Econom/cGeo/og

Vol. 80, 1985, pp. 1669-1688

Mineralized Veins and Brecciasof the Cripple Creek District, Colorado

TOMMY B. THOMPSON, ALAN D. TBIPPEL, AND PETEBC. DWELLEY*
Departmentof Earth Resources,
ColoradoStateUniversity,Ft. Collins,Colorado80523
Abstract

The CrippleCreekdistricthasyieldednearly21 milliontroyounces

ofgoldsinceitsdiscovery
in 1891. The orebodiesoccurasnarrowveinswithin PrecambrianandTertiary rocksand as
bulk tonnagedepositswithintectonicandhydrothermalbreccias.
The districtislocalizedwithinandadjacentto a27.9- to 29.3 ___
0.7-m.y.-oldnesteddiatremeintrusivecomplex.Two magmas,
phonoliticandalkalibasalticin composition,
generatedvolcanicflows,subvolcanic
intrusions,
andphreatomagmatic
breccias.
Magmamixingis suggested
by intermediate
composition
latite-phonolite
andsyenite.Subsidence
of the diatremecomplex
rocksisindicatedby (1) a thickfluvial-lacustrine
sedimentary
sequence
in the easternsubbasin,
(2) the presenceof carbonaceous
debris,ripple-laminated
rocks,and dessication
cracksin
sedimentary
rocksat depthsmorethan300 m belowthe presentsurface,(3) by the fracture
systems
nearthe diatremesubbasin
marginsthat reflectbasementrockinfluence,and(4) by
flat-dippingveinsnearintrusivebodiesor smallbrecciabodies(e.g.,the Cressondiatreme).
The vein depositsas exemplifiedby thoseof the Ajax mine cut Precambriancrystalline
rocksandTertiary rocksof the diatremecomplex.Within the Precambrianrocksthe veins
are radialto the marginsof the diatremesystemandare sheetedzoneswith rockdissolution
andopen-space
fillings.Wherethe veinscutthe CrippleCreekbreccia,theyareanirregular

anastomosing
fracturezone.Themajorveinsexhibitremarkable
verticalcontinuity,
extending
to morethan 1,000 m belowthe presentsurface.Vein-relatedhydrothermalalterationoccurs
in a narrowselvagethat extendsoutwardno morethanfive timesthe vein width. Secondary
K-feldspar,dolomite,roscoelite,andpyrite occurwithin aninner zoneadjacentto the veins,
whereas an outer zone containssericite, montmori!lonite,magnetite, minor secondary
K-feldspar,andpyrite.Thereis no expansion
of the alterationzonesin the upperlevelmine
exposures.

Five stagesof mineralsarerecognizedin the Ajaxmineveins:(1) quartz-fiuorite-adulariapyrite-(dolomite-marcasite),

(2) basemetals-quartz-pyrite,
(3) quartz-fluorite-pyrite-hematiterutile, (4) quartz-pyrite-rutile-calaverite-acanthite,
and(5) quartz-fluorite-dolomite.
The proportionsof eachstagevary within andbetweenveins,but the ore mineralogyis consistent
throughout
theverticalextentofthedeveloped
veinsystems.
Horizontally,goldvaluesranged
between0.5 and 1.0 oz Au per shortton.
Fluid inclusionanalyses
havedocumented
the presenceof earlystageI salinefluids(33>40 equiv.wt % NaC1)with the highersalinitiesfoundin the upper 300 m of the Ajax mine

levels;the fluidswereboilingandcontained
CO. Stage2 and3 fluidinclusions
exhibitprogressively
lowerhomogenization
temperatures,
andsalinities
aremarkedlylower(0-8.3 equiv.
wt % NaC1).The tellurideorewasdepositedfromweaklyboiling,dilutefluids(1.4-3.5 equiv.
wt % NaC1)with temperaturesbelow 150C.
The bulk tonnagedeposits,asexemplifiedby the GlobeHill area,consistof mineralized
tectonicandhydrothermal
brecciascuttingpyroxene-bearing
alkalitrachyte.Fourstructural
eventsoccurredat GlobeHill: (I) emplacement
ofhydrothermal
brecciabodiesalonga north-

west-trending
1,800-by 700-mzone;(II) intersecting
tectonic
adjustments
alongsteepvariablestrikezonesonthewesternmarginofthe stage1 breccias;
(III) intrusivebrecciaemplacement
at the major stageII fault intersection;and (IV) hydrothermalbrecciationcenteredto the
immediateeastof the GlobeHill pit andcharacterized
by a matrixconsisting
of anhydrite,
carbonate,
fluorite,pyrite,andbasemetalsulfides.
Two hydrothermaleventsgeneratedgold-silvermineralizationand associated
wall-rock
alterationin the bulk tonnagedeposits.The preciousandbasemetalsoccurwith alteration
productsin brecciaclastsor in matrixmineralswithinthe hydrothermal
andtectonicbreccias.
The fluidsresponsible
for alteration-mineralization
wereboilingasindicatedby wideranges
of fillingtemperatures
in fluidinclusions
of the samemineralgrain,extensive
development
of "explosion"texturein quartzandcelestite,andlargevariationsof liquid/vaporratiosin
fluidinclusions
withinindividualcrystalgrowthzones.Temperatures
werebelow200Cas
indicatedby minimumfillingvalues.Cappingof boilingshallowhydrothermal
fluidsappears
* Presentaddress:FMC Corporation,1801 CaliforniaStreet, Denver, Colorado80202.
0361-0128/85/448/1669-2052.50

1669

1670

THOMPSON,
TRIPPEL,
ANDDWELLEY

to havebeenenhanced
by the alkalitrachyteporphyryintrusionat GlobeHill, whichacted

asa permeability
barriertoupward-migrating
fluids.
Vapor-dominated
fluidsdeveloped
overpressuring,
leadingto hydrothermal
brecciation
andlow-gradegolddeposits.
On the other
hand,the veinsystems
in the CrippleCreekdistrictformedalongstructures
opento the
surface;hence,hydrothermalbrecciationdid not occur.
Introduction

in a southwest-striking
palcovalley
immediatelysouth
of
Victor
(Tobey,
1969;
Wobus
et
al., 1976)thatapSINCE
the1891discovery
ofgoldintheCrippleCreek
pears
to
have
headed
on
the
Cripple
Creek volcanic
district,almost21 milliontroy ounceshavebeenreerosionand/orvolcanicactivity
covered(Gott et al., 1967). The orebodiesoccuras complex.Subsequent
narrowveinswithin PrecambrianandTertiaryrocks seemsto have removedany trace of suchfluvial dealthoughsomeorebodieswere localizedwithin brec- positsin the immediateCripple Creek district.Ash
cia bodies.A reconnaissance
geochemical
program flowsof latite porphyryoverlyingthe conglomerate
by the U.S. GeologicalSurvey(Gott et al., 1967, depositsin the palcovalleyto the southwestof Victor
1969)indicatedtherewaspotentialfor bulktonnage were thoughtby Tobey (1969) to havebeen derived
deposits
withinthe district.The development
of one from a Cripple Creek eruptivecenter;similarrocks
not beenrecognizedwithin the Cripple Creek
suchdepositby The SilverStateMiningCorporation have
district.
(Lewis,1982) atteststo the viabilityof suchdeposits.
The Cripple Creek volcaniccomplexconsists
of a
We intendto presentdatalinkingthe vein andbulk
large
mass
ofbreccia
intruded
by
bodies
ofphonolite,
tonnagedeposits
anddescribing
theirrelationships
to
latite-phonolite,
syenite,andalkalibasalt(Fig. 1). The
brecciasof variousorigins.
brecciafills an irregularbasin(Loughlinand KoschPreviousand PresentInvestigations
mann,1935) that appearsto haveat leastthree subbasins.
The subbasins
are indicatedby the presence
Numerousinvestigators
haveworkedin the Cripple
within the
Creek districtand the publishedresultsare volumi- of Precambrianbasementrockexposures
nous.The earliestaccounts(CrossandPenrose,1895; brecciacomplex(Fig. 1). The brecciais knownto be
Lindgren and Ransome,1906) pictured the district at least1,000 m thick.Alongthe easternandnorthern
asan explosivevolcaniccraterin Precambrianrocks. partsof the CrippleCreekbasin,lacustrineandfluvial
rocksare interbeddedwith the Cripple
Later (Loughlinand Koschmann,
1935), the role of sedimentary
subsidence
in formingsomeof the brecciacomplex Creekbreccia(Figs.1 and2).
wasrecognized.The controlsof basementstructures The Cripple Creek breccia is a heterolithic unit
of angularto subangular
fragments(Fig. 3
in localizingvein systemswas clearly defined by composed
Koschmann
(1949) andthe occurrenceof oresat con- A, B, andC) of PrecambrianandTertiary rocks.The
siderable depths was documented by Loughlin brecciahasinterfragment(I):fragment(F) ratiosthat
(1927). A wealthof minemapsfor the districtis con- are high (>1:1), with a well-sortedmatrixconsisting
tained in an unpublishedU.S. GeologicalSurvey of quartz, microcline,and rock fragments0.5 to
Open-FileReport (Koschmann
andLoughlin,1965). 2.0 mmin diameter.Carbonizedtree (conifer)trunks
Detailed accounts of vein- and breccia-hosted ore deand local coaly layers are reported in the breccia
positmineralogyhavebeenprovidedby Lindgrenand (LindgrenandRansome,1906, p. 31) at depthsof as
great as 800 ft (244 m). The brecciais massivein
Ransome(1906).
for shortdistances
The presentreportsummarizes
field andlaboratory outcropandexhibitsstratification
studiesinitiatedin the CrippleCreek districtin 1982 whenpresent.In the easternhalfof the CrippleCreek
by graduatestudentsandthe seniorauthorfromCol- basin complex, the Cripple Creek breccia is inoradoStateUniversity.Studiesto date have focused terbeddedwith lacustrineand fluvial sedimentary
appearto havebeentransported
on vein-golddepositsin the Ajaxmine (P.C.D.) (Fig. rocks.The sediments
into a shallowlacustrineenviron1), bulktonnagebreccia-hosted
golddeposits
at Globe by fluvialprocesses
Hill (A.D.T.) (Fig. 1), and on district-widegeologic ment.Ripple-laminatedsiltstones(Fig. 3D), leaf imprints,dessication
cracks,andanimalfootprintsattest
mapping(T.B.T.).
to a shallowbodyof standingwater.Localoccurrences
Regionaland Local Geology
of similardepositsare knownthroughoutthe entire
The Cripple Creek district(Fig. 1) is localizedin basinarea.Often the lacustrinerocksare overlainby
a compressionally
formedLaramidedomeat contacts typicalCripple Creek breccia,and fragmentsof the
between Precambrian
intrusive and metavolcanic
sedimentaryrocksare presentin the breccia.
bodies(Fig. 1; Wobuset al., 1976). During the LarThe body of Cripple Creek breccia is known
amideuplift,all PaleozoicandMesozoicsedimentary (Loughlinand Koschmann,1935) to occupya basin
rocks were eroded from the dome centered in the
onthe eastwith shallow-dipping
walls(Fig.2) whereas
Cripple Creek area.Oligoceneconglomerateoccurs the westernhalf of the basinhassteepwallsthat 1o-

