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ECONOMIC GEOLOGY

AN'D THE

BULLETIN OF THE SOCIETY OF ECONOMIC GEOLOGISTS

Vo.. 65

JuNE-JuLY, 1970

No. 4

Lateral and Vertical Alteration-Mineralization oning

in PorphyryOre Deposits

j. DAWDLOWELLAND JOHN M. GUmBERT

Abstract

The geologichistory of the San Manuel-Kalamazoo deposithas provided an oppor-

tunity for the examination of vertical and horizontal zoning relationships in a por-

phyry copper system. Precambrian Oracle "granite," a Laramide monzoniteporphyry,

and a Laramide dacite porphyry are hosts to zones of potassic,phyllic, argillic, and

propylitic assemblages hown to be coaxially arranged outward from a potassiccore

through phyllic, argillic, and propylitic zones. Alteration zones at depth comprise an

outer chlorite-sericite-epidote-magnetiteassemblageyielding to an inner zone of

quartz-K4eldspar-sericite-chlorite. Mineralization zones are conformable to the

alterationzones, he ore zone (with a 0.5% Cu cutoff) overlapping he potassic nd

phyllic zones. Occurrenceof sulfideschangesupward and outward from dissemination

at the low-grade core of the deposit through microveinlet to veinlet and finally vein

occurrence ndicating the progressively ncreasing effect of structural control.

Several aspectsof San Manuel-Kalamazoo geology suggest hat it is exemplary of

the porphyry copper depositgroup. To test that idea and to evolve three-dimensional

aspectsof these deposits, table of geologiccharacteristics f 27 major porphyry de-

posits is presented. Considerationof the table indicates hat the "typical" porphyry

copper deposit is eraplaced in late Cretaceous sediments and metasedimentsand

is associated ith a Laramide (65 m.y.) quartz monzonitestock. Its host intrusive

rock is elongate-irregular,,000X 6,000 feet in outcrop,and is progressively ifferen-

tiated from quartz diorite to quartz monzonite n composition. The host is more like

a stock han a dike and is controlled y regional-scaleaulting. The orebody s oval

to pipelike, with dimensions f 3,500 X 6,000 feet and gradational boundaries.Seventy

percent of the 140 million tons of ore occurs n the igneoushost rocks, 30 percent in

preore rocks. Metal values include0.45% hypogeneCu with 0.35% supergeneCu,

and 0.015% Mo. Alteration s zoned rom potassic t the core (and earliest) outward

through phyllic (quartz-sericite-pyrite), argillic (quartz-kaolin-montmorillonite), nd

propylitic (epidote--calcite-chlorite),he propylitic zone extending 2,500 feet beyond

the copperore zone. Over the same nterval, sulfidespecies ary from chalcopyrite-

molybdenite-pyritehroughsuccessivessemblageso an assemblagef galena-sphalerite

with minor gold and silver values in solid solution, as metals, and as sulfosalts.

Occurrence haracteristicshift from disseminationshrough respective onesof micro-

veinlets (crackle fillings), veinlets,veins, and finally to individualstructures n the

peripherywhich may containhigh-grademineralization. Breccia pipes with attendant

crackle zones are common.

Expressionof zoning is affected by exposure,structural and compositional omo-

geneity, and postore faulting or intrusive activity. Vertical dimensionscan reach

10,000 eet, with the upperreaches f the porphyryenvironment erhapsonly at sub-

volcanicdepthsof a few thousand eet. The vertical and lateral zoning describeds

repeatedwith sufficient onstancyhat depthsof exposure t many deposits an be cited

against the model of San Manuel-Kalamazoo.

373



374 .t. D. LOWELL AND J. M. GUILBERT

Several ines of evidence uggest elativelyshallowdepthsof formationand signifi-

cant variations n water content n the porphyry environment. Shallow emplacement

is consistent ith the appearance f brecciapipesassociated ith ring and radial diking

and with vertically telescoped oning. Models of the sourceof altering-mineralizing

fluids are considered.

Contents

PAGE

Introduction ................................. 374

Genetic modelsof porphyry deposits .......... 375

Geologyof the San Manuel-Kalamazoo eposit . 376

Fresh rocks ................................ 378

Alteration zones ........................... 381

Mineralization zones ........................ 385

Comparison f porphyry deposits ............. 386

Deposits (column 1) ....................... 386

Preore host rock (column 2) ................ 386

Igneoushost rock (columns3-11) ........... 386

Orebody (columns 12-19) .................. 399

Hypogenealteration (columns 0-27) ........ 400

Hypogenemineralizationcolumns 8-35) .... 402

Occurrence f sulfides columns 6-42) ....... 403

Supergene ulfides column43) .............. 403

Genesisof porphyry deposits ................. 403

Conclusions .................................. 404

Acknowledgments ............................ 406

References ................................... 406

Introduction

Exv•.o1•,•T•oNf the Kalamazoo ortionof the San

Manuel-Kalamazoo istrict,Pinal County,Arizona,

has presented n unparalleled pportunity or the

studyof a porphyrycopperdeposit n three dimen-

sions. The coaxialsymmetry f alteration nd min-

eralization oneswhichwas the basisof the explora-

tion model has been verified in the exploratory

drilling Lowell, 1968) of the Kalamazoo ortionof

the district and in exploitationof the San Manuel

portion. As explorationproceeded,t became n-

creasinglyapparent that many elementsof min-

eralog-y, ccurrence,nd geometry f other porphyry

copperdepositswere explicitly represented t San

Manuel-Kalamazoo. Zoning patterns here can be

considered refinedbase or the studyof mineraliza-

tion and alterationrelationshipsn other porphyry

copperdeposits, nd this is the subjectof the study

reported here, with compilationof data from 27

major porphyrycopper nd molybdenumepositsn

North and South America. Most significants the

emergence rom the many descriptions f a more

generally applicableunifying theme of large-scale

alteration-mineralizationoning in these large de-

posits hanhasgenerally een ecognized.Stringham

(1953, p. 990) stated hat "a review of hydro-

thermal studiesof porphyrycopperdeposits hows

as many dissimilarities s similaritieso the hydro-

thermal features at Bingham Canyon." We now

take the opposite osition hat there are many char-

acteristicswhich link Bingham Canyon and many

other depositso the generalporphyrycopperdeposit

type. There appears o have been ittle published

effort specificallyo compareand contrast he por-

phyry deposits s a group.

The first portion of this paper describesboth

lateral and vertical alteration-mineralization relation-

ships at San Manuel-Kalamazoo. The exploration

model includedand substantiatedpproximately 0

degrees of postmineralization ilting. Thus this

geologic system provides information concerning

both vertical and horizontalaxes of a porphyry de-

posit. A three-dimensional ynthesis s given of

hydrothermal lterationmineralogyand assemblages,

of the distributionand quantitativeaspectsof sul-

fides, and of the structural occurrenceof sulfide and

oxide minerals. Vertical treatment of alteration and

mineralization eometry s still tentative,but some

vertical zoning changescan be identified.

Comparison f other major porphyrybase-metal

depositso San Manuel-Kalamazoo y meansof pub-

lisheddata assembledn Table 1 permitsdevelop-

ment of a generalized ateral and vertical zonation

model or the depositgroup. Finally, that model s

used to examine the genesisand environmentof

formationof the porphyrydeposits. The data sug-

gest that it is sometimespossible o estimate the

position of the present erosion surfacesof other

porphyrydepositswith respect o their originalcol-

umns of mineralization. Depth parametershave

beenassignedo nine deposits, nd it is hoped hat

both scientific nd explorational se can be made

of three-dimensionallteration-mineralizationoning.

The porphyrycopperand molybdenum eposits,

hereaftercalled"porphyries,"must first be defined.

A necessarilylexibledefinitionemerges rom con-

sideration f many deposits nd descriptionsf a

"typical" one.

A porphyrydeposit s here definedas a copper

and/or molybdenum ulfide depositconsisting f

disseminated and stockwork veinlet sulfide minerali-

zation emplacedn varioushost rocks hat have been

alteredby hydrothermal olutionsnto roughlycon-

centric zonal patterns. The deposit s generally

large, on the scale of several thousandsof feet, al-

though smaller occurrences re recognized. The

relativelyhomogeneousnd commonly oughlyequi-

dimensionaldeposit s associatedwith a complex,

passively mplaced tockof intermediate omposition

including porphyry units. It containssignificant



.4LTERATION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 375

amounts f pyrite, chalcopyrite, olybdenite, uartz,

and sericiteassociated ith other alteration,gangue,

and ore mineralsand metals ncludingminor lead,

zinc, gold, and silver. Mineralizationand alteration

suggesta late magrnatic-mesothermalemperature

range. The deposit s generally associatedwith

brecciapipes,usually with a large crackle breccia-

tion zone,and is surrounded y peripheralmineral

deposits uggestivef lower temperaturemineraliza-

tion.

The grade of primary mineralizationn typical

porphyry opper epositsanges p to 0.8% Cu and

0.02% Mo, and porphyry epositsn whichmolyb-

denite s the chief economic ineralhave grades

ranging p to 0.6% Mo and 0.05% Cu. All por-

phyry copper deposits ontain at least traces of

molybdenite,nd all porphyrymolybdenumeposits

containsomechalcopyrite.Many deposits ontain

recoverablequantities of both minerals, either in

separate rebodies r in ore with approximately

equal copperand molybdenum ollar values. Al-

though ypicalporphyry opper epositsiffer rom

typicalmolybdenumepositsn some espects,he

existence f gradational haracteristicsn metalliza-

tion suggests common rigin.

This definitions somewhateneralizedecauset

must permit considerationf many deposits hose

localgeologicircumstancesary as expressedy

their geometries nd physical haracteristics.We

believehe porphyry epositso be a petrological-

mineralizationallass, nd ndividualorphyry e-

positsare best nterpreted s greateror lesserde-

partures from the unifying model of the above

definition s elaboratedponbelow.

Genetic Models of Porphyry Deposits

Several eneticmodels avebeenproposedo re-

late the characteristicsf porphyrycopperand

molybdenumeposits.All of the modelsecognize

the important nvolvement f porphyriticntrusive

rockswith oredeposition,ndall are fundamentally

magmatic-hydrothermal,iffering n the sequences

of events, epths f intrusion,he timingof deriva-

tion of fluids, and the sourceof fluids. The models

considered ere are the orthomagmatic odel,

Fournier's model of intrusion of a water under-

saturated melt, and the White model of multilevel

circulation f brinesadjacent o a heat source.

The orthomagrnatic odelhasbeenbestdescribed

in therecentwritings f Burnham1967) andNiel-

sen (1968). It is the geneticmodel acitlyadopted

in mostdeposit escriptions,s for example,hose

describedn Titley andHicks (1966). It sometimes

involves enetration f the source o levelsas shallow

at 1,500 eet (Nielsen, 968),but morecommonly

to depthsapparently n the order of 3,000-5,000

feet. The modeldepends n a melt derivedat some

greaterdepth,probablynear the mantle-crust oun-

dary, which becomes aturatedwith water as it ap-

proaches he upper surface. Releaseof that water

may occur when internal vapor pressuredeveloped

by supersaturationxceedshe lithostatic oad pres-

sureor when he intrusive ystems rent by external

stresses. Crystallization hen proceedspresumably

along he linesof Emmons' 1933) cupolaor R. H.

Sales'ssub-hood upoladevelopment.

As described y Nielsen (1968), the sequence f

eventscan be paraphrased s intrusion,early mar-

ginalcrystallization hichproduces solidshell,and

ruptureof that shell o produceporphyritic-aphanitic

textures n subsequentlyrystallized ocks. Volatiles

released y the quenchingmigrateoutward hrough

crackle, stockwork,and brecciatedzones n the cooler

marginswhere, augmented y diffusioneffects, lter-

ation and mineralization ccur n responseo gradi-

ents"from near magmaticemperatures t the center

of the stock to relatively cool temperaturesn the

wall rocks" (p. 37). Silicate sulfide reactionsof

the typedescribedy HemleyandJones 1964) pre-

vail. Other authorswould not necessarilyimit the

separationof volatiles to the period of quenching,

but rather would consider volutionof the hydro-

thermal fraction a quasi-continuouseparationof

volatiles n responseo the many variables elated

to temperature nd pressure. The loss of volatiles

from near-surface ortionsof a melt may permit the

upward and outward replenishment f mineralizers

from greaterdepths.

Fournier (1968) suggestshat the initial deep

porphyry copper melt was unsaturatedwith water

at one to three percent, that it was intruded to

depthsof less han about4,500 feet, and that rup-

ture by faultingwould causesudden, venexplosive

loss of water and supercooling f the silicatemelt.

Crystallizationwould then abruptlyhalt the upward

progress f the now dry melt. Subsequent exten-

siveargillicalteration hownby mostporphyrycop-

per depositss probablydue to a superimposedir-

culatinghot-springsystem, ed mainly by meteoric

and cormatewater" (p. 101).

White (1968) in a particularlystimulating aper

suggestshat circulationof sulfur-deficient a-Ca-C1

brines, with salt contentsgenerally equivalent o

5%-to 40% NaC1, are responsibleor many base-

metal deposits. Such brines may be produced n

porphyry systemsby deuteric reaction of residual

liquids with earlier formed plagioclase nd ferro-

magnesianminerals o achievehigh contentsof cal-

ciumand basemetals. AlthoughWhite in his paper

doesnot develop specific pace-time odel or the

porphyry deposits,he implicitly developsa model



376 .r. D. LOWELL AND J. M. GUILBERT

involvingmultilevelcirculation f deutericallymetal-

enriched or cormate-meteoric sulfur-deficient metal-

lizing solutions nder he influence f thermalgradi-

ents established y an adjacent or subjacentmag-

matic heat source. The model differs importantly

from the orthomagrnaticmodel in that the source

of the solutions,and perhaps the metals, is almost

completely xternal to the magmaticsystem,with

convective overturn of circulating solutions pro-

ducingalteration-mineralizationnvelopesnd zones.

Geology of the San Manuel-Kalamazoo Deposit

The San Manuel-Kalamazoo deposit (Lowell,

1968), located in Pinal County, Arizona, is here

accepted s the type porphyrycopperdeposit, nd

its geologyand other characteristicsre presented

for comparison nd contrastwith others (Table 1).

Precambrian quartz monzonite of the Oracle

Granite batholith in the San Manuel area was in-

truded in Laramide time by swarmsof monzonite

porphyry dikes and irregular massesof monzonite

porphyry, more properly termed biotite latite por-

phyries, although ong-establishedmonzonitepor-

phyry" terminologywill be followedhere. Closely

related in time and space to the activity was a

porphyrycoppermineralization vent hat produced

the San Manuel-Kalamazoo rebodyand its associ-

ated concentric lterationzones. The hydrothermal

system ppears o have beencenteredn the middle

of the monzonite orphyrydike swarm,and metal-

lization is almost equally distributedbetween he

monzoniteporphyry and the Oracle Granite host

rocks Fig. 1).

Followinghydrothermalmineralization nd alter-

ation (Fig. la), the whole districtwas tilted to the

northeast, nd the block ncluding he San Manuel-

Kalamazoo rebodywasprobably elativelyelevated.

Erosion of this block exposed he top of the ore-

body, and supergene ctivity formed a thin chal-

cocite enrichmentblanket. At this time, the long

axis of the orebodymay have plunged at about

65øSW. Shortly thereafter, errestrial sediments

began o cover he deposit.

Further tilting, perhaps15ø followeddeposition

of the lowermost Cloudburst Conglomerate. An

erosion surface formed on the Cloudburst sediments

was later coveredby the Gila Conglomerate. A

third-stageilt of about30ø gave he Gila Conglom-

erate ts present nclination nd brought he origin-

ally verticalaxis of the San Manuel-Kalamazoo re-

body nto a 20ø southwest-plungingttitude. The

San Manuel ault then diagonally ffset he original,

nearly cylindrical rebody nto two roughlyequal-

sized ieces,he SanManuel nd he Kalamazoo

portions.TheupperKalamazooortionmoved bout

8,000 feet in a down-dip,S55øW direction.

Small,high-angle,orthwest-trendingormal aults

later displacedothhalves f the originalorebody,

and erosion trippedmostof the Gila Conglomerate

from the east end of the presentSan Manuel ore-

body (Fig. lb).

The original,unfaulted rebody, s defined y a

0.5% copper imit, formeda slightly lattened r

elliptical ylinderwhichwasat least7,700 eet ong

and from 2,500 to 5,000 feet in diameter. The top

of the cylinder, t the eastendafter ilting,mayhave

been rounded,with the bottom,at the west, having

an irregularshape. The centerof the orebodys

poorlymetallized,o that ore actually ormsa hol-

low cylinderor cylindrical hell. The shell sur-

roundinghe ow-gradeenter ariesromabout 00

to 1,000 feet in thickness. Mineralization nd alter-

ation zonesare approximatelyoaxial.

The alterationassemblagesn the San Manuel-

Kalamazooepositormregular, moothlyounded

zones,which, as in most porphyries, re locally

gradationalnd difficulto placewithina hundred

feet,althoughheyare well defined n a broadscale.

The boundaries re more clearly defined han they

are in mostporphyrydeposits, resumablyecause

the mineralizingluidsaffectedntrusive, ssentially

homogeneous,sotropiclutonic ndhypabyssalost

rocksof intermediateomposition. hese ocks e-

spondedo the indicatedlkalichemistry ithout

important ainsor losses.No marginal ediments,

compositionallyontrastingntrusive ocks,planar

rock fabrics,or prominent ectonicelements ro-

duced teep hysical r chemicalradientso influ-

ence the uniform zoning and symmetry.

Mineralogiconing t Kalamazoond elsewhere

suggestshat at least ouralterationssemblagesre

easily iscerniblen theporphyry opper ndmolyb-

denum eposits. he termspotassic,hyllic, rgil-

lic, and propylitic avebeenadapted r adopted

from he iterature Burnham, 962;Creasey, 966;

Meyer and Hemley, 1968) to describehe four

principal ssemblages.he terms "argillic"and

"propylitic"re well knownand widelyaccepted,

broadly describingquartz-kaolin-montmorillonite

chlorite-biotite nd chlorite-calcite-epidote-adularia-

albitealteration ssemblages,espectively. Phyllic"

is here applied o the assemblageuartz-sericite-

pyritewith ess han5% kaolin, iotite, r K-feld-

spar,and "potassic"s suggestedGuilbert nd

Lowell, 968) o includentroducedr recrystallized

K-feldsparndbiotite,withminorsericite ndhighly

variable ut persistentnd generallyminoramounts

of anhydrite. Each of theseassemblagesill be

more ully describedelow, speciallys theyoccur

at San Manuel-Kalamazoo. ther assemblages



.4LTERATION-MINER.4LIZATION ZONING IN PORPHYRY ORE DEPOSITS

377

pCqm

OREBODY

12

SAN M•NUEL FAULT

sw

• . Cc• - NE

•qml •{ SAN •

• KALAMAZ• SEAMEN _ •.•.'

lb

0 10•00'

I I

Approximofe Scole

Fxa. 1. Schematicrawingof structural istoryof San Manuel-Kalamazooeposit. (a) at time of emplacement

and (b) at present. Note the umbrella-likelare of dikeswarmand the chalcocitenrichmentone CCa). pœqm--

Oracle Granite, TKrnp= monzonite orphyry,Tcb= Cloudburst ormation, gc = Gila Conglomerate.

rarely encounteredn the porphyry nvironmentre

the advancedrgillic (Meyer and Hemley, 1968)

and pegmatoid,espectivelynvolvingquartz and

pyrophyllite,ith races f dickire r kaolinire,opaz,

and zunyite, nd quartz-coarseericite-K4eldspar,

with or withoutcarbonate,nhydrite, nd apatite.

Hydrothermalalterationassemblagesn the San

Manuel-Kalamazooeposit re summarizedn Fig-

ure 2, which showsalterationchangesmineralby

mineraland assemblagesn AKF-ACF diagrams.

Supergene ctivity is limited to a 200-foot thick

zonenear the top of the deposit.

The alterationzoneswere separated uring Kala-

mazoo exploration as follows. The inner limit of

the propylitic onewasplacedwhere he total quartz-

montmorillonite,quartz-kaolin, or quartz-sericite

content in plagioclase ites exceeds he total of

chlorite and epidotereplacingmafic minerals; here

the color usually changes rom green to light gray.

The argillic zone, n which kaolin or montmorillonite

predominatesn plagioclase ites and chlorite re-

placesbiotite, was not generallymappedseparately

and is least significantquantitatively. The inner

limit of propylitic alteration is locally the outer



378 J. D. LOWELL AND J. M. GUILBERT

SHALLOW-MODERATEEPTHSSEMBLAGES'

FRESHIM, PROPYLITICONE ARGILLICONE PHYLLICONE POTASSICONE

PORPHYRIES

Quartz NoChange Augmented Augmented Augmented

Orthoclase- Recry•tallized,npart eplaced

Microcline NoChange Flecked ithSericite Sericitized byalteration -felclspar-quartz

Plagioclase Tr. Mont, lecks& granules p, Fresh o completelyeplaced y

(An35.45) zois, car, chlorite, aol. Montmorillonite, Kaolin Sericitized brn-grn lt'n biotite,K-spar,ser.

Fresh or recrystallized ta sucrose

Biotite Chlor, ois, car, leucoxene Chloritized, leucoxene,tz Sericite,pyrite, utile brn-grn ranules, chlorite

...

Hornblen_d..e.._.p,car, mont, hlor 2 types) Chlaritized Sericite, yrite, uffle(?) Biotite,+ chlorite•utile

Magnetite trocepyr re Pyritized Pyritized Pyritized

A-K-C-F •Ac.(kaol} •A•.kool A A

A=A' ,a•a- ?•Cpx.•,•Fy,•,,.•••[,•,e/•

=Casalts C K ,•..•/,,;•car r?

= Fe,Mg r •..•

ß I•i '•.•-- py, pt•,mb

•rt . F "• P trocef

Veinlet Fillings O-cal- K-spar-chlor-rareb-rt Q-ser-py-chlor O-ser-py Q-K-spar-bi-ser-anhy-cal-ap

DEEP-LEVEL ASSEMBLAGES

OUTER INNER

•uar•z SlightlyAugmented Augmented

Orthoclase-

Microcline Dustedwith race sericite AlterationK-sparwith sericite, elicts common, inor uartz

Plagioclase

(An35-45) Dustedwith sericite, ohiorite,epidote Sericitized,with alterationK-s•r-quartz, relicts uncommon

Biotite_ Largelychloritized,minor pidotemag dded Chloritized, are primary elicts

,

Hornblende Chlorite Epidote Carbonate Chloritized;racecarbonate

•9•t•te Augmented Mostly yritized

A A

A-K-C-Fer••

= K, Na

K C K

C = Ca salts

F = Fe, Mg r?

• /• car?

ab,k-spar•_chl

•mag,py k-•ar mb

Veinlet Fillings •mag-py • Q-ser-cal envelopes Q-K-s•r-ser-chl, tr mag,py, cp• mb

Fro. 2. Summary of hydrothermalalteration assemblagest San Manuel-Kal,amazoo.

limit of either the argillic or the phyllic zone

of pervasive conversion o quartz, sericite, and

pyrite. The inner limit of the phyllic zone is the

outer limit of the first continuous section of sec-

ondary K-feldspar and secondary biotite, even

though the total quartz and sericite content here

ordinarily exceeds he total K-feldspar plus biotite

content. The zoningpatternsand intercepts an be

projectedremarkablywell from hole to hole. Sub-

sequent etrographic tudyhas contributedo these

descriptions f the zones,and subsequent ublica-

tions by J. M. Guilbert describinghe chemical nd

structuralmineralogyand physicalgeochemistry f

the alteration-mineralizationrocesses re planned.

In the following sections,he fresh rocks at San

Manuel-Kalamazoo are first discussed and alteration

zones exposedon a horizontalplane at moderate

depth are described uccessivelyutward from the

center. Alteration and mineralizationchangeswith

depth are discussedast and are summarized che-

matically n Figure 3a.

Fresh Rocks

The unaltered rocks at San Manuel-Kalamazoo

includePrecambrianOracle porphyriticquartz mon-

zonite and two varieties of much younger biotite

porphyries. The. Oracle "granite" is coarsegrained

(Fig. 4) with anhedral subrounded uartz units

about a centimeteracrossand commonly angential

to their nearestneighbors, ectangular o irregular

plagioclaseablets (Anas_45), nd interstitial quartz

and K-feldspar. K-feldspar species ncludemicro-

cline,orthoclase,nd microperthite. Severalauthors,

especially anerjee 1959) haveconsideredhe rock

palingenic, lthoughmany other workers accept ts

orthomagmatic rigin. Accessoryminerals nclude

biotite and hornblende,with trace amountsof zircon,

apatite,sphene,magnetite, nd very sparsemonazite.

The porphyriesare of at least two types. One

(here called Type A) is a quartz monzonite or-

phyry distinguishedy its zonedand twinnedoligo-

clase-andesinehenocrysts hich averageabout 5

mm and range up to 15 mm across Fig. 5), its

quartz-K-feldspar roundmassommonly ontaining



ALTERA TION-MINERALIZA TION ZONING IN PORPHYRY ORE DEPOSITS 379

SAN MANUEL FAULT

KALAMAZOO

SEGMENT

/

/

/

/

ARGILIC

I

SAN MANUEL

SEGM.•.ENT

PROPYLITIC

Chl- pi- arb

AduiAib.

•HYLLIC•'•

- Ser-py

\

\

)TASSIC \

Q K- feld Bi- •

-+ er•anh •

%

VEINS

PERPHEAL PERIPHERAL

p-gal,sl

Au-Ag

cp-gel-el

Au- Ag

mag +

VEINS

VEINLETS

DISSEMII•

DISS

DISS

'4-

MICRO VLTS

VEINS

ED

Fro.3. Concentriclteration-mineralizationonest SanManuel-Kalamazoo.a) schematicrawingf alteration

zones. rokenines nKalamazooidendicatencertainontinuityr locationnd nSanManuelide xtrapolation

fromKalamazoo.b) schematicrawingf mineralizationones. c) schematicrawingf theoccurrencef sulfides.



380 .T.D. LOWELL AND J. M. GUILBERT

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Figure 4

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Figure 6

FT6. 4. Fresh Oracle quartz monzonite. Quartz grains along top, microdine acrosscenter, and biotite at lower right.

Andesine unit at extinction at left. Both feldsparsmottled but essentially resh. Crossednicols, 15 X.

FT6. 5. Fresh Type A monzonite porphyry. The stippled sucrosequartz-K-feldspar groundmass s studdedwith com-

pound ectangularwinnedplagioclasehenocrysts. he white rectangular nit is a biotitephenocrystnd the blackblebs

immediatelyabove and to the left are quartz "eyes." Negative photograph,crossednicols, 3.2 X.

FT•. 6. Fresh Type B biotite dacite porphyry. Plagioclasephenocrysts re square, rai•ezoidal,or rectangular. They

are twi•_ned but generally unzoned. Negative l•hotograph,crossednicols, 3.2 X.



.dLTERATION-MINERALIZAT10N ZONING IN PORPHYRY ORE DEPOSITS 381

fine-grained, mbayedquartz "eyes" with stippled

overgrowth rims. Few quartz eyes exceed 1 mm

in diameter. Accessory iotite, hornblende, patite,

ruffle, zircon, and minor magnetite are generally

euhedral, the first two reaching 5 mm in length.

No K-feldspar phenocrystswere observed. The

groundmasss that of the widespreadquartz latite

porphyry and quartz monzonite porphyry of the

porphyry deposits. Its grain size averages .1 mm

and its texture is granularsucrose. Though ocally

variable, t averages 5 percentquartz and 45 per-

cent K-feldspar,so that the overallwhole rock feld-

spar compositionverages bout 35 percentplagio-

clase and 25 percentK-feldspar. The K-feldspars

are anhedral, granular, and mutually intergrown

with quartz; granular, often euhedral apatite and

rutile and shredsof mafic mineralsare sparse.

A secondporphyry (here called Type B) is a

biotite dacite. Plagioclase henocrystsn Type B

are generally oughly square o rectangularor even

trapezoidal n cross section (Fig. 6) rather than

compound nd zonedas in Type A. Rarely do they

exceed mm on a side. Biotitephenocrystsp to

3-5 mm are prominent. Quartz pheno:rysts re

absent,and the biotite-to-amphiboleatio is slightly

greater than that of Type A. The groundmasss

composed f intergrown microcrystals f sparsely

twinned plagioclase ith quartz, apparentlyslightly

later, and sparse K-feldspar. Rutile and apatite

accessoryminerals are rare.

It js difficult to estimate from drill core the rela-

tive abundances f the two varietiesof porphyry.

Type A predominates long the core of the San

Manuel-Kalamazoo system. Porphyry units form

an umbrellaor mushroom-shapedutwardexpan.sion

of diking at higher evels (Fig. la). Althoughpor-

phyry-quartzmonzonitecontacts re predominantly

sharp, hey may in somecases ppeargradational n

diamonddrill core, and the porphyry "dikes" must

be highly sinuous nd variable n attitude,especially

at greater depths. Indeed, an approach o wholesale

mobilization f porphyryconcurrentwith the potas-

sic alteration is suggested y coarselyvermicular

and diffuse contactsbetweenquartz monzoniteand

porphyry seen in drill core from deep within the

orebody.

Alteration Zones

Alteration zone boundaries re not affected by

rock type interfaces, t leastat the scaleof study o

date. Systematiccomparisons f fresh and altered

rockson either side of a particularcontacthave not

yet been made, but the various starting material

compositions,tructural characteristics,nd fabrics

seem o have responded early identically o alter-

ation processes.

Potassic one.--Several uthors, specially em-

ley and Jones 1964), Creasey 1966), and Meyer

and Hemley (1968), have discussedhe potassic

alteration nvironment.Hemleyand Joneshavede-

limited an environmental interface between K-feld-

spar and sericitestabilities,he latter with higher

HC1/KC1ratiosat a given emperature, n environ-

ment consistent ith late magmatic r early hydro-

thermalconditionsn the K-feldspar-sericite-kaolin

(pyrophyllite) ystem. nclusion f iron and mag-

nesium houldbringbiotiteor chlorite nto consider-

ationwith K-feldspar, ericite, ndquartz, n assem-

blagencreasinglyotedn porphyry opper eposits

(Creasey, 966) and assignableo a late magmatic-

early hydrothermal"deuteric"environment. Such a

biotite-K-feldsparlteration ssemblageith quartz,

sericite, nhydrite, yrite,chalcopyrite, olybdenite,

and tracesof bornitegenerally onstituteshe low-

gradecenterand part of the ore shellof the Kalama-

zoo deposit Figs. 7, 8, 9).

This innermostlteration one Fig. 3a) involves

pervasive nd veinlet eplacementf primarymin-

eralsby secondaryiotite,K-feldspar, uartz,seri-

cite,and o a lesser xtentanhydriteFig. 9). K-

feldspar ccurswith quartzas microveinletillings

that healminutestockwork-likeracturesn the pri-

mary rocksand also replaceoriginal eldsparso

varyingdegrees. "Rock" orthoclases fleshcolored

when fresh, turning slightlyorangewhere exten-

sively eplacedy alteration -feldspar.Typically,

quartz heals quartz grains, and K-feldsparheals

orthoclase,ith K-feldspar lsocommonlyeplacing

andesinelagioclasextensively,itherby rimming

or by advance long win planes. K-feldspar lso

locally eplaceslagioclasen the porphyry round-

mass. No albitizationasbeen ound, lthough re-

liminaryexaminationf alteration -feldsparndi-

catest to bemoresodichan heprimaryorthoclase.

Alteration iotiteoccursn four mportantmodes:

(1) as hairline einlet illings longwith chalcopy-

rite,alterationilicates,ndanhydrite;2) assparse

to massiveeplacementf plagioclasehenocrysts;

(3) as brightblackeuhedral nitsmegascopically

nearly denticalo primary ockbiotite; nd (4) as

locallypervasiveeplacementsf groundmasseld-

spars (Fig. 8). Alterationbiotite s recognizable

both by its fine-grained, ucrose, ubhedral o euhe-

dral form and by the coexistencef two distinctive

color variants, one a light tan to brown which

mostly redominates,he othera light applegreen.

Shagreens notpresent,ndbirefringences slightly

lower than that of the rock biotite. Chlorite inter-

grown with biotite is common.

The altered ocks,especiallyhe porphyries, re

distinctively igmented y groundmassiotitization.

Porphyries egascopicallyhowinghe smoky ray



382 .t. D. LOWELL AND J'. M. GUILBERT

1• .-":4.

•.,•

..•

•. -•. • .:•.•

.

.. •

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.

Figure 7

Figure 8 Figure 9

Fro. 7. A ',•" veinlet of mosaic quartz, K-feldspar, anhydrite, and biotite in potassicalteration assemblage.

feldspar (stippled, lower left corner) and anhydrite (vertically twinned) in veinlet. The white stippled ablet to right of

center in lower half of photo is a K-feldspathized-biotitizedplagioclasephenocryst n Type A porphyry. Crossednicols,

15 X. (b) The same field in plane light, showing shreddy brown biotite pervading he potassic ssemblage nd replacing

the plagiodase tablet describedabove. Plane light, 15 X.

Fig. 8. A veinlet of quartz, K-feldspar cutting Type A porphyry n the potassic lteration zone. Note rivulet replace-

ment of plagioclaseby alteration K-feldspar at upper center adjacent to veinlet. Groundmass s biotitized. Crossed

nicols, 15 x.

Fro. 9. A veinlet of dominant calcite, anhydrite, K-feldspar, and opaque minerals (pyrite-chalcopyrite) in a per-

vasively biotitized Type B porphyry. The finely shreddy groundmass s composed f fine biotite with scattered chal-

copyrite (black). Crossed nicols, 32 X.

(a) K-



ALTERATION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 383

color normally found with advancedpotassicalter-

ation generally also carry significantbase metal

values. Such rocks also show K-feldspar-richvein-

lets up to ¬ inch wide (Fig. 9).

The potassicalteration assemblage enerally n-

volvessparse o trace amountsof anhydrite,carbo-

nates,and apatite. Rutile and wolframitehave been

observed n several veinlets. Anhydrite, not pre-

viously reportedas a widespread lterationmineral,

commonly orms granules n the quartz-K-feldspar-

rich gash veinlets and in microveinletswhich cut

individual ock feldspargrains. Unlike biotite, t is

not generally a replacementmineral. It is wide-

spreadbut rarely abundant. Carbonates ccur both

in veinletsand as bits and shredsdispersedhrough

the entire rock. Apatite, thoughnot yet well studied,

occurs both as a veinlet mineral and as minor but

pervasivelydistributedanhedral units.

Phyllic Zone.--Surrounding and to some extent

overlappinghe biotite-K-feldspar one s a zone n

which alteration minerals include quartz, sericite,

pyrite, hydromica, minor chlorite, and traces of

rutile. This zone (Figs. 3a and 3b) generally n-

cludespart of the ore zoneand all of the marginally

mineralized nd pyritic zonesand is nearly coexten-

sivewith strongpyrite mineralization. Sericitepre-

dominatesn the inner part of this zone, clay min-

eralsand hydromican the outermargins. The most

distinctive assemblage,both megascopically nd

petrographically Fig. 10), is that of complete

sericitization f all silicates xceptquartz. Original

rock plagioclasend orthoclase re both pervasively

replacedby a felted mat of fine-grainedmuscovite

with abundantultrafinegranularquartz. Vestiges

of cleavage, oning,and twin planesof plagioclase

are retained n most instancesn preferredorienta-

tions of sericite lecks. Original biotitesitescan be

identifiedby relatively well-orientedalterationseri-

cite flecks,by less abundantalterationquartz, and

by either anhedralor sagenitic utile or leucoxene,

presumablyepresentingitanium from the original

biotite. Primaryquartz s unaffectedut generally

overgrown.

K-feldspar s totally sericitized n the innermost

phyllic zone, but shredsand scrapsof K-feldspar

persist n the outer part. Pyrite is abundant; hal-

copyrite s variable,generallyoccurring s dissemi-

nated grains,commonlyn sericitized ites. Pyrite

formsveinlets nd generally ranulardisseminations

in the pervasively hyllic-alteredmaterial. Pyrite

content anges rom 2-30 percentby weight, aver-

aging5-10 percent.Apatiteand utileagain ppear

to havebeen ecrystallized nd redistributed. Silