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8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
1/20
Econom/c eo/og•
Vol. 80, 1985, pp. 1669-1688
Mineralized Veins and Brecciasof the Cripple Creek District, Colorado
TOMMY B. THOMPSON, ALAN D. TBIPPEL, AND PETEB C. DWELLEY*
Departmentof Earth Resources, oloradoStateUniversity, t. Collins,Colorado80523
Abstract
The CrippleCreekdistrict asyielded early21 million royounces f goldsincetsdiscovery
in 1891. The orebodies ccurasnarrowveinswithin Precambrian ndTertiary rocksand as
bulk tonnage eposits ithin ectonicandhydrothermal reccias.
The district s ocalizedwithinandadjacento a 27.9- to 29.3 ___.7-m.y.-oldnested iatreme-
intrusive omplex. wo magmas, honolitic ndalkalibasalticn composition,enerated ol-
canic lows, ubvolcanicntrusions,ndphreatomagmaticreccias. agmamixing s suggested
by intermediate ompositionatite-phonolitendsyenite. ubsidencef the diatreme omplex
rockss ndicated y (1) a thick luvial-lacustrineedimentaryequencen the eastern ubbasin,
(2) the presence f carbonaceousebris, ipple-laminatedocks,and dessicationracksn
sedimentaryocks t depthsmore han300 m below he present urface,3) by the fracture
systems ear he diatremesubbasin arginshat reflectbasementock nfluence, nd 4) by
flat-dipping einsnear ntrusive odiesor smallbreccia odies e.g., he Cresson iatreme).
The vein deposits s exemplified y thoseof the Ajax mine cut Precambrian rystalline
rocksandTertiary rocksof the diatremecomplex.Within the Precambrianocks he veins
are radial o the margins f the diatremesystem ndare sheeted oneswith rock dissolution
andopen-spaceillings.Where he veinscut he CrippleCreekbreccia, heyare an rregular
anastomosingracture one. he major eins xhibit emarkableertical ontinuity, xtending
to more han 1,000 m below he presentsurface. ein-relatedhydrothermal lterationoccurs
in a narrowselvagehat extends utwardno more han ive times he vein width. Secondary
K-feldspar, olomite, oscoelite, ndpyrite occurwithin an nner zoneadjacento the veins,
whereas an outer zone containssericite, montmori lonite,magnetite, minor secondary
K-feldspar, ndpyrite.There s no expansionf the alteration onesn the upper evel mine
exposures.
Five stages f minerals re recognizedn the Ajaxmineveins: 1) quartz-fiuorite-adularia-
pyrite-(dolomite-marcasite),2) basemetals-quartz-pyrite,3) quartz-fluorite-pyrite-hematite-
rutile, (4) quartz-pyrite-rutile-calaverite-acanthite,nd 5) quartz-fluorite-dolomite.he pro-
portionsof eachstagevary within and betweenveins,but the ore mineralogys consistent
throughouthevertical xtentof he developed einsystems.orizontally, oldvaluesanged
between0.5 and 1.0 oz Au per short on.
Fluid nclusion nalysesavedocumentedhe presence f earlystage saline luids 33-
>40 equiv.wt % NaC1)with the higher salinitiesound n the upper 300 m of the Ajax mine
levels; he fluidswereboilingandcontained O•. Stage and3 fluid nclusionsxhibitpro-
gressivelyowerhomogenizationemperatures,ndsalinitiesre markedlyower 0-8.3 equiv.
wt % NaC1). he tellurideorewasdepositedromweaklyboiling,dilute luids 1.4-3.5 equiv.
wt % NaC1)with temperatures elow 150øC.
The bulk tonnage eposits, sexemplified y the GlobeHill area,consist f mineralized
tectonic ndhydrothermal reccias uttingpyroxene-bearinglkali rachyte. our structural
events ccurred t GlobeHill: (I) emplacementf hydrothermalreccia odies long north-
west-trending,800-by 700-mzone; II) intersectingectonic djustmentslong teep ariable-
strike ones n he westernmargin f he stage breccias;III) intrusive reccia mplacement
at the major stage I fault intersection; nd (IV) hydrothermal recciation entered o the
immediate astof the GlobeHill pit and characterizedy a matrixconsistingf anhydrite,
carbonate,luorite,pyrite,andbasemetalsulfides.
Two hydrothermal ventsgenerated old-silvermineralization nd associated all-rock
alteration n the bulk tonnage eposits. he precious ndbasemetalsoccurwith alteration
productsn breccia lasts r n matrixmineralswithin he hydrothermal nd ectonic reccias.
The fluids esponsibleor alteration-mineralizationereboilingas ndicated y wideranges
of filling emperaturesn fluid nclusionsf the samemineralgrain,extensive evelopment
of "explosion"exture n quartzandcelestite, nd argevariations f liquid/vapor atios n
fluid nclusions ithin ndividual rystal rowth ones. emperatures erebelow200øCas
indicated y minimumillingvalues.Capping f boiling hallow ydrothermalluids ppears
* Presentaddress: MC Corporation,1801 CaliforniaStreet, Denver, Colorado80202.
0361-0128/85/448/1669-2052.50 1669
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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1670 THOMPSON,RIPPEL, NDDWELLEY
to havebeenenhanced y the alkali rachyte orphyryntrusion t GlobeHill, whichacted
asa permeabilityarriero upward-migratingluids. apor-dominatedluids evelopedver-
pressuring,eading o hydrothermalrecciationnd ow-grade olddeposits. n the other
hand, he vein systemsn the CrippleCreekdistrict ormed long tructurespen o the
surface; ence,hydrothermal recciationdid not occur.
Introduction
SINCEhe 1891discoveryfgold n theCrippleCreek
district,almost 1 million roy ounces avebeenre-
covered Gott et al., 1967). The orebodies ccuras
narrowveinswithin Precambrian ndTertiary rocks
although omeorebodieswere localizedwithin brec-
cia bodies.A reconnaissanceeochemicalrogram
by the U.S. Geological urvey Gott et al., 1967,
1969) ndicatedherewaspotentialor bulk onnage
deposits ithin he district. he developmentf one
such eposit y The SilverStateMiningCorporation
(Lewis,1982) attestso the viabilityof such eposits.
We intend to presentdata inking he vein and bulk
tonnage epositsnddescribingheir elationshipso
breccias f various rigins.
Previousand Present nvestigations
Numerousnvestigatorsaveworked n the Cripple
Creek districtand the published esultsare volumi-
nous.The earliestaccountsCross ndPenrose, 895;
Lindgren and Ransome,1906) pictured the district
asan explosive olcaniccrater n Precambrian ocks.
Later (Loughlinand Koschmann,935), the role of
subsidencen formingsomeof the brecciacomplex
was ecognized. he controls f basement tructures
in localizingvein systemswas clearly defined by
Koschmann1949) and he occurrence f oresat con-
siderable depths was documented by Loughlin
(1927). A wealthof mine maps or the district s con-
tained in an unpublishedU.S. GeologicalSurvey
Open-File Report (Koschmann nd Loughlin,1965).
Detailed accounts of vein- and breccia-hosted ore de-
positmineralogy avebeenprovided y Lindgren nd
Ransome 1906).
The present eportsummarizesield and aboratory
studiesnitiated n the CrippleCreek district n 1982
by graduate tudents nd he seniorauthor rom Col-
oradoStateUniversity.Studies o date have focused
on vein-golddepositsn the Ajax mine (P.C.D.) (Fig.
1), bulk onnage reccia-hostedolddepositst Globe
Hill (A.D.T.) (Fig. 1), and on district-widegeologic
mapping T.B.T.).
Regionaland Local Geology
The Cripple Creek district (Fig. 1) is localized n
a compressionallyormedLaramidedomeat contacts
between Precambrian intrusive and metavolcanic
bodies Fig. 1; Wobuset al., 1976). During the Lar-
amideuplift,all Paleozoic ndMesozoic edimentary
rocks were eroded from the dome centered in the
Cripple Creek area. Oligocene onglomerate ccurs
in a southwest-strikingalcovalleymmediately outh
of Victor Tobey,1969;Wobus t al., 1976) that ap-
pears o haveheadedon the Cripple Creek volcanic
complex. ubsequentrosion nd/orvolcanic ctivity
seems o have removedany trace of such luvial de-
posits n the immediateCripple Creek district.Ash
flowsof latite porphyryoverlying he conglomerate
depositsn the palcovalley o the southwest f Victor
were thoughtby Tobey (1969) to havebeen derived
from a Cripple Creek eruptive center;similar ocks
havenot been recognizedwithin the Cripple Creek
district.
The Cripple Creek volcaniccomplexconsists f a
largemass fbreccia ntrudedby bodies fphonolite,
latite-phonolite,yenite, ndalkalibasalt Fig. 1). The
breccia ills an irregularbasin Loughlinand Kosch-
mann,1935) that appears o haveat least hree sub-
basins. he subbasinsre indicatedby the presence
of Precambrian asementock exposures ithin the
brecciacomplex Fig. 1). The breccia s known o be
at least1,000 m thick.Along he eastern ndnorthern
partsof the CrippleCreekbasin, acustrine nd luvial
sedimentaryocksare interbedded ith the Cripple
Creekbreccia Figs.1 and 2).
The Cripple Creek breccia is a heterolithic unit
composed f angular o subangularragmentsFig. 3
A, B, and C) of Precambrian ndTertiary rocks.The
brecciahas nterfragmentI): ragment F) ratios hat
are high (>1:1), with a well-sortedmatrixconsisting
of quartz, microcline,and rock fragments0.5 to
2.0 mm n diameter.Carbonized ree (conifer) runks
and local coaly layers are reported in the breccia
(Lindgren ndRansome, 906, p. 31) at depthsof as
great as 800 ft (244 m). The breccia s massiven
outcrop ndexhibits tratificationor shortdistances
whenpresent.n the eastern alfof the CrippleCreek
basin complex, the Cripple Creek breccia is in-
terbedded with lacustrineand fluvial sedimentary
rocks. he sedimentsppear o havebeen ransported
by fluvialprocessesnto a shallow acustrine nviron-
ment. Ripple-laminated iltstonesFig. 3D), leaf im-
prints,dessication racks, ndanimal ootprintsattest
to a shallow odyof standing ater.Localoccurrences
of similardeposits re known hroughout he entire
basinarea.Often the lacustrine ocksare overlainby
typicalCripple Creek breccia,and fragments f the
sedimentaryocksare present n the breccia.
The body of Cripple Creek breccia is known
(Loughlinand Koschmann, 935) to occupya basin
on he eastwith shallow-dippingalls Fig.2) whereas
the westernhalf of the basinhassteepwalls hat 1o-
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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CRIPPLE REEK ISTPdCT,EINS& BRECCIAS 1671
YPP
/+++++++++++++++++++++•+
+ ++++++++++++++++++*++++•
+ + +
•+++++++++++++++++++++++++++++
•+++++•+++X•d+ + + ß + + + + + + + +
•++++++.+.+++++++++++++%+++++++++
++++++++++++++++ + + + + +
I 0.5 0 I Km
VI C TOt?
+++++++
+ + + +
+ + + +
++++
+ + ,
+
+
+
+
+
+
+++++++++++
,+,++ Xgd +++++++ + +
v /+
+ + + + + + + + + + + + ,
+ + + + + + + + + + + +
'.':':::::::t';'""
Geology mapped in 1983 with
. +++[+•++++ 0 parts daptedrom indgren
+ ,
I -• ond Ransome1906) and
•____J • Louõhlinnd oschmann(
I -
ROCK UNITS
- T•] Alkaliasalt
:TJ•"'• yen,te
;T•-• Latite-honolite
?.,'•.• Phonolite
• Cripplereekreccia
s, lacustrine and fluvial
-- facies
EXPLANATION
Y•I Pikeseakranite
o •VY•'•'-•Cripplereekuartzonzonite
i ß++r-•-G...iorite
::X:• B,otiteneiss
SYMBOLS
..... Dike
• ß -- Vein
......_.• . Contact, dashed where approximately
located, dotted where concealed
• Fault
ß & Breccla
• '-'/ Line of cross sechon
•/_/////////•...f hydroth... b ...
///////bod,es
B Shaft
FIG. 1. Geologic map of the Cripple Creek district, Colorado.
cally (Fig. g) dip beneathoverhanging recambrian
country ockon the southwest.he overallgeometry
of the CrippleCreek breccia s that of an upward-
flaringmasswhichappearso have ts deepest xtent
in the vicinity of the Cresson iatreme Figs. 1 and
2). Local idges ndbenches eldup by Precambrian
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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1672 THOMPSON, TRIPPEL, AND DWELLEY
A
E leva tion
(m)
3.,150
2,650
1,650
Bendnsection
'/:':':':':':':':':'
• + + *'•..-• + + .i- "•"• •-I + • + + + +
ß ' ... .... -,
+ + + + + + + + +.+ + x /+'•----A V
.. ...', .... , /.':'"",',*'Z.
+ I + Xgd +++lL+s + *- + + + + *
:::::::::::::::::::::::::::
•lO. •. CooIonicross ection -A'acrosshe CrippleCreekdiatreme omplex. ymbols
s3meas hose n •i•are ].
countryrock extend nto the basin,suggestinghat
irregular ault blockswere responsibleor the floor
ontowhich he brecciaaccumulated. he widespread
occurrences of carbonaceous debris and lacustrine-
fluvialsedimentaryocksat depth n the brecciamass
clearlydocument subsidenceasin.Explosive ol-
canism ccurredduringshort ntervals,but the basin
floor was collapsingand trapping the bulk of the
brecciadeposits.Shallowbodiesof water were pres-
ent, into which ashdeposits nd fiuvially transported
sedimentswere deposited.
Numerous gneousmasses ave ntruded he Crip-
ple Creek brecciaand Precambrian ountryrocks.
Theseoccuras tabular,upward-flaring, r stocklike
bodieswhich may havehad eruptive deposits. hey
appear o represent magmaseriesbeginningwith
phoneliteand followedsequentially y latite-phono-
lite, syenite, and alkali basalts Fig. 4). Chemical
analysesLindgren ndRansome, 906) for the Crip-
ple Creek igneous ocksappear o cluster n three
groups: honelites,atite-phonolitesndsyenites, nd
alkalibasalts. he trendsexhibitedby these ocksare
not normaldifferentiationrendsandsuggesthat two
magmas,epresented y the phonelites ndalkaliba-
salts,mayhavemixed o form he ntermediateatite-
phonelitesand syenites.
Potassium-argonateson aegirine-augiteor sy-
enite (McDowell,1966) suggesthat the rockswere
crystallized 4 +_1 m.y. agowhile wo sanidine am-
ples from phonelitewere dated at 27.9 +_0.7 m.y.
and29.3 ___.7 m.y. Webus t al., 1976).Thesedates
and he bimodalalkalicmagma uite ndicate hat the
CrippleCreekmagmasmaybe associatedith early
stages f extensionalectonism, epresented y in-
ceptionof collapsingasins long he RioGrande ift.
Similarbimodalmagmatisms representedn the San
Juanvolcanic rovince o the southwestndat the
Climaxand Hendersonmolybdenum epositso the
north (Shannon t al., 1984).
Phonelite s the mostwidespreadgneous ock in
the CrippleCreekdistrict.t occurs ot onlywithin
thebasin ut up to 7 km away rom he districtn the
formof dikes, f upward-flaringomes ith ocalvol-
canic utpourings,ndas abular,iat-dippingodies.
The rock s light gray o beige n colorandcontains
1 to 3 percent mall
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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•dPPLECREEK ISTRICT,EINS BPd•CCIAS 1673
c
FI•. 3. A. CrippleCreekbreeeia xhibiting eterolithie atureof fragments.ndhigh nterfragment/
fragment atio. B. CrippleCreekbreeeiawith phonolite top center) ragmentsn a granular uartz-
microclinematrix derived from Precambrian rystalline ocks.C. Cripple Creek breeeiawith minor
sehistosieragmentsbottom enter) ndmoderatenterfragment/fragmentatio.D. Ripple-laminated
lacustrineock (view normal o bedding) rom the eastern ubbasinn the Cripple Creek diatreme.