CRIPPLE
CREEKDISTPdCT,
VEINS& BRECCIAS

1671

YPP

/++++++++++++++++++++++

+ ++++++++++++++++++++*+++++
++++++++++++++++++++++
+ +++++++
++++++++Xd+ + + + + + + + + + +

++++++.+.+++++++++++++%+++++++++
++
+++++++++++++++
+++++++

+++++++
+

++++
+

+
+

+++++++++++

,+,++ Xgd +++++++

+ +

v /+
+
+

.
I

0.5

I Km

VI C TOt?

+
+

+
+

+
+

+
+

+
+

+
+

+
+

+
+

+
+

+
+

'.':':::::::t';'""
'

Geology mapped in 1983 with

+++[+++++
=0 partsadapted
fromLindgren
,
I

____J

ond Ransome
(1906) and

Louhlin
and
Koschmann(1935)

EXPLANATION
SYMBOLS
ROCK

UNITS

.....

- T] Alkali
basalt

Dike
--

......_.

located, dotted where concealed

:TJ"'Syen,te

YI Pikes
Peak
Granite

;T- Latitephonolite
?.,'. Phonolite
--

Fault
&

Ts, lacustrine and fluvial

Breccla

o VY''-
1 Cripple
Creek
Quartz
Monzonite
'-'/ Line of cross sechon

....lb....Ja
i x++r-1G
....
diorite/_/////////Z....f hydroth

Cripple
Creek
Breccia
facies

Vein

. Contact, dashed where approximately

::X: B,otite
gneiss

////////bod,es
B

Shaft

FIG. 1. Geologicmap of the Cripple Creek district, Colorado.

cally (Fig. g) dip beneathoverhangingPrecambrian flaringmasswhichappearsto haveitsdeepestextent

countryrockonthe southwest.
The overallgeometry in the vicinity of the Cressondiatreme(Figs. 1 and
heldupby Precambrian
of the CrippleCreekbrecciais that of an upward- 2). Localridgesandbenches

1672

THOMPSON, TRIPPEL, AND DWELLEY

A

Bend
insection

E leva tion

(m)
3.,150

2,650

.'....

+ *'..-

' + + + + + +
1,650

..

.... -,

+ + .i-'""

-I

+ + +.+ + x

/+'----A

...',..... , i
:::::::::::::::::::::::::::

'/:':':':':':':':':':':

+ + + +

/.':'"",',
t*'Z.

I + Xgd++++lL+s++ *- + + + + *

lO. . CooIonic
crosssection
A-A'across
theCrippleCreekdiatremecomplex.
Symbols
s3measthosein iare ].

Phoneliteis the mostwidespreadigneousrock in

countryrock extendinto the basin,suggesting
that
irregularfault blockswere responsiblefor the floor the CrippleCreekdistrict.It occursnotonlywithin
ontowhichthe brecciaaccumulated.The widespread thebasinbut up to 7 km awayfromthe districtin the
occurrences of carbonaceous debris and lacustrine-

fluvialsedimentaryrocksat depthin the brecciamass

clearlydocumenta subsidence
basin.Explosivevolcanismoccurredduringshortintervals,but the basin
floor was collapsingand trapping the bulk of the
brecciadeposits.Shallowbodiesof water were present, into which ashdepositsand fiuviallytransported
sedimentswere deposited.
Numerousigneousmasses
haveintrudedthe Cripple Creek brecciaand Precambriancountryrocks.
Theseoccurastabular,upward-flaring,or stocklike
bodieswhich may havehad eruptivedeposits.They
appearto representa magmaseriesbeginningwith
phoneliteandfollowedsequentiallyby latite-phonolite, syenite, and alkali basalts(Fig. 4). Chemical
analyses
(LindgrenandRansome,1906) for the Cripple Creek igneousrocksappearto clusterin three
groups:phonelites,
latite-phonolites
andsyenites,
and
alkalibasalts.The trendsexhibitedby theserocksare
not normaldifferentiationtrendsandsuggestthat two
magmas,representedby the phonelitesandalkalibasalts,mayhavemixedto formthe intermediatelatitephonelitesand syenites.
Potassium-argon
dateson aegirine-augitefor syenite (McDowell,1966) suggestthat the rockswere

crystallized34 +_1 m.y. agowhiletwo sanidinesamples from phonelitewere datedat 27.9 +_0.7 m.y.
and29.3 ___
0.7 m.y.(Webuset al., 1976).Thesedates
andthe bimodalalkalicmagmasuiteindicatethat the
CrippleCreekmagmas
maybe associated
with early
stagesof extensional
tectonism,representedby inceptionof collapsing
basinsalongthe RioGranderift.
Similarbimodalmagmatism
is representedin the San
Juanvolcanicprovinceto the southwest
andat the
ClimaxandHendersonmolybdenumdepositsto the
north (Shannonet al., 1984).

formofdikes,ofupward-flaring
domeswithlocalvolcanicoutpourings,
andastabular,fiat-dipping
bodies.
The rockis light grayto beigein colorandcontains
1 to 3 percentsmall(<2 mm)phenocrysts
ofsanidine.
LindgrenandRansome(1906, p. 67) reportsodic
sanidine,
nepheline,analcite,aegirine-augite,
andsodalite asthe modalconstituentsin the trachytic-textured,holecrystalline
phonelite.

Latite-phonolite
wasrecognized
by Lindgrenand
Ransome
(1906, p. 68) asa distinctlyporphyriticalkalicgroupof rockswith orthoclase,
oligoclase,
and
sodicpyroxenephenocrysts
up to 1 cmin size(Fig.
3E).Thelatite-phonolite
occursasdikesandfiattabularbodiesintrudingtheCrippleCreekbreccia(Figs.
1 and2). It mayoccuraslocalflowsinterbedded
with
the breccia as well.

Syeniteoccursas dikesand stocksintrudingthe

CrippleCreekbreccia(Figs.1 and2). It is a finegrainedrockwith orthoclase,
aegirine,hornblende,
biotite, andminorfeldspathoids
(LindgrenandRansome, 1906). Apatite, sphene,and magnetiteare
commonaccessories
in the syeniteaswell asin the
phoneliteandlatite-phonolite.
Alkali basaltsof at leastfour typeshavebeen re-

portedin the CrippleCreekcomplex(Lindgrenand

Ransome,1906). They range from aphanitic to

stronglyporphyriticandhavebeentermedtrachydolerite,vogesite,monchiquite,
andmelilitebasalt.
Somevarietiesare distinctlyamygdaloidal
(Fig. 3F).
Furtherworkis neededto documenttheir mineralogy

and distributionclearly.The alkalibasaltsoccuras

dikescuttingall other rocksof the Cripple Creek
complex.They appearto overlapin agewith an unusualbreccia,the "Cressonblowout"(Loughlinand
Koschmann,
1935;Figs.1 and2), composed
of allthe
rock typesin the complex,includingPrecambrian

dPPLECREEK
DISTRICT,
VEINS6 BPdCCIAS

1673

FI. 3. A. CrippleCreekbreeeiaexhibitingheterolithienatureof fragments.

