noted; is the most important economic 

feature of the veins, as the richer ore 

bodies are dependent upon it.) The 

veins run nearly northwest, and are generally vertical or dip steeply .southward. The vein filling· is quartz and pyrite, with more or 

less enargite. In so1ne places the veins have apparently been the cause of displacement of 

older veins, but in others- this displacement is only a feature of contemporaneous forn1ation 

of t~o sets of fissures. In most of the northwest veins, particularly in those of the Ran1s and 

Bell-Diamond areas, the reopening of the veins has left little of the original vein filling intact, 

so that in most places the fault material is readily recognized and the old filling is liable to be 

overlooked. This is particularly true· of the Greyrock and others in its neighborhood. 

Veins of this class are often distinguishable fron1 the east-west ·veins by the presence of 

enargite, which extends upward to the oxidized zone; in fact, the enargite veins are less deeply 

oxidized than the east-west pyrite veins and carry fresh enargite at levels in which the ordinary quartz-pyrite v~ins are completely oxidized. 

The age of this northwest system is ·probah(y son1ewhat less than that of the east-west Anaconda system. In some of the veins it is difficult if not impossible to distinguish an original 

quartz-pyrite character. In n1ost of them, however, the criteria are readily recognizable and 

there is no difficulty in establishing their relative age in one part or another of their extensive 

workings. 

SILVERBOW LODE. 

The Silverbow lode is extensively worked in the Pennsylvania and Silverbow n1ines, 

being continuously developed from the western boundary of the Pennsylvania property for 

4,500 feet. eastward and to a depth of more than 1,400 feet. In both mines it has been con-
SILVERBOW SYSTEM. 

tinuously stoped to a depth of 600 feet. 

It has been known as the Pennsylvania 

No. 1 vein in the Pennsylvania 1nine, 

and it was correlated with the :Moonlight lode by Emmons in the Butte folio 

(No. 38). 

CHAl~ACTEU AND DISPJ~ACEM:ENT. 

It outcrops about 150 feet north of 

the Pennsylvania shaft, but its apex, ' 

though developed at different points by . 

. open cuts and pits, is not easily followed, being largely conce~led by surface debris. Its general co~1rse is N. 

65° w.,·but it curves with a northward 

convexity in the Pennsylvania· ~line, 

owing to a distributed displacen1ent in 

the Ran1s fault zone. The dip is southward, and outside of the Ran1s zone is 

very constant, averaging 68° at the Silverbow shaft. The tl}iclmess varies considerably in different places; in the · 

Pennsylvania mine it measures 10 to 15 

feet between wal1s, and in the deeper 

levels of the Silverbow it. is 20 feet 

across. (See fig. 60.) 

The v:ein apparently joins the Pennsylvania vein westward near the wor~­

ings of the St. Lawrence n1ine, but separates again. The junction niay be 

seen in the 100-foot level of the Pennsylvania n1ine, where the vein dips 45° 

to 50° S., and shows sharply defined 

walls with clay selvage, particuhirly on 

the hanging wall. 

The distributed displacement of the 

Silverbow vein by the Rarus :fault is 

shown in the upper levels of the Pennsylvania mine, where the vein, though 

apparently continuous, is cut by a multitude of small cross breaks with slight 

displacen1ent, so that the plan of the 

vein on the first to the fifth levels shoWf) 

a bow or curve very unlike the normal 

straight course; the dip also is materially flattened. The larger cross faults 

(for example, one with 15 feet throw 

north on the 300 ancl400 foot levels, 75 

feet west of the Pennsylvania shaft) 

shows the southward 1noven1ent of the 

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158 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT', MONTANA. 

hanging wall by drag. The direction of throw is not always the same, for in places a fault is. 

encountered beyond which the ore fails for a few yards and then resumes beyond a second cross 

slip. These many lesser faults come together downward, so that the Silverbow slrows decided 

shifting on the 800 and 900 foot levels. (See fig. 61.) · 

The ground for 100 feet or more south of the Silverbow vein is traversed by several small 

east-west quartz-pyrite veins; on the tenth level five of these veins are over a foot thick, but the, 

ore is irony and low grade. From these veinlets, which are mostly to be considered as hahgingwall streaks of the lode, south to the Iron or Glengarry vein, the ground is cut by 1nany fault. 

slips. In the crosscut south on the tenth level (fig. 62) ten such faults are cut; seven run N. 40° 

to 60° E., with steep southerly dip; two run east and west; and oneruns northwest. These 

faults reach a foot or more in thickness and are filled by clay, in places holding friction breccia. 

or pebbles and uncommonly streaks of secondary ore. . 

VEIN FILLING AND RECENT DEPOSITION. 

The vein filling is oxidized to a varying depth, averaging about 60 feet below the surface 

(200 feet in the Silverbow). The leached matter .is not rich enough in silver to warrant its 

extraction, but it has beneath it, above the solid pyrite, a thin layer of partly altered and replaced 

pyrite that carries argentite and assays 80 ounces or more of silver to the ton. 

The primary filling of the vein is quartz and pyrite, which in n1any parts of the vein is 

still solid and unbroken and carries relatively low '\alues in copper. In general the vein is but 

-IIOOft.to-. 

s. B. No.3 shaft: . \ 

FIGURE 61.--Plan of east end of 50G-foot level of Silver bow mine, showing Iron vein (No. 3 vein) cut by fault. 

little crushed and broken by either strike or cross faults, but the richest ore consists of crushed. 

vein filling cemented by glance. In general the copper and silver contents decrease downward·, 

except where local fracturing has permitted the ready access of downward seeping waters with 

the formation of secondary glance. Chalcocite is the most abundant copper mineral and in 

the upper levels contains native silver on fracture s1;1rfaces. Eriargite appears but sparingly. 

Oxidation has extended to a depth of 200 feet or more below the surface in the Silverbow mine, and its action is particularly interesting owing to the large amounts of copper sulphate deposited in the mine workings. At the west end of the n1ine free-milling ore was found 

to a depth of 160 feet; eastward the lower limit of oxidation goes slightly lower, following the 

contour of the surface. · 

In the zone of oxidation the changes have been very complete. The oxidized matter 

consists of a mass of coarse spongy quartz, the crevices of which have been partly filled by iron 

oxide and by small amounts of silver chloride. No other minerals are present. In the lower 

levels, beneath tl?-is completely oxidized. material, the different stages of oxidation are traceable. 

Blue chalcanthite, the hydrous sulphate of copper, is seen in large quantities in the unused 

() 
SILVERBOW SYSTEM. 

drifts of the 300 and 400 foot levels, where it collects in large 

quantities on the walls of the drifts and as stalactites and staln,gmites ou the roof and botto1n, coats mine ti:r;nbers, and impregnates the wood itself with 1netallic copper. This deposit is . 

collected from tin1e to tin1e and smelted; it is found to contain 13 per cent of copper. The water in the bottom of the 

drift has a clark greenish-blue color and is so rich in copper 

that the iron rails have been deeply corroded and for some 

distances have been found to be entirely replaced by metallic 

copper. 

On the deeper levels, where the oxidizing waters h~ve 

penetrated as a result of artificial workings, the oxidation is 

son1ewhat different. The blue sulphate of copper, chalcanthite, is almost never seen, but the oxidized forms of iron are 

plentiful, and large stalactites are formed, especially on the 

800-foot level (Pl. VIII, B, p. 82.) These stalactites have been 

observed 2 to 3 ·feet long. They grow ·w1th gr~at rapidity, 

s01ne of them increasing 1! feet in less than three months. 

They are typicnJ stalactites and are apparently formed without the aiel of algous growth. Commonly they are hollow 

pipes con1posecl of concentric rings of a light-brown to deepbrown lin1onite and are usually coated with a thin \Vhite film 

regarded as the oxidized form of iron, freshly deposited from 

the waters. Continuous strean1s of water fl.o\v clown their interiOI·s and, in addition, a considerable mnount is always flow-

..ing on their outer surfaces. The growth is mainly from the 

outside. · 

BAILEY VEIN. 

In the older parts of the Steward1nine two quartz-pyrite 

veins are developed. The first (Bailey vein) 1nay be considered 

a Inember of the Silverbow systen1, since it has a course·of 

N. 62° to 64 ° W. and a clip of _70° to 7 5° S. It is a dry and 

tight quartz-pyrite vein, about 4 feet wide, with a. 1 t to 2! 

foot streak of pay ore, which carries 1nuch sphalerite, partly 

replaced by chalcocite. The chalcocite is friable and soft and 

occurs mixed with pyrite and partly decomposed blende. 

Though the vein is solid and unbroken, it has clay seams on · 

·both walls. The vein was worked on the 50, 100, 150, 200, 

250, and 300 foot levels 'only. 

OTHER NORTHWEST PRIMARY VEINS. 

The Johnstown (North Connecting) vein is a good exanlple of the Silverbow systern, as in it but slight later opening 

has occurred to obscure the character ·of the earlier vein filling. It runs parallel to the Mountain View fault, but, unlike 

that fracture, it is a solid, unbroken vein, which intersects but 

does not fn,ult the east-west veins. · 

The Windlass, Wild Bill, and other veins of the Silverbow 

systen1 are described on pages "171 and 218 in connection with 

the Rarus'a!!d Bell-Diamond areas. 

e-JO 

Q.JO 

Qj<D 

"'"' 

159 

0 0 0 g 0 ~ ~ 0 

"It 0 co Ill Ill Ill "' "It 
160 GEOLOGY AND ORE DEPOSITS OF BUTTE· DISTRICT, MONT AN A. 

SYNDICATE LODE. 

COURSE AND DEVELOPMENT .. 

The Syndicate lode is one of the most regular and 'veil defined of the Butte copper lodes. 

In the property of the Anaconda Co. it has been opened by a practically continuous set of drifts 

f_or about 3,000 feet along the strike, to vertical depths of 1,000 to 2,200 feet. It has been 

followed westward about 1,500 feet farther by nearly continuous drifts through the Estella, 

Poulin, and Moscow 1nines, but in this extent its exploration has been mainly confined to upper 

levels within 400 feet of the surface. It outcrops· on the south edge of the terrace on which 

Centerville is built, but its apex is topographically inconspicuous, rising but little above the 

general surface of the granite. Its course, however, is easily traced, either by the exposed vein, 

by the collapse of the nll.ne workings which reveal the vein walls," or by numerous shafts which 

mark its course fron1 the Poulin !nine on the west to the Wake-up-Jim n1ine on the east. The 

outcrop consists of a firm, somewhat brown quartz, more or less stained by green copper carbonate, but showing no workable bodies of copper ore in the oxidized zonB. 

No positive correlation has as yet been established between the Syndicate lode and the 

veins worked in the Bell and Greyrock mines, but, as stated elsewhere (p. 177), there is reason. 

to believe it to be identical with the Diamond ledge. A vertical section through the Wakeup-Jim mine shows that the Syndicate lode is traceable to a depth of 700 feet, but that below 

that point the vein seems to change from N. 80° E. to aN. 80° W. line of fissuring, which would 

carry it away from the workings of the Bell and Greyrock. It is possible, however, that the 

·mine workings have followed lean cross fractures. 

The lode has a general N: ·soo E. course, the outcrop being. crescentic. The lod~ is the 

resultant of the intersection of two sets of fissures, mineralization following first one and then 

the other, and as this has been modified by cross fractures and slight displacements the actual 

course of the. lode diverges son1ewhat fron1 a straight line. 

The vein has been developed to a depth of 500 feet for 4,000 feet. On these levels the 

workings extend from the Moscow mine ea.stward to the Wake-up-Jim. The zone of ,veathered 

and leached ore is apparently shallow; thus, near the Mountain Con. shaft the lode was workable 

on the tunnel level (6,140 feeO, the. outcrop being only about 60 feet higher. At an elevation 

of 6,050 feet the vein. was continuously workable from the No. 1 shaft to the Wake-up-Jim 

shaft, a distance of 4,500 feet. 

In the Anaconda Co.'s ground (see Pl. XIV, B, p. 114) the lode is worked through the following shafts, which were mined at the time of examination (1906) to the depths given:. · 

Shafts on the Syndicate lode in the Anaconda Co.'s ground in 1906. 

Distance 

east of west Elevation 

Shaft. boundary Depth. of bottom 

of Buffalo level. 

claim. 

Feet. Feet. Feet. 150 500 5,530 

600 1,200 4,944 

Buffalo .................................................................................................... . 1-fountain Con. No. 2 ................................................ · ....................................... . 500 2,200 3,940 

1,000 . 2,200 3,535 500 1,000. 5,150 250 600 5,550 

Mountain Con. No. 1. ...................................................................................... . Green Mountain ..................................................... , ............... .' ..................... . 'Vake-up-Jim ................................................ : ............................................. . Easternmost ........... · .................................................................................... . 

The table shows that the workings are deepest in the central region and shallower at either 

encl. The reason for this is that at the east end, as will be shown below, the lode is either 

displaced northward or the fracture system spreads out into a series of small veins and the ore 

apparently ends. At the west end, although the lode continues strong and well defined as far 

.as it has been developed, it became so poor in copper and so high in zinc on the lower levels 

as to be unprofitable. 
SYNDICATE LODE. 161 

The lode clips 65° to 75° S. in the greater part of its exte~t. Near the surface, back of 

the :Mountain Con. No. 1 shaft and around the Wake-up-Jim shaft, it assun1es a somewhat 

shallower anglo, and at places in depth it bends down to or even past the perpendicular for 

short stretches. 

SPLITTING OF THE LODE. 

In tho upper levels the Syndicate lode is practically single, that is, it does not consist, as do 

numy of the prmninent lodes, of two or n1ore distinct veins separated throughout the 1nine 

workings by a considerable extent of fresh or only slightly altered granite. Lower down, howover, it splits into two branches, but the depth of bifurc.ation differs in different parts of the 

lode. In a cross section through the :Mountain Con. shaft the split is seen at the 900-foot level, 

in a similar cross section through the lode at the No. 2 shaft it is on the 1,100-foot level, and 

at the Green :Mountain shaft it occurs at 1,200 feet. 

The two branches or splits of the Syndicate lode are kno,vn as the North and South veins, 

respectively. In one cross section an intennediate split is seen, which is locally called the 

:Middle vein. 

THICKNESS. 

The lode is unusually thick. For considerable distances along its length ore has been stoped 

to a width of 25 to 65 feet and in places even to 100 feet, and points have been observed where 

the zone of vein matter is as much as 200 feet wide. On the other hand, in many intermediate 

portions it narrows to less than 6 feet. A very considerable part of the wider and poorer portions, however, is 1nerely impregnated or but partly altered granite, and in some parts it is 

bnpossible to determine defmitely whether introduced or original n1aterial predominates. In 

the richer portions the lode is generally of more moderate width, say frop:I15 to 20 feet. In a 

broad way, banding or sheeting parallel to the general plane of the lode is everywhere recognizable, though where metallic n1inerals are most abundarnt it· is sotnewhat effaced. These 

minerals :fi.rst fill small veins that traverse the lode material in every direction, an.d are finally 

so concentra..ted as at times to form a solid mass in which all evide~ce of original structure is lost. 

FRACTURES. 

The general trend of the Syndicate lode is a few degrees north of east, with a slight southward bend at either end. In the general map (Pl. X, pocket) the curve or bow of the lode is 

unduly emphasized because the ground on which it outcrops is much higher in the middle than 

at either encl. As the dip is· to the south, the middle of the outcrop lies farther to the north than 

if it were on a horizontal plane. A truer idea of the actual' strike of the lode is given in figure 

63, which is a horizontal tracing of part of the lode plotted from maps of the mine workings 

and which shows the relative width of the ore bodies (not necessarily, however, of the fractured 

zone) on the 700-foot level (.5,350 feet elevation) of the :Mountain Con. mine. An analytical 

'study of the fTactures in the mine shows that their planes both dip and strike in two ruling directions. These directions generalized are N. 80° E. and N. 80° W., the courses varying within a 

few degrees. The N. 80° E. fractures are predominant in the lode, but a critical study of the 

1nine n1aps shows that no definite law can be laid down as to the relative width or richness of 

the veins in either systen1. 

In many places the ·fractures form mineralized spurs running out from the veins, the ore 

bodies thinning out. and disappearing at short distances-200 feet or so. This is especially 

true in the upper levels, where the replaceme11-t and deposition of glance has gone so far as to 

obscure the lesser fault planes. There is no reason to doubt that the breaking up of the lode 

Jnto short blocky segments (as is well seen in the 700-foot East Greyrock vein) also prevailed 

here, but it is no longer recognizable, owing to the deposition of secondary ore. 

The following directions of fissuring are recognized: N. 10° E., dip 73~ E. or W.; N. 80° W., 

dip 80° S.; N. 80° E., dip 80° S.;. N. 56° W., dip 65° S.; N. 40° vV.,.dip 75° S., cut~ing all 

. others; N. 60° E., a eross vein-recognized on the 500-foot level between shafts No. 1 and No.2 

of Mountain Con.; and N. 65° W. · 

90427°-N o .. 74-12-11 

• 
• 

162 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

Westward the lbde is cut off by a great cross fault developed in the Moscow mine. The 

exact condition of this cut-off is not known, owing to the fact that the low-grade or unworkable 

character of the vein in the lower levels of the Poulin mine 

has led to only meager development. 

In dip the fractures have a general inclination of 70° S., 

but vertical fractures also occur. The conjugate north-dipping fissures associated with the south-dipping fissures are 

not prominent in the upper levels, but at a depth of 2,000 

fe~t or more are abundant and 'vell defined. Between the 

Buffalo and the No. 2 shaft-that is, at the west end of the 

lode-the clip is vertical or northward, but is reversed in 

passing downward and in a short distance becomes normal. 

In studying the variations of the lode it is necessary 

here, as it is throughout the district, to discriminate sharply 

between the original fractures with east-west course and 

primary quartz-pyrite filling, and the later fault fissures, 

which have played so important a part in forming the work- oJ 

~ able ore bodies by their enrichment of the lean primary ores, 

~ either by adn1itting ascending solutions or by affording a 

:g channel for descending waters to reach and ·enrich the 

tfl primary sulphides. Only by actual inspection can this dis- c.l 

::J · tinction be satisfactorily detern1ined; sections can not be ~ 

~ constructed with certainty from mine maps or stope sheets. 

:3 Secondary fracturing and faulting has played an impor- ~ 

~ tant part in the ore development of the lode, which is known 

t to have experienced ·more than t'vo periods of secondary ~ 

fA movement. ·Son1e secondary fractures· are parallel with the <¢ 

e plane of the vein and others cross it at a decided angle. It 

~ seems certain that the latter are earlier than the former; at ~ 

any rate, some of then1 fault the vein, and they do not necessarily influence its n1ineral contents. The parallel fracture 

planes or strike faults, on the other hand, generally occur 

within the lode, most frequently in the middle or in the 

hanging-wall portion. Some of them form a zone of broken 

granite and vein n1atter fron1 a few inches to several feet 

wide, and some form a simple clay seam only an inch or two 

thick. One or the other form is almost invariably found to 

accompany the formation of chalcocite or copper glance. 

That all clay Bean1s or selvages are necessarily of secondary 

·origin can not be definitely assun1ed, but all the evidence so 

far obtained points in this direction. . 

The lode seems to be generally impoverished in depth 

in its westward extension. In the Buffalo and Stella mines 

the upper levels contain large ore bodies of high-grade material, but the copper content gradually diminishes downward, 

and ~t. depths of a few hundred feet is too lean to pay. Similar conditions prevail in the Poulin mine, whose good or~, 

was all obtained from the upper levels; and the same is true 

in the Moscow mine at the western end of the lode. That 

this change in value is not alone clue to the tightiless of the 

vein or to lack of fracturing is easily seen in the Moscow, 
SYNDICATE LODE •. 163 

which is traversecJ by many fault fissures, so that the original vein is crackled and wet. It is 

therefore evident that the center of n1ineralization, fTom which the enriching waters spread 

out, was somewhere near the vicinity of the ]\fountain Con. shaft, for the lode traced eastwarci 

yielded good ore for a depth of 300 feet beneath the surface at the vV ake-up-Jim 1nine, but 

became lean and unworkable in its eastward extension in that property. 

WALL ROCKS. 

The Syndicate 1nines follow the system of working by "laterals"-thn.t is, of cutting 

working drifts in the footwall about 50 feet from and, as near as n1ay be, parallel to the vein, 

from which at given distances crosscuts tap the vein-a 'system that affords numerous opportunities to study the character of the country rock. This is generally of granite, but dikes of aplite, 

generally parallel with the plane of the vein,. are also observed. 

The most pron1inent and well marked of these dikes, near the Buffalo shaft, is 40 to 50 

feet thick. On the Buffalo 500 and 600 foot levels it forn1s the footwall of the vein, on. the 

700-foot level it is a little distance fronT it, and on· the 800-foot level it is no lpnger seen. In 

longitudinal extent it was traced from 50 feet east of the Buffalo shaft ·west to the end of the 

clailn, a distance of about 200 feet. Although its disappearance in either direction n1ay be 

readily accounted for by probable divergences in strike and clip between the dike and the vein, 

causing the forn1er to pass out of the range of observation in 1nine drifts, it is probable, judging 

frmn observations of si1nilar dikes elsewhere, especially ftt the surface, that the actual extent 

of the dike sheet is not very n1uch greater than that proved by the above observations, say, 

under 500 feet long and not n1ore than 50 feet thick. 

Although, as compared with other copper veins of the district, the dividing line between 

vein material and country rock is unusually well defined in the Syndicate lode, places are not 

wanting where th~ change· frqn1 the one to the other is so gradual that it is difficult to say 

exactly where one ends and the other commences. The country rock is ordinarily impregnated 

with pyrite for son1e distance on either side of the veins·; but the extent of the impregnation 

is extremely variable, ranging fTmn a few feet to nearly a hundred. The distance is genera1ly 

proportionate to the mnount of n1etallic minerals within the vein zone. 

, Although pyritization leaves the rock hard and fresh looking to the eye, it is always accmnpaniecl by a certain amount of sericitic alteration. Alt~ration accompanied by decomposition, 

on the other hand, appears to bear a genetic relation to the east-west fractures; in the immediate vicinity of the latter it is very pronounced both in vein matter and in country rock. 

There is but a narrow zone or band of altered rock on the vein walls of the Blue and Steward 

systems, in marked contrast to the great extent of alteration about the Anac.onda, Rarus, 

Pel)Ilsylvania, and Leonard veins. 

Pyritization, with or without copper values, is not ordinarily found to have affected the 

·aplite dikes, possibly because of the absence of basic silicates. In some places, in footwall 

crosscuts, the aplite immediately adjoining the vein was free fron1 pyrite·but the granite beyond 

was strongly impregnated with it. In the stopes, however, a few veinlets of pyrite and 

chalcopyrite were observed penetrating the aplite that adjoined the ore body. 

In the primary veins the general alteration of the country rock is less along the hanging-wall 

side than it is on the footwall side. This statement does not apply to the later fa.ult fractures, 

in which wall-rock alteration is a minor feature. 

In the Green 1\1ountain workings the alteration of the country rock extends into the hanging 

wall for 25 feet and is intense in the footwall for 50 feet or more. Between the branches of the 

vein is a horse 1 to 8 feet wide, composed of much-altered pyritized granite. In general this 

· intcrvein rock is smncwhat n1orc altered than the hanging-wall material, but it does not show 

the crushing and nutshing cha.~·acteristic of the latter. The.clay seams between the 1\1iddle and 

North veins of the Green :Mountain mine, the granite horse, and the footwa~l rock all indicate 

faulting, and that the South ledge may be a downthrown part of the North vein. 
164 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

ORES. 

Large ore bodies were found in the first five levels of the :Mountain Con. n1ine. The largest 

was from 50 to 60 feet wide, several hundred feet long, and had a nearly 'east-west course. It 

showed a flat dip and was n1arked by a large branch or spur vein running off to the southwest. 

It was evidently form'ed by the intersection of a northwest fracture with the normal east-west 

lode, but no reason is apparent why it should terminate so abruptly westward, and its flat di') 

does not conform to the normal steep dip of the main vein. These ore bodies, which are the most 

notable on the upper levels, are believed to be due to comparatively shallow enriphment, in 

which the surface waters deposited glance in the broken ground at fault intersections. . 

In gene~al the Syndicate .lode is rernarkable for the continuity of its values. Broad and 

lor:g ore shoots witl\ a general southwest pitch pass downward from the 400 or 500 foot level 

to depths of 1:000 feet or rnore, the line of pitch of the largest shoot passing through the Mountain 

Con. shaft. In addition, however, to this large rich body, the lode carries workable ore from one 

end to the other. The large shoots appear to be connected with northwest fractures similar in 

direction but not identical with that forming the spur to the big ore body found near the surface. 

Another well-defined ore shoot is found near the Wake-up-Jim shaft; it occurs at the intersection 

of the N. 80° E. and N. 80° W. fractures and pitches N. ·60° W. 

Specimens fron1 the lode consist of primary quartz-pyrite vein filling fractured and impregnated with glance and bornite. :Much distinct cavity filling appears along later fissures in the 

vein, the crusts showing quartz, bornite, etc., the quartz being either comby, with isolated 

crystals in the bornite, or dull and reddish, resulting from replacement of altered rock. 

1\:fuch primary quartz-pyrite vein n1atter is visible in the unworked parts of the lode, as well 

as at the east and west ends of the drifts. In such places the massive pyrite is but little fractured, 

or if broken the fractures are healed by white quartz. A sainple from the east face of the 1,800-

foot drift show~ clearly that all the bornite and glance is confined to these quartz stringers and 

that the workability of the lode entirely depends on them. 

The quartz is not always pyritous. In many places it carries but little pyrite and grades 

over into sericitized granite. . The partly altered granite shows.pyrite developed from hornblende. 

As the sericitized granite has less pyrite, part of that formed from hornblende rnay have been 

dissolved. · 

1\:fost of the specimens from the deep levels show that bornite and other sulphides are still 

forming in fractures, even in capillary fractures, in the vein and in the altered granite (2,200-foot 

level, third drift north), and that the+ solutions are oxidizing and depositing sooty glance and 

ferric oxide in places. It is evident that ore formation has been interrupted by the draining 

away of the '¥ater by drifts and stopes. 

SUBORDINATE VEINS. 

Besides the Syndicate lode proper certain veins which occur in the Syndicate area may 

properly be considered part of a broad lode zone and described here. The most i1nportant is 

the l(eegan. 

KEEGAN VEIN. 

The Keegan vein lies south of the Syndicate ledge, being the first vein south of the drain 

tunnel in the 1,600-foot level, Buffalo crosscut. The course is S. 40° W. and the dip 58° S. 

The ledge, where cut by the '1,500 south crosscut of the :Mountain Con. mine, is about 12 feet 

wide, but the hanging wall is not exposed; the footwall is defined by a clay gouge several inches 

thick. As a whole, the ledge is well banded and is generally very solid. It is composed of 

quartz pyrite, with banding parallel to the walls.· In places there is much clear, glass}~ quartz, 

carrying sphalerite. The or~ occurs in bunches in the vein, one shoot being 5 to 6 sets high 

(35 to 42 feet), and running 6 to 7 per cent in copper. The shoot is markedly lenticular and the 

vein itself pinches and widens along its ·course. Above the 1 ,500-foot level the lode becomes a 

mere seam without ore and is not recognizable as a vein. 
SYNDICATE LODE. 165 

The vein appears to be a solid pyritic vein, cut by vertical fractures and penetrated, to the 

g;reatest depths n1~ned, by water, not only in fissures but also in the apparently solid ~ein. 

These :fissures are 1narked by chalcocite, and the pyrite itself is generally spotted and is fractured 

by incipient, almost n1icroscopic, capillary cracks whose surfaces are glazed with sulphides. 

The ledge cu.rried 26 per cent ore on the 1,700-foot level and good ore on the 1,900-foot,·though 

in the east face it shows a netting of the fractures, with granity quartz between, and is evidently 

playing out. ·The vein ·is ·worked on the 1,.500, 1,700, and 1,900 foot le-vels of the ~fountain 

Con. 1nine. 

DERNIER VEIN. 

The Dernier vein, though worked in the Syndicate 1nines (seep. 184), belongs to the Greyrock 

systmn .. It is well exposed on the 1,900 and 2,100 foot levels of the :Mountain Con. The vein 

consists of a n1ass of quartz-pyrite ore, with secondary bornite, associated quartz, and enargite, 

the lust 1uunecl being seen here for the ftrst ti1ne in the Syndicate workings. The vein is 10 feet 

wide und expands as it approaches a northwest fissure which cuts it and practically terminates 

n1ineralization in this direction. This fissure is a n1ere dry crack, but beyond it the vein, which 

appears to go on without displacement, is narrow and lean. This is a remarkable example of 

the effect of a fault fissure devoid of ore or gouge, which deflects the enriching solutions and by 

their stagnu,tion causes an enla.rgen1ent of the adjacent ore body. 

OLD GLOH.Y VEIN.-

The Old Glory vein, which in recent years has yielded small mnounts of copper ore, is 

located in Centerville, near :Main Street. The vein splits downwn,rd into two veins, the southerly 

averaging 5 feet in thickness and dipping about 60° S., and the 1nain vein standing nearly vertical. 

The ore contains n1anganese, zinc, and silver 1ninerals, with some lenticulnr bodies of copper ore, 

and is thus a trn,nsition or composite vein sin1ilar to the West Greyrock vein. 

The lode is faulted by the La Plata fault vein, so that its downward continuation beneath 

the fuult lies to the north. The latter runs north-south, dips east, and shows in the north crosscut fTon1 the 800-foot ~fountain Con. level, the first east of the Buffalo shaft. In the drift on 

the fifth level fTOlll the inclined shaft. on the Buffalo the vein strikes N. 70° w.', with a flat dip 

from the 200 to the 900 foot level. The 500-foot level of the Buffalo has a long northerly 

crosscut to the Snoozer vein whose course is N. 70° E. The san10 vein is worked on the 1,200-

foot level, where it splits into a north vein and a southern 2 to 3 foot vein, exposed. in the crosscut 

south fTom the east end of the level. · · 

H.A VEN VEI':N. 

The Ruven vein, lying north of the Sy~dicate lode, has a general east-west course and a 

. dip of ttbout 58°, rolling considerably between the surface and the 323-foot level. It is a 

contact vein between n.plite on the north and Butte quartz n1onzonite on the south. There 

has been so1ne 1noven1ent along this contact, and the 227-foot level shows clayey fault 1natter, 

but no ore or other vein n1atter. 

On the 323-foot level the vein shows 2 to 4 inches of sulphide ore, besides an impregnation 

of the granite wall rock. The ore carries sphalerite, galena, pyrite, and some copper. ·It has 

been opened on the 140, 227, and 323 foot levels. ·The vein has an average dip of 58° S. frmn 

the surface to the 1.40-foot level. Below the average is ·about the san1e, hut the vein straightens 

up between the 140 and 227 foot levels, and then flattens between the latter and the bottom 

level. The botton1 level shows several inches of sulphide ore very rich in silver, with silver 

ore running out along fntetures in the granite. 

MINES. 

In considering the features observed in different parts of the Syndicate lode, the sections worked in the various 1nines, namely, the ~1oscow, 0 Poulin, Stella, Buffalo, ~1ountain 

Con. Nos. 1 and 2, Green :Mountain, and Wake-up-Jim 1nines, will be considered in turn. 
166 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA • 

. MOSCOW MINE. 

The extreme western end of the Syndicate lode was worked in the Moscow mine, a property 

that has been idle in recent years, so ·that but few new notes are obtainable. The property 

was, however, thoroughly examined in 1896 by S. F. Emmons, by whom a considerable part 

of the description of the Syndicate lode was written. The n1ine workings show .that a large 

ore body existed on the 100-foot level, extending downward to the 250-foot level, (fig. 64) the 

ore shoot lying along a secondary fissure known as the Poulin fault, an easterly fault fissure 

belonging to the Steward series. In this property the primary lode filling· is too lean to pay 

fo:r working and need not be further considered. 

POULIN 1 STELLA, AND BUJ!'F'ALO MINES. 

The Poulin mine lies next to the :Moscow; its workings go down to a depth of 1,200 feet. 

East of the Poulin lies the Stella, follqwed by the Buffalo .. 

On the Stella and on the 400 and 500 foot levels of the Buffalo the drifts extend nearly 

to the Poulin shaft, and develop large ore bodies of low-grade ore fro1n the surface ·down to a 

depth of 400 feet. In the Poulin mine no pay ore has been taken out below a depth of 600 

feet; from the 600-foot level to the 1,200-foot level the lode has a strike of N. 70° to 80° E., 

a dip of 75° S., and is a thick but lean and dry quartz vein. Though crossed by a northeast 

fault fissure with crushing and shattering, neither :.the Syndicate lode nor the fault fissure 

contain pay ore. (See fig. 65.) 

The 1,200-foot crqsscut from the Poulin shaft southward is cut through hard, very fresh 

granite, showing joint planes that are well n1arked but are devoid of clay fractures or other 

evidences of n1ove- 5 2 

FIGURE 04.-Cross section of Syndicate lode, Moscow mine, 250-foot level. 1, Quartz monzonite; 2, breccia; 

3, porphyry; 4, clay; 5, pyritized quartz. 

1nent or decoinposition. Near the south 

end of the crosscut a 

zone of zi11c veins 

crosses the level . in a 

general east and west 

direction. These 

veins are dry and consist of quartz, a little 

pyrite, and considerable zinc blende. The quartz is crushed in part of the vein, but it does llOt show any clay. 

Eastward along the level the walls show pyritized granite, with several very s1nall slips., At the 

point where the level, after bending southeast, takes a general easterly course, a clay fault 12 

feet wide forms the footwall of a hard quartz-pyrite vein which, runs with the drift. The fault 

is traeeable eastward, showing in a little crosscut running northwest fron1 the n1ain 1,200-foot 

level, and reappearing to the east. Beyond this point it passes out of the wall to the north, 

but shows again in the Buffalo crosscut. In general the rock through this level is somewhat 

altered granite, which shows numerous joint planes, along which the rock has been softened for 

a thickness of 1 to 4 inches,' so that it yields as readily to the pick as a sand. There is no 

evidence of movement and the deco1nposition is plainly clue to the infiltration of \Vaters. 

Along the joint planes, in a little vein seen in the northeast crossc.ut runni~g out from the 

1,000-foot level, an excellent specimen of vein formation is taking place above a clay slip, the 

granite being replaced by waters flowing along the fault plane. At several places in the level 

the granite shows patches or veinlike masses of altered rock resembling porphyry. This shows 

greenish feldspars softened to the consistency of cheese and is probably a thoroughly altered 

n1ateriaL :Much semiaplite was also seen, but as the boundaries were indistinct and the rock 

fades into granite, the places have .not been marked. 
SYNDICATE LODE. 167 

MOUNTAIN CON. MINE. 

In the :Mountain Con. mine the lode consists of two 1nain veins known as the North and South 

ledges. As the stopes above 1,100 feet are inaccessible exact conditions in them are unknown, 

nnd an examination of the stope sheets throws but little light upon the subject. The level 

maps show that the· South ledge has been worked continuously from the outcrop downward, 

but that the ore body stoped out in the upper levels had a different course frqm that of the 

ni.ain ledge at deeper leve,s. The tunnel level 

and the 100,200,300, and 400 foot levels in the N 

vicinity of the Mountain Con. shaft were all 

driven on very large ore bodies with a nearly 

due east-west course. Below the 400-foot 

level the ore shoots seem to pitch southeast. 

As bearing upon this feature, the wellmarked ore shoot found between the :Mountain Con. and the Green Mountain mines is of 

importance. This shoot seems to come in at 

an intersection of aN. 80° E. set of fractures 

(the course of the main Syndicate ledge) and 

a N. 80 ° W. set of fractures developed on the 

deeper levels. The mnps show ore bodies extending f-rom the 500-foot level down to the 

1,200-foot level along this intersection, which 

in depth is of course progressively farther and 

farther east. 

In the Mountain Con. mine the North 

u.ncl South ledges come together at the· 900-

foot level, but as no prospecting is done to 

the south in the upper levels, whether the 

veins ~ross or simply coalesce is not known. 

The stopes are continuous on the South vein 

fron1 the 1,300 to the 1, 700 foot level, and 

are practically connected from the 2,000-foot 

level up. . 

'rhe North Ledge is nearly vertical frmn 

the 1,300-foot level down almost to the 2,000-

foot level, on which it bows to the south very 

strongly enst of the shaft, so that the levels 

show co~1stant offsets until, near the end, the 

drift runs nearly south. This is believed to 

be due to an intersection of tbe southeast fault 

STELLA 

SHAFT 

L£V£L 

s 

6000 

5300 

5200 

5100 

4900 

4700 

4600 

of the Steward system. The 2,000-foot level FIGuRE 65.-Cross section through Stel,la shaft, showing the Synd.lcate 

leaves the vein on account of this southerly lode and the faults that cut it. 

trend and crosses north to meet the raise from 

the 2,200-foot in the Green Mountain mine. The South vein splits forming the l\1iddle ledge 

and the South vein proper on the 1,300 to the 1,500 foot level. 'The raise is mostly, however, 

in fault breccia. 

Rich glance ore occurred only where the veins were wet or showed signs of having recently 

been so. Thus, the barren fault breccia in the raise from ~he 1,500 to the 1, 700 foot level 

is dry and dusty, and the vein is dusty generally near the raise and is devoid of good ore, but 

farther off, where it is wet, .it holds considerable glance; in other words, the wet veins are most 

likely to carry ore, though they do not invariably do so. 

In the lower levels sooty sulphides and films of glance coat pyrite. That the ore comes frolll 

above and is deposited by descending waters is shown by the North vein on 2,000-foot level, 
168 GEOLOGY AND .ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

which was drained dry ·within a few days after it wa:s first cut. The vein consists of a brecciated 

quartz-pyrite ore, with dull, opaque quartz, showing the characters of replacement quartz, but 

crushed to an ~utoclastic breccia and cem~nted together by secondary crystalline silica which 

shows comb structure or banding and holds numerous vugs. This brecciated material holds 

some glance as veinlets, spots, and cementations of crushed pyrite (fig. 66). The most striking 

feature, however, is the presence"'of crystalline scales of glance on the fracture surface of the white 

quartz, or, more rarely, spotting the forms of late quartz crystals. The crevices in the older 

quartz and in the quartz-pyrite ore are coated with sooty glance, and\he whole ore body shows 

n1ore or less of this incoherent sooty matter. The druses of quartz crystals rest upon zinc blende 

or in some places on enargite. It is evident that extremely minute fractures in the ore and in 

the glance · are filled with the 

quartz rather than with the 

films of such sulphides. Some 

covellite was also seen. · 

Organic matter can be 

practically eliminated from 

the reactions involved in the 

formation of the secondary ore 

just mentioned. Some of the 

deep workings seen are not FIGURE 66.-Section of Syndicate lode, 600-foot level, Mountain Con. mine. 1, Quartz monzo- l th · k 

nite; 2, altered rock; 3, pyritized quartz;' 4, pyrite and glance; 5, glance; 6, clay; 7, breccia. unc er any 0 er. mine wor - ings, and the surface overlying 

the veins is devoid of all vegetation. The North vein on the 2,000-foot level west evidently 

formed a watercourse which when visited had just been deserted. It was moist but not 

dripping. There are no lower workings, and if ·the waters came from below they would show 

in the floor or in the lower part of the face at least. There is no escape from the conclusion 

that the waters forming the glance 9res are descending waters, and that they were still active 

and were depositing glance when the vein was cut and the action stopped. The action is, 

however, one of leaching, that is, one of solution and of corresponding deposition, the waters 

probably dissolving and depositing at the same time, a phenomenon seen in the Skyrme vein, 

in which skeletons of 

mossy residues showing dissolution occur. 

The statement 

often expressed in the 

clis.trict that the footwall ore streak is richer 

than the hanging-wall 

band does not hold 

true in the Mountain 

Con. veins because the 

0 . 5 

4 3 

10Feet 

FIGURE 67.-Section of Syndicate lode, 1,100-foot level, Mountain Con. mine. 1, Quartz monzonite; 2, clay; 

clay gouge shuts off - · 3, altered rock; 4, pyritized quartz; 5, glance. 

access to the footwall 

gra:qite, and solutions do not penetrate it. The footwall of the South and North veins on the 

higher levels is granite, and the change from ore to granite is rather sudden, as shown particularly in the North vein. The granite of both walls of the vein is rather scaly, and the fractures 

are curved and marked by films of clay (figE!. 67 and 68), so that when the rock is mined it 

slacks off in lumps and exposes smooth bossy surfaces. As the water is drained off this hardens and becomes solid and as a rule stands well, though occasionally the ground runs badly. 

Some flat fissures have a prevailing dip of 45° more or less, but as a rule these do not markedly affect the ore. An exception is on the 1,900-foot level of the Mountain Con., where the 

fissures appear to throw, or rather drag the vein to the north. 
SYNDICATE. LODE. 169 

Between the two Mountain Con. shafts the Syndicate lode diverges markedly to the southeast on ·the 600-foot level (see fig. 63), though this divergence becomes less with increasing depth. 

The vertical elmnent in clip is n1ore pronounced with depth and results on the 1,000-foot level 

in a widening and splitting of the ore zone into two veins such as were found at the botton1 

of the No. 1 workings 

(p. 167) .. Tlus feature of 2 __ ,....,.....,._:.,...,.,...,....,..,...,... 

the lode has thus been 

traced over a horizontal 

extent of 1,200 to 1,500 

feet. "'What it will develop in depth ren1ains to 

be proved. (See fig. 69.) 

West of the Mountain 

Con. No. 2 the lode has a 

very regular strike in the 

nonnal north-of-east diFIGURE 68.-Section of Syndicate lode, fourth floor above 1,0QO..foot level, Mountain Con. mine. 

1, Quartz monzonite; 2, clay. 

rection, but its clip is steeper than the normal, and with this steepening seems to go a widening 

of the ore zone. In the lower levels explorations have not yet been carried to the western limits 

of the Anaconda Co.'s ground. . 

A modern cross fracture running north and south nearly on the line of the Buffalo shaft has 

be~n noted on each succeeding level down to the 800-foot; it admits s~rface waters freely and 

N 

1 

LEGEND. 

11!3 Ore 

ba 

Faults 

FIGURE 69.-Pian of part of 2,100.foot level, Mountain Con. mine. showing spraying or ore. 

carries a wlute mud of decomposed rock material. It.pitches slightly to the east. It does not 

throw the lode nor have any appreciable effect on. the character of .the ore. It thus seems later 

and distinct frmn the secondary fractures which follow the plane of the 'lode and are traceable 

wherever notable enriclunent occurs. 

0 

·. 
170 GEOLOGY AN•D ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

GREEN MOUNTAIN MINE. 

The various crosscuts of the Green Mountain mine show several sn1all veins and clay searris 

north of the main ledge .. (See Pl. XV, B.) The lode is cut on each level but is not stoped, 

because the vein is too poor to work. In general, the lod.e is unworkable below the 900-foot 

level, and even above this level is lean east of the shaft. The ore is very largely pyrite, associated. with a dull white to gray quartz, very hard to drill, and lacking the usual fractures of rich 

ores (fig. 70). The vein on the 1,600-foot and 1,800-foot levels shows some glance, but it is 

mostly either in films or cracks in the pyrite or in platy veinlets in the fractured quartz, or else 

it is in vugs of white quartzite. As a rule in these veins the glance and the pay ore occur only in 

quartz and the irony ore is too lean to pay. Though this does not support the chemistry of the 

secondary theory, it is evident that it is due to the fact that the quartz ore can be concentrated 

f;tnd the pyrite ore can not. The actual copper value of the pyrite ore may be as high as 

that of the quartz and yet the ore be not available. 

The 1,800-foot level is dry, and inspection confirms the view of the writer that the water 

all comes from ·above and that there ·is no uprising water. This is easily seen in the new 

workings ·driven underneath the old workings. In such cases th~ waters drip from the roof 

and sides of the drift, but the amount soon lessens and in a few weeks the workings are relatively dry and in a year are perfectly dry. If the water came from below, the level would 

FIGURE 70.-Section of Syndicate lode, 800-foot level west, Green Mountain mine. 

remain permanently wet, which seems. to negative the idea of uprising deep-seated waters. 

Moreover, one need not look at the 2,000-foot Mountain Con. a second time to see that' the 

water has recently left it. The structure of the ore indicates that it is still being formed, and 

there is a marked coincidence of wet vein and good ore, the solid tight vein being dry and 

unworkable, though explored by a few drifts. The main ledge of the Green Mountain is, however, not dry, though it is not cracked and crushed, and hence is not a good water channel. 

Samples of water were taken at the diamond drills at the 2,000-foot north, at the north end 

of crosscut, and the analysis has already been given (p. 101). 

In· the Green Mountain workings, on the 1,200 and 1,300 foot levels, the South ledge thins 

out at a point 240 feet west of the crosscut, but is a strong vein, richly mineralized, east of 

the crosscut. In the Wake-up-Jim workings the vein is double, as already noted; the North 

branch is lean, and the South branch is small but rich. 

The big Syndicate ledge, where cut on the 2,200-foot level of the Green Mountain, about 

150 feet south of the shaft, is 60 feet wide, consisting of altered and silicified granite, with a 3 

or 4 foot band of solid but barren quartz in the center and a 5-foot footwall band of pyritic 

ore. (See fig. 71.) 

In the Green Mountain mine the lode is very irregular, changing rapidly in width from a 

few feet up to 70 feet. The ore appears to be distributed in chimney-like channels within the 

vein matter. Westward, toward the Mountain Con. lode, it separates into several ore-bearing 

bands filling overlapping fissures and tending to pinch out successively. Eastward, on the lower 1 

• 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE XV 

A. MOULTON MINE. 

Shows g reat dump heap of low·g rad e zincifero us si lver ore and wast e. See page 244. 