E. Latite-phonoliterophyrywith plagioelasendorthoelasehenoerysts.. Amygdaloidailkalibasalt.
Amygdular illings re calciteand minor luorite.
rocks. he rockhasa significantomponent f alkali
basalt ragmentsut is cutby steep o fiatbodies f
basalt Fig. 2). The blowoutalsocontains arbonized
tree fragmentst depth,clearly ndicatinghat sub-
sidence as major actorn ts ormation.hemajor
basalticcomponent f the breccia,as well as cross-
cuttingbasaltdikes,suggestshat a basaltic ody at
depth was he sourceof the energyessentialo the
development f the brecciabody.The Cresson low-
out bifurcatesat depth (Loughlinand Koschmann,
1935; Fig. 2). Its geometry, horoughmixing ofrock
types,andsubsidenceequirements uggesthat the
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1674 THOMPSON,TRIPPEL,AND DWELLEY
No20 K20
FIG. 4. Triangularvariationdiagram or the Cripple Creek
magma eries. wo variation urvesare shownby CaO-K20-Na20
(solid symbols)and SiO2-K20 + Na20-Fe•O3 + FeO + CaO
+ MgO (opensymbols). he arrowspoint in the directionof de-
creasingage. Chemical data are from Lindgren and Ransome
(1906).
body sa diatreme enerated henhotbasalticmagma
contacted roundwater n the deeperpart of the main
Cripple Creek basin.
The overallgeometry f the Cripple Creekbasin,
alongwith its contents, uggestshat the complex is-
tory involvedperiodic explosive olcanism nd flu-
idizationactivity accompanied y significant ubsi-
denceand gneousntrusions. he district s centered
over a gravityand magnetic ow, interpreted Klein-
kopf et al., 1970) to reflecta largebatholithicmass
at depth.The systems bestdescribed sa complex
diatremewith relictsof tuff-ringmaterial n isolated
bodiesaway rom the source. he draped acustrine
and luvialsedimentaryocks f the eastern asin e-
mained ntacteven hough hey subsided smuchas
300 m, a feature ecognized orldwiden manydia-
tremes Lorenz,1973; Lorenzet al., 1970). Accre-
tionaryapilliup o 8 mm n diameter ere ecognized
by LindgrenandRansome1906, p. 99), whodid not
know he significancef suchproducts. he lack of
fine silt- or clay-sizematrix in the Cripple Creek
breccia rguesor selective innowing, ccretionary
development,nd ineashexpulsion uringepisodes
of fiuidization ndsubsidencef the CrippleCreek
diatreme. xperimentaltudiesWoolsey t al., 1975)
suggesthat fiuidization rocessesangenerate, n a
laboratory cale, ll of the features eenn the Cripple
Creek diatreme.
Mineral Deposits
The renownedCripple Creek deposits ave been
described n detail by Crossand Penrose 1895),
Lindgren ndRansome1906),Loughlin ndKosch-
mann 1935), and Koschmann1949). We will not
reiterate heir findings ther han o note he distri-
butionand ypesof deposits. igure 1 showshe gen-
eral distribution of veins in the district. The veins oc-
cur in distinctbelts hat overlieburied ridgesof Pre-
cambrian ock beneath the Cripple Creek breccia
(Fig.2), occurmarginalo stocksFig. 2), occurpar-
allel o steep iatreme alls Figs., and2), or overlie
basement rock contacts that extend beneath the
CrippleCreekbreccia Fig. 1). All vein systemsp-
pear o be extensively eveloped t the surface ut
become ocusednto majorstructures elow600 m
(Koschmann,949).Thisdiscussionill focus nvein
deposits f the Ajax mine n the area mmediately
north of Victor and on bulk tonnagedeposits n the
vicinityof GlobeHill (Fig. 1).
Veins of the Ajax Mine
The Ajax vein systems exposed ver a vertical
rangeof 1,025 m with no apparentchange n ore
tenor. Wall-rock alteration, vein mineralogy and
paragenesis,nd fluid inclusion tudieswere con-
ducted Dwelley,1984) in an attempt o define he
significantharacteristicsf fluids esponsibleor ore
deposition. he veins n the Ajax cut Precambrian
rocks swell asCrippleCreekbreccia,withsignificant
changesn both he extentof alteration nd n vein
formbetween he two wall-rock ypes.The Ajaxmine
beganproductionn 1895 andproduced 47,917 oz
of goldbetween 895 and1921 (Henderson,926).
The total productiono date hasbeen n excess f
700,000 oz with vein gradesof 0.60 to 1.04 oz Au
per ton.
Vein mineralogy
Five stages f minerals re recognizedn the Ajax
mine veins (Fig. 5). The proportions f each stage
varybetween ndividual eins swell aswithineach
QUARTZ ....
FLUORITE -- -
ADULARIA
DOLOMITE -- --
PYRITE
HEMATITE
RUTIL E t t
SPHALERITE • •--
GALENA
MARCASITE
CHALCOPYRITE
PYRRHOTITE
CALAVERITE
ACANTHiTE ....
VOLUME %
FIG. 5. Paragenetic iagram or the BobtailandNewmarket
veins,Ajax mine (Dwelley, 1984).
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CRIPPLE CREEK DISTRICT, VEINS & BRECCIAS 1675
o 2 ft.
openvug
FIG. 6. Compositecross ections,ookingnorth, of the New-
market 2600 level) andbreccia-hosted1600 level) veins.Note
the restricted ein-related lteration alo n the Ajax granite in-
formal mine nomenclatureor the Precambrian ranodiorite)
comparedo the alteration alowhere he CrippleCreekbreccia
hosts ein mineralizationafterDwelley, 1984).
vein; all five stages re seldompresent n any one
vein. Concurrent racture openingand minor brec-
ciation of vein mineralsoccur throughout he min-
eralizingstages. wo veins, he Newmarket and Bob-
tail, are present hroughmostof the Ajaxmine evels.
The Newmarketcutsnot only Precambrian ranodi-
orite (Ajax graniteof local terminology) Fig. 6) but
the Cripple Creek breccia, oo. Within the granodi-
orite the veins are narrow, well-defined sheetedzones
whereas n the Cripple Creek breccia they become
an anastomosinget of irregular branching ractures
(Fig. 6). The Bobtailvein (Fig. 7) displayshe typical
Cripple Creek sheetedvein structures n the Precam-
brian granodiorite swell as n the contactzoneswith
Tertiary dikes.Typically,dissolution f the granodi-
orite (Fig. 8A) or phonolite ikesalong racture ones
generatedvuggy fracture zones within which the
open-space ein mineralswere precipitated. Gold/
silver ratios vary between 23:1 and 0.20:1 with no
consistent ertical or horizontalgradients.
Wall-rock alteration
Wall-rock alteration related to vein mineralization
is of limited extent Figs.6, 7, 8B) andcanbe divided
into two zones Fig. 9): an inner zone dominatedby
secondary -feldspar, olomite, oscoelitevanadium-
bearingmica),and pyrite and an outer zone typified
by sericite, montmorillonite,magnetite, minor sec-
ondaryK-feldspar, ndpyrite. There is no expansion
of the alterationzonesas the upper levels of mine
exposuresre reached; owever, he Cripple Creek
breccia has more extensive alteration due to its in-
herentpermeability Fig. 6).
0 2 ft.
I i
borren fracture
;"-'.•", ' mineralized fracture
• apen vug
E XPLANA TION
• vein-relotedlteration
• phonoliteike
:/F-• Ajaxranitc
FIG. 7. Compositecrosssections,ookingnorthwest,of the
Bobtailvein (2000 and 3350 levels).Note that veinsdevelopad-
jacent to dikes 2000 level) or completelyndependent f them
(3350 level) (after Dwelley, 1984).
