f ‘ E T — DEPARTMENT O HE mTEEIOE U . s. GEOLOGICAL SURVEY C H A R L ES l) GEOLOGY AND ORE DEPOSITS O F T $ E MININGD ICT J RS NC NTY MONTANA ISTR . EFFE O QU , ’ NV A L T E IR I—I A R V E X \V E H U ‘ V IT H A N A P P E N D IX O N THE MICROSCOPICAL PETROGIH PHY OF THE DISTRH‘ T ’ J O S F J I H 1 3 1 \ l { I i I CL L EX R A C F R O M T H E WEN Y -S EC O N D A N N UA L R E PO R O F T H E S U R V E Y 1900- 1901 T T T T T . PA R T II—O R E pE PO S IT s W A S H I N G T O N G O V E R N M E N T P R I N T I N G O F F I C E 1 9 0 2 GEOLOGY AND ORE DEPOSITS OF THE ELKHORN MINING D C J F F N UN Y MON ANA ISTRI T , E ERSO CO T , T W A L T E R H A R V E Y W E E D WIT H AN APPENDIX ON THE MICROSCOPICAL PETROGRAPHY OF THE DISTRICT J O S E P H B A R R E L L C N N O T E T S . h a r Introd u tion C pte I . c F ield work and acknowl edgm ents G eographic pos ition h t r II G n r eo i eatur f h C ap e . e e al g log c f es o t e district and its relation to th e sur rounding region a t r III I n rock f th i C h p e . g eous s o e d strict G ranitic rocks G ranite (quartz-m onzonite ) D efinition Exte nt and character of surface D escription C hem ical com position A plite-granite D efi nition C h em ical com position O ccurrence D iorite D escription E xtent and area covered Q uartz-diorite-porphyry D efinition E xtent and character of surface A ndesitic rocks Extent and character of surface D escription IVeathering D iorite-porphyry r D escri tion of th e se dim entar rocks C hapte IV . p y A lgonkian rock s Turnley hornsto nes ( Spokane shale?) C am brian rocks A lpreston quartzites ( F lathead quartzites) Starm ount lim es tones H obo G ulch lim e-shale 22 G E O L PT 2— 01 26 , 402 C O N T E N TS . — r IV D tion of th e sedim entar rock ontinued . C hapte . escrip y s C — C ambrian rocks C ontinued . C em etery lim es tone Elkh orn h ornstone Siluro-D evonian rocks U nion shale M adison lim estone Q uadrant form ation C row R idge series r ation f ro k m C hapte V . R el s o c asses Sedim entary foundation of th e district G abbro stock of Black Butte D iorite stock of C em ete ry R idge D iorite -porphyry laccolith of Q ueen G ulch Turn ley R idge quartz-diorite-porphyry stock A ndesite m asses of E kh orn Peak ueen C re ek and Elkh om G u c l , Q , l h A ndesite M arble cliffs G ranite batholith G laciation V nera c of rm m m i f k f th C hapter I. G e l effe ts the al eta orph sm o the roc s o e district A rg illaceous rocks C alcareous rocks F um arolic alte ration M in ra s of th e o de o its of th distri t C hapter V II . e l re p s e c O re m inerals G alena ( sulphide of lead ) Bournonite T tr ed ri e r co r or antim onia u i f r e a t a e e s de o co e . h (g y pp , l lph pp ) Pyrite ( iron sulphide ) Tetradym ite ( sulphide and telluride of bis m uth ) Bism uthite ( sulphide of bism uth ) Blends s a erite zinc su ide ( ph l , lph ) C alam ine ( hydrated silicate of zinc) C erussite (lead carbonate ) L inarite ( hydrated sulphate of lead and copper) C halcopyrite G old Sil ver P ro us ite b ack ox ide of man anese y l ( l g ) 0 A zurite ( blue carbonate of copper) M alachite (green carbonite of coppe r) H em atite and m agnetite Lim onite (bro wn hematite ) D escloizite ( vanadinite of l ead and zinc) A urichalcite ( bas ic carbonate of z inc and Oopper) P rr otite m a netic rite iron su hide y h ( g py , lp ) G angue m inerals Q uartz (crystalline silica) wa n ] C O N T E N T S . 403 f — th re de sits o th d i n n . C hapter VII. M inerals of e o po e istr ct C o ti ued n u m — i Ga g e inerals C ont nued . C alcite (lim e carbonate ) D olom ite ( carbonate of lim e and magnesia ) G arnet ( variety grou ularite ) Diopside (lim e-m agnesian pyroxene) Serpentine ( hydrated silicate of magnesia) A x inite ( boro-silicate of alum inum with varying am ounts of iron nd m an a s a g ne e ) . Tourm a ine bas ic or subsiicate of boron a um ina otas im e l ( l , l , p h , l , m agnesia ) E idote ort osiicate of im e a um ina and iron p ( h l l , l , ) Wollastonite ( silicate of lim e ) M icrocline Th E k m in C hapte r V III . e l h orn e H isto ry of the pro perty G eneral features of the ore deposit Topographic relations G eological relations O utcrop H anging-wall h om stone F oot-wall dolomite Th e ores G eneral characte r Value Mine workings O re shoots and cham bers G eneral characters M ain ore s hoots F orm s of th e ore shoot Peculiarities of th e hanging wall N orth ore shoot South ore shoot Interm ediate ore bodies G eneral characte r of th e ore of the m ain ore sh oots Isolate d ore bodies in th e dolom ite or foot-wall lead cham bers O ccurre nce F illing D escription of a foot-wall ore body N ature of the ore deposit Structural relations of th e ore shoots O re shoo ts constitute saddle depos its A lteration of country rock M ode of form ation of ores O rigin by replacem ent E vidence of re placem ent sh own by thin sections of the ore Source of th e m etallic contents of th e once Secondary sulphide en richm ent Age of th e ore depos it r I N ot s on o r m in of th e di trict C hapte X . e the es s in C . and D . m e Keene m ine 404 com . — Notes on the oth er m ines of th e district C ontinued. C hapter IX . U nion mine Dolcoath m ine R elief m ine H omestake and D unsto ne m ines n r L axenbur and M ountain iew M o te C ist o, g, V J acquem in m ines E lkhorn Q ueen F uture of th e district i tr ra b J ose Barre ] A endix . M icrosco ca e o pp p l p g phy , y ph l Introduction U naltered igneous rocks R ocks of th e Ce m ete ry R idge sto ck D ifferentiation in place A ndesites E lkhorn M ountain intrus iv e andes ites E k orn M ountain lavas breccias and tufts l h , , Turnley G ulch andesites Diorite-porphyry laccolith T urnley R idge stock Batholith at Elkhorn V ariations in com position Elkhorn M ountain aplite A plite stock A plite dikes north of Black B utte A plite dikes south west of Black Butte C ontact dikes of aplite in T um ley G ulch Segregations of to urmaline Alte red sedim entary ( contact-m etam orphic) rocks U se of nam es Pure quartzite s Q uartzitic Lim e-silicate group O rder of crystallization of th e lim e-al um ina-silieate group O ccurrence of m inerals M arbles L L U A N I S T R T I O S . T r hic m a of th e E k orn district P L A TE XL II . opog ap p l h Th E kh orn m ine and m i XLIII. e l ll I Taiin s dam s of th e E k orn m ine XL V . l g l h V G i m a of th e E k orn district s owin area distribu L . o c X eol g p l h , h g l V I T ica ranite area at ead of T urn e C reek sh owm bow ders XL .