Profess10nal Paper No 26 Senes (A, Ewnomtc Geology, 34 

I B Descrtpbve Geology, 38 

DEPART11ENT OF THE INTFR!OR 

UNITED STATE8 GEOLOGICAL 8URVEY 

(,H 1\RI,F~ D 1,\- ALC01 T DIRFCTOR 

EOON OMIC RESO UROES 

OF THE 

__.,~~ORTHERN BL_L~CI\._ HII~LS 

B\ 

.T. D. IRVING 

\\I1H CO'-TPIBUTIIf\fo; Bl 

S F. EMMONS ,m<l T A J AGGAR, Jr 

WASHINGTON 

GOVERNMENT PRINTING ()FFICE 

190± 
I 

~\ 

72 3656 3 09 
I 

CONTENTS. 

Page. 

PART I. GENEIUL GEOLOGY, BY T. A. J.\{~(T.-\H, JR--------------------------------·----------- 7 

PAnT II. llhNING GEoLoGY, Jn' .T. D.lRYIS{{ .\sn S. F. E:\nro:-;s.............................. 4B 

INDEX - - - - .•• - - - - . - • - - - - - - ••• - - - - - - - - - - - - - - - - - • - • - - - - - - - - - • ----- --- ----- • -- - -- - - - ----- -- - - 2Hl 

LETTER 0~' TRANSMITTAL. 

DEPARTMENT OF THE lNTERIOit., 

UNITED STATES GEOLOGICAL SuuvEY, 

mushinqton, D. 0., June 24, 1903. 

SIR: I have the honor to transmit herC\vith the manuscript of a report on 

the "Economic Re"ources of the Northern Black Hills," by .J. D. Irving, with 

chapters by Mr. S. F. F:mmons and Dr. T. A .• Taggar, jr. I would re~peetfully 

recommenrl that it be published as a professional paper. 

Very respectfully, 

HoN. CHAi<LEs D. ·wALcoTT, 

c. w. HAYES, 

Geologist in Oharqe nf Geology. 

• 

1 Director United State• Geological Survey. 

5 

ECONO~HC RESOURCES 0~' THE NORTHERN BLACK HILLS. 

Part I.-GENERAL GEOLOGY. 

By T. A JAGGAR, Jr. 

; 

C 0 NT EN T S 0 F PART I. 

Page. 

IIttroductlon •••••.•. ----------.-----•...•••. ___ . __ ........•... __ ......•. ____ . •. ••. •••• •.•• 13 

B1bhography .. _ ................. __ ... _ ............ __ . ___ . _ ....... _. __ .. _. _ .......... _ _ 13 

General structure ........•.......... _ .. _ .. ___ ............ ____ . .............. ... .......... 14 

Topography and drainage ...•. ---- ..•. ___ .... _ .......... _ ............. _____ ......... ___ ... 14 

Topographic type~ ... _. __ .. _ ............. _______ ....... _____ ............. _ .......... _ _ 15 

Stratigraphy .•••.......•. ___ .....•.... . ..... ______ ........ _______ ...... _______ ........ __ . 17 

n'ynarnic sigmficance of stratigraphy ... -.-.--.--.---.---.----.-.----.. -------.- ------- 17 

Vanations In tlnckness •••••.•••....... __ , ___ •..... __ . __ . ___ ..•.•...••........ _____ .. .•. 18 

Intrm:nve porphynes ..... ___ ........... __ .. ___ ......... __ . __ ....•. _ .. _. __ ...••..... __ .... 22 

Lithology . ___ .. __ •...•• ___ · _ .......... ______ . __ ......... __ .• _ ••. ___ . __ ..• _ ••... _____ .. 22 

(-irorudite ..•..•..• _ .. -••.......... ____ ....... ________ ...... ________ ..•.... ___ . 22 

Phonollte ___ .••••..... _____ .......... ______ ....... __ .......... __ ......... _ .• _ 22 

Rhyohte-pmphyry and dac1te ..... __ _ .... : ..... ___ ·-- ..... _. _ .......... ___ .... 22 

Andebtte~porphyry, dwrite-porphyry, and diOrite .. _ ....... _. _ ... _ ....... __ .. _.. 22 

Lamprophyre ..... _. _______ ..••..•. ____ ...... ____ ........ _____ ....... ____ .. •. 22 

Relative age .... ______ .••.••.. ______ ....••• __ .......... __ ..••........ _ ...... _____ .. •. 23 

Geologteal age •.•..••. _. ~- __ ........ _ ... _ ...... ' ... ___ ....... _ ......... _. ___ .. .•••..... 25 

Dtstnhution of tgneou~ bodies ... _____ .. _ ..•.• ___ ....... _. _ .......... __ ....... _. ___ •••• ~6 

Homestake dikes . _. __ •. _ ....... _____ ...•.... _ ~ ........ ___ . _ ....... __ . __ ...••• __ •••••. 27 

Pseudo-<"onglomeratel:l ____ ........... __ ....•..... __ ...... __ ................... .••.. •••• 27 

Sun1mary of dynanuc hil:ltory ..•••.•••• ____ ...••••. ___ ....... ___ ...............•.... _ ... _.. 29 

History of IntrusiOn ... ______ •...•••.. ___ ....••.•. _ ........ __ ........ ___ ......•. ___ •... B1 

Descriptive geology of mintng di~tricts ........ _ ••••.••••. __ ... _____ ..... __ . ___ •. . . . . . . . . . .•. 33 

Algonkian ...... ____ ...... ____ .. _____ ... _. ____ ... __ .. _._ ........ __ ...... ___ . ___ ... _._. 33 

Sch"t.e showmg 'ynclinal structure north of Home<take mine ____ .. _ ... _____ .. __ ... __ 33 

Schu;ts showmg sudden change of strike near Clo\er Leaf ore body ..•. _....... . ___ •. 33 

Carobrmn, Ordovtctan, and Carboniferous---------------------------------------------- 34-

Terry Peak >ection................................................................ :l5 

Englewood section ..•••..•••.... __ •••••••••••••• ------ ..•••..•••.. __ ....•. ---· ___ . 36 

Galena section .•.. ------••••..•..•.... ____ .:...................................... 39 

Tertiary and Quaternary •• ___ ... _ ••.••••• ____ •••••.• _ ••• ____ .••••... __ .......••••••••• 40 

9 

IUUSTilATlONS TN PART I. 

PI,<\.TE I Geologic map of northern Bla{'k Hlll-, ··················-···-----------------------

Fw 1 Generalized. C'Olnmnar ~;eution of northe1n Bla(•k Htlhl ......••..•.•.. ____ ........•.... 

:! Green phonolite cutting rhyohte .... ---- __ ...... __ ................. _____ .. _ ........ . 

, 3 Rh)ohte cuttmg green porph) ry ............................. ---- ... __ ............. . 

4 Geologic sectiOn through Hume':ltake mme .......................................... . 

5. Upper eontaet of ~<Ill cuttmg hmestone breectas, Galena 

• 11 

Page 

H 

lR 

24 

24 

28 . 

\ 

ECONmHC RESOURCES OF THE NORTHERN BLACK HILLS. 

P.ART I.-GENERAL GEOLOGY. 

By THOMAS AuGUSTUS .TAGGAR, .Tr. 

INTRODUCTIOX. 

The mining district of the Black Hills. compri,ed within the Spearfish and 

Sturgh, quadrangles. wa.s surveyed geologically in the summers of 18!18 and lSH\l 

nnder the direction of Mr. S. F. Emmons. • The following pages present a brief 

summary of the geologic features. more especmlly with reference to ore-hearing 

formations. These are confined to the Algonkian an<;l Paleozoic strata and their 

associated eruptives. 

BIBLIOGRAPHY. 

Descriptions of the general geology of the Black Hills may be found in the 

following publications: 

' 1. ExploratiOns m ~ehra~ka awl Dakota Ill 18fl5, 1856, 1857, hy G-. K Warren, Engmeer Department, U S A , 1875, p 30 

2 Geological report of the exploratiOn of the Yellowstone an1l l\hssoun nYers, 18.59-60, by F V. 

Hayden, 1869, p 42. 

3. Geologtcal report on the Black Htlls, by~- H. "'mchell Report on a reeonnat~&mce of the 

Black Hills of Dakota made m 1the :,ummer of 1874, by ~Wilham Ludlow. captam of Engmeerf', 

U S. A., 1875, pp. 17, 37 

4. Report on the geology anrl re~ources of the Black Htlls of Dakota, hy Henry Ne\vton anrl 

, ·walter P Jenner U S. Geog. and Geol Surv Rocky :i\Ionntam Regwn, 1880, pp lRil, 219, 283 

5 Geology of the BI:ick Htll:,; of Dakota, hy 'V 0 Cro~by. Proc Boston Soc. Nat Hist , vol :?3, 

1888, pp 488-517, vol :!-1, p 11 

6. Not'es on the geology of the Black Hlllt-, hy F R Carpente1 Preliminary report of the Dakota 

School of :i\Iines upon the geology. mmeral re::~ources, and null~ of the Black Htllf' of Dakota, Rapid 

CitY, lSSH 

. 7 A t•ontnlmtwn tu the geology of \he northern Black Hills, hy 'John Duer Irving. Ann. New 

York Acatl Sc1., vol 12, Xo 9, p 187 et seq , 

8. The laccoltths of the Black Htl!,., hy T A Jaggar, Jr, w1th a chapter on experiments Illustrating intrusiOn anrl erosion, by Erne:;,t Howe ~TwtJnty-fir::!t Ann R~pt U. S. Geol Survey, pt 3, 

1900, p. 163. 

13 
14 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

9. Preliminary descriptiOn of the geology and water resources of the southern half of· the Blaek 

Hills and adjoining regions in South Dakota and Wyoming, by N. H. Darton: Twenty-firEt Ann. 

Rept. U. S. Geol. Suryey, pt. 4, 1900, p. 489. 

10. The Oelrichs quadrangle, hy N. H. Darton: Geologic Atlas U. S., folio 85, U. S. Geol. 

Sun-ey, 1902. 

GEJ'."'"ERAL STRUCTURE. 

The Black Hills are well known to constitute the type of dome structure. 

They rise like an island in the midst of the Great Plains, with culminating peaks 

of pre-Cambrian granite intrusive in Algonkian schists, and t~ese same schists and 

granite may b~ followed· outward from. the -center of. the Hills to an encircling 

esea.rpment ·of Pale?zoic rocks dipping ~Lway on the northern, ·southern, and eastern 

sides, and mantling over the schists to form an extensive forested limestone plateau 

on the we13t. The center of activity of the younger porphyry intrUt:;ions and of ore 

depo•ition is Terry Peak, a summit rising 7,069 feet above the sea, in the northern 

portion of t,he schist area exposed on the eastern side of the uplift. Northwest; 

north, and northeast of Terry ~eak occur a large number of intrusive bodies in 

beds ranging from Algonkian to Benton Cretaccou:-;. The structure and forms of 

these igneous bodies ntry chiefly with .the horizon of intrusion. 

TOPOGRAPHY A.c~D DRAINAGE. 

The drainage of the northern Hills follows in general radial courses consequent:upon the original slopes of the uplift as a whole. 1Vhere erosion has gone 

deepest this drainage has become modified by the development of valley• along 

the softer rocks, and,. in corisequence, subsequent valleys having_ courses concelltric 

to the dome tend to ,follow along the strike of the Paleozoic and Mesozoic beds. 

The !)lOSt conspicuous of these mlleys is the well-known Red Valley, which forms 

a continuous depression around the Black 'Hills uplift .. 

Four streams drain the Terry Peak eruptive center, flowing east, northeast, 

and north; these are Elk, Bear Butte, Whitewood, a~d Spearfish creeks. The 

drainage system of each of these. has eroded away strata which capped igneous 

intrusives; and the porphyries, by rea.son of their more resistant quality, usually 

fo~m prominent emine,nces ab-ove the general level. 

The westernmost of the streams mentioned, Spearfish Creek, forms for 20 miles 

an. impre:-;sive canyon in the --limestone plateau, from which the stream 'emerges 

into the Red Valley at Spearfish. For a portion of its course this stream, which 

is to-day one of the most powerful in the Hills, flows along the contact of the 

Algonkian schists with the basal beds of the Cambrian; above the mouth of Annie 

Creek the stream leaves the last outcrop of schist, and from here to the mouth 

of Robison Gulch, under Spearfish Peak, flows on Cambrian beds, cutting into 

porphyry masses at Annie, Squaw·, and Rubicon gulches; then, entering the zone 

; 
TOPOGRAPHY 15 

ot nmth-<hppmg P.1lcoz01u,, progres..,nely cutb tt-, ,\,ty across Ordovtcmn, CarbonlfeiOno, and Pmm1an bed, heto1e emergmg on the Tna"1c lowland of the Red 

Vaile) (See PI I ) 

"\Vhtte\\ ood and Beat Butte t.reek... winch flow to the notthea.;,t, traverse a , ' 

more vaned topog1aphy heto1e they eme1ge from the Hlllo They take thmr rhe 

.1mong Cambrian -=-tr.-da and porph) ne-.., .tnd thetr headwntm branche-, have as..,r.:;;ted 

1n carvmg out the nm thmn pm bon ot the exposed Algonkmn cm e ot the Black 

H11l-. uphtt Through pol twn' ot thc1r couhe; deep V -sb,;ped gulches h,tVe been 

cut m the F.c,hrst ..... and wall can)Oll" tn the C..trhomtciou-, hmestone Each tmmatwn In tutn ha .... rt-, cbaracten-.,tH_, eto..,wn fmm, whtch V.t1le ... httle throughout 

' the nm thern H11l,, and b u'ualh dnectly dependent upon 1ts 1elatlve capae1ty 

±or te::,tsttng ero;;;;wn Indeed, the dt.un.tge .t.., ,L whole. \\htle tetammg con~e4.uent 

Gour..,e'!tn genmaJ ±or the nM-,tei -..tre.Lm;, -,bo"'" ma,ny mudtfic.:ttwn ... hy ad]U'!tment, 

more espemall} m the tnhut.uy hr.tncbe ... , and o<..,ca~wnllj ~tnkmg m~tance-, ot 

c..tpture .ue evrdent 

Elk Creek, flowmg east, drams on the ,outh the h1gh Algonk1an plateau land 

wh1ch m.nk, a portwn ot the a1ea of max1mum uphft The uppe1 porbon' of 

It"l COUrSe .ne dutradeuzed hy broad me8.dow hottom-, .md gentle &lope':> from 

upland "flats" con,htmg ot Camhu,m 01 porphyry < ap' over 'lhlot. 'Vhm e the 

:::-tlec1m entm:, the lnne ... tone 1 \\hiCh l':l here of cAtraordmary thrckness, a magmhrent canyon w1th vert1cal walb rNng ,hee1 trom 2UU to ±110 teet has been cut 

Through th" can)on the engmee1:, ot the Black HJ!J, and Fo1t P1ene Ha1hoad 

ha' e bmlt one ot the mo't pJCtme,que wnte, ot traHI m the count1y Steammg 

thwugh th" lmpre,SJYe gorge the t1aveler movmg ea,tward find' 1t dJflkult tor 

-:orne tlme to dt-,covm any con-stderable dtp m the ma.,o;;n~c hme-,tone .... whtch 

tet.nn for :,everal nnle-.. the .tppearance of umtmm thKkne;::.:-3 Ut the ptet.,tprtou-: 

chfh that wall ,m the tor1ent Eventually, howe\m, the <anyon w1den' out and 

the hmestone chff, are replaced by bnght-colored hed' ot the l\hnneluoa ' alternate 

sene~:' and then o;;uddenlv the ch,uacterr...tl<.., gateway of .i\Imnekaht.1 hme-.,tone 1~ 

pa,,ed and the t1am eme1ge, mto the broad lowland of the Red Valley w1th 1ts 

1ed ma1h and tJ!Ied fieldo 

TOPOGRAPHIC TYPES 

The Algonkun 'chJSt& tm m flat uplands, and when they occur "' ma,slVe 

upturned qu.:titztte...., hel1nently ]Ut out m colo .... .,al wall.., Neat Elk Cteek one of 

thc':le (1U.trt7rte wan~ may he bJ.ced tm mrle:,. :,trongl~ Je-..ernbhng a dtke El~ewhele the Algonkl.ln form< the bottom' ot olleam' that have 'ut through the 

softe1 Camhn<1n bed'3, 01 form" "1th rtr.., c,haradeuo;;tlc ... teepl) rndmed handmg. 

the ,]ope' ot <teep gulche<, hke Wh1tewood C1eek along the lme of the Burhngton Rarlroad The many hr,mcbe.., ot the railway f..y-,tem~ afford excellent ~<..,tron~ 
16 ECONOMIC RESOURCES OF NORTHERN BLACK RU,LB. 

of the Algonkian as they wind in and out along gullies and sparR to maintain 

th~ir grade, and these railway branches and loops are now so numerou~ in the 

mining district as to form a conspicuouf' artificial feature in the topography; the 

same may be ~5aid , of the ~nnumerahle tunnel1-1 and prospect holes with their 

dumpil juttmg out from the steep gulch slope,, tl1e size of the dump an index of 

the depth of the digging. Thanks to this artifimal ·'honeycomb" nllllerground 

and the clean railway cuts abo\·e, much is now exposed to the geol0gist that was 

completely magked twenty yeais ago. 

The Camhrian section, ·where exposed beneath a protectillg cover of limestone, 'frequently forms wall cliffs of red and hrown eolor, striped parallel to the 

stratification, o~e notahle red band in the upper part of the formation being 

conf'picuous in many places. The type loeality oceurs on the west side o£ \Vhitewood Creek. just below Deadwood. \Yhere its protecting· limestone cover has 

been eroded away the Camhrian is likely to' weather mto rmlmled foreRt-covered 

hills of inconspicuous outcrop, like those occurring- south of Elk Creek in the 

vicinity of :Meadow Creek. Immediately heneath the Ordodclan limestone the 

Cambrian m;nally forms a bench, oceasioned by the hard and sahent •' wormeaten" (Scol1"thus) 4uartzite ji1tting out from heneath thick, soft, green shales 

~~1). ' 

The Ordodcian limest~~Ef: in consequence of this relation and of another shale 

band above it, is frequelltly masked by talus, hut, where its thickness is sufficient, 

forms a yellow bench, well shown in \Vhitewood Canyon on the route of the 

Fremont, Elkhorn and l\Iissouri Valley Railroad. Thil:l bench is rarely seen west 

of Deadwood, and the Ordivicmn b dilllcult' to identify in Upper Spearfish Canyon. 

It occurs north of .A .. nnie Ureek at several poinb in the canyon. at Crown Hill, 

and at Carbonate. 

The Pahasapa formation, equintlent to the :;\ladison limestone· of the Rocky 

J\lountams, is naturally the principal cl_iff-maker, and its escarpment forms a conspicuous feature in the land~eape cve'rywbere. A more irregular and variegated 

cliff'. colored purple, red, :.nHl white, an(l presenting m~e of the most picturesque 

color effects, is made by the l\Iinnelu~a sandstone, forming the ·• sand hill-;" 

encountmed in dri'l'lllg out from the' Hills just b~fore reaching the Red Valley. 

The sandy soil of the Minnelusa frequently produces holes anu 'and in the roads 

winch traverse thi~ zone. 

The l\linnekahta limestoue of tho Permian forms one of the most striking 

topographic featnr~s of the Hills. Dipping away with wonderful uniformity from 

the uplifted dome, the outJlowing- streams mvariahly cut through it a V -shaped 

gateway, making in the inter~tream ~:.pace:-; croscent-~hapetl ~carps of the 30-foot 

limestone over the soft red sandstone that underlies it. The outer slope of the 

jointed limestone i~ usually washed bare and on the inner ~icle of t,he Hed Valley 
~TRATIGR.U'HY. 17 

iotms what ha~ been apt,\y called a tessellated paxement The ·· Ht~d Bed~" them-

'belvcs ntrely present gootl expo-,uies. though oct~a~ionally tht~ ~tream" whic..:h 

mcandet through the ntllcy cut them mto bllt:dl buttes or me~a". t:appetl hy gyp"um, 

'vhit;h exhibtt a heddcd cro:-.~ section. f.;ncl1 ~ bPction may he SCL'll ea~t. of 

Wlutewood. 

Cuntmuing outward from the Hillb. t}w .htras::.Je hed::. onkrop on the infal'e 

of the Crctaccou::. esc:u·pmcnt that mti.kc-. the oute1 wall of the Red Valley. and 

a eon::.pkuonb feature of 'these heel~"~ ii1 the bnngi-.; dtstriet i-. a hard quartzite which 

form~'~ angular blocks upon the :-:-lope. Tlw trcst of thi:-. :-.lope i-., u.;.nally a rotk 

fae.;c of coffee-colored 01' JL~llowi"h stmlhtone of Low~¢r Crl'taceon" agt>. This 

~ancbtone ~lopes away toward trregutar hilb formed of o1her liH::•mUer~ of tht~ 

serw~. The Dakota 1:1andstone i15 the 1a~t harcl. ~alient bed. and thi;S iu turn cf1p-, 

gentl)7 beneath a \\icle. adJ. trac~t of UE~ntou hlal·k -..bale, the monotony of whit~h 

i~ broken only hy di-stant buttes of Niobra1a linu::>:-.tone that ar>peat upon the ~ky 

liitc far out acros~ the p1ams. 

STR~\TlfnlAPHY. 

DYNAMIC SIGNIFICANCE OF STRATIGRAPHY. 

ln the columnar ~edion. tig. l, are showu the avetage thkkness ancllitholog:ic 

charactei of Puleozoie and :\Ie~ozoic rocks. ln t•onnedwn with the mteqnctat,ion 

of dynamics of intrusion and aceompa11yiug mmera~ization: t.lw di-:-trihntwn of 

thm-LedUed and thiek-heddecl ~trata in tlu' colunm is of great importanet'. h·ying 

hus ~huwn the imprntunrc of ~hale hed., a:-:. :fa,·orite honzmb of lntru-,wn: they 

arc the readiest tu yield to a Yi~eun~ wedge oi igneous mattl~l'. · Th~! c~lumnm 

secttnn shows three thkk bed~ qf :-.nft matcnal, one at. the top of the Camhrian. 

th~~ Pmmo-Tnas-:ic rerl lu~J~. and the Benton shale:-:.. The lirst umledie~ the mo~t 

tm~~~iYe ··competent., 11 JIH'mher n-£ the whole '-el'h!-.-i. e the f.?l'l'at limestone. 

inelndmg both OnloYtcian anrl. Crn bonife1un~. The lowet H·d l1pt\ mulcrlH~" the 

massive layer knowu as J\limwkahta u1 purple lmwstone. wlw·h h oYPrlain by 

easily deformed thick hed-; of red mntl. while t.he -..oft. hlavk Benton ~hale~ 

underlie the ~whrara lime~tonc 

ln. addition to these three eonspwuou-, :-.hale horizon;;.. other -..tratigraphic relatwn:-. 

wbn:h 'vuulEl tend to mtlnence intt n ... ton are a~ follow ... : The Algonkiau _lam1Jn1t.ion 

ahnt:-. abruptly upward again~t the hanl ha~nl Cn.mb_riau ttntl.rtzltc nr eonglomerate, 

and thb stllll' lan1ination, while failly uniform iu it~';) ~t.dke ~~::\\\' ). \·arie-. in ih 

inclination east nnd we:-.t of tho Yertlcal. though tt i-.. prennlin~ ly" we-,tf~rly in the 

Teny Peak region. An example of vlmnge 1n <tip of the :-.ehi.,t-.. O(·enr.-. at Central. 

''WilliS, HaJk), The IUC( ~anKo> of Apioa.lachmn ~tructnrt!, Thirteenth Anu lllpt I; ~ Eie••< ~un e1, }•t !, 1~!12, 

p 2:iU ''.\. thrustwg layer tum enough to tnm~m1t the effectl\t: :torLe' lJl ~tr.:<t.:t tol•llll!i UJJflLr Ltter.ll cuwprl'~~uni h 

callul 1> "compLtcnt" stratum The ~ttllll'\\>Jrd rnu\ "toe ai>phc•l tu a, ~trntu:n rcsl~taut to tlw 11\oll,tr>lprn!l"re"~ "! JUI 

lntru~t\e magma, awl thu~ cornpetlnt to ol<•rnu 1\[11\:Ho\ lather tban ~pllt and Illll'-h llle •hnl• 

4B8i-.So 20----0-i---2 

• 
18 ECONOMIC RESOURCES 0~' NORTHERN RLACK ,HILLS. 

in Deadwood Gulch, nearly opposite the De Smet open cut. (Sec section, p. 33.) 

Throughout tl1e Cambrian, thin-bedded paper sh~les alternate with flags and sand-, 

stones~ forming innumerable thin parting planes. Thin shUles occur also above tho 

Ordovician and in the l\finnelu:m, .lura, Hlld r ... ower Cretaceous. 

VARIATIONS IN THICKNESS. 

The columnar section (fig. 1) '.shows an; rage thicknC.$':i Jor the northeastern part 

uf the Black Hilb. r_r:hesc iigureH arc generalized from .':'ectiom; measured in SpearMinneh..IS~ 

''cuterl7afe'' 

series.Joo 

M/nneiUSi!t 

£"":,;:J.sr017e 100 

Croy 

lime,o;f<)ntJ Z00-700 

Fm. 1.-Geueralizcd columnar section ,;f northern Black Hi;ls. 

K. B.-The bed~ here designated Silurian huvc recently been deter· 

mined to-belong ruther to the Ordovician. 

fish, Whitewood, Bear Butte, and 

Elk eanyom;, The progressh·e 

varhttion in thb seric::; of mcasnrcwents, which is most significant in counection with the intrusives, is .sho\vn in the diagrammatic strike section (vertical 

exaggeration X 2-. 5) from northwest to :southeast inserted on the 

. map, Pl. I. From a thickriess 

at Beaver Creek of probably not 

more thnn ±00 feet, just west 

of the mapped are.a, the SllnroCarlJoniferOus massive li111estone, 

grouped a.-; a single competent 

member, thickens to more than 

700 feet in Spearfish Canyon. 

The Cambrian beds maintain 

. throughout thi.s reg-ion a rather 

unlform thickness, but probably 

diminish where the limestone i:; 

thickest. There is some evidence. 

that, the present course of Spearfish .Canyon marks the ::lxiUl 

region of a gentle syncline of 

deposition under the great limestone. For this reason the thicknesse.-, in the section hnxe been referred to an upper 

datum !e,'el, ,namely, the top of the gray Pahasapa limestone. 

The Algonkian surface thus sectioned is seen to be_ warped jnto undulations. 

That some such undulations occur, and of much more pronounced relief than th~t 

· represented in the .seution, is amply proved at several points. One of these i-; 

between Englewood and Nevada Gulch 1 where there is a rise in the Algonk_ianCambrian contact of 4-00 feet in u northwest Uireet.ion; that is, along a line tangent 
VARIA~'IONS IN THICKNESS 0>' BEDS. 19' 

to the curvature of the elliptical area of the Black Hills uplift. Similarly the schist 

surface beneath the Cambrian nt Bro,,vnville, on upper Elk 9reek, sho":'S a very 

rapid rise westward toward \V oodville. Coarse Cambrian conglomerate tills hollows 

between ancient Algonkian q~artzitc reefs on the upland 4 miles southeast of 

Virginia, on Bear Butte Creek, so that irreg·ular relief in the original Algonkian 

surface, as well as irregularities induced by deformation, may be safely postuiatcd. 

\Varping of the schist surface in post-Paleozoic time probably proceeded largely hy 

small slipp_ings on lamination planes. These movements, when communicated to 

the flat-lying Cambrian beds above,· produced innumerable small fractures-the 

"verticals" of the niines. The coincidence in trend between verticals and -Algonkian lamination plane:-; (NN\Y.) is remarkable. The thickness of the Algonkian is 

unknown, but there is good reason for supposing that its nearly vertical structure 

marks a ::;eries of isoclinal folds in which eventually some recurrent h<?rizons may be 

identiti~tble. ·As is to be expected in isoclinal strneturc, the schistosity usually 

conform.':! to the original bedding, but in places where the axial region of a fold is 

·exposed the lamination is seen to be distinctly trans\'erse to the bedding, tls in 

Deadwood Gulch, near the town of Central. (See 1'!. Ill.) 

East from Spearfish Canyon the great limestone shows a remarkable thinning, 

fr.om 700 feet to a total thickne::;s o-£ probably not more than 100 feet on the flanks. 

of Polo' 1\iountain, a distance of 6 miles. The Cambrian thickens, but not in the 

same proportion; at Deitdwood it has a thicknes.s of between 400 and 500 feet. FrOm 

Polo Peak, where the limestone stratigraphically overlies the greater porphyry mrtSses 

of the Terry Peak complex~ thb nut.ssive member steadily thickens southea:-::tward, 

reaching 300 feet at \Vhitewood Canyon, ab~~mt ;)00 _feet in' Bear Butte Canyon, and 

probably more than 800 feet ln Elk Creek C~tnyon. Tlie Cambrian beds thickel1 ut 

B.ear Butte Creek, and ther; ·thin tnvay to between J 00 and 200 feet south of Elk 

Creek; and farther ~outh, on the· flanks of the I-Iarney Range, the Cambrian 'almost 

disappears. 

Swmnarizing thi:-3 section from BeaYer Creek to Elk Creek, the thick limestone 

in Spcarfi.':lh Canyon separates two areas ?f igneous irruption and _A_lgonkian elevation, 

namely~ the Bald 1\:lountain and Nigger Hill mining districts. The Terry Peak center 

of irruption underlies the thinnest l)ortion of the limestone. The Two Bit region of 

maximum development of sills is where the Cambrian is thickest, and tl!e RunkCl 

region of large porphyry masses in and above the limestone is where the Cambrian 

thins and the limestone heeo~nes thickest. A study of the map will show these relations. The Nigger Hill Algonkian area lies outside of the mapped area, on the ~vest. 

(Sec Pl. I.) 

The paleontologic, lithologic, and topographic characters of the geologic column 

are best expressed in tabular form. Local formation, names ·arc a\'oided except 

where already in the litcratmc of the Black Hills. 
l't•ri•••l Fpoch Formation 

lJu.tter nary ..... 

Tertl.uy ....... ·I Eo<'l•nc? ... I \YintP Hwer _ 

( ()\t~H-

('PIH') 

I BPnton ~h.tlc ...... . 

D.tkota FlmHIFltonu _ . Un'hH·eono: ..... . 

........... l""''"''-''"''"''00< .. 

.Jnra~~lt' ....... ·•····· ·- ····· 

Trws~Je ....... . 

I'e1rman _ .. 

1

1\Iorn-.:nn ......... . 

l \TnnnL• .lura ..... . 

'' Heol Beoll'l'' •...... 

\hnnLk.thta lnne-

"tone 

G;olog!c forwdwns m northern Blad Jlills 

Lithologw 1 lmracter 

~heam giavPl:,, pwbahly {'fl.ff\ lllf! plater 

~"'hlm pla<.,-e~. 

Clay~. wink, r•mk, or b~1ff Small fragHJC'nt.« ol white rhyuiltP 111 t•on~lmner~ 

atH· l.tyPr~ 

Topogrnplur 1 httnw\!•r 

I<tll~ saddle~ anol hoiIowa, 1~nually th\'ltle•. 

seattereJ bowlJers on 

the plain~ 

Snnilar tn above, hut 

]p-.., almwl:mt Oftf'll 

uwler t hP Plel~tn<'t-'111-' 

gra \•p}~ 

Fo~~Ils 

Vt-rtelnate reinainR, 

::\Te.~ohlppu", T~dJylOillYH typu~ 

il;u k ~ha]pq or t•lay ....................... I I' lam~ ................. I F1'lh ~~ aieR and tPPth. 

Brol\\'11 t'lanobtone '' tth lnnnmti<' no.lnlP~. __ ( ( )nh•I l'~t·arpnwnte- of 

B\a('k Hill" 

Plant. 1 emam~ 

I . I P ~an1l,;tmw", huff. wh1tu, and gr:w, limP- l re-.:t, nf onter \\.lll of 1 lant~, eyo·aols, ek 

"tonL·-.:,, L'<•k•le~l ~·\,\):,, ~!'et'll :-:hall·, t•arhunat'COU"\ het\>l 

FH"·h-w.tter dl'JlO"Jti'1, !!fC'I'lt -.:halP!<, f',tml-

"11111l'"' anti cl.tyP 

Huff mar I, fo.an•l"'totJC, un-tpr hnw.:;tone~. 

gret·n a;1d red el01.y~, m:nll", aw 1 ~1-l.tie:=-

Hed JHarl '\Ith g\p~nm ...•.•............ 

Uniform ptn ph«h hant It'd lmw:=-toue, \\ eathl'lM "lntt), ~tl'Ong lntnmmnus otlor when 

etn~hetl. 

Ht•tl Yalll'y antltrrPgnlai h\llR .lntl t>:-t·m pIneuts 

An llwon ... pH·nonfl lK·d 

In ontt•r ",til uf Red 

Valin 

l.O\\l'l bt>d" 111 ontt•r 

\\all of HP1l \' aller 

Rt>tl Yal!Py ........... . 

TP~""'lated pavpment on 

nnwr Plope o t Hud 

\ralley, t-'Mt'al pntell t 

and "gatcwny~•· of 

RtreamR. 

Fl.anrmn rem:uus 

Ht·lPmnih·~, o~trf'a, 

'l'IJ.l)CJ'IUfll, l'~entl!)· 

ntnn•)tJ~, Tanuetlut, 

CmJJO('eras, ' Lm-

~nla lm•virostl'i~ 

B.1kewellm, Yoltlia 't 

Ednumtll<l~ 

"" c 

"' 0 

~ 

~ ~ 

0 

, 

"' en 

g 

5 

"' if. 

0 

"' 

~ 

~ :II 

gj 

z 

"' "' > 

c 

~-

.t:J 

'"' rn "'
Carbomferous •.• 

Unlovwmn 

Cam!Jnan 

Algonkmn .. _ ... 1-- •• - _ ••• - •• 

Ltm er red hed ... _-I H.e4l satH_bttme, f.Oft IUHl lllarly ........... ·I T nner slope of :\lmne1\hnnelu:::;a .......•. j AltPrnate hnH.:'i:!tone::; anU thtcket s.tnclstonet3, bOtne\\ hat tolorecl 

l'ahat<apa. etJillV.tlent tt, )latll~t lll ot 

Hocky l\Jountams 

:\Iasf,I\'e lmtP~tone, gray, p111 k, or lJntf, 

~umetuues cht>It)- ~muehnw:,~ sthuhetl 

and Ote Leming 

EtJglewoml lttlll'- ll'mk or !lllflllu;h thm-h~dclecl limebtune 

~tUliP, Eo(',lJ bontletOU>", eqllt\.-t1 eu t tu Lu\\ ei:!t 

1HtHi:!ll-l!-,Jpptan 

(Chouteau 01 

Kmclerht•ok) 

\\'hth:!\\'tliiC] li IHl'-

Stone, eqm\alent 

to Upper Trenton 

Veach·\ ourl Fortnat.ton, equnalent 

to 1\hddle c~unLnan of the 

Rocky l\lonntams 

w 1 t h tt•cl ttolH'>tamed lol4i:!J I mollusks 

Pnn•le PI' g1eeu shales Lclow. 

Peen !tar ~pc d tPtl HH1.8si \I" l11w 'HI one, lll'lld !!_,. 

bnfi Wtth lno\\ 11 ut teddJ1-h rl}•ot.·-, :,atHI)-·. 

Vel} huge fu::;stls. ' 

(JonglmnPtate, quartzite, ferrngtnons tl.tnd-

::;tollel:!, many alternatwn::; of gn--'Pil r~lt.llt•, 

ltJneJ:ltnJl(• lllt'l'CIJ.jo:, tnemclal lillll'ElicnH' 

tlagi:!, at the top Seoltt1ms ~awlstorw or 

(1u.:utz1te, awl th1ck grt•en ~hales Ores 

Lomnwnly neai- the bato~-

1\ltca, gWI•lnte, J.ll(l hornblende sdnsti:!, 

ml'taruurphie 11uartztte and cunglc•Juerate, and some pre-Cambnan 1ntrmotve~ 

Locally I•yrttifcioUB and canymg iwe 

gold 

kahta ei:!('ttl pment 

\Tuue~rate1l :,tnpecl ehtfH 

,mtl sawly lnlls 

)ltli:!t'IVC t.Jif£:,, the 

gri::'Utet est,u pment 

F'!Pilltl'llti)' ClllHCl':th--'t} 

1 •t·ne.tt h taln~ t:;hu\\:, 

an .lpp.ut'nt mwunft~runty •>f t.'IO~tlln be· 

t\wen It aw I the gwy 

]JIUt~~tone .thu\e 1 

though 1ltp m al'eonlant 

Jlenl'l1 11'-llaih· ma:-kt->tl 

],\. tJ.ln:, 

'\'ttlJ,,. c 1f Tl'l'Pllt t'8Jl\ 4lll" 

or 11l1l gJ~Hh·tl .,]ope~, 

u~u.Jl!y a prorwmwed 

!Jeuch 

J<lat-toppt>d plateaus 

awl ht•a1lwater valley 

bottoms. 

HptrtfL•r, f:.yJllll,!:OJlOfll, 

l'nuludt;..,, ;-)ellllnula, i'.upluentiS, 

etc. 

F~nebtt->Ha, ( )rthc •thetPC! IL'pt.ena, Sptp· 

fe1, Chnnete::; logan!, H.t;'tu~nl.ula 

peLnhatJ~, 8'vllll¥o· 

thyr1s earteri, erinclld8. 

J•:wloeerasJ 1\Iadnrea, 

lteet~ptaen 11 tes, 

llal)- Httejo:, Streptehtflnta, Lit1utes, 

Orthu'l, annelul 

traiJq, Llnthotrepln~, ~lnrdn:,oma. 

Oho)u,.·, IJyohtlms, 

llJeellomn:,, A~a~ 

l'hl:,t'Ut-~, Olcnotdes, 

Ptyt:hoparm, Acrotreta. 

:;l 

"' 0 

,., 

0 

" ~ 

0 

"' 0 

" ,.. 

~ 

8 

~ 

"' :;; 

z 

~ "' z " 

" ,., 

>-

~ 

~ 

~ 

"' ,_. 

!' 

• 
• 

22. ECONOliiO RESOURCES OF NORTHERN BLACK HILLS 

INTRUSIVE PORPHYRIES 

LITHOLOGY 

The porphynes \

7

ary m kmd f1om 1hyohte, lhonte-porphyry, and "lyemteporphyry to moiC ,tlb.ahne 1 ock-;, \\ hrch mrty he da-,•;eli a-. phonohte..., and gtor udtte" II nnga ha& de-..c,uhed 111,1ny ot the type':!, and there 1':1 hme a remarkahlc 

sene<:. ot gr,td,ttlOn"l whi< __ h lender-- the 1egton p:xceptwnJ.ll) ht\orahle f01 ~tudy of 

magmdtiC dlfleientlatwn He ha, d!'tmguhhecl the iollowmg htm1hc" 

(hoJ uddt: -Htghh7 alkahue Iock-; contammg orthoda .... c, qw11t7, .cegirme-augrte, 

and regnme In '-ome t, pes acce~-,m.r alhttP, mH .. rodme, and lnotrte Locaht~e ... 

Terry Pt>ak, B..tld 1\Iountam. Elk l\Iountam1 Lo..,t (),unp Cicek, AnmP CrePk, 1-'heet 

on the Burlington H,uhoJ.d ea ... t ot Teuy Pe,1k, and Ill the Sun..,et mmc 

Phmwlzte -Rot,k,_, ncb m ..,odJ., iormmg the mme hasiC pha"'e ot the grmud1te ... 

Composed ot orthoda ... e, anorthoda.,e, nuum hne, regirme-augJte, .:egnme, ncphehnc, 

OO'·H~an with ac< c%ory hau} ue, b10t1te, m..lgnehte, t1tamte, melanrtc garnet, and 

po.,..,Ihly lenCJte Locuhtw., R,1gged Top n.iountam, Sl{naw and Anme c1eek..,, Ualanllt) Gulch, M~to Tepee, Green Mountam (peak next wetlt of Bald l\Iountum), 

'Vhitetaii Gulch, ea•t ,]ope of Bald l\Iountmn, unci Fal&c Bottom 'tock 

Rl1-yolde-porphy1y and dauh ~Phcnouy..,b ot orthoclabe plagwda .... c and 

quai tz 111 J. fine-g1amecl gr oundma .... ., ot <jlMl tz ancl tcldgpar, hOI n blende and biOtite 

m ,arymg amount.., Lo< <thtie::;. Head ot S<1uaw C1eek, Foley Peak, Tcxana, Cn..,tel 

Pe.tk, Butche1 Gulch, Deadman lae< ohth, north ,,de ot V anockm ldcwhth Two B1t, 

Pluma, Beat Hutto, lowm pOI twno;;; of Shet,p 1\Iountam, ".,..lntcwood Canyon lau.ohth, 

drkeg m many llOrtwn..., ot Teny Peak dto;;;hJt,t Crow Peak Inyankara, ~undance 

Mountam, and "'Yancn Peak., 

Andt>..,dtJ-pot'jJfitJI y rlwrde-p01ph1J1 y, and dwt'ltl"" -Porphyntw rot_,k" t,Ont.:unmg 

phenooy.::;tg ot pllgiOcla.,c, oJthocla.,P, hOI nhlendf' and bwtJte In a fme-guuned 

groundma% ot pl.lgwd;v;:e, quart.t, ,uul rhloute The 1oc.k f--howK tran•·ntwng to 

tlachybc tonns "hwh nM ,. be (ailed '} emte.porphj ry LocahtleS s.n, lll Squaw 

C1eek and m RubY Ra...,UJ, at the Needle:,. and 1n the Iegwn o± the VanoGker 

Iaccohth 

Dwutf' fmm ... the DPad\\oud Gulch ':!toc.k aho,re the town ot Ccntutl It b 

a gra} 1 ock ot gramtmd texture, ..,}IO"\\ mg a tf'ndent_}, ho"" C\ e1, to automorphl':!ffi 

w the component mtnel,tl..,, rt contam.., hornblendE>. plagwcla ... f', quart?, bwbtc, and, 

acce~sory OI thodase 

Lamplnpltyl'' -A ha>Ic 10ck m small d1ke~ cuttmg the d!Outc.porph} 1y of 

the Nt.edle~, and agam nPfil the head ot lion Creek, 1t Ib < ompo.,ed ot a fine 

automOI plnc aggt egatc ot augite anU telUHpat, 'Hth d.Ct,Cb':!Ol y hOI nblcmlc and 

nMgnetite II nng COthi<lci., It the finJ.l and habit, repre..,entattn.~ ot the ::;.oda-uch 

magma that con,titute• the pnnupal Black Hllh eiUptlve bCrie" 

ainmb J Il .\nual~J\L\\lorlA<..!L<l "'u '<lll2,J\o 9,p244Lt"Ul 

f 
u. s. GEOLOGICAL SURVEY PROFESSIONAL MPER NO. ~6 PL I 

GEOLOGIC MAP OF NORTHERN BLACK HILLS. 

LEGEND 

COVERED 

~ 

~ LACCOCIT" 

oo"E5 

PO .. ~HYRY 

-(LACCOLIT.,IC) 

PORPHYkY 

-STOCK~ 

D JURA-CR<TA.L[OUS 

-

P[R ... O-TRIASSIC 

""'·'~~' "''" 

51 LURO • CARBON,_ [ ROU~ 

LIM~STON£8 S~~DSTO~<S. 

CAM6RIA' 

~ 

~ "'TH PORPhYRY 

SILLS 

= CAMBRIAN SANOSTON<S 

FI._A(i' AND SH>l£5 

SECTION 

SILURO-CAR ~ BON I r !:ROUS 

LIMESTONE: 

C£2] 

CA1.16RIAN 

ALC.ONKIAr-11 

-

~ 
INTRUSIYE PORPHYRIFS 23 

It will be "een hom the ,tbm.e that the IoLkq 1ep1e..,ented ne not uuhke many 

othe1" that h,t\e been de-.,cnhe(l hom l.ucohtluc nwunt.un-., ot the RoLky 1\lountmn 

regwn,a and It I':> not po""thle .tt ple..,ent to -.,t,ltc pu-.,ttn ch whcthc1 .t "'hat p dt"~­

tmctwn, matkmg thffment PtuptHm perwd...,, may lw (h.l"'n llPtwef'n the phonolite~ 

gunudtte .md the th\ohte-,Iude-.,Ite rnagma~ The P\HleiHe pomts Iathct to a 

gradual h._tn-.,Itwn between tlw t"o The teun-., IhJohtP .1nd phonolite are unfortunately .1-.,"0Giatetl with e"Xti u:::.wn •• tnd 1t might he le-.,q Lonfu-.,mg to -.,peak ot tlw-.,e 

rock" tb gtamte-porphyne" .md mon.lomte-poi phynf'-., hut then ~t1 uLtuie \\ ould 

h.·udlv "a11.1nt -.,uc.h ,t teunmology In dt..,tubntwn the dtb..e Icgwn ot the -.,chJ:,t 

arPa contain-, hoth phonohtiC ctnd rhyohttc Iod\." thP ':!Ill" ot '1\,o Btt and Squ.1w 

Cteek dhtJH..t-, ,ue Ill genetal an<leo;;;tte-potphvty .1wl dwntc>-pmph}IV, the outlytn~ 

thick 'plug-like_ l.ucohth,, as well,,, a g1eat p01t10n o± th~ gieatei Teuy and 

BPallodge complexe" .tiC mot:~th thyohte But O\et the th,ohte on many hill", 

a.., Tmty, Dem, B.l.ld1 and Sheep monntam" OICUL phonohtr<:.. c.1p.., and t.hc ma,-,.., of 

Rtgged Top, the Spe.u ftsh Pe~k g10up ot bccohth' m the C.ll bomimou,, and Malo 

TPepee are phonolite The rlwute magm.t I.., tepte..,cnted hy .t gte.lt ... tock Ill DP•td-

\\Ood Gulch, ,1nd 1t' pm phH' form' the nM" ot the Needle, to the we't .tnd 

portwn" o± the Vanod\.el l:u < uhth to the ea-.,t 

RELATIVE AGE OF PORPHYRIES 

Dt:ffmence-., 111 relatne .tgP .unong the pmphJ ue" ccit.unly oc.cn1 1± the tran'3cctwn ot one (hke by .1nothei 111.1' he con...,tdeted condu":.IVe evtdence th.:tt the ... econd 

t:, JOUnget tlun the :fh..,t Thi-, endence howmei. ha-, 110 cont,hbn~c ,.due lila 

smgle nhtance fot one po1t10n ot t lll.lgma might IeaJily ciy ... t.1ll17e tnd ...,pht up 

to recen e latct I~]Cctwnr;; ot thfiei entmted m.1tenaJ ouglilallv put o± the ... a me Igneou~ rlmd Between the 'uhdlt} mg ot No 1 ,md the JtJ]C~tion o± No 2 the t1me 

elapr;;ed may not h.t\e been gtedt enough to covc1 the \\hole peuod ot ... ohdth(ation o± the l.ugm mar;;-,e" of No 1 It thh "ete tine a late1 In]ectwn ot 1.\u 1 

might ebewhme c.ut .tn ahe.td} ... ohchfied bodJ o± No 2~ m • which < .t ... e the 

apparent telatwns Hl .tge \Yonld he IC\GI...,ed The. ptepondm.mce ot eVIdc.nce 

would :,eem to "how th tt m the Black HtlJ.., the phonuhte nMgma as .t ''hole 1::, 

youngf'I th.m the thJ-ohtP m.tgma 

"1\I.mv occunence-, m the helcl ot dtkP ... ot one kmd of potphyiy cuttmg 

anothet mdJ- he uted In the Two Bit (h ... tuct the gie.1te1 ma..,-,e.., ot -,,emtcporphyty VU!J- hom .t hmnhlende ±.tclP.., to one th.nadPilZI~d thiPffy hy l.uge 

orthoda~e phenoGLJ st ... 'Hth p01k1htic mtmgruwth" ot plJ.g101 ]a ... e 1nJ other 

mmeta,l-., D1ke~ vthtch cut thh lUI h ,ut m gcnoal hke the m.b'3 ot Bc.ti Den 

aSc'- Cross, \\lntman, The laccohthH.. moun tam group" of Colorado, Utah and An zona Fourteenth <\.nn RPpt U ~ 

Geol 5unc), pt 2, 18!13 Also \\eed and Plr~~on Judith Mountmns of 'lontana E~.ghtc<nth \nn Rept U '< rTLOl 

Survey, pt s, lil98 
24 EC0~0)£IC: RESOURCES OF NORTHERN _BLACK HILLS. 

~fountain, which i::: an outlying subordinate lacco1ith. They are o£ trachytic, liihtGOiored porphyry, showing pink microcline ;phenocrysts. They may bear some 

relation to the phonolitCs. A ::-imilar rock with :u~tbcr-colorcd feldspar phenocrysts 

in a gray 

the Terry 

IWltrix cuts rinc-gTained w-hite aphanitic rhyolite in a sma1l dike on ' - . - branch of the Fremont, Elkhorn and·1!issonri Valley Railroad, on the 

FIG. 2.-IJ-reen phonolite cutting rh)·olite-porphyry, .Fremonf. Railroad, near Xevadu (iuleh. 

spui' between Fantail and :Nevada 

gulches. (Fig. 2.) Near Alkali 

Creek, on the divide from Vanocker Creek, nmn~-WOllti dikes cut 

the fine-grained rhyolite mass. 

These are n purplish trachytic rock, 

with glat;sy feldspar phenocrysts, 

showing stril~tion · (prohably oligoclase) and a decomposed bisilieate. 

Othci· cases of the rock with phenocrystic pink (microeline) feldspar 

cutting the rocks of the rhyoliteandesite .3crics: occur on the ~pur south of \Vhite Hock, just above .Deadwood~ 

and on the ridge we.:;t of t.he he~td of 8pruce· Guleh~ Near the sawmill north of 

Kirk Hill a gray rock couhiinilig muei\ mica and yellow feldspar occurs as a dike 

'cutting light-gray rhyolite which .:;bows ~omc hornblende. It is probable that these 

are mostly phonolitic rocks which cut rocks of the rhyolite-andesite magma. 

FIG. 3.~Rhyolite cutting green porphyry near Aztec. 

Irving has de.::crihecl four ease . ., of phonolites Cutting quartz-porphyries and 

diorite-porphyries. 

A very unusual case (rig. 3) is shown in a seetion near Aztec, on the Burlington 

Railroad (Spcm·ti,h branch). Here a mass of green phonolitic phorphyry is 

apparently cut by an irregular swelling intrusio~ of white rhyolite of the fine-
INTRUSIVE PORPHYRIES. 25 

grained decomposed type so common in- the region. Both occur, as shown, at a 

sloping dike contact with Cambrian shales. All the evidence in this case would 

show the rhyolite to be the younger, or cOntemporaneous with the phonolite. 

The second alternative is the more prohahle. The two magmas may grade illto 

each other, and in this case perhaps the green regirine rock was still viscous when 

the stream of. white rhyolite was injected through it. It is hoped that more 

extended study of the petrography of the region will throw light on these relations. 

GEOLOGICAL AGE OF PORPHYRIES. 

The geological age of the porphyries may he stated in only the most general 

terms. The Bc[tl' Butte and Little ~fissouri Buttes ·l!lcColiths were intruded· into 

Benton Cretaceous and were unquestionably cove1;ed by Niobrara limestones . 

. Jenney has found pebbles of Black Hills porphyries in the conglomerate at the 

base of the 'Vhite River beds to the southeast, and· similar. _fragm.ents occnr in the' 

Tertiary beds at Lead. The Le;td Terti>iry clays (Oligocene 1) are deposited in an 

old topography l,SOO feet below the present porphyry summit of Terry Peak and 

on diddes 300 feet above the adjacent gulches. As these clays were flood-plain 

or lake ( ?) deposits, of a mature stage in the early Tcrtinry dissection of the region, 

an additional 206 feet may be considered a most conservative estimate of height for 

the original porphyry upper limit of the Terry Peak .niountains. This porphyry 

at the time of its intrusion was covered hy a thickness of strata not leSs than 

that of all the formations below the hig·hest beds invaded; a minimum esti'mate 

would make this c not I~ss than 2,500 feet. This would imply a total thickness 

of rock eroded away.abovc the present Tertiary beds at Lead of 4,500 feet (2,000 

erosion+ 2,500 thici<!!~s.s); accordingly, the ·later limital epoch of the intrusion 

per~od may be expressed as the beginning of ·a ±,500-~oot erosion period prior to 

the. Oligocene, while the earlier limital epoch is the Nio~mra. Between these 

there is the ehoice of Pierre; Fox Hills, Laramie, and Eocene times for the 

intrusion . 

. B.r analogy with !he Rocky :\Iountains the greater uplift. i;,' .the Black Hills 

probably took place after the close of .the Laramie. The Only evid.en.ce in the immedia~e Yicinity of the Black Hills hear-ing 011_the queStion ~h·ether: Lar~mle beds ever 

extended over the present site of the hilis is the .factth~t they are tilted up by the 

Black Hills uplift on the west side; if they did so ~xtend they may have attained a 

··thickness of se\·eral thousand feet. The thickness of the .Tum-Cretaceous below the 

Laramie is ±,000 feet. a If the first uplift ~f importance was in Eocene time and 

Larumic beds were present, the erosion depth. at Lead may be increased· by several 

thousand feet. There are analogous intrusions of Eocene age in the Rocky Mouna The wi-iteris indebted to Mr. X. H. DMton ior data and disc,ussion on this question. 
26 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

tain district in bUfficient numher to renrlcr Ycry prohahle t.he occurrence of igneous 

actidty, concomitant with uplift, in the Black Hill" at that time. That orogenic 

dis~urhanccs took place concomitant with mtrusion is proved by the relation of 

the Algonkian-Cambrian contact to the porphyrie-, at many place8, the latter filling 

fault fissures. After the energetic crosi~:m that led to ilepo~ition of Oligocene hed.-; 

and probably reduced the topogmphy of the Hills to much lower relief than that 

of the present duy, "·there wa-s a further uplift, \Yhich has given a very strong 

tilt to the 'Vhite Riv<'r deposits.'' a No porphyry now rm~ealed can ha,~c accompanied this last uplift, wh1ch may sti11 he in progress. By this laRt movement the 

Olig~eene beds at Lead ha\re been lifted and the pre~ent gulches have since heen 

carved below them. The following is a ~ummary of the evidence for the Eocene 

age of the erupth·e,· 

{

Laccohth::> m the Benton 

Endence from geology ... ~ •• _ DeformatiOn concor~1'tant wtth intruswn. 

Porphyry pebbles m Ohgol'ene sethments. 

fPost-Laramle uphft of Rocky )lountams Evtdence from analogy .. -..._.- •

1 

• • k ' Post-Laramie mtrn!<IOllS ot Roc y l\Iountams 

!

Probable ernsion ot 6,000 to 8,000 feet of strata from ahove leVel of 

Evidence from physwgraphv.. · · present Tertmry clay at Lead , 

DISTRIBUTION OF IGNEOUS BODIES. 

The intrw-,ive rocks occur as stocks and dikeb in the Algonkian Rchist. sills in 

the Cambrian shales where that formation is thick, and" laccoliths, which thin out 

' into Elills in the Cambrian, hut ri:,e into thick domes of limited horizontal extension 

where the magmu has broken through the 'mas.s.ivc Carhoniferous limestone and 

escaped to higher horizons. The,e relations will he best understood by reference 

to the map (Pl. I), where Custer Peak, the \Yoodville Hills, Deer Mountain, Dome 

l\tlountain~ and the Iron Creek mas~ represent laccoliths in the Cam hrian a-,sociated 

w1th the broad sill district: thi:-; in turn surrounds the schist area of ~tock~ an'd 

dik~s. Outlying masse", of steep rlomical form, which have hroken through the 

lime, tone are Ragged Top, Citadel Rock, Crow Peak, \Yhitewood Canyon laccolith, 

Pillar Peak, Bear Den .Mou~tain, Deadman laccolith, Tilford laccolith, and Bear 

Butte. The great mass of the Vanacker laccolith on the east is an exceptionally 

large body which in part has broken across the limestone. To the north Crook 

Mountain and Elkhorn Peak are domes of :Minnelusa sandstone, where erosion ha~ 

not yet revealed the porphyry. 

In the schi~;t area mariy hundred dikes occur1 trendmg usually about N. 30° ,Y., 

parallel to the Algonkian lamination, and this trend m a general way corresponds. 

with that of some of the larger laccohthic groups. 

a Quoted frum Mr Dart<m Jetter to the \\nter 
INTRUSIVE PORPHYRIES. 

Thus a line of porphyrie8 may l?e drawn from Custer Peak to 

Crow Peak, from the Tilford laccolith to Elkhorn Peak, and from 

TwoBit to Polo Peak, pru;sibly indicating an alignment of conduits 

beneath. At four points ~:;tocks have been indicated on the map, 

namely, at False Bottom Creek, Deadwood Gulch, Pluma, and a· 

snmll mass east of \Vest Strawberry Gulch; there ·ar<: prohahly 

others in the hills west of Lead. 

dike for a portion ·of its Course, 

The mass nt .. Pluma is a 'great 

but becomes complicated with 

stock-like bodies, nud is of S\!Ch size as to warrant independent 

mapping. The area of' sills in Cambrian shales has its bc~t exposures on Two Bit Creek, Spruc"e Gulch, on the ridge southeast of 

Deadwood, on False Bottom Creek at Garden, along Squaw Creek, 

and on Annie Creek. 

~OMESTAKE DIKES. 

A section from south west to northeast through the Homestake 

and Caledonia open cuts (fig. ±) serves ., illustrate the frequency 

and thickness of dikes in the schist area 

westward-spreading sills and laccoliths. 

that \Vere conduits for 

Here the schist dips to 

the east· and contains much quartz, which in places is distinctly 

quartzite, else'Y"here is massi\Te quartz. The schist is red and 

ferruginous in this region, but talcose, slaty, or graphitic where 

less altered. The dikes average 35 to ±0 feet in thickness. Three 

dikes in the I-Iomcstake section ar~ associated with breccias: in one 

case on the foot wall; in a;wther the fragments of schist arc 

embedded in the igneous rock; and in the third case n breccia 6 

inches thick occurs on the hanging wall of a small ±-foot dike high 

~1p on the eastern slope of the main cut. These breccias sometimes contain frag·mcnts of both· schist and porphyry~ and therefore might be the product of. faulting subsequent to intrusion: 

In other cn.ses they are unquestionably the product of brecciation 

concomitant with intrusion. 

I 

PSEUDO-CONGLOMERATES. 

Besides the dip away from the core of the Black Hilb, which, 

on the rim of the uplift, uniform!)' indicates deformation of once 

horizontal sediments by forces other than those immediately generated by the recent intrusives, there is interesting evidence presented 

by the limestone breccias which are so abundant in the Cam-

! 

l 

' ! 

j 

! •. 

;· 

i 

l 

27 
28 ECON01IIC RESOURCES OF NORTHERN BLACK HILLS. 

brian. The.sc occur in lentieuhlr l!Ut.s~e:-5, ~ometimcs ll_lorg·ing iuto unbroken "limestone flags interspersed among hetis of green· shale, the flagS carrying trilobite 

fragments. ·These £raiments of trilobites may also he seen in ~he flat or rounded 

'"pchble.-3" of the limestone breccias, ·and this bars the possibility, suggested by 

Crosby:a that these breceias arc· conglomerates derh~ed :from an Algonkian limestone. The breccias in .question werC' formed by crushing, accOmpanied in some. 

cases by minute folding·~· of t,he limestone hand~, the hrittle lamin::-e breaking on the 

most acute flexures, or else breakitig into flat pieces under the influence ·of pressure 

without any considerab~e tlexure. 

Infiltration of wttters which dissoh~ed off. the edge~ and corners of these broken 

fragments later cemented the ma:::;s ·by depo~iting crystalline dolomite a.s a. matrix 

for the pseudo-eon glomerate. These :'intraformational broeciat5" are' abundant in 

. the Two :Bit distriCt, where are also lwtny sill~ and dikes of porphyry, and the quesFIG. 5.-Upper contact of ~ill cutting limestone brecdaR, Galenn. 

tion frequently arises in t.he field .whether the deforma.t,ion which fractured the 

limestone beds, and the waters which eementcd .t.h.em, were in any way associated 

with the.intrusiYes .. A negat.i\Te answ9r to t.his question was clearly afforded by the 

upper contact o:f the sill figurcrl (fig. 5). In the lentkular masses of limestone 

breccia here ,;;;;hown there arc deyelopc_d locally distinct foids, which pass by gradations into a breccia, holfliug fragments t.ilted at all angles, frequently without order 

or armngement. Careful examination sho"\ys that often these· may be resolved into 

former folds hy joining· ~he adjacent "pebbles." The work of solut!oi1 and recrystallization on the .fracfured heds has nearly obliterated the original crumpling. 

This locality, showing distinct crumpling occn.sioncd by the porphyry in some of 

the beds -and the ancient crumpling associated with the development Of thC .. ps~ucloconglomerates, offers nn exCellent opportunity to test the· question whether the 

porphyry was immediately the occasion of the brecciation. rrhe cont~ct shows 

« Proc. Boston Soc. X at. Hist.. vol. 23, p. 49i. 
SUli:YARY OF DYN Al\liC HISTORY. 29 

distinctly tlmt it, wa"' not. 

porphyry hoth on the old 

The hme;,tone bu~cdas ate nregularly cnt aero:,~ by the 

fol<l:o, and Ill pla<'e~ where all trace of folding ha-, <li~ap- " . peare<l. In othe1 <·ase~ where fragment ... of the breccm still renuun hori.wntal the 

porphyry cuts actUS':- ftagment~ and matrb. alike. The nnhrecciated limeE-tonc 

bands are occtt.swrutlly folded ttll(l fraeturctl hy the purph~T,Y, and un the frat.:turei; 

.there i::, evidence of some rccrystalhzatwn. :-o that it l& not impo~~1ble that iu places 

a newer Lre<'Cta may owe it1:l origin to Jefotmation by mtru~ton: hut in mo~t ca~es 

the limestone breeGias of the Camhrian wore formed hefure the intru::,ive:o,. Thi& is 

further evidenced by the faet that the~e hreccta~ occtu· in many part~ of the Hill~ 

where tho younger etnptive., are ah':lent, ~o that it h fan to concllulc that the 

• evtdcnec 111dtcate:-. a period uf deformation Iuter than the Cambnau and earlier than 

the laccolithic iutru~Ive~. Smnlar lune-,tone hreecia-, oecur le~;;, ahnndantly m the 

Carboniferous and Permian lime.~ tone:;,. ''r et>d hn-, tig-nred '

1 a Ca111lJrian limestone 

conglom.eratc from the .Tudith l\Iountain ... that in the photographic illn-,tratwn is the 

exact connteqmrt uf the Blaek Hill~ Camhrian l1ed::,. He helie-..·e~ it to have heen 

formeU on a ~->hingly beac...,h. The• writer woultl ::,ugge~t that po~::,Ihl:'.- many snppo~ed 

conglomerate~ may be mtraformatioual hreccia;;. 11 compo'-'ed of luue~tone fragments, 

formed hy CI u::,hing and recrystalli.t.:ution of I~ultr~x, a':l deseriLed, rather than hy 

uplift abo\ L' sea lcn~l. 

•' 

The geologie map uf the Sturg-tc;-Spearti~n-qundrauglc:; (Pl. 1) nnow::, a regwn 

of concentrated 1gncou~ actin(\ nhoi1t the t•Ity of Lead. Tbt., region i~ aEo a 

center of Ote depusitwn, th~ sulphide's ·awl: their (l~riyath'eS being cl~'sely :t'->sociated 

with the poli:Jhyrie::,. The preeJOil&·llletal& are knowi1 to:oecur in A1gonkian ::,cl1l~t;;;, 

in the pre-Camhnan granitw eruptive rock-, a::,::,oeiatcd -.;vith tho...,c ~dn&h. throughout the Cambrain, and a-,-,oci;lterl with lneculitlllc ho~lie-, There are ;;,nme productive mine'-' in Silnro-Carboiliferuu~ 1ilpe~tone.;;;. awl ores ot·ctu· m tlte Tertiary 

porphynes them~elve-.. 

Struetnrally, the Lead eruptiyc ccutor 1~ an area of· laccolith~ in and below 

the ma~sive 1une~tone/'. of later Pa1eu.t.:oie age and uf dike:, and stoek.:; Ill upturned 

schist& founing the eondmt:-< of -::ills in the tlun-beclded Cambrian .~trata. From 

Custer Peak to Hichmoml HilL where ero-.ion ba,., gnawed dt~epe:,t into the erupti\ e 

region, stock"' and dikes in ::,ehi~t arc abundant. Surrounding thl:, tnea the 

Paleozoic ~ectwn bhmvs t-i1l-, in Cambrian :,trata, awl laccolith., at the hasc of the 

great hmef.tonc~. 

It ha-. been shown that the Igneous inti:n":ilOn;;, of thvohte ancl phonohte 

porphyrie':l aecompanied or immedmtely followed a gteat mo\·cmcut of upltft m 

a Weed an<l l'lr~~on, Turhth ~fonntum~ uf ~rontuuu El!{ht"'tonth .\nn TI••pt U S fiL•ll SnrYe\·, pt .3, 1~~8. P! LXX 

Also, Little Bdt Mount..tlll!> T\\ t>ntwth Ann l:t•pt U 'o (,.•,Jl ~un·L \, pi {, 1000, Pl XXXIX 

1>\\akntt, C ll, Hull Cfeol Soc AmcrJt:>t, \itl ;,, ]']' 141-1\J' 
30 ECONO"MIC RESOURCES O.F NORTHERN BL.A:CK HILLS. 

the area now occupied by the Black Hills. a This uplift arched the horizontal 

strata of the plains into an elongn.te dome; schists beneath, with nearly vertical 

bedding a_nd lamination, mo,·ed up hy faulting and slipping, frequently on planes of 

schistosity. Erosion has completely .removed a portion of the sedimentary cover, 

exposing twO kinds of sections whereby the solid geometry of structures within the 

uplift may be studied. One is a beveling acros.s the top of the dome, exposing .a 

ground plan; the other is a deep trenching h~T streams· throug·h the flankS, exposing 

vertical cross sections. The igneom; matter rOse through the steeply iticlincd schist 

laminro and spread out among the scdimcnt.s which lay across them unconformably. 

Erosion beveling has exposed dikes in the schist and fiat m.asse:s in the later :;hatu. 

The. walls of erosion trenches show the thicknes:-3 of the sills and lenses and. 

' sometimes their junction with feeding dikes. 

The intrusives are eonfined to the northern portion of t~c uplift. The ,'Jouthern 

portion was occupied by massive ancient pegmat_ite granit~s, themselves pre~Cambrian 

intrusives in Algonkian strata. Probably they acted as a rigid cemei)ting and · 

hardening agent to prevent. fracturing in the southern schist.'5; the northern, le.':l:-3 

indurated phyllites cracked and faulted more readily to permit the younger intrusives 

to rise from the depths. The northern exposed schist areas contain many hundred 

dikes and some stocks; these must have imlnccd movements of horizontal extension 

in the schist, and such mo,~ements are attested by bedding phtne. faults at the base of 

the Cambrian. ThO dikes have a common trend and clip prtrallel with schistosity. 

The dip gave them tendency to, spread in the Cambrian in One direction more readily 

than in another. In Cambrirtn thin~bedded 8trata with many shale horizons ~ills 

formed in great number. Abm'e.lay the thick limcstor~e; it resisted upward mo\·ement of the porphyries und locally became domed ancl arched. Beneath it' were 

formed the principal laccoliths of ·larger size, the lru-g-est where the limestone '~Tas 

thinne.-,t. Some of them were unsymmetrical, partl'y because they were injected into 

strata possessing an initial dip, partly be~cunsc their emlduits sloped and thfJ magma 

was forced :forward in one direction. On one side the limestone 'vas flexed beyond 

the breaking point; a .:fracture opened and admitted the igneolu:; fluid to higher 

horizons, forming subordinate laccolith,.,. The subordinate laecoliths are eharae.-

terized by still greater lack of symmetry; their sides nre steeper than those of the 

main laccolith; they fault and crumple. the heels about them. Assoe.i:ttC'd with dikes, 

silL;, and laccoliths are breccias composed of fragments of the rocks throug·h which 

the igneous magma passecl. Thel'c is no evidence that the intrusives were connected 

with surface volcanics. In general the phonolites are younger than the rhyolites; 

none of the larger main laccoliths ,are formed wholly of phonolite; the phonolite 

broke through the larger bodies of rhyolite-porphyry and solidified in smaller 

aJaggar, T. ~.;Laccoliths of the Blaek Hill.~: Twenty·firi't Ann. J{cpt. U.S. Geol.(surver, pt. 3, 1901, p. '280. 
.. SUXMARY· OF DYNAMIC HISTORY. 31 

masses at higher. h?rizons. 

a!·c of rhyolitc-pophyry;. 

The greater number of subordinate laccoliths, however, 

th.ese include Bear Butte, Deadman, and \Vhitcwood 

Canyon laccoliths, Cro-..v Peak, Inyankara, and Sundance :Mountain. The magmas 

whieh formed the subordinate laccoliths were beginning to ::;olidify and hence were 

·more Yi.-,cons; this is proved in part by fewer sills, by domes of smaller ground plan 

and greater convexity, and ~).Y diminution in totnl volume of intrusive rocks in the 

higher strata. The eharacteristic forward and upward movement of int,rusive 

through strata is by ''my of strike fi:::;surcs. The lower contact of sills and larcoliths 

frequently' truncates or bevels strata obliquely across the bedding. The horizons, 

where a single stratum is followed for some distance, are eotnposed o:f soft shale 

confined bet,veen harder hedl:l. 

Erosion has left laccoliths covered, partially rinco\·ered, and deeply dissected,. 

and in plac.cs has removed them entirely or loft only scattered remnants. Conduit, 

basement contact, '"·edge, flank, crest-all parts of the laccolith are exposed, in plan 

and section, in different iJlaces in the Black HiUs. The edUence quoted points to 

Eocene time as· the nge of intrusion. There .,verc sm·eral thousand feet o:f strata 

above the laccoliths, and the soft Cretaceous ::;hales absorbed laterally the doming 

produced hy individual intrw;ive masses. Tnmk drainage consequent on the lllack 

Hills uplift was deflected hy adjustment to the domed hard strata that were gradu· . ' 

aJly uncovered; branch drainage, dependent on t,he relat~on of rainfall to form and· 

texture of i:iurface, eontinually changed with the, discovery of hard and soft strata, 

producing hills in hard domed beds and annular valleys in soft ones. Sueh annular 

valleys wore eventually supcri>osed on porphyry," and persist in several deeply dis-

::;ected laccoliths, such as Cn::;ter Peak and the .\Vooclville I-Iills. "There an annular 

·\·alley on the contact of porphyry and' flanking sediments becan,le superposed ori the 

basement Stratum, its course preserved appr:oximatcly the outline of the laccolith 

after the same was in great part eroded a\vay. 

HISTORY OF INTRUSION. 

The history of intrusion in the northern Black Hills is believed"to he intimately 

associated with the history of the larger deformation." Intrusion is not conceived 

to have been in any sense a cause of the greater uplift, but an effect. The 'intrusion~ were a small incident in a great movement .of elevation. The greater uplift · 

probably· took plaCe after the cloi:ie of the Laramie·, along with ::;imilar movements 

in ~the Bighorn Hange and the Hocky J\founta.ins. \Vhatever their cause,· these 

movements were colossal and involved a considerable section of the earth's crust; 

doubtless there had been similar rnovc.mcnts about the hard granite core of the 

Black Hills from the earliest P>tleozoic times. There wa8 unquestionably some 

deformation prior to the laccolithic intrusions, £or these broke across previously 
32 ECONO.:'IIIO RESOURCES OF NORTHERN BLACK HILLS . 

. brecciated Cambrian flags and encountered clips already initiated. The postLaramie uplift W<L::.i accompanied· by profound fracturing. The fractures rcaehed 

downward to a zone 'vhcre rnolten rock was under press~n·e. The liquid shot 

upward into every ramification of the· fracture system; .tUgonkian, Paleozoic, and 

l\ilesozoic beds were in some sense under compressiYc stress, rising slowly, the hard, 

competent members supporting the arch, the ~oft beds folimving the lead of t.l.1eir 

more re~istant neighbors. Diversity Of structure :.m4 consistency produced minor 

differential movements of faulting. and folding. ·The upturned schist b~ds slipped 

··like cards on edge to make undulations in the basal Cambrian quartzite, which \Yas 

also .faulted in 'places. Springing into e\·ery weak place, ~prcadltlg' the beds and~ 

crumpl~ng th~ soft ones wherever there was tendency to gaping by reason of the 

greater burden assumed by the more rigid strata, the igneou~ magmas reached the 

Cambrian throu&·h countless fissures in the schist beneath. The chauge in structure 

at the Algonkian-Cambrian unconformity was especially f:_tvorahle to the dm·elopment of .local weakness that would give adnmtage to an igneous wedge. The l')aleOzoic horizon least compressed lav under the Carboniferous limestone. The thick ' . limestone member, most "competent" to support load under lateral pressure, 

relieved the soft shales beneath in many plaees. The porphyry magma \Vas itself 

probably under pres::;ure and eapable of independevt dynamic action relative to individual beds in~;adcd;. ,vhether that pressure wa~ in :.m;· 1\·ay limited hy the actual 

volume of magma anlilable, or what hydrOstatie or thermal la-w governed it, we 

have no means of knowing, but it i~ q11ite certain t.hut the pressure of igneous fluid 

rellltive to the condition of the limestone was sufficient- lOcall~· to arch up and break 

. through that stratum and some. of the 'superj:lcent. hed.s. That it did not do t·.his 

until it was beginning to solidify is in part suggested by the faet that or.lly a relatively small Yolumc of porphyry broke through the limestone to higher horizons. 

The fact pf local don.ting- ancl. fracturing of the limestone by the porphyry does not 

of neecssity imply that the lm~a in eneh of those domes lifted the load; ~t bent and 

pimpled the limestone within an arCh of enormOusly greater .magnitude, co_mposcd 

of several competent mcmhers that were collectively supporting the total weight of 

sediments. The fad that the greatest: doming of limestone over porphyry at the 

Terry-Polo complex took place wher~ the limestone wa~ t,hinnest shmvs that it was 

·not the wcig·ht of superincumbent becl's, but: the inflexible quality of the thicker 

linlcstone which resisted doming. lt is cqunlly dear that ~he siZe of the ·laecolith 

i.::: entirely independent of load; the snitlller · Hagged Top and the greater Deer 

l\fonntain 1aceoliths arc both intruded at the ~ame horizOn; the Vanoeker iJorphyry· 

mass, probably the largest single laccolith exposed, reaches the Upper Carboniferous, while comparatively srnall sub~rdinate laecolith:s: like Crow .Peak and the 

one in "\Vhitewood CanyOn, are int,rudcd under ·obolus beds at the base of the 

Cambrian. 
GEOLOGY OF THE REGION 33 

DESCRIPTIVE GEOLOGY OF 111INING DI!>TRICTS 

A few t1 p11. .. al sectwn.::., made hom surface mea:surements ot bell.., m .:;trabgraphtc. ..,uc.ce ... ..,ton among the ore-bearmg hmrzons, w1ll sufhc.,e to IndiCate the 

nature o± the Algonkum and lower PaleozOic ... trata. 

ALGONKIAN 

The two mo't stnkmg Algonkmn >ectwns ate tho'e adJacent to the two largest 

ore bodte", namely, the Home•t.tkc and the Clove1 Lea± 

GCHISTS SHOWING SYNCLINAL F-TRUlTURE ~ORTH QF BOl\IEf.TAKE MINE 

A ~eLtlOn ±rom west to e.1"'t on Deadwoorl Creek near Central Rhows the 

folio" mg Algonkmn wck' 

.T ugt we't ut Cent tal there 1' a wntact ot graph1t1c 'ehtst on the wegt wtth spotted 

mrc..t--..clnt.t on the ea-,t, trenfhng N 10::1 'V Oppo•nte Blackston<' ... hou-,e occur '3 

<t hea.' y ±errugmou~ blat.k c;,chr-.t w1th qu.:utztte band-:, 1 to 2 mt...heg wrde ( ut hy 

n 1 eg-nLu "lute quartz hodiC'> wlnch ±orm a drstrnct zone The ':!.tnd<;tonc bands 

dP.uly lnc.tea-,e m b17e on .1pp1on.Ghmg the De Snwt of.Jen t..ut hom the ''est 

F,ttther do"n the gulch, opp<Nte the DeSmet cut, terrugmou, '<hht on the "e't 

1"' found m rontad with gra) IDlUL-schi-,t on the Past, .tt..,compamed llj a ~->udden 

change 1n dtp The dtp httherto ha~ been towatd the ea,t at htgh angle,, but 

around the pomt m Sawptt Gulch the ontmopg me .lll gtav mw.l-'-t..ht-st, with a 

fc\\ very thm ".tnd<::.tone stnnge1"' and ha' e a unlfounly \\P~tcrly dip Tlu.;;; 

sudden < hange ot dtp JU't oppo,tte the De Smet and Homestake ute hod1c' h 

"gmfieant and buggest' that per hap' the gte,tt ore houy may fill a'} nc\m,tl sadrlle 

pttebmg to the &uutbeast A bhort dhtan< e np Sdwptt Gulch ±rom Centtal, on 

the Columhu~ 

1ng N 3±0 W 

worlnng-. 

ground, a trench ha<::. been opcnPd tlong a pyntl±C'IOU..., ...,bc,Lk trendThis trench h dnectly m the hne ot the DeSmet and Homc,take 

bCHISTq RHOWING &UDDEX CJIA}I.lrF OF bTRIKE KEAh. CLOVER L} .\F ORE BODY 

Ea>t f10m Perry the Algonkmn g,lrnet bLhbt >t11kes S S5° >Y , mth mat ked 

l.uninatwn Thu, trend 1'3 tran':!Vel~e to that of the Clo,er Le.t± open t..ut "outh\\c-,t 

ot here Ea>t\\ ud ,tlong the udge on the nmth stde ot Elk Creek there 1:, e'po,ed 

g.nnetl±crous mHa-bdu~t w1th numrtou" lluart7 lcn-:,e~ ~ome o:t them toldPd, J to 6 

Jnche..., thtt..,k The qu.trtz t.hows Iotmded granulebl It 1::, dlflkult to deteunmc-

" hethet they .tre <:.,<Ltada-,tiC 01 bCdimrntat y The lammatwn I" w.1vy. ttendmg 

S 50° 'y, but van Ing g1e1tly m .1 smgle ?utc1op, even to north-.;;;outh &hikes 

.T ust :,outh of tln"3 outcrop ate C'lO...,SPd gr.1plnhc sch1~t .... , feu ugmon~ tlU.ll tz1tc, .1nd 

amplubohte w1th" bend ot R b2° 1\T 

4987-No 2b-04--3 

f 
' 

I 

34 ECONOMIC RE::,oURC:ES OF N4>RTHERN BLACK HILLS 

The next ~pur to the e,"t ohows to the notth 8U to lUll teet o± \\lute <Juart< 

above w1th .tmplubohte ticndm~ we.;;;t-southwe...,t on the pomt o± the ~pur F.nther 

ea:,t I '::I found a. ledge o± mH a-:,c.h.Jbt with l.muncttwn N 53° '\\r , arttl a. wh1te 

barldmg (hstmct -from sdu"tosit) trendmg ~ 75° E The btlltdmc .tp}Jioa,Lhes a 

dt.twn-out hnear pa.rallel "t.hi.::tosity The white qua.rt.t 7ono 1.., on the o;;outh, lmth 

on thib bpur itnd the next -,pul to the t t.,t, thP -..outhern C"'(trenut} o± the ..,ptu 1~ 

oct.npied hy a. well-marked told o± IUKk-.chi-,t "howmg hght .md Ja1k }Mnd., and 

pttdung to the south Follo"mg out the udge we come to an SO-toot ledge 

ot ±euuguwn-::. <tnartzite, .,howmg conturtwn., .wd J<l'I!Jety tcAture On both 

5H1c::. o± this sahent teet ocun great mt...,..,e.., ot ampluhohte t1endmg northc.:t-,t-

">onthwc-,t, wrth "'outherly drp Thrs d1p 1"' charJ.deu'ltu, ot the whole ~">cctron 

There rs here agam .1 north\\e"lt-trenrlmg l.urunatwn'dhtrnc,t hom the h .. mdmg On 

thP f'.l'5t ot the lrttle gulch to the north ot tlu., udge occur.., mH.:t-~1 hro;,t 'utltlayms 

ot mrc.u.eou., oand...,tone Both tmunatwn ..tnd bedUmg~ here trend N 10° ,y Thrs 

nm thedy otuke 1':! repe.tted In tiH~ ..,cbr-,t., u± Elk Creek Canj on, a . .short chstJ.IH.e 

±urthm c.t-.,t 

Suuunmg up tho Al~onkiJ.n ':!ectruu .tlong th~.., r ulgc nor thea,-,t of thP Clover 

LeaJ mnw, we -,ee th.tt tho we.,t-southwcst l'trrkc ro unn'"u.tl. :,ugge~tmg th.tt there I'! 

oome -.,udden ch.mge 111 the ... tructme e,tst '-md woot of the ud~e m q_w'lhon Thm 

ch.tngP, on the we...,t. take.,, place lll the lllJmedr,tte numty ot the Clover Le.t± me 

hudy The <..,f'ctron .tcros-, the ... tuke, hom nor th-n01 th" eot to .,outh-~outhea:"t, lb .IS 

±olio"·.., 

lrJ.rnetJterous mH <l·'H hJ..,t 

Crr.1plntu.. <.(.hi-,t 

Ferrngmous qu.trt..:Itt> 

,.tmplnbollte -

1\Itw-schi~t 

\\ lnte quart..: 

1\IICit·"ChiSt 

.\.mpluh(llltt> 

Quart7ltL 

Amph1hohtc 

CAMBRIAN, ORDOVICIAN, AND CARBONIFEROUS 

Thf' tollowmg t<~.hulated seLtwn ... ...,Jw,, the ch.UJ.I tPllt-.tic det.ul-., ot the lo1\-er 

P.t!Po..::oil. 1o._,k~, wluc.h .-tie retcned to on the toregomg p.lge-:,, tn the dr.tgtam 

~- (hg 1) . .uul m the ta.hl(' o± tm matwn ... (p 2U) The tn ... t ot the-.,e ~:oectwnb 1:, m the 

mmmg dr-:,tuct ne.tt Teny PeJ.k, the ..,ecoml r., truthet ... outh ne.11 Englo"oo<l (the 

t} pe locaht} tot the Eotathon!±mou' June, tone), ,md the thml lb on Beat Butte 

U1eek, nPM the town ot G.tlPn.l, whetc tho Deadwood .wd Englewood ±ornmtrons 

are \\ell e.xpu~ed m .:t-:,:::>OLr.ttwn wrth &Ill'! and dike,;;; 
,. 

CAMBRJ;A N SECTION ... 35 

'l'EURY PE~\.K .;;,EC'l'IOX. 

8rrt1on 1n lower p11rt of Cambr-t_an ter,:rw]e, 8pt'rufish &ranch of the Rttrlui[Jion uud J[umnun Rwlruud, 

j1um nurthgrnt Rlnpe uf_.Terry Pc(/1. to new· EnyleU'und. 

Fcrrugmuns f:UTI1lstone m :!-mch layerb With green t.hale partlllgs __ ... _ .. ___ ~_. ___ .. _______ _ 

Cuar~<f', ma~;,stYe, ferrugmom; r:anibtune With ohve-grPen l"'haly surtacP'l. _ .... _____ ... _. _____ _ 

G-ray, fine ::;and~tum•, m placeR greenish, irrl.'gularly blt~tehcrl w1th purple, and euntmmn):! 

limumte Contain!:! a ft->w Hcattert"'ll \\'Ollll borll1!-!"f'. ___________ .... _. ________ .. _______ _ 

Lunomtic earth:_ .... ! ... __ .......... ____ .... ____ .... ----· ---- .. _. -------- .. _ ...... ___ _ 

Yery glaucumbe, loui'c, ferrugmoml :,o;uHlstuw· ....... ___ . ------ ...... ___ . __ ------ ......... . 

:\[nf'h deemupo':led stliceon:,; f-.J.ncb.tune, \Veath"ere1l lo1·ally .to '-hale:,; awl hermHttw earth .. _ 

Gray. f'tlleeous, ('bert-like, fiue-qrained, compad s~nlll'tone Ill •heel:, of :! to -l mchf'q _ 

Ft In 

.5 0 

4 0 

0 10 

0 10 

.5 0 

·' 0 

.] 6 

8mglc he,l, gray, exceptionally sth('euu-., Pawl•4one, Yery httle eement, ~mne wam~ ot hmo: ,· 

nttlc earth ... __ ... __ ......... ____ ........ ------- ... __ .. --. ___ ........ ------ .... __ ... . 

Fwc-gratneO, rlnt:~ty,.glau('onitic o:awl"ltone ......... _____ ------ ...... __ .... __ .... _ ...... . 

Limomhe glaucuntte pawh1tone, le~~ rn~ted th.1.n below, mnre t:ltlweouf'. toward the top 

}la~Eot\"C R to -l mch beU".----'-------- ---·-------------------------------------------

)laB'3i ve glau('omtw rust eel f.andstone ...... _. . ..... _ .. _ ·- .... _:. _. _ ................... __ .. 

~[asstve ruE:>tetl glaucomtle :,:.:~,n,lootnne in bene he" with a iew mh~I he<l!lerl. f'hale:,; ... _ ....... _ .. 

Altere1l fiag8 anti brown Pand:;:tone Di1•, 12° ~W . _ .... ____ .. -.... ______ . _ .. _______ .. _ ... : 

Coari,Je, Urown, ma:,'3I\ely hedde<l ferrugmouoo :-awl~tonP ----------------------------------

Thin-beililecl glaucmlltw hrm\11 sanrh-tnne ------------------

Cr<•e.e~-lwrl<led brown ferrngmoUI" paJHbtone "tth fnf'OHlt-: .......... : ... -----------=--------- ' 

Thm-beclrlell,' :,h.lly. glauenmttt: sanrl..:tune \Hth two ur three 2~I;wh layert> of brown s~ul<l-

~>tiJne ........... _ .. _____ -- .. ---· ... -... --- .. -------------------- .. ------- -----------

Yery rusty glaucomtw hro\\n ~antlstnne. ____ ...... ____ ................... ----.----------

Tlunly lanunated ferrugnwus eawlstunP"\\lth ~lancomtic l.tyer:-..: ..................... .' .. . 

Same U'l above; Ill a to :lmeh lw·rl-. ---~----------------- -----------------------------

S.une as above, very rusty, an•l 

Rrmvn sandstone With Irregular 

m sume ptu.:e'l be1l<le1l m Jllfli",:tve blocke. .... __ = _ ••••. __ • 

:! to :1 meh IJPtb .......... ---··----------------------·-

)fwsiYe re1ldu;;h and glancombt• ~q11rl~tone ............ __ .. __ ............ :. ____ ..... _ .. . 

Thm, gr~y, ~haly :-.:.tndstone. highly glaucornth m place.", \\eathermg plllk, purplP, aud blue. 

Talnt< ~lope, E>howu~g th_ree lnas"-n e lune:-.tunc~ hree{'Ja memb~r~. ~l\ eragmg 1 toot each. ___ . 

Thm-hetl<le<l lnnestmw hreccw;,. _ ------ .... -------- ......... _ ....... ----------- .......... , 

Gray, fnable, f-and) tlag..,tonf'o> Ill thm t-mch ]Jpob .......... -.------······----------------

Thinly htunmttPtl. tnw, green-gtay, ooluly <-antl:,;tonc,_mure foh,ily bel<!\\, t--m•ly ahuYe. 

SQalc'l "Ith mterhe,lth~d flagstone brecl'la, fine, gmy-~rePn, ~an1ly partnig be1ls among the 

Phales llel'reat.e from here eat:ob\anl ......... ------------- ......... --- __ . ____ . ________ _ 

Paper ~ha.lPS \\Ith a few:! tu 4 mch.l•ethl ot hme~tone hreeu,t 

SenncrystallllltJ Impure luue:-:tone s!Jghtly Lr~-·t c·tatecl, th\ Hlecl 

wtth trilobite iragments _. 

mto -l-mch baiHl:,l ;;f--~~~ii:' 

Lrnwn, red, and green ____ ._ .... ____ ............. _ ....... _ .. __ ...... ___ ._. ______ .... __ 

Paper ~hale:, with 1-wch hmf'Ptone bech: ---------·-: ......... -------------------------· 

Thm-Uah<lPd ~enncrystallme hme:,tune tlagc; Ju} tu ;{ mrh bet!-; ·------------- ---------

Calcareom; dark-brown ~euHcry:,talhne ~awbtone t•rmtamtug ubohlb awl tnlolnte:.! ( DtcellQn1us nana) ........... _______ ............... ------- .. __ ... . 

0 

0 

0 

2 

30 

15 

2 

3 

6 

.5 

R 

R 

20 

4 

n 

6 

.5 

5 

40 

H 

8 

11 

0 

0 

0 

0 

0 

3 

0 

0 

0 

0 

0 

0 

0 

0 

() 

0 

0 

0 

s ... 0 

16 0 

5 0 

2 0 

3 0 

3' 0 

0 

·= 
36 ECONOMIC RESOURCES OF NU:t\THERN BLACK HII,LS. 

Brown glauconitic and calcareous sandt-.tone, partetl by finf' black slaty f'halct; mto layerf' 

one-half mch to 4 inchet'l th1c.k ·--------····-··--·----·····-·-------····---------····· 

Fme, gray-black, '"ell-Jointed paper shale~, t•rnmplcd.• ....... ---------····---------------

Limestone flags contammg hmefl.hme• hreccia, w1th t,\·o 2-inch "hedo; of black l'laty shales 

above and helo\v .... __ .............................................................. . 

Rm~ty calcareou~ t:~andstone m 1 to Smch band~ beparatctl by layers of light-green Rhale, :-ornetimes glaucomtu:, 1 to 3 mchet_o. Huck Both memhers are glaucomtic, the ~antlstone more 

so than the shaly members ................................... : .... ................... . 

Rusty calcareous .Randstone m be(ls 3 to 15 tn('hes thick Highly ferrugmou<;, lemon-yellow 

Ft In 

1 6 

5 0 

--~·1· 

2 0 

7 0 

to ochBr colors anrl dark red brown A~ a whole this Coarse memher "eather~ dark rerl .. _ f. 0 

Much diSmtegrated red, hrmvn, awl yellow ferrugmous Rtndstone Small crystals of hematite, 

mueh hmomte,'vmns of a carbonate and a mangane»e (") mmeral............ ...... ...... 0 10 

Fine-gramed lunonihe qnart?ate, open ~tructure, wlutish, m betlH 4 to 6 inrhes thiCk. 1\Imerahzed upper r<urfaee uf hasal quartzite.................................................. 4 2 

Eight to 10 beds, gray-green paper J:JhaleH above, 4layerl'l of limestone flag!!> he low . . . . . . . . . . . 6 0 

Quartzite carrymg trilobite slnelds anrl quartz m clruses, upper surfa('e red With P.cohthnr< 

l1onngs ................ ------ .. ---.- ·-·---- · · · · · · · · · · · ·- · · · · · · · · · · · · · · · · ·.· · · · · · · · · · · · · 1 0 

Pure siliceous saml:-tone, showlilg round gralils and pradwally no cement, nearl~· a quartzite. 

_·weathers rusty mto massive beds and is slickensided, the shckPnsiJ.es show horizont~l 

movement along a vertwal plane....................................................... 10 2 

t~nartz1te blocks in talus below, carrying tnlobite shields. This near base of basal quartzite 

of the Cambnan _ The tanna IS middle Cambrian. Talus of Algonkian schist. ..... 30 0 

In lo.wer Paleozmc rockR, on Burlmgton und J[issoun Rtrer Rrulroad, 2 mile11 .~OIItltn'I'B of Englewood. 

PAHASAPA LDIEHTOXE 

Gray limestone f>hO\\ s a dip rllscor1lant w1th the EnglewoOd limestone below and an unconfOrmity on it along an almost horizontal !me lJ1p, "~ 28°. The Paha~apa heds at the 

contact are progressiv~ly truncated to\\ard the north. The ~hr<cor~I~nee IS not ·wholly one 

of unt:ontormahJhty, be('am'<e deformatiOn at the south end of the ent affeets both formFt' In 

tttions alike and therf' IS probably some thru!ltmg ................................... c.250 0 

ENGLEWOOH Llli-IESTO:SE 

Purphbh limestones. At north en1l of cut 1lip If'< Bi'l0 to 50° easterly, at south end 2i0 

S 80° E ............................................. ~----~------····· ............... 50 0 

Greemsh·gray shales m railroad cut unclerlying the Engle\\ ood lnnestone The shale Is 

lumvy, hght green on fre!lh ~nrfaces, With da1 k-purple markmgs tbat show c1rcular 

sectwn,across the bed1lmg anJ.lmear, fueoi1l-hke, eyhnclncal hocbes on the heddmg plane~ 

Ao tlns almost ('ertamly overlies the orange-colore,} Xaphrenl1s·bearing rock, It Is prohably 

Lower Ca~honiferous .................................................................. 14 0 

IIRJJOVTCIAN _('?) OR EXGLE\\OOD 

[The follo\\ mg beds are from a!Jont the Or,lovian limestone honzon dowm'\·artl, gomg north 

acro:::o strata tlippmg about 4° SSW , Imme,hately under the great lnuestone quarry J 

Orange-colored arenaceous limestone bearmg Zaphrertt111, crmoid otems, and brachwpoc.ls, 

appdrently in place 
LOWER PALEOZOIC SECTION, 

LA:\IBRIA~ 

Talus ....... ~ ............••....•............... -- .. ---.- .. -- .. -.-.-- .• -

Ft 

40 

GrPen paper shale-.. ....................•..........•.......•..........•...............•.. 10 

'falnf'l .. _ •..•.......•.. ____ ...•.•..•••••••.••••••....•..•..• ---------- •.•..•..•....•.••. 80 

)fa:,~IYlJ "pmk fut..oulal lJUw,tom• _ ................•. _ ....... __ ..... . .......... _ .. _. . . . . . . 0 

37 

In 

0 

0 

0 

40 

PapE>r t,hah'B ancl cal( areon~ flag........................................................... 0 12 

0l'her-yellow calcareous "andstnne ...•..................... :. . . . . . . . . . . . . . . . . . . . . . . . . . • . 0 26 

Green paper "halE-s._ ...... __ ................... __ ..•........... -------· ...... _____ ...• 0 6 

Arenaceotu; ltmt>.,:tone w1th 15r~cn ~hale l'nrfat·e, E,howmg mud cracks With filhng ('Olort>d rerL. 0 1 

Massive·hanl arenaceuu:,: ltme-,ton~-> .•.•.....•.•...•.••••.•.•••. _-------------------------- 0 Bk 

L1ght-green paper :,hale:5 awl thin limestone tlagt-, w1th nreg-ular fucoulal surfaces and mutlcracks ...•......•......................•.................••....... -~--- .. .. ..... ..... 0 17 

).lat3sive caleart:!OUfl qnartntc cx1.tetl with calcite on JOll1t surfaces Retl on iresh suriace, showmg much crvr-talhne carbonate ........ ------ ...... -------- ........ ------ .......... ---- 0 24 

'GlaueomtiL· sawl::~tone. l.unmatctl on Cf()SS-betldmg planes. vdth fuc0Hl:,;, Ill }'art deep green 

antl full of glauconite In other plact>'l tlark n•<l or lunomttc yellnw Sotnt' 0i the lngher 

belh! shov.· Scnl1tltw! (?) hofmg"l D1p, 3° t~~ 4° south_erly ................................ 16 6 

Yer! coan-e, loose, antl in able santh;tone, '' Ith lim om tic t•ement antl smne glaucumtc .. _ .. _. _ 0 3 

Ripple-markctl glauconitic an•l fprrugmous 8.1ntl..,tone, mas-,lve as a whole, hut separa1etlmto 

npple~marked Hliibs The !:!labs are t'oah·tl "1th hemahtc. Evidenu::, of tl1sturbances, 

~uch as cross bedrlmg antl ripple markmg, mcrcase Ill the upper memhcrs ot this section as 

a \vhole ....... · ...........•...................... i................................... 0 20 

Dark-green, gl.aneomttc, arenacPon8 ~hale, vt>ry tun '1f g:lam·omte . . . . . . . . . . . . . . . . . . . . • . . . . 0 3 

Ft·rrugmons ~andst<me m t"o tna'-~lve beth;, t<eparakrl by tt thm bawl of ~hah·... il3 0 

Bright-ret! :,1Rndt=tone, prohably the ''Rerl Rantl, Carbon,tte occUI'tl m vems an<l tlrnses 

Lunomh~ oecnrs m irregular ~pots, as \veil ajo:, ,throughout the ma~s u( the rock, a· httle 

g:lanc_orpte. Rock Is maf'"l\'e, t--howmg snmt-> beUtlmg lirwfl and "lightly '.Vavy Up}H2r ~urhtt·e. 3 0 

Glaucomte shalE>. The hecldmg 18 here Irregular antl variable \'.Ithm short thstances, cross 

hetltling I:, common, tln'3 shale hand tluns nut, awl is replat•Ptl, hy the retl bantl above .... _. 0 ]0 

MM-,1\'t:,glanc.onitH. ~ant1stone. V.wi.1.hon m thicknt's"' is tlue to ndges rcseiTLLhng wtwc mark::1 

uf 2 tu a feet wave length antl ~ t(J :1 m_che'! height.· ~Rnck ~hoW8 ero~os hcdrlmg . _ ... 9 to ].t Inf'ltPS 

Glauconttw shale ....... _ ......................................... --..................... 0 7 

:\IassJ\'e glaut'nn!hc samlstunt" ................... ____ ..... __ ............................. . 

Arenac~otts glanenrntic ~halt> ....... __ ._._ ..... _. ___ ._ .... __ .. _._ ....... __ ............ _ ... . 

),fass!Ye terrugmous sand<-torw, ),lhowmg hnwmte, qnartz, and red matnx Very little glaucumtc. Coan,e crm,., betltling tllppmg S"~, c:nt off "X_ •. _ ..•.••.••.•.•• _. ______ .•.• ___ .•• 

Htghly glaucomtlc ancl tu.l~tiiYe ~alltlstone ' ............................................. .. 

)lal"e!lve ferrugmons .. antbtone, with a 12-lilch quartztte herl helov., showing quartz grams 

Ill a hematltw matrtx awl 8nme glant·onlte The quartnte 1~ ma-;sl\'e \Vhile the upper 

members weather m ~-inch. humnre ............................ -- ................ -... . 

tllancomtic sancl:,tone Ill irrt>gular lamnue, capped hy a f-erlet'l of red ferrugmom~ r-antlstone:;:, 

showing no glai:wumte anrl mmh wm ... -----·-····--·-------------·-------····----·-

Gray arenaceou::~ !:lhale!3 awl Irregularly liPrldecl glauconitic :,;haly 8awh:tones .....•......... 

lilaucon1tic ~antlr-tone >Hth very abundant glatwonite, m two ma.%1\'e bands, with tendency 

to part on the ~dthng ...... _ ........................... __ . _ .. _ .•........ _ ~ ........•. 

0 11 

() fij 

0 21 

0 10 

3 0 

4 2 

0 20 

0 14 

\ 
38- ECONOiiLIC RESOURCES- OF Ji-ORTHERN BLACK HILLS 

Ft In 

MaB'liVe fprrngmou-. -.,mrl~tone, ~ho"m!:r h-'S'3" glautomte than 111 bed heltm ----·----------- 0 .!1 

l\Lt">'HVe glauromh,, '".lwhJorw, "lio"mg: r_,tr)';~ LPdthng 111 plrtu~.., "here the cro-.b herlrlmg 

bmtn,c drpto tlfe <,onth""l.rtl _______________________ --------- ----·------------------ 0 IJ 

.FUfOHial, pmk anrl green, loo"e -,ott, :-.halv, gl<~.nr orutH f>,lnd.,to-ne 1n d. dJf'.tJ.nr e of (1 teet tht<> 

hPJ thm.., out (0tnpletelv anrluH•rge<J mto the llld~"'l\e r-.1-nrl..,ttme <tllo\P --------------- 0 s 

G-Jant.nmtJL l'l.:tnd-,tone \\ rth pink anrl gra-... &eamt10 mchf'-. m tlw kne..,-. Htp, 6"' SB"\Y •• _. _ .. 0 

Pmk ,uul grePn, tw ntdal, loo..,e, "Jott, 'lhal}, gl,tut.omtlt -.,md-.tntw, "\\Ith penrhar properh' ot 

hre.tb.mg up wtu many ]Pnbl" un 1\Pathererl '-llrtacP, hu't ._JHnHng a IIJd':l~n·e fa<f' .. ----- d 2 

1t!as:;n e glaw omtJL, "l,tnrJ..,tnnc, "lhowmg rn.my "311!all '' onn3 fueut4l mark" m cro"':; ... ec t10n 

Upper f!nrfac e (O<ttecl n1th green :-halt' \\ luch tJw\\"' < unt'a\ e Hnpret-:-wnf! ot < oar<-c rop\ 

tuLoHl~ one-half to threvfourth-; mch m· Jumeter, llllXPd \\ 1th Irregular lurn1n ma'-"'t'"-. 0 f) 

Thml) lammaterl green "'Jule <on~unmg one h.:tnd \\Inch 1., pmkt"h anrl ~anclv ---------- 0 

Ma.'-'-lVe glaw.oiHtl<' f',trlll..,tone, Jomt snrfat e < o\'ererl "tth globular ancl botn mclal c oatmg ot 

''hat .t!Jpe.tr-, b • },p .t Lr) stalhne L.trhnn,tte tn 

part of tlu.., ht>rl ~ho\\.., pmk tnc otrlul markmg" 

:-urfate 4 tpet Jon~ __ :: ______ _ 

"lntP m.1""e" Cror-'- FCchon ot lcmer 

!htn::. i>Outh ancl r-ho"~ < ur\e<l upper 

Shaly glancmutJc ~anrl'!tone "'1th ahnncl.mt gray day, lentltorm fr.tcture, fre"lh 'lurta~e IS 

5 

greem<:h gray 'lpeckled wtth gl.me,onUP _____________ ------------- ---------- 0 HI 

Alternate ntd""" e lJan!l':l of glauf'omte l>anrl .. tonc ancl gra) "'ttalP The ll!MlBIH' bantll'l average 

.~me he-, m thrcknel'ls Seen on a frel'h tnt the.;e heel~:> appe tr db .t blllgle was<:.n•e hancl .. _ ti 8 

Fme-gramecl r .-t.lcarenus glau< omtrc "awh·tmw nrpgularl; bancletl pmk awl greeDI"'h gra} 

The pmk b) ers repre'-~ent the finP-gr.unecl m,ttenal ot thP ropy iuLoiil l'lterm ___ • __ •. _. _ 0 4 

Evenly t.mnn.:tte<l .tltPrnatt' byers ot gl.:tnumttH, ~antl,.tnne, thm gra) paper '!hales and pmkrsh' 

.;,awly hme<,tone flag!' \ Rf) mg 111 tluc kne~" trom on;-ha1f lll< h to :1 mche"' ' The 1'1\lrfacPs 

of the~eil.tg~tone..,are<o\ered\HthsnJJllrop) tucuuls __ --------------- ·----· ----- 0 15 

Ma."lsl\e terrugmous glanf'onrtiL sand..,tone '\uth <;In.tlJ \ellllet~ of carhonate, 2 con'-plcuou<; 

heel..,-------- --·--·- ------- ---·----------------- __ -------·-·------- ---------- :! o 

ThmlJ la.mmatecl, \ery ,trgi1ldtPOU~. glaue,omte "hale, green gra} m Lolor, \\lth 1'11lall '\\ofluy 

tmoul':l ... ---· 0 

Glaucomhe sanrl<~tnne \\ 1th lmli)Illte 4 •ct-nrrmg' In '-'trPab.<: In c ro'-s ~et bon ~hdJlf'rl bke bl.ulel' 

ut gra..,':l Surtace ot a o;l.tb '3ho\~~ iuLm<l'l m rleprt'"'3Hm'-, .twl rulge:; like the muci-tnuls oi 

aga::.teropocl. --- ----------------- ---------· --------------------------- 0 8f 

Glaucon!tic l'hJ1e \\Jth 1l.1y ::.eJJHI'l .mtl grJ"'l·hke ftHottlt< mcru<..'l Ret bon------ ------------- 0 10 

'coaNe luuomtH gl.me,omte :-ancl«tone :\fa!'sl\P, \\Ith bome },relci.tt!On hke the U':!Ual hme-

"ltone hreu I<tH of thP Camhrun. ___ _ 

Spt-ckk~l gr.1y-g-reen glauwmtJc sand ... tone 

Hanl glauc omtJC ~<anrl-,tone, wtth pretlo~unant quart,r, l'.tnrl All ot thi" fPrteE of sanclstonec; 

\\'e.tthPr retlrhsh hrm\ n "1th the gra) ·grPt:'ll wlur" ll1 the :;h.tle~ _. __ 

Irregul,lr leuttld ot "haly glancomtw <:anrl:-tun~· \\Ith llJU< h gr.tv d.1\ Fre~h ::ml:ate greem!lh 

0 

0 

0 

~ra)' "PeLklerl \\Jthg-lautomte _______________ ·--- ------------- - _ ---------------~ 0 i 

Yery Lak.treuu<.J glaucomttc r.and~tone \\Ith murc> tarhon,1tt Vl"llJh• unrlPr tlw hanrllt>ll':l than 

tJU.trtz Y dlm\ d.n on mtedamtnat bt'dltl" Snr±.tt f' gr.t} ,mrl rPcl "PPckled, \\ 1th "Orne 

appt'.trance ot fucmcl~" .E,·enh lammated m onP-lult to l-1ilch hanrlfl .• __ . _. __ . ___ . _ _ 0 :1! 

MasE>lVe hmomtJc gl.tutomte ".lnrl"tone, Jnghh L.1lcareonr-, r-urt.tCP t-t..tuwrl \\Jth Iron r.treak"l 

Fttf'otcl tmpre<..<:Hltl'l not prow •nnLecl. ____ . __ II 
I 

I 

J,OWER PALEOZOIC SECUO". 39 

.Ft. In, 

Similar .to next below, hut more massive, with hematitic 'bands and h1co~d Curves slw.,vn in 

, cross section ... _._ .. _ ............................. _ .....••.. · .. · ...•... :............... 0 2 

I~oot:e shaly glauconitic sandstone1 gray s_peckletl with dark green. Breaks into irregular 

lentiform pieces with one 2-inch massive hand. Much gray day--··-····-··-·-··-·-. 0 6. 

Talus ... _ .. _ .... _ ...........• ~ ...•........... -...........•.••...... , ........ _............. 0 6 

Impure 'glanconitic BandHtvne, calcareons and argillaceous. Fncoidal surfaces. A ma~sive. 

bed, -\vith a minute day-seamed lenticulur structure .............................•.•.. _ 0 10, 

Talll!·: ............• _ •... _ ... " ....................•....•.•..•....... : .•. -.-................ 1 0 

Coarse glanconitic sand!ltone, showing Under the lens abundant tri~nsparent rm~nded quartz 

grains, with interstitial smaller grains of limonite and- glm~conite. Parallel to the 

stratification there are hands of ~nor~ abundant glauconite a_nd !3omecrystalline carbomite.·. ,., The whole bed is massive with smne interlaminar.slickensides .............•....•..... 0 15 

Similar to the bed below, \Vith greenish-1vhite clay on fracturO sur!" aces. There· are smal) 

fucoids and some appearance of flat ~<pebbles," or breccia fragments; indicating proximity 

to the horizon of limestone breccias. La~nime one-half. to 1 inch thick. __ ._ .. _. __ .. _. 0 7 

Massive speckled .glauconitic sandstone, purplish on weatherc(l ~urface, ·with pinkish 8pots. 

Variegated color on fresh snrface. Whole series. here i.: more, or less fucoidal ... __ ... 0 6 

Railroad c•1ts north of this .point show fragments of the gl_auconitic series .. Lowest bed 

exposed glallconitie shale. Apparent dip, 9°, S. ~7o \Y. 

GALENA S.ECTIOX: 

Section ;·n lrw1e'r -Paleozoic rockH, up Bedr Bu'tte CrCek }rain road junCtion ea.st of G(flen.a-: 

EXGJ,EWOOD, LDlER'l'ONE. ,._.',ry. .Ft. In. 

· Ma~ive limestone Of grayish·yellow color with blotches of purple hematite .that.frequently 

form a coating on the fossils found in this bed; some calcitB (\ruses. Dip, 8°,.N. 70° E ... s 9 

'Alternating speckled yellow and pink bands of friable thiniy laminated limestone, with mu~h 

crystalline calcite _ ........ -.- ......•....................... ·;_ ...•..... -... -............ 3 5 

More massive pnrple limestone; 40 feet above is the base of the cliff of Pahasapa limestone._ ~ · 6 

},.~~sh·e }mrplish and yellow beds, above.a cliff of Whitewood litil~stone ........ _. _. __ .. ~. _ .. 4 4 

..._ Wlll'I'EWOOl) LIMES'I'O'SF: (ORDO\"ICIAN). 

1\laEsh·c g~ay. limest~n~; spotted. yello\~·.; irregular, w.it~t len~icnlar_ lami_nre prod?-ced by 

\\·eathering ........... _ ... _ .. _. __ . _ .• _ .. _ ....... _. _ ...... _ ........•.. _ •... _. _ .. _. _ .. ~ 15 0 

Buff-colored sandy limei:3tone hecorning increasingly siliceous downward;_ massive, weathering 

to thin latnitu-e ....•....• ___ ·_. _. _ ......... _ .. _ .· ... .'.· ......... · .• -~---: _.: •... _ .. ~ .. ·. __ 6 0 

CA)lJlRL\.::0.: ( llEADWO~)D FOR::.lATto,~). 

"X, ell ow .and gray limoni~iC calcareous sandston.e _ .. · .. _ .... _. _ .. _ ~ _._. _ ... ~ _. _. _. __ . _ ....... =· 2 0 

Massin~ brownish sandsto"J?.e, with traces of seolithus borings._ .. :.:.:·.·- ...... _._.·.~ .... _ .. _._ 

Ha~(l, ·white1 ·,ScolitlwH quartzite, with well-marked gasteropocl hori~1gs thinning to the ... vest" .. -

0 10 

Q, 1 

Bro\\'ll sandstone . : .... : . . :. _.. ___ .. · _. ___ :. _ ..• _. __ · _ _. ... __ . ~ :. ___ . · __ . _. _._._._. __ • :·.·-- •..... o. ·.4·' 

Hard white ' ' quartzite, /~'cutitiw.~ borings in upper surface, thinning toward th~ west _. _ .... _. c· 0 4! 

Pink and orange-~olo~ed quartzite . .:: . .:.: ..... _. _ .. _. _ . . :.. _. _ : ... __ r_.~ ..... _. __ . _. __ _. ___ ._. __ 0 2' 

Shale .....•....... -.-.- .. -: .. -'~--.-.- _. _. ~.-.: .. : . • ---:-.-.--. ~·~·-."- .·.- -·-----.-- : . . ~--- ' ... 0 • Pink qu~rtzite varyil:~g to white, without borings·----··-·--·'·---~--:··-----------~-~·---·- ·'0 1 

·rink ~audstone- ...... : . .... _..;; ... ~---:.- .... _.:-.:---.:-; .. -. --'-- --- .. -.... -.. -. -·--- .. - 0 4" 

,• 
40 :ECONOMIC 'RESOURCES OF, NORTHERN BLACK HILLS. 

-white quartzite 

Pink and yellow fine-grained sandstone. All of these beds show a tendency to converge 

\Vest\vard. _. __ . _. _ •... _. _ .. _ .. _ ... _. _. __ . _ .... _ ·- _ .•.. _ . _ .. _. _ .. _ ... _ •. _ •• _. _ .. _ ..• __ 

\Vhite quartzite ... ~ ... _ .... _. _ .. _. _. __ . _. _ .. _. _ .. :. _ ... _ .. _ ... _ .. _. _ .. _ ---- ....... _ ... . 

Pink sandstone ............. ~ .................................. -.. -.- .. ---.-.-.-.. -.... -

\'fhite quartzite ......... _ ............. _.: ....... _._._ .. _._ ............ _ ................ . 

·white quartzite, weatherin~ reddish on its upper l'lUrface ......•. ~ ..•.•..•...•..•.•.•..•• 

Yellow quartzite, weathering pink .. ---- ........... __ ............ __ ..................... . 

Pink, yellow, and white sandstone, becoming more calcareous downward .... ~.-····-·--·-

Gray calcareous Bhales, becoming thinner bedded and wore shal_y downward, with fine gray 

slaty shales at the base; scolithns borings occur throughout this sericl'l. _. _. _. ____ . _. _ 

Persistent white sandstone beds showing ripple marks in cross section, and veneered on 

"its upper surface with gray shale carrying fucoirls ______________ ··-------------···-·-· 

Bfown shales wit.h Iight-greell Surfaces and interbedded gray shales, showing ropy fucoids .. 

'Cliff of massive .brown sandstone, with glauconite beds on the south !!ide of the creek. 

Dip due E., 8° on the E., 20° on the""·-----·-··-·-·--·---·----·-··-··--···------

Brown ferruginous ~andstonc, very_ glauconitic above and massive; below the rock becomes 

more laminated and contai!ls less glauconite. Dip, 8° cine E .. _._._._~ __ . ___ .. _. ______ . 

Massive dark-bro\vn sandstone forming a single bed,· with siliceous infiltration:; . _ .. ___ . _ .... 

Glauconitic sandstone, with a more thinly laminated middle band-·-····-·---~----····· 

Pale rose-colored sa~dstone, as below ... _. _ .. __ . __ ... ____ ... _. _. _ .. _ ... _ .. _. _. _. _. _ .. ___ ~ 

:Massive brown sandston'2.. __ ... __ . _ .. ____ ............ _ ..... _ ......... -----· .... _ --------

Palo ros"e-colored, thinly laminated; :,:haly sandstone, \Vith gray fucoid.<;. This series seems 

to be thinning toward the west, and shows in that direction increasing shaly 'lamination.· 

Brown sandstone _____ . _ ...•. _ ........ ____ -~ _. _ .•................ _ ----· ___ . ___ -----·-. _. 

Brmvn sa~dstonc filled with yellowish fu~oid~ .. __ . _. _ .... _. _____ . __ . ~. _. __ .. __ . _. _. _. __ . _ 

Strongly glauconitic hard sandstone._._._ . __ . _. ~ .. _ . _ .. _. _. _. _. __ . _. _. _. _ ... _ ...... _. _.:. 

Yellow and green shales, with fucoids and glauconite •........... -----·-·-·--·-·-------· 

Soft rotten· glauconitic shale . __ .:. _. ____ . _. ___ •. _' ~ ___ .. _. _. _. __ . __ _ .: __ ; .. _. ___ .. _. _. _. _ 

Hard glauconitic quarb::ite .... ___ . ----·-·- _ ·---- ...... _ --·-·- ____ .• ---·-· ··-.--- ____ . ---·-

Soft shales . _. __ . _. __ . __ ... _. ___ .. _. __ ... _. _. __ . _. _. ______ • _. ____ . ___ . _ ... _. _. _. _ ... __ . _ 

'\ Speckle(t brown and green sandst~ne, with glauconite---------·-···-····---·-·---------· 

Thinly laminated glauconitic sl:iale1 with fucoid markings ?f yeJiow limonite. The whole 

~cries of rocks here is calcareous .... · .............. : .............. , ................. . 

.l\Iassive red-brown sandstone,· yery ferruginous, 1vith some ?lauconite. _. _.: .. _____ ... _. _. 

Ocher-colored fucoid shale, with black blotches and thin films of green shale .. ____ ._. __ _ 

Glauconite shales, thin bedded, showing coarse i-ipple-rnarked surfaces covered with limoniti"c 

fucoids of ochpr color ..... _ ..... _ .. 

Bright-gre"en massive glauconitic -sandstone . _. _ .• _. _. __ ... _. _ .... _. _ ... _. _ .. _. _. _. _: ___ .• 

Ocher shales .................... ·_ •.. -- ....... -.. 7 ••• - ••••••••••••••••••••• --•••••• _. _ ••• 

Hard glauconitic sandstone, apparentl~ thinning westward, with small yellow fucoid 

Illarkiugs .. _. __ • _. __ . _ •. _. _ .... _ .. ·- ........ _ .......... · ... _. _ ...... _. _. _ .. _. _. _. ___ . _ 

Glauconitic fncoid shale, thinly laminated .......................................... : ... . 

Yellow and green shale with_ large grainS of glauconite ..........•....................... 

Thin-bedded glauconite shale~._._ ... ____ . __ ._ .. _._._._ .... __ .. _ .... _. __ .. _· ____ ..... _ .. _. 

Ft, In, 

0 1 

0 9 

0 • 0 2 

0 2< 

1 2 

1 ,! 

6 0 

6 0 

0 6 

0< 2 

25 0 

8 1! 

,! 3 

3 10 

0 8 

1 1 

0 1! 

1 1 

1 9 

0 8 

0 4 

0 1 

0 9! 

0 6 

1 0 

0 10 

5 0 

0 8 

4 7 

0 10 

0 5 

0 4~ 

3 10 

0 3 

60 0 
TERTIARY AND QUA~'ERNARY. 41 

Ft. In. 

Light-gray quartzite, wfth ocher-colored cement and fucoids an~ entirely without glauconite. 

This absence of glauconite very conspicuous in contrast with adjacent beds __ ....... _· 0 8 

Red, ferruginous,_shaly limestone, carrying crystalline calcite, hematite, ycllmv fucoid traces, 

and near the base thin green lenses, slightly glauconitic, covered with fucoids ... __ .. _:. 2 10 

Similar to _abo\'e, but more massive ............ : .... , ..... : ...... --------··--··---------: 3 0 

Thinly laminated, light-brown, dolomitic shale, 'vith some ghiuconite; weathers red on , 

edges-·····----------------------~------------···--------···--: ..................... 3 0 

About 40 feet below this the gray shaly dolomitic limesto~es outcrop in thin continuous 

laminate(~ flagstones. The surfaces sh(nv fucoids, IUud cracks, rind glauconite, ::l.nd there 

are interlaminated limestone breccias or "intraformational conglomerates." . 

TERTIARY AND QUATERNARY. 

The ·Tertiary and Quaternary formations have an indefinite thickness, occurring, as they do, only in the form of eroded remnants. Tertiary occurs as white 

clay in the basin where Lead has been built and in thC saddles between neighhoriilg hills. This clay contains fossil vertebrates, and also fragments of 'porphyry, 

hence is the product of erosion after the porphyries were intrudcd. This is further 

proved by the fact that the clays are depositcd in a topography eroded far below 

the present porphyry sum"mit~, The material here called Quaternary consists of 

rounded stream bowlders and gravel, occurring in masses sometimes 50 to 100 feet 

thiek, usually filling divides between the present streams. These remnants show 

the location of more corisiderable qeposits of the same sort along ancic/tt stream 

channels. The courses' o:f these ancient s~rcams in several cases show a significant~ 

relation' to elbows of capture and valley trends which mark ·the changes the drainage 

has undergone. o 

The thickest masses of Quaternary gravel lie at the head of Boulder 'Creek, east 

of Deadwood, on the divide southeast of Crook ~Ionntain, at the head of Park 

Cteek, on the divides west and southwest of Sheep Mountain, and at the head of 

Whitewood Creek, along the Burlington and Missouri River Railroad. There is 

reason to suppose that these anei8nt stre'ani gravels may contain placer ggld, but 

they have not been worked to any extent,.as co·~lp"red with. the gravels of the 

present gulches. 

ECONmliC RESOURCES ·oF THE NORTHERN Bl~ACK HILLS. 

Part IL-JYHNING GEOLOGY. 

By J. D. IRVING and S. F. EMMONS. 

43 

CONTENTS 0~' PART II. 

Png., 

l~TRODUCTIO:X ~ •••••••••••••••.• -- < ..• - ...•. -........................................ • • • . . . 5.~ 

Ackno"' ledgment:s _ .•. ___ ..... __ .... __ ..... _ ... __ . _ .. ___ . fi:{ 

I~ocation of the mmmg re¢on ... __ .... ____ .. ___ .... __ .... _ 54 

CHAPTER I. ORE llEPO~ITS IX ALGONKIAX noCKS ···-····--···--·········----·----·----------- 5.3 

Gold ores ...... ----~- .. ·,· .. -·----..................................................... 55 

Home~take mmes, hy S. F Emmon~-------------------------·--------------------- 55 

])u::covery and development ..........•........... ·.............................. 5fl 

DtscoYery .. _ .........................•..............•.•. _• ____ .... .... .... ft."i 

lte1luctwn oi ore'd ·····-··············--····-·········-···············-··-~ 08 

l\hning 1levelupn1ent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 

:l\lean'd of comrnunwabun •.•..... _ .. _ ...... _ .................... _........... 61 

ProJuetton ·······:······················································· H2 

Geological Jesenpbon .......... _ ..... _ ......................... ·,.............. 66 

Surface geology ................. _......................................... 66 

Ore minerals.............................................................. fiS 

Gangue mmerals __________________________ ,- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ liS 

Incli•Stng rocks ..•......•.......... _....................................... 61-l 

Form and manner of nc·currence of ore bodtei'l......... . ................ :. . . 71 

Smfaceworkrnga.............................................. 71 

Underground Viorkings........................................ 74 

Cale1lon1a ore body........................................................ 78 

Condu'dJOBt-~ .............. ............ ......... .......................... 78 

PetrographH' E'huly of the Homestake oret'\, by J D Irvmg ---··················· SO 

:\Ietamorphosed seclnnents ............... _.................................. SO 

Metanwrphu:,;ed Ignel)ru; rnckr............................. . . . . . . . . . . . . . . . . . . SO 

Rclatwn'3 of ore:,; to the Algonkran-ruc,ks. _ .. _ .. _ ........ _ .. _ .. _____ .. ___ .... 81 

Detatle1l ~~~.,~i.fj)twn-:-~-~-~~--- ............. ~ .... _ .... __ .. _ ... __ ........ 81 

\Yall rock ........ __ ...................... -.:;. -~- .7: ... ---- .... ·. _ ... ?"~~s1:: 

Ores~-----~----·---··--······-----------··--····-···~~~~~---~~ _, - 82 

Handed ore __ .• __ .. __ .... _ ..... ---· ......... - .. ---·-- .. -::-:,_--- 82 

Contorted ore ••. _ .. __ .......... ---- ......... - .. -.. -- ...... -- ~85 

l\Iat-~Ive ore. __ ... _ ... _ .•. _ ................. --................. ~\:;.. 

Porphynes _ .-. _ ........ _ ... _. ___ .., __ .. _. __ .. _ ....... --................. 8S 

Porphyry breccia .. __ ... _ ........... __ ... _ ... _._ ... _ ... ,...... R\:l 

Sunrmary ... _ ... _ .. _ ............ _ .. __ ........ : •. ........ _ ............ -... l.JO 

l":fold ... _ ... ___ ...... _ ... _ ........ _ ... _ .. _ ...... _......... 91 

Dnlom1te ... _ ...... _ ..... _ .. __ ... _ .•. _ •. _......... 92 

.J,,j 
--=-,_ 

46 , CONTENTS OF !'ART- n: 

CnAPTER 1. Om~ DEPOSITS 1:-.r ALGONKIA.S ROCKS-Continued. 

Gold ores-Continued. Page, 

Clover Leaf miue ... ~ ........ ---- ...................... --.-- ..... : ...•. ----........ 92 

RelatioM to surface geology ...................... · ........... _·_ ........ -.... 93 

Character of 'the ore ..••......... ---- ...... :.-.: ..... -....................... 94 

Copper ores .. -••.................. -.---.............•.•... -- ..................... --... 94 

Tin ores_ ...•.......................................•... --- .. -........................ 95 

Stream tin,- _______________ ---------_----_ - ____ --- ~------- ----- ____ - _____ -- __ ---- _ 96 

:1\[iscellaneous deposits ....•.................•....... -: .... -.'.. ..................... -.... 97 

. CHAPTER 11. ORE DEPOSITS IX CAliiHRIAX ROCKH............................................. 98 

Gold and silv~r ores .............. ······-------------···-------------.................. 98 ' . Gold-beanng conglomerates~ ......... -- ........... -- ...... --- ... -- ............. ---- 98 

Generil statement. ___ ._ .. _ .... ·- ...... _ ................. _: ..... ___ •.......... _. 98 . 

Detailed description ..... : ...... _·_ ... -............ --._._-_....................... 101 

Literat_nre .................... -.. -- ... --- .... --- --· ..... ·_ ...... --.......... 101 

• Location ...... _-_ .......•........... ____ ...... ___ ....... _ ......... _._ ..... . 

Topography _________________ ---- ____ -------------- _______ . ___________ ----- 10:1 

Geology ___________ -- _---------------------------------- ___ ---- __ --- _---- _ lOR 

Algonkian ..........••........ 1 .•. -- ...•.•....•... ----........ 103 

Carnbrian ....................... ! ........................... ·. 104-

. Distribution of conglomerate areas.~ .............• _ ...•.. _ •... _. 10-1-

~ithological composition .. · ............ --- ........•.... _ .•. _. ... _ -107 

Pyritic conglomcntte ._ ........... -.•.....••• ~ ....... ·.·........• 107 

Conglomerate eemcnted by iron oxide.......................... 108 

Alteration of the conglomerate ... ---···········---~----········ lOS 

The contained gohL ..................................... ---·.............. 109 

.Jiechanically deposited gold ................... _ ..... ·._........ 109 

Chemically rcprecipitated gold ...... · ........ _._ ..... _ .. __ . __ .... 110 

Gold introduced with pyrite .......•.... ----···········--····-- 110 

Refractory siliceous orcs ..................... : ......... ---- ..... .- ..........•.... --. 111 

General statement .. __ ... _ .......... _ ... _ .... _____ •. __ . ___ .....• __ ..• ___ ... _ .. Ill 

_Deta~~:r~~{:~:i~~-~~,~ ~ ~~ ~ ~-~~ ~ ~:: ~ ~~~ ~ ~~~ :: ~ ~ ~ ~:: ~:: ~ ~::: ::::: :·:::::: :~ :::::: 

History and dev~lo£m,c,!t~~- --~~-=-~'- :':.~-~ ... ~ --~~- ...... --;-:.· .. -.'- _ ... ___ .- .. _ ... _ Proclnction._. •.. -." •• -: .. -.... --- ... ------ .... ---- : ••. -- ... -~ ........... ." ...... . 

-----~-=--~ /otiilrif(f~r a.n"clr_osition of the beds in which the ore occurs . __ ... ___ .• · .. ____ _ 

113. 

I 13 

116 

117 

118 

IIS 

118 

119 

120 

121 

122 

122 

. . ).;r - . Physical character ..... __ .... ___ .... _ ...... ____ .. ___ . _ •• __ ... _ 

_/T . Macroscopic appe'arance' ............... ___ .... __ .. __ ... --~-

/"' 

{~ 

-t;.•~ 

Microscopic appearanCe ............. ------ ___ . _ .. _ .. ___ .. . 

Alteration . ___ -- ... _____ .••. ____ ... ____ ... __ : _ .. ____ .... __ . 

Chemical composition ..... _ ....... ---·· ....... ___ .. ___ ...•. _. _ 

.Geol9gical position .•••.. __ ..... _ ..•. __ ._ •.... __ ... ___ .... ___ .. 

Lower contact··-------· __ ------------ ____ ..... __ .... _ .... 

Upper tontaet . ____ ...... ___ ... __ . _. __ .. __ ..... ___ .... __ •. . 123 

The ore bodies. ___ ..... --------- ............ -- .. ------ .... __ ....•... ------ lU 

Fonu and size ............................. --. -......................... 12-l-
CONTENTS OF PART II. 47 

CnAPTER II. ORE DEPOSITS rN CA:\IBRIAX .ROCKs-Contiriued, 

Gold and ~ilvcr ores-Cot~tinued. 

}{efractory siliceous orcs-Continued. 

Detailti<l description-Continued.. 

The ore bodies-Continued. Page . 

. Fracture~!\ .. : .•.............•..... ------ •.••. __ ............••• · ...... __ . 126 

Vertil:al extent .................... ----- .......... _ ...... _ ... _ 128 

~mount of opening ..................... ---- ....... --- ..•. ---- 129 

Direction ______ ......... __ ._ ............. __ . __ .......••... ____ 130 

Grouping ____ ·_ ........... ·. ____ ......... _ .. _. ___ .. __ .... _____ ._. 130 Intersection . . ..... .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . .. .. . . . . 1:31 

Relation to eruptiYe rock~ ______ .......... _ ... _ ...........•. _.. 132 

Origin ........ ____ ..•.................. · ....... __ ....... · ...•.. : 1:34 

Relation to n~ineraliza.tion .................. _· .. ~................ 134 

The ore ...................................•.... -......................... 136 

1lac"i'copic characte; ................... _ ................. ."....... .. . . . 136 

::\licroscopie character ...•......•...... _ ....... ___ ......••... _ ......• _. 137 

Minerals ______ .......•.... __ . __ . ·. : ___ ... _. _ . : ....... ___ . ___ .......... _ 138 

Quartz _______ ....•... _____ .•..•..... __ ... ____ ----. __ •...• 138 

Chalcedonic silica. ___ . _____ ..•. ·--~ .. ___ . ____ ......... ____ . 138 

Pyrite ................................•........... ·······.· 138 

Arsenopyrite . ___ .. _. _: .... -- _ ... ___ ............. ___ .. _... 138 

Barite.: ............ ·----- .............. ______ ... · ... ··---· 138 

Fluorit'e ____ . __ ... __ .... · ••.... _ ..... _ ......•...... :. __ .... 139 

Gypsum........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Stibnite ................................. .-.............. .. J:l9 

Uraniun1 n1ica .••...•.... _. __ ......................... __ •. 140 

Alteration. ____ ._ .. _.- ............ :_._ .•.......... ·. ___ .......•.. _____ •• 140 

Chernistry _. _. ____ • _·_ .. _ .. _ .... __ .......... _ •...... __ .....•.•....... ~. 141 

V'ariations (rom the usual type of. ores._ ........... · ...•.... : . . · .......... _ 143 

. Auriferousclay ........................................... 143 

Auriferous gouge ................ !':.·.! ................ ; .... __ 144 

... Quartzite ore·----·"'··:--··;·········-···----·········--·- 144 

.·o_,.·o.._.Areal.,list:~~lil!_on.oLre!r~tO!-y-siliee~S:::of'es ..•........................ _ 144 

Bald~~::~::t~:·~~~:~tgr~~~;:::·:::::~:'~:-~;~::~~-~::· -~~·· . . . Alpha-Plutus-::\l_ogul group ...................... : ... -~~-,.- 146 

Portland distriet -~--- ......... · .............. ~ .........•. --- -~ 149 

.. 'Isolated n1ines -·-··---·····--··········----"·---···--··--····- lw 

150~~. 

151 ""'. 

151 ~-

Garden an•a ... ········----- ···········-~---·· ············--------

1 -· --· 

Lead area ........ _ .................. ~ ....................•• ·- _ ...• _ 

•. Ye!low Creek area ... .' .. ; ............... -................. --.... .. 

Squaw Creck_area ......... _. __ ._ ..................•...•.. --- ..•... __ 152 

Sumnn1ry .................................. _ ..•...... __ ....•....... 153 
<.·-=-

4S ( ·CONTENTS OF P.ART II. 

CHAPTER .II. ORE DEPOSITS IX CA:>.JBRrAX ROCKs-Continued. 

Gold and silver ores-continued. 

Refractory siliceous ores-Continued. 

Detailed description-Co~tinued. 

The ore-Continued. !>age. 

'ralue _______ ......... _. _______ ... ~ .................... __ .. . . .. . . . . . . . 153 

.Age of mineralization. ________ -~---- ...•......•. ____________ ...... ____ 154 

Origin. ___ .-----......•... __ . _____ .... _·_ .......••... ______ . ___ .. _ .... _ 154 

. The mineralizing process ..•..•. __ . __ . __ ........••......... o •• ':.. 155 

Direction 'of flow of mineraliZing waters ......... _. ______ . _...... !56 

Derivation of ore minerals .•.. !>.~ •• ____ •• __ ••••••• __ •• ___ •••••• 157 

Methods of treatment ... __________ .. ______________ 00 __ .. 00 00 _ _ _ _ _ _ _ _ _ _ 160 

l\Iethods of mining_-_ ................... __ ..•..•....... _. ____ ._ .. ~ ..• ___ 160 

Prospecting. ___ .· ............ _______ .. _ ....... _________ . __ . 161 

Future of refractory siliceous ores ................. : .. __ ......... _.............. 161 

Pyritous o~es ....... ------. ______ .......... ----~- ..•......... _ _-______ .·. .•.. ......•. 162 

Two Bit district..~ ......................... _._ ... _ ... __ .'.. 162 

Tungsten oces. _____ -----. _____ ------ ______ -· -------- _ ----· ------------------------- ___ 163 

\Yolframite .......... _ .. -------- .. ____ ......... -~--- ____ ............ _____________ : 16:~ 

History ..... : . ..........•................. __ ... •••.. .. . . . . . . . . . . . . . . . . . . . 16:~ 

Occurrence ______ -.- _ ...... _____ .. _ ........ _____ ... __ ..... _ ..•.......... _ _ _ 164 

Character __ . _____ ........ ______ .......... ___ .... _....... .. .. .••. .. . . . . . . . 165 

Chemistry__________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 166 

Coneentcation __________ - _ _ _ _ __ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 168 

\ralue.. •. . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 

Discus!'lion .................. _ ............. ________ ... __ •.......... _. _ _ _ _ _ _ 168 

Lead and silver ores ... _ ............................... __________ !._ ••••••••••• · •••• _.'.__ 169 

Ores of Galena and vieinity: ___________________________________ .:. __ _-_ _ _ _ _ _ _ 169 

Age of mineralization ... _-_. _____ ........................... 171 

CHAPTER Ill. ORE!,; IN CAnnONJFEiwus ROCKs •••••••••••••• : .•.•••••••••••. ~--------------- 172 

. Gold and sih·er ores ..... ______ ........• _ .. ____________ . __ ...•.....•... " ___ .. _ ...... _ .. 

Ragg-ed Top district __ :.:~->-. __ . _______ ........... ____________ ....... _._ ......... . 

. Dacy group ........ -::'-_ .. ··;·· ______ ......... ---""~- ........... _.! •••••••••••. 

Microse3pi1::appearanCe of~the,ore. _.: _ . _ .- __ .. ·. __ .-.. , ........•.. _ 

__ _ -~-;_mic3.1 character of the ore._._.~:· __ ·--~ _______ . _______ ... ___ .. 

~ -?f~r~mlltC~treak mine •... ___________ ·: ___________ ..•...... __ ........ ____ :.: .. . '-" 

172 . 

172 

17:l 

174. 

·y Ulste~ mute. ____ .. _ ...... _. ________ ....... ___ . _____ ........ _____ ._ ....... . 

c . /-~df~:o:~::~~;~s~~;~l~~:o~es-:::::---::-:-: :::::::::::::.::::::::::::-:::-::::::: ::~:- ~ CHAl-'TER IV. ORES IN ROCKS Ol-' RECE_NT ORIGIN ••••••••••.••••..••••• ~---------------------

174 

175 

1 i6 

176 

177 

177 

/;} Placer de 'posits._ ....................................... _ ...................... -•....•. 

.//' CnAi'TER V. DETAIJ.Jm nEsCRIPno;-;-., oF m:-;-Es •• , •••••.•.••.•••••••..••••• ;-----------! •... 

~·/' 

179 

179 

181 

181 

182 

182 

/ ~c;/ 

~lines in auriferous Camhrian eonglomcratc ......... _. _. __ . _ ......... ___ ...... _. _______ _ 

Pinney open cut ........•............. --------------------

On_1ega mine __ ·: _______________ .......... ____ ....... _____ _ 
CONTENTS 0~' ~ART II. 49 

CHAPTER V. DETAILED DE&CRIP1'Iox~ oF )11'\"&,-Contmue!l 

l\Iinps m auriferrtU::l Camlman conglomerate-Continued. Page 

1\Iomtor, G~ntle Anme, and Hawkeye-Pluma mines......................... 182 

:Monitor .....•. _ •... _. _ ..... ___ ....... ___ ...... __ ••....... 182 

Gentle An me _____ ------ _________________ ._________________ 1SR 

Ha'\'okeye-Pluma ..... ___ .... ____ .•..... ____ ..... ___ ...... 183 

Mmes in refractory :::thceou-, ore<~. ____ ...... __ .... _____ ..... __ ....•.. ____ ...... __ ...••.. 184 

Bald :Mountain arE>a __ ......... ___ .. ____ ...... _. __ ...... _____ ..•. ____ .. · ........... _ 184 

Buxton mtne ····--------···-----···-------·--------···--- 184 

Retriever nnne ... ~ .................................... : ·•. 184 

Stewart m1ne .............................. .._..... ......... 185 

Golden Rewurclmme............ ....... ........ ... ..... ... 185 

Btg Bonanza mine . •. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. •. 186 

Fannte nune .... _ ...................... . 186 

Little Bonanza mme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . 187 

:-:;outh Uolden Rewarll mme ...... '....... . . . . . . . . . . . . . . . . . 188 

I><t<lomh unne.---------------------------- -------------- 188 

SmHlan<'e mine •• . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ISS 

Billy mme.............................................. .. 188 

Rnby Bell!Hme .......................... ,. . . . . . . . . . . . . . . . . 18~ 

Luctlle llllllC.... .. . .•......•••••.. ...•.•.. ...•... .. .. .... ISH 

Ro:,s-Hannibalmme .................•.................... 18\:J 

Union mine .............................................. 1HU 

Alpha-Plutu-;-::\lognl goroup............................................... .. HH 

Chnton tntne .... :........................................ 191 

Alpha-Plutns 11111)('..................................... .. . 19~ 

Turnaclo t-Aine -------·······--···················-------·· 192 

Great Mogul mine________________________________________ 196 

Little TornadP mme ....................... :. . . . . . . . . . . . . . . Hl7 

Double Stan1lar1lmine..................................... 197 

Bot"~('Obel nune ................... :·........................ 19g 

HaHlscrabhle mme. _...................................... Hl9 

""ekome n11ne............................................ 199 . -. Harmony mine .............. :.. ......................... 149 

Tien Hnr mme ....... ·----···---·····--·-······--·····--·-- ~00 

Baltuuore mine........................................... :!00 

l\lines on the upper ore-h·armg beds................................................... :!00 

DaJ~"=Y 111tne. ____ ... ___ .... · .. _. _ ....... __ .............. _ ... ....:--~oo- _____ / 

Upper Welcome min~---···------··-----····=--:.·.··-=-·---'·--··· ~00 

Portland Ui-,trtet • _................... • . . . . . . . . . . . . . . . . • • . . . . . . . . . . . . . • . . . . . . . . . . . 201 

Dn i1lentlmme ........ _ ........ ____ .................... __ .. 201 

Sno\\ storn1 1mne .. __ .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :?02 

Two.TohnatnJne ......••................••................ ~0:! 

Ci-nc;hnn-t and ::\Ian chester mines........................... :?0:! 

l.ahrador !nine.------•................... :................ 203 

Decorah llllne .••...•.............•................•.••... 203 

4987-No 26-0':1-4 
50 CONTENTS OF PART II. 

CIIAPTER Y. DETAILED DESCRIPTIOSS oF MINEE.-Continued. 

Mines on the upper ore-bearmg•beds-Continuerl. 

Portland dtl:ltrid-Continued. Page. 

TroJan unne. _ .... _ ..... _ .... _ .......•..••..... 20:1 -.---.--- -- Alarneda nunt• .............•.... : ..•. ___ ...... •. . . . . . . . .•• 203 

Folger tutne ..... __ ..... _ ............... ---.- __ ••.. __ .... •. 204 

Perseveran('P IIIHW ....•••..••••..•••....•...•••....•....• - 204 

Entptrc mwe _ .... _ .......... _ .... _ ..... _ ... __ .... __ ...... ~04 

)lark T\\~In Intne ......•.•..... __ ......•.. ___ .•..••. _ .... _ :?04 

Leo1Jard antl Jesl:lte Lee mine._ .... __ .......••. _ .. __ ..... _. :!05 

Burlmgtonanol Golden Sawls nunc........................ :!05 

Portlawl mtne ..•.....................•.....•..........••. :.?05 

Clinton nnn~· . -,................. . . . . . . . . . . . . • • . • . . . . . . . . :.?06 

Gunmson mtnP •.....•...••...•...•.....••..•••. --------- ~06 

South Dakot.ct nnne........................................ 20fl 

Lead area -----·. _________ ....................... · ............. _ ............... ____ 206 

' 

Sula 1nnw .......... ~ ... o •••••••••••••••••••••••••• _ ••• ___ 206 

Harn~on mine .... -.•....•............... _ ........ _........ :!07 

Iowa and Golden Crown mllw ... .--......................... :!07 

Dea(h\ood-Terra mme ............•............ _ ....•.. _. •• 207 

Btg l\h~o>souri nnnP .. ------------------------·----------···· 208 

Swamp Eagle mine ................... : ............. _ .. ____ 208 

Hidden Fortune mme ........ __ .. __ .... _. _. _. _ ... __ . _·_ .. _ _ :!OS 

Du rang:o llllllt-' •..•••• ';. • ~ •••••..•.•••••.•• _ .••••••• _ ~. ___ • • ~08 

Garden area ..••. : ••••••...••. ____ .... : ..... -............... : .... _ ..•. _ .... ___ -___ . :.?09 

Penobscot rrnne ............ · ------ __ .... ------ ...... ...... 209 

Keyt-.tone anti other nnne:-: ........ .:....................... 209 

Harn1.on rmne ......................•. ___ .. __ .. __ .•.•. ___ . 209 

Golden (1ate wme ...... --------------------------------- 210 

KICkmg Hon-e mme .... __ ... ___ .. ___ .. __ . ___ . __ ....... ____ :!10 

Bla(·kta1l nnne --------------------------------·----------· :no 

'Veils Fargo 1n1ne. ------------- __ . ------ ....... _ .. -------· 210 

Amenl'an ·ExprCl'll-1 HJIW-' •• _ •.•• _ .•• __ •• _ •• ___ •• __ • __ •• __ • _ _ 210 

Yellow Creak area ................ -- ... -- ... --- ......... ·.......................... :!11 

' ...... lJonelt.un tradwn ___ . ____ .. __ .. _ ... ___ .. __ .. _ .• _______ . __ _ 

,,·a~p No 1 ... _ ......•. ----·- -------- ___ .. _ .. _ .. __ .. ___ •.. 

211 

211 

""asp No.2, L1ttle Blue, and Little Blue fraetwn. ___ .. ____ .. 211 

Two Rtnke nnd Little Pltb,burg.~ .. ___ ...... _ ... _ ... _. __ .. . 

Squa\v.Creek area.------ ................................. ____ .... _._-___ .. __ .. ____ _ 

212 

:!12 

---- Cleopatra uune -·----------··-----:....................... 212 

PL.\TE<: II TO xx . .-: ...... · .... •;-';.-:;:o.--"o'.·--------- -----------------'------------------------ :!14 

INDEX •••••••••••••••••..•••••. - ••• -·..:::- ••. ---.-----.--- •.• --·-••••••.••..••.•••.•••. _'. __ _'_ :!15 

... 
ItiUSTRATIONS IN PART II. 

' ' 

'' 

PL\.U' H :-4outlKrn De.:vh\ooll-Tt rr.tupen ~.,nt________ •••••••••••••••••••••••••.•.•• 

1U :-4pt:!clluPn ot -,Ltte -,hm\lllg r~btwn of fol•hng to l.uwnatton .... 

IV Sketch rn.tp ol a pnrtton ot the northern nt,u k I!lll"~, ~ho\'illlg' the loL<llHJn uf the 

"1\LrJ.l "Peu<~.lm.tp'3lndude•lm tlus pa,per ......•.••••••...•...... 

\' l;encra\ "eoJog>L m.tp ot the northern Black H>IJ,, 'hO_)V>ng the \oca\Wll O[ the \af!OUe 

pr•HlUt tl\L 1\HillllK -tre.L'~ .11111 tht~Ir rel.lt10n to tlw ~echmentary furmatwn-; 

VI ll-E>ologH map ot Lt!acl arHl \'ICJnlt\, sho" mg the lo• .ttwn nt the .tllrlferou<: gravel" at 

the ll.l"P of the C.un bnan and the general tr,Pologv m th~_. ne1ghburhoo1l ot the 

Homestake IO(lL .......••..... ' 

YH l-i-arnetlierun" ure lrom the P1erce ~tope, Home~t.1ke wme, 'lhO\\IIlg se<onriary 

Page 

214 

214 

214 

~14 

214 I 

<IUJrtf wtfo,lntt>d lJetween (~1) 'lhatter~o>d garnet aJHl (B) !'<.attere<l<~1TLonate _ 214 

VIII Sketch map of the Clu\t>r lAat llllilL, '3h<,\\tng rel.ltlon to "iUrfau"' Keologj _____ • . • • 214 

lX )lap ~hm\tng the pnnupal f<hoob, uf refrd.l tot) '-thceuulo ore lll the Bald )lotllltam 

a,rPa ,m• l thf'lt relJ.twn to ::.nrfa<.e geqJug\ . __ . _ 214-

X Dolonnte nr orL-bea,rmg rm k .1, xenomorphlL Y.tnet), n, autmuorplH(' y,tfld). 214 

XI 'r, pc cro" 'e< twn, ot <tln eo no ore ehoots siH>\\lng \arwt>o [ormo L<ken Lv ')nner•l· 

I.l.ltllm l'rntLc<lmg uut\\J.r<l trom the suppljmgn~--urc~ ---------- . 21-l 

XII ~1, C•Hup<•""Ite trHtnrc or '',ertHRl,'' •t" <-lCen ln open ;ut ot the Cleopatr.t mlllP, 

bqua\\ Cnek n, :\hnerah7e<l fracture::. or . \ettual-;'' lll porph)ry flLdf tbe 

:X Ill 

:XIV 

mouth ot the Ltttle Tionanta nnne un t:l•mth P.Hlc ot FanUul (htlch 

Plan ut a. pnrtwn ot tlu \Velcome mme 

}!111 fO'-lUplC bl.LtlUB'-~ ut ">)\H UllHl Oft trotn• the 

the 1•ul.tnnr H. \\lth the j•nlotrlter -·--· 

Ro>.~-.-I-lanntlJ.lJ mnw .I, \\lthout 

XY ~flLro...,<OplC "L<'twn-., uf --IhteoU>.~ ore, "hm\tng the pcrfet.-t pre.,cnailon of the dctatlH 

11t tlw orJgm.:tl r11ck tcxturP after t<>mplete rf'pl.u·enwnt loy ...,Jlua A, '\o\Jtltout 

214 

~14 

214 

the po!,mter, B, \\Iththepol.lnter. --·-·- ·-·-- 214 

• 

XYI Bande•l "'hceon> me, N" 2 'hoot, Umnn unne, shmHng the preoenatwn o[ 9eoh-~ 

rnent.Hj beti<hng m the ort"' ---- __________ : ________ -:_ 214 

'XSll (n~ol<Jgtc m.lp of RJ.gge<l T;,p )lunntam a,nd 'H llllt,, >.~bo\\ mg po!'ltwn and thret•hun 

ot the ma,m R1.gged Top "\ertH'al'3,!.'.<t.h·0-t\w hll'atton of the 1Jl<.ter mme ... 214 

XYUI Pl.1.n <~.n<l t ro"'S 1'-Lltwn ot tht-> H.n\ kej e-l'lum,L mme, ::.ho" lllg the genlogH, relatwnt:~ 

of the golcl:he<Lnng l'amlman conglomerate ... _. __ 

XIX East~\\t>"it cru-.t:~ '-CCtwn uf the Torncv1o mmt< 

XX Plan and eat:.t-v.e'-t crot-., :sechon of the hrt>at ).!o6ul mmc 

ol 

~\4 

214 

214 
52 

Fm 6 

7 

8 

9. 

!0. 

11 

I'' 

J:J. 

14 

Hl 

]6. 

ILLUSTRATIONS IN l' ART ll. 

Folded awl eompres~ed quartzite band In slate .. _. _ ... _ .................. . 

SectwmJ of ore body, Father rle Smet mine. ____ ._._ .............................. _. 

Plan:;~ of Hnmet'take ore lJOfllt's on 300-5,00 f{}(lt lt:!veh> ..•...••.•...................... 

Star-Oltl A he ~edttm of porp~yry an1l ore ........ ; : _ ............................. _. 

Banding of Algonk~an ~late due to l'arallel arraHg-ement ot graplnuc matertal . __ ..... . 

D1rectwn of ~l'hl:-.tmnty m mmerahze1l J-Chb,ts ....... _. _ ................•... _ ...... . 

Approxl!Ilate gt>ologwal sectiOn from I [omestakp W-'in eaJo<tward (after W R. Devereux). 

SkPh·h of "vertteal," a."J bPen meros~ Jo<ectlon, Mhow1i1g the manner lJl which it, projectR 

from the :;urroundmg eountry rock on ..tcr·onnt of the rel'lbtant character imparted to 

the adjoimng material by Slht'lficatwn _- _--- ___ . _. 

l\flcro-draWlllg' of fl~"ure Ill rlel'OIJl{lo"lP<l trachytmci phonolite, ~hO'\·~'IUg the character of 

a "vertical" aftt'r pasl:!ing- mto the phonoltte ailJOinmg thfJ ore, from a large rbke 

I'ag~ 

72 

'iii 

75 

76 

~::I 

84 

102 

12!1 

on the we~t .-;ide of the Tornado ort> hotly ..... _. ___ ._ .. _ ...• _. ___ ._ .... _. ___ ._ 1::12 

lrleal sertwn to ~:>how rPitlttom~ of greatest latt!ral extent of ore to the tllrectwn ot flow 

of tnlnerahzin~ v.,ater:'. _____ .. -... -...... --.-. _ ... _ ....... _ ....•.•.•. _. ____ . ___ . _ ];}j 

Cro~'l ~"chon of a portwn of No 4 flhoot, Union nnne, showing the eonf'entratwn of 

ore Ueueath an Irregular rhonoltte root. .. --- ... __ .... -.-.... _ ... _- •.. _ ... _. Hll 

--. 

--------

·" 
I -

ECONOMIC RESOURCES OF NOR'I'HERN BLACK HILLS. 

PART li.--nliN.ING G-EOLOGY. 

By J. D. lnvr:om aml S. F. Emru>1s. 

INTRODUCTION. 

This paper is intended to embody a description of the economically important 

ore deposits in the Sturgis and Spearfish quadrangles, in the northern Black Hills. 

Inasmuch a~ thh,; area includes the major portion of the mineralized and productive 

territorv, and as those few ore bodies that fall without its limits have heen ' I 

described, the title has heen expanded to cover the mining region of the northern 

Black Hills. ~he tin and gold ores of the southern hills are not included. The 

work is chiefly of a descriptive character, and theoretical discussions are either 

excluded or made as brief a:-; pos~ihle. Generally the discussion of each cla&s of. ... 

dcpooit is preceded hy a general statement of most of the important fads embodied 

in the more detailed description, so that the esoential facts may he readily grasped. 

Acknowledgments.-The tield work upon which the mining portion of thrs 

paper is hased was carried on during- the tield season of 18~~. The work was done 

by :Mr. J. D. Irving under the direction of :Mr. S. F. Emmons, who has written the 

report on the Homestake mines. Valuable assbtancc Wl\8 rendered by }..Iest-;rs . 

• T. ~1. Boutwell and l'. S. Smith. Conjointly with the im·estigation of the mines, 

the areal geology was studied by Dr. T. A . .T aggar, under whose personal direction 

the tield operations were conducted and to whom the "-rrters are indebted for many 

valuable criticism~ and suggestion~. 

It is with great pleasure that the writers acknowledge tlie uniform courtesy 

with which the owners and operators of the mineo of the northern Black Hills have 

placed at their disposal information and facilities for im:Cstigation indispensable to 

the preparation of the work. Acknowledgments are especially due to :Messrs. T . 

• T. Grier, of the Homestake Mining Company. Angus R. McKay, C. W. Carpenter, 

and Colonel Franklin for their endeavors to further the work carried _on in their 

mines. Many valuable suggestions are also due to the kindness of Dr. F. R. 

53 
\ 

54 ECONOMIC RESOURCES OF NORTHERN BLAOK HILLS. 

Carpenter. It is imposElihlc to make Rpccial acknowledgmentt~ to ail from whom 

courtesies and qssistancc were received, hut of sneh as have not hccn separately 

mentioned too nnwh can not be said in return :for the aid which has hcen so willingly 

rendered. 

Location (Jf the un'ninq reqt'on.-The main productive- mining region of the 

northern Black Hills i' inclurled within an area of about 100 Sl[Uarc mileo. Jt 

extenrls from the town of Perry. on Elk Creek, northwestward tu the town of 

Carbonate, on the cast bank of Spearfish· Canyon, while it::; wirleRt as \veil as its 

mo'.st Producti \"C portion lies hetwecn Terty Peak on the J-'Onthwest anrl Garden on 

the '\wrthea':lt. Ont'3ide of this ar~a IS a small and eomparatin•ly undrYelopeJ 

district to the '~c>t in the ,·iclnity of Nigger Hill. 

'\Vitbin the maii1 min,ing region oeeur 'many ancl,very dhrcrse types of ore 

depOsits, some of whwh oecur mamly in the rocks of the olUer gcologi<'al formations. . ' - TheRe depm;its in each ease lmYe features charaeteristie of the geological formation 

in which they oecu.r, so that for purpo~cs of rleScription they muy he most logically 

classified under the h~ad of th"c,e geological formations. In this way the following 

fiv~ main dhrisions may he distinguished: ta) Ore Jcpo~it'3 in Algonkian rock.,, (b) 

o~·e deposits in Uambriall rocks, (l') ore dcpo~its in CarhoniferouR rol'k~, (d) ore 

deposits in eruptive rocks, (c) ore deposits in roeks of recent formation. 

The relaLions of the'c different groups of ore deposit" to the rocks of the "everal 

fo!·m~tions of the Black Hills are shown in Pl. V (p. ~H) a~d fig. 1 (p. 18). 

\ 

. ' ... 

.. ,., 
CHAPTER I. 

ORE DEPO:-llTS IN ALGONKIAN ROCKS. 

The ore deposits oecurrmg in the metamorphic schi~ts and other rocks of . . 1.\Jgonkian age constitute the most Important a::; well a-, mo~:;t permanent factor 

in the mineral prorluetion of the northern Black Hi\ b." They may he subdivirle'd 

' mto golJ. ore~, copper oreEl, and tin ore~. 

Of theee three divisions the tirot, or that of tl:e gold orcs, has thus far been 

the only one of importance. There are three mines that have yielded orcs-the 

Homestakc mine, the Clover Leaf mine 1 and the Columbus mine. PI VI show::; 

the location of the Algonkian lodes and their relation to the stratigraphy. 

HOMESTAKE MINES. 

By S. F E:~.n.IO!':., 

The Homestakc belt of mines extend, from the town of Lead and Gold Run 

Gulch northwestward aero::;" Bohtail Gulch to Deadwood and Sawpit gulches, 

covering thus an area over a mile in length and about 2,000 feet in widtll . 

. The gold product of this group of mines ha" always O\'ershttdowed that of 

all the other mines of the Black Hills together. .:For a Ion!( time it constituted 

ahout ~0 per cent of tho total product of the ,hills, altho~gh it was "omcwhat 

le:,s in the early Jays, when placer mine:-; were more productive. Since 18!10. 

howe\~er, with the increasmg Uevelopment o:f the siliceous ores of the Cambrian~ 

this proportwn ha" gradually decreased to lj() per cent, m spite of the fact that 

the act,ual product of the helt has steadily increaser!. 

DISCOVEitY. 

For many years reports had l1een currPnt among "T estern pioneer~ aild prospectm's of the occunence of gold in the 13\ack Hllb,"reports that became unduly 

n None of the ore <lt>po~Its nf \\hat 1~ known a, tht! southern lull~ arc Included 1n this treatment, a" they are entlrcl) 

w1thont the area mapped This "Ill fnxonnt for the omi..,o<HJn of many of the now quite nnportant gold-producmg 

propcrtie« that occur ~outh of the town of Perry 

55 
56 ECONO)flC RESOURCES OF NOR'rHERN BLACK HILLS. 

magnified for the ,-ery rea,on thttt they could not be verified because of the 

jealous care exercised by the Sioux Indians in keeping miners and pro1spector.s 

from this the mo;,t valued portion of their great reservation, which, by the treaty 

of 1058, compri::•ed all of South Dakota lying west of the l\Iissouri River. These 

report' were, doubtless, mainly founded on the story of Father de Smet, a .Tesuit 

missionary of Belgian birth, resi<ling among the Sioux in the firot half of the 

nineteenth century. He otated that nuggets of gold that came from the Black 

Hills were shown him, and that he was assured that there \Vas a mountain of 

gold where the nuggets came from. Subsequent in\'estigation proved that the 

Indian mountain of gold was nothing more than a formation of yellow mica; but 

this probably found fewer reporters and believero. 

The military reconnais-sance by General 'Custer in the summer o£'1874, which 

actually penetrated the hills, was accompanied hy a geologist (Prof. N. H. Winchell) 

and several miners :tnd prospectors,.and actually did discover gold in the stream 

beds of the Harney Peak region. After the, return of the expedition the miners 

who hag accompanied it organized a party supposed to be strong enough to protect 

itself against the 1 ndian_s and established themselves in a stockade on French Creek. 

Under the treaty of 1858 the Government had bound itself to protect the reservation against the encroachment· of white men, so this party was brought back to 

Fort Laramie by a company of United States cavalry in March, 1~75. Steps were 

taken to prevent the inrush of miners whi'ch seemed likely to follow, it being generally understood, howe\-er, that the Go\'ernment would take the neces&11;ry steps to 

secure a recession of the hills by the Indians so that they might be thrown· open 

to pe":ceful and legal occupation. 

As som~ doubt was felt by persons of high authority .whether gold did exist 

there in remunerative quantities, the Secretary of the Interior authori~ed a geological examination of the hills to determine the true facts regarding the nature and 

value of the mineral deposits. Accordingly, the geologists, >V. P .• Jenney and Henry 

Newton, with a strong military escort, were sent there in May, 1875. This expedition, who~e final report for vatious rea.sons 'vas not published until, 1880. made a 

less thorough examin~tion of tpe northern part of the hills than of the region farther. 

south, where gold was first discovered, because the northern portion was so thickly 

co\·ered with forest growth as to render it almost inaccessible. 

The region of the Homestake mines was not even reached by the part,\" of 

Newton and .Tenney in 1875, but some of the men' attached to this !?arty remained 

behind to pra&pect after it was hroken up for the winter. The first mention of the 

region in print is found in a letter from T. H. Mallory to 1V. P .• Tenney, dated 

January 31, 1876." Mallory stated that he had found abundant gold in the gravels. 

•"' ''axewton, Henry, and Jenney, W P, Report un geolog)' and reRourceY oi the Black Hills U S Geog and Geol Surv. 

Terr , 1880, p 282 
-' 

HISTORY OF HOMESTAKE MINES. 57 

of the variou::; stream!::\ around '\Vhitewood and Deadwood gulches, and characterizes 

the region as the best place in· the hills for a poor miner. 

The Homestake and Old Abe deposits are said to have been discovered in 

April, 1876, by two· French boys, :Nloses and Frederick Manuel. The Highland, 

Golden, Star, and other claims now included in what is -kno\vn as the Hpmestake 

belt were located later in the same. year. Dul·ing that summer the work was 

mainly that of the prospector. At the surface was found a great ext~nt of ironstained rock (cbloritic slates, quartz, and pot:phyry) which carried g~ld, sometimes 

as much as $16 per ton, but in general of much ·]ower grade. ·Although it was 

difficult to make such determination of the form or boundaries of the ore bodies :ts 

would give an idea of their probable value or permanence, yet public expectation 

ha,d been so excited with regard to the assumed mineral worth 'of the bills that four 

of these claims found purchasers within the year at prices varying from $30,000 

to $165,000. In 1877 they 'vere examined and reported u,pon by such well'known 

and experienced mining engineers as "Tilliam B. "Farish,.Louis and Henry .Janin·, 

and Augustus J. Bowie, jr., in the interests of prominent mining operators and 

ca,pitalistS, among whom were J. \V. Gashwiler, George Hearst, J. B. Haggin, and 

Lloyd Tevis. 

At the time these examinations were made -the deVelopments consisted only 

of open cuts, or shafts not over 50 feet in depth, yet by the follO\ving year the 

various claims within the -belt had been purchased and four large gold-mining 

companies had been organized and were in active operation. Three-the Homestake, the Father de Smet, and the Highland--had been incorporated in California, and one-the Deadwood-Terra Company-in New York. Thefr properties 

were compri,ed in a belt about H miles long, exter\ding in a northwesterly 

direction from Gold Run on the south to Deadwood Creek on the north. The 

group of claims constituting the Homestake mine occupies the southern end of . ' 

the belt and is succeeded on the north by the Highland, Golden Terra, Deadwood, 

and Father de Smet mines, in ·the order named. .Not long after the mines were 

opened it was found advisable to work them 'under ·a single management, and as 

time went on the Horuestake Company came either irito Control or into actual 

possession of the Other properties in a manner and to an eXtent not generally 

known to the public. The result' has been that the' name "Homestake" has been 

applied to the whole belt and the other properties are often spoken of as if they 

'were simply parts financially, as they are geologically, of one great property. 

This practice will be followed here, except so far as it bas: been possible from 

acccssi ble published reports to segregate the bullion output of •· the different 

companies. ., 

The history of the Hoinestake properties, could it be given in full from 1878 
58 ECONOMIC. RESOURCES OF. NORTHERN BLACK HILLS. 

until the present day,. would be. a most instructive one. It, would describe the 

development of very. low-grade bmlies of ore in the face of great natural obstacles, 

and ·with a margin of profit necessarily RO small that a very slight error might turn 

it into a loss; yet the company.has hee~ RO uniformly successful that at no timP- has 

it been fQund·necessary.to ·SU.':>penrl the regular monthly dividends to stockl;wlders. 

As it has been the policy.of the coinpany not ~o n~ake public anything more than the 

general finan~ial Te~mlts Of its hu~im~s:-;, the puhlishcd data with regard to it are so 

incomplete that it is only possible here to give a g~neral l"ketch of its history; which 

may.not·hc strictly corrcct.in all its iletail~ ... 

. · ~In a lai·ge degree the uniform success of the vropcrties has douhtles~ hcen due 

to the:faet that tho~e who furnished .the .capital for their ilevelopmcnt_wcre men of 

practical experience in, the management of large mining_ e_ntcrprises. Both in p~rw 

chasing ami developing their pr_operty they took the be::;t scientific ad vie'e, and were 

willing to Hpend· money freely in accorO.ance with this"addee. Furthermore 1 after 

. having convinced themselves that their 'manager at the mines was a man_ of ability 

and integrity1 they. ga\~e him ._free hand and did not hamper him i~ his work .. To 

the two men who have had the entire management of it~ !t.tfairs since their inception, 

Samuel 1\riclVIa:-;ter np to 1885 and T .. J. Grier since that time, is due a gr;at part .of 

the credit for the remarkable success of. this mine. 

REDUCTION OF ORES. 

It was evident that for a profitahle working of :-mch very low-grade ore as was 

fonlld ,here it was necessary to handle very large quantities and at very !ow ~cotit. 

It Watl possible to.mine at very loyi' co~t, for the ore bodies, lying ou rather steep 

hill slopes, could he worked in open cuts or actually qwtrried. The ore, ·moreover, 

was free milling and of a nature to he ve:·.v r~adily crushed, hence ti:e proper way 

wa:-.; to increase the mill capacity as fafit as was consistent with successful working 

and a judicious expenditure o-£ capital. Timber was ahundant in the hills, though it 

had been clefired away,or burneJ. off from the immediate vicinity of the mine. Other 

supplies 'ha~ to be hauled-from the Union Pacific Railroad, oi:· from the ~Hssouri 

River, a distance, of 200 to 400 miles . 

. In the summer of 1878 two St:lmp :nilll:l, one,of 80 stamP.~ at the Homestake mine, 

and one of 100 stamps at. the Father de Smet, were put in operation. In 1879 the 

Homestake Company. had a second mill of .120 stamps running, and mills of SO 

stamps each were huilt at the Deadwood and <.Caledonia mines. In 1880 'the Highland 

mill of 120 stamps· and the Terra mill of 80 stn.mps were added, making at the close 

of .that year, a total of 7±0 stamps employed in crushing tl10 ore from this be1t, with 

an actual capacity of 2 to 3 to?s each per twenty-four hours . 

... According to the first report of .the Homestake C0111pany, which gives Un account 

of the operation8 for twenty months up to Septen!ber, 1880, the average yield.of the 
REDUC'l'ION OJ!' HO)r1E~TAKE ORES. 59 

ore_ had hecn $9.6D p~r ton·np to .Tune, 187D, hut whfm al~ th~ ore hetwecn the wall:-< 

wa~ taken without sorting, thus deerea>;ing the co:-;t of mining. thi~ ~~ield was rednecd 

hy ~H to $5 per ton. It increased- again later, when highm··grade ore was found in· 

the 100-foot level~ tu $7.fl5~ a meanwhile, the cost uf milling had been hrought down 

'to 90 cents per ton in the 80-stnmp mill, and 71- cents in the·l~O-stamp J,uill.; ·-To 

·hring ahout such low costs it wa-:; quantity rather than quality of work that had 

bcCI!. :timer! at; hlankets and eoncentratioi1 machinery were not ernploy(~d, hec•ttnse· on 

the concentration of the small amount of pyrite contained in the ·ore it was funnel 

that the pyrite assayed only $8 per ton, hence was not richer than the ore. l\foreover, 

by an assay of the tailings, it was fo~1t1d that the mills ~vere ·extrnding 75 to 80 per 

cent of the g-old in the ore, which was a sati~faetor.Y yield umlcr the eircumstanct~B. 

In an m~e of this chn.raeter it .i~ impus~ihle. to distinguish by the ~ye alone that 

which will pay to mill from that 'vhich will not, and the practice bas been rt<lopted of 

panning ca~h day a 2-ponnCl sample of ore from every fre~h face in the mine. Power 

is used to manipulate the pe3tle, which reduces the fragments of ore to a sand. fine 

enough to he ea~ily pannccl 1 and the man who does the panning has hy long. experience acquired sueh skill that he ean pin GO Rample:;; per day and estimate their ~ . ·\-alne h_y the eye within 2:') to 50 cent:-l. The::5e c:stimatcs are chcck0d ·from time to 

time by fire assays of the riclt'~andtl left in the pan: · Although thi~ method o~ valuation appear~ very crude, it ha-, the sanction of twenty years' practical experience, 

during which it has evidently given satisfaction to those employing it. 

The mill capacity of the Homcstakc Company) 'which hitd an aggreg~te of 200 

f'tamj>R in 187\1, was increased as time went on hy the "enlargement of existing mill~ 

and the aCLJniring of new ones~ until, as the· report of 1Sns ~hows, there were: on 

J\IIay 1, of th.at year, 54:0 st~1mps dropping on Homestake ores alone. ·The Father. de 

Smet 'and Caledonia mill,.,, with an aggregate of 160 stamps, had long since ceased 

·working~ as no more ore wa:-:~ heing produced from those mine:-; and they were not 

readily accessible from Lead, which the sonthwanl pitch of the ore rendered the 

mo:-:~t central point in 'vhid1 to concentrate the work of the mines. 

As greater depths were attained in the mines the rtmount of unaltered pyrite 

in the ore incrcaReJ. somewhat, though not as nnwh a:-; in most mine~, nncl although 

the management still claims that these sulphillcs contain no more ·gold· than the 

average of the ore. it is evident-'that it was not Co'nsidered good polky to neglect 

·this part of the product, whose gold was not extracted ·by amalgamation.· The 

· eoncentJ·ates from the mills wei·e sold for a time to the pyritic smelter at .. Deadwood, 

and to the chlorination· works at Plmna, while a small cyanide plant had heen erected 

bithe conlpany for experimental \vork. lt is signitil~ttnt that, as is•slwwn hy the 

report of 1goo, another large cyanide plant of 1,200 tuns daily capacity wa8,building 

by the <·~mpany and exPected soon to b~ in running ~rder. 

a !<"luther detail>! l'l.'l to ywld of ore will Le Iuun-1 in t~tble~ given on page 63. 
60 EOONOillC RESOURCES OF NORTHERN BLACK HILLS. 

The number of tons milled has increased anrnmlly from less than 200.000 in the 

early years to nearly 900,000 in 1900, but the costs chargeable to milling, as well as 

-can be dctel'mined from th~ financial statements in the reports~ still amount to about 

80 cents per ton in romid numbers. a 

l\IINING DEYELOP:'\IENT. 

The erosion of Deadwood, Bobtail, and Gold Run gulches had made cuts 25Q 

to 400 feet be,Jow the base of the Cambrian beds, or the highest points of the 

ore remaining on the intermediate ridges, and ~is the ~lopes of these ridges wer~ 

quite.stp,ep the first.mining was done Ly open cuts or quarrim;; then tunnels \Yore. 

run. on a levci 'as near the bottom of the gulcl~ as was practicable a~d the ~re 

dropped through chutes into cars in the tunnels. On either face of the porphyrycapped ridge between Deadwood and Bobtail gulches, which cut across the mineral 

bed nearly normal to its strike, the quarries exposed rock faces about 200 feet 

in height, which afford admirable opportunities for studying the structure of a 

mineralized rock. Between 'the Highland shaft and the Star shaft of the Homestake mine, where the ravine r\}nS approximately with the strike of the ore belt, is 

the greatest open cut in the region. This cut is about 800 feet long and 200 to 300 

feet deep, its bottom being 100 feet below the collar of the Star shaft. On its side,, 

also, there are g'ood :rock sectiOns· which show the porphyry bodies coming up· 

through the slates and spre~ding out in horizontal sheets betwee·n the Cambrian beds. 

As an instance of the scale on which these quarries were mined in the early days, the 

record shows that in 1882 a mass of mineralized. rock 100 feet long by 70 feet wide 

and 100 feet deep-say about 5,000 toris-was broken down by a single shot.. There 

was necessarily a limit in. depth to which this method of mining colild be carried, 

and vertical shafts have subsequently been sunk at various points within the belt, 

from which levels, at vertical intervals of about 100 feet, run out under the quarries. 

As will be shown later, the ore bodies pitch rather rapidly to the south; hence 

the northernmost mine, tlie Father de Sn1et, was the first to reach the bottom of . . the pay shoot, and this mine ceased producing in 1886. On the other hand, the 

Homestake properties at the southern end of the belt have not yet reached the 

bottom of the_ shoot, the Golden Star, or central. shaft, being. 'now 1,100 feet deep. 

A new shaft, the Ellison, is-being sunkabontl,OOO feet south of the Star shaft on 

the south side of Gold Run, and is intended to be used. for working the lower 

portion of the ore belt .on its southern extension beyond where any ore shows at the· 

imme.diate surface.~ In Working .. the 'great bodies of ore it is often necessary to 

leave chambf!rs'several hundred feet in length and width,' and the Comstock system 

of sq~re §ets of timbers, or else huge timber cribs filled with waste rock, are used 

_,_, . ' 

/- a These figures are obtained by dividing the gross amount of expense assumed to be chargeable to milling by the 

number of hms milled. Doubtless the costs might be figured considerably less if they were striCtly confined to tlie 

actual runriing cost of each mill. 
MINING OF HOMESTAKE ORES. 

to "upport the roof and walls. In the Homestake mine the waste rock is taken 

from the hottom of the great open 'cut and sent down to the slopes through a shaft ' 

or rock chute. It is evident that- mining costs must increase with depth attained. 

On the other hand, the inc1·cased cost has been offset in a measure by improved 

tramportation facilities, which ba,·: lowered the cost of supplies of all kinds. The 

amount of \Vater in the mines iR not excessive, except in the spring, when the 

melting of the Rnow &end'3 a considerable amount Uown through the open cuts. 

Jt is not, however. a disadvantage to the mines, since it can he used in the mills, 

for one of the principal costs in milling oPerations b that of obtaining a sufficient 

supply of water. 

The actual' cost of mining per ton of ore millecl is not known to the writer, hut the 

aggregate cost, as taken from figureS given i"n the HomeRtak:c report~, and counting 

in all mining work, exploratory al"3 well a~ the direct' cost of, extraction, would 

appear in late years to have heen a little over $2 per ton, whereas in the report of 

September, 1880, it was giYen as $1.33, or, calculated on the above basis, $1. 70. 

1\IEAKS OF COMl\f'UNICATIO~. 

As has already heen stated, when the mines were first opened the nearest rail 

or \vater comm1mwation washy the Mis~mnri RiYer~ about 200 mile~ distant, or the 

Union Pacific R::tilroad, ahout 400 miles distant. Af- wood \Yas u&ed for fuel as well 

as for mine timbering~ a large amount was necessarily consumed, and the company 

Hoon began the construction of a narrow-gage railwily, which at first only ran from 

the mine openings to the milb, hut was later extended through the tun her belt in 

the direction of Rapid; 25 mile, of tbi, road was completed hy 1882. By 1886 the 

Fremont, Elkhorn apd Mis,ouri Valley Railroad, now a part of the Chtcago and 

Northw;~tem_ system, was within 50 miles of Hapid, and in 1887 had reached 

Whitewood. About this time, however, the tenor of the Homestake ores. was falling 

off. ancl they were carrying 7 to 10 per cent of Rulphnrcts, which dhl not amalgamate~ 

and hence yielded nothing. 1 This probahly accounts for the slow progre~s of the 

various roads in the immediately subsequent years. By 18ll0, however, prospects 

were better in the '-mines; the Chicago and Noi'thwcstern Railway-had- reached 

:bead wood, and the Bnrli-;;gton -and=~'frs;;uri -Ri~er..:.RailToad, -cOming up from the 

t'Onth, had reached Rill City on its way to the ~ame point~ a narrow-gage raihvay 

connecting Deadwood with Lead had hcen built, and the Hmpcstake Railroad had 

been extended to Piedmont: on the lme o-f the -Chicag1) and_NorthwPstern Railway; a 

pyritic smelter had been huilt at Dead wood, and a large chlorinati~i'pl"ttt at Pl~ma. 

Since 1891 there have hcen two nvul trnnk lines, the Northweste'?n'>..a,d the 

Burlington, eom[>eting for the mining business of the Black Hills, and spur~lm>o,_~. 

been built to every mine of m1portance, so that in the last decade transportation -~ 

charges have probably heen much lower than ever before. 
62 ECONOMIC RESOURCES OF .NORTJIERN· BLACK JIILLS. 

o< Water has always Qeen. a considerable item of expense ·with the Homestake 

·Company becaus~ of the. large amount required for their stamp mills. It early 

acquired all the sources of water supply in the neighborhood; then a water.company 

was organi~ed,_ ,vhich constructed pip~ Jines and ditches to. the heads of the nearest 

s~reams," and finally to. the head of Spearfish Ri,·er. This company, together with 

~he Homes take Railroad,. which was tilso .organized .as a separate company, bas 

recently by consolidation been merged into the Homestake Company. 

' 'PHODUGTION. •. 

Th~ follo.wing ttllilc; niade \ip from data contained in the financial rcports.of th~ 

Home.Stukc Company, giv-es its production fror:n .January, ll?78, to .Tune, 1900, 

together with the amount of dividends distributed to stockholders. The record 

speaks of only one assessment, of $200,000, which was apparently the total outlay of 

cash for developing the· mine and putting it on a paying basis. In the twenty 

months' period froni J'anuary, 1878, to September, 1880, $600,000 had been paid in 

dividends, and $1,4u5,675 for plant and working expenses, leaving a balance of 

$107.48 in cash on hand. Cost of plant is charged as $50:3,±75. 

Pmduction of tl~e IIomesta_ke Mining Company . .. 

I Toud val no of Year ending. Ore milled. Bullion. Gold. Silver. gross prod- Dividend!>. uct.a 

Tons. (hmces. 

Juno 1, 1881 b ---------- 411,3.\8 167, 86l $2,801,026 $29, 4:{6 $2,831,890 $990,000 

June I, 1882.· ..... ------·- 180,514 -72,920 1,222,'400 13, ;{66 l, 237, 161 422,500 

Jlme 1, 188:L.~--------- 179,074 (0,341 I, 18:1, 689 12,{545 1, 196, 394 GOO,OOO 

June 1, 1884 ....... ----- 191,505 67, ii6 1,142,599 11,898. 1, 154,681 400,000 

Jtinel, 188h ....... -~·-.-- '213;190 '72, 347 1,224,484 12,468 1,236,967 343, 750 

Jnne 1, 1886 ............ 219, 165 76,592 1,294,960 12, 029_ ---,-1,306,989~ ~-=-eo.~612, 500 

June 1, 1887 ............ 219,~0 56, 178 050, :l43. 8,189 ~58;5:12- 450,000 

June 1, 1888 ...... : .. · ... 24B, 355 52, 737 . 895,822 7,-585 903,407 300,000 

Juhe 1; 1889 .... : . ...... 285, 774 56,846 961,907 8,117 970, 744 275,000 

June 1, 1800 ........... " 297,557 .5~,356 980,243 l 8,597 988,840 150,000 

June 1, 18n1 ............ 319, 130 65,987 1, 110, 361 11,115 I, 121,476 150,000 

June 1, ISH:! ......... ~ .. 321,495 72,630 1,217,958 11,106 1,.230, 546 150,000 

Jun.e 1, 1893 ..• ~:-.-:_s..;.;.~: - 29..J:, 5:~0 ,. 66,905 1, 118, t102 . 9, 347 <;;"1,127,949 "150, 000 

June], !Sp..J: .. ,-----·-:-- ::l'-.!.-=Jl09,.2~_0J" ~-8:!065 ""),:!fl;568 9,-341' 1, :~98, ssq 181,250 

Junel, 18H.') .... ~------·: 31Rl;ll2()"' ;,:---no: 991" 1,~'50H;·o4H" f"-'·'..-9, 397 1,546,138 318, 750 

.Tunel, 1896 ............ ~·~45, 220 69,322 lf156; 785 8,099 1,177,616 375,000 

J.unel, 1897.--- .. ---···-· / 395,530 . 110,851 -f'""1, 840,674 13, 112 1,899,725: 375,000 

Junel, 1898 ............ 548, 390 I:tf), 28.1. 2, 4_67, 9fl7 15,377 2,518,026 500,000 

Junel, 189\L.: ...... ~ -·_:.;_620,,1_r~~ ~ l7Z; 543 2,667,281 18,559 2, 725,196 750,000 

~'~~The flgnc" in the column "gro&<produot" nee •lightly in exce&;of thc,om of tho, in tho "gold" and "miw" 

4 / columns, becau~c they include the prcmlum of exchange, and in the la~:<t ~ix years also the amount received from-~ule of 

June I, 1900 .... ~~"-· - 89L 585 227,695 3,557,387 26,338 '3,658,956· 1,175,000 

-~-- 5, 085, 771 ! 1, 870,'719 I 30,"674,132 I _:....-):ot-a'l -------·-··· 256,019 31,190,083 8, 668, 750 

~· 

// concentrates. , /f7 . b From January, 18i8, to June 1, 1881: · • ·· · · .-

\ 
., PRODUCTiON OF HOMESTAKE MINES. 63 

The following table gives the average yield of ore per ton milled at different 

annual periods during this time. There arc no data .from which to determine 

accurately what th.e aetual content of t?e ore was, or 'Yhat the loss has been. 

The method followed of assaying the tailing' from time to time is not entirely 

accurate, for it does not take into' account what , loss there may have been of 

float gold, which, as its name indicates, would have floated Off with the water 

and not :,ettled .with the tailings, and hence in such an ore might have ·beeh 

conElidcrabl€'. The table also gives for the ,.;arne _pcr~od the relatiYe portions of 

gold and stlvcr in the bullion produced, both by ,weight and hy value. 

~ ll'l'rii[Jf' y1eld uf on' 11nd relntn•e prupurtwrlll oj gold and s1lvn. 

A\erage Fmenel:ll! of 

Ratw oi g,old to Silver in bullion. 

Penod y1dd of ore bulllon trcuterl Ry \\-eight By value 

. Paton 

Up to SeptemLer, 1880. ____ . ___________ . _ ...... ____ $6 90 815 1 4 90 to 1 96.4 to 1 

June, 1881, tuJnne, 188:! ----------------------···- 6 Sfi 808 6 4 6-! to 1 H-!.3 to 1 

.T nne, 1882, to .T nne, 1 SHB ____ •• __________ ••• ___ •••• 6.60 80H.O 4 60 to 1 91 4 to 1 

June, 1897, to June, 18\:18 __________________________ 4 60 7fl:~. 0 4 2!i to 1 160.0 to 1 

June, 189K, tu June, 18<JH -------------------- ----- 4.40 758 0 !l 98 to l 143.0 to 1 

June, 1889, to.Tunc, HJOO .... ---------------------- 4 10 770.0 3.R8tul 135.0 to 1 

Tntal protluet to .Tune, HJOO •••••••• _ ••• ------ 5.485 ---------- ----------- 119 81 to 1 

It is claimed by the management that there io no appreciable falling off in 

the tenor of the ore with depth, yet the above figure~ Eleem to ~how a remarkably 

uniform (lecrease in its average yield. It mu:,t be admitted, ho~ever, that these 

figures Ui·C' not neces~aril_y eonelu:o,ive. During the tirRt three penods the •ore 

would naturally- haYe heen somewhat richer than that found at grcate!' depth•, 

becttu:,e it ~ould have heen enriched hy the oxidizing action uf :,urface waters. 

For the last three annual periods it is neee:-.sar_y to i·emcmber that the, number 

of tun~ treated has been increasing- very rapidly, and it is very posbihle that the 

averag-e yield has be,£n lowerrd hy the milling every year of :t___}_~gget"- amount of 

low-grade rock. It is' qu_ltc=...po~sihl~fnfOfeov-er;=that.:.w.hen the .~ornpany treats its 

own L'oncentrate:-:; there may l)e a ::,~LYing that may ~ensibly increase the average 

_yield of its ore. As yet it can not h~~:,::ud that there is. any conclu:,ive evidence 

of a decrcaEle in value 'vith depth in the \'ttlpltid9..,or lln!J.ltet:Cs!~one. , . .• 

The other columns in the table vt·ere arranged fOr the purpo~of determining 

wh~ther there wao any uniform change with ·depth in the propor~o,,~f gold 

anil sih·er in the bullion. ~~or this purpo~e the figures in the la:,t column !'U ~-£)f~ 

no value, sinee they are based on the commercial value of an ounce of silver, whic~....:: 

has been too variable to make it worth while to reduce it back to a t•omm~n unit. 
r 

/ 

64 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

The others are deduced from propot'tions of gold" and silver which are tabulated 

in the reports for each bar of bullion. In this case the average during one or more 

selected months has been given to represent thw character of the bullion during • 0 ' 

the year. The bullion is- remarkably-free from impurities other than siker, th8 

average o£ such impurities being less than 2 per cent, the ore yielding about 80 

per cent gold and 18 per cent silver. 

In considering the earlier and later groups of years the decidedly iarger ratio 

of gold in the upper over the lower levels would be accounted for by the superior 

solubility of the silver, in consequence of. which a larger proportion would have 

leached out, but in the last three years in the lower .levels there appears to be a 

slight, though not absolutely certain, tendency for the proportio'n of silver to still 

continue to increase. It will be of interest _to observe in the future ~whether this 

tendency still continues with greater depth . 

. Thc.next table gives the total yield of all the mines of the belt up to .Tune, 1900, 

from figures kindly furnished by the officers of the Homestake Company. The 

dividends paid in the same year .are also given, as far as it has bcell found possible 

to ascertain them; but it is evident that they arc not complete, especially ·in the 

case of the Highland mine. 

The product of the Columbus mirie should he added to the total, as it forms 

part of the. belt. Its amount is, however, not known. The United States Mint 

returns for 1891, 1892, and 1893, gh'e an aggregate of $88,618.41 for this mine; 

for other years its product wns not segregated. 

Tutal product ofthe Ilomesloke belt 1tp to June, 1900, 'With relation of product to dividends. 

. Name of company. 

Homes1:.ake . -~ ·_ ............•........ _ .. _ ....... _ .. _ ...... . 

Deadwood-Terra (ceaseO in 1898) ........................ . 

Highland •............................................... 

Father de Smet (ceased in 1886) .......................... . 

Prod net to June 1,1900. 

$31,190,143 

11,073,065 

12,018,610 

3,259,383 

Caledonia (ceased.in.18(3) .. ~ ... :......................... 2, 345, 6¥1_ 

Total •.......... ~-~-.:~-~~~~~c-~-~"':~i:--:"""•··59;-s56,822 

Dividend~ in~ -Per cent of same period. ·product. 

$8, 668, 750 27. 7 

1, 500, 000 13. 5 

. 1,110,000 

194,000 

11,472,750 

34.1 

8.3 

The dividends oytlw Homestakc and· Father de Smct mines arc probably correct. It will ~oticcirthatthc·percentage of dividend to product is greater in the 

case of the)atter thardn"tl;;;-former. This is due, probably, to the fact that the De 

___ S~?~~i~vorked ~nly on the richer ores ncar the sn:·face; which have been more 

: ~~easily milled than those of the Homestake. No attempt has been made to calcnlnte 

' ' the percentage of dividends to product for the whole belt, inasmuch as it is cYidcnt 

{'/. 
PRODUCTION OF HO)lF.ST AKE MINES. 65 

that the Highland mine mu~t haYe paid ~ome diddends and prohahly of ~imilar ratio 

to the Homestakc, but it is not kr_1own what the,v were. 

It may he inl:'ltrudi\·c to <'om pare the result-:; obtained in working thi~ mine with 

those of sotuc mine of an opposite type, wh'ose ore instead .of being exceptionally· 

low grade is unusually rich. For thb purpose the ~ortland mine, o£ Cripple Creek 

di~trict, Colurad<), has been t~Iw~en. ~ince it. pul1li~hc.s very full reports UIHl ha~ 

been under one mauagment from the ~tart. The J-igure.s given helm\· arc taken 

from the eighth annual report. whit:h .~·iye~ dnta up to December 31: 19tH. 

Colllf!ll!"alh·,.; yield 1/nrl din'dewls r:(Jfrm!t'dol..f~ rmd l'orfhwd miw::.~. 

I Portlnnrlmint•. 1-----

:!2 years 5 Juunt,h~"L-1 7 yPars ~ IHonth~. 

Home~take mine 

Length of perio1l eonsiUereU ......... __ ............... . 

l:rroi!s yiel!l !Jf ore in n:(';pet·tiw period,.: ............... . s:n. 1no. 1-!3 ~ ...... -I :SI:~. 1::!8.'525. 

SH, t-itJS, 75() ___ -.--- ·I $4-, 0:!7, OHO. . 

$::?tn$1li ••••...... ~fitu~4fl0anrlupward." 

$5.4K .............. 1 $4-ll: • . 

Dividends !Jai<i in re~pPdiYe periotl~----················ 

Range in \'alue of ore per ton ... : ..................... . 

AYerage yielcl per ton of or•! treatecl tlnring peri11tb ..... . 

~et yield uf ore during la'it year of rcspedin_. pPriod, ... . $-!.10 .............. :S23. 

DiYidcnrls to gros:-; protlnd ............. ____ .. _ ...... __ :!i. i per eent .... _ .. 30 per eent. 

----------------------------------~------------'---------------~--------~-"·~70~~-----

These figures arc of interc:-ot to thu::-e who prup<!:-oe to irwc~t in ·mine~. but of 

lesH \Talue to the student of uh~ depo:-.its in gencrall since they Jo not giYe the 

actual contents of the ore in eaeh ca::.-t~, hut o.nly the amount vdlich his been extracted. 

On the other hn,nd. they do gh·e the ;tdual commercial re;.;ulb of t,~,o·o important 

and well-managed minCs. The .figure~ giYen for the range in yaluc. of the respectiye 

ores are .sume"·hat arbitrary, hut they are such a:-; might he· giYen hy a 'conH<~ientious promoter. Prohahly still higlwr ntl~tes might fairly have been gin~i1·for 

the Portland ore~, and to the a \·erage inyestor the~e high value~ would pr,f~:,ent 

incomparably· greater attraction..; than tho~e fnruished by the~Homcstake tig·ures, 

which are pos-:;ibly put rather hig·h. 

The actual result.s of umuy year~' mining work :tl'e of eomparahle proportion~:~, 

$±1i per ton average yiel<l fur the Portland orcs again~t uot quik $ii.fi0 for the 

Homcstake ores. or nearly nine time~ as mueh, ":bile the per<'t!ntagc of di,·idemls 

to gTo::.-~ yiel<ll whid1 eorre...;poml~ as nearly a~ pos~ihle to thP perc<~ntag-e of profit 

in an ordinary business. b only 80 per cent as against :!7 ~TI per eent, ur le~s than 

10 per cent more, £or the rieher ore. 

It may he suid that the Home:;takc i::: a free~mi1ling m:e, while the. Portland ore, 

being a telluride, is not. anrl hctwf! l'Osts more to treat. On the other han'd, the 

~ortland mine has hcen running only about one-third as many yean"' us the Hon~estakc, and on comparing the average,yicld for the la~t year \Yith the average yield 

4987-No. 2U-04---o 
ECONOMIC RESOURCES OF NORTHERN llLACK HILLS. 

since the inception of work, it i:-; seen that in the Portland mille the yield has 

fallen. off ~0 per cent from the average and in. the Hornestake only about 25 

pei· ~.:ent. 

This is ~nerely a prae_tical demonstration by actual figure!:! of what is well 

known by a_ll eXperienced mining men-that as a purely hu~in~ss proposition a 

very large body of low-grade ore is preferable to a moderate-sized body o£ very 

rich or~. 

GEOLOGTCAL JJE8CRII'TIOiY. 

SURFACE Gr~OLOGY. 

The town of Lead, which has a population of ·about 4,;)00, made up mainly 

of person:-3 directly or i~1clirecttv d~pendent on the Home~take mine, occupies a 

basin-like valley at the head of the narrow ravine of Gold Hun, down whieh runs 

the narrow-gage railroad that connect~ the town with the trunk line in Whitewood Valley, about 350 feet below. The rather flat-top ridg-es that overlook the 

town on the north and south are occupied by remnants of the horizontal Camhrian 

strata and their included sheets or sills of porphyry that have escaped erosion~ 

while on the divide directly southeast of the town is found a body of Tertiary 

clays and marls containing vertebrate remain~ that identify it as belonging to 

the 'Vhite River formation: Below thet'e capping· rocks, whot:le uut~i-mum thickness in this vi~inity is abou~ 200 feet, the \-alleys arc entirely carved out of the 

· Algonkian slates. . ' 

The main street of the town of Lead follows the general direction of Gold 

Run westward up the ravine, while subordinate streets cro.ss it nearly at right 

angles. The lowet~ or easter~most of these cross :;ti·eet::; i.s~ apJroximittely in the 

di,recticn and po;ition· of the original Olltcrop of the HomeStake lode. East of 

it, extending am·os~ the heud of Gol~ Run Ravine, are the main offices, mills, 

and hoisting workt:5 of the Homestake Compnny. The mine openings extend up a 

northwest branch of1 the gulch, in the upper pa;·t of which, aho1'e the ·Star shaft, is 

the ·great open cut of the I-Iomestake ·mine, while another smaller opP.u cut lies 

. farther eastward, back of the Homestake mill an<l between the Star and Old 

Abc shafts. 

The eastern and northern Walls of the· Homestake open cut present a cliff 

section, 200 to 3UO feet in height; of the mineralized slates which {orm the 

Homestake ore. ln. this section are seen many veins and lenses of quartz nnd 

intrusive dikes and stocks of. white porphyry. These stand ?ut in strong contrast to the- dark iron-stained slates, but their outlines ,arc much obscured by 

the talus slopes of broken rock which is being drawn off from the bottom of 

the cut and ,]ent down thcongh chutes to the mine below to fill the cribs that 

support the walls of. the great ore chambers. 
GEOLOGY ' OF 'l'HE HO~l.ESTAK:E BELT. 67 

At the northern head of the cut the apex of the ore zone is well exposed 

where it passes under the, Cambrian beds. The basal conglomerate of the Cambrian is here wanting, and :-;andy shales with some brecciated material rest direCtly 

on the Algon~ian surface. The porphyry here o~curs in several parallel sheets 

a short distance above the base of th~ Cambrian, and by following them eastward 

along the railroad traCk one ~an di8tinguish points where a sh.eet bends "doWn to 

connect with a dike coming up through the Algonkian slates. Remains of a still 

lat:ger sheet cap the ridge,. forming small hills. 

Still farther north are ot.lwr open cuts. one on either side of Bobtail Gulch 

above the old mining hamlet of Terraville--the Deadwood-Terra cuts-and one 

on the south "'all of Deadwood Gulch above Central-the De-Smet cut. These 

are on_ the main Homcstake zone~ and farther east, so~th 

another cut on the Caledonia ore body. 

vVhilc these cuts are not so deep as the Homestake· 

of Term ville, there- is 

' 

cut, not going below 

the beds of the respective gulches in which they are situated, they present an 

even better opportunity for studying the structure of the· ore-bearing slates, the 

contact o-f the overlying Cambrhm beds with the Algonkian stu·face, and the 

intrusive bodies of white porphyry within these beds. On the west side of the 

cuts what is called the west wall .of the ore- body, the only one that is fairly 

well detined, is gencmlly easy to distinguish. lt dips eastward at approximatel.Y the sa~e angle as the lamination of the slates 1 and on it the lines of 

pitch, which incline southward at an angle of about 2:3°, normal to proillinent scrie!i 

of .]oint planes, are readily distinguish~d, at3 shown in the view of the Tcrra"cut 

on Pl. II (p. 214). In this view also the base of the porphyry bo(ly is "een to ·cut 

across the Cambrian:bcds at a low angle, leaving a wedge-shaped mass between it 

and the Algonkian surface. 

The northernmost extension of the outcrop of the Homestake lode is in Sawpit 

Gulch, northwest of the De Smet open cut, where are the workings of the Columbus 

mine. Beyond this the Homestakc lode disappears under the capping of Cambrian 

beds in the hills to· the north, but a vertical in these beds, apparently on. the 

same line of fracture, has g·iven rise to a deposit of l::liliceous ore in the latter beds . 

. Tbc Columbus mine has been· abandoned· for some ·years, and its Underground 

workings were not accessible. They are said to extend: from the bed of Saw pit 

Gulch to Deadwood Gulch, and are opened by a 200-foot shaft in the former 

gulch. There are trench-like open cuts on either "side of Sawpit Gulch which 

show rocks similar to those of the De Smet cut with abu.ndant quartz lenses, and 

the mineralized ore body appears to be about 40 feet wide. ··'"· 

South of LCad there doe~ not appear to· have been much evidence of ore o'ri . ' . the surface along the line of the Homestake ore, zone. ~Nevertheless, as it was 

' 
• 

68 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS .. 

g-enerally nnder~tooll that thio ore body was pitching to the southeast, fL tunnel 

wus run in from tho level of ~Whitewood Gulch at the base of the steep face of 

the· ridge th~lt divides it from Lead Valley. It \VaS iutendcd to intersect- the 

southern extension of the l-Iomcstake body and runs dia~ronally acros~ the ·slates 

and in a direction more to the west of north than the trend of the latter. It is 

2,500' feet long tmd said to connect with the BOO-foot Ic\rcl of tho Homestitke 

workings, being now the property of that company. 1t was not accessible at 

time of vi.sit, and it is Hot, knmvn whether i~ found payable ore or not. 

~The best .-,urface exposures of tho slates and intrush'c porphyry dikes ,are 

seen between the Star t-;haft and the Caledonia open mit. A eros:; section On this 

g"eneral line was very carefully measured by the geologists engaged in mapping 

the areal geology of the r~gion, and tho result is gi\'on in ~g. 4 (p. 27). The section 

shows ten different dikes or stocks of porphyry crossed. 

OHE 1\liNERALS. 

The ores of the Homestakc zone are rather ill-defined masse·s: of rock sufficiently 

_impregnated with gold to· pay for working, but otherwise hardly to be ,distinguished from the country' rocks in which they occur. They are singularly barren 

of the mmal ore· minei:als. The gold occurs in so finely divided 3: state as rarely 

to be visible, e\·en with a magnifying glass. "\Vhcre observed, it was found in 

the leaf form and without evidenee ·of · crysta1line structure. B~sidcs gold, the 

only other metallic minerals are pyrite and arsenopyrite-the former by far the 

more almn_dant-which are irregularly dis~cminated through the ore, generally in 

very small crystals. \Vhile their presence is an a priori indication of values, 

they can hardly be considered as esscntiul constituents of the ore, for they are 

often wanting in the relatively rich portions. 

I 

GANG Ul<; MINJo~RALS. 

The nonmetallic or gangue mineral-quartz-is the most abundant. :rt occurs 

in v~ins or lens-shaped masses often of considerable sb:e and of se\Teral different 

periods of formation; also in grains or crystals mostly of smnll size. In the 

crystalline form it is ger~era.lly disseminated throughout the ore~ and may be an 

original constituent of the quartzite qr a later impregnation of secondary origin. 

Calcite t:~nd dolomite are also common gangue minerals, generally of secondarJ.,. 

origin, hut are_ not universally present. 

Tremolite and garnet are also of frequent occurrence in mo::.-t portions of the 

ore body that are probably of original igneous origin, but can not be considered 

ltll essential part of the ore. Where, the relnt11'e age could be· determined gold 

' is found to be of later formation than the gangue minerals. 
• 

H<H1EST AKE )ti~ ES. 69 

IXCLOSI~G l{OCKS. 

The Algonkian slates, in ·whieh the Homestal.;:c "ore, bodie~ oeGqr, are sehistose 

tocks, for the mo:st part of 'sedimentary origin, one variety alone being recognized 

as a metamorphosed igncons rock. The latter may be classed as an amphibolite, 

amphibole l)eing the most prominent eonstitncnt. 

The amphibolite:::; occur as dikes or irregular masses in the other Algonkian 

rocks. They arc generally of grecni:;h eolor, of massive and rather dcn_sc texture, 

with )JOorly rleYelopcd schistosity. 'J~hey arc made up in general of actjnolite,-

plagioclase, secondary quart;.;;, and orthoclase in subordinate amount, with zoisite, 

ilm~nite, titanite, let~coxcnc, and calcite as accessory minerals. The original rocks 

were probably basic, with pyroxene and ferromagnesian minerals as original constituents. Kernels of augite show the hornlilencle to he of nralitic character. 

The metamorphosed sediments are qwtrt?-ites, quart:~.-sehi.st:;, mica-schists, phillites, and graphitic, ganictiferous, and ehloritic slates, with intermediate varieties. 

A common variety o£ the barren 8lates, known among· the miners as wood-yard 

slate :from its resemblance in fracture to split firewood~ is very schistose and shows 

'~avy c:·enelations trtwersing the surfaces of schistosity. These slate.'! consist of 

quartz and mica, (hmsely aggTe~ated, with finely divided gT~lphitc i1} ·co.nsiderahle 

abundance in the denser varieties. In the vicinity of the ore bodies pyrite occurs ' ' ' 

as thin film::; on th~ planes of schis~osity, or with (pmrtz as the nucleus of small 

knot (augen)-like mas•es, 

J\tloTe recent ernptives o£ rather acid type cut through aH these rocks, as well as 

indiscriminately through tho ore bodies, in irregular masses, often having a dikelike form. The~e orupth·es arc of two varieties, 'vhich have been designated · (1) 

rhyolite, (2) tmchytoicl phonolite, 

The rhyo'\ite-porphyry, which is by far the more common rock, is a tine-g-rained, 

granular aggregate of quartz and orthoclase with rare phenocryst8 mostly altered "to 

kaolin. The rock i~ Yery like the Leadville white porphyry in habit and composition. 

Small crystals of pyrite occur ,~ery abundantly, even in the- freshest 8peeimens. It 

cuts through the .A..lg'onkian 'and spreads in sheetS or sillS between the nearly horizontal strata 0£ the overlying Cambrian series. 

The trachytoid phonolite is . a brownish-drab porphyritic rock composed of 

phenocrysts of salmon-colored sn.nidine in aph"anitic groundmass. Small cry::;tals of 

~egirine-augite ciln also be identified in th~ hand specimen. The microscope shows 

that the gToundmass is made up of· small rods of orthoclase, and that the rock contains a few crystals and irregnla1: masses of identifiable nepheline, not enough, however, to bring it a;nong the normal photiolites. This rock thus far 'has ~nly been 

seen at the 800-foot level of the llomestake mine, though it. is elsewhere known 

as a not uncommon rock in various parts of the northern Black Hills~a 

a )lore detailed petrographic de~criptions of both ruck!; tLlld ore minerals will he found on page 80 
\ 

70 . ECONO)fl(J RESOURCES OF NORTHERN BLACK HILLS. 

The prevailing J:itrikc of the laJ.nination planes of the slates ls N. lOu to 45° ";-·, 

w:ith a dip of a?out. '75° NE., hut there arc many local variations in both strike and 

dip, the former in pl~ces ''cering to the northeast. \Vhile the ore bodies are generally assumed to conform to the lamination or bedding of the sl!ttes,.this is probably 

not strictly the case, though it was not possible to definitely prove or disprove this 

assumption, as both t.he ore bodies and the slates arc rather irregular and ohscurl~d · ' - . I 

by letter movements. \ 

Where .the porphyry bodies are of the dike form they shown tendency to confor~n to the dip an~ strike of the slates, but the larger hodies arc very irregular in 

~ori4, ~hough ~n eas~ern d~p ·is almost n;lways diseernible. They show a depided 

tenden.~y also, like the ore bodies, to pitch to the ·southeast. Thi;' pitch is a structural feature that has been observed in the crystalline schists of the Appalachians 

and boars the same relation to the dip of the lamination planes that the pitch of 

the a><;is of an· anticlinal or synclinal fold does to the dip"of the sedimentary strata 

involved in the fold. 

In the Hornestake lode the pitch is best seen in strongly marked structuml 

planes on the generally rather well-defined foot wall of the various open cuts. Its 

angle is 23° SE., which is also the general pitch of the ore bodies. (See Pl. II, 

p, 214.) There also appears to be a tendency on the part of the porphyry to eon-

. form in a genet:al way with this pitch, but it is less susceptible 'of. direct proof t.han 

in t,he_ case of the ore bodies themseh·es. The general deductio~ made by the writer 

from the above fact~ in their bearing upon the. original mineralization of the,region 

is as follows: 

The original complex of Algonkia1i sediments, with its included sheets of 

igneous rock, was slowly ~ompressed into anticlinal and synclinal folds, having a 

general northwest ~_stri~e and southeast pitching aX!JS. As the compression went 

on, probably with increasing intensity, these folds were squeezed into isoclines, 

a~d finally differential movement set in .al~ng plane.s of lamination. rThis movel!lent_was.most marked a.Jong the general axis of the present _ore body, and resulted 

i~ c~msi_derable displacement a~d some fi-acture. It had both a vert,iCal and a lateral 

component, which caused a displacement vertically along the steeper sides of- the 

. folq_ an~ la.ierully along thQ ~xes. Irregular branching· channels were thus opened, 

which. had at the same time n "teep dip to the east along the plan~s of lamination 

and a pitch to the southea"t, both dip and pitch followir;g in a general way lines 

of least I~esistance_ .t~at re:5ulted f~om an original tendency of the heds to slip on 

their dividing planes, 

At present it io difficult to determine to what extent the ·porphyry intrusions 

conf~rmed with the pitch, hu.t it is very evident, that in a general 'vay the.): eame 

up along the lamination planes, which dipped to the east. ·when the intrusions'· 

' 
·'. 

HO)iE~T A KF. 1-1 INER. , 

reached the orerl.ving Camhri:w hcd:-3 tJ1e.'· ·"Pl'Ctid out in a ~enernl westerly 

dircdion, following the softer ancl more rcn,dily yiehling membCrs of that serie$:;.. 

The only IUO\""emcnt phmes that can be \Vith _certainty rts~igne<l to the pu~tporphyry period arn breccia plane~ ('fU rying fragment~ of. porphyry and slate; 

that follow or arc parallel to-the conbtet of porphyry. am\ shtte. 

The description:-' Of the ore hodies wh.ieh follow arc ncccssftrily · imperfeet for 

the following reason:-;:· At the time of visit the greater portion of the tlpper 

mine workings on the~c ore bodies Pad lung ~incr~ beeit ahanth)neU and were" no· 

long-er accessible. and fe\v pcr~on8 coulU he found who w~re familiar witli t.hcin. 

at the thnc they were in operation. The examination of deeper workings, moreon~r. 

hail not hecn completed when, ln the nntnmn of tS09, the management withdre·w. 

the permi~sion to .study them which harl pnwiou~ly been accorded to memhers. of 

the Survey. Since lKtl!l there may hare been development~ in the1 0eeper mine 

workings whieh~ if known to the writer, might hrwe inoditied his conclusions. 

141il{JI.\('E WORKINGt>. 

The nmm 1-lom~J~take hod.y~ a.;; detined by the open cuts of the Father de 

Smct 1 De~tlhvoud-Tcrra, High!and, and Hon~estake claim:;, has ;t trend of about 

N. goo VV. A ~econd ore hody, as rather imperfectly deti.nctl by the Old Ahe and~ 

Caledonia open eutf.l., has a direction nearl)· north and south (N. 10° \Y.) and converge:-; with the main ore body under th~ eastern portion of the town of ~ead. 

The ore hodies on both these lines haNe a general <lip to the eaf't, a; defined h\ ' . their re~pecti ve foot wnJls. 

In the De bmet open eut hot.h wallt> of the ore ho<l.v are fairly we1l derined, 

the hanging or casi wall t-:tanding nE>arly vcrtieal, and tht~ foot or wet5t wall 

dippi11g 55° to 00° ~~. in the mas~ of ~late~ that .. constitutQ what is left. oT the 

ore body on the south face of the cnt, the original bedding calt he traced by the 

chttnge in color and material of the respective hed8~ and i~ ~een to cOnform in 

generul to the lamination or schisto ..;ity. 1n Plticet5,' however, :-;harp1 clo$ely 

apprc:-;sed fold8, which are cut through by the lamination planes,_ can he detCcted 

in the ,original bedding. The foldR are mostly h;oclimtl, Rometimes, however, 

assuming a fan shape. Three di~tinct phases. of quart!'- veins or .lensc~ may he 

di,tingnished: (1) Material which apparehtly formed thin, siliceous layers in the 

original sedimentary material, and which has pa~sed thru~1gh the quartzite stage 

into a quartz that in the hand specimen can hardly he di:itinguished fror~1 vein fJnart.r. 

(see fig. 'l). (2) Srnall scams of \'ein quart?< which are parallel to the lamination 

and for the most part parallel to the hed<ling n\so, hut which in the folds cut across 

·I 

,. 
72 ECONO.MIC RESOURCES OI<' NORTHERN BLACK HU ... LS. 

·it, a:;: .shown in 'pt. III, a photog;mph of the crest of one of the small folds crossed 

hy a rpmrt:r, Yein ·of this chtss. (8) Qnartz n~in~ Or lenses a.i·c sometimes obsel'ved 

which t.mt acroBS hoth hunituttion and bedding; these are. generally larger, very 

irregular in shape, and appear to lut\rC been t.dfeded by differept.ial nw\rement 

within the' inclosing roek m:tss. 

No porphyr_\ hodies are vb;ible in tbe Hlates exposed within the open Cut, hut 

a considerable thickness of porph,,.-ry remains on the crest of the ridge ab<nrc aS 

a ~hcet intruded. i_n the capping Cambrian bed.-5. A 12-foot dike of porphyry, 

whieh strike~ northeast and dipt! 60° to "7tJO .N\\r., is ent in the tunnel which runs 

in from below the opeu eut near the bottom of Deadlvood Uulch, and, following in 

general tbe strike of the ore body, connects with the BOO-foot leve·I of the HomeFIG, 6.-l'~oldcd 'und compressed quu_rt.:itc baJHl 

stake "~orkiug·t>. This is the only porphyry 

hody oh .. :H:rved ni1dci:ground in the northern 

p:trt of t.lw Home~t.akc working-s, a.nd nmy 

lw,-c hecn one of the feeder ., of ~he sheet or 

.sill in the Camhrian beds on the rldge above. 

The porphyry sill is not strictly parallel with 

. the hedd.ing, lmt riseH g<:mtly to the west, 

lead11g in that direetion an in~~rea.sing thicknc~.s of Cambrian beds hetween it and the 

Algonkian rocks.. The hasal conglomerate is 

W[Lnting- above the· apex of tho Homestake 

body, hut i~ found in unusual thickness farther eastmm! toward the point of the didding ·ridge between Deadwood and .Bobtail 

gnlehes. 

I11 the Cam brian beds beneath the porphyry sill and a little to the west of the apex 

of the Tlornestake body some siliceous gold 

in slate. 

ore has been mined, whieh is ne~essarily of 

later forniation than the or.iglna) ore )u the Algonkian rocks, and is probably con-

_t.emP,oraneotts with the o~·~'bodies forn;ed along 'rertieals in the Terry PCak reglon. 

In these open euts it is impossible for the unpracticed eye to distinguish the 

slates whieh u.re sufficiently mincrali7.ed to eonstitute pay ore from those which nrc 

practieally barren. \Vithin the Ore zone the rock· appeal'S to. he. rather more 

silicified and "is more frequently stained by, iron oxide, and there is more evidence 

·of dynamic action. The so-called walls are apparently p.Janes along which ditfcrentifd movement has taken pluce, especially on the foot Wall. The flutings which 

define the direction of pitch are \rery e""tident~ as shown in Pl. 11 (p. 214). 
/ 

FORl\1 OF HOM EST AKE ORE BODY. 7·3 

The :form of the ore body HH mined iE"> _g·iven ln t~o aecomnwying seetions~ which 

are re~nced. (!opiQS .o£ those prepared by the engineers in charge of the early work (t 

(fig. 7). It will he seen from these sections that not all of th1! ·material hetween the 

walls is :'lnffi.cientl.\T rich to l'OI.tstitute OJ·e, 

which, while not absolutely barren of values, are too poor to 

work. Snch irregul_ar masses 

or horses of rela.ti n~ly harren 

material are found in all the 

large ore bodies of the zone and 

enhance the difficult}' of forming 

a correct idea of their shape. 

The general form shown in theHe 

seution.s rcsem hle.s that of the 

hull of" deep-keeled vessel, and 

the nort,hern p:ut of the Homcsta.tte ore zone, as well as can 

, he determined, correspondH in 

general to this shape. Bnt in 

the southern portion, where the 

pre::-~ent extraction is being carTied on, there wa~;, at the time 

of visit, no evidence of the closing togethe~· of the ore hody in 

dept~. This may have heen due 

to the numerous porphyry hodies 

which have eut through and displaced it~ or to the Rteepening o£ 

the southern pitch, which has 

carried the bottom far below the 

present workings. 

In the other open cuts the 

phenomena, .as far a.-; can be 

seen through the covering of 

' as the ore hody lnelurle:-; irregular lllttsses 

FlU. 7.-Sectium; of ure body, Father de Smd mine. 

talu~, are e~sentially the snme as in the De Smct. In the Homest.a.ke open cut 

the Ro-called we~;tcrn.wall is 1:emarkably well defined, but it does not s_eem to necessarily form the limit of the ore hody on that Hide. On the ridge at the northern end· 

of the HomeBtake open cut five sill~; or ~hcet~ of porphyry ean be distinguished in 

"I tlm indebted to .:\lr. Richard BlaekstOite, engineer of the Home~tuke Company, for the original drawings f~u~~ 

which these sections were copied. 
·ECONOMIC RESOURCES OF NOR'l'HEHrf BLACK HTLLS. 

the Cambrian, one of which caps the higher. points of the ridge. The connection ·of 

:;onw of these ~ills with dikes breaking up through the Algonkian can he more or 

less distind.ly traced Ol; the northeastern faee of the cut. At the bottom of the~ 

lowest sill i.-; a hreccia.-likc material that apparently represents the tlow breccia 

which WtL.S·t,he forerumH~r of the int,rusion of the sill itself. 

\Yhci·en~r the orig·inal ont.t~rop of the lod_e can he ~een under its eovering of Camhriari beds the basal congl<~rnerate appears to he wanting directly over it,. but is 

found in tulll:;nal thickness at a little d i . .;:.tance on either side iu channel-like depressi<lns containing· almndant,_ fragment~ of auriferou::-: quartz. Hence, as is more fully 

explained ir~ a later chapter, it is asSulllcd thn.t this (Jutcrop was for a considentble 

time exposed t.O erosio_n al~ovc tht: waters of the gradually rising Cambrian ~ca. 

UXDEH(:JHHi:\"ll WOHKIXnS. 

The underground working~ of the Cofumbus mine were inaccessible, but from . . . 

nceimnts given by those who had ~een them, it seems the ore.stmngly resembled that 

in the De Smet, :lnd, 1ike it, was somewhat richer thn,n the average ore of the belt, 

freC gold being often d~ihle to the naked eye. In the deeper port.ions the ore contuins con::oidcmble sulphides. ' 

The gre.atest horiz:ontal exten~ion of oTe in the Homcstake mines is shown on 

the 300-foot [eye[, so reckoned from (,he Star Hhaft. This IC\·el connectH with the 

t~umel which runs in fr"o111 6eadwood Gulch below t,he De Smet open cnt, and .is the 

only one that extends so far north~ fo.r ~he rca~on that no pay ore was found below 

the De Smet open eut at fhis level. Henee it lm~ l~een assumed that the ore -body 

has wedged out, as the form ~hown. in the sections (fig. 7) su~·gesb thftt it might. 

lt is to he r~nuuked that the funnel or wedge-like form shown in these sections is 

that· whieh theoretically 11 might have been cxpected.as the result of a normal f~ulting mo\·cment along the gi:meral axis of the Homestake body. The records Hi1ow 

that the ore in the .be -Smet-min~~ was considerably rieher on thc.average than that 

in the mines farther S~nth. This sug·gesb:; that such dmvnward leaching in the oxidir.ed zone n:; took place hnd here been arrested in the bottom of the funnel by the 

con,·erging walls and the ore was therefore relatively more e11riched. In fig. 8 the 

general form of the ore body in horizontal section i~ given as far as shown by the 

groprid fLctnally stopecl on the 300, {00, and 500-foot lcveb. As there showr1 the 

~ nm,-thernmo~t· portio.n <_>f the ore hody for 1,000 to· ll500 feet is in the form of a 

narrow trough from 10 to 40 feet in ,width, whieh widens rapidly to the Houth 

between the Terra and Highland shafts to about 150 feet and then to 300 or 400 feet 

as the Star shaft is approached. Jn the latter portion, however, no distinct walls 

conld be traced and consideral)le portions of the ore body within these limits are 

left sta11ding because the ore wa:s of t~o low grade. [n the htingi\Jg·wall eountry are 

"Becker, G. F., Comst?ck lode: Mon. U.S. (-leo!. Stnve~·. vol. 8, 1882, pp. liS et ~eq. 
FOR~l OF H0.\1ESTAKE ORE llODY, 75 

. I 

many large lenses of white (jWtrtz, sometime::; 10 or more feet in thickness, ·which, 

howe\·er, :;ho\r no metallic mineral ..:, t~wngh pyrite seems more abundant in the 

slates immediat.el? adjoining them. The laminatiori of the slate.~ in general .strikes· 

somewhat nearer north than the ore hodics, and the latter shown tendency to overlap 

each other en echelon~ leaving barren ground between the tongues of Ore. 

ln general in the country northwest of the Star shaft the form of the ore body 

fulfills fairly well. the idea of 'a hoat-shaped mass pitching to the southeast, and 

' 

.,., 

FH;. b.-l'iau~ of Homestuke ure bod !e.'> on the 300, ·lOU, 1111d 500 foot levels. 

henec on n g·h,en horizontal section gTowing actual\}; wider in that direction. \\_rit.h 

the appearance of the porphyry bodies in the vieinity of the Star shaft, however;·a 

disturbing factor hi introduced. Not only is the main ore body split' up into ~everal 

distinet part:-; 1:>.\· the intrusion of the porphyry sheets,' but there .arc separate 

detached ore bodie.':l or ehimncys \vh.o .;;c f'trncturnl dependence on ~ach other could 

not be determined from the examination made. These bodies lie south of.the Star 

:;l_mft, the principal ones: going· etl:;;tward~ heing the Independence' body near the 
76 lWONOl\HC RESOURCES OF ~ORTHERN BLACK HILLS. 

shaft of that name, the Pierce stope, the E~ts.L.._ stope, the Lincoln, and the Amicus 

body, the latt~r near the Old AIJc shaft. 'l~hc main working shaft at· time of Yisit 

wa1::! tho Star shaft, frOm which levelR are opened at 11)0-foot intervull:'l and drifts run 

out to cut the ore hodics that \\''ere worked in the next level ahov'e. The sy~tcm of 

mining pursue.d involves the opening of large chamber:; in the ore zone, rapid 

extr~ction of the pay on~, and prompt tilling up of tho .o:.topes with waste, so that no 

detailed study of the indiYidual bodies wa:; prad~icahlc. The mo~t important data 

were' furnished hy the drifts whieh are run on each lend eastward from the Star 

~Porphyry 

gon 

FH;, ~.-Stur-Olll.\Ue ~ectiun of porphyry and ore bCH.liel;. 

shaft to the Old Abc or Pump shaft. These hnYe been w:>eJ rts the eommon ordinates 

for ~he_ successive mine plans gi,,~cn in fig. S, and from them a cross ;;eetion of the 

different porphyry sheets that· intersect the main ore body has been .constructed, 

which is reproduced i~1 fig. 9. Although based on accurately determined data at 

each level the representation of the form of the bodies is necessarily somewhat 

diagrammatic, for ~t is not possible to trace. their Outlines between the levels. 

Nevertheless, from this section, .combined with other llata partly shown on the 

horizontal sections,. it is evident that the portJhyry· bodies have a :fairly uniform dip 
PORPHYRY IN HO~lES'l'AKJ<~ l~ELT. 77 

to the east in general accordance with~ though somewhat ·steeper, than the lamination of the ,-;late::;. Furthermore, it is seen that they pitch to the southeast as do 

the ore bodies, and, finally, that they fend to spread out more an'd oe9upy a wider 

horizontal ::;ection as they approach the surface. lt, is probably due to their southern 

vitch that many of these ore bodie::; appear to wedge out in depth, ·and if a parallel 

,-;{~etion eould be made on a pbne somewhat farther HOuth it would probably bwfdund 

that the point of ~he wedge i.-; successively deeper in each section. The only other 

~:ross section of the porphyry dikes observed wa.-:; in a cross.:ent drift on the 300-foot 

level running from the north he~uler or drift of the Star shaft eastward about ~00 

feet to the Caledonia workings. This drift cub six dike-like bodies of porphyry 

from 12 to 70 feet in thicknes8 nnd with an, ag·grcgate thickness o£ about 200 feet. 

Comparing this cross section with the eight section!'i obtained in the Star-Old Abe 

drifts, it is seen t~at while each differs some\vhat i11 the number and thickness of 

i'mliddua~ dike~ the aggregate thickness of all of theni cut on these .various lines 

present::; a rather rcritarkable uniformity, ranging only bet.wccn the extreme limits o£ 

150 and 225 feet Und a\~eraging ahout 200 feet. The dike:-:; may, therefore, be regarded 

as' representing a single intrusion of porphyry, which had been forced between the 

lamination of the slates and cu.t across the eastern edge of the ore body, entirely 

inclosing in some cases large masses of ore-hearing ground. A most interesting and 

instructiYe feature Of the dikes is the frequent occurrence at ~heir contllct with the 

slates of a line of breccia, generally conforming with the plane of contact, but sometimes branching otf into the body o£ the slates. "\Vhile some of these breccia seams 

may be, as Doctor .Taggar suggests, flow brc?cias ·or broken material which was 

pushed ahead of the 1imgma nt 'the time of its first intrusion, they are, for the most 

part, true friction breceias and contain broken fragments of the porphyry, as well as 

of slates.· In one case a seam of hreceiated slate and porphyry fragments was found 

iu the slates at a distance of 15 feet from the porphyry contact. The breccias thus 

indicate clearly that there have heeu dynamic_ movements within the mass of slate 

and porphyry since the intrusion and consolidation of the latter. They are found 

generally on but one .side of the dike, but in a few cases were observed at either 

contact. A study of these friction breccias show that mineralizing solutions must 

haye entered along t~e channeb proUuced by these movements. Panning fests 

pro\·e that the breccias contain gold: yalues, though gener:ally less than the adjoining " 

slates, while th~ porphyry on the opposite wall is generally found to be practicall.f -

barren of go!d. On the other hand, hoth l~·eccia and adjoining slate-~ arc-abt~ndantly 

impregnated with pyrite, as is the porphyry to a less degree for a short distance 

from the contact. There has also been a certain amount of silicification accompanying this later mineralizing actiOn. Not o!lly the breccias and slates hut also the 

porphyry it8elf have bf?en ~ilicitied in the neighborhood of these seCondary fractures,-

\ 
78 ECONOMIC RESOURUEB OF NORTHERN BT~ACK RILL~. 

and some of the large quartz len::;es in the hanging-wall portion of the horly are 

apparently of more recent origm than the pm·phyry. 

On the 800-foot levd, a little sonth of the Star shaft, the miuc drift~ h,l\-c rlisclosed the top of a bodv uf phunolit~ whieh ero::5ses the lamination of U1e :-.latcs in " ' 

a northeasterly direction. ...:'ls seen at time of d:-5it. it consisted of two detached 

masses with the same general strike On their northern cuntads. The-.,e HHtSt<,e~ are 

prohably projecting knobs of the upper surface of a ~ingle body. aml may he 

expected to join below: 'fhey are preso.1mahly of later origin than the rhyoliteporphyry. Whether they have bad any influence ou oro depo~ition i:-; nut known. 

CALl<~DONI.A O}{E BODY. 

This ore body was only observed o~ the 3ou and 600 foot leyel.~. It lie:, entirely 

to the east of the porphyry intrusion which is cut hy the other mine \\-·or~;:ing~. and 

the porphyr~· body seen nt the surface nenr the open eut did not appear in the lowtW 

working~ of thi::. mine. A narrow dike of porphyry striking N. 10° ,y, is, howe,·er, 

cut hy the somewhat curving drift which reachc::; the CaleUonia workings from t,he 

Old Abe Hhaft on the 600-foot level. The slates in this portion of the workings have 

the same g·eneru,l strike, namely, a little west of north, though it loeally hends a 

little to the cast of north. Their dip is about 4;) 0 E., apparently .-;omewhat les~ steep 

than that of the porphyry. The. ore hody has the usual eastern dip, which also 

seems to be rather steeper than that of the slate~:~. The inclosing rocks are amphiholitic and abundantly impregnated with pyrite. 

CONCLUSIONS. 

From the observations made in the underground \Vurkings. of which only a haJd. 

statement of the most important has heen gh·en above. the following- eonl·.lnswnH 

have been drawn as to the form and probable origin· o:f. these ore bodies. The 

determining cau:o;e of the original ore deposition would appear,t.o have been a eonF 

pression and crushing of th~ rocks along two eom·ergiug· lines. a line of major 

crushing, trending about N. 30° \Y., and a line of minor movement. running ahout 

N .. 10° ,y, and crossing the line o{ major ~rushing just south of the Star shaft, where 

now are opened the shafts and most exten~:~}ve ore hodies. The movement which 

produced this crushing must have been very gradual and of ~i. nature similar to that 

""" · -.--,. - ----which produced the lamin:ition of the Hlates. lt resulted not in hn·ge definite frac- '- . tlli;es-or-in-brecdation· of the rock~ as in vein fissures or <~rushed zones~ where 'ore 

generally accumulate:::, but in a differential movement along the already determined 

planes o-f ·lamiuation and pitch, the effects of whieh, however. extended through 

zones or belts tlutt were somewhat more steeply inclined than either of these structures, especially at the jm~etion of the 'lines of major and minor crushing, where 

the rc:-;ultant crushed zone seem.-; to ha\'e a nearly ,·er"tical ·direction. 
.ORIGIN 0.1!' HO:MESTAKE ORES. ' 79 

;raggar ha.-5 ~ug·gested that the general zone of crnshing 18 nearly coinciden5 

with the change of dip of the lamination of the slates, but no fn.cts bearing 

directly upon this theory were observed in the underground workings. ·I( how:.. 

ever, a strong line of folding l~ad been developed in the original sedimentary serie~ 

prior to the compression which produced the; lamination; it is ,·ery probable that 

during the compression the limb~ of the folds would have Uet~ll lines of '"~eaknes~ 

along which _the strain might have resulted ~n some difi'erential movement ~tnd special 

crushing and dynamo-mctamol·phisn_t of the rocks. Along ·thetle lines of movement 

the solutions rose from which were precipitated the original deposits of iron .sulphides and gold. There is no definite evidence as to the source of UlCse metab. 

The presence of garnet-amphibole rocks is suggestive of contad metamorphi~m, 

hut neither magnetite nor specular iron, ,.,rhich arc usually chara.~teri:-;tic of contact 

minetalization, is found with the ore, nor in' its distribution wa~ the ore observed t.o. 

have any specialTclation to the older intrusive bodies. The ore is distinctly of later 

formation than the garnet and assoeiate.d minerals, and the latter are seen by.micro-· 

~copie study to have been formed since the dyitamic action which produced lamination 

or schistosity.in the rocks. The metals may be assumed, therefore, to have hcen 

derived from the leaching of roeks at some di~tance below the surfaCe by percolating 

·water.-;, and" to have been precipitated in contact with thi.'! gr;aphitie matter~ a.JHl 

possibly also with original pyrite, present in the !'lates. 

The se~on.d mineralization which .came after. the later intrusion of rhyo1iteporphyr)~ evidently followed the same g·eneral chai:mels and consisted essentially 

of the same materials, iron sulphide, and ·gold. It did not stop at the Cambrian 

contact, however, but.continued on through cr:wks or iiS~ureR into the·Cambrian 

roeks and deposited abundant auriferous pyi·ite in the basal conglomer~tte adjOining 

and in the calcareous beds immcdi~tely o\-'erlying the outcrop of the I-Iomestake belt. 

The most important difference as yet noted between the two periods of deposition is 

the local fo,rmation in the-~onglomerates of .tungstate of iron 'Yhich seems t.o replace 

the-{ulphide. In these later deposits n_o evidenee of pneumatolytic action has been 

observed. As to whether millerulir.ation went on· during the period hetwec.n the preCJ:!mhrian and Tertiary deposition, there is also no evidence. 

The deposits in general ri.re remarkable for their freedom from metals other 

than those already inentioned. There is said to be 0.11 ounce of silver per ton in 

the ores and not over 0.05 per cent of copper in the cq_ncentrates. Secondary·---' 

enrichment of the ores by snrfa?e leaching has also been of relatively--small impoi·-

tance.· Some of the stn·face ores of the llomestake body are sai4 to have assayed as 

high a::r$16 per ton, and the ore taken froin DeSmet and Columbus mines is ~aid t.o 

have averaged about $1. per ton rich~r than the ores of the more southern mines. 

It is said that th~ concerJrates in the upper workingS of the~Homcstake mine, where 

the ore was almost completely oxidh.::ed, carried only about $.1 in gold per tonl but as 

• 

) 
- ~-~~-

80 ECONOMIC RESOURUES OF NORTHERN BLACK Hll.J .. 8. 

oxidt4tion has decreased in depth the amount of gold in the concentrates ha:; increased 

until in the lower levf!ls, .where oxidation has not penetrated, the concentrates carry 

$8 in gold per ton, while the ore taken a" a whole ,{veragc" $5.50. Under the,;e "conditions there is no eddellee of any deui'CUt::ie in Lhc vnlues with depth, while the .size 

of the ore borly appears to be iuercasing rather than decreasing. On the other hand. 

it '\'Ould appear from :>uch evidence as was ohtainecl fluring this examination that 

the pitch of ore i:; not as regular as ::;eemed to he the caf'e in the upper and northern 

portion of the workings, but that at present it has steepened so a~ to nearly 

apprqaeh the vertieal, while the eastern dip has al.-.n stccptmed. Thh; might have 

been expected if, as .sugge:-:ted above, the present result 1s devendent on the 

eon,~erging or crossing of m~\rement on two distinct line~. 

PETlWI!RAl'HlC STUDI" OF 1'1/R JTOME8TAKE ORES. 

'By J. D. TRYIN<<. 

The orcs of the H')mcstake mine oeeur in the rocks of the Algonkian, which 

consist of a ntried series of highly altcrPd and, in most ca.ses,- ery:-;talline rocks. 

They may be divided into t~rvo group:-:.,-nwtatnorphosed :;ediments, and metamorphosed igneous rocks. 

1\IETAlHOiti'HOHI<:I> SEDil\1~<;:-l"T.S. 

The rocks of this group eon.stitute by far the g-reater portion of the Algonkian 

:;eric~. They arc quartzites, quartz-:schist..,, mica-schists, phyllites, graphitie ~latei":.i 

aml ;-:.ehists, chluritic slates and schists, and man}· varieties intermediate in 

position. 

l\1J<iTAl\10RPHOSJ<::D l(~NI<X>UH HOC:KH. 

U ndcr this head are plaeed a series of varyingly schisto::;;e rocks of uniformly 

basic l"haracter. They arC here grouped tog·cther under the comprehcn:-3ive term 

'·amphibolite,'' as amphibole i:-: the most noticeable constituent. As a whole theY ' . pre!-:lent a_- greenish appearance, a !IH1!-:!SiYo and. i·ather dense texture, and in the. 

majority of cases possess a schistosity hut poorly developed. They occur a~ 

dikes or irregular masses in the other Alg-onkian rocks, and in many cases :show 

a ma:'.lsh~c core with the' schistmlity increa~ing toward the periphery.· Mineralogically they con~ist of pale-groci1ish amphibole (usually actinolite) with .-;orne original 

Phtg·ioclas~z_~:s£!Id~I~Y -quart?., and orthocl.as~ in :.:.ubordinate amount, with acc~ssor_\. · zoil:'ite, ilmellite, titanite. leueoxcne, and calcite. Original kernels of augite 

show the hornblende- and . t;etinolitc to be of a ul·ulitic eharaeter. Some of the • , I , 

more highly metamorphosed rocks show a development of hiotite. "• fi ' 1 

In texture the metnmorphosed igneous rocks vary from a fine-grained dense 

rock, though diabasic, tO one ,·ery c<?arse \vith a eharacteri:-3tic mottled appearance 

• 

.. 
PETROGHAPHY OF· HO~LESTAKE HRLT. 81 

resemhl_ing the skin of a leopard. The ~oarscst specimen's possess a texture nnd 

general appe.arance suggestke of gabl.n·os 1 pyroxenites~ and other plutonic rocks 

of hasie character. In t.he less extensiYc and dike-like ocennenc~s the yestiges of 

an original diahasic texture are often well detinecl. There seems little reason to 

doubt that the amphibolite group as here exposed is referable to an original 

series of basic rocks wllo:;e chief mineral was }l.n·oXcne. 

IU~LATIO~ OF THE C>RI<:f-' TO THE ALGOSKIA'S R.OUKS. 

The ores of the Homestake mine, taken as a whole, can not he.said to prCScnt 

any constant _features that will serTe to distinguish them from the characteristic hut 

barren rocks of the Algonkian. 

Pyrite is by far the most itwariable indication of mineralization~ but is notably 

absent from many of the richest portions o-f the ore. Quar~z, dolomite, calcite, and 

arse~~~pyrite-are abo of frequent occnrn:nee and :-;ometimes eon:-3titute the main body 

of thc'ore, hut. no decrease in yalucs can be noticed when they arc nLscnt. .. A.gain, 

·garnet and trcmolite will he pr'esent in so great abumlanee a~ to constitute the .larger 

portion of the g:1ngue mineral, hut hodies of ore will occur at no appreciable distance 

in which no trace of these minerab ean be obsCITed. Thn~, it will appear that 

a}thmig'h we find pyrite, qnart.z~ llolomite~ calcite, arsenopyrite~ tremolite~ and g~lrnet 

frequently con:;;titnting e.ither separately or in comhination the gangue of the ore, 

no one "of these minerals can be stated to be a sine qua no'n to the occurrence of the 

gold. In general, however~ it may he said that, compared with the barren areas of 

the same ~ormation, the orcs oc.enpy a zone which -presents a greater number of 

secondary minerah; a more constant oceurrcnce of sulphides, dolomite, quart.z, 

cal~lte, and arsenopyrite; and, tinnll~·, a more ndxanced de~ree of contortion and 

di~tortion. 

DETAILEI> l>ESUlUPTIOX . 

. li"AJ .. I. RO(;h-. 

In the set of collected rocks were two specimens of that varlet~T of wall rock 

known among the miners as ''woodyard'~ slates. These were take.n from the 

north end of the ~00-foot le,-el in the long cro.sscut. 

One specimen (No. 45) is an extremely fine-grained, evenly sdlisto~e rock of a 

blacki~;h-gray color. It splits more easily along tl-~ose planes Which ~how an abundant development of extremely tine mien .. to the arrangement of. which in parallel 

pia.tes the schistosity ~s due. Cross jointing frequently occUrs, and the rock gen~ 

erally shows wa\·y crenelations tra\·ersing the _surface of schistosity. Thin films of 

pyrite occur here and there in the ~econdary planes and the same 'mineral may 

occasionally be·observcd in srnall isolated masses. The microscope shows this i·o~k. 

to be a dense aggregate ~f quartz, mica, and a ·ve.ry finely divided dull-black 

4987-No. 26-0-l--G 
\ 

.82 J<::CON'O:MIC RESOURC:ES OJ:<' NORTHERN 'BLACK HILJ,S. 

D?.aterial, whiCh is presumably graphite. This graPhitic material occurs in such 

abundance as to make microscopic sections very opaque. Occasional lenses Of small 

size occur in which irregular uHtHses of pyrites and quartz may he obse_i-ved. 

The coarser mriety of the so-cnllcd "woodyard" sl<ttes (No. 4±) shows lig~tercolorcd, rather larger flakes_ of mica, and a more marked evidence of crumpling. It 

contain.<; considerahlc chlorite, ·and between the micaceous layers are intercalated 

bands of a. more quartzose character. The quartr. grains nrc small and show ·con~ 

siderablc reccmcntation. The mi<':t is musco\'ite. The light color of the rock is due 

to the absence of the graphitic constituent. Considered us a ·whole, these specimens 

'show tt less di~t~rbed eondition than the ores; they eontain far less pyrite and are 

mueh more evenly sehistose. 

ORE . .:::. 

In the se"t of Specimens collected the following three varieties of ore can be 

distinguished: (1) Banded ore; thnt is, ore wherein the mineralization has not b'een 

accompanied by dl~fortion of the original struct.ur~s of the rock. (2) Coritorted 

ore; f,hat is, ore where tho original rock ha.-, undergone \·ot:y great distortion. This· 

distortion has generally been accompanied by the introduction of numerous mjncrals 

not an essential part of the Algonkian series. (3) J\llasshrc ore; that is, ore where 

few, if -any, traceto of either the original structure or the original ingredients in the 

Algonkian rock can· be observed. These three varieties a1·e separated from one 

another by no sharp line~ of demarcation~ but transitional Varieties occur sbowing 

ail stage~ of d_istortion and mineralizatiou. 

Jl,L\"DI<CJJ Olm. 

A specimen of ore taken from the middle hreast of the 800-foot level shoWs 

complete preservation of tlH; original structure.-; and characte.ristics of the Algmikian 

rock after mineralization. It is a black, schisto.-;e rock (specimens 4 and 5) in which 

. the original sedi_nwntary ban.diug is _very pronounced. Tli·e band.:-! are caused by the 

·alternation of narrow and exceedingly den::;e layers of a slaty aspect with broader 

bands of coarse tcxtur? and slightly lighter color. The narrow bands have a slaty 

cleavage at a con.-,iderahle angle to the bedding. Th~ microscope ~bows _them to he 

composed Of irregular blades of biotite parallel to the cleavage and a confused 

aggregate of very finely divided black material of presumably graphitic character. 

Small grains of quartz and orthoclase occur together with the hiotito. .Along the 

planes' of schi~tosity in these dark bands occur broad and extremely thin films 

of py1:itc. 

The ·coarse1: layers a~·e composed of irregularly h<;>Unded .grains of orthoclase 

Of considerable. sjze and irregular patches of biotite. The orthoclase grains contain many incluBion~ and ha\·e originated. from the metamorphism of the primary 
' 

PETROGRAPHY OF H0)1ESTAKE OltE8. 83 

ingredients of the roek. The biotite is interstitjal between th~ orthoclase individuals and IS in very irregularly bounded patche~ arranged without any Bpecial 

orientation. They arc generally of sufficient Hize to be identified in the hand 

Hpecimen. lt is interesting to note that the graphitic material in the body' of the 

· orthocla~e/is arranged in very narrow bands of :iltcrnat.cly darker and ligh.ter color 

according to the greater or less abundan~e of the graphite (see fig. 10, 1). These 

baud.s follow the original bedding planes of the rock, causing the contrast in color 

which makes the handing prominent. The schistosity has fractured them so. that 

their continuity is interrupted by a sncces:::;ion of Hmall displacements (see fig. 10, 2) . 

• Joint planes ean be freqncntly ohsctTed running in directions at various ang~es to 

the prevailing schistosity. In some of the::;e seams carbonates-probably calcite 

and dolomite-occur; in others, pyrite. 

A slightly more oxidized variety, of handed ore is seen in specimen No. 25 

from the north end of the c!OO-foot lm·cl ncar the 

De Smet. It is a blackish-gray rock with a pronounced sedimentary banding and poorly developed 

schistosity. Small crystals of arsenopyrite and 

pyrite are scattered .-;parsely through it with no 

semblance of regularity. ThO p~·rite o{~curs also in 

irregularly dist.rihuted masses or in thin films. 

There is htter deposition of pyrite, together with 

conr:;iderable limonite, aloi1g- see_ondary fractures. 

Viewed under the microscope the rock i.:; seen to 

consist of biotite, quartz in grains, and numerous 

lenticular masses or crystals of pyrite and arsenopyrite. The speeimen has suffered little or no 

deformation, and but for the oeeurrcn~e of the sul-

" FIG. 10.-Banding of Algtlllkiun slate duo 

to parallel arruugement of graphitic 

material. ' 

phides presents no notieeable features which ,,,rould 1-:>erve to characterize it as an ore. 

Nos. 15 and 16, taken from the north end of the 400-foot level, show still 

another variety of bandeJ o~·e. In No. 15 the _sedimentary banding is scarcely 

notiecable and the roc~ closely resemble~ the .'"woodyard" slnte~ in its general 

appearance; It. is a fine-grained grayish phyllite, with hands of. somewhat more 

graphit.ic character lccurring without ·regularity.' Pyrite is present in· very thin 

' films along the planes of schistosity. 

No. 16 is a rock of very similar character, hut exhibits two directions of 

schistosity. The first, or that parallel to the original handing, causes the rock to 

break into broad flat t;labs. The second il:l at fin angl? to this and exists only between 

the first described. The microscope show~ the rock to be composed of quartz grains, 

fine blades of museovite, hiotite, and ehlorite, together with considerable calcite ill 

irregular ptttchct:i and some pyrite. 
84 ECONOMIC RESOURCES 0.1+' NORTHERN BLACK "HILLS . 

. No.-2± .show.s,still a· different ynricty of handed ore. It is from the Lincoln stope 

on the 400-foot level. . -It i8 a dcn8C rock composed of alternating light and dark 

bands. The dark bands have a blauk slaty appearance and show numerous small flakes 

of biotite, together with minute crystals and masses of mispickel and pyrite. The 

lighter· bands are of an extremely fine quartzite, ~omewhat friable in character, and 

colored light green from contained chlorite. The whole specimen is cut by a cross 

vein of quartz and pyrite which shows a distinct vein structure and is almost 

perp~ndicular to the schistosity. The quartz of this vein is of glassy character and 

the ,J?y_rite occurs chiefly in the cen_ter~ filling_ the space between .two quartz masses 

on the sides. The section .,bows only a limited portion of the specimen and is taken 

from. the light-green band. This.~onsists of fine grains of quartz, showing considerable recementation, some inter~titial_.calcite, and very l!Ulllerous extremely thin 

shredded flakes 9f chlorite. A few isolated pi!tches of titanite may aloo be observed. 

No. 8, from the ·south breast of the 700-foot. lm·el, is a dark-green schistose i·ock, 

shot through with tine lenticular masses of pyrit~, whose longer diameters are in the 

directi9n of lamination. Fibrous trcmolite can abo be obsenyed in small radiating 

bundles. The microscope shows .. the rock to be n laminated aggregate of quartz 

grains, tremolite, chlorite, and lenticuhir masses of pyrite; a litt.le 

biotite was also observed. 

Specimen No. 6, from the middle 

west ~hoot on the 800-foot level, 

shm,·s a transition from that ore 

which presern~8 the original Algonkian s.tructure to ore of a more contorted character.. 1 t i~ a ~narkedly schistose rock· 

consisting of grant.Ilar q~mrtzite, glassy q':Jartz, and hea,·y bam:Js ~f iron sulphide 

Il).ingl~d together in~ confused manner. The sulphide is of u slightly pinkish tinge 

and may be l?yrrhotite. [ntiniate~y mixed wit,h the quartz is considerable ·dolomite 

R~owing curved faces a_nd_s!Jt.u~times a slightly yello~vish color. Under the microscope 

the sulphides show shattering, t~iotite, qlllli·tz, and calcite occurring between the 

fragments. In the portion which consists mainly of quartzite the grains are noticeably rec~mented! In the micaceous portion, green amphibole, chlorite, biotite, and a 

l_ittle _titanite oeeur. All of- the minerals shm~' strain phenOihena, and the· entire 

Speciinen is distorted, so that tlie ·relations of tho various layers are very confused. 

Specimen NO. :10, from the. west stope'on the 500-·foot·levcl, is a dense granular 

·quartzite heavily impregriated with pyrite, ci-ystals of arsenopyrite·, and carbonates. 

'Traces of a. laminated tcxtlirt~ at~e observable in the parallel alignment of.hiotit? and 

other micas which occul' i"n ~1 narrow· band. :The· greenish color is due to thin 

~nicroscopic blades of chlOrite. Under pbe n_1icroscope the separate grains of quartz 

·show recemezltation. There is present cousiderahle hiotite and pyrite in iri·egular 

masses, arsenopytit.e always. in characteristic cry:4als, and some calcite. 
.. 

PETROGBAr'HY . o:F Ho.MES'l'AKE· ORES.' . . 85 

No .. ~::f.-is a tine~gmined compact quartzite, colored dark ·green by extTemely 

minute microscopie blades of chlorite ~uid containing, scattered hunches of radially 

arrangc(b,trcmolite n~~cdles. Th{~ microscope .shows the rock to be made up ·of ail 

aggre~·atc -of :"mall quartz grains, all showing secondary enlargement, scatter.~d 

nutsses .o.f. titanite; and a ·little caleite. All of the original quart;~, grains ~liow .. 

indications of hcaYy strains. 

CO~TORTlW ORK 

The te~·m •• contorted~' ore has been used to designate that· \'aricty of ore ilt 

whiCh the orig·inal se.histosc cha.l·actcr of· the Algonkian has hecn greatly distorted, 

and in whi~h milwrals not commonly, forming 'an essential part "of the .AlgOnkian 

rocks have been introduced in greater or les.~ ahundance. 

Specimen~ "No~. 32 and n:3± illustriltc th.is variety of ore. They are extremely 

"fine~grained, chlorithj schists, \vith satin~likc luster, di~torted ·and gnarled ·so as 

to resemble the tcxtui·e of knotted wood. Lenticular ma~ses and itugen of 

dolomite, ealtite 1 and quartz intimately mixed tOgether, or of gla~sy quai-tz, 

pyrite, U:nd mispickcl a.re abumlant; radiating nmsses of tremolite occur sparing I)< 

\Vhere the distortion has not gOne so far that nO definite ::;tructure cari he 

rceognized, the- knots or augen are beautifully _developed. A hlow with the 

hamme1· will generally reveal the presence of a kernel of arsenopyTite or pyrite, 

to which the knots owe their origin. These kern'?ls ·of sulphide are Often one-. 

half or three-fourths of an inch in diameter. They are genernlly well"·crystallized, 

and the schist passes up over them iu Yery even curvCs. Iri other instances the 

distortion has go-uc so far (e. g.,- specimen .No. 2G) that ·_,he original structure of 

.the :schist has heen eompletely obliterated, and masses of quartz, sulphides, 

chlorite, tremolite. dolomite, and ealcite occur together in very confused rclatim~s. 

In specimen No. 2G a very htrgc apd irreguhu maSs of quartz may be· seen. 

embedded in the chlorite. The arsenopyrite is almos.t alw3..Ys in cli~tinct Cry8tah;·, 

or ·groups of crystals, atul the PSTite is sometimes in crystal~, but mOre 

frequently in large irregular ma~ses. ln many instances pyrite and ar:::;enopyritG 

are· mingled together in a single nms~, each mineral being recognizable hy ib; 

characteristic color~ but neither showing any definite relation to the oth0:r. 

Ocea.sional patchc~ of garnet may be seen in the chlorite. hut they are n~·thci 

sparingly develope_d. The microscope sbo,vs the grem~ish portion to be composed. 

mainly of chlorite, with some few needles of adinolite or hornblcn~e, of which 

the chlorite seems to be the alteration product. The crysmls of arsenopyrite 

arc frequently slightly shattered and their interstices filled with quartz,- but the 

fragments are never yery distant· from one ,anothe:f, and it is probable .that ~he 

movement which produced the shattering -~as very slight. 

In a section of specimen No. ·a2 secondary ·veins of calcite can ·be observed 

cutting directly across chlorite, sulphides, and quartz indiscriminately. This 

\ 
86 ECUNO)fiC RESOURCES Ol<' NORTHERN BLACK HILLS. 

shows that there has beer\ an introduction of calcite subsequent to. all of the 

early mineralization. 

In one specimen of this chlol'itic ore (No. 896) a considemble development of 

free gold was observed. This g·old occurs in two distinct relations to thegangue 

minerals; first, contai.ncd in the quartz in extremely thin lea,~es follOwing apparent 

fracture lines; second, contained completely in the chlorite-schist. In some instanceH 

the gold leaves in the quu.rtz extend up into the chlorite of the main rna.ss. ln 

neither case is the gold associated with sulphides, but small fr~gments of quartz, 

some of them completely surrounded by gold, occur with all of those masses of gold 

in the chloritic portion of the ore. A specimen of the gold in the chlorite was seen 

in the mine inspector's office in which a leaf of gold about o,;e-half inch in breadth 

and one sixty-fourth of an inch in thickness projects from the chlorite and curves 

over on the outside of the rock. In. one instance a leaf of gold extends from the 

quartz into the chlorite hy which the latter was surrounded and occurs there 

together with chlorite, filling the interstices between irregular grains of quartz. 

:Most of thi::; g·old is in exceedingly thin lea\'es, none of i.t mrer showing nugget-like 

·appearance. A distinct crystalline structure could not be observed in any of the 

gold, but its manner of reflecting light suggested the presence of minute crystalline 

faces. 

Under the name of "maSsive" ore has been placed that Yariety of ore in which 

all structures-both of handi11g and ::;chistosity, which characterize the Algonkian 

rock-have been completely obliterated. This variety of ore consists chiefly of 

minerals which have been introduced either :J.Y deposition in spaces left between 

Algonkinll rocks or by replacement. Such 1pinen1ls as arc characteristic of the 

metamorphosed Algonkian oceur either in this ore as broken frag·ments or in t~e 

Algonkian rock which forms the walls _of the ca vit.ies in which the ore was_ found. 

One of the most interesting varieties of this ore is that composed of dolomite and 

quartz. A characteristic speciiven of this variety of ore (No. 925) was taken from the 

south breast on the 800-foot level. It consists of a large irregular mas' of coarsely 

crystalline dolomite confusedly mingled wi.th chlorite, tremolite, in:egular masses of 

glassy quartz, and some pyrite. The main dolomite muss is intersected by joint 

planes filled with glassy quartz and evidently of a much later age than the rest of 

the ore. The microscope shqws the dolomite to be made up of a great number of 

separate individuals, no.ne of them· with crystalline boundaries, but impinging upon 

one another in very irregular lines. They show very great dynamic stress in their 

wavy extinction and distorted cleavage. A few identifiable masses of calcite occur 

with "the dolomite. The quartz which fills the joint planes is seen to be composed of 

many small individuals, but is 'Tery clear and shows no indication of strain. 
PETROGRAPHY OF HO~IESTAKE ORES. 87 

Another variety of massive ore is seen in that taken from the west 8hoot on 

the 800-foot level (specimen 7). It is composed of a confused aggregate of radiating 

tremolite of a brownish-green color in hand speciment5 but almost colorless by 

transmitted light, biotite, quartz gTains, dolomite, and chlorite. Tremolite iH the 

most noticeable· mineral in the ore. U ndct: the microscope the quartz grains and . - dolomite a·re seen to he mingled together in a confused manner, neither ingredient 

exhibiting crystalli'ne boundaries. lt5olated grains of titanite, ragged flakes of biotite, a little green.hornble.nde, and some quartz arc also present. A most interesting variety of massive ore is that occurring- in the Piere? stope and known as 

•• garnetiferous" ore (No. 18, No. 19, and No. 20). It is a confused grayish mass 

of tremolite, glassy and granular quartz, dolomite, pyrite, arsenopyrite, and garnet.· 

The microscope shows garnet, chlorite, dolomite~ quartz, pyrite, and arsenopyrite.' 

The garnet is \'ery largely broken and shattered, especially so when occurring in the 

qua,rtz and dolomite. Tho~c nias~es which are entirely contained in the tremolite 

arc les.~ ~battered. As a whole it is very much broken. and is often partially 

altered to chlorite and a green, pleochroic hydromica, perhaps_related to ripidolite. 

The garnet fragments are surrounded and inntded along fracture lines by dolomite, quartz·~ and pyrite, showing that these three minerals were f~rmed later than 

. the garnet; which is itself probably, the product of metamorphic action. In sotlle 

cases the garnet has gone so far in alteration that only a green confused mass ~f 

chlorite and hydromica remai'us~ with perhaps a kernel or two of garnet to indicate its origin. Fragment~ of garnet occnr completely isolated from the parent. 

mass and surrounded by quartz. The quartz consists of an aggregate of irregult_tr. 

grains whose boundaries have beeu recemented .in many cat5es: ,The granular 

aspect it5 probably due in large nteat5nre to shattering~ of which the hcnYy :strain 

phenomemt are an additional eyidcncc. Pyrite grains occur ScattereU through. the 

quartz. The dolomite, when seen in a hand specimen, presents many curved faces 

and under the microscope :showt5 wavy extinction due to dynamic stress. It has 

never developed the twinning planes parallel to -t R. which are so characteristic 

of strained caleite. It is broken so that large fragments are often isolated and 

imbedded in a quartz matrix, the separate faces being eaten into at time::5 by the 

·quartz. This phenomenon 'of quartz occurring later than the dolomite is again 

.:3een on the 800-foot level, where a large mass of dolomitic ore is cut hy smal~ 

~tringers of glassy quartz rarely more than one-sixteenth of an inch ·in -\v-idth, hut 

dbtim:tly filling joint planes in the dolomite (No. 925). 

Specimen No. 19 ~hows large and distinct cube" of pyrite embedded partly in 

one of the ingredients of the ore and partly in another. The arsenopyrite is present 

in small crystal~ of characteristic shaPe,. but is not so prominent in the garne.tiferous 

portion~ as in the rest of the ore. The dolomite in Specimen No. 1\l i,; ~lightly ycl-

\ 
88 ECONO'lUQ RESOURCES 01!'. NORTHERN BLACK HILLS. 

low ish in:Color and probnbiJ'.bas sm~i~ of the ~iderite molecule in its '·composition. 

The trei.;~~lite sometimes penetrates t·hc garnet and in some cases has been replaced 

. by calcite. The dolomite of the· main ore mass is to be sharply distinguished from a 

few later calcit~ .seams which ent b?th (lnartz and garnc~ indiscriminately. The 

quartz frequently contains little porous and fl.niclal inclusions arrangeU in lines at 

.varyi~g angles to one another. In this .varict}" of ga1:netiferous ore, therefore, is 

se~n the folJowing· sequence of events: 

(1) The metmnorphic action which produced the tremolite and the garnets. 

(2) The shattering of the original rock which· gave rise to the broken condition of 

the f£arnets. (3) The ·introduetion of the dolomite between the fragments of the 

garnet. (±) The shattering of the rock as then formed and the introduction of the 

quartz into the spaces thus left vacant. These relations will be well illustrated by 

Pis. VII, A and B. 

It is probable that most of the pyrite was introduced at tho same time as the 

quartz~ h~t, except to say that it is later than the garnet, no definite evidence as to 

it:; age is available:. Lritcr than ull these eyent.s occurrec~ considerable movement 

and crushing \l,rhich produced strain phenomena in the quartz and the subsequent 

recernentation of the shattered i!HliYidunlr:; hy quartz. 

FORP!f}"RIES. 

The erupth'e rocks. occurring in the Homestake mine arc rhyolite and trachy· 

toid phonolite. 

The rhyolite, which is by far th~ most abundant of the two, is a dense, almo.st 

aphanitic, grayish-white rock resembling novnculitc. Under the microscope it shows 

an· extremely fine aggregate of low polarizing. individuals in granuhtr arrangement. 

None of them arc large enough· to be accurately determined, but they are probably 

quartz and orthoclase. Phenocrysts are scattered ,.CIT sparsely through the rock 

and are unifor1nly small in_size and sho\V Yery advanced ::;tagetJ of alteration. In the 

very numerous sections examined all of the phenocrysts were either completely 

kaoliniied or weathered and the spaces filled by secondary ealcite. The only basic 

mineral present is pyrite, which occurs abundantl~7 even in the freshes~ specimens. 

It generally shows small· dodecahedra or pyritohcdra~ or is in irregular rounded 

· mUI";t-iCS of no definite form. The::;e cry::;tals and mas::;es are generally extremely 

small~ so that t_hey appear in hand specimens mere_ly as minute, g·listening specks. 

No da'rk silicates of any' kind ean·be seen in the slides. There is a general resemblance of this roek to the rhyolite or white porphyry which" occurs in the vicinity 

of'Lcaddlle and elsewhere. 

A second variety of porphyry b a rock belonging to the phonolite family. It is 

a porphyritic rocl{ exhibiting a dense, brownisl;.grecn; almost aphanitic groundmitss, 

in which are embedded glassy or salmon-colored erystals of sanidine. Small crystals 
\ 

l'E'l'R'oGRAPHY· OF HOl\IES'l'AKE. ORES. 8\! 

of acgil'ine-augite can aL;o be identified in the hand :-;pccimen. The· micro;;;copc 

. shows the grotindmass. to be made up of small rods of orthocla8c arranged in flow 

strneturc, together with innumerable shredded masses 1 of aegirine. A few crystals 

and inegular masses of identifiable nepheline occur. The large aegirine·angit.es i1re 

gcneptlly well hounded and show the char~wteristie deayage ~wd optical characterS of 

this variety of pyroxene. The rock has 1:-learccly sufficient nepheline to Ue classed a:-) 

u phonolite, and yet the proportion of" that mineral is too large nnd the amount of 

soda. pyroxene i-; too great to allow its clas:'>ificrition with the· .~oda tnwhytes. It is 

distinctly t~ transitional type and. belongs to that vru:iety of rocks whiCh b very 

common in the northern Black Hilb and has been classified as •: traehytoid 

phonolites." 

l'Oi{PilYltY BRECCIA. 

On the border Of many of the dikes of· rhyolite occur varying \vidth~ of 

brecciated rnaterial consisti~g of angular fragments· of porphyry, 'ore, and. di~tortcd 

schist. On the uPper level8 these breccia.-, are· too much oxidized to afford any 

satisfactory evidence .from their 8tudy. Tho::~e from the lo\ver levels, howevei-, 

present some interesting features. 

No. 78 Occurs on the contact of tln~ dike with barren ::~lates. It consists --of 

~harPly ~tngular fragments of porphyry, glassy quartz, and dolomite embedded in a 

matrix of black comminuted schist of a ve~·y graphitic character and more or le~s 

heavily impregnated with pyrite. 

No. 29, taken from the east stope on the 500-foot level, shmvs a grayish mass of 

brecciated material eontaining mueh fine-grained pyrite and ::;mall angular masses of 

poi·phyry. ]n this are embedded large and ::,mall more. or less broken angula~· 

fragments of gla::~sy quarb:. Pyrite occurs in the quartz rather·more sptuingly than 

in the interstitial muteriill. The .latter is an extremely tine, black, graphitic 

aggregate, which, by rea::~on of its \·cry yielding eharacter, has heen thrust into the 

minutest crevice~. The pyrite Oeeur.':l n;w.st abundantly in this matrix. 

Specimen No. 31 t;how~ frag·nwt.lts of porphyry· eompletely embedded in glas.'3y 

quartz and pyrite of the ore muss. The quartz fragments arc made up of many 

separate individuals with very irregular boundaries, an(_! in polarized light give 

m·idi:mce Of great dynamic stress. "l\Iuch ealcite has been introduced between the 

fragments of quartz and also occurs in irregular patches in the breccia matrix. It 

is worthy of note that the pyrite in thC matrix, even where present in distinct 

Crystals and large ma~ses, Shows no evidence of shatte~·ing. It is therefore probable 

that' this mineral·was introdu~ed either subsequent to or ccmtemporaneou·s with the 

brecciation. 

Specimen No. -!'7 ·is a breceia showing a more advanced degree of commmution. Under the microscope.wc are ~lble. to detect fragments of qunrtz, angular 
90 ECONOMIC RESOURCES Ol!' NORTHERN HLACK HILLS. 

fi·agments of porphyry, and irregular pieces of quartzite and schist. In the 

interstices between these ditferent frag·mcntS is a matrix composed of black 

m·nshcd material of graphitic c~wraeter. Some calcite and a little elay resulting 

from. a decomposition of the feldspar are ;dso prcserit. The quartz shows the 

wmal strain phcnom~na. The softqr material in this case, as in .the other specimenS 

of ·breccia, has suffered the oTeatest deformation and ba):l been introduced between \ . b ~ 

the harder fragments withimt destro.ying their angularity. 

SUMMARY. ,/ 

Although a careful study of the collected specimens fronl the Homestake 

mwe docs not lead to nny very positive conclusions, it i:"~ possible to got from the 

relationship.':'i of the different minerals ::50IIIC evidence a;:.; t~o th~ general nature 

and origin of the mineralization. The orcs oeeur along- a definite zone which 

follows roughly the general tren_d of the schistosity of the AJgonkian series. 

This zone hm; been the line along which Successive periods of differential movt~­

ment and fracturing have occurred. That these periods of movement were 

subsequent to metamorpb~c action is pt:oved-first, by the partial_ or complete 

obliteration of metamorphic strnctnrcs in much of the Homestake ore,. :wei, 

second, hy the shattering of many of .f,he minerals which are the characteristie 

pro~ucts of me~amorphic action. Thus, for instance, the gnarled and kllotted 

structures of the chlorite-schists from the Pierce stope; the departure of the 

schistosity from the even ~md regular direction so eharacteristic of "woodyard" 

slates- to one wholly \Vithout regularity; the occurrence of various foreign 

minerals in distorted and confused relations; and, finally, the complete obliteration 

of all metamorphic structures in some of the more massive varieties of ore must 

be assigned to disturbances which have occurred long after metamorphic agencies 

had ceased to operate. i 

For the better understanding of the relations of the different ingredients of 

the orcs and the conclusions which may be drawn froni their study ,the following 

general summary is introduced. The minerals of which the ores are Composed 

fall into the following three well-defined groups: (1) Minerals which are an 

essential pa_rt of the Algonkian rocks, either as original ingredients of the series 

prior to metamorphic action -or !~S pro~ucts of regional metamorphism. These 

include quartz, orthoclase, hornblende~ biotite, garnet, tremolite, actinolite, titanite, 

and graphite. {il) Minerals that are the result of min~ralizatio!l as distinguished 

from metamorphism, pyrite, arsenopyrite, quartz; dolomite, calcite, and gold. (3) 

Minerals that arc the result of the oxidizing and decomposing action of surface 

waters, iron oxide., and calcite. The minerals of this group! except in so far as 

it is necessary to distinguish them from U1e others,· are unimportant. 
PARAGENESIS OF HOMESTAKE ORES. 91 

It, i~ readily 8een that quartz ocenr~ a~. the most abundant and characteriEtic· 

mineral in both Sl~rie~, nor ha\·c we, except in it~ strudural relations, any means 

of determining to which da::;s it belong::;. lt oecurb in three form::-;: 1. As a relic 

of the ynartz of the original rock prior to metamorphism, in which ca~c it may 

generally be~clbtingnished by it.s· ocCurrence iu somcw·hat stretched grains which 

ha.\"c been cemented by later dcpo;.;itions of ~ilica. btrain phenomena and other 

indication::; of metamorphie action are hci·e nt their maxinmtu: 2. As a by-product , 

of mctamorphi::-~m tilling inter~tices Uetween the laminae uf schists and forming 

grains in the schi~ts thcmsclYe8. Quartz of this yariety is seen to be composed 

o-f separate indi\~idual grains ::;ometimes cemented together by additional silica and 

always shows-at least, in all of the orcs taken :from the Homcstake mine-evidence 

of dynamiC stress. 3. As n Yein mine1;al intersecting all schistOt:lity and other 

superinduced metamorphic structures and therefore entirely subsequent to thesC. 

How many periods there inay ha\'e h~en during ,,,rhich thi~S vein quartz was introduced it i.s impos~i ble to say. 

Garnet and\ tremolite uf the tirst or metamorphic group are undoubtedly older 

than some of the quartz, pyrite~ and dolomite that arc attributed to mineralization. 

The garnet especially often oecurs shattered and broken, the interstices between the 

frugmCnts being tilled with dolomite, quartz, and pyrite. 

l:lyrite occurs in rnany different rela.tions, such as: 1. Alor1g planes of secondary 

schistosity and other metamorphic structures; it i~ he1:e unaffected hy subsequent 

lllO\'emcnt. 2. In irregular masses. and crystals having no d(~finite relation to the 

schistosity. a. ln irregular ma~se.s and crystals which have been s.hatterCd by 

t'uhsequent moYemm1t and the intcn;tieeS between fragments filled by quartz. 

4. In the porphyry in minute crystals and rounded grains. 5. As·the eentral and 

y9ungcst ingred.icnt .;f quartz ,·cin.::: which cut ·across the prevailing lamination. 

G. J n joint planes cutting the ~chistosity and cddently long subsequent to other 

mi!1eralizing aetion. 

It will thus appear that the pyrite has been introduced at differerit periods. 

One of these periods undoubtedly occurred later than· the movements which ohat-

· tered certain of the metamorphie minerals 

whcth~r pyrite belonging to other periods 

It can not, however, be determined 

of mineralization may not have been 

introduccil at the timc.of metamorphism. Again, some of the pyrite is later than 

the intrusion of the rhyolite~, but that belonging to other periods may have ,been 

introduced earlier. 

Gold.-The relations of the gold afford no evidence ~s- to the date of its 

introduction. It i~ associated with quartz, and may ha\'e been introduced with the 

quartz or subsequently. Furtl~ermore, there is no evidence as to the manner in 

which the g·old was deposited. 

. ' 
'. 

92 ECONOUTO RESOURCES OF NOR'l'HERN BLACK HIJ ... LS. 

Dolomite.-ThB doloiilite 8eem:; tO lun·e been the product of a single period 

of mineralization. lt::3 relation to fragments of metamorphic minerals sho\vs that 

it was formed later than the metmuorphie action. Its occurrcnt~c. n~. fragments 

in porphyry breccia.., shows that it was present previous to the movement that 

shattered the dikes. Again, very heavy straiu phenomena, the ·distortion of 

cleavages and twi.ning lines, together with its oceuncnce in lenticular ftnd augenlike masses in bodieS of schist, .~how that much movement ancl distortion has 

occurred since its introduction. The relation of the dololnite to some of the 

quartz is also interesting, for fmetnres or joint planes filled with gla~:s.r (iuartz 

occhr in the dolomite, and frequently clea\·ngc rhomb~ and angular fragments of 

dolomite may be seen surrounded by glassy •1u:lrtz. The relation of the dolomite 

and pyrite can not be determined. 

The general conclusions which 1mty he dravnt from the study of these specimens 

arc as follows: .1. There have been suCcesshTe periods of mo\rement since the 

metamorphism of the ·Algonkian series. 2. There have been successh'e, periods 

of Inineralization whieh occurred later than the metamorphism of the series. 

Others may have occurred prior to metamorphism, hut of these we have no 

proof. 3. Though no definit.e evidence b at hand to show that the gold was 

introduced into these ores after the metamorphism of the rock, it seem's most 

reas~nable to refer it to this period of mineralization. 

CLOVER LEAF MINE. 

The Clover 'Leaf mine (formerly the U nclc Sam) is situated on the south side 

of Elk. Creek, at Perry station, on the· Black Hills and l<~ort Pierre Railroad. 

The country rock it-i mica-schist and the wmal associated rocks of the A lgorikian 

formation-mica-slates, chloritic schists, amphiholites, and qua.rtzites. The mine 

is :;ituated in the Algonkian area' at a ·considerable distance, in all- dit·ections, from 

exposures of 'higher geological formations. Pl. VITI (p. 214) shows _-the ·geology 

and genert:tlmode of oceurrencc of the ore body. The mine was first operated under 

the name of the "Uncle Sam mine,:' hut was abandoned in 1880 on account of the 

difficulty in handling· the 'rater. It '-VtlS idle for ten yea~·s, and \Vas then opened in 

J.,8Q9 by a new company. The depo~it was originally worked by an inclined shaft 

extending southward from a point a short distance north of the large open cut 

to a depth of 150 fe~~----:I~his incline, •,we! all of the workings connected with it, are 

now inaccpssibl~. At It point about 200 feft s.outh of the olU incline a ycrtical 

shaft was sunk to a depth, of 260 feet and the quartz body was th~n mined in 

levels from that point. The .ore, howe,Ter, dipped so sharply in. a southeasterly 

directiot 'that it was soon carried beyond working distan(:e from the shaft, and a 

new incline was opened on a 200-foot level. This .followed the ore in a direction 

S. 6±0 E. and dipped at an average angle of ±0°. This incline had attained a depth 

of <;omething over 30.0 feet vhen the mine was abandoned. 
CLOVER J,EAF MfNE. 93 

The ~ndatc working.-. of the Clon~r Leaf mine comprist~ two open euts connected hy ~t tunnel. One uf the~e if' 12(1 feet :::;lightly we~t of north from the shaft~ 

the otlu~r ahont 50 feet farther we~t. Tn the fir~t or prineipal ent is exposed a 

ledge of iron-stained quartz 5 to 0 feet, in thickncs", ttnd rong·hly parallel tn the 

lamination of the schist. ft ~tril\eS N. r>:(.J ,v., and <lipfl about 60° to ·j(J0 s"r· Thi~ quartz leUge wuR followed downward along the dip, anrl _increased greatly in 

thicknes~ to the ~ontheast. The inelosing schi~t~ and :-;lates, a~ well as the quartz of 

the ore hod.\· itself. are heaYily impregntlted with pyrite, w-hieh at the Rnrface is in a· 

higl~ly oxictizell condition. 

From the snrfnee to a dPpth of 300 feet extenl~~ a large inclined stope. 

Through this one may descend a:::; far as t.he ~f)O-foot len~.!. heyonrl which. water has 

rendered the workings inaeces~ihle. A horizontal ~ection of .the quart;, hody, as 

exposed on the !350-foot len~l, has the appearance of the let£cr U, -with ::;lightly 

flaring arms.· The apex uf the U strike~ S. fi--1? E.: the'northern arm, N. 40°, ,V., 

and. the .~outhcrn, S. 75° '~r. The :-:lutes ctnTe oYer the roof and. eouform to tl,le 

strike of the qmntz hody, appearing on both sides of thn northwestt~rly and the 

southwesterly arrns. They are not, howeyer~ exposed in the tloor of. thP stope ... , from 

which the qun.rtz has not been complete}~- excavated. Botl; arms ·of this 1-1nartz 

ma~~- when followed out fro,m the crest of t.he eastwardly dipping- anticline, become 

much narrower ihnn the main quartz hody. The northweHterly lm~ an axe rage 

width, where exposed, nf 20 feet; the ~onthwesterlY: a hunt 10 to 1:3 feet~ narrowing· 

as it is followell along the strike. 

·UELATIONS TO Sl..~Hl'~AUE Gi'XlLOfiY. 

At a point along the l'ailrmul ::;witd1. !~50 feet in a direction N. 8:J0 ,V, of the 

shaft, tlle lamination of the schists strikes almost eitst :twl \rc!it \\·ith a southerly dip 

of 44°. Thi:-; dip and strike seem to prentil along the r:~ilrmul cut for about 500 to 

i30U feet·, hut as o11e approaehel-:' the open cut the ilip hccomes steeper. ttltd tlie Strike 

ha~ turned to a direction N. 5:1° \\'. On the north ~ide of .Elk Creek, 800 feet 

north of the shaft, is a prominent expo:-:o~n·e of suhist, and here the dip is 53° toward 

t.he northeast, and the :-:;trike N. 15° 'y. The same ~trike seem~ to prevn..il to the 

northeast of this point. Again. directly south of the ~haft, and ahout SOO=£~et___­

di:-:taut, the lmnination of Uw ~ehi~h ~trikes N. 35c \\'.: and dips a~45° SVY. 

All uf these ohserYations, When eo11sidered togcthe~·=:,~ith--those made underground, 

~re strongly suggcsth:e of 'thC-prest-.:.t.~~e o~ a-;-outheastwarrll]~(lipping. nntidine, at 

the erest- of which lies the thiekc~t po-rt(~·~~ of the ore hody. Tf1e narrowdr arms 

would then P.Xtenrl outward, and coincide with the d1p and. strike, a:-; imlieated on 

the sketch map. 

There i~ a striki!1g resemblance between 'thi..; ore hotly and the so-called saddle 

reef..; of A mtralia. 
94 "RCONO".MIC RESOURCES OF NORTHERN BLACK HILI .. S. 

Owners and ?rerators have indulged in some :"ipeenlation ns to the probable con-

. nection of this ore body with that operated by the Homestake Company in Lead. 

The distanee between the two is slightly over 7 miles. The ~trike of the }lomestake 

ore body is approximately N. 34° " 7 ., and this, if extended~ wonid pass a little les.:; 

than 2 miles west of the Clover Leaf mine. The two mine.-; mny perhaps be situated 

on the same general zone of mineralization, but no con elusions regarding the ntlue 

o£ the intervening country can he La.sed upon sneh :;;peculation. 

The mine is sing-ularly isolated from region.':l of igneous activity, the nearest 

outcrops of porphyry being about a mile distant,. Jn the' miue itself tbi.., · roek 

is entirely absent. 

CHARACTER OF TH}~ OltE. 

The gossan is a ledge of rusty~. irorl-stained quartz, much fractured and 

bearing, in l~and specimens, no truces of a sedimentary origin. The i11elosing roeks 

nrc ehlorite, hornblende, graphitic schist, and mica-schists of endless variety. 

These likew.ise are much stained with iron. At great-er depths, however, the rul:lt.Y 

stai~s gradually give place to a heavy impregnation of pyrite, both in the <1uartz 

mass and in the inclosing schists. 

The gold in. the quartz is free nnd almost in\rariably associated with galena. 

A specimen _taken £rom the famous paJ; stretl.k of the mine, which occurred in the 

thid<e~t portion of the quartz body as it was follmved downward to the southeast, shows a t};ree-eighths inch · .,treak of galehn, in a matrix of milky white 

quartz. In this streak, and completely snrronnded hy. galena, oecitr nugget-like 

and irregularly rou·nded ma,-,ses of gold, some of them .attaining a diameh~r of 

one-fourth of an inch. Throughout the entire quartz muss of these spechnens are 

scattered isolated patches of galena, in the center of which could generall)~ be 

detected a ·small speck of gold. These smaller masses of g·old frequently showed 

crystal faces. 

The average value of the ore is 8tated to ha''" been from S+O to $+00 to tbe 

' 

ton, the silver1 contents being so small as to be geuerally_ disregarded; a fA.et 

which is rather siugular in the presence of so lmteh lead. 

---~· --="~ COPPER ORE15. 

There have been found at several localities wit,bin the schist area ., small deposit.-; 

of C?~e:o~ iS~ti""'the~east""SiUe of _9J'3~Creek, n~~lr the crest of the hili 

- north of Deadwooa. The country rocK~_is~·Ttblad~ graphitic schist: in places highly 

silicified, and in the credces of this schist' occur thin tilms of native copper. They 

are scattered through the rock rather .sparsely, and occur in patehes without regularity; the copper having· prohahly been redueed hy the action of the. graphite on 

copper-bearing solutions. 
COPPER AND TIN ORES. 95 

On _the crest of the diddc between \Vhitcwood and Yellow_ Creek there is a 

small prospect in ,,rhich the rtnartz-t-ichists and laminated Algonkian quartzites are 

heavily stained with malaehite and a little azurite. Patches of unaltered tetrahedrite 

also occur. The deposit i::; sn~all rmd extremely local. Other ar~as of Schistose 

rocks m the dcinity of Hoehford and a few reported from the southern hill~ show 

quartz and schi:::;ts throi1gh which is scattered chalcopyri~- mingled with pyrite. 

The average pereentagc of copper is very lo~'· 

As coppCr ore i~ used in the su1elting of the refractory siliceous orcs, later 

discussed, these deposits have given rise to some excitement, but none of them 

has yet proved to be of sutticiently high gr3:~e n~r unifm:m occurrence to be profitably worked. If found in large enough bod~es the concentration of the chalcopyrite 

might bt•, earried on with ' some profit on tt~count of the expenbe of importing copper 

ore~, hut as there is no definite kno\vledge as to .the length of tim~ that the refractory siliceous orcs will continue to be productive, the exploitation of copper deposit~, 

unless in extremely large and uniform bodies, should be carried on with great 

caution. 

TlN.OR~JS. 

Tin has heen known to occur in the southern hilt., since 1876, when attention 

was first called to it by.Richard Pearce, who had· (letect.ed it in some gold du::;t sent 

him for examination; bnt its presence in the Nigger Hill district does not seem to 

have·been appreeiated until the discovery Of tin at the Etta mine (originally a mi~a 

mine) in 1883. This discovery stimulated tl~e search for other deposits, which 

resulted in several finds in the vicinity of "Nigger Hill and Sand Creek and the prosectltion of quite a little development work. The enormous expenditure of capital 

ana the collapse of the tin enterprise in the southern hills, howev.er, brought all 

operations for the exploitation of tin ores to an ahrupt termination. Since that 

time but for .a few inc±Iectual attempt~ to interest caPital in these deposits little 

or no work of any .kind has been attempted. At present \Vriting~ however, t.he 

writer i~ inforn.ICd hy J\Ir. \V. S. Tangier Smith that there has been a renewal of 

activity iu the prosp.eeting in and about this _northern district. 

!n general~ Nigg~r Hil,l comprises a celltral ar~a of_ cr~'8tallin~ A_Igonkian ~·~~~ 

altd mtrnded porphyne~ of probable Eocene age, from whwh the se~mentary-r<)C:Ks 

of Cambrian, Silnrbtn, and Ca.rboniferont~ age dip away in all directi.Ons-a repetition 

in miniature of the main Black Hills uplift. For=-this~aLupliftecl region the .. _._.~"'-'-~- -~ ~ . name _Nigger Hill is frcquentl.Y11Red;...,,but- m?re correctly applied, ~it-indicates-aslightly elevated ridge of limited areal extent sitnuted between the headwaters of 

Sand Creek and Bear Gulch. lt. is on this ridge .that the twJst exten~ive hodies of 

tin-hearing granite have heen found. The eountry rouk throughout the major 

portion of the uplifted area is prophyry of Tertiary age, which haH heen intruded 

\ 
96 ECONOMIC RESOURCES 0~~ NORTHERN BLACK HILT.S. 

into the ... ...\Jgonkian rock~ in such extci;sivc masses as to have left only Hmall portions 

of them exposed. Of the:::oc remaining portions pcrhap~ about one-half is crystalline 

schist, the other ha.lf being irregular, lenticular masses of a coarse~ pcgmatitie 

granite which is, composed of feldspa1· (orthoclase 01: ttlbitc) 1 muscovite, and <pmrtz. 

Both granite aud schist, as weir as the acidic types of porphyry, arc cut hy basic 

dikes. The granite masses trend in a g·cneral north-northwest direction. The 

larg·e.;;;t of them has been found orl Nigger Hill. [t is completely surrounded h_,~ 

porphyry, being more in the _nature of an inclusion in the intruded porphyry than a 

lenticular muss ·in the Algonkian schists. The exact form unrl character of this, as 

well as the other granite nu~sses, has not been determined, for the country is headly 

cloaked by Yegetation and the mines at the time of examination were completely 

inaccessihle. 

The ca5siterite occurs in two forms: (1) In the pegmat,itic granites and (2) as 

stream or placer tin, which has been derived from them. 

In the fir.st 111ode of occurrence it is found ·in irregular grains, which range from 

one-eighth to· one-half inch in diameter. The grains arc most frequently without 

crystal faces, but occasional large and fairly perfect crystals have been found. 

They are most frequently embedded in t,he. white feldsp~r ·which forms the major 

portion of the grv.nitic nmtrix, but .. they also occur in those portions of the· granite 

which consist-almost entirely of quartz and mien. No spodumene har-; yet been 

reported, but columhite and tantalitc havC been ~etccted both in the lode orcs and 

in tho stream tin; s?mo tourmaline and wolframite are also found. 

'Vhile it has not been possible to form any very satisfactory idea as to the exact . ' ""~ '"'•lP•....-,'. . 

character of these deposits, it ~eems probable t~at 'they, wore formeci contemporurieo~sly with the granites in which they occur.' 

\Vhether these ores may or may not be profitably worked is a question which 

only extens~ve exploration will determine. The percentage of tin in the rock is 

small~ probably no~ exceeding 2 per cent, a and the distribution of the cassiterite in 

the rock is extremely irregular, so that a profitable exploitUt,ion at ?no time might 

readily become a losing enterprise at. another. If oPerated. upon u small scale it is 

possible that these 1oi·e ~bodies may be~'s'li:Cessfully worked. ' 

STREAM TIN. 

The strea1~1 ti~w:hich-=-o"c-curs=-in:~lc.qiuwtity in the g~lches in :this region has 

· ---occasioned-Jlflli~h~~nnoyance to the miners .jn"their·g·Oid" pa;ming- since .the early SQVen- · . .. r: .. . . - ·~:J' ~: 

ties. It wa~, as Doctor Carpenter describes, kno,vn as "'iron" until 1883. :Nlany . ., il! . ,• 

attempts ha \·e -been made to work these graycls ~J..nd .with some success, but nO cXtensi\·e shiPments have been· made .. The ti;1 oceurs in subanglilar fragments, '"~ hich . . ' . . . 

a Blake. W. P .. Tmn~. Am. Inst. Min. Eng., vol. 13, p, _691.. Carpenter, F. R., Trans. Am. Tn.~t. l\Iin. Eng., vol. 17, 

p. 572 et seq. Hendden, W. P .. Proc. Colorado Sci. Soc., vol. a, pp. ilp-350. 
ORE DEPOSI'ICS IN ALGONKIAN ROOKS. \17 

range from an inch or more in size down to extremely minute grains. They are 

mingled with many sm:;~,ll red garnets;--pieces of columbite and tantalite, and minute 

crystals of topaz. The cassiterite rarely shows the dark reddish coating so freqnen~ly observed in stream tin, but it is generally in l)lack shining fragments, which 

llre only slightly rounded and bear evidence of having been transported to no great 

distanee from their source. 

~IISCELLANEOUS DEPOSITS IN 'l'HE ALGONKIAN ROCJ{S. 

'. ,, 

At several localities within the productive mining region or?s have been 

found which may be properly described with the Algonkian lodes. They occur 

partially in eruptive rocks und pa_rtially in brecciated material composed o-f 

schists and porphyry, while at times they f~:n·!n veins which pass from one 

rock into the other. At other points they pass from porphyry into Cambrian 

rocl~-s. VVhile none of these has yet attained any great importance, there are 

two that deserve special mention. The first is in Strawberry Gulch, where a 

numbe~· of small mines have been intermittently worked) among them the 

Hoodoo, Gilt }<;dgc, ,Jupiter, Dakota Maid, and Union Hill. The ore generally 

occun; iu a decomposed porphyry in the form- of thin aurifm·ous limonite fillings 

of small fractures, or of impregnations in the adja~ent rock. In general, these 

pass downwai·d into unoxidized pyritC, ·while ·in a few cRses sphalerite- itnd 

galena have been reported. The porphyry mass in which these orcs are found 

is extremely large 'and so irregularly iu.trndcd into the schists that its relations 

to them can not be readily made out. Some of the ore obtained from the 

mines is reported to have been \rery rich, but it has so far been to() irregular 

in its occ~uTcrwe to form the basis of extensive mining. 

The 8econd locality where ore has been found in porphyry is at the Old 

Ironsides mine, near the mouth of Squaw Creek. · Here there is exposed in the 

side of the creek a sheet of mica-diorite-porphyry about 40 feet thick with beds 

of Cambrian rock both above and below. 

Through these rocks nm a series of vertical_fractures, striking about N. 85° E., 

along which silicification has occurred aild from which telluride of g·ol<l has been 

introduced into the adjacent rock. often to considerable distances from a fracture. 

Some of the ery:::;tals of telluride (presumably sylvanite) arc very large. 

The deposition has occurred chiefly in the dioritc-piirphyry, but also to a minor 

degree in the Cambria11 rocks. At t~e surface, where the rocks arc highly_ oxidized,"__;d 

gold may be·scen·along the fractures in the free conditiOn: ···~ ... ~. -

There are other places in·which. o_re. has b~nd ·i!i·enq;t~ves,~-eit.h .... Ci· :is fillings 

. of fiss~res or as impregnations, bnt-""they arc not of. any ·economic valuC. The 

eruptives, as a whole, however important they niay have been in connection with the 

genesis of the ore bodies, have not them8elves been the loci of constderable deposits. 

4987-No. 26-0~7 
• 

CHAPTER II. 

. ORE m;POSITS IN CAMBRIAN ROCKS. 

The ore deposits .in Cambrian rocks are second in importance only to those of 

the Algonkian. They have of late years produced heavily, and have closely approximated the Hmnestakc mine in their aggregate output. They may be subdivided 

as follows: 

!

Gold-bearing eongloruerates. 

Gold am~ silver ores Refractory siliceous ores. 

I'yritous oree. 

Tm1gsten ( wolf~aroite) orcs. 

Lead and silver ores. 

GOT~D A~D SILV:F~R ORES. 

GOLD-BEARING CONGLOMERATES. 

GENERAL 8TATE~liE.N'l' .. 

At the base of the series of Cambrian strata, which lie unconformably upon 

the upturned metamorphic schists o·£ the Algonkian, a conglomerate is usually 

present. It varies in thickness from a few inches to marC than 30 feet. At a few 

localities jt is entirely absent, but· in general is so prominent a :feature of the 

series that it has been recognized as·ti separate formation. Throughout the larger 

number- of areas where the Cambrian strata yet i·emain uneroded this conglomerate is characteristically about 3 or 4 feet thick and passes upward into a hard, dense 

quartzite that hits a vertical range of from 15 to 30 feet, the conglomerate itself 

being often cemented ·by more or less ·indurated sandstone of a quartzitic nature. 

It is present in this development in the vicinity of Bald .Mountain, Garden, Woodville, and many other places. There are,, however, -two localities where it attains 

an uri usual thickness. The first is known ikl ''Cement Hidgc~" and is on the west side 

?£-Spearfish Canyon; the s"econd is the region in and about Lead. In the latter 

· -lOcality 9ply it is auriferous and has yielded large amounts of gold.· The conglomeratelle~·e has a t,hiekness of from 2 to 30 feet and lies tit the base of small outliers 

of Cambri:in·s~~-t~at retilaill_upon_the.sumtjlib;-of 7divides. The region is one ~f 

prevailingly Algonkia~ rocks, into which~~sf;Cams have can·e:! deep and irregular · 

98 . 
GOLD-BEARING CONGLOMERA~'ES. 99 

gorges. The conglomerate 1s overlain by cross-bedded beach sands and quartzites, 

which are in turn conformably 1 overlain by the higher members of the qambrian 

series. It is underlain unconformably by metamorphic schists and slates. In these 

underlying Algonkian rocks is a great mineralized zone of relatively indurated 

character, which strikes approximately N. 34° W.-ahnost parallel to the lamination 

of the schists. This zone was probably a reef in the old Cambrian sea at the time 

of the deposition of the conglomerates, ·as it offered more resi.stq..ncc to erosion 

than the eneompttssing schist.~ on account of the hardness imparted to it by prCCambrian m_ineralization. 1 Upon this zone are the workings of the Homestake, 

Father de Smet, Deadwood-Terra, and Columbus mine~, and about it are the 

productive portions of the auriferous basal conglomerktcs of the Cambrian. They 

are five 'in number; on:~, comprising the Durango arid Harrison mines, is west of 

the H'omestake lode near it~ southern extremity; the other four, east and north of it~ 

include the Hawkeye, Monitor, Gold Finch-Gentle Annie group, the Bobtail Gulch 

groups, and a fifth mine on the divide between Deadwood and Blacktail gulches 

(sec Pl. VI, p. 214). The g·old-bearing conglomerate occupies depressions in the old 

Algonkian surface, but thin:':! out to nothing along the strike of the Homestake lode,' 

~here the higher mr:asnres of the Cambrian "lap over onto the miner~.fized rocks Of 

the Algonkian. A general downward inclination of_ the Algonkian snr'face toward 

the northeast also exists, but a·s this corresponds to a northeastward dip in the Cambrian it is probably due to later distortion of the Algonkian surface. Beyond the 

limits of the area in which this thick, gold-bearing conglomerate occurs the basal 

Cmnbrian conglomerate becomes very thin a~d quartzitic .. ]t is impossible to give 

th~ exact boundaries ~f its originaJ extent on account of the. dissected nature of 

the aretts now remaining. Lithologicn)ly _thi:;; auriferous conglomerate i.s formecl of 

rounded waterworn pebbles of quartz or Algonkian quartzite with an intersprinkling of schir--t .fragments which seem. to decrease in abundance as. one proceeds 

farther from the. Home8takc lode. It may he at once distiugnished .from tbe nongold-bearing portions of the basal conglomerate, as it. is cemented by either oxide of 

iron in the1_:\"·eathered portions or by pyrite when it has not snfi'ered alteration. 

The nonauriferous conglomerate, on the other hand, has always a quartzitic, or in 

rare instances a 8lightly calmu·eous matrix. The pyritic cement occurs in all_ the 

productive m·eas except one, and as all degrees of oxidation arc pr.esent it can he 

a::-Smned that the nmtrix of all of the gold-bearing conglomerate, was once·pyrite. 

l\Iueh of the gold in the richest conglomerates is detrital, as proved.hy its water~· 

worn. condition and. its ~oneentration near the ,.bed -rock. This gold w~defiVCd "'-.~ . 

undoubtedly 

mecb:u_1ically 

from 

deposited 

the erosion 

in dcprcssior~~"ilong 

of ay_~ifero~13 

the 

lodes 

old, 

in 

Algonkian 

~thT:(IgoDKian·-rock.<.;_and 

shore linm . Some 

yms 

o_!_---· 

~ 

-

the gold was dissolved by ferric sulphate resulting from the oxidation of the pyrite, 
100 ECONOMIC RESOURCES OF NORTHERN BLACK HIL£8. f ~ 

and from this solutiOn was redeposited in thin films in the schists below. Thii('has 

also produced an enrichment of the lowermost layer.s of conglomerate. In addition 

to these it is possible that gold was introduced with the pyrite that once form~(:! a 

·large portion of the matrix of the pebbles. To determine this, careful assays' ,;;g~e 

made in the only productive area now completely accessible-that which includes the 

Gentle Annie, Monitor, Gold Finch, and Hawkeye mines. The mode of occurrence 

may be seen in Pl. XVIII (p. 214). It was found that alo"ng definite Jines in tlie 

center of the stopes there were values of from $5 to $12 per ton in the conglomerate, while at a distance of from 10 to 100 feet from such lines the values 

sink .to between $1 and $2 per ton. Iron-stained fractures are found in "the roofs 

of these slopes. A possible. inference is that the gold which has low and fairly 

uniform values distributed through the mass is of detrital origin, and that the 

additional values have been introduced into the conglomerate together with the pyrite 

along zones of fracture. This is rendered still more probable by the fact that much 

'of the gold does not yield to simple amalgamation, the conglomerate being treated 

largely by the cyanide process. The introduction of the pyrite was subsequent to 

the deposition of the conglot.ncrates, since mineralization extend:; into fractures in 

the quartz pebbles. The pyrite is probably a replacement of the original cementing 

material, w'hich elsewhere consists o£ quartzos~ sands. 

Intrusions of rhyolite eut the conglomerate in Home places. They are much mineralized with pyrite, which is thought to be of post-intrusive origin: This would 

place. the pyritic mineralization sub~equent to the rhyolite intrusion. 

These gold-bearing eonglomcrates must have been either of fluviatile. or of 

littoi·al origin. All of the evidence is in favor of the latter view,~for (1) the rocks 

immediately above the cqngl'omerates contain marine fossils and were unquestionably 

deposited in an extensive Cambrian sea; (2) the area covered by the heavy conglomerates is very Hmall and quickly passes in all directions into regions ~vhere finer 

material with marine shells shows that the conditions were marine; hence, a land 

surface sufficient to support a dr~inage exten:-:;ive enough to deposit such hea\TY 

conglomerate could hardly have existed; (3) eross-beddcd sands and quartzites were 

deposited upon the conglomerates with perfect conformity so that they are to be 

considered as an integral part of a typically marine sCries; (4) conglomerate is absent 

from the ·outcrop of the Homestake"lode which must therefore have' projected above 

the old pre-Cambrian surface; (5). schist fragments, such as could only have been ·------., . pi·eserve_d·mear the source from which they originated, decrease in abunda~lCe as one 

~ / ·;,;.()c~~ outward from_the Homcstake lode. ·while, therefore, these were littoral deposits the.{\~~:~~-cxcerrlio:uil in-that-they ~ere-"not uniformly deposited along the 

- -----shore, but(lowere eonfin~d to the vicinity orthe outcrop of a large gold lode, and the 

detrital material from that lode 'va,s held in irregular depressions in the submarine 

surface in its vicinity. 
GOLD-BEARING CONGLO)!ERA~'ES. 101 

The points in which the views herein expressed differ :from those of previous 

writers are: (1) The recognition ot pyrite as once· the matrix of these auriferous 

gravels; (2) the reference of a considerable portion of the contained gold to the 

actioll of mineralization long· subsequent· to this deposition. 

DETAILJW DESCRIPTION. 

LlTEltATURE. 

In the only previous description of these ha~al conglomerates or "fossil. 

placers," as they have been te~·med, ¥l. B .. bc\'Cr~ux·a has described in a general 

way their geologieal occurrence and the manner in which the gold is pr~sent 'in 

them. Since gold-bearing ~ongl?merates as :feat~n·cs of stratat of very early geological periods have nowhere else been found, this paper has been widely quoted 

in many publications relating to mi~eral deposits. Since its puhlic~ti~n many of 

these mines have been worked out and are now in mo.st cases abandoned, so that 

they afford but poor facilities for investigation. In not a few cases,_ however, 

examination has been possible and several important features not observed by 

Devereux have been noted. DevereuX's paper is too long for complete citation at this point, but a short statement of the main facts and the conclusions 

deduced is given below. For fmther detail the re'ader is referred to the original. 

In the vicinity of the Homestake vein in the Black Hills are a series of 

detached areas of Cam brian strata with beds of conglomerate at the base and 

resting unconformably upon metamorphic schists, from which the materials 

requisite for the formation of the congloti1erates have been .derived. They 

consist of quartz, pebbles, and schist fragments, with frequent hematite bowlders,. 

and are cemented ,by oxide of iron, but in some insta1lces tak~ on· the character 

of a breccia. They contain gold and have been extensively mined, most ·of the 

prodUCtive deposits being foun!i on the east side of the Homestake lode; a single 

depo~~t occurs on the west side. The Algonkian !:lurface upon which they rest is 

slightiy undulating and slopes away from the Homestake lode in a northeasterly 

direction, at an angle of about 10° and nearly perpendicular to the the strike of 

the Homestake lode, so that the Cambrian sediments form a wedge thinning out 

to nothing on top of the Homcstake lode, where the cap of rhyolite comes in 

contact with the vein matter itself. This proves that the thinning was not due 

to subsequen~ erosion. Toward the ei1st this wedge-shaped mass becomes rin1ch 

thicker. A section (fig. 12) is given to illustrate this. The richest deposits wer~ 

mined from the divide between Deadwood and Blacktail gulches. The gold was a 

mechanical deposit of water-worn scales and "shot" gold, riCher near the base of 

the conglomerates, so that only the lower"5 o'r 6-f;;~t paid for milling and mining. 

il Trans. Am. Inst. Min. Eng., vol. 10, pp. 465--475. 
I 

! I 

102 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

Local channels and depressions in the Algonkian surface caused concentrationS 

and enrichments, hut the richest portions were sometimes found a little to one 

side of th-:- center of depressions, as if caused by wave action. Alternations of 

rich and poor ·material occurred, due to currents. Tlic gold was in a finer state 

of divisiori than that in the Homestake vein and carried less silver; probably on 

account of the solution of silver by sea waters ut the time- of deposition and the 

solvent action of the ferruginous solutions that formed the matrix of iron oxides 

that cements the pebbles. Intrusions of porphyry produced heat. that later 

assisted this solution. The proof of this is that the gold near the porphyry was 

either completely dissolved out of the conglomerate or exhibited a pitted surface 

clue to solvent acti(Jn. The gold was almost always coated with a film of iron 

oxide. A further proof of the solvent action of the waters on the gold is that 

.it is often ChCmically precipitated in thin, continuoll:s films· in the schist~ below the 

Conglomerates. Placers of recent formation occurred in Deadwood and Blacktail 

~Schist ~Cement mines 81 Porphyry Iiiii Potsdam 

gulches, and were 

formed by the disintegration of the fossil 

placer;"! ahovP- and, 

\Vith the exception of 

Blacktail Gulch, by 

additional accessions 

FIG. 12.-Approximate geological section from Homestake eastward. (After W. B. from the erosion of 

the Homestake ledge. 

free-milling methods. He 

Devereux.) 

Cement gold yields 89 to . 93 per cent extraction by 

then concludes as follows: 

••If we now endeavt;>r to group together the facts noted above, it does not seem 

a difficult undertaking to form a history which ,ball give a rational account of the 

successive geological changes which took place. First, we have the proof that the 

gold grain~ and the contained gold were in existence, in much their present condition, 

prior to the Potsdam period. Then, we have the Potsdam seas washing away the 

debris resulting from the disintegration of the quartz veins, and depo8iting it in 

deeper water in accordance with ib various .specific gravities. At the .':lame time the 

. g~·adual. wave action earned the gold to the bed rock in the same man,ner that it is 

f?Cttled in a nlincr's pan. The Homestake vein~ ,by reason of its g~·cater durability, 

formed a reef or Jo;v island whiCh never became deeply submerged. After a time 

these sediments became in,sular, and as such remained undisturbed, gradually becoming· cemented into rock until the-recent eruptions of porphyry took place causing 

·intense local metaphoric actiOn. The gold, which up to th1s time suflerecl perhaps 

loss in ::-liver on!y, now became itself partially dissolved where the solvents were 

sufficiently powerful, and was .again at Jea~t partlally precipitated as thin films in 

the .:o;chi~t~ heJow. 

"'Once more a pe1:iod of rest occupied the t.ime until the crosiye action of fresh· 

water stream:o; cut through the upper strata and began to disintegl'atc the mati;ix of 
• 

GOLD-REARING CONGLOMERATES. 103 

tlw gold and ~+fforded ·material for a new concentrating process. Disintegration and 

concentration has been going on until now, when the_hand of. man has hastened the 

work of nature. 

"This gold from the conglomerate, which found its way down the slopes to the 

gradually lowering bottom of Deadwood Gulch, was joined with new supplies brought 

from the Homestake vein through lateral gulches, and the re,ult was the great Deadwood placer. That in Blacktail Gulch, however, received no new accession and 

remained a placer, which had received its gold entirely from the Potsdam sediment." 

The remainder of the paper i~ devoted to the refractory siliceous ores and does 

not concern the present discm;sion. 

J_,OCA'l'J0!'-1. 

The area in which the auriferou~ conglomerates occur is a restricted one, 

emb"rncing only a little over 2 square miles, extending from the southern edge of 

Lead northward to the northeast side of Blacktail Gulch. The accompanying map 

(Pl. VT, p. 214) shows the location and extent of the area, also the ,Hstrilmtion \ . . of the gold-bearing- conglomerate. 

' 

TOPOGRA!"IlY. 

After the erosion of the cover of Paleozoic sediments which formerly overlay 

the region ~tream:s trc~ched deep and irregular gorges into the scllists, slates, and 

quartzites of the Algonkian. The deepest of these is the gorge, Deadwood· Creek, I 

which flows .toward the east about a mile north of Lead and empties into Whitewood 

Creek at the city of Dead wood. Through Lead a pamilel gulch of less depth, 

known as Gold Hun Gulch, extends toward the town of Pluma, where it empties 

into \Vhitewood Creek. Poorman Gulch is a transVerse valle.v that runs northwest 

into Deadwood Gulch upon the west side of Lead. Blacktail, Sawpit, and Treasure 

gulches, join Deadwood Gulch from the northwest. Bobtail Cluleh and a corresponding valley on the south side of the divide that intervenes between the two 

first-named streams empty into Deadwood Gulch and Gold Run Gulch, respectively. 

GEOLOGY . 

Al.GOXKIAN, 

As the Algonkian rocks have been descnbed in detail in the fo~·egoing pages 

they will npt be again referred to here except with reference to the Homestake 

ore body. 

The Homestake ore body consists of a series of brond lenticular masses .. o.f 

Algonkian rock in part silicified >Ind impreg·nated with pyrite. It forms a broad , 

band in the schists of ·an average width of 150 ( ?) feet and strikcsal5ont N. 34° W., 

approximately following the schistosity of the Algonkian series. 

Taken us u whole this ore body form.s a long zone that pitche::i in a general way 

toward the southeast and bas, on account of the induration imparted to it by 
104 . ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

minernlization~ been much more resistant to erosive action than the inclosing rocks. 

For this reason it probably formed at early geologic periods a prominent feature in 

the old pre-Cam brian surface. 

,. CAMBRIAN. 

Upon the crests of the Algonkian divides 'that separate the streams above 

described ;est small detached area" of Cambrian strata. The pre-Cambrian surface 

was of an undulating character, and in the depressions of this surface lie the thickest 

and richest portions of the auriferous conglomerate. Passing verticalLy upward 

from the_ Algonkian the conglomerates are overlain by fine-grained, cross-bedded, 

and ·now consolidated ?each Sand containing many scales of mica; some argillaceous 

matter, and little, if any, carbonate of lime. These in turn pass into quartzite, often 

cross-bedded and containing subsidiary layers of conglomerate, none of which a~tain 

any considerable thickness. Still above the quartzite are beds of variable width, 

composed of a banded, somewhat impure dolomite of crystalline texture, now stained 

red and yellow by oxide of iron. Above· this in turn lie argillaceous and often I 

slightly glauconitic shales. Over the shales is a heavy cap of line-grained rhyolite, 

which is often connected with dikes that extend upward from the Algonkian through 

the Cambrian. The regularity of sequence is interrupted by two disturbing conditions. First, the rhyolite cap often takes a slightly downward flexure so as to cut 

out much, if not all, of the Cambrian rocks; and, second, the higher portions of the 

pre-Gam brian surface rise so that co~glomerate, beach sand, quartzite, and finally 

dolomite and shales lap over onto the Algonkian measures. 

DISTRIBUTION OF THE CONGLOMERATE AREAS. 

Ou the divide west of the Homestake outcrop and between the heads of Poorman and Gold Run gulches is a broad trident-shaped area of Cambrian strata with 

its three prongs extending eastward along the tops of the ridges between Bobtail 

and Homestake gulches. ·The northern arm lies above the ·De .Smet cut, and its 

connection with the main area ha~ been severed by erosion. The central arm is 

capped by a remnant of rhyolite sill, mentioned above, the porphyry forming three 

elevated knolls connected ,by a narrow ridge of the same rock. The Cambrian is 

here very thin, and the basal conglomerate b almost entirely absent, the dolomitic 

shales being separated from the schists by only a small 6-inch layer of pebbles. The 

southern arm is short and broad and is intermpted by a rhyolite sill and capped with 

a remnant of the same rock. The rhyolite has been eroded from the main area with 

the exception of two small outliers. Along the western edge of this area the conglomerate is from 4 to 6, feet thick, but increases toward the southeast to 15 feet; 

thence it pinches out so that the dolomitic beds lap over onto the western side of the 

Homestake outcrop. At the head of Homestake Gulch the conglomerate is absent 
• 

I 

GOLD-BEARiNG CONGLOMERA'rES. 105 

except for a fe·w in?hes scarcely worthy of mention. On the central arm the conglomerate is also absent. On the detached northern extremity, between Bobtail 

and Deadwood gulches, it is lacking in the 'immediate vicinity of the DeSmet and 

Deadwood-Terra cuts, but appears just east of them, and thickens as it is followed in 

a northeasterly direction until it has attained a thickness of perhaps 20 feet. -, 

Another large area of Cambrian is that cast of this and situated between Gold 

Run and Deadwood Gulch. At the western end, in the neighborhood of the Caledonia eut, the conglomerate is absent, but it ~hickens to the ea8t until about 400 feet 

from the Caledonia it has attained a maximum thickness of 8 or 12 feet. Eastward 

from hiwe the AlgOnkian RUrface rises slightly ngain, and the conglomerate, while 

present, becomes so interrupted by beds of quartzite and com;olidated beach sand as 

to have afforded no woi·kable deposits. The rhyolite cap is 150 feet thick between 

it and the Algonkian, but t~ere is a considerable thickness of Cambrian. South 

of Gold Run is another exposure where conglomerate wit!) a thickness of 8 feet 

has been found. North of Deadwood Gulch is a wedge-"haped area of Cambrian 

extending southeast onto the narrow divide between Deadwood, and Blacktail 

g-ulches. T~e conglomerate here is upward of 30 feet thick, but is interrupted by 

quartzite beds at the east end of the divide. The Algonkian surface dips northeast 

and is lower in elevation than on the south side of the gulch by upward of 150 feet. 

In the head of Hidden Treasure Gulch the conglo~erate is 'reported to have been 

very thick. On the north side of Blacktail Gulch the Algonkian surface slopes 

northeast, and 22 feet of conglomerate is here found considerably lower in elevation 

than that south of the gulch. An extensive sill of rhyolite, 350 feet in thickness, 

covers all of the country to the north and comes down to, and in places through, the 

conglomerate. 

There are five localities at which auriferous conglomerate has been mined (Pl. VI). 

The only deposit mined on the west side of the Homestake outcrop-is that which lies 

just west of the porphyry knoll upon the southern arm of the Poorman Gulch area. 

There arc here two mines, the Durango and the Harrison. The· Durango is opened 

bv a shaft which is north of the Black Hills and Fort Pierre Railroad, and exposes . . 15 feet of conglomerate lying upon the Algonkian schists. Pyrite forms the cement 

of portions of the conglomerate. Not far east of the Durango is the shaft of the 

HaiTison mine, in which is also exposed 15 feet of gold-bearing conglomerate. The 

Algonkian rocks that underlie these deposits are reported to slope upward on the 

east, and the conglomerate itself, as expOsed on the east side of Poorman ~ulch, 

is much thinner, so that it is probable that this coarser material lies in a northwestwardly trending depression in the Algonkian surface, parallel to the Homestakc 

outcrop. 

The next deposit of conglomerate is that which lies east of the Caledonia cut and 
106 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

upon it there are three large mines-the Monitor, at tho head of tho •mall gulch 

which connects with Bobtail; the Gentle Annie, at the head of a northwardly flowing 

stream that joins Deadwood Creek, and the I-Iawkeye, which comprises a large set 

of workings on the southea•t side of the ridge. These mirics haye been operated 

upon a bed of conglomemto rnnging from 2 to 12 feet in thickness:, and lying in 

irregular channel-like depressions in the Algonkian, from which the rocks of that 

series rise sharply to the west and more gradually toward the east. The larger ' . portion of the conglomerate is cemented by pyrite. The Monitor workings comprise largo stapes, often more than 100 feet in width, and sometimes over 12 feet in 

height.. In the Gentle Annie mine a sill of porphyry underlies the greater portion 

of the conglomerate and gradually rises toward the south. Tho gold in these minos 

occurs along definite lines and usually beneath an even bed of loosely compacted, 

slightly argillaceous sand. In the roof of the stapes many intersecting fractures 

can be. observed, but their directions were not accurately determined. 

-The third productive area is situated upon the northeastwardly sloping 

Algonkian surface of tho divide between Bobtail Gulch and Deadwood Creek. In 

the vicinity of the Deadwood-Terra mine this conglomerate partakes of the nature of 

a· breccia. It b all of the oxidized \"ariety and the pebbles are imbedded in a matrix 

of iron oxides. It comprises three mines-the Deadwood-Terra mine, nearest to the 

IIomestake ore body; the Omega mine, lying to the northeast, and the Pinney open 

cut, which has been excavated from the yery narrowest part of the divide upon a 

portion of the conglomerate which was exposed at· the surface, but has now ?eon 

completely removed. 

North of Deadwood Gulch, and on the divide between it and Blacktail Gulch, is 

· the fourth and richest area of gold-bearing conglomerate. Upon this area there were 

operated three mines-the Baltimore and Deadwood on the extreme eastern end of 

.the divide, the Esmeralda. upon the north 'ide a little to tho west of the Baltimore 

and Dead wood, an4 the Hidden Treasure 1nine on the western edge of the area. 

None of these mines i::; now accel:lsible, but the conglomerate in the Hidden Treasure 

mine is reported to have yielded extremely large amounts .of gold. The Algonkian 

surface slopes upward gradually toward the northwest, and is reported to have tin;tlly 

~ncountercd tl northeastwardly trending rise, which cuts out all but the upper 

measures of the Cambrhin serieS. The conglomerate at this point is not now to be 

seen, .tJut is reported us of great thickness. -# 

·The ·fifth area is on the north side of Blacktail Gulch, northeast of the last 

aRmed. It comprises the 1\fine:f\·a and the Deadhroke mines. From the tunnels of 

'these two mines, which run northerly from the base of the hill slope, the Algonkian 

surface slopes sharply downward toward the northeast. At the entrance niost of the 

~onglomerate is cut off by a capping of rhyolite which comes completely down to the 
I 

GOLD-BEARING CONGLOMERATES. 107 

Algonkian, but it thickens to more than 22 feet at the northern end of the mmes, 

about 600 feet northeast from the entrance. Part of the conglomm'ate in the 

]\'linerva mine hi still in an unoxidized or pyritic condition~ but the larger portion 

of it is cemented by iron oxides. 

Of these five productive areas the richest was that upon the divide between 

Deadwood and Blacktail gulches. Some of the conglomerates taken from there, 

according to Devereux, yielded $50 per ton. a Ore from the Pinney open cut, on the 

didde between Bohtail and Deadwood gulches, is also reported to have been·very 

rich, and likewise some of that taken from the Deadwood-Terra mine. That from 

the area east of the Caledonia open cut was characteristically lower in gold coritents. 

That on the northeast side of Blacktail Gulch does not, as·a rule, yield more than $4 

'"per ton, while in the Durango, on the. west side of the Homcdake vein, -it is also of 

low grade. 

LITHOLOGICAI, C011POSITION. 

The gold-bearing conglomerate is composed, as stated by Devereux, of the 

debris derived from the disintegration of the Algonkian rocks. Rounded, waterworn bowlders and pebbles of quartz and\ laminated quartzite are the most common, 

and range in size from one-half of an inch to 1-foot in diameter. The larger ones 

are iwt very frequent, and a fair average size for the·majority of pebbles is probably 

·from It to 3 inehcs. Many smaller and many larger ones occur, but they are insignificant in number. Fragments of sthiSt~ often 3 or 4 inches in length and more or 

less rounded, occur intermingled with the other pebbles, but they are not abundant. 

They occur with greater frequency in the Omega and Hawkeye-Piuma mines than 

in the Dcadbroke and Minerva-that is, they are in greater numbers near the old 

shore line from which they were derived. <Devereux mentions many pebbles and 

howldcrs of hematite, hut none were ~bserved by the writer. Between the pebbles 

and schist fragments are many small, rounded grains oL waterworn sand, scales of 

mica, and smaller pebbles. The whole is cemented together by mi"tterial \\'hich, in 

the gold-bearing m·eas, is in large part either ·pyrite or iron-oxide, while the noniold-bearing portions are cemented by a quartzitic matrix. · 

., PYRITIC CONGL0)1ERATE. 

When the matrix is pyritous the conglomerate is ~xtremely tough and br~aks 

with difficulty. The spaces between the pebbles are often incompletely filled, so 

that ·cavities arc left in the pyrite with the.ir interiors coated with drusy crystal~ 

of the same mineral. Such c~tvities as this ar~ fr~quently encountereQ. in ~nineral 

deposits formed by the replacement of one mineral by another where the aggTegate 

volume of the material introduced .is less than that removed. TPcy may be considered 

an in~portant proof of replacement action. Extensive bodies of this pyritic con· 

tl Trail!;. Am. lust. Min. Eng., vol. 10, p. 468. 
108 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

glomerate a_re found in the Pluma, JV[onitor, and Gentle Annie mines and isolated 

patches occur· in the :Minerva mine on the north oide of Blacktail Gulch; also 

in the Durango mine on the west side of the H~mcstake lode. In othc~ words, 

all of the area;~ where the auriferous conglomerate has been mined show greater 

or less· amounts of ~n. unoxidized pyritic matrix, the single exception ,being the 

Dcadwood-Terra-Pinney urea, bet~een Bobtail and Deadwood gulches, ,\v~ere the 

cement is whqlly Jimonitic. This pyritic matrix was not observed by Devereux, 

probably on account o£ the limited amount of dcvelopnicnt attained at the time 

his observations :were made. 

COXGLI.DIEH.ATE CEMENTED BY IH.OX OXIDE. 

Of the gold-bearing conglomerate already mined probably four-fifths of the 

total bulk has been oxidized. This oxidized conglomerate has a eement of ir01; 

oxide, sometimes exhibiting cavities, but most frequently constit,uting a moderately 

hard~ uniform material of reddish to dark-brOwn color. In cases where oxidation 

has gone very far, the conglomerate is loosely compacted, but in general blasting 

is neces!:lary to remove it. In places it has been resilicified by waters that have 

' penetrated it along lines of fracture. 

The continuity of these conglomerates is 'frequently interrupted by beds of 

quartzite, often cross bedded ttnd containing subsidiary layers of pebbles; also 

by bands of loosely consolidated somewhat clayey sand in thin flaggy layers, 

which contain many scales of mica. Such interruptions are always accompanied 

by a decrease in the gold contents. Iu places quartzite beds become so abundant 

that the conglomerate gradually dwindles to nothing. Again; there may be two 

beds Qf coarse, ferruginous conglomerate separated by a parting quartzite. In 

general, however, the gold-hearil).g port}ons of. the conglomerate lie in more or 

lesS channel-like depressions, and a transition latera11}' into quartzit~ and sand 

. layers, where seen, is accompanied by a rise in the Algonkian surface. 

ALTERATION OF THE CO:SGLCl.'!fERA'rE. 

There is little que~tion that the matrix of all of these ores w~s at one time 

pYritic, for _pyrite is still present O\~er extensive areas. It disappeU.rs gradually as 

one passes into the oxidized material occurring in isolated patches in all but one of 

the areas of oxidized conglomerate. 

The process of oxidation'is st.ill going on in many places. In the Pluma mine a 

drift had been run through completely fre~h pyritic conglomerate and was left for 

some years. The walls are now coated with a thick layer of glistening c~ystals of 

inelanterite, many of them of singlllar beauty and perfection: A fine whitish-gree~ 

layer of the same mineral is often present and may be identified by its slightly acrid 

taste. This indicates that ferrous salts are the first to form in the oxidation of the 

I 
GOLD-BEARING CONGLOMERATES . 109 

. pyrite, and such is in accord with recent investigations by Dr. H. N. Stokes. As 

will be later apparent, these sulphur-iron compounds have an important bearing 

upon the sOlution and repr~cipitation of a portion of the gold. 

TilE CONTAIKED GOLD. 

The gold is known· to occur in two conditions: detrital gold and chemically 

reprecipitated gold; in addition much of it may have been introduced with pyrite. 

:<.tECHANICALLY DEPOSITED GOLD. 

Apparently the detrital gold was in the early dm·elopments the most important 

source of value in the ores. Of it Devereux remarks:" "The gold had all the 

characteristics of 'placer' gold and was generally what is called 'shot' gold, or 

smooth, rounded grains slightly flattened. I observed one nugget of nearly 3 

pennyweights in weight." 

The writer has noted occurrences in which gold, such as that described, was 

found in ·considerable quantity. A nugget of about the size of the one mentioned was ~een embedded in the iron-oxide cement. It is well rounded and 

nearly one-half inch in diameter, and is of undoubted detrital origin. Many fine 

scales, showing the characters of waterworn gold, may be seen in addition to the 

coarser grains. As a rule; gold can not be seen in the conglomerate either in 

the sulphid'e or •. oxidized variety without the aid of panning. The distribution of 

this detrital gold through the cong-lomerate is dependent on two conditions: First, ' . . 

that of specific gravity; se?_<;,~ld, that of th_e alternations of rich and poor materials 

·due to varying conditions of deposition. The gold occurred largely near the bottom 

of the conglomerate and not far from its contact with the schists. '"In general," ~ 

says Devereux, "only 5 or 6 feet"'-in,_tliickfi.CS-s~ pay for mining an~ milling." 

It is usually distributed more thickly at the bottoms'of _the stapes immediately overlying the slates. Devereux remarks: a -.....::..~- :.._~=-~~= ~--~-.:.. 

".In general where conditions had been such as to allow the subsidence of other ~ · 

materials of high specific gravity the gold was most abundarlt; ·ordinarily with large _ /~----~~ quartz bowlders or with pebbles of hematite. The latter were seldomJound without . 

gold being >Lttached to them, the pebbles themselves having a smooth polisl!ed sgrface. / 

In general, the position of the gold was always sueh aS to point to its great sPcCj_~~· " 

gravity as the locating cause and not to solution or precipitation. In fact, the many 

Curious positions in which I observed the gold were such that no satisfactory explanation could be found except the one noted a.bove. ·Upon one quartz bowldeJ.:·, :which 

had lain directly upon the .:;chists, I found, after removing the decomposed talc ±)·om 

the bottom, that graiils of gold of almost exactly the same size were arrangeU"'i.n 

ribbon-like layers in such quantity that half Jill ounce <:ould probably h>we been co,'-" 

ered bv the hand. EaCh gTain of gold is generally covered with a thin coating of 

oxide ~£ iron·, which needs a blow to-loosen. it." 

a Tram<. Am. Inst .. Min. En.:., Yol. 10, p. 469. 

r 

- -----.._,_ 
• 

110 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

It is to be regretted that the writer wa~ unable to see more occurrences of 

detrital gold in ,these conglomerates, but the mines arc now but little V{orked and · 

such oPerations as arc being carried on invo.lve leaching in cyanide tanks, little or 

no free gold showing in t,hc ore. The opinion of Devereux, however, as to the 

detrital nature of the gold is based on a wide range of observations made while 

engaged in 1ilining work and may therefore be assumed ~<Y be accurate. Furthermore, they are in accord with such observations and panning tests as the writer was 

ahle to make, and there seems to be no doubt that a large port,ion of the gold in 

these conglomerates, especially in the richer workings in the pyritic or oxidized 

condition, is of detrital origin and has been derived from the erosion of the Algonkian 

lodes. 

CHEllliCALLY H.EPREClPI'l'ATED GOI,n. 

A number of aSsays made by Devereux seem to show that the detrital gold 

contains less silver than that irl ihe neighboring lode ore depp~its, and this is in the 

li~e· ~f ohSernttions in other regions,(/, placer gold generally being purer (-containing 

less silver) than that oceurring in veins. This is usually attributed to the greater 

solubility of silver over gold. Devereux supposes that the solution may have been 

due to the action of sea wate'r at the time of deposition, or of later ferruginous 

waters. The former is possible bl1t not susceptible of proof; for the latter 

Devereux himself cites instances where thin films of gold ar_~ _p_!esent- along the 

lamination planes in the suhists below the conglomerate, and-.. gives instances where 

as much as 10 feet of bed rock paid for mining and ___ inilling; yhc writer has also seen 

depos;its in the Dead broke· mine where ~~\hists for a ~th- ~L3_feet below the ory 

are reported to carry about $3· per ton in gold .. _Similar eonditions u.re also said 

to obtain in other oxidized loca_l~tiet-;;=--No_.J:'¥:,~aR..,-has been sho,vn, the matrix of the \ 

conglomerate is pyritic. As;ttiis was oxidized ·from the surface downward solutions 

0f"'ferrie:su1phate,_,)_Y-9.!!ld~bf'iormed by descending surface waters, which 'vould take 

up iiwsolution ·both gol¢L.and silver. At> this ferric sulphate came in contact with 

pyrite the dissoh•ed-,;{etals would have heen precipitated, the gold more readily 

~ than the silver;1owing to the superior solubility of the latter. Thus, the bottom of 

. \ _ the.conglornft:ate ·beds and the underlying schists 'vould have been enriched by the 

--repf8cipifll.tion of the gold, hut -the Rilvcr would have been carried farther; 

/ 

GOJ,D IXTHOJHJCED WI'l'H PYRITE. 

)t is cvid~nt that the ip,tro~u~tion. o£ the pyrite into the c~nglomeratc~ is . . . tpy:result of mi~eralizing a~tion subseq~ent to deposition, for it oceurs in -fractures 

/in the pebbles and cm~tains. c'a,~itics. lined with crystals, such as may frctJnently 

be observed in replacement deposits. That gold was actually introduced with the . . . 

. . /"/ 

/ 

J ·a Tran~. Am. lnRt. Min. Eng., vnl. 9, p. fo:'lti •. 

/ 

• 
REFRACTORY SILICEOUS ORES. 111 

pyrite seems probable, but is htudly susceptible of definite proof. The facts 

bearing upon this !?oint are as follows: In the Hawkcye-Plnrna mine there is .a 

stope 500 feet long in which large pillars haye been . left to. ~mpport the roof. 

The conglomerate is from 5 to 8 feet thick and is larg·ely oxidiz~d, hut passes 

into the pyritic variety at the north end. A seric~ of assays made in this stope 

f!howed values of about $0 to $8 per ton eon fined almost entirely to dJle pillars,_ but 

no values in the sides of the stope::; higher than $2 per ton, although in many 

instances there was little Change in the character of the conglomerate. T'vo other 

stopes in this mine showed the s~une phen~nnenon. Fractures, stained with iron 

and somewhat si!icitied,_ occur in the sandy material that fonu:-; the roof. In this 

ca~;c the rock is riehm· where the pyrite is most abundant-that is, along the medial 

lines which appear to he lines of fracturing and hence chatmels for the admission 

of solution:-;. Unfortunately, it doe:-; not seem possible to determine what proportion of gold in the pyritic conglomerate b detrital or was there before the pyrite 

was introduced. . There is also a possibility that some of the gold in the lower 

and unoxidized portions may he rep~·ecipitated gold resulting from seco~dary 

concentration. 

REFRACTORY SILICEOUS ORES. 

GENERAL 81'A Tb'.J!EJ.Y'l'. 

Of all the ?res occurring in rocks of later age than the Algonkian the refractory siliceous ores._ have thus far been the most in}portant, factor in the gold production of the northern Black Hills. Their yield has increased rapidly and is now ~ =~ . 

equal to about two-thirds of the output of the Homestake mine. They exhibit a 

very marked uniformity in ocC_urrence and may be con:sidered to be of rather 

unique character. ','->-*-.:_,~~~_;·~~ 

These ores have been variously termed ''Potsdarn.~gold ores" a and "Siliceous 

ores," the latter munc' having prevailed more widely thtih~the_$?~!!t.::dno-mining~arld"'":~ 

geological circles. 0£ these the name" Siliccon.., orcs" alone, based upon the minera-0 

logical composition of the ore, is inapt, as it does not serve'to distingui~h the ores. 

:from others wh~se charactcris~ic quartz~s~ gangue io unaccompaniee\. 1,~ refract~ry /_ 

eh•u·aeter. Agam, the term '"Potsdam'' 1s to be· excluded, hecausc the~Cambrmn4 / · 

rocks of the Black Hills region have been recently proved to belong to an age earlie-;:;_::_c 

than the Potsdam. The term "refractory" is open to the least objection, in that 

amalgamation hat' proved uniformly tmKatisfactory in the treatment of this class of . " 

orcs. lt does not, hO'I\-'evcr, serve to exclude those orcs of a more ba~ic composition which are· of frequent oc_currence. For the purposes of this papct·, then, the. 

tP-rm "'refractory siliceous ores" ha.s been adopted aS expressive of the most strik--...., 

ing features of the ores and as lea."t at variance \•lith the· names now m use. \~ 

a Trans. Am. lnst. Min. Eng., vol. 2i, 1897, pp. 404,428. ~. 

/ 

.~ 
\ 

112 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS.· 

I 

The ores are widely distributed over a broad, irregular. belt extending from 

Yellow Creek on the southeast to Squaw Creek on the northwest. This belt 

includes five produethTe areas, which have been severally designated as the Bald 

M~:mntain area, Lead area. Yello\V Creek area, Garden arctt, and Squa\\"' Creek 

area, the last named being little more than n prospect a and situated at the junction 

of Squaw and Sp~arfish creeks-' 

The ore is an extremely hard, brit~lc rock, composed largely of secondary 

siliCa. and ca~rying, when unoxidized, pyrite, fluorite, and other accessory mineral~. It occurs in flat, banded masses, in which the banding is continuous 

with f,he bedding planes of the adjoining strata. The1je masses possess a regular, 

channel-like form and follow zones of fracture that vary in their general' direction 

in the different districts, but have. a very· uniform trend in any single productive . 

. area. 

These channel-like ore bodies are known as "shOots" and have a width of 

:frOm a few inches to, in rare instances, 300 feet. The length is· in all cases many 

times greater than tho breadth; and in one instance reaches nearly three-fourths 

of a mile. The vertical dimensions vary from a :few inches to ~ maximum of 18 

feet. The average thickness is about 6 feet. The ehannels generally follow 

either single zones of fracture, which ·arc parallel to their longer ~iameters, or 

broad areas of parallel or intersecting fracture. A series of typical~cross sections 

of these ore shoots may be seen in Pl. XI (p .. 214). --·< 

The country rock in 'vhich the ore occurs i~:~ a dolomitic limestone of finegrained 'crystalline texture and varying, like the ~,-""'in·-it.':l degree of oxidation. 

It is termed "sand rock" by the miners. In its fresh condition it is a dense, 

gray, crystalline rock showing~n..;_mcrablo ___ s_mall cleavage faees of dolomite and 

generally interrupted by bands of greenish-black shale of varying- width. When 

oxidi~~<!.)t-has~a ...... deey·cd~color, '""" but presents the same glistening facets, while 

~ith very advance,dUlteration it passes into a~ red, earthy material termed "goug·e:~' 

~~,......._ Dolomite beds· of thiS eharacter' have sO far been found to contain oro bodies at 

~- ~ tw~ positions jrl the Cambrian series; the first being immediatc1y over the bttsal 

~. ql~~..r~tzite_,Jfrtr?~.15 to 25 feet above the Algonkian schists, and known as the "lower 

~C~ntact. 'j/ The second is from 18 to 30 feet helmv the Scolitku.~·, or ~o-call_ed "wormeaten'' ,.sandstone that forms tho top of the Cambrian series, and is termed the 

'' uppel- contact.~~ Other beds-of dolomite occur at intel'\1'ening levels and httve 

~As thi~ paper goes to press the writer 'is in receipt uf !l pape; by c. C. O'Ilarru, in which this Squaw Creek ftren, ,'< . 

where the Cleopatra mine is situate~l,' is shown to have become !l 1very important producer since thC writer vi~ited the 

~gion. 

/ bA small !ldditional area in Spruce Gulch hilS been shown on tht map, but the ore~ here found arc so lll\lch 

more Jmsie than the normal siliceous ore und are Or such small importance th!lt they are omitted from this 

di.<-cussi011. 
REFRAm'ORY SILICEOUS ORidl. 113 

prod need a little ore at some few localities. They have .been hut little prospected; 

more exten:-,ive exploration may show them to be frequently mii1eralized. 

The beds that form the roof of the ore arc generally shales of ~t more or less 

impervious character, or not infrequCnt~y sills of eruptive rock. 

1 The floor upon wbieh the ore rest~ i::; sometimes the basal Cambrian quartzite, 

but in many eases varying thicknesses of dolomite intervene l>etween it and the ore. 

ln Ruch cases the widest portion of the shoot is directly beneath the iinpervio.us ro0k 

of the roof, the solutions having spread out and replaced the dolomite to the greatest 

distance along the under surfaec of the rock which checked their upward _progress. 

In a few instances the or~ lies on a -floOr of eruptive rock. On the upper cont~ct 

the floor is either' dolomite or shale. 

The.gradc of the ore is different for the separate productive districts. For 

the main or Bald Mountain area and for the Garden area the average yield is 

about $17 per ton; for the Lead and Yellow Creek areas it is possibly $45. 

The ores are mainly ores of gold, but oecasionally carry quite high values in 

silver. 

DETAILED DESCHIPTION. 

LITl<~ltATURE. 

'.Vith three exceptions the litera~ure relating to the refractory ores is of a 

very fragmentary character, such reference as is made to them being only incidental. 

The first of the three exceptions referred to is a p>1per by W. B. Devereux," entitled 

'"The occurrence of Gold in the Potsdam Formation, Black Hills, South Dakota." 

This paper is mainly concerned with the auriferous conglomerates described in the 

·foregoing pag~f5, but in,dudes a brief discussion of these ores, at that time but 

little developed and less understood. ln this papei·.occurs the following description: 

'" * * · * Several milesdi:::;tant gold occurs in the same formation in considerable 

q·uantityl and with such characteristics as to justify its being classed as a chemical 

constituent. 

"This locality is known as Bald l\l(li.tiltain, and comprises ·ari ef~v:~'tCd area of· 

several square mil~s~ through which quite an cxt;llsi\~C mineralization has taken place. 

The same geologlca.l features' are here met with that I have already described; a hase 

of schists, upon which arc typical quartzites, from which the sedimentary_chara_~ter 

has been almost obliterated by metamorphic action. These are penetrated in evm.:y.-..___ 

direction hy porphyritic dikes, the overflow from which has, in places, formed high -. 

peaks. There is generally a small stratum of conglomerate next to the schist, but 

the sediments were generally quite fine. Through the area mentioned m·es of gold 

· and silver are quite common, although l do not know that their treatment has proved 

to he a financial success. The ores seem to he impregnations; and not confined. to 

veins with well:defined walls. In fact, tr.ue vein quartz is rare, and r am not sure 

a Trans. Am. InsL Min. Eng., voL 10, 1882, pp. 46fr-475. 

4987-No. 26----04--8 
114 ECONOMIC RESOURCES 0~' NORTHERN BLACK HILLS. 

that I ha,·e seen any, althongli some of the quartzite would be taken for <gmrtz if 

examined without a knowledge of its occurrence. The tdl\~er occurs as chloride, more 

rarely native. and il:i confined to small fissures in the rock. Copper stain i~ also 

common. Gold occur:; nathTe, but in so fine a state as to be seldom visible. I have 

noticed it as a brown sponge in cavities in the quartzite, and ,,rith no metallic appear~ 

ancc until compressed with a knife, wheu it immediate1y a:;;surned the luster and color 

of ·gold. These cadties arc very common in the quartzite and arc gener.dly lined 

with quartz erystals. 

'•The ratio of gold to silver i~variable, and ranges fron1 a small pen:eutage of 

the total value to half. Continuous hodies of rich ore seem to be rare, although speci· 

mens gidng high assays can ea..,ily be ohtained. From it.':i appearance the sponge 

gold described should he nearly pure, hut I have never been able to tcot it. At the 

time of my obsernttions, which was se,~eral years ago, the developments through the 

region were very limited, and 1 was nnahlo to form conclusive opinions reg-arding 

the character of these deposits. Certain facts sceme<l to he pointed out: First, that 

the metallic. constituents seemed to be segt:egatcd along certain strata through which 

there seemed to have been less resistance to the pas.•mgc of the minera1 solutions; 

secondly, that in these planes there i.'l a concentration along certain vertical planes, 

which planes ar'e contacts of the quartzite with. porphy\·y dikes. Almost all of the 

opening:; showing ore conform to these two comlitions. I ha\~c sampled portions of 

decomposed porphyry which were yery rich iu "sih·er, and gold or silYcr seelned to 

be found in almost every opening made along a certain plane within certain limits. 

I have also examined these dikes below the ~ontact of the quartzite and the schist, 

and fonnd them, to a certain extent; lines of mineral segregation.. It, therefore, 

seems doubtful whether the minerals came from below, or were derived by segregation from the sediments themseh·es. I am inclined to think that hath causes were in 

operation. In one place we found that the lower sedimentary stratum was highly 

charg-ed with oxide of iron, and that a sample gave over twenty dollar,; in gold per 

ton, although it was so fine that no gold could he obtnined in the pan, an almost· 

universal characteri.':.itic of thet5e or~s~ aml one tvhieh bars the use of the simple stamp 

mill 'vitbont amalgamating pans for reduction. 11 

In this statement Devereux has cmhodied two, 1·ery important facts: First, 

these 9.re2..-Q.c_cur in certain we1l-detinecl bed::;; and, second., they follow definite 

·vertical planes 01: di~~~ip_n~"· ... .q • .fuoO .so~fal-:~ ~~· he connect~ these ,~ertical planes or 

directions with porphyry dikes the evidence does not support hi~ assumption, 

nor does the ore usually o~cur in quartzite. Furthermore, the instances in which 

>nttti~Vc gold -r; found have proYed to be very exceptional, and only one or two 

very doubtful occurrences ha,~c come to the observation of the .writer. a The fact 

that the ores are difficult to treat hns since been thought to be due in part to 

the coh1hination of the gold with tellurium as well as to its very line state of 

division. 'Chloride of silver luis heen reported from a ,·ery few of the siliceous 

u In the Hidden fortune mine, north of Lead, native golll ocrur~ in great abundance in the ore, hut the condition~ 

here muy be con~ldereJ somewhat exceptJOnul, ~o that the above ~tatement is ~tccnrate for ~til other occurrences. 
REFRACTORY SILICEOUS ORES.;· 115 

ore bo'dies with relatively high silver-c,mltent, but is' Rn extremely rare constit!lent 

of these orcs. 

The sccoml paper relating to these ore hodie:-: i8 that hi F. H.. Carpenter~ ·and i':l 

entitled '"Ore Depo8it~ of the Black 1-Iills of Dakota>~ '

1 UnflerJhe heading '•Contact 

deposit:-:;" Carpenter desvrihe-:; the ores a8 replacement:; by silica and pyrite of the 

limy portion.-:; of the cc.mtry roek, whh:b he dc3crihes as l:'andstone or <lunrtzite .. 

He draw8 attention .to t:·-~ fact that they are in no sense due to the filling of • - I 

preexi~ting c~vitic~, anrl fntther t:tatcs that golll is more widely developed 'in the 

lower, anil sih-er in the upper, strata uf the Cambrian. 

The eruptive rocks arc J'Jnshlered ~Ls of earlier ag0 than the ore ~ep_u.-,it.iotl. 

The orcs are described as jntht:'~tcly associated with the igneous intrusions to which 

he considers they owe their origin, and he belieVeS that the refractory OJ'CS' Wilf be 

found coextensive with the distribution of the intrusives throughout th~ Cm~lhrian 

rock:-3. 

Tho .conelusions o£ Carpeutcr iu regard to 'replacement, aH well a.::; other uf the 

essential :features of this paper, hm·c been_ confirmed by recent investigatio.u, .but 

certain modificatiOn~ have heen suggested l1y studies of tho writer. Tho l'a:'les in 

which the siliceous orcs are mineralized quartzite are confined to a few localities 

where the· latter roeks cont.ain unusual ·amounts 'o£ carbonate of lime.. Tho 

majority are undoubtedly mincralizecl dolomite which, in some cases, contains 

sufficient quantities of i':iftndy material to he terll~t{l a c:~lcarcous sandstone,' hut it 

is rather impOrtant to recognize that the original country rock before mineralization 

was rt limestone, and that the grade of tho ore ha8. been lowerCd in thC same pr~portion that it was contaminated hv sallliV or :-:;halv material. Sollie. confu':liou seems \ ... ... ~ 

to have existed on this point in the mindi':i of most early "Titei~s .. 

As regards the rebtion o£ ore bodies to· eruptives, it i~ quite' true that they 

occur only in tho vicinity of the latter aml are of later int,roil.uction,' but that 

the orcs arc the effect, and thc-eruptivCS 'the cause, has llO't been 9-enionstrited. 

The thir~l and most recent discw;sion~ these ores is jn .. a paper-hy .!!~. C. 

Smith;" cntitle<l: "The Potsdam g-old ores orthe,Black- Hilb of South Dakota." 

Parts of thi~ paper have been quoted in full in the following page:-3 . ... Professor Smith ·discUsses the geology of the siliceou:-3 ore::; of what_he_terms · 

the '"northern connected district," an area that includes the. Bald n.-ionntain t;~ 

of .his paper, but ontits the Yellow Creek, Lead, 1aml_ Garden- areas. He then ·, 

adds a discussio:O of the orcs,· of which the following is a short dige:-it: 

The Potsdam ores are "thoroughly reorganized sandstones showing, under tho 

microscope, _many druses -lined with innumerable quartz cry:'Stals, and containing 

a Trull>< .• \.m. In,;t. ~Hn. Eng .. vol 17, 1S89, pp. 582-588. 

I>Ibi<l., vol. 27,1897, Pi'· 420 etseq. 
116 ECONOl\1IC •REt:!OUROES OF, NORTHERN BLACK HILLS. 

calcite and fluorite.,, He rlivide~ them Into blue or •unoxidizerl and red or oxi;lized 

ores, giving analy:-;e:-; to prove the origin of the latter from the former. and Ht:tte:; 

that hoth Vt~:rictles are "very hrittle and hard to break or pulverize." He finds 

Py many careful aJutl,v:-<e~ tellurium and gold ami s1h·er in q_uantitic:; reqni~ite 

for the formu.tion of telluride~ There are two ore-hearing hed~ or honzons. In 

dil:'cu:-;sing the ongin he :o;ays -the •' nnneru.lization i:-; unUoubtedly rcferahle to the 

igneom.; action: which is ~'~<> stroiigly marked m their vicinity.'' This ,eonnection 

he' de~eribes in detail as follows: •• \Vhercver rnineraltzation of the Potsdam hcds 

hal:! occurred it can alway.-, be traced to a quartz-porphyry or rhyohte dike or 

'}:·ertical,'. which itself' ito usually mineralized, staiued with oxide of iron, and ::-.o 

much· broken and decomposed that its rock character it~ distinguislmhlc with 

difficult)'." He then further discns.:,e~ the influence of the mtrmn,·es and adds 

certam conclusions which, as they do not Lear directly on the question at is5ue, 

ar'e 'here omitted. 

rrofessor Smith's descriptions and conclus~OnH as to the charaeter of the ore 

have been fully borne o~t by later investigation, and it sePms probable that the 

refractory character of the ores is in part due, as he supposes, to the"' combination 

of the gold with tellurium. The orc.'l are 1~ot, hO\Ve\·er, .. thoroughly reorganized 

sandstones" except in so far as the replhced dolomite lm:-. Hhown locaily a slightly 

sandy character. His 5tatement as to the relation of ores to the eruptives it:! also 

incorrect, since the so~called ~·verticals, are fractures, not decompos_ed dike~. 

An additional di:scussi!Jn of these ores WR':3 pnbhshed by the writer ll just 

prior to the year in which the fieldwork for thi? paper was completed, hut aR 

the results there "et forth are largely embodied in thts paper they will not be 

further discussed. 

HISTORY AND DEVJ<;LQPl\IENT. 

The following brief history of the ores is found in Professor Smith's paper b 

and is quotcd-ill__0ll: ." 

"The history of the~P-otsdam ore;·~~~~tences m 1877, when :Mr. A. ,J. Smith, of 

Portland, S. Dak., located the Empire mine on Green .i\lountain and later th~ Trojan, 

Perseverance, and Indispensable in thp 8ame dcmity. In 187B the first e'nginc wa~ 

_ -"'ereCteCf tO suTpply power for the treatment of these ores. \Vith it an arrastrc was run 

~ ~- upon ores from the_Empire mine averaging about $35 per ton. The Having in 

precious metals was little or nothing, anil the attempt wa:-:. discontinued ufter about 

two months. In 1880 the Portland l\lining Company, owning the Portland., GuE-tavu::~, 

and Pilgrim mming claims, huilt a mill (which still stands idle near the olrl town of 

Portland) for the treatment of these orcs by pan anutlgamation; later this eompan)' 

purchased the Empire, Trojan, Indispen~ahle, Per::;e\·crance, Folger,· and Olh·e 

''Ann Ne\\ York AI'H!l ~ci \ ol 12, pp ~"97-Jll 

h Trun~ Am In~t )lm Eng, vol 1.7, pp 420-4:.U 
• 

Rl<~FRACTORY SILICEOUS ORES. 117 

claims. Pan al-mtlgamation ~aYed ahout 50 per cent, of the sih:er and 30 per cent ~f 

the gold, and various other proce%eS, such as •• free mil1ing, '' kiln roa:-:ting, chlori-

. nation, and eyanide lixiviatiun were tried without success. In 1:--18:1 the \V clcOme 

J\.Iining Company passed through a ~imilar history of unfortunate metallurgical 

experiment upon their property near the head of Fantail Gulch. In 1880 th8·Bnxton 

mill was built by the Buxton :\lining Cmnpauy, and expcrunenb·• made there hy ).lr. 

0. P. Ankeny, hy the usc of hromine, scemctl to lmvc,stopped just short of success~ 

. probably on account of clisadvantages which at the present elate would riot ~urround 

the experiment. Ah(Jut thi:-. time the l"iliceous ore-, were sncceH:o.fully treated h.)~ the 

Plattner prol'C/"'S In the metallurgical department of the School of l\Iinc~. In 188H the 

Gol<len Reward Goltl J\Iining Company erected a plant in Deadwood for the treatment of the Pot~dam oreB hy harrel chlorination, commencing in April; 1891, with a 

ca}mcity of 50 tom~ per clax. In 18!10 tlH' Dcad,vood antl Delaware Smelting Company huilt the smUll experimental silwlting plant in Deadwood which ha .... Rmcc grown 

:;u larg-ely. Two year::. later, or in 1~!12, a ':lmn.ll vyanide plant wa::. erected in Deadwoo<! hy the Black Hills Gold and ~:xtractwn Company. and in .Novemhe1, 18B5, the 

Kildunan J\Iilling Company ~tarted ehlorination works at Pluma, S. Dak. (a short 

fhstu.nce from Dl:"adwood), with a capacity of ahout 75 tons per day. 

'' Quring the time from the fh -:;t disaHt.rous attempts at the trPatment of the Potsdam ores until more :-;killful exper imeut had firmly c::;tabli::.hed the Deadwoorl and 

Delaware and the Golden_ Reward plants, although considerable amounts of orC were 

sl1ipped outoide of the Black Hills for treatment, the fact that ores of le" value than 

about $30 per ton eould not he mined and shipped with an\' profit, together w1th 

a :-;uper:4itious feeling that there wa~-; Romething '· unc;mn~-~~ ahout the:-.P ores and 

that they could not he treated succcRHfully, pre,·ented an active rlcn .. dopment of 

the Potsdam me bodie:-;, Only within •the last three yeart-. haYc the old eonditions 

heen changed, anrl minert-. can tiO\V generally ohtain a profit from ores carrying $15 

}Nl' ton. Naturally the earlier mines in the Put::;dam ore hodw~ were located "=here 

the Potsdam rocks were eas1est,of attack, in the Yicinitv of Green ami Bald mountams and to the ea::-t of Terry~ Peak in Ne-\:ada, Fa.ni:aii. and \Yhitetail gulcheH In 

the,e localitJes the three large companieo .which handle the Pot~dam ores (the Deadwood and De la ",rare, Golden Rewar,d.. and Horseshoe) own and operate a )~rg~ n~HJ!her 

of yery valuable mines, and- smaller companies and individual owners hold the 

remainder.,. .._ --~ ·- H • 

PHODUUTIO~. 

The ohtainahle 'data on the prodnCtwn of. these orcs are ,of the most meager 

de&criptwn. The report of the State mine inspector lor the year 1897 gives the 

following: 

Prodnctwn of sil1ceom< ore m northern Blu.rk Hdl.s 

.Golden Reward .. _._, ___ -~-· ..•... ____ .--···- .... ___ ·----· .. -.·:.______ $6R2, 205 S2 

Dea~wootl and Delaware ........... __ ... ___________ ..... __ ... __ . ___ .... 504-1 000 00 

Horl:le1'1hoe •••••.. ____________ --------- .. ·--·-----·····---------··-······ 304,500 00 

Bonant:a ..... --- _. ___ ...... _ ............ __ . _~ __ . . ... ___ . __ ....... _. _ _ _ 134, 561. 24 

Wabp No 2 -------···--------- 182,84fi.l2 

'' 
• 

118 ECONOMIC RESOURCES OF NORTHERN 1lLACK HILLS. 

Dtvtdend .....................•............................. --,----.--. 

Cltnton and Ashland ..................... __ ....... __ .................. . 

Carrol Group. __ ..... ___ ....... _____ ... ____ ... _____ ...... ___ ...... __ .. . 

Ha:.rrxson ......•••••...•••• -- ....••••• --- ••••.....•••.......•••• ------

Little Blue ........... ' ..... · ............................ ~ ..... ____ .. ___ _ 

"'a~p :\Itning Company ....................... __ ........... __ .... ____ .. 

''rasp ~o. 4 •. __ •.•.•••• ___ ••••••• ___ .••••. __ .. _ .••• _ ••••••• ____ ..•• _____ ' 

Rua .................................................................. . 

Balmoral ...... ---- .......... -- __ .. ---- ........... __ ........ · .......... . 

$6~,017 54 

60,il80.09 

50,000.00 

41,106.80 

52,000 00 

4,500.00 

•1 .Buxton---------------- ······------,-----------·-·········--·········· 

1, 200 00 

20,000.00 

16,821.38 

10,897.71 

12,000 00 

24,152 38 

E\·a H ................. -- ....... : . -- ... ---- ................ --.-.--- .. . 

Yellow Creek Gold l\Iming Company ...... -.. --··· ......... _ _" ___ ......•... 

Total ..................................... : .................... :. 2,1,64,287 58 

As the total 'gold output of the Blaek ·Hills for the same year is gh~en as 

$5,631,237, it will be seen that the siliceou' ore' production for that year was 

abo\lt two~thirds that of the Algonkian ores. Since this report it has steadily 

' increased. 

• CHARACTER AND POSITION OF THE BEDS IN WHICH, THE ORE OCCURS. 

PHYHTCAL CHARAG'TER 

The rock in w~ich the refractory .siliceous ore occurs 1~ a crystalline magnesian limestone or dolomite. It form~ bed:-:; of variahle thickness at difi'erent 

positions in the Camhrian series. and i:-:.. knOwn amo~g the miners as "sand rock.~' 

· .1"l£ac:roscopio appeurance.~Jn ib -fresh and completely unaltered e~ndition it 

i::5 a ·dense. massive rock of light hluish-gray color. ('On:-.isting chiefly of an aggregate of small glistening grainl:l of lime-magneHiutiJ <.:arhonate, among which ar9 

Rcattcrerl minute masbe~ or eryt:;taJs of pyrite. Little irregular tlecks of glauconite often gi\~e it a greeni.::;h tinge, hut they nre rarely preftent in .sufficient 

abundance to hecomC a <.:onspicuow; feature. Alternating with the heds of this 

dense, nmrhle-likc rock is d~rk, ireenish-hlack ~hale, which ig arranged ~ome,times 

in even, parallel haml::.;;, and sometimeH in extremely irregnlfir or di&torted patcheH. 

In some places the.ge shale band:-:; _arc Ro nearly ab~ent that the rock resemhle-, 

a finc-grai~ed homogeneouf- marl1le with thin lines or trace~ o£ Hhale in just sufficient amount to hring out the ~tratified nature of the roek. In other ca:,e~ the 

shale beds arc much thicker and not infrequently occur in sueh ahundance that 

the str~ta partake more of the nature of highly dolomitic shah•. than o£ cry&tnlline iimestone. All gradations exist ~h?tween thc~e two extremes, hut. the prevailing oct:urrence i.s where the dolomitic herl"' arc in the preponderance. The 

shale kwdt:; are· then extremely thin and !lt ntrving di&tanceH from one another. 

They often c::xhibit a very marked ero~;. hcdding aml hrmg out Clearly the ~erli-

'0 

' 
REFRACTORY SILICEOUS ORES. 119 

mentary origin of the rock. Regularity o£ banding b,"howcYer, rarely continuous,. 

for it is interrupted by .crm;hed and contorted layers, by irregularly distributed 

little faults, and· often by a confused hrecciater\ structure. These brecciated 

structures· become at times very pronounced, so that the stratification is com~ 

pletely obliterated, and the broken .fl·agments ~re often rounded in such a way 

as to give to the rock the appearance of a conglomerate. 

_3Ilcroserpir; rppearance.--Ulld~r · the microscope the ore-hearing rock, or 

dolomite, is seen to be of two different mrieties: (1) An aggregate •of interlocking anhedraa of dolomite, none of them po.sses!5ing crystalline boundaric·s; 

and (2) an aggregate composed of rhombs of dolomite, all of them compl~te 

crystal individuals. 

Dolomite of the first variety is composed of an aggregate of anhedra of 

dolomite impinging upon one another with extremely irr~gular boundaries. 

Among these are scattered irregular rounded grains o£ quartz, ma!5scs or cry::otah~ 

of pyrite in the unoxidized varieties, minute speck~ of magnetite, irregular 

patches o£ green glauconite, and an occasional mass of ralcite. The main hody 

of the ·rock b made np of the dolomite. ·It clearly shows rhombohedral cleavage, 

but never, even when strained; i~ there twin lamellation. Calcite whep present 

can be readily ,distinguished from it hy this means. The rounded grains of 

quartz s~ow all the attributes of detrital material. and probably remain as, they 

":ere prior to the marhleization of the rock. They sometimes occur in great 

abundance. In the' speeimcn taken from the Two .T ohns mine, they are segregated into-.. detin'ite layers where they formed· almost no per cent of the roek. As 

a rule they 'are, howm~cr, much less frequent in their occurrence and at times 

a1·e completely ahsent. The magnetite 'occurs iu sudt excecdingl~· minute u.tas~es 

. that it can with difficulty be recognized. l+lauconite is present generally in a 

small quantity. It forms irregul.~uly 'rounded masses of con.'3iderahlc size, showing the usual aggregate polarization, and. almost invariably in a very fresh con~ 

dition. In one or two of the most highly oxidized spcdmens it, Shows ~ign~ of 

decomposition. The pyrite is absent from oxidized specime-ns, in which the iron 

content i.'3 a limonite distributed along intcr.~tices het.ween indi\"idnals of carLon~ 

ate and alOng the C\enxagc cracks of th~ same mineral. The aggregate amount 

of iron is probahly insignificant, u~though the rock b often yery deeply ~tai11ed 

with iron oxide. In sume specimens, notably those frorn heds ahm~e the De 

Smet cut, and from the Belle Elrlridge mine hi Spruce Guleh. the microscope 

re,·eals fragments o£ shells and small irregular plates perforated with many 

minute holes. The latter are prol~alJly some form of Foraminifera and their 

aAnhedron is here u~ed to designate a mineral grain nr indn·idnal which, wh1le it is crystulhne in its internal 

structure, so that it polanze!:> light, etc, has been preventc!l from duYolupmg crystal faces hy the pre~encc of contiguous 

grains of the >arne or other minerals. It sil:llply fills up the irregular ~pace between the other mineral grains . 

. • 

. ' 
120 ECONOMIC RESOURCES 0>' NORTHERN BLACK HILLS. 

,presence indicates that 'the rock originally consbted of the rcm~ins of organ-, 

isms, the greater part of which have been completely obliterated by sub~equcnt 

marbleir.ation. 

A micro-photograph of this rock is shown in Pl. X, A, facing p•ige 214. 

The second \·a~iety Of structure olJserved in the dolomite is that where tPe 

rock consists o~ an .agg,rcgate of' automorphic e.rystals 11 of dolomite. Indusions 

and staining by oxide of iron ha::; produced dark bands in these crystab, that 

give to them a marked z;otlal appearance and hriug out distinctly the thoroughly 

crystalline character of the rock. These rhombs arc sometimes exceedingly small 

1tnd. of uniform size, but in ()ther instances irregular bands 'of larger individuals 

. arc distributed through the roek. (Sec Pl. X, B, p. 2H.) In other respects this 

variety show.s no essential differences 'from that first dcseribed. 

The first variety of dolomite or "sand rock" i:; mor_e common on the lower 

contact, the second on the upper. The two, ~owever, grade into each other and 

~re not to be distingui~hcd without the aid of the microscope. 

Alteration . .....::..The ·alteration of the dolomite produces a progressh·e serws of 

changes in the appearance and condition of the rock. The fir~t mineral attacked 

is· the pyrite, which becomes rapidly oxidized. The ·limestone then becomes 

stained with oxide of iron, so that it changes to a deep Venetian r~d, or yellowish 

brown.' The, flashing cleavage ·faces remain unaltered, and, together \vith the red 

color· and peculiar eve~1 texture, give the rock a very peculiar and easi.ly recognized appearance. The black shale bands become stained to dull •'ed by iron 

oxides, and where very impervious freque-ntly exchange their black color for a 

light gray.. The glauconite does not seem to have been much affected by altera· 

tion, being frequently found in the most decomposed specimens. It i::~ impl'obable 

that all of the iron oxide that stains this rock urises from the decomposition of _ 

the pyrite; much of it has· probably been introduced by oxidizing waters that 

have ~eeped downwnrd from the Leds above. 

The next step in. the oxidation of the rock after the pyrite has been rem oven 

and the rock stained red is the grRdual solution of a portion of the carbonate:-;. 

By th~s means' the rock lose~ its masshTe structure and Passes into a red or 

yellow earthy mater.ial composed of disintegrated fragments of lime and magnesiu~ carbonate, limoni~e, i1_ICiuded sand grains, and whatever clay originally 

existed in the rock. This completely decomposed material is known to the 

miners as •• gouge/' and is especially well developed on the edges of ore bodies, 

even when the ore and wall rock are comparatively unoxidized. One of the 

most noticeable features of this gouge-like alteration i::~ the prominence given by 

it to the banding of the rock. The dolomite bands become darker by reason of 

the introduction of iron oxide, but the Shale bands, on account of t,heir impervious 

"-Crystalline mineral grains which have fully developed crystal faces are termed automorphic. 
REFRACTORY SILICEOUS ORES .. 12i 

nature, retain the greater portion of their original material ttnd are therefore of 

light~r color. Thus with~ the increasing alteration the banding of the rock ha:s 

hcen rcndcn~d more pronounced, and it is often supposed that red ores· come in 

shales and blue ores in the limestone. Gradual transition:;, f!owever, betw(~cn the 

gouge and the or,iginal blue, unaltered rock are frequently observable, no ~ingle 

step in the alteration being absent. At time::; the rerl. gouge has ph::served the 

structure of th~ rock from whieh it wa:s derived, so that angular fragments will 

present the appearance of a hard, massive }ime~tone, wbile ·in reality a touch 

will serve to cause them 'to ·crumble into a loose mu:-;.<..; of soft ·earth. 

CHE:IliCAL C0)1PO~lTIO:-;-., 

An analysis was made by Nil-. W. F. Hillebrand of a 'pccimen of th~ hluc 

unaltered dolomite taken from the long crosscut of the Tornado mine knowti us 

the '·' Bx" erosseut. 'l'he portion UnalyzeU 'va~ taken from a layer fr~e from 

shale hands, and sho'_Ved dolomite,_ calcite, quartZ, pyrite, and glauconite, with n 

few minute ~pecks of magnetite. A-fter~. treatment with hydrochloric and s\.\1~ 

phurie acids, the residue of quartz grains, pyrite, and tpagnctite was further 

c~:unined t~nder the _microscope. The quartz grai~t:-:< w~rc ror{nded and without , 

doubt of ·detrital origin. The pyrite was in irregular masse~ and ocea~ional 

crystals, and the magnetite in such au extremely fine state of di\Tision that it 

merely imparted to the residue a slight grayi:l\ tinge, and could only be 

recognized as ~ncb by mean~ of the magnet. 

The analysis gave the following results: 

Analy;;is of unallerPd dolomite fnim 1'orrwdo" mine. 

Per cent, 

~\~6~~ ~ ~ ~~~~ ~ ~~ ~ ~ ~ ~ ~~ ~·~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ ~ ~ ~-~ ~: ~ ~ ~ ~-~ ~~ ~ ~ ~ ~-~ ~ ~-~~~ ~~ ~ ~~ ~~~ ~ ~ ~ ~ ~ ~ ~: ~~ Fe20s ....•............................. ; ............. -....................... . 61 

FeO .•.... : ....... ------ ........•.... ____ .......... ____ -----·-- . . : .... -~--- ____ o. 47 

FeS, -·--------- ... _ .... ---·· ..... ·--- _ .. , ............ ---- ...... ,. --·-·· -·---- . 69 

1\'lnO ..... '...... -- . ." ...•..•..... · .. __ .....•.•.•............•..•. -----.----- ;... . fli 

1\lgO _________ . _____ . ____ .. _____ .•. _________ ..•... ______ . ______ • ____ ~---. _____ t4. in 

CaO .... __ . --·-- .. __ : .... _ .. -- ·-·- ........ ·-·-·- .................. -----· ..... . 26.81 

~-a~(J- .••.•....•.....•......•.•. .. : •. ...•...•..• ------ .....•..•....... _· _____ •. .07 

K 20- ...... -......... - ~ ............... · ................. : . .... :. : . ......... :. . . . 53 

I-1 20-lO,'l()C ____ . ----- .... • ...... ------ ......... : .. ------·--· .........•.. -----· . 3-! 

l-1~0+ lOil()C ............... _. ............................•.. ~ ........ _ .... _ .. _. . tli 

!'205 . ------ ~------------ -·----- .. -----------:--- ---------------------.--.----- . 08 

co, .. ----.----... -- ..... -.. ------.. -.-.----.--'------.--.-.--·.-.--.-----.. --.- 40. ll 

Total ....•... ~ •.•......... , ......•....•................ _. __ . _. __ . _ .• _ •. _ 99. 89 

It has ·not been possible to calculate the exact mineral composition on 

account of the variable composition of the glauconite, but it will at once appear 

' 
122 ECONOMIC ·RESOURCES OF NORTHERN BLACK HILLS. 

that the proportion of carbonates present is much" in excess of all other minerals. 

If the lime, magneSia, ferrous oxide, and mangan'ese oxide be calculated so as to 

combine with total carbonic acid present, the aggregate a.mount of carbonates 

represents about· 87 per cent of the rock. These elements probably do not exist 

as separ~te mineral species, but occur as isomorphous mixtures, the iron and 

manganese replacing a part of the calcium . and magnesium of the normal 

dolomite. Some distinctive calcite does, however, occur; but the amount is small. 

The formula would probably be about as follows: CaMg(l'IInFe)(CO), where 

small quantities of Mn and Fe occur in the dolomite molecule. 

The alUmina is too high fqr glauconite of normal composit,ion, and indicates 

that a small amount of kaolin is present." This wo.uld consume a portion of the 

silica, potash, and combined water. The remainder of the. alumina, potash, and 

combined water, part of the silica, considerable magnesia, and all of the soda 

and phosphorus are probably contained in the glauconite. The balance of the 

silica· is present a~ sand grains. 

The percentage of glauconite and shaly material increases with the increase 

in the quantity of shale bands in the rock, and ,as they always persist unaltered 

in. the ores, they are to be regarded· ns impurities in the normal ore-bearing rock. 

GEOLOGICAL POSITJOS OF OHE-REAIHNG REDS, 

In the Cambrian group these dolomite beds most frequently carry ore at 

two level.s, which are locally known as the ~'lower" and ~• npper ~' contacts, although 

it is probable that other beds will be found within the inten·ening portion of the 

sedcs, but such haYe not yet' been carefully sought. . 

Lmoer contact.--The lower beds lie geuerally directly ,upon the basal quartzite 

of the Cambrian and are from (i to 30 feet thick. The bands of impervious blue 

shale whieh interrupt the continuity of this rock 'i·ary greatly in thickness ~nd 

occur at i~1terva~s .which increase or diminish without reg·ularity. The result is 

that if traced for any great distance. the dolomite' beds show a lenticular form, 

passing from' a thick mass into thinner· and thinner bands until 1 they finally 

disappear in the .surrounding shales. Frequently such, lenticular heds are 

arrang·cd so that one. passes latera11y beneath the next succeeding one above, but 

dwindles -to nothing, while the higher or lower hed continues. It therefore 

happens that the lower heds vary in their exact g·eologieal position; at some plrtces ' . 

they lie directly on the quartzite and at others are.sorne distance above it, the 

intervening space being occupied by thin alternating beds of shale and impure 

limestone. · The beds of dolomit~ and their intercalated shale are in some places 

overlain· by a series of extremely impcrYious blue shnJe~, which break with a 

triangular clea\7 age and never show any indication of niineralization.· At times 

the limestone becomes so thin that the blue shales lie but 5 or 6 feet above the -· 

' 
REFRACTORY SILICEOUS ORES. 123 

basal quartzite; generally the distance is much 'greater. It very rarely happens 

·that shale horizons of this extremely i_mpervious character lie directly on the 

quart~ite. Although the aggregate thickness of these ore-bearing beds is sometimes as much as 30 feet, their continuity is always interrupted by shale beds, 

often of considerable thickness, and it is usually such a bed o~ shale that forms 

the roof of the ore bodies. · 

The dolomite beds that lie upon the lower quartzite are remarkably uniform 

in their distribution. They occur in Garden, Ruby Basin, Portlanfl, Squaw 

Creek, Lead, Yell ow Creek, and recently a drill hole has revealed them' to a 

thickness of 12 feet at the base of the Cambrian that underlies the Carboniferous 

limestone of the Ragged Top plateau. On the west of Spearfish Canyon, in the 

vic~nity of the porphyry masses known as the "needles," a tunnel has rm~ealed 

the same dolomite series. In the Two Bit district, however, in the Detroit and 

Deadwood shaft, this rock iS absent, and it probably does not occur in the region 

to the east and southeast of Deadwood. Its distribution in a direction westward 

from Lead is, however, very uniform. 

Upper contact.~ The position of the upper beds of dolomite is about 12 to 

18 feet below the Scolithus sandstone that lies near the top of the Cambrian 

series. 

There are in most of the mines on the upper cmitact two beds of this dolomite separated by 3 to .4: feet of shales. In many instances-such aS the :Mark 

Twain and the Burlington mine,_ ncar Portland-the ore that occurred in the 

lower of these two beds was completely removed before the parting of shales 

had been broken through, and the ore of the upper bed discovered. It is stated 

that in the South Dakota mine, at tbe head of Annie Creek, H.S many as five or 

8ix separate beds of ore replacing blankets of dolOmite~ 1 f<>ot in thickness, 

occurred. Two blankets of ore also QCcnrred in tl~e Divide,nd mine, and in a 

portion of the l\lark Twain 1nine the same duplication occ~rs. Occasionally 

shales which lie between beds of dolomite have been slightly silicified and carry 

aman· quantities of gold. The large proportion of clayey material which they 

co~tain has, however, prevented their complete minentlization, aud it is only in 

the purer and more massiye bands of limestone that workable ore bodies oceur. 

The dolomite beds of the upper eon tact, as exposed- 'at ·Portland, bare been 

discovered in the region of Ruby ·Basin and in the headwaters of Annie Creek~ 

but their occurrence at ot,her localities has not· been determined. Intermediate 

beds of dolomite-such as that seen in 'the Belle Eldrjdge mine, in Spruce 

Gulch-are mentioned by 1\fr. Tower as ·occurring in the. yicinity of Galena ·and 

Strawberry Gulch, but their exact position is not definitely determined~ and that 

these intermediate beds do not. earry ore when present in mineralized locahties 

ha:s not been proved. 

/ 

' 
124 ECONOMIC RESOURCES OF NORTHERN BLACK HIJ,LS. 

The two eontact~ mo.st connnoiiiy known ha,~e boon de,Tcloped hccau ..,e .they 

have been. the most easily accessible. The exploita.ti.on of the lower contact 

especially has been extremely 'easy on account of tho almost invariable occurrence 

of that series of dolomite beds' directly oYer the quartzite, thus permitting the 

use of the latter rock ~~s a basis for expl<!rati~n. Indeed, so much ha.s thi.-, 

occurrence on or ·clo.':lc to the qu'artzite been .emphasized that it ha.s hcc~mle ·the 

dognu! among mine1·s to. "sink to quartzite" before prospecting for ore. The 

Ore-bearing beds ~f the upper contact near Portland and the ore occurring in 

the~l qutcrop all a~·Ound Green MounUtin and along the l'ailroad, so that ~re 

bodies On that contact were ea~ily acce:-5siblc. The existence of ore shoots in 

beds lying· betw.een these. horizon~ IH not only possible, but prohable, _and future 

prospecting may re,veal them. 

ORE BOlHES. 

FOR)£ ASJ> SlZE. 

The ore ·occurs, ·as stated above, as flat, more· or less banded ma~ses, which 

hav~ a 'channel-like form and are parallel or nearly parallel to the bedding 

planes oCthe strata in which they are found. Such hodie.s ai·e locally known as 

"'Shoots/' a term \VhiCh it \\'ill he convenient to u:;e throUghout thiB paper for 

anJ~ single body of refract9ry siliceous ore of whate\rer form or size. 

-Viewed in horizontal projection the larger-- nuinber of :::;hoots shows a long 

lenticular :form, slightly bri>ad(~l" at 'th-e ce·nter and beconiing ··narrower at either 

end. As shoots are seldom mined to their extremities~ theSe relations can not be 

fully'appreciated from thc·map.(Pl. IX, p. 2H). Broad shoots are more irregular 

in 'shape t,han the·smal.ler hodies, and, as they arc in· reality formed by the jnnction 

of intersecting· or parallel shoots· of smitller size, have rio absolutely constant form 

(Pl. XILI, p. 214). They arc, ho\vever, generally longer than broad. Vie;ved in 

cr'oss section~ there is a complete gradation· from a narrOw lenticular shape with 

longer ~~is i;1 7t "'~rtical position to a g1:cat Hat bed remarkably conformable to the 

hedding planes of the strata and with -'it~"wicttli"';nany tim~s greater than its. thickness. Between these t1Vo extremes shoots possess va.riablti and often very irregu.lar 

foni1s. _Some of these are shoWn in Pl. XI (p. 214), which gives a series of cross 

sections- and illustrates. the gradation between large and small ore sho0ts. 

Only where ore h~dies are -very wide is there an absolute conforri1ity to the 

bedding- 'planes of the .:"t.rata, a'nd then only in the r·oof of the ore. The lower 

boundaries gei1Edally. 'cross the strata ·at an angle and. extend downward a 

great distance along the· fraCtures; above the ore usually tormhlates against a 

bed of shales that seems ·'to have been a barrier to the far~her upward passage 

of mineralizing waters.' At times when shoots are interrupted by many shale 

beds they ha,'e the form shown in Pl. XI, G (p. 214). 
REFRACTORY SIL!OEOUS ORES. 125 

The length of the shoot:s varies from a few feet to about. four-fifths of a 

mile. The Tornado-Mogul shoot, which. is probably the largest single body of 

refractory siliceou:s ore yet mined1 had a total length of ±115:1 feet. The Bottle~ 

son Khoot, including that por~ion th~t extends into the Alpha:-Plutus mine,. wa~ 

3,2\JO feet in total length. The large No. 1 shoot of the Union mine, cxelnsh·e 

of its prolmhle contimu~tion in the Ruby Bell, had been mined when visited ·t~ a 

length of 1,750 feet, ~nd 'va~ not then completely worked out. The Ross Hannibal 

shoot was 1,500 feet long; the Steward, 1,160; the Boscobel, 1,050, and the Double 

Standard, \JOO.. On the upper contact the shoots of the Mark Twain and Empire ' State· mines, 'vhich practically constitute a ~ingl_e ore body, ~how a total length 

of 2,000 feet.· Shoots having a length of from 600 to soo feet are of frequent 

occurrence, while those between 600 ·and 100 feet co~stitute perhaps one-half of 

the total number of shoots mined. In general shoots hav.ing a length less "than . ' 100 feet are not very often 

and poor to pay for mining. 

encountered: and when found are often too narrow 

Thb is especially true in the mines of' the I\ald Mountain nrea wlwrc the ore i~ not of very high grade. ln the Yell ow Creek and 

Lead areas: the ore i~ higher in gold content and occ'urs iu 1n1.wh_ smaller bodies, 

so that shoots of very small Size are often workable. 

In width shoot:5 Yary from a IULITOW film of Hilica lining the sides of: an 

almost imperceptible crevice to great flat bodies 300 feet or .more in width. The 

widest shoot mined i~ that of the Golden Reward mine on· the south bank of 

Nevada Gulch, ·,vhich. tneas1u:c~ 3±0 feet ·at ·the- broadest point: The Tornado at 

its widcot point is 180 feet. Shoots 100 "feet in. width arc of quite frequent 

occurrence, and those from 100 feet d~wn to .4 or 5 feet are 1~1ined iE___iT~any 

places. Perhaps, ~wwcYer, the most ;1sual width of ore. shoot throughout the 

region is from 5 to 20 feet, .such occurring with greater frequency than any of 

the other widths cited. The width of a shoot varies a little from point to point,~ 

and in many easet-i is greatest about midway of its course, gradually diminishing . 

toward the extreiuities. -Th~ Tornado-lVIogul shoot is 180 feet wide·sliglitl~; 11_,th . ~~ _.-o-0"___,·~ 

of the central poiut~··but ·it tiitfi·O""'s~to"'lW'feCtliCih; nort~ern outcrop and pinch~~ • 1 • · X~ 

out entirelY at the' south end. Very wide shoots like the Golden Reward are . . . 

generally form~d hy the convergeuce of many snm~ler ore bodies having slightly 

discordant trends; thus the total width is dimi_nished in any particular· dir_ection 

by the i.nti·oduction of ,,,edge-shaped areas of unrnineralized rock. 

In general, there js' no constant relation between length and breadth. Ex~ept 

in a few c~ses \vhere very wide shoots, like the Oolden Reward and the inclined 

shoot of the I~ittle Bonanza, arc nearly as broad as they are long, the length is 

many .times greater than the breadth. The longest s~oot~. are so~netimes broad, 

as in the case of the Tornado-1\logul, hut there are ~uany ca!:Ses like the .Bosc"Jbel, 

where a shoot 1,±50 feet l9ng never shows a greater width than 10 feet. 
~-

' . 

126 ECONO),!IC RESOURCES OF NORTHERN BLACK RILLS. 

The ,~ertical dimensions· arc the least variable, because the ore deposition 

being due to the rePlacement of certain more solnhle sedime~ttary beds is 

limited only b~T the thickness ·of those beds. Consequently tho thieknesi:i for 

narrow ore bodies is as great as for wide ones, at lea::<t in the same loca1ity.a 

iVhere the ore-hearing bods are rcry thick the ore is likewise thick. :From '5 

to 10 feet h a couservati\rc estimate for the Bald 11onntain area, us also for the 

Garden area. In the Port,land distriet the thickness of the ore is not -often 

more than 3 feet tutd often ranges between that and 1 foot. lt rarely ~appcns 

that .the ore in a sh.oot of any considerable siZe is continuous from tho floor to, 

the roof~ for it i8 a~most always interrupted b}; partings of nnmine'ralized shale. 

_These are termed '' wa~te" by the miners and haYe to be carefully remm'cd by 

sorting. " 1here such "waste:) Oeds are thicker than the oro there are practicaiiy 

t,vo ore shoots or h1aukets one above the other. The thickness of a shoot often 

diminishes at the rims, where the ore thins to a feather edge. Other .cases 

occur where the transition from ore to 

country rock is f'uch. that the shoot l·etains 

it., full thickness to the rim. 

FRACTURES. 

In all of the stopcs from which the ore 

ha.s been completely excavated discolored 

1!<~---~--~~~·~~,.~seains ma}"'be observed: These are gcncri_dly ~ cOt)SpicuO,ii::;~hoth..,.on-.<o..~ccount of their 

.slightly iron-stained appearance and on aceount of the resistant character of the material of which they are composed~ the latter 

FIG. 13.-Sketeh of · yerticnl" ns seen iil cross section, ~bowing the manner in which it project~ 

Irom-the·surrourtding e0untry rock on account of 

the resistant charncter imparted W the adjoining 

material b~- silicification. 

feature having frequently caused them to pro-. 

~ject from the sOfter, unmineraiized country rock. The.r may be most readily 

obs~rved in the beds oYerlying t.he ore 1 as these arc of slightly lighter color and 

·of a~ltalr":dmfUCter than those-in which the ore itselL-ocCurs~ hut if eare- ,- ... --------~~. ~uli~· followed to the si~e or end of"'tho~'stope=nitty ... htf-traced downward into the 

_.-.=~~ndcrlylng quartzite~ shale or dolOniitc, whet~cvcr mining opera-ti~ns have reyealed 

=-· the rock belO\Y the ore. These seams are known to the ruiners as "~ertical.~" 

(Pl. XII, p. 214). 

In a "vertical" there arc two features to be distinguished: 1. The original 

.fracture. 2. The mineralization along or proceeding from that frac~ure. 

The original fracture is a result of rupture due to strains· in t~e .country 

rock. ·It may have been a simple crack with no perceptible open space between 

a The exception is wh~re narrow and e.:dremely high ore bodies u.re forme(l along very open fractures, as in the 

l'enobscot mil}e (see PI. XI, 0, p. 214). 
REFRACTORY SILICEOUS ORES. 127 

the walls 01: a crevice a:n inch or more in \ridth. 

eralization the frncture is often tilled by si1iccous 

Secondly, as a result of mindeposits and sometimes stands 

out as a small ridge in _softer material, or it may be lined with quart;.: crystuls 

and not completely filled. · Often it is not clearly distinguishable· in the mass 

of the or8. As a result ·or- the replacement of the country rocl;: on either side 

of the creYicc a sheet of hard silieeous rock is formed which ·may extend for 

considerable distance.~ on either side of a fracture. 'If extcm;ivc it forms an 

ore shoot; if slight, a "~Tertical.:: Thi.s vertical is often confused with the fracture, but it is important not to confonnil. the two. The fracture admits the 

solutions' and, the ore body is fonncd by them. 

Th~ origin3.l fractures ~~rc e~thcr simple or composite. 

The simple fractures have slight displacenient along surfaces which are sometimes· perfect planes, but more fr_eqnently arc slightly warped or curved surfaces. 

No unevenness or hrecciation oceur~ along fntcturcs of this typcl and verticals which 

result from their mineralization ,arc generally extremely narrow and regular. 

A composite fracture is canBcd by the intersection of many small, irregular 

fractures running in all· planes and at all angles to one anotherl and C_onstituting a 

zone of fracture. This ean not be described as a breeqiatecl zone, because fragments 

have not been perceptibly moved froui their res:pective positions. 

Simpl~ fractures when followed to the limits of _the ore,'whcre their tr;t~es can 

be di~tinguished in the wall~ of the ;topes, show·that they are planes of movement. 

The faulting that has t{_t~en-place"'-iS hi .... ~h~ ~~lajority~of cases extremely small, but 

is almost always cle~LrlY disc<;rnible. ~t ·generally averages from ·one-quarter of 

one inch to 6 inches. The differential movement that takes place alopg such _ 

fractures may be hotli vertical and horizontal. If the movement iS -·verticat it ·is 

usually shown hy a very pronounced drag in the extremities of the dislocated 

strata; if horizontal it is indicated hy horizontal striations in the underlying 

quartzite. · ~ 

The plane~. of ,movement of these faults are, ,as is usual in·fanlt_pln.nes, .. curviri~ or slightly warped surfaccs., .. ;They..J~I:e,,:f\n·ther,~fRults""Of-blitSiight displacement;_, 

faulb of_ larger displac.ement-in one instance of 300 feet---occur! but show no ' 

edclence of mineralization ·and a're probably of later elate. 

All gradations from the simple to the composite type exi~t.. A single and 

simple fracture rarely continues for any distance as such. In many ore shoOts a 

single tis8ure, though showing a very constant direction, may change. into a. composite fracture and still .farther on split into a large nmnber of fissures not quite 

parallel, so that by gradual divergences and convergences they form an interlacing. 

netvmrk in the roof of a stope. At times the vertical, which has' resulted from 

the mineralization of a series o:f 'parallel fractures, occupies the entire roof of the 
128 

stope, the 

silicified. 

ECONOMIC RESOURCES OF NORTHERN BLACK ,HILLS. 

space betwe~n the individual fractures having become more or less 

Silliple fractures arc generally vertical, or nearly so. 

VERTICAL EXTENT OF FRAGrURES. 

Tho fractures somCtimes extend into the ro<;>f overlying th~ ore, and in all 

inStarice.s where it wa~ possible to make obseiTttiions~ could be traecd into the underlying beds. In a few cases it was possible to trace' their continuations inio the 

Algonkian rocks below. 

in the :Mogul 1pine a drift was run into the slates directly heneath the ore 

body !tself. ~~vhlences of silicification can be detected in the phyllite~ of the 

Algonkian, showiug that the mineralization extended into the rock.s underlying 

the Caruhrian, hut where the .~Ugonkian rocks are quartzite, or like insoluble 

rocks, little or no s~condary replacement can be observed. 

In the llig l\IiSsouri mine the ore-beadng heds lap over into direct contact 

with the Algonkian, and verticals can be seen passing into the schists which underlie 

the ore. 

In the .tlawke_vc-Plllma mine verticals from 3 to 4- irichcs ·in thicknes:;, consisting of red-stained silicified phyllites, and showing many dr~sy cavities, extend 

many feet helow the C~mbrian into the Algmlkian. Siliceous verticals were also 

detected in the Dividend mine, near Portland, passing from the Uambrian rock:; 

into the Algonkian. It seems, then, ver~c probable that these fractui·es extended 

into the Algonkian underlying· the Uamhrian --quru:tzite. It is to be observed 

that the Algonkian rocks are not generally composed of' :;-ohihle nor easily 

replaced,material, so that only when the fl-acture:; pa~s into soft white micaceous 

rOck~ flo silicified bands hecome prorninellt. ~Ioreo\~er, the vertical position of 

-~~ _ the Algonkian lmnination Imtkcs it difficult to distinguish banding due to secondary alteration from that characteristic o:f the original rock. · 

_ The upward extent of the fractures seems to be conditioned by the rock~::i 

through_which;ti;P.y-pa8s. That they extend at times almost,-if=not~quite, thr~ugh 

the Caml1rian ~e~"I"eS'is renilered~'prol,ahlt~o-hy=their -<>c1~urrence in those ore bodies 

which ure on the upper contact. Thi.., is at least 250 feet above the base of the 

Cambrian. Again, the fmctures which occur in the Uarbonifet:ous limestone, hoth 

in t.he lead-silver district of Carbonate and in the vicinit)' of Ragged Top 

J\T01intain, may be the upward continuations of fracttires in the Cambrian below. 

It is not known bow much farther they extended into the series that has been 

eroded away. On the other hand, there arc many instances in which the fractures 

.do not pasn through the rocks immediately overlying the lower contact ore •hodies. 

In the Huhy Bell minC verticals, or fractures, were obse;ved in the ore; that is, 

displacements along definite lines or offsets in the handing of the ore, which did 

' 
• 

REFRACTORY SILICEOUS ORES. 

not extend ·into the shales overlying the ore. In. those stopcs, Of course, where 

the ore ·had been mined out, ycrticals that did not extend beyond the ore~ bearing 

beds could not be seen, as the material in Which they occurred had been rcmove_d. 

Thus the. roof of the greater paft of the Ross-Hannibal mine .is of a smooth, 

m~cn shale, showing only a few fraCtures, and these at great distances frOm one 

another. l\iany of the wider and more extcnsiv~ ore bodies occurring itt Portland 

show the. same phenomenon.' Jn some· o~·c bodies of ~'ery ·consfde~·able siz.c. i~~~ 

fractures of an.)' kind can be observed, and it is difficult at. first to :iccount for the 

occurrence of tile ore ·body. In ·such inStances, ho'wever, i_t may. frequently be 

noticed, where ore has been left in the inine, that the han.ding shows Sli-ght 

dislocations ~tlong vertical. planes. 

·It will thus be seen that \vhilc the fractures max gencrall.)' be shown to extend 

down into the Algonkian, their .uPward 'continu~tion is sOmewhat variable; they die 

out i~ less massive beds where movement has .been productive of plastic 11C:w ;.ather 

than fracture, or where the shattering forces· ha,;c ·been stronger the.)' .extend for 

greater distances upward, and probabl.)' freque~tl.)' reach the massi"ve limestones' of 

the Carbmiifcrous. 

Al'tiOUNT OF OPENING 0~' FRACTURES. 

The aniount to which the opposite walls of fractures ·have. been .removed from· 

one another is variable. Openings_ arc either. original or l~ave been secondarii}T 

/ prodnc~d after the minei~a.!iza~ion 9f a f~·ac~nre .. Primary openings are almost 

always extremely narrow, ·thread-like crevices, t~c a(~tua.l opening between the 

opposite walls being general!.)' less than one sixtx-fomth of an inch. There are, , 

'however, a number of instances in whic9 it is as. mqch as one-eighth· to one-fourth 

of one inch and in a 'few .~ascs even -greater.·. Thus in_ the Ben Hur miJ!C a fracture 

passes from the ore-bearing beds into porph.)'ry and ,in the latter rock .~hows an 

opening of froin 2 to· 3 inches. The interspace i,; filled with large crystals of· 

quartz ttnd' ~t goo_d deal of secondary silic~. In the ~olden R~:v~u:9- .. w.ine, .whq_rc 

fractures pass into porphyry, ~!le.~pae~-.b~~~T~~f! .. adjacent 'Yttlls is as _much .as on~­

fourth inch. 

In the Alpha-Plutus mine many Of the fractures s~ow consicl_erablc openingssometimes as muc~ as one-half ir:ch in width,- and w~"en a ·fraeturc sl:tmving an 

opening of this_ size is composite, or composed of. many. -fis~ures occupying the_ space 

of a foot or more in width, the aggregate amonn~ of, op~ning Jn~y be_ Ycry great. 

Sncl~ instances as these arc, however, rare, anc!, open sr>aees- have seldom.attaincd 

any consi~erable size. Innumerahle)nstanceR,II~ight be cited wl~erc the walls·, arc so 

closely pressed together that only capillary spt~_(_!9S ren_1~!n. As a general rule, those 

fractures tha:t arc ~o he seen in large, flat_ m;e bodies are much smaller a·nd ,tigl;lt.e~· 

than those in long narrmv shoots. 

4987-No. 26-04--9 
130 ECONOMIC RESOURCES Q]'. NORTHERN BLACK HILLS. 

niRECTIOX OF FRACTURES. 

:Fractures are generally arranged in parallel groups, each group following a 

single direction with comparatively little div~rgenee. Such groups may be termed 

fractur~ systems. Two or more sueh- systems may be distinguished in aJI, of the 

productive areas of siliceous orcs. Some systeri1s show great persistence and are 

heavily mineralized; these correspond in direction to the trmld of the greater 

number of ore bodies, while othe~·s arc c.omparatively insignificnnt, arld do. not seem 

to have beeri productive of ore bodies of any size. .Fractures of the first variety 

haVe been termed ''m3.jor" fractures; those of the Roeond, "minor'' fractures. 

GROUPINCi OF FRAC'I'tiRR'3. ' 

The minera)ized fracttn:es arc. divided up into scp:irate and distinct groups, 

which correspond closely to the difl'erent productive areas of. siliceom; ore. These 

groups. ftre separated from one anOther by intervening areas in whichl as far a:; 

known, mineralize~l fractures do not occur. In any one group t~ere arc present 

two or more syStems of well-defined fracture which· preserve direction:; .that are 

constant within the limits of ·that group, but different from those of the neighboring group. 

·The spacing of the fractures within any one group is generally without 

re'guiarity. A -t;ingle group usually show:; all gradations from a spacing so close 

that the individual fractures can hardly be distinguished as such, to one ,;o broad 

th3.t an unmineralizcd area of from 400 to 500 feet intervenes bet\vcen a fractm;e 

and its nearest neighbor. 

In some of the groups of- fracture there is a close relationship between the. 

fractures and the structure of the· Cambrian rocks. Thus in some mine~ ore 

shoob- occur upon the crcstb of lmv anticlinal ridges, and the fractures from which 

they ·ha.ve originated are strongly developed, while in. the ~hallo\V s_ynclincs 

between them mineralized fractures do not oceur. 

There n:re five important groups of fractures~ two in the Bald .Mountain areai 

and one each iri the Garden, Yellow Creek, and Lead areas~ 

.The fractures in the Bald Mountain area constitute two groups occurring in the 

vicinity of Ruby Basin and Portland. 

In the Huby Basin distriet there are two systems of major fracture: One ha~ a 

direction ranging from N. 15° \V .. to north-south. The prevailing and strongest 

fissures .of this system are N. 12° W., and are followed by the long E shoot, tho 

Big shoots .:Jf the Tornado mine, the Bottleson shoot, and many other shoots of 

cOibJderable si:.-:e. The other direction of major fracture is from N. 25° E. to N. 30.J 

E. Fractures belonging to this system may var);. 5° on. the t?nc side or other of these 

directions. :Minor fractures nm N. 30° to 50° "r. and occasionally N. 65° E. Otper 

fracture~ of minor charactCr ocCur, but they arc confined to extremely broad stopes 
REFRACTORY SILICEOUS ORES. 131 

where the network· of v_ery small fractures is so i?tricate that there is no predominant 

direction. In the Bottleson shoot and in the St. Louis ore body there are other 

maj~r fractures which trend N. 5° E. In the group of mines west of the 300-foot 

fault, designated the Boscobel-"T clcome group, the fractures follow the same general 

directions, but vary possibly within wider limits than those of the Alpim-Plutus-Mog~l 

group ju.st discussed. 

In the Portland" distri.ct the preva_iling direction of the pmjor· fractures and the 

resultan_t trend of the ore bodies is between N. 20° "B~. toN. ±5° E., the most constant 

direction being a.bout N. 35° E. .Minor fractures trend north-south, ~- 50°-55° E., 

N. 130° E., .N. ·80°-86°. E., N. 13° E., .N. 30° E., and in rare instan'ces .N. 35° \V. 

Hence the prevailing trend is strongly toward the northeast. 

In the Garden area 5 general systems are important. These· run .N. :30° E., .N. 

40°--45° E., N. 55°-57° E.; N. 60°-65° E., and N. 85° E. The·rllimber of fractures 

following the other .direction::; is very much less.and they may, therefore, be regan.led 

. ,is comparatively unimportant in the part that they have played in the production of 

ore bodies. 

In the mines of the Yellow Creek and Lead' areas the Cambrian rock:; ~re so 

eompletely 'veathered that. the accurate determinatio~ of fracture~ apart from ore 

bodies 'vas not attempted. The major fructures here, as :elsf!where, follow in 

gene~al the direction of the longer diiuueter:;. of the ore shoots, but eren theSe are. 

:;omewhat small and disconnected, so t_hat it i.-, difficult to settle upon their prevailing 

direction. Presumably, however, in Yell ow Creek t_heir directions are N. 12° ,V., 

N. 60° to 80° E., N. 33? to 40° K, and north toN. 3° E. ln the vicinity of Lead, so 

far as could be a::-~certained, fraetures follow with considenible constancy the strike 

of the lamination of the underlying Algonkian schist1-:l--:that is, .N. 25° to 30° ,V. 

Other systems of }ra~ture probably exist, but "'ere not detcct~d. 

INTERSECTIO!\ Of? FR~CTURES. 

' Intersections of fractures occur both -in vei-tical and m horizontal planes. ' . Vertical intersections are comparatively rare,· because they 

fracture:; exhibit pronounced dips, ancl such arc infrequent. 

can occur only wheri 

An intersection of .this 

character occurs in the western· workings of the 1\iogul mine, and an ore body o.f 

c~nsiderahlc size is found at the jUnction of the· fis~ures.. No displacement 'vas 

-observed. Another_ place where an intersec~ion of two compoSite fractures in a 

vertical plane 'vas observed is in the "' Do~tblc Standard." mine. No displacement 

occurs at this ii:1tersection. 

At intersections in a horizonhtl pli:me di::;placcmcnts arc ·.sometimes observ~d, 

but are frequently absent. In the big shoot of the Tornado mine, on the west ~ide 

opposite the Tornado shaft, a small fracture trending N. ±0° E. can be seen faulting· 

from its direct course a large ore-bearing vertical running directly north and south.-
J ' 

I-32 ECONOMIC RESOURCES OF .NORTHEI;tN BLACK HILLS. 

·In the Clinton _mipc, near Portland, two. small parallel' fractures running 

N. 20° E. arc intm~seeted by a la~ge ore-bearing ye~tical striking N. 65° E., and the. 

two small fractures are displaced_ for a distance of_S inches. 

In the north end of the "A" shoot of the Tornado mine a st.rong manifold 

fracture, trcndiilg N. 15° .b;., which had_pCrsistontly formed a large ore body from 

ami to 800 feet, is displaced 3 to 4 inches to the ·west on the north side by. a minor 

vertical trending N. 30~ W. 

In the Donelson mine, in Yellow Creek, an cast-west vertical terminate_s against 

on~_ running dir~~tly no,rth and south, and can not be obscrvecl a! all on the other 

side. A few: oth_cr instances may be ~itcd where intersections of fractures arc 

accompanied by slight displac~ment, but it is much more usual for intersections to 

be without.itppreciablc dislocation. When fractures-intei·scct at small angles it is in 

most cases_ difficult to observe any iritersections at all, because they curve into One 

another, and so _many auxiliary crevices are developed ·connecting those ruiming 

in. one direction with those running in the other that it. would. be difficult to say 

whether the fractures had intersected one another or simply coalesced. Such interFIG.14.-!\ficrodrawingof tissure-in decomposed truchyioid phonolite, showing 

character of "vertical" 

after passing into. the pho-

·. nolite adjoining the ore . 

From a lurgc dike on the 

s~ctions become more confusing when the fractures arc of a 

; manifold and composite character. 

UELATIOX (II<' FRACTURES 1'0 ERUPTI\'E ROCKS. 

Evidence as to the rela.tivo age of fractures and eruptive 

rocks is ·conflicting. Fractures younger than. eruptive rocks 

·were obsen~ed at tho places mentioned below. 

In the south end of tho Golden Reward mine an ore-· 

bearing· fracture passes directly from the limestone and o~erIyiug Cambria.n, where i~ had. been prod.uctive. of a very C(!·,~-

. sidcrable ore body t into a slOping floor of phonolite below. 

west side of the Tornado 

or~ body. 

Tn this rock it ;tppea.rs as' a number of elosely spaced, parallel 

fissures one sixty-fourth to one-fourth of an inch in width, 

which are filled with .secondary ·silica and often ::;how narrow, vug-like cavities 

at the center and parallel with the walls of the fissure. A similar passage of a 

vertical, into a shee~ of phonolite occurs in the l\Iark· Twain mine, near Portland, 

·also in the south end of the Tornado mine (see·fig. 14). ln the No. 3 shoot of the 

Union mine the phonolite which oVerlies t~c o~·e is scam.ed with intersecting fiss_nres 

caiTying secondary silid1. In the H.Ctri~ver mine~ on· the divide bCtwecn Nevada 

arid Fantnil gulches, the or~ lies hctweeh a cap Of rhyolite and a floor of quartzite, 

and the-feeding verticals can be· tt:~tecd into the porphyry cUp '~here their ironstai.ned· appearance- ·has rendered them extrenwly prOminent. In the J\iail and 

~xpi'css mine, in Sheeptail gulch~ intersecting Yerticals may be traced "from the 

ore ii1to the·rhyolite roof, hut become extremely fine and thread-like iw the latter 

roc~. 
REFRACTORY SILICEOUS ORES, 133 

In the "1\-logulmine fraetureS extend from .the ore into the henching- dike that 

form" the wc,t wall of the ore hody. · They do not occur in that rock ·with ye\·y 

great fre,quency, however, and considering the number of fracture~ ihat occur in the 

surrounding country rock it h; the more remarkable that they are not more\/ 

numerous in these larger porphjry maSses. 

In the Ben' Hur mine a fracture in porphyry alxmt i to 3 inches wide carries 

rich ore for a considerable distance and then passes frorri the porphyry dow·nward 

into the rlolomite, which here lies· immediately above the Algonkian. 

In the following instance:::; fracturEs older 'than the eruptive rock~ \v'e"i·e 

observed. In the Tornado mine in the north end of the V. N. drift ·a fracttire 

heavily mineralized. terminates abruptly against un· cast-west dike. the silicification 

co\·ering a Slightly inCI;eaSed area at the point of c~ptact: It can be observed 

again on the Opposite siJe of the dike, hut- there is no evidence of fracturf'. in 

the Porphyry. In the Two .T ohn:-3 mine, in Sq~mw Creek, a fracture trending 

N: nso E., which had carried Ore for morC:than 420 feet, is interrupted hy two 

small phonolite dike::;. These dikes arc "about 20 feet apart, and the fractures do 

not pass through them but terminate abruptly against them on either side. The 

porphyry at the contact i". "lightly silicified. l n the western drifts of the -Two 

.Tohns mine· three ore shoots terminate agai,?st a sloping wall of dark-colored 

rh,-olite-porphyry. The fractures do not extend from the ore into the porphyry. 

A further indication of' fractures older than eruptive" is the parallel alignment 

of dikes and the northwest system of fractures in the Ruhy Basin district, 

showing that the fissures through which the erupti,·es had gained access to the 

Cambrian ~trata were probably· due to the same causes as those producing the 

other fissures of the same ::;ystem. 

From tlie data, then, it is to be infened that either. there are two sets of 

fractures, one older and one younger than the erupti\·e rocksl or thnt there have 

been several Periods·~£ intrusion. Jt ha:-; been shown that the erupth·es are d~c to 

a :;ingle period of igneous activity .during which ~nany types of .rock were produced, 

and that the transection of one rock by another may show one sequence at one 

point and the reverse at no great distance. It ha!5 abo t:een shown that 'the 

intrusions followed "lines of weaknesses developed hy orogenie movements~the 

same movements that produced the fractures. It is not, therefore, necessar).~ to. 

assume that fracture::; older than eruptive:; at one point were formed at a period 

widely. ~eparated from those which show the re,·er:-;e relationship at another. 

The £rapturing, in~rusion, ·and orogenic movement wer<? probahly coeval and 

occurred during one long period of mountai?-nmking movement::;, so that the 

di~erences in relative age of the fractures a.nd eruptives were due rather to 

irregularities in the sequence o£ the porphyries than to separate period~ of 

fracturing.· 
134 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

Throughout the northern portion of the Black Hills not .only does the Cambrian 

lie unconformably on the eroded surface of the upturned Algonkian rocks, but it 

rarely retains its original horizontal position. LO\V undulations or incipient folds of 

, irregular form are characteristic feature::-{ of the lower members of the serie.s. \Vhcn 

revealed. by the mine workings the lower beds of quai·tzitc arc generally found to 

dip at a slight angle in ~t dir9ction that is sometimes at right angles to the prevailing 

:-:Jtrike of the A.l~·onkian rqcks; at others without definite relations to them. Slight 

·dip~ in one direction soon gi\·c place to corresponding dips in another direction,- so 

that the wliole lower surface of the Cambrian is composed of a succession of depressions at~d undulations with much attendant fraeturc and slight faulting. In explana· 

tion of this yhenomenon Dr. T. A .• Jaggar has suggested that during the uplift of 

the Black Hills orogenic mov·emcnts were accompanied. hy. a difi'erential gliding 

of tho Algonkian rocks upon one another along plane.s of schistosity: This prodtlced 

an elenttion at one point and a sii{mltmie'ous d~pression at another, so that the result 

has been a general distortion of the horizonthllayers of the Cambrian. During :mch 

·.difl'erct~tial movement the harder. beds of the Algonkian have exerted a powerful 

upward thrust on the O\·crlying series, the softer adjacc'nt layers being distorted 

against the rocks abO\·e. Such distortions have been ohsen'ed nt sevCral points. 

~he mos~ striking instance may be seer; in the long \.vest crOsscut f~·om the Mogul mine, 

\\'hich penetrates the contacts of the two series. The softer rocks of the Algonkian 

are. here crus~cd ·against the overlying quartzite and distorted·, while the more rigid 

mer:r;tbers of the. same series have not· sufl'ered appreciable deformation. It is not 

h_nprobahle that some of the breccias that occur along many of the intr'!ded dikes . 

· 'arc to be attributed to t,he same cause. Such ·a distortion of the Algonkian surface 

could not but have prqdl10ed strains iri the hori~ontal rocks above, and probably it is 

in large part to such strain that the frftctnres. with 'vhich are ·assOciated the siliceon!:i 

ores, Owe their origin. 

RELATIO.\" OF 'I'HE FHACTUHES. TO THE .'lfiNEHAJ,IZATJOX. 

The mineralization that has occurred 'al~·ng the fractures manifests itself in 

·two ,different ways: First, ft has replaced the wall rock whenever that was composed 

of soluble material; .second.l it has filled sueh open spaees as existed in the fractures. 

The di~tance to which replacement has extended from the fractures varies with the 

character of the hed.s through whiCh they pass and the intensity of the mineralizing 

action. Jn compam.tively impervious _roeks, like shales and eruptivcs.·replaccm":nt 

has extended characterist\cally to nry slight distances, so that the result has been 

the production of narrow verticals .• In the d.olom~t_e or ore-bearing beds pt-oper, 

if slight~ it has likewise produced narrow shoots or verticals; if of gi·eatcr inte~sity, 

ore bodies of workable size. 
REFRACTORY SILICEOUS ORES. . . 135 

In the latter case the evidence seems to point to a limited distance for 

mineralization arising from a single fracture." In mos.t of the ore bodieS which 

occur in Ruby Basin the mineralization has not exte.nded n~ry far. Ten feet 

may -be considered a yery fair a ,·m·age.. Ore bodie~ o-f greai.cr width than this are 

dne eithCr to the coalescence oi. a number of parallel shoots or to the existence of 

a large niunber of intersecting! fractures. There are instances -where mineralization 

seems to have extended to much greater distances. Thus in the vicinity of 

Portland extremely wide shoots were seen in whieh the ore extends to at lca:?t 

59 feet on either side of a t-ringle fracture, a~d a few cases were noted where no 

fraetures at all could be detected in lhe ·beds overlying· the ore. In these cases, 

ho,vever, it is probable that the fractures terminated ii1 the ore~bearing rock. . . lndecd, such could often be inferred from offsets in the banding of .the ore, so 

that there seems little probability that mineru1iztltion hns extended to a greatei· 

distance than 20 feet from the supplying fissure. 

It will thus appear that the relation of the fractu~es to the separate shoots 

of ore depends upon the ~anner in which the fractures arc. grouped. Ore bodie~ 

occurring along single fractures are long and narrow and rarely attain a width 

greater than 20 feet; they aTe gepcrally from 6 to 10 feet wide. Instance~ of 

this kind are the Boscobel shoot, which is 1,050 feet long with an avemge \~idth 

of 10 feet, and the E shoot of the Toruado mine, 835 feet long by 12 feet wide. , 

There are also many others. \Yhere a number of fractures lie close· toget~1er, 

so that the mineralization from ·one fracture has coalesced with that from the next 

succcedit_1g fracture, shoots have a width determined by the number of fractures . 

present. Of the 1\mny large shoots formed in this way two distinct types are to 

be found. The first includes those shoots in which the fracture~ are parallel, m· 

nearly so; ·the second, those in ,vbich they intersect. ·Of the former a typical 

instance is the northern end of the ~Velcome_ mine, where a shoot nearly 100 feet 

wide is formed by a series of almost. pamllel or slightly diverging fissures (PI. 

XI~I, p. 214). Of the latter->wd in general it is by far the most usual type of 

large ore body-there are nuiny instances, of wl~icb perhaps the most striking 

is the great Tomado-Mogu\ shoot which b 180 feet wide at, the broadest point 

and over 4,000 feet in length. 

There arc few shoots of large size-unless it be those formed along a narrow 

single fracture-that conform throughout to any one of these type~; for in one 

part of a :::;hoot one grouping of fractures will prevail, and at some d.i~t~nce 

another. in general, however, these four relationS of fractures and ore are 

sharply defined and may be ·readily distinguished. 

The filling of open spaces i~ seen in a few cases, hut is then ~ubordinate to 

the action of replacement. The material that fills such spaces is generally a finely 
136 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

diddcd aggregate of silica. Whore the crevice is narrow the silica i,.-; without 

definite arr!lngement. .\Vith an inCi-ease in width it is noticeable that fine silica 

lines the walls and incrca;singly Jarge individuals occur towardr the center. giving 

to the vertical a very _diRtinct. vein-like structure. When the fractures _arc as. 

much as on~-eighth of an i11ch in width the center.i~ often left vacant and_ druses 

of quartz crystals project inwa.rd from the walls. A specimen from the Ben Hur 

mine shows a fracture 3 inches in 'vidtb in porphyry. Along the walb on either 

side is a one-half~inch lining of. silica from which large crystals of quartz project 

inward, interlocking with those on. tl:ie opposite :;ide. These cry:-;tals are oft~n 

onc-l;alf inch in diameter and It inches in length. Similar verticals of varyi~g 

width were ol~:-;erveU in" the Two ,Johns mine in Squaw Creek, in Rlacktail Gulch, 

and at other localities. Calcite, clay, manganese, and iron oxides often fill the 

. central cavities. In some of the fractures observed in Yellow Creek the material 

filling the fissure is almo:;t, if not elltirely, chalccdonic Hilica, and the cavities 

are lined with even, parallel bands of this mineral. In the Dividend mine, near 

Portland, ~nd in the D~nelson mine, near Yellow Creek, are fractures of considerable width containing fragm~nts of Algonkian slat~s and s'chists, which have ' · 

probably resulte'U from· the differential movenlf'nt. occurring along the fi:ssure:-;. 

Filled fissures rarely po:-;sess :-;ilicificd walls, for the free. circulation of mineralizing 

waters has nOt usually been fa\'orhble to the action _of mineralization. 

Besides the primary filling of open spaces,. a secondary iilling is sometimes 

found; for \\rhen fractures_ have once been mineralized they ha\'e 'not infrequently 

been· a ::;econd t.ime the seat of slight movement, and a reopening of the fissure 

has taken place. Into the cadty thus formed fillings of calcite, manganese, and 

iron oxides and clay have often been introduced, so that the appearance of a 

banded vein is not infrequent. Such ·s~condarily filled scams are especially abun-

' dant in oxidized localities, and often much of the filling material has 

\Vay ,into cavitie:; in the ore itself, 

an essential .ingredient of .the ores . 

giving rise to the erroneous belief 

. THE ORJoJ • 

• t!ACROSCOPIC CIIARACTE,If. 

found its 

that it is 

"\Vith a few unimportant exceptions, the siliceous ores are e'xtremely uniform 

in their general appearance and Structure. "\Vhen seen in large matSscs the ore is 

general!y ·a more or less banded rock, exceedingly hard and brittle. The banding 

is due to the persistence of the stratified structure of the ore-bearing beds in the 

ruinei·alized rock, the· shale bCds usually remainirig in ·nearly unaltered condition, 

while the dolomite layers have been completely replaced. Cavities of irregular 

form lined with crystal ·druses of vttriou~ minerals are in\.Tariably· present alld give 

t? the' ores a very cavernous. appearance. These may generally be seen in bodieS 

of mineral formed- by the ~aCtion· Of replacement. 
REFRACTORY .SILICEOUS ORES. 

· The hardness and density of ·the ore a!;e so great that it can be crushed only 

with great ditliculty. Its hard'and brittle character causes it to give a harsh, grating 

:-;ound when struck by steel; :;o that, even when it can not be seen, a blow with· a 

pick or other !mplemcnt will often sen·e to distinguish it from the country rock. 

The texture of the ore is dense and compac~, and the colOr· when unoxidlzed 

-·is generally grayish blue. At times a greenish tinge~ is impa:ftcd t;y disseminated , 

glauconite in minute grain~. Ores -from YellOw Creek and- the ·vicinity of Lc:ld 

are often white, or grayi~h ,vhitc, on accou-nt of the I?resenee of large fiuantitieS'. 

of barite. Sulphides sometimes occur in recognizable patches in the more cOarsel)r. 

textured ore, but generally they ar~ Present in' too· fine a s·tate of divi,o:;ion"'io be 1 

visible in halld specimens. 

MICROSCOPIC CHARACTER. 

Under thC microscope the ores at:c seen to consist of an aggregate of irregularly bounded individuals, chalcedonic silica and quartz, through which is disseminated 

'pyrite (see Pl. XIV, p. 214), generally withouf crystalline houndarie~ and in a ,tate 

of tine division. The proportion of the cha~cedonic silica to the. quartz varies, sometime~ one an.d Rornctimc~ the other. bei~g in. the p·reronder~~ce; in the majority-of 

cases, however 1 the quartz is present in the largest amount.· The si~c of the pyrite 

masses ranges from tho~e- which :tre distinguishable in the ·hand ~pecimen to such~ 

an extremely tinely divided aggregate that the mineral·i:-; scarcely recognizable 

even under the microscope. It is this extremely fine pyrite that impart.::; to the 

ore its peculiar bluish tinge. · Residual i:nass~s of glauconite, often of con.,iderable 

size, are scattered thrqugh this with greater or· less frequency. 

_The cavities or vugs are generally 'lined with druSe:-; of perfect qua-rtz crystfllS. 

Such dru~cs are generally free from pyrite and are probo,hly the latc,t added and. 

purest portions of the. silica. They are often n?t~ccaLle in the hand specimen. In 

some instances the center of a cavity is filled with silica resembling that of the main 

body of the ore. In ores from ccr_tain parts_o£ the Tornado mine original detrital 

quartz grains arc seen here and thet:e through the ore, being readily distinguishable 

on account ~f their rounded character and the fractures and cracks that pe~1ctrate 

them. Fluorite is very fre(_1uently present; it it" s~metime~ purple, sometimes green, 

and again completely colorless. It is <il)Vays irregularly bounded, except when pro-, 

jecting into cavities, when i_t is found in· eubes often of great beauty and perfection .. 

. Ore~ containing app1·cciable • amount"3 of alumina frequently show light-colored 

masse~ of transparent material that polarizes· as a_n aggregate, and this kaolirr-likc 

material i~ almos·t always pre:-3ent in'.these ores in greater or less amount, and 8Cen,l::lto vary directly with the a~nount of alun~ina. and residual impurities. In .;;;orne 

specimens ihe indi~·iduals of :-)iliea arc of difl'erent :-<ize. and, the. smaller' and larger 

arc grouped together so as to forrn dctinite hands with irregular bou11;da~·ie~. The 
138 ECONOMIC RESOURCES OF· NORTHERN· BLACK HILLS. 

1 

finely disseminated pyrite is sometime:-3 ,c.;egreguted into irregular hands and patches 

showing peculiar swirls and eddies, and often assuming subflorescent forms. (See 

Pl. XIV.) Shaly layers in the ore show the usual indeterminnble aggregate of 

finely divided minerals. Glauconite generally favors such shaly laye~s and appears 

a~ ~reen to yelloWbh-green n~asses, fre<gwntly of considerable ~ize . 

.lf1SERAL8 OF TllR nRES. 

In the order of their relati\~e .abun'dan~.;e the minerals of the ores al'C ahout 

as,follows: Q.~mrtz, calcedOnic ~ilica. pyrite, a~senopyrite·, barite, fluorite, gyp~~m, 

•siil;nitc, uranium mica (ntriet,T undetermined).' .. ' . . . ., . . Quartz (S/0 ).-Thi~ is the _most widely distrihuted anU ,invariahle ingredient of the 'ores. It occurs, a~ aho,·e described, a.::; an aggregate of tinel.r di•i'ided 

individuals, generally of microscopic size. Clear glassy c:.a:,,·stals form druse:; 

lining the interior of cavities, and u.re often very perfectly developecl. 'Yhen the 

ores are extremely tine grained the silica sometimes :;how.s a marked iridescence. 

Instances of tbb kind can he see~ in the ore in the Ho.':1s-Hannibal mine, in · 

\V'hitetail Gulch. In its orig-in the silica is both Jetrital and the product of mineralization, the latter va.riets · g·encrall.r l)ein~r in far greater proportion. The . . . detrital quartz plays hut a small part in these orcs, :~nd w4en in large proportion 

materially lo\ver~ the grade of the ore. Quartz m·ystal..; of large size seldom 

occur, those obsen·ed in the Ben Hur mine being the single exception. 

Ohaleedonic 8ilica ( Si O,+n TT, U).~Silica of this character occurs in . the 

same general relations as the quartz, all:hough it . .., proportion i~ usually mueh 

.smaller. It can 1lot be 'distinguish£.d hy the eye eXcept when it lines eadties . 

. Pyrite (Fe82) Pyrite occurs in· very considerable quantities in all unoxitlized 

orcs. It can often b~ observed in the hand specimen~ hut is most frequently 

present in an exceedingly fine state of division. In many of the ores it is so . . ' 

finely divided- that it ean not he observed without the microscope, and it1 then 

. imparts a peculiar dark~b]ue color ~o the ore. 'J;'he segregation of pyrite into 

restricted areas of the ore sometime~ occurs. An important instance of this kind 

is reported from the Hoss-Hannihal mine, in Whitetail Gulch. where a bed of 

pyrite is Said to have underlain the ore. 

Arsenopyrite (FeAsSJ.-Arsenopyrite .can never he ob~erved in the hand 

specimen. and often it is not present at all. In those cases 'Yhcre it occurs the 

. percentage varies within wide limits. but is always "less than that of the pyrite. 

If the rock be ground up and the sulphides isolated the white color of the · 

arsenopyrite may oft~n be 

be determined by analysis. 

of this mineral. 

recognized. For purposes of treatment arsenic must 

Th.e u~alysis given on page i±2 shows 4.10 per cent 

Bffrite (BaSO,), hea-vy spar.~Barite is in the greatest deyelopment in the 
REFRACTORY SILICEOUS ORES . 139 

. Lead and Yellow Creek area~. ·It occur~ in flat, hla.de-like crystnl:; which have 

.sometimes a clear glassy appearance~ with dtreous luster or a white· opaque 

~spect. In the orcs :f.rom the Lead area it is alway~ of the latter variety and in 

fiat crystals which form an interlocking aggregate and frequently exhibit ~t 

rough rarlial arrnngement. A.t times its re]ath~e abundance is so great that it 

forms more than ;')0 per cent of the ore, and the crystals arC' generally ahout 

one-.,ixteenth to one-eighth of an inch in thickness an,d one-fourth to one-half 

inch in width. Extrerriely large crystaL; one-half inch wide and g inches in 

leng-th were taken from the Hicldcn Fbrtunc mine uear Lead. Bnrite ~ometin';c~ 

oceurK in massive aggregates which may be readily recognized hy their ·g-reat 

,weight and- the peellliar pearly appe~rance of their clea\-age faces. Crystals · 

from the vicinity of Yellow Creek are generally glassy and line the iritcriors of 

cadties. This mit.eral is rare in the Bald ]\fountain and Garden areas. hut was 

found in the Boscobel ::;hoot between Fantail and Nevada gulches. It occur~ in 

large, fiat crystab \2 inches in width and three-eighths of an inch thick. lt was 

the earliest :formed 'ingredient of the ore, as the rest ot the rock masses close)y 

filled the iuterstices between 'the interlocking plates. In the ore· from the 

Penohscot mine, in the neighborhood of Garden, small quantities of this lnin~ral 

were ohserved. Barite shows no definite relation to the occurrences of the gold, 

hut it i~ one of the mo:-::t widely distributed mineral:; in those areas that have 

prod';!-ced the richeHt ores, and b an indication of very strm;g mineralization. 

Flunrltl.' ( 0rr]i?2).-Fluorite is ~n invariable ingredient of the ::;iliceous ores, 

nlthough often in very small r:tnnntity. 

cavities in the ore. Ore from the 

It frcllUent1y oecnrs in cubes lining the 

Ro::;s-1-Iannihal mine shoWed clusters of 

white, transparent cuhes one-sixteenth of an inch in diameter. In some instances 

it is a briliiant-grccn ·color. b~1t most frequently occurs in cubes of a bright 

purple. These are especially well developed in the Bald Mountain area. Besides 

the ·distinct crystals, fluorite is disseminated throug-h the hody of the ores in 

fine microscopic masses which never possess r.rystalline boundaries. \Vhere the 

ore i:; in contact ·with other roeks, such aK porphyry or :shale~· fluorite often 

extends bej~ond the ore and lines .the c::witie-:; and crevices in the adjacent rock. 

{i-ypsum ( Ca80~).-Gypsnm, though not a common ingredient of the siliceous 

ores, occn~ionally occurs. Ores from the Douhle Standard shoot, between Fantail 

and Ne\~ada gulches, shm,;ed irregular masses of gypsum, some 'of which are a:; 

much as .an inc~ in diameter.· F. C. Smith '

1 also mentions gyp:smn as an ingredient 

of these ores. 

StiUnit~J (8b2S3).-Analyses frequently~:,lww the presence of antimony, l?ut it 

is only in exceptional instanees that is in ~uffil:ient quantity to be seen. Siliceou::; 

ore~ from Yellow Creek and nlosely nssociated. with tungsten deposits show large 

"Tmn~ .. -\m. Imt. Min. Eng., vul. 27,1897, p. 415. 
140 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

masses of this mineral composed of slender radiating needles oftet;t 2 inches in .. 

length. They are embedded in the silicifieq limestone and seem to be the earliest 

formed of the minerals present. 

Ura.niwn mica.-Largc quantities of a greenish uranium mica arc reported 

to have occurred in a~sociation with the ores of the Ros::;-Hannibal mine in 

'Vhitetail Gulch. _ Uranocircite occurs in several localities in tho productive mining 

region, and it· is possible that this occurrence is similar. 

ALTERA'l'JO}l OF THE ORES. 

The general appCarance of the siliceous ores is so much changed by oxidation 

that the commonly rtccepted classification in mining circl~s is a··division into blue 

Or unoxidiz~d orcs and red or oxidized ores: The blue ores arC those just descri?ed, 

and grade by gradual tran~itions into the more oxidized yarieties; All stages irdhe 

, process of oxidation are well represented. The red ores arc so called on account 

of the heavy staining with iron oxides that has resulted from the alteration of the 

' pyrite and the infiltration of iron from other soilrces .. Th~y are often of an 

extremely ferruginous aspect, ·but when broken the more solid portions are found 

to contain b~t small quantities of iron oxide. dften the oxidation has begun 

alo'!g the line. of demarcation between the dolomite and the ore, so that a very 

narrow lil1e of iron-stained rock intervenes between the two. Examples of this 

were obser~Ted in the Ross-Hannibal mine in \Vhitetail ·Gulch. In a fmv cases . . oxidized zones were obsenTed a~jaccnt to creviceS iii. bodies of blue ore. The 

changes which oxidation produces in the mineralogy are quite noticeable. Pyrite 

is the first mineral to be attacked, and rapidly passes through a series of ·alterations that eventually produce oxides. In most cases where the change is complete 

much, _if not all, the sulphur has disappeared, or, if present, _is changed t_o sulphates. 

In many of the· ores are cavities lined with small druses of jarosite, which has 

formed by the oxidation of the pyrite i;, the presence of the potash ~ontaimid in 

the residual shales. Calcite is an extremely common mineral· in the oxidized Ores, 

frequently occur"ring in such large quantities that reduc'cd rates for their treatment / . 

can be obtained from smelti~g companies. It almost always fills seco1_1d~ry crevices 

or cavities which have been previously vacant, and its ~ractical absence :from the 

sulphide orcs ,is strong evidenc~ that it has been one of the 'minerals intr?duced 

by oxidizing water8. Black oxide of manganese- mixed with limonite has :frequently 

been 8imilarly introduced and occurs in cavities ~nd fissures. Its derivation, like 

that of the calcite, is probably due to the oxidation of the .dolomite, in which the 

ore bodies occur. Hematite sometimes occurs in distinct scales and crystals, but 

iS not often a noticeable mineral. Very'advanced stages of decomposition produce 

in the ores a concentric and subCorlchoidal parting that causes the ore to break 

into kidney-shaped masses. Such s~rudures arc seen if! the. Big Missouri mine 

near Lead, the Steward mine in Nevada Gulch, and many .others. 

• 
REFRACTORY SILICEOUS ORES. 141 

CIIE.lliSTR Y OP TJIE ORES. 

The :f~llowing table includes fonr analy~etoi of refractory RiliCeou~ ore: 

' .AnalyRes of rejrn.ctory xiliceo1ts orf'R. 

L II. . III. i:v. 

Sulphide ore. Oxidized ore. OxHlized ore a 8ulphide ore.a 

SiO~ ..••....... __ . ____ ................. \. ..... . 

TiO~ ______ _ ... : _ ~ ______ .............. ~ ....... -.. 

Al20 3 ••••••••• -- ••••••••• -.- •••••••• -- ••••••••• 

;::~~ ~-~ ~ ~ ~ ~ ~ ~-~ ~~ ~ ~ ~~ ~ ~ ~ ~: ~ ~ ~: -:::::: ~::: ::::::: r 

.l'"e _-.- ••• :-----.--.-.--------- •••••• -.----- •••• -

l'cr f't'nl 

75.2B 

013 

B.61 

.13 

)!nO._ .................... -................ _ ... -----...... . 

~1g0. __ . __ ...... _____ . _ ...................... _ _ Trace. 

Ca(l --------·-···--------------· -----------··· 

SrO ...... : ................................... . 

BaO ···-·r·····------·······--·-···········----

Na~O ... : .............. --------::-·······: ... . 

K 20 ··-·--·.·······---·········----··--········ 

1. 7.5 

Trace. 

0 05 

0 05 

2.38 

Prr ernt. 

{j.5. 1-!2 

3.924 

20.3G4 

. 0611 

Traee. 

. 77\l 

5. 711' 

Trace. 

Trace. 

Per cent. 

B4.45 

4.07 

7. 28 

0 25 

. B.~ 

Per cent. 

68.748 

·3.072 

13.2R9 

J_,i~(l__ ----------------·· Trace .........•••• ······----·· --------·---

H~0-1050 ·····------·-····------············· .47 .476 -------····· .••.•••..... 

1120+105° ..... :._ ................ ·-----------·· .87 1:83\l ·······----- ···-······-· 

1'205 -------·········-----·········-----------· .21 .832 ---····· .... .'842 

SOa--------·--------------.-: ................. : .61 .073 3.71 ···---------

CaS04.- ...•. ~.' •... ------ .....•...... -.--.-.-....••••......• -.----- .. __ .. --- •.•... - ~ . 8!{!{ 

s ·······--·······------···········---------··· 5. 8.5 . 27\1 ---·······-- 11.728 

}'! .... - _____ , ........ ---- ....... -------------

CaF12 : ••••••••••••••••• ----------------------: ------------ •••••••••••• ····-------· • 784 

Cl .................. ~---···--------·-········· Trace. -----------· ............ ------··-··· 

A~---- .... ---·- ....... -----····· .. ----.----·-. 

Sb ......................... --- -----· ...•... .' .. 

Cu ....... -----· ................•.. : ........... . 

Lees 0 for Fl ................. : ............... . 

Total···--------····-···-----------·-··· 

(iol1l ........ ___ ....................... _____ .. . 

-silver.~:. ___ ........................ -- ....... . 

Telluriun1 ..... _. ____ . __ ....... .'.· ............ _. · 

I. 89 

b. 02 

,., . 02 

99. 7~ 

• 2\-1 

0 010 

Trace. 

'rrace. 

0:: .'fliT ton. .- Oz.1J~-~o~t. 

-2~95-' 0. 42 

4. 75 . 62 

100.01 

0:: per ion. 

0. r174 

2.875 

99.2~6 

0;. pe~ ton. 

0.32il 

10.55 

4:03 

"Tnkcn from pnpcr "Potsdam gold orcs uf the Rinck Htlls of South Dakota," br }'.C. Sm1th: Tmns Am. Inst. Min. 

Eng., vol. 27, p. 410. 

/>Approximate. 

cEnough present to form telluride with the golil if not with·the silver. 

------
. ' 

142 ECONOl\llC RESOURCER OF NORTHERN BLACK HILLR. 

Analysis I is of sulphide ore from the N9. ± shoot, Duuhle Standard mine. 

This specimen ,Vas <'ompletcly unoxidized, showed con~idcrable pyrite, visible ~n 

the hanJ specimen, ::;orne ar:-:;cnopyrite, kaolin, and other residual shaly material 

of indeterminable character. Analysis was made hy IV. 1'. Hillehmnd. It was 

not pos!:lihle to calculate the percentage of all the mineral:-; present on account of 

· the uncertain compo..,ition of the shaly material, but the following minerals ~ould 

' be ensily estimated: 

. . . . Jfineral cumpu.~ition t:f ;,;ulphide ore froru .;.Yo. 4 .~hoot, Duublt> 8l1111drtrd mine. 

Pyrite .......... ____ ......... _______ ..... !: •••. ______ ._· ___ .• ·----- __ ...••... ____ 9. 4/ 

Afse:q.opyritt· . _______ .... · .... ________ ......... ___ ------- ... ______ ... ____ ..... _ 4.10 

Stibnite ....... ~ ................ ~ .. • ............... ·.·......................... . 03 

FluOritt· __ .......... ----- .................... ------ ......... ___ ----------. ___ _ 1. 36 

Gypsnn1 .... ________ -------- ______ .. -------- ______ ........ ______ ... ____ . _____ 1. ~1 

Barite'? .. ·.· .... ____ . __ .... 

Apatitt>'' __ ...... ____ ... __ 

Rutile"-------------·----------------------------------------------------- ___ _ 

8_ilit'a, together with dPtrital day, ettc .. : . .................. __ .... __ ...... ______ _ 

. 08 

.. 49 

. 13 

R2.46 

Total ..•................................................................ · 89. 4:3 

\ . 

The_pota~h, alumina, ~nd traces of lithia, magnesia, and strontia are probably 

contained in the :-:;hale. Phosphorus has been estimated as apatite, on' account of 

a slig-ht excess of lime over that necessary to comhinc with the residue of 803 • 

Apatite could not he distingui:-:~hcd as such, ·but as phosphoru:-:; is present in the 

umi1ineralized country rock and ore in approximately C<!Ual amount,'' and so often· 

occurs in shales, its presence may he justly assumed. The titanium may likewise he present in the shaly material, possibly as rutile. The percentage o-f potash 

in thi:-; _ atialysis i.':l rather unusually hig-h, and, taken in . _connection with t~1e 

aluminum, might he regarded as indicative of orthoclase. As:-:~nming the presence 

of orthoclase and· about 2t per cent of kaolinite, there \vould lle about GO per 

cent of free.:-.:dlica. 

Copper never occurs in any considerable quantities and in much o.f the ore 

can not he detected at all. Arsenic i.'5 present as arsenopyrite anrl antimony a~ 

stihnite. Gold and silver can not he irlentitied hy -the micro~cope~ hut tellurium 

iS-pi·eSeift -ir~ffieient-qnantity to eombine with them to form tellurid~~. Thi~ -~- .---

is also shown by Professor t:hnitli·.~\Vllo hus enlcl~latecl the percentage of tellurium, 

gold, and silver and ~hown them to he present in tl~e proportions retlUi§ite.,..for 

the comi)osition of sylvanite. There seems to be little rea~on to doubt that gold 

and silver are pre:-,cnt _in this combination. One of the most imporbtnt. features 

o:f this analysiS is the complete abse!1c.c of carbon dioxide and the correspon<lingly 

a Compare nnalr5is of rlolomite on p. l~l. 
REFRACTORY SILICEOUS ORES. 143 

low percentage of. lime, mang~n~!SC,' and :ferrous iron, ::;bowing that the soluhle 

constituent::; or carbonates. have been nJmost, if. not. completely, removed during 

the process of silicitication. , _. 

Analysis II, of · oxidi"ed ore ·from Blacktail Gulch, wa' furniohed hy the 

courtesy o:f 1\Ir. Dorr, of the Golden, Gute ~lining Company-, .and i~ published by 

permission of the company. Thh; analysis is, chiefly interesting as illustrating 

the chemical changes hronght ahout hy alteration. ~~hC great increase in iron 

oxide, lime, and magl)esia, with the corresponding ·fall in silica and l'lulphur, are 

the most conspicuous features.·' The im~rcasc in iron oxide, lime, ·and magnesia 

are pr~bahly due in large part 'to the intiltration of these ingredients from without by the action of :-<nrface wttters, the iron in the form of oxides a.nd the lime 

and magnesia in the form of carbonates.· The moisture .is also much higher. The 

ot,ht~r ingr~dients have probahly not sufferct.l appreciable change. 

Analysc.s III and IV :LL:e of oxidized and un~xidize<l ores, respectively, and 

:-:how in general the same series of chan~e::;, but in, this case the hlue ore, lV, is 

much more ba:-:ic ore than III, so that the incre:ise in iron 'vould at first seem to 

be revCrsed. In general an examination '.of about 05 :L?alyses. furnished by the 

Dead-wood and Delaware Smelting Company ;;howCd a range in ::;ilica from 60 to 

86 per cent and. of ii·on from n to 1 T per ·cent, or an ::iY~rage of 73.3t: ,per eept 

silica ami 12.17 per cent. iron.· ' 

It is difficult to offer any sati,factory explanation of the failure of the gold 

in these ore~ to yield to ordinary methods of extraction. In the cU.:::~e of the hlue 

or unoxidizcd ore::; its probable l~ombination With tellurium may he considered a 

snffieient reason, hut for the red or oxidized variety, or the hlne when subjected 

to u thorough roa::;ti.ng, hy whieh it i::; to be sttppo:::~ed that the gold ir; either 

wholly or at least in part relea::;ed.fron~ conlbiriation, this 'vill not answer. That 

the gold is; a~ originally suppo~ed by Devereux, in an ·extremely tine :::~t~te of 

divi~iol1 and i~ uniformly distributed through a roek not readily permeable hy 

8o'lutions and yielding \Vith diffienlty . to crushing may he offered U13 a partial 

explanation of the refractory natm·~~ of the ore. It nmst, howeveT, ·he admitted 

that. with all of the ende~yor::; to ·solve this prolJIClll the exact condition in whieh 

the gold exist~ in these ores i:-:; not 'vel! understood. . __ ____---·-....__,__ 

l'.IRI.I TIUX8 FROJI THE- USU.lL TYPE-OH oiE.~- ~ • , ,.__ --- _ _.. . 

Four varietie:-; of ore are fonlld intimately ass~ciated with these siliceous 

orcs, but can nof he considered Characteristic.·· 

... turU~n'Oil.'i ·clay.-In the l\Iogul ttnd Tornado ·mine.s there occlir~ interbedded 

with the hard siliceous o~·e, bands of a soft white_ clay which frequently carry 

higher values in gold than the main body of ore. Seams of this kind ure reported 
144 ECONOMIC RESOURCES OF NORTHERN BT~ACK HILJ,S. 

to have contained at times from $±0 to :;l6o· per ton in gold and to have yielded 

free gold on panning. 

It is not possihlc from an examinatiOn ~£ the q1ate~ial to form any very 

definite idea of its origin,, hut the clayey matter is prol.mhl.y the result of the 

decomposition of intercalated shale or of small included layers of porphyry. For 

the introduCtion o'f t,hc gold the writer can suggest no satbfactor.r explanntion 

unless it be the result o£ the secondary adion Of ~nrface waters on the 'ore material above. 

Aurij'eroi"'~ Mnd.~Below the' ore and. lyinlt' in the quartzite in the Wasp 

No. ~ mine in Yellow Creek, or directly upon the Algonkian in the Dividend 

mine near .-Porthtnd, was found much loose i'ncohercni sand containing comdderable 

val~1es in gold. In both case~ it was p~rtiallj~ cemented, by 1imon1tc or carhonatcs 

and often yielded v~ry. high_ v~Iues. When washed ·-and ·examined ·under the 

microscope the grains of sand from Yellow Creek were found to be loose and 

often perfect crystals of quartz and only held together hy the cementing material. 

Aur(t'e-rrnts gnuge.-~n the ,Dividend m!ne. ncar Portland, much of th~ decoinposed dolomite is heavily charged wHh oxides of ·iron, together with ::;ome sandy 

fluorite and Iilangancsc. It carries. workahle qimntities ?f gold. The- values 

are, however~ always JOwer than thOse of thR silicified rock occurring· in their 

immediate vicinity. It is not· improbable. that this gouge material is the result 

of both prim~ry and secondary. mineralization. ThC presence of fluorite, which 

is a mineral that often extends beyonll the limits of silicification into crevices 

in the adjoining rocks, 'suggests that the values were partially introduced into 

the dolomite at the time of first mineralization; the presence of manganese, that 

n secoiu1ary concentration of such values h.r :mrface waters has taken place . 

. Qtun'tzite orP-.-Tbe quartzite that underlies mueh of the siliceous ore of the 

lower ore-bearing bellS contains a hiih percentage of carhonates. ~nd it. i::;. not 

infrequently mineralize<! so as to form ph.y ore. 1t ·i:; ne':er as high in grad~· as 

the ore that lies above it, hecause there is more insoluble material in the original 

rock than in the purer dolomite beds aho,·c. 

AREAL DISTRIBUTION OP TilE REFRACTORY SILjCEOUS OR~'S. 

The produeti\·e areas of refradory· siliccops orcs are five in number (see 

Pl. V). and have 'bee-;; sev~rally._ designated· the Raid Mountain area, J~ead area, 

Yellow Creek area~ Garden· area, and Squaw' Creek area. The last-named area \vas 

at the time of exumina.tion little ·inore tha!l a jJrospeet, but ha.':i since become an 

importunt producer. 

·B.U,n ItiOU~'T.UX .~IU-:A. 

This is by far the largest and most-important area, and has just!~, been considered the type dbtrict for this class of orcs. Jts. name has been derived from 

Bt1lrl Mounttiin, which lies at ,the center of the northern edge of the area. 
REE'RACTO~Y SILICEOqs ORES. 145 

As will be seen from Pl. V, it i~ a northwest-southeast striking belt of about 

1 mile in width and 4t miles in length.· As it corresponds closely to the inner 

rim of exposed Cambrian stratu, it lies hebvecn the contact of th,at rim with the 

underlying Algonkian on the northe'ast and the nearly parallel line of contact of 

the Cambrian with the .overlying Ordovician on the southwest. Across this belt 

the Cambrian beds have n general downward inclination from northeast to south· ' . west. They have been eroded from the higher portions of the. Algonkian area 

to the northeast (with the exception of a few isolated outliers), and pass on the 

sot~J,h beneath the heavy, overlying rocks o£ the Ordovician and. Carboniferous 

formations. 

This belt of Cambrian rocks extends on to the southeast beyond the present 

limits of the productive area, but is cut off from the Yellow Creek a·rea by the deep. 

gorge which the waters of 'Whitewood Creek have cut far down into the Algonkian. 

Toward the northwest the Ordovician and Carboriifcrous approach much nearer to 

the edge of the Algonkian afea and the rim of the Camb~ian turns toward th~ north. 

In its northern end, in the vicinity of Crown Hill and Portland, the Cambrian is 

expo,ed in nearly its full thickness, so that as yet it is only the upper ore-bearing 

beds that have been thoroughly developed. As ,,dll appear from Pl. IX, great numbers of intrusive sills, dikes, and irregular bodie~ of igneous roc.k are interbedded 

with the Cambrian rocks of this belt. 

The topography of this area is very rough and irregular, the steepness and 

irregularity of the gorges having been much· accentuated by the presence of eruptive bodies, which have offered great resistance to erosion, while the softer inclosing 

Cambrian rocks hri.ve be~n more readily removed. • 

From a northwest-southeast line through Terry Peak the drainage is to the 

southwest into Spearfish Creek, to the northeast into Whitewood Creek and to the 

northwest into Squaw Creek. 

The headwaters of the southwest drainage· appear just at the edge of the area, 

and have cut down through the ·Carboniferous rocks into the Cambrian, leaving 

heavy cappings of the former on the divides between the streams. The northeastward draim1ge comprises a series of gulches w"hich empty into \\'hitewood · Creek. 

These streams head up into the Cambrian belt and cut down into' the underlying 

Algonkian, so that the lower ore-bearing beds, which are about 10 to 25 feet 

above the Algonkian, outcrop in a very sinuot;s line, and allow long, narrow 

embayments of Algonkian schists to extend far up into the mining district. The 

southeastern portion of the district has been m'ore deeply dissected, so that the 

· orc-bCaring beds have here been rendered easy of access on the divides between 

these gulches, espe9ially on Nevada, Stewart, and•Whitctail creeks. In the northeastern portion, erosion has not progressed so far, and the lower ore-bearing beds 

4987-No, 26-04--10 
146 ECONOMIC RESOURCES O.B' NORTHERN BLACK HILLS. , I . 

are still in large · pa~t deeply .buried, the so-called upper contact having been 

most extensively developed. \ 

With relation to the ore bodies, therefore, the area may be divided into two 

portions-the Ruby Basin district and the Portland district. In the first-named, 

or southeastern district, the mines arc .largely upon· the ~lower ore-bearing beds; in 

the !?Ccond, or northwestern, Jargely upon .the upper. The mines of the Ruby 

B~sin district are op.cratcd mainly .by. one cbmpany-thc Golden Reward. Two 

~nines belong tO the Po~'tlan~. Company, name~y, th~ Big. Bonanza and Bux.~on, 

~h.,.il~ a ~.ew. small mines _ar~. op?ratcd by i!ldividual owners. These relations _may 

qe ci~arly made ' out-from _PI. ,IX. 

RUBY BASI)[ DISTRIC'l'. 

ll). the Ruby Basin distrid there arc a lai·ge number of long chanp.el-like ore 

bodies or 'shoot..; resting on or. ncar the basa~ Cambrian quartzite and trending as 

~ whole }n a roughly north-south direction. These o!·e ,bodies fall into two distinct groups, withiq which or~ shoots are situated relatively close to one another. 

These arc the Buxton-Union group and the Alpha-Plutus-Mogul group. 

Buxton- Union group.-This is the more easterly of th_e two, and comprises • • I ' • . • 

15 mme~. Naming ~hem from the east to the west, b~ginning on the north, these 

are: The Buxton; Rctrie.yer,_ Steward, Tony and Maggie, Golden Reward, Big 

Bonanza, Little Bonanza, Gla9-stone, South. Golden Rmvar4, .Fanny, Isadorah, 

Sundance, Billy, Rub)· Bell, Lucille, Union, and Ro•s-Hannibal (or Mikado). 

(S~e map, Pl. IX.). The ore shoot, operated in th~se mines number 39 in ·all, of 

which 21 are large and extensive ~~d the remaining 18 comparatively insignificant. 

}_'he . general ~rend o~ these . sh~ots. is about .n~rt.h-northwest, with a ~ew' large 

intersecting shoo~s trending ~. ~5° E., or nearly so. 

The ore-bearing bed~ upon which the mines of _this. group are situated .are 

not. continuous in a north-south direction, but are cut through by Fantai! and 

Stewart gulches, ~o that the .ends. of the' ore bodies outcrop on either side of the 

~ivide sep~r~ting th~_se stre~ms, rendcrjng. t~em ca..;ily accessible. The ore-

. bea~'i_ng be9s, however, are a~ a nuich low.er e~_evation at the southern end of the 

groU:p, _o;o_ tl~at ·t'hc_ shoot~ in the Union mine h~v~ been worked by means of a 

shaft. 

At the southern Cl)d of the· group a large oill. of phonolite hao been int1:1!ded 

in .th~ Cambrian, and ex.tends '"'esbvard as. far as· the Fanny ·mine. It may be 

se~n ~aking .ahi·upt clifl's in Stewart .and Whitetail creeks. South of Whitetail 

Gulch this sill has c~t the ore-bearing beds into two portions, so that the ,;hoots 

of the .Union mine .lie below a9d that: of the Ross-Hannibal above, the phonolite 

forming in the' one case the roof and in the other the .floor of the ore. The 
RE~'RACTORY SILICEOUS ORES. 

workings of the Isado!·ah and South. Golden Reward are also above the phonolite; 

but they rest upon the quartzite so that (as may be seen iri the Billy tunnel) it 

is evident that· the phonolite has crit downward toward the west and· inCluded all 

of the ore-bearing. beds above itself. This sill is extreme!)· irregulat', and presunuibly terminates at the northern end of the South Golden Reward; ivhere it 

extends. upwtird in ·a dike-like· mass Separating the ore bodies of the north and 

south end ·of the Golden Heward. It extends nm;tbwest, h~wcver, hcncath the 

southern end of the Big Bon~nza, nncl sends· ()ut a -dike tOward· the· north Which · 

separates· the Big and Little Bonanza mines; the formei· .heing i1hout 50. fe~t 

above the latter. The ore bodies of the North Golden Rewanl and Tok;- and 

1\faggic outcrop in ~he ~outh ~ide of Fantail Gulch, and are· on the lower. Cambrian quartzite, ~vhieh is separated from the_ Algonkian by a heavy sill of 

eruptive rock. The Big Bonanza· is at about the Same elevation, and i;5 separated 

by· the same sill from the Algonkian:. Owing to the alJJ'upt termination of the 

.thick phonolite sill previoui-5ly mentioned, the_ ·ore hOd)- ~f the fanny mine is 

mueh lo''{er in 'elevation than ~hat· 'of the mines· directly east, and it is at aboUt 

the oamc elevation·>as the shoots of the Alpha-Piutuo-Mog·ul group to 'the ·west. 

The shoots of the Li'ttl~ Romi.nr.a outcrop ju~t west of the Big 'BOnan~a, and are 

much c·omplicated hy h;reghlar porphyry bodies. As their relation~ arc tllore. 

fully discussed on page 187, ·they will not be fiirther inentioned at this point. 

AJpha-Pl-ntHs-J.l[oqul group.~-Thi~ group b ~eparated from the. mo~·e easterly, or Buxton-UniOn group·~ by a wedge-shaped area of comparatively barren 

country situated with its broader ·end· toward the south, so that the twri groups 

approach each other on .the north, but diverge 'in ·a southerly direction.~ This 

grOup comprises 14 mine~. Frqm eaSt to ·west beginning at the n'orth, they are 

a:; follows: Clinton, Alpha-Plutus, SmiJy ttnd Lundt, Bottlc::son, Tornado·,· Little 

Tormldo, Double ·standard, Boscobel, Dai~y, HarmOny, ·'I·Iardsc.rabblc, 'Velcome, 

Upper Welcome, and Great ·Mogul. There are 71 shoots iil all, of which about 

25 arc of large size, th~ remainder being small,· thoUgh yielding- collectively a 

lai·ge amount of ore. One,- the Tornado-Mogul shoot, is larger than any yet discovered. 'Vith two exceptions all of the·. ore bodie:; of this group lie in the 

lower ore-bearing beds close tO the Algonkian, or not· more than 30 feet aho,ve it. 

Two small ore bodies, the Daisy and Upper Welcome, the first situated on the 

diddc between Fantail ·and Stewart gulches, and the. second on: the north Si~e of 

Nevada Gulch, itrc ·on an upper contact, which- prObably corresponds to tha1 of 

the upper ore bOdies of the Por'tland · distr~d. 

As wiWbe,seen from ·pJ. IX (p. 2H), 'the shoots of this group trend northwestsoutheast and are comparatively close to 'one anOther, relatively fc\v of them 

beii:tg disconnected. The ·group is brokei1 intO two'. pOrtions by a heavy farilt 

, 
148 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

by which the ore-bearing beds on the west side are elevated about 300 ,feet and 

offset against the higher measures of the Cambrian. On the lower, or east· side, 

of the fault the same beds are offset against the Algonkian. This fault:mppears 

as a single and dearly cut displacement in the west workings of the Troy,··shaft 

where it h~ts been well ·exposed in tho several crosscuts that connect the ·Horseshoe shaft with the stopes of the Great l\fogul. From this point it passes 

northeast, but becomes in part divided into many small step faults between the 

workings of the Hardscrabble and Tormtdo mines; thence H runs north across 

Nevada Gulch .sopnra~ing the workings o£ the AlpLa-Plutm; from the small tunnels of the Smily and Lundt mine: This fault is not clearly defined on the surface, bcc~use th.cre are so many comp1icating masses of intruded rock that 

distort and confuse the relations of the strata. It appears, however, in Nevada 

Gulch at the point where the Fremont, Elkhorn, and :Missouri Valley Railroad 

makes a hoi·seshoe bend, the· Algonkian ex,tending far up the gulch but coming 

against the upper Cambrian at this point. Just south of Nevada Gulch this fault 

is immediately on the west side of a large dike of eruptive rock, but diverges 

from it in a southerly direction so that in the Troy workings· the two are separated by an intetTening area of about 800 feet. That this fault diverges thus 

from the porphyry suggests that it is widely separated in age from the intrusion, a fact that is well b;,rne out by other evidence. A second fault also appears 

just west of the. :Mogul shoot, at the extreme south end of the group, and on 

the west side of the large porphry dike that extends north as far as Nevada 

Gulch, forming the western boundary of the great Tornado-Mogul shoot. The 

downthrow of this fault is to the west; the reverse of ·that just described. It 

lowers the ore-bearing beds fully 100 feet at the extreme south end, bnt gradually dies out northward until, at a point. about the center of Fantail Gulch, it 

·has completely disappeared. A thil·d fault occurs at the north end of the group 

about 300 feet east of the 300-foot fault and with the central ppint of its course 

just below the bed of Nevada Gulch, the downthrow being about 72 feet on the 

east; It has a general north and soUth direction, hut curves to the west as it is 

followed south, cutting the Tornado shoot into two portions and uniting with the 

300-foot fault. Upon the fault block thus formed are the north end of the 

Tornado, otherwise known as the St. Louis shoot, and the most \vesterly ·ore 

bodies of the Alpha-Plutus. As may be seen by consulting Pl. IX, only three 

of the shoots of the part of this group below the 300-foot fault show in outcrop, 

the gulches not. having been. cut deep enough to dissect the ore-hearing beds. 

Of these three the ·Clinton oittcrops in Nevada Gulch, hut as it is about 

midway between this group and that first described it can not be rightly said to 

belong to either of the two. The other two, the St. Louis and Upper Alpha-
REFRACTORY SILICEOUS OR]~S. 149 

Plutus, are on the small elevated fault block and outcrop in Nevada Gulch. The 

remainder are all deeply buried and· have, therefore, been· worked by means of 

shafts. The relations of these faults to one another may be understood by 

consulting Pis. XIX and XX (p. 214). 

1Vest of the 300-foot fault the ore shoots outcrop all along the south side of 

Nevada Gulch. Two mines, the Little Tornado and Harmony, outcrop also, one 

on either side of Fantail Gulch. To the southwest, however, the ore-bearing 

beds are not exposed and mining is carried on. by means of shafts. 

PORTLA:XD DISTRIC'l'. 

·with one exception-the Dividend mine-the ore shoots of the Portland 

district are on the so-called "upper contact." They arc separated from the 

lower ore-bearing bods by a vertical interval of 527 feet, and are about 15 to· 25 

feet below the Scolitkus or "worm-eaten" quartzite. \.They comprise [L series of 

shoots all closely grouped together and striking with almost no exceptions about 

east-northeast, thus sho~ing a marked difl'orenco in trend to those of the Huby 

Basin 'district. The following mines have been operated: Dividend, Decorah, 

Trojan, Empire State, Folger, .Perseverance, Alameda, Leopard and Jessie Lee, 

1\fark Twain, Burlington and Golden Sands, Clinton, Portland, and .Gunnison. 

There are about 46 productive shoots in this group, but they are so ofter~ connected 

with one another that it is difficult to say \Yherc one ends and the other begins. 

Tho ore-bearing beds dip slightly to the southwest, so that they outcrop around 

Green .Mountain and westward just above the two milroad lines at the head of 

Squaw Creek, and also at the head of Nevada Gulch. To tho southwest they 

. are more,Aecply buTied. These shoots m;e as a rule _rather broad aml fiat a~ 

compared with those of the H.uby Basin di"strict. Little or no faulting occurs, 

so that the 1 geological relations of the group may be readily a·ppreciated fi·om Pl. 

. DC (p. 214). The lower ore-bearing heds outcrop 527 feet below, at tho base of 

.Green J\'Iountain, around the head of Deadwood Gulch. The workings of the Dividend mine are situat<od here, but have uot yet been extended suflicientJy Jm· to the 

southwest to fully explore this contact direetly below the upper workings, and 

it is therefore not pos~iblc to say whether the presence of these oTe bodies Jn 

·the· upper beds may be considered a:s evidence that· a correspondingly productive 

group of ore bodies will be found below. The ore from this group is ·"in 

much thinner shoots than that occur~ing in the R_uby Basin district, and the ores, 

taken as a whole, yield. rather lower values than the general run o£ lower 

contact ores. This difference. in value is especially noticeable when t_hc comparison is nmde between them and the orcs from the Dividend, which belongs to 

the same group. Orcs from this mi!1e :yield between one-third and twice as 

high values as those from the upper group. 
' 

150 ECONOMIC RESOURCES. OF NORTHERN BLACK HILLS • 

. Hcav.v sills . of erUptive rock lie at varying-. distances he low· the beds upon 

which the mines of this group are operated, and the summits of Green lVIountain 

and the hills to the south .are capped U.l' a mass of the same character. Dikes 

:ire Hoticcably absent from the workings, only one having been encountered. .. In 

the workings of the Dividend, howm~er, the Jikcs are extremely abundant, a 

fact which shows that there is a strong tendency for intrusires to as:-3ume horizontal position~ as they ascend to higher. horizons in .the Cambrian. Al5 compared 

with the Ruby .Basin distriet the ah~encc of dikes in this area is significant, as it 

shows that the occurrence of the:-;c orcs is in no way dependent o'n their presence. 

Besides these large groups of ore bodies there are several h;olated mines that 

nuiy properly he cla~seU as in. the Ralrl 1\.Iou~tain area. Two of these are in 

Nevada Gulch~ about midway hetween the Ruby Basin and Portland districts. 

These are the Baltimore and Ben Hur. The former has a series of small shoots 

lying on the lower contact, whid1 is at this point .some distance vertically below 

the bed of Nemda Gulch. The workings are largely to the south of the guleh . 

. The Ben Hur is some distance farther down the gulch, just at the head of the 

Algonkian exposure (see Pl. IX, p. 21+). A small north-south fault has lowered 

the strata .on the west so that the single Rhoot of thi." mine is worked by means 

of a tunnel through the. schh;t.. 

The area between the Alpha-Plutus-Mogul group and the Portland group 

IS ahout 3,000 feet in width anrl bus hecn quite extensively prospected, notahly 

by the Snowstorm mine, hut as no other than these two ore bodies have been 

founU it seems not improbable that it may constitute a con~parati\'ely barren area 

like that between the Buxton-Union and Alpha-Plutus-J\fogul groups. 

Another i.·mlated mine is the Two .Johns. operated on the lower ore-hearing 

beds which outcrop on the we~t sicle of upper Squaw Creek. The shoots ·trend · 

cast-northea~t. hut arc all comparatively small. A little ore has also been found· 

in the South ·Dakota mine' in Annie Creek and at other points along the cour:-;c 

of Squaw Creek, notahly in the Labrador miuc, hut thb western portion of the 

Bald l\Iountain area haA not yet heen thoroughly pro.::;pcctcd, though it may m 

future become proUuctive territory. 

GARDKX .-\RJ.:A. 

The mines of the Garden area arc ~ituated m Blacktail and Sheeptail gulches, 

and at the head of a small tributary of Fabe Bottom Creek about two-thirds of 

a mile east of south from Garden. To the ~outh,vest lie~ the Algonkian nucleu~ 

of the northern portion of the hills. To the Borth the country is eo\·ercd hy a 

heavy cap of rhyolite which obscures the i·elations of the Cambrian strata. Still 
( 

REI<'RACTORY SILICEOUS ORES. 

farther no~th tho Cambrian- paHscs hcneath the on~rlying formations. 

dip quite sharply to the northeast and arc co,'ere<l by the rh>'olite 

151-

The strata 

cap before 

mentioned. · The relations of the strata are much confused -hy irregular intru•_dycs 

and hy a series of small north-south faults which ele\·ate the ore-bearing bed:o; on • 

the \~r·ecit side. The following mines hn.vo heen operated in. this area: Penobscot;. 

Golden ·Gate, "Tells Fargo. Kicking-- Horse,. Keystone, ..._~merican Express, 'Chicken 

Lode 1 and another mine -of conRiderahlc size whose name is not known. 

The trend of· the shoots is about ca~t-northeast by cast or nearly east-west, · 

although t.hcre is con~iderahle dh·crgencc from this direction. The Hhoots are 

~on1ewhat narrower than those of the Bald J\.I<?.tmtain area, hut generally of con8iderable 1ength. The· grade of the ore i::: comparatively low on account of the 

prevalenc~ of :;hale bands in the ore, hut ,-,ome high values have been reported. 

Dikes nrc seldom if ever encountered in the workings. The exposed area of 

Camhrian upon which these mines are. situated is very limited, and it 1s not 

known how far the. ore: bearing bed:-; . extend bmieath ·the rhyolite cap to the 

northeast. 

J,EAD AHI-:A. 

' Iri the vicinity of Lead there still remain uneroded on the· crestH of the 

Algonkian ridges a few srilall iHolated outliers. of Cambrian st1:ata: A heavy sill 

of fine-grained rhyolite capi-' the Cambrian, leaving a ntr~ ing· thickness of shales, 

dolomite, and conglomerate hetween it and the Algonkian, hut .as we approach 

the Homestake zone, first this rock and then the hasal conglomerate thins ont so 

that the ore-bearing heds lap oYer first upon the conglomerate anrl tinally 

directly npo11 the schists. The ore bodies are exposed at the :5Urface upon the 

westernmost edge of this area, hut lie beneath the shales in an easterly direction. 

1tlnch of th_e ore from this district· contain:; great <tuantities of barite and is 

uniformly rich in ¥old. From the Hidden Fortune mine wa.~ taken ore which, in 

addition to its. refractory -content, yielJed immense quantities of tincly diYided 

and crystalline native g:old. 

the l'>e Smet qut, and helow 

From the thin parting of ore-bearing hedt::l aboye 

t.he ·rhyolite• cap, great masses of Yery rich silice0ns 

ore were wined. while to the west of the Homestake open cut the _Big :Missouri 

mine has yielded great quantities of ore of the same character. In those mines 

where the conditions permit of their determination the fractures with which the 

ores' arc as:5ociated ·conform in strike to the lamination of the undcrlvincr - b 

Algonkian schists. YELLOW (;RF.EK AUE.\.. 

This area is situated a littlC more than 2 miles slightly caSt of South from 

the city of Lead. 

The ores are found in a thin Capping uf Cambrian strata on the didde bet'Yeen 

Whitewood Creek on the west and Yellow Creek on the east. Above the Cam-
152 ECONOMIO RESOURCES OF NORTHERN BLACK HILLS. 

bri~n rocks -is an extensive sill of fine-grain~d rhyolite which attains a thickness 

of 350 feet as it is followed in a southerly direction. A small detached area of 

this eruptive rock remains uneroded to the north and there forms-a small elevated 

knoll. Between this knoll and . the larger southern mass of porphyry the 

Cambrian measures lie uncovered, and within this area-generally not more than 

30 feet below the surface-have been found small but rich bodies of refractory 

siliceous ore. Farther to the north on the extreme end of the divide is a large mass 

of phonolitic rock intruded irregularly into, the rocks of the Algonkian. On the 

northeast side of Yellow Creek small areas of Cambrian still remain upon the cres~ 

of the divide between that creek and the west branch of West Strawberry Creek. 

Siliceous orcs have recently been found on this divide, but have not yet been much 

developed. The ord of the Yellow Creek area lie directly upon the basal quartzite 

of the Cambrian and about 15 to 25 feet above the Algonkian. They follow fractures 

varying somewhat in their direction, but the more extensive shoots generally trend 

northwest and southeast, following the strike of the Algonkian rock8. In the greater 

number of the mines the loose incoherent character of the roof has completely 

obscured the supplying' fractures. The average value of the ores is about $40 to $50 

per ton. ' ln the J\finnie mine tho· grade was much lower and in· other mines much 

higher. Fluorite. is gei1erally not a prominent constitu.ent, but barite occurs with 

great frer1uency.. The mines which have so far been operated here arc the Donelson 

fraction,, Wasp No. 1, Little Pittsburgh, Two Strike, ~Iinnie, Little Blue, Little 

Blue fraction, Wasp No. 2, and Wasp No.4. 

The Yellow Creek district, though a very restricted one, has been extremely 

product~vc on account of the high average yield of the ore. The district is closely 

related to that near Lead. The grade of the orcs in botll cases is high; the occurrence of barite and tungsten minerals is ~imilar, and tho two areas bear the same 

general relation to the strike of the Homestake ore body. To a less extent it is 

similarly related to Garden area. 

' SQUAW CR,EEK AREA.a 

This area is situated in Sqmnv Creek, a sho.rt distant cast of its junction with 

Spearfish Creek. It is one of the few where rnining has been begun in the bed of a 

deep gorge, with a very narrow outcrop of Cambrian cupped by heavy Carboniferou::5 cliffs, so that mining will soon carry the workings beneath great thickness~s of 

overlying rocks. A few vertical:5 may here be seen and. some small bodies of ore 

have been encountered in the Cleopatra mine, although at· a considerable distance 

above the base of the series. In view of the heavy mineralization of the overlying 

Carboniferous it is not improbable that ore bodies of workable size may be found 

here. At prcsei1t it is little more than a prospect. 

crAfter this paper huol gone to pre;;~ C. C. O'Harra's paper "The mineral weulth"of the Bluek Hills," was received, 

showing that this Squaw Creek un•a lmd become an important producer since the writer visited the region. 
REFRACTORY SILICEOUS ORES. 153 

SUllMARY. 

The refractory siliceous orcs are restricted .to certain soluble strata of the 

Cambrian series. Such development as has taken place has naturally been directed 

to those areas of Cambrian strata where erosive agencies have rendered the orebearing beds most readily accessible. 

The Cambrian rocks are not widely exposed, as they yield readily to erosive 

agencies when unprotected by a capping of massive limestone. They therefore 

remain only as a rim around the inner . edge oi the Carboniferous (tiee Pls. V 

and IX), and ~·apidly thin- i~tward until onlj isolated outlicrH remain upon the 

Algonkian highlands, or they pass outward beneath the heavy massive rocks of the 

Carboniferous. In the former case ore-bearing areas· arc isolated on account of 

the removal of the Cambrian strata from the intervening' country. .In the httter 

case the ore-bearing beds lie so deeply buried that it is difficult to say how far in 

these directions the mJneralized area may extend, a.nd 'exploration involves a 

greater expense than the uncertain conditions would seem-to justify. 

VALUE OF THE ORES. 

The gold contents of the ores in the Bald Mountain area nm from $3 or $4 

per ton to, in rare instances, $100. The general average for. the ores in this 

district is about $17, and those containing from $10 to $20 are of· the most 

common occurrence. Ore carrying $85 per ton is considered high -grade. Some 

of the ore from the Ben Hur mine yielded upward of $60 per .ton in gold. As 

compared with the ores of the lower beds those from the upper contact are 

slightly lower in g;·ade, so that much of tho ore is often left in the mines. The 

orcs from the upper contact have also been reported to carry a higher relative 

proportion of silver, but although this is true in individual instances, in general, 

si1ver orcs are as frequent in the lower as in the upper beds. The distribution 

of the values in the ore is far from uniform. Ore which carries $25 at one point 

will fall, within 10 feet, to roek yielding ~nly $10. This is especially true of the 

upper contac.t. In general, the larger ore bodies arc of lower but more uniform 

grade. No general rule as to the distribution of values in a single shoot can be 

laid down, for the poTtion near the supplying fracture is sometimet:i higher and. 

sometimes lower than that farther remove~ therefrom. , The extreme ''rimsZ' of 

the ore arc generally lower tha.Ii the main ore mass. In the Tornado· mine the 

ore in tho vicinity of the· complex of dikes nnd faults north of the shaft 

carried higher values than that in ~l{e less distnTbed heds to the south. In the 

Hoss-Hannibal mine, on t~e contrary, the ore carried ,~ery big~ values and the 

shoot was remarkably uniforrH and undisturbed. The larger ore bodiCs often yield 

increased values where they are joined by smaller ·shoots entering them at an 

angle. Instances of this are to be seen in the Tornado mine. 
154 ECONO)!IC RESOURCES OF NORTHERN· BJ,ACK HILLS. 

The thi'ee smaller areas of siliceOus ore; Y cllow Creek, Lead, and Garden, to 

the west of the Homestake ore body, or its continuation, produce ores of uni:formly 

higher' grade than those from the Bald ]\fountain country. Those of the Lead 

area, such· as tlie Big- :L\fissonri, DuraOgo, and Hal-rison, yield~d ores carrying 

between $25 and S500 per ton;· much ore was shipped that carried an average of 

$50 per ton. The unusual instances are the IIiddcn ·Treasure, Golden Crown, 

and lmva mines; portions of the Durango and Harrison also ·produced ore containing· large quantities of fr~e go1d besides that. in the refractory condition, 

Tb~ gEade here ran up into th~ th'ousaf.lds, so that one _car 6£ 10 tons is reported 

to haye yielded $65,000. High-grade ores are also found in Yellow Creek where 

a conservatiye average ~or ores heretofore mined is $40 ~,o $50 per ton. 

The Garden area, which bears the same general relation to. the continuation 

of the Homestake as do the Yellow Creek and Lead districts, also carried some 

ores with rem~rkably high valu~s, bU.'t the general avcrag~ in this district is not 

high on account of· the larg~ a.mount of waste in the ore due to the greater 

proportion of shale bands iri the. ore-bearing beds. 

AGE OF TJJB .lliZ.oFE[lALJZATIO.:.Y . 

. The .fractures have heen shown to be .older than some of the eruptive bodies 

and younger than others. Where fractures .cut eruptivcs fillings 'of ore . extend 

uninterruptedly from the main ore body into and through the porphyries. Mineralization along fractures that '!U'C cut by eruptivcs has always exercised an influence 

on the porphry, either by producing a slight silicification at the point of contact 

or by the· extension of the more' powerful of the. mineral,izers, like fluorite, 

beyond the ore into the minute crevices of the eruptive rock. Eruptives h~ive 

never been observed to contain angular fragments of ore, which would probably 

have been the ca~m had magmas broken through such an extremely-brittle material. 

These conditions have been observed to hold good for all of the varieties of 

eruptive rock., The mineralization is, therefore! later than the igneous activity. 

As igneous rocks cut strata of the Benton Cretaeeous and pebbles of fhe 

~ame roek have been found in the basal conglomerates of the Ncocene it v.rould 

seem that the mineralization oceurred somewhere between the Benton and the 

.Neocene and it probably, represents ~he finnJ phase of vulcanism that was concomitant with the elevation of the Black Hills. This occurred while the Cambrian 

was still deeply buried beneath itS covering 'of later formations. 

. I · . • .. . ORIGIX OF THE OR~ES. • 

The evidence that is furnished by the facts cited in the foregoing pages as 

to the origin of these ores falls into two classes, tha"t which relates to the manner 

in which t.he or~s have been formed, and that which relates to the source from 

which the ore minerals ha,,e been derived. The first has to do with the changes 
• 

REFRACTORY SILICEOUS ORES. 155 

that have taken place in the country rock thrOugh the agency of mineralizing 

action. and with the chemical and physical nature of the process by which these 

changes have been wrought. The second treats of the channels" through which the 

mineralizers have gained access to the beds which they have nJtercd, the direction 

. of flow of mineralizing waters through these channels; and, finally, the immediate 

source from which these water:; ·have dcrh·ed· their mineral contents. 

THE )IIXERAJ,IZlXO PROCE1:\S. 

The ore did not in ~~ny sense fill pi·cexisting ca~·itics, :for there is no cvidenc:e 

to show that such ha.ve existed in the ore-bearing: r~ck at a~y tiri1e; the·:.'onl}· 

ca,:ities present being the minute credce~ or fiss1~res which)~a\'e been termed "ver-

~.icals.'''-"-,Tbe ore has been formed by a proeess. which involved the gr-adual 

reinoval of the original rock sUbstance and the 'simult'ancous substitution 'of the 

ore mineral~. Th_is ~as ofte~ proc~ed.ed with ~o~ lit_tle d_isturbane_e of the .oriiin;l 

n-iaterial that" the stratification of the countt:y roCk is, continuous with the banding 

of the ore, and at times so perfect is the preservatiOn of_ this. structure that it is 

difficult to determine, without a detailed examination of the substance of the rock, 

:tt what point the ore terminates and thC unmilleralized rock begins. A very good 

idc!t of this handed structure can be obtained from Pl. XVI (p. 214). lri other words, 

a-complete alteration of the mineral substance of the'rock has taken place without 

~my change in its external form; still further, ·when viewed under the -microscope, 

the ore shows· an even mo-re faithful reproduction· of the original microscopic 

structure. One type of ore-bearing rock (described on page 120) consists of an 

aggregate of minute but conq~lete ·crystals of dOlomite. This -rock is shown in 

Pl. X, B (p. 21±). \Yhen a transformation of this material into ore has taken place 

the process has been eanied on with such nicety that ·these little rhombs ·appear 

as distinct in the ore as in the unaltered rock (Pl. XV, A). When, however, the 

· 'polari:wr is applied to the microscope it is at. once seen that the ore is composed 

entirely of silica and pyrite and that no ,trace of the original material is left, 

althoug·h its form is as perfect as before alteration (Pl. XV, B, p. 21±). 

During this mineralization n marked decrease in volume has occurred. This 

is shown by the great number of cadties or vugs that occur in the ore., and the 

resulting contrast with the dense texture of the origirial Tock. The intensity of 

the ore deposition seCms to have been directly· proportional to the confinement 

of mineralizing waters; the rnore open the fracture the smaller is the ore shoot, 

and the more even and uninterrupted the shale or porphyry above, the grcate~ 

is the lateral extent of the ore. 1:\.gain, \vhere 'ore shoots, like the great Tornadol\1ognl, lie in contact with large igneous bodies, there seems to have bCen an 

additional confinement of waten; which may ha,~c .bad some eonnection with the I 

great size of the ore body. 
• 

156 ECONOMIC RESOURCES OF. NORTHERN BL.,CK RILLS. 

DIRECI'ION OF FLOW OF :t>HNERAL WATERS. 

These ore mi~erals have been transp.orted by circulating waters to the dolomite, 

whether it was present as comparatively pure beds or as cementing material of 

sandy and shaly ro'?ks. Such waters have found in the fractures, ~r "verticals,". 

trunk channels hy means of' which they have been enabled to penetrate the 

encompassing and comparatively insoluble rocks and reach the more readily 

replaced material. Whether the direction of flow in these fractures has been 

upward or downward is extremely ?ifficult to detc:mine, for there are certain 

facts that arc not to be readily cxplain~d Oil either assumption. ]n the opinion 

of the writer, hOwever, the mass of evidence seems to favor a mineralization by 

ascending waters. 

ln the first place, the ore generally lies immedi,ately below a comparatively 

impervious rock (see Pis. XI, XlX, XX, p. 214); this may be a bed of extremely 

argillaceous shale, sometimes quite thin and again of considerable thickness, or a 

sheet of porphyry, hut in alt"cases a rock competent to act as a barrier to the further passage of uprising waters. On the other hand, such a close contact with the 

quartzite or other impervious rock below rarely occur:9, for there often intervenes 

between the next lower impervious bed and the under boundary of the ore an 

unmineralized area of dolomite of the same soluble character as that which has 

been repla~ed. Excellent instances of this may be seen in the Union mine, the 

E shoot of the Tornado mine, in the Mogul mine, the W clcome mine, the American Express mine., the Two Johns mine, and in innumerable other cases. If 

the mineralizing waters had come' from above it is reasonable to suppose that 

such a stoppage of circulation would have taken- place just above, not beneath, 

an impervious bed, and that tho, umnincralized portion of dolomite \Vould have 

been aboye, and not below the ore. It is, of course, to be observed that there 

are many cases where this unmineralized area js not present, for the ore often 

completely fills the space between thg roof and underlying impervious bed. This 

is. especially true where ore bodies arc very extensive, for the aggregate amount 

of material introduced has been sufficient to completely replace . all of the 

soluble rock which interYenes. 

In the second place, directly beneath this impervious roof the lateral extent 

of the ore-the horizontnJ distance to which ore solutions h:.L\re spread from the 

supplying fissure-is generalljr greatest, diminishing with increasing downward 

distance until it pinches ~o a mere vertical. It is clear that the intcrposi~ion of 

an impervious layer across a chanllel of circulation will produce just such a ]atera\ spreading, and that where circulation has been upward, it will take place 

\ • on the under surface of the layer; where downward, on the upper. The two 

'diagrams below (fig. 15) bring out these relations. 

In the third place, theie seems ~n general to be a .connection between the 
REFRACTORY SILICEOUS ORES. 157 

lateral expansion 01 mineralizing waters and the amount of open space available 

for their circulation. Thus, where fractures arc -large .and open and pass uninterruptedly upward through the capping shale or porphyry the soluble rocks are 

comparatively little altered and ore shoots are narrow and confined chiefly to 

the immediate vicinity of the fracture. a In other words, the mineralization of 

lower beds has not been great where large and open verticals have permitted the 

free passage of waters to higher levels. Such a stoppage of flow in mineral: 

~caring waters would also t~nd to increase the extent of rock mineralized along 

the barrier, owing to the increased ch.e.mical activity of the waters due to the 

absence of rapid motion; for it has been frequently , remarked by .writer8 on 

ore deposition that the quiescence of mineralizing waters is essential to an 

active deposition of mincral.b I 

DesfJendind water-s AscetJding welters 

Impervious bed 

FIG. 15.-Jde'aisection to show relation~ of g'reatcst lateral extent of ore to_4~!ection of flow of mineralizing waters. 

\Vhile these three groups of facts are not sufficient to prove that these ores 

were deposited by ascending waters, they must at least be explained before a 

deposition by descending mineralizers _can be advocated. 

DERIYATJOl'( OF ORE -1\HXERALS. 

There arc. no facts which serve to indicate with Certainty the source from 

which the circulating .wat8rs derived __ their_-.mineral contents . ..P However, from a 

~ 0 

a L.·uge ore shoots occur along open fractures, but only where they are present in large numbers anrflirc closCly 

spaced, so that small amounts of mineralization along fractures have coalesced, forming a large body limited hy the number of fractures. 

bEmmous, S. F., Geology and inining industry of Leadville, Colo.: Mon. U.S. Geol. survey, vol. 12, 1880, p. 570. "It 

will be readily apparent *· * * that such precipitation will be most abundant where for any cause there ls some 

interruption in the regular flow of the enrrent, as ·rapidly moving waters deposit Ill.nch less readily than those whose 

movement is very slow." 
158 ECONOMIC RESOURCES OF NORTHERN BLACK HILJ,S." 

corisideration of the sevci·al rock formationS, it it; possible to· form some idea 

of their relative importance as a possible· source of ore minerals. · ft is now 

'· 

generally admitted that meteoric waters by' descent to and contact with heated 

rock ·masses at great depths may' .be transformed to ascending· waters; therefore, 

the minerals which constitute these· orcs·, sO fai·, at leasl, as their positi~m relative 

to_ that' ~f the ore bodies- is concerned, may have had their origin either wholly 

or in part in any of the cotihtry rocks that ·remained uneroded at the time of ore 

lleposition. The region was ·then presumably deeply buried b)' rocks now rcmo,·ed, . 

corisisting ·of small areas Of ·th'e Algonkian. and Cambrian, of tho Ordovician and 

CarboniferOus limestones, Minnelusa sandstoneS, and CretaCeous rocks, together 

with much intrusive porphyry, i:n'aking in all a1i aggregate thickness of probably 

4,000 feet. To these, as a ·possible source of ores, must be added Algonkian 

schists and their ineluded eruptives to indefinite thicknesses below the level of 

the ore· bodies. The ore· n:tinerals to be derived· froin these roCks are, in the 

"relative order. of _their abundance, Silica, pyrite, fluorite, wolframite, barite, 

tellurium, torbernite, gypsum, stibnite, gold; :Lnd silver. 

For. the silica, so many different sources can he suggested ·that its origin 

does not deserve speeial- consideration.· The same :rimy be said, though in lesser 

·degree, of tlfe pyrite which, while· present in corisiderablc amount in the oreS, is 

too· '\videly distributed a min·er~l to hU\~e its origin exclusively in any of the 

country rocks. 

The flum;ite, perhapS more than any other mineral present, may he Uscribed to 

pneumatolitic emanations from the erti'ptive rocks at the time of int:usion. Barium 

may have origina'ted from ··small 'quantities ·in the feldspart"i of the igneous rocks, 

in which it is known to· occur in co~siderable quantities .. For the rarer eleme~ts, 

such as tungsten, tel1ui'ium, arsenic, antimony, and, in fnstances, uranium, no 

tests have . been made. Since" these miner~Is ean not readily be supposed to 

ha,·c been ·original constituentso-of~· the · sedimentS:r)r rocks, their origill must be 

sought in the· Algonkian or eruptive· masses. 'Yolfrarnite occurs in sonsiden1ble 

-qt~antitics .in rocks of the Algonkian," associated with the tin deposits, both in 

·Nigger 'Hill and ·in the southern hills. Its· occurrence suggests that similar 

deposits arid bodies of eruptive granite may exist below the sehish; in the 

vicinity of the tUngsten deJ:iosit~:~ near Lead; and if so~ they may readily be 

supposed to have· srippliCd ·this min-eral t6 ftscendiiig thermal waters. It ·+s·, of 

coun~c·;-·:Possible~Jtmt tungsten ·also is present in·· the enlptivc r"ocks, ·but if so,· it 

is···yet"-·m!detectcd'In--tlie''Iighlo{ the eviae-!lce· as- to--dii·ection of flow of 

-mineral solutions ·no such assumptioi1 is ··essential. 

Ar~_?enopyrite is known to occnr""in the auriferous lodes of the Aigmikian 

·. ----~~(see..,...-dcscription of Homestake orcs, p. GS). Tellurium, arsenic, antimony, and ~~-
R~FR.ACTORY ;SILICEOU_B ORES,· , 159 

uranium may, have .had_ their origin in either eruptiv·e rocks, or 4-lgonkian 

schists,. but their presence in either is not reported: 

Of the gold and silver contents of... the various rock formations more is 

known. Among the sediments the only series which undoubtedly_ contained gold at 

the time of the ore formation is the Cambrian. This g-~ld occurs, (1) in the form 

of auriferou::; conglomerates at the base of the Cambrian; (2) as small a1ll~unts 

of free gold widely disseminated .through ·.unaltered sediments, presumably 

contemporaneous with their deposition. Of this latter type of gold the writer 

has seen no occ~rrences in person, but mt1ny instances of the kind are_ repC!rted, 

and as they originate :from_ reliable sourc~s, th~y are probably aeCurate. 

That the schists of the ~-\lgonkian were mineralized with gold and silver 

prior to the deposition of the Cambrian, the study of the Homcstake and other 

Algonkian deposits has placed beyond question. ~Many~ other instances of small 

quantities of gold at different places in the Algonkian· series have come under tQe 

notice of the writer, although never in sufficient quantitie:;;, nor of high enough 

·grad~, to ,be of economic importance. 

-~whether gold and silver were original ingredients of the e_ruptive rocks, it 

is much more' difficult to determine. These ~rocks ,frequently yield appreciable . 

amounts of g9ld an~ si~ver on assay~a fact which is attested by a nUmber of a:;says 

made for the writer, as !V"ell as by examination of assay returns from several mines. 

Such n.ssayl':l, however,_ were confined to eruptives so eloscly associated \Vith areas of 

mineralization that these values ma}r have been introduced into them at the time of' 

ore deposition. It seem..,, ho,yever, possible that ~here may have been some :::;mall 

quantity of these metals .in the original rock, although -it can not-:be defi~nitely 

proved. 

Jt will be seen from these data that the country rocks of the ore-bearing areas 

. coritai~cd at the time of t-he ore dePositio,n most of the ore minerals in qmmtities --

su:fficiet~t to have constituted au adequate source:o.--f. B~~P~.Y,.~nd in the opinion of the· 

writer, it is very probable that each of these rock divisions has contributed t~~ the 

ore formation, one adding one element to circulat.ing waters, and one another.: l-l~)v~ 

the metallic con.tents have been. derived from these. rocks------:-sch~sts, sediments, ftnd 

· eruptiv<;!s~\\:hether exclusively through a leaching. bJi- purely meteoric waters, or 

by tpe additional aid of occluded moisture or g-ases rel_easeci from,eruptive magmas, 

it i::; not possible to say. The- pn~sence of ~mch large quantjties of. fluorite in the 

orcs certainly leads one_ to suppose _ t~at ~he _latter action has_lJeen an important 

factor in the ore g-~ncsis and .. .in ,_th.~inion of-the· wrife~:-- it has-:h~d~ much . ·--- clo8el' connection with the origin of these ores than is generally admitted. lt' is 

further probable, :;!nee the ore depo~ition foll<?.wed so clo::5ely tbe eruptive actidty, 

• 
• 

160 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

that the heat imparted to mineral \Vaters by igneous rocks served to increase in no. 

small degree the activity of circulation. 

~lfETHODS OF TRE.!TJfENT.a 

After the fail nrc ~f the earlier attempts to trcut these refractory siliceous ores 

by amalgamation~ a plant :for the treatment of the ore:5 by chlorination \Vas erected 

by the Golden Reward Company at Deadwood, in 188~, and a second plant of 

similar character was hnilt at Pluffia, in 1895, by the Kildonan ]Hilling Conipany. 

This process waE; attm~ded with a greater degree o£ suc~ess than any before tried, 

and until recently has been largely used. )Vith the increase in the understanding 

of the chemical character of the ore other processes were found to make so much 

better saving o-f the precious rnetals that chlorination has now largely given place to 

them. 

In 189g a cyanide plant was built in Deadwood, but seems to have been in 

operation only intermittently. In 1890 the Deadwood and Delaware Smelting 

Company b"uilt the plant in Deadwood for the treatment of the orcs by mattesmelting, and under the efficient management of Dr. 1<'. R Carpenter this method 

of treatment became one of the most Rucce~sful that had yet been tidopted. Since 

its erection the plant has been purchased by _the Golden Reward Company and much 

enlarged. Another is now in process of .. construction at Rapid. 

Within the last three years the cyanide process has been used with increasing succe8s on these ores. The percentage o:f extraction is somewhat lower than 

that attained by smelting, but the saving in expense is so great that orcs may 

often be profitably handled, even, though of lower grade than those economically 

treated by other methods. There are now in operation in the Black Hills eight 

cyanide plant::~ treating the refractory siliceous ores, while numbers of others are 

in process of construction. b 

llfETHODS OF JIINING. 

The methods of mining followed in the siliceous ore regions are extremely 

----~ simple. Shafts are not deep, and in many instances the ore outcrops so ncar 

the surface that the mining operations may he carried on hy means of drifts. 

The loose, incoherent nature of the Cambrian rocks necessitates some timbering, 

but that is generally of a very simple character. Lagging is necess~ry in the 

larger stapes, owing to the lack of rigidity of the shales that often form the roof 

of the-ore; but in_the smaller· shoots the_ entire ore body is frcque~tly extracted ~--·...-·· without-the use of supports-of any kind. Irc•mueh oxidized and decomposed 

a Detailed ?'ccounts of the treatment of the ores will be found as follow~: F. R Carpenter, TranR. Am. Inst. ~lin. Eng, 

vol. 17," pp. 570-ii98. F. C. Smith, Trans. Am. Inst. 1Iin. Eng., vol !:!i, Pl-'· 4::!:.!-42!1. Charles H. Fulton, Bull. No. fi, 

South Dakota School of Mines, February, HIO:'!. 

- b Fulton, C. H, Bull. No 5, South Dakota School of Mines, p. Ui>, February, 1902. 
REFRACTORY SILICEOUS ORES. 161 

areas more careful support o:f the roof is necesl:lary. in a few mines difficulty 

has been experienced in handling the water, largely on account of the imen:n 

and und'ulating character o:f .the quartzite on which the ores oce~r, so ihat the 

location of a sump is never permanent~ but mus.t be shifted from f-,imc to time. 

In large bodies of ore the center of a shoot is generall}r rcnu~ved first, pillars 

of ore .being left to. support the roof it the timhc1·ing itself iH insufficient~ the 

rims and, finally~ the Pillars arc then remm·ed; a:nd all ~vaste material in the ore 

is deposited in the cente1: of the. stope. Cadng is son~etimes res~rted to after 

ore has hecn removed, and gangways left along· the edges of shoots, "the 

e'xpcnse of maintaining a large am<?tmt of ·timbering· l~eing· thus avoided. . . . . ~ . . ' · 1~Jyj.pectr'ny.~Mining propCl·t.r: i!l the siliceous ore region is o_ften sol(l 

· without regard to ore' "in sight,'' so that the method and intelligence \vith \Vhich 

~yste.miltie pro:~pccti~g iH carried ~n haS an extremely important bt~~~ring, on the 

profitabl9 working of the orcs.· The ,first· st'ep i:-; tl1e determination of the orebearing heels. • This having 'been dedUed, the beds· are opened np by a :-ihaft, if 

below the surface, or hy tunnelt' if exposed; drifts are then run at right angle~ 

to tho prm·ailing direction of ore shoots i_n. the region. Verticals or ore hodict' 

intcrt'ccted arc follmved or mined ·ont" along their strike, and other cro:-i:-icnt drifts 

are rnn at considcrtthle distanc?s. from and para1le1 to the fir;;t. In thi::; waj~ an 

cxceeding~y cxter~~ive. area may he :(i"i·Ospeete-d f~r ap except shoots of c~trCr_nclysmall size at a nominal exp~nse. Intrusive porphyries occasion ~ome inconn~nienee, hut thi:; can generally be O\'erconw by intelligent \\-'Ol'k. lVIiniilg ~~o·mi:mnies 

that· ha,·e kept their Systenmtic prol:lpecting ir~ ildnwee of their ore 'cxtl~action 

h:n:c opened up new .shoots_ before old one:; were mined o_ut, thus enabliug them 

to prod nee cOntinuously, while those companies that· have n~t adopted -this method 

have been subjected to an i~xpensh'c and discouraging i)criod of dead work and 

• inaction when their <~re '"in ~ight'~ ·was exhausted. 

PUTURE OF THE REF'RACTOR1. 8ILICEJOU8 ORES. 

'Vhile there are con~iderHlJle tr:~cts of the o~·e-hearing_ beds· of the two knOW!; 

horizons still nnprospt!cted ·within the exposed rim of Ciunhrian strata ahon~ 

mentioned, the de,·elo{nnent ~f such ore bodies as may there be discovered (~Hn 

not maintain the production for .any great length of time. But there arc man.\· 

included dolomite beds between the so-called lower and- upper contacts .wl~ich 

have been hut little, if at all, explored, and whieh there is every reason to helien~ 

. ? . 

arc mineralized. Upon the prospecting in these. beds and th.e dis<.;overicM which 

exploration may make where ore-hearing beds are dcepl.)~ buried bcneath.:..-th•~=-~---:-_.' 

overlying limestOnes ~:f the Carboniferous will depend the future of this-·Chss of 

ores. It is therefore necessary to ~m.swer_.thc- question,· How far. in- these.-.dirce4987-Xo. 26-04--11 

~-·= 
' 

• 

, 

162 ECONO~IIC RESOURCES OF NOR'fHERN BLACK HILLS. 

' tions does the mineraliZed area extend~ Thi:-; i~ a difficult question. . Three 

cmHlition::; determine the occurrence of these ores: (1) The.., presence of the 

ma.rblei~ed dolomite or <;)l'e-bcaring beds; (2) fractures by means of which mineralizers may obtain ae~ess to such beds; (3) the percolation of mineralizing waters. 

As bef?re state"d, . it has been pro\'ed that the ore-hefl:ring dolomite occur:; 

under .much of the .limestone to tl~c west of Portland, and the same beds ha.Yc 

been detected far west of Spearfish Canyon, so that it b prohable that the ,orebearing rock is uniformly present over extensive area~. 

· .. The pre:;ence of fractures is. a condition which would also seem to be fulfilled, at.. 

least so far as the ~astern s~de of. Spearfish Can yon is concerned, for the occurrenee 

of mineralized fractures hf.the limestone of _i':::Ik ~fountain, Ragged Top, and Carbonate indicate that verticals may be likewise. present in the Camhrian below. 

The third and, pc~·haps, mm;t essential eondit"ion, however, that there should have 

be_tyn mineralizing .~ction upon these clee~)ly !-m_ried 8trat~ i8 ?He which only _d~velop~ 

nwnt. can determine: -~If we are to consider the .Ragged Top ores, Which arc of the 

same general character as the majority of refractory siliceous o1·es, to he the work o£ 

a~cending waters, then it is not iiupr<.lbable that these deeply buried beds have 

beep _mineralized; but as the evidence on this point is by uo mean~ conch~sivc no 

argument crin be based. on t:mch tlll assumption. That refractory siliceous ores have 

been found in ·the Cleopatra mine in the bed of Squaw Creek and" are alsq reported 

by Carpenter a from Cold, Creek to the east may be taken ~s an indication of the 

future value of the region, and are certainly Sl!fficie~t grounds fo'r a careful and 

extensive Jn·ospecting. In general there does not seem to be any reason why ore 

bodies should, not occur beneath ·the C!trboniferous, and if they rlo this class of ores 

may continue to be an important factor in the gold production of the Black Hills for 

many years. 

PYRITOUS ORES. 

Under this head are included ores· of gold that show usually a heavy pyritic 

contm~t with which are sometimes associated otper ::mlphides, such as sphalerite and 

galena. These orCs oe.cur at v~rious pOints \Vithin' the Spearfish quadrangle and 

have heen intermittently mined, but, on account of the small size, irregUlar character, 

and low g-rade of the ore bodieS, have never been au ·important factor in the gold 

production of the region. 

I?.vo Bit d£strict.-The best-known <;lCCurrences of these gold-bearing pyrite 

or:es are in Two Bit Gnleh. The cou.ntry rock is h~re Cambrian shale of va-rying 

t~ickness, consisting chiefly. of fine gray shale, glaliConitic in places; iron-stained, 

;;..""~""=- =shaly-~sandstones sometimes calcareous in character; and some few lavers of dolomitic 

breccia. 'Interbedded with these Camb~ian strata arc manJ: sills of·s;enite-porpbyry, 

a:rrans. Am. Inst. :Min. Eng., vol.l7, 1889, p. 570. 

• 
• 

PYRITOUS ORES. 163 

coarse rhyolite- or granite-porphyry and other varieties of eruptive rock. 'At ~he 

ha~c of th~ Cambriari Beriel"3 i:-:~ a heayy and much indurated quartzite, but at no point 

oh:-;ervcd hy the writer docs the banded dolomite or charaeteri.~tic horizon of the 

silieeom; ores occur upon thi~ quartzite. 

The ore hodie:-; g~ncrally are the result o£. mineralization along fractures qr · 

vel'tical:-; which cut erupth-es .and Cambrian strata indiscriminately. The ores are 

co~mposcd. ]argely of pyrit~~ which t;cCurs in heavy, almost amorphous mas~cs in 

the Cambrian shales on or ne:.tij the basal '1uartzitc, and is reported to have been in 

the forin of shoots of considerable width in the Hardin mine. \Vhen :fractures 

·intersect porphyry the pyrite often ·occurs in c~rystalline dru.ses and at tiines is 

'"cattered thiekly through the hotly of the erupth·e rock. .The quartzite b also 

in places he~nrily impregnated with pyrite. This pyrite is reported to have yielded 

low values in gold, although no authoritative data as to the exact yie_ld are an{il~ 

ahle. As pyrite i.:; essential to the smelting of the refractory siliceous ores it Was, 

hopecl that· these low-grade ores, if cmwentrated, might find· a. local marketl btit 

for ~ome ca.u:-;e.:; not well understood several trials pro,rcd them unsatisfactory: 

The Hardin shaft is the only mine in which bodies of pyrite of workable,. size 

have been found. :Much ill-advised mining- has ·been carried on in this· district' 

and, although in future these ores may possibly prove to be· of value £or smelting purpose::; should other ::;ources of :mpply beconie· unavailable, in the light 

of the present development operators would, do well to exercise caution in their 

exploitation. . 

In their occurrence "these Orcs show quite a ::;trong resemblance to the refractory ::;iliceous ores. The fracturing is of later age than the igneou::; activity and 

so· also the pyritization. The mineralizing process seems to ha,re been in the 

nature of a replacement by pyrite of a portion of the djfferent rocks through 

which the fractures pass. 

TUNGSTEN OUES. 

WOLFRAMITE. 

HISTORY • 

.Fm: some years prior to 18H!=l large quantities of what wa~ localiy knoWn as 

.~black iron" were mined. together with refractory siliceous H~ld m:e, froni 

w·o.rkings in the Lead and Y ello\v Creek siliceous-ore areas, a~ desCr~bed on page 

V>l. In most ca::;e::; this material containeU very low value~ ·in gold, and ·was 

sorted from the ~re·, ,.,o that it Rcciunulated in considerable amount on the' waste _____ 

heaps of the mines. Some of that from Yellow Creek, however; is rep()rtec(fO . .~~~~--

have yielded workahle gold mlues. '[his was shipped to the_ smelter-":~d.ther; 

treate9. among other hasic ores without sU:':lpicion o£ its :;pecial value. In .January, 
164 ECONOMIC RESOURCER OF NORTHERN BLACK HILLS •• 

189[1, however, its great .weight attracted the attention of a local mineral collector 

and a few :simple tests serv~d to reveal its true character. Its ini'portanee was 

quickly recognized hy manufactures of tungsten steel, and the eXploitation of 

the deposits has now developed into an industry which, ~Llthongh not extensive, 

·ha::< yielfled considerable profits to indivi<lnal own~rs. 

OCCUHHENCI<j 0.1:!~ THE 'VOLJ<'HA:\liTE. 

This mineral has hcen found thus far at t\vo localities. 'l'hc first iS upon 

the .Cambrian outlier immediately north of Lead, un the top of the high' hill 

which form~ the crest of the divide hetween Hold Run and Deadwood Gult:h; 

the second is in the narrow tongue~ like area of Camhrian which~ a~ a thin capping· 

on the divide between Yellgw and 'VhitewooU creeks: projects north into' the 

centmJ area of Rchists. The two lie in a line which trends ahont N. :!fi0 to 30° ,V .• 

, and follows very closely the Rtrike of the schistosity of the upturned metamorphic 

Tocks below. In the latter rocks, just east of the northern deposits, _are the 

open cuts of the Hornesbtke mine, whieh lie in a line nearly parallel to that 

connecting the wolf_ramitc areas, and on a gr.eat mineralized, gold- bearing -zone 

in the ~chists. The Yellow Creek 'occurrences lie jn~t west of the projection of 

this zone, bearing the same relation. 

A.s stated above the wolframite is found in much the ~rune relation~-> aH the refrac· 

tory siliceous ores already de1:wribed. 

lt_occurs in flat, horizontal hut rather irrcgulal" nutsses up tu 2 feet in thickness. 

They frequently eo,·er considerable areas, of whiCh perhaps the largest so far 

diseovered. may have an extent of ~0 to 30 ~->qnare feet; bnt they arc so extremely 

irregular that it is clifficnlt to form an exact estimate of their lateral extent. The~c 

masses.lie upon or nea; the ba.-:ml quartzite of the Uamhriuu or where t.hnt is ah~ent 

upon the conglomerate that separates the upper member~ of the series from the rocks 

of the Algonkian. The beds in which it lies arc an impure dolomite 1"30llletime.':' .-;o 

full of sand grains a3 to grade into quartzite-a fact that lms n/>t infrequent]y given 

riSe to the erroneous opir~ion that the ore~ are mincr~lizt>cl quartzite. 

Above the dolomitic beds generally fH'<mr layers of shale, which become much 

more argillaeeous, and often contain considerable glawxmitc. ai:i one passes Yertieally 

upward. Aboye these ~hales. both in the \'ici;Jity of Lead and Yellow Creek, arc 

found remnants of a rhyolite sheet, ::;bowing in many cases a well-developed colum· 

nar structure. 

The wolframite is to Le considered more ht the nat~1re of ,a basic phase of the 

refractory ailiceous ores than as a separate and distinct depmdt, for it occurs a1ways 

in intimate association with tl~em. At time~ it forms a rim around the outer edge 

of the siliceous ore shoots. often extending inward an<l upward so as to fo!m a thin =----- - ·:-' 

• 
TUNGSTEN ORES. "165. 

capping to that ore. _ It t,hu.., appears as a ,'lor~ of envelope to the silicPons-ore mass, 

which it incloses, or nParly incloses. on all cxeept the lower Ride. ~'iargins of this 

kind are often frOm 2 to 2~ feet thic~{' hut the capping portion is generally thinner. 

At other time..; the wolframite occur~ in irregular masse..,, scat.tererl through the 

siliceous ·ore, o1· iu stringe1·:::; and. thin, contorted layer::; in tbe partially silicified 

do!omite. In the "\Yasp No.~ mi11e, in Yellow Creek, it wa.., ob~mTed in lenticular 

or kidney-shaped 1~1a~se,.-; in the ~hhl.'' dolomite. An exeellent im;tance of the first 

or envelope type of oeenrrence is to he ~een in t~e Harrison mine, ncar Lead. In 

the· Two Strike mine in tJH~ YelJow Creek area it was seen in thin, irregular layers 

replacing the uppermo~t and wore cnleareou~ portion of the hasal Cambrian 

l[mlrtzite. " 

' [n general the ore, i:-3 separaterl from the nonmineralized roek by a f~tirly sharp 

line of demarcatiun; hut in not a few ea~es it gracle.:; off so that, the ore. becomes 

leaner and passes hy ~careely perceptible tran:-:itious into the conntry rock. I 11 almost 

all cases e~m~icterahlc silieitication ha~ extended beyond tlw \volframite deposition so 

that, without the airl of the mit~ro~eope. it is difficult" to dbtinglli.sh the orig-inal rock 

from quartzite. 

CHAHAGTEH. OF w0LFHAl\1ITE ORE. 

As takeu from the milte~, thf~ wolframite is a clonse, hlack~ mas~·d\Te rock of 

fine, grannl:Ll' texture nllll ,g-reat wsight. It closely n~semble~ •tt'!tinc~grnined magnetite: but it~ greater ::;pecitic gravity and I!Iiihtly browniSh ~treak, t9gether 

with the as..,uciated mineral~;, g·enerally render its identification po~sible. The 

component gTain:-> are: in the majority of cases, about one thirt,y-second ineh in . 

diameter, and alway:-; ~~xhibit brilliant, eleavage face~. ln the portimls having 

coarl':'er texture, the grains are one~eighth to one-fourth inch across, and han~ 

slightly enn'ecl" snrfacf~~ with an extremely brilliant metallic luster. They do not 

possess erystnlline houndarie~; except whe1~ the replacement ha~ been hut· partial 

or when erystals project into ca.vities. Halliating ng.!(regates or Single tahular 

crystals of barite :trc pre!-3er~t in considcraUle abundance embedded in the body of 

the wolframite, hut are more sparsely distributed in the more ma.s~dve portion~. 

They havE~ alway:-, attained a perfect crystalline development, which ~;bows that 

they arc the earlier formed ingredi'ents of the ore. Irreg-ular f•avities or vngs, 

.. such as are generally to he seen in deposits originating from the replacement of 

one mineral b~, anothm~, are present throughout the ore in great numbers. These 

arc of all sizes, sOme of them Yery ·intricate in form, arid often of conl'jidernble 

aggregate volume. Th~ir interior 1L1rfaces arc usually coated with small but 'veilformed crystals of wolframite, not unlike marca~ite in their form and in the 

mann~r of their grouping, an9 v.:ith crystal druses of yellowish or hright~green 

·scheelite. The crystals of the lntter minei:ar are often of great ·beauty and per·· 
166 ECONOMIC RESOURCES OF NQRTHERN BLACK HILLS. 

fcction. In some cases, cavities are filled 'vith white or glassy crystals of barite. 

In a· few instances, the leaner wolframite from Y~llow <;reek shows long, s-lender 

crystals of stihnitc~ radiating from a common· cent~r, much iJ\ the manner of 

the spicules of a ptdiolarian .. 

Despite the decomposed and gouge-like character of the country rock~ alteration has not generally taken place to any noticeable degree: "Then the ore· has 

been long exposed to- atmospherie conditions, lioweyer, a mineral of gold-yellow 

cOlor, in glistening ·druses of extremely rr,linutc crystals, Yery often coats the surface·. This has been considered by Forsyth a as snggestiYe of tungl:ltite, · or 

tungsten trioxide; but none of that collected by the writer gave satisfactory 

results to tests for ~nngsten, and its. true .character has not yet been ·determit{cd. 

Under the microscope the ore, when v~ry pure, sho·ws little besides the dense, 

opaque wolframite. Occasionally, interstitial masses of clear, glassy- quartz are 

observed, filling the space;. 'formed by the crystal faces of wolframite. When 

sufficiently lean to permit the· use of transmitted light, however, the wolframite 

may be seen to be made up Of innumerable small_ crystal~, \vhich are generally 

well developed, .b1~t interfere with one another at their extfmi1ities. There are 

thus left between the wolframite indivicj.nals r:tmny irregular spaces, always bounded 

by plane surfaces a1id usually filled, either with secondary quartz or by grains 

of original detrital·quartz, about which enlargements caused by later added silica . ' . . 

have f?rmed complete crystals. 1n some specimens ·large crystals of barite arc 

to be seen. Scheelite occurs interstitial to the wolframite. Sections of ·the ore 

cut from the portion where it passes into the unreplaCe~ roCk show a moderately abrupt transition from massive wolfmmite ·to partially replaced material, 

with interlocking crystals, which gradually become more sparsely scattered, until 

they finally disappear in the barren rock. The latter is generally heavily silicified 

be.rond the limits of the wolframite, so that the microscope shows, if polarized 

light be used, that the rock is almost wholly composed of silica. If, howm·er, 

the polarizer be removed, nothing can be seen but the sharp outlines of irregular 

rhombs, such as constitute the bod_y of the mmal type of dolo~nite before mineralization, the original carbonate having been replaced with such delicacy that its 

structure has been perfectly presen·cd. 

CHEJ\IISTRY. 

The following analyses were made by Mr. \V. F. Hillebrapd in the laboratory 

of the United States Geological Survey. Both analyses a;·e· of specimens of the 

purer and more massive portions of the wolframite. .No. I is of a sp~cimen 

taken from the Two Strike mine in Yellow Creek, It is ·complete, and II!"Y be 

assumed to show the average composition of the wolframite. No. II i~ a speci-· 

uB\n.ck Hills Mining Re\'icw, vol. 5, No. 32, pp. 14. 15. 
TUNGSTEN· ORES. 167 

men from the Harrison mine, near Lead. It is~ only partial~ hut IS inserted to 

show the relatively high percentage of lime. 

Analpse11 of U'nlfranide nre .• 

Si02 • __ ••••• • •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 

'V03 ••• -••• ---- •••••••••• •••••••••••••••••• -.·-· •••••••• ------ •••••••••••• -. 

Fe2C•a-·- .. -- ----------- ---··-- --···---- ---- ......... -.... -.- -'---- ---- .. ---. 

Fe0 ........ ·-----------·-··-----------------------·----······------------·-

~-\.}20s •• - -·_ - - - - - - - -- ~- - - - - - - - - - - - ~ - - - - - - -- - - -- - - - - - - - - - - -.'- - - -- - -- --'- - - -- - --

l\fnO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................................. . 

CaO .............................................................. , ....... . 

SrO ........................................... , ..................... · ..... . 

BaO ...................................................................... .. 

1(20 -f-.Na20+ Li 20 ........................................................ . 

Ill), below 105° C .•.................................. · .... · ................ . 

H 20, above 105° C ....... ____ : ____________ ..... ~.: ....... ·--··--- _________ _ 

·~\t>205 _· __ -- ·-·--.- ............... --.------ ··------- ---------- :···· ----- .... . 

~-2~;5- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ : ~ ~ :: ~ : : : : : : : : : : : : : : : : : : : : : : : : ~ ~ ~ : : : : : : : : : : ~ ~ : :·: -:: : ~: ·: : : : : 

S or S03 •••••••••••••••••••.••••••••••••••••••••••••••••••.• -- ••••••••••••• 

I. 

Per cent. 

12.R/ 

61.50 

3. 85 

9. IR 

.52 

8.21 

. H3 

.02 

:o< 

. 08 

. 20 

. H7 

1. 25 

. 12 

Trace. 

Trace. 

II. 

l'er cent 

~.60 

61. 70 

(/ 12. fii 

------···· 

----······ 

7. 21 

5. :~~ 

·--······-

. ..... ---- .......... 

-.. -..... -

....... -.. 

·········-

.......... 

b. 10 

. .... -.. -. 

.............................................. ! 

----1·---

Total ............... . 

AssayS of I.~Gold, 0.05 oz. per ton; silver, 0.2.5 oz. per ton. 

Extremely minute traces of -:\Ig, Zn, Cu, Sb, and Sn were al~o found. 

99.64 -..... -.. -

b :-pproxrmate 

'Vhile it is not possible to calculate :from these analYses the exact mineral 

domposition of the ore, on account o:f the difficulty of determining the form in 

which the minor ingredients are present~ the relative proportions of the more 

important constituents may he roughly calculated as follows: 

Proporliuns of principal mmerals. 

'Volframite (Fe-;\:l:n) WO~---···-.. ····-·······-······--------: .. · .............. . 

Quartz, Si02 ---············-···-···········---··········-·· ••••••••••••••• 

Scheelite, CaW04 ----~----------·-·············---·······-··········--····· 

Barite, BaS04 •••••••••• ---- -· •• -····· -·,-··- :. -- ··---·------ • • • • • • • • • • ·- • ·- · 

Ferric oxide, Fe20 3 •••••••••••• ---- •••••••• --·· ••••••• - •• --- •••••••••••• -.-. 

'Vater, H 20 ............................................................... . 

Arsenic oxide------ ....................................... ---~--~---- ..... . 

Residual clay (kaolin) ••••..... · ............................................ . 

I. 

Per l'enl. 

75.60 

12.54 

4. 77 

. 06 

3.85 

.20 

1. 2.5 

1. 34 

II. 

Paccnt. 

lil. 58 

9.60 

t27. 68 

...... -.-. 

·········· 

. ......... 

-- ....... -

.. , ·'· .......... 
168 ECONOMIC RESOURC:ES' OF NORTHERN BT.ACK HILLS. 

It will· at om:e appear from those tables thfi:~. ~he. o~·e is coritaminated chiefly 

by scheelite and quartz. The first has probably· bCCn formed hy the combination 

of -some of the tnngstic. aeid with tl!e orig·inal lime of the .. inineralized beds, wl1il~ 

the silica may ha\re been cithe'r a portion of the unrcplaced quartz, :which occurs 

in grains throughout the coni"ltry roek 1 or later formed silica, introduced at ~he 

time of •mineralization. 

For meta1lurgiet~l purposes it is probable that the minor constituents: such 

as arsenic, vanadium, and especially phosphorus, maj; ~eriotisly impair the utility_ 

of the ore. A.rutlysis No. 11 iS interesting. as showing a relatively large proportion 

· of scheelite. 

CONCENTRATION. 

As only the purer and .more nu1ssive ore carries a sufficiently high· percentag·e 

of tungstic acid _to meet the requirem!3nts of the smelter~, _i.f_ ~a.., been found 

necessary to concentrate a _con:~~dderable portion of .the rnater~al I_uined .. At. some 

of the mines the erude method .of _hand sorting and trimming off of gangue 1JY 

hammers is adopted. For this purpose a considerable number .of men must be 

employed and the cost must he heayy; hnt the yalne of thO ore seems to justify 

even this expense. Of Ittte, · experiments have been made with various wet 

methods of concentration; and Forsvtha clisent~se~ in f:;Ollle detail the several 

processes which have been tried. He showl:l that the ~hie£ difficulty lies in the 

production of slimes, and that, in cases where considerable 'gold· values occur iu 

the ore, they pass into the concentrates ~ind not into the tailings. This difficulty 

is, however, of mihor importance, as the ore rarely carries any apprecialJle 

amount of precious metals. ·At the time that the mines were Yisited it Was 

suggested that thcsC orcs, wh!ch arc quite ~trongly magnetic, might readily be 

separated by the \Vetheri1l concentrator; and in the opinion of the writer th~ 

difficulties ~hat have been encountered might thus be obviated. It will be 

interesting to note the result of such expl~riments: 

VALUE. 

The :Mineral Industry for 18~9 shows that the tungsten market is a somewhat 

fluctuating one, and it is not therefore possible to g-ive any exact idea ?f the· 

value of the ore;. hut it is reported to ha\·e hccn sold at from ()LOO to $250 per 

ton ttceording to the percentage of tungstic acid presei1t and the date o£ sale.b 

DISCUSSION. 

'\Yolframite is not a common mineral, and its occurrence in bodies of suffieient 

size 'to be profitahly .,vorked 1s rare. Deposits have been fom~d· ·.re<~ently in 

.Arizona aud Nentda and at a few other loe~tlities in the U llited States.': 

uBlnck Hills ~iining Review, vol. 5, p. li'l. 

l>lbid., p. 15. 

,. A very comprehensive summary of tlw tungsten deposits of the United States may be found in the volume of the 

U.S. Geol. Surycy on )Iineral Resources for 189}-1000, pp. 300-!c\04. 
WOLFRA>liTE ORES. 16\l 

So fnr as the \Vritcr has been able to determine, the associations in which 

wolframite ~res arc found iu·e two: 

1. A.-; a constituent o-f pegmatitic gr'atlitcs, usually of the· type known as 

greiscn. and frequently more or less closely associated with ot·c:s of tin: Such 

deposits occur in the Black Hilis in the Nigger Hiil and Etta tin districts, hut 

the material ii':'i there crystalline, and i.::; generally beli{h;cU to have resulted hon~ 

rneumatolitic action. 

2. In quartz veins, hi granite or other rock of related character. "i\loSt of 

the more recent discoveries belong in this class; for instance, tho~e in the .J)rag-oon 

1\'lountains of Arizona; at :Murray, Shoshone County, Idah_o; Osceola, Nev.; San 

.Ju~n County, Colo.;. etc.a 

The familiar ca~m of the wolframite of the Connvall tin region 1s in part 

comparable with both ·of these typ<;.~. 

]twill at· once appear t,hat neither of these tv;'o elasses· of deposits bears any 

resemblance to tho.':.le under discussion, and it is cddcnt from the manner in 

which the ore occurs that it' is to be ascribed to the Hame mineralizing agencies as 

the deposition of the -siliceous ores. The association of the latter with fracture.:s, 

the occurrence in an easily replaced rock, and the manner in ... which original 

strnctlll'eJ; haxe bee.n preserved in the ore have been ::;hown to prove. that they 

are due to the replacement of carbonates by Siliceous material. In the <'.Use of 

the \Vo1framite there secrp::; no. rea::;on to doubt that the same series of eycnts has 

•taken place, although a partial replacement of quartz may have oecurred at the 

sanHi time. First there wa::; !\. fraduring of the country rock, then the replaeing 

action of mineralizing water:-3 which gained acces:-3 to the re.placeab,le strata by 

means of. the fractures, aud finally a gradual interchange of carbonate (and 

possibly of some quartz) for wolframite, molecule hy molecn,e. 

:Ll<:.Al! ANl) SlT ... Yl~H OHES. 

LEAD-SILVEH. OHES OJ<.~ GAI:..ENA AXD YICINTi'Y. 

The greater part of the llata upon.whieh the discu::;sion o-f these ores-at least, 

10 the vieinity of Galena-i~ ba~cd i~ taken :from the field notes of ltJ1;. G. \\T. 

Tower, formerly of the United States Geological Snrn~i The writer hn.::; merely 

assembled · J\tlr. Tower's descriptions anc{ formed :from them the generalized 

statements that follow. 

The lead-silver ores .of Galena and vicinity once tillCd a.n important place in 

the mineral producti<?n of the northern Black Hills. Ahout twenty years ag'o. a 

~melter was· in operation, and se,·eral mine8 were producing headly, thC Hichmond 

or Sitting. Bull mine especially having figured lluite prominently ~n the silyer 

production. Smith' gives the total output as "little short of $750,000." 

n !\Ullcrrtl He~ources, 18\19-1900, JlP· :c!00-304. b'rrans. Am. lnst. )lin. Eng., vol. 27, Jl. 427. 

• 
170 ECONOMIC RESOURCES OF NORTHERN RLKCK HILJ,S. 

After a bdef period of activity, howev-er, operat_ions were rather abruptly 

diseontinued, and the district· v.ras idle until the year 1806, when operations tv ere 

resumed, althoug-h upon a somewhat smaller scnlc. 'Vork is now bei~1g conducted 

in rather a dcsultoi-y manner. 

i\tines that have produced· this character of ore arc situated in and about the· 

town of Galena, mqst; if not 'all, of them. being- upon ore bodies that occur in 

strata Of (}unbrittn _age . 

. In· order of their importance, the principal producing mines are as follows: 

Richinond (Sitting Rull), Florence, Hester A., Coletta, :i\ferit No. 2, Cora, Carpenter, Alexander, Romeo, El· Refugio, and Washington. 

The ore that occurs in these mines is as a, whole of a much more basic ctlarllCtcr than any :fouud in the more westerly ore deposits heretofore deScribed. 

"~hen uuoxidized it eonsists chiefly o-f pyrife, whieh is either massive or more 

freqttcntly disseminated through the body of the country rock. With the pyrite is 

a~soeiated argentiferous galena and not infrequently small qnat)tities of sphalerite. 

In many cases the galena occurs in seams iri the pyrite or_ as druscs of minute 

cry~tals lining tl}e interiors of cavities~ In all cases where found nnoxidized tbese 

two minerals arc associated irr this manner. The galena is, therefore, of later 

origin than. the pyrite. Occ:v;iona1ly the latter earrics low values in gold, hut these 

are miimportant,: the. values that render the mines workable heing contained in 

argentiferons galena. ltr most eases there is but little silica as~ociated with the 

oreo, but in the Florence and Richmond (Sitting Bull) considerable amounts of 

secondary silica are found· in intimatt~ association with the deposits. In such 

case.;;; the body of the ore is composed largely of secondary ~ilicn and pyrite and 

re.<::emblcs in the mode of its occurrence the refractory siliceous orcs. Through 

the silicified material are scattere(f irregular bunches u.nd stringe1·s of argcntiferous galena and pyrite~ but the ~~elatiOns of the tWo can not be ~efinHeJy. determined. The sphalerite is not an essential ingredient, hut ocenrH at times in smaU 

amounts. The ore li~s in shoots or long lenticular bodie.s of varying thickness 

or width. These follow vertical fractures which traverse the Cambrian :"trata and 

the intruded porphyry bodies i_ndi1':lcriminate1y. They sometimCs strike in a single 

Q.irection; at others, form several intersecting systems. The trends of the fractures 

are usually constar;t 'rithin any single inineralized p.r~a. pisp~acerncnt along the 

fractures is generally ,~ery small, but in some cases t.ln·o,vs of as much as ·4 feet 

are observed! 0 q'J-Jw shoots ,·ary in width from scareely perceptible seams to flat 

bodies as mu\'h as-20 feet wide; the thickness is generally from " few inches to 2 

feet~ thoug~·~·~n some instances it is as much as 4: feet.. 'Vhen the fractures are 

open the ore generally fills the intervening space. The rock in which tbe ore 

occurs is either a quartzite eontaining eonsiderable calcite as a cement to the 
LEAD AND BIL V:F$ ORES IN CAMBRIAN ROCKS. 171 

') sand grains or a shaly limestone ~hat is presmnahly dol~mitic. The ore bodies 

usua1ly lie ii-I the. up1~ermost layers of these ore-bearing beds and ir;•mcdiately 

beneath a capping shale, the fractures sometimes extending hcyond the tihale bed::; 

atHl sometimes terminating in them. This ore-he~ll"ing rock ·in thO Florence and 

Hichmond, El Hefugio, and Alexander mines is ahout 300 feet aboYe the Algonkian, presun.mbly ncar, the top of the Cambrian series. In t,he Carpenter and 

"Tashington the m:e-bcaring. rock is about 100 feet above the schists and is an 

impure and sandy lin~estonc; in· the ~Im·it. No. 2, Co~a, Hester A., Horseshoe, 

Comet, t'tnd Romeo it is ·a calcareous qua.rtzite at or near the b!tsc ·of theA~::ambrian and not more than 30 feet a hove the Algonkian 8chists. • . 

The lead-silver values in these .Ol'C8 are \'Cl'V unc\~enly distributed. Much of . . . the ore from the Sitting Bull . mine was rich, containing 2,000 rmnces of silver per 

ton, but genera1ly the grade was very mueh lower and considerable quantities of 

the ore yield~d only G or S ounces per ·ton. 

In the mode 9f their occurrence these sulphide deposits hear a strong resemblance to the refractory ..,Hiccous ores, but are of much more basie ·composition. \ ' . ' 

Both occur in the form of shoots· whieh follow vertical fractures and constitute 

chiefly replacements of the calcium and magnesium cllrbo~atcs o£ the country rock. 

It is, ho\vcver, probable that the replacement in case o! these more basic ores 

has not been entirely confined to these more readily' .soluble Constituents. 'Vhile 

the oxidized condition of. most of .these Ore hodies renders it difficult. to obtain \ 

evidence on this point, it is not improbable that a considcrt\blc portion of the quartz 

in the country rock has heen replaced hy pyrite arid galena. 

Afle r~f the mineral't'.sation.~The fracttu;es along- which the ore deposition has . ' ' taken place Cl)t the eruptivcs, a1id fillings of sulphide frequently extend into the 

porphyries. The mineralization is, therefore, subsequent to their intrusion . 

• 

., . 
CHAPTER III. 

ORES IN CARBONIFEROUS ROCKS. 

T_hc gray limestone of the Carbmiifcrons eanics two distinct yarictics of.. ore: 

(1) Orcs of.gold and silver; (2) ores of lead and silver. The latter claS8 of ores was• 

in past years of very considerable importance; but the single locality from which 

·they were obtaincrl has ·long· since been 'tvorked out and they are n"ow chiefly of 

historical interest. · The gold· and silver ores are of the refractory type .and of 

comparatively recent disco\Tery, hut they arc of small ~ize and of minor importance. 

ln general tb.e Carboniferous rocks have not figured larg~ly in the mineral production of the region. 

GOT.D AND SILVlcR ORES. 

As stated above, these ores Rrc of the refractory siliceous type. They include 

the deposits found in tl;tc vicinity_of Ragged 

found in the ·neighborhood ofGalena. ' 

Top ~fOuntain and a small ·prospect . . 

RAGGED TOP DISTRICT. 

>Vest of the elevated region, about Crown Hill tmd Portland, i8 a broad, flat. 

plateau into which streams. ha\~c incised deep canyons with abrupt, precipitous walls. 

This plateau is formed. by the thick, massive strata of gray Carbonifei·ous limestone 

which extend with a olight northerly and westerly clip as far west as the edge of 

Spearfish Creek, being then cut through to the u~derlying Cambrian by the deep 

and precipitous gorge through which the :vaters of that creek find ogres~ to the 

surrounding ]o,vlands. ~rust east· of this canyon there rises from thut portion of 

the limestone plateau that lies between tbe two fork:; of Calamity Gulch and the 

l~w, rounded dome of Ragied Top _Mountain, a laccolith (,f phonolite intrndqd at 

the base of the Carboniferou:::; formn.tion, and llow exposed above the surrounding 

country by the erO-sion of the uplifted covering. In the flat limestone'that surrou'uds 

this phonolite masH 'are the ore borlies 1 upon the strength of whose discovery the 

tmyns of Baimoral, Preston, and Haggcd Top were built. It was formerly thought 

that these limestones would yield only lead-silver ores similar to those found about 

4: miles north at Carbonate: but in 18$16 a miner named \Vall made the 'accidental 

discovery of ric4 ore~ of gold occnring as irregulur bowlders of silicified limestone 

upon these limestone flats. A typical mining· excitement followed and a rush of 

prospectors to thC region caused the rapid growth of the above-named towns. 

li2 
GOLD AND SILYRR ORES IN CARBONIFEROUS ROCKS. 173 

The mines that h~Ye yielded ore are the ·Dacy group, the Ulster, the Pete 

Hand prospect, and some small mines on the southern slope of Elk Mountain. 

DACY GUOUP. 

The Dacy group comprises a series of seven nearly equally spaced vcrt,ical 

frac~nres just north of Hagged Top .i\lountain and separated from it by .Jackass 

Gulch. Taking them up· from cast to west they ha\·e the following strikes: 

"""(J0 1" ··,,... "9° E' "' ''~ " " ·so"' " 0 u0 E d N 5'"'0 J...'\, :->_ ~ ~.:., ..LY:_n_. ., 1"1. ~)I ['_.,_, J'\, n r ... , 1,. <) ., an . .1 "' .JCJ. 'l'l . _ 10 seven tb 

is·of'Conlparath:dy sm~ll importance. Numbers of small -fn1~turcs of comparatiycly 

insignificant size were also observed. Pl. XVIl (p. 214) gives an idea of the 

relation of these. fracture~ to the geology. 

These fissures are of variou~ widths at the surface, a maximum heing ahout 10 

feet~ from whiCh the~' range down to extremely minute crevices. In the lower 

portiOns, 'vherc surface ~Iteration has 'not been cxtl";n9ivc, the ore can be ohserved 

to pass laterally. int? the limestone 1ra!l.s '"'ithout disturbing the strueture of the· 

latter rock. It is of a uniform. light-buff tint which h.l so nearly the color of 

the ~urrounding limestone and so perfectly preserves tiic structure that hy the 

eye alone it can· be distinguished from the unmineralized country rock only b)r 

superior hardness and slight yellow tinge. NeverthelesS the lines of demarcation 

at citl~er 8ide of the . ore b'ody, if cxri:minecl closely, are sharp and somewlmt 

undulating. The mineralized: zone geuentlly narrows downw.ard so that at a 

maximum depth of about GO feet(1) the ore bodies are represented by mere 

~treaks. 

The ore when followed up to the sur-face hecmnes more and more bowlder-like 

and broken on acco.unt of the irregular manner in which the· disintegration has 

occurred. The gossan itself is compo:-:'ed of large irregular bowlders of extrem~ly 

hard :.;iliceous material, stained red and brown by iron oxide, and composed _of 

hrecciated and irregular fragments of limeston~, nm•t' wholly altered· to silica and 

co1~taining many sharply ~angular cfw1ties lined- with. dru.ses of quartz crystals. 

Cavities containing· calcite crystals are not inf_reqnently encountered, but occur, 

so far as knowh, in the poorer qlfality Of .. oi·C:- These bowlders are grouped 

in \incnr arrangement so that they outline the position of the fissur~. 

lHuch of the ore is cori1poscd of angular hrecgiated fragn~cni~ of whaf was 

formerlj~ limestone, but has been wholly altered to. ~iii";;a:-. The ore hc:trs strong· 

\ 

resemblances to the brc~ciated limestone that is found at many·"" poh).ts __ in the 

• Carboniferous areas where .there han~ been dvnamic disturbances but t~fller-- ---- . . ........_,_ alization. :Many fine thread-like crevices, stained _by a peculiar pil;kish-brown , 

oxide, in addition to the silicifiet~ion, bav_e been~-f0und associated \Vith these ores. 

All of this was formerly Supposed to be iro~ oxide, hut considering the large 

amount of tellurit_un present in the ores it is not imvrohable that it may contaiii 

an oxide of that metal. 
174 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

)1ICJiO~COPJC .\I'PEAHA:"CE • 

. Examined under the microscope the oro is found to consist chiefly of secondary quartz in irregularly bou~ded indi~'idual.s, which do not show crystalline 

_boundaries except where open space:; have nJlowocl their formation. .A little' 

·opaline silica is also present. · The yellow color seems· to be due to the presence 

-~f a .uniforml.1; distributed pinkil:;h-brown pigment, which is spr~ad between. the 

.grains of quartz in such thin films that its character can not be defini~dy deter-

. mined. Some of the richest portion.s of the ore show excessively millut.e opaque 

Partieles, that ;nay be m<;tallic. In on~ specimen .Qf ore, 1 carryh~g. $3.05<·per ton, 

a smftll ~p~ck of metallic mineral rcscm~lin'g SJ~h anitc was· detected, but·· in general tellurides, if present, have' been_ completely oxidized. ? 

CHE~IICAL CITARAC'I'ER. 

0 0 

Two analyses are given below. No. I was taken from the paper by F. U. Smith.• 

No. II was made by W. F. Hillebrand in the laboratory of the United States 

Geological Survey. 

SiO~ ............... -.· .................................... . 

Al 20:1- •••••••••••••••••••••••••••••••••••••••••••••••• 

L 

Per cent. 

90.990 

2.970 

Fe20.1 •••••••••••••••••••••••••••••••••••••••••••••••••. . ••••••••••••••••• 

FeO ~ ~ ~ ~ ~ .. ~ ~ ~. ~ .. ~ ..... ~ .. -~-~- ~. ~ _ ~ ~. ~ ~~~~. ~. ~ _. _ ~ _ ~ .. ~ _ ... _. ~ ~ _ ~ :J. 024 

l\fgO . . . . . . . . • . . . • . . . • . . . . . . • . . . . • • . . . . . • . . . . . . . . . . . . . . • . . . . . . . . . • . Trace. 

CaO ... ~ .... ~. ~. ~ ... ~. ~. ~. ~. ~- ~- ~~ ~ _ ~ _ ~ _. __ --~ ~ ~ ~ _ ~ ~. ~. _. _. ~ ~ ~ ~ ~ ~ _. 

BaO. ~ ~ ~ ~ ~ ~. ~ ...•... ~ ~ ~ ~ ~ ~ .. ~ _ -~ -~ -~ ~ ~ ~~ __ . ~ ~ _ ~ _ ~ ~ ~ _ ~ _ ... ~ ~ _ ~ .... __ 

Na./) .. --- ... -.- .. -- ... - ..... -.-.-.---.-.---.. -.- ..• -... -.-.- ....•. 

K 20 .... --·- .... -... -.-.- .............................. -. ~ .......... . 

1. 1~8 

Not det. 

Not det. 

Not det. 

Li 20 .......... ~............ . .......•.•. -•.. _ ...................... _ Not det. 

::~~~~~: ~ ~-~ ~ ~ ~ ~ ~~-~ ~ ~ ~ ~ ~ ~-~ ~ ~ ~ ~-~ ~ ~ ~::::::: ~::: ~:: ~: ~:~:: ~~ ~:: ~:: ::} . 110 

C02 - •••••••••••• - ••••• - •• -.-••••• - ---~--- ~ ----. o : • •• - ._ •• -.-.- .·.- -;- ------ •••• -. 

Volatile nmtter ..................• _· ....... ? .... _. __ ....... __ ... _. _. . 802 

::\ot. det.. 

b. 0.52 

/), 002 

'· 091 

II. 

Per ce7lt. 

\ 

96,27 

.:26 

0 19 

.19 

1.16 

. 06 

• Q.j 

.11 

Strong trace. 

• O:J 

1.42 

. 96 

. 05 

c. 06 

c.02 

rl.08 
• GOLD· AND SILVER IN CARBONIFEROUS ROCKS. 

By assay (ouncP.R per ton of 2,000 }JOIIUd~)-

Te ___ .•. ____ .... _ ... ---- _. _____ ~ ------ ___ .•.. ~ ___ .. ______ .. ______ . 

• .\u------ ------------.--- _·_-. ---- _· __ . ---.--------- .. --- --~-.----- -- . 

Ag----- ------ •• ··,------------ ---------.---- •• ~------- •. ----- ••• ----

]. 

29.26 

17.:l4 

1. 21 

II. 

175 

15.2.') 

4. 75 

The silica wilr be at once seen .t,o constitute nh~wst' the entire bo~y 

rock, only a small amou~t of calcium a_nd magnesium remaining unrcpJaced. 

of the 

The 

Alumina probably represents some original impurities in the replaced lime:sLone, 

as also the soda, potash, and lithia. The vobt~le ~natter ·in analysis N~. I iS 

probably equivalent to the CO, in No. Il, the latter i~gredient resulting from a 

small amount o£ carbonates in the ore. It scmi~s Probable that the irOn in No. I 

is .not all ferrous, but some should be given as ferric iron. It is customary in 

the analyses of these ores, ,yhieh are nu_1dc for conun.ercial purposes, ·to calenlate 

all the iron as ferrous. The alkalies .were probably contained in the original 

limestone and the small ~1mount of barium may have existed in that r:oek or have 

heen introduced at the time of mineralization. 

At the foot of analysis No. I in the paper on these ores Professor Smith 

makes the following statement: 

Combining the gold, l'lilver, and tellurium in the above analysis we find ihem existing in the 

following relative percentages: 

I'er cent. 

Telluritnn _____ ... ·---- _ .. --------- .. __ .... ---- ....•.....•••......•. -------... 61.20 

Gold _______ -----. _____ .----- .. ---·. _____ ------.----- ..••.•...... _........... ;{6. 27 

Silver ... _ ... _----- ____ .----- ____ ---------- .. ------ .. --.-- .. _ .. -...... ------- 2. fi3 

---· TotaL. .......... : .•.•.••••........................•••...•••......•.... 100. QO · · 

This dosely approximates the composition of Hylvan"te according to Kla.proth's analysiE. 

It will be noticed that in Analysis II the proportions are different, the per-

,centage of silver being greater and that of tellurium relatively 1ow. Some o£ 

the tellurium may, howeYer, have been remove~ during the process of alteration. 

·The sulphur shown in Analysis II ·may -perhap; be combin~ with a portion of 

the ferrous ir~m in the form ·of. pyi·ite. • 

On the whole the presence of telluriunt in these o~~- seems to offer the most 

plausible. e~plana.tion of thCir refractory character, and 'in-the~ ~igbt o£ present 

knowledge it is not easy to suggest any other cause that will account -for_ the 

~-~- difficulty of treatment. 

::\1ETALLIU STRJ<JAK MINE. · · 

This mine is situated on the sOuthwest 

~--. --

side 

-,c---. 

of Ragged Top Mountain, .just across 

• 

'\-

~ 

Calamity Gulch, on the top of the liniesto~e plateau. It comprises a series of shal-~·. '"-~ 
176 ECONOMIC RESOURCES OF NQR'l'HERN .BLACK HILLS. 

low diggings from which arc quarried flat bodies of red-stained limestone that are 

reported to carry as high as :i\10 to .$25 per ton in gold. Associated with this 

ore arc certain irregular patches of silic~ou1; material resembling· the Ragged Top 

ores in many respects, but carrying less gold, aml often hea,·il_y impregnated 

with purple fluorite. The latter material also occurs in dense, sandy mas~cs and 

in general doe::; not carry much gold. In n, few cases. there arc masses of brecciated niaterial· parallel ,with the bedding, <~cmcntcd hy bro\vn-stained silica. The 

deposits are small and irregular and now :-;o decomposed th~t their relations can 

not be readily appreciated. 

ULSTER MINE. 

The Ulster mine is situated on the n0rth side of Long -Valley ahont one-third 

of a mile north from the town of Preston. The c~mntry ·rock is Carbo'niferous 

limestone .. A little north <:f the· mine 1~ an irregul~ir hill composed of eruptive 

rock, while 'the mine is also intimately n.s~ociated with irreg.ulnrl,\' intruded masses 

of rhyolite and phonolit~. The ore occur:-; as irregular mas~es of silicified limestone with which fire a8~ociatcd quantitie~ of brilliant, purple: fluorite. These 

masses are generally iJ! the limestone at the contact of that rock with irrcg.ular 

bodies of porphyry. The porphyry is often· :-:o decomposed as to be lit-,tlc more 

than soft clay. The portion containing fluorite is u~mLlly lower in gold than 

Other parts of th~ roek, and the highest values :u:e contained in the dark-colored 

silicified limestone. ·Much of the ore frotn this mine carried yery high values, 

some of it yielding us much .as $2,000 per ton in gold. .The greater part of 

the ore w·as taken from :-;udace workings and from a large number of shallow 

shafts, hut tile conditions are now imch that but little can be made of the general. relations of the ·ore. 

Irregular bodies of silicified limestone have been· found at many loealitics 

at various points. on this 1iriiestone plateau, both northwar4 a:.; far as the junction 

of Spearfish and Squa·w creeks, and southward to a point south of the Burlington and 1\'Iissouri River Railroad .. Many of them, such as the Pete Hand prospeet, . ' 

carry a moderate amount of gold~ but none at present writing sufficieii't to admit· 

· of ~ini.ng operat!on . 

. ~~. 

~ -~.~=-.,__-ORIGIN OF TIIJ<.J ORES. 

;r:-:-· . -'~he ge~_ra( character of the ores iS such that they may be readily seen to 

'~-~be...-l~~~tents of limestone by silica and fluorite with small quantities of gold, 

_./"' ~er~ and tellurium. \Vh·e~eyer sufficiently exposed to admit of ob~enration the.r 

-~~'"'" arc associat"ed with fi~~ctures which, .. in .the_c~se_ ?f Hagged Top deposits, have been 

traced downward-for' more than 300 fe~t. If it .is assumed that the deposits were 

~--"""fOrmed by ascending solutions the differing 1ithologic conditions "\vill account for 
LEAD AND SILVER ORES IN CARBONIFEROUS ROCKS. 177 

their differenee from the :siliceous ore bodies, which is chiefly one of form. The 

country rock here i.s a IIU1ssive, homogeneous limestone in \Vhich there secn.I.s to 

be nothing that would favor a concentration of ore at any particn~ar horizon, 

whereas, in the Cambrian deposits, there have been irilpervious ~hale beds or sheets 

of porphyt•y which have caused the mineralization to spread out away from the 

yerticals at definite horizons. 

:r.~~AD AND SILYER ORES. 

CARBONATE biSTRICT. 

On the north side of Squaw "creek, ncar the point where it enters Spearfish 

Canyon, is the town of Carbonate. This was a flourishing camp in L8S6 and 

pro~uccd considerable silyer and lead. A smelter was built and during a number 

of years wa~ in acth·e .operatwn. The production o{ the Iron Hill mine, the 

largest and most important mine in the district, is given below. It is probable 

that considerable ore was produce.d by other mines \vhich were· Uctive from time 

to ctimc. For the years 1889 and 1890 no output is reported, and it is probable 

that the mine was idle during thttt period, although the writer could· obtain no 

definite information on that point. 

Production of Iron Hill mine, Carbonate camp. 

1885 -----------------------------·----------------------·· ; ________________ _ 

1886 ...........•.....•................ ." •••....•..••................ ... : ..•. 

188i .... --- .. ---- ....... -.- .. -------.-- .... ---.---... -- ... -.- ... -..... -- .. . 

1888 ....••...•••...•.•....••.....•...•..........•....•...•.....•........... 

1891 ······················································'·············~·-

!513,394 

:nz, 120 

259,942 

15,000 

6, 762 

Total.---- ___ ........... ____ .......... ____ ........... __ ...... ___ .. -.--_. 60i, 218 

The country rock that carries the ore in the Iron Hill mine is the gray 

Carboniferous limestone in which sills, dikes, and irregular masse.\:i of porphyr_r 

have been intruded. The ore· bodies arc of two kinds: hlrge, irregular bodies of 

lead carbonate, which pass in places into more or less unaltered galena, generally 

in close contact with porphyry masses; and partially filled' crevices which rese~1l~le 

in a general way the verticals of Ragged Top described on page 173. 

The first type of·deposit is that which has formed the chief source of silver in the 

district, and1 silver, as shown above, was largely obtained from the Iron Hill mine. 

In this mine the or,e \Vas a large mass of argentiferous lead carboimte which ·ex~----­

tended down for 300 feet on the east side of a thick dike of nne-grained' white 

porphyry. Much galena was also found together with the carbonates, and after 

the ore Was worked _out 11 scam or vertical' was detected extending downward 

from the main mass. Other pockets of ore were also found at ·different 

points, and·. in one place a pocket of_l vanadiniteo c~ntaining 4 or 5 tom; was en4987-No. 26-0-t-12 
178 ECONOMIC RESOURCES 0>' NORTHERN BLACK HILLS. 

countered: :;_ur. Fo,vler report:; ·the occurrence of the following ti1inerals: Galena, 

cerussite~ ccra_rgyrite, matlockite, wulfenite, pyromorphite, plattnerite, atacamite, 

and vanadinite. This type of o-re t'Bsembled in its general eharacter and in its 

as::;ociation with porphyry bodie::;,, the deposits described -by l\'I r. S. F. Emmons, 

from Lead,;iii~~, Colo. a Too little is knmvn, however, regarding the details of the 

ore oc(:unence to afford any more definite iclea of the UHtnnet:,.. in which it originated than the .simple fact that it i.s probably a rcplacmnont of th'e limestone. 

Of the second type of occnrt·enGc the most importunt case is that at the Seahury 

mine. This consists of an irregular crevice striking S. 85° ,V. and running 

through the Seabury, Iron Hill, Segregated Iron Hill, and Adelphi mine:s with 

a possible continuation in the Spanish lt, a mine in which some ore was obtained 

but at too great a distance for its relation to the others to he clearly made out. 

This crevice ''aries from 1 ·to 20 feet in width. The sides con.sist of a ferruginous 

jasperoid material ,~hich replaces tbc limestone often for .2 . Or 3 feet from the 

cre\'ice and contains at .... time~ galena, lead carbonates, and ccrargyrite. in sufficient 

amount to he profitably- worked. Cerargyrite most frequently occurs as a thin 

film c<nrei·ing drnses. of fine quartz crystals which form linings to car·ities. 

The center o·f the credce was loosely filled by a soft, ferruginous, gougelike pinkbh-red matter containing gold. A .large quantity of this ore is 

reported to ha,·e been mined from the Seabury, an~ also from the west· side of 

the porphyry dike in the Iron Hill. 

To the north of the Seabury mine is a series of shafts situated along a line 

which strikes N. 74° W. These are the Far West, Hattlcr, Enterpri.se, \\' ilkerson, and Hartshorn shafts. None· of .them are uow acces.sible~ but they a1e 

reportyd, to ba':"e been sunk on a :-:econcl crevice of t<imilar character to that just 

de~cribed. Only small amounts of ore were obtttined from -these workings. 

Numerous other small iron-stained seam:-; or partially opened crevices may ·be 

observed in different places on the surfaee, but they do not seem to have been 

productive. 

Since 1891 there _seems to have been but little work done in this district, no 

output being recorded for that period. Within the last year, however, a small 

35-ton cyanide plant has been erected to treat the tailings from the old smelter.' 

aEmmon~. S. F., Geology awl l\Jfning Industry of Leadville, Colo.: )Ion. U.S. Geol. Survey, Y<?l. 1:2, p. 886. 

bFulton, C. H., Bull. South Dakota School oi )Jines Xo. 5, p. 6;'). 

--------------..- \ 

\ 
• 

CHAPTER IV. 

ORE DEPOSITS IN ROCKS OF lUICENT ORIGIN. 

PLACEH DEPOSITS. 

At many points throug-hout the hills auriferous gravels of comparatively 

recent origin have been· worked, and constituted m early day:.; the most 

important source of gold in the region. Here, as in uumy mining· districts, 

their discovery evidently led to that of the large and more permanent .lodes. 

Nearlj· all of the large gulches that lie well withii1 the Black Hills uplift contain 

gold in some quantity, b~tt it is chiefly those that head up in the areas of 

Algonkian rocks that luwc yielded large returns. The productiye placers have 

been found in greater numbers in the southern portion of the hills than in the 

northern, hut of those in the latter region the famous Dead wood placer and 

Nigger Hill ·placer~ lmvc been important. The gold in thc~e placers is all derived 

originally from the Algonkian rocks 1 for as the siliccou~ orcs contain free gold 

only in rare instances it is not probable that they have added to the placer gold r 

derived from other sonrce!S. The great comparati,·c riehness of the Deadwood 

placer ha~ been shown by Devereux to he the result of a double concentrationfirst, in the formation of the fossil placers or cement deposits at the ba~c of 

the Cambrian, and, later, in th~ sorting of the material derived by their disinte- · 

gration; The Nigger Hill placers arc comparatively small hut numerous and 

ha,·e yielded rich returns for the area mined. \Vhen the gold from tl~c~: ores ----

is panned it is f01~1d to Uc m_ingled with great quantities of tourmaline -itnU 

ca~~iterite and innumera!>le small red garnets~ typieal minerals of the _Algonkian 

rocks, while to many of the nuggets and grains of gold, are found attached 

fragment~ of glassy quartz, anU in a few cases flakes and small masses of talcose-- _ 

schist. Some speculation has taken place regarding the riehness of the lode from 

which the placers of the Nigger Hill region seem to ha\·e, o!·iginated rmd 

prospectors have been at considerable loss to exphtin the continued failure to 

find the mother lodes. It is w~ll, howeverl to bear in mind tlFtt nature is a 

natural Concentrator and that rich placers lllay readily have been deri,·cd from 

1 i9 
180 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

quartz ledges in which the gold was so .<;parsely dbtrilmted as to offer· no 

encouragement. to -the 1 prospector. The continued action of erosive agenoie~ 

through great geological ages by operating on great qnantitics of material bas· 

concent·rated the nuggets 0£ (gold hnd made them easily aece:;siblc to the miner, 

when in their original condition they may have been separated b.r :;o great areas 

of barren rock as to admit of no mining operations. In general the placers are 

not now productive. -Many of tho~e ,worked out are still yielding very .small 1 

quantities of gold and enable some of the poorer miners to earn a livelihood~ 

but as a factor in the mineral wealth of the hills their importance is largely 

hh:torical. 

• 

I 
CHAPTER V. 

DETAILED DESCRIPTIONS m' MINES. 

This chapter is designed to include detailed descriptions of mines which have. 

not been separately treated in the previous pages. The mines have been grouped 

together comformably with the general arrangement of the paper; that is, basal 

Cambrian conglomerates arc first treated, and then the refractory siliceous ores. 

As the mines working upon the other types o£ deposits are but few in number, 

their descriptions have been given with their general discussion and are not 

repeated here. 

MINES IN AUHH'EROUS CAJIIBRIAN CONGLOltiEHATE. 

These mines are situated in the vicinity of Lead on the gold-bearing conglomerates at the base of the Cambrian series, isolated remnants of which lie on 

the tops of hilb of schist, such hills forming an old Algonkian surface which 

dips in a general way eastward from the Homestake outcrop. 

There arc five productive areas~ all but one of which are located on the east 

side of the Homestake lode. The remaining one is on the hill between the Home· 

stake open cut and Poorman Gulch. 

Beginning on the north the following mines have been worked on the four 

areas to the east of the Homcstake (see Pl. VI). On the north side of Blacktail 

Gulch, beneath the heavy cap of rhyolite, the Minerva and Deadbrokc mines have 

opened up a large area of gold-bearing gravel. These mines have'been described 

on pages 106-110. Between Blacktail and Hidden Treasure gulches are the 

Baltimore and Deadwood, Esmerelda, and Hidden Treasure 'mines. These are 

nmv inaccessible. On the area next south, which lies on the crest of the divide 

between Blacktail and Deadwood gulches, are the Pinney open cut, Omega, and 

·Deadwood-Terra mines. The first two are described below and the third was 

not visited. 

About 1,600 feet southeast of the last-named area, beneath the thick cap of 

rhyolite which forms the top of a high hill just cast of the Caledonia 'open cut, 

are the Hawkeye-Pluma, Gentle Annie, and Monitor mines, which have opened 

181 

• 
182 ECONOMIC RESOURCES OF NORTHERN RLAOK HILLS. 

up a large area of g~ld-bearing congldmcratc.. These three mines, the :Monitor 

in particular, have been ve(r important producers, and they are described in 

detail 1 below. 

On the west side of the Homestake lode, between the Homestake open cut 

and Poorman Gulch, is the remaining" area which was ,vorkcd hy the Durango 

alld Harrison mines. Desci-iptimm of those mines will he found on page 105. 

P/nney op(._,>J~ cut.-This is thC most northeasterly of the 3 mines operated on 

' a small area of conglomerate occupying the divide between Deadwood and Bobtail 

gulches. It is located on the extreme north end of a small spur, hence just east 

of the buried outcrop of the Homestake lode. It was one of the earliest ope~ed 

.mines of gold-bearing conglomerate' in the region and y'ieldr.d much rich ore, all 

highly oxidized. White quartz in the nature of broken ledge matter is said to 

have been mined from here, yielding very rich returns. 

Omeqa mine.-Southeast of Pinney open cut are the workings of the Omega 

nunc. A tunnel runs west £ron the upper Tcrraville road through A1gonkian 

schists and the ore is mined through rabes into the conglomerate above. The 

conglomerate is about 12 feet thick and lies under a roof of friable, shaly sands. 

The stopes of the old mine are largely caved. The conglomerate was oxidized 

and contained a great number of fragments of schists of somewhat angular 

character; the remaining material was oxide of iron. Lenticular masses of quartz 

were encountered in. the schist. They strike northwest and dip cast, and are 

said. to carry free gold in \vorkablc amount. They are supposed to be small 

,·eins parallel to the main Homestake ore body. The ralue of the ore in the 

Omega mine is reported by the management to be "$6 per ton 1 of which $1.80 to 

S2 C:Ul be sayed by amalganw.tion. The ret;t is refractory and can only be 

extracted by cyaniding. 

MONI'l'OH., GE_XTLE ANNIE, AND IIA WKEYE· PLU.:HA JIIXES. 

These three mhtes open up the area of gold-bearing conglomerate that lies 

beneath the heavy porphyry cap on the hill east of the Caledonia ore body. The 

floor of this area slopes sharpl.i· east away from the summit of the hill. 

_Monitor.-The most northerly of these three, the Monitor, is opened by a 

tunnel at the head of the South Fork of Bobtail Gulch. The tunnel extends southeastward and the workings run east and south so as almost to connect with those 

of the Gentle Annie and Hawkeye-Ph.ima. mines. The tunnel which opens up themine is in the A1gonkiau schist some distance below the conglomerate outcrop. 

It pusses southeastw~rd through :;chist into a large lmsin-like'~mass of conglomerate ii1 which great chambers, often 20 feet high and 100 feet wide, have been 

exCayated. The roof is a friable, cross-bedded ~:~and, often loosely coherent and 
MINES IN AURIFEROUS CONGLOMERATE. 183 

interrupted by bands of a finer texture compo~ed of sand, scales of mica, and argillaceou~ material. ln the roof is a series of iron-stained fracture~ :following many 

different directions and intersecting one another. Some of these can be traced 

down into the ore, where they become lo8t among the pebbles of the conglomerate. 

The latter contains many very hirge bowlders and ·numerous fragments of schi::it. 

lt is cemented ·by ·oxide of iron, but in many places thi.s pa8scs gradually into n 

.matrix of pyrite. 'Vhere the working.s approach those of the Pluma mine little 

or no oxidation has taken place and the quartz pebbles are embedded in a solid 

pyrit~c matrix sometimes showing cavities lined with druses of th~ same mineral. 

The conglomerate is frequently interrupted by interhedded layers of quartzite. 

Gentle Ann/e.-The workingi-i of this , mlne ~tro s.ituated east and slightly 

north of those of the ~Monitor. They are opened by a tunnel at the head of the 

g•1lch next east from Bobtail, which is tributary to Deadwood Creek. The 

conglomerate in this mine is underlain· by a sheet o:f rhyolite which has been 

intruded between the conglomerate ~tnd the schists. As the porphyry tli~s south 

the drifts cut throug_h it into the ovcrl.\:ing conglomerate, and at the extreme 

southern end of the mine the latter rests directly upon the Algonkian s·chi~ts, 

the porphyry having passed downward into the roc~s of this senes. The 

conglomerate, where exposed in the :-3topes, shows a thickness of :from 2 to 6 

feet, hut only the basal portions have been mined and the actual roof has not 

generally been reached. The greater part of the (~onglomerate is nnoxidized, 

the pebble~ being imbedded in a matrix consisting largely ~of pyrite. The 

porphyry is itself impregnated with pyrite, ~tlthough no increase in this mineral 

c<;ml<l he detected near its immediate contact with the overlying ore. 

Ilrtwkeye-Ptnma.-To the south of the Gentle Annie is the third of the three 

mines operated upon the Caledonia conglomerate a~·cu. Here the hill is cupped 

by a hmwy sheet of rhyolite, under which is dolomite, qmtrtzite, loosely bedded 

sands, and finally ab?nt ±0 feet of conglomerate, the lower portions o-f which 

are gold bearing and rest npon the Algonkian schist. The mine is opened by a 

shaft and four ~unnels. The tunnels rnu westward from the brow of the hill ~ ' through the ;3_9hist into a baSin of conglomerate, the gold-bearirig portion of 

':vhich forms a channel trending in a general way north and sonth, and with an 

average width of 60 feet. This channel is 'nearly· 1~8(10 feet long, and strikes 

about N. 60° E. for about 400 feet in the southern and " few degrees west of 

north in the northern1 BOO feet. It lies approximately 200 feet west of. the 

outcTop. On the east side ot thi~ channel the schists rise very gradually, so 

that the three n'?rtherl.Y tunnels soon pass from it into the ovcr·lying conglomerate, 

hut 6n the west the rise is extremely steep· and the ore is cui off ·hy the 

sandy beds that form the roof. An indinc has been run on this western contflet~ 
184 ECONOMIC RESOURCES 01<' NORTHERN BLACK HILLS. 

and_ farther south a tunne-l has _been driven for 875 feet into the schists, upraises 

having· been mndc to the eontnct above. Tbc .. ;c relations may be readily made out 

from Pl. XVJII (p. 214). The ore is nearly .J.O feet thick in places, but the average 

would probably not be more than 0 cu· S ·feet. In the northern end of the workings 

the greater part is still in the·pyritic condition, the oxidation hadng been confined 

to the southet·n portion of the ore body. When panned both pyritic and oxidized 

ore show tine 8cales of ,v_atcrworn gold. ~tatemeuts arc conflicting as to the. 

value of the material which has been' removed, but from the 'fact that the mine 

was profitably worked in very early days it is probable that the grade was quite 

higli. A series of assays of the ore now exposed in the workings~ made during 

a systematic sampling of the mine,- shows that the high ,·alues of from $10 to $12 

per ton ure confined to the material forming pillars in the center of the .stopes, 

while the marginal conglomerate docs not contain sufficient gold to be profitably 

worked. The mine has now been idle for some years. 

' 

l\IINES IN REFRACTOUY SILICl<JOUS ORJ<JS. 

As previously described, the refracto_ry siliceous ores occur in five fairly welldefined areas, each of which is separately considered in the following, pages. The 

individual mines are described ·and no attempt has been made here to give a 

general geological treatment of these area~,. because such will be found in the 

main body of the text under the heading "Areal distribution" on page l.J..J.. 

BALD MOUNTAIN AREA. 

The Bald Mountain area is the largest and includes the greatest number of 

mines from which ores of this class are obtained. The ore bodies are taken up 

and described according to rough groups in which they may for convenience of 

description be div1ded. These are shown and named on the' map, Pl. IX (p. 214). 

The indiddual mines are described from north to south· within the limits of each 

group·-excep~ where_ a mine occupies intermediate position. 

Buxton mine.-The Buxton mine is situated on the eastern extremity of the 

didde betweer; Nevada and Fantail gulches, just above the loop in the Fremont, 

Elkhorn and Missouri Valley Railrond. The workings are upon the basal quartzite 

and were opened by ·tunnels On opposite sides of the didde; they are now inaccessible~ The ore shoot is very near the surface and is reported to have had a 

generO.l north-~outh direction. The mine was· an extremely rich one, having· 

pioduced high-grade ore in considerable cfuantity. 

J-letrie~Jer 1n~ine.-About 800 ·feet west of the Buxton is the Retriever mine. 

The ore is in or near the basal Cambrian quartzite, on· the sam~ divid~ between 

Nevada and Fantail gulches, upon which a long tongue of still unerodcd Cambrian 
MINES OF BALD M.OUN'.rAIN AREA. 185 

lies between the Algonkian measures· exposed in the· gorges to the north and 

south. It il':l opened by two tunnels; one at the north and one at the south end 

on opposite sides _of the divide. -Below the quartzite which forms the floor of 

the ore body is a thick sill of diorite-porphyry. Above the ore is another sill 

of the same rock. The dolomite intervening between the quartzite and OYer lying 

porphyry is,up to 5 feet in thickness. One ore :-;hoot onl}'~ 'vhich follows a fracture that trends slightly west of north, was found in. the mine. The fracture or 

Y-ertkal extends upward from the ore into the porphyry, proving that not only 

the ore, but also the fracture, is of later age than the porphyry: ·• 

Stewart mJne.-The Stewart mine is located on the divide between" St.ewart 

and Nevada gulches and extends through to Stewart Gulch. The country rock is 

Cambrian shale and dolomite, with underlying basal quartzite. The ore shoot 

is 'opened by two "tuimels~ one at the north and the other 'at the south end. lt 

is 1,160 feet in length, and. strikes slightly east of south, with a width Yarying 

between 10 and (iO feet. For the first G80 feet it follow' two main parallel northsouth fractures. Four hundred and eighty feet so~th of the north end there is a 

small ore Rhoot to the southwest caused by a N. 3()0 E. fracture whieh intersects 

the main vertical. The mairi shoot her8 becomes n~rl'O\\' and follows a fracture 

running north-south, then N. 30° E., and finally it follows a second fracture 

,.,..ith a north-south <lireetion. 'The cross fracture intersects eaeh of the others, 

and the ore extends only short distances beyond the intcr:-;ections. The floor of 

the ore is (piartzite; the roof a tine impervious shale. To the east the mine is 

connected with the Golden l{eward by drifts through the barren country rock. 

The workings arc all very close to the surface. The ore from the Stewart is 

highly oxidized and contains higher values in gold and. ~ilyer. It exhibits in 

many cases a peculiar shell-like, subconchoidal parting resembling the exfoliation 

of weathered granite bowlders. Thb is a feature which is freque?tly ohsern:!d 

in the highly altered . siliceous ores. No sulphide ore has-_::·beeu found in the 

Stewart mine. The Stewart body is probably a southward continuation of the 

Bnxton, the intervening portion having been removed by the erosion of Nenula 

Gulch. 

Golden Reward m£ne.-The Golden Reward mine is located ou the didde 

between Fantail and StCwart ~ulches, just east of the Stewart. It comprises t,wo 

distinct and dise.onnccted serie8 of \vorkings, one forming the south end and the 

other the north end. 

The northerly workings of the Golden Reward mine and those of the closely 

adjoining_ Tony and ~Iaggie claims are upon· the ·same ore shoot and· comprise a 

series of open cuts pas_sing in n southerly direction into stopes a fmv feet below 

the surface. The underlying rock is the basal Cambrian quartzite about 25 feet 

• 
186 ECONOl\IIC RESOURCES Ol<' NORTHERN BLACK HILLS. 

above the Algonkian, but at the :;outhern end of the. mine it gi\·es place to 

porphyry, which gradually rises from the floor until the ore i.s completely cut 

off. The roof is shale. At the north end the Golden Reward shoot attained the 

unusual width of 3±0 feet, a width greater by lGO feet than that of any ore 

.-,hoot in the region. Thi~; ore l1ody extended south into the Golden Reward 

mine for 125 feet 1 and then it divided into three :-;mallei' .':'hoot.~, the tfo v .. ·e.sterly 

following S. 30° \Y. fractures, and the other:-; run_ning in a direction :-:;lightly 

east of south. ~lmost all of the working·.-; rtrc now inaccc.-;sible, but the fact that 

it seiJarate~ at its southern end into two scric':l of ore.hcaring fracture~ haYing 

the usual directions make.-, it probable that its great .si:-:e is due to the intcr.-;eetion 

of numbers of north-::;outh and N. 30° E. fractures. A north-south fault oeeurs 

neal' the eastern side of the· Golden Heward ore hod.r and tht:ow.:; the oro do~n 

on the east side;· the. throw is 8 feet, gradually deerca..,ing to nothing at the 

south end of the mine. There b a space between , the t\vo faulted portions of 

country rock of about 18 inche:-; in wichh which i . ..; tilled with fmgmcnts of sehist 

· and porphyry. 

B·t:q Bonan.za m£ae.-Th_b mme 1 . ..; situated on ~he divide Separating Fantail 

and ·stewart. gulches between the workings of the Golden Heward on the west 

and tho:;e of the Little Bonan:-:a on the east. The ore outcrops on the north side 

of the divide, where ~t is opened by a. tunnel. The shoot is very (~xtcnsh·c. It 

oceupies nlmost the entire claim, ancl is oftci1 15 feet in thicknes:-;. It rest:; on 

quartzite and comes in contact with a large dike of phonolite on the west side. 

The workings are now inaccessible. Thi..; has bee·n a yery productive nJinc. 

Fannie mine.-Thc Fannie mine i::; opened by a shaft situated on t.hc Honthern 

side of ~h~ broad diridC between Fantail nnd StC\vart gulche.-, to the northwest 

of the Little Bonanza~ northeast of the Big Bonanza, and about 600 feet cast of 

the long shoots of the South Golden Heward. The 'haft is 265 feet deep, and 

according to F. H. Carpenter affords the following ::;edion: 

Section in Fannie shaft. 

Feet. 

Cambrian shales ............••..................................••.. ____ .•.. __ .. 70 

Cambrian shales, containing a little ore .........••.•.. '.......... ------ ____ ..••.... 6 

Cambrian shaleH .......••............•.••... ----· ...... ---- .... ~ ..... __ . ____ ..... 4 

Trachytoid phonolite .................................. ,: .............. _____ ...... 165 

Cambrian shale~! awl dolomite ......... _ ..... __ ...... _ ..........•.. __ .... ____ .... 12 

Ore ..............•....... : . ........•...........•............................ .: . . 10 

The mine is now inaccessible~ hut .from the forcman1 Mr . .lt. Rodda.1 the 

following statements have hcEm obtained: There are four bodies of oi:e. One. 

small shoot trends about N. 12° ,V,, is 10 feet, 111 t,hic~ness, and about 30 feet in 

width. It lies on porphyry. West of thi.' i' a hroad shoot about 65 feet in 

• 

\ 
l\UN.ES OF BAJJD "l!OUN'TAIN AREA. 187 

maximum width trending likewise nhout N. 12° \Y., und dividing into 3 narrow 

shoots toward the north. This shoot was pos.:dbly ±0 feet higher than that to 

the cast, hut was sittUlt.ed on or near the basal quartzite. Both of these shoots 

are about 150 feet lower than the wo~·kings of the mines to the north and 

west, but ftrc on ~he same lcYel with the Sundance shoot to . the south, with 

which the more easterly is probably connected. To the ettst arc two other 

small ·ancl low-grade shoots trcmling about N. 10° 'V-~ and almost north of the 

large shoot of the Little Bonanza 111ine. The probable ('ause of the difference 

in altitude of the ~hoot~ lying in and -about the Fannie mine is the intrusi<;>n of. 

a sill of traehytoid phonolite from the cast. The phonolite has hroken irregularly ncross the Camb,rian so that the orc-bcarin~ beds sometimes\ lie below and 

som~times abon~ the eruptiYe. The ore from the main shoots of the Fannie 

was· of good grade and contained much fluorite. 

Lz'ttle Bonauzrt m£~1e.-On the nyrth side of the divide between Fantail ami 

Nevada gulches is the Little Bonanza mine. It i.-s separated hy a larg~:c~ phonolite. 

dike from the workings of the Big Bonanza mine on the ca~t. On the west side 

of this dikc1 i.-; a fa,nlt that throws the lm~al Cambrian quartzite dmvn 40 feet on 

the west side, thu~ producing a corre~ponding difference of eim'ation in the Orebearing hed_s of the ,two mines. The Little Bonanza i:s opened at tho north end 

by t\vo tunnels. These follow 1Ull'l'O\\' oro shoots, which trend north and south 

and are sepan1ted from each other hy a slight fault of possibly 2 feet with the 

downthrow on the cast ~ide. A.-; one follows these shoots ~outbward they unite 

and the shoot hccomes hroader until 750 feet, south of the opening it is 200 feet 

witlc, althoug·h interrupted hy a northwardly projecting tongue of unmineraliz(~d 

dolomite that clidd,c.-; it into 'two portions. From the no~th, end of the mille 

southward the quartzite nssmnes an· increasingly steep dip to. the southea.;;._;t,. which 

at the widest portion of th~ ore body ammmb; to 30~. Together with this 

dip a serie.s of mineralized fradnrcs ·with ·small displacements diverg-e fr01n 

the slight fault at the north end~ so thnt in the widest portion of the stope to 

the south the ~n·e on the ca:;t :::ide is 1(-)0 feet below that on the west. The 

amount of displacement along the.-:e fractures is generally small, thoug·h it some-

. time~ anwtmt:; to G feet. The difference in elevation of the two sides of the 

ore body at the south end is brought about hy dip and increase in the number of 

diverging fractures mther thm~ by inc":.·ease in displacement. The most westerly 

portion of the shoot continues south at abOut the :-:;ame elevation as at the mouth 

of the tunnel, but diYides into three almost parallel shoots. The central shoot 

is 540 feet long and widens out to about 25 feet, and is in contact with a Hmss;:; 

of phonolite on the west side. A large pnrt of the ore mined was of the blue 

or sulphide ntriety. 
\ 

ECONOMIC RESOURCES ()}<' NORTHERN BLACK 'HILI-'S. 

SontA Gplden Rewttrd nu"ne.-The South Golden Heward is opened by four 

tunnels sitmtted on the south side of the divide between Fantail and Nevada 

gulches and directly opposite those of the hadorah on the sonth. The workings 

are on quartr.ite and above the phonolite sill that extends westward from Sugnrloaf 

J\IIonntain. The ore was obtained :from two large shoots trending a little west of 

north, which avcragCd 600 :feet in length by 60 in breadth, but <hvindled away at 

\he northern end. Two small shoots lay to the west of 'these larger ore bodies. 

[:he mine is now inaeeessible. 

Isadora!~ mine.-The lsadorah is worked through t,vo tunnels that open in 

the south "ide of Stewart Gulch just south of the opening of the South Golden 

Heward. Two small shoots were mined. · The easternmost trends north and 

south and rests on quartzite which lie::; above the sheet of phonolite that extendt> 

eastward from Sugarloaf 1'lountain; the westernmo~t trends :N. 10° \V., and lies 

upon Hhalcs about 4 feet above qnnrtzite. · A small auxiliary shoot lies on quartzite 

·a few feet west of the second ore body. It trends N. 20° \V., but is very 

small. The mine has not been very productive. 

Sundance uLine.-The Sundance mine is worked f1:om' a shaft situated in 

Stewart Gulch about 280 feet west of its junction with Whitetail Creek. lt is 

265 feet deep and penetrated the snme phonolite mass as that cut in the Fannie 

' shaft, probably the weste-rn extension of the Sugtirloaf mass. The ore i~ 600 

feet east of the shaft and lies on ,or near basal Cambrian quartzite. It occurs in 

_a single shoot 10 :feet thick and of very considerable sir.c, and follows a r.one of 

fracture striking north and south. The shoot had not been explored at the time 

the min~ was vhiited, but it has since proved to _be a very extensi'\'e ore body. 

The strata oL.the Cambrian arc horizontal nbo,;.e an·d below- the ore~ but dip 

slightly away on the east nnd west sides. The. ore wa~ completely oxidized and 

of very good grade, averaging a?out $25 per ton and in individual instance . ...; 

containing much higher values. This ~?hoot is probably ·<;:onnected with the more 

westerly of the two shoots in the Fannie mine. 

Billy mine.-This mine is opened by a tunnel located on the west side of 

Whitetail Creek just north of the mouth of the north fork of the same creek and 

opposite the openings of the Ruby Bell. It runs west and intersects three smalr 

ore shoots that trend north and south to N. 7° W. and follow groups .of parallel 

fractures with the same trend.· · The ore lies on the basal Cambrian quartzite 

beneath 'the heavy sill of trachytoid phonolite that extends northeastward below 

the workings of the· lsadorah and Golden Reward mines. This sill gradually 

breaks down across the Cambrian until 800 feet west of the mouth of the tunnel 

it completely cuts off the ore-bearing beds. The Billy has not been a productive 

mme. 
MINES 01:!' BALD MOUNTAIN AREA. 189 

Ruby .Bell mine.-:-The Hnhy Bell mine i~ opened hy two tunnels-one -in 

1~'hitctail Gulch trending 'outhwest, the other in the North Fork of 1Vhitctail 

trending southeast. There are two shoots of fairly good size, the ca~terly running 

a little east of south and probably <~OmH~cting with the large No. 1 shoot of the 

Union mine, and the wc:sterly running a· little west of south: ' Between are three 

small shoots, which are little more than verticaL-; and which extend upward 

some. distance into the ~hales that form the roof of the usual ore-bearing beds. 

They arc nearly parallel to the eastern shoot. The two more westerly are in 

contact. with a dike of phonolite 1 one on either side. 

In the south end of the mo:-;t easterly ::;hoot the ore lies beneath an C](tremcl;y 

e~T~n bed of tine, imperdous -,hale, in whieh no \'erticab could be detected. 

Careful examination of the ore in the breast of the shoot :showed· that fractures 

were present in the ore as 'Tery slight displacements to the handing of the 

but that they did not extend upward into the shales that formed the roof. 

ore was of the oxidized variety. 

rock, 

The 

Lucill~J m.ine.-The workings of tho Lucille are slightly to the west of the 

Isadorah above the phonolite sill alJoye mentioned. The mine was not accessible 

at the time the region was ·visited.· 

RoJ5:<--Ilamu'hal ·m£11e.-Tbo sill of trachytoid phonolite that extend:-; westward 

and northward from Sugarloaf AJonntain has been cut through by "\Vhitetail 

Creek draining north, and hy the North Fork of the same creek, joining it from 

the west. In these two ·creeks arc exposed the elitfs formed by the phonolite 

sill whieh ba~ -cut the ore-bearing hed~ in two. The shoots of the Union mine 

lie in the dolomite parting bCncath---Lhis· 1:5ill al;d above tho ha.sat quartzite, and """ . ~-~~--- - 'the long shoot"--of......_t~H.Oss-Hanuihal is abo,~e_ tPe sjJ]. __ --"'The~Jf!_~ter shoot 

therefore lies almost .directly abm·e the No. 3 shoot ~f the UniOI~~--=Which::-:i~ 

separated from it by this phonolite parting. lt i~ opened hy tunncl~-one on the 

south banK of the North Fork of \Vhitetail and the other running westv'"'ard 

from 'Yhitetail Gnleh. The ,;hoot i,; 1,5<)Q feet long and is 100 feet wide at the 

northern end, from which point it trend:::: alliwst due ~outh and narrows to an 

extremely slender ore body, So nth of thi~ narrow portion it widens again and 

bends east, assuming a dirP-ctioil ahont S. 27° 1~~. The ore i:; from± to 8 feet.thick 

and lic:s n.t all points obserT:~le dircctly_,L~neath a shale roof and upon a floor. either 

of dolornitt? or phonolite. T~a.Pping --~h;-lc~ is extremely .even 1tnd unbroken 

by Yerticals: except in the narrower portion of the ore body, and even: then 

fractures arc ,·cry :;mall. Silicified fractui·es in tho No. :1 :;hpot of the· Union 

below show that the ore wa~ formed after the phonolite intrusion. Those fracture~ 

have probably supplied the Ross.Hannilml shoot. 

Thre.e hundred and fort.'' feet from the south end of the shoot the ore rested on· 

\ 

' -.-..,..., __ _ 
\' 

190 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

a floor of crystalline dolomite, but '~ras dosoly in contact with an even roof of blue 

shales above. This phenomenon is repeated in nutny mines and seem~ to sb"ow that 

where an impervious stratum has prevented t}w upw~trcl rlow of mineralizing waters 

the silicificatiOn has ~xtended from such impervious bed.~ downward, reaching the 

floor of unreplaceable rock that underlies the dolomite only along the lines of 

fracture. 

The ore of the Ross-Hannibal was unoxidizcd sulphide ore. It carried about 

80 per cent of silica, and C·O~ltained much fitwritc. A segreg~ttion of pyrite at 

the bottom of the ore .body is reported by the owners. Some of the ore contained 

uranium, and, according to ~~. C. Smith, a 255.08 ounces of silver per ton, wi.th' 

but 0.44 ounce of gold. This was exceptional, however, as the ore 'vas characteristically 'an ore of gold. The ·shoot was a rich one and Ls_ reported to have 

yielded an average of $35 per ton in gold. 

Uniou m,ind.-The Union mine is opened by a shaft situated in. the bed of 

Whitetail Creek about 1,750 feet south of its junction wit,]{ Stewart Gulch. To 

the east i.s Sugarloaf Mountain, to the west is the broad, sloping area that forms 

the east declivity of Terry Pe:tk, known ail Ruby Basin.· The shaft passed through 

the following rocks: 

Section of Union .~lwjt. 

.Feet. 

Phonolite ....•...••.. _ .•. _ .•.. _. ___ . __ .. __ . _ .. _ ... _ .. _ ..... __ .•.. ___ .... _ ... __ . _ 80 

Shale a~d dolomite . __ .. _ .. _ .. _ ... __ .. _ .• __ . __ .• __ .. _ ..... __ . _ ... __ ..... _ ... _ .. __ 20 

Quartzite __ .. __ .. __ ._ ... __ .. _ ..... __ . __ .. __ .. _ .. _ .. __ •. _· ... _ ..... _ .. __ .. _ .. _ .. __ . 7 

. The phonolite encountered in 'thc};haft _.!s_part of a large eruptive mass of laccoiithic character which .was intrnded.f.i.n-th~=c·t~lirian-.. series a short_distRriCe above 

~---J!fp~a.l:::::-L(Uilrtzi~Tl~·e=wOfKff;g·s of the mine have-l~in·the dolomite 

that intervenes between phonolite and quartzite. 

From the bottom of the shaft ~t long crqs~cut extenas east and west. In an 

easterlv direction it runs 500 feet, then turns south and follows a S. 50° E. 

" I 

course for 600 feet, connecting with the National shaH. No ore bodies were 

found on this side of the shaft.· To the west it extends 2,~60 feet and in thiB 

distat~cc four ore bodies are encountered; known as Nos. 1, 2, 3, and 4. The 

first or No. 1 Bhoot lies about 100 feet west of the shafj,_ It is the largest ore 

shoot of the mine, ranging jt;!_>l.!'_ 50-to-200"feet-in-widtll""by about 8 feet in thicknesB. It was worked at' the time of inspection to a length of 1, 750 feet. Its 

trend is nearly due north and sOuth and it is probably connected at its northern 

end with the Ruoy Bell shoot. On the west of the o're body a porphyry dike 

appears at intervals and. anot,lier may be seen in the ore ~outh of the shaft cross- ~-

a Trnns. Am. Inst. :\lin. Eng., voL 27, p. 419.' 
MINF.S OF RALD !10UNTAlN AREA. 1\Jl 

ing the ~hoot in a sonthwc::5tcrly direction. The ore in this 8hoot rested upon or 

Ycry close to the basal qt:artzite and bcm;ath· a roof of fine~ impcrviou~ blue shale. 

The other three shoots of the mine lie (i:l!\ 1~500, :ind 1,~125 feet \VC8t· of the 

shaft nnd all trend in a general north-south direction. They differ from_ the 

No. -\ shoot in lying from ± to G feet above the basal quartzite upon a floor of 

dolomite through which the m·? cxtcndci down\rard only along the supplying 

fractures. The roof is of shale or phonolite. ln places the latter ·rock is 

extremely irrcguht~·, o-ften bulging down into the ~we and sometimes ·passing completely acros~ it and through the quartzite below. A good eXample of this is 

givPn in the ~ketch (fig. lH), which 1~ a portion of a longitudinal·8ection of the. 

south end of the No. ± shoot. 

A general cross section of the No. ~ shoot is given on Pl. XI, H (p. 21±). 

These shoots arc abo mnT_owcr than the No. 1 shoot, hut n.s they are not completely 

mined out their length has not been determined. The ore of the No. 2· shoot was all 

sulphide ore. Between the No. 2 n.nd the No. 3 shoots the crosseut intersect:-; a 

' 

• 

hody of phonolite n.botit 500 feet in 

thickn~ss, w~1ieh is probably con~ 

. ·neeted with the large phonolite mass 

cnconntcrcd ·in the shaft, or that 

which forms the Sugarloaf 1\'Ionntain laccolith. According to tho::;;e 

who worked the mine assa.y:-5 of this 

¢ phonolite· were made from time to . 1rm. lt\.-Cro;!,; section (lf a portion ol ::'\11. -! ~lulnt. Union mine,_....--:-;· l h l l · · ~howing:,.the~oncentrutiun oi ore bencatll un:::irrcglil~r_l.JhO~>f,lJUe :lll( 8 OWe( Vll UeS rang1ng 

nulite roof. ~?~·- _.=-v from a few ss.nt..'>..._t<;u~s much nS $2 . ~,.., ____ ="' ~~ ~ 

in gold. The rock is extremely fresh and if the8CvUliies have been introOucetl~at_._-~ ---~ -= ~=== 

the time of ore deposition thCy have -heen accompanied by no visible alteration. 

ALPHA-l'LUTU8-~10GUL OUOUl'. 

Olinton ?JU;Ild.-On the :;outh side of Nevada Gulch slightly -farthcT below 

the op~ning of the Alpha-Plutus mine arc the workings· of the Clinton. The 

tmlnel i~ situated at the bottom of the gulch on the bas1i.l Cambrian qnartzitel tl5 

feet below the pm:ph)T:y-silt~lkh~j'~".:<P?Sed along the railroad on the south 

side of t.hc gulch. To the east thbl intrusive-sill breaks down across the Cambrian, so that the workings of the Hctrie.ver and Buxton mines to the ca.st are 

elevated to a horizon ~tbove the porphyry to which the naiuc of upper contact 

has been enoneously applied. Oue hundred feet fr91~1 the mouth of this· tnnucl 

t\VO narro·w ore shoot:-3 arc exposeU, separated hy abmit ~5-~-feet o-f umniner'alized 

rock. The longest. tr~nds due nOrth and south; the other slightljr ea..;t-of north.-=-
'' 

192 ECONOMIC RESOCROES OF NORTHERN BLACK HILLS, 

The countr.r rock is an extremely decomposed gouge-like alteration of the dolomite or "sand -rock." At the south end a t;ross shoot o~cUJ'ti following a vertical 

trending N. 22° E., and another very small shoot tren~ing north and south lies 

a few feet to the east. The shoots dip slightly to the l'}Onth. This mine has not 

been a rery productive one. 

Abpha-Plutu8 mine.--The workings of the Alpha-Plntus lie beneath Bald 

Mountain on the north side of Nevada 

Fremont, Elkhorn and :Missouri Valle\r ' - northward extenSion of the Tornado mi,nc . 

Gulch and extend from the loop in the 

Railroad enstward. They constitute the 

The mine is opened by a long west 

. crosscut which extends from the north side of Nevada Gulch westward for 

1,150 feet: The country rock is the usual dolomitic limestone that lies directly 

upon the basa] Cambrian quartzite hut is all iu a hig~ly oxidized conilition. 

Nine hundred feet west of the opening it~ a fault which throws the quartzite up 

SO feet on the west; again to the west of this is the continuation of the great 

Tornado fault that throws the quartzite up about 300 feet on the west side. On 

the space between these two faults are three long, narrow ore shoots lying at the 

aame elm;ation as the northern end of the big Tornado shoot. One of these i:s 

the continuation of the Tornado shoot and trends N. 20° E., the interrening portion having been cut :nvay bj~ the erosion of Nevada Gulch. Thi,.., shoot i.-; cut in 

two by. the SO-foot fault, which 1 se<).U" to he post-mineral. West of this about 

100 feet is a shorter parallel shoot from the n~rth "end of which a shoot trends 

S. 12° _E. intersecting the fir8t-namcd ore body. On the enst or down thrown side 

of the 80-foot fault are siXteen narrow shoots ntrying from 50 to 600 feet in length 

and trending N. 20° ,V.; N. 15° ,V.;-N. 00°-·,V.; ~- S.; N. 25° E., and~onc small . . . ~---

shoot ~~~ N. 45° )\~.=A:Jcw ~ small dikes of grortidit({ strildng__N.-7°-,Y. were ent in - . -=~--~=~~=~-=---thee:nol-thern portion of the mine. These shoots are widely spaced and uni-

' 

\ 

fonuly nanow~ few of them exceeding 5 feet ir width, and arc often \'ery high, 

sometimes being stoped up for 15 feet. The fractures were open and manifold 

a~d no displacements could be observed at intersections. ..All of the shoots dwindled 

to mere verticals in a northerly dit;ection. 

This mine has produced considerable ore,~ hut most of it of slightly lower 

grade than that on the ·south side of Nevada -Gulch. This is the only mine on 

the north 8ide of Nevada Gulch in which any appreciable-aii;-;,unt of ore has been ~- -·~·~ 

found. -.~, ·-o--· ~~- - ~· - .-

Tornado mine.--The Tornado mine is worked through a shaft 315 feet in 

depth, situated 720 feet west of the railroad trestle in Fantail Gulch. There are 

36 distinct shoots of ore i~thC- mine, \Yhich lie upon or close to the ha.~nl 

quarizite of the ~;trnbi"iarf··~~d about 25 feet above the Alg~nkian. ...4. ver.Y good 

-~idea" of the rela.tive position and size of these· ore shoots can be obtained fl'om 
· ALl'HA·PI,UTUS·MOGUL GROUP. l\J3 

the map, · PL IX (p. 214). Two of them were of exceptional size, and have furnished the larger portion of the output Of the mine. The main; or ''Big." shoot, as . . 

it. i~ termed hy the owner8, is the largest single body of refractory siliceous ore 

yet mincll. From its outcrops in Nevadfi: Gulch beneath the railroad trestle it 

extends in a direction slightly ca:;t' of south for a distance o-f 1,225 feet. It then 

turns to .a direction s .. 15° E., which it follows for the balance of its. course. 

At th.e north end it is about 10 feet in width, but widens as it is followed 

inward until at a point 210 feet directly west of the Tornado shaft it,attains a 

maximum width of 180 feet. Frmfi. thh;· point south. it nalT9WS to about 10 feet 

and again widens at the southern ;end, where it pa~sc~ into the property of the 

Horseshoe Company. The thickness of the ore betwCen quartzite and overlying 

shales i, about 6 feet, hut increases at some points . to upward of 14 feet. 

The roof of the ore is shale .for the greater part of the length, but at several· 

points this is replaced by a sheet of igneous rock. The floor upon which the 

ore rests is in most eases- quartzite, which at several points gtvcs place to a 

projeeting sill of trachytoid phoriolitc, connected •with a dike on the west. In 

the south end of the mine the Algonkian projects up into the ore, and is. itself. 

reported- to have carried refractory values which in some cases reached $12 pe~ . 

ton. Seven hundred and fifty feef south of its outcrop in Nevada Gulch, the 

Big shoot is thrown down 72 feet' on the south by a fault, striking N. 22° K 

l<'or some distance north of this fault, and through the northern end of. the 

downthrown portion to the· south, .the continuity of the ore .is broken by many 

north-south porphyry dikes of varying thickness.· From a point directly west of 

the shaft the ore comes closely in· contact w:ith .a large 60-foot dike of trachytoid 

phonolite on the west. side, This dike extends far south _into the workings of~~ 

the Mogul mine, where it finally. dwindles. to n9tbing. Tl;w_direction-of..t\!e. ore. 

bodv from the point where it joins the dike ~S:--12° E. for the rest of its '."-

cou;·se.. Many Bmall shoots of ore, with varying strikes,· join thi~ large b~dy on 

the east side, and the grade of the ore is increased at such .j_unc~ions. The ore 

is partially sulphide and partially oxidized, and carries averag~ ·v~li1es of about 

$17 per ton .. lt is higher in the vicinity. o£ the dikes and faults at the northern 

end, but bce'omes considerably lower at the point where the. shoot attains its 

greatest width. 

The other large shoot of this mine is that kno,vn as the B~ttleson shoot. It 

extends from a point 600 feet north of Nevada Gulch for a distance of 1,500 

feet to the Bottleson shaft and is there deflected to the west. Three hundred 

feet south of this shaft it terminates in an ore -shoot 30 feet in width, trending 

S. 47° E., which occurs along a fault fissure that throws the southwest side down 

8. feet. At the southeast end of this cross shoot are two other ore bodJes, one 

4987-No. 26-0--!--13 
194 ECONO)!IC RESOURCES OF NORTHERN BLACK HILLS. 

small and extending 700 feet to the northeast; the other large and irregular and 

extending 1,100 feet to the southwest, with a strike of N. 25° to 30° E., finally 

uniting with the long narrow ore body k1~own as the '" E" shoot. This has heen 

considered on the map as a part of the Bottleson shoot, nlthough really a eeparate 

ore body. The width of the Bottleson shoot ,·aries from 25 to 65 feet. The 

roof is shale, and the floor at times quartzite and at times dolomite. i\Iany 

inte~eSting- fractures occur in the roof. following the longer diameter of the ore 

body. Twelve of the other smaller ,boots of the mine are parallel to the >outhern 

end of the Big .':.\hoot, and trend hetween N. 12° and N. 15° ,V.; thirteen trend 

between . )/. 15° E. and ---N> 30° E.; one trends N. ±7° \V. 

One hundrerl feet east of the Tornado shaft is an ore body 700 feet in 

length, known as the ·•A" l:lhoot, ·follo,ving a manifold fra.cture with a N. ~W0 E. 

trend. Between this shoot and the Bottleson shoot, a distance of 500 feet in an 

eatltcrly direction, is a long cros~cut, whiCh run,.; upon the batial quartzite and 

intersects no ore· hearing. fracture::!. This barren region , forms a .sy'ncline in 

which the quartzite and overlying limestone' dip away from the ore bodies in 

either direction at angles of 20° and 15°, respectively. 

At the south, end of.. the mine, tmd about 350 feet east of the phonolite dike, 

is a comparatively narrow 'ore boUy 950 feet in length~ known a.s the "E '' shoot . 

. The ore in thb ~>hoot was of good grade, often averaging as much as $35 per 

ton. It followed a strong vertical, which shows little or no displacement. The 

ore-like much of the ore in this part of the mine-does not rest on the 

quartzite, but lies at a distance of perhaps 4 or 5 feet above it at the north 

end of the &hoot. r£his intelTal incre::l'"'C~ Jo_l2-feet where the shoot pa~ses into 

__ the Mogul grounrl. The floor consists of dolomite. 

··~. Besides· these-four shoots, described, there are on· the east of the large 

phonolite dike previons-(v'nleirlioncd twenty-eight other ore bodies that have added 

materially to the production of the mine. While not separately considered here, 

a very good genernl,idea of their relative size and importance may be obtained 

from the mttp CPl. IX, p. 21±). 

On the west side of the large dike which forms the west wall of the large or 

main ore shoot the conditions are somewhat different from those to the east. At 

a varying di.stanc.e west of the porphyry the crosscuts \vhich penetrate this Uike 

encounter a di:-.placemcnt which throws the wes_t .side up for a dmtance of nearly 

300 feet. In Nevada Gulch this fault is reported to have been very near the west 

side of the phonolite dike, but at a pomt northwc,t of the Tornado shaft it diverges 

from the d1ke, which is deflected to the east, so that on the boundary between the 

Golden Reward anrl Horseshoe properties the two are "eparated by an interval of 

700 feet. This fault continues into the Horseshoe property and ap,,ears just west 

-' 
TORNADO MINE. '195 

of the Troy shaft, where it shows a clear offset of 300 feet. At the point of 

divergence it i,; joined by a 72-foot fault that cuts the large ore shoot into two 

portions with a downthrow of 72 .feet on the cast. Directly on the west side of 

the large phonolite dike there is another displacement by which the west side is 

thrown do\Vn for ±0 :feet tLt the south end of the mine. The amount o£ disp~acemcnt 

dccrcasc:s to the north, however, until due wc8t of the Tornado shaft" it is practically 

zero. Thi.':l displacement, unlike. the others in the mine, seems to have occurred 

at the time of the porphyry. intrusion, as it is accompanied by no brecciation or 

slickensides. The porphyrys and scdimeittaries show ~L cloS~ and typical intrusive 

contact, often exhibiting considerable metamorphiSm .. ---~---

Directly West of the shaft there arc between .these two main faults a series of 

·small displacements which form narrow hench·cs as one passes westward from the 

phonolite dike. By two of these the quartzite is elevated on the west side successively 30 and 40 feet; others are much smaller. The ·actual ofl'set in these dispht~ements is extremely small, and much of the difference in elc\~ation i~:~ absorbed in an 

extremely steep easterly_ dip. c 

On the separate benches between these displacements are six small ore bodies 

which trend about N. 3° .to 5" E. Considerable ore of good grade was found in 

these shoots, which arc of smaller size than those generally encountered in thn mine. 

Pl. XIX (p. 2H) gives an cast-west cross section of the mine and will bring out 

these relations clearly. 

The ore from the Tornado mine was .partly red or oxidized and partly blue or 

sulphide ore .. In the early history of the mine the oxidized m·e was especially sought 

·on account of the additional ·difficulty_of _treating the unaltered sulphides, but with 

the more complete understanding of smel~i~g this preference carric_to-be disregard~?-:..-------

The ore from the Big shoot is · very markedly banded_on account of the 

_persistence of beds of shale in a,comparatively ~Ite.red' condition. In some of ',--.....__ 

these the shale bands contain soft white clay, which has presumably resulted from 

the decay of thin seams of porphyry. This clay not infrequently contains high 

values in gold. A partial analysis of it gav~ the following rcsrtlt~;- -

AnalyBi., of cla!} from Big shoot of Tornad19 mine. 

Si01 ••••••••• ~· ___ :_ ••••••••••••••• ~--- •••••••••••••••••••• _. ____ •••••••••••••• 36. s· 

FeO ____ .. _.-.-. ___ ------------------------.: ... --- ..... ____ - _- _---------..... . 19 

Al20 3 •••••••••••••••••••••••••••••••••••• : ••••••••••• :·············--········· 16.5 

ll20 (combined) .. __ ..•••. --- ..... ---- ....... ----- .••............ ~- .•.......... 15. B 

Ounces of gold ................... · .......................... _ ........... 2.47 ($49.40) 

Ounces of eilver ..••••...••................. -.- ...........• _. .. •. •. .• .• . . . . . . .. . . . 9 

It is stated that in some ·cases this clay carries values as high as $200 or 

• $300 per ton in gold. 
196 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

In general, the ore from this mine averages about $17 per ton in gold. In 

the northern end of the Big shoot, where many faults and a large number of 

dikes interrupt the continuity o£ the ore, the contained values are higher, often 

averaging $35 per ton; in the large flat body directly west of the Tornado shaft 

they are comparatively low, much of the ore mined carrying only $10 per ton. 

The ore here is little broken or disturbed. The grade is higher where the large 

ore body is joined by lateral shoots. Little or no secondary enrichment has taken 

place in the mine, for there is little relative difference between the values yielded 

by filtered and unalte.red ore. . 

Great, fl'fi,gul mine.-The Great Mogul mine is opened by a shaft 305 feet in 

depth, situated in Stewart Gulch, at an elevation 5,986 feet above sea level and 

about 1,600 feet west of the loop of the Fremont, Elkhorn and Missouri Valley 

Railroad. The shaft penetrated two sills of porphyry, separated by about 15 feet 

of Cambrian shales, the upper being relatively the thicker. Between the lower 

sill and the basal Cambrian quartzite occurred interbedded shales and dolomite, 

the more completely marbleized layers of which rested . on the quartzite. The 

Cambrian rocks dip east at an angle from 12° to 15°. The mine comprises two 

large ore bodies. The first was encountered 250 feet directly west of the shaft, 

and by reason of the strong eastward dip is worked by a horizontal drift that 

connects with the shaft 30 feet above quartzite. It is the southward continuation 

·of the large shoot of the Tornado· mine. It is 110 feet in maximum width and 

about 5 to 10 feet i.n thickness. At the north end it is dhcided into two. portions 

by a long neck of unmineralized rock. Toward the south it gradually narrows, 

until about 1,350 feet south of its· connection witli the Tornado it dwindles out. 

·~On the west side is a dike of trachytoid phonolite sloping slightly east and benching 

- out-beneath the ore. Fr~ts. contact with this dike on the west the ore dips 

eastward at an angle whiCh increases slightly in an easterly direction away from 

the dike. This dike, like the ore shoot, pinches out to· the south. The majoi· 

fractures in the shoot trend north and south, but often there is so intri~ate a 

network of minute yerticals in the shale roof that it is impossible to distinguish 

any predominant direction. 'Vest of this dike is a fault which throws the west 

side down t'or 40 feet at the north end and increases in amount·as we proceed south, 

until at the end of the dike the displacement amounts to 100 feet. On the downthrown side of this fanlt is the second large ore shoot of the mine. This shoot 

is 75 feet in maximum width at the north end and lies against the phonolite 

dike on the east side. Farther south it ·leaYes the contact with the phonolite 

and narrows until finally it dwindles to a mere vertical. On the west side of 

the ore is a ledge of Algonkian quartzite,. and beneath the ore for the larger 

part of its southerly course is a· floor of the same rock. The basal Cambrian 
' 

GREAT MOGUL MINE. 197 

<!uartzite, 'vhieh became very thin below the ore in the upper shoot~ is hcTc 

entirely absent.'' ·• This shoot is connected with the. shaft by a drift which p~ss~s 

T_ beneath ~he. main shoot through the Algonkian. Iron-stained fractures may be 

seen beneath the easterly shoot parallel to the lamiimtion of the schists. These 

may he the downward continuation_s of the mineralized fractures or verticals in 

the stope ahm-.,.e. A cross section· of this mine in an cast-west direction is given 

in Pl. XX (p. 214). The ore from the 1\lognl is partially oxidized in some places ' and completely so in others. At several points, presumably in the lower shoot, 

the ore contained gre·at numbers of angular fragments of Algonkian rock, among 

'which were scattered crystal~ and isolated masses of -jarosite. In the upper or 

"''"tern shoot layers of very rich clay were found interbedded with the ore. 

These often carried several htindred dollars per ton in gold. The Mogul has 

been a very productive mine. 

Little Tornado mine.-To the west of the 300-foot fault on the divide 

between Nevada a·nd Ftwtail gulches are the dismantled workings of the Little 

Tornado mine. They are pre~umahly upon the basal Cambrian quartzite, as that 

stratum is exposed at the same elevation in the Double Standard tunnel, a short 

distance to the south west. 

There are two small shoots striking N. 10° E., following strong, rather open 

fractures, which converge toward the north and together extend through to 

Nevada Gulch. These shoots are separated by a slight fault which throws the 

eastern shoot down 10 feet, while from the south end of the latter a third small 

ore body trends N. 3±0 E., to be intersected midway of its course by four very 

small ore bodies parallel to the first two. The strata have a pronounced easterly 

clip, which, together with many slight displacements having downthrows on the 

east side, marks the approach to the great 300-foot fault (mentioned on page ·127). 

Two small dike:; of rock related to gro·rudite and striking N. 80° E. cut directly 

across the ore shoots of this mine. Country rock and ore were alike extremely 

oxidized. The mine has not been a heavy producer. 

IJonble Standard mine.-ln. the head of Fantail Gulch, above the town of 

Terry, on· the north side of the gulch, is the tunnel of the Double Standard mine. 

The tunnel i:::; driven upon tho basal Cmnbrian quartzite, trends slightly north of 

west and intersects seven long, narrow shoots of ore at 100, 150, 200, 287, 312, 

412, and 500 feet west of the opening, respectively. 4 

The ·first two are small and strike N. 10° E .. and ~· 22° E. with ·a largo 

dike of coarse-grained rhyolite between. The third or main Double Standard 

shoot trend.':! N. 4° E. and extends north 900 feet, where it outcrops high np on 

the south side of Nevada Gulch. The ore lay in dose ·cimtact with a dike of 

rhyolite on the east si<lc for 300 feet and then a slight fault has brought the 
198 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

4-lgonkian schists into contact with the ore. The other •hoots are short and 

narrow and trend N. 25° E., N. 30° E., and N. ·7°-E. All follow strong and rather 

oPen fractures, which are mai_nly vertical in pOsition. TwO of these sh~oots converged 

toward the south, and at the ·point of intersection formed a large body of ore 5 

feet thick with an extremely even shale roof. Where the fractures come together 

they have ~lightly discordant dips and intersect one another in· both horizontal · 

and vertical planes, but no displacements could be detected at the intersection. 

There is a prevailing southwest dip in the mine and· slight undulations interrupt 

its regularity, the shoots· always lying on the crests of the anticlines. The shape 

of the ore bodies in 'cross section throughout this mine varied considerably, some 

being elliptical and others so irregular that the ore extended out in thin shelflike mass~s into the country rock. A shoot was observed in which a shelflike mass of this character, about 1 foot in thickness, Jay immediately beneath 

the shales that overlay the ore and extended from 3 to 6 feet beyond the main 

body of the shoot. Much of the ore: from this mine was unoxidized, and that 

from the shoots to the south of the crosscut carried large quantities of gypsum 

and green fluorite .. 

Boscobel rnlne.-At the extreme west end of the Double Standard crosscut 

tunnel a 10-foot fault hru; thrown 'the basal quartzite up on the west. On the 

upper side of this fault is the long shoot of the Boscobel, which extends south 

400 feet, where it dwindles to· a mere vertical, and north for 1,050 feet to its 

outcrop in ·Nevada Gulch. l\fid,vay· along its northerly course there is a small 

vertical ore shoot, a few feet to the west, striking N. 35° E. 'Vest of tho·main shoot, 

where it outcrops in Nevada Gulch, three small ~hoots are situated. The t\vo most 

westerly arc a~ a high angle to one another, so that they conyerge to the south, and 

together for!n an ore body parallel to the wain Boocobel ,;hoot. The most 

easterly of the three is between the latter and the converging shoots. The 

fractures of the Boseobel mine are prominent and often inclined at a slight_ 

anglo to the east. [likes of rhyolite lie in contact with the ore of the main 

shoot on both sides and. in many cases divide the ore into two portions. 

Throughout the entire country Uetwecn the Boscobel and Double S_tandard 

shoots, and thence eastward .as far as the mouth of the Double ·standard crosscut, great numbers ·of north-south dikes of rhyolite occur. The ore sonwtirnes 

li~.s in- contact with them and at others diycrg~s from them- at considerable 

angles, showing that the occurrence of tho ore is . independent of this ig~oous 

activity, so far at least. as the direction of ore -shoots is concerned. 

The· ore from the Boscobel shows great quantities of brilliant green fluorite, 

together with extremely large crystals of barite, the latter embedded tightly in 

the ore. 
ALPHA-PLUTUS-MOGUL' GROUP. 199 

Ilartkcrabble rnine.-In the end of Fantail Gulch, just below the sharp 

.southward bend in the stream, is a long open cut from the west end of which a 

tunnel leads westward into ·the Hardscrabble mine and thence through to the 

- Welcome shaft. South of this open cut, and south also from the tunnel, is a 

series of irregular stapes, open to the north, from which low-grade ore was 

mined. These bodies passed into fairly regular stopes toward the south, but in 

the neighborhood of the open cut the ore was included between an inextricable 

tangle of dikes, sills, and irregularly bounded masses of rhyolite. 'the workings 

'are presumably near the basal quartzite of the Carribrian, for that rock is exposed 

in the Welcome mine to the west. Fractures pass through rhyolite, shales, and 

dolomite indiscriminately. To the north of the tunnel and open cut are a series 

of narrow shoots following fractures that trend N. 20° K, and probi1bly conned 

with the shoots of the Double Standard. Southwest of the Hardscrabhle workings 

is a long' shoot trending horthcasterly, and connecting with the workings ·a£ the 

1V elcome mine. It is inclined sharply south, following the dip of the quartzite, and 

on the east is in contact with a dike of rhyolite. . The ore from the· Hardscrabble 

mine contained great quantities of purple fluorite, and some of the rhyolite itself 

'vas so. heavilY impregnated with this mineral that it contained wOrkable values. 

lVelcome mine.-The 'V elcome mine i.':l opened h.r a shaft situated on the 

northwest side of Fantail Gulch, ju~t abo\7e its bend toward the south. It is slink 

on n fault which .':!trikes north and south and throws the w·est side down 30 feet, 

but dies away to the sotrtb. The strata dip to the south at an angle of from 10° 

to 12°. About 25 feet west of the shaft is a shoot 100 feet wide hy· 10 feet in 

thickness and· 625 feet in total·Iength. This lat:ge ore bod.)· ·is cansed h.r. the 

occurrence of innurnera.ble parallel fractures whicli, ''Thile they nrc. strong and 

display Considerable ope{ting, are so clo:;ely spaced tha,t the.\· ha,·e ·produCed an ore 

body of great. size. (Sec Pl. XIIJ, p. 214.) So close arc the_,. to one another that 

the shale roof hat~ been sufficiently silicified between to carry considerable values. 

Thi.':l shoot terminates against nn eastward-dipping dike or crosscutting sill on 

the west side and gradually ·dwinU.lcs to a more vertical on the :-;outh. 'Vest of 

the :;outh end of this large shoot. are a great·number of small shoots on fractures 

striking north ~nd south, N. 10° ,V., N. J.;JO E., and N. 80° f1~. .Much of the ore 

in thi~ mine was separated from the quartzite by from 2 to 3 feet of red dolomite. 

The Welcome has been a heavy producer. 

IIarmony mine.-This mine i~ opened by two. tunnels on the south si,dc of 

Fantail Gulch above the to\vn of Terry. The workings arc now inaeccssibl'e, but 

frOm the mllp there seems to be a series· o{ 8mall shoots. trending N. 5° to 10° 

E. The workings are directly south of the Little Tornado and just west of the 

great 300-foot fault. 
200 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

Ben IIur mine.-On the south side of Nevada Gulch, some distance north. of 

the opening . of Cherry Creek -1is the tunnel of the Den Hur mine. It runs a 

little south of west down a gentle incline through tho schists of the Algonkian. 

It then encounters a dike striking parallel to the schists. On the west side of 

this dike a fault has thrown 'the Cambrian down so that the quartzite is on a 

.level with the adit and the porphyry dike bus turned O\·er into a sill toward the 

west, so that abou"t 5 to 6 feet of Cambrian-lmndcd dolomite and shales intervene 

.between quartzite and CruptiYe rock. Lying directly against this eruptive rock 

on the cast and beneath the sill is a large .shoot of ore. South of the tunnel 

the ore body turlls sharply southwest, presumably following a coordinate fracture 

and then sharply south, so as to resume its original direction which it maintains 

for a considerable distance. 

The fracture which octpplied the ore passed up into the porphyry and was 

about 3 inches in width and filled with a mass of largo· intedocking quartz crystals, which projected from a narrow band of silica into the open space between 

tho walls. This quartz-crystal ore was reported to have yielded high values. In 

the extreme south end of the mine the ore lies against the Algonkian schists, 

probably on account of slight faulting. The ore from the Ben Hur was oxidized 

and carried high values, sometimes yielding $60 per ton in gold. The mine is 

·still productive. 

Baltimore mine.-The Baltimore shaft is situated in the bed of Nevada Gulch 

south of the saddle between Bald and Green mountains. The country rock is an 

eruptive~ probably related to the grorudites. This is intersected in the shaft' to 

a thickness of 60 feet; below is a parting of Cambrian shale 40 feet thick, another 

sill of eruptive rock 20 feet thick, and then 110 feet of Cambrian shale and 

dolomite. The .shoots are scarcely more than verticals and lie in the dolomite 

~bovc the basal Cambrian quartzite. Two trend N. 20° K, two N. 25° vV., and 

one N. 70° E. These verticals have not been indicated on the map in Pl. IX (p. 214) 

on aCcount of the uncertainty as to their exftct location. 

JIUNF~S ON THE UPPER ORE-BEARING BEDS. 

Daisy mine.-The workings of the Daisy mine arc situated. on the divide 

between Fantail and Stewart gulches just east of the 300-foot fault and directly 

. over the most westerly shoots of the Tornado. They are hut a few feet below the 

surface. The country rock is a green glauconitic shale, containing band::; of dolomite, 

but exhibiting no heavy beds of the latter. type. The ore is colored green by 

much included glauconi.te and contains many large cavities or vugs distributed 

without regularity. 

Upper Welcome mine.-West of the vVelcome shaft and far up on the north· 

west slope of Fan tail Gulch are some small workings that are at a much higher 
MINES. OF UPPER ORE· BEA.RING BEDS. 201 

altitude than the workings of the ·welcome mine. The country rock is Cambrian 

shale containing great quantities of glauconite and interf'alated layers of a dolomitic 

character, none of whjch are very thick. The ore was mostly in the nature of 

narrow silicified shoots following small north-south fractures, ~ut extending only 

short distances laterally from them.· :l\fuch eruptive rock occurs. in rather confused 

relations. The geological position is probably about the same as that of the 

Daisy mine and may correspond to the upper t~ontact of the Portland district. This 

aud the Daisy mine tO the east are the only ore bodies in the Ruby Basin district tllat 

are in what may be properly termed upper ore-bearing heds. The fact that the 

country rock js such an impure variety of dolomite, interrupted by many shale 

bands, indieates that· ore-bearing beds which eXhibit considerable uniformity of 

textu~e and freedom from impuritie~ at one l~cality may give place to comparatively 

unreplaceable rocks at another. 

PORTLAND DISTRICT . 

.Dividend 1nine.-The Dividend mine is situated upon 'the northern slope of 

Green Mountain, a little north of east from the town of Port.Jand .. It is operated 

by two tunnels running into the hillside and opening into a small tributary of 

the north fork of Deadwood Gulch. The workings are about 20 feet above the 

Algonkian upon the basal Cambrian quartzite, which dips slightly west of south 

at an angle at from 4° to 6°. Two small flat bodies of ore were mined from the 

northeast end of the mine. They occurred at the intersection of many small 

fractures which trended N. 25° K, N. 4-±0 E., and N. 18° 1\'. The ore rests on 

quartzite and beneath a thin- bed. of shale, but ends abruptly on the west against 

soft Algonkian phyllites, which are faulted up· by a slight displacement trending· 

about N. 78° W. The ore in these two bodies was irregularly bounded and 

~tbout 5 or G feet in thickness. i\fineralizcd fractures pass from the ore into the 

Algonkian, in which rock they have yielded some pay ore. Another small ore 

body occurs in the extreme southwest end of the mine at the intersection of 

fractures trending N. 30° E., N. 38° E., and N. 36° W. This ore body is about 

500 feet northeast from. the nearest mine, in the_ upper ore-bearing heds, and is 

:;epar~ted from them by an interval of Cambrian strata and intruded porphyries 

527 feet in thickncstl. • The othc"r ore bodies of the mine were narrow shoots, seldom more than 5 feet in \Vidth, which followed rather open fracture:; Uut often 

extended to considerable disb1nccs in a vertical direction, in one ~.:ase as much atJ 

4:0 feet from the quartr.ite. The largest of these fracture..; contained fragments of 

Algonkian schist, and was .sometimes 6 inches in width. It trended N. 53° E.l 

and carried ore for 7-J.O feet. Other omall ore shoots followed fractures trending 

north and Routh, N. 15° E., N. 25° E., N. 44°-53° E., and N. 3-P--40° W. The 

fractures are open a.'J;1d but little mineralized when compared with those occurring 
202 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

on up_per contact and in mines where the ore bodies are extensive flat masses. 

Dikes of decomposed eruptive rock of a few feet in thickness occur in great num~ 

hers; many of these have brecciaS along their contact:;. The dikes appear to 

intersect the v~rticah,, but/ the rocks are too de"composed to give positive evidence. 

The ore is of three ,-arieties: The first is a gouge-like decomposed material 

heavily charged with oxides of iron and manganese, and often ·containing 

considerable sandy ·fluorite; the· second is a sandy material resulting from the 

disintegration of the basal quartzite and often mined to its contact with the 

underlying schists; the third is the usual bard refractory siliceous ore. The first 

two varieties of -ore carried values of from $10 to $25 per ton, but the siliceous 

ore generally contained from $25 to $50 in _gold with hut little ,i'·:er, which 

is strongly in contrast with ore of the same character in the upper beds, the 

latter yielding uniformly low values and a rehitively high silver content: 

A peculiar, hard, ferruginous j~spcr occurs in this mine in the same banded 

masses as the ore, but it carries no workable values. It is termed "liver-colored 

rock" by the miners. 

Snowstorm mhu.-The Snowsto.rm shaft is located in the extreme head of 

Nevada G~lcb. lt is about 3±5 feet deep and h~s produced no ore: It i~mportant" in that it comprises fin extensive series of· barren· 'workings on the bas~i 

Cambrian quartzite and indicates that ore bodies are probably absent in the barren 

region lying east of the Portland district. 

Two Jdw8 1nine.-The. Two .JOhns mine b located in a southwest tributary 

of main: Squaw Creek,_ about 1 mile east o~ north from Crown 'Hill. · The basal 

quartzite and about _20 feet of the Cambrian rocks are here exposed and outcrop 

all along the ~vest bank of Squaw Creek, dipping southwest\\:ard from the great 

porphyry mass that forms \V :ir Eagle . Hill. A bo,'e the shales is a thick sill of 

rhyolite. The, mine is opened by two. tunnels on the basal quartzite which 

diverge at the mOuth, one running ~outheast anJ the oth~r southwe~t. There 

are two long, narrow shoots of ore, the southern trending· N. 50° E., and the 

northern composed of two portions, of which the eastern trends N. 70° E. ai1d 

tbe western N. 25° E. At the junction of the two portions the ore body is 20 

feet wide, the ore of the small shoots followir~g fracturps that strike between 

N. 70° and 50°-E~ Two small dikes of eruptive rock cross one of these ore bodies 

and the fractures do not pass through them. On ·the 1vest side all of the shoots 

are cut off against an eastward-sloping wall of dark, coarse-grained rhyolite. 

The mine has not been a very productive one . 

. Ouskurst and ...L1£anchesh'1',-0n the quartzite rim that is exposed in the head 

and on- the west side of Squaw Creek arc a few small workings that belong to 

the Gushurst and ~fanchcster rnine. There occurred in these, workings in the 
MINES IN PORTLAND DISTRICT. 203 

dolomitic shale a few isolated masses of jasperoid rock in which in·~gular patches 

·of galella and cerussite were found. These mines haYe not produced much ore. 

Labrador mine.-In Labrador Gul~h at an elevation of about· 5,500 feet abm·e 

sea· level is an exposure· of Cambrian rocks much distorted b'y intrusi\'e sills 

and dikes. , There arc a few workings that have yielded ~ome refractory ·siliceous 

ore. These are now inaccessible. 

Decorah min.e.-The workings of the Decorah mine lie on the eastern side 

of Green Mountain. They are opened at the north end b}" two tunnels about 50 

feet above the railroad and follow two long narrow ore bodies southward for a 

distance of 650 feet. The workings are about 20 feet below the Scolith:uB sandstone 

which lies at the top of. the Cambrian series. The country rock dips slightly to 

the south-southwest, and the ore bodies trend S. 35° W., following the dip. 

The easterly shoot· is from 25 to 30 feet wide at the south. end, but gradually 

narrows to a mere vertical at the north. A little ~outh of n~id_way along its 

course it widens to the west until it ha:; attained a rnaximum width of 100 feet. 

Shales form the roof of the ore body and the floor upon which the ore rests. 

The fractures are ·extremely 8trong and opCn_, sometime.':! occupying. the entire 

roof of the stope. The. ore is from 2t to 3t feet thick and' corresponds exactly 

to the thickness of the replaced bed of dolomite. The more westerly shoot is 

narrower and at tho south end the Ore extends up into the shales that form the 

roof, thus fOrming a verY narrow vertical ore hody. 

T1·ojan mine.-Thc Trojan is opened by a tunnel running S. 35° E., and 

situated on the north side of Green J\Iountain cast of the. 'ivorkings of the Decorah. 

rrhc country rock is hero Cambrian shat.es, yerJT glauconitic: with an. interbedded 

layer of dolomite about· 4 to 5 feet in thiekness. Tho mine con~prises a broad, 

flat stope about 700 feet long and 85 feet in maximum width, but narrowing 

toward the southern end. ~~t the south end the oro is clidded hy a dike of coarse 

rhyolite striking N. :15° E., which is itself greatly silicified in places, and often 

st~ined dark brown wlloro ·it comes in contact with the ore. The ore from the· 

Trojan yielded _rclath·cly high vnlues in silver, thus contrasting 8trongly with the 

·ore taken fro.m the DividCJid mme to the north and lying upon the basal Cambrian 

quartzite 527 feet belmv. 

Alameda.-Tho Alameda is an open cut at t~c soUth side of Green MountaiuUl1d is probably a continuation of the Decorah. Fra.etur~s run about t:i. 35° -"'· 

and the country rock dips about 8° ir~ a direction 8.---go "'· There is a bed of 

considerably oxidized fine-grained dolomite 2 feet in thickness, above 'vhich arc 

14 feet of glauconitic ~hales with thin interbedded byers of ~~ dolomitic character. 

The vertical seen in this open cut :.;hows u heavy bed of ore ·replacing the nlain 

dolomite layer, but upon passing into the shales alHn'e the 8ilicification i.-; 
204 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

confined to a slight replacement of the thin dolomitic layers. The ore;from the 

Alameda· is of low grade, not generally averaging more than $9 to $10 per ton. 

Folger m,hze.-The Folger mine' i:; on the south side of Green :Mountain about 

150 feet west of the Alameda. The ore shoot is small and trends :N,. 30° E. but 

divides into two portions at the norther~ end. A few fractures arc present hut 

the roof as a whole is an eXtremely uniform and unbroken bed of shales: 

Perseverance 1ni1~e.-The·· Perseverance ·mine is opened by a tunnel situated 

about 200 feet west of the Folger and rum1ing N. 35° E. from the south side 

of Green 1\fonntain. There are three ore shoob, the central one of which is 

very narrow. It widens at the north end into ft broad, flat stope about 50 feet in 

·width in which few, if any, ve1~tic:ab cau be ohscrved in the shale that forms 

the roof. The other ore shoots tr.end in the same general direction and the ore is 

about B feet in thickness. It lies between two beds of shale. In the more westerly 

shoot there are twO blankets of ore, one above t_he other, separated by an 

interval of unmineralized shale. 

Em:pire State m.ine.-The Empire State !nine is opened by a long tunnel 

extending southward from the north side of Green ~lountain· completely through 

the hill and connecting \Vith the workings· of tlle Mark 'Twain on the southwest. 

The ore is from 2t to 3 feet in thickness and lies between two beds of irnpcr-

'dous shal~s. In places it comes in contact with irregular beds of coarse-grained 

rhyolite. Fractures trend N. 25° E. and :N. 35° E. ~lany of the shoots occurring 

in this mine are very broad and flat, the roof being interrupted by few fractures. 

The average"'thickness of the ore is from 2t to 3 feet. 

Mark Twai-n 1n£n_e.-The JVIa.rk T\vain mine is opened by a series of tunnels 

running from the head of Nevada Gi.1lch in a northwesterly direction. The 

· country rock is a Cambrian shale with two interbedded layers of dolomite sep-

, a rated by about 5 feet of shale. The lower layer of dolomite· is 3 feet in thickness; the upper is 2 to 2t feet. The ore forms a .large, irregular channel-like 

mass 1,200 feet in length. It lies in two hlankets 'of extremely even upper and 

lower contacts and replaces t~o bed_s of dOlomite. . ).luch glauconite occurs .in 

the shales. Fractures are present· in tbi.., mine intersecting one anoth.er in an 

irregular manner. The nlost frequent of these trend .N. 35 to 40° E. l\Iany 

____ oth~_r~ occur striking N. ·S5° E., N. 60° E., N. 50° E., ?-L 80° W., N. 330 E., 

and N.'10° W.- Th~ irregular character of the ~lark Twain stapes is due to the 

intersection of these ft:U:Cture•. At the south end of the mine the strata of the 

Cambrian bend upward sharply toward the southwest. The ore is largely sulphide ore, and the values which it contains arc often -distributed with great 

.regularity. The :1\"lark Twain has been a very procluctive mine. 
' 

MINES IN PORTLAND DISTRICT. 205 

Leopard anrl Jessie Lee ?n-ine.~This mine ·is entered by a ~unnel on the north 

side of Green Mountain, a few feet east of the town of Portland. The workings 

lie about 20 to 25 feet below the Scolitlws sandstone which is exposed in the 

cut of the Burlington and Missouri RiYcr Railroad near the railroad station. 

The. ore occurs in large irregular flat masses, about 40 feet in maximum width 

and about 2 feet in thickness. It lies tlpparently upon a 3-foot sill of coarsegrained rhyolite and beneath argillaceous and glauconitic shales. The fractures _.,:.- . . in the roof are extrc_~1_ely-smalltlnd follow directions N. 20° E., north and S<?.uth, 

and N. ~0° W. 

Burlington an<l Golden Sands mines.-The Burlington and Golden Sands mines 

are opened by a tunnel that enters the north side of the hill just above the railroad. A few feet from the mouth of this tunnel is a long crosscut that runs 

southeast and connects with the workings of the Leopard and .Tessie mines. In 

the shoot there b intersected a series of broad shoots of ore trending as a whole 

about N. 35° E., and lying about 18 feet below the ScoWh:us sandstone that forms 

the uppermost layer of the Cambrian series. The ore-bearing· beds are about 2t 

to 3 feet thick, but are int~rrupted by more than the usual number of shaly 

luyers. They are overlain and underlain by glauconitic shale. There is a slight 

southwesterly dip throughout the mine. The fractures are widely spaced but 

extremely strong, for the siliciticat~on has often extended for 6 inches from them 

in the shales that ov~rlie the ore-bearing beds. The shoots follow fractures whichtrend about N. 35° E., and arc inter~ected by others running N. 13° E. and ~cc~-­

siona~ly N. 60° E., the largest bodies of ore occurring_in_th~~\'icini~--;~ch 

intersections. The ore is about 2t to 3 feet thick,~t the southeast end of the 

mine another blanket of ore was discovered about 6 feet above the first and 

separated· from it by glauconitic argillaceous shales. 

Portland mine.-The Portland. mine~is'sitnntccl west Of the_ town ~f PortlunJ . . . / ·.- - ---· 

just south of the crossing of the narrow and wide gage railroads. There 

are two dolomite beds tl;at-cal~.f ., ore, all dipping slightly southwest and interbedded with argillaceous and glauconitic shales. At one point there is a small 

bed of dolomite 8 inches thick inte1:veniiig betwe.~n the other two. These beds arc "-< ,..__ 

not continuous over any very extended area, for they Often Uecome shaly qr_ gra_~e 

into comparatively unreplaccable rock. The more easterly portion of the .work~ 

ings is about 20 feet higher than that to the west, and comprises an open cut and 

three yertical very narrow and high ore bodies, all in the shales that overlie the 

principal ore-bearing beds. The ore from tlu~se workings contains Yery high 

values in silver, but, as is ':lsual with ore bodies in· the comparatively impure· 

dolomitic shales, extends but short distances from the supplying fractures. There 

are three . large ,·erticles of this type trending N. 25° E. a1id a smaller one 
206 ECONOMIC RESOURCES OF NORTHERN llLACK HILLS. 

N. 40° E. In the western 'vorkings which arc opened by a long southeast crosscut are several small shoots containing blankets of ore, generally not more thatl 

2 feet in thickness ai1d follmving.....,:':-ltrong fractures ,vhich trend .N. 20° E., N. 25° 

~., N. 30° E., N. ±0° E:, :N. 55~ ~~~-;-- :N. 80° E., and N~ 35° \V. Intersections are 

generally without appreciable displacement. TheN. 25° to 30° E. fractures are the 

stronger and the most. of the ore bodi~s trend in that direction. The Scolitlurs 

sandstone lies about 25 ·feet aboye the-, lowermost blanket of ore. The most .. "'- . 

westerly stope. of this .mine is .a small shoot 20-feet-high but of small horizontal 

dimensions. It yielded very high values in silver: A~siderable amount of 

ore has been mined from the Portland. 

Clinton mine.-The Clinton mine is located about 1,500 feet west of the town 

of. Portl~ncl and is wo~·ked through a tunnel_ connecting 'vith the Portland mine 

to the· northeast. The country rock is the glauconitic shale of the Cambrian and 

inter-bedded ]a,·ers of dolomite that .lie. about. 20-.feet. he! ow the Scolithus sltnd- ·- . ~ l. "' --~·. ·. . • ..•. -_; ·' .. -·· _,. ·. ''• .. "J 1 -

_s_~?R~ ~I}-~. ~8q~ti~.vt~ .. t~y · ~q~c_!tll~_g.,.~~pppei~ .c:onta~t_.;: •. _.~ , , ~ . 

.. , 1.t,here are,th_ree Jarge .shoo.ts·~in the mine ... 'J:~e ,more easterly shoot is G to 8 

fee~_.wide, t_r~nds, N ... ~4° E., and· is .about. 300 feet long. The ore is 3 feet thick. 

·The major "fractnr~s trend-~· 2~ . ~.; N. 32° .E.,.N. 44:::..E.,_and. N. 50':_E.; minor 

fractures run north and south, N .. 86° E., N. 85° W., and N. 58° W. , The large 

_ sh9ot is formed. by the intersection .. of major fractures running N. 32° to 44° E., 

-and minor fractures running N. 50° to 85° W. This large shoot divides at the '·· - ... ::.n~rth,end- into two portions. The other- shoot is · 30 feet northwest and trends 

N.~32°E:-;-.£~g_,pamlleLfractures with· ~he same trend. Forty feet east of 

the long nU:rrow shoot~..::'Shoot trending ·N. 53° E., and crossing at a smallangle a series of parallel fractur~~striking N. 32~ E. The . Clinton has been 

\ 

quite a productive mine. -\ ./ 

--=--C-umf£son -~rdne. --:---The Gunnison-o-ii:i~-a--si~'lll but compara __ !.~rely unproductive 

mine about 400 feet west of the Portland and=;;;:mth of the'railroad. The tunnel 

. h. h I h h ·'h /.'". f . ·.I IS upon _a onzon somew at ower t an t at 9f t e....-maJOrity o mmes m t 1e 

region. The Ore is lmY grade and oecurs)n~t~,~ _blankets, replacing beds of 

dol~mite and separated by vnry!_.ng.-inte{vals of glauconitic shales. Th8 'mine 

ha~ produced -.hut-little-ore~~ 

=-~-;:th Dakota -rni-n'e.:_ This mine is· on the northeast side of A;.nie Creek on 

a spur that juts out from Foley :Mountain. It has yielded but little ore and 

that of low grade. As many as six small blankets of ore· are reported to have 

occurred in the mine. 

LEAD AREA. 

Sula mine.-The Sula mine comprises an open cut north of the junction of 

Poonnan Gulch and Gold Run excavated directly upon the basal measures of 
)liNES IN LEAD AREA. 207 

the Cambrian. The ore i.., of two varie"ties, one -contnining much barite rnn_d 

carrying refractory values in gold -ranging sometimes as hig·h as $2_5 per ton, 

the other canying irregular pfttches of granular wolframite. The mine has not 

been very productive. · __.,-- . 

IIarri:-:;on n_rine.-Thc Harrison 'mine i::; situated on the top of the hiil just 

north of Leall. It is opened by a tunnel that trends northwarll anll the ore lies 

hut a few feet below the sm·face. The •trata dip quite sharply toward the east . 

. There are three' varietiesO{ o"l·c·-int'hc minc-~·c~ractory-.siliccous. ore, tun~sten 

ore, and ~turiferous cong·Iomerute. 

The· refractory siliceous ore lies in the dolomite dir~ctly on the basal 

Cambrian conglomerate and beneath a roof of shales. It forms a hlanket_about 

3 feet in thickness. [t is a whitish granular-looking rOck, often. mistaken for 

mineralized quartzite, and carries great ·quantities of l~arite in crystals ~nd 

irregulo.r masses. The. average yield of this ore iS $60 per ton in gold. 

The second variety -of ore is a granular wolframite whieh appears as a rim 

around the refractory ore· and generally forms a capping of rari_able thickness 

to the latter. It also appears as ·irregular patches throughout the siliceous ore. 

This wolframite:...contains- many cavities. tn which crystals of wolframite together 

with white and green scheelite occur in considerable abundance. Fine radiating 

aggregates. and a few dir;tinet crystals of barite. are scattered thrqugh it, and a 

drusy coating of gold-yellow ferric . sulphate, which is often mistaken for---

/ 

tungstite, .covers the more oxidized specimens. ~---

.The third· variety of Ore. is the auriferous cong~?merate,~as a thick- _ 

ness of 15 feet and lies below .the refractory~Ofe~ a depression upon the . / 

Algonkian surface .. This conglomerate was all highly oxidized·: and consisted of 

wat?r·worn pebbles of quartz and Algonkian quartzite with a few,fragments of 

schist> embedded"'-~- a matrix comp_Q:>d...:of-...:fineJ.J~·d detritftl quartz and- irol! 

oxides. Some, fre-;gold. occur~,-i-;; the conglomerate, which is richest· in the basal 

portions. · The depres~in~c~l- this occurs is 78 feet '"·ide and trends north-

·west. It is reported to have been'~h!'.._~ded by slight elevutions in the Algonkian 

surface. · '---..----......_. 

This mine has been prodncti,·c for more than ·cightcen~ycars. 

Iowa and Golden C'rown mine.-North of Lead· and just above the Black Hills 

and Fort Pierre Hailroad is the tunnel of the Heddy mine. A great quantity of 

whitish siliceous ol-e, containing quantities. of barite, was mined from small shoots 

that trended northwest. The workings extend through to the opposite side of 

the hill. 

Deadtwoorl-Terra mine.--In the Cambrian strata that lie beneath the rhyolite 

cap on the divide between the De Smet and Deadwood-Terra open cuts great 
208 ECONOMIC RESOURCES OF NORTHERN BLACK HILLS. 

quantities of rich siliceous ore were found r~sting almost directly upon the Alg~mkian schist. To the west ue the great chambers from whieh t,hc auriferous 

conglomerates were mined. • .. Big .JJlissou'l'i rnine.-The Big Missouri. comprises two tunnels far up on the· 

west side of the Homestake open cut and ru;..ning into the decomposed dolomite 

of th,e Cambrian that here lies directly on the schists. The ore occurs in small 

bunches in thb rock and exhibits a shell-like concentric parting. It contains . ....__ ·- extremely high values. ·Fractures were observed- at the-west end o{ the tunnel 

pas;ing from the Cambrian rocks into the schists of the Algonkian. 

Swamp Eagle mine.-On· the west side of the divide, ·between Poorman and 

Bobtail gulches, is an open cut on the Swamp Eagle claim. I rrcgularly bounded 

masses of siliceous ore, carrying much barite and some wolfraniite, but comparatively low values in gold, were. mined from this cut. 

7Iidden Fo,rtune mine.-Tlie Hidden Fortune mine, at .the tin_1e it was visited, 

was .a small open cut in the basal measures of the Cambrian, at the head of 

Bobtail Gulch. The ore was exposed on the surface and lay like most of the 

siliceous ore, almost horizontal. . It contains barite, sometimes in extremely large 

white crystals measuring 3 inches ·in length. · It is much· oxidized, and disseminated through it in ·great numbers are scales and crystals of native gold. This 

ore is so rich that a single car of 10 tons is rep,orted· to have yielded $65,000. 

Considerable wolframite occurs in this ore. 

-~D.Jl!":ngo ·111ine.-The Durango mine is located upon the north side of Gold 

Run, jusCabove_the~Black Hills and Fort Pierre Hailroad, with the workings of 

the Heddy adjoining it ·o~~east and of the Harrison on the west. It is one . ' of the oldest ·mines of the hills, being first managed by W. B. Devereux in 1877, 

and is still profitably worked. There are three \'ftrieties of ore-auriferous conglq_inerate;·'· wolf!!!l!!.~~,~~efractory~Sili~,':Q!!_~· The aurifJ.rous_ congloll~erate 

was first mined. It is 15 feet thick and rests dii·\ctly upyn the sc;hists, probably 

connecting eastward with that worked in the . Harrisfu Devereux reports that . .; ___..- much· gold ocenrred free, was richest at_jts contact with the slates, and was 

often dissolved and reprecipitated in· cr~;,f~es in the latter rock. He reports that 

the riche:?t portions~ofjt,.reS[;d on a surface inclined -upward tow.ard the west .-.-- ·--· . 

away from the lowest point of the· channel. The Cambrian rocks all dip east at 

this point, however, and it is probable that this inclination was the result of 

differential movements in the Algonkian rather than a feature of the deposition 

of the conglomerate. Devereux reports coarse, shot-like 1masses of waterworn 

gold clinging to the under~surfaces of large rounded bowlders at their point of 

contact with the Algonkian. Stamp milling extracted 90 to .95 per cent of this 

gold. These woi·kiugs are now· caved m. At the upper limits of this conglom-
)liNES IN GARDEN AREA. 209. 

crate small 'patches still in an unoxidized condition occur, showing pebbles 

embedded in a m.atrix of pyrite, with cavities· lined with cryE;talt; of this mineraL 

A hove the conglomerate and in the c_lolomitie beds lie 8 inches to 2 feet of 

refractory ·siliccom; ore which occurs in broad sh~ots following fractures trending 

generally northwest, but not often discernible in the shales abm·e the 01:e. It 

consists of interlocking crystals of barite embedded in a matrix of secondary 

Hilica and detrital grains of quartz. It grades into wolframite in places~ espedally 

on the rims of the ore. The wolframite i.., gran_ular,.._:,and. carrie:-: hut little gold·; 

the white baritic ore contains between $25 and $60 gold per ton. At se\·eral 

points in the mine the· portion of the . conglomerate immediately ·underlying the 

siliceous o{e consist~ of a mass of pebbles embedded in a matrix of sand grains 

and secondary silica through which were scattered great quantities of native gold 

in sharp and bral)ching forms. 

GARDEN AREA. 

1)'-'>nobscot mine.-Tbe Penobscot n~ine · i:-:; oPened' by a tunnel situated on a 

northwestwardly projecting spur that lies to the southeast of Garden. The 

tunnel i~ · up,on the ba~al Cambrian· quaetzi_te, which dips 10:..:·_ \V.; it follOws a 

:-;hoot of ~iliceous ore 12 feet thick by 12 feet in maximun\ width, which trends 

N. 40° E. A strong manifold fracture may be obser\'ccl in the roof. The ore 

lies in separate blankcbi of varying but rather small thickness, separated from 

one another by band~ o~ unmincralized shales. The ore shows many cadti'ci-3 lined 

with erystals of jarosit_e and contains small quantities of lmrite. It b all of the 

oxidized type. 1\vo .n~inor verticals occur .to the ea.':lt, ~;tri~ing N. 54° E. 

){eystone and othet' m-ines.-Southwest from the .:Penobscot the outcrop of 

basal Cambrian quartzite cxtend:-5 around the ridge and south-i.nud ·tOward th~ 

diddc between the nortlnvardly flowing tributary of False Bottot{I Creek an4_-.r-~-."'."' 

Blacktail Gulch. On thi~ outcrop are many small productiYe woridngs following 

fractures which trend N. 38° E., N. 45·.::. E.~ N. 55° E., and N. 60° E. Ore bodies 

arc small b_ut often quite profitable. The largest masses ocenr at intersections. 

Jf(u'l'ison 111-iue.-Between the south tributar·y of False Bottom· Creek and 

Blacktail Gulch i~ a diYidc upon whieh about 65 feet of Canihrian strata remain. 

A shaft on the center of this didde G5 feet deep constitutes the opening to. the I 

llline.· There are three small ore shoots between 5 and :30 feet wide by 10 feet 

thick fo11owing fractures trending N. ±P E., N. 71° E., and N. 85° E. Sereral 

minor fractures trend N. 20° E. The ore bodi<:s are largest at the intersections . 

. -Face samples of "ore from this mine carried sometimes as much"' as i\88 ·per ton, 

and the ore averaged' about $30 to $35 per ton in gold, with some sil,·er. On 

the bill southwest of these workings is an open cut, in which the basal quartzite 

4987-No. 26-0>-14 
.210 ECONOMIC RESOURCES OF NORTHERN Bf,ACK HILLS. ' 

is exposed, dipping northeast. Two long shoot-s trending N. 70° E. occur here, 

one of them tiOO feet long. The~e com·erge at the southwest end and are 

intersected by a third shoot trendmg N. 38° E .. the three forming a stope GO 

feet wide. 

Oulrlen G1de m.int>.-Thc Gulden Gate mine 1~ worked hy a :-:haft on the 

north side of the head of BlacktaJI Gulch. It is now producing a good deal of ore. 

The mine was inacce~->-;ihie when vi:..;ited. 

li7cki~'(/ llor~:Je mine.-----:-This mine 1.s al':io on the north :-,ide of Blacktail Gulch, 

not' far from the Golden Gate. 'rt is opened hy a ~haft~ from whtch a crosscut 

run::~ northwest. It it:l -,tated by the foreman that there are ~~ Hlllall ore shoots 

in this mine, and the <lnart:atc i~ l'trongly faulted up to the northwest at the end 

of the Cros~;cut tunnel. 

B/rwldail (?).-Directly south of the Golden Gate shaft and on the south 

side of Blacktail Gulch i-, a mine whwh has produced a consid~1'ahle amount of 

ore, but for whieh the writer could get no di~tinctive JJame. It i:-; opcncJ hy 

four tunnel_s, separated from one another by slight· northeast-,outhwest faults. 

There are seven ·small shoot~ following fraetures, which trend N. 30° E., N. 43° 

E .. N. 20° E., ami N. 5U0 E. The largest· stope occurs at the intersection of 

a system of N. 20° E., with N. 50° E. fractures. 

Wells Fargo mine.-The Wells Fargo mine is located on the south side of 

Blacktail Gulch, west of the eruss roads that lead into Tetro Gulch. There are 

two t~et~ of workings, of which the \Vestern r.cries i::; higher in elm.~ation than the 

eastern on account· of the strong easterly dip of the Cambrmn strata. The 

western series of workings i':l opened bv a cros-scut trending ':;outhcas't and com~ 0 -

pri.'3c~ ten :-;mall niirrow. shoots that follow small fracture.-. which trend N. li5° E. 

and N. 5 7° E .• with a few minor intersecting Jo,hoots trending N. 21Y:' E. and 

N. 32° E. The lower working~ are eal-3t of those just deseribed. and compril'le 

one large shoot of ore trending N. !55° E. and, three f..maller .shoots trending 

N." ±7° E., N. !\11° E., and N. 6!1° K The fractures are very tight, and cun not 

be seen except in the faces uf ore at the end of the :-.hoott-. They do not extend 

into the ~hale:-:- that overlie the ore. 0' 

Amf:t·i('(/11 l!.~''JH'eN-: mln.t:'.-'The America'n Expre.-,~ mine 1s opened hy a t.unnel 

running northward from the bed of Shceptail Gulch nbou.t one-half mile west of itl'l 

junction with Bhwktail. The working-~ whi<'h lie ju ..,t south of tho.-,e of tlle 

\V ell& :Fargo are upon the h~~al Cambrian quartzite and in dolomite of the hard, 

blue cry:-;t.allme nuiety. Aho\rc the ore-hearing heds about 15 feet from the 

quartzite i~ a sill of tine-grained rbyohte. The :-:-trata dip to the east at an ~ 

angle of 10° to 15°. There are nine ore hodics In the mille, of which foui· ~trc 

of ':ont-iderable :-.ize. Thl' largest is 50 feet wtde at the eenter and Wati formed 
MINES IN YELLOW CREEK .AREA.· 211 

by four systems of fractures trending N. 40° to ±5? E., N. 50° to 55° E., N. 60° 

to 65° E.; and N. 85° E. · From the east end of thig large ore shoot a crosscut 

runs north and intersects twelve small shoots;.of. which· three trend N. 85°;. three 

N. 40° ~o 45° E.; two N. 50° to 55° E.; and four:N. 60° to 65° E. The· ore 

bodies become larger where the fractures striking N. 85° E. int~rsect th.ose 

striking N. ±0° E. The fractures passed from the ore into the overlying sill of 

rhyolite .. All· of the ore bodies in this mine except the large shoot on the 

east lie from 5 to ,.., -feet above the quartzite .. the ore resting on\ a floor of blue 

dolomite of exactly the same character as the walls and immediately beneath a 

a roof either of fine. impervious shales or o£. rhy_<;>lite.. The ore mined was all 

of the sulphide variety and yielded fair. average values. 

, YELLOW CREEK AREA . 

. . .Donelson fractlon.-The Donelson fraction .. comprises two ore shoots, the 

larger following the zone of fracture with a general dii·ection of N. 12° vY.. It 

is opened by drifts at two points; the first is a little north .of the porphyry 

knoll which ·occupies the center and narrow southerly portion of the divide 

between Whitewood and Yellow creeks; the other is an incline· a little more 

than 700 feet southwest of this point. · About 300 feet southwest of the north 

opening of the mine an ore body, following a fracture whose strike it; about N. 

60° E., enters the main shoot. This fracture extends northeast. as far as .that 

which has produced the main ore body by which it' is .abruptly cl)t off, not 

app~aring upon the other side. At the south end of the mine the .ore body bends 

slightly to the southeast and divides into two portions, which trend S. 20S E.; 

·and extend into the Kickapoo claim. At the north end the fracture is of an 

. extremclJ~ irregular form. The ore body varies from. 6 to 30 feet in width . and 

is nbout 1± feet· in .thickness. The roof is a decOmposed· shale;. the \Valls are 

.oxidized, iron-stained, and banded dolomite. The ore is reported . .to havc:yielded 

values a\·eraging about $50 per ton. At rmmy places in t~is mine the quartzite 

which underlies the ore carries from $15 to $25 per ton in .gold, but is always 

mueh lo\vcr in grade than the main body of the· ore. 

Wasp lVo. i.-Directly east of the Donelson fraction is the vYasp -No. 2. 

Two series of o~e bodieo of very small size, but often of considerable length, 

were here· mined. Fractures are completely obscured by the very deComposed 

character of the roof .. Five of tho. ore shoots trend N .. ±5° W.;. three of the 

... ~ger shoots N. 33 to 38° E.; two, N. 80° K . Two small shoots trend N. 3° 

E.,· and complete the series . 

.. , Wasp .No.!&, Little Blue, and Little Blue .fraction.-Four liundred feet southwest 

· of the·south end of the Donelson mine arc ·the Wasp No. 2, Little Blue, and Little 
212 ECONOMIC RESOURCES OF NORTHERN Bf,ACK HILLS. 

Blue fraction, while south of these mines a short distance are the 'Vasp No·. ± and 

J\.iinnie mines. The working:; of all these mineS are connected with olle-anothcr. 

The ore lies directly upon the quartzite, and except in ~crtain portions of the-Minnie 

mi~e carried high values. The shoOts vary -from 5 to .f.O feet in width 1 and are 

generally 5 to 6 feet in/thickness. In all but a' few cases the roof is a much decomposed shale. Lagging has generally obscured the fractures, but tl)e ore bodies 

trend generally N. 37° to MP E. There are minor or~ bodies Rtriking north aml 

south and N. 12° IV. A few other shoots are present which follow directions 

undetermined. Quantities of barite occur in the ore, and irregular porphyry 

dikes are found with considerable frequency. 

In the IV'asp No. 2 mine a large irregular porphyry mass, striking slightly west 

of north, faults the Cambrian about 20 feet. As it proceeds toward the south it 

becomes divided into two dikes, on the west side of eith01: of which is a fault with a 

small downthrow of ahout 8 or 10 feet. Between these two dikes is a small stope 

about 40 feet wide and 60 feet in length. One of the porphyry dikes cm·,-es up m·er 

the ore so that the space is almost entirely inclosed in porphyry. This small bod)' 

of ore is reported to have yielded $75,000. l;'rom se,·eral of these min~s deposits ~f 

granular wolframite were mined. 1~ occurs iu nodules anJ·as rims to the main hod~: 

of the ore. In one case the wolframite was ol?setTcd forming kidney-shaped masses 

in the decomposed do.lomite heds a few inches from the quartzite. l\I uch of this i:; 

reported to have contained high values in gold, and was shipped tO the smelter !tnd 

treated fm: that mineral heforc its yalue as an ore of tungsten wa!" re6ognized. 

Two Strike and Little I.litt.>:~lnu·y IIIIHes.-The:;e mines hayc yielded hut :;mall 

quantitie~ of siliceuu~ ore and arc more important in connection with the tungsten 

deposits discussed on page 16±. The ore lie~ on the hasal quartzite and carries barite 

and quantitieS of granular wolframite~ which it~clf contains radiating ~rystals of 

__ l)_arite and cavities lined with ~cheelite. S0mc of the siliceous ore contains long. 

acicular crystals of stihnite radiating from a center like 'the spicules of a radiolarian. 

SQUAW CREEK AREA. 

Olenpcdra. mine.-Th.e Cleopatra mine is situated on Squaw Creek, just above its 

junction w~th Spearti8h Urcek. The ore occur:-:\ a:; a replacement of dolomite along 

fractures which strike nearly east and west. There were some small bodies of flat 

siliceous ore opened at the time the mine was Yisited, hut no large ore Shoots were 

disco\~ered. Since thi~::.~ report was written this mine has become an important 

producer. See page 152. 

I 
• 

PLATES ·rr TO XX.· 

213 

"' 
() 

II. 

III. 

IV. 

Y. 

YI. 

PLATES II TO XX. 

Southern Deadwood-Ter~·a open cut. 

Specimen of slate showing relation of folding to lamination. 

Sketch map of a portion of the northem Black Hills, showing the location of the several 

special maps included in this paper. 

General geologic map of the northern .Black Hills, showing the location of the various 

productive mining areas and their relation to the sedimentary formations. 

Geologic map of Lead and vicinity, showing the location of the auriferous gravels at the 

base of the Cambrian and the general geology in the neighborhood of the Homestake· lode. 

VII. Garnetiferous ore from the Pierce stope, Homestake mine, showing secondary quartz introduced between (A) shattered garnet (B) and scattered carbonate. 

VIII. Sketch map of the Clover Leaf mine, showing relation to surface geoJogy. 

IX. Map showing ·the principal shoots of refractory siliceous ore in the Bald 1Iountain area 

and their relation to surface geology. 

X. Dolomite or ore-bearing rock: A, xenomorphic variety; R, automorphic variety. 

XI. Type cross sections of siliceous ore shoots, showing varying forms: A, Simple fracture 

"';ithout mineralization (from occurrence in the Penobscot mirie, Garden area); B, 

Slightly inclined fracture v..-ith inCipient minerali?.ation (Little Bonanza mine, Bald 

Mountain area); C, Showing the great vertical and limited lateral extent of ore shoot 

arising from the minerelization along a strong open fracture (Penobscot niine, Garden 

area); D, Showing conCentration of ore beneath shale roof and its tendency to narrow 

M followed downward to the quartzite; E, Nearly circul:ir shoot in clearly marked 

dolomite ·beds (the E shoot, Tornado mine, Bald Mountain area); F, Showing coalescence of minera~iza~ion a~ong adjoining fractures, which become extremely tight above 

(Isadorah mine, Bald Monntaih area); a-, Showing bands of waste in _the ore produced 

by the oc<':urrence of less easily mineralized shale between beds of dolomite; ll, No. 3 

~hoot of Union mine north of the crosscut, Bald Mountain. area, showing manner in 

which the greatest thickness of ore occurs. along the "vertical" or fracture; I, Manner in which beds of impure dolomite above the main ore body are partially replaced 

(Alameda open cut, Portland- district); J; Manner in which a large flat ore body arising from -a single complex fracture is concentrated beneath a beJ of shale (No. 5 

shoot, Double Standard mine, Bald Mountain area);· K, Cross section of Tornado shoot 

at the widest point, showing formation of immense flat body of ore on zone Of intersecting fracture. 

XII. A, Composite fracture or "vertical,". as seen in open cut of the Cleopatra mine, Squaw 

Creek; B, Mineralized fractures or "verticals" in porphyry near the mouth of the 

Little Borianza mine, on south side of Fantail Gulch. 

XIII. Plan ·of a portion of the Welcome mine.· . 

XIY. Microscopic section!l of siliceous ore from the Ross-Hannibal mine: A, without the polarizer; B, with the polarizer: 

XV. Microscopic sections of siliceous ore, showing the perfect preservation of the details of the 

original rock texture after complete replaceme'nt by silica: A,, without the pqlarizei'; 

B, with the polarizer. , • 

XVI. Banded siliceous ore, No: 2 shoot, Union mine, showing the preservation of sedimentary 

bedding in the ore. · 

XVII. Geologic fnap of Ragged TOp Mountain and vicinity, showing po'Oition and direction of the 

main Ragged Top ''verticals," also the location of the Ulster mint:. 

·XVIII. Plan and cross section of the Hav;rkeye-Pluma mine, showing the geologic ·relations of the 

gold-bearing Cambrian conglomerate. 

XIX. East-west cross section of the Tornado mine. 

XX. Plan and. east-west c~oss section of the Great :Mogul mine. 

214 

' 
U. S. GEOLOGICAL RURVEY PROFESSIONAL PAPER NO. 26 PL. II 

SOUTH E RN DEADWOOD-TERRA OP E N CUT. 
U. S. GEOLOGICAL SUrli/EY PAOFESSIONAL PAPER NO. 20 PL. Ill 

SPECIMEN OF SLATE SHOWING RELATION OF FOLD ING TO LAMINATION. 
\ 

: 

,. 

1 

I, 

.~· 

/ 

/ ___ ,.,:· 

i 

-.~ 

4Y" 

\..... 

.) 

~- ~ \ 

i /' 

.. / 

( 

I 

r 

\ 

i 

' 

" i 

/ 

\ 

i 

\ 

., 

.... 

/ .. 

,..' 

(' 

\ 

._) 

/ 

/ 

\. 

) \ 

.\ 

i 

i 

__ ) 

r 

; 

! 

\ 

/ 

; 

ogicat Survey Topographic Sheets SKETCH MAP OF A PORTION OF THE NORTHERN BL.ACK HILLS 

SHOWING THE LOCATION OF THE SEVERAL SPECIAL MAPS INCLUDED IN THIS P.Af!ER 

Tf1F: NOIUll'> PFTERS CO. PHOTO·UTHO .. WASHINGTON r, <: 
MAP OF THE NORTHERN BLACK HILLS 

SHOWING GEOLOGIC STRUCTURE AND THE LOCATION AND RELATION OF THEY.ARIOUS PRODUCTIYEMINING-.AREAS TO THIS STRUCTURE 

BY J. D.IRVINGScale ~ )t ~ o 2 .._ s m:il.es 

~~~--~======~------~·======~------~·==~ ~ 

LEGEND OF PRODUCTIVE AREAS 

P.roductive areas ofTefractmy siliceous ares of Cm:nbrian_ 

Prodnctive 

-

areas of &old -bearing 

lodes in the ~rikian. 

Productive areas 

-

oflead- silver o:::-es 

LEGEND OF GEOLOGY 

c:::=:J 

l'ost-Carribrian. ( Carboniferuu.s 

l:Unestones in 91'M.t- pa:ro} 

c:::=:J 

Ca:mbrian conta:iningmuchpm:phyry 

NAMES OF AREAS 

1 Carbonate area 

2 Squaw- Creel< area 

3 .Areaofprospects of sylvanite 

.t\ Ragged Top area 

6 ElkMom.1.tain. area 7 Bald.Moun.tain. area 

A. Portland. district 

B. RubyBasin.district 

8 Garden. area 

9 LeadCit.varea 

10 Yellow Ci-eekarea 

ll Spruce Golch.area 

12 TwoBitCreekarea 

13 Strawberry Gulch area .ttl Galena district 

16 Hom.est.:ke area 17 Clo-rerleafarea(Un.cleSam.) 
U. S. GEOLOGICAL SURVEY 

GEOLOGIC MAP 

OF 

LEAD AND \l'ICINITY, S . DAK. SHOWlNG THE LOCATION OF 

Au"R.IFEROU 8 GRAVELS AT THE BASE 

OF THE CAMBRIA.' .AND THE GENERAL GEOLOGY 

fN THE NEIGHBORHOOD OF THE HO:MESTAKE LODE 

GEOLOGY BY 

T . A . JAGGAR JR., cT.M. BOUTWELL ,AND J .D.IRVJNG 

EC,ONOMIC GEOLOGYBYJ.D.IRVING 

Scale 1000 1000 zooo 3000 

P R OFESSI ONAL PAPER NO . 2& PL. VI 

L E GEND 

Cam "brian 

Basal Camoria:n. 

c ong:J.on1.erate 

~ 

~ 

Areas un.Qei'lain oy 

gold-:produ.cl:ng basal 

C a=brian con,Slomerate 

Eruptive rocl<:s 

(chiefly rlryali te) 

Dikes 
U . S . GEOLOGICAL SURVEY PROFESSIONAL PAPER N0. 26 PL.VII 

THIN SE CTIONS OF HO;M.ESTAKE ORE 
u . s . GEOLOGICA L SURVEY PROFESSIONAL PAPER NO .2 6 P L. VI II 

NOTE 

Position of' outcrops determined ·by 

llrteraec tion 

Dips and str-ikes are those oft he lan1ffiation 

oftl:te.Algonlrian 

The redhatcbing in the :m.i:ne irulic ates the quartz body as dete-nnined 

Scale 

200 100 0 

SKETCH MAP OF THE CLOVERLEAF MINE 

BLACK HILLS, S OUTH DAICOTA 

SHOWTNG ITS RELATION TO THE SURFACE GEOLOGY 

200 4oofeet 
LEGEND 

ECONOMIC GEOLOGY 

Ore bodies in. 

lower ore-bear.ingbeds 

or"lower contact' 

Ore boilies in 

"lower contact:' 

Posit:ion.an<le:xact· 

outline -uruieterrrrined 

Ore bod:ies in 

upper ore-beari:ngbe<ls or "upper contacts" 

Ore bodies in 

"upJ?er contacts'.' 

Pos1tton. =d exact outline undetermined. 

Ore bodies :in"low-er 

contact': but restll:tg orr 

a floor ofphonollte. Thenta:i:n llowert:onlact~' 

bodies lie below-·the 

phonolite 

-u .s. G EO LOG\ CA SURVEY 

2000 

Scale 

3000 4000 5000 

MAP SHOWING THE PRINCIPAL SHOOTS OF REFRAC~~ORY SILICEOUS ORE IN THE BALD MOUNTAIN AREA 

AND THEIR RELATION ) THE SURFACE GEOLOGY 

PROFESSIONAL PAPER N0.26 PL . IX 

LEGEND 

S URFACE GEOLOGY 

D 

Massive g~LL.. r gray lil:nestone 

11 Englewood. limestone (pink l:llnestone) 

z . 

H P:irik- spotted. 

1:i1nestone 

i

:::!: { c al

~~~:L careous sandstones 

~ and quartzites 

H Sclrists,plgnlites 

a:mplu.oolites 

quact.zites, etc. 

Porphyry 

(msheets a:ruL 

irregu-lar bodies) 

Fault lines 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 26 PL. X 

A 

B 

DOLOMITE, OR ORE-BEARING ROCK. 

A. Xenomorphic variety. Shows cleavage of the dolomite, which forms the greater part of the rock; also grains 

of detrital quartz. Analysis on page 121. 

B. Automorphic variety. Shows complete rhombs or crystals of dolomite, of which the rock is made up. This 

structure may be seen preserved in the ore shown in Pl. XV, .A. 
U . S . GEOLOGICAL SURVEY 

A B 

F 

G 

K 

H 

JJ 

Sbales an.d 

intercalated 

la;yers of :llnpure dolomite 

Sketch o.f:m:i:n.eralized :&acture s 

in.Ala:m.eda :urine near Portland 

s"hovving repl.acemeni of' In.ain. 

dolonrite bed and partial replacement 

ofim:pure layers of dol.o:mit.ic a bales 

I 

EAST 

PROFESSIONAL .PAPER NO .2 6 PL . XI 

E 

TYPE CROSS SECTIONS 

OF 

ORE SHOOTS 

By J.D. Irvill.g 

Scale 

2a5&&-===~--c=~--~=================·~•-.BMaa~~~~---·-O£eet 

LEG E ND 

I M 1:\:J:;:;q 

Co:mparativeo/ Dolomite 

impervious Slate ~-Algorilrian. 

schists 
U. S. GEOLOGICAL SURVEY 

A. COMPOSITE FRACTURE OR ·· vERTICAL, " AS SEEN IN OPEN CUT OF THE 

CL EOPATRA MINE, SQUAW CREEK. 

PROFESSIONAL PAPER NO. 26 PL. XII 

B. M I NERALIZED FRACTURES OR "VERTICALS " IN PORPHYRY NEAR THE 

MOUTH OF THE LITTLE BON~NZA MINE, ON SOUTH SIDE OF FANTAIL 

GULCH. 
U.S.GEOLOGICAL SURVEY PROFESSIONAL PAPER N0. 26 PL . XIII 

. I 

PLAN OF 

A PORTION OF THE WELCOME MINE 

BlACK HILLS, SOUTH DAKOTA 

Showing a £lat ore body of considerable ho-rizontal extent 

form.ed bythe contbin.ed action. of solutions rising through a 

:number of closely spaced fractures 

ByJ.D. Irving 

Scale 109 so o 100 zoo:feet 

bo==±===cl========±======~ 

LEGEND 

c__ _ __,l Um:n:ineralized country rock 

t__ _ _.Jj Ore 

L-..-.. _ _l, Porpbyry 

IWJJ%1 "Verticals" 

N 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 26 PL. XIV 

A 

B 

SILICEOUS ORE FROM THE ROSS-HANNIBAL MINE . 

.A. Seen without the polarizer. Shows the dark m1neral, pynte, and the l1ght mineral, quartz (h). 

B. Seen with the polarizer. Shows the separate individuals of si li ca forming the ore. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL. PAPEA NO. 36 PL. XV 

A 

B 

SILICEOUS O RE, 

A . See n without the polarizer. Shows th e perfect preservation of the form of ihe dolomite rhombs afier comp lete 

replacement by si!!ca. 

B. Seen with the polarize r. Shows \hat th e rock is compl etel y changeJ to silica . 
.. 

U. G. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 26 PL. XVI 

BANDED SILICEOUS ORE, NO.2 SHOOT, UNION MINE. 

:.hows the preservation of sedimentary bedding in the ore, the banding here seen being contim.ous with that of the inclosing stratified rocks. 
MAP OF RAGGED TOP MOUNTAIN AND VICINITY, BLACK HILLS, S. DAK. 

SHOWING THE GEOLOGY, POSITION, AND DIRECTION OF THE MAIN RAGGED TOP "VERTICALS" OR SILICEOUS 

GOLD VEINS, IN THE LJARBONIFEROUS LIMESTONE; ALSO THE LOCATION OF THE ULSTER MINE 

Scale o soo 1000 zooo aooo ~feet 

b-~~~~======~----~~====~ 

LEGEND 

.CARBONIFEROUS 

w 

Refractory 

siliceous ore 

Keavy gray lim.estone 

OROOVICIAN 

Pink spotted 

limestone 

CAMBRIAN 

IGNEOUS 
U. 8. GEOLOGICAL SURVEY 

Sect/on on lt'ne A 8 

Sect/on on line C 0 

Scale 

o.e:~=5oE=~~~oeo~=====ieio=o=======3=oo~=====5+a5aofeet 

PLAN AND CROSS SECTION OF THE HAWKEYE-PLUMA M , SHOWING THE GEOLOGICAL. RELATIONS OF THE GOLD-BEARING CAMBRIAN CONGLOMERATE. 

'\ 

\ 

'\ 

PR,OFI,SSIION~L PAPER NO. 28 PL. )CYIII 

\'\ ' 

'~,j 

Adi~1.1 I 
U.S.GEOLOGJCAL ~URVEY PROFESSIONAL PAPER NO. 26 PL. XIX 

WEST 

.Algonlrian 

scl:U..sts,etc. 

CROSS SECTION OF 

PORTION OF THE TORNADO MINE 

BLACK HILLS, SOUTH DAKOTA 

THROUGH THE TORNADO SHAFT 

ScaJ.e 

w ..... •-=0~30~2~0 1=0 ======s::Eo~~~~ .... 10m0f"eet 

Basal 

~ 

~ Cambrian 

quartzite 

LEGEND 

Dolomite. 

-

often 

shaly so as -to lirade 

into shales in places 

hnpervious shales 

containing many 

dolomite beds 

OJ] 

Porphyry dikes ~ I \ \\ I Ore Faults 

EAST 
U.S. G EO LOG I CAL SURVEY 

A----

A 

PLAN AND CROSS SECTION 

OF A SMALL PORTION OF THE 

GREAT MOGUL MINE 

BLACK HILLS, SOUTH DAKOTA 

Algonkian 

sdU..sts, etc. 

Scale ~~·~0~30~?=o="~o~o===========S~O~~=-~~"O~Ofuet 

LEGEND 

IIIII Basal Cambrian Dolomite, often 

quartzite shaly so as to 8rade :into shales in places 

Impervious Shales 

containing man~,. 

dolomite bed.s 

PROFESSIONAL PAPER NO. 26 PL. XX 

N 

t 

I 

'j 0 

' --0---- ---- -----

INCL!N£ ON 

f Ore 

B 
' ' 

INm~x. 

A, 

Page. 

Alameda mine, description of ..................... 203--20-t 

Alexunder mine, ore in, stratigraphic position of. 1il 

Algonkian formations, character and thickness of, 

columnar scction showing.. ... . .. .. . . . ... 18 

Algonkian rock~, character of......................... 21 

gold in, mines yielding... . . . . . . .. . . .. . . 55 

origin of....................... . .. ... . . . . .... . 159 

Homestake ore body in, form and character of. 103-107 

mineralization of .................................. 90-92 

ore deposit!! in , .................................... 5 ..... 9i 

relation between ores of Homcstake mine and.... 81 

section of, ca~t from Perry.... . .. 33-34 

northeast of Clover Leaf mint: ........ :.... a3-3-t 

on Dead wood Creek, near Central.. . 33 

ycrticnl fractures in . . . . . . . . . . . . . . . . .. . . . . . . . . . 128 

warping of surface of. ...•........................ 18-19 

Algonkinn schi;;ts, direction of schbtof!ity in, figJlre 

showing .......... . 

mineralization of, date of ..... . 

stocks' an<l dikes in 

,, 

159 

26 

topographic f..;ntures of 15--16 

Algonkian slat..;s, banding of, llgure showing......... 83 

dip and strike of...... 70 

ore bodies in........................ G'J-71 

porphyry dikes in ............... :.. . iO 

quartzite band in, figure showing... . . . ..... i2 

Alpha·Plutns group of mines, ore ~;hoot~ of, descrip-' 

tion of • .'............................... 1-17-1'\19 

Alpha-Plntus mine, des<.:!riptlon of . .. . . ... . .. . . .. . . .. . 192 

American Express mine, dcsNiption of......... 210-211 

Amphibolitcs, character and occurrence of ......•• 69,80-81 

Analysis. ,See substance analyzed. 

Andesite-porph~·ry, mineral composition ~md localities of................................ 22 

Ankeny, 0. P., expefimcnts by, on use of bromine in 

ore r..;duction..... . . .. . ... . . . .. .. . . . .. . . . . 117 

Arizon!t, wolframite ore in, occurrence of. ......... 168,169 

Arsenopyrite, occurrcn~e of, in refractory ~ili..;eou.~ 

ore~. ............. 138 

origin of, in refractory siliceoU!! orcs ........... 158-159 

Aurif..;fous grun:ls, etc. See Gold-bearing. 

Azt..;c, rhyolite cutting grE:cn porphyry near, figure 

showing . . . .. . . . . .. . • . . .. .. .. .. 24 

JJ. 

Bald )iountainurea, Cambrian rocks in:exposuresof. 145 

drain!tgt:l of............... . .... 145--1-iG, 

f.racture groups in......... 1:30 

geologic features of......... 113 

location of................. ...... .... . . H4 

mines of, location and developm..;nt of......... 1~5--150 

Portland district in .............................. 149-150 

• 

l'age. 

Bald )fountain area, refractory siliceous ores of, average yield of ............... 113 

refractory siliceous ores of, gold in .. . 114 

map .showing principal shoots of...... 214 

occurrence of. . . . . . . . .. . . . 112 

ratio of gold to silver in .. 1•• lH 

valueof........... 152 

Ruby Basin district in...... 1-16--149 

topographyof_....... H5 

Balmoral mine, gold production of. 118 

Baltimore mine, description of..... 200 

location and workings of...... lflO 

:Baltimore and DeadwOod mine, location and working~ of....... . ...................... lOG 

Bande-d ore. · ,'l!'e Homestake mines, Qres of. 

Barite, occurrence of, in refractory siliceous orcs . . . . . 139 

Barium·, oiigin of, in refractory siliceous orcs......... 158 

Rear Butte Canyon, Cambrian ..rocks in, thickncss 

of ........ 18 

geologic section measured in...... 18 

-Bellr Butte Cr~;ek, course und features of. 15 

geologic section on . .. .. . . . . . .. . . . . . .. .. 39 

Be~tver Creek, Siluro-C1trbonifcrou~ limestone~ in, 

thickness of ........... :. .. 18 

Ren Hur mine; 'deSCi-iption of....... 200 

fractures in, relation of, to eruptive rock 133 

location and working~ of..... 1f.O 

or..; of, value of . . . . .. . .. . .. . .... . . . . .. . . . 154 

Benton f.Jrmation, po:,ition and thickness of, columnar 

section showing . . . 18 

Benton shale. clw.racterof..... 20 

fo~sils in. . . . .. .. ... . 20 

B,ibliography of Black Hills literature...... U-l-i 

Big Honanza mine, description of 1S\l 

Big 1-lissouri min..;, description of. 208 

ore of, value of . . . .. . . . . .. .. . 1.')4 

refractory siliceous ore in . . . . . . . 151 

vertical fractures in . .. . • . . .. . . . . .. . . . . 128 

Billy mine, description of.......... 188 

Black Hills, northern, drainage of. 14-Fl 

geologic formation~ in, fos~ils of ...... 20,21 

· lithologic and topographic character of, tab!~ 

showing............ . ........ 20-21 

geologic map of . ... . .. . .. . ... . 214 

igneous intrusions in, history of 31-:~3 

literature relating to . .. .. . 13-14 

mining region in, location of.,..... 51 

sketch map of portion of, showing location of ~pechli maps (plate) . 2-il 

stnltigraphic reluticms in. 

stntctural features of ..... 

topogntphic types ill 

uplift of, date of .................... .. 

215 

17-22 

14 

If'>-li 

2.'i 

• 
216 INDEX. 

Page. 

Black Hills Gold and Extraction Companr, smelting 

pl~lnt of.................................... 117 

BlacktaifGulch, gold-benring conglomerates near.. 103, 

106-107 

ore from, analysis of .................... ~.......... 143 

Blacktuil (.') minc:dcscriptlonof...................... :no 

Blake, W. P., cited on tin ores in southern Black Hills. 96 

:Bobtail Gulch, gold-hearing conglomerate between 

Deadwood Creek and...................... lOG 

Bonanza mlnc, gold production of..................... 117 

Boscobel mine, description of.......................... 198 

·fractures in, relation Of, to mineralizlltion . ... . . . . 135 

ore shoot of, dimensions of........... 125 

Bottleson sho?t, length of ..•..•.••...• :............... 125 

Boulder Creek, Quaternary gravels !tlong. ... .. . . . . •.. 41 

Boutwell, J. M., acknowledgment to .... __ .........•.. 53 

Bowie, J, Augustus, jr., gold ores of northern Black 

Hills examined and reported on by....... 01 

Breccia, porphrry, occurrence of ................. ·'··· 59--00 

Breccius, intraformational, occurrence and character 

of .•........................................ 27-29 

Burlington and Golden Sands mines, description of:. 205 

Buxton mine, description of . ... .. . . . . .. . . .. . .. . .. ... 184 

gold production of. .................. :.-............ 118 

Buxton )fining Company, development work by, history of..................................... lli 

Buxton-Union group of mine~. ore shoots of, description of .................................. 146-147 

c. 

C1tlcitc, occurrenCe of, as a gangue· minerai:: •. ':.,:.::: . 6$ 

Caledonin cut, dikes in, character and thickile&i of... 2i 

gold-bearing conglomerate near .... :~·:." ...• • .. ·.~:.: 100 

Caledonia mine, ore bod~· of,- character of............. 78 

stampinilisat..................................... 58 

Cambrian formations, character of .•... :.· ............. 18,21 

fossil.~ in........................................... 21 

thickness of, columnar section showing........... 18 

topographic features of.._ .. __ ..... __ .............. 16 

Cambrian rocks, character and thickness of.......... 1\J 

gold ore in ................ :........................ 72 

gold and silver ores in ............ : ............ __ . 98--1G3 

lead aud silver ores in ...... : ...... : ............. IG9--1il 

l'rritous ores in ................................. 162-163 

section of, near .Englewood ........................ 37-39 

near Galena ...•............................... 39--41 

itettrTcrry Peak ......•........................ 35--36 

tungsten ores in .................................. 163--169 

type locality of.................................... 1G 

vertical fractures in ···•···········.················ 128 

wolframite ore ln ................. -:--........ 166 

Cambrian shales, volcanic sills in ............. ·.... 26 

Carbonatedi~;trict, eountry'rockin ............... Iii 

locationof......... ........................... 1i7 

ore of, charucterof...................... . lii-178 

C>trbonlferous formutiOJlS, character and thickness of, 

columnar section showing................. 18 

charactcrof. ....... :............................... 21 

fossilsin ............................... :·: .. :..... 21 

Cltrbonlferous limestones, orcs in ............. ; ...... li2-178 

yertical fractures in......................... 128 

Cttrboniferous rocks, gold and silYer ores in. li:l-lii 

lead and silver ores in............. · 177-178 

Carpenter, C. W., acknowledgment to....... 53 

Carpenter, F. R., acknowledgment to..... 54 

cited on occurrence of refractory siliceous Qre~ ln 

Cold Creek.. 1W2 

Page. 

Carpenter, F. R., cited on refractory siliceous ores.... 115 

cited on tin ort>s in sonthem Black Hills...... 96 

cited Qll treatment Qf refractory siliceous orcs ... : 160 

Carpenter mine, ore in, stratigraphic position of. lil 

Carrol group of mines, pfQdnction of ...... _........... 113 

Cassiterite, occurrence of... . .. . . . . ..• . . . ... . .. . .. .. . . \J6 

Cement Ridge, Cttmbriun conglomerate ncar, thickness of.................................. 98 

Chalcedonic silica, QCcurrcnce of..................... 1:38 

Cl1emical analyses. See suUstance aiialp:ed. 

City Creek, copper ore ncar............................ 94 

Cleopatra mine, locution and workings of............. 212 

refractory siliceous ores in, occurrence of ........ 152, 162 

verticalfracturesin....... --·-···-······-·· 152 

plate ~bowing ................... 214 

. Clinton mine, description of ................... 191-192,200 

· fractures in, intersection of........................ 132 

Clinton und Ashland mine, production of............ 118 

Clo>cr Leaf mine, Algonkinn section northeast of, 

· churucter'of ····-··-···-······-············ 34 

country rock at ................................• :. 92 

history of de>elopment of. ............. ·.........•. 92 

locution ?f........................................ 92 

ore of, clmracterof ........ .................... 94 

dipof. ..•. .-.................................... 92 

relatiQn.;: of, to surface geology................ 93 

value of....................................... 9~ 

sketch mup of, ~bowing relation to surface gcol· 

ogy ........................................ 212 

surface workings of ................................ 9"2-93 

Cold Creek, refractory siliceous ores on,occurrence of. 162 

Colorado, wolframite in, occurrence of................ 169 

Columbus mine, ore of, character of . ..• . ....... .. ... . 74 

-~~-cl ··········· ········· 3 

workingsoL..... ................................. U7 

Comet mine, ore in, stra.tigmphic position of .... ..... 171 

"Competent" member, definition of.................. 17 

Conglomerate, gold-bearing. See Gold-be!~ring conglomerate. 

Contorted ore. See Homestuke mine, ores of. 

Copper orcs, occurrence of . . . . • . . . . . . . . . • . . . . . ......• 94-\!5 

usc of, in smelting siliceous ores . . . . . . . . . . 95 

Cora mine, ore in, stratigraphic po~ition of . ...•.. .. . . 171 

Cornwall tin region, wolframite in ......... :.......... 169 

Cretilceous formations, chamcter of................... 20 

character and thickness of, section sh~wing . ... .. 18 

fossilsin .... ··--·········--··-······-············· 20 

Cretaceous (Lower) formations, character or.......... 20 

fo,-silsin................ .......................... 20 

thieknes~ of, columnar section showing........... 1S 

Crosby, W. 0., cited on pseudo-conglomerates of the 

Bhtck Hllls ..... :.......................... . 2.3 

Cross, Whitman, cited on intrusive porphyries in the 

Rocky .Mountains......................... 23 

Cnster, General, reconnaissance by ..........•...•...•• 

D. 

Dacite, min&rul composition nnd localities of ......... . 

D~1cy group of mines, location of ... ·: .••.............•• 

ore of, character of ............................... . 

ehemic~tl composition of. .................... ~. 

microscopic appearance of ..................•. 

Daisy mine, description of. ........................... . 

Dukota fgrmlltion, position and thickness of, columnar 

section showing ........•...•.............. 

Dakota snndstone, character of· ..... : .....•........... 

fossils in 

56 

22 

173 

1i8 

li4. 

174 

200 

13 

20 

20 
INDEX. 217 

Page. 

Darton, X. H., acknowledgment to.................... 2f> 

quoted on age of White River deposits...... 26 

De Smet cut, ore hody in............................. i1 

refract Dry siliceous ore in . . . . • . . . . . . . . . . . l·'il 

De Srnet mine, banded ore from............ S3 

ore of, value or . ... .. . . .. .. . . . . . . . .... . . . . >9 

ore body of, figures showing secUom of i3 

Dead broke mine, ore of, value of. . .. . . . . . .. . . 110 

Dc!nlwood, Cambrian rocks at, thickness of...... 19 

Deadwood Creek, .Algonkian rocks along, section of.. 3:3 

gold-bcuring conglomcntte near................... lOll 

Deadwood formation, character aml equivalents of 21 

fossils in . . .. . . . .. . . . . .. . . . .. . .. .. . . .. .. . . .. . . . .. . . . 21 

section of, near Galena . . ................... 39-U 

Dcudwood Gulch, Cambrifln conglomerate ncar, thiekness of 105 

gold-benring conglomerate north of........ 101\ 

Deadwood mine, stamp mill~ at. . . . . . .. .... . ... . . . ... OS 

bcadwood plncei deposits, source of gold in. 179 

Deadwood anrl Dcl1Lware mine, gold production of 11> 

Deadwoo>l nnd Delaware Smelting Company, nnaly~es 

furnished by.. . .. .. .. .. .. .. .. .. . .. .. . 113 

plnnt of, for treatment of ores ................... lli, 1(>0 

Dearlwood-TernL Company, organization and properties of................................... :y; 

stftmp mills of.. ... . . ... ... . .. .. . i>8 

Deadwood-Terra mine, deScription of ............... 20i-208 

Deadwood-Term (Southei.-n) open cut, plate showing. 21-t 

Decorah mine, description of. ............... ,......... 203 

Devereux, W. B., cited on Deadwood placers.......... 1>9 

cited on derivation of gold-bearing conglomerate. 107 

citedongold-bearingconglomeratesin Black Hills. 101 

cited on silver in detrital gold deposits . .. .. ... . .. 110 

quoted on gold in Cambrian conglomerate........ 109 

iJUoted on origin of the gold-bearing conglomerates ............... .-................. , ... , 102-103 

quoted on refractory siliceous ores ....... , ..... , 113--114 

Diorite, mineral eomp0sition and locnlities of........ 22 

Diorite-porphyry, mineral composition and localities 

of.......................................... ~ 

DiYidend mine, description of ......... : .. .......... 201-202 

frnetures in, relation of, to mineralization........ 136 

gold-bearing gouge in . . . .. . ... . .. . .. . .. . .. . . . . . . . . 144 

gold-bearing sand in ............................. : 14-l 

production of...................................... 118 

refractory silieeom; ores o'f, yield of...... . . . 1~9 

Dolomite, analysis of.................................. 121 

occurrence of, as a gangue mineral . .. . . . . . . . . . .. . 68 

in Homestake mines . .... . ... . . . .. . . . . .. . . . . .. 92 

plate showing varieties of . . . . .. . . . . .. . . . . . . . .. . . .. '.:!14 

Dolomite, Cambrian, alteration of........ 120--1~1 

chemiCal composition of ....................... 121-1'22 

lower contact of ............................... : 122-1'.:!3 

macroscopic appearance of ...................... 118-119 

Inicroscopic appcumncc of . ... . .. . . . 119 

mineral composition of. .. :............ . .... 119-120 

nppcr contact of. ................................ 123-12-t 

Donelson fril.cture, description of... 211 

Donelson mine, fructnres in, in'tcrsection of 132 

fractures in, rc~ation of, to mineralization 13G 

Dorr, Mr:;acknm\·ledgment to................... 143 

Double Stand!trd mine, description of .... .' ........ 19i-198 

ore from, mineral composition of........... 142 

0re shoot of, length of................ 125 

Durango mine, description of . . . . . . . . . . . . . . . . . . .... 208-209 

locntion and workings of.:................. 105 

ore of, value of.......... ................. l&J. 

E. 

El Refugio mine, ore in, stratigraphic position of •••. 

Elk Creek; course und features of . . ......... . 

garnctifcrou~ mic!l-schist along, exposures of. ... . 

Elk Creek Canyon, Cambrian rocks in, thickne!'S of ... 

geologic section metl.>mrerl in .................... . 

Ellison shaft, depth of............... . .............. . 

Emmons, S. F., cited on ore of Leadville, Colo ....... . 

quoted on mineralization t1f ores (note) ..... . 

report by, oil the Homcstnkcmincs ............... . 

Empire minC, gold production of ... __ .... __ .. 

Empire State mine, description of. ........... . 

c ore shoot of, length of.... . ......... . 

Englewood. geologic section ne,u .. 

Page. 

Ii1 

15 

33 

19 

18 

60 

178 

157 

5.">-80 

116 

20·1 

}:!;) 

3fi----3\l 

Englewood limestone, equivalents oi . 

chnrueter rmd thickne~s of 

fossilH in ..... 

-21 

21,36,39 

21 

Eocene formati(ms, chnmcter of ....... . 

fos~ils in. 

Esmeralda mine, locution and workings of .......... . 

Etta mine, tin discoycred at. ..................... .. 

Eva H. mine, gold production of ................. __ . 

F. 

20 

20 

100 

95 

118 

Fannie mine, description of. ........................ 1SG---1.Si 

geologic section in................................. 187 

Fantail Gulch, fractures or verticals in, plate showing. 214 

Farish, William B., gold ores of northern Black Hills 

exumined nnd reported on by.:........... 5i 

Father deSmet Company, organization and properties 

of ........... :...................... 57 

stamp mills of..................................... 58 

See also be Smet. 

Florence mine, ore in, stratigraphic pOsition of. .... ·.. 171 

Fluorite, occurrence of, in refractory siliceous ores... 139 

origin of, in refractory si1H~eou8 ores ....... : . . ___ . 158 

Folger mine .. description of............................ 204 

Forsyth,--, cited on methods of concentration of 

wolframite ore .................. : ......... 168 

Fossil placers. Sec Gold-bearing coilglomerate. 

Fowler,--, cited on ore mineral>i in Carbonate district...... ................................ liS 

Franklin, Colonel, acknowledgment to............... 53 

Fractures, amount of opening of. ..................... _ 129 

direction of.................. .. . .. . . . . . .. 130 

grouping of.................. . .......... 130-131 

intersectioll of. ......... ·..... . .... 131-132 

originof..................... 134 

relation. of, to eruptive rock~ .......... 132-134 

to the mineralization. . ......... 134-136 

types of .................... :..... . .... 126-l2i 

verticnl extent of. ........................ , .. . . . 128-129 

Fultun, C. H., Cited on methods of treatment of refraetory silicem1s ore~ ....... . 160 

G. 

Galena, geologic section near, along Bear Butte 

Creek .......................... -~-- ......... 39-41 

lead-silver mines near, location and development 

of .................... ·.................... 1i0 

lead-silver ores of vicinity of .................. 169-171 

Garden area, countryrockin.......................... 150 

fracture groups in........ .................. 131 

locution of... ................. ................... 150 

mines in, description of . . ...................... 209-211 

location and development of. ............... 150-151 
218 INDEX. 

Page. 

Garden area, ore of, grade of............. . ..... ...•.. 151 

oro shoot:! in, trend of............................. 151 

refractory siliceous ores in, average yield of . . . ... 113 

occurrence of·········'"···-·····-············· 112 

valueoL ..................................... 154 

Garnet, occurrence of . . . . . . . . . . . ..................... 68, 91 

Garnetiferous ore, Home;;take mine, plate showing... 214 

occllrrcnce and ehantcter of. ...... :............... Si 

Gashwilcr, J. \'\'., reference to......................... Eii 

Gentle Annie mine, description of . ... .. . ... . . .. . ..... 183 

location and workinggof ......................... 106 

pyritic conglomerate in . . ... ..... .. . . . . . .. . •.. .. . . lOS 

Gold, discovery of, in northern Black Hills.:; ........ 50-57 

occurrence of, in Clover Leaf mine . . . . . . . . . . . . . . . 94 

mo"de of occurrence of, in Homestake mines ...... 68,91 

production of, l>y Homcstuke .Mining ComP~~y·.:. 62 

native, occurrence of ....................... "···· 114,151 

Gold and sil\'Cr orcs, in Cambrian rocks, discussion 

of .......... .' ............................. ." 98-163 

in Carboniferous rocks, discm~ion of ........... 172-177 

Gold Run, Cnmbri!m conglomerate between Deailwood Gulch and................... 105 

Gold-bearing clay, occurrence of, in Mogul and Tor· 

nado mines ............•................. 143-144 

Gold-bearing conglomerate, alteration of ........... 108-10!.1 

derivation of....................................... 107 

geologie features of .................. ::..· ... ~-- .... 103-107 

gold in, derivation of ............................. 99-100 

distribution of ...........•.. :. . . . . . . 100, 10!.1 

originof .............. : ........... _...... 110 

literature relating to .......... ~--- .............. 101-103 

lithologic character of......... . ........... 107-109 

locution and distribution of........ .......... ... . 103 

matrix of .... . •• 107-108 

mines in..... . . ... .... ... . . ... . . . . . 100,105-107 

_desc-ription of. ....... : ...................... 181-184 

occurrences of ...........•...................... 104-107 

origin of • • • . . • • . • . . . • • . • . . • • • . . • • . . . • • . . • . . • . • • . . . . 100 

pebbles of, Size of.................................. 107 

po~ition and thickness of .........•................ 98-99 

rhyolite intrusions in.............................. 100 

topography associated _with....................... 103_ 

;alues in .. . . . ... . .. . . .. .... .. ... ............ ... ... 100 

Gold-bearing gouge, occurrence of, in Dividend mine. 144 

Gold-bearing gravels, occurrence of................... 179 

source of gold ln ................ :.................. ·179 

Gold-bearing stLnd, occurrence_ of, in Yellow Creek 

and ncar Portland......................... 144 

Golden Crown mine, ore of, value o~. ... .. . . . . .. .. . ... 154 

Golden Gttte mine, description of . . ... . ... .. . . . . ... . .. 210 

Golden Gate Mining Company, acknowledgment to.. 143 

Golden R.oward Gold l\-fining Company, development 

workby .......................... ~ ........ 117 

plant Qf, for treat_ment of orcs ............. ."....... lGO 

Golden Reward mine, description of ............. : .. 185-lSG 

fractures in, relation of, to eruptive rocks......... 132 

gold production of. ..........•..•.................. · 117 

ore shoot of, ~width o{ ................... : .. .... .. . . 125 

Golden Reward mine, South, de~c:ription of........... 188 

Golden Star shaft, depth of. . . .. ..... .. . .. . ... .. . ..... 60 

Great :.\logul mine, cross section of, plate showing.... 51 

description of. ......... ·······.:············· ..... 196-197 

Grier, T. J., acknowledgment to....... ............... 53 

Grorudite, mineral composition and localities of...... 22 

Gunniwn mine, description of . . . . . . . . . . . . . . . . . . . . . . . . 206 

Gushurst and :Manchester mine, description of ...... :202---203 

G~·psum, occurrence of, in reirnctory siliceous ores... 139 

II. 

Page. 

Haggin, J. B., reference to....... . . . . . .. . ... . . . .. 57 

nardin shaft, pyritous ores in, work on....... 163 

B:ardscrabhlc mine, description of........... 199 

B:armony mine, description of.............. 199 

Harney Peak region, gold discovered in . . . . 56 

Harney Range, Cambrian rocks in, thickness of. 19 

Harrison mine, Garden area, description of........ 209-210 

Harrison mine, Lead area, description of ............. 1 207 

location and workings of. ..... ................... 1 105 

ore of, value of .•••••.••...... --· · ···. -· · ·- · · · · · ii ~; 

production of.................. . . . . . . . . . . . ...... :,; , 

wolframite from, analyst~ of.............. 167 

Hawkeyc-Pluma mine, description of. ............. 183-18-i 

gold-hearing conglomerate in, as..'l!lys of... Ill 

plan and cross section of, plate showing.......... 214 

vertical fractures in . . . . . . . . . . . .................. ." 128 

Hayes, C . .,Y., letter of tmnsmittal by................. 5 

Headden, W. P., cited on tin ores in southern Black 

Hills .... :.................................. 96 

Hear!it, George, rEference to .....•....... .'............. 57 

IIe!:iter A. mine, ore in, stmt!graphic position of...... lil 

Hidden Fortune mine, description of .......... ,...... 208 

native gold in. . .................. 114 (ncite), 151 

Hidden Trensure mine, location and workings of. .. .'. 100 

oreof,valueof .................................. :. 154 

Highland shaft, open cut between Star shaft and..... 60 

Highland Com puny, stamp mills of................... 58 

Hillebrand, ·w. F., analyses of wolframite by .....•. 166-167 

analysis by, of dolomite Irorn Tornado mine...... 121 

of ore from Dacy mines........................ 174 

Homest!lke lode, pitch of. ......................... :... 70 

Home.«t!lkc mine, Algonkian schi~t.s showing synclinal 

structure south of........ . .. .. . . ... . .. .. . . 33 

Homestuke mines, dikes in, figure showing ...•....... · 27. 

dikes in, thickness and character of. ............ ).rl 27 

discovery and de_velopment of ........ : .......... ~:· 55-58 

dolomite in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 

extent and location of. ......................... :.. fJ5 

gangue mineral.9 in................................ C.8 

garnet and tremolite in........................... 91 

garnetiferous ore from, plate showing............. 214 

geologic de~cription of ....•................. , ..... 66-78 

geologic section eastward from, figure showing-.:.. 102 

history of development of ......................... 57-58 

mining development of. .... _. ...................... 60-61 

ore bodies of, discovery of......................... fi7 

. form and cha.raetcr of..... il, 73-74, 103-11)4 

horizontal extent of..... • 74 

origin of...... . . . . . . . . . . . . . . . . . . . . . . ......... 78-80 

plans of.............. . .......... ......... ,::', 75 

relations of, to Algonkian rocks .............. :,-) 81 

rocks inclosing ................................ G9-7I 

ore minerals of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 

origin of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 

ores of .....•............. ::... . ................... 8:.!-88 

o. verage yield of . . . . . . . . . . . ................... f:>c'!-:'i9 

banded vu.riety ....•.. _ ...•.............. '...... 82-85 

character of................ . .. . . . . . . . . . . . . . . . . 65 

contorted variety •.............•............... S."i-86 

C08t of mJning of.. ..... ;: ..............•... :.:. -61 

massh·e variety ..................... , .......•.. SG-88 

occurrence of, mode Or •••..••••...•...•••.•• ~---•~ .' 1 9!> 

petrogmphic study of, by J.D. Irving ..•..... ; .. 80-92 

reduction of ......................•.....•...•• VS-60 

relative proportions of goli! and silver in. ·---~-I~~ 

vnlue of . .. . . .. . . . . .. . . . .. . ..... .... .. . . .. . . ... iS 
INDEX. 219 

Page. 

Homestake mines, phonolite in, character of .........• 88-89 

pQrphyries in ...................................... 88-90 

production of, statistics· of. ........................ 02-65 

compared with that of Portland mine. Cripple 

Creek .......... :........ .................... 65 

pyrite in .............................. : .. :......... 91 

quartz oL ........................................ ~. 91 

reporton,byS.F.Emmons ...................... ~. 55--80 

rhyolite in, character of................... 88 

dikes of. .... (........................ 89 

stamp mills at ..................................... 55,59 

~urface workings of........................ 71-74 

trnmportation facilities of. .. :::.:.:............... 61 

underground workings oL ................ · ......... · 74-78 

wall rock of,deseription of .............. '.... · ...... 81-82 

water supply of. ........ ::.............. 62 

Homestakc Mining Company, dividends distributed 

~--······················ ............ ~.~M 

organization and properties of...... . . . . . . . . . . . . . . . 57 

stamp mills of .................................... 58-60 

average yield of· .. · ............................. 58-59 

Homcsta.ke open cut,.dimensions of................... GO 

geologic section exposed in ...... , ................. 66-67 

Hol'lle~ilOe mine, gold production of................... 117 

ore in, stratigraphic position oL ...... .':. ..... ..... 171 

I. 

Idaho, wolframite in, occurrence of . . . . . . . . . . • . . . . . . . 169 

Intrusive porphyries, age of, geologic ................. 2fr-26 

age of, relative ... _........... . ............ 23-25 

distribu_tion of..................... . .............. 26-27 

lithology of ....................................... 22-23 

Iowa mine. ore of, value of............ . ............. 154 

Iowa and Golden Crown mine, tlc~cription of ..... _.... 207 

Iron Hill mine, country rock at....... ............... 177 

ore of, character of ........... 177-178 

minerals of .. .. . .. . .. ... .... . ...... . .. ....... 178 

_. production of.. .. ..... .... . ... J77 

Irving, J.D., work of... .............. ............... 53 

Irving, R. D., cited 011 intrusive porphyries........... 22 

Isadorah mine, description of......... .... ...... .... . 188' 

J. 

Jaggar, T. A., cited on porphyritic intrusions in the 

Black Hills .............................. . 

report by, on the g~neml geology of the region .. . 

Jan in, Louis lind Henry, gold ores of north'ern Bllu;k 

Hills CX!tmined and reported on by 

Jeriner, W. P., cxpcditi~n Df Henry Newton and , .... 

J11rn-Cretaceous beds, thickness of, below the Laramie. 

Jurnssic formations,· character and thickness of, section 8howing .................. . 

fO<;sils in............. .. .................... . 

K. 

Keystone mine, description oL ...................... . 

Kicking Horse mine, dcscriptiO!l of .. _ ... _ ............. . 

,Kildonan Milli~g ~ompany_, sme_lting plaJ:!.t of ..•..... 

L ........ 

Lab!ador mine, de8cription of.:.::.: ............... : .. 

location of ............ :: ... : ... :: ............ : . ...• 

Lat:riprophyre, mineral composition and localities of .. 

Laramie form1ttion, e\·idcncc of former presence of, in 

· Black Hill~ ... :.::.· ....... : .............. . 

30 

7-41 

57 

5<3 

25 

18,20 

20 

. "" 

210 

160 

203 

150 

22 

Page. 

Lead, geologic map of vicinity of . .. .. .. ... 212 

geologic features nC!lf ........................... 6G-67 

gold·beariug conglomerate near, position and 

thicknc;;s of . !lS 

Homesta.ke open cut near . . . . .. . .. .. . . . .. . .. . . .. . 66 

location of................ . . . .. . .. . .. 66 

map of region about .... : ......... . 

mines in vicinity of, description of.. 

population of 

Lead 1trea, fracture groups in .............. . 

mines in, description of .. 

location und development in .. 

ore bodies in, exposure of ....... . 

refractory siliceous ores in, a vernge yield of 

•occurrence of. ... : ... · ......... : .... . 

181-18-1 " 

G6 

131 

2(1(\-209 

.. !-: 151 

151 

llfl 

112 

·vttlUC'Of .......... ........... . .......... . 154 

";olframHe in, discovery of .......... :.· 163 

Lead and 'silver ores in Cambrian rocks, discu~-

sion of . ... .. . . .. . . ... . . .. . . . . .. . . lf>9-li1 

in Carboniferous rocks, discu~sion of. .......... 177-178 

Lco.d-sih·er ores, nge o~. ... . . . .. . . . . . .. . . .. . .. . . . . ... 171 

character of .. . .. . . . . . .. . . . . . . .. . . .. . . . . . . .. . 170 

minerals of ...... : .... 170 

valueof...... .............. ...................... 171 

Lead eruptive center, structure of 29-31 

Lead Tertiary clays, deposition of..................... 2-'i 

erosionof ....................... ~ ............... :.. 25 

Leopard and Jessie Lee mine, description of... W5 

Lirne~tone breccias, character and occurrence of ..... 2i-29 

sill cutting, upper contact of, figure showing . . .. . 28 

Linc>~ln stoPe, banded ore from ............ :.. ... ..... 84 

L-ittle ntuc mine, description of ... :· ................. 211-212 

gold production of................................. 118 

Little Bonanzu mine, description of................... 187 

fractures or verticals in. porphyry near, plat'e 

showing . .... . . . . .. . . . . ... . .. .... . ..... .. .. 214 

Little Pittsburg mine, description of . . . . . . . . . . . . . . . . . . 212 

J...ittle Tornado mine, description of .....•....•..... :.. 197 

Lower Cretaceous formations, character and thickfo~sils i:~~~ -~~·. ~: ::~: ::::: :::~: ::::-~~':: :::-: ~: :::~:: ' ~~ Lucille mine, description of. ..................... ·. ... 189 

M. 

McKay, Angus R., ackn~wledgment to. . ... . . . .. . . .. . 7>3 

)I ail and Express mine, fractures in, relation of; to 

eruptive rocks............................ 132 

Mallory, T. H., gold discovered by, in Whitewood and 

'Deadwoodgulches ........ .... : .... ....... [16-7>7 

Manuel, Moses an<l Frederick, di~covcry by, of Homestake and Old Abe dePosits........... .)7 

Marine Juru, character and thickness of .............. 18,20 

fo~silsin.................................. :.W 

Mark Twain mine; descriptiou of.. . . .. .. .. . . . . 20-t 

fractnres in, relation of, to eruptive rocks .. 13:! 

ore shoot of, length of....................... 12.-l 

)fassh'c nrc.· &e·Homcstake mines, ores of. 1 

:Merit No.2 mine, ore in, stmtigraphic position of. 1il 

Mesozoic rocks,·lithologic·chaructei and thickness of, 

columnarsectioi1 showing......... ' r;, 18 

stratigraphy of ............................ . :. : •. . : 17-lS 

Metallic Streak mine, location and workings of. ... 175-176 

ore of; value of· ...... · ..... .' .................. ·..... 17G 

Mineralizing waters, direction of flow of. . .. ' .... 1f>6-157 

)Iinnekahta formation, position and thickness of, col-

.· umnar section showing . . . . . . . .. . ... 18 
220 INDEX. 

Page, 

1\Iinrlekahta.limestone; character of.................. 20 

fossilsin ..... "''·········· 20 

topographic featurCs of.... . . . . . .. . . . . . . .. . 16---17 

:Minnelusa formution, character of........... 21 

position and thickness of, columnar seetion show· 

ing ....... . 18 

~Iinnie mine, grade oi ore in................... 152 

~Iogul mine, auriferous clay in, occurrence of 143 

fractures in, relation of, to cruptivC rocks . . . . . ... 133 

vertical fractures in .. 

.:'>Ionitor mine, dc.~cription of.. 

loCation and 'n)rkings of .... 

. . . ... • . . ·-.-. 128 

--- 182-l&-! 

lOG 

pyritic conglomerate in lOS 

::Uorri!>on formatioi1, character of..... . . . . . . . . . . . . . . . . 20 

fossils in. ................ 20 

position and thickne~s of, c~lumuar section showing ........... . 18 

X. 

Xevada, wolfrnmite ore in, occurrence of.. . .. 168,169 

Xevad~t Gulcll, phonolite cutting rhyolite-porphyry 

ncar, figure showing . . . .. .. . . . ..... 24 

Xewton, Henry, expeditlon of W. P. Jenney and..... 56 

Xiggcr Hill dbtriet, geologic features of .............. 9t,_96 

tin orcs in, discovery of...... . .. . . . .. . ... . 95 

Xigger Hill ph\Ccrs, origin of........... . . . ...... ..... li'il 

yield of ............ •.. ...... ... . ... . . . . .. . ... .. . ... 1i9 

o. 

O'Harrn, C. c., cited on ore production in Squaw 

Pinney open cut, mining operations in ........ . 

Page. 

l82 

Pirsson·, L. '-:., W. H. Weed and, cited on limestone 

conglomerate from Judith ~fountains..... 29 

l'laeer deposits, occurrence and character of ...... 1;9-180 

originof. ..................... :... li9 

yield of.. . . . . ... . .. .... . . . .. . . .. . ... . 179 

Pluma mine, pyritie conglomCmte in 108 

See also Hawkeyc-Plumn. 

Polo ~Iountain, Siluro-Carboniierons limeStone on, 

thicknesS of .............................. . 

Poorman Gulch, gold-bearing cOllgiOmcrate in...... 10.5 

Porphyries, in Homestakc mines, oCcuri-cnce and character of.:.. · · - ' ............... S&--90 

intrmive, age of, gcolo!i-ic .. . .. . ... . . . . . :2-5---26 

age of, relati\·u. -~ .. ~ ......................... _ :23-25 

distribution of. ...... ~--· ...................... 2f,_27 

lithology of .. :: ..... : ......................... 22-23 

Porphyritic intrusions, historr of. ..................... :n-32 

Porphyry breccias, occurrence of ..................... 89-00 

rc'lrtland di~trict, fracture groups in . ..... 131 

m!ncs in, description of. ......................... :201-206 

refractory silicc'ous ores in, occurrences of ....... 149-150 

Portland mine, description of ........................ 205-206 

ore of, chunwter of............... . . . .. . .. . . . . ..... 65 

Portland mine (Cripple Creek (listrict), production, 

etc .. of Homest1tke mines compared to.... 65 

POrtland )[ining Company, development work by .. 1lf>-117 

Pot~dam gold orcs, rcfmctor~- siliceous ores so termed. 111 

Sec ttf~o ftefrnctory siliceous ores. 

Pseudo-conglomerates, occurrence and character of. .. 2i-29 

Publication~ relating to Black Hills, list of ............ 13-14 

Creek area ............................... . 1;,2 Pyrite, occurrence of, in Homestake mines . ... .. . . . . 91 

Old Abe deposit~, discovery of.. . .............. .. 

Old Abe ·shaft, ore bodies in, figure showing section of. 

Old Iromides mine, ore of, character of 

57 occurrence of, in refractory siliceous orcs.......... 138 

iG tyritie conglomerate, gold in, origin of ............. llG--111 

9i occurrence and character of ..................... 107-108 

Omeg~t mine, description of.~ ........................ . 

Ordovician formations, character of ....... . 

fossils in ......................................... . 

Ordovician(?) limestone, character of. 

topographic features of ....•...••.... .' .. 

Ordovician rocks, section of; neur CTaleua ... 

Qre-beari~g rocks, position and thickne~s of, columnar 

><ection showing . . . . . ............. . 

P. 

Puhasapa formation, dwracter of . .' .. 

fossils in................... . ............... . 

topographic features of ................. . 

Paha~apa limestone, character and thickness of ..•... 

Paleozoic rocks, lithologic character and thiCkness of, 

columnar section ~bowing ........... . 

sections showing details of, tabul~tted ............ . 

stmtigrnphy of .................................. . 

Pearce, Richard, tin discovered by, in southern Black 

Hills ..................................... . 

Penobscot mine, description of .. 

Permian formations, character of .................... . 

182 

21 

2l 

36 

16 

39 

18 

21 

2l 

16 

" 

17, 18 

SE--41 

li-1S 

fossils in... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

position and thickne&> of, columnar section 

~;bowing.............. ................. 18 

topographic features of. ... .' ....................... 1(',_17 

Perry, Algonkian schists east of, character and occurrences of. . . . . . . . . . . . . . . . . . . . . . . . . 33--R! 

Pei'8eYerancc mine, description of..................... 20-l. 

Phonolite, character and occurrence of............... 69 

dike of, cutting rhyolite-porphyry, figure showing. 24 

mineral composition and_ localities of............. 22 

I'yritous ore~, character and occurrence of .......•.. 162-163 

resemblance of, to refractory sllice,ous ores........ 163 

Q. 

Quartz, occurrence oi, in refractory siliceous ore~. 

Quartzite bLind in slute, figure showing .....••.•...... 

138 

72 

H4 

41 

20 

Quartzite ore, occurrence o£ .......................... . 

Quaternnry formntions, ch1tmctcr ltnd thickness of .. . 

character of, table ........................ . 

H. 

Rngged Top district, location and topography of.. 172 

mines in, development of... . .......... 1i3-176 

ores of, origin of.. . .... , ........................ 176-177 

Rugged Top )Jountnin, geologic map of, showing ver-

. ticals ...................... . 

Recent rocks, ore depo~its in .......... . 

placer deposits in .............. . 

,. Red Beds." ch1t;actcr of ............ .. 

Refractorr siliceous orcs, alteration of 

annly~es of .......... . 

arcul distribution of .. . 

·churncter of ......... . 

chemistry of. ..... . 

copper in ............ . 

conn try rock of ....... . 

214 

181-182 

179-180 

20 

HO 

Hl 

H4 

112 

......... Hl-143 

142 

112 

distribution of. . . ... .. .. . ........... .. . .. . . . . . . . .. 112 

floor and roof of................ . . . . . . . . . . . . . . . . . . . 113 

fractures in, character of ........................ 126---127 

direction of................ . . . . . . . . . . .. .. • . . .. 130 

grouping of. ................................. 130-IS! 
INDEX. 221 

Page. 

.Refractory siliceous ores, fractures in, intersection 

of ....................................... 131-13:.! 

fractures in, origin of.. ........................... 134 

relation of, to eruptive rocks ..... -- 13:.!-133 

tomineralil'.ution ............ . 

-..~crticalcxtentoL ............. . 128 

width of ..... ............. 1:.19-131 

future prospects of: .... . ..••...•... 161-Hi:.1 

gold in, origin of ........ . 

hi;oton· awl de,·clopment of ...... . 

li!Cf!lt-~rc relating to ........... . 

159 

116-117 

113-116 

macroscopic charucter of. 136-137 

map showing principal ~hoots of, in Raid Mountalnarea .............. · ..................... 212 

microscopic charucter of . . . ... . . . .. . . . . ... . ... . 137-138 

micro~copic >;ections of, plate~ showing........... 2H 

mineralization of, uge of.......................... 151 

processe" of .................................. 155-157 

minerals of .. . : .... ......•. 138-140 

derivntion of ................................ 157-160 

mines in, dc~cription of. ......................... 18~:.!00 

mining of, methods of ........................... 160-161 

names applied to ........... ~ .............. :...... 111 

origin of ......................................... 154-15.') 

production of, table showing .................... 117-118 

prospecting for .. .. .. .. .. .. . .. .. .. .. .. .. .. 161 

relations of, to eruptive">...... 115 

resemblance between pyr}tous orcs and. 1(;:3 

rocks inclosing, alteration of............ 120-121 

chemical compo~ition of................. 121-!2'2 

geologic position of........ 12:!-1'24. 

macroscopic !lppeurn.nce of...... 118-119 

micro>Jcopic appearance of...... 119-120 

shoot~ of, form and sir.e of........... J:!J-1'26 

pl!lte showing......... ................ 214 

~ilver in, occurrence of.......... 11:'!, 114 

treatment of, methods of....................... 159 

type cross sections of shoots of. ............. , ..... .' :!12 

variations from type of ......................... 143-Hl' 

yield of, in gold ..................... _ ...... ,. . . . . .. 11~ 

RetricYer mine, description of......... · ..... 184-JS,J 

fracturcH in, relation of, to crupti\'e rocks........ 132 

·Rhyolite, porphyry cut by, near Aztec, figure showing........................................... '24. 

Rhyolite-porphyry, character and occurrence of 69 

dike of phonolite in, figure showing 2,1 

mineral comPo~ition an<lloc!llities of............. :!2 

Richmond mine, ore in, stmtigraphic position of. 111 

RoOda, R., cited on ore bodieS in Fannie mine 

Romeo mine, ore in, stratigraphic position of .... 

Ross-H1mnibal mine, description of. 

ore of, microscopic sections of, phtte showing_. 

...-alue of: ......... .. 

ore shoot of, length of ............. .. 

Run mine, gold production of .. 

Ruby Basin di~hict, fracture groups in . 

fractures in, rel1ttion of, to eruptive rocks ... . 

relation of. to mineralization ........... . 

r,efr!lctory siliceous ores in, occurrences of 

Ruby Bell mine, description of. · 

s. 

186 

171 

18\l-190 

214' 

V'i3 

125 

liS 

130-131 

133 

135 

HG-H9 

189 

Pagb. 

Silica, origin of, in refractory siliceous ores........ 158 

~iliea, chalcetlonic, occurrence of, in refractory si\F 

ccous ores ..... . 138 

Siliceous ores, rcfm<'torr. Sec Rcfructory ~iliceous ores. 

Sitting Bni'lminc, ore of, laluc of . . . ... .. . . .... . 171 

Silurian formntions, character !Llld thickness of, columnar section showing . .. . . . . . . . . ... . ... . JS 

Siluro-Carboniferous limestone>!, chantcter and thickness of, colunmur ~cction showing . . . . . .. . IS 

Siln:r, production of, byHomestake )lining Company. 62 

Silver and gold ores, in Cambrian rocks, discus~ion of.· 9g...ltl3 

in Carboniferous ror:ks, di~cussion of. ........... li2-177 

Sliver and lead ores, in Cambrian rocks. . ..... 169-171 

in Carboniferous rocks . .. ........ 177-178 

Slttte, quartzite hnnd in, figure showing............. 72 

~pecimen of, illustrating relation of folding to lamination................... .............. 212 

Smith, A. J., mines located by.... ................... 116 

Smith, F. C .. !Umlrses of refractory siliceous ores 

quoted from............................... lH 

analysis quoted from, of ore from Dacy_ mines ... . 174 

cited on gypsum in refractory siliceous ores....... 139 

cited on lead-silver production (If Hichmond or 

Sitting Bull mine.......................... 169 

cited on methods of treatment o[ rdractory siliceousores ............................. •.... 1GO 

cited on rcfructory siliceom orcs ........... 115-116 

qu01ed on analysis of ore from Dacy mines....... 175 

quoted on history awl developml.!nt of rcfntctory 

. siliceous orcs . . ......... .. 

Smith, P. S., n.cknowlcrlgment to .. 

Snow~torm mine, del:>cription of 

location nnd ·workings of.: ... 

South Dakota mine, rlE'~crlption of 

location of. 

116 

53 

'202 

150 

206 

}[1(1 

South Golden Rew!lrd mine, description of...... 18S 

Southern Dcadwood·'l'crra open cut, plate showing... 21..1 

Spearfish Canyon, Cambrian conglomerate in......... 9S 

geologic section measured in .................... """-~IS-~ 

Siluro-Carboniferous limestone in, thiCkness of .. . lS 

Spearfish Creek, course n.nri'fentures of............... H-15. 

Squaw Creek, or"' in, chfiracter of. 97 

Squaw Creek urea, Cambrian rock~ in, ex}oosures of.. lf:o~ 

loca!ion of.... .. . . .. . . . . . .. . .. 15:.! 1

mincs in, location and deyelopm~nt of.. 15:.! 

mining opcmtion~ in...................... 212 

refractory ~iliet,ous ores in, occurrence of........ 112 

Star shaft, open cut between Highland sh!lft and.. 60 

ore bodies in, figure ~hmving section of..... 75 . . fonn a nO character of....... 7:~,_;1) 

Stewart JHinc, description of . ... .. .. . . . . . . .. . 1:3;) 

Stcwurd ore shoot, kngth of . . . . . . . . . . . .. . .. . J:!.) 

Stibnite, oCCI}rrcncc ~f, in refmctorr ~iliceous ores .. 139-140 

Stmwberr~- Gulch, mines in, work on 

ore in, cluun.eter of ......... . 

Stream tin. See Tin. 

Snlu mine, description of. ...... 

Sundance mine, description of .. 

g; 

97 

.. ~06-207 

........... lSS 

Swamp Eagle mine, description of .................. . 20S 

'.r. 

Terry Peak, ultitudc of. 

Sand Creek, tin discovered on 

Sand rock, definition of . 

95 geologic ~ectiou near. 

14 

34,35-313 

H 

He~ also Dolomite. 

Seabury mine, ore of, character of 

112 volcanic character of 

Terry Pcuk ~fountains, porphyry intn1sion~ of ... 

178 Tertiary eluys. deposition of. 
~ 

222 INDEX. 

Tertiary formation~. eharucter of 

erosion of ......... . 

fOISSll~in ....... . 

thicknes;; of. ............. . 

Tevis, Lloyd, referent"<' to ... . 

'fin, disrovery of, in Xiggcr Hill di~trict 

Tin ores, occurrence of ..... 

value of------······----

Tornado mine, 1turiferon~ clar in. oecurrence of 

cro~~ ~eet10n of, plate showing .......... . 

ole~Priphun of. ... -------···--

<lolomite from, llilalysis of .... . 

fructnres in, inter~cctiou of. .. . 

relation of, to eruptive rork~ ... 

to mineralization . 

ore of, value of·---------··--------· 

Page. 

20,41 

20 

41 

.17 

95 

y,')...'J7 

9ti 

14:.:-144 

:!14 

1!J:!-191i 

1:!1 

131,132 

ore shoot of, width of. .................. ~ .. ~:· .... -:--:. • 

13:\ 

135 

153 

12fl 

Tomado-~Iugul mme, frachirc~ In, relation of, to mmeralization ....................... _ .... __ 

ore shoot of, dimen~ions of ......... . 

T<Jwer, G. W., notes of, un lead-HilYer ores of (i-ulcua 

1i5 

1:.!5 

16'J 

Trachytmrt phonolite, ocl'urrence and charact<'r <tf ::;S-S!J 

Tremolitt•, occurrence~ of . . .. .. . . . . • • . . . . . • . . til',, !J1 

Tr1a~~ic formtttions, ch~ractcr of . . . . . . .. 20 

fo~~u~ in. 20 

Trojm1 mine, dc;.eription ttf ... __ 2U3 

Tungste'n ores, occurrence of, discu;.~Jon of ........ 1fi3-1G'J 

Two Bit d!~trict, Cnmbrh1n rocks in, thick_ne~~ of. 1'J 

country rock in ....... ___ .............. . 162 

pyntou~ ore~ in, oceurrence and chH,nt<!ter of ... lG:.!--1(;;)_ 

Two Johns mlnl·, de!>crlption of .. ____ ...... 202 

Iracture~ ill, relation oi, to erupli\ c Joe!.._,,.. 1.-;,-; 

relation of, to minemhzation ... __ . .. . . .. . . .. .. 13G 

location of.............................. 150 

Two Stnke mine, description of ........ . 

wolframite from, analysis of. .. 

u. 

' ~l.Jll'ter mine,-cou_!.!.try rock at ........... . 

--- geolQgic map o.li'in\"ing ltwa!i'?n of .. . 

location of .... 

ore of, cluuucter •mtl value ••f ...... . 

21:.! 

----- 166,167 

liG 

214 

17(; 

17fi 

· Unwn mine, cross section of ore ~hoot in 191 

description of.......... I!J0-191 

gcologiesectionin. . ........... 1\N 

ore shoot of, length of . .. . . . .. .. .. .. 125 

Uppa contact, mines ou, tlcscnptiun of ............ :.!00---:..'01 

Upper Welcome mille, description of.. . ... ____ .... 200-2Ut 

· Urnnium m1C:?-• occurrence of, m refractory Hliccou~. 

orcs.. .............. HO 

Y. 

V1mocker l!tccohth, character of .... 

Verueals, Cleopatra mine, plate ~howing 

tlefinition of .............. --- ......... ---

26 

:.!14 

120 

figures showmg ...................... __ .......... 12tl, 132 

Little Bonantu mine, plate showing ..... :......... :.!H 

Ragged Top )Iountain, plate showmg .. :.. .. 214 

;)ec nlso Fracture~. 

w. 

Page. 

Vi"nlcott, C. D , cited on intraformationnl brecciill!. ... 29 

W11shmgtun mine, ore m, ~tratlgraphw position of.... 1il 

Wa~pXo lmine,tlescriptionof. ..................... 211 

\Va~p Xu. 2 mme, de,cription of......... :.!11-212 

prorluction of ............................... ._.... 117 

wa~p ~u. 4 mine, gold prutlnctlun of. ...... . 

Weed, "'· II, 1tnd L. V. Pirs~on, cit8tl on llmc.~tone 

conglumer•lte from Jndith )[ount!tins .... . 

"'elcome mine, description of ................. __ .... . 

fractures in, relation of, to mincmhzation . ___ ... . 

J->lan of,-plate showmg ..... __ .... __ 

Welcome )fining Company, development ,\·ork by,-

historyof ......................... . 

Wt!lls Fargo roinf', description uf 

\Yhitc River rlcposits, 11ge of. ...... 

tiltiugof......... --~ 

\Ylnte River f<ormatwn, character of ... 

WhiftU:\~~~:tlc~~):~;~: ·c~;~~ri~-~: ·;,;~k~ ·i·~.- ti;~~-k~~:~ -~f _ 

' gculultic ~ection mea~urerl in .................. . 

Whitewood Creek, COJ•pcr ore between Yellow Creek 

anti ....................... . 

cour~e !Ulil features of ... 

Whitewouil limestone, ch'arncter !tn<l th1ckne~" of ... . 

equivalents of............. . ............. ! .. . fo;.~ils in ..... . 

\Villb, Bailey, cited on .lctinitinn of "competent" 

113 

:.!!) 

190 

1;)5 

2H 

117 

210 

" :!6 

20 

~0 

19 

IS 

\lf:o 

15 

:.!1, 39 

" 21 

stratum.................................. 17 

\Vlnchell, X. H., reference to work of, in Harney 

Peak region 

\Volfr>ttnlte, occurrent•e and uri gin of . . . . . . . . . . . . • 1.58 ·" 

Wolframite ore, analy~cs of........... .. . ____ . ...... 1il7 

character of, macroscopic and micro:-.copic. __ ... 165--166 

chemkul cumpositio.!_l of.· ........ : ............... ~66-167r 

conccntrauon of ............................... .'... 168 

discovery of, hi;.tory of .......................... 163-164 

p1ineral rompo~ition of. .................... 166,167-168 

ocrurrenre;.of.......... 1 164 

relations of, tu bturounding rocks 1G4 

rock~~~sodateil with.............. 169 

valucof................. . .......... 168 

"Woorlyard" slates, character nnd oecurrence of ..... !_;1-B2 

Y. 

Yellow Creek, t•nppcr ore between Whitewood 1;rcek 

anti .............. . 

gold-bcaring~allllin ............. . 

Yellow Creek 1trPu, fracture group~ in. 

location of. 

mine~ in, rle~ciiption uf 

lOC!ttion und rlr:vclupmeut of .... 

refractory ~iliceou~ <>re"' in, a \"Crnge ~ Icl<l <lf 

gmdeof 

95 

1-14 

131 

151 

:.!11-21:.! 

1.'}2 

11:.! 

15:.! 

o<"rurrence uf .. _ 11:.! 

positioJl tlf .... 

valnt!tof 

------------ 1Col-15:! 

----·;·---- l5:!,I.i4 

rhyolite ~i!l1n, thil'kllt'~-~ of. 1;)2 

wolframite in, di~covery of. . ............ __ 1G3-1t:4 

Yellow Creek Golrl )lining Companv, gold production 

Uf. . .... · .................. : 118 

0 
PUBLICATIONS m' UNITED STATES GEOLOGICAL SURVEY. 

[Professional P_nper X f}. :!6.] 

The serial• publications of the United States Geological Survey consist of ll) Annual Reports, 

(2) ::\Ionographs, (R) Professional Papers, (4) Bulletins, (5) l\Iineml Resources, (H) ~Vater-Supply 

and· Irrigation Papers, (7) Topographic Atlas of the United States-folios af}(l separate ~h,.. ... ts 

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The Professit~nal Papers, Bulletins, and Water-Supply Paper::; treat of a variety uf subjects, and 

the total number issuetl is large. They have therefore been classifit>tl into the following l'erie~: A, 

Econ~mic• geology; R, Deseiiptive geology; C, Systematic gt->ulogy aiHl pal(:'ontology; D, Petrography 

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is the thirty-fourth in Series 4 anil the thirty-eighth in.Series B, the complete lists of.which follow. 

(PP=Professional Paper, B=Bulletin, "~S=W~ter-Supply Paper.) 

SERIES "A, ECONO:\fiC GF.OLOG¥ 

R 21. Ligmtt:s of Great Sioux Rt:~t:rvatiOJ): Report on region bt>tween Grnn<l and Moreau rivers, Dakota, by R1tilcy WililR. 

1885 Hi pp., 5 ph (Out of ,:tuck,) 

B ·Hi. N~ture and origin of deposits of pho~ph.ak of lime, hy R, A F Penro~l', Jr., wuh introductioH by N, S. Shaler. 1.':\~S. 

143 pp (Out of ~tock.) 

B 65. Stratigraphy of the bituminou« eoal field ~f Pennsylvania, Ohio, 1UHl \\'e"t VIrginia, t>r I. C. Whtt<>. 1~\11. 212 N•, 

• 11 pls. (Out of ~tork.) " 

B 111. Geology of Big Stone llap 'coal field of Vuginia and Kentucky, by ~1. R. Campbell 1X!J3. lOti l'J>., r; pi~. 

R 132. The di!>5emmated lead ore~ of ~outheastern hh~Mmri, br Arthur Win~low. 1i\!Jti. :n pp, 

B 138. Artesian·well prospect~ in Atlantic Coastal Plain region, br X. H. Darton. 189r.. :.!:.!~ pp., HI pls. \out uf ~toek.J 

B 139. Geology of Castle )lountainmining distriet, )Jontana, by W. H. Weed anrl L. V, Pu~~on, 18% 164 pp., 17 pl~. 

B H3. Bibliography of chtys and the ecmmic art.~, by J. C. Rrnnner. 1~96. 114 pp 

B 164.' Reeonnaisrumt'e on the Rio Grande co!tl fields of Texa~. by T. 'IV \'aughan, ineliH1ing a report on igneous rock~ from 

the Sun Carlos coallielrl, by E. C. E. T,ord, 1900 100 pp .. 11 pi~. 

R 178 El Pa-~o tin dep05its, by W. H: Weed. 1901. 1."1 pp, 1 pl. 

B 100. Occurrence and distributiOn of corundum iu United State5, by .r. H. l'ratt. 1901. \IS pp,, 14 pis 

B 182. A report on the economic geology of the Silverton quadrangle, Colorado, by I<', L. Ransome 

~ (Out of stock.) 

lOut of stock.) 

1901. lti6 pp., 16 pis. 

ll 184. Oil und gas fields of th~: western interior !Llld northern Texa>. Coal ~[easnn:s und nf the Upper Crctlll'<'ons tuul Tertiary of the western Gulf roast, by G. I. Adams. 1901. 04 l'I•·· 10 pl~. (Out of .~tock.) 

B 193.'The geological relatiOn~ and. dlstr:Ibntion Or platinum and assoCiated mdal~, by J. F. Kemp. 100"2., -y5·j~};,;·r, jJI("'". 

(Out of stock.) · .... ,... __ . · •· 

B i98. The Berett gnt Oil.'.and in the Cadiz !jUadrangle, Ohw, by W 'r. Gn~wold 1902. -~a ·pp .. 1 pl. 

PP 1. Preliminary report on the Ket{'hikan mmmg district, .\lu~ku, with un introduetory ~ketch of the geology of south· 

eru:.tern Alru;ka, by Alfred Hulse Brook~. 1\IOC!. 120 pp., 2 pl>', 

R 200. Reconnaissance o~ the borax deposits of Death Yallcy anrl ·Mohave De~ert, t>r :11 R. Campbell. 190'2. ;3 pp., 1 pl. 

(Out of stock.) 

B 202. Tests for gold and s~lver In ~hale~ from western Kansas, by Waldemar Lmdgr~n. 1002. :.!1pp 

PP 2 Reconnai~nce of the northwe»tcrn portion of Sewarrl1'cnml-ula, Aln~ka, by A . .J. C••llier. 100:.!. 70 pp, 11 pis. 

PP 10. Reconnnissanl'e from ·Fort Hamlin to Kotzebue Sound, Alu~ku, by \1 ay of Dr. II, Kanuti. Allen, awl Kowak r!vers, 

by W. C. :\Iendcnlutll. 19tl2. t\8 pp .. 10 plR. 

l'P n.' Clay~ of the Unite!l :;tnte~ en~t of~thc ~Ii~~i~sippi R1ver, loy Heinrich Rie~. 190a. C!9il pp , 91-'b. 

PP 12: Geolog-y of the Globe {'opper o.lbtnet .• \rizonn, by F. L Itansome. 1\!0a. 168 pp, 27 pi~. 

11212. Oil Jiclrl~ of th~ Texa~·Loubiann l;n]f Coastal Plain, l.>y C. W. Ha~·e«and William Keunefly 

B :!13. Contributions to ct;onomic geology, l!Jtr2 3. F. Emmon~. C. W, Ht;ye~. goeolog1~t~ Ill <"harge 

l'P 15. The mmcrul re~onrce~ of the Mount Wrangell f!i~triet, Ala;,ka, by W. C. :'II~ndenhall und 

1\!0'J 

1!!03. 

174 pp, llJ<ls. 

H!lpp. 

7I pp , 1U pl~. 

B 218. Coal rc!-ourccs uf the Yukon, .l..laska, hy Arthur .T. Collier. 1903. 71 pp., ti pi~ 

B 21!l The ore dqoo~Jt~ of Tonopuh. NeYada (prclirninary report), loy .J. E Spurr. 1\;i():l, 31 pp., 1pl. 

l'l' 20. A reeunuai,:~ance in northern AlaSka in l!lOI, l.Jy F. C. Schrader, 19(}l 13\J pp, Hl pis. 

F, (', Sehrarlcr. 

l'l' 21. 'l'hc geology and ore dcpo~it:; of the Bisbee qunrlran~le, .Arizolltt, hy F L Ran.'-omc. HIU4. 1G8pp., :!'J pis · 

B :.!23. Gypsum dq•o;-It~ in the United Btnte~. by G.I: .-\<1am>~ nnd other~. 1\104. 12g pp., 21 pl~. 

190~. 

PP 21. Zine nnd lead depo~its of northern Arkan~u~. by G. T. .\.dams, U:>H~te•l hy .\.H. l'nnlnt: nrul E, F, Burehurd, with a 

section on the determination und ('orrelation uf formation~. l.Jy E, 0. l;lrkh 1801. 11.~ J>!' , :!'7 pb. 

I'P 25. The copper dcpo~it~ of the .Eneampmentdistnet, Wyo::.ninc;, by A C. Speneer. 1\lW. lUi l'P, 2 pl~. 

B 2:!.') Contributions tu economk geology, 1\lO:-l, by f'5 .F Emrnun~ nnd C W. H11~·e~, gL•nl"g-t~t~ Ill dutrg"t', 1!104 .. "o.!.7 pp., lpl, 

PP 2b. E!·onomic rcsourct:S uf tile northcru Black Hilh, l.Jy J.D. In·ing, wlth t·ontnbutlon~ Ly S F. Elllmon« !illd T, A . 

.Taggur. jr. 1904. 222 pp,, 20 pl~. 

' 
II PUBLICATIONS OF UNITED STATES GEOLOGICAL SURVEY. 

SERIES B, DESCRIPTIYE GEOLOGY. 

B 23. Observations on the junction between the Eastern sandstone and the Keweenaw series on Kewe"enaw Point, I"ake 

Superior, by R. D. lr\'ing and T. C. Cbamlterlin. 1885. 12-! pp., li pis. (Out of stock.) 

B 33. Xotcs on geology of northern California, by J. S. Diller. 1886. 23 pp. (Out of stock.) 

B 39. The upper beaclle~ unrl deltas of Glacial Lake Agas~iz, br Wnrrep Upham. 1887. 8-t pp., 1 pl. (Out of stock.) 

B 40. Change~ in river cour~e.s in Washington Territory due to glaciation, by Bailey Willi~. 1887. 10 pp., 4 pl~. (Out of 

stock.) 

B 45. The present condition of knowledge of the geology of Tcxa:,, by R. T. Hill. 1887. 9-1. pp." (Ou~ of stock.) 

B 53. 'fhc geologr of Xantucket, by~- S. Shaler. 1880. 55 pp., 10 pi~. (Out of ~tock.) 

B 57. A geological reconnaissance in sonthwestem Kansas, by Robert Hay. 1890. 4!:1 pp., 2 pis. 

R 58. The glacial boundary in western renns~·lvnnia, Ohio, Kentuek~-. Indiana, and Illinois, by G. F. Wright, with introduction by T.-C. Chamberlin. 1890. 112 pp., 8 pis. (Out of stock.) 

B 67. The relations of the trups of the ~ewurk system in the New Jersey region, by X. H. Durton. 1800 .. 82 pp. (Out of 

stock.) 

B 104. Glaciation of the Yellowstone Ynlley north of the Park, by ·w. H. Weed 1893. 41 pp., 4 pis. 

B 108. A geological reconnaissance in central \\·"fishii;gton, by I. C. Russell. 1893. 108 pp .• 12 pis. (Out of stock.) 

B 119. A geological reconnaissance in northwest Wyoming, by G. II. Eldridge. 1894. 72 pp., 4 pis. 

B 137. The geology of the Fort Riley 1filitary Reservation and yici~ity, Kamas, by Robert Hay. 1896. 35 pp., 8 J!l.'. 

B 144. The moraines "f the Missouri Coteau and their attendant deposits, by ,T. E. Todd. 1896. 71 pp., 21 pis. 

B 158. The moraines of southeastern South Dakota and tlicir attendant (leposits, by J. E. Todd. 1899. 171 pp., 27 pi~. 

B 159. The geology of ea_~tern Berkshire County, Ma&<achusetts, by B. K. Emerson. 1899. 139 pp., 9 pls. 

B 165. Contributions to the geology_ of )Iaine, by H. S. Williams and H. E. Gregor\. 1900. 212 pp., 14 pis. 

WS 70. Geology and ,mter resources of the Patrick .and Goshen Hole quadrangles in eastern Wyoming and western 

Nebmska, by G. I. Adams. 190'1. 50 pp., 11 pls. 

B 199. Geology and water resources of the Snake River Plains of Idaho, bj· L C .. Hu~~cll. 190"1. 192 pp., 25 pis. 

PP 1. Preliminary report on the Ketchikan mining district, Alaska, 'vith an introductory sketch of the geology of southeastern Alusku, by A. II. nrooks. 1902. 120 pp., 2 pis. 

PP 2. Reconnaissance of the northl\'estern portion of Seward Peninsula, Alaska, by A. J. Collier. 1902. 70 pp., 11 pis. 

l'P 3. Geology and petrography of Crater Lake Xational P~uk, by J. S. Diller and II. B. Patton. 190'1. 167 pp., 19 pia. 

PP 10. Reconnaissance from Fort Httmlin to KotzP.hnE>· 8onnd, Alaska. b~- wny of Dall, Kanuti, Allen, and Kowak river~, 

by W. C. )lendenhall. 1902. G8 pp., 10 pls.· ' 

rP 11. Cluys of the United States cast of the "1Iississippi River, by Heinrich Ries. 1003. 298 pp., 9 pls. 

PP 12. Geology of the Globe copper district, Arizoll!t," by F. I .. Htmsome. 1903. 168 pp., ?.7 pls. 

Pr 13. Drainage modifications in southeastern Ohio and adjuecnt parts of West \'irginia and Kentucky, by W. G. Tight. 

1903. 111 pp., 17 pis. r 

B ::!08. Descriptive geology of Nevada south, of the fortieth parallel and udju.cent portions of California, by J. E. Spurr, 

1903. 229 pp., 8 pls. 

B 209. Geology of Ascutney 1Iountain, yermont, by R . .A. ·Duly. 190:3. 122 pp., 7 pis. 

WS 78. Preliminary report on artesian basins in. southwestern Idaho and »outheastern Oregon, by I. c. Russell. 190:3. 

-~---··=-----51 pp-., 2 pis.·. . ! 

PP 15. Mineral re~ourCes of,the l\Iount Wrangell di!!trict, Alaska, hy W. C. 1Iendcnhall and}'. C. Schrader .. 1903. 71 pp., 

10 pls. 

Pr 17. Preliminary report on the geology and water resources of X ebra~ka west of the one hund~ed and third meridian, 

br X. H. Darton. 1903. G9 pp., 43 pls. 

B 217. Notes on the geology of southwestern Idaho and southeastern Oregon, by I. C. Russell. 1903. 83 pp., 18 pis. 

B 219. The ore deposits of Tonopah, Kevndn (preliminary report), by J. E. Spurr. I903. 31 pp., !"pl. 

PP 20. A reconnais~nce in northern Alaska ill 1901, by F. C. Schrader .. 1904. 139 pp., 16 pis .. ~ 

Pr 21. The geology and ore deposit~ of the Bisbee quadrangle, Arizona, by F. L. Ransome. 1904. IGS pp., 29 pis. 

WS 90. Geology and w>tter re~ourees of part of the lower James River \'alley, South Dakota, by J. E. Todq and C. M. Hall. 

1904. 47 pp., 23 pls. • . , 

PP 25. The copper deposits of the Encampment district, Wyoming, by A. C. Spencer. 1904. 107 pp., 2 pls. 

PP 26. Economic resources of the ·northern Black. Hills, b~· J.D. In·ing, with cC'mtributions b~- S. F. Emmons nnd T. A. 

Jaggur, jr. 190·1. 222 pp., 20 pls. 

Correspondence should be addressed to 

THE 

Ju:NE, 1904. 

DIH:h.'C'l'OR, 

Uxr~Ev STATES GEOLOGICAL SuRYEY, 

'YASHIKGTON, D.C. 
LIBRARY CATALOGUE .SLIPS. 

[~.fount eaeh t;lip upon a l:lep~rate card, placing tite s_ubject at the top of the 

secoll(l slip. The name of the series should not be repe:;tted on the series 

card, but additional numbers should be added, as received, to the first 

entry.] 

Irving, J [ ohn J D [ uer] 

. . . Economic resources of the northern Black Hills; 

by J. D. Irving, with ·contributions by S. F. Emmons 

and T. A. Jagger, jr. Washingtm.;; Gov't print. off., 

1904. , 

222, III p. illn~., 20 pl. (in d. maps) 2H~ x 2:{""'. (U.S. Geological survey. , 

Profe~~ional p~per no. 2G.) 

Subject series: A, Economit: geology, :3-l; R, Descriptive geology; RR. 

"Bibliography": p. lR-14. . 

"Literaiure": p. 101-Im, 11:3-"116. 

Contepts.~pt. 1. Genera_l geology, by T. A. Jagger, jr.-pt. 2. )lining 

geology, by J. D. Irving :md S. F. Emmons. 

Irving, ][ ohn J D [ uer J 

. . . Econon1ic resources of the northern Black Hills, 

by J. D. Irving, with contributions by S. F. Emmons 

and T. A. Jagger, jr. Washington, Gov't print. off.,· 

1904. 

t> 

222, m p. ill us., 20 pl. { incl.inaps) 29! x 23cm. { U ·, S. Geological f!llrvey. 

Professional paper no. 2{).) .• 

Subject series: A, Economic geology, ::H; B, nescriptive geology, il8. 

"Bibliography": p. 13-14. 

"Literature": p. 101-10:{, 113-116. 

Contents.-pt. 1. General geology, hy T. A .. Jagger, jr:-pt.. ~- ::\lining 

geology, by .J. D. lrving and S. F. Emr~om;. 

U. S.· Geologic;al survey. 

~ Professional papers. 

"' 

no. 26. Irving, J. D. Ec.onomic resources of the 

northern Black Hills. 1904. 

U. S. Dept. of the Interior. 

see also 

U. S. GeologiCal survey. 

4987-So. 26-04--15 

.. 

nr 
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AUG9 1972 

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