andhighinterfragment/
fragmentratio.B. CrippleCreekbreeeiawith phonolite(topcenter)fragments
in a granularquartzmicroclinematrix derivedfrom Precambriancrystallinerocks.C. Cripple Creek breeeiawith minor
sehistosie
fragments
(bottomcenter)andmoderateinterfragment/fragment
ratio.D. Ripple-laminated
lacustrinerock (view normalto bedding)from the easternsubbasin
in the Cripple Creek diatreme.
E. Latite-phonolite
prophyrywith plagioelase
andorthoelase
phenoerysts.
F. Amygdaloidai
alkalibasalt.
Amygdularfillingsare calciteand minorfluorite.

rocks.The rockhasa significant

component
of alkali cuttingbasaltdikes,suggests
that a basalticbodyat
basaltfragments
but is cutby steepto fiatbodiesof depthwasthe sourceof the energyessentialto the
basalt(Fig. 2). The blowoutalsocontainscarbonized development
of the brecciabody.The Cresson
blowtree fragments
at depth,clearlyindicating
that sub- out bifurcatesat depth (Loughlinand Koschmann,
sidence
wasa majorfactorin itsformation.
Themajor 1935; Fig. 2). Its geometry,thoroughmixingofrock
basalticcomponentof the breccia,aswell as cross- types,andsubsidence
requirementssuggestthat the

1674

THOMPSON,TRIPPEL,AND DWELLEY

LindgrenandRansome
(1906),LoughlinandKoschmann(1935), and Koschmann
(1949). We will not
reiteratetheir findingsotherthanto notethe distributionandtypesof deposits.
Figure1 showsthe general distribution of veins in the district. The veins oc-

cur in distinctbeltsthat overlieburied ridgesof Precambrianrock beneaththe Cripple Creek breccia

(Fig.2), occurmarginalto stocks(Fig.2), occurparallelto steepdiatremewalls(Figs.,1 and2), or overlie

basement rock contacts that extend beneath the

CrippleCreekbreccia(Fig. 1). All vein systems

appearto be extensively
developedat the surfacebut
becomefocusedinto majorstructures
below600 m
(Koschmann,
1949).Thisdiscussion
will focusonvein
depositsof the Ajax mine in the areaimmediately
No20

K20

FIG. 4. Triangularvariationdiagramfor the Cripple Creek

magmaseries.Two variationcurvesare shownby CaO-K20-Na20
(solid symbols)and SiO2-K20 + Na20-FeO3 + FeO + CaO
+ MgO (opensymbols).The arrowspoint in the directionof decreasingage. Chemical data are from Lindgren and Ransome
(1906).

north of Victor and on bulk tonnagedepositsin the

vicinityof GlobeHill (Fig. 1).
Veins of the Ajax Mine

The Ajax vein systemis exposedover a vertical

rangeof 1,025 m with no apparentchangein ore
tenor. Wall-rock alteration, vein mineralogyand
paragenesis,
and fluid inclusionstudieswere conducted(Dwelley,1984) in an attemptto definethe
significant
characteristics
of fluidsresponsible
forore
deposition.The veinsin the Ajax cut Precambrian
rocksaswellasCrippleCreekbreccia,withsignificant
changes
in boththe extentof alterationandin vein
formbetweenthe two wall-rocktypes.The Ajaxmine
beganproductionin 1895 andproduced247,917 oz
of goldbetween1895 and1921 (Henderson,
1926).
The total productionto date hasbeen in excessof

bodyisa diatremegeneratedwhenhotbasalticmagma
contactedgroundwaterin the deeperpartof the main
Cripple Creek basin.
The overallgeometryof the Cripple Creekbasin,
alongwith itscontents,suggests
that the complexhistory involvedperiodicexplosivevolcanismand fluidizationactivityaccompanied
by significantsubsidenceandigneousintrusions.
The districtiscentered 700,000 oz with vein gradesof 0.60 to 1.04 oz Au
over a gravityandmagneticlow, interpreted(Klein- per ton.
kopf et al., 1970) to reflecta largebatholithicmass
at depth.The systemis bestdescribedasa complex Vein mineralogy
diatremewith relictsof tuff-ringmaterialin isolated Five stagesof mineralsare recognizedin the Ajax
bodiesawayfromthe source.The drapedlacustrine mine veins(Fig. 5). The proportionsof each stage
andfluvialsedimentary
rocksof the easternbasinre- varybetweenindividualveinsaswell aswithineach
mainedintacteventhoughthey subsided
asmuchas
300 m, a featurerecognized
worldwidein manydiatremes(Lorenz,1973; Lorenzet al., 1970). Accretionarylapilliupto 8 mmin diameterwererecognized
by LindgrenandRansome(1906, p. 99), whodid not
knowthe significance
of suchproducts.The lack of
fine silt- or clay-sizematrix in the Cripple Creek
brecciaarguesfor selectivewinnowing,accretionary
development,
andfineashexpulsion
duringepisodes
QUARTZ

....

FLUORITE

--

ADULARIA

DOLOMITE

-- --

PYRITE

HEMATITE

RUTIL E

SPHALERITE

--

GALENA

of fiuidizationandsubsidence
of the CrippleCreek
diatreme.Experimental
studies(Woolsey
et al., 1975)
suggest
that fiuidizationprocesses
cangenerate,on a
laboratory
scale,allof thefeaturesseenin theCripple

MARCASITE
CHALCOPYRITE
PYRRHOTITE
CALAVERITE
ACANTHiTE

....

Creek diatreme.
VOLUME %

Mineral Deposits

The renownedCripple Creek depositshave been

describedin detail by Crossand Penrose(1895),

FIG. 5. Paragenetic
diagramfor the BobtailandNewmarket
veins,Ajax mine (Dwelley, 1984).

CRIPPLE CREEK DISTRICT, VEINS & BRECCIAS

o

2 ft.

1675

generatedvuggy fracture zones within which the

open-spacevein mineralswere precipitated.Gold/
silver ratiosvary between 23:1 and 0.20:1 with no
consistentvertical 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
K-feldspar,dolomite,roscoelite(vanadiumbearingmica),andpyrite and an outer zonetypified
by sericite, montmorillonite,magnetite, minor secondaryK-feldspar,andpyrite. There is no expansion
of the alterationzonesas the upper levels of mine
exposures
are reached;however,the Cripple Creek
breccia has more extensive alteration

due to its in-

herentpermeability(Fig. 6).
0
I

2 ft.
i

openvug

FIG. 6. Compositecrosssections,lookingnorth, of the Newmarket(2600 level) andbreccia-hosted

(1600 level) veins.Note
the restrictedvein-relatedalterationhaloin the Ajaxgranite(informal mine nomenclaturefor the Precambriangranodiorite)
comparedto the alterationhalowherethe CrippleCreekbreccia
hostsvein mineralization(afterDwelley, 1984).

vein; all five stagesare seldompresentin any one

vein. Concurrentfracture openingand minor brecciation of vein mineralsoccur throughoutthe mineralizingstages.Two veins,the NewmarketandBobtail, arepresentthroughmostof the Ajaxminelevels.
The Newmarketcutsnot only Precambriangranodiorite (Ajax graniteof local terminology)(Fig. 6) but
the Cripple Creek breccia,too. Within the granodi-

E XPLANA
borren

fracture

orite the veinsare narrow, well-defined sheetedzones

TION

vein-reloted
alteration

whereasin the Cripple Creek brecciathey become

phonolite
dike
an anastomosing
set of irregular branchingfractures
apen vug
:/F- Ajax
,ranitc
(Fig. 6). The Bobtailvein (Fig. 7) displays
the typical
Cripple Creek sheetedvein structuresin the PrecamFIG. 7. Compositecrosssections,lookingnorthwest,of the
brian granodioriteaswell asin the contactzoneswith Bobtail
vein (2000 and3350 levels).Note that veinsdevelopadTertiary dikes.Typically,dissolutionof the granodi- jacentto dikes(2000 level) or completelyindependentof them
orite (Fig. 8A) or phonolitedikesalongfracturezones (3350 level) (after Dwelley, 1984).
;"-'.", '

mineralized

fracture

1676

THOMPSON,TR/PPEL,AND DWELLEY

FIG. 8. A. Dissolutioncavitiesin Precambriangranodiorite

adjacentto faultsin the Ajaxmine.SmallroundholesareXRD

sample
sites.B.Vein-related
alteration,
Ajaxmine.Vein(farright)
with biotite-feldspar
destructivealterationselvage,grading
abruptly
intobiotite-plagioclase
stable(leftofscale)Precambrian
granodiorite.
C. Photomicrograph
illustrating
"explosion"
texture
withinan annularzonein quartz.Marginof quartzcrystalis intergrownwith fluorite.Fieldof viewis 1.0 mmwide.

