1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado

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


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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-


3/20

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


4/20

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


5/20

•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


6/20

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).


7/20

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).


8/20

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-


9/20

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


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-


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


12/20


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


13/20

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


14/20

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


15/20

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


16/20


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


17/20

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.


18/20

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


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 (


20/20


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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1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado

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Transcript of 1669.fullMineralized Veins and Breccias of the Cripple Creek District, Colorado