B. GENERAL VIEW OF GREEN MOUNTAIN MINE. 
ANACONDA-PARROT BELT. 171 

levels, it disappears 200 to 300 feet beyond the shaft, its place being taken by a zone of impregnated granite and by southeast striking veins of pyrite a few inches in width and 30 to 40.feet 

apart. · 

·The development of southeast fissures is a characteristic feature of. this part of the lode; 

they appear in the developed ground mainly as spurs making off in a northwesterly direction 

into the footwall country. One on the 900-foot level was followed 225 feet in a northwest 

di.rection, when it pinched out. Another running northward and extending vertically ·100 feet 

above the level was traced 60 feet northward to where it was cut off by a recent fault, fresh 

granite appearing beyond a clay seam. This vein carried a rich chalcopyrite ore but no bornite 

or chalcocite. Five s1nall southeast-striking pyrite veins were cut in the footwall country by 

the crosscut from the shaft to the vein. (See fig. 67, p. 167.) ' 

Another unusual feature of this part of the lode is the occurrence of faults transverse to the 

plane of the vein; in one, east of the plane of section, the fault plane dips north and throws the 

northern or upper portion of the lode downward about 10 feet; in another, east of the plane of 

section, the fault plane dips 15° S., and the 

lode above it is thrown 10 feet south; thus 

both are normal faults. · · 

The lode is cut by a clay fault seam, 

breaking and slightly shifting the ore. The 

crosscut'for 450 feet south of the shaft westward is cut by nun1erous slips and dislocated 

fragn1ents of quartz-pyrite veins; it probably 

represents a ground ready for vein formation but not yet enriched, for the ore body 

west is siinilar, except that later 1nineraliza-. 

tion has replaced and in1pregnated the granite. 

WAKE-UP-.liM MINE .. 

In the W ake-up-Jiin ground the two sets 

of fissures, one northeast and the other southeast, are more distinctly developed, as is' also 

the vertical and inclined dip, producing. very 

c01nplicated conditions. The ore near the 

surface appears to have concentrated mainly 

FIGURE 71.-Section of Syndicate lode, 2,200-foot level east, Green 

Mountain mine. 1, Solid black quartz and pyrite; 2, vert.lcally 

banded black quartz and vugs; 3, banded quartz, mostly dark, 

and pyrite; 4, white clay; 5, white quartz; 6, vug, lined with 

quartz; 7, quartz monzonite. 

on the northeast fractures, but below, on the 400-foot level, the lode trends southeast, the northeast fissures constituting only ~pur veins. One of these, about 170 feet east of the shaft, has been 

cut in both 300 and 400 foot levels, which correspond to the 2oo and 300 foot of the :Mountain 

Con. It stands vertical and carries about 2 feet of quite unaltered pyrite and quartz. At its 

crossing the main vein is unusually wide and rich and has apparently faulted the spur vein. A 

~ shnilar spur vein SO feet west of the shaft, which is in places 5 feet wide, ends in a country 

rock that has been ~hattered by secondary action and exceptionally carries chalcocite. Fifty 

feet west of tllis spur the main vein narrows to a clay seam, and the ore continues west in 

an echelon or overlapping fissure 20 feet to the south. 

· In this n1ine the main ore-bearing lode has not thus far been traced n1ore than 250 feet east 

of the shaft nor more than 800 feet downward. The strong and relatively well-defined fissure 

S)7-stmn appears to be replaced in either· direction by a few narrow and diverging fracture planes 

carrying b1._1t little ore. 

DIAMOND-BELL GROUP. 

GENERAL RELATIONS. 

The Dia1nond-Bell group of veins, situated in the northern part of the copper· area and _ 

worked in the Dimnond-Bell, High Ore, Speculator, East and West Greyrock, and Corra mines, 

has not only been a large producer for a long t~e, but has become of increasing importance in 
172 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTA:NA. 

recent years through the discovery of new ore bodies in some of the deeper levels; . The Diamond vein can be tentatively correlated with the Speculator lode to the east, but the extension 

of the veins t() the southwest is not satisfactprily established. It is reasonable, however, to 

suppose that the large and persistent veins worked in these mines extend as fractures both to 

the southeast and the ·northwest and if not workable themselves have greatly influenced the 

mineralization of the other lodes in these ar~as. 

The vein relations in the group are complex, no less than four systen1s of fracturing and 

vein formation being well developed; but when these are differentiated the _apparent complexity becomes relatively simple. Briefly summarized, the mines show an east-west vein, the 

Speculator, broken into segments by several northwest fault veins of the Greyrock group (Blue 

Vein system), the displacement being 300 feet east on the hanging wall of the Skyrme vein and 

less on the footwall veins south of the Skyrme. A. third vein system, the High Ore, is a 

varian~ of the east-west veins; it has a course intermediate between the east-west and the 

Blue Vein systems and appears only in short detached blocks, ending agamst the walls of the 

fault veins of the Blue system. 

These vein systems are broken by the Bell fault (Steward system), which shifts the entire 

block of ground north of this fault to the northeast. This fault, so· far as known in 1906, is 

not ore bearing, though veins of this system are liberally mineralized in the Steward and 

Ane.conda mines. · 

The veins of the Blue Vein system having a generally northwest trend, constitute what 

may be called the Greyrock group, of which a· prominent representative is the Covellite vein. 

A parallel_vein south of it, known as the Bell vein (not Bell fault), or the North Greyrock vein, 

is the next most prominent v~in of the series. Both the Covellite and .the North Greyrock 

are fault veins; the former is correlated with the Skyrme vein, which has been worked eastward 

from the Bell shaft to the High Ore shaft, but is broken and displaced by a later N. 70° E. 

fault vein, which throws the east portion of the Skyrme vein south of the Covellite and Bell 

vems. 

The High Ore system, earlier than the Blue V em system, is represented by the High Ore 

and Wild Bill veins, with a course of N. 65°-70° W. 

The Anaconda system includes the Speculator vein, with a general course of N. 65° E., 

the best-knoWn representative of the system in this group of mines. Some observers have 

thought the Speculator and Covellite veins are faulted parts of a once continuous vein, but 

the mine maps show plainly they differ considerably in strike, and. a study of the veins themselves shows a decided difference in physical character and in mineralization. 

The Bell fault vein, the prominent member of the Steward system, passes through the 

center of the "Diamond and Bell workings and extends eastward into th9 Speculator ground, 

where it is encountered in the w~rkings of the mine of that name; westward its direction corresponds to that of the Poulin fault vein, though the crosscuts of the Green Mountain, shaft do 

not afford definite correlation in this part of the camp. (See fig. 72.) · 

The dip of the veins is generally steep, those of the High Ore and Greyrock being exceptions 

in showing flat southerly dips. The others have a steep southward dip, but in the deeper 

levels the Covellite vein splits and- its north branch dips northward. (See fig. 73.) 

The principal veins of this part of the district are: Wild Bill, Covellite (or Bell north), 

Bell, Gillie, Middle, Winchell, and Greyrock. All these lie northwest of. the cross or Bell fault 

vein, which runs north of east, is nearly ver,tical, and cuts the Greyrock and Covellite veins, 

passing through the Bell shaft. Southeast of the Bell fault are the Higgins, High Ore, Skyrme, 

and Speculator veins. Several others appear in the lower levels, but not being distinctly recognized above, have been given specific names. These include the Sisters, Diamond ·(which 

may be the Middle),· Vale, and Christian veins·. 

The Covellite vein is worked. to the northwest in the Corra mine, but the other veins found 

in· that mine seem to correspond to the silver veins of the West Greyrock mine rather than to 

those of the Greyrock group. The Covellite is worked on the 2,200-foot level of the Green 

Mountain shaft,· being reached by a long north crosscut. It is interesting to note that at this 
DIAMOND-BELL GROUP. 173 

() 

depth both the Covellite vein and the 

supposedly faulted eastward extension of 

this vein-the Skyrme vein-contain an 

abundance of enargite, n. 1nineral almost 

unknown in the upper levels of all the 

veins of the gro.up. 

Minern.logically the veins of this 

group of 1nines present n. certain indiviclun.lity. The prevailing type of ore shows 

abundant chalcocite in a mixture of 

quartz n.nd pyrite, but bornite is common, though not in large amount; enargite occurs only in the deepest levels, 

2,000 feet or 1nore beneath the surface. 

The reln.tively rare minern.l, covellite, is 

very o.bundn.nt in one vein, called by this 

nn.me, in the En.st Greyrock mine and is · 

present in small amounts in other veins. 

No typicn.l enn.rgite veins occur, though 

the deep Edith May and Jessie veins contn.in ln.rge an1ounts of this mineral. 

The veins show the usual differences 

obse1:vable throughout the district between the primary. quartz-pyrite veins 

and the later fault veins. The former 

are vn.luable only when broken by later 

.movement n.nd enriched; the latter carry 

ore in lenticuJn.r shoots, separated by 

stretches of barren fault matter. Friction breccias are common, but the conglomerate ores !3een in the mines on the 

Parrot lode are rare. The immense ore 

bodies found in the Bell and Diamond 

mines occur at the inter.sections of the 

various fissure systems and are apparently the result of several distinct periods 

·Of min,eralization. 

In genera] the tendency of the veins 

:seen in the lower levels-as, for example, 

the 2,100 and 2,200 foot Bell and DiaJnond-is to split up; the granite between 

these fractures shows silicification but no 

·Ore, and the veinlets or individual frac-

. tures get leaner in depth. The 2,200-

'foot Bell-Dian1ond is a remarkable exam-

·ple of this tenciency. The Covellite vein 

on this level is seen west of the crosscut, 

where it is very lean, and is mainly 

·composed of a friction breccia, usually 

.. \vithout quartz. Eastward the Covellite 

vein splits, and east of this bifurcation 

is cut off by a cross fault, beyond which 

it hll.s not been definitely located, though 

it seen1s to correspond to the Skyrme 

·vein. 

LEGEND 

~ Ore 

Faults 

1100· FT. lEVEL 

1200·FT.lEVEl 

''. 

==:::#;2,j~/p.>:::;.·/ • =/ =;~;r;m"'"fjj#'""f#"IJ.=t'''l---;:==t=.==;t;t:::::::::::::n:::::::; l.?.i!!i .. ;":,sz ;;~ /,;:>; 

,.(/ 

,..;:// 

==========--=-~-=-.-=-.-=..-=-.-=-.--=lOJ!:-FT.LEVll 

FIGURE 72.-Section through Green. Mountain shaft, showing Syndicate lode. 
174 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The 2;200-foot, or drainage, level of the I-Iigh Ore n1ine shows aplite in abundance at a point 

300 feet north of the shaft. It also shows a granite porphyry, or rhyolite porphyry, in which 

the quartz phenocrysts lie· in a groundmass much more granular than usual throughout the 

district. This level also· shows much brecciated grn.nite, ·which apparently represents the first 

stages in vein formation. · 

FAULTING. 

The interest in the Bell-Diamond-High ·ore group of vema lies mainly in their structural 

features, the record of faulting and succeeding mineralization being exceptionally clear. Neither 

in mineralogic nor economic relations do the veins present any especial novelty. 

FEET 

DIAMOND 

6200 

6000 

5800 

5600 

5400 

5200 

5000 

4800 

4600 

4400 

4200 

4000 

FIGURE 73.-North-south section through Diamond shaft, showing veins of Diamond mine. 

The Greyrock group of veins, including the Greyrock, Bell, and Covellite veins, are of 

variable width and show clear evidence of shifting along their walls. They consist largely 

of altered granite and friction clay, with 'long ore bodies which feather out at ei;tch end, but 

are of great vertical extent. 
DIAMOND-BELL GROUP. 175 

. . The veins of the Greyrock system (see fig. 73) are shattered and sliced by northeast fractures, producing frequent displacen1ents of small amount, a feature ,vhich seen1s most marked 

in the lower levels, probably be'cn.use close timbering, crushing, and filling prevents its recognition on the upper ones. The shift is almost invariably to the west. As. noted on the Parrot 

vein, tlus fnulting in places produces a marked variation in the amount of rich ore, the vein 

being lean west of the fault. The faults are generally of steep dip, and the filling consists of a 

few inches of clay, with pebbles of country rock. Owing to the extreme crushing in the vicinity 

of the Bell shn.ft the relations of the Ditunond vein (part of the Speculator vein), which comprises 

the gren,test ore body of that mine, can not be satisfactorily determined; but there seems little 

doubt thnt it is formed by the juxtaposition of the Diamond vein .and the faulted Bell vein. 

These relations are best shown by the map giving the horizontal section of the 5,100-foot level. 

The relations of the displaced veins are best shown on the 1,600-foot levels of the mines. 

The displaced segn1~mts of the Speculator vein are six in number, the Diamond being one of the 

centrnJ ones. The Greyrock group displaces the Specul~tor, and· as it is .displaced by the 

Bell fault the resulting structure is apparently complex. If, however, the Covellite vein be 

correlated with the'Skyrme, the Vale vein with the Sales, and the Winchell with the Teague, the 

correlation is perfect withou.t any vertical movement. In this case the Bell vein corresponds 

to an unworked vein lying between the Sales and the Skyrme. To correlate the displaced 

seg1nents of the Speculator one must assume an eastward throw on the south or hanging-wall 

side of each of the northwest veins. This results in a complete correlation and shows that the 

Speculator vein was once continuous westward beyond the working;:; of the East Greyrock n1ine. 

The faulting of the Speculator vein by the northwest veins is repeated westward, where 

the Wild Bill is cut off by the Covellite vein, and this in turn by the Bell and other fault fissures 

lying to the southward. The 1,500-foot East Greyrock shows a cut-off of this kind, with a shift 

of the vein sunilar in amount and displacen1ent to that produced by the Skyrme vein and by the 

Covellite vein on the Speculator vein. These facts, which are difficult of verbal expression, are, 

it is believed, clearly brought out by the maps. 

The persistence and straightness of the northwest fractures are very marked, the most notable 

example being the Skyrme vein, which has been developed on several levels for a distance of 

4,500 feet, drifts being run from the High Ore mine to the Bell-Diamond, and on some levels 

eastward to the I-Iigh ·Ore shaft. This vein has been developed fron1 the ::mrface to a depth of 

2,400 feet and has also been cut in the 2,800-foot level of the High Ore mine, where it is ore 

bearing. Counting in its westward extension the Covellite, it has a total workable length of 

ovei· 4,000 feet, being worked in the Corra mine and probably cut westward of this property in 

other workings. The other fissures have not been so well developed, but there is no reason to 

doubt that when they are drifted upon they, too, will be found to contain pay ore. The future 

of this section of the camp rests entirely on the development of the deep levels of these northwest fractures. · 

The rich ore bodies in which not only streaks of high-grade ore but intervening sections of 

mineralized ·granite have been largely worked in the Bell and Diamond mines, are due to the 

shattering .of the ground by the northwest and northeast fractures. As the latter are later than· 

the northwest fractures it is probable that we have here to d~al with two periods of mineralization, the last of which is still going on, as .the mine waters, even at the greatest depth, are clearly 

descending waters and are depositing glance. 

Of all the veins opened up in these mines the most productive has been the Covellite and 

the next most productive the Bell. The Covellite is a fault fissure, but, unlike many of the 

others, it carries good ore near the surface, which feature is wholly absent in its eastward con.;. 

tinuation in the Skyrme. It has been continuously worked to the deepest levels, yielding good 

ore il1 the westward extension of the vein· on the 2,200-foot level of the Green l\1ountain mine. 

Of the I~orthwest veins, the southernmost, called Winchell west of the fault and Teague east 

of it, has proved very productive in the deep levels, whereas the faulted section of the Specu-

" 
176 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRTC.T, MONTANA. 

lator, designated J. B. on the map, yielded comparatively little ore in the upper levels, but at 

1,400 to 1,600 feet is characterized by a large and rich ore body. 

The Bell fault is the latest fracture of this area. It belongs to the Steward fault system. 

It displaces the Skyrme vein, which, as already noted, is equivalent to the Covellite vein, and 

it also cuts through ·and displaces the Higgins, which is the eastern portion of the Bell vein. 

The workings of the West Greyrock and of the East Greyrock mines show many small fractures 

parallel to this Bell fault, and these fractures displace the older veins a few feet, though fortunately they do not interrupt the continuity of the workings, but have apparently played an 

important part in producing rich ore. The fault runs somewhat north of .east. 

fdffr / ........_ 

____--/ 100 

'"roo 1- I= 200 

r I 30C ,~~ 

/.;:·l J ,. 

·;~I 1 5900 

·-Jf! I ( 

: 

d II I "' ff::_ II/ I ~700 l!f , L ... """ 1/ ~~1 I 5600 

~~~ *7 # I 

II I 7UU 

~¥ l~f/ !, ff 800 / H .E 

~u l.:>f I a > 5400 

/ I ~,<::-/ .E/1 9~0 

5300 // / .:;,"Z f: . :!: '1 1000 // I ~L \ J 

/ I il '\i f/ 5200 

.... ':\\ ~~· 100 

II 1150 5100 II /(/ I " I tl '::·,J~r' , II 

'I li!UU 

·~~ 

/ I 1300 

/ I or 4900 

y 1400 

/ I p: 0 

k/ 1500 

4700 / l~ ' 1600 

I .Vf , , Diamond 1700 

I /) I 4500 

I I 

I J n'/ 'Diamond 1800 4400 

I '· .. 4300 

'I 

4CO'O 

FIGURE 74.-North-south section through vein and faults. of Diamond mine on line of Bell shaft. 

EAST-WEST VEINS. 

The east-west veins include the Speculator and its supposedly detached faulted portions, 

the Diamond, Swede, Flood, J. B., etc. The old vein filling consists of quartz and pyrite, the 

latter in places prevailing. When not broken by fault movements and enriched by glance 

deposited. later, these veins are very low grade. When enriched they form large and riGh ore 

bodies, the so-called Diamond vein being the largest and most valuable ore body of the group. 

All the· east-west veins encountered in the mines are now believed to be merely faulted portions of the Speculator (and possibly Syndicate) ledge. Of these, the Diamond has been the 

most productive. In the Speculator mine the vein dips north down to the 300 level and below· 

this changes to a squtherly dip. 
DIAMOND-BELL GROUP. 177 

The largest of the east-west veins is the Speculator, which is worked in the Speculator 

mine, and extends westward in a nearly straight line to the workings of the Greyrock, and Bell. 

The Speculator vein is broken and displaced by the northwest veins, and the result is that the 

detached fragment of the Speculator vein found near the Diamond shaft, and generally ]mown 

as the Diamond ore body, is limited both on the east and on the west by fault fi~sures. 

There is some question as to whether the great Syndicate ledge is not the westward continuation of the Speculator vein. The Syndicate ledge termina.tes abruptly eastward, 'but· 

owing to the barren nature of much of the vein the workings hfl; ve not .been developed up t6. 

the point where the Bell fault is supposed to cross. When account is taken of faulting, however, the Syndicate correlates very well with the Diamond, and the Diamond in turn with the 

Spec.ulator, so that there is a probability· that these three ore bodies were once a continuous 

vein. This implies a very considerable shifting of the· hanging-wall blocks of the hill. The 

displacen1ent by the Skyrme vein is estimated at 300 feet eastward on the hanging wall. The 

displacement by the Bell fault vein is estimated at 200 feet north on the west side of the fault. 

The Diamond is a Wiele vein, varying from 30 feet on the 1,100-foot level to 100 feet on 

the 1,200-foot. It is exceptionally rich in copper sulphides, inclosed in massive quartz-pyrite 

ore. Much of the ore consists of altered granite, peppered with glance ari.d bornite and netted 

with thread-like veinlets of these minerals. Postminera] or fault clays are absent in the big ore· 

body of the 1,200-foot level. The Di~mond vein is not seen above the 500-foot level, but from 

.the 500 to the 1,300 foot levels, carried very rich ore and was the mainstay of the Diamond 

nune; below the 1,300-foot level it is composed of hard, compact quartz, ·carrying much pyrite 

and very low values in copper. The vein is a typical example of replacement and belongs to 

the Anaconda systen1. On. the 700-foot level the vein shows no walls, the ore merging by 

insensible degrees into the altered sheared country rock, but the heart of the vein is a clay 

sean1, with quartz and pyrite bands on either side. In places the vein shows bands of altered, 

partly replaced granite separating quartz-pyrite layers. The central clay seam and bunchy 

nature of the rich ore shoots .are ·characteristic. The ore body is delimited by faults. The 

other faulted blocks of the east-west veins, all of which are parts of the Speculator or of the 

Syndicate lodes, are sin1ilar in character to the Diamond, and, though designated on the maps 

(Pis. XXXV-XL) by separate names, do not merit individual description. · 

The faulted block designated the J. B. vein is unusually wide. It consists of crushed 

quartz and pyrite, with long slivers of this material cemented by newer quartz carrying pyr~te 

and s01ne specks of glance. 

The Bell shaft is at the. intersection of veins whose broken ground has furnished material 

for the large stopes. Owing to the very soft nature of the ground these stopes were all filled 

and the faces can not now be exanlined. In fact no ground is allowed to remain open except 

in lateral drifts in all·this mine, as it is essential for the safety of the miners that the excavated 

space should be promptly filled by waste. This area is crossed by the Skyrme and the South 

Bell veins, as well as the Diamond, but the latter makes the big stopes and is the largest ledge 

of the Inine, though the Covellite vein has yielded the most steady output of first-class ore, 

containing pay ore from the surface down. The Diamond vein ends eastward against a northeast fissure cutting off the East Bell vein. This cut-off makes the vein. shorter on the 1,000-

foot level than on the 700-foot level, a:p.d of course prop·ortionately so between these two. Below 

the 1,000-foot level it is not cut off but extends farther east, as shown on the map of the 1300-

foot workings. 

HIGH ORE GROUP OF VEINS. 

. . 

The I-Iigh Ore series is a variant of the An~concla east-west system. It includes the High 

Ore, Bell, and Wild Bill veins. 

HIGH ORE VEIN. 

The Iligh Ore vein has a flat clip and extends west to the Diamond on the 200-foot and 

300-foot levels, where it forms a junction stope. Its flat dip takes it farther south of the 

Dimnond shaft going down, a~d thus there are no intersections or fault cut-offs. (See fig. 7 4.) 

90427°--~o. 74~12----·12 
178 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT~ MONTA~A. 

The High Ore vein is neither an east-west nor a northwest fault vein, but has a course of 

N. 70° W., corresponding to that of the Wild Bill vein in the upper levels of the mines. These 

veins are older than the northwest veins and have been displaced by then1. 

The IIigh Ore vein has been continuously and extensively worked down to the 1 ,000-foot 

level, where it becomes lean. The upper levels show great stopes in the ground east of the Bell 

shaft, among them of an ore shoot 1,200 feet long on the 300-foot level. The vein has a very 

constant strike and uniform dip, but the walls are curved and locally irregular and are cut by 

a multitude of small quartz veins. 

The vein filling consists of quartz arid pyrite, with enriching bornite and glance, the richest 

streaks being near the footwall. · The usual abundance of fault clays and slips of other veins 

is lacking, and the ore shoots end abruptly in lean quartz and pyrite. 

The vein varies in width from 7 to 40 

,..-----:-:-:-..,....--:=-~-;-i,~-:::----::::-r~-:-4-:-::---:.~---n------::---rr.-:-::o.G::-771 feet, and has held large bodies of very rich 

ore at depths of 200 to 700 feet. Underground it appears to split both longitudiw:tlly and vertically, the two branches 

coming together again. There is some doubt 

whether these splits are not in reality the 

crossing of fault fissures, the High Ore 

belonging to one of the older periods. The 

east-west course found at the surface changes 

toN. 70° W. in the lower workings. Above 

the 200-foot level the vein beco1nes less and 

less distinct ·as the surface is approached, 

and at the surface, like the other veins in 

the vicinity, it is hard to recognize. FIGURE 75.-Section of High Ore vein, stopes of 2,200-foot level, High Ore 

mine. 1, Mashed quartz monzonite; 2, blue clay; 3, fault matter One thousand feet below the surface the 

(breccia and clay); 4, hard vein quartz; 5, vugs or quartz; 6, quartz High Ore vein is lean and consists· of quartz monzonite. 

and pyrite, with large vugs lined with 

quartz and pyrite crystals, the latter often tarnished with some associated enargite (fig. 75). 

On the upper levels the largest ore bodies of the Bell and Diamond mines found were those 

of the High Ore vein. The strike makes an angle of about 20° with the Skyrme vein. The 

vein has.been very regularly developed fo:r: a distance of 1,000 to 2,000 feet on its strike and 

from the 200-foot level down to the 1 ,000-foot level. Below the latter level it is said to be 

barren, but the cross sections indicate that the vein is cut off by one of the northwest fault 

fissures and is not ended by impoverishment. On the 1 ,600-foot level such a cut-off may be 

observed westward, the drift following the fault vein. This cut-off is exactly like that seen 

where the Speculator vein IS terminated westward by the Covellite vein, as shown on the 

400-foot level. 

:MODOC VEIN. 

The Modoc ·vein passes· westward from the mine of that· name into the Sunnyside, and 

enters the High Ore ·and Bell ground, where, however, it has not proved workable. As this 

vein accompanies a quartz porphyry dike, it is readily recognizable. 

BELL VEIN. 

The Bell vein lies next to the High Ore, outcropping about 250 feet to the north. It strikes 

N. 75° W., and dips from 70° S. to vertical. The vein has not been worked to as great depths 

as the fault fissures, and in fact the observations in this part of the camp confirm the general 

observations gathered elsewhere, that the east-west veins have been the great producers in 

the upper levels, that is to 1,000 feet below the surface, and that at greater depths the fault veins 

have been and are likely to prove in the future the ·great producers. In the Bell-Diamond 
I 

DIAMOND-BELL GROUP. 179 

workings a cross vein with a course of N. 55° W., duts off the west end of the Bell vein. It 

runs parallel \yith the Diamond vein, which has held a large ore body in the intermediate workings. ·The Diamond vein is only known on and below the 500-foot level of .the Bell mine, its 

upward extension being limited by the fault plane lmown as the Bell fault. The Diamond 

has a course of N. 65° E. and a steep southeast dip. It has been worked for·a distance of ·500 

feet, and has an average width of workable ore of 15 feet, which increases in the big ore shoot, 

being formed by the intersection of othe~· veins, with accompanying mineralization of crushed 

rock. . 

The I-Iigh Ore vein can be traced westward on the surface by various outcrops and 1nine 

workings, and runs int~ the Old Glory clain1. · . 

~ 

WILD BILL VEIN. 

The vVild Bill vein runs parallel to the I-Iigh Ore (N. 70° W.) on the northern border of 

the group. ·It is a typical fault vein, carrying shoots of glance-pyrite ore. It is separated 

by a clay selvage from the normal granite of the footwall and fr9m the altered slacky granite 

of the hanging wall. This granite becomes normal and unaltered 3 feet from the vein. The 

Wild Bill resembles the Skyrme; for long distances it carries no ore, and. when ore is found 

it is in sinall bunches. On the 1,300-fo.ot level the fault character is less apparent, and the 

vein is a nearly solid, tight, and dry vein of pyrite, which appears to be composed partly of 

an old vein fuling and partly of new quartz and glance in fractures nearly but not quite parallel 

to the vein. Westward the vein turns over and dips 70° to 80° N. Where wet it shows 1 to 

2 feet of Cl'ushed granite, with endogenous white quartz, blende, and pyrite, but where dry 

and dusty is dense, has but little quartz, and is low grade.· 

The vein is worked on the 900, 1,100 1,300, and, 1,500-foot levels ·of the Diamond mine. 

On the 1,100-foot level west it is but 8 to 15 inches wide and is a distinct fault vein, with mashed 

granite but without pebbles, containing endogeno-l1s streaks of glance. The walls are marked 

by clay films, and the country rock is a slacky decomposed granite which fades into a normal 

granite 3 feet away from the vein wall. The vein is a typical fault vein, and for a long distance 

carried no ore, or at most· ore bunches or kidneys. The black normal granite forms the footwall. 

North of the Wild Bill, a parallel vein 2 feet thick is tight and hard and shows no selvage. 

It consists of black quartz with pyrite in small bunches and patches, and 4 inches of it is slightly 

mineralized. 

So far a~ the underground evidence affords any indication of the character of the vein, 

it appears to be an older quartz-pyrite vein fractured by a later strike fault, and carrying good 

ore only where fractured. 

A crosscut north of the 1,100-foot Corra goes SO feet north of the Covellite lode, cutting 

a fault vein 2 to 3 feet wide, with a banding of white quartz, pyrite, and zinc. This vein is 

tight and has a good hanging wall of pink Inanganese spar. The footwall is ill defined. 

GREYROCK GROUP. 

GENERAL CHARACTEH. AND RELATIONS. 

The northwest veins of the Blue Vein systen1 are the 1nost pr01ninent lodes of tllis s·ectiou 

of the Butte district, and are now the most productive veins of the Bell-Diamond group of 

mines. They include the Greyrock, Bell, and Covellite veins. . 

The members of this system are all fault veins, rec~gnizable as such not only by their 

structural relations, but also by the character of their filling. They have a general northwest 

course, are of long extent and quite regular strike, and dip steeply, usually southward. The 

walls are generally undul~ting, and the granite shows varying degrees of alteration, ~side 

fr01n the relatively small amount directly attributable to vein formation. The ore shoots 

consist partly of solid and partly of brecciated ore, the former in part at least primary but 

not necessarily part of -an old northwest vein reopened by strike faulting, for ore endogenous 
180 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

to the fault would be crushed and broken by movement and adjustments of later date than 

that of this system. . 

The veins of this system having been severed and shifted by later movements along the 

.Bell fault, have been given different names on each side of this fault. 

, Southeast of the Bell fault there are the Skyrme, Custer, Higgins (or Middle), Sales, and 

'Teague veins. Northwest .of the Bell fault are the Greyrock, Winchell, Vale (or Gillie), Bell, 

·Covellite, and Dernier veins. The correlation of these veins across the Bell fault is nearly 

perfect in dip, strike, and mineral character. The largest and richest vein of the series, namely, 

the Covellite, corresponds to the Skyrme vein east of the fault, where it carries only small 

.and detached shoots of ore down to the 1800-foot level. The High Ore vein does not belong 

to this system but makes an angle of 20° with it. 

SKYRME VEIN. 

The Skyrme vein is the most prominent member of the northwest series south of the Bell 

fault. It has been developed by long drifts on many levels, which connect both with the 

High Ore shaft and the workings of the Diamond and Bell mines. These levels have developed 

:but little ore (or some 1,600 feet beneath the surface. A few ore shoots were found on the 

1,600-foot level, bu't the lenses were short, having a vertical extent of 40 or 50 feet, a horizontal 

extent of not mote than 300 feet, and a width of 6 to 12 feet. Thus on the fourth floor stope 

i: 

I I I I 

Drift : '.' ' ----·---------·---------...... ./ ' ..... __ _ -~~i-------------- ---------,, ,-----------.. :·-

' ~ _,: ~~\ 'J.-..,.._ ~~: 