aturesfor stageI fluidinclusions

rangefrom206 to
510C.The largevariationis dueto widerangesof
Primaryfluid inclusionsfrom stages1, 2, 3, and 4 fillingtemperatures
in the shallowlevelsof the vein
wereanalyzedby heatingandfreezingstudies.Quartz system.
Stages2 and3 fluidinclusions
exhibitprogressively
(four stages)and fluorite (stages1 and 3) are widetemperatures,
andsalinities
are
spreadin the veins,and locally,stage2 sphaleriteis lowerhomogenization
sufficientlycoarsegrainedfor study.Figure 10 sum- markedlylower, rangingbetween 0 and 8.3 equiv.
marizesby stageand elevationthe homogenization wt percentNaCI (Dwelley, 1984). Stage4 quartz,
metalstage,exhibitsa fillingtemperature
temperaturesfor the Ajax veins.Stage1 fluidswere theprecious
salinewith equivalentNaCI valuesrangingfrom 33 rangebetween105 and 159C,with a meanvalue
percenton the 2,055-m level to greaterthan 40 per- of 140C.Salinityvaluesrangebetween1.4 and3.5
cent in the upper 300 m of the mine. Weak boiling equiv.wt percentNaCI. Fluidsof stages2, 3, and4
isindicatedby theincreased
salinities,
variableliquid/ were weaklyboiling.A plot of meanand minimum
temperaturesfor fluidsof stages1
vaporratiosin individualgrowthzonesof quartz,and homogenization
temperatures
thewiderangeofhomogenization
temperatures.
Most and3 (Fig. 11) illustratesthe decreasing
stage1 fluidinclusions
containdaughterhaliteanda with time. There is, however, an increasein the minfew exhibitincreasedsalinitiesby the presenceof syl- imumtemperatureabovethe 7,537-ft elevationfor
to the contactzone
vite and hematite.In the upper mine levels,homog- stages1 and3. Thiscorresponds
enizationtemperatures
in mostsamples
wereby halite (Fig. 12) betweenthe CrippleCreekbrecciaandthe
dissolutionrather than by vapor homogenization; Precambriangranodiorite.Higher temperaturesare
however,samples
belowthe 2,300-mlevel (7,777 t presentin the CrippleCreekbreccia-hosted
portions
Fluid inclusion studies

elevation;Fig. 10) homogenizedby disappearance

of
the vaporphaseafterhalitedissolution.
A doublemeniscusis exhibitedin the largerfluid inclusion
vapor
bubbles;freezingstudiesindicatedthe presenceof
CO2 hydratewith clathratemeltingpointsof 8 to
9C (Dwelley, 1984). The homogenizationtemper-

of the vein system.

InternalCO2pressures
for the variousstageshave
beenestimated
by freezingstudies.Stage1 fluidsare
NaCl-saturated
underfreezingconditions;
therefore,
internalCO2 pressurewithin the inclusionsis estimatedat 27 bars(Collins,1979). Internal CO2 pres-

CRIPPLE
CREEKDISTRICT,VEINS& BRECCIAS

1677

Inner zone

Biotite totally replaced by pyrite, magnetite,dolomite, secondaryorthoclase,

roscoelite-sericite, minor fluorite

Plagioclasereplaced by montmorillonite-sericite-roscoelite,
minor carbonate
Quartz unaltered to total recrystallizationnear vein

Microclinerimmed and veined by adularia--up to 80 percent

Outer
Outer

limit I to 3X vein width

zone

Biotite replaced by up to 95 percent sericite, secondary orthoclase,

magnetite, pyrite, and carbonate
Plagioclasereplaced by up to 95 percent montmorillonite-sedcite,minor
carbonate

Microclineand quartz--generally fresh, microclineweakly veined by

adularia and quartz
Outer
Deuteric

limit I to 5X vein width

zone

"Fresh rock," biotite weakly replaced by chlorite and magnetite

Plagioclaseup to 50 percent covered by sericite-montmodllonite

FIG. 9. Summarydiagramof vein-relatedalterationin the Ajax mine (after Dwelley, 1984).

sure in stage3 and 4 fluid inclusionsis estimatedat

explore the vein potential at depth beneath Globe

44 bars(Collins,1979) basedon clathratemelting Hill. The tunnel is about 1,280 m long and extends
temperatures.
Trappingpressures
for stage4 precious from PovertyGulch eastwardto the PlymouthRock
metalsdeposition
were estimatedfromunpublished i shaft.Althoughno high-gradeore wasdiscovered,
curves(R. J. Bodnarand C. A. Kuehn,unpub.data) highlyalteredand oxidizedbrecciacontainingtrace
for H20-rich inclusions.The trappingpressuresand low-gradegold was noted over a considerable
rangedbetween360 and 400 bars.
distance(Argall, 1905).
By 1905 three smallopen pits were developedto
Globe Hill Ore Deposits
a depth of 50 m alongintersectingveinsand strucGlobe Hill (elevation,3,183 m) is locatedin the tures.Theseincludedthe Globe and Deerhornpits,
northernsubbasin
of the CrippleCreek district(Fig. near the summitof Globe Hill, and the Ironcladpit,
1). The Globe Hill area is characterizedby hydro- half a kilometer to the southeast. From 1916 to the
thermal and tectonicbrecciationdevelopedin Ter- mid 1970sthere waslittle productionfrom the area.
tiary igneousrocksthat postdatethe Cripple Creek Numerousexplorationprogramswere conductedto
breccia.Thesebrecciasare extensivelyalteredand evaluatethe low-grademineralizationby meansof
oxidizedand hostseverallarge tonnage,low-grade bulk sampling,trenching,anddrilling.
gold deposits.
From 1977 to 1981 Newport Minerals,Inc., a subProductionfrom the area beganin 1891. Incom- sidiaryof Gold Resources,Inc., mined 680,000 tons
plete recordsshowthat about80,000 oz of goldhave of low-gradeore from the Globe Hill pit, which is
beenproducedfromthe minesnearthe crestof Globe centeredon the old Globe and Deerhornpits (Fig.
Hill, excludingthe mostrecent open-pitoperation. 13). The operationwas halted in 1981 to allow TexEarly productionwas concentratedin high-grade asgulf,Inc., a joint-venturepartner,to conducta deveins and fault structures in the Deerhorn, Summit, tailedevaluationandfeasibilitystudyon the deposit.
and PlymouthRock 1 mines(Fig. 13), as well asin The evaluationincludeddrilling,trenching,sampling,
the shortGlobetunnelwhichintersectedthe upper and mapping.
level of the Deerhorn mine.
Since March 1982, the Silver State Mining CorBetween1899 and 1902 the Chicagoand Cripple porationhasoperateda 1,000 ton per day open pit
Creek tunnel (elevation,2,957 m) was extendedto located at the old Ironclad pit (Lewis, 1982). The

1678

THOMPSON, TRIPPEL, AND DWELLEY

AJAX

VEIN

SYSTEM

HOMOG[NIZATION

414

O)

TEMPRATuR[

RANGIS

IO

114-

84

o-----

-P-

---o

8170--

....

IO

'0

7777-

Nte:

Number over range b4r IndIcolel

number of incluliOfie efialyzed

,

7256 -

3
O-- ,I--0

0-------7

8985

....

o..4
ZO

.-o

H4

m
IOO

ZOO

300

400

500

TEMPERATURE

FIG. 10. Homogenization

temperature
rangesin the Ajaxveinsby minelevelandstage(after
Dwelley, 1984).

alkalitrachyte(referredtoaslatitegeologyandmineralization
is asyet unstudied,
but pyroxene-bearing
districtwide).Visibleflowtexturesareunbrief visitsby the authorsindicatemanysimilarities phonolite
common;however,the aphaniticgroundmass
often
to featuresexposedin the GlobeHill pit.
microscopic
flowlineations
aroundthepheNumerousreports and publicationsdiscussthe displays
The extentandgeometryof thisintrusion
Globe Hill area, mostnotableof which are Crossand nocrysts.
Penrose(1895), Argall (1905, 1908), Lindgrenand is not known, but examinationof nearby prospect
indicates
thatsimilarintrusions,
andequivalent
Ransome(1906), Keener(1962), andPeters(1982). dumps
are widespread.
Theserocksintrudethe
This paperpresentsnew informationfrom ongoing extrusions,
studieson the interrelationshipof structure,altera- CrippleCreekbrecciaof thenorthernsubbasin.
The alkalitrachyteporphyryaverages
lessthan15
tion, andmineralizationof the deposits.
modalpercentpotashfeldsparphenocrysts
lessthan
Host lithology
2 mm in size. An aphanitic,trachyticgroundmass
and pyroxenelessthan
The Globe Hill depositis hostedin porphyritic consistsof alkali-feldspars
subvolcanic
intrusiverock,dominantlycompos,ed
of 0.05 mm in size. Core from a diamond drill hole im-

CRIPPLECREEKDISTRICT,VEIHS6, BRECCIAS
AJAX
MEAN

AND

MINIMUM

VEIN

1679

SYSTEM

HOMOGENIZATION

TEMPERATURES

9688-2954 m

9414

--

8662--

8485-

8157 EXPLANATION

--

Stage I

minimum

Stage I

mean

0----0

7777-

Stage 3 minimum

e- ---...

Stage 3 mean

/
7537

72587137-

6985-

67422055m

I00

200

300
TEMPERATURE

400

500

oc

FIG. 11. Meanandminimumhomogenization

temperatures
forAjaxveins,stages
1 and3 at different
elevations.
Note decreasing
temperatures
betweenstagesaswell astemperaturereversals
abovethe
7,537-ft elevation.

mediatelynorthof the pit doesshowtexturalgrada- alkalitrachyte,alkalisyenite,mafic-richalkalisyenite,

tionsat depthto granularalkalisyenite.
basalt (?), and Precambriangranite also occur
Local portions of the subvolcanicmasscontain throughoutthe hostintrusive.
abundant
smallfragments
of texturallydifferentalkali Structure

trachyte.Someof thesefragments
exhibittrachytic
flow orientationsof phenocrystsand others are
Four separatestructuraleventsoccurred at Globe
aphanitic.A few fragmentscomposed
of mafic-rich Hill (Table 1). The earliestevent (stage1) createda

1680

THOMPSON,TRIPPEL,AND DWELLEY

BOBTAIL

VEIN

N. 40E

CROSS

SECTION

looking
N.50w

shaft

:400'

collar

10105

elevation:

ft.

Axg
EXPLANATION

O, ,
.*......:.. -.

--

3350L

elevation:

phonolite

dike

Breccia- Ajax granite contact

,

--

40,0 ft.

6742

vein

ft.

FIG. 12. Crosssectionthroughthe Bobtailvein. Note vein-dikerelationshipand the fiat contact

between Cripple Creek breccia (Bx) and Precambriangranodiorite(Axg) at the 2000 level.

zoneof hydrothermal
brecciabodieswhichwerelater
cut by a seriesof tectonicstructures(stage2). Intrusivebreccia(stage3), probablydike- or pipelike in

form, then invadeda major stage2 shearzone, and a

separatehydrothermalbrecciabody(stage4) formed
withinthe stageI zone.Minorreadjustment
occurred

CRIPPLE CREEK DISTRICT, VEINS & BRECCI.4S

1681

Globe Hill (elev.3183m)

-i-

r]Summit

Stage IV

A'

Explanation:

[] Deerhorn

shear

zone

fault

hydrothermal

breccia

hydrothermal

crackle

'.

60%
/

vein

76 m

to

Plymouth Rock
No.1 shaft

Stage
I

chal-celest-py
(matrix filling),
ser-chl-carb-

rnont-py (alt)

Stage
I

&

50m

Stage
II
Stage
IV

A
3150m.

Stage
IV

3100 m.

3050

FIG. 13. Generalizedmapandsectionshowingstructure,mineralization,andalterationat the Globe

Hill area.

chl-ser-py-qtz (alt)
ser-mont-carb-py
(alt)
anh-carb-celest-

fluor (matrix
filling)
rnont-chal-hern

(matrix filling),
rnont-qtz-lirn(alt)

1682
TABLE

THOMPSON, TRIPPEL, AND DWELLEY

1.

HydrothermalMineralizationandAlterationAssociated
with the Major StructuralStagesof the Globe Hill Area
Stage I -

Structures

Hydrothermalbreccias
alongearly tectonic

Stage II

Stage III
Intrusive

Tectonic faults, shear

breccia

Stage IV

Hydrothermalbreccias

zones, etc.

structures

Mineralogy

Breccia matrix and veins:

chalcedony,quartz,
celestite, fluorite,
carbonate,pyrite,
sphalerite,galena,
chalcopyrite,
pyrrhotite, specularite,
rutile, calaverite,
sericite,
montmorillonite

Alteration

Brecciafragmentsand
adjacentwall rock:
sericite, chlorite,
carbonate,

montmorillonite,pyrite,
quartz, apatite

Surroundingwall rock:
chlorite, sericite,
pyrite, quartz,
montmorillonite,
apatite

Veins: quartz, eelestite,

fluorite, pyrite,

Granular to rock flour

matrix:

no

mineralization

carbonate, adularia,

galena,sphalerite,
ealaverite, ehaleopyrite,

core breccia

matrix:anhydrite,
carbonate, celestite,

fluorite,pyrite, galena,
sphalerite,
chalcopyrite,pyrrhotite
Peripheral breccia matrix

sericite

Disseminated

Central

outward

from gangue-free

and veins:

structures: pyrite,

montmorillonite,

sphalerite,galena,
ehaleopyrite,
pyrrhotite, speeularite,
ealaverite(?)

fluorite, opal,
chalcedony,hematite
(spherules),fluorite
Matrix and fragments:

Wall rock adjacentto

veins: quartz, sericite,
pyrite

Wall rock adjacentto

gangue-freestructures:

chlorite, sericite,

Fragmentsof central core

breccia:pyrite, fluorite,

specularitc,hematite
(spherules),quartz

Fragmentsof peripheral

carbonate
breccia and wall rock

sericite,

adjacentto veins:

montmorillonite,

carbonate,pyrite,

montmorillonite,
limonite, hematite,

quartz, apatite

quartz

Mineralsin assemblages
are listedin decreasingorder of abundance

alongthe stage2 structuresfollowingthe four major bodies.Vertically,mostbodiesprobablygradeupstructuralevents.The followingdiscussion

detailsthe ward from a steepfault or vein to crackledandbrecnature of the structures associated with each event.

StageI: Hydrothermalbreccias:The earliesthy-

ciated wall rock.

Mostbrecciafragmentsrangein sizefrom 1 mmto

3 cm; they are generallymonolithic,clearly rotated
or as coalescingirregular bodies in a northwest- with subangular
to subrounded
shapes,poorlysorted,
trendingzonewhichmeasures
about1,800 by 700 m andgradefrom beingfragmentto matrixsupported,
in surfacearea (Fig. 1). Two largeclustersof hydro- with interfragment/fragmentratios that are low
thermal breccia bodies are found, one at the Globe (<1:3) to high (>1:1). The matrixrangesfrom rock
Hill pit andthe otherat SilverState'spit to the south- flourto fine-grainedwall-rockfragments.Mostof the
east.The bodiesin the GlobeHill clusterformedalong fragmentsoriginatedfrom the immediatewall rock
preexistingfaults,at fault intersections,
and at joint either as platesalong sheetedstructures(Fig. 14A)
intersections.
Eachbody (Fig. 13) approximates
an or asirregularangularformsin the crackledareas.A
upward-flaringcolumn,roughly equidimensionalin few of the matrix-supported
breccias,however,conplan view but with numerous extensionsoutward tain fragmentswhich have clearly been transported
alongplanarstructures.The largestindividualbreccia over a considerabledistance.These fragmentsare
body is 50 m in diameterat the surfaceand extends heterolithic,wellrounded,poorlysorted,andlessthan
75 m downward; the smallestonesare lessthan 10 cm 5 cmin size.The mostcommonlithologyispyroxenein anydimensionandoccuralongjoint intersections. rich (as much as 20%) alkali syenite. Other compoMost breccia bodies exhibit crude lateral and versitionsincludebiotite-rich alkali syenite,porphyritic
tical texturalzonation.They gradelaterallyover sev- and aphaniticvarietiesof mafic-richalkali trachyte
eral metersfor the largerbodiesto a few centimeters (someof whichdisplaywell-developed
flowtextures),
for the smallestbodiesfrom a breccia-dominatedcore, and quartz-fluoritevein material. Accessorysphene
through a crackle-dominated
halo, and into highly andtopazare commonin the syeniticfragments.
The brecciamatrixis completelycementedby hyjointed wall rock. The frequencyof the joints and
fractures continues to decrease outward from the
drothermalmineralswhichdisplayopen-space
growth
drothermal breccias in the area occur as either isolated

CRIPPLECREEKDISTRICT,VEINS! BRECCIAS

1683

FIG. 14. A. Stage1 hydrothermalbrecciaalonga sheetedstructure.Matrixis dominantlychalcedonic

quartz.B. Stage1 hydrothermal

brecciain well-jointed
wallrock.Samplegradesfromjointedwall
rock (left), to matrix-supported
(center),to rebrecciatedfragment-supported
breccia(right). Matrix is
dominantlychalcedonicquartz.C. Stage4 hydrothermalbrecciaof the centralcorezone.Gray matrix

0eft) is.anhydrite,
whichhasalteredto gypsum(right).Fracturedbrecciafragments
andmatrixare
alsocementedwith gypsum.D. Stage4 hydrothermalbrecciaof the centralcorezone.Matrix isentirely
alteredto gypsum.Note variationin igneoustextureof the fragments.

and
textures.'
Some
ofthematrix-supported
breccias
ex- difficultto trace owing to their discontinuous
hibit texturesindicativeof a secondhydrothermal
brecciationand matrix-fillingevent (Fig. 14B).
StageII: Tectonicstructures:The secondstageis
characterizedby steep tectonic structuresconcentrated alongthe westernedgeof the stageI hydrothermalbrecciazone.The mostrecentproductionat
Globe Hill has been from this area. There are four

crosscuttingsubstagesof tectonic structures.The

earliestis highlyirregularpinchandswellfaultsconcentratednearthe centerof the pit. Theseare cutby
numeroussteepfaultsand shearzones,which are in
turn cut by a major north-southshearzone,The last
substageis representedby faultsthat cut all earlier
tectonicstructures(Fig. 13).
Relativedisplacement
alongthe stageII tectonic

pinchandswellnature.Severalsplayat eitherend,
includingthe north-southshearzone, which also
splaysupward.Moststructures
havenearlyvertical
slickensides,but the north-south shear zone contains
horizontal slickensides as well.

StageII tectonicstructures
areusuallygougefilled
and have intenselyjointed and fracturedhalosof
variable width. Fault breccia occurs within some

(especially
withinthenorth-south
shearzone)andoften at the intersection of two or more structures.

These breccia bodies are small, discontinuous,and

variablein form.They are tabularto lensshaped

within shearzonesand columnshapedat structural

intersections.
The formerare mostcommon;they are
lessthan0.5 m wide andtraceableup to 10 m along
structuresis unclear. Marker structures,veins, and strike or dip.
dikescutby the north-southshearzoneare notfound
The breccia fragmentsare unsorted,angularto
on the oppositeside,either at the surfaceor in core. subrounded,less than 2 cm in diameter, and supMost of the structures,thoughroughlyplanar, are portedby a inatrixof gougematerial.The matrix

1684

THOMPSON,TRIPPEL,AND DWELLEY

gougeis a mixtureof unsorted,very smallwall-rock hydriteand otherhydrothermalmineralswhichdisfragmentswith rock flour. This tectonicbrecciahas playopen-space
growthtextures.
interfragment/fragment
ratiosthat are low (<1:3) to
The peripheralbrecciahalo, which is about60 m
intermediate(2-3:3).
wide,consists
of fragment-supported,
angularto subStage III: Intrusive breccia: The third structural angularwall-rockfragments
generallylessthan2 cm
eventproducedintrusivebreccia.Core datafrom an in size;it hasintermediateto low interfragment/fraganglehole documents
its presence90 m beneaththe ment ratios.The brecciaat the outer marginof this
centerof the pit; it is alsofoundasfragmentson the zonegradesinto crackle-dominated
wall rock.It has
pit floor.The brecciaoccurswithinthe stageII north- anopenmatrixpartiallycemented
by montmorillonite
south shear zone but is not sheared.Therefore, this andhydrothermalminerals.
The smallhydrothermalbrecciabodieswhichare
brecciatypeisinferredto postdate
stageII. It isprobably pipe- or columnlikein form,but sincethere are isolatedfromthe mainbrecciabodyare characterized
little dataconcerningits form, it is termedintrusive by angularto subangular
wall-rockfragments,
usually
breccia.
lessthan 3 cm in size.The fragmentsare suspended
The intrusivebrecciacontains
unsorted,subangular in a matrixof the samehydrothermalmineralsfound
to well-rounded,heterolithicfragmentslessthan 8 in the peripheralhalo zone.
cmin size,whichare matrixsupported,havinginterBrecciasimilarto thatof the peripheralzoneisalso
fragment/fragmentratios that are intermediate foundalongthelast100 m of theChicagoandCripple
(2-3:3) to high(>1:1). The fragments
are composed Creek tunnel (Argall, 1905; LindgrenandRansome,
of aphaniticandporphyriticalkalitrachyte(someof 1906). This suggests
either an extensionof the main
whichexhibitflow texture),alkali syenite,and gab- stage4 brecciabody southeastward
to the Plymouth
bro(?), as well as mafic-richvarietiesof each. Some Rock i mine or the presenceof a separatebody of
of thesefragmentsshowevidenceof havingbeenal- late-stagebrecciationcenterednearby.
tered prior to brecciation.
The matrix of the intrusive breccia consists of rock

Mineralization

flour andvery fine fragments,mostof whichare less

The preciousmetalmineralizationof the GlobeHill
than 1 mm in size. Locally, the matrix is banded depositis epithermalandpolymetallicin nature(Tashowing
alternating
fragment-rich
andfragment-poorble 1). The mineralizationresultedfrom three sepazones.
rate hydrothermalevents.Thesecoincidewith three
StageIV: Hydrothermalbreccia:The final structural of the four major structuralstagesdiscussed
above;
eventat GlobeHill wasone of intensehydrothermal stage3 is unmineralized.The mineralizationoccurs
brecciation centered below the Deerhorn shaft. The either as breccia matrix fillings, veins, or as minor
brecciabody formsa verticalpipelike massabout replacementbodies, dependingon the degree of
220 m wide andat least180 m deepwith a rounded structuralpreparationof the wall rock. Although
top (Argall,1908) and hasdike- and pipelikeapo- Ag/Auratiosare commonlygreaterthan3:1, they are
physes
whichextendoutwardandupwardalongstage lessthan 1:1 in zonesof significantgoldmineraliza2 tectonicstructures(Fig. 13). Thismainbodyis not tion.
exposedat the surface;however,somesmallisolated
Mineralization associatedwith stage I structures:
bodiesare.Thesesmallerbodiesformedalongstage Mineralizationin the stageI hydrothermalbreccia
II tectonicstructuresand are foundthroughoutthe zoneoccursasveinsand breccia-matrixfillings(Fig.
entire area.
13) and as weak disseminations
within brecciafragTexturallyandcompositionally
the mainbodycan mentsandadjacentwall-rock.
The open-space
vein-fillingassemblages
consistof
be dividedinto two zones,a centralcoreanda peripheralhalo(Fig.13).Thecentralcorebrecciabegins either chalcedonicquartz-celestite-carbonate-fiuo23 m below the surface and extends at least 100 m rite-pyrite or quartz-fiuorite-pyrite-(celestite-cardownward;it is 100 m in diameter(Argall, 1905, bonate).The latter quartzvarietycommonlyexhibits
1908). It containsheterolithic,subangularto sub- explosiontextures,consistingof radiatingvoidsberounded,matrix-supported
fragments,
upto 10 cmin lievedto be formedby displacement
of attachedvapor
size, which are often rebroken(Fig. 14C and D). bubbles during boiling of the hydrothermalsoluThesefragmentsincreasein abundance
fromthe cen- tion. The other mineralscoprecipitatedwith the
ter to the marginof the core, suchthat the breccia quartz immediatelyoutsidetheseexplosiontextures
hascorresponding
interfragment/fragment
ratiosthat (rig. 8c/.
are high (>1:1) to intermediate(2-3:3). They are
The brecciamatrixfilling is composedof chalcecomposedof severaltextural varietiesof alkali tra- donic quartz-celestite-pyrite-(fiuorite-carbonatechyteporphyry(theseshowvariabledegreesof pre- quartz). The quartz occursas narrow rims on fragbrecciation
alteration)
andcuriousbrokenaggregates ments in the well-rounded, heterolithic breccia. Acof celestite.The matrixis entirelycementedby an- cessorymineralsfound throughoutall assemblages

CRIPPLE
CREEKDISTRICT,VEINS&BRECCIAS

1685

include:sphalerite,
galena,chalcopyrite,
pyrrhotite, montmorillonite. Much of the montmorillonite is
specularitc,
rutile, calaverite,sericite,andmontmo- white or stainedbrownby limonites,but someisbrilrillonite. The total sulfide content of the mineralized
liant yellow-green.As with the anhydrite-cemented
stageI structures
rarelyexceedsa few percent;tel- corebreccia,geochemicalanalysesrevealonly trace
lurides and primary oxides are present in trace amountsof gold.
amounts.
Crossand Penrose(1895) report gypsumcoating
Mineralization associatedwith stageII structures: the seamsand fragmentsin the peripheralbreccia

central
The mineralization
alongstageII structures
is of two zoneabovethe anhydrite-gypsum-cemented
types:asveinsalongthe earlieststructuresor, more core in the Deerhorn mine. Recent core data, howcommonly,as disseminations
throughoutwall rock ever, indicateno visiblegypsumor anhydritein this
zone.
adjacentto the later structures.
The veins formed as discontinuous lenses less than

Alteration

20 cmwide,whichhavea pinchandswellcharacter,
alterationeventsatGlobe
andare concentratedin a 15- by 45-m zoneexposed Therewerefiveseparate
(Table
in thepit.Theveinsarecomposed
of quartz-celestite-Hill. Eachofthefirstfourtypesishydrothermal
fiuorite-(pyrite-carbonate-adularia)
which was de- 1) andisrelatedto oneof the majorstructuralstages;
weathering.
The
positedin multipleevents.Galena,sphalerite,
calav- thefifthtypeisrelatedto supergene
erite, chalcopyrite,and sericiteoccurwith this as- last hydrothermalevent as well as the supergene
but irregularoxidation
semblagebut generallyare only found in trace weatheringformedextensive
amounts.All of these minerals exhibit open-space to a considerabledepth.

The fraggrowthtexturesand the quartzcommonlyexhibits Alterationrelatedto stageI structures:

brecciabodiesconexplosion
texture.The othermineralscoprecipitated mentsin thestageI hydrothermal
with quartzwithin andimmediatelyoutsidethe ex- tain weak to moderate sericite-chlorite-carbonatealteration
plosiontexturezone.Initial total sulfidecontentin montmorillonite-pyrite-(quartz-apatite)
the veinswas only a few percent;telluride content (Fig. 13). Intensesericite-pyrite-quartz-(carbonate)
alterationis commonlydevelopedin a rind around
locallyexceededseveralpercent.
The latter structuresare mineralizedchieflyby py- breccia
fragments
lessthan0.5 mmwide.Occasionally
rite disseminated
outwardthroughthe adjacentwall they alsoexhibitan irregularrind of silicification
rockandbylocalpyriteconcentrated
alongfractures. aroundtheir outermargin,but it is lessthan0.1 mm
The halosadjacentto individualfaultsare commonly wide.
the hydrothermalbreclessthan3.0 m wide.Overlappinghalosfromseparate The wall rocksurrounding
structures within the shear zones create wider areas

cia bodies containsextensive,moderate chlorite-ser-

of disseminatedmineralization.Accompanyingthe
pyrite,whichrarelyexceedsa few percent,are trace
amountsof sphalerite,chalcopyrite,pyrrhotite,specularitc, and (probably)calaverite.
Mineralizationassociatedwith stageIV structures:
The centralcoreof the stageIV matrix-supported
hy-

icite-pyrite-quartz-(montmorillonite-apatite)
alteration, the extent of which has not been delineated

(Fig.13).Chalcedony
veinletsareoccasionally
found
throughoutthis zone and displaynarrow, intense
chloritichalos,whichgradeoutwardto the chloritesericite-dominated

alteration.

Alterationrelatedto stageH structures:

The veindrothermalbrecciais cementedby an assemblage
of
anhydrite-carbonate-celestite-fiuorite
(Fig. 13), each filled stageII tectonicstructuresdisplayhalosof
of whichexhibitopen-space
growthtextures.The ce- moderatequartz-sericite-pyrite
alteration,lessthan
lestitc showscrudelydevelopedexplosiontexture as 5 cmwide.The gangue-free
structures
exhibithalos
well. Accompanying
the ganguemineralsare minor of weak to moderate sericite-montmorillonite-caramountsof disseminated
pyrite, galena,sphalerite, bonate-pyrite-(quartz-apatite)
alteration,up to 3 m
chalcopyrite,and pyrrhotite.Geochemicalanalyses wide.The alterationextendsto a depthof 75 m within
revealonly trace amountsof goldin the rock.
the majornorth-southshearzone and to shallower
(Fig. 13).
The stageIV peripheralzone, composedof frag- depthswithin smallertectonicstructures
ment-supportedhydrothermalbreccia, is partially
cemented and veined by massivemontmorillonite
(Fig. 13). The montmorillonitealsooccursas veins
and as breccia matrix filling in the stageII tectonic
structuresthroughoutthe entire deposit;it is accompaniedby minor amountsof opalineto chalcedonic
quartzandtiny hematiticspherules.One 5.5-m-long
core interval is comprisedof montmorillonite,but

No ohiorite-dominatedassemblage
has been recognized.

Alterationrelatedto stageHI structures:The stage

III intrusivebrecciais characterizedby intensechlo-

rite-sericite-quartz-hematite
alteration throughout
the matrix.Brecciafragmentscontainweakchloritic
alteration and often exhibit a rind of moderate to in-

tense chlorite-sericite-hematite-quartz
alteration as

well. The degreeof fragmentalterationvarieswith

andigneous
textureof thefragments.
wispyveinletsof fluorite are foundcuttingthe vein thecomposition
most veins are less than 5 cm in true width.

Minor

1686

THOMPSON,
TRIPPEL,
AND DWELLEY

Severalfragmentscontainfracture-controlled
adularia Additionally,the anhydriteis partially convertedto
and have intense sericitic alteration. These anomalous gypsumby hydration.
fragmentssuggesta prebrecciapotassicalteration, Supergeneweathering of alteration and mineralpresumablyat depth.The hematitein boththe matrix ization productsrelated to stage I structureshas
andthe fragmentsoccursasblades(specularitc)and formed an assemblageof fracture-filled and disassphericalaggregates.
seminatedgoethite-manjiroite-wad-(hematite-j
arosAlteration related to stageIV structures:In the ite-celestite-autunite).
The autunite is found along
stageIV centralbrecciazone,alterationof the frag- oxidizedveins.Weatheringof alterationand minermentsrelatedto the anhydritematrixfilling is mini- alization productsrelated to stageII tectonic strucmal.Nearlyall of the heterolithic
wall-rockfragments tures has producedan assemblageof hematite and
containprebrecciasilicification
in varyingdegreesof jarosite, with lesseramountsof goethite, and manintensity.Somefragments
displaynarrowrindsof py- ganeseminerals.

rite-fluorite-carbonate
alteration.The prebrecciacelestitcaggregate
fragmentsarepartiallyalteredto an Fluid inclusions
assemblage
of anhydrite-(fiuorite-carbonate-pyrite) Fluid inclusions are common in minerals from the
alongmarginsandgrainboundaries.
three stagesof mineralization.Primaryand pseudoThe wall-rockfragmentsin the peripheralbreccia secondaryfluid inclusionsoccurmostoftenin the fluzone contain weak to moderate montmorillonite al- orite within the stageI veins,quartzwithin the stage
teration,with minor quartz and limonite(Table 1). II veins, and anhydrite within the stageIV breccia
The alterationintensityincreases
towardthe anhy- matrix filling. Most are of approximatelynegative
drite-cementedcentralbreccia.The brecciafrag- crystalform andlessthan 10 tamin maximumdimenmentsand the wall rock adjacentto the montmoril- sion.Fluid inclusionsin the stageI fluoriteandin the
lonite veinsalongstageII tectonicstructurescom- stageII quartz containboth liquid and vapor. They
monlycontainonly weak montmorillonitealteration. havevariableliquid to vaporratiosbut are generally
Oxidationof preexistingsulfidesand telluridesin liquid dominated.Most fluid inclusionsin the stage
the fragments
of the peripheralbrecciazoneincreases IV anhydriteare entirelyvapor,but a few are liquid
toward the unoxidizedanhydrite-cemented
central dominatedwith variableliquidto vaporratios.Nearly
breccia.The relativepercentage
ofpyritecasts,
how- all anhydritedisplayscurvedcleavagesresultingfrom
ever,doesnotincreaseproportionally
with increased postdepositionalstrain. No daughter products or
montmorillonitealterationand matrix filling. This doublemeniscuses
were observedin any of the fluid
zonationwithintheperipheralbrecciaisalsoreported inclusions,
indicatinglower salinitiesandvaporpresfromobservations
madein the Deerhornworkings suresthan observedfor the early vein fluids.
(Argall,1905, 1908). Similaroxidationis presentin
A crushingstudywasconductedto testwhether or
narrowwall-rockzonesadjacentto the montmoril- not the fluid inclusionsare overpressured.Polished
lonite veinsalongstageII structures.
platesof eachsampleimmersedin mineraloil at room
The natureof thisoxidation,the relativelyconstant temperaturewere viewedwith a petrographicmicropreoxidation
pyritecontentof the fragments,andthe scopeandcrushedwith a dentaltool. Fluid inclusions
occurrenceof hematitespherulesin the montmoril- within stageI fluorite and stageII quartzwere both
lonitebrecciamatrixfillingstronglysuggest
a hypo- foundto be overpressured,
withthelatterconsistently
geneorigin for this oxidation.
yieldinglargerandmoreabundantvaporbubblesthan
Alterationrelatedtosupergene
weathering:
Super- the former. Fluid inclusionsin stageIV anhydrite
gene weatheringhaspartially oxidizedthe rocksat yielded no vaporbubblesuponcrushing.
Globe Hill to a depth of at least270 m, some45 m
Only preliminaryhomogenization
temperaturedata
belowthe ChicagoandCrippleCreektunnel(Lind- are available, owing to the problems of locating
grenandRansome,1906). Little or noremobilization workable-sizedfluid inclusionsand to the decrepiof precious
metalshasaccompanied
the weathering. tation which commonlyoccursupon heating. HoThe effectsof thisweatheringare mostpronounced mogenizationtemperatureswere recordedfrom five
alongstageI hydrothermal
brecciasandstageII tec- fluid inclusionsin fluorite from stageI chalcedonic
tonic structures,where permeabilityis sufficientto quartzveins.The fluidinclusions
containvariableliqallowdownwardpercolationof meteoricwaters.
uid to vaporratios,with vaporbubblesoccupying1
The mostcommonreactionwith oxygenatedme- to 50 vol percent.All homogenized
to liquidat widely
teoricwater is the alterationof pyrite, galena,chal- scatteredtemperaturesbetween 371 and 425C.
copyrite,andcalaveriteto limonites,anglesite,cov- The rangeof temperaturesindicatesthatthe fluidmay
ellitc, and nativegold,respectively.The oxideand havebeenboilingandthat the true trappingtempersulfateassemblage
varies,dependingon the amount ature is probablywell below 371C.
ofpreoxidation
sulfides
andtheirdegreeof oxidation. Homogenizationtemperatureswere alsorecorded

CRIPPLE CREEK DISTRICT, VEINS & BRECCIAS

from sevenfluid inclusions

in quartzfrom stageII
veins.Theseinclusions
occurimmediatelyoutsideof
a zoneof explosion
texture.The liquidto vaporratio
is variable,with 5 to 50 vol percentbeingvapor.Six
of the fluid inclusions
homogenized
to liquid at an
averagetemperatureof 203.5C,with valuesranging

1687

1 fluidswere salinewith temperaturesof more than

300C (Fig. 10), allowingfor chloridecomplexing
as
a meansof gold transport;however, the ore-stage
fluids were dilute and less than 160C. As ore fluids

became dilute from meteoric water influx, the con-

centrationof metals,particularlygoldandtellurium,
mayhaveled to tellurocomplexing
of gold(andminor
mogenized
to liquidat 331.2C.Apparentlythefluids silver). Precipitationappearsto have been induced
boiled weakly or effervesced;therefore, the true by simplecooling.
temperatureof trappingis at, or slightlybelow,
In the major fault zones,ore fluid flow was un198.6C.
impeded upward to the surface,often movinginto
The vapor-dominated
inclusions
in anhydritefrom subsidiaryfracturesthat were of greaterabundance
the stageIV brecciamatrixfilling neitherhomoge- nearerthe surface.The latter yieldedveinswith a
nizednor decrepitated
uponheating.The few inclu- lesserverticalextentthanthe principalfaults.In other
sionswith a visibleliquidphasehomogenized
to liquid cases
orefluidflowin faultswaspartiallyreducedand
at temperaturesbelowthatwhichis requiredto form divertedwherethe faultscutpermeablesedimentary
anhydrite.From theseobservations
it is evidentthat and volcaniclasticunits (Koschmann,1949). In still
the fluid inclusions
musthaveleaked,perhapsin re- other cases(e.g., Globe Hill), fluid and gasflow besponseto the samestresses
which createdthe curved cameimpededby vein mineralprecipitationandby
cleavageplanes;a few mayhavebeenpartiallyfilled a thick trachytesill.The permeabilitybarrierto fluid
by later fluids.
and gasflow allowedoverpressures
to develop.The
upper part of the systemwasprobablyvapordomiDiscussion
nateddue to the great depth at which COerelease
Mineralizationin the Cripple Creek districtpost- began.Vapor-dominated
systemshave higher fluid
dateddiatremedevelopment,includingthat at the pressures
thanliquid-dominated
systems,
a condition
Cresson.Early mineralizingfluidswere saline,sug- thatcreatesoverpressures
greaterthanlithostaticload
gestinga magmaticorigin.They were CO2 bearing, to depthsof asmuchas 1,000 m (Nelsonand Giles,
andthetrappingpressures
of 360 to 400 barssuggest 1985). Once fluid overpressures
exceededlithostatic
thatfirstboilingof theoresolutions
couldhavebegun loadandrocktensilestrength,hydrothermalbrecciaat 4,000 m depth (utilizinghydrostaticconditions). tionensuredat GlobeHill. Fluidfocusing
onreopened
It is apparentfrom the fluid inclusionstudiesof the faultslocalizedmuchof thehydrothermal
brecciation.
Ajax vein systemthat boilingof ore fluidsoccurred Vein and mineralizedrock fragmentswere transthroughoutthe entire vertical interval of 1,050 m. ported upward in fluidized columnswhich flared as
Thereis no knownbottomto the gold-bearing
vein thesurface
wasapproached.
StageI breccias
andstage
systemandthe largeverticalintervalof gold-bearing II tectonic zones at Globe Hill contain minerals that
veinandorefluidboilingindicates
thatflashingof ore are equivalentto thoseseenin the deepervein sysfluidswith rapidprecipitationof metalswasnot the temsof the Ajax; however,no direct comparisonof
ore-formingprocessat Cripple Creek. Continuous stagesis possible.The shallowhydrothermalfluids
boiling of ore fluids allowsfor volatile releaseand were enriched in calcium, strontium, and sulfate
leadsto metalconcentration
in the remainingliquid. comparedto the deepervein systems.
This wasdue
The behaviorof stagei fluid inclusionsabovethe to the introduction,possibly,
of calciumandstrontium
7,537-ft elevation(Fig. 11) with an increasein min- from an alkali basalt heat source, and the sulfate is
imumtemperatures
appears
to be theresultof energy clearlythe resultof near-surface
He oxidation.
derivedfromsteamcondensation.
The homogeniza- Clast and wall-rock alteration is more extensive in
from 198.6 to 210.6C. The seventh inclusion ho-

tionof fluidinclusions,
asnotedabove,changes
above theshallow
hydrothermal
breccias
(Fig.13)compared
the 7,537-ft elevation. Above that elevation, fluid in- to the narrow,deeperveinsof theAjaxmine(Figs.
clusions
homogenize
by halitedissolution,
a phenom- 6, 7, and9). The shallow
alteration
iszonal(Table1)
enon that Roedderand Bodnar(1980) believed to andreflectsmoderately
alkaline,oxidizedfluids.The
haveresulted
whereinclusions
weretrappedathigher ore fluidscontinued
to boilepisodically,
becoming
pressures
thanthoseinclusions
wherehomogenizationparticularly
focused
duringstageIV fromthe central
occurredby vapordisappearance.
The conditionsof anhydrite-cemented
corearea(Fig. 13, sec.A-A').
fluid flow with high CO2 contentmay haveled to Continued
evolution
ofCO2,SO4,andHe gases
resteam-driven
boiling(P.T. Holland,in prep.),yielding ducedfluidpressures
sufficiently
sothatanhydrite,
ore throughouta largeverticalinterval.
carbonates,
andcelestite
wereprecipitated
in open
CrippleCreekveinsare low (<3 vol %) in total spaces.Minor sulfideswere formedin the centralcore
sulfides,
sothatthiocomplexing
wasminimal.
Stage zonewhereH2Sremainedunoxidized.
Anhydriteas

1688

THOMPSON,TRIPPEL,AND DWELLEY

1969, Distributionof goldandothermetalsin the Cripple

a matrixin the corezoneappearsto havedeveloped -Creek district, Colorado:U.S. Geol. Survey Prof. Paper 625in upward-growing
columnsasboiling,hydrofractur- A,
p. A1-A17.
ing, and sulfate precipitationoccurredconcommi- Henderson,C. W., 1926, Mining in Colorado:A history of dis-

tantly.
Thus, the relationshipbetween veins and miner-

covery,development,andproduction:U.S. Geol. SurveyProf.

Paper 138, p. 56-60.

alizedhydrothermalbrecciasat Cripple Creek is in- Keener, J. H., 1962, Cripple Creek, Colorado,StrattonCripple
Creek Mining and DevelopmentCo., unpub. rept., 21 p.
timate.Restrictionof fluid andgasflow within a vein Kleinkopf,
M.D., Peterson,D. L., andGott, G., 1970, Geophysical
systemled to shallowmineralizedhydrothermal studiesof the Cripple Creek mining district, Colorado:Geo-

breccias.

Acknowledgments

The authorsgratefullyacknowledgethe cooperation and supportof the Hecla Mining Corporation

andthe TexasgulfMetalsCompany,includingSteve
Peters,StanCoombs,Lou Knight, CharlesMatteson,
Charles Brechtel, and Alex Paul. In addition, we

greatlyappreciatethe cooperationand financialassistanceprovidedby Gold Resources,Inc., andNewport Minerals, Inc., including Brian Hestor, Peter
Reed, andKen Ennis.StandardOil Companyof Californiaalsoprovidedfinancialassistance
for the Globe
Hill researchthrougha generousfield-orientedthesis
grant.The costof supplyingandmaintainingfluid in-

physics,v. 35, p. 490-500.

Koschmann,
A. H., 1949, Structuralcontrolof the golddeposits
of the CrippleCreekdistrict,Colorado:U.S. Geol.SurveyBull.
955-B, p. 19-58.

Koschmann,A. H., and Loughlin,G. F., 1965, Mine mapsof the

Cripple Creek district,Colorado:U.S. Geol. SurveyOpen-File
Rept. 65-90, 18 portfolios(528 maps)and index.
Lewis, A., 1982, Producinggold for $160/tr oz in Victor, Colorado: EngineeringMining Jour., v. 183, p. 102-107.
Lindgren,W., andRansome,F. L., 1906, Geologyand golddepositsof the CrippleCreekdistrict,Colorado:U.S. Geol.Survey
Prof. Paper 54, 516 p.
Lorenz, V., 1973, On the formation of maars:Bull. Volcanol., v.
37, p. 183-204.

Lorenz, V., McBirney, A. R., and Williams, H., 1970, An inves-

tigationof volcanicdepressions.
PartIII. Maars,tuff-rings,and

diatremes:NASA ResearchRept. NGR-38-003-012, 198 p.

Loughlin,G. F., 1927, Ore at deep levelsin the Cripple Creek
district, Colorado:Am. Inst. Mining Metall. EngineersTech.
clusion analysisequipment was supported by the
Pub. 13, 32 p.
EconomicGeologyDevelopmentFund at Colorado Loughlin,G. F., andKoschmann,
A. H., 1935, Geologyand ore
StateUniversity.Our sincerethanksare alsoextended
depositsof the Cripple Creek district,Colorado:ColoradoSci.

to BenLeonardandRalphChristianat the U.S. GeoSoc. Proc., v. 13, no. 6, p. 217-435.

McDowell, F. W., 1966, Potassium-argon
datingof Cordilleran
logicalSurveyfor the useof laboratoryfacilities.
intrusives:Unpub.Ph.D. dissert.,ColumbiaUniv., 246 p.
Reviewersof an earlier draft of the manuscript, Nelson,
C. E., and Giles, D. L., 1985, Hydrothermaleruption
clarifiedour presentation.We are responsiblefor any
mechanisms
and hot springgold deposits:ECON.GEOL.,v. 80,
shortcomings,
however,that may remain.
p. 1633-1639.
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Peters,S. G., 1982, Evaluationof Gold Resources,Inc. property,

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Argall,P., 1905, ReportonGlobeHill properties:Cripple Creek,

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Cross,W., and Penrose,R. A. F., Jr., 1895, Geology and mining
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Gott, G. B., McCarthy, J. H., Jr., Van Sickle,G. H., andMcHugh,
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