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1676 THOMPSON, TR/PPEL,AND DWELLEY
B
FIG. 8. A. Dissolution avities n Precambrian ranodiorite
adjacento faults n the Ajaxmine.Small oundholes re XRD
sampleites. . Vein-relatedlteration,jaxmine.Vein far ight)
with biotite-feldspar estructive lterationselvage,grading
ß bruptlyntobiotite-plagioclasetableleftofscale) recambrian
granodiorite.. Photomicrographllustratingexplosion"exture
withinan annular one n quartz.Marginof quartzcrystal s in-
tergrownwith fluorite.Field of view s 1.0 mmwide.
Fluid inclusion studies
Primary luid inclusionsrom stages , 2, 3, and 4
wereanalyzed y heating nd reezingstudies. uartz
(four stages) nd fluorite (stages and 3) are wide-
spread n the veins,and locally, stage2 sphalerite s
sufficiently oarse rained or study.Figure 10 sum-
marizesby stageand elevation he homogenization
temperaturesor the Ajax veins.Stage1 fluidswere
salinewith equivalentNaCI values anging rom 33
percenton the 2,055-m level to greater han 40 per-
cent in the upper 300 m of the mine. Weak boiling
is ndicated y the ncreasedalinities,ariableiquid/
vapor atios n individualgrowthzonesof quartz,and
the widerangeofhomogenizationemperatures. ost
stage1 fluid nclusionsontaindaughterhaliteanda
few exhibit ncreased alinities y the presence f syl-
vite and hematite. n the upper mine levels,homog-
enizationemperaturesn mostsamples ereby halite
dissolution ather than by vapor homogenization;
however, amples elow he 2,300-m evel (7,777 •t
elevation;Fig. 10) homogenized y disappearancef
the vaporphase fterhalitedissolution. doubleme-
niscuss exhibitedn the larger luid nclusion apo
bubbles; reezing studies ndicated he presenceof
CO2 hydratewith clathratemelting pointsof 8 ø to
9øC (Dwelley, 1984). The homogenizationemper-
atures or stage fluid nclusionsange rom206ø to
510øC.The largevariations due to wide ranges f
filling emperaturesn the shallowevelsof the vein
system.
Stages and3 fluid nclusionsxhibitprogressively
lowerhomogenizationemperatures,ndsalinitiesre
markedly ower, rangingbetween 0 and 8.3 equiv.
wt percent NaCI (Dwelley, 1984). Stage4 quartz,
theprecious etalstage, xhibits filling emperature
rangebetween105ø and 159øC,with a meanvalue
of 140øC.Salinityvalues angebetween1.4 and3.5
equiv.wt percentNaCI. Fluidsof stages , 3, and 4
were weaklyboiling.A plot of meanand minimum
homogenizationemperaturesor fluidsof stages
and3 (Fig. 11) llustrateshe decreasingemperatures
with time. There is, however, an increase n the min-
imum temperature bove he 7,537-ft elevation or
stages and3. Thiscorrespondso the contact one
(Fig. 12) between he CrippleCreekbreccia nd he
Precambrian ranodiorite.Higher temperatures re
presentn the CrippleCreekbreccia-hostedortions
of the vein system.
InternalCO2pressuresor the various tages ave
beenestimated y freezing tudies. tage1 fluids re
NaCl-saturatednder reezingconditions;herefore,
internal CO2 pressurewithin the inclusionss esti-
matedat 27 bars Collins,1979). Internal CO2 pres-
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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CRIPPLE REEK ISTRICT, EINS& BRECCIAS 1677
v E I N
Inner zone
Biotite totally replaced by pyrite, magnetite, dolomite, secondaryorthoclase,
roscoelite-sericite, minor fluorite
Plagioclase eplaced by montmorillonite-sericite-roscoelite,inor carbonate
Quartz unaltered to total recrystallizationnear vein
Microcline immed and veined by adularia--up to 80 percent
Outer limit I to 3X vein width
Outer zone
Biotite replaced by up to 95 percent sericite, secondary orthoclase,
magnetite, pyrite, and carbonate
Plagioclase eplaced by up to 95 percent montmorillonite-sedcite,minor
carbonate
Microclineand quartz--generally fresh, microclineweakly veined by
adularia and quartz
Outer limit I to 5X vein width
Deuteric zone
"Fresh rock," biotite weakly replaced by chlorite and magnetite
Plagioclaseup to 50 percent covered by sericite-montmodllonite
FIG. 9. Summarydiagramof vein-relatedalteration n the Ajax mine (after Dwelley, 1984).
sure n stage3 and 4 fluid inclusionss estimatedat
44 bars Collins, 979) based n clathratemelting
temperatures.rappingpressuresor stage precious
metalsdeposition ere estimatedrom unpublished
curves R. J. Bodnarand C. A. Kuehn,unpub.data)
for H20-rich inclusions. he trappingpressures
rangedbetween 360 and 400 bars.
Globe Hill Ore Deposits
Globe Hill (elevation,3,183 m) is located n the
northernsubbasin f the CrippleCreek district Fig.
1). The Globe Hill area is characterized y hydro-
thermal and tectonic brecciationdeveloped n Ter-
tiary igneous ocks hat postdate he Cripple Creek
breccia.Thesebreccias re extensively lteredand
oxidizedand host several arge tonnage, ow-grade
gold deposits.
Production rom the area began n 1891. Incom-
plete records how hat about80,000 oz of goldhave
beenproducedrom he mines ear he crestof Globe
Hill, excluding he mostrecent open-pitoperation.
Early productionwas concentrated n high-grade
veins and fault structures in the Deerhorn, Summit,
and PlymouthRock 1 mines Fig. 13), as well as n
the shortGlobe unnelwhich ntersectedhe upper
level of the Deerhorn mine.
Between 1899 and 1902 the Chicagoand Cripple
Creek tunnel (elevation,2,957 m) was extended o
explore the vein potential at depth beneath Globe
Hill. The tunnel s about 1,280 m long and extends
from PovertyGulch eastward o the PlymouthRock
i shaft.Althoughno high-gradeore wasdiscovered,
highly alteredand oxidizedbrecciacontaining race
and low-gradegold was noted over a considerable
distance Argall, 1905).
By 1905 three smallopen pits were developed o
a depth of 50 m along ntersecting einsand struc-
tures.These ncluded he Globe and Deerhorn pits,
near the summitof Globe Hill, and the Ironclad pit,
half a kilometer to the southeast. From 1916 to the
mid 1970s there was ittle production rom the area.
Numerousexplorationprogramswere conducted o
evaluate he low-grademineralizationby meansof
bulk sampling,renching,and drilling.
From 1977 to 1981 Newport Minerals, nc., a sub-
sidiaryof Gold Resources,nc., mined 680,000 tons
of low-gradeore from the Globe Hill pit, which is
centeredon the old Globe and Deerhornpits (Fig.
13). The operationwas halted in 1981 to allow Tex-
asgulf, nc., a joint-venturepartner, o conducta de-
tailed evaluation nd easibility tudyon the deposit.
The evaluationncluded rilling, renching, ampling,
and mapping.
Since March 1982, the Silver State Mining Cor-
porationhasoperateda 1,000 ton per day open pit
located at the old Ironclad pit (Lewis, 1982). The
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
10/20
1678 THOMPSON, TRIPPEL, AND DWELLEY
•414 -
•114-
84•
ß
•J
,• 81•7-
7777-
7256 -
8985
ZO• m
AJAX VEIN SYSTEM
HOMOG[NIZATION TEMP•RATuR[ RANGIS
O•) I IO
o----- -P- ---o
IO
0-- .... '0
, 3 ,
½ 3
O-- ,I--0
0-------7 .... .-o
N•te: Number over range b4r IndIcolel
number of incluliOfie efialyzed
o.•.4 H4
IOO ZOO 300 400 500
TEMPERATURE
FIG. 10. Homogenizationemperatureangesn the Ajaxveinsby mine evel andstage after
Dwelley, 1984).
geology ndmineralizations asyet unstudied, ut
brief visitsby the authorsndicatemanysimilarities
to features xposedn the GlobeHill pit.
Numerous eports and publications iscuss he
Globe Hill area, mostnotableof which are Crossand
Penrose 1895), Argall (1905, 1908), Lindgrenand
Ransome1906), Keener 1962), andPeters 1982).
This paperpresents ew informationrom ongoing
studieson the interrelationship f structure,altera-
tion, and mineralization f the deposits.
Host lithology
The Globe Hill deposit s hosted n porphyritic
subvolcanicntrusive ock,dominantly ompos,edf
pyroxene-bearinglkali rachytereferredo as atite-
phonolite istrictwide).Visible low extures reun-
common; owever, he aphanitic roundmassften
displays icroscopiclow ineationsroundhephe-
nocrysts.he extentandgeometry f this ntrusionis not known, but examinationof nearby prospect
dumpsndicateshatsimilarntrusions,ndequivalent
extrusions,re widespread. hese ocks ntrude he
CrippleCreekbreccia f thenorthern ubbasin.
The alkali rachyte orphyry veragesess han15
modalpercent otasheldspar henocrystsess han
2 mm in size. An aphanitic, rachyticgroundmass
consists f alkali-feldsparsnd pyroxene ess than
0.05 mm in size. Core from a diamond drill hole im-
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
11/20
CRIPPLECREEKDISTRICT,VEIHS6, BRECCIAS 1679
9688--
2954 m
9414 --
8662--
8485-
8157 -
7777-
7537 -
7258-
7137-
6985-
6742-
2055m
AJAX VEIN SYSTEM
MEAN AND MINIMUM HOMOGENIZATION TEMPERATURES
/
/
EXPLANATION
0 0 Stage I minimum
-- : Stage I mean
0•----0 Stage 3 minimum
e- ---... Stage 3 mean
TEMPERATURE
FIG. 11. Meanandminimum omogenizationemperaturesor Ajaxveins, tages and3 at different
elevations. ote decreasingemperaturesetween tages swell as emperatureeversalsbove he7,537-ft elevation.
mediately orthof the pit doesshow exturalgrada-
tionsat depth o granular lkalisyenite.
Local portions of the subvolcanicmasscontain
abundantmall ragmentsf texturally ifferent lkali
trachyte.Someof these ragmentsxhibit rachytic
flow orientations f phenocrysts nd others are
aphanitic.A few fragments omposed f mafic-rich
alkali rachyte, lkalisyenite,mafic-rich lkalisyenite,
basalt (?), and Precambriangranite also occur
throughout he host ntrusive.
Structure
Four separatestructuraleventsoccurred at Globe
Hill (Table 1). The earliestevent (stage1) createda
I00 200 300 400 500
oc
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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1680 THOMPSON,TRIPPEL,AND DWELLEY
BOBTAIL VEIN
looking. 0øw
:400'
N. 40øE CROSS SECTION
shaft collar elevation:
10105 ft.
Axg
EXPLANATION
O, 40,0 ft.
.*......:.. -. phonolite dike
-- Breccia- Ajax granite contact
, vein
-- 3350L elevation: 6742 ft.
FIG. 12. Crosssection hrough he Bobtailvein. Note vein-dikerelationship nd the fiat contact
between Cripple Creek breccia (Bx) and Precambriangranodiorite Axg) at the 2000 level.
zoneof hydrothermal recciabodieswhichwere ater
cut by a seriesof tectonicstructuresstage ). Intru-
sivebreccia stage3), probablydike- or pipelike in
form, then invadeda major stage2 shearzone, and a
separate ydrothermal recciabody (stage ) formed
within he stage zone.Minorreadjustmentccurred
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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CRIPPLE CREEK DISTRICT, VEINS & BRECCI.4S 1681
N
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
Globe Hill (elev. 183m)
-i-
ß
r]Summit
[] Deerhorn
'.
ß
76 m to
Plymouth Rock
No.1 shaft
A'
Stage IV
/
60%
Stage
Stage
StageI
StageV
StageV
150m.
3100 m.
3050
&
50m
A
FIG. 13. Generalizedmapandsection howing tructure,mineralization, ndalterationat the Globe
Hill area.
Explanati
shear zone
fault
hydrotherm
breccia
hydrotherm
crackle
vein
chal-celest-
(matrix fillin
ser-chl-carb-
rnont-py (al
chl-ser-py-q
ser-mont-ca
(alt)
anh-carb-celes
fluor (matrix
filling)
rnont-chal-hern
(matrix fillin
rnont-qtz-lir
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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1682
TABLE 1.
THOMPSON, TRIPPEL, AND DWELLEY
HydrothermalMineralizationand AlterationAssociated ith the Major StructuralStages f the Globe Hill Area
Stage - Stage II Stage II Stage IV
Structures
Mineralogy
Alteration
Hydrothermalbreccias
alongearly tectonic
structures
Breccia matrix and veins:
chalcedony, uartz,
celestite, fluorite,
carbonate,pyrite,
sphalerite,galena,
chalcopyrite,
pyrrhotite, specularite,
rutile, calaverite,
sericite,
montmorillonite
Breccia ragmentsand
adjacentwall rock:
sericite, chlorite,
carbonate,
montmorillonite,pyrite,
quartz, apatite
Surroundingwall rock:
chlorite, sericite,
pyrite, quartz,
montmorillonite,
apatite
Tectonic faults, shear
zones, etc.
Veins: quartz, eelestite,
fluorite, pyrite,
carbonate, adularia,
galena,sphalerite,
ealaverite, ehaleopyrite,
sericite
Disseminated outward
from gangue-free
structures: pyrite,
sphalerite,galena,
ehaleopyrite,
pyrrhotite, speeularite,
ealaverite(?)
Wall rock adjacent o
veins: quartz, sericite,
pyrite
Wall rock adjacent o
gangue-free tructures:
sericite,
montmorillonite,
carbonate,pyrite,
quartz, apatite
Intrusive breccia
Granular to rock flour
matrix: no
mineralization
Matrix and fragments:
chlorite, sericite,
specularitc,hematite
(spherules), uartz
Hydrothermalbreccias
Central core breccia
matrix:anhydrite,
carbonate, celestite,
fluorite, pyrite, galena,
sphalerite,
chalcopyrite,pyrrhotite
Peripheral breccia matrix
and veins:
montmorillonite,
fluorite, opal,
chalcedony, ematite
(spherules), luorite
Fragmentsof central core
breccia:pyrite, fluorite,
carbonate
Fragmentsof peripheral
breccia and wall rock
adjacent o veins:
montmorillonite,
limonite, hematite,
quartz
Minerals n assemblagesre listed n decreasing rder of abundance
along he stage2 structuresollowing he four major
structural vents.The followingdiscussionetails he
nature of the structures associated with each event.
Stage : Hydrothermalbreccias: he earliesthy-
drothermal breccias in the area occur as either isolated
or as coalescing rregular bodies in a northwest-
trending onewhichmeasuresbout1,800 by 700 m
in surface rea (Fig. 1). Two large clusters f hydro-
thermal breccia bodies are found, one at the Globe
Hill pit and he other at SilverState'spit to the south-
east.The bodiesn the GlobeHill cluster ormedalong
preexistingaults,at fault intersections,nd at joint
intersections. ach body (Fig. 13) approximatesn
upward-flaringcolumn, roughly equidimensionaln
plan view but with numerous extensionsoutward
alongplanarstructures. he largest ndividualbreccia
body is 50 m in diameterat the surfaceand extends
75 m downward; the smallestones are less han 10 cm
in any dimension nd occuralong oint intersections.
Most breccia bodies exhibit crude lateral and ver-
tical texturalzonation.They grade aterallyover sev-
eral meters or the largerbodies o a few centimeters
for the smallest odies rom a breccia-dominated ore,
through a crackle-dominated alo, and into highly
jointed wall rock. The frequencyof the joints and
fractures continues to decrease outward from the
bodies.Vertically, mostbodiesprobablygrade up-
ward from a steep ault or vein to crackledand brec-
ciated wall rock.
Mostbreccia ragmentsange n size rom 1 mm to
3 cm; they are generallymonolithic,clearly rotated
with subangularo subroundedhapes, oorlysorted,
and grade rom being ragment o matrixsupported,
with interfragment/fragment atios that are low
(1:1). The matrixranges rom rock
flour o fine-grainedwall-rock ragments.Mostof the
fragments riginated rom the immediatewall rock
either as platesalong sheetedstructures Fig. 14A)
or as rregularangular orms n the crackled reas.A
few of the matrix-supported reccias,however,con-
tain fragmentswhich have clearly been transported
over a considerabledistance.These fragmentsare
heterolithic,wellrounded, oorlysorted, nd esshan
5 cm n size.The mostcommonithology spyroxene-
rich (as much as 20%) alkali syenite. Other compo-
sitions ncludebiotite-rich alkali syenite,porphyritic
and aphaniticvarietiesof mafic-richalkali trachyte
(some f whichdisplaywell-developedlow extures),
and quartz-fluoritevein material. Accessory phene
and topazare common n the syenitic ragments.
The brecciamatrix s completely emented y hy-
drothermalmineralswhichdisplayopen-spacerowth
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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CRIPPLECREEKDISTRICT,VEINS • BRECCIAS 1683
FIG. 14. A. Stage1 hydrothermal reccia longa sheeted tructure.Matrix s dominantly halcedonic
quartz.B. Stage hydrothermalreccian well-jointed all rock.Sample radesrom ointedwall
rock (left), to matrix-supportedcenter), o rebrecciated ragment-supportedreccia right). Matrix is
dominantly halcedonic uartz.C. Stage4 hydrothermal recciaof the centralcorezone. Gray matrix
0eft) is.anhydrite, hichhasaltered o gypsumright).Fractured reccia ragmentsndmatrixare
alsocementedwith gypsum.D. Stage hydrothermal recciaof the centralcorezone.Matrix sentirely
altered o gypsum.Note variation n igneous exture of the fragments.
textures.'ome f hematrix-supportedrecciasx-
hibit textures ndicativeof a secondhydrothermal
brecciation nd matrix-filling vent (Fig. 14B).
Stage I: Tectonicstructures: he secondstage s
characterizedby steep tectonic structuresconcen-
trated along he westernedgeof the stage hydro-
thermalbrecciazone.The most ecentproduction t
Globe Hill has been from this area. There are four
crosscutting ubstages f tectonic structures.The
earliest s highly rregularpinchandswell aultscon-
centrated ear he centerof the pit. Theseare cutby
numerous teep aultsand shearzones,which are in
turn cut by a major north-south hearzone, The last
substages represented y faults hat cut all earlier
tectonicstructures Fig. 13).
Relativedisplacement long he stage I tectonic
structures s unclear. Marker structures,veins, and
dikescutby the north-south hear oneare not found
on the opposite ide,either at the surface r in core.
Most of the structures,houghroughlyplanar, are
difficult o trace owing to their discontinuousnd
pinch ndswellnature. everal play t eitherend,
including he north-south hear zone, which also
splays pward.Moststructures avenearlyvertical
slickensides, ut the north-south shear zone contains
horizontal slickensides as well.
StageI tectonic tructuresreusually ougeilled
and have intensely ointed and fracturedhalosof
variable width. Fault breccia occurs within some
(especially ithin henorth-southhear one)andof-
ten at the intersection of two or more structures.
These breccia bodies are small, discontinuous, nd
variablen form.They are tabular o lensshaped
within shearzonesand columnshaped t structural
intersections. he formerare mostcommon; hey are
less han 0.5 m wide and traceableup to 10 m along
strike or dip.
The breccia fragments re unsorted,angular o
subrounded, ess than 2 cm in diameter, and sup-
portedby a inatrixof gougematerial.The matrix
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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1684 THOMPSON,TRIPPEL,AND DWELLEY
gouge s a mixtureof unsorted, ery smallwall-rock
fragmentswith rock flour. This tectonicbrecciahas
interfragment/fragmentatios hat are low (1:1). The fragmentsre composed
of aphanitic nd porphyritic lkali rachyte someof
which exhibit low texture),alkali syenite,and gab-
bro(?), as well as mafic-richvarietiesof each. Some
of these ragments howevidence f havingbeenal-
tered prior to brecciation.
The matrix of the intrusive breccia consists of rock
flour and very fine fragments,mostof which are less
than 1 mm in size. Locally, the matrix is banded
showing lternatingragment-richnd ragment-poor
zones.
Stage V: Hydrothermalbreccia:The final structural
eventat GlobeHill wasone of intensehydrothermal
brecciation centered below the Deerhorn shaft. The
brecciabody formsa verticalpipelike massabout
220 m wide and at least180 m deep with a rounded
top (Argall, 1908) and has dike- and pipelikeapo-
physes hichextend utward ndupward long tage
2 tectonic tructuresFig. 13). Thismainbody s not
exposed t the surface; owever,somesmall solated
bodies re. Thesesmaller odies ormed longstage
II tectonicstructures nd are found throughout he
entire area.
Texturally ndcompositionallyhe mainbodycan
be divided nto two zones, centralcoreanda pe-
ripheral alo Fig.13).Thecentral orebreccia egins
23 m below the surface and extends at least 100 m
downward;t is 100 m in diameter Argall, 1905,
1908). It contains eterolithic,subangularo sub-
rounded,matrix-supportedragments,p to 10 cm n
size, which are often rebroken Fig. 14C and D).
These ragmentsncreasen abundancerom he cen-
ter to the marginof the core, such hat the breccia
hascorrespondingnterfragment/fragmentatios hat
are high (>1:1) to intermediate 2-3:3). They are
composed f several extural varietiesof alkali tra-
chyteporphyry these how ariable egrees f pre-
brecciationlteration) ndcurious roken ggregates
of celestite. he matrix s entirelycemented y an-
hydriteand other hydrothermalmineralswhichdis-
play open-spacerowth extures.
The peripheralbrecciahalo, which s about60 m
wide, consists f fragment-supported,ngular o sub-
angularwall-rock ragments enerallyess han 2 cm
in size; t has ntermediate o low interfragment/frag-
ment ratios.The brecciaat the outer marginof this
zonegradesnto crackle-dominatedall rock. t has
anopenmatrix artially ementedy montmorillonite
andhydrothermalminerals.
The smallhydrothermal recciabodieswhich are
isolatedrom he mainbrecciabodyare characterized
by angular o subangular all-rock ragments, sually
less han 3 cm in size.The fragments re suspended
in a matrixof the samehydrothermalminerals ound
in the peripheralhalo zone.
Breccia imilar o that of the peripheral one s also
foundalong he ast100 m of the Chicago ndCripple
Creek tunnel (Argall, 1905; LindgrenandRansome,
1906). This suggestsither an extension f the main
stage4 brecciabody southeastwardo the Plymouth
Rock i mine or the presence f a separate ody of
late-stage recciation enterednearby.
Mineralization
The preciousmetalmineralization f the GlobeHill
deposits epithermal ndpolymetallicn nature Ta-
ble 1). The mineralizationesulted rom three sepa-
rate hydrothermal vents.Thesecoincidewith three
of the four major structuralstages iscussedbove;
stage3 is unmineralized.The mineralizationoccurs
either as breccia matrix fillings, veins, or as minor
replacementbodies, dependingon the degree of
structuralpreparationof the wall rock. Although
Ag/Au ratiosare commonly reater han 3:1, they are
less han 1:1 in zonesof significant old mineraliza-
tion.
Mineralization associatedwith stage structures:
Mineralization n the stage hydrothermalbreccia
zone occursas veinsand breccia-matrix illings Fig.
13) and as weak disseminationsithin breccia rag-
mentsand adjacentwall-rock.
The open-space ein-fillingassemblagesonsist f
either chalcedonicquartz-celestite-carbonate-fiuo-
rite-pyrite or quartz-fiuorite-pyrite-(celestite-car-
bonate).The latter quartzvarietycommonly xhibits
explosionextures,consisting f radiatingvoidsbe-
lieved o be formed y displacementf attached apor
bubbles during boiling of the hydrothermalsolu-
tion. The other mineralscoprecipitatedwith the
quartz mmediatelyoutside heseexplosion extures
(rig. 8c/.
The brecciamatrix filling is composed f chalce-
donic quartz-celestite-pyrite-(fiuorite-carbonate-
quartz). The quartz occursas narrow rims on frag-
ments in the well-rounded, heterolithic breccia. Ac-
cessoryminerals ound throughoutall assemblages
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CRIPPLE REEK ISTRICT, EINS&BRECCIAS 1685
include: phalerite, alena, halcopyrite,yrrhotite,
specularitc,utile, calaverite, ericite, ndmontmo-
rillonite. The total sulfide content of the mineralized
stage structuresarelyexceeds few percent; el-
lurides and primary oxides are present in trace
amounts.
Mineralization associatedwith stage I structures:
The mineralizationlong tageI structuress of two
types:asveinsalong he earlieststructures r, more
commonly, s disseminationshroughoutwall rock
adjacent o the later structures.
The veins formed as discontinuous lenses less than
20 cmwide, whichhavea pinchandswellcharacter,
and are concentratedn a 15- by 45-m zoneexposed
in thepit. Theveins recomposedf quartz-celestite-
fiuorite-(pyrite-carbonate-adularia)hich was de-
positedn multiple vents.Galena, phalerite, alav-
erite, chalcopyrite, nd sericiteoccurwith this as-
semblage ut generallyare only found in trace
amounts.All of these minerals exhibit open-space
growth extures nd the quartzcommonly xhibits
explosionexture.The otherminerals oprecipitated
with quartzwithin and mmediately utside he ex-
plosion exturezone. nitial total sulfidecontent n
the veinswas only a few percent; elluride content
locallyexceeded everalpercent.
The latter structures re mineralizedchieflyby py-
rite disseminatedutward hrough he adjacentwall
rockandby ocalpyriteconcentratedlongractures.
The halos djacent o individual aultsare commonly
less han3.0 m wide.Overlapping alos romseparate
structures within the shear zones create wider areas
of disseminatedmineralization.Accompanying he
pyrite, which arelyexceeds few percent,are trace
amounts f sphalerite, halcopyrite, yrrhotite,spec-
ularitc, and (probably)calaverite.
Mineralizationassociated ith stage V structures:
The centralcoreof the stageV matrix-supportedy-
drothermal reccia s cemented y an assemblagef
anhydrite-carbonate-celestite-fiuoriteFig. 13), each
of whichexhibitopen-spacerowth extures. he ce-
lestitc shows rudelydevelopedexplosionexture as
well. Accompanyinghe ganguemineralsare minor
amountsof disseminated yrite, galena,sphalerite,
chalcopyrite, nd pyrrhotite.Geochemical nalyses
revealonly trace amounts f gold n the rock.
The stage V peripheralzone, composed f frag-
ment-supportedhydrothermal breccia, is partially
cemented and veined by massivemontmorillonite
(Fig. 13). The montmorillonitealsooccursas veins
and as breccia matrix filling in the stage I tectonic
structureshroughout he entire deposit; t is accom-
panied by minor amountsof opaline to chalcedonic
quartz and tiny hematiticspherules.One 5.5-m-long
core interval is comprisedof montmorillonite,but
most veins are less than 5 cm in true width. Minor
wispyveinletsof fluorite are found cutting he vein
montmorillonite. Much of the montmorillonite is
white or stained rownby limonites, ut some sbril-
liant yellow-green.As with the anhydrite-cemented
corebreccia,geochemical nalyseseveal only trace
amounts f gold.
Crossand Penrose 1895) report gypsumcoating
the seams nd fragmentsn the peripheralbreccia
zoneabove he anhydrite-gypsum-cementedentral
core in the Deerhorn mine. Recent core data, how-
ever, ndicateno visiblegypsum r anhydrite n this
zone.
Alteration
Therewere iveseparate lteration vents t Globe
Hill. Eachof he first our ypesshydrothermalTable
1) and srelated o oneof the majorstructural tages;
the ifth ype s elated o supergene eathering.he
last hydrothermal vent as well as the supergene
weatheringormed xtensive ut irregularoxidation
to a considerable epth.
Alteration elated o stage structures: he frag-
mentsn the stage hydrothermalreccia odies on-
tain weak to moderate sericite-chlorite-carbonate-
montmorillonite-pyrite-(quartz-apatite) lteration
(Fig. 13). Intensesericite-pyrite-quartz-(carbonat
alteration s commonly eveloped n a rind around
brecciaragmentsesshan0.5 mmwide.Occasionally
they alsoexhibitan irregular ind of silicification
around heir outermargin,but it is ess han 0.1 mm
wide.
The wall rocksurroundinghe hydrothermal rec-
cia bodies containsextensive,moderate chlorite-ser-
icite-pyrite-quartz-(montmorillonite-apatite)ltera-
tion, the extent of which has not been delineated
(Fig.13).Chalcedonyeinlets reoccasionallyound
throughout his zone and displaynarrow, intense
chloritichalos,whichgradeoutward o the chlorite-
sericite-dominated alteration.
Alteration elated o stageH structures: he vein-
filled stage I tectonicstructures isplayhalosof
moderate uartz-sericite-pyritelteration,ess han
5 cmwide.The gangue-freetructuresxhibithalos
of weak to moderate sericite-montmorillonite-car-
bonate-pyrite-(quartz-apatite)lteration,up to 3 m
wide.The alteration xtendso a depthof 75 m within
the majornorth-south hearzone and to shallower
depthswithin smaller ectonicstructuresFig. 13).
No ohiorite-dominated ssemblage as been recog-
nized.
Alterationrelated o stageHI structures: he stage
III intrusivebreccia s characterized y intensechlo-
rite-sericite-quartz-hematitelteration throughout
the matrix.Breccia ragments ontainweakchloritic
alteration and often exhibit a rind of moderate to in-
tense chlorite-sericite-hematite-quartzlteration as
well. The degreeof fragment lteration arieswith
thecompositionnd gneousexture f the fragments.
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
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1686 THOMPSON,RIPPEL, ND DWELLEY
Several ragments ontain racture-controlled dularia
and have intense sericitic alteration. These anomalous
fragments uggest prebrecciapotassic lteration,
presumably t depth.The hematite n both the matrix
and he fragments ccurs sblades specularitc) nd
as spherical ggregates.
Alteration related to stage V structures:n the
stageV centralbreccia one,alteration f the frag-
ments elated o the anhydritematrix illing is mini-
mal.Nearlyall of the heterolithic all-rockragments
contain rebreccia ilicificationn varyingdegrees f
intensity. ome ragments isplay arrow indsof py-
rite-fluorite-carbonatelteration. he prebreccia e-
lestitcaggregateragments re partiallyaltered o an
assemblage f anhydrite-(fiuorite-carbonate-pyrite)
alongmargins ndgrainboundaries.
The wall-rock ragmentsn the peripheralbreccia
zone contain weak to moderate montmorillonite al-
teration,with minor quartz and limonite (Table 1).
The alteration ntensity ncreasesoward he anhy-
drite-cemented entral breccia.The breccia rag-
mentsand the wall rock adjacent o the montmoril-
lonite veins along stage I tectonicstructures om-
monlycontainonly weak montmorillonite lteration.
Oxidationof preexisting ulfides nd tellurides n
the fragments f the peripheral reccia one ncreases
toward the unoxidizedanhydrite-cementedentral
breccia. he relativepercentagef pyritecasts, ow-
ever,doesnot ncrease roportionally ith ncreased
montmorillonite lterationand matrix filling. This
zonation ithin he peripheral reccias also eported
fromobservationsade n the Deerhornworkings
(Argall,1905, 1908). Similaroxidations present n
narrow wall-rockzonesadjacent o the montmoril-
lonite veinsalongstage I structures.
The natureof thisoxidation,he relatively onstant
preoxidation yritecontentof the fragments, nd he
occurrence f hematitespherulesn the montmoril-
lonitebrecciamatrix illingstrongly uggest hypo-
geneorigin for this oxidation.
Alteration elated o supergeneeathering:uper-
gene weatheringhas partially oxidized he rocksat
Globe Hill to a depth of at least 270 m, some45 m
below he Chicago ndCrippleCreek unnel Lind-
grenandRansome, 906). Little or no remobilization
of preciousmetals asaccompaniedhe weathering.
The effectsof thisweathering re mostpronounced
along tage hydrothermal reccias ndstageI tec-
tonic structures,where permeability s sufficient o
allowdownwardpercolation f meteoricwaters.
The mostcommon eactionwith oxygenatedme-
teoricwater s the alterationof pyrite, galena,chal-
copyrite,and calaverite o limonites, nglesite, ov-
ellitc, and nativegold, respectively. he oxideand
sulfateassemblagearies,depending n the amount
of preoxidationulfides nd heirdegreeof oxidation.
Additionally, he anhydrite s partially converted o
gypsumby hydration.
Supergeneweathering of alteration and mineral-
ization products related to stage I structureshas
formed an assemblage f fracture-filled and dis-
seminated goethite-manjiroite-wad-(hematite-jros-
ite-celestite-autunite). he autunite s found along
oxidizedveins.Weathering of alterationand miner-
alization products elated to stage I tectonic struc-
tures has producedan assemblage f hematite and
jarosite, with lesseramountsof goethite, and man-
ganeseminerals.
Fluid inclusions
Fluid inclusions are common in minerals from the
three stages f mineralization. rimaryand pseudo-
secondaryluid nclusions ccurmostoften n the flu-
orite within the stage veins,quartzwithin the stage
II veins, and anhydrite within the stage V breccia
matrix filling. Most are of approximately egative
crystal orm and ess han 10 tam n maximumdimen-
sion.Fluid inclusionsn the stage fluoriteand n the
stage I quartz contain both liquid and vapor. They
have variable iquid to vaporratiosbut are generally
liquid dominated.Most fluid inclusionsn the stage
IV anhydriteare entirely vapor,but a few are liquid
dominated ith variable iquid o vapor atios.Nearly
all anhydritedisplays urvedcleavagesesulting rom
postdepositional train. No daughter products or
doublemeniscuses ere observedn any of the fluid
inclusions,ndicatingower salinities ndvaporpres-
sures han observedor the early vein fluids.
A crushing tudywasconducted o test whether or
not the fluid inclusions re overpressured. olished
platesof eachsample mmersedn mineraloil at room
temperaturewere viewedwith a petrographicmicro-
scopeand crushedwith a dental ool. Fluid inclusions
within stage fluorite and stage I quartzwere both
found o be overpressured,ith the atterconsistently
yielding argerandmoreabundant aporbubbles han
the former. Fluid inclusionsn stage V anhydrite
yielded no vaporbubblesupon crushing.
Only preliminaryhomogenizationemperature ata
are available, owing to the problems of locating
workable-sized luid inclusions nd to the decrepi-
tation which commonlyoccursupon heating. Ho-
mogenizationemperatureswere recorded rom five
fluid inclusionsn fluorite from stage chalcedonic
quartzveins.The fluid nclusionsontain ariable iq-
uid to vaporratios,with vaporbubblesoccupying
to 50 vol percent.All homogenizedo liquid at widely
scattered emperaturesbetween 371 ø and 425øC.
The rangeof temperaturesndicateshat he fluid may
havebeenboilingand hat the true trapping emper-
ature is probablywell below 371øC.
Homogenization emperatureswere also ecorded
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
19/20
CRIPPLE CREEK DISTRICT, VEINS & BRECCIAS 1687
from seven luid inclusionsn quartz rom stage I
veins.These nclusions ccur mmediately utside f
a zoneof explosionexture.The liquid o vapor atio
is variable,with 5 to 50 vol percentbeingvapor.Six
of the fluid inclusionsomogenizedo liquid at an
averageemperature f 203.5øC,with values anging
from 198.6 ø to 210.6øC. The seventh inclusion ho-
mogenizedo iquidat 331.2øC.Apparentlyhe fluids
boiled weakly or effervesced;herefore, the true
temperatureof trapping s at, or slightlybelow,
198.6øC.
The vapor-dominatednclusionsn anhydrite rom
the stage V brecciamatrix illing neitherhomoge-
nizednor decrepitated ponheating. he few inclu-
sions ith a visibleiquidphase omogenizedo iquid
at temperatures elow hat which s required o form
anhydrite.From theseobservationst is evident hat
the fluid inclusionsmusthave eaked,perhaps n re-
sponseo the samestresses hich created he curved
cleavage lanes; few mayhavebeenpartially illed
by later fluids.
Discussion
Mineralizationn the Cripple Creek districtpost-
dated diatremedevelopment,ncluding hat at the
Cresson. arly mineralizingluidswere saline,sug-
gesting magmatic rigin. They were CO2 bearing,
and he rapping ressuresf 360 to 400 bars uggest
that irstboiling f the oresolutionsould avebegun
at 4,000 m depth (utilizinghydrostatic onditions).
It is apparent rom the fluid inclusion tudiesof the
Ajax vein system hat boilingof ore fluidsoccurred
throughout he entire vertical interval of 1,050 m.
There s no knownbottom o the gold-bearingein
system nd he argevertical ntervalof gold-bearing
veinandore luidboiling ndicateshat lashing f ore
fluidswith rapidprecipitation f metalswasnot the
ore-formingprocess t Cripple Creek. Continuous
boiling of ore fluids allows or volatile releaseand
leads o metalconcentrationn the remainingiquid.
The behaviorof stage fluid inclusions bove he
7,537-ft elevation Fig. 11) with an ncreasen min-
imum emperaturesppearso be the resultof energy
derived romsteam ondensation.he homogeniza-
tionof fluid nclusions,snoted bove, hangesbove
the 7,537-ft elevation. Above that elevation, fluid in-
clusions omogenize y halitedissolution,phenom-
enon that Roedder and Bodnar (1980) believed to
have esulted here nclusionsere rapped t higher
pressureshan hosenclusionsherehomogenization
occurred y vapordisappearance.he conditions f
fluid flow with high CO2 contentmay have ed to
steam-drivenoiling P.T. Holland,n prep.),yielding
ore throughout large vertical nterval.
CrippleCreekveinsare low (
8/19/2019 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado
20/20
1688 THOMPSON,TRIPPEL,AND DWELLEY
a matrix n the corezoneappearso havedeveloped
in upward-growingolumns sboiling,hydrofractur-
ing, and sulfate precipitationoccurredconcommi-
tantly.
Thus, the relationshipbetween veins and miner-
alizedhydrothermal reccias t Cripple Creek s in-
timate. Restrictionof fluid andgas low within a vein
system ed to shallowmineralizedhydrothermal
breccias.
Acknowledgments
The authorsgratefullyacknowledgehe coopera-
tion and supportof the Hecla Mining Corporation
and the TexasgulfMetalsCompany, ncludingSteve
Peters,StanCoombs,Lou Knight, CharlesMatteson,
Charles Brechtel, and Alex Paul. In addition, we
greatlyappreciate he cooperation nd financial s-
sistance rovidedby Gold Resources,nc., and New-
port Minerals, Inc., including Brian Hestor, Peter
Reed, and Ken Ennis.StandardOil Companyof Cal-
iforniaalsoprovided inancial ssistanceor the Globe
Hill researchhrough generousield-orientedhesis
grant.The costof supplying ndmaintainingluid n-
clusion analysisequipment was supported by the
EconomicGeologyDevelopmentFund at Colorado
StateUniversity.Our sincere hanksare alsoextended
to BenLeonardandRalphChristianat the U.S. Geo-
logicalSurvey or the useof laboratory acilities.
Reviewersof an earlier draft of the manuscript,
clarifiedour presentation.We are responsibleor any
shortcomings,owever, hat may remain.
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