~~~~ ~~ :· t 

~,~'\,. - 0; J ,~ ~~.., Q1 I • • 

'"-~. 1.!)/ I • . 

~~~ _,I 

~-~~?_~+~~~~:-_-:~;~~-4~~~~-,..-- : i 1600' level _______ ~'---.-:: 

/ , ',v, 

:, 'Y~ 

\r-'"\ 

above the 1,600-foot level the ore consisted of 

pyrite and a little quartz, and no secondary sulphides, and was so lean that it barely paid working. There is some doubt as to whether this ore, 

which is nearl:y solid pyrite, was deposited in the 

fault fissure, or whether it was a remnant of an 

earlier vein filling similar to that. found in the 

Johnstown (~ orth Connecting) vein of the Rarus 

group. 

In general the deeper levels, 1,800 to 2,800 

feet,· show that the better grade of ore consists 

of a dense massive mixture of very fine grained 

quartz intimately intergrown with pyrite, bo~·n- FmuRE 76.-Plan showing cut-ofi and displacement of Skyrme vein 

by east-west Modoc fault vein, 1,600-foot level, High Ore mine. ite, and a little enargite. These minerals are 

not banded, but occur irregularly scattered 

'through the mass. The quartz is clark colored and all of the replacement type, showing none 

of the coarse crystals or vuggy character of a cavity filling. The ore. is fractured but is not 

badly crushed, and the minute joints show mossy deposits of glance. 

An ore shoot, developed on the 1,600-foot High Ore level near the boundary line between 

the Diamond workings, shows 2 feet of ore that is very pyritic., but is incased by 5 to 8 feet 

of loose granitic mate:dal that has a netting of clay seams on the north side. The shoot is 

evidently true quartz-pyrite ore, showing a ·banding due to the arrangement of the quartz and 

pyrite into leaner and richer streaks, but shattered somewhat irregularly by faulting with crushed 

quartz and breccia in some parts of the vein; the north wall is indistinct and has much mashed 

granite where the vein is widest .. The glance occurs as films or very thin plates in fractures 

cutting the original ore and also as spongy masses in the ore where the crevices are most 

abundant. It is certain that it is in part of secondary origin and is deposited in ·favorable 

places. On the contrary, the inclosing apparently solid ore is specked with particles of glance 

and is emphatically a glance-enriched v~in. The vein is wide where stoped, being 20 to 25 

feet across west of the crosscut that leads south to the drain tunnel to the High Ore mine. 

At (his place it shows probably what is enargite mixed with glance. The faces of the stopes 

were carefully searched for galena, but none was found. Throughout the extent of the long 

1,600-foot level the vein can not be over a couple of feet wide, including the clay seams. At 
DIAMOND-BELL GROUP. 181. 

any rate, the walls are hard granite and show no clay except near the south crosscut, where, 

it is possible that the strike fissure crosses the vein. 

'I'he Skyrn1e vein is a fault fissure. In the stopes which were seen the vein is a fairly 

solid n1ass perhaps 2! feet wide, with a well-defined hanging wall, the glance-bearing streak: 

being on the north or footwall side of the vein proper; there is 10 feet or more of mashed 

granite north of the vein 1nined as waste for filling. The vein is apparently traceable to the. 

South Bell workings. It is cut off and displaced in the High Ore mine by the east-west Modoc. 

fault (fig. 76). 

The east end of the Skyrme ledge, ~hown in the High Ore workings, indicates that the. 

vein, though persistent in extent, occupies a ·true fault. The vein has not been a great producer fror~1 the surface dow:n to the 1,600-foot level, though son1e good bunches of ore have 

been found on it. In October, 1907, N 

the Ffigh OL'e shnJt W11s 2,860 feet 

deep and showed good ore at that 

depth i.1\ the Skynne vein. 

COVELLITE Vl~IN. 

EAST GREYROCK MINE. 

The section (fig. 77) through the 

shaf-ts n,ncl crosscuts of the En.st Greyrock mine clearly illustrates the relative positions of the n1ain· _veins 

worked. The section has been c11refully constructed fr01n detailed notes 

made on each level of en,ch crosscut through both the East Greyrock and the Dimnoncl mines. The 

northernmost vein is the Covellite 

(or North Greyrock). It appears to 

be cut.by a northward-dipping clay 

sliphn,ving a general northwest direction, which displaces it; shifting it 

along the fault plane for 50 feet. In 

the upper· levels this fault fissure is 

not clearly shown, but it n1ay be 

seen in the raise between tlw 700 and 

900 foot level!3 wherever· the timbering permits. It dislocates the Covel-· 

lite vein and, as it is ore-bearing 

below the line of intersection, it has 

generally ·been assmned that it is 

the Covellit~ vein, which is supposed 

to have changed fron1 its norn1al 

. steep southerly clip to a northerly 

dip. The workings extend clown.:. 

ward on tllis fault slip to the fourI 

~/ I 

I 

I 

I 

s 

LEGEND . 

CIIl 

Veins(Gooct ore) 

Faults 

r---:z--1 

LLi_j 

Minor faults 

L_ ...1.19_0 _2...J9_0_3--J9L0 __ 40L1 o_~S?O Fe'et 

FIGURE 77.-Cross section through East Greyrock shaft. 

teenth level, where the top of a cut-off vein, known as the Dernier vein (see p. 184), is 

encountered. In reality the Covellite maintains its norn1al clip and has been developed beneath 

the fault fr01n the 1,100-foot level to the 1,700-foot level. 

The 9ovellite vein is typically developed on the 1 ,500-foot level of the East Greyrock 

mine, where it varies in width from a few feet to 15 to 18·. The 'Yalls are irregular in dip, 
182 GEOLOGY AND ORE DEPOSITS OF BUTTE .DISTRICT, MONTANA. 

but are generally sn1ooth, with clay selvage present on both sides of the vein. The prevailing 

dip is toward the south, for the workings g9 toward the north, though the south wall is nearly 

vertical. · 

The occurrence of covellite in the Covellite vein is unusual, inasn1uch as the mineral is 

som~wliat rare, not only at Butt~, but throughout the world. It is found in abundance in the 

Covellite vein, where it is associated with glance and in some places with s1nall a1nounts of 

chalcopyrite. It is found on the l,100-foot level, where the a1nount of reducing n1aterial 

s~e1ns to be greater than that fonning glance. The mineral occurs only .in the fault clays and 

is associated invariably with sericite and not with the blue and unreduced clays con1n1only 

found in the fault veins. Bornite is found, but is not abundant. The evidence indicates that 

the covellite is formed by descending solutions and that its presence is due to the abnonnal 

conditions which prevail in certain sections of the 1nine. · · 

CORRA. MINE. 

The most westerly workings on the Covellite vein are in the Corra nline, whose drifts are 

continuous with those of the Greyrock. An ore shoot passes from the Greyrock into the Corra 

and extends westward for 50 to 150 feet. The vein is 5 feet wide, and appears to be a fault 

fissure along an old quartz-pyrite vein of hard, dense, uniform-textured, 1nassive pyrite and 

quartz, cracked but not brecciated, with s1nall strike slips of blue clay~ these newer cracks are 

filled by secondarily deposited milky-white quartz and glance. The prin1ary quartz is dark 

and is easily distinguished from this 1nilky-white quartz of later deposition. The pyrite is 

mostly primary, is abundant, and occurs partly in streaks, but n1ostly in patches irregularly 

. flecking the quartz. These pyrite patches are not sharply defined, but show a fading at the 

borders, arid in places where they are in1pregnated with glance and bornite a spongy texture 

is observed. Sphalerite also occurs, but it is secondary, and n1ost abundant in the footwall 

clay slips. These observations apply particularly to the 1,000 and 900 foot Corra levels. 

DIAMOND MINE. 

Eastward from the 900-foot Corra into the Dia1nond mine (the connection being on the 

twenty-fourth floor or 1,100-foot level of the Diamond n1ine) the vein expands to 15 feet in 

width. In the western part of the Dia1nond workings the vein shows a greater a1nount of 

faulting than in the Corra. Possibly the fault passes into the hanging wall westward and the 

crackling of the ore body in the Corra is simply due to sympathetic strains-that is, to footwall 

stresses. 

The vein is really con1pound; one ledge is composed of a footwall band 5 to 8 feet wide, 

with films and threads of quartz and specks of glance, deliillited by a clay footwall; its hanging 

wall shows 2 :i'nches ·to 6 inches of black clay selvage. The other ledge is a prirnary, older 

quartz-pyrite vein, 10 feet thick, co1nposed n1ainly. of dark, granular pyrite, carrying some eyes 

of quartz and here and there bu.nches and patches of solid glance. The hanging wall of tllis 

c01npound vein (that is, of the old vein) shows slickensides and a band of crushed quartz and 

granite. As tllis wall rolls very decidedly, it is evident that the hanging wall of the old vein 

was fissured when the acco1npanying strike-fault vein was formed. In n1any places the rolls 

pinch the vein and cut out the old or pri1nary quartz-pyrite vein filling. The newer fault vein 

shows friction bowlders and clay. One· section showed (a) footwall clay slips; (b) 10 feet of 

crushed granite, carrying a little quartz, with crushed quartz and pyrite and glance filn1s; (c) 2 

feet of solid vein; (d) three h~nging-wall slips in mashed granite 3 feet wide. A notable feature · 

is the making of ore along barren southwest-northeast fissures, dipping 60° s. 

The vein wall in the Diamond, like that seen in the Corra, lin1its the decomposition of the 

granite; that is, tllis alteration extends only about 5. feet into the wall. 

The deepest develop1hent is on the 2,000-foot and the 2,100-foot levels of the Dia1nond 

mine. On the 2,000-foot level the drift run on the vein west of the n1ain crosscut shows it to 

be about 6 inches tllick and to be formed of clay and gouge, without any quartz or pyrite. 

This applies to the portion of the vein nearest the upraise to the 1,400-foot level. West of this 
DIAMOND-BELL GROUP. 183 

raise, however, the streak thins ou~ to about one-half inch of clay, and the quartz-pyrite streak 

c01nes in, the ore body sending out spurs to the west into the hanging-wall granite. The 

extrmne west face, at the time the property was visited (1902), showed 12 feet of vein matter, 

with the south or footwall streak of nearly black quartz-pyrite ore, carrying bornite and calcite 

in nodular masses. The main streak shows a seam of clay one-fourth to 1 inch wide, lying 

between the normal quartz-pyrite ore body and the altered granite of the hanging wall. :A 

fault vein of low .dip (45° to 50°) comes in from the north and intercepts the vein immediately 

below the level. This quartz vein crosse.s a streak of zincky black quartz containing pyrite. 

The Covellite vein is supposed to be the extreme northern~ost- vein worked on the north 

crosscut from the 2,000-foot level of the Diamond. If this is so, the vein must be worked in. a 

faulted block. A raise goes up on the vein to the 1,800-foot level, establishing its continuity 

upward. The vein is vertical and tern1inates eastward against a fault running N. 55° E., with 

a dip of 65° S. The eastward continuation of the drift is through granit~ cut by a number of 

clay slips but showing no vein of any kind. 

HIGGINS (EAST BELL) VEIN. 

The I-Iiggins or East Bell vein is the Bell vein east of the Bell shaft. It is seen only on 

the maps on the 700, 800, 900, 1,000, and 1,300 foot levels but has apparently yielded considerable bodies of ore. It seems to be cut off by the Bell fault fissures running northeast and 

southwest. (See fig. 78.) The vein ·is very irregular in dip fr<;>m the 700 to the 1,000 foot 

levels, but must straighten up between the 1,000 

and the 1,300 foot levels. On the other hand, 

the South Bell vein is practically vertic~! from 

the 900 to the 1,200 foot, but takes the southerly dip between the 1,200 and 1,300 foot levels. 

MINES. 

EAST GREYROCK MINE. 

GENERAL RELATIONS OF VEINS. 

In addition to the Covelli te vein the section FwunE 78.-East-west Speculator vein, with 12 to 14 feet or ore and 

(fiE?. 77) throuE?h the East Greyrock workings two parallel footwall veins, terminating abmptly against the ._, ._, northwest Bell fault on the 1,600-foot level or the High Ore mine. 

shows several subordinate veins, known as the 

Sisters, Dernier, Vale, and Greyrock. The Sisters vein, which lies benea'th the north fault, has 

a dip of about 60° S. It is exposed from the 900 to the 1,700 foot levels and is workable in 

places. The Vale vein lies east of the shaft and underneath the Greyrock vein. It is known 

fron1 the 1,000-foot level to the 1,600-foot level and carries good bodies of pay ore in the deeper 

levels. The Dernier runs parallel to the Covellite. The Greyrock, next to the Covellite, is 

the chief vein of 'the mine; it is more fully described in connection with the West Greyrock 

mine (p. 184). 

All the veins have a general northwest course and are more or less similar in character, 

being fault veins in which remnants of an older quartz-pyrite filling appear to be recognizable 

at intervals,. The walls are well defined, generally smooth and slickensided, and the granite 

appears to be fresh. The thickness of the veins varies from 2 or 3 feet to ·25 or 30 feet. . On 

the 700-foot level the Greyrock vein, for instance, has walls but 4 to 5 feet apart and the fissure 

is filled with crushed. granite and clay, with occasional balls of hard ore. Followed along its 

course, shoots of newly deposited ore occur and the vein carries good values. In general, the 

Greyrock vein shows a very hard footwall, with a dip of 79° to 86° to the south. The foot- · 

wall has a clay selvage lying between the solid vein matter and the normal granite. The hanging wall of the vein is generally marked by a clay gouge or a series of clay seams, and this wall 

rolls so that at times it has a dip opposed to that of the footwall. 
184 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

SISTERS VEIN. 

The Sisters vein is a hard quartz-pyrite vein 3 to 5 feet wide, having a course of nearly 

N. 50° W. and a dip of 61° S. It shows a clay selvage on the hanging wall, but this is not 

constant, and when present is in places separated by the crushed· granite from the main body 

of the vein. Including the mineralized rock lying between the ore streaks, the vein has a total 

width of about 20 feet. It is cut by flat fault slips, which appear to be strain cracks, due to 

the settling of the fault blocks,.and are not persistent fissures. These fault cracks have not ·only 

produced slight displacement of the ore bands, but haye had a marked effect on the richness of . 

the mineralization. · · DERNIER VEIN. 

The Dernier vein, which is also worked in the :Mountain Con. mine (p. 165), is parallel to 

the Covellite, which it closely resembles. It is generally marked by clay selvage on both walls, 

and has a width of 5 to 10 feet, with 3 to 4 inches of clay on the footwall. It dips 88° N. 

or is vertical, and its general course is N. 45° W. Northwest its northward dip is quite pronounced, but as shown on the 1,300-foot level this may be merely due to the intersection of 

the ore-bearing fault. 

The ore from this vein is an exceptionally dense mixture of glance, sphalerite, bon1ite, 

and enargite, with·scattered specks of pyrite. It occurs on the 1,900-foot level where the vein 

is cut off and is evidently associated wit4 faulting, as the ordinary ore of the vein is a mi-xture 

of quartz and pyrite with patches and irregular smearlike masses of bornite and enargite. Vugs 

in the ore show masses of white quartz· crystals associated with and inclosed in but not inclosing 

~nargite. The zinc vein near the Dernier on the 1,300-foo't level of the Diamond consists of 

good. comb {]_uartz and zinc blende, with much less chalcopyrite, the whole forming a typical 

silver. vein. 

VALE VEIN. 

The Vale vein, which is extensively developed on the 1,400-foot Greyrock, is a composite 

vein, in which. an old quartz-pyrite filling 15 to 18 feet wide has been shattered by strike faults 

and slightly_ displaced by cross faults. The strike fault has produced clay slips, lvhich follow 

first one wall and then the other, or may pa:ss off into the country rock entirely. These slips 

h~ve a general course of N. 40° W., a d_ip of 80° S., and carry from 1 to 2 inches of clay as a 

selvage. Northwestward the east and west slips, or, more properly speaking, those having a 

course of N. 80° W., have displaced this vein to the west, producillg an irregularity in the workings, which makes the course of the vein, as shown on the mine maps, appear somewhat more 

sinuous than it is in reality. 

WEST GREYROCK MINE. 

In the West Greyrock mine five veins, all of which have a northwest course, are developed 

within a width of 200 feet. Four of these veins are of similar mineral content and are best 

classed as silver veins. The southernmost contains important copper values, but the ore is 

nonpersistent, occurring in lenses smaller than but similar in character to those of the Covellite 

vein. The next vein north (the southernmost silver vein) is persistent throughout the mine 

and has been developed for 2,000 fe.et or more. It narrows eastward to a thin fault fissure and 

is not recognized in the Diamond workings. 

All the veins of this mine carried copper in the upper. levels but changed to normal silver 

veins in depth. Tliis peculiarity is also observable in the veins of the Corra mine, where copper 

ore was mined from the 200 and 300 foot levels, below which the veins changed to typical manganese-bearing silver veins. These observations are directly opposed to the current belief that 

the silver veins carry copper ores in depth. Similar evidence was obtained .in the Flag, Sisters, 

and Josephine claims, where the upper levels have yielded rich ores with high copper values, 

and deeper development has shown a marked change in mineral character. 

Examination of the workings of the West Greyrock mine ~as limited to the upper level's 

· by flooding of the mine. The southern or copper vein was found to have a course of N. 45° W., 

and a variable dip of 87° S. or less. The vein .consisted of quartz and pyrite, with considerable 
DIAMOND-BELL GROUP. 185 

zinc blonde and some copper glance, and showed an average width of about 10 feet. Between 

this vein and the silver vein next north, an east-west vein with a southerly dip has been developed on the upper levels, but was too lean to warrant working. The silver vein most extensively worked is badly shattered by cross faults, but shows a general course of N. 45° to 60° W. 

It luis a width of 2 to 7 feet, and contains typical silver minerals and considerable zihc. Cross 

faults and slips are abundant and have played an important part in the formation of ore, but the 

displacement along the smaller fractures is not great, and the drifts therefore may be assun1ed 

to follow approxin1ately the general direction of the vein before faulting. 

'fhe cutting of the Greyrock veins by east-west (N. 80'0 W.) fault fissures which are vertical or steep is very plainly seen in the Greyrock mine. The shift of the displaced veins is 

always to the east along the north side of the fault, in this differing materially from conditions 

elsewhere in the district. On the other hand, the east-,vest fissures cutting the ·vein, whose 

course is regarded as c01nplementary to that ·Of those just noted, have a reverse shift, the 

displaced vein on the north side of the fault having moved westward. This is observed on the 

1,416 raise of the Greyrock 1nine, where the Vale vein is displaced. In general these displaceInents semn to correspond to an overthrust n1oven1ent rather than to normal fa:ulting. The 

displacement by these lesser cross faults is fortunately not great, varying from a yard to 12 or 

15 feet, so that in drifting along the vein it is not necessary to change the course of the drift 

:materially. · 

The highest-grade ore shipped from the West Greyrock mine in 1900 went 2.8 per cent 'copper. The veins worked in the East Greyrock mine have very good ore, but the glance and bornite lessens toward the west on the Covellite and Bell veins. One cross fault shows a shift of 

15 to 20 feet ancllilnits the pay ore. In the Con·a mine the ore fron1 the southern vein carries 

only 1.5 per cent copper, but the silver values are good. The Sisters vein shows good copper ore 

on the upper levels, but tlll.s plays out in depth. The \yesternmost end of the Flag claim was 

prospected by clian1ond-drill holes for 200 feet each way and showed no P.ay ore in the veins ·cut. 

Copper ores are, however, extracted from the west end of the. Josephine claim. 

SNOWBALL MINE. 

The Snowball mine is 250 feet deep, and develops a vein of zinckx quartz ore with spongy 

cavities showing a little rhodonite, galena, and chalcopyi'ite, assaying 2 per cent of copper. 

CORRA MINE. 

The Corra mine is situated on the lll.gh ground forming the ·extreme northern limit of the 

copper belt. The nll.ne has workings on several veins, but the copper ore comes mainly from 

two, one of which is the vVild· Bill vein, the other the western extension of the Covellite or 

North Greyrock vein. The latter splits below the 1 ,200-foot level in the Greyrock workings 

and forms the south vein of tlu} Corra nll.ne. The new shaft on this mine was sunk on the ore 

shoot lying near the east line, and forming the western termination of the shoot worked in the 

Greyrock. I~ is well developed between the 800 and 1,200 foot levels. Both the veins of the 

Corra consist of blackish quartz with sphalerite and pyrite, and show a well-develqped, banded. 

structure, uncomn1on in this district. Where the ore occurs at the east end of the claim this 

quartz is crushed and shows the typical clay selvage brecciation and other features common to 

fault veins. The pr~n1ary black quartz is cemented by wlll.te quartz, and the pyrite is replaced 

by gl~nce, with an accompanying relatively high silver ·value. The ore had an average of 5.7 

per cent copper, with 11 ounces per ton silver, these figures being the average of 20 assays . 

made on carload samples. The copper varied between 3 al).d 25 per cent; silica, 58 to 59 per cent; 

iron, 5~9 to 6.2 per cent; alumina, 4 per. cent .. 

The veins have sharply defined walls, with only a tlll.n border of pyritized granite between 

the vein wall and the fresh normal rock. 

The ore produce~ came from ·a large ore shoot in the Cov.ellite fault vein. Tlll.s shoot had 

been worked in the Dian1ond mine and was stoped out from the 800 to the 1,100 foot level of 
186 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

the Corra mine. It shows about 5 feet of fault matter and clay gouge on the 100-foot level, 

but does not contain pay ore until a depth of 300 feet is reached. From this point downward 

to the 600.-foot level the shoot is lean but workable, and it reaches its greatest horizontal extension on the 900-foot level. 0 • Three veins are developed north of the shaft on the 1,100-foot level, but none of them can 

be correlated with the Covellite fault vein. The one nearest to the shaft is a hard quartz-pyrite 

vein, which has been developed on the 800, 900, and 1,000 foot levels; it shows several feet of 

high-grade glance ore on the 1,000-foot level, where the vein is devoid of any of the features of 

faulting. The second vein lies 160 or 170 feet north of the shaft; it sho\vs 18 to 20 inches 

of 4 per cent ore in a reopened primary vein. The Wild Bill vein, which lies. still farther' north, 

carries about 5 feet of 1 to 2 per cent ore. As already shown (p. 179) the Wild Bill is a fault 

vein belonging to the Covellite group. 

SPECULATOR AND ADIRONDACK. 

The Adirondack is a nearly vertical east-west vein; 4 to 5 feet thick, consisting of a 1 to 2 

foot band of quartz and pyrite in a soft granite mass inclosed in well-defined walls. It is probably developed in the Speculator as well as in the Adirondack, but the Speculator workings 

were not accessible at the time the field work for the report was being made and so notes can 

not be given. 

MINERS UNION. 

The :Miners Union vein is cut on the 700-foot level (5,362 feet elevation) of the Speculator, where it shows a thin seam (1 to 2 inches) of quartz and calcite. 

JES~IE-EDITH MAY GROUP. 

IMPORTANCE. 

The discoverJ of the high-grade ore bodies in deep levels in the two fault veins, the Jessie 

and Edith :MaJ, is·most important. Not only do the veins constitute an important addition to· 

the wealth arid producti0n of the district, but they also demonstrate that the fault veins contain 

lenses of high-grade ore with long barren stretches between them and that such veins are worthy 

of development, not only bJ crosscuts and by drifts upon then1 200 or 300 feet apart, but by 

systematic drifting for long distances. on levels comparatively close together. The discovery 

is not entirely new, as the Covellite and the SkJrme veins are both fault veins on which extensive 

drifting has developed ore bodies. The future of the copper mines of Butte seems to depend 

upon the exploration of these fault veins, which in the upper levels have so generally proved 

disappointing and unprofitable. 

JESSIE VEIN. 

The Jessie vein is a tJpical fault fissure, with northwest course, and it is tl:ferefore considered a member of the Blue vein series. It has been developed in the workings of the Jessie 

mine to 500 feet and in the workings of the Speculator mine to 1,800 feet. The vein contains 

lenses of ore of remarkable extent and richness. Their maximum thickness is 25 to 30 feet, 

tapering clown to nothing. Beyond the ore shoots the vein contains lenticules of ore, in places 

consisting of nearly pure copper glance, and these lenticules continue for 100 feet or .more 

beyond the shoot and finally disappear.. Beyond these the vein is filled with barren crushed 

granite and fault material extending for indefinite distances with variable widths of from 5 to 

10 feet. 

The vein is peculiarly dry, especiallJ where it contains anJ quartz and ore; indeed, very 

little water was encountered either in this vein or in the granite for 1,000 feet on each side of it. 

The mineralization indicates that the Jessie vein follows in part an old vein which has 

been shattered and partly included in it. In the upper levels. the fault material contains 
JESSIE-EDITH MAY GROUP. 187 

considerable bornite, son1e chalcopyrite, son1e gray c'opper, and fragments of manganiferous 

ore. · In the deeper levels the ore shoot consists of copper glance, enargite, some zinc blonde, 

a very s1nall mnount of galena and quartz, with n1ore or less. iron pyrite. Enargite is particularly abundant on and along the footwall. There is a streak of zinc blende along the hanging 

wall, which varies in thickness fron1 a few inches to 2 feet and is persistent for several hundred 

feet. Tlus zinc blonde is conunonly associated with or replaced by copper glance. 

The walls of the vein are generally well defined and marked by black clay selvages. Very 

large grooves, with horizontal n1ftjor axes, were noticed Oil. the hanging wall where it is perpendiculn,r. · 

The lower levels of the Jessie 1nine contain no 1nanganese 1ninerals except s1nall amounts 

of hi.ibnerite. The rfttio of silver to the· copper is very constant, being 1 ounce of silver to 

each per cent of copper. The greatest ore shoot of the vein has been developed for a length of 

1,000 feet or n1ore on the 1,600-foot level, and for 1,000 feet vertically. The vein has been cut, 

and is understood to be ore bearing, in northern crosscuts from the Amalgamated properties. 

The working of this vein on the Jessie clain1 proved unsatisfactory, the only ore found 

being in too small quantity to pay a profit. The discovery of the big ore shoot was n1ade by a 

crosscut driven for about 1,000 feet northward fr01n 'the Speculator shaft ,on the 1,600-foot 

level. The extraordinarily high-grade ore encountered by this crosscut led to rapid development by raises and winzes, and by drifts extending several hundred feet in both directions. 

Transverse fissures cross the ore body in both veins, and it appears that extensive and 

crushing n1ovement occurred subsequent to the formation of a portion of the ore, and that 

these n1oven1ents rearranged the vein, filling 

fTactures, dislocating solid n1asses of ore, and in 

many places bringing high-grade ore into j.uxtaposition with low grade or with barren n1asses 

of s®ftened and altered granite. In n1any places 

the vein is banded vertically and the ore in the 

widest places contains strips and wedges of waste, 

but despite this, the percentage of first-class ore 

in the vein is much greater than in any other 

now mined in Butte. (See fig. 79.) 

In the Jessie n1ine the 400-foot level shows 

the vein to have a thickness of 6 to 8 feet, a FI~tURE 79.-Displacement of Jessie vein by fault of Steward system. 

dip of 75° S., and a st:t~ike of N. 45° W. The vein on this level shows only the usual fault !naterial, except near the west end, where an ore shoot is developed that extends northwestward 

into the Sioux and Tuolun1ne claims. Tlie stopes showed an ore body 10 feet wide, consisting 

of bornite and chalcop)'rite with son1e glance and iron pyrite. Another sn1alllens was encountered above the 400-foot level, but did not extend to the end line. On the 450-foot level of the 

Tuolun1ne 1nine the Jessie vein faults a hard quartz-pyrite vein that is rather lean and has a 

width of about 2 feet and displaces it toward the west on the hanging-wall side. The vein 

flattens eastward above the 400-foot level. 

The specin1ens from the Jessie mine show secondary bornite mixed with tetrahedrite and 

chalcopyrite, or as stringers and veinlets deposited in arotten and loose granite found in the 

fault breccia or fornung· the vein walls. :Masses of mixed bornite, blonde, chalcopyrite, and 

tetrahedrite also occur, and vugs in the vein show crystals of chalcopyrite and tetrahedrite 

·coating the cavities. The ore is unlike that of the Gen1 fault vein in that it contains an abundance 

of bor11ite and a relatively small proportion of chalcopyrite and but little tetrah~drite; its 

·physical texture and occurrence are also unlike that of the Gem mine. In general, however, 

the upper levels of the Jessie vein show many balls of rounded fragments of bornite, which were 

evidei~tly torn off fr01n so~ne preexisting ore n1ass by the faulting, and which form the most 

conspicuous feature of the present vein. It is this occurrence of faulted ore which should have 

led to the finding of the great ore bodies on the 1,200 to 1,800 foot levels. 
188' GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

EDITH MAY VEIN. 

The Edith May vein is a northwest fault vein lying south of the Jessie and greatly resem-· 

bling the latter in its mineralization and general features. It has a steep southwesterly dip 

and shows an ore body on the 900, 1,000, 1,200, 1,600, and 1,800 foot levels. Like the other· 

veins of this system, the Edith May has well-defined walls of almost unaltered granite, between 

which the fissure is filled with fault material in which lenses of ore occur. The main lens, so 

far discovered, has a maximum thickness of 30 feet and a lengtl~ of about 1,000 feet, with. a 

height as yet unknown, but certainly 600 or 700 feet .. Between the ore le~ses the vein is filled 

with dry crushed granite and clay. 

The Edith May vein is peculiarly a chalcocite vein. Enargite is of rare occurrence and is fotind 

only in small vugs, associated with drusy quartz. Zinc blende, galena, and manganese minerals. 

r--:~-,--,----:---7--r-:----:~-:----:--~-:---:-. -.-r:-":"-.-.;-~,......-r-:-~ seem to be entirely wanting. Quartz and a 

FIGURE 80.-Level on Edith May vein, showing abrupt change from 

small amount of pyrite are present. The silver 

content of the Edith May vein is just one-half 

that of the Jessie ore, that is, one-half ounce of 

silver to 1 per cent of copper, the ratio ·being 

very constant. The vein walls are well defined, 

one of them in many places acting as a boundary to the ore. (See fig. 80.) The country 

rock on either the footwall or the hanging wall 

may show two or more strong fissure planes. 

high-grade ore to low-grade quartz-pyrite ore where vein is cutting through the country rock parallel to 

•crossed by clay seam. 1, Quartz monzonite; 2, quartz; 3, high- the bounding planes of the· ore body and thus 

grade ore; 4, fractures. constituting the ultimate and intermediate 

hanging and foot walls. The material between these outside walls and the ore 'is usually a. 

bleached and much-altered and softened granite, little of which contains ore minerals. Bike 

the Jessie vein, the Edith May shows vertical banding and includes strips and wedges of 

altered granite. Transverse fissures cross the ore body, and there is evidence of extensive, 

crushing and movement, with rearrangement. of vein material. 

Although these two veins are comparatively close together and belong to the same system, 

they are quite different in the character of their mineralization, the Jessie vein having a pre-· 

ponderance of silver values and containing silver minerals 

with associated zinc blende and galena, and the Edith May 

being essentially .a copper vein. 

GEM VEIN. 

The Gem vein is a well-marked fault fissure belonging to 

the northwest ·or Blue vein system. It has a well-defined, 

easily tra:ceable quartz outcrop, barren of copper and recognizable for a distance of several thousand · feet through 

unaltered granite. The vein varies in width from a foot or 

so up to 30 feet. In the Gem mine it was developed to a 

depth of 500 feet at the time visited. In the upper levels 

it contains much zinc blende and a little galena. .Lenticular 

FIGURE 81.-Section of Gem vein, 400-foot level,. 

fourth floor, 75 feet west of shaft. 1, Solid hard. 

qu.artz monzonite wall; 2, quartz, crackled; 3, 

gray and yellow copper; 4, sheeted quartz monzonite; 5, crushed quartz with tetrahedrite and 

chalcopyrite; 6, black clay (! inch). 

masses of ore formed in the fault fissure are composed of rhodonite, sphalerite, tetrahedrite, 

and chalcopyrite. (See fig. 81..) These lenses lie embedded in the fault breccia and occur· 

most commonly where the vein rolls or shows enlargements due to rolls of the vein walls. From 

the surface downward to the 400-foot level the vein carried but little pay ore, the sulphide· 

mass consisting mainly of sphalerite. In the lower levels an increasing amount of gray copper· 

and.of chalcopyrite were found. The only pay shoot observed was at the west end, where it 

was worked not only in the Gem mine but in the Jessie. 

The vein shows well-marked slickensides on the hanging wall, indicating a shifting along· 

the wall as well as a vertical displacement. Where the vein fissure narrows to 6 or 10 inches. 
EAST BUTTE BELT. 189 

:across no ore Qccurs. Pay ore .and water are markedly associated. The vein fissure contains 

rounded balls of bornite and other primary ores and appears to .be a i·eopened and brecciated 

.silver vein occupying a fractured vein of an earlier generation. A. secon:d and parallel vein 

lies a few yards to the south, but so far as exploration has indicated, is entirely barren of 

· pay values. 

On the 400-foot level two ore streaks are observed incased in clay and separated by. 6 feet 

·Of sheeted gtanite that is devoid of clay. The ore shoots consist of crackled quartz carrying 

tetrahedrite, rhodochi:osite, and chalcopyrite, with a silver content of 3! to 4 ounces to each 

per cent of copper. The vein carries about 2! feet of soft fault matter, consisting mainly of 

crushed granite, and the ore streaks are from 2 to 4 feet in width. Eastward on the 400-foot . 

. drift the vein shows a 2-foot streak of banded zinc blende and rhodonite, impregnated with 

·copper; it carried about 2 per cent of copper and 5 ·ounces per ton silver. The west drift 

.show~ a 4-foot vein of mashed granite, With irregular lenses of quartz and rhodonite deposited 

in the fault fissure. The lode walls are very hard normal black granite. On the 500-foot 

.level the vein has a width of 30 feet and is well defined by clay slips. In general it is a dry 

fault vein which in places is composed of a breccia of quartz fragments cemented by pink 

manganese. 

The specimens obtained from the Gem mine show chalcopyrite and tetrahedrite in a highly-

.alterecl recemented material composed of crystalline quartz and altered granite. One speci-. 

men shows much purple fluorite and quartz, some of the latter occurring in a mixture of 

tetl'aheclrite and chalcopyrite. Masses of fluorite occur inter banded with white and dull-gray replacetnent quartz. The ore from the 500-foot level 

consists of an intimate mixture of mottled gray and 

white quartz, carrying n1ossy patches and grains of 

·Chalcopyrite, massive but not very solid, and showing 

·no crystal outlines. In vugs in this ore chalcopyrite· 

is observed coating quartz crystals and tetrahedrite 

-coating the chalcopyrite. This tetrahedrite shows 

·vitreous luster and well-marked cleavage and is 

massive and coarse, inclosing unreplaced fragments 

and mineraJized particles 'of granite. The ore ap-

.pears to be a replacement of, 'crushed granite, prob-. 4 

2 

ably part of a fault breccia. A little zinc blende FIGURE 82.-Section of Gem vein, 400-foot drift, east face. 1, 

' th 1 tl 0 tl 500 f t 1 1 Mashed quartz monzonite; 2, quartz and pink manganese lS seen roug l 1e ore. n 1e - OO eve spar with streaks of gray copper ore, distinctly banded; 3, 

the ore bodies lilay be regarded as solid endo- fault, mashed quartz monzonite and quartz; 4, clay; 5, 

_genous ore deposited in a fault. Although the ore quartz ~onzonite. 

is original in this vein it has been shattered by later movement. The tetrahedrite sho~s 

patches and irregular broadly crystalline aggregates of chalcopyrite, these two minerals being 

'interlocked with glass and white quartz. Vuglike masses of pinkish. carbonates also occur. 

Specimens of the hanging-wall rock proved to be a highly altered granite, with large flakes of 

muscovite replacing the former biotite and hornblende, one with abundan~ cubes Qf pyrite, 

the balance of the rock being white sericitic material resembling clay. The rock looks.porphyritic, but is merely a broken-down and altered granite. (See fig. 82.) 

EAST BUTTE BELT. 

GENERAL CHARACTER . 

The East Butte belt includes the Number Three mine, south of the Silverbow, and all the 

territory lying between Silverbow Creek and the ~naconda belt. The most extensive workings, aside from the Number Three, are those of the East Butte and Davis-Daly companies. 

'The ~fontana Consolidated and other companies also own tracts in this belt. The principal 

mines are the Number Three, Glengarry, Ground Squirrel, J. I. C., Otisco, Anderson, Cambers, 

·Oneida, Gopher, Lizzie (I-Iayes), Colorado, Belmont, Prefe1rencia, and Green Copper. In 

() 
190 GEOLOGY AND-ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

general these properties have rich secondary pyritous ores for a few hundred feet below the· 

surface, whiclr change to lean.and zincky quartz-pyrite ores in depth. 

The deepest development work is in the Belmont mine, but both the Number Three and 

the Colorado mines have workings at a depth of 1,000 feet or more below the surface. 

A large part of the southern part of the district is held by the Davis-Daly Copper Co.; 

which· has explored the ground by crosscuts from the deep levels of the Moonlight and Original 

mines, as well as from the Belmont, Smokehouse, and other shafts. The results of this work, 

so far as known to the writer, confirm the general conclusions primarily reached, viz, that this 

part of the district carries distinct, well-defined veins, but that the ores are zincky and carry 

only low values in silver and copper. 

The belt shows sever.al well-defined east and west quartz-pyrite veins. The Rarus and Blue 

veins cross the belt, and numerous lesser cross fault~ have broken the ground. These.lesser 

fault veins have been developed in the Colorado, Belmont, and several other mines, but have 

thus far been disappointing to their owners. The ore produced in the belt has come mainly 

from the east-west veins, which show more or less crushing and alteration, with some soft black 

glance. The primary ore of the deeper levels is lean in copper, consisting of quartz and pyrite, 

with much zinc blende, the latter in places forming 30 per cent of the ore. In the crushed 

groun~ the lodes show relatively high silver values, but the ores are bunchy .. 

The veins show no evidence of an iron belt, or so-called zone of pyrite and blende, capping 

richer glance ores, and the deep development work in the Colorado (1,000 feet) and Belmont 

(1 ,800 feet) discloses only the same low-grade zincky pyrite veins found above 

VEINS. 

GLENGARRY VEIN. 

EXTENT AND DEVELOPMENT. 

The most important vein of the belt is the Glengarry, also variously known as the Ground 

Squirrel, Number Three, and Iron vein, the. southernmost of the larger productive veins of the 

.district. It traverses the low ground southeast of the Anaconda mines and immediately south 

of the Silverbow mine. The vein has been continuously worked underground from a point 

under Silverbow Creek westward for 3,400 feet through the Glengarry, Monitor, and Ground 

Squirrel milles to the J. I. C. mine, where it is cut off by the Rarus fault. Its continuation beyond 

this fault is not positively kn<?wn . 

. The lode outcrops about 600 feet below the Mountain View shaft house. It has been 

opened in the Number Three mine to a depth of 1,100 feet, in the Glengarry·to 800 feet (4,730 

elevation), in the Grouncl·Squirrel to 600 feet, and in the Harrington to 150 feet. Its average 

strike is N. 80° W. and its average clip is 5Q 0 to 60° S. Besides this, the n1ain vein, there are 

two lesser veins 200 feet apart, which parallel it and are sin1ilar in character, a.ncl several smaller 

veins. In none of them do the richer copper sulphides extend downward n:tore than 350 feet. 

below the surface. 

NUMBER THREE MINE. 

In the Number Three mine the Glengarry :vein has a general east-west course, with a somewhat curved strike. It belongs to the Anaconda system, being a typical quartz-pyrite vein, 

with an unusually large amount of pyrite. Its width varies from 8 to 20 feet, the ore merging 

into the wall rock, except where secondary fractures occur. In the east end of its course, 

under Silverbow Creek, the vein cuts through rhyolite porphyry, and in the Glengarry mine 

it traverses aplite, but elsewhere it is incased in pyritized granite. Through much of its known 

course the vein is free from strike faults, crushing, or clay selvages, and is remarkably regular 

in width, dip, and character; it, however, is displaced by several cross veins. The lesser vein 

south of the lode has parallel strike but steeper dip (averaging 80°), so that it rapidly diverges 

from the Glengarry in depth .. 

0 
EAST BUTTE BELT. . 191 

In both the Number Three mine and the Silverbow workings the Glengarry vein has been 

developed to a depth of 1,100 feet. It maintains an average thickness of 6 feet, with extremes 

of 2 to 14 feet, and dips very regularly at ~5° fron1 the 200 to the 900 foot level. In the eastern 

workings the proportion of pyrite increases ,until the ore carries but little or no quartz, with a 

decrease in the copper content to 1 per cent or less, except where fracturing and local em·ichment occur. In general the richer ores extend 300 to 350 feet below the outcrop, occurring 

in bunches of wet and friable pyritic ore, blackened by soft ''sooty" glance. In many sections 

across the vein it consists of two regular and well-defined seams of ore separated by a thin 

layer of pyritized granite. To the east the vein appears to join the Silverbow, whose dip is the 

same, but whose course is northwest. To the west the vein is continuously worked into the 

drifts of the Trerise shaft. The vein filling is massive and varies from ·the usual nuxture of 

quartz and pyrite to nearly solid pyrite. The leaner parts show banding, and when cross s·eams 

of clay cut the ore chalcocite occurs. 

The Glengarry vein in the Number Three mine is cut and displaced by several larger and 

numerous minor faults. On· the 300-foot level the vein splits eastward into two narrow bands, 

separated by 1 t feet of pyritized granite, and it shows bu.t 2 inches of ore, though 25 feet to the 

west it is 5 feet wide. Everywhere else it carries at least 10 inches of ore. On the 400-foot 

level and below the vein is a solid mass of pyrite, with scattered and disseminated quartz, which 

on this level is rather abundant, mostly white, opaque, and secondary. The sulphides show 

alteration, with ft.lms of black chalcocite on fracture surfaces. To the east the vein is oxidized 

down to the 400-foot level. The richer ore occurs where the vein is crackled and fractured, 

and in such places a bulbous expansion of the vein shows 15 feet of 6·per cent ore. 

In the stopes a few feet above the fifth level the vein is quartzose and is crushed to a 

friable mass of white quartz and black sulphide, composed of disintegrated pyrite and freshly 

deposited glance. The vein on this level sl1ows a footwall seam of clay a foot wide, with 4 

feet of 16 per cent ore between this and the pyritic vein matter. As a rule this soft glance 

occurs in spots and bunches from the size of a pea up to 18 inches across, .scattered through 

the mixture of. quartz and pyrite. Enargite occurs scantily in streaks banding the ore where the 

vein has been reopened. 

The Glengarry vein splits eastward and is cut and shifted by a fault of the Steward series, 

whose relations are well shown· on the fifth level about 1,100 feet east of the shaft. The fault 

runs N. 80° W., and dips of 70° S. It displaces the vein so that the ends overlap 150 feet, the 

faulting being norn1al. The 700-foot level runs 2,000 feet east of the shaft and under Silverbow Creek. The inflow of water. here is heavy, averaging 200 gallons a minute in 1905, and 

as the ground eastward is soft and wet further exploration is unlikely. 

On the seventh level the rich ore is confined to local bunches and the vein generally consists 

of massive iron pyrite or of a n1ass of shattered pyrite, carrying n1uch water, but devoid of coppe1· 

glance. The eastern end of the workings on this level shows overlapping ore shoots of sn1all 

size, pinching to clay slips. The v.ein is also crosscut from the 1,000-foot level of the· Silverbow mine. The extreme eastern. workings show 3 feet of pay ore in a vein 7 feet thick. The 

vein is mushy and wet. The same drift westward shows a vein 5 feet to 7 feet thick, of very 

uniform dip and character to the surface. On this level (1,000). a south crosscut shows the 

vein 800 feet south of the Silverbow vein to be 5 feet ·wide, with clay selvages on both walls. 

The footwall slip runs northeast and dips 70° S., whereas the vein ·clips 60° S. 

GLENGARRY MINE. 

West of the Number Three mine the Glengarry vein is continuously developed in the 

Trerise, Glengarry, Ground Squirrel, and J. I. C. workings. It is cut off and displaced by several 

minor faults. . 

In the GlengaiTy mine the vein shows the usual east-west course and a dip of 65° to 70° S. 

· The width vuxies from 6 to 15 feet, with "swells" and "pinches" along its course. The filling 

contains an unusual amount of whi~e quartz, in many places iron stained in the upper levels. 
192 GEOLOGY AND ORE .DEPOSITS OF BUTTE DISTRICT, MON'fANA. 

In t.he stopes the vein is 5 to 15 feet thick and is double, having along the footwall a thin band 

of pyritic ores less than a foot thick, separated by 8 feet of softened sericitized granite from a 

hanging-wall streak of pyrite, carrying enargite and chalcocite, 5 to 6 feet wide. Cross fractures making" spur veins" are seen on the 200 and 3oo foot drifts. 

The workings disclose a quartz-pyrite vein shattered and impregnated with enargite and 

chalcocite to a depth of 200 feet. These minerals become less and less in amount below that 

level, the .vein becoming a solid mass of pyrite and quartz of remarkably uniform character 

and carrying but 2 to 3 per cent copper. The hanging-wall rock is highly altered several feet 

from the vein wall, but the footwall shows only slight decompositiop, and that only for a short 

distance. 

Two other veins 150 feet apart are cut on the 100-foot level, but show no pay ore. The 

first,· cut 220 feet north of the Glengarry shaft, is a fault fissure a few feet Wide, carrying only 

bunches of ore. The second is a pyrite vein 2 feet thick, cut some 50 feet north of the shaft 

and traversed by a strike fault. 

GROUND SQUIRREL MINE. 

The Glengarry vein extends westward into the Ground Squirrel mine, where it has been 

opened from three different shafts and developed westward till cut off by the Blue Vein fault 

and its sympathetic fractures, along which the drift turns northwest because these carry seams 

of rich ore. · 

In this mine oxidation has extended from the surface downward to a depth of 45 to 75 feet. 

The ore immediately und~rlying the ~xidized material is black and consists of a friable aggregate 

of pyrite crystals coated by chalcocite. The ores of this part of the vein average 12 per cent 

copper and 13 ounces per ton in silver and nearly $1 per ton in gold; the richer portions carry 

23 per cent copper and 53 ounces silver. The oxidized part of the vein consists of a somewhat 

iron-:stained spongy quartz, carrying an average of 20 ounces silver per ton. 

In the lower levels this vein shows no features of especial interest. The dip is 65° to 70°. 

The vein is 2 to 6 feet wide and shows the same double structure seen in the Glengarry. On 

the footwall three bands of altered granite-unreplaced parts of the sheeted zone forming the 

lode-carry veinlets of ore. Secondary fracturing of the vein by strike faults is shown by clay 

selvages and seams, which in places are 8 inches thick and are accompanied by seams of glance 

of equal thickness. · 

In general it may be said that· the rich ores do not extend more than 50 to 60 feet ·below 

the 300-foot level and that the vein, though as wide or wider than above, consists of pyrite, 

with but little quartz and very little copper. The altered granite north of the vein is netted 

by veinlets carrying copper values. Cross faults . are common, and in one case two parallel 

northwest fractures drop the vein between them, so that the drift shows no ore. 

J. I. C. MINE. 

In the J. I. C. workings the vein averages 7 feet in width and dips 70°. It shows the same 

characters as the Glengarry. G~YMAN VEIN. 

The Geyman shaft is near the Ground Squirrel. .The Geyman vein lies about 300 feet south 

of the Iron or Glengarry vein, with which it is parallel. It is 5 to 8 feet wide and consists of 

crushed and altered quartz-pyrite vein filling, with rich glance and enargite ore in the upper 

levels, but the high values do not go down. 

BELMONT VEIN. 

The Belmont vein dips 62° to 67° S. It is a lean quartz-pyrite vein, 5 to 9 feet thick on 

the 800-foot Belmont and 8 feet thick on the 900-foot Belmont, showing streaks of pyrite and 

quartz in ·mineralized granite, the main quartz streak being 4 feet thick. 
EAST BUTTE BE~T." 193 

MINES. 

OTISCO MINE. 

In the Otisco mine the only- ore developed comes from ~egments of an east-and-west lode, 

not yet identified, between the walls of the Rarus fault. 

IDUNA MINE. 

The Iduna mine is located immediately west of the Ground Squirrel mine, in southeastern 

Butte. The workings are confined to a single vein belonging to the Blue Vein system, having 

a northwest-southeast course and tl pron.ounced southerly dip. The vein on the 100-foot level 

widens from a strong clay wall to a breadth of 12 feet, forming an ore shoot that had been drifted 

on (1905) for 100 feet eastward, and at the breast gave distinct signs of pinching to a clay wall. 

Tlus shoot is composed of the characteristic copper vein minerals, chalcocite, enargite, pyrite, 

chalcopyrite, and 1nore or less sphalerite. The chalcocite and enargite form the matrix of an 

ore extremely heavily laden with pyrite. The structure of the vein is well seen in figure 83. 

The footwnll and hanging-wall bands are rich in sulphides and quartz, and between them are 

numerous bands of fair definition where the body is distinctly an altered granite; the 

rest of the shoot is composed 

of varying amounts of sulphides and vein quartz. In 

places the vein has a very 

heavy clay seam, which has . 

beeri developed by movement 

subsequent. to the vein formation. It contains a large 

amount of broken or groundup vein material and altered 

granite. 

COI. .. ORADO MINE. 

The Colorado claim is 

south of the Baltic and the 

shaft is clue south of the Blue 

0 10 Feet 

FIGURE 8.1.-Cross section of lduna.vein, 100-foot level; width, 6~ feet. Vein or ordinary type, 

with thin clay seam and notable enrichment on hanging wall. 1, Quartz monzonite; 2, 

pyrite; 3, altered quartz monzonite; 4, quartz-pyrite; 5, altered quartz monzonite, with 

quartt and pyrite. 

Jay. Four parallel veins with a general east-west course cross the property. These veins have 

been penetrated by a shaft located in the extreme southeast corner of the claim which is over 1,000 

feet deep, with north and south crosscuts on the 300, 500, and 1,000 foot levels. The first. vein 

is cut at a depth of 45 feet, the second at 75 feet, the third at 230 feet, and the fourth at 300 

feet. The vems dip 60° S., and consist of quartz and pyrite, with considerable zinc and very 

low copper and silver values. A long east level cuts several veins of the Blue Vein system at 

210 feet and 500-540 feet east of the crosscut. These veins carry ore streaks from 1 to 2 feet 

wide, but hold only 2 or 2! per cent copper .. The property is now owned by the Davis~ 

Daly Copper Co. · 

LIZZIE MINE. 

The Hayes shaft, 750 feet clue south of the :Moonlight, develops aQvein traversing the Lizzie 

claim, which is probably the vein worked in the :Moonlight mine on the 1,200 and 1,300 foot 

levels. The vein, which runs northwest and belongs to the Blue Vein series, is from 2 to 5 feet 

wide and carries 2 to 2! per cent copper, with much zinc. In the Moonlight drifts it is also 

90427°--~o. 74--12----13 
194 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

narrow and bunchy. Similar veins are cut in Belmont 50Q-foot level. The crosscut running 

2,000 feet south from the Original shaft on the 1,800-foot level cuts 30 feet of fault matter 

in a member of the Blue Vein series at 710 feet south of the Original drift, and other similar 

veins at 870, 960, 1,110, 1,590, and 1,730 feet south. These veins have. not been seen, but 

according to the reports of reliable engineers carry only low-grade zinciferous ore. 

CAMBERS MINE. 

The Cambers mine is -worked to a depth of 230 feet, connecting with the stopes of the 

Belmont mine. The Cambers vein has a general east-west course, with a flat dip· of 30° to 38° S. 

It is from 2! to 3 feet in width, w1th a hanging-wall gouge of 3 inches or more of soft and wet 

clay. In the upper workings the ore was quite rich, car samples from the 185-foot level showing 

16 per cent copper and 13 ounces of silver. In general, however, the vein is of much lower grade, 

the ore from the 230-foot level, averaging between 3 and 4 per cent copper, with 3 ounces of 

silver. This vein is opened up and stopedeontinuously from the 100-foot 'level of the Cambers 

down to the 200-fo.ot level of the Belmon't. Near the Cambers shaft the vein is cut off westward 

by cross slips, the orie on'the 100-foot level of the Cambers having a course of N. 40° E. and a 

dip ·of 85° w., showing little over a foot of clay, with some pyrite, limonite, and copper stains. 

On the 100-foot level a northwest fracture, with a dip of 55° to 58°, shows and cuts off the vein 

on the west. 

The ore consists of friable decomposing pyrite, with soft black chalcocite, and n1ore or 

less sphalerite. 

ANDERSON. MINE. 

The Anderson' mine: is situated in southeas'tern Butte, immediately south of the Belmont 

mine. It is 400 feet .deep·; a crosscu·t to the south extended 600 feet and. showed only a sm.all 

vein of pyritifero_us nature. To the north a crosscut extended 250 feet, revealing more satisfactory conditions. The middle vein, which warranted exploration, was cut just south of the 

shaft, and its course to the east was explored for several hundred feet. It was notable only for 

its high per cent of pyrite; the copper content rarely exceeded 4 per cent. 

HESPERUS MINE. 

The Hesperus mine is situated in the Flat almost due south from· the Anaconda. In· the 

development work a vein striking east.:.west and dipping 60° S. was cut. This vein was nearly 

8 feet in width and carried 1! per cent copper, 1 ounce silver, and 30 per cent zinc. The granite 

which composes the country rock is to all intents and purposes free from alteration arising 

from mineralizing agents. 

VALLEY MINE. 

Th~ Valley mine is immediat~ly south of the Hesperus. At the time of visit a shaft had 

been sunk SO feet. Two vei:J;ls in the immediate vicinity have an east-west trend parallel to the 

vein system of the district. The main vein is 15 feet in width; its dip is 60° S. The vein 

minerals are principally silica, together with zinc, galena, chalcocite, and iron pyrite. Alteration of the granite is very slight. · 

HENRY GEORGE MINE. 

The Henry George mine is north and slightly west of the Hesperus. The shaft was sunk 

not more than 50 feet at the time it was visited .. No veins were encountered and it is mentioned 

chiefly because re.d oxide of copper was observed on the fracture planes of the granite. This 

oxide was not found in large amounts but is interesting because it is somewhat unusual in the 

heart of the Butte district. 
EAST BUTTE BELT. 195 

ADAMS MINE. 

The Adams mine is located just south of the Pennsylvania. ·Workings have been extended 

300 feet below the surface and have cut three veins. The croppings of these veins are concealed, 

but their development undergrouncl.shows them to be normal, with a course slightly south of 

east or north of west and a constant dip to the south. The northerly vein varies in width from 

· 6 inches to 10 feet and the south vein up to 2 feet. Near the surface the veins, which are similar 

in character andn1ineral composition, have been found to carry a high percentage in silica and 

a profitable amount of copper. Both the copper and the silica diminish with depth, and at the 

botton1 of the 1nine the mineral content is aln1ost entirely pyrite. The size of the veins also 

markedly diminishes: 

PREFERENCIA, GREEN COPPER, AND ALLIANCE MINES. 

The Preferm1.cia or Green Copper vein lies near the western portion of the belt, on the 

extren1e southern border of the proved copper area. It extends through the Preferencia, 

Green Copper, and Alliance workings, striking east and west and dipping 65° to 80° S. Its 

average width is 5 feet, 3 feet of which is ore carrying 3 to 7! per cent copper·and about one-half 

ounce silver to each 1 per cent copper per ton. The lode is traceable for 1,000. feet or more 

across the Flat, and has been opened at intervals by shallow shafts. 

Development work was stopped in 1906 by litigation. The Preferencia shaft is 125 feet 

deep and has developed 4 feet of ·ore for 100 feet along the drift west. The Green Copper sluift 

is 'but a few yards to the east. In the Alliance mine the vein has been developed by 235 feet 

of drifting on the vein on the 200-foot level and by 100 feet of drifting on the· 300-foot level. 

It varies between .5 and 8 feet in thielrness and carries 3 feet of ore averaging 2 per cent copper, 

3 ounces silver, and 70 cents in gold per ton. 

TALBOT & JONES CLAIM. 

The Cosgrove shaft, on the Talbot & Jones addition, develops a flat east-~est vein which 

shows 1 to 2 feet of good ore. This vein has a south dip of 45°, which carries it into the 500-

foot west crosscut of the Silverbow No. 1 mine. In the Cosgrove shaft it is developed on the 

170, 205, and 285 foot levels. The 205-foot level of the Cosgrove lies 220 feet above the 500-

foot level of the Silver bow No. 1. ·The second vein lies 30 feet south of the former. It is from 

4 to 8 feet wide and shows from 1 per cent to 10 per cent copper. 

WASHOE MINE. 

The Washoe mine is situated immediately south of the western extension of the Parrot; 

it appears to be upon the Blue Jay vein. A number of shafts have been sunk; those at the 

eastern end-the vVightman and the Washoe-have developed a vein which corresponds .in 

position and n1ineral content to the Bellona. (See p. 121.) A spur· vein has a general course 

considerably n1ore to the south of east. 

GOLD HILL MINE. 

On the Gold 1-Iill.clainl, which is in1mediately south of the Washoe, two shafts have be.en 

sunk. These have developed but a singie vein, which appears tD be a westward continuation of 

the Blue Jay vein. It has a norn1al course nearly due east and w~st and dips between 65° and 

80° S. In places it is 10 or 12 feet in width, but its average is probably under 5 feet. 

The characteristic mineral of this vein is sphalerite. Quartz and galena also occur. The 

· perc~ntage of copper is,almost invariably below the pay liJ?it. 
196 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

MOUNTAIN VIEW-SHANNON-COLUSA BELT. 

The Mountain View-Shannon-Colusa belt extends from the :Mountain View fault to the 

edge of the flat north of :Meaderville. It is traversed by the once continuous Shannon and 

Colusa-Le·onard lodes, which with others are worked in the Mountain View, Colusa, Leonard, 

and other mines. 

MOUNTAIN VIEW MINE. 

LOCATION AND CHARACTER. 

The :Mountain View mine is located on the summit of Anaconda Hill, north of the St. 

Lawrence mine. The workings (1,400 feet deep in 1905) have developed a network of veins, 

embracing the Molintain View south vein, which js an eastern dislocated segn1ent of the 

, Anaconda lode; the Shannon, a member of the Anacond~ system; the Johnstown (north connecting), a northwest vein; and a number of minor north-south veins belonging to the :Mountain 

View system (p. 202). All these veins are cut and displaced by.the Mountain View fault vein 

and by other members of the Blue Vein system, as well as by others of the later Steward 

system, w~th accompanying enrichn1ent of ~.he ores. . ' 

2 

.. ----- --- Shannon 

~Vein 

--Fault 

FIGURE 84.-Shannon vein cut into blocks by Blue Jay fault, No. 12 fault vein, and Rarus fault. 

N 

The mine has been- a heavy producer for many years, the ore supply coming for a long 

time from the Shannon, the most northerly vein of the mine, from the two veins of the :Mountain 

View south (Anaconda) lode, and from the Johnstown vein. Since 1905 the ground between 

these veins has also been productive, and great ore bodies have been found along the fault 

fissures. This network of veins is well shown in the vein maps, particularly the one showing 

the 5,100-foot plane. Figure 86 ·also shows the relations of the veins of the Mountain View 

mine to those of the Rarus and Pennsylvania. · 

The surface outcrops of the lodes are not readily· traceable, as the zone of oxidation is 

deep, extending generally to the first level, 500 feet beneath the surface. The vein filling in 

this zone is a coarse spongy-textured quartz, more or less iron stained, but containing residual 

unaltered masses of pyrite and carrying from 2 to 4 ounces of silver per ton. It is a notable 

fact that the enargite ores ~re less oxidized than the glance-pyrite ores, both in the Johnstown 

and Shannon veins. In the latter a pillar of fresh or but slightly altered enargite ore 50 feet 

wide extends upward for nearly 200 feet through leached and barren oxidized material. 
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 197 

· SHANNON VEIN. 

·GENERAL CHARACTER. 

As exposed· in the :Mountain View mine, the Shannon (north) vein consists of .a . group of 

overlapping blocks, separated by fault fissures, producing an echelon structure. The vein 

narrows and is apparently dying out 

in the west end ,of the mine, but 

throughout the main workings the orebearing zone is 10 to 40 feet wide and 

shows remarkably little barren ground. 

The vein has a steep southerly dip, 

varying fro~ 70° to 90° in different 

parts of its course; in the 1,000-foot 

level and for 60 feet below it dips north. 

Though considered a member of 

the Anaconda system the Shannon has· 

a general eourse of N. 70° E., the san1e 

as the fault veins of the Steward system. The dislocations clue to cross 

faulting have not only shifted large 

blocks between the major faults, but 

have also proclucecl n1any minor changes 

in direction and curves. 

The vein shows well-defined walls, 

whose ore is separated by clay seams, 

developed during the adjustments acconlpanying block faulting. The vein 

filling is quartz, carrying pyrite, with 

son1e glanee and considerable enargite. 

In the lower levels the latter is the 

main copper-bearing mineral. 

The Shannon is abruptly truncated 

westward by- a northwest fault near 

the ~1:ountain View shaft, the displaced 

lode west of tlus breal\: carrying ore for 

a few yards and then changing to a 

barren friction breccia. 

The Shannon has been continuously worked for 2,000 feet eastward 

fTom the :Mountain View shaft, increasing in width and richness eastward. It: 

is undoubtedly continuecl·in the Colusa 

lode, but as a big northwest double 

cross fault (the Gambet.ta-No.12, which 

is probably equivalent to the lligh 

Ore) sepa.rates ~he two portions by a 

displacement of between 200 and 300 

feet, the names used by the miners of 

the district are retained. Figure 84 

shows the fault blocks as disclosed 

underground. 

LEGEND 

L::ill 

~ 

Outline of workings 

Veins 

~ faults 

~ 

~ 

Timbers 

Granite carrying 

specks of ore 

Granite carrying 

specks of ore 

FIGURE 85.-Sectlon In West Colusamlne,323 ralse,showlngcharacter of Colusa vein. 

Eastward, in the West Colusa mine, the vein expands into an ore body 60 feet wide and 

minable from the 290 to 'the 400 foot levels, but its values give out, except <;>n the foo~wall 
LEGtND 

I~ [lZ] N 

Quartz porphyry Clay fault Ore 

s 

55ool I / '~':<:~ ... ~:._"'-~~~"':);~:dv .0J I CiH?"/ fl!ff____ -r 1M J-p---Q---r-~--- " 15500 

StlOOI . ~.'{/.' I ~:1 ,"t-Ier, 

4500 ., 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I I~ 

c 

'Qj 

> 

c 

0 

c 

c 

<0 

.s:: 

FJ • <"<-"'P"'~ :rf>"~'~ ~ ... -~. ~9'-''" ,if,l I I t:.l ({)CI 15000 

.. ' 4500 

400.0 " 4000 

0 50 100 200 300 Feet 

FIGURE 86.-Cross section through Mountain View, Rarus, and Pennsylvania mines. 

1--' 

co 

~ 

~ 0 

8 

~ 

> !2: 

t::;j 

0 

!;d 

t%.l 

t::;j 

t%.l 

1-d 

0 

m 

H 

1-3 

U1 

0 

~ 

to 

q 

1-3 

1-3 

t%.l 

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m 

~ H 

0 

~1-3 

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0 

z 

1-3 

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?--
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 199 

streaks, below 400 feet, ·probably because the glance enrichments of the "spray" do not 

extend downward. In the upper levels of the West Colusa mine the Shannon ore body is a 

great mass of enargite ore in a crushed quartz-pyrite vein. Solid enargite occurs on the 

footwall, but the ore body is crossed by northwest (not north-south) streaks, carrying quartzG R A N 1. T E 

G RAN I T E. 

GRANITE 

.0 100 200 300 400 500 FEET 

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

FIGURE 87.-Cross section. through Pennsylvania mine. 

pyrite ftlling that shows soft black glance coating the pyrite. The ore bqdy must be the result 

of rock shattering following an older vein, with mineralization co1;1fined to upper levels. (See 

fig. 85.) 

Near the Mountain View shaft the Shannon lode is but 2 to 5 feet thick, but it widens 

eastward by spur or branch veins to 15 to 25 feet, and maintains th.is thickness in the great 

ore body stoped out above the 900-foot level. (See figs. 86 and 87.) 

.. 
200 GEOLOGY AND ORE DEPOSITS OF· BUTTE DISTRICT, MONTANA. 

These spur veins carry high-grade glance-enargite ore, and as the 'intervening granite is 

altered and impregnated with particles of ore, the entire mass is workable (fig. 88). Not all 

the veinlets are fault veins, for many of them do not cross the lode but are the result of the 

settling of the hanging-wall block over the Blue- Jay fault. 

o 10 zo 3o 40 so Feet 

LEGEND 

~I Veins 

Faults 

Pyritic 

~ 

~ 

granite 

L::£J 

~ 

Outline of 

~.orkings 

FIGURE 88.-Section of Mountain View south vein, showing streaks of 

first-class ore, consisting of quartz, enargite, pyrite, and chalcocite, with 

a little bornite and tetrahedrite, 1,055-foot raise. 

The ore body is peculiar and unlike anything else in the district except the Leonard 

(see p. ~11), which is regarded as a faulted 

part ,of the same mass. 

In the :Mountain View mine the continuity of the vein is destroyed by three 

veins, the Smelter, Sullivan, ~nd Combination, considered by the writer to be members 

of the Blue Vein system. These cross veins 

are ore-bearing in the deeper levels, but 

lean or unworkable for the first. 500 feet or 

more beneath the surface. 

FAULTING. 

Noteworthy. in the·· workings on the 

Shannon vein are the northwest faults which 

terminate against the east-west faults. An 

example of this is seen on the second and 

third levels of the West Colusa mine; . the 

true relations being very well shown in the 

stopes on the fourth level, where it. is quite 

clear that the diagonal northwest fault does 

not extend beyond the Shannon vein,. A 

reasonable interpretation appears to be that 

a block of· ground of pyramidal shape, with 

its apex downward, has been moved. as a 

result of faults. The north wall of this block 

is a hanging-wall fault of the Colusa vein.· The south wall is a more or less vertical fault 

cutting through the Shannon on the ,upper levels. In depth the intersection of these two 

walls advances eastward and meets the Rarus fault somewhere about the seventh or eighth 

level, forming the apex of the pyramid. The east side of the pyramidal block is the Rarus 

fault. The block appears to have been produced by a thrust upward. A crushing pressure 

would cause such a block to move upward, and a relief of pressure would allow it to drop 

downward. The great abundance of crushed granite could hardly be explained on the ba.sis 

of a settling of the block, even were its weight to rest against irregular sides, with more or 

less tearing off of irregularities. ~1:oreover, the fault shows on the first level that ore has been 

dragged north from the Shannon vein, whereas settl~ment would have caused an eastern and. 

southern drag. The faulting of the Shannon ore body is marked only on the three uppe!most 

levels. . . . 

Such an upward movement might be the result of a strong north-south pressure or of a 

thrust from the east. The latter would force the wedge westward and upward but would also 

have left its impress upon the country rock on each side of the block in question and would not 

have produced such differential motion. 

MOUNTAIN VIEW SOUTH VEIN. 

The Mountain View south vein, the greatest ore producer of the Mountain View mine, 

is the extension of the Anaconda lode east of the ~!fountain View fault. It shows the usual 

pyritous siliceous quartz· vein filling, with good definition between ore and country rock on 

the footwall, and a steep southerly dip conformable to that of the lode in Anaconda ground. 
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 201 

It extends eastward to the west wall of the Rarus fault, where it is abruptly truncated. (See 

fig. 89.) The vein has the typical character of the Anaconda in mineralization, structure, 

direction, and dip. It is a double vein, but the branches appear to split up and play out eastward and are not recognized east of the Rarus fault, except in the deepest levels opened. 

In the :Mountain View ground the lode differs 

fron1 the. other veins, usually lacking much enargite 

but being rich in pyrite and chalcocite, and also· 

carrying ·bornite. It is cut by the Blue Jay fault 

vein with but slight djsplacement, but is broken; with 

considerable cracking, n1ashing, and subsequent enriclunent and the forn1ation of n1uch clayey 1natter, 

which masks its original character. On the tenth 

level (fig. 90) the ore consists of crushed and crackled 

quartz and pyrite containing considerable enargite. 

The vein is somewhat vuggy along fracture planes, but 

has neither round nor large cavities. The chalcocite 

occurs in thick, persistent sean1s and bunches (see Pl. 

XVI, A) and is solid and unshattered. Enargite, 

though persistent,. does not form continuous streaks 

but is associated with s1nall bunches of white quartz 

and in fu1ns and seams in the masses of altered and 

crackled granite included ih the vein. It is clearly a FIGURE 89.-Truncation of Mountain View south vein by 

later Inineral. Rarus fault, 2,200-foot level of High Ore mine. 

The relation between the ~1ountain View south lode and the rhyolite porphyry is shown 

on the fifth. level of the n1ine, where the lode cuts through a dike, ·with in~poverishn1ent, narrowing, and splitting of the vein. The footwall or north branch of the vein runs parallel to 

. the Anaconda lode, but the southern branch fi_as a southwest course and shows westerly spurs 

1naking off on the north side. The ~1ountain View fault. cuts across the narrowest part of the 

/ 

( 

· lode, so that both in the St. Lawrence and MounN 

tain View ground th~ · veiii apparently thins near 

the fault. The tenth level shows the branching 

very clearly, No. 1 being north and No. 2 south. 

The vein is double eastward to the Blue Jay (~1icldle) fault, but single beyond it. 

The vein has been very productive but throughout the workings shows crushing and fault movement, with fault clays and breccias, so that it is 

difficult to assign the proper importance to the old 

lode itself. The complex relations of the vein to 

the Blue Jay (No. 16) fault and to the Rarus are 

shown in figures 89 and 90. · 

JOHNSTOWN (NORTH CONNECTING) VEIN. 

The Johnstown (North Connecting) vein runs 

parallel to the Mountain View fault. It varies 

somewhat in chara~ter in different places but is FIGURE 90.-'l.'runclltion of Mountain View ore body by Blue Jay 

(No. Hi) rault, tenth level, Mountain View mine. essentially an old quartz-pyrite vein, the quartz 

carrying pyrite masses and little veinlets. 

In ~1ountain View ground it is narrow, carrying 16 inches to 2 feet of ore, with rather 

irregular walls of hard, pyritic granite. On the 500-foot level it shows no ~ale and no enargite, 

but to the southeast it carries enargite in scanty amount, though it is not a fault vein and seen1s 

to lack any fault clay or crushing. It gets poor and tight tq the northwest. It dips 72° S., 
202 GEOLOGY AND ORE. DEPOSITS OF BUTTE DISTRXCT, MONTANA. 

and farther east, near the Rarus fault, it has a good wall, with selvage and good ore. On the 

500-foot level it dies out before reaching the Rarus fault. Within the Rarus fault it is not 

definitely recognizable. 

East of the Rarus fault the Johnstown is correlated with the Windlass vein. IIere it 

has a clip of about 80° S., and an average width of 8 feet of vertically banded quartz, abundant 

pyrite, and some enargite. The north end of the vein, 150 feet from the main crosscut of the 

mine, is sharply cut off by a fault running easterly. Beyond this fault the vein has not proved 

workable. 

The Johnstown is essentially an enargite-bearing quartz-pyrite vein in which the rich ore 

occurs in lenses within clay walls. As it is ,nearly vertical, while the South ledge or Anaconda 

has a clip of 60° S., the veins must intersect in depth. It becomes narrow, pyritic, tight, and 

lean, and loses its clay walls as it nears the cut-off by the easterly fault on the fourth and fifth 

levels. Its course is parallel t'o a porphyry dike about 50 feet s()uth. From the company 

records it appears that it carries 6 feet of glance ore on the tenth level, gradually changing up·warcl 

to enargite, the third level showing practically no glance. This is contrary to the conditions 

. ew vein (Anaconda 

South Mtn. y, 

Penns vania No.8 v~ 

Snohomish 

FIGURE 91.-Diagram showing relative positions of veins and faults of the Mountain View and Rarus mines. 

prevailing in other veins. If the descending copper-bearing waters contained arsenic it is 

easy to see how they would become more and more basic or reducing in their descent and would 

therefore deposit glance above and enargite below. · 

MOUNTAIN VIEW AND BLUE JAY FAULTS. 

The Mountain View and the Blue Jay faults· have already been described (pp. 142, 152). 

They are structurally and productively important features of the Mountain View property. 

Their relations to the veins of the Mountain View area are best understood by reference to 

figure 91. 

MOUNTAIN VIEW SYSTEM VEINS. 

The cliff~rent crosscuts driven south from the shaft of the Mountain View mine to the 

main south ledge afford excellent sections of the granitic country rock and of the lesser fractures 

which traverse it. (See Pl. XVI, B.) 
• U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE XVI 

A. SMALL VEINS OF PYRITE IN GRANITE. 

Mountain View mine, 10Q.foot level, South or Anaconda vein. Veinlets are s lightly displaced by 

secondary fracture plane, which is nearly parall el to main vein, but pyrite veinlets follow jo int 

planes nearly at right angles to main vein. Th ey diverge, cross, and converge again, as do the 

seams which make up th e large veins. Li ght part is vein granite; streaks are pyritous ve in s low 

in copper. Vertical slip planes separate vein from impregnated country rock. See page 201 . 

.B. FAULTED VEIN LETS OF CHALCOCITE AND QUARTZ-PYRITE ORE. 

Mountain View mine, 600.foot level, sou th crosscut, north vein, east vein. 
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 203 

One set of the fractures strikes about N. 35° W. and dips about S0° S. These small fractures 

are occupied by hard quartz-pyrite veinlets frorri 2 to 6 inches wide. · They supposedly represent 

the earliest period of fracturing of the granite. The sections do not show conjugate fracturing, 

the dip being always to the south and varying from 60° to 80°; the strike varies from 30° to 

45 ° west of north. 

The earlier fractures are faulted by a multitude of fault fractures belonging 'to the Mountain View syste1n, which run from N. 70° toN. 90° W. and stand nearly vertical. These faults 

are filled by crushed, fu1ely ground granite, 'for1ning a claylike paste, containing numerous 

pebbles of pyrite ore and son1e slabs or dragged particles (Pl. XVII, A), up to 6 inches in dianleter. They vary greatly in width, running fron1 one-half inch up to 2 feet or n1ore. A few of 

these }t1ountain View fault fissures are themselves fractured by a later 1novement which follows 

along the earlier pyrite veins; but in general this 1novement appears to have been slight and 

the dislocation insignificant. They are considered to be the result of contraction and perhaps 

of settling. 

The number of fault fractures increases with depth, and the number of pyrite-fijled seams 

appears to lessen. Water follows these fractures, depositing considerable limonite on the 1,200 

and 1,300 foot levels, but this seems to be a case of surface water draining downward because 

of the artificial opening. As with. the Parrot seams these fault fractures, whose prevailing 

course is about N. 75° W., have a southerly clip, in places as flat as 65° and in places approxiInating the vertical. These fractures are all in the footwall country rock of the Anaconda vein, 

· here known as the }t1ountain View south ledge. 

The north-south veins of the }t1ountain View system developed in the ·west Colusa, }t1oun-

. tain View, and Rarus ground are of comparatively recent recognition. They form narrow but 

rich enargite-glance vein's in granite, with little or no quartz, but inclose angular fragments 

and balls of pyritized granite. A good exmnple is seen in the 1,203-foot north crosscut of the 

West Colusa. 'rhey are not so. rich above the Ranis fault as they are below it, which probably 

accounts for their retarded development. Beneath the Rarus fault they appear close together; 

in the Leonard ore body the entire mass between the veins is taken out, particularly within the 

Rarus fault, whereas above the ·Ranis fault only the individual veins can be worked. 

COLUSA-LEONARD LODE. 

EXTENT. 

The ·section of the district containing the Colusa, Leonard, and }t1innie Healy mines is traversed by a n1aze of connected veins, forming a productive zone that might well be considered 

one great lode. The northern limit of this zone is the Colusa vein, and its downward (southfaulted) continuation in depth, the Leonard. The Tramway vein· delimits it on the south. · 

Eastward the productive area exte:t;1ds as far as Silverbow Creek .in the upper levels, but falls 

1nore and n1ore short of that boundary as depth is gained. Westward the mines and veins 

terminate against or merge into those of the Mountain View mine. This· area is not only travel'sed by well-defined veins arid cross v~ins but is shattered by a network of fractures how filled 

with ore, so that in places all the ground between veins is workable. 

COLUSA LODE.· 

GENERAL CHARACTER. 

The Colusa lode, one of the great veins of the camp, is a northeast and southwest vein, 

with steep northerly dip and a thickness varying from 10 to 40 feet or more. It is an enargiteglance vein, which may be regarded as tl1e "trunk" vein of the belt, as it is the one from which 

the others ·seem to diverge. It is large, even for Butte, being worked for a length of 2,400 

feet in stopes 20 to 40 feet and, in the fault section, even 150 feet wide. It is continued westward beyond the Gambetta fault as the Shannon vein. 
204 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The course of the Colusa vein at the surface is easily traceable. At one place it outcrops 

strongly as a tough spongy limonite., almost 'the only good limonite cap found on any of the 

productive veins. . Generally the .footwall is well exposed, owing to movement and settling 

over the old workings, the entire hanging-wall block for several hundred feet out from the foot 

wall having settled, with serious disturbances of the surface and damage to buildings and 

machinery. The footwall granite is solid and is unfractured save by the usual joint planes. 

The alteration of the wall rock is relatively more pronounced on the south or hanging-wall side 

of the Colusa vein. . 

The vein has been mined to a depth of 1,400 feet, its downward extension beneath the 

Rarus fault being distinctly recognizable, though it merges into the Leonard stockwork. Its 

general course is N. 65° E., but several cross faults and minor fractures have deflected the vein 

from its normal trend. The dip is steep, averaging 75° down to the walls ·of the Rarus fault, 

but the vein is flat through the fault, resuming its steep inclination beneath it. The vein varies 

between 20 and 50 feet in thickness, except in the flat interfault ore bodies connecting the 

Colusa and ·Leonard veins, where the stopes are wider, and has been worked for its entire width. 

The lode is a normal quartz-pyrite vein, which, with the crushed country rock accompanying it, is netted with streaks of enargite, pyrite, and chalcocite, and by numerous clay ·slips 

and seams. Little solid uncrushed ore is found, for adjustments since ore deposition have been 

marked and vigorous. Enargite is the most prominent mineral, but on the upper levels chalcocite is equally abundant. 

Rhyolite porphyry, part of the Modoc dike, forms the footwall of the lode for a few hundred feet, both vertically aP.d horizontally, near the East Colusa shaft. The granite acco~npanying the lode is generally well sericitized and peppered with pyrite~ In places it appears 

completely altered to a clay-like inass, in which th~ original minerals have entirely disappeared, 

but the granitic texture is still recognizable. As would naturally be expected from its structure, 

the lode is wet and yields a heavy flow of water, espec~ally where rich second~ry ores are found. 

FAULTING. 

The crushed character of the locl~ is clue to n1overnent along various strike and cross faults. 

These faults belong to the three systems recognized throughout the district, but the northwest 

or Blue vein system is the inost prominent and. has produced the nlost profound changes. A 

great double fault (the Gambetta and No. 12 veins), belonging to this system, cuts off the 

Colusa oil the west and separates it by a shift of nearly 300 feet fron1 its continuation in the 

Shannon. (See fig. 84 and p. 200.) The Rarus fault cuts through the Colusa and all its neighbors, and the movements along it have further crushed a lode already shatt~red and altered 

by cross and strike faults. To the Rarus, moreover, is due the production of the peculiar flat 

·ore bodies which have been observed generally along its course and which are particularly large 

and important along the Colusa-Leonard lode. Fissures belonging to the Blue Jay system 

also appear. · . 

The relations between the Colusa and the adjacent veins is well shown in the horizontal 

section along the 5,100-foot plane (Pl. XXXVI), in which the Colusa .is shown to form the trunk 

lode, with the No. 12, Piccolo Discovery, Gambetta No. 2, and No. 8 veins, apparently branching or diverging from it on the south. These correspond to the Gambetta, Minnie Healy 

(Betty), and Piccolo fault veins below and east of the Rarus fault zone. 

The structural relations of the various veins are best understood by reference to the plans 

and cross sections through the rather complex group of veins (figs. 92 to 97). · Minor fractures 

are omitted, owing to the small scale used, but there· is a marked breaking of the veins by a 

multitude of cross fissures varying from mere joints to clay and breccia filled fissures, some of 

the larger of which carry ore: Many streaks of rich ore come up to these cross slips and stop, 

and though the vein continues with slight displacen1ent it is comparatively lean immediately 

west of the slip. These fissures are abundant for a few hundred feet on either side of the West 

Colu~a shaft, where the vein shows a marked curve in its cottrse. The s~rike faulting, on the 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE XVII 

A. FAULT BRECCIA, MOUNTAIN VIEW MINE. 

Shows cross slips and o re bowlders in north crosscut , e leventh leve l. Breccia 45 inches wid e. See page 203. 

B. MINERALIZATION ALONG JOINTS IN GRANITE. 

Rarus mine, south crosscut , seventh level. Incipi ent vein formation, vein lets of quartz and pyrite. See page 224 . 
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 205 

other hand, is later than the cross faults, and, thopgh movement along its plane has not been 

pronounced and has not brecciated the vein, it has broken it and formed the crushed mass of 

ore and granite that constitutes so large a part of the ore shoots. 

~-----------J~--~----------~------------------L-~--~-----4300 

Ore Faults 

FIGURE 92.-North-south cross section through Leonard and Colusa mines on 5,100-foot coordinate east. 

BLUE VEIN FRACTURE SYSTEM. 

The most interesting features of the lode are the northwest fractures of the Blue Vein 

systen1, which appear to be southeast extensions of these so prominent in the Bell, Diamond, 

and Gre.yrock mines. Very generally the nlinor fractures cut off the rich ores westward, and 

even where displacement is not noticeable the lode west of the fracture is lean (fig. 93). The 

combined effect of the lesser slips near the West Colusa shaft is to give a curved course to the 

lode. · 
206 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

NUMBER 12 FAULT VEIN. 

The largest of the northwest veins of the mine is the No. 12. With the Gambetta, a parallel 

vein 100 feet fQ-rther west, it cuts off the Colusa vein and separates it from the Shannon vein 

on the west. Both faults are nearly vertical and are parallel to the Skyrme vein of the High 

Ore mine; They cut and shift the Shannon ore body in the Mountain View mine (p. 196). 

The No. 12 vein is ore-bearing in some places· arid has been worked. - It is well exposed on 

the 200-foot level of the Colusa mine and on several of the underlying levels above the Rarus 

fault (figs. 94, 95). To the west it is abruptly truncated by the Rarus fault, but is probably 

I Faults '"~J 

~ Enargite 

Pyrite •• and glance 

0 25Feet 

continued beyond by the Minnie 

Healy (Betty) vein. On the 200-

foot level of the West Colusa 

mine it cuts the Colusa vein and 

apparently displaces it slightly, 

but the main displacement is by 

the parallel Gambetta fault . 

GAMBETTA VEIN. 

The Gambetta is one of the 

principal veins of the Leonard 

mine. It lies beneath the Rarus 

fault, above which its upward 

extension is called the Gambetta FIGURE 93.-Loss of value in vein approacping fault vein. Leonard mine, 500-foot level, No.2. Downward it enters into near 514 chute; Gambetta vein cut by PicQolo vein. 

the complex forming the great 

stockwork of the Leonard lode. (See fig. 94.) It is a nearly vertical vein, having a thickness 

of 5 to 25 feet, and a strike of about N. 75° E. In vertical cross sections it shows considerable 

variation in dip, its course being somewhat sinuous. It is characteristically a fault vein, which 

in part follows an old quartz..:pyrite vein, but in the main consists of crushed granite, with 

streaks and impregnations of enargite. The vein has an average of about 3 feet of first-class 

enargite ore. Close examination shows included wedges of granite, with fragments of quartzpyrite ore belonging to the earlier .vein :filling; the workings show, however, that the vein 

does not follow an earlier vein throughout its entire course. Enargite occurs in nests and 

druses and coats nucleal masses of rock and quartz. Tllis enargite has been shattered by lat~r 

. movement and the cracks filled by films and veinlets of glance. The vein extends eastward.to 

the Piccolo fault vein, a northwest fracture which apparently terminates the m·ineralization 

of the Gambetta. 

The vein is abruptiy truncated by the Rarus fault, but it is believed that development work 

will show that this vein, like the Piccolo Discovery, will have a flat ore body within the limits 

of tl1e Rarus fault, which should be encountered between the fifth and sixth levels. 

Westward the Gambetta splits into two prongs, which are well shown in drifts 505 and 511 

of the Leonard mine. The south prong affords a good example of an old vein enriched by 

enargite deposition. It is well shown on the 400-foot level of the West Colusa mine. Above 

this level the vein is narrow and ·consists of lean white and dense quartz, carrying abundant 

pyrite. This primary vein filling is traversed by a strike fault, the mashed granite alongside 

of the fault being impregnated and its cracks filled by seams of solid black enargite. Tllis 

mineral occurs almost pure, fills the cracks, shows little or no trace of replacement,· and is accompanied by little or no quartz or pyrite. The granite alongside of the enargite is unaltered or 

shows no alteration due to the deposition of this mineral. Between the 400 and 500 foot levels· 

this Gambetta south vein shows 2 to 3 feet of solid enargite. It should be mentioned, however~ 

that the footwall streak on the vein consists of crumbled pyrite mixed with copper glance. The 

Gambetta vein proper consists of white quartz, with pyrite and nests of enargite, partly in druses, 

and coating nucleal masses of older rock. The amount of enargite varies greatly in different 
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 207 

parts of the vein, and secondary glance is observed filling cracks and films both in the ore and 

in the wall rock. 

The specimens of ore fron1 the Gambetta vein consist of solid enargite, with disseminated 

grains and irregular streakings of pyrite and occasional nests of friable decomposing pyrite, 

which may possibly represent an unreplaced portion of the old pyrite vein before the enargite 

was formed. The evidence ·afforded by the specimens is not conclusive, bt1t indicates that the 

l!"llff/11 

Ore Faults 

FIGURE 94.-North-sout.h section through Leonard.and adjacent mines, 4,Soo-root coordinate. 

vein filling began in the replacen1ent by enargite of an old pyrite vein devoid of quartz, and 

was continued by the replacement of the granitic rock. · 

The Gambetta No·: 2 vein is peculiar because what appears to be one contint~ous quartz 

and pyrite vein is worthless above the 300-foot level, carries good ore for 300 feet below that 

level, flJld becomes zincky again and poor beneath the 600-foot level. This peculiar feature is 

believed to be clue not to a change in mineralization but to an abrupt truncation and dislocation 

of the vein downward by one of the fissure pl~nes of the Raq.1s fault, the Gambetta vein lying 

above another vein of different characte~, and containing a large excess of zinc. 
208 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

PICCOLO VEINS. 

The name Piccolo is· applied to three veins,· distinguished as the Piccolo, the Piccolo Dis:.. 

covery, and the Piccolo fault. The Piccolo lies beneath the Rarus fault. The vein has a 

width of 4 to 5 feet, .and consists of fault clay and breccia. It has a clear-cut and regular 

hanging wall, with crushed and mashed granite on the footwall, very solid granite lying outside 

of the vein. The filling consists of fault matter, with crushed ore and scarf-like masses of 

·broken and dragged ore." Its course is N. 45° W., and its dip 80° SW., in places becoming 

c 

-~ 

>-

~ E 

(Q 

L 

Is 

[lY 

Ore 

N 

FEET 

----------~~~--~---------------------------L----~--~---4500 

FIGURE 95.-North-south section through Leonard and adjacent mines, 4,90D-foot coordinate. 

steeper or vertical. Where exposed on the twelfth floor of· the 500-foot level of the Leonard 

mine, the vein is 10 feet. wide, consists of mashed granite, crushed quartz, and pyrite, with a 

little copper glance. Enargite is absent. Endogenous ore is not observed, the only ore streak 

consisting of crushed ore and clay. 

The Piccolo· Discovery vein lies above the Rarus fault and is well exposed on the 400, 

500, and 600 foot levels of the West Colusa mine. Its course is nearly east and west, but the 

vein is unquestionably a· .fault fissure which cuts abruptly through and dislocates the lodes 

intersected ·by it. The vein is not known north of the Colusa vein nor south of the Rarus fault, 

but as it is known to be deflected by the Rarus fault in the deeper workings, it almost certainly 
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 209 

extends eastward beyond this fissure. The ore found in the vein is not solid enargite, but is 

crushed and slightly displaced by the settling of the hanging-wall block over the Rarus. fault. 

The ore is not brecciated and, though mashed granite and clay occur above it, shows no fault 

breccia or muck. 

The Piccolo fault vein is a local fissure, important only as delimiting the mineralization on 

the east. It is a fault ledge and not ·part of the stockwork series. In the last few years it 

has been found to possess a flat or.e body corresponding to that of the Leonard vein, and like it, 

due to the Ran1s fault. The Piccolo fault vein is itself fractured by a northeast fault. On 

the 600-foot Leonard it cuts off the 602, the Gambetta No. 1, and the Gambetta No. 2 veins, 

but is itself cut off by a N. 45° E. fault with a 30° dip. 

Several neighboring veins have been distinguislu~d by numbers. 

No. 1 vein shows 2 inches of crushed granite and quartz, with scarfs of crushed ore. It 

has well-defmed· walls of firm granite, the hanging wall being hard and solid• pyritized graniet 

and the footwall a leached silicified granite. 

'fhe No. 2 vein shows 5 feet of crushed rock, with bunches of black ore, mainly crushed 

pyrite, partly replaced by glance. 

The No. 4 vein consists of solid quartz and pyrite, with soine secondary glance, the streak 

of rich ore being 4 inches wide, and lying in a hard pyritized granite. 

The No. 5 vein is a solid pyrite vein, carrying but lit,tle quartz, and dipping 70° S. It has 

a hanging wall of soft and mushy fault matter, and is itself cut off by a fault. 

The No.8 vein of the Leonard and West Colusa 1nines is a fault fissure which has been developed on a number of levels. (See figs. 94-97 .) It has a general e~st~west course and a rather 

flat dip to the south. It is a fault vein which is wet and mushy but contains irregular bunches 

of enargite and streaks of enargite and glance 4 to 6 inches thick, so that the entire vein has a 

workable width of about 10 feet. In places portions remain of a primary vein filling of white, 

dense quartz, thicldy inlpr.egnated with pyrite. Tllis old vein must have been very narrow, 

as the workable portion of the vein at present is only about 1.4 feet wide. The No. 433 drift 

shows a sheeted wall rock in wllich the mineralization gradually fades out away from a streak of 

pyrite and quartz carrying enargite 1 foot to 2 feet thick. A footwall streak of crushed enargite 

with clay and fragn1ents of earlier yein fliling lies against a clay gouge,. with mashed granite on . 

the footwall. As the cracks in the broken vein filling are filled by solid black enargite it is 

evident that the early vein has been enriched by later mineralization in which enargite has been 

the principal nlineral formed, and that both the earlier ores have been enriched by later deposition of glance. MINNIE HEALY VEIN. 

- The :Minnie I-Iealy (Betty) vein is a good, strong, quartz-pyrite vein 6 feet wide, crushed 

by a strike fault, and showing secondary enrich~erit, with recent streaks of white quartz, and 

large masses of black, ·soft, decomposed material, with 

pyrit As shown in figure 96, it cuts off the ore streaks 

of the Leonard stockwork in the west drift to No. 822 

of the Leonard mine. 

MINOR FRACTURES. 

The northwest fissures of t~lis complex correspond 

only in part to those of the Bell-Diamond group. A 

large number of nlinor fractures (particularly well shown 

on the 300-foot level) are due to the fracturip.g of the 

hanging-wall block of the easterly fault (No. 16 vein) 

supposed to be the continuation of the Blue Jay, This 

0 5 10 15 20 25 FEET 

FIGURE 96.-Leonard ore body cut by Minnie Healy 

(Betty) fault vein. 

dips 65° S., whereas the diagonal fissures are vertical or dip ·steeply north. One of the most 

prmninent of these diagonal fissures is well exposed on the 200-foot level. It extends across 

the ve~n, but stops at the footwall fault, cutting off the ore on the first, second, third, and 

90427°--~o. 74--12----14 
210 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

fourth levels. A reasonable explanation appears to be that the strike fault caused a splitting 

of the southern ·or hanging-wall block. This adjustment might be due to normal downward 

movement, the cracks being reopened and intensified by adjustments due to the later Rarus 

fault. The facts show (1) an abundance of crushed granite, indicating upthrust and grinding alo~g walls; (2) a northward drag of ore from Colusa vein into the fault, showing a 

northwestward movement, whereas if the wedge had moved downward it would also move 

eastward and southward; (3) o.nly slight displacement except on the four upper levels, a condition according best with a hypothetical upward movement due to strong north-south pressure. 

The veins of this section differ from the quartz-pyrite ·veins of the Anaconda type. The 

enargite veins of the Leonard mine carry little pyrite and practically no quartz, and are incased 

in pyritized granite, the only quartz of any moment being present either as inclusions or as a 

thin film between the granite and the enargite. '(See fig. 97.) 

These conditions are well exposed in the Gambetta vein on the 400-foot level of the West 

N 

LEGEND 

FIGURE 97.-Cross section of part of Leonard lode, from 1,000-foot level upward for 7'/ 

feet. The ore streak on the left is main footwall ore, running east-west. The central streak with south· dip is a new fissure, containing much pyrite and enargite. 

The streaks on the right run N. 75° W., dip 67° N., and show 6 to 7 feet of solid 

enargite. The intervening ground is altered silicified quartz monzonite richly impregnated with glance and enargite. the glance usually filling small cracks and the 

enargite appearing in bunches. 

Colusa mine, where considerable enargite occurs in· cracks in the granite, apparently without regard to 

the former presence of quartz. or 

pyrite vein matter. Where the enargite is clearly the result of replacement, pyrite nests and cavities occur 

in it. The vein between the 400 

and 500 foot levels shows 2 to 3 feet 

of solid enargite. 

BLUE JAY FRACTURE SYSTEM. 

The largest of the N. ·~0° E. 

fractures is either the northeastern 

continuation of the Blue Jay-Middle 

fault or a parallel fissure of the same 

series which cuts through the northwest cross faults, both great and 

small. This fault shows much clay 

and fault breccia, but little shifting 

of the vein structure. The veinlets 

of rich ore which branch off from the Colusa may be mineralized strain cracks due to this fault. 

RARUS FAULT • 

. The wide northeast fracture known as the Rarus fault is described and discussed on. 

pages 228-230. In this part of the district it cuts and displaces not only the Colusa, but all 

the lesser neighboring veins. J'he veins are sharply cut off, but the displacement instead of 

being concentrated along the two walls of the fault is distributed through its width, probably 

as a result .of slipping and some torsional movement along many fractures. The result is a 

step faulting of the lodes and the formation of flat bodies. (See also p. 229.) This is well 

shown in the cross se~tions, figures 94, 95, and 99. 

These ore bodies connect the Colusa and Leonard veins by an abrupt elbow, the lode being 

seemingly bent almost at a right angle (fig. 94). .This feature is most apparent in the Colusa 

vein, owing to the latter's great size, but it is found also in the other veins of the group, and the 

position of such ore bodies on all of them can be determined by calculation before development 

work is begun. The Rarus fault is very well defined in the deeper levels, but is less easily identified above the 600-foot level, and its displacement near the surface appears to be slight. 

Between the limiting planes of the Rarus fault the flat ore bodies of the Colusa have been 

immensely productive, the stope floors being in places as much as 150 feet across. The ore 
MOUNTAIN VIEW-SHANNON-COLUSA BELT. 211 

body has a dip of only 10° to 15°, and its connection with the overlying lode and its continuation 

down,~arcl were difficult to understand by any ordinary process of faulting. Figure 94 shows. 

that the ore body consists of a mnss of crushed ore and rock netted with clay slips and seams. 

The planes of displacement parallel to the walls of the Rarus fault are obscured by cross slips 

and can seldom be definitely locat.ed, but there seems no doubt that there has been some movement of the mass since the Rarus fault, withJurther crushing. 

The flat ore body seen in the stopes has a main ore streak, is undulatory in cross section, 

and rests upon a flat fault that has a course of N. 80° E. toN. 70° W. and a clip of 35° to 55° S., 

and is therefore a n1e1nber of the Steward fault series. It has 4 to 6 inches of pebbly clay and 

2 to 3 feet of crushed brecciated granite. This fault cuts off N. 35° E. slips, with 50° S. dip. 

Farther north the ore body consists of a mass of crushed granite, with ore balls and a band of 

enargite crushed to powder. The granite contains numerous blue clay sl~ps, striking mostly 

N. 45° W., N. 35° W., and N. 40° W., with conjugate dip north and south. :Much of the 

ore is a cracldecl n1ixture o:f quartz, chalcocite, pyrite, and crumbly crushed granite. Beneath 

the flat ore body the granite is crushed, with more or less clay. 

J~EON ARD LODE. 

GENERAL CHARACTER. 

The nrune "Leonard" has been applied to the continuation of the Colusa lode beneath the 

Rru·us fn,ult, but n1ay perhaps be better used to designate the great ore body of the Leonard 

1nine, c01nposecl of various veins and cut by several faults. Though it might be called a stockwork, it is not a network of interlacing veinlets in rock, but rather a trunk vein with a unilateral 

developn1ent of branches. As prev~ously stated, it is limited northward b}r the Colusa and 

southward by the Trmnway veins.· As the Tramway vein has a north clip and the Colusa a 

south dip, the ore body is ·wedge shaped and narrows down\vard. This great ore body shows 

stringers of rich ore spraying off fro1n the Colusa vein and bending around until they take a 

north and south course. The best general section is that developed on the 1,000-foot level of 

the Leonarcl1nine. The map (Pl. XVIII), which represents a horizontal cross section of the ore 

body on. the 1,000-foot level, shows only the actual rich ore streaks. The granite between 

these streaks is altered and, though solid, is specked with ore, so .that it is all mined. 

The Leonu.rd difrers very n1arkedly in cha1•acter from any other lode or ore body in the 

Butte district. It 1nay be likened to a plume_, in which the rib is the Colusa vein and the various 

north a11CI" south offshoots curving around from it the .small feathers. The entire ore body as 

mined really consists of the Colusa vein, with stringers spraying off to the ·east and turning until 

they go south and end against the Tramway vein. There are no ore shoots in the ordinary 

sense of the word, but streaks of ore having a northwest to north course run off from the Shannon m1d Colusa veins in the upper levels and bec01ne stronger and richer going downward, until 

at a depth of 1,000 feet or n1ore they become thinner and pinch out. These stringers of rir,h 

ore consist of enargite in altered granite, the definition between ore and granite being sharp.· 

As, however, the intervening rock is impregnated with pyrite, partly ot wholly replaced by glance 

and enargite, the space between the ore streaks is also mined, so the ore body is practically a 

stockwork. This intervening granite, though highly altered, is unfractured. 

VEINS. 

The extrmne northern lin1it of the ore body (fig. 98) is the downward continuation of the 

Colusa vein, whose faulted upper portion is the Colusa vein proper, which farther westward is 

known as the Shai1non. The other veins which form part of the stockwork and which, above 

the Rarus fault, are independent veins, coalesce downward into the great Leonard ore body, 

but are still recognizable. One of them, the PiccQlo Discovery vein, passes vertically downward apparently without deflection by the Rarus 'fa.ult, as its termination directly overlies 
212 GEOLOGY AND O:&E DEPOSITS OF BUTTE DISTRICT, MONTANA. 

another vein. The level maps of the Leonard and Colusa mines show these veins. Some of 

them are n~med; others are, for convenience, designated by nun1bers. 

FAULTING. 

The relation of the Leonard lode to the Colusa lode is best shown in the vertical cross 

sections 1 (figs. 92, 93, 94, 95, 98, and 99), which show that the supposed cut-off or fading out· 

~ Ore Faults 

FIGURE 93.-North-south section through Leonard mine, 4,50Q-foot coordinate. 

downward of this vein does notreally exist, but that the Colusa vein is displaced by the Rarus 

fault, forming the great flat ore bodies of the Leonard stopes, and makes up the wall of the 

great Leonard lode underneath that fault. These relations are, however, c01nplicated by other 

faults, one of these being the middle or No: 16 fault, which in this ground follows the footwall 

1 These figures are based on cross sections kindly furnished me by :M:r. R. H. Sales and checked and amplified by myself. 
MOUNTAIN vnj)~V-SHANNON-COLUE?A BELT. 213 

of the Colusa lode. Another, here called the Corbett fault, has a flat southerly dip and limits 

seconclai·y mineralization to the south. 

Figure 99 shows the. veins lying south of the Colusa vein and composing the complex which 

underneath the Rarus fault is so heavily mineralized. The veins known as No. 12, the Sales 

vein, the Gambetta No. 2 vein, the Piccolo Discovery, and the No. 8 or En~rgite vein, net the 

ground lying south ·of the Colusa lode, and beneath the Rarus fault reappear as the Minnie 

I-Iealy (Betty) vein (a nearly vertical lode), No. 12-A vein, No. 2-A vein, and others to which 

no defmite designation has been_ affLxed. The whole area lying between the Tramway vein on 

~ 

~ 

Faults 

FIGURE 99.-North-south section through Leonard mine, 4,700-foot coordinate. 

the south and the fault limiting the Leonard ore body on the north is. shattered by faulting of. 

different periods, and has been so impregnated with copper that it forms a vast stockwork of 

low-grade ore, cut through by veins and streams of high-grade material. Considering the 

:faulting i( is rather remarkable to find. such a close matching of veins. The formation of the 

flat ore body by the Colusa as a result of the Ran1s fault has been confirmed by search made 

for the flat portions of other veins also displaced by tllis fault, and it has been found possible 

to direct new drifts to locate such ore bodies from the plats made in the office. 

On the Le~nard 400-foot level the Rarus fault appears to split and a branch coalesces. 

with the footwall strike fault of the Colusa. On the 600-foot the Rarus fault is a strong break 
214 GEOLOGY AND ORE DEPOSITS OF BUTTE. DISTRICT, MONTANA. 

with slight displacement, the only abnormal features being those due to the northwest faults. 

On the 700-foot level, however, the Rarus fault has produced a very marked displacement of 

the vein, and the flat ore body is here due, as it is within the workings of the Rarus mine, to 

step faulting or block faulting of the lode, the distributed displacement bringing short tilted 

blocks so close together that they apparently form one flat dipping mass of crushed but continuous ore. In the horizontal plane of this level the lode apparently swings around to the 

south as it approaches the limiting fissure of the Rarus fault. These features are best seen in 

the cross sections (figs. 92, 94, 95, and 98) which show very plainly the strong and well-defined 

Colusa vein, with its footwall fault dipping downward to the cut-off by the Rarus fault. A 

strong south-dipping fault is also observed in the crosscut from the sixth level at a distance of 

100 feet from the hanging wall of the Colusa vein. The same cross sections show the nearly 

vertical Tramway vein, with its slight northerly dip limiting the mineralized ground on the 

south underneath the fault, with the undulating but nearly vertical Gambetta vein to the north 

of the Tramway, the parallel No. 2 vein to t~e north of this, and the Piccolo fault beyond. 

ORES. 

The ore body in many places consists of a mass of crushed granite, with ore balls and bands 

of enargite crushed to a powder, and the granite alongside contains nun1erous clay slips, 

mostly with a northwest course and conjugate north and south dips. The main mass of the ore 

.0 5 10 1s Feet 

Impregnated granite Vein Faults 

FIGURE 100.-0re body in south crosscut, 700-foot level, Leonard mine. Shows soli.d ore (glance and enargite) cut by fault 

slips dipping with vein. · 

body is composed of a crackled mixture of quartz and pyrite, with some copper glance, together 

with crumbled and crushed granite. The granite beneath the flat ore body is crushed and shows 

more or less clay. · 

In south crosscut No. 772, from the 700-foot level of the Leona~d mine (fig. 100) thick bands 

of solid ore are cut off by sympathetic fault slips parallel to the main displacement, and the ore 

generally consists of a shattered mass of quartz and pyrite vein filling, netted by clay seams 

and enriched by ·glance. Text figure 100 gives an idea of the broken nature of the ore body 

and plainly shows how the hanging-wall block has been broken ana ·secondary slips formed by 

the settling of the main hanging-wall block of ground. In the deep levels of the mine the ore 

bodies show solid streaks from 3 to 4 feet thic-k, of bornite, glance, and covellite. These streaks 

are in solid but highly altered granite, and are cut and displaced by northeast fa~lts, usually 

steeply dipping, having a displacement of 2 to 6 feet. · 

An examination of the deep levels of the Leonard mine and the stopes showed that the 

ground between the veins is netted and that lesser streaks are abundant, and that, in many 

cases, the granite is not actually impregnated nor spotted with glance and enargite, but is 

·cobwebbed with ore. One is impressed With these facts: (1) That many of the veinlets show comb 

quartz with enargite between the crusts, and more rarely bowlders incrusted with cockade. ore 

and quartz; (2) that there is no absolute regularity of planes; (3) that the fissures must be 
MOUNTAIN VIEW-SHANNON-COLUSA BELT •. 215 

open, as N. 65° to 75° vV. fractures show clots or spangles of enargite and glance. The larger 

streaks show noticeable banding. 

In the. deeper levels, 1,100-foot and 1,200-foot, vein fotn1ation seen1s to have been arrested. 

The intermediate granite looks as if in a short time geologically it would have been completely 

mineralized and replaced; the veinlets show arrested filling, with crumbly pyrite crystals and 

open-textured enargite, etc. The emirgite is t,tllloose textured and full of pyrite. The glance 

appears secondary, and so does the covellite. Vugs are abundant, and barite, hi.ibnerite .. 

tetraheclrite (bronze) occur, though sparingly, and the covellite forms veinlets persistent from 

floor to floor. 

The ore is markedly impoverished from the 1,000 to the 1,200 foot levels; the ore streaks 

becoming more siliceous and irony and the pitch of the ore body is to the west, though there 

is no apparent reason either for impoverishment in depth or fading out eastward. Assays of 

san1ples taken at 5-foot intervals on the sill floor of the 1,000-foot level show that the entire 

mass carries 7 per cent copper. The curves of the silver and copper values, when platted by 

coordinates, follow each other up and down very closely, and · 

though the ratio varies somewhat it is in genera] about 1 per 

cent copper· to 1 ounce silver. 

The Leonard ore body shows streaks and lenses of black 

enargite in the altered granite. As seen in the stopes, the bulk 

of the ore n1ined is an altered granite, carrying disseminated 

grains of pyrite partly replaced by enargite and glance. Pyrite, 

however, is not the only mineral replaced, the thin sections indicating a direct replacement of hornblende and biotite by the 

arsenical sulphide of copper. Direct evidence of replacement 

is shown in sac-sha peel bunches of ore like the one shown in 

figure 101. 

Several systems of fracturing are noted in the ore body. The 

most important ore bodies occur at the intersections of northwestsoutheast fractures with others running northeast and southwest. 

The northwest fractures commonly dip 60° to 70° N., but con-· 

jugate opposed fractures, having the same course, but a contrary 0 . 5 

-

Pyrite 

IDJ 

Enargite 

\ .Granite ~ with 

quartz streaks 

10 Inches 

dip, also occur. So far as observed, the ore occurs only in shat- FIGuuE 101.-Enargite bunch, soo.root 

1 · level, Leonard mine. tered roc \:1 where fractures intersect, and is not found along either 

set of fractures away fron1 the intersection. The rock in the crosscuts is pyritized granite very 

n1uch like that coinn1on throughout the district, and would be called waste if it were not for the 

great stopes which have been minctcl. The mineralization seems to be n1ainly by enargite shn,ttered and cemented by glance. · 

TRAMWAY VEIN. 

The Tramway is a northeast fault vein, which, u:p.like most of the veins of the district, 

has a steep dip north. It has been mined.in the Tramway, :Minnie Healy, and Leonard mines, 

where it forms the southern boundary of the great compound ore bodies of the Leonard mine. 

The vein is composed of a mix:ture of crushed pyrite and white, opaque, siliceous matter, 

representing an earler vein filling that has been crushed, recemented, and indurated. It contains glance streaks, which cross the vein, the streaks appearing to fill torsion cracks. The 

vein has been extensively developed in the Minnie Healy mine, where· it varies from 6 to 20 

feet in width, with bands of high-grade glance ore ·from 1 foot to 6 feet thick. In general, 

there is a clay hanging-wall selvage 2 inches or more thick, a 2-foot band of rich ore (5 to 10 

per cent).; a central band of brecciated but hard vein matter; streaks of solid glance and 

clay slips, 5 feet of low-grade pyritic ore, and a footwall streak of mashed ore,· quartz, and 

blue clay. The walls roll and the vein swells and pinches. The ·conditions indicate thn.t an 

old indurated fault vein 2 to 3 feet wide has been reopened and widened by a strike fault, 1n 

which glance and enargite have been deposited. 
216 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The vein in places shows a matrix of light-colored or mottled material apparently of granitic 

·composition, but really ~ade up of white, nearly pure silica -that has a chalky appearance and 

texture. Isolated fragments of an earlie:r fault breccia, well indurated, so that the fragments 

retain their form, occur in this silica. Between these fragments later enargite has formed, 

constituting the chief value of the ore. · 

' 

MINES NORTH OF MEADERVILLE. 

:MODOC :MINE. 

The Modoc mine is located near the eastern end of the copper district, immediately north 

of Meaderville. It has two shafts, but only one has been used in recent years. The Modoc 

is a single vein 5 to 20 feet wide, dipping quite uniformly south at an angle of 55° to 60°. The 

incasing rock is either quartz monzonite, usually pyritizt::d, or rhyolite porphyry. The rhyolite 

porphyry forms a series of dikes, which unite at the surface in a single outcrop 100. feet wide 

at times, forming the Modoc dike. Underground, the vein is nearly parallel to the dikes but 

. cuts through them in places. · 

The lode is not continuously ore bearing, but consists of a banded mixture of solid quartz 

. and pyrite that is workable -only where broken by faulting and enriched by secondary glance 

and bornite. Chalcopyrite also occurs, and secondary bornite is deposited on the ends of 

quartz-pyrite crystals.. The vein is bro.ken ·by numerous transverse northwest fissures, by 

which it is slightly displaced. The pay ore occurs in shoots, which generally pitch westward 

and do not extend either laterally or vertically for more than a few yards, the largest being 100 

fe~t in horizontal and less than 40 feet in vertical extent. These lenses only exten<;l downward 

to the 600-foot level. Below this depth the mineralization is still seen, but it becomes less 

and less until on the 1,000-foot level the vein is scarcely recognizable and can only be traced by 

reason of its passage through the quartz porphyry. The only mineralization seen on this_ 

level is at the extreme western end, where there is a lens of pyrite 25 feet long and 2 feet wide. 

The mine workings show that the country rock is crossed by three of the rhyolite porphyry 

dikes. The one -n~arest the shaft has a width of 10 to 15 feet .and is cut by the vein on the 

upper levels. A second dike lies some 35 feet to the south of this and has a width of 30 to 

35 feet. A third dike lies about 50 feet ~outh and has a ·width of 8 to 15 feet. These three 

dikes have a general northwesterly course approximately parallel to the vein. They are well 

exposed on the 1,000-foot workings in the crosscut from the shaft.· 

In general, the vein has been disappointing and unprofitable below the 500-foot level. 

A connection has been made westw~rd with the High Ore mine, but the only ore extracted in 

recent years has been by men working it on a lease who weJ;e therefore able to mine small ore 

b~dies that were unprofitable when the· property was worked on a large scale. Fault veins 

occur in the mine and intersect the Modoc vein at a slight angle. Three small parallel veins 

are cut on the crosscut on the 600-foot level. One of these veins has been drifted on, but has 

not shown any pay ore. On the 700-foot level the drift follows a fault slip 'in which a zone 

of very rich ore extends for 40 Jeet east of the main crosscut. This ore shoot is nearly vertical, 

and the ore is composed of bornite, with quartz and pyrite. Another well-defined shoot of 

ore extends downward from the 600 to the 700 foot level, being well exposed on the twelfth 

floor above the 700-foot level, where it. has a width of 10 feet and consists of bands of pyrite 

and chalcopyrite, bordered on each side by a 2-inch _seam of rich copper sulphides, separated 

by 2 inches of gouge from the country rock. 

In this mine the rhyolite p_orphyry contains numerous inclusions of granite which show 

no melting or other evidence of assimilation and effectively prove the intrusive nature of the 

porphyry. 

REINS COPPER CO. MINE. 

The Combination vein, worked by the Reins Copper Co., in the claims lying directly east 

of the Leonard and Minnie Healy mines, had been developed to. a depth of 800 feet in 1904. 
, 

MINES NORTH OF MEADERVILLE. 217 

It is a fault fissure, showing 7 to 8 feet of clay and crushed vein matter, with an 8-inch streak 

of high-grade ore, consisting of glance and bornite, with an abundance of native silver in 

curly wires and mossy masses, lying in fractures and in nests in the crackled copper sulphide. 

In general, the ore of the vein carries secondary bornite and glance, with more or less zinc 

bleride, but the streak of rich ore just noted, which lies along the hanging wall, also has curly 

crusts of chalcopyrite, w)lich in this connection are regarded as accompaniments of the silverbearing solutions. The vein also holds much curly quartz, with crushed and recemented vein 

matter, the quartz of the latter type carrying specks and stringers of copper glance and a 

little pyrite. The vein filling shows the best example seen in the district of the replacement 

of crystalline pyrite by bornite. The .pyrite occurs as tiny cubes and crystalline aggregates 

lying in a n1atrb: of. yellow clay and shows the various stages of replacement from the underlying pyrite to the solid bornite; · 

On the 400-foot level a 65-foot dike of quartz porphyry .is cut at' a distance 9f 100 feet 

north of the shaft. This appears to be east of the Rarus fault. · 

On the 800-foot level, at 35 feet north of the shaft, a 7 to B foot ledge is cut. Samples 

taken from an 8-inch streak of frrst-class ore showed glance fractured and with curly native 

silver particles scattered all over the fractured face. The grains of crystalline pyrite scattered 

through .the waxy yellow clay showed a remarkable replacement by bornite. The ore shows 

glance and bornite, with some zinc. The hanging-wall streak has curly crusts of chalcopyrite 

ore .. 

The second-class ore of the Reins vein is a rather curly quartz, with crushed and recemented 

quartz carrying glance in specks and stringers and but little pyrite. 

SUNSHINE MINE. 

The Sunshine n1ine is located at the head of the gulch west of the Modoc mine. The shaft 

is 300 feet deep. A vein, seen on the 100-foot level 20 feet south of the shaft, r_uns east and 

west and dips south. It is small and shows the usual characteristics of a copper vein; 

MAT MINE. 

The Mat 1uine lies immediately north of :Meaderville, a few hundred feet north of the eastward extension of th~ :Modoc mine. Its career has been somewhat erratic; it has been worked 

and abandoned; worked again, and again abandoned. At the 'time· of visit the shaft was 

400 feet below the surface, and all the ore came from the lowest level. The country rock is 

basic quartz monzonite, i'esembling that i:p. the mines east of Silverbow Creek. 

On the 400-:-foot level a cross.cut 50 feet south from the shaft encounters two veins; the 

first, which runs 16 feet fi·oin the shaft, is the mainstay of the mine and has be,en drifted upon 

extensively. Beyo.ncl this in the crosscut tlie granite is greatly altered, decomposed, and profounclly shattered. Along these fracture planes a certain amount of vein material has been 

developed,. whether by mechanical or chemical processes it ·is not possible to say. At one. 

place this concentration was so marked that it has been considered to constitute a vein. The 

two veins continue for 300 feet, where they unite; they also unite 50 feet above the crosscut. 

To the east but one vein has been found, and this abruptly dies to a clay wall, carrying little 

or no vein 1ninernl. . . . 

'"!''he vein throughout its course is somewhat erratic. At the west end the dip for 200 feet 

from the surface is to the south; below this.it is reversed to the north at an angle of 70°. Midway . 

. between the Adelaide shaft and the Mat shaft the vein is as crooked as a squirming snake; at 

the Mat shaft the clip is persist~nt 80° S. The width of the vein varies somewhat; it averages 

4 feet and in few places exceeds 10 feet. The· vein materials occur in long, narrow lenses with 

a vertical extension of never more than 40 feet, and a horizontal length varying up to 100 feet. 

In the eastern end of the workings immediately over the crosscut from the main shaft the 

north wall con·sisted of altered granite; adjoining ·this was a zone of shattered granite, highly 

altered, containing stringers of ore and quartz 15 inches in width; succeeding this was a 7-inch 
218 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

band of very zincky ·ore running high in silver and low in copper. Adjacent to this was an 

irregular 4-inch band of manganese spar, extremely pure but rarely solid; and succeeding this 

was an 18-inch zone of altered granite containing numerous veinlets of sulphide minerals. Last 

came a 2-inch seam of clay lying on a footwall of profoundly altered granite. Constantly associated with the band of manganese spar ·was a threadlike seam. of clay. The alteration in the 

wall rock at this point extends not more than 12 inches on either side. of the vein. 

At the point of junction of the two spurs of this vein, 20 feet above the latter, the vein 

is 3! feet wide and dips 85° N. The south or footwall granite was absolutely fresh; succeeding 

this was a 4-inch band of rhodochrosite and clay; next a 6-inch irregularly defined band of 

siliceous ore; then 1! feet of ore composed largely of iron and copper pyrites and some bornite; 

overlying this a 1!-foot band of altered, broken, and sheared granite; and, finally, a l-inch clay 

seam, immediately underlying freshgranite. The country ro.ck had not been attacked by the 

mineralizing agents, differing in. this from that in the vein section at the eastern end of the 

mine. Both walls showed distinct and strong seams of clay, and examination showed them to 

be polished and faintly striated. It seems almost certain that the vein has been greatly changed 

from its original condition by physical rearrangement of the minerals of both the country rock 

and the vein. 

Farther west the drift has been run in the hanging or north 'Y·all for a distance of 50 feet; 

subsequent work has been through a crosscut 20 feet to the S()uth, and then to the west indefinitely. 

The crosscut to the south has developed two walls, one at either end, in comparatively 

fresh country rock, the immediate zone being occupied by. profoundly altered and broken 

granite, interspersed by numerous nonp-ersistent seams of vein material; in one case almost 

entirely quartz, in another almost ·entirely chalcopyrite or pyrite.· On the main south wall, 

which her~e is the footwall, one of these veins attains a maximum width of 12 inches. On the 

300-foot level a crosscut, now inaccessible, was extended to the north 100 feet and cut an additional vein. 

The most striking feature of this mine is the association of its minerals. At the eastern 

end is tetrahedrite, and consequent~y a high percentage in silver, but the amount of c~pper 

is not sufficient to warrant its removal. Associated with this is a certain amount of sphalerite 

and rhodochrosite, minerals characteristic of the silver veins. At the western end the per-

·centage of copper is high, and the silver is in the ratio of the .northern copper mines. The 

copper minerals are chalcopyrite and bornite. Th~ vein minerals are, in the order of their 

abundance, pyrite, quartz, sphalerite, chalcopyrite, bornite, rhodochrosite,. and tetrahedrite, 

an association not to be expected in a typical copper mine. The mine, then, is remarkable for 

the irregularity and nonpersistence of its ore shoots; the irregularity of the zones of alteration 

in the wall rocks, which in one place extend a number of feet on either side of the vein and in 

other places are entirely absent; and, last and most important, in the association of its minerals. 

ALEXANDER SCOTT MINE. 

The. Alexander Scott mine is immediately north of the West Colusa. vVork on it in 1906 

had not progressed to any considerable extent. On the 200-foot level a small vein was 

encountered north of the shaft. On the 400-foot level a similar vein was encountered, also 

north of the shaft. Thjs vein was in hard, fresh granite and within a few feet passed into a 

thin seam of soft, gray granite, impregnated with pyrite. There were a number of small cross 

faults, but none of them seem to have any large displacement. The ground should be well 

mineralized below. 

RARUS GROUP OF VEINS. 

DEVELOPMENT AND GENERAL CHARACTER. 

What may, for convenience, be called the Rarus group of veins is in many respects the 

most interesting, as well as the inost complicated ~etwork in the Butte district. The veins 

are usually continuously ore bearing, lie close together, and belong to two systems of different 
RARUS GROUP OF VEINS. 219. 

direction and age, in which the later veins fault the earlier ones, and all of them are cut and 

displaced by the Rarus fault. 

The veins of this group extend westward into the Anaconda ground, northwestward into 

the Mountain View mine, eastward into the Berkeley, and northeastward into the Minnie 

I-Iealy, Snohomish, and Tratnway properties. In all these mines the veins have been productive, 

and as their ownership has been a question of bitter litigation, thei1~ development and study 

has been unusually thorough, a large amount of work having been done to determine geological 

conditions, irrespective of ore development.. Fortunately this development-" legal development "-has proved of great economic value, new and formerly unknown ore bodies having 

been found. It has also shown that few of the veins have well-defined outcrops; that the complexity of structure, resulting from fauJting, have rendered continuous development necessary 

to determine the apex of any particular vein; and that many veins show a subfault apex. 

Briefly, a series of neady parallel northwest-southeast veins belonging. to the Silverbow 

system traverse an altered, sheeted, pyritized granite. Several east-west veins of the Anaconda 

system, including the Pennsylvania, oc.cur but do not cross the northwest veins. The Mountain 

View fault (Blue Vein system) cuts and displaces the veins crossed by it. It is parallel to the 

older (Silverbow) veins . in strike, but has a flatter 9-ip and is not continuously mineralized. 

The Blue Jay fault (Middle) vein of the Anaconda mine dips eastward toward this ground, and 

movement along this fault led to readjustment in the ground, producing new cracks, which 

run N. 30° E. All these fissures are mineralized, the later fault veins being, as a rule, workable 

only at depths greater than 800 or 1,000 feet, and the earlier veins losing their values at about 

that depth. The ground between the veins is highly altered and often plated, showing pyrite 

films along the shear planes parallel to the northwest veins and in a few cross veinlets; the 

inclosing rock also contains scattered grains of pyrite. The east-west veins and joints show 

as spurs running off into the walls of the northwest-southeast veins. This area is cut by the 

gr~at Rarus fault, the most interesting and important feature in this vicinity. 

Although 13 distinct and continuous veins traverse the Rarus area, practically no outcrops 

are recognizable. Railway cuts and trenches have cut the veins within 3 to 5 feet of the surface 

and have found them narrow and composed of rusty quartz. · 

The ore from the veins of the Rarus area varies considerably in character. In the Windlass 

and Enargite veins the high-grade ore averages about 9 per cent copper and 2 ounces silver per 

ton, and the low-grade ore varies from 3 to 3~ per cent" and 0.9 ounce silver The No. 16 vein 

(Blue Jay system), which is worked from the 1,100 to the 1,600 levels of the Rarus, yields 

high-grade ore, which carries 10 per cent copper and 18 ounces silver per ton, and low-grade ore; 

which averages 4 per cent copper and 8 ounces silver. The ore from the fault veins varies 

in hardness, yielding in concentration about 900 tons of soft ore to 550 of hard ore. · In general 

the ore mined in 1902 a~eraged 4 to 5~ per cent copper, and 3.5 to 5.5 ounces silv~r. In passing 

through the 1nill this is concentrated to a product holding 10.5 to 13.5 per cent copper and 6.8 

to 9 ounces silver. The silver loss in concentration is greater than the copper loss. As a 

whole, the high-grade ore derived fron1 the deep levels varies between 9.5 and 15.5 per cent 

copper and 6 to 8' ounces silver. 1 . . 

For the purpose of discussion the area in which the Rarus veins occur may be divided into 

three parts, one west of the Rarus fault, one east of it, and one between its walls. 

CORRELATION OF THE VEINS. 

In the areas w.est and east of the Rarus fault two sets of veins can be distinguished, one 

running nearly clue east-west (Anaconda system) and the other northwest (Silverbow and 

Blue Vein systems). The former includes the Iron and Powder veins, on the west side of the 

Ran1s, and the Berkeley, Flat, Enargite, and Cross veins east of the Rarus. In general the. 

northwest veins have a steep dip and regular course, and the east-west veins a flatter but 

regular dip. At least one of the northwest vei~s, the Mountain View fault vern, i~ a plane of 

1 '!'hose figures were furnished by the late George H. Robinson. 
220 GEOLOGY AND ORE DEPOSITS OF. BUTTE DISTRICT, MONTANA. 

movement along which fracturing and dislocation of the east-west veins has taken place, leaving 

shifted ends which were for a long time regarded as spur veins. The other northwest veins are 

old primary lodes, which do not, so far as proved, dislocate the east-west veins. The latter, in 

fact, appear to stop them, as is the case with the Enargite and Windlass veins. The relation 

of these veins to one another is shown in figure 91 (p. 202). 

sw. 

Rarus shaft No2 

FIGURE 102.-West wall of Rams fault, showing projection of intersecting veins; dip 42° SW. 

The veins 'of the northwest (Silverbow) system are the more important; they include the 

Johnstown (North Connecting) vein, which shows two branches on some levels; the Johnstown 

No.2 lying next to it; and the Pennsylvania No.8 farther south. The Mountain View fault 
' RARUS GROUP OF VEINS. 221 

vein is parallel to these but belongs to the Blue Vein system and is of later age and different 

character. East of the Rarus are the North vein (north branch of the Johnstown); the Windlass, correlated with the Johnson; the South, correlated with the Johnstown No. 2; and the 

Mountain View fault; others which are either not developed, or are not present to the west, 

are the 612 v.ein, the Snohomish, and the Snohomish diagonal fault (between the Windlass and 

the South). (See figs. 102, 103.) 

Of the east-west veins are the Pennsylvania No. 2, the Enargite, the Powder-Iron, and 

the Cross. · 

The veins and faults ~f the area have been broken and shifted by movement along the northeast Rarus fault. This is a double fault, having two thick; clay seams for walls, with crushed 

sw 

SURFACE 

\\~ \ ,~ 

\\ \ 

NE RARU5 SHAFT 

50 

60 

134 300 

250 

210 M.D 

350 R 

400 R 

450 R 

500 R 

• 600 R 

700 R 

..r 

\ 

\ 

\ 900 R 

FIGURE 103.-East wall of Rams fault, showing projection of intersecting veins; dip 54° SW. 

vein and country rock between. The faulting was normal, but oblique, with a northward shift 

of the hanging-wall block. Moreover the two walls are not parallel, but diverge in depth, so 

that the space between them increases. In the dislocation of the veins the portion of each vein 

between the Rarus walls has been broken by minor, subordinate faults parallel to the walls, 

and the net result of this step or distributed faulting has been to produce fiat ore bodies, as if 

the veins had each been bent almost at a right angl~, forming an elbow. 

In the Rarus ground the fact that on. some levels one could stope a vein up to the wall of 

the fault and, cutting through the 2 feet or so of clay, find ore on the other side, led some observers 
222 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

to believe the veins were everywhere continuous through the fault. As a matter of fact, however, none of the flat ore encountered in the Rarus ground was a part of the adjacent vein; 

.everywhere it showed a widely differing dip, disturbed orientation, and different characteristics. 

(See figs. 102, 103.) 

M.any of the veins show marked individuality, particularly the Winillass, the largest of 

the veins worked in the Rarus mine. By means of these marked individual characters, by the 

porphyry dikes, and by the aid of extensive drifts and raises, the correlation of the veins on each 

side of the Rarus fault·is now satisfactory. 

STRUCTURE. 

INTERRELATIONS OF THE VEINS. 

The relation of the older east-west veins (such as the Powder-Iron, Pennsylvania No.2, and 

Enargite) to the northwest veins-Windlass, Johnstown (North Connecting), and other parallel veins-is not everywhere clear, but the northwest veins are believed to be later and to 

interrupt and dislocate the east-west veins. Seemingly they cut off the east-west veins. Thus 

/ 

· the Enargite runs into the Windlass, 

N 

5 

· and if shifted by it should appear east 

of the latter, forming the Cross vein, 

which, however, lacks both the size 

and the characteristics of the Enargite. 

It is therefore regarded as possible 

that ·in this part of the Butte district the forces that produced the 

great east-west fissures of the district formed at the same time northwest fissures·, which were here dominant, and that the east-west fissuring shows only as cross joints or fissures between the master (northwest) , 

fractures. 

FIGURE 104.-Veins of Rarus area, east of Rarus fault. 

Throughout the Rarus ground one 

may observe slips and veinlets running off into the hanging walls of the 

veins, and these are commonly called spurs of the vein. Some corresponding .. droppers on 

the footwall side are seen, but it is not easy to correlate the seams; and faulting, though the 

easiest explanation, has· not been proved. · 

F4ULTING. 

In the Rarus area the true relations of the veins are difficult to depict, since three faults, 

the Mountain Vie'\v, the No. 16 (Blue Jay or Middle), and the Rarus are involved in the dislocation. Figures 86 and 91 give details of- the intersections.. The section given in figure 104 

shows that three veins join near the surface, viz, the Berkeley vein, the Enargite vein, and the 

Windlass vein. 

The Mountain View fault vein splits or branches into three lodes east of the Rarus fault. 

On the Pennsylvania 1,000-foot level it fOrms veins Nos. 11, 7, and 10 (named inorderfromnorth 

to south), disclosing that fact that the Enargite and the No.3 Pennsylvania veins are the same, 

and that two dislocated blocks occur between the No. 7 (Middle) fracture of the l\:f:ountain View· 

fault and the Nos. )0 and 11 veins. The No. 10 vein is a cru~hed zone replaced.by quartzpyrite and some enargite, and as it is well mineralized it hardly resembles a fault vein. No. 11 
RARUS . GROUP OF VEINS. 

vein shows but little, if any, mineralization in the Pennsylvania ground. No. 7·shows some ore 

in places; it varies in width and is locally no thicker than one's finger. 

· The deeper levels of the Rarus mine (below 1,000 feet) derive their ore supply from wholly 

different veins from those so extensively Q.eveloped in the upper levels, most of the latter being 

impoverished and unworkable at a depth of 1,000 or 1,200 feet (p. 226). The ch~ef supply comes 

from the vein known as No. 16, which is regarded as the eastern extension of the Blue Jay 

(Middle) ledge. It is, however, interesting to note that the deflection of ore along intersecting 

fractures, a feature observed in the upper levels, is here quite prominent, the principal systems 

along which ore has been made being N. 60° E., N. 60° W., N. 30° W., N. 80° W., and N. 80° E. 

The 1,100 and 1,200 foot levels show extensive development along these fissures. Thus, the 

1,100-foot level shows a S. 80° W. vein (the No. 16), which is strong and well-defined and has 

been extensively stoped westward to a point where it intersects a N. 30° W. fracture, whence 

it extends northwest to the Rartls fault. The S. 80° W. fracture continues, but is barren. 

~)' I 

~ 

~ 

Porphyry 

IP"l Veins F"eults 

l!~IGURE 105.-Plari of veins on l,lOD-foot level, Mountain View mine, aud 1,20D-foot level, Rarus mine. 

The No. 16 v~in is the principal ore producer of the 1,100 and 1,200 levels of the Rarus mine. 

Its course is N. 70° E. and its dip is 53° S. It is a distinct fault vein, varying in structure from 

a mass of mashed granite cut by interlacing clay seams with bands of glance and pyrite on the · 

footwall, to a vein 7 to 10 feet or more wide, of which 2 feet is pyrite, impregnated with glance. 

The displacement of the veins opened up in the Mountain View and Rarus mines by the 

No. 16 fault vein, which is itself displaced by the Rarus fault, is well shown on the 1,100-foot 

Mountain View level, ·which lies about 15 feet above the 1,200-foot Rarus level (fig. 105). In 

these workings the principal ore bodies are found as northwest veins, displaced by the ·No. 16 

(Blue Jay) fault, the shift varying from 20 to 60 feet to the east. West of the Rarus the No. 16 

fault dips about 50° S., and east of the Rarus about 65° S". The Rarus fault appears to contract where it crosses the No. 16, and in the broken ground lying between it and the Blue Jay a 

large. body of ore is found that appears. to have been form~d recently. The Rarus fault in 

crossing splits, one branch running nearly northeast and dipping 60° NW., and. the other branch 
. 224 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

turning nearly north, with a dip- of 45 ° W. and· producing a second dislocatinn of the northwest 

veins. 

The No. 14 vein lies on the footwall side of a rhyolite-porphyry dike. It is itself a fault vein; 

but of the· older Silverbow generation, to which the Johnstown (North Connecting) vein belongs. 

The displacement by the northwest-dipping Rarus fault, and by the southeast-dipping Blue Jay 

fault, is similar, which seems to indicate that the latter is an overthrust fault. 

A second fault fissure, parallel to the No. 16 (Blue Jay), lies about 250 feet to the north. 

But little development has been made on this fault fissure, and its relations to northwest veins 

is not known. So far as indicated by the workings, it does not ·fault them. The chief significance of the observations on this level lies in the fact that the Blue Jay is shattered by .the Rarus, 

and that the block between the intersections of these two faults is intensely shattered, indicating that down-seeping waters have filled this block of ground .with glance and enargite whose 

downward extension is limited by the plane of the Rarus fault. A detached, isolated portion 

of the No. 16 fault is found between.the two walls of the Rarus. 

In the Rarus min~ the No. 16 vein ~hows 6 feet of fault material. The veins displaced by 

it are two.· The southernmost, known as the No. 17 vein, is a hard quartz-pyrite vein, dipping 

from 85 ° N. to vertical; ·it has a width of 2 to 3 feet and seems only slightly enriched. The 

northernmost vein shows 1 to 2 feet of ore, but is lean and unworkable in the faces seen. It also 

is a hard and solid quartz-pyrite vein incased in granite and is not recognized westward. It 

dips 60° S. This same vein is cut on the 1,200-foot drift along the No. 16 (Blue Jay) fault, 

and in both instances the displacement is to the south on the hanging-wall side. The Rarus 

fault at this level shows 18 inches of tough blue clay, carrying pebbles. It is very clearly defined 

and readily traceable th~oughout the mine. 

DEFLECTION OF MINERALIZATION. 

The hypothesis of intersecting fissures with mineralization that follows one fissure line for 

some distance and then turns off to another accords with the facts observed on the Syndicate and 

Parrot lodes, where N. 80° W., and N. 80° E. fissures deflect the mineral channels, the forsaken 

line continuing beyond the intersection as a tight and barren crack. At the Rarus one can , 

recognize fractures coursing N. 60° E., N. 60° W., N. 80° E., N. 80° W .. , and N. 30° W. 

Where faulting has occurred ·and the fault is ore bearing, the ore along a N. 80° E. vein 

may turn northwest along aN. 30° W. vein; in many places only a barren crack continues the 

first vein, perhaps to become ore bearing again where the crack intersects another N. 60° E. vein. 

In the Rarus-Pennsylvania part of the district it has been found that ground in which the 

walls of drifts are coated by iron oxide or where much iron oxide occurs is uncongenial for ore. 

The altered granite from the crosscuts of the Rarus mine is streaked and banded by films 

of pyrite coated by black and sooty glance. These films occur in minute joints, too small to be 

noticed were it not for the mineral. The films vary from pure pyrite to pure glance according 

to the amount of· replacement; on joint surfaces in cross fractures between the pyrite films 

dendritic masses of sooty glance are seen, so it is evident that the glance is not entirely an actual 

replacement, but that the mine waters are depositing chalcocite directly. (See ·Pl. XVII, B, 

p. 204.) 

VEINS WEST OF THE RARUS FAULT. 

In the ground west of the Rarus fault half a dozen veins are worked in t)le Rarus and the 

Mountain View mines. The strongest are those of the northwest series, embracing the Johnstown or North Connecting (the most northerly vein worked which splits near the. Rarus into two 

branches), the Johnstown No.2 vein, and the Mountain View fault vein (called the Orange or 

South vein in the Rarus and :Micha~ Davitt trials). Farther south the Pennsylvania No.8 vein 

occurs and is extensively developed. Besides these four veins there are several small parallel 

veins which have not been worked. · 

All these veins extend eastward to the west wall of the Rarus fault, which cuts then1 off 

abruptly and in most cases brings the end of the vein against barren granite. 
RARUS GROUP OF VEINS. 225 

The veins of the quartz-pyrite series include the Cross, the Iron-Powder, the Pennsylva:u.ia 

No. 2, and others as yet unnamed. These veins are mostly lean and workable only near the 

Ran1s fault. 

NORTHWEST VEINS. 

JOHNSTOWN (NORTH CONNECTING) VEIN. 

The most i1nportant vein in the area west of the Rarus fault is the Johnstown (North Connecting) vein. It has a northwest course, parallel to the Mountain View fault. The vein is 

about 8 feet wide, and in the Mountain View has a dip of about 80° S. It is an old vein wh()se 

charactQr varies somewhat at different places, but is essentially an altered and partly enriched 

quartz-pyrite vein, without clay selvages or other evidences of faulting. Though not a fault 

vein it carries enargite, which is characteristic of the f!lult veins of the district. In the Mountain 

View mine the 500-foot drift on this vein at first shows no enargite, but going southeast enargite 

occurs more and more abundantly. To the northwest the vein is n~rrow, carrying from 16 

inches to 2 feet of ore,' lying against rather irregular walls of hard, pyritized granite, the vein 

'filling becoming progressively poorer iLlld more ~assive. The dip in tllis portion of the vein is 

72° S. To the southeast the vein becomes richer, and as it approaches the Rarus fault has been 

reopened and shows a good wall with selv~ge clays, though the values fade out before the Rarus 

fault is reached. · 

The Johnstown vein has a tendency to split, showing a number of branches. The apex of 

the vein is 30 feet wide, and the bifurcations begin in the Lloyd tunnel, despite whlch the vein 

is united and solid a few hundred feet beneath tills tunnel. West from the Rarus fault this vein 

has a dip of 47° to 55° S., changing finally to 70° S. at~ point 179 feet west. Toward the surface 

the dip becomes reversed and is northward. 

· This vein, though not definitely recognizable between the two fissures of the. Rarus fault, 

probably forms the Cyclone, a flat ore body; east of the Rarus fault it is correlated with the 

Windlass, wllich is the widest as well as most persistent and regular vein of the Rarus series. 

JOHNSTOWN NO. 2 VEIN. 

The Jolmstown No.2 is like the Jolmstown (North Connecting) vein and is parallel to it. It 

is a comparatively narrow vein, averaging 4 feet across, with one-half inch to 2 inches of ·clay on 

the hanging wall and with lenses 6 to 8 inches wide of quartz-pyrite ore, the latter coated by 

glance. The dip is 70° to 80°, being steeper to the west. It is developed by drifts on the 300 

and 500 foot levels of the ~1ountain View and St. Lawrence mines. The walls are distinct, but 

the footwall granite is plated by pyrite films one-fourth inch thick at intervals 1 to 6 inches 

apart. (See Pl. XXVII.) Where workable it shows 1. to 2 feet of ore. In the 509-foot Mountain 

View it has 6 inches of fault clay and 3 to 10 inches. of lean ore. The vein as a whole shows wavy 

walls, the vein widening out only to, narrow again along its course and showing many clay slips . 

that run across from wall to wall. Though parallel to the Mountain View fault vein, it is not 

seen in the south crosscut on the 500-foot level of this mine, and must pinch out. 

Between the Johnstown vein and the Mountain View fault vein the rock is a soft and white 

leached granite for 50 feet, then harder. It is cut by at least three small northwest veins, which 

have received no names. 

Eighteen feet south of the Johnstown No. 2 vein lies a parallel vein 12 inches thick and 

dipping 90°. Another east-wes~ vein about 30 feet north of the Mountain View fault is 6 to 8 

inches wide, with walls of sheeted granite. The vein dips 62° S. 

MOUNTAIN VIEW FAULT VEIN. 

The Mountain View fault vein and its relation to the Anaconda and Mountain View south 

veins are described elsewhere (p. 202). It is not important as an ore producer in the Rarus 

area west of the Rarus fault, but its eastern continuation, in the deep levels east of the Rarus 

fault, contains valuable ore bodies. · Its dip is nearly vertical and parallels the Johnstown vein 

90427°--~0. 74--12----15 
226 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

in the Mountain View mine; where it cuts off the Mountain View south vein it dips 70° S. and 

is quite uniform on all levels, but nearing the Rarus claim line and farther eastward it bends or 

arches and dips less steeply in depth than it does near the surface. 

PENNSYLVANIA NO. g· VEIN. 

The Pennsylvania No. 8 vein lies southeast of the Mountain View fault vein .. 

EAST-WEST VEINS. 

POWDER-IRON VEIN. 

The Powder-Iron vein is in two segments, separated by the Mountain View fault. 

PENNSYLVANIA NO. 2 VEIN. 

The Pennsylvania No. 2 vein (South ledge of the Anaconda mine) swerves northward in 

approaching the Rarus fault, near which it lies on the 

footwall side and parallel to a strong dike of the rhyolite 

porphyry; it is dislocated by the :Mountain View fault, 

beyond which it reappears as the Enargite vein. 

VEINS EAST OF THE RARUS FAULT. 

The area east of the Rarus fault is as extensively 

fissured as that to the west. Not only are the veins 

close together and netted by cross veins, but the rocks 

a~e plated, fissured, and thoroughly decomposed. 

This extensive shattering· has led to equally extensive mineralization of the ground, which has proven 

I'E--------7' wonderfully productive for a depth of 800 to 1,000 feet, 

below which the veins become l~aner and leaner and FIGURE 106.-Section of Windlass vein, face of 600-foot 

level, Rarus mine. Altered granite cut by streaks of finally unworkable. Other veins, however, appear in 

enargite, and pyrite coated by enargite. the levels below 1,000 feet; and the north-northeast fault 

veins, which are not seen in the upper levels, are especially productive. 

NORTHWEST VEINS. 

WINDLASS VEIN. 

The Windlass vein has been the most productive in the Rarus n1ine (fig. 106). It is a large, 

Well-defined fissure vein, varying in width from 3 to 40 feet, with an average of about 20 feet. 

It has been developed continuously to a depth of 1,400 feet and a length of 3,000 feet in the 

· Rarus, Berkeley, and Silverbow mines. It is the most persistent, regular, and liberally mineralized lode of the group. It lies south of the North vein, but in some places unites near the 

surface with the North, Enargite, and Berkeley veins, the last two of. which strike east-west. at 

an acute angle with the Windlass. In the deeper levels, 1,000 to 1,800 feet, the vein is lean 

and composed of quartz and pyrite, with little .or no glance or enargite; and even in the upper 

levels the ore yielded by this property comes from the .so-called No. 16 fault vein (correlated 

with the Blue Jay fault vein or Anaconda iniddle ledge). On the 1,200 and 1,300 foot levels 

of the Rarus mine the Windlass is a vein of white quartz, with patches and dendritic aggregates 

of enargite and glance scattered through it. ' 

The structure of the Windlass vein is particularly interesting on the 1,600-foot level, where 

it shows a shattering of the rock between definite walls and impregnation by enargite along the 

joint planes. These joints show the multiple fracturing commonly observed when a blo9k of 

rock is fractured by steady pressure-that is, they are conjugate fractures. 

Of the older veins the. Windlass seems to be the master fissure, and the east-west veins run 

up to it and appear to stop. Thus the South vein of the Rarus mine is not found beyond, though 
RARUS GROUP OF VEINS. 227 

calculation shows it to correlate fairly well with the Cross, only the latter does not come to the 

Windlass. The Enargite, the dislocated east end of the long, strong, and persistent Pennsylvania No.2 vein, appears to end against the Windlass, as also does the Berkeley. One can not, 

however, make a correlation· of the veins on both sides of the Windlass, as is so easily done with 

the Mount~ View fault vein, and the inference is that the Windlass vein is of the same age as 

the Pennsylvania, but older than the :Mountain View fault. The Johnstown (north connecting) 

vein is ~ndoubtedly the conti.nuation of the Windlass northwest of the Rarus fault, but is cut off 

.by the Blue Jay (middle) fault of the Steward series and ends. against the South vein of the 

:Mountain View mine. As this South vein parallels the Anaconda east of the :Mountain View 

fault, it seems probable that the northwest-southeast and east-west fissures were formed ~t the 

srune time and that they fault and d~limit each other. 

SOUTH VEIN. 

The South vein, which is extensively worked in the 210,450, 500, 600, 700, and 800 foot levels 

of the Rarus mine, merges eastward in the Windlass vein. West of the ·Rarus it appears as the 

Johnstown No.2, but may possibly be the Powder vein. On the 800-foot level of the Rarus the 

vein is wide an.d strong and carries 2 to 8 feet of solid enargite. 

BERKELEY VEIN. 

The Berkeley is a particularly interesting example of an earlier vein, fractured and faulted, 

and containing large 'blocks of the original vein filling, lying distributed somewhat irregularly 

through the fault clay, but not broken into the small fragments and bowlders· characteristic 

of fault veins generally. The vein shows well-defmed clay walls on both the north and south 

sides. The vein has a width of 6 to 8 feet bet,veen walls, but carries ore only in bunches and in 

the fragments just mentioned. It is worked in the deep levels of the Rarus mine (800 to 

1,600 foot) where it is an important ore producer. 

NORTH VEIN. 

The North vein is less regular than the Windlass. It lies north of the Windlass vein, with 

the Snohomish Diagonal, a narrow fault vein, between. The vein has a width of but 1~ to 2 

feet at the surface, but is 15 feet across where the sulphide ore begins and has an average thickness of 10 feet in the stopes. ' 

It has been worked for 600 feet vertically, but becomes narrow and lean a~ 1,0.00 feet. 

The dip is north for 300 feet beneath the surface, and then straightens up and becomes south, 

until it unites with the Windlass vein on the 900-foot level. On the upper levels of th~ Rarus 

mine (450 and 600 foot) the. vein (becomes lean and narrow as it approaches the Rarus fault, 

contracting to a 2-i?ch streak of quartz and pyl'ite inclosed in sheeted granite. Eastward it 

splits up and dies ·out 100 feet east of the Cross vein. · 

The 1,100-foot level of the Rarus ·mine shows a long \vestward drift on the North vein, 

which is from 1 ~o 2 feet wide and sh.ows rather lean values. This vein appears to cut off ·an 

east-west vein and several parallel streaks lying north of it. The drift passes into and through 

the Rarus fault; and the branch of the drift turning eastward cuts an east-west vein that is 

faulted and displaced by the No. 16 (Blue Jay) fault. 

SNOHOMISH VEIN. 

The Snohomish vein has been stoped in several levels in the Rarus mine, but is not lmown 

west of the Rarus fault, though the altered g:ranite north of the Johnstown (north connecting) 

vein shows a thin quartz-pyrite vein that may represent its westward extension. It is a wet·· 

vein, with well-defined walls of hard granite, showing spurs running off to the northeast. 

VEIN NO. 612. 

Vei:ri No. 612 is 3 to 4 feet wide and has irregular rolling walls of hard granite. It is a 

granite vein, consisting of crushed. rock, with a 2 to 4 inch streak of pyrite, enriched on the 

hanging wall by bunches of chalcocite ore. The vein averages 30 inches of 6 per cent ore, 

carrying 6 ounces of silver. · · 
228 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

EAST-WEST VEINS. 

CROSS VEIN. 

The Cross vein runs approximately east and west, its general direction being N. 80° E. 

and its dip 82° S. It is a fault vein showing 6 to H> inches of ·brecciated country rock and clay 

and some bunches of ore;'· but is seldom workable. It cuts and slightly displaces the North 

vein, ·a northwest fracture, and faulted veinlets of pyrite show the north wall to have a horizontal 

shift eastward of 10 feet. The vein appears to end at the Snohomish Diagonal vein (another 

northwest vein) and does not extend to the wall of the Windlass. Neither in character nor 

dip does it correspond to the Enargite vein. 

SNOHOMISH DIAGONAL VEIN. 

The Snohomish Diagonal is another small vein of the northwest series, averaging about a 

foot in thickriess but showing swells and narrowings along its course. It sho"ws fault clays 

with quartz-pyrite bands. The dip is 65° S. , The vein is well developed on the Rarus 800-

foot level. · '-

RARUS FAULT. 

IMPORTANCE. 

The Rarus fault is the most recent and in many ways the most important fault of the 

entire district. It cuts and displaces not only the veins of the mine from which it takes its 

name, but extends northward through the Leonard and Colusa mines and southward to the 

Belmont, and on its dip it cuts through the Anaconda lode arid its congeners. This, unlike 

other great faults of the district, is not mineralized, but it has played an important role in 

producing the great flat ore bodies of the Colusa, Leonard, Rarus, and St. Lawrence mines 

by its intersection with east-west lodes. 

An understanding of the Rarus fault is essential to the proper development of many of the 

mines, and no single feature of the structural geology of the district has been the subject of 

greater or more bitter controversy. In 1896, when the district was first studied, this fault was 

clearly recognized by the geologists of this Survey, but a few years later its existence, at least 

as a displacing fissure, was strenuously denied by many witnesses in the celebrated Rarus lawsuit. 

Time and the development of the mines of the district have shown that not only was the 

Survey's interpretation of the fact correct, but that faulting of the lodes is so common a feature 

throughout all the mines that no intelligent development can be planned without a recognition 

of the fact and its influence. GENERAL CHARACTER. 

The Rarus fault is known by mine development work for a distance of over 5,000 feet 

_along its course and to a depth of 2,400 feet vertically. Its apex is indistinct and can only 

·be recognized as narrow iron-stained streaks of indurated clay, but in underground development its presence is easily recognized, as it cuts off the veins crossed by it cleanly and.sharply. 

The deepest development of the Rarus fault is o~ the 2,200-foot level of the St. Lawrence 

mine, where it has a width of 125 feet, being cut by a drift 400 feet north .of the shaft. At this 

point it has a wall composed of rhyolite porphyry and of aplite .. It is noticeable that in the 

country rock there are many slips parallel to the Ranis and many others t~hat lie at right angles 

to the first set, cutting and displacing them; from this it is supposed that they are due to the 

"adjustment of the blocks (Mountain View system) and not to any fault movement subsequent 

to the Rarus. · 

The Rarus is a double fault, that is, it has two clean-cut and distinct fault planes, with 

broken and crushed material between. As these two fissures have a dip diverging as they go 

down, the space between them widens with depth, and the fault becomes one of increasing importance as the mines are deepened. 
RARUS GROUP OF VEINS. 229 

The width of the Rarus fault varies greatly from pla<?e to place, even at the same elevation; 

on the plane 5,000 feet above sea level, for instance, it varies from 30 feet to 300 feet. The 

east or foot wall is the more regular of the two fissures, the variable width being largely due to 

a curving of the west fissure. 

On the Anaconda 2,400-foot level the fault fissure is 40 feet wide, but on this level, as on 

the 2 20.0-foot the fissure is only a part of the broken ground which at this depth represents ' ' ' the fault. The Anaconda vein within the fault is here definitely -recognizable but is lean and 

ahnost valueless. · 

On the surface the two limiting fissures are from 15 to 40 feet apart. They have a general 

northeast course, with marlred local curving. The outcrop having been developed for legal 

purposes, is well determined in the Rarus and adjacent clain1s, and may be seen in the railway 

cut on the :h1ichael Davitt claim. Elsewhere it is recognizable with difficulty, though underground developnmnt fu::es its position within narrow limits. 

INTERI!'AULT FILLING.· 

. The walls are everywhere marked by seams of blue clay or by its.ox~clized and hardened 

equivalent, fron1 a few inches to 2 feet or more in thickness. The footwall. or east fissure is 

particularly well defined and sharp. 

T~e blue clay carries not only rounded pebbles of ore, quartz, pyrite, and glance, but also 

others of granite, aplite, and rhyolite porphyry, where these rocks are near by and are cut by 

the fault. The rock alongside of this clay is often striated, in some places slickensided, and 

many of the major grooves run downward at an angle of about 42°. The west or hanging-wall 

fissure is well defined and clear cut, shows clays and friction breccias, and sharply cuts off the 

vein. 

Evidence of movement may be seen along both walls and in the interfault mass. Parallel 

to the fault walls are many sympathetic or subsidiary fractures, some of which appear locally 

outside of the fault proper and have cut and slightly shifted the veins; others appear in the 

fault, bounding blocks of ore. · 

Within the fault walls is a mass of broken and crushed rock, which as a rule is more altered 

and softened than that outside of' the fault and which contains detached irregular pieces and 

blocks of ore that once forn1ed parts of veins but have been broken off and dragged fron1 their 

places. These deta~hed fragments have a disturbed orientation, being tilted and turned partly 

around. The large flat ore bodies appear to be a succession of blocks, a p·art of the veins broken 

and step-faulted by distributed displacement. They are never large and unbroken n1asses. 

The identity of the veins within the interfault n1ass is destroyed by the tilting and cracking. 

l\1or~over, the ground has been much shattered and serves as a water channel, so that granite 

and ore are altered and unlike the materials outside of the fault. 

Dll' AND DISPLACEMENT. 

1'he average dip of the east wall of the Rm·us, measured along the cut-off of the Windlass 

vein fron1 the surface to the 900-foot level, is 52° 44'; the average dip of the west fault, fro1n 

the surface to the 900-foot level, is 44° 49'. · 

The total displacement of the Rarus fault on the 500-foot level of the Michael Davitt appears 

to be 200 feet to the north and 230 feet vertical. The hinge point of the interfault blocks 

appears to be the 1,100-foot level of the Rarus. In the Rarus mine the country west of the 

fault has gone down 210 feet on the clip of the fault, and probably moved northward 195 feet 

horizontally. The slip is not normal to the strike, but inclines to it at 42°. · 

There is some doubt as to the amount of tilting of the hanging-wall block (i.e., the scissors 

movmnent along the fault) of the Ranis fault. In the Pennsylvania mine the displacen1ent 

along the Ranis fault seems gradually to lessen. At the 600-foot levels it is well marked, is 

much less on the 700, still less on the 800, and practically lacking on the 1,200. 
230 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

In the St. Lawrence mine the Rarus fault is steeper and has a greater throw in. the upper' 

levels than it has at a depth of 1,600 feet or more. On these deep levels the two bounding or 

wall fissures are no longer distinct, but the fault has split up into many slips, though in general 

the foot-wall fissure limiting the fault ground is well defined and persistent. The average dip 

is about 30°, but varies in each slip. The 1,600-foot level of the St. Lawrence shows six welldefined fissures composing the fault, and the same flat· ore bodies are found here where the 

Anaconda lode is faulted by the Rarus as are fou~d in the upper levels of. the Rarus mine, notably the 450-foot, and in the workings of the Leonard mine, where the Rarus fault breaks through 

the Colusa, Gambetta, and Piccolo veins. The progressively western pitch of the ore bodies is, 

of course, due to the northwestern dip of the fault, combined with the southerly dip of the vein. 

In some of the cross sections constructed for use in court the ore bodies are marked as passing 

downward through the Rarus fault, without deflection, but in each case where development work 

has been done to prove the actual conditions, flat ore bodies have been found, so that there 

seems no reason to doubt that the explanation here given is approximately correct. On the 

other hand, it must be remembered that there are numerous northwest fissures which cut through 

. the ground; further, in the Leonard mine there is an intermediate vein fissure, with a course 

of N. 45° E., which corresponds to the Rarus fault but has dips of about 45°. As the Rarus 

cuts all the veins of the camp, including postmineral faults like the Blue, Mountain View, and 

others, the resulting structure is very complex and an exact matching of the .veins can not be 

obtained. ORE BODIES. 

The area between the two fault walls contains workable ore bodies of great value, not only 

in the Rarus ground, but notably northward in the Leonard-Colusa ground and in the deep 

levels of the St. Lawrence mine. 

North of the Rarus mine the Rarus fault, in passing through the Leonard ground, undoubtedly cuts and displaces the veins. This is well shown in the upper levels, where in passing 

through tl:le Colusa vein it has produced a flat ore body, due to a distributed faulting, by which 

the Colusa vein is spread out in a series of blocks arranged in steplike form. On this assumption 

it was reasoned that a similar flat ore body should be found in the immediately contiguous 

veins, and to prove this exploration work was started on the Piccolo Discovery. The· wo.rk 

proved successful, the 600-foot crosscut encountering a streak of ore which was found to correspond in position and in shape to the flat ore body whose existence was demanded by the 

theory. The ore is solid enargite, but it .is crushed and not hard like the ore of this character 

in unbroken veins. The block is, however, not brecciated; though mashed granite and clay, 

clearly fault matter, occur above and below it, the ore itself does not appear to be so badly 

broken. 

South of the Rarus area, in the Silverbow area, the fault does not interrupt the continuity 

of the ore, though it shatters and step-faults the vein, flattening it on the dip and changing its 

course on its strike. 

VEINS OF BUTTE FLAT. 

DEVELOPMENT. 

Between the prodtictive copper area and the high mountain ridge of the continental divide 

on the east lies t4e Flat, a broad, nearly level valley bottom draine~d by Silverbow Creek. 

The copper veins are mined up to the western borders of this Flat and . in the Silver bow mine 

out under it, but their eastward extension across it has not been established, though much 

prospecting has been ·done at many points. As early as 1896 the Atlantic shaft was sunk at a 

point almost due east of the Colusa mine and by 1900 a number of other shafts l).ad been sunk 

in the same region. Those known as Butte & Boston shafts Nos. 5 and 7, together with the 

workings of the ·Ella mine, situated in the Flat east of Meaderville, showed that veins exist in 

this area, but did not reveal any that were profitable. The more extensive cl,evelopment of the 

Pittsburg & Montana Copper Co., which included two shafts 1,200 feet deep, with winzes down 

to 1~450 feet and over 25,000 feet of underground crosscutting and drifting, showed the e~stence 
VEINS OF BUTTE FLAT. 231 

of several veins with workable bodies of copper ore that do not extend upward to the surface. 

Other companies owning ground in the surrounding section have sunk deep shafts, especially 

along its eastern border, at the base of East Ridge, bu't though numerous small quartz-pyrite 

veins have beep. cut and, a large number of fault fissures founq, no large ore bodies of commercial value have been deve'Ioped. 

Owing to the thick mantle of debris filling the Flat, prospecting has been both difficult and 

costly. In the Atlantic shaft this "wash" is nearly 500 feet deep, a log being found 480 feet 

below the surface. The saturation of this debris by water has made shaft sinking extremely slow 

and troubl~some. On the foot slopes of East Ridge conditions are not much better, as the wide 

north-south fault 'zones found there are filled· by crushed and ·altered rock; that, requires close 

tin1bering, as the ground is loose and dangerous. 

PITTSBuRG & MONTANA PROPERTY. 1 

The Pittsburg & ·Montana property is the most important property of this area. In 

this n1ine the two upper levels of the south shaft show practically nothing of value,. In t4e 

other workings several veins have been found, three of which carry well-defined shoots of 

shipping ore. The lodes are not continuously ore-bearing, a condition predicated by the work-

, ings on the Silverbow n1ine. 

The veins developed in this property belong to the three systems, the Anaconda or quartzpyrite system, a northeast ,fault-vein system, and the Blue or northwest systmn. 

The Donner is a lean quartz-pyrite vein,. having a course of N. 40° E., and a steep northerly 

dip (80° or about 50 feet in 200). It is developed by drifts and stopes from above the 1,000-foot 

level down to the 1,350-foot level, showing a mean of 3! feet, with extremes of 1 to 6 feet in 

thickness. On the 1,350-foot level the vein is 12 inches thick at the winze, and 7 feet wide 

at the face of the drift. The ore shoot is 135 feet long, the vein being lean beyond the shoot. 

The ore contains enargite and glance, the shoot averaging 5 per cent copper and 13 ounces of 

silver as n1ined. 

The Reed vein. courses N. 65 ° W. and dips _north. It is developed from the 500 to the 

1,200 foot level, but is low grade. 

The Rossell and ~1otherill veins are nearly parallel fault lodes 500 feet apart, which cut 

off the others. The Rossell courses N. 60° E., and dips steeply north, with an average thickness of 3 feet, varying from 1 to 11 feet along the drift. It has been stoped from 1,200 feet 

up, the ore shoot being 400 feet long on the 1,200-foot level. The Motherill vein runs N. 45° 

E. and varies from 2 to 6 feet in width, averaging 3 feet. It .shows an ore body 150 feet long, 

developed from the 1,000-foot down to and below the·1,200-foot level. 

ATLANTIC MINE. 

'rhe Atlantic shaft is between the East Ridge and the town of ~1eaderville. The shaft 

was sunk to a depth of 600. feet by the Boston & ~1ontana Mining Co. in a search for the supposed eastward continuation of the veins of Anaconda Ifill. The granite bedrock is covered 

by 400 feet of slide material and valley wash. On the 600-foot level a crosscut to the·south 

9o feet long shows three small veins, the most northerly of which has a general southeast 

course and stands nearly vertical; its maximum width is 4 feet. It has been drifted upon to . 

the east for 75 feet and throughout was found to be a typical quartz vein, s~udded with irregular· 1nasses of chalcopyrite and pyrite. As much as 4 per cent copper and 15 ounces of silver 

to the ton have been found in portions of this vein. South of this vein the crosscut has been 

extended a short distance, but the two veins encountered are extremely small and without 

value.· A crosscut has been extended 30 feet north, ·at which distance a vein 2 feet in width 

was encountered. This. yein, like the more southerly ones, is a lean pyrite-quartz lode. 

BUTTE & BOSTON NO. 7 MINE. 

The Butte & Boston No. 7 shaft was sunk 410 feet by the Butte & Boston Co. in a search 

for the eastward extension of the . copper veins. According to the mine foreman, the shaft 

was sunk through wash for 140 feet ~efore reaching bedrock. At 200 feet down it cut a small 

1 Since this report was written Important discoveries have made this mine a large and profitable producer. 
232 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

vein of iron-stained quartz 6 to 15 inches wide, running N. 60° E. and dipping 50° N. This 

vein was explored by a west drift, which was closed at the time of visit. The vein has an 

aplite hanging wall, the rock being cracked and the fractures coated with red iron oxide. The 

footwall is silicified granite. 

In the shaft, on the 400-foot level, which was being cut at the time of visit, the rock is 

fresh granite, cut by fractures running in all directions. The largest seen is a small clay seam 

15 feet north of the shaft, dipping 60° S. and coursing N. 70° E. On the west side the rock 

is a pyritized granite, cut by a northward-dipping clay seam. 

VEINS OF EAST RIDGE. 

CHARACTER AND DEVELOPMENT. 

The mountain ridge commonly called the East Ridge, which forms the e~stern wall of 

Silverbow Flat, is seamed by many mineral veins, which are commonly believed to be the 

eastern continuations of the copper veins of Butte. The veins can not, however, be traced 

across the Flat, as this is covered by a deep layer of .debris and mountain waste; moreover, 

the Continental fault, with its sympathetic fractures, has so displaced the ground on each side· 

of it that no direct connection is probable. The evidence now available indicates that the 

Butte copper belt does extend eastward beneath the Flat, but that the great veins worked in 

the Anaconda and Rarus areas have lost their strength and are not definitely recognizable. 

The development work since 1900 has shown that numerous quartz-pyrite veins, carrying very 

low values in copper and seldom more than 2 feet thick, traverse the lowest foot slopes of the 

mountain ridge, and that these veins are cut by veins of the Blue Vein series and are truncated 

· by broad and barren north-south fault zones. In the Pittsmont ground shoots of high-grade 

ore have be~n found; elsewhere the deep workings have not (up to 1906) developed ore enough 

to pay for working. 

In the East Ridge proper, east of the Continental fault, the veins are unlike those of the 

copper belt, but greatly resemble those of the Butte silver district. They are quartz-filled 

fissures, carrying silver minerals and some copper ore. At the I-Iomestake and Clinton mines 

considerable chalcocite was found, Lu t it occurred in the central or open and vuggy part of a 

vein of comb quartz containing rhodochrosite and some tetrahedrite. Elsewhere development 

work on many veins has failed to show any extension of the Butte copper veins. Though the · 

mineralization of the East Ridge has not as a whole proved remunerative, there is no sound 

reason to assert that this area contains no good properties. It may safely be said, however, 

that. the veins show no evidence of beGoming copper-bearing in depth. As the Continental 

fault depressed the Butte area proper, the veins of this East Ridge must be far more deeply 

eroded than those of Butte. 

The entire East Ridge area has been staked out in mineral claims, and more or less prospecting has been done. The most extensive work appears to have been cnrried on along the lowest 

part of the ridge, which lies between the gulches which score the mountain front. 

Many of the surface showings along these claims are more attractive than any on the grea:t 

mines across the Flat. The granite is stained and impregnated with copper oxides and silicates 

over considerable areas near the Altona, J\1ontgomery, .and Bertha claims, on the ridges on 

. either side of the. Columbia Garden gulch. V einlets and, bunches of cuprite and chrysocolla · 

occur, and small shipments of rich oxide ores have been made from several claims. It has been 

found, however, that this mineralization is due to ·alteration and leaching of small and most1y 

lean veins and, mainly, of the copper so generally distributed as chalcopyrite through the granite 

beneath the limit of oxidation. · The lack of pyrite and the presence of chalcopyrite appear to 

be unfavorable conditions for large accumulations of copper ore, and this despite the fact that 

the dark a_nd fresh granite contains an average of nearly 1 per cent copper. 

The entire foothill area was actively prospected in 1896, but the lack of favorable results 

led to the gradual cessation of work until 10 years later, when the high price of copper, the 

Pittsmont discoveries, and the importance of the fault veins as ore producers all led. to active 

prospecting work. Of the earlier work that on the Alt~na was the deepest and most important. 
VEINS OF EAST RIDGE. 233 

ROCKS. 

The rocks resen1ble those of the Bluebird silver area rather than those of the Anaconda or 

Syndicate hills. They show large quantitltes of aplite, with the usual associated darker transition to Butte quartz n10nzonite, and numerous quartz and pegmatite segregations, whose 

presence has given rise to false hopes, as the quartz is generally supposed to be vein quartz, 

but is really local, not mineralized, and similar in occurrence and origin to pegmatite. 

Wherever aplitic granite occurs in this ridge, copper seams appear. The silver values are 

rather high, being 2 ounces of silver to 1 per cent of copper, whereas generally the proportion is three-fourths OUJ?.Ce of silver to f per cent of copper. 

The aplite fr01n near Columbia Gardens is the typical aplite of the Butte district, showing 

n1ore or less alteration and no biotite. This rock is cracked and the fissures filled with malachite, 

with cuprite in the center. No replacement has taken place, and it is evident that the oxidized 

n1inerals form actual cavity flilings. This is readily understood, as in the western part of the 

Butte district the aplite of n1any of the masses crack into a network of fissures, similar to mud 

cracks, which are believed to be due to the strains developed in the weathering of the rock. 

The derivation, however, of this n1alachite and cuprite is difficult to explain, as it must come 

from the surface. The n1ost reasonable hypothesis is that the chalcopyrite-bearing granite on 

the higher hillsides is decomposed and that solutions traveled along the base of the disintegrated 

1nantle lying above the solid rock deposited their burden on encountering the cra<?ks in the aplite. 

No reason, however, for precipitation in these cavities is apparent in the specimens, as there 

is no evidence of replacement of the rock and none of the presence of pyrite. It is, of course, 

possible that the seams represent oxidized, enriched, and subsequently reoxidized pyrite seams. 

The rock from the Clinton n1ine consists mainly of aplite. The dump heap shows s01ne 

granite, which is nearly normal in character, but has the porphyritic tendency. and facies so 

ovten observed in the borders about aplitic n1asses. 'The biotite in the rock gives ~t a porphyritic 

appearance. 

MINES. 

SIX O'CLOCK MINE. 

The Six o'Clock n1ine is situated on the foot slopes of the East Ridge, just below the Great 

Northern Railway. The old shaft was down 1,000 feet in 1907. At 400 'feet down a crosscut 

south 100 feet long traversed several belts of alt.ered granite, associated with which are numerous 

stringers and veinlets of n1anganese spar. Studies under the microscope show an apparent 

ratio between the an1ount of n1anganese and the ferromagnesian minerals, especially the biotite. 

On the 1,000-foot level crosscutting showed several veins, which have not been examined, but 

are said to be s1nall east and west quartz-pyrite veins, cut by lar~e northerly trending fault 

fissures. 

NORTHWESTERN 1\II~E. 

The Northwestern mine. is situated just east of the Butte ·quadrangle, at the 1nouth of the 

canyon .which opens fr01n Elk Park. When visited the shaft was only 300 feet deep, with a 

crosscut running 25 feet north and an equal distance sot1tl1 fr01n its botton1.' In sinking the shaft 

two east-west veins were cut, dipping steeply to. the north. The granite is of a transition type, 

rich in ferrOinagnesian minerals and plagioclase and rather n1ore coarsely crystalline than the 

conunon rock. It is co1nparatively fresh and unaltered, the zone of decomposition extending 

only a foot or so fro1n the veins. Twenty feet north of the shaft, on the 300-foot level, a 6-inch 

vein was cut, which carried a large an1ount of pyrite and some chalcopyrite, fresh and massive. 

Several crystals of quartz an inch in diameter were e~sily broken fron1 the mass and left a mold 

which showed· every detail of their shape. The pyrite is everywhere distinguishable from the 

chalcopyrite, the lines of division between the two minerals being sharp and the contrast in color 

Inarked. The iron pyrite occurs in more or less crystalline masses in the vein and in the 

country rock inclosing the vein for as much as a foot, possibly 2 feet, away from the veins. 

This pyrite is closely associated with the ferromagnesian minerals of the granite; it is observed 
234 GEOLOGY AND ORE DEPOSITS OF BUT';['E DISTRICT, MONTANA. 

to occur along cleavages in the hornblende and biotite and in regular masses within these crystals; it may therefore be either a replacement of the ferromagnesian minerals or a reduction 

from them, as the minerals associated with the decomposed ferromagnesian minerals and the 

pyrite are those formed by the decomposition of the biotite, hornblende, and augite, it seems 

probable that the iron of the pyrite at one time belonged to the iron-bearing silicates. 

On the surface of this mine two veins have been found. Both of these have an east-west 

course and a northerly dip; this _last, however, is not persistent and in all probability averages 

vertical. 

Nearly every joint plane or fracture surface in the granite-and there are many-carries 

some form of ·copper. In many this is c;halcopyrite, though much· native copper is found, 

everywhere in thin plates, dendritic in form and showing a very weak tendency to crystallize. 

CLINTON MINE. 

At the Clinton mine the vein is developed by aN. 80° W. drift. The vein is wet but only 

contains ore at intersections with N. 80° E. ·fissures. The canyon itself is eroded along a fault 

fissure. 

HOMESTAKE MINE. 

The Homestake mine has the greatest development of any of the East Ridge properties, 

but it has been· full of water for many years. Good ore is said to occur on the 500-foot level 

1,300 feet belo~ the Clinton tunnel. The ore is tetrahedrite and glance and is found in welldefined quartz veins, whose general character more nearly accords with that of th~ silver than 

that of the copper veins. 

The Homes take mine is situated nearly a mile east of· the Northwestern mine. Development work has· been carried on in a desultory way for a number of years; at first a· tunnel was 

run into the side of the hill, and granite, considerably altered, together with numerous veins of copper ore was found; subsequently a shaft was sunk on the side of the hill 75 feet above the tunnel. 

This shaft is 550 feet deep. From the shaft three veins have been develop~d, all of which 

have a general northwest and southeast trend. They are not more than 200 feet apart. The 

middle vein is the best developed. It stt~tnds nearly vertical. At the bottom of the shaft it is 

7 feet wide, ancl is composed of very white, hungry-looking quartz, which contains bunches of 

chalcopyrite, pyrite, and gray copper. Analysis of this ore yields 1 ounce of silver and $2 in 

gold.per ton, together with 4 to 8 per cent of copper. A number of tons of ore taken from this 

mine s~owed close association with the country rock, that is to say, the heart of the vein is 

composed of very low-grade quartz, and the walls of .the vein, both hanging and foot, yield a 

grade of ore which is valuable when concentrated. Studies of this ore und.er the microscope 

showed only small amounts of iron pyrite, together with some sphalerite, tetrahedrite, and 

quartz. The pyrite was apparently the first mineral to form; it is in crystals more or less 

rounded and is at times highly shatt'ered. Closely associated with it are quartz inclusions. 

The sphalerite is rich golden yellow in color, and shows a full development of octahedral cleavages. 

It is of later origin than the iron pyrite and than much of the .quartz. Gray copper (tetrahedrite) occurs plentifully, associated with chalcopyrite. In general it does not show crystalline 

outline, out, in the thin section studied, traces of a tetrahedron form were found. One' such 

cryst~l is composed in greater part of tetrahedrite, covered by a crust on two sides and by chalcopyrite on the others, as if the chalcopyrite.were a reduction from the tetrahedrite. 

BULL WHACKER MINE. 

The Bullwhacker vein shows well in the Bullwhacker discovery shaft, where the good ore 

is 5 to 8 feet wide and e·xtends down 50 feet west of and against a no!th-south slip. 

Above the 100-foot level the same ore body .was stoped, carrying 3 to 4 per cent ore quite 

like that of the Bertha claim. On the 200-foot level the values are too low to work, and nothing 

was found on the 400-foot level. It appea:r:s that this ore body is a concentration of material 
VEINS OF EAST RIDGE. 235 

leached out of the copper-bearing rocks and veins of the slope above the vein, and concentrated 

in this fault zone by absorption by the fault clays. 

· The same vein shows in the :Maggie Fraction, where a shaft 30 feet deep. at .time of visit 

showed good oxide and silicate ore on a north-south fault at the bottom of the shaft. A drift 

east developed a lean east-west vein, 3 to 6 inches thick. 

BERTHA GROUP. 

The Bertha group of claims, embracing the Bertha Fractional claim,· the P~;tcific, Copper 

Queen, Sarsfield, and Lillie claims, covers the gentle foot slopes of East Ridge, where it is cut 

through by Park Canyon, the deep cut by which the Great Northern Railway crosses the Continental Divide. 

These claims are traversed by several quartz-pyrite veins, having a general easterly course, 

and by north-south fault fissures and zones belonging. to the Continental fault series. One 

strong fault fissure in the Bertha claim can be traced at intervals in a northerly direction across 

the Copper Queen, Sarsfield, and Lillie claims. Southward thi~ vein crosses the Bullwhacker, 

Maggie, and probably the :Montgomery claims, but is disturbed by cross faults in the latter, and 

lost beneath rock debris or flood "wash." · 

BERTHA MINE. 

. The Bertha mine is situated on the foot slopes of East Ridge, north of the canyon leading 

to Columbia Garden. The workings show a wide fault vein, with a general north-south course, 

with workab,le ore 20 feet across. The development consists of a tunnel with a winze 50. feet 

deep, f.rom.the bottom of which drifts are run for 45 feet north and115 feet south. 

The ore body lies in the fault. It includes 20 to 25 feet of granite, cut by veinlets and 

stringers of copper silicates, oxides, and carbonates, etc., inclosed between well-defmed walls. 

The wall rock, which is impt·egnate.d for 1.5 to 20 feet fron1 the hanging wall, carries 1 to 2 per 

cent copper. 

The ore body is developed for 140 feet in length and for 120 feet in depth. Shipments of 

nearly 1,800 tons fron1 between the tunnel and winze levels gave 5.2 per cent copper. On the 

bottOin the ·ore carries but 2 to 3 per cent, and the south drift is part]y barren, showing that 

the ore is fringing out. Two east-west veins also outcrop. One o.f them, explored h}r drifts from 

the shaft, 200 feet below the surface, shows, a vein 6 inches to 3 feet wide, with a narrow stringer 

of ore running 6 to 30 per cent copper. 

The ore of the Bertha-Bullwhacker vein consists of crackled granite alqng a fault fJSsure, 

with nun1erous clay slips intercepting the rock. It consists of chrysocolla and 'tenorite, filling 

fractures and replacing the granite. The ore is acidic, carrying 80 per cent silica and about 

5.1 per cent copper. On the 100-foot level the ore body has been stoped for a width of 20 feet. 

The bulk of the ore is not a true fault breccia, but may be more fittingly called a mashed granite 

with the spaces fuled by waxy, solid chrysocolla. Part of the ore consists of block-]ointecl 

granite, in which the body of the rock has been altered and impregnated with chrysocolla and 

tenorite, both us fiJn1s along fracture planes and as patches replacing portions of the rock. 

About 2! feet of crushed fault matter is seen, but the bulk of the ore body gives no evidence of 

the fault and is not recognizable as true fault material. An east-west crosscut shows the character of tl~e walls, and. indicates that the impregnation. of chrysocolla fEtdes out gradually from 

the vein. The drift on the ore has a general course "of S. 10° E. 

LILLIE CLAIM. 

This claim shows a broad surface capping of limonite and iron-stained rock that forms a 

"blowout" connected with a fault vein that may be the extension of the Bertha. The gossan 

extends downward very irregularly, but as the shaft on this property is not on the fault, but 

west of the vein, nothing is determinable. The iron stain is apparently the work of an old 

spring, now dry, and shows no evidence of being true gossan. 

\ 

\ 
( 

236 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

SARSFIELD CLAIM. 

The Sarsfield shows the extension of the Bertha fault, and also another north-south fault 

vein carrying a little pay ore. The rock shows a peculiar transition forn1 between granite and 

aplite. It is, ~n fact, almost a porphyry, with fresh biotite,. uralitized hornblende, and accessory 

pyrite and molydenite, the latter forming a half-inch veinlet of quartz, marked by bands of 

molybdenite on each side. 

PACIFIC CLAIM. 

In the Pacific claim, which adioins the Bertha on the east, two north-south fault f1Ssures 

occur. The westernmost, or Pacific vein, appears to be parallel to and not far fro1n the Bertha. 

It has been developed by a vertical shaft to a depth of 399 feet, with drifts on the vein. Both 

the Bertha and Pacific fault veins extend northward, probably crossing the Copper Queen and 

Sarsfield claims. 

COLLEEN BA WN MINE. 

A crosscut tunnel on the Colleen Bawn property intersects two small east-west quartz.:. 

pyrite veins, which have been developed by drifts 75 feet long. The veins are narrow and show 

little ore and have no commercial value. 

EXEMPTION CLAIM. 

Two small east-west veins on the Exemption claim are cut by a tunnel and by drifts at a 

depth of 100 feet in a shaft 130 feet deep. The vein seen showed 6 inches to 3 feet of vein 

matter, and in the shaft is said to carry a foot of 10 per cent ore. Shipments or selected ore 

are said to have aggregated 26 tons that carried 12.6 per cent copper, 38 tons that carried 3.1 

per cent, and ·1 ton that carried 48 per cent. 

SINBAD MINE. 

The Sinbad mine lies south of the Altona, near the second canyon south from Columbia· 

Garden. When visited in 1905 it had a shaft about 500 feet deep, with levels at 410 feet and 

490 feet. The upperlevel shmved aN. 72° E. fault vein in rotten brown granite. The vein is 

soft, carries no values, and'ht~t little quartz. 

MONTGOMERY 'CLAIM. 

Considerable prospecting was done on the Niontgon1ery claim in 1906-7. · A shaft over 

100 feet deep, with crosscuts north, south, and west, was sunk, showing a fault vein 18 to 24 

inches thick, overlying a few inches of greenish granite, impregnated with copper. 

A cr:osscut was driven 282 feet west through more than 100 feet of altered white granite, which 

gradually changed to less-altered granite with fresh biotite, cut by 1 to 2 inch seams of aplite, 

and with aplite in the breast. A fault cut 74 feet fron1 the shaft ran aJmost clue north and 

south and dipped 42° W. A drift running south 30 .feet on this fault disclosed the cut-off end 

of an east-west vein on the hanging wall of the fault, and led to the discovery and working of a 

vein averaging 4 feet in width carrying 3 per cent copper. 

A north-south crosscut, 164 feet long, cut a fault zone running N. 45° W. The footwall 

slip dips northeast in the crosscut, but fa:J:ther west clips southwest, parallel to the hanging wall. 

Between the fissures the granite is broken, mashed, and altered and shows green spots, colored 

by chrysocolla and carrying 2 per cent copper. · 

· MAGGIE MINE. 

The l\1aggie.mine, which is situated on the :Maggie Fr~ction claim, showed, in 1906, a shaft 

30 feet deep, containing a distinct ore body of oxide and chrysocolla ore similar to that of the 

Bertha. This ore is cut off by a strong north and south fault, marked by clay and fault pebbles .. 
VEINS OF EAST RIDGE. 237 

An east-west vein, cut off by t~1is fault, runs through the center of the drifts. The ore body is 

about 20 feet wide. 

Although the :Maggie shaft is not over 125 feet from the Montgomery tunnel (N. 92° E.) 

and is on the direct extension of the Bullwhacker vein, the tunnel shows only dry and barren 

disi.ntegrated fault 1natter and granite. Throughout the clain1 quartz films and blebs of aplitic 

material are com1non; the quar.tz is probably largely magmatic, but is in part masked by silica 

relen,sed by sericitization of the rock. 

ALTONA MINE. 

The Altona mine is: situated on the slopes of the first canyon south of IIorse (or Columbia 

Garden) Canyon. The shaft is 360 feet deep~ and has a very heavy inflow of water, so that wlien 

the mine was pumped out the springs of the neighborhood dried up. The mine, at 200 and 360 

foot workings, has developed an east-west quartz vein, cut and displaced by north-south 

faults. This, the Altona vein, has a true east-west .course and dips 55° to 60° N. It varies 

from 6 inches to 3 feet in thickness and carries a 3-inch to 30-inch streak of ore, with 1~ per cent 

to 4 per cent copper. It has a persistent clay selvage which carries 1 to 3 inches of breccia, 

which cuts out the ore to the east. The vein is cut 92 feet north of the shaft, and is continuously exJ)osed for 230 feet. Ninety feet east of the north crosscut a cross fault cuts off the 

vein, which is recovered 25 feet to the north, but is again thrown by a second parallel fault, 

30 feot east of the first. These two faults are 10 and 15 feet thick respectively, run N. 10° E., 

and dip 65° and 70° W. They outcrop northward, an inclined shaft going down on one for 25 

feet or n1ore on the ~1acarona claim. The vein is recovered about 200 feet east of the faults. 

On the 360-foot level the Altona vein is cut 230 feet north of the shaft, and is developed by a 

short drift. It is fron1 2~ to 3 feet wide, but carries less than one-half of 1 per cent copper 

and only low values in silver. · 

Another s1nall vein less than a foot thick, cut by a south crosscut on the 360-foot level, 

carries 6 inches of 9 per cent ore, but is cut off eastward by the fault found.'on the 200-foot level. 

Ntunerous northeast a.nd north~vest clay-filled fault fissures are encountered. 

The granite in the vicinity of the Altona 1nine differs fron1 the normal rock of the district, 

appearing to be a transition fonn to aplite. In the specimens obtained fron1 this mine, both 

fr01n the surface and the deep levels, no pyrite was observed, but chalcopyrite is abundant· 

.both as dendritic· 1nasses on fracture surfaces generally, and in the deeper levels as particles 

disseminated through the rock and especially abundant in connection with the fresh or but 

slightly altered ferron1agnesian 1ninerals. Specimens of the ore from this mine show a banded 

quartz-pyrite vein filling 6 inches thick, separated fron1 the granitic wall rock by films of nlolybdenite, which material also impregnates the wall rock for one-fourth to 1 inch; accompanying this iinpi·egnation is a marked sericitization for an inch or n1ore fron1 ·the wall. The central 

portion of the vein shows comb quartz, with the -points of the crystals coated by glance. This 

structure is characteristic of the Clinton and I-Iomestake ores, and indicates that the Altona 

does not differ markedly from the other veins of this .portion of the district. 

IDA MINE. 

The Ida n1ine adjoins the Altol).a on the south, covering both sides of a ~all gulch debouching westward into the Flat. The property is developed by two shafts, on opposite sides of the 

creQk. The southern shaft was 110 feet deep when this property was visited in 1906, with 

levels at a depth of 40 feet beneath the surface, running 36 feet west and 32 feet east. The 

shaft and drifts are in aplite rich in n1olybdenite, resembling the aplite of the Altona mine. 

The ore shows tetrahedrite and chalcocite, secondarily enriching a quartz-pyrite vein filling 

{}arrying accessory galena and sphalerite; it is therefore a typical silver-vein ore. 

The mine workings disclose a s1nall vein, averaging less than 8 inches thick, running north-

·east and dipping northwest at a very steep angle (80°). · The yein filling is banded rhodonite, 

with streaks of ore-a normal silver vein. A second parallel streak, ~ inches thick, carries the 

quartz-pyrite molybdenite ore noted above, enriched by glance, etc. 
238 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MO~TANA. 

These veinlets are cut off and dislocated by an· east-west fault 4 inches thick, filled with clay 

and dipping 60° S. This fault shows·in the shaft. 

SCHWEITZER-MONITOR TUNNEL. 

The Schweitzer-Monitor tunnel is in Elk Park Canyon, midway between the Homestake and 

the Northwestern mine, on the north side of the gulch. It runs north for 1,500 feet. The first 

80 feet cuts aplite; succeeding this for approximately 200 feet is granite of the basic variety; 

· the n~xt 6 feet is composed of iron pyrite and decomposed granite; then from 286 to 400 feet 

the tunnel is i~ granite; next comes a 60-foot zone of intensely altered granite, containing many 

veins and veinlets, some of which carried as much as 5 per cent copper. As is common in· 

veins of this sort, iron pyrite is abundant. For 750 feet to 800 feet from the mouth of the tunnel 

granite was encountered; then a small .vein; next 300 feet of granite; then a vein 8 to 10 

feet in width; then 100 feet of granite; then a 3 to 4 foot vein, and finally granite to the breast 

of the tunnel, 1,500 feet in all. The veins are all parallel or nearly so, and their average trend 

is east-west. 

The first 30 feet of the tunnel follows a 3-foot quartz vein running N. 80° W. and dipping 

64°'S., with a 10-inch band of fault clay on the north wall. The second seam is a quartz-pyrite 

vein 2 feet thick, running N. 82° W. and dipping 82° S. The line between aplite and granite is 

indistinct. In the granite 80 feet from the aplite a vertical east-west 4 to 6 inch quartz-pyr~te 

vein is cut, and a few feet farther a 4-inch streak of quartz and rhodochrosite. At 730 feet from 

the portal a big northeast vein is crosscut. It is 11 feet wide, runs N. 65° E., dips 70° S., and 

looks fairly promising. Thirty-five feet farther in, an east-west vein (N. 80° E.), 5 to 6 feet 

wide, is cut~ This vein carries a 10-inch streak of ore that assays 13.3 per cent copper and 3.4 

·ounces per ton in silver; it dips 70° S. Beyond these veins the granite is hard and blocky to 

. the face of the tunnel. A lean northwest vein, cut at 320 feet from the breast, is 5 feet wide and 

dips 65° N. 

Though two veins have beeri cut, no drifting has been done to determine their value. It 

will be noted that the trend is similar to that of Butte. 

COLUMBIA GARDEN. 

The fault knobs back of Columbia Garden stand up in front of long, flat-topped spur 

ridges, largely of brecciated material, showing quartz and decomposed silicified granite. Where 

fr~sh granite occurs it appears broken and shattered. Some aplite is also seen. The Homestake and Clinton ore bodies occur in· this shattered rock. No rounded pebbles or extensive 

bodies of clay or breccia are, ho~vever, seen, and it is believed that the fault is a compound 

one of a distributed type, or possibly a very close sheeting. The breccia at the west end of 

the tunnel is slide rock and shows no definite, well-defined outcrop. 

Back of Columbia Garden the .Mountain Lion ledge shows a course of N. 65° E., and the 

rock is stained by manganese. Above the mine the granite is sheeted into thin slabs, the course 

of the joints being N. 10° E. and the dip 80° S. A seco-ndary summit south of the main top of 

theTidge is composed of aplite blocks, with flat veins of pegmatite having a dip of 19° W. and a 

course of N. 50° E. On the main summit, however, the sheeting isS. 10° W. and the dip 80° W.; 

the entire course is N. 30° W., with a dip of 70° S. A very promiment, closely sheeted area 

shows fractures running N. · 10° W. breaking the rock into thin vertical plates. 

The veins on the summit of the ridge between Elk Park and the Flat have a general eastwest course. The Major Burke vein, which is exposed in the first gulch south of Elk Park, 

has a course of N. 70° W. On the ridge southeast of the :Major Burke mine the vein runs N. 

70° E. 

The veins are typical silver-bearing fissure veins, showing manganese and comb quartz, 

and like the veins of the Rainbow lode, they carry but little replacement quartz. The veins 

follow a direction of early fissuring, marked by large dikelike masses of aplite. 
• 

CHAPTEn XL-THE SILVER LODES. 

PRODUCTIVE STATUS. 

The silver lodes of the Butte' district have been· extensively and profitably worked, but 

their importance has been overshadowed by the immense production of the copper lodes. From 

1881 to 1890 the four principal producers of the district yielded 28,704,310 ounces of silver, 

but in 1896 the practical demonetization of silver, together with the change in character of 

the ores in depth, ·led to a sudden and almost complete stoppage of nlining, and since that date 

the silver lodes have not been regularly worked. At present (1906) the silver production of 

the district from the silver lodes, excluding the metal recovered as a by-product of copper 

smelting, is comparatively small. Lessees are at work on many properties, and when rich 

ore bodies are found,.as occasionally happens, the discovery stimulates a renewal of exploration 

work on many of the properties, especially those adjacent to that on which the find has been 

made. As a whole, however, the industry is deca.dent and the great mills and mining phints 

are idle. · AREA AND SUBDIVISIONS. 

The silver-bearing area is much larger than the copper-bearing area, which it laps round on 

~he north and west, silver lodes o~curring as far north as the boundary of the Butte special quadrangle and as far west as the borders of the Silver Bow lake-bed district. In this large area 

the veins occur in bunches or clusters, and are therefore best discussed in si..-x: different groups, 

each of which takes it~ na1ne from its :p10st prominent mine or from its locality. · These groups are 

(1) Lexington, (2) Rainbow, (3) Northern, (4) Missoula. Gulch, (5) Western or Aplite, and (6) 

Southern and Eastern. 

LEXINGTON GROUP. 

VEINS. 

The Lexington group lies just north of the copper area, between the Syndicate lode area and 

the lodes of the Rainbow group. The Lexington mine comprises five claims, developed by 

extensive unclerground workings from a shaft 1,450 feet deep. The veins of this group must be 

arbitrarily distinguished from those of the Rainbow group inasn1uch as there is Iio intervening 

barren ground. The veins have been traced continuously fron1 J\1issoula Gulch eastward to the 

West Greyrock mine, a distance of 5,500 feet. 

Though the'group includes numerous veins, they do not seen1 to be closely related. They 

do, however, as a whole, follow a course similar to that of the Rainbow lode, but lack the latter's 

minor distortions. Their course varies from N. 75° E. at the west end to nearly east and west 

in the center, and to southeast or S .. 65° E. at the east encl. 

BLUE WING LODE. 

':Che Blue Wing lode is the northernmost member· of the Lexington group. It consists of 

two veins,. separated by 50 to 100 feet of granite, which are cut in the workings of the Lexington, 

Paymaster, and Blue Wing mines. The northernmost vein of the lode splits between the 100 

and 200 foot levels, forming two veins or branches 20 feet apart. The clip is nearly vertical and 

the veins rarely exceed 5 feet in width. The southern vein of this lode lies parallel to the 

northern· one, and is. a single fissure veinvarying in width up to 20 feet, and containing exceptionally rich but very irregularly distributed silver and gold ores: At a depth of 300 to 600 

feet the sp,ace between . these two veins con tams a number of smaller veins, which it is not 

necessary to distinguish. 

239 
• 

0 

240 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRIC'I\ MONTANA. 

LEXINGTON MINE. 

The workings of the Lexington mine show three principal veins, the Allie Brown (Atlantic) 

on the north, the Wappello, and the La Plata (South) vein. 

"ALLIE BROWN VEIN • 

. The Allie Brown outcrops about 400 feet north of the Lexington shaft and about 200 feet 

north of the Wappello. It is a persistent well-defined vein, with a course slightly north of west 

and a nearly vertical or slightly southerly dip. To the west it extends into the Blue Wing 

claim, splitting into two veins which diverge until they are 75 feet apart, continue separate for 

about 500 feet, and reunite westward. To the east the vein extends to the Corra mine. The 

average width is 5 feet, with lenticular expansions ·to 20 feet, in places inclosing lens-shaped 

horses of altered granite. · WAPPELLO LODE. 

The W appello lode consists of a number of close, parallel veins, one of which, called the 

·Main vein, is persistent throughout the workings of the Lexington mine, but near the surface to 

the north splits into a number of small veins which diverge downward. These spur veins are, 

not persistent, but where they die out many of them are replaced by other small lenses of vein 

matter. Westward the Wappello is encountered in the Eveline workings, where it is cut by 

numerous very small fault fissures running parallel to it and dipping north; their maximum 

throw is 20 feet. Eastward the main vein splits into a number of smaller fractures, which are 

nearly parallel to the main fracture. These lesser veins are worked in the Sisters, Flag, Josephine, and West Greyrock min~s, where they have yielded notable amounts of copper, mostly 

as chalcopyrite, from the surface downward for some 200 to 300 feet. 

The Wappello has an average width of ·5 feet, but locally broadens to several times this 

width. The ore is solid and frozen to the vein walls. The dip is southward at an angle of 

55° to 70°. The West Greyrock lode is parallel to the Wappello, but dips south at a smaller 

angle. The two south veins of the West Greyrock mine unite westward to form this vein. 

LA PLATA LODE. 

The La Plata lode is the most southerly member of this Lexington group. It consists of~~ 

number of short connecting veins which may be traced on the surface from :Missoula Gulch to 

Main Street. It is nearly parallel to the Wappello, but differs from it in having clay selvages, 

4 to 5 inches thick, between vein matter and wall rock, and is wet and difficult to keep open. 

(See Pl. XLI, B.) 

COST OF MINING. 

The following data, obtained from the books of the Lexington mine, help to explain the 

abandonment of silver mining in the Butte district: · 

Table showing production of Lexington mine. 

Years. 

1897 .................... : ............................. · ...... _· __ ....... . 1899 .................................................................. . 1901 .................................................................. . 

1902 .................................................. ················· 

Gross 

product. 

Tons. 

2,240 

1,443 

2,815 

3,091 

ORES. 

Cost of 

mining 

per ton. 

Cost of Cost of 

transporta- reduction Total value Net return ti~~rf.er per ton. per ton. per ton. 

$15.79 ........... . 15.57 .......... .. 9. 30 $0.76 11.46 .83 $8.00 

7. 50 7.10 

7.12 

$27.96 

23.29 

19.47 

16.41 

0 +4.17 

+0.22 

+2.37 

-3.00 

The average copper output of the entire mine is ·5.3 per cent The ore runs about 1 ounce 

of gold to 100 ounces of silver, though of late years it has increased to 2 or 3 parts to 100. The 

high-grade chalcopyrite ore averaged about 19.8 per cent copper, 43.3 ounces of silver, and a 

trace in gold. The gold values appear to be greatest in ore showing brilliant facets of fine 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 74 PLATE X Ll 

A. BRECCIATED SULPHIDE ORE EMBEDDED IN LATER QUARTZ. 

Lexi ng t on min e. On e- half natural size See page 241. 

B VEIN STRUCTURE, LA PLATA MINE, FIFTH LEVEL, SOUTH VEIN. 
THE SILVER LODES. 241 

seconcJ.ary quartz, which are regarded by :Mr. Ruger, the manager, as a sure indication of highgrade ore, and this is the ore which is now being searched for by the leaser. The copper ore 

consists of chalcopyrite 1nottled with quartz and. showing considerable zinc. 

The Allie Bro,yn and the W appello. veins are mineralogically aln1ost identical. They 

appear as remarkably uniforn1 open fissures in the granitefrom 1 to 5 feet in width, rarely 

larger, which have been filled by vein material. The veins consist of quartz, iron pyrite, sphalm·ite, galena, chalcoyprite, argentite, and some form of gold, presumably a sulphide. Associated 

with these are the silicate of manganese, rhodonite, and the carbonate of n1anganese, rhodochrosite, which are typical of the silver lodes. Both are very abundant, and serve quite generally 

to distinguish the silver from the copper veins. The n1etallic sulphides occur in bunches or 

spots throughout a matrix of quartz and n1anganese minerals. In certain places the heavy 

sulphides forn1 almost the entire vein, but this is uncommon. (See Pl. XLI, A.) Rhodonite, 

the silicate· of n1anganese, is much more abundant than the carbonate, rhodochrosite. It is 

easily recognizable in the hand specimen by the·greater hardness and by its nonoccurrence in 

large crystals. It is very fine grained, massive, and tough, and has the general appearance 

of an opaque rose quartz or jasper. All the carbonate of manganese, rhodochrosite, is crystalline, with conspicuous rhombic cleavage; it gives off C02 feebly when treated with dilute hydrochloric acid. The workings have failed to develop any sulphide of manganese, and none of the 

evidence indicates conclusively that these manganese minerals are alterations fron1 the sulphide. 1'hey 1nay be, therefore, a final stage of deposition from solutions which pass through 

the smne channels that the earlier and more strongly mineralizing solutions traversed. No 

definite order of formation of the sulphides of the heavy n1etals can be traced, for both n1egascopic 

and 1nicroscopic study show an apparently indiscriminate a~:rangen1ent. Crystals of pyrite 

carry inclusions of the n1ore valuable sulphide, argentite, and pyrite also has been found inclosed 

with crystals. of this san1e sulphide. 

Several epochs of deposition probably occurred, as the veins are in many places beautifully 

banded. One specin1en fr01n the 300-foot level of the W appello vein, found frozen to the 

hanging wall, consisted of a crystalline band of quartz, dotted abundantly with crystals of fine 

iron pyrite and chalcopyrite; a s01newhat sn1aller and less fully defmed band composed almost 

entirely of the sulphides of the heavy n1etals; a band of almost pure rhodonite; and finally a 

cap of quartz, presenting in the heart of the vein an open cavity lined with the typical hexagonal 

prisn1s and pyranuds of quartz. These quartz crystals are interesting be~ause they are coated 

with little clusters of a rh01nbic mineral, which is probabl): rhodochrosite. The succession of 

the vein fr01n the outer wall to the heart is identical with that just described. Frequently 

the vein is found band~d in a simila~r way, but with no order of deposition. J;>late VII, A 

(p. 72) shows a speciinen, 9 inches long and 4 inches wide, in which the line of contact of the 

vein n1aterial with the grmute is well marked, though there is no selvage. The vein is composed of alternating bands of more or Jess pure quartz, the darker portions being the less 

pui·e, the in1purity consisting of the sulphides of the heavy n1etals already described. 

Associated with the fonnation of the veins there has been much movmnent. A specimen 

taken fron1 the hn.nging wall of the Wappello vein on the 300-foot level, near the once fan1ous 

Butte & Boston raise, shows a fine-grained rock, consisting of rounded and angular frag1nents 

of quartz, feldspar, and vein 1naterials. The rock is thoroughly impregnn.ted with iron pyrite. 

1\ficroscopically it reveals frag1nents of quartz and feldspar, wluch are widely separated by a 

n1ass of unrecognizable Inaterial having a strong resemblance to the nucrofelsitic ground1nass 

of rhyolite. None of the heavier silicate minerals, such as hornblende or biotite, appear in 

the slide; and if these were ever present they are now represented by traces of chlorite. Iron 

pyrite in well-defined cry~tals,- unbroken and unworn, is abundant. A slide of a granitic 

fragrnent of this breccia showed all the characteristics of decon1posing granite; biotite had 

turned to 1nuscovite, the feldspar·, which was nearly all orthoclase, having .decomposed to kaolin 

and epidote. This alteration of the feldspars begins along the cleavage cracks or in the heart 

of the crystal, the o~~lines of the crystals always remaining intact. The quartz is fresh and 

90427°-No. 74-12--16 
242 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

normal. Both slides reveal certain amounts of micrographic intergrowths of quartz and 

feldspar. The presence of fragments of vein quartz and fragments of granite in the same 

specimens indicates that this breccia was formed after a period of mineralization. The condition of the pyrite, the matrix. of the breccia, and the fact that the rock is now solid and 

corripact indicate subsequent mineralization. 

A specimen taken from one of the intermediate levels of the mine consists of a number 

of angula1~ bowlders of ore, cemented by almost pure crystalline quartz. It is a striking illustration of the intermittent character of the mineralization which formed the vein deposit. 

On the 500-foot level an interesting condition has been found. Son1e disturbance of 

the vein has taken place since its deposition, and as a result the vein minerals, principally 

the galena and sphalerite, have arranged themselves in a series of narrow, parallel veinlets, 

separated by narrow bands of highly altered country rock. This arrangement is particularly 

interesting because the galena forms numberless series of twins, ahnost identical in appearance and characteristics with those described by Cross 1 from Bellevue, Idaho. The adjacent 

country rock is highly altered. The heavier silicates have been removed ·almost entirely; . 

the feldspars have been reduced in varying degrees to zeolites, sericite, or kaolin; the quartz 

has been attacked by the mineralizing solutions. Both the quartz and the feldspar 

appear under the microscope in extremely irregular crystals, the process of this change being 

seen in the pitted faces of otherwise fresh crystals. In some specimens the accessory minerals, zircon, apatite, and titanite, have either been removed or rendered unrecognizable. 

This change in the country rock extends for varying distances from the veins. It is rarely 

ever h~ss than a foot, and it may be as much as 25 feet. Associated with these changes is the 

impregn~tion of the country rock with iron pyrite, which occurs near the veins wherever the 

minerals of the granite have been altered by the vein solutions. It occurs largely in association 

with the heavy silicates, generally in a series of minute crystals parallel to their cleavages. 

Pyrite is also seen in larger masses with less definite crystalline boundaries, replacing the whole 

of what was once a crystal' of biotite or hornblende. It has also been observed with more or 

less frequency associated with feldspars and even with quartz. The changes in the rocks a:q.d 

veins, which have been brought about by normal weathering, apart from the mineralizing 

solutions, have extended into the country rock to depths of not over 50 feet, and in country 

rock associated with veins to as much as 200 feet. The veins are oxidized for about 100 feet, 

below which any oxidation is the result of e!ther nune workings or natural channels produced 

by recent movement in the count:r;y rock. 

The La Plata (South) vein is characterized by a s1nall a1nount of the manganese minerals, 

a very high per cent of zinc and galena, and a peculiar Qccurrenc·e of veinlets of zinc and galena. 

Nearly all of these are 2 or 3 inches wide, in groups of perhaps five, separated by bands of highly 

altered country rock. The vein is further characterized by a larg~ amount of clay and fault 

material, showing conclusively that much more movement has taken place along the plane of 

this vein than in either of the other veins. So"me evidence goes to show that the minerals 

occurring in this vein are secondary in origin. They. n1ay have been introduced fr01n other 

veins through chemical processes associated with oxidation. 

In brief, the phenomena seen in the Lexington mine include (1) a highly sheeted granitic 

country rock, much decon1posed and altered along fracture planes and planes of jointing, 

containing many large masses of pegmatite; (2) a series of aplite dikes, varying in width, 

inclination, and regularity; (3) a series of nearly east-west veins, clipping nearly vertically or 

to the south at a very high. angle, and carrying quartz, silicate and carbonate of manganese, 

the sulphides of the metals iron, silver, zinc, and copper; (4) alteration and oxidation of these 

minerals, extending as much as 200 feet from the surface, and producing psilomelane, wad, 

goslarite 'and other minerals; (5) movement parallel to the course of the veins, but dipping in 

the reverse direction, producing local displacement and fracture; (6) movement parallel to the 

plane of the veins, producing vein brecci~s; (7) movement occurring after the first mineraliza·· 

1 Cross, Whitman, Proc. Colorado Sci. Soc., voL 2, 1887, pp. 171-174. 
THE SILVER LODES. 243 

tion and previous to the final nuneralization; (8) increased percentage of copper in the 

lower levels, especially in the lowest level; (9) heavy percentage of zinc in the more southerly 

vein; and (10) banded structure in.the ores. · 

RAINBOW GROUP. 

The Rainbow group, which takes its name from the great Rainbow lode, incluJes· other 

veins w:hich outcrop on the hill slopes north of Walkerville, where they attain their greatest and 

most important development. From the central portion, where the strikes vary but a few 

degrees from east and west, the veins have been traced. eastward to the banks of Silverbow 

Creek, curving gradually, until they trend S. 6qo E. Westward the veins extend along Oro. 

Fino and Beefstraig4t gulches, where their course changes to south of west. 

VEIN SYSTEMS. 

In the vicinity of Walkerville the grQup includes three distinct vein clusters-(1) the Valclemere, a system of nearly parallel southeast to east veins; '(2) a system of northeast cross fissures; 

(3) the Rainbow lode. The latter crosses the veins of the Valdemere system in a direction 

somewhat north of east, dividing it into northwestern and southeastern portions. 

V ALDEM:ERE SYSTEM. 

The southeastern division or the Valdemere system includes the Valdemere, ~loose, l\1agnolia, IIawkeye, Garfield, and Curry, which lie at nearly uniform distances of 200 feet apart, 

and strike N. 75° to 80° W. Their clip is uniformly 75° to 80° S. Those near the Rainbow have 

thus far proved the richest. The Valdemere and Moose have been very productive,· the latter 

having been \vorked even during the low prices of silver. The I-I~wkeye vein has also been productive. All these veins have been disturbed by secondary cross faulting, as is well seen in the 

Belle of Butte mine, where four cross faults were noted, the largest fault displacing the vein 

60 feet southward on the east. 

The n·orthwestportion of the Valclemere group includes the Silver Safe, Moulton, Amy,· and 

Goldsmith mines. These veins are less uniform both in· strike and in clip than those first mentioned. The dip in the Silver Safe mine is 45° S. at the surface, steepening to 60° at 200 feet 

in depth. The :Moulton and Amy veins have nor1nal southerly dips, but the Golds~ith dips 

. 80° N. for a distance of 200 feet below the surface, and then changes to a southerly dip. The 

strike of the veins changes weshvard· and finally bows around to the south. The veins have an 

average width of 4 feet, with extreme v~riations of 1 to 7 feet. 

NORTHEAST SYSTEM. 

The series of northeast cross veins is particularly well exposed just east of the Magna Charta 

shaft, where they connect the Valdemere vein with the Rainbow lode. They dip south at a 

comparatively low angle. Their average width is about t~1at of the southeast veins. 

RAINBOW LODE. 

DEVELOPMENT. 

The Rainbow lode, which is the largest and most productive silver lode of the district, 

received its nan1e f1~om its crescentic course. · 

The outcrop of the lode shows a great number of ledges of quartz stained a deep black by 

oxides of manganese. Its course is marked by nu1nerous prospect pits and open cuts, by which 

the veins are readily traced for several thousand feet.· Where these veins merge together in 

about the center of the lode they have been developed in th~ Alice mine, 'to the east of which 

lie the Fraction, :Magna Charta, Valdemere, and the Poser, and to the west the l\1oulton, AmySilversmith, Goldsmith, and Rising Star. These veins can be traced eastward as far as the 

al1uvial bott01n of Silverbow Creek, and westward to the point where they are hidden by the 
244 GEOLOGY AND ORE DEPOSITS OF. BUTTE DISTRICT, MONT AN A. 

overlapping rhyolitic rocks. They traverse normal Butte quartz monzonite, which shows much 

less alteration in the vicinity of the silver veins than in the copper-bearing portion of the district. 

Dikes of aplite and small areas of pegmatitic granite are also found. Plate XV, A (p. 170), 

shows the waste dunip at the Mou"Iton mine. The great size of the dump indicates the extent 

of the n1ine workings. , MINES. 

ALICE MINE. 

The principal·development of the Rainbow lode is on the group of claims worked by the 

Alice Gold & Silver Mining Co., and collectively known as the Alice mine. 

In this part of the Rainbow lode the bolQ. outcrops consist of heavily stained and blackened 

quartz, porous arid honeycombed in places (the cavities indicating the former presence of pyritic 

material), in layers and parallel masses, differing somewhat in composition and hardness. The 

more compact quartz rises 20 feet or more above the surfa·ce, but the softer layers have been 

worn down to the general surface of the ground. 

The Rainbow lode has been the great ore producer of the mine, and is remarkable among the 

silver veins for the great width to which mineralization has extended, reaching ·in some pla~cs . 

nearly 100 feet. It consists generally of two distinct fissures, known as the north and south 

veins, respectively, which stand nearly vertical, the north vein tending to incline a few degrees 

north, and the south vein as much south. The veins are separated by a varying width of 

granite, impregnated in many places with vein materials and cut by small veins to such an 

extent as to constitute one great ore body, with streaks of richer and poorer ore. · 

Numerous breccia zones carrying fragments of o~e are accompanied by secondary fault 

fissures and clay seams. These zones are generally parallel to the primary veins in strike, but 

commonly diverge a little in dip. . 

The vertical throw on the secondary fissures, as far as determinable, is quite small, but the 

direction of the striations on the abundant slickensided surfaces indicates lateral movement. 

Ti1ese fe.atures show a reopening of .the vein and a sliding of one portion on the other . 

• The htrgest and richest ore bodies were found in the oxidized zone, quite near the surface, 

and generally accompanied by the breccia zone. Down to the 100-foot level the ore is all 

oxidized; on the 200-foot level a mixture of oxides and sulphides is found; and in places along 

the breccia zones oxidation extends even deeper. Rich sulphide ores were found at considerable 

depth, but decrease in amount with depth. In general a decrease in silver is accompanied by 

an increase in zinc; this seriously interfered with amalgamation, so that before the .1 ,000-foot. 

level was reached the ore was no longer remunerative. The shaft was sunk to nearly 1,500 

feet, ·and considerable drifting done in search of new ore bodies, but the lower workings we~e 

soon abandoned and allowed to fill with water. 

1n the oxidized zone, associated with cerusite and other oxidation products, some.carbonates 

A,nd a little oxide of copper were found, and in the mine drifts some chalcanthite was seen on the 

walls, indicating the presence of a small percentage of copper in the ore; but no accun1ulation 

of copper ore of merchantable value. has been found. 

The ore below the oxidized zone consists of white quartz carrying iron pyrite, galena, 

sphalerite, and argentite, with much rhodonite and some rhodochrosite. These minerals being 

in many places arranged in parallel bands or crusts. The quartz is subcrystalline or at places 

is in distinct crystals, showing that it filled open cavities. The rhodonite and rhodochrosite 

occur locally in large masses orin bands or layers of pale to deep-pink color, in some places dotted 

with metallic sulphides and again forming with secondary quartz the cement in breccia zones. 

Silver sulphide occurs as films upon cleavage planes and in cracks in massive pyrite; near the 

water level it has decomposed and formed filaments and wires of silver, some of which are several 

inches in length. Generally, however, they are very fine and lie curled and matted over the 

ore surface like a mass of wool. A few flakes and scales of silver also occur. The silver contains 

a small amount of gold; in the bullion from oxidized ore, which averaged $74.22 per ton i:p 

value, 87.26 per cent of. the value was in silver and 12.74 per cent in gold; in the bullion from 
THE SILVER LODES. 245 

roasted ore, representing the average yield of sulphide ores, with a value of $56.95 per ton, 92!93 

per cent wa:s in silver and only 7.07 per cent gold. Up to 1879 the mine had yielded $837,539. 

On the 200-foot level of the Alice mine bi1t 135 feet below the surface, the Rainbow lode, 

eas~ of the shaft, is 80 feet wide, and contains three pay streaks; and the south vein consists of 

two closely adjoining fissures. West of the shaft the north and sQuth veins come together, 

forming a thin lode 2 to~3 feet wide, but they separate again and are 40 feet apart at the Moulton 

line. The north vein dips 70° to 80° N., and the south vein as much south. The breccia or 

secondary fault plane is less marked than in the level above and occupies a different relative 

position. Similar conditions obtain on the 300 and 400 foot levels, but on the latter several 

secondary fault planes cross the lode at· somewhat steeper angles than do the original veins; 

they have distinct striations on their walls which dip 24° SW. 

The granite horses include considerable bodies of rhodochrosite and some veins, 1 to 2 feet 

wide, of rhodonite and quartz. Though the individual veins are as a rule distinctly filled fissures, 

in son1e places they grade through partly replaced granite to norm.al country rock. Specimens 

examined under the microscope show that quartz and feldspar have been attacked and secondary 

quartz and sericite formed, and that the ferromagnesian minerals have been replaced by p'yrite 

and spluilerite. · 

A n1easured section across the vein at one point gave the following divisions: 

Section across Rainbow lode in Alice mine. 

Hanging wall, granite. Ft. in. 

Clay gouge, with quartz fragments .......................................................... 4 

Hard quartzose ore ....................................................... · ................... 4 

Clay sean1................................................................................. 1 

Black quartz, with ore and clay seams......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Clay sean1 ...................................... : ........... ·............................... 1 

Rich ore, quartz and massive rhodochrosite, with sulphides ................................... 1 6 

Granito, with veinlets of ore, forming horse .................................................. 6 2 

Massive pyritous ore, carrying native silver ................................................. 2 4 

Massive sulphide ore, galena, sphalerite, and pyrite, with filaments of native silver..... . . . . . . . ~ 

Massive quartz, with a little pyrite, and veinlets containing native silver ...................... 3 

Massive quartz, with patches of ore ........................................................ 3 

Shatt9red quartz, white, but carrying disseminated sulphides ........................... · ...... 3 

Low-grade ore, with white quartz.~ ........................ : ................................ 5 

Clay sean1 ......... : .................................... ~.................................. 2 

Crushed and soft ore .......... ~ ............ : ............................................... 3 

Footwall granite, with small veins of quartz, fading out in country rock. 

On the 500-foot level east of the shaft there are two streaks of rich ore, with· 30 feet of 

impregnated granite between. 

The I-Iawkeye vein, which is 240 feet south of the Rainbow lode on the 200-foot level, strikes 

about S. 80° E., and dips 80° S., shallowing to 65° S., in depth. It has yielded co.nsiderable highgrade ore, being in places as much as 15 feet in width. In the lower levels it is a strong vein 

of low-grade ore, consisting mainly of quartz and rhodonite. 

The Garfield vein a.t 550 feet and the Curry vein at 625 feet south of the Hawkeye are strong 

veins, generally parallel in dip and strike with the ·latter and from 2 to 3 feet in width, but 

have not been important producers. Their ore is oxidized to a depth of 200 feet or more. 

The paragenesis of the ores of tl~e Alice mine is the same that obtains in the other silver 

veins. The vein minerals are, in the order of their abundance, quartz, iron pyrite, rhodonite, 

·galena, sphale1~ite, rhodochrosite, and argentite. A study of thin sections of the ore shows that 

quartz belongs to n1any generations and may be both the oldest or the youngest 1nineral forn1ecl. 

The iron pyrite is probably of at least two generations, but is usually younger than part of the 

quartz, and in part at least younger than the argentite. The .argentite is genera:lly without 

crystal outline, nniCh of it occurring within iron pyrite. The pyrite occurs in well-defined cubes 

and dodecahedrons, both in the quartz and in the altered country rock. Sphalerite and galena 

are of later age than pyrite. They ·occur in irregular n1asses lying along cleavage planes and 
246 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONT AN A. 

jo4tts and also in thin films along fractures in the ferromagnesian minerals. Rhodonite occurs 

both crystallized in rhombs and in massive form. Rhodochrosite occurs also as an alteration 

'product from the rhodonite; it can hardly be distinguished from calcite when of pale color; little 

of it occurs crystallized. 

1\:IAGNA CHARTA 1\:IINE. 

East of the Alice 1nine the continuation of the Rainbow lode is worked in the ~Iagna Charta 

mine, a· sn1all fraction 200 feet wide separating the two properties. In this 1nine the Rainbow 

lode shows five principal veins, comnwnly called the North, Tunnel or McGinty, South, :Magnolia, 

and Copper, corresponding to those worked in the Alice mine. West of the shaft these veins 

have ~n almost due east-west course, but east of the shaft they turn markedly to the north. 

The mineral content of all of them is entirely similar to that of the other silver properties; they. 

have been oxidized for a little more than 100 feet below the surface~ 

The north vein shows an uncommonly well-developed series of branches and spurs. It 

dips steeply north and the branches from it also clip north but at a lesser angle; as they lie 

in .the footwall country they rejoin the vein before any great. depth is reached. At the shaft, 

however, the North vein splits in depth, and the north portion is the larger and more persistent, 

though the south branch contains the higher-grade ore. The Tunnel vein and the South vein 

are closely allied. The former is less persistent and is not seen below the 300-foot level. The 

·two veins are traced eastward to the Valclemere shaft, but are not continuously developed. 

The Magnolia vein is remarkable for its persistence in depth and in outcrop; it is not split 

and shows no unusual features. The Copper vein is interesting because it ·carries bunches of 

chalcopyrite ore which have been worked in recent years. 

MOOSE MINE. 

In this mine three veins are developed. . One of these is the V alden1ere vein, which extends 

eastward from the V alclemere mine into the :Moose, though in the absence of continuous drifts 

between the two properties the identity of the two is not absolutely established. Tllis vein 

has a steep dip, w'llich varies fron1 north to south in different parts of its course. The second 

vein lies 150 feet' south· of the V aldemere, and, like the former, has an exceedingly steep dip, 

which varies'fron1 north at the surface to south in the deeper levels. This vein splits westward, 

the two branches clipping to the south and uniting below the 300-foot level.: This second vein is 

probably the eastern extension of the :Magnolia vein cut in the :Magna Charta. A tllird vein 

is cut at a distance of 300 feet south of the shaft. It is vertical and extends westward, and is 

probably the eastern extension of the Belle of Butte vein running into the Amador mine. The 

Moose mine has been worked almost continuously for the last decade, even while the other silver 

properties of the district were idle.· These veins are well-defined fault fissures, but the quartz 

is largely a filling and not a replacement of the country rock. It is well banded and contains 

the usual pink manganese minerals. 

The Valclemere vein shows in the ~loose workings a tendency to split, the ends overlapping 

and connecting l;>y curved strain cracks carrying ore. On the second level the vein near the 

shaft is a mere seam of quartz and rhodonite, carrying 5 inches of ore for a few feet westward; 

100 feet or so from the shaft the vein has been stopecl for a distance of 260 feet, until it apparently ends in a small slip; a short parallel ledge, 10 feet to the north and separated fron1 the 

vein by north-dipping clay seams, carries a body of good ore; the main lode is continued by a 

ledge parallel. to the main drift, showing in the stopes 3! feet of zincky quartz-pyrite ore. Eastward the Valclemere changes to a mere clay seam in crushed granite, showing a foot of ore for n. 

few feet but being mostly barren. On the third level tllis vein has been developed for several 

hundred feet west of the shaft, the drift and stopes showing the vein to clip 7 5° N. and to vary 

from a foot or two up to 15 feet. The ore shoot at the west end shows a width of 8 feet, n1ostly 

a mixture of quartz, with pyrite and sphalerite, carrying silver. Generally, ho·wever, the vein 

consists of numerous stringers an inch or two in width, with many spur slips running off to the 

north to the parallel north vein of the lode. . The north branch of the vein shows a width of 4 to 5 
THE SILVER LODES. 247 

feet and clips 7 5° N. The south branch ends in a 6-inch seam of poor ore and has walls of hard 

and but little altm•ed granite, the northern one cut by n1any !-inch stringers of rhodochrosite 

running northwest up to the north branch. 

The :Magnolia, the· n1iclclle of the three veins worked in the lVIoose, has been n1ost extensively 

developed on the third level. It has a curved, somewhat irregular course, in contrast to the 

straighter course of the copper veins, and at one place splits and passes around a large horse of 

granite. It is developed but slightly on the 200-foot level, as the ore is low grade, but is worked 

for a total distance of 1,200 feet on the 300-foot level (6,124-foot elevation), showing a width 

of .2 'to 5 feet and an average width of 15 inches of ore, with good bunches where splits occur. 

The walls are sri1ooth, showing in places slickensides clipping at 25° W. The vein is cut, but 

not shifted, by aN. 40° ,¥.fissure dipping north, having clay walls and a 10-inch seam of black 

stained quartz. · 

To the east the vein becomes double, a south brt;tnch showing 6 to 12 inches of ore. 

Throughout its course the vein has clay gouge, usually on both walls, and dips north. The 

ledge i~ 2! feet wide at the east face and consist.s of rhodonite, with little or no quartz. The 

hanging--\vall granite is crushed in many places and shows joints dipping at 45° NE. 

BELLE OF. BUTTE MINE. 

' . 

The southern vein in the Belle of Butte n1ine varies up to 3 feet in thickness, with a few 

inches of ore, and dips 75° S. It has been stoped frOIJ-1 the surface to nearly 30 feet below the 

300-foot level. It contains ore in short shoots and also a persistent but narrow streak of rho-, 

.donite varying fron1 3 inches to 1 foot in 'thickness. The cross cuts show normal Butte quartz 

monzonite cut by a few northwest clay slips, some of which carry fault breccia and rhodochrosite with alteration 9f the wall rock. 

AMY-SILVERSMITH MINE. 

vVest of the :Moulton rnine the Rainbow lode is worked in the ::Moulton clairn of the AmySilversmith rnine to a depth of 500 feet or more. Three veins have been developed, of which 

the north and south veins luive been the most productive, and the middle vein has contained 

pay ore in the eastern encl. The north vein clips about 80° N., becoming vertical in depth, and 

then clips south. This vein varies from 1 to 3 feet in width and is chiefly notable for the uniforniity and persistence of the ore shoots; the ore, however, is of rather low grade and the bunches 

of high-grade material found in the other veins are lacking. The middle and south veins, 

which lie south of the shaft, are not well defined in depth and do not carry pay ore. In part 

at least they are represented by fractured planes, marked by clay walls and slightly mineralized 

material, opening in places into n1asses of quartz and rhodochrosite too low in grade to warrant 

exploration. 

East of the Amy shaft the rnicldle vein has been cut and drifted upon continuously to the 

:Moulton shaft. The south vein is very persistent and has been drifted on to the limits of the 

ground both east and west. Tllis south vein has shown extremely rich ore in pockets and 

bunches, separated by stretches of brecciated material and inclosed in well-defined walls. It 

.shows postmineral brecciation, the vein filling consisting of well-banded layers of quartz, 

rhodonite, and iron sulphide, with silver n1inerals, the bands being from one-si..-x:teenth to onehalf inch in tlliclmess. Later n1oven1ent has sheeted the granitic breccia alongside the vein into 

plates varying fron1 1 to 4 inches in width, and these plates are now cemented b:y veins of 

quartz, which show scattered crystals of iron pyrite and argentite. This records an internlittent opening of the veins and is in line '\vith the evidence found in the Lexington mine. • 

GOLDSMITH MINE. 

West of th,e Amy-Silversmith nline the Rainbow lode is worked in the Goldsmith, in which 

two veins have been developed, the so~thern of which has been the more productive. This 

south vein has a v.ridth of 8 inches tq 3 feet, is persistent throughout the length of the claim, 
248 GEOLOGY AND ORE DEPOSI.TS OF BUTTE DISTRICT, MONTANA. 

dips about 80° S., and is but little disturbed by postmineral movements. The north vein lies 

north of the shaft; it dips north for 120 feet below the surface, at which depth it is faulted, and 

is assumed to be continued by a steeply southward dipping vein 1 to 3 feet wide. At the east 

end of the claim the level driven on the north vein is connected with the Amy-Silversmith; at 

this point a northeast fault with a northwest dip produces a throw of 100 feet to the south.· 

A similar displacement is observed on the south vein at the west end of the workings. The 

ore extracted from the Goldsmith north vein has been extremely rich, varying from $100 to 

$200 per ton in gold, with an unusually high percentage of silver, but in general the average 

for the mine is not higher than that from the other mines of this lode. · 

NORTHERN MINES. 

The Wabash group lies at the extreme northern end of the Butte district, west and north · 

of the Rainbow group. In this portion of the district the outcrops are more prominent than 

in any other portion, but although the veins are_ so conspicuous in outcrop and abundant in 

number their exploration has been disappointing, inasmuch as workable ores occur only in· 

small amount and extend only to comparatively shallow depths. It is, indeed, doubtful if 

any of the mines in this portion of the district have returned the cost of equipment. 

WABASH 1\IINE. 

The Wabash lode outcrop is one of the best defined and strongest in the neighborhood. 

The lode lies just south of the Black lode. Its course is about east and w~st. At the point 

where it has been developed by mine workings the vein splits into three branches, which join 

at a depth of 200 feet, on the west at a distance of 150 feet, and on the east at a distance of 

100 feet from the shaft. The mine has not been worked in recent years, and the workings 

have not been examined since 1900 or thereabouts, as the mine has been under water.· Oxidized 

ore extends downward for 100 feet. In general the vein belongs to the silver series and has 

the same general character as that already given . 

. The Black lode, which is on the Wabash claim, has an outcrop of black stained quartz 

that is readily traceable by its color and by the prominence of its outcrop, which rises 10 feet 

above the surface and has a width of 2 to 3 feet. The vein dips 80° S. and the outcrop forms a 

curved line. 

SPRINGFIELD 1\IINE. 

The Springfield mine is situated north of the Wabash, its nearest neighbor. The workings 

show but one vein, which runs east and west, clips 80° S., and is about 3 feet wide. The vein 

filling consists of quartz with but little manganese, and carries small pockets and streaks of 

iron pyrite, together with a little sphalerite, and very small amounts of chalcopyrite and galena. 

Ruby silver and argentite occur as tiny black and red specks impregnating the quartz. The 

vein matter is everywhere shattered and separated. from the hanging wall by a persistent clay 

seam an inch or two thick. A s·econd vein parallel to the first ancl100 feet north of it has .been 

cut on. the SO-foot level. This second vein is composed entirely of quartz and iron pyrite, is 

well banded, and shows included lenses of granite. The walls of both veins are well defined, 

and the country rock is fresh and unaltered except for a width of 3 or 4 inches next. to the wall. 

Ruby silver (proustite), found in fracture planes in the vein filling, is probably of secondary 

formation and is believed to result from the oxidation of tennantite. 

SNOWDRIFT-GLENGARRY. 

The Snowdrift and Glengarry mines are situated on the south side of Oro Fino Gulch, near 

its head. Though once extensively worked, these rillnes are at present abandoned, and the 

information obtained in 1896 is all that is available. At that time the·property _was opened by 

a shaft near the boundary line between the two claims. The vein is well marked for 1,500 

feet, and can be traced at intervals with f.air identification for 7,000 feet. Many spur and 
THE SILVER LODES. 249 

parallel veins accompany the main vein, but they are less.persistent and rarely contain pay ore. 

The vein dips about 70° N., and when visited had been developed to a depth of but 75 feet, 

with east and west drifts at this depth. A fault fissure with a N. 45° E. course and a dip of 

60° NW., belonging to the Rarus series, cuts through the vein and displaces it for 25 to 40 feet. 

East of this fault the vein consists of quartz and rhodonite containing disseminated pyrite, 

with gray copper and small amounts of gold and silver, the manner of occurrence being entirely 

similar to that observed in the Rainbow lode, with the common oxidation products, limonite, 

psilomelane, and some calcite. In the development of this lode the rich ore, running 100 

ounces or more in silver, occurs in small lenses or pockets. The vein filling contains small 

amounts of galena and is almost free from sphalerite. The gold value is, however, low, and 

for this reason the ore has not been as extensively sought as that in less prominent veins. 

SILVER LICK MINE. 

The Silver Lick mine is situated on the hill next north of the :Moulton. The vein has a 

.general east-west course, and a dip of 80° .. Its average width of 3 feet is extremely constant., but increases to 15 feet at the west end of the 200-foot level. The n1ine is developed by 

an inclined shaft 250 feet deep. The vein is a filled fissure containing quartz and iron pyrite, with 

rhodonite and complex sulphides of silver, the ore shipped averaging about 35 ounces in silver 

and $1 or more in gold to the ton. 

MISSOULA GULCH GROUP. 

The mines of the :Missoula Gulch group lie west or slightly north of the west end of the 

Anaconda-Parrot lode. · LATE ACQUISITION MINE. 

The Late Acquisition is generally regarded as a silver mine, although it lie~ on the borders 

of the copper belt, and up to 1906 had not . been sufficiently developed to prove that 

copper minerals do not occur in the deep levels. The mine is situated immediately north of the 

Gagnon, and has been developed by three shafts to a depth of 150 feet only. The workings ,. 

reveal the presence of one vein 1 to 3 feet wide, striking east and west, and clipping 78° S. 

Oxidation has extended downward for 80 feet, below which the unaltered ore resembles that 

of the other silver mines, except that it contains more galena and somewhat less zinc sulphide 

than do the silver veins of the Lexington group. Rhodochrosite and i·hodonite a:re both abundant, occurring in places as pockets of extremely rich ore, which are, however, small and not 

persistent vertically. 

MOUNT MORIAH MINE. 

The western extension of the Late Acquisition vein was formerly worked in the :Mount :Moriah 

mine, on which a number of shafts were sunk to depths of 100 to 200 feet. . These workings have 

been inaccessible for many years, so that the conditions underground are not known. The vein 

is wider on this claim than it is to the east, but has broken up or branched into a number of 

smaller parallel vei:qs, and the ore bodies so far mined (1906) have not been so rich as those in 

the Late Acquisition mine. At the extreme west end of the claim recent workings along the 

bed of :Missoula Gulch have encountered several pockets of rich ore along fault planes in dull 

dark quartz stained by iron and zinc but free from manganese. 

ANSELMO .MINE. 

The Anselmo claim, next south cf the Mount Moriah, has been opened to 150 feet below the 

surface by means of an incline following an east-west course, dipping 45° S. and gradually flattening to 30° near the bottom. A crosscut was driven south from this shaft for 150 feet. 

The vein, which is only. fairly productive, varies in width from 1. foot to 4 feet. In the crosscut 

three small veins have been cut, none of which were found to be persistent nor large, consisting 
250 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

for the most part of an association of broken vein material and clay walls, developed by post-

. mineral movement. Probably the ores are the result of mechanical, and possibly of chemical, 

concentration of the v~in minerals. 

CALEDONIA AND JASPER MINES. 

West of the Gagnon mine a great. many small silver veins, none of them extending mqre 

than 300 feet either vertically or laterally, carry rich ore in small pockets.· In width they vary 

from 1 inch to 3 feet, but their marketable ore is small. This ore is simil~r to the ores of the 

other silver veins, except that the amount of mangane~e and sphalerite is somewhat less. The 

Caledonia ~nd Jasper n1ines, located on these properties, are worked intermittently by leasers 

and show no extensive developn1ent. 

SILVER KING MINE. 

The Silver ICing mine shows a strong and well-defined quartz vein, too zincky and too low in 

value to pay for working, whose outcrop, though quite strong and easily traceable over the bare 

slope on the east side of Missoula Gulch below. the Gagnon claims, shows almost no quartz. 

The vein that is worked appears to be an offshoot or spur from this vein, and is believed to run 

northwestward into the Gagnon vein. The vein, which shows no outcrop nor· surface indication, was discovered while digging the foundations for a house. 

The vein splits.as it passes eastward, one branch passing out of the Silver King claim into 

that of the Plymouth. Surface developments and levels driven 8 or 10 feet beneath the surface 

traced both branches of this vein for several hundred feet. The hanging wall is rem·arkably 

smooth and regular, and in places shows slickensides. It marks the outer of a se?ies of three or 

four planes sheeting the granite. This granite on the hanging-wall side is nearly fresh, very 

hard, dark in color, and is unmistakably tlie normal and almost typical Butte quartz monzonite 

of the district. The footwall, on the other hand, is irregular and rolling, and the granite is more 

or less decomposed to a soft and clayey material or to a whitish granite impregnated with Inineral. The vein dips 60° to 65 o. Its width varies from 3 to 6 feet, owing to the irregular footQ wall. The pay streak runs across from the hanging wall to the footwall and is marked in the 

oxidized zone by its rusty color and the presence of manganese. In the deeper workings it· 

is recognizable only by scatterec;l quartz streaks and by the presence of well-defined minerals. 

The ledge is remarkable for its richness and for the amount of gold which it carries. The ore 

runs as high as 333 ounces in silver, and $294 in gold; as a rule, however, the ratio is $3 in gold 

to each 10 ounces of silver. The ore is not only remarkable for its richness, but for the fact 

that a large amount of it, though of very high value, is nothing but a granite, carrying minute 

particles and bunches of ore scattered through it; much of the ore looks like an ordinary decomposed granite. It contains a little quartz, it is true, but this quartz is more in the nature of a 

leader; that is, it marks the occurrence of the ore on its under side rather than being an ore 

itself. Most of the footwall ore, however, is dark-colored, decidedly quartzy, and easily distinguishable by its toughness from the granite .itself. The quartz streak on the hanging shows 

very well on the 250-foot level, east face, where it is lean and carries no values. A cross fault . 

running diagonally across the face, but more in the nature of a strike fault, seems to terminate 

the ore abruptly. · 

Westward a strong, well-defined, very zincky vein, with much clay, comes into the Silver 

King vein. West of the junction no pay ore has been found. This zinc vein has been explored 

for some distance on the 250-foot level and has so far failed to show up any ore shoot of value. 

The vein matter is soft and clayey, and it is with difficulty that the level has been kept open. 

The Silver King vein, on the contrary, needs but little timbering, and though not dry is 

not clayey. The dip of the vein is south, and the dip of the cross fault is also southward, but 

at a less steep angle. The Silver King vein strikingly contrasts with the veins of the silver 

mines farther north, such as the Moulton, Alice, and Lexington. In these last the ore occurs 

as minute black spots, few of them large enoug,tt to be distinctly recognizable, scattered through 

a quartz which is quite clearly a vein filling .. In the Silver King, on the other hand, the vein 
THE SILVER LODES •. 251 

filling is n1ore in the nature of a replacmuent, or in the ordinary language of the miner, an impregnation. By tllis it is not 1neant that the interstices of the rock have been filled with n1ineral, 

but rather that portions of the rock have been replaced by n1ineral. This distinction must 

be emphasized because n1any authors use th,e tern1 replace1l.1ent only where the entire rock 

htts been replaced, and in tllis case the granite texture, and, indeed, the granite nature of the 

rock is not only apparent, but is very striking .. The rich ore, which occurs in lenses in the 

grmlite, is composed very largely of clark ttnd amorphous-looking quartz, having none of thn 

chttrttcteristics of filling quttrtz. On .the contrary, the quartz stringers wllich accompany 

the vein are crystalline and show comb· structure, and are undoubtedly the filling of open 

·co, vi ties. 

The yield of the Silver King vein has been r.ather phenomenttl; and there \vas probably 

something like $150,000 wqrth of ore in sight at time of visit (1905). 

WESTERN GROUP. 

NETTIE AND PHILADELPHIA 1\fiNES. 

The Nettie and Philadelpllia mines were worked .for many years by the Colorado :Mining 

& Smelting Co., which also controlled the Gagri.on mine. They are situated about a mile 

southwest frmn Big Butte and 2 1niles from the city courthouse. Both are typical silver mines, 

in which the veins httve been reopened by faulting, with n1uch crushing H,nd the formation of 

lttrge mnounts of soft fault n1aterial, largely a clay or granite so thoroughly decomposed that 

when wet it runs badly and co,uses difficu~ty in 1nining. 

VEINS. 

GENERAL CHARACTER. 

The veins. have a general east-west course and show in \veil-defined outcrops. They are 

developed by three shttfts, the easternmost known as the Nettie, the 1uiddle. as the West Nettie, 

and the west as the Phil~delphia. The first shaft is 300 feet deep; the second, wlllch lies 700 

feet to the southwest of the first, has an inclined shaft 54°, 450 feet long, equivalent to a vertical 

depth of 370 feet. · 

The 1nine workings reveal the presence of three veins. The· Nettie (or north) vein varies 

from 6 to 8 feet in width, and consists of quartz, separated fron1 the country rock by tllick 

settms of gouge or fault clay, the country rock being decomposed aplite, altered for a distance 

of 12 to 20 inches outwttrcl fr01n the vein walls. 

The Philadelpllia vein, which is the southernmost of the three, carries· the principal workings. The drifts, which ttre largely to the west fron1 the No .. 2 shaft, extend for 300 feet to 

a rhyolite dil\:e. The vein htts an average width of 5 feet and carries exceptionally good ore. 

The three veins developed in the Nettie 1nine are all in aplite and are cut across by a dike 

of rhyolite just north of the :Nettie No. 1 shaft. This dike has a northwest and southeast 

course, is approximately 200 feet tllick, and splits in the lowest level of the No. 3 shaft into 

two branches septtrated by 140 feet of aplite. This rhyolite invariably cuts off the veins. It 

is not 1nineralized except where oxidized iron and manganese 1ninerals have formed by recent 

surface Wttters, and even these products contain no precious metals. (See fig. 107 .) 

In the earlier workings of the 1nines theN ettie (north) vein was the principal one developed. 

Later, when the inclined shaft was sunk, the Plliladelpllia (south) vein was opened up, and, 

as good values were encquntered; a third shaft was driven at the east end of the claim. 

NETTIE VEIN. 

The Nettie vein has not been developed west of the rhyolite dike. It has an average 

width of 3 feet. Ore shoots on the 300 and 200 foot levels are separated by 7 feet of barren 

cltty ttnd 1nashed granite. These two shoots are roughly heart-shaped, that on the 200-foot 

level being 100 feet in lateral extension, 90 feet in vertical extension, and having a nlaxilnum 
252 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

thickness of 10 feet. This shoot occurs directly south of the main shaft. A similar shoot on 

the 300-foot level is 100 feet long, 70 feet high, and has a maximum thickness of not more than 

10 feet. East of these shoots there is a barren zone 300 feet in length, then two persistent 

and well-defined ore shoots which stand vertically or have a slight pitch to the· east. The 

more westerly, which lies just west of the Hibernia shaft, is 140 feet wide, and has been stoped 

from the surface down to the 400-foot level of the Philadelphia shaft, a distance of 470 feet. 

The more easterly shoot extends from the surface downward and joins the west shoot on the 

400-foot level of the Philadelphia shaft. It is in places 400 feet long. Beyond these ore shoots 

the vein abuts directly against and is cu~ off by the rh)~olite dike. 

MIDDLE VEIN. 

The Middle vein has been somewhat developed at the east e:r;1d of the Nettie, where it 

has been most productive, and at the extension of the vein into the Hibernia claim. The 

vein is lean in the workings from the Nettie shaft, but becomes richer, developing an important 

ore body on the line separating the Hibernia and Nettie claims. The vein is developed on 

the 100, 200, and 300 foot levels of the Nettie shaft. It is a comparatively narrow vein, nowhere 

rich, which becomes lean at a depth of 300 feet, where it is merely a narrow veinlet composed 

N 

I ... 

~ 

~ . 

17SHAFT ,,.·:··,, • . ~• 

../ 

f : . 

[}3 ' [3] ~ ED 

Rhyolite Granite Rhyolite porphyry Veins Outline of workings 

50 100 ISO zoo zsoFeet 

FIGURE 107.-Plan of workings of Britannia mine, showing silver veins cut but not displaced by rhyolite dike. 

of valueless quartz impregnated with iron pyrite. In the upper course it carries small bunches 

. and pockets of pay ore, especially in the west end riear the rhyolite dike. This vein is probably 

encountered in the workings of the No. 2 shaft 100 feet north of the Philadelphia vein, though 

this correlation is not proved. 

... PHILADELPHIA YEIN. 

On the Philadelphia vein the workings show a long ore shoot extending the entire length 

of the development work from the No. 2 shaft. This vein is thicker than either of the other 

veins, attaining a width of 25 feet in places. It has been better developed than either of the 

other two veins, except for an interval between shafts Nos. 1 and 2 in which the rhyolite 

dike cuts off the· vein .. FRACTURES. 

The mine workings show at least three periods of movement. The first produced a series of 

parallel joint planes sheeting the aplite, and along these joint planes mineralization took place, 

forming the veins. Subsequent to this a series of northwest-southeast fault fractures were 

formed, faulting the veins and forming lines of weakness, along which the rhyolite dike was injected. These fractures appear to have been due to the volcanic outbreak of the Butte, and 

1nust have been in the nature of a sudden shock, as the aplite is not sheeted, nor is there a dislocation of the veins parallel to this plane of movement. The last period of fracturing resulted 
THE SILVER LODES. 253 

in displacement, producing three well-defined, persistent faults, which· cross the veins at right 

angles and throw their eastward extensions up to 150 feet northward. These faults run north 

and south ariel clip 45° E.; the most easterly shows a series of minor breaks or sympathetic fractures, with slightly steeper clip and distributed displacement, tllis being well shown on the east 

workings of the 550-foot level of the Philadelphia shaft. 

The veins are remarkably persistent fr01n one end of the mines to the other; they clip 

from 45° to 60° S.; they occur in aplite and vary in width from 1 inch to 25 feet. The 

vein filling, like that of all the silver veins of the camp, consists of quartz with associated silicate 

and carbonate of 1nanganese, and the usual sulphid~s, galena, sphalerite, pyrite, and probably 

argentite and proustite. The Nettie vein has a persistent and conspicuous outcrop, but is not 

workable below a depth of 300 feet. The Middle vein has a well-defined and strong outcrop, and 

has been worked to a depth ·of 500 feet, but has not proven particularly profitable. The Philadelpllia (south) vein has an ill-defined outcrop, but has proved very productive in the lower 

levels. It narrows westward and widens eastward. 

ORES. 

In the veins of the N ~ttie and Philadelphia property oxidation is complete to a depth of 200 

feet or n1ore, and extends along fault planes and fractures to the lowest levels. Its products 

consist of 1nanganese and iron oxides and silver chloride. Gold, though present, is not visible, 

and native silver is not abundant. :Manganese is extremelycabundant, especially in the upper 

levels, and it is forn1ing in the deeper levels as the r~sult of percolation of surface waters downward along the strike faults. The prin1ary ores consist of pyrite and complex silver sulphides, 

en1beclclecl in a 1natrix of quartz, rhodonite, and rhodochrosite. A diminution in manganese is 

noted \vith depth, the 550-foot level showing. a predominant quartz gangue. The ore contains 

sulpllicles of zinc, lead, iron, and silver. A typical cross section on the :Middle vein shows a 

sn1ooth hanging wall, devoid of clay selvage, with a streak 2 feet in width of nearly solid metallic 

sulphides resting upon a 4-foot band of quartz ore cut by innumerable veinlets fronl' one-fourth 

to one-half inch thick, rulllling approximately parallel to the vein walls and composed of rhodonite ai1cl rhodochrosite. The footwall streak is a fault fissure 6 inches thick, composed of finegl'ained ore and aplite in a clay n1atri..-x. 

The South vein, which gips 45° S., is 11 feet 3 inGhes wide on the 550-foot level. Where 

revealed by a crosscut on this level it shows a solid and fresh aplite hanging wall, with a 5-inch 

sean1 of clay separating the country rock from a band 2 feet thick of low-grade quartz ore containing metallic sulphides. This rests, in turn, upon a band 6 feet 9 inches thick of high-grade 

sulphide ore containing relatively small amounts of quartz; and this in turn is underlain by a 

10-inch band of barren white quartz frozen to the aplite footwall. In some places the ore forms 

small tongues which extend into the aplite, the 1nineralization gradually fading out. In general, 

the richest ore occurs nearest the hanging wall, and the footwall streaks ar~ lean or barren. The · 

banding of the vein is largely a true ribbon structure, clue to postrriineral fracturing, but there 

is also original crustifica~ion. 

MOODY & SANKEY, I.OWA, AND KOSSUTH MINES. 

The Moody & Sankey, Iowa, and l(ossuth mines, located near the western limit of the 

Butte quadrangle, are situated· on the crest of the knolls of granite which mark the limits of the 

lake-bed depression. To the north and east rhyolite covers the granite; westward the lake beds 

cover the bedrock; to the south an aplite inass is found. The area in which the veins occur is 

thus an island-like mass of granite, in which si..-xteen veins outcrop. Only six of these veins are, 

however, shown on the map, the others being too small or lacking i~ persistence to warrant it. 

The veins have a general east-west course, turning slightly north of east, and clip from 70° S. to 90°. 

The I\::ossuth shaft develops, to a depth of 90 feet, a typical silver vein whose features differ 

in no way from those already described. · 
254 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

The Moody & Sankey shaft was 270 feet deep at the time of examination, but has been 

filled with water for many years. The veins exposed in the upper .levels vary .from 1 to 3 feet 

in width, and consist of completely oxidized ores, composed chiefly of manganese oxide, lying 

on the hanging and. foot walls of the veins with impregnated quartz between. 

N 

0 

The Iowa shaft, near the east end of this 

s granite area, develops a vein 16 inches wide that 

lies on a contact between a granite footwall and 

an aplite hanging wall. The vein has an eastFEET 

5600 

5500 

5400 

5300 

west course, clips 80° S., and is developed to a 

depth of 80 feet. A parallel dike of aplite is 

encountered 20 feet north of the vein. 

In general, the veins of this vicinity show 

pronounced oxidation to a depth of a.t least 100 

feet. The most abundant minerals are psilomelane, wad, and pyrolusite, with less abundant 

n1alachite, the silver values occurring as cerargy-

. rite. Psilomelane occurs in radiating aggregates 

of crystals and mas~ive botryoidal forms. Pyrolusite is abundant as a crystalline coating on 

fracture planes on the vein. Wad is much more 

abundant than either of the other minerals, and 

is, of course, n1assive. :Malachite occurs only as 

minute needle-like crystals, filling cavities in the 

manganese oxides. Cerargyrite forms a thin 

coating which discolors the surface of the other 

n1ine.rals. 

KIT CARSON MINE. 

The Kit Carson mine, located in the gulch 

east of the Nettie, has four veins, which outcrop 

on the crest of the hill immediately north of the 

52oo shaft. These veins have an east-west course, and -H------------~ dip 70° S. They have been developed to a 

depth of but 100 feet. The workings lie north 

of the shaft, the crosscut developing an eastwest fault. The vein materials consist of abundant chalcopyrite, carrying crystals and mossy 

5roo aggregates of native silver on fracture surfaces. ~~-H----------~~ This is. the only vein encountered in the silver 

area where ·chalcopyrite exceeds iron pyrite 

in abundance. Galena is present in small 

amounts, and sphalerite· is abundant. String-· 

ers encountered in the veins show very high 

-----r--------------.::.:so:..:o:...:...o values in gold and silver. 

SOUTHERN AND EASTERN GROUP. 

50 100 ISO Feet ELLA MINE. 

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

FIGURE lOS.-Vertical section through ~lla mine. Although the Ella n1ine lies along the direct 

easterly continuation of the veins worked in 

the West Colusa and Leonard 1nines, its veins are typical silver lodes. The 1nine is situated 

!ri the flat valley bottom of Silverbow Creek, east of the Leonard mine. vVhen examined 

it was developed to a depth of 600 feet, and showed a well-defined silver-quartz vein, continu-
. THE SILVER LODES. 255 

ously exposed from the second to the sixth levels (fig. 108). The vmn has a width of 15 

to 25 feet, of which 4 feet may be reg~rcled as ore. 

The vein filling consists of well-banded or" crustified" quartz, rhodonite, and rhodochrosite, 

showjng in places as much as 6 to 10 feet of solid pink n1anganese ore, without quartz and 

devoid of banding. ·A quartz band 3 to 12 inches thick generally lies next to the selvage. 

This ore carries from 1 to 20 ounces in silver, with only traces of copper and gold, showing 

a progressive decrease in silver values downward. The walls are well defined, with clay selvages, 

but show no evidence of movement, the clay gouge being without pebbles or crushed granite 

and being probably due mainly to alteration. (See fig. 109.) The Wf.tll rock is but slightly 

n1ineralized for a few inches, being mainly hard, fresh granite, much of which shows veinlets 

of pink m.anga.nese. On the third level 6 feet of clay is seen on the foot wall. On the ·s.~cond 

level the vein has been developed by drifting for a distance of about 400 feet, but has not been 

stoped, as the values were low.. On the third level the rather irregular workings a.re mainly 

within the vein. 

The general strike of the vein is N. 65° E. and the dip 70° N. The vein is defined by 

fault slips, but is not a typical fault vein. A sample taken across a width of 3! feet gave only 

traces of copper and gold and 9 ounces in silver. 

The fourth level exposes a vein having a width 

of about 20 feet, marked by considerable pink 

manganese and quartz, and carrying 3! to 4 feet 

of ore that averages 40 ounces in silver. The ore 

consists mainly of pink manganese, with some 

colorless quartz mi."\:ed through .it. 

On the second level a crosscut driven north 

from the shaft euts a parallel vein; consisting of 

quartz, with pyrite, zinc, and galena, which has a 

width of 1 to 2 feet and dips 60° S. The granite 

walls are impregnated with zinc and galena, and 

a san1ple cut for a width of 1 foot y~eldecl 1.4 

ounces i1~ silver, with mere traces in· copper. A 

second vein cut in this north crosscut at a distance 

of 100 feet north of the shaft showed 2 to 4 feet 

of vein n1atter, mostly quartz. The vein dips 65° 

NE. and trends N. 70° W. It carPies no copper 

and low values in silver. Near the breast of this 

FIGURE 109.-Scction of Ella vein. 1, Granite; 2, rhodochrosite; 

3, quartz. · 

north crosscut a clay slip occurs, and a quartz veinlet running N. 70° E. and dipping 40° N. 

cuts through :fresh granite. 

On the fL:fth level the main vein lies north of the shaft, and is exposed not only by the 

crosscut but by a drift to the west. A 13-foot sample cut across the vein in the crosscut 

showed 2! ounces of silver. A south crosscut fr01n the 500-foot station (5,126 feet above sea 

level), 50 feet from the shaft, showed a banded quartz and rhodonite vein 3 or 4 feet wide (fig. 109), 

trending N. 85° E. and clipping 6.5° N. This vein carried low values in silver, with neither 

copper nor gold. The adjacent rock is fresh and blocky granite, showing a few veinlets of 

pink 1nanganese. At the 600-foot level the main ledge north of the shaft has a width of 13 

f~et and an ~verage silver content of less than 2 ounces. The vein walls here clip 80° N. and 

the granite lying south of the vein is cut by stringers of pink manganese. 

ANCIENT OR EMMA MINE (BLACK CHIEF). 

The big manganese outcrop of the Ancient (Emma) vein crosses South Washington Street 

two squares south of Silver Street. It is one of the most prominent silver veins of the district. 

Its outcrop consists mainly of black-stained quartz, with clecompos~cl clayey material forming 

para.llel streaks on each. wall. The outcrop is between 4.0 and 50 feet wide, as seen in cuts 
256 GEOLOGY AND ORE DEPOSITS OF BUTTE DISTRICT, MONTANA. 

made in the excavation of the streets. In the prospect pits it shows the usual sulphide ore, 

the mineral occurring in streaks and films in white quartz and being itself cut by later filling 

of secondary quartz. The vein has a pronounced southward dip. In the large ridge the 

outcrop shows occasional slickenside surfaces which cut across the vein. The main outcrop 

ends in a high knob which overlooks Missoula Gulch; a smaller outcrop continues across the 

gulch and becomes lost under the placer-ground flat, though still farther west, about a half 

mile beyond the gulch, a similar reef occurs that may be the same vein. Granite shows in 

the pr9spect shaft near Missoula Gulch immediately north of the lode, and granite also occurs 

across the gulch, where it is covered by 3 to 5 feet of clayey placer gravel alongside of a dike 

of rhyolite porphyry i25 feet wide. The prospect shaft on the sumn1it of the hill formed by the 

vein has cut through the footwall, and the dump shows fresh undecomposed granite and some 

quartz porphyry. 
~NDEX. 

A. 

Page. 

Aclmowlcdb'lncnts to those aiding ................................ Hi-Hi 

Adams mine, development or.................................... 195 

Adirondack mine, development of................................ 186 

Age, or fractures, ovidonoo of ..................................... 58-.59 

Alexander Scott mine, development or........................... 218 

Allee mine, dovoloprnont of .................................... 244-246 

section act·oss HoJnbow lode in ......... .'..................... 245 

AllhU1CO mine, development or................................... 195 

Allie Brown vein, character ol.................................... 240 

Alluvium, character and thickness or. ............ ~............... 46 

Alteration, variation in........................................... 92 

Altona mine, development of..................................... 237 

Amy mine, veins or.............................................. 243 

Amy-Silversmith .mine, development of.......................... 247 

Anaconda Co., shafts or, on Syndicate lode....................... 160 

Anaconda lode, Blue vein cutting, figure showing................ 109 

detailed description of.. .................................... 114-126 

faulting or .................................................. 125-126 

intersection or, with Blue vein ............................. 138-140 

figures showing ..................................... 109,117,137 

mineralization or ........................................... 122-125 

sections through, figures showing ....................... 118, 123, 124 

Sec ltlso partiwlar veins. 

Anaconda mine, analysis or cupro-alum stalactite from........... 81 

section through, figure showing............................... 115 

shaft or, plato showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 

Sec also particular veins. 

Anaconda-Parrot belt, lodes and veins of ....................... 114-1.54 

Sec also particular veins. 

Anaconda-Parrot lode, veins or ................................. 114-136 

Sec also part.icular vein.~. 

Anaconda shaft, sections through, figures showing .............. 115,119 

Anaconda system of veins. gem oral features of..................... . 107 

Anaconda vein, cut by l~luc vein, plato showing................. lOS 

ideal cross section of, plato showing........................... 110 

orcs and wall rock of. ...................................... ll4-ll6 

relation of porphyry dike to, figure showing.................. 61 

sections along .......................................... 115, 116, 117 

splitting or ................................................. 11fr-117 

figure showing. . . . . . . . . . . . . .. .. . . . . . ... . . . . . . . . .. . . . . . . .. . 118 

variation in charactm· and richness or, figure showing......... 116 

Ancient lode, outcrop of, plato showing.......................... 84 

Ancient mine, development or. ...... ·.· ......................... 255-256 

Anderson mine, development of ..... : .................. :.......... 194 

Andesite, character and distribution of. .......................... 27-28 

Anselmo mine, development or. .............................. · .. 249-250 

Aplite, alteration or.............................................. 90 

character and distribution or .•............................... 36-40 

' inclusions or.............................. . . . . . . . . . . . . . . . . . . . . 38 

intrusions of, figure shO\Ving.................................. 39 

origin of ...................................................... 39-40 

petrographic features or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-37 

relation of, to copper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

variations in, analyses and figure showing ................... 37-38 

weathering or, effect or........................................ 38 

Areal distribution of orcs, general conclusions regarding .....•.... 66-67 

Arsonic, occt"irronco or, in ores.................................... 70 

Atlantic mine, development of. .. . . .. . . . .. . .. .. .. .. . .. .. .. .. .. .. . 231 

D. 

Bailey vein, character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 

Banded oro near Lexington mine, plate showing. . . . . . . . . . . . . . . . . 72 

Bnrito, distribution and character or.............................. 84 

Betty vein, character of and figure showing ........ .'............. 209 

90427°-No. 74-12--17 

Page. 

Bello of Butte mine, development of............................. 247 

Boll fault of Speculator vein, in High Ore mine, figure showing... 183 

Boll mine, vein outcrop near, plate showing ................... ·... 54 

Bell shaft, north-south section through, figure showing........... 176 

Boll vein, character of. ......................... ~ ............... 178-179 

Belmont vein, character of....................................... 192 

Bench marks, changes in elevations of... . . . . . . . . . . . . . . . . . . . . . . . . . 50-51 

Berkeley vein, character of....................................... 227 

Bertha group of claims, development of ...... .' ................. 235-236 

Bertha mine, development of..................................... 235 

Big Butte, rhyolite complex at, character of...................... 45 

structural relations of.. . .. .. .. . .. . .. . . .. .. .. . . . . . . . . . . .. . . . .. 56-57 

Biotite, analyses of ....... ~ ...................................... .' 35 

Black Chief mine, development of .............................. 255-256 

"Bluebird granite," character and distribution of ................. 36-40 

See also Aplite. 

Blue Jay fault, relation of, to Mountain View-Shannon-Colusa belt. 202 

truncation of Mountain View south vein by, figure showing.. 201 

Blue Jay fault vein, character and development of ............. 152-154 

Blue Jay fracture system, character of............................ . 210 

Blue system of veins, and Steward system, comparison of ...... 108-109 

Blue vein, cutting Anaconda lode, figure showing .......... 109,117,137 

cutting Anaconda vein, plate showing........................ 108 

detailed description of ............... ~ ..................... 137-142 

development and general character of. . . . . . . . . . . . . . . . . . . . . . . . 138 

intersection of, with Anaconda lode ........................ 138-140 

with Steward vein ................................. :..... 140 

judicial investigation of .................................... 137-138 

orcs of. ..................................... · ... : ........... 140-142 

sections through ........................................... 117,137 

Blue vein fracture system, minor fractures of. ..... ·.· ........... 209-210 

veins of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205-210 

Blue vein system, veins of. .................................... 136-145 

Blue Wing lode, development of................................. 239 

Bornite, distribution and character of............................ 74 

paragenesis of. ....... · ....... ~ ............................. , . . 85 

petrographic relations of, figures showing ..•.................. 74, SO 

Boulder, aplite near, figure showing texture variations in. . . . . . . . 37 

Boulder batholith, chemical and mineralogical relations of ........ 33-34 

rooks of, analyses of .......................................... 33,34 

sheeted granite of, plato showing............................. 26 

Brecciated sulphide and quartz in Lexington mine, plate showing. 240 

Britannia mines, world.ngs of, plan showing...................... 252 

Buffalo mine, development of.................................... 166 

Bullwhaoker ffiine, development of. ..•........................ 234-235 

Butte, description of............................................. 17 

geologic and vein map of ................................ In pocket. 

Butte & ~oston No.7 mine, development of ................... 231-232 

13 utto district, derivation of name of. . .. . .. .. .. .. .. .. .. .. .. .. .. .. 1 7 

geologic map of region near .............................. In pocket. 

western part of, plate showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Butte Flat, veins of ..................•......................... 230-232 

Butte minos, diagram showing elevations or. ................ In pocket. 

Butte quartz monzonite, alteration of ............................ 86-90 

character and distribution of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-36 

chemical and mineralogical character and analyses of ......... 33-36 

composition of, by volume .•................................. 91-92 

contact metamorphism of, effect of.. . . . . . . . . . . . . . . . . . . . . . . . . . 87 

distribution of. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 32-33 

intrusions of aplite in, figure showing. . . . . . . . . . . . . . . . . . . . . . . . 39 

metasomatic alteration of, effect of ......... -.. . . . . . . . . . . . . . . . 87-80 

petrographic features of ...................................... 31-32 

rhyolite porphyry surrounding, plato showing............... . 32 

texture or, plato showing..................................... 32 

weathering of ................ ! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86-87 

257 
258 INDEX. 

c. 

Page. 

Calcite, distribution and character of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 

Caledonia mine, development or.. ................. ·............... 250 

Caledonia vein, character of and development along.............. 152 

Cambers mine, development of................................... 194 

Chalcanthite, distribution and character of....................... 81 

stalactites of, plate showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 

Chalcocite, distribution and character of ......................... 75-76 

formation of, by secondary enrichment....................... 102 

of Leonard mine, specimen of, figure showing. . . . . . . . . . . . . . . . 76 

veinlets of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 

figure showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 

paragenesis of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 

Chalcopyrite,. distribution and character of....................... 75 

in quartz, in enargite veinlet, figure showing .............. ~.. 75 

occurrence of, in wall rock ..... , ...... , . . . . . . . . . . . . . . . . . . . . . . 93 

paragenesis of ............................................... , 85 

Chapman, R. H., leveling by. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 

Chrysocolla, distribution and character of........................ 81 

Classification of vein systems, discussion of ..................... 106-107 

Clear Grit fault, displacement of, by Steward vein, figure showing. 149 

displacement of Rialto vein by, figure showing............... 149 

Clear Grit vein, character of...................................... 144 

Climate, features of .............................................. 17-18 

Clinton mine, development of.................................... 234 

Colleen Bawn mine, development of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 · 

Colorado mine, development or................................... 193 

Columbia Garden, veins of........................................ 238 

Colusa-Leonard lode, extent, character, and faulting of ......... 203-216 

Colusa lode, character, faulting, and veins of.. .................. 203-211 

Colusa mine, section through, figu~e showing...................... 205 

Colusa-Parrot shaft, sectlon through, figure showing ......... ·..... 128 

Colusa-Parrot vein, sections through, figu.re showing ............ · 121,125 

Colusa vein, in West Colusa mine, figure showing .... ·............ 197 

Composite copper veins, general features of. .................... 109-110 

Composition of vein, changes of, in depth......................... 111 

Qoncentration, of copper ores, from wall rocks .................... 93-94 

Concentration processes, character and effects of ............... · .. 97-104 

Conglomerate ore, of Steward fault vein, plate showing........... 110 

Continental fault, changes induced by............................ 4.7 

evidence of. ...... , ................... ~ ....................... 47-49 

Copper, amount of gold and silver in ores·of. ..................... 67-69 

area of deposits of, location of................................. 66 

composite character of veins of ............................. 109-110 

concentration of, from wall rocks ............................. 93-94 

occurrence of, in basic minerals............................... 94 

primary source of. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 93-97 

relation of, to aplite.......................................... 96 

to rhyolite porphyry .......... , .......................... 95-96 

Copper area, location of. .............................. ~.......... 66 

Copper lodes, detailed descriptions of. .......................... 113-238 

method of treatment or.. ...................... : ............ 113-114 

nomenclature and subdivisions of............................ 113 

sections of. ................................................. 113-114 

See also particular lodes and veins. 

Copper mining, development of .................................. 19-22 

Copper ores, metallic composition of .............................. 67-71 

minerals of ........ , .......................................... 72-82 

paragenesis of ......... : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84-85 

sources of. .................................................. 93-104 

structure of ........................... :...................... 74 

tenor of...................................................... 67 

weight of ................... :................................. 71 

Copper pitch, distribution and character of....................... 81 

Copper-vein systems, classification and general features of .. : ... 106-109 

Corra mine, development of. ............................... 182, 185-186 

Cost, of copper mining, figures showing........................... 24 

of silver mining, statistics of. ....................... ,......... 240 

Country rock, influence of, in vein filling ................ · ....... 110-111 

Covellite, distribution, character, and analysis of ................. 76-77 

occurrence of, in quartz-pyrite and enargite, figures showing.. 77 

Covellite vein, mines on ........................................ 181-183 

Cross faults, character and distribution of. . . . . . . . . . . . . . . . . . . . . . . . 63 

Cross vein, character of........................................... 228 

Cuprite, distribution and character of............................ 80 

Cupro-alum stalactite, analysis of.. ............... ·................ 81 

Curry vein, character of .•...........•............. ·:·.............. 243 

D. . Page. 

Dacite, occurrence and origin of.................................. 29 

Decomposition of granite, effect of................................ 54 

Dernier veln, character of .............. ·. . . . . . . . . . . . . . . . . . . . . . . . . . 165 

cut-off and spraying of, figures showing.. . . . . . . . . . . . . . . . . . . . . 112 

in East Greyrock mine, character of.......................... 184 

Development of Butte district, account of ........................ 18-22 

Diamond-Bell group, general relations and faulting of .......... 171-176 

. veins in .................................................... 176-186 

Diamond mine, development o·f. ............................... 182-183 

veins in, figures showing ................................... 174, 176 

Diamond shaft, section through, figures showing................. 174 

Diamon·d vein, description of.. ................................. 176-177 

Dike of rhyolite porphyry, figure showing........................ 42 

Discovery, of Butte district, account of.......................... 18. 

Disintegration, of granite, effect of.. ......................... : .... 53-54 

Disintegration bowlders, manner of formation of, plate showing.. 5 

Drainage, general features of. .................................... 16-18 

E. 

East Bell vein, character of...................................... 183 

East Butte belt, mines and veins of ............................ 189-1!)5 

East Greyrock mine, development of ........ : .................. 181-182 

section through, figure showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 

veins in, character of. ...................................... 183-1817 

East Ridge, evidence of faulting afforded by ..................... 48-49 

rocks of. . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 

structural relations· of. ....................................... · 55-56 

veins of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232-238 

East-west system of veins, general features of..................... 107 

East-west veins, of Diamond-Bell group, description of ......... 176-177 

of Rarus group, character of ............................•..... · 228 

locations of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 

Edith M:ay vein, character of..................................... 188 

level on, where crossed by clay seam, figure showing......... 188 

Elevations, of levels of Butte mines, diagram showing. . . . . . . . In pocket. 

recent changes in ............................................. 50-51 

Elk Park drainage, evidence of faulting afforded by.............. 47 

Ella mine, development of: ................................ : ... 254-255 

vertical section through, figure showing...................... 254 

Ella vein, section of, figure showing.............................. 255 

Emma mine, development of .................................. 255-256 

Emmons, S. F., work of .......................... :.............. 15 

Enargite, distribution, character, and analyses of ................. 77-7~ 

formation of, by secondary enrichment ..................... 102-103 

inclosed in bornite, figure showing ......................... ~. 74 

in Leonard mine, figure showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 

occurrence of chalcopyrite in.................................. 75 

paragenesis of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 

relations of, to covellite and quartz, figures showing.......... 77 

to pyrite, figure showing ................... ·............... 78 

Exemption claim, development of ....... .-....................... 236 

F. 

Fault breccia, in Mountain View mine, plate showing............ 2Q4 

of Original mine, plate showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 

Faulting, character and extent of ................................ 47-51 

continental, effects and evidence of ........................... 47-49 

mapping or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 

present effect of ........ : ............. .-...... : . . . . . . . . . . . . . . . . 50-51 

See also particular veins. 

Field work, account of............................................ 15 

Fissure systems, classification, directions, and relations of, ....... 59-62 

early and late, relations of ........................... ·. . . . . . . . . 63-64 

relations of, to jointing in granite ............................. 60-61 

Flat, evid~nce of faultin~ afforded by ............................ 47-4.8 · 

Flood vein, description of. ...... : .............................. 176-177 

Fluorite, distribution and character of ...... · ............ ~ ........ 83-84 

Fractures, age and occurrence of ................................. 58-64 

directions of ........................ :. . . . . . . . . . . . . . . . ... . . . . . . . 60 

'extent of ..................................................... 61-{)2 

regularity of ....................................... , .......... 59-60 

spacing of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

Future of Butte district, deductions regarding .•.••..•........... 24-25 
INDEX. 259 

\ 

G. . . Page. Gagnon mine, fault cutting primary quartz-pyrite vein in, plate 

showing_............................................ 110 

faults, veins, and ore bodies in ............................. 134-136 . 

relations of minerals of. ...................................... 84-85 

sections through, figures showing............................. 135 

Stowurd vein ln ................... ·........................... 151 

plate showing............................................ 110 

Gagnon shaft, sections ncar, figures showing ................ 140,141, 146 

Gagnon vein, section through, ncar Gagnon shaft, figure showing.. 140 

Galcrm, distribution and character of. ... , ............. ,.......... 79 

occurrcricc of, with zinc blende and quartz, figure showing.... 79 

Grunbctta vein, character and composition of .................. 20G-207 

cut by Piccolo vein, figure showing.......................... 206 

Gangue, inincrals of. ............................................. 82-84 

Garfield vein, character of........................................ 243 

Gem vein, character of. .............................. · ........... 188-189 

scc.tions or,_ on 400-~oot level, figures showing ................ ISS, 189 

Gcogro.phy, general features of ................................... IG-18 

Geologic features bf Butte district, summary of................... 30 

Geologic relations, general features of. ............................ 26-27 · 

Geology of Butte district, map showing ..................... In pocket. 

Gcyman vein, character of....................................... 192 

Gillie, John, assistance rendered by.............................. 15 

Olcngarry mli1e, development or ....................... 191-192,248-249 

Glengarry vein, mines on ... ~ ................... : .... .' ......... 190-192 

Gold, in co'ppc.r orcs, occ.urrc.nco of. .............................. 67-GS 

in orcs, distribution and character of.. . . . . . . . . . . . . . . . . . . . . . . . 79 · 

Gold Hill mine, development of. ...... '............................ 195 

Gold mining, epoch of.. ........................................ :. 18 

Goldsmith mine, development of. .................... • .......... 247-24~ 

Goslarltc, distribution and character 9f........................... 82 

Goodale, C. W., assistance rendered by........................... 15 

Granite, cluuactc.r and distribution of ............................. 28-29 

fracturing or, figure showing ...................... :........... 98 

mineralized joints in, plate showing.......................... 32 

quartz veins in, figure showing............................... 96 

relations of jointing in, to fissure systems ..................... 60-61 

Granite area, structural relations of .............................. 52-54 

Gmnitic. rocks, character, age, and subdivisions of. ............... 31-40 

Green Copper mine, development of.............................. 195 

. Green Mountain mine, development of. ................. :.: .... 170-171 

plato showing................................................ 170 

sections of Syndicate lode in, figures showing .......... po, 171,173 

Groyrock group, veins and mines of. ........................... 179-186 

Ground Squirrolmino, development of........................... 192 

Gypsum, distribution and character of .................. :........ 83 

H. 

Hawkeye vein, character of. ............................... ·...... 243 

Henry George mine, development or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~94 

Res per us mine, development of. .............................. .".. 194 

Biggins vein, character of. .................. ·..................... 183 

High Oro group, veins of. ........ ; ............................. 177-179 

High Oro mine, Bell fault of Speculator vein in, figure showing... 183 

displacement of Skyrmc. vein in, figure showing.............. 180 

section showing faulting in ................................... · 201 

High Oro system of veins, general features of .............. · ..... 107-108 

See also Silvcrbow system. • 

High Oro vein, cha.racter of. ................................. :. 177-178. 

figure showing section in..................................... 178 

Hillebrand, W. F., analyses by .................. 35,38, 77,81,82,88,101 

on composition of mine waters .............................. 99-101 

Hogan vein, description of ............................... •........ 122 

section through, figure showing.. . . .. .. .. . .. .. .. .. .. .. .. .. .. . 126 

Homc.stako mine, development of................................ 234 

Homestead tunnel, sheeted granite near, plato showing........... . 26 

Hornblende, analyses of.......................................... 35 

HUbncrite, distribution and character of ......................... 80,85 

Hyde Pa.rk dike, analysis of rhyolite from........................ 44 

I. 

Ida mine, development of. .................................... : 237-238 

Iduna mine, development of..................................... 193 

I(Iumi vein, cross section of, figure showing....................... 193 

Igneous rocks, character and distribution of ..... : ..... ·........... 26 

See also specific varieties. 

Inclusions in aplite, character of ............. ~ ....... : .. : .. ·;.... 38 

Page. 

Intermediate copper belt, mines and veins of. .................. 154-156 

Investigations, account of........................................ 15 

Iowa mine, development of. ................................... 253-254 

Iron vein, in Silvcrbow mine, figure showing..................... 158 

J. 

Jasper mine, development of..................................... 250 

J. B. vein, description of ................................... · .... 176-177 

Jessie-Edith May group, veins of. .............................. 18G-189 

Jessie vein, character of. ...................... · ................. 186-187 

displacement of, by fault of Steward system, figure showing.. 187 

J. I. C. mine, development of. ............... ·.................... 192 

Jolmstown No.2 vein, character of............................... 225 

Johnstown vein, character of ........................... 159,201-202,225 

Jointing, in granite, o1Icct of.. ...................... ~............. 53 

in granite, figure showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 

relations of fissure systems to ........ · ..................... 60-61 

K. 

Kaolin, distribution and character of .. ,.......................... 83 

Kcc.gflll vein, character of ............ ~ ......................... 164-165 

Kit Carson mine, development of:............................... 254 

Klondike crosscut, section through, figure showing .......... ":.... 159 

Kossuth mine, development of ........... · .................. '. . . . 253-254 

L. 

Lake beds, character, distribution, and origin of.. ................ 4£;-46 

origin and geologic relations of................................ 29 

La Plata lode, dev~lopment of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 

La Plato mine, vein structure of, plate showing. . . . . . . . . . . . . . . . . . 240 

Lassonose, from Big Butte, analysis of ......... _.................. 45 

Late Acquisition mine, development of.......................... 249 

Lead, occurrence of, in ores .................. ~.................... 70 

Leonard lode, fissure containing pyrite and enargito in, section 

. showipg ......... · ............. :....................... 210 

· general character and veins of. ............................. 211-215 

Leonard mine, chalcocite specimen and vein let at, figures showing. i6 

character, faulting, orcs, and veins of ....................... 211-215 

cnargite in, figure showing................................... 215 

fracturing of granite in, figure showing. . . . . . . . . . . . . . . . . . . . . . . 98 

Gambctta vein cut by Piccolo Yein in, figure showing........ 206 

oro body of, fib'Ure showing ......... ,......................... 2H 

relations of minerals of. ...................................... 84-85 

relations of minerals of, figure showing. . . . . . . . . . . . . . . . . . . . . . . 85 

sections through, figures showing ............... 205, 20i, 208,212,213 

silver and copper values in, figure showing................... 69 

vcinlcts of chalcocite in....................................... 95 

Leonard ore body, cut by Minnie Healy (Betty) vein, figure showing ................................ ,.................. 209 

Leveling, indications of present-day faulting shown by ... · ........ 50-51 

Levels of Butte mines, diagrams showing .................... In pocket. 

Lexington mine, ban~ccl ore near, plate showing................. . 72 

brecciated sulphide and quartz in, plate showing............. 240 

cost of mining at............................................. 240 

Lexington mine, development of. .... ·............................ 240 

ores of ...................... : ............................... 240-243 

Lexington group, veins of ...................................... 239-243 

Lillie claim, development of.. ... , ............. :.................. 235 

Limonite, character, distribution, and analysis of. .............. : 82 

stalactites of, plate showing ............................. ,.... 82 

Little Mina mine, development of. ............. .'................. 141 

Liz~ie mine, development of. .................................. 193-194 

;tJocation of But to district, index map showing................... 16 

M. 

Maggio mine, development of. ................................. 236-237 

Magna Charta mine, development of............................. 246 

Magnetite, distribution and character of .................. :....... 83 

intcrgrown with pyrite, figures showing....................... 84 

Magnolia vein, character of....................................... 243 

Malachite, distribution and character of ......................... ·.· 81 

Manganese, occurrence of, in ores................................. 69 

Manganese minerals, distribution and character of................ i9 

Mapping of faults, ·method of..................................... 47 

Marcasite, character of............................................ i4 

Mat mine, development of. ..................................... 217-218 · 

Matte, composition of and loss of in smelting, tables showing..... 71 
260 INDEX. 

Page. 

Meadcrville, mines north of. ................................... 216-218 

sheeted granite north of, plate showing....................... 54 

Melaconite, distribution and character of ... ,..................... 82 

Metals, in ores, amounts of. ...................................... 7Q-71 

Middle vein, of Nettie and Philadelphia mines, development of.. 252 

Mineralization, along joints in granite, plate showing............. 204 

deflection of, in Rams group of veins......................... 224 

Mineralized joints in granite, plate showing....................... 32 

Minerals, of gangue, descriptions of. .............................. 82-84 

of ores, descriptions of. ....................................... 72-82 

Miner's Union mine, development of............................. 186 

Mines, production of, statement and tables showing .............. 22-24 

Mine temperature, records of..................................... 104 

Mine waters, composition and analyses of ....................... 99-101 

Mining, cost of ............... ,................................... 240 

in Butte district, future of. .................................. 24-25 

Minnie Healy vein, character of and figure showing.... . . . . . . . . . . . 209 

Missoula Gulch group of mines, development of ................ 249-251 

Modoc dike, plate showing part of................................ 32 

Modoc mine, character and development of....................... 216 

Modoc vein, character of ........ :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 

Molybdenite, distribution and character of....................... 79 

Montgomery claim, development of.............................. 236 

Moody & Sankey mine, development of ............. : .......... 253-254 

Moonlight vein, description of. ................... : ............. 120-122 

faulted by Blue Jay fault, figure showing..................... 121 

Moose mine, development of. ................................... 246-247 

Moose vein, character of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 

Moscow mine, development of.. ..................... __ ........... 166 

section of Syndicate lode in, figure showing................... 166 

Moulton mine, plate showing ...... .-.................. ;........... 170 

veins of- -. -- -................ --. - . ---.. ' . . . . . . . . . . . . . . . . . . . . . 243 

Mountain Con. mine, altered quartz monzonite from, figure showing................................................... 84 

development of.. ........................................... 167-169 

sections of Syndicate lode in, figures showing ............... 168, 169 

spraying of ore in, figure showing............................. 169 

Mountain View fault, relations of, to Mountain View-ShannonColusa belt ............................ ·............... 202 

Mountain View fault vein, character of. ........................ 225-226 

development, character, intersections; and ores of .......... 142-143 

Mountain View mine, fault breccia in, plate showing............. 204 

faulting of veinlets of North vein in, plate showing........... 202 

location, character, and veins of. ........................... 196-203 

quartz-pyrite vein in, plate showing.. . . . . . . . . . . . . . . . . . . . . . . . . 202 

relative positions of veins and faults of, figure showing........ 202 

section showing faulting in................................... 201 

section through, figure showing............................... 198 

veins on 1,100-foot level of, figure showing. . . . . . . . . . . . . . . . . . . . 223 

Mountain View-Shannon-Colusa belt, mines, veins, and lodes of. 196-216 

Mountain View south vein, character of .................. : ..... 200-201 

section of, figure showing..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 

truncation of, by faults, figures showing...................... 201 

Mountain View system veins, character of.. .................... 202-203 

Mount Moriah mine, development of............................. 249· 

N. 

Nettie mine, analyses of aplite from.............................. 37 

development of.. ........................................... 251-253 

Nettie vein, character of ........................................ "251-252 

Neversweat mine, Blue vein cutting Anaconda vein in, plate showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 

from southeast, plate showing................................ 114 . 

sections at, figures showing ................................. 123, 125 

Nickel, occurrence of, in ores...................................... 70 

Nipper mine, development of. ............ ~...................... 140 

No.3 mine, development of.. .................................. 19Q-191 

No.3 vein, in Silver bow mii1e, figure sjlowing.................... 158 

No. 6 raul t, character and development of........ . . . . . . . . . . . . . . . . . 152 

No. 12 fault vein, character of.................................... 206 

cutting Shannon vein, figure showing........................ 196 

North Connecting vein, character of. ................... 159, 201-202,225 

Northeast system, of Rainbow group, character of veins of........ 243 

Northern mines, development of. ............................... 248-249 

North vein, character of............................ . . . . . . . . . . . . . . 227 

·in Mo;untain View mine, plate showing....................... 202 

Pa.ge. 

Northwestern mine, development of. ........................... 233-234 

Northwest veins, east of Rams raul t, character of... . . . . . . . . . . . . 226-228 

west of Rams fault, character of.. .......................... 225-2 

0. 

Old Glory vein, character of...................................... 165 

O'Neill ledge, description of. ....... ~............................. 122 · 

o'res, character, types, and distribution of. ............... -.. --.-. 65-85 

Original mine, fault breccia of, plate showing..................... 108 

ores and veins in ............................................ 133-134 

section across ore body in, figure sho\\ing..................... 133 

Steward vein in.............................................. 151 

Steward vein and Parrot lode in, figure sho\\ing.............. 150 

Otisco mine, development of..................................... 193 

Oxidized minerals, distribution and character of. ................. 80-82 

P. 

Pacific claim, development of.................................... 236 

Paragenesis, conclusions regarding ............................... 84-85 

Parnell mine, character and development of. ................... 154-156 

cross section of Schweitzer vein in, figure sho\\ing............ 156 

Parrot lode, development and general character ................. 126-136 

fractures of. ................................................ 129-130 

in Gag~on mine, charaqter of................. . . . . . . . . . . . . . . . . 135 

sections through, figures shO\\;ng ................... 127. 128, 129. 132 

splitting of. ................................................ 128-129 

Steward vein cutting, figure showing......................... 150 

Parrot mine, face of drift in, p)ate showing....................... 84 

occurrence of silver at, figures showing....................... 80 

ores, fractures, lfind faulting in .............................. 13Q-132 

sections in, figures showing ............................. 127, 129, 132 

Parrot shaft, section of veins west of, figure sho\\ing.. . . . . . . . . . . . . 148 

section through. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 

Parrot vein, cut by Blue vein fault, figure sho\nng ... ·.·.......... 117 

faulting of, by Steward and No.6 veins, figure showing....... 147 

in Original ntine, character of................................ 133 

section through, near Gagnon shaft, figure showing........... 140 

Pennsylvania mine, sections through, figures sho\\ing .......... 198,199 

PennsylvaniaN o. 2 vein, geologic relations of.................... 226 

Pennsylvania No.8 vein, location of.............................. 226 

Pennsylvania vein, description of .............................. 117-120 

Philadelphia mine, development of. ............................ 251-253 

Philadelphia vein, character of................................... 252 

Piccolo vein, character of ....................................... 208-209 

cutting Gambetta vein, figure shO\\ing....................... 206 

Pisanite, distribution and character of............................ 82 

Pittsburg & Montana property, development of.................. 231 

Porphyritic dacitic pitchstone, analysis of ............... :........ 45 

Porphyritic rocks, character and distribution of .................. 40-45 

Porphyry dike, relation of Anaconda vein to, figure showing. . . . . G4 

Poulin mine, development of..................................... 166 

Precious metals, in copper ores, occurrence of. .................... 67-69 

Preferencia mine, development of................................ 195 

Previous work, account oL... ... . .. . . . .. .. . .. .. .. .. .. .. . ... . . . . . 15 

Primary minerals, descriptions of. ............................... 73-80 

Production of Butte district, amount of .......................... 22-24 

by mining and smelting companies, table showing............ 23 

• by years, table showing...................................... 23 

in May and June, 1907, table showing........................ 24 

Pyrargite, distribution and character of.. . . . . . . . . . . . . . . . . . . . . . . . . RO 

Pyrite, distribution, character, and metallic content of ........... 73-74 

occurrence of, in granite, figure showing.. . . . . . . . . . . . . . . . . . . . . 73 

in wall rock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 93 

with other minerals, figures showing ......... 74, 76, 7i, 78, 79,81 

secondarily inclosed in bornite, figure showing................ 74 

Pyrite vein, in Original mine, character of........................ 134 

Pyritization, effect of ............................................ 91-92 

Pyritized granite, fracturing of, figure showing................... 98 

Q. 

Quartz, in gangue, distribution and character of. ................. 82-83 

Quartz monzonite, character, distribution, and analyses of. ....... 31-36 

See Butte quartz monzonite. · 

Quartz-pyrite vein, fault cutting, plate showing.................. 110 

in Mountain View mine, plate showing....................... 202 

Quartz veins in silicified granite, figure showing................. 96 
INDEX. 261 

R. 

Page. 

Railroo.ds, cfl'ect of construction of................................ 20 

Hainbow group, vein systems of.. .............................. 243-248 

Hainbow lode, development of. ................................ 243-248 

section across, in Alice mine.................................. 245 

Ran1s area, veins of, cnst of Harus fault, figure showing.......... 222 

Rarus fault, character of. .............................. 210-211,228-230 

cutting Shannon vein, figure showing........................ 196 

dip, displacement, filling, and ore bodies of ................ 228-230 

cnst wall of, figure showing................................... 221 

trunco.tion of Mountain View south vein by, figure showing.. 201 

veins cnst of, character of.. ................................. 226-228 

figure showing........................................... 222 

veins west of ......................................... :. . . . . 224-226 

west wall of, figure showing.................................. 220 

Rams group of veins, character of .............................. 218-238 

correlation of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219-222 

development of .................................... : . ...... 218-219 

structure of. ............................................... 222-224 

Harus mine,, unalysis of enargito from............................ 77 

minorulizution along joints in granite in, plate showing....... 204 

partial analyses of oro samples from.......................... 67 

relative position of faults and veins in, figure showing........ 202 

sections through, figures showing ................. · .......... 157,198 

veins on 1,200-foot love!, of, figure showing.... . . . . . . . .. . . . . . . . 223 

'Vindlnss vein in, figure showing............................. 226 

Raven vein, character of......................................... 165 

Heins Copper Co. mine, development of ........................ 216-217 

Rhodonite, distribution and character of......................... 84 

Hhodochrositc, distribution and character of..................... 84 

Rhyolite, alteration of. ................. : ......................... 90-91 

character and distribution of. ................................ 42-45 

complex of, at Big Butte .......... :.......................... 45 

dikes of, character and occurrence of. ......................... 44-45 

occurrence and origin of...................................... 29 

Hhyolitc-dacitc, character and occurrence of...................... 4 

Rhyolite pOIJ>hyry, altcmtiqn of ................................. 90-91 

charucter, distribution, and analyses of. ...................... 40-42 

dikes of, direction and occurrence of. ................ : ........ 41-42 

figure showing characteristics of.. . . . . . . . . . . . . . . . . . . . . . . . . 42 

relation of, to copper ......................................... 95-96 

relation of fissures to dikes of................................. 63 

surrounding Butte quartz monzonite, plate showing.......... 32 

weathering of, effect of....................................... 41 

Rialto vein, displacement of, by Clear Grit fault, figure showing.. 149 

displacement or, by Steward vein, figure showing............ 149 

in Original mine, character of. ............................. 133-134 

Hock alteration, character and effects of .......................... 86-92 

Rocks, occurrence and character of............................... 31 

Sec also 7Jarticular varieties. 

Rutile, dlstrl button and character of............................. 83 

s. 

st: JJawrenco mine, alten>d and mineralized. granite in,. figure 

showing.............................................. 124 

plan of, at 1,400-foot level, figure showing..................... 153 

Sales, Heno, nssistanco rendered by.............................. 1G 

Sarsfield claim, development of................................... 236 

Schwoltzor-Monltor tunnel, development of...................... 238 

Schweitzer vein, cross section or, in Parnell mine, figure showing.. 156 

Secondary enrichment, general nature and effects or. ............ 101-104 

Secondary fissures, character and distribution or .................. 62-63 

relation or, to rhyolite porphyry dikes........................ 63 

Scdlmcntaryrocks,charo.ctcr,dlstributlon,and general relations of. 26-27 

Sec also Lake bods; Alluvium; etc. 

Sericite, distri bu tlon ami' character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 

Shannon vein, cut by Harus fault and No. 12 fault vein, figure 

showing.............................................. 196 

general chanictcr and faulting of ............................ 197-200 

Shcctcci granite, ncar Homestead tunnel, plate showing.......... 26 

north of 1\fcadorvlllc, weathering of, plate sho\\1ng ........ .'... 54 

Silver, occurrenco.of .............................................. : 80 

occurrence or, at Parrot rnine, figure showing................. 80 

In copper ores... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68-69 

Silver area, location or............................................ 67 

Sllverbow lode, character, displacement, vein filling, and deposition of. ............................................. 156-159 

Page. 

Sllverbow mine, sections through, figure showing ........... '157,158,159 

stalactites of chalcanthito in, plato showing.................. 82 

stalactites or limonite in, plate showing....................... 82 

Silver bow system, general features of. .......................... 107-108 

veins and lodes of .......................................... 156-159 

Silver King mine, development of ....... .' ...................... 250-251 

Silver Lick mine, development of. ............................... • 249 

Silver lodes, production and subdivisions of .................... 239-25() 

Silver Inini:Ug, epoch of.. ......................................... 18-19 

Silver Safe mine, character of..................................... 243 

Silver vein, typical outcrop of, plate sho\\1ng.. .. . . . . . . . . . . . . . . . . . 84 

Silver veins cut by rhyolite, figure showing....................... 252 

Sin bad mine, development of..................................... 236 

Sisters vein, in East Greyrock mine, character of................. 184 

SL'\': O'Clock mine, development of.............................. 233 

Skyrme vein, character of. ............................. : ....... 180-181 

displacement of, by Modoc fault vein, figure sh0\\1ng. .. .. . . . . 180 

Snohomish Diagonal vein, character of........................... 228 

Snoho.mish vein, character of. ................... ,................ 227 

Snowball Inine, development of.................................. 185 

Snowdrift-Glengarry mines, development of. ................... 248-249 

Southern and eastern group of silver Inines, development of .... 254-25() 

South Parrot vein, description of................................. 132 

South vein, in Mountain View Inine, plate showing.............. 202 

of Harns system, character of................................. 227 

Speculator mine, development of.'................................ 18u 

Speculator vein and Bell fault in High Ore mine, figure showing.. 183 

Sphalerite, distribution and character of .......................... 78-79 

occurrence of, with quartz and galena, figure showing........ 79 

Spraying of ore, figures showing ............................ 109-112,1()9 

Springfield mine, devclopmcntoL............................... 248 

Stalactites, of chalcanthite, plate sh0\\1ng........................ 82 

of limonite, plato showing.................................... 82 

Stella 1nine, development of...................................... 1G6 

section through, figure sho\\1ng............................... IGu 

Steward fault vein, conglomerate ore of, plato showing............ 110 

nlincs on ................................................... 146-152 

sections along, figures showing............................... 147 

Steward mine, displacement in, figure showing................... 149 

ore body from, figure showing................................ 150 

section through, figure showing............................... 150 

veins and ores of ........................................... 147-151 

Steward system of veins and Blue system, comparison of.· ...... '108-109 

Steward vein, displacement of Rialto and Clear Grit fault vein 

by, figure sho\\1ng... .. . . ..... . .. .. .. .. .. . ... . . .. .. .. 149 

in Gagnon mine, character of................................. 136 

in Original mine, character of................................ 134 

section through, near Gagnon shaft, figure showing......... 140 

Steward vein system, veins of. ........................... -...... 145-156 

Stokes, H. N., analysis by .. · .......................... 33,35,38,41,44,45 

Strike faults, character and distribution of. ....................... 62-63 

Structural history, summary of................................... 57 

Structural relations, general features of ........................... 51-57 

Structure, changes in, with veins in depth ...................... 111-112 

Structures of orcs, classification of................................ 72 

Subsidence, in Butte district, results of leveling showing ......... 50-51 

Sulphur, occurrence of, in ores.................................... 70 

Su.pslline mine, development of. .... 1........... •• • .. • • • • • ••••••• 217 

Swede vein, description of.. .................................... 176-177 

Syndicate lode, course and development of....................... 160 

fractures of.. ............................................... 161-163 

nlines of. ................................................... 165-171 

ores of. ....................... , ....... , ........ ·................ 164 

plan of, figure showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 

sections of, figures shomng ................. 166,167,168,169,170,171 

shafts of...................................................... 160 

splitting of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 

subordinate veins of.. .......... : ........................... 164-1(35 

tllickness of. . . .. . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 

wall rocks of. ............................. .'.................. 163 

T. 

Talbot & Jones Inine, dilvelopment of............................ 195 

Tennantite, distribution and character of.......................... 78 

Tcnoritc, occurrence of........................................... 82 

Tetrahedrite, distribution and character of. ...................... 78,85 

formation of, by secondary enrichment. ................... 103-104 
262 INDEX. 

Page. 

Texture of aplite, variations in, figure showing................... 37 

'I'opography, general features of .................................. 16-17 

Toscanose, analyses showing alteration of........................ 90 

Tower, G. ,V., work of. ............ ,............................. 15 

Tramway vein, character of. ................................... 215-216 

u. 

Underground water, amount, and movement of. ................. 97-98 

effect of, in concentration processes ...................... : ... 97-104 

v. 

Valdemere system, mines of.. ........... ;........................ 2-13 

Vale vein, in East Greyrock mine, character of................... 184 

Valley mine, development of. ............. ~...................... 194 

Vegetation, former growth of..................................... 18 

Vein, incipient formation of, plate showing....................... 204 

Vein filling, types of and general features of ................... ·. 110-llf 

Vein formation, relation of to source of copper .................... 94-95 

Vein No. 612, character of........................................ 227 

Vein outcroppings, occurrence of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

Veins, changes in composition and structure of, in depth ....... 111-112 

mapping of.. ..................................... .' . ." ....... 104-105 

of Butte district, map showing .......................... In pocket. 

Vein structure, map showing ............................... In-pocket. 

of La Plata mine, plate showing.............................. 240 

Vertical distribution of ores, general conclusions regarding ........ 65-66 

Virginius vein, description of..................................... 132 

w. 

Wabash mine, development of................................... 248 

Wake-up-Jim mine, development of.. ............................ · 171 

Page. 

Wall rocks, c.oncentration of copper ores from ..................... 93-94 

Wapello lode; development of.. .... ~............................. 240 

Washoe mine, development of.................................... 195 

Water supply, character of. ...................................... 17-18 

Weathering, effect of, on aplite................................... 38 

·effect of, on rhyolite porphyry................................ 41 

of sheeted granite, plate showing............................. 54 

Weight, of ores, general conclusions regarding.................... 71 

West Colusa mine, quartz veinlets in granite in, figure showing... 96 

section of Colusa vein in, figures showing..................... 197 

section through, figure showing............................... 157 

Western group of mines, development of ....................... 251-254 

West Greyrock mine, development of .......................... 184-185 · 

Wethey, A. H., assistance rendered by........................... 16 

Wild Bill vein, character of....................................... 179 

Winchell, H. V., assistance rendered by.......................... 16 

temperature readings by..................................... 104 

Windlass vein, character of ..................................... 226-227 

in Rams mine, figure showing................................ 226 

Wulfenite, occurrence of.......................................... 85 

Wurtzite, occurrence and analysis of ............................. 80, 85 

Y. 

Y vein, in Original mine, character of............................ 134 

z. 

Zinc, occurrence of, in ores .. .' ........... : .. :..................... iO 

Zinc blende, distribution and character of ........................ 78··79 

occurrence of, with quartz and galena, figure showing........ 79 

'Zinc vein, in Original mine, character of.. ............. ·........... 134 

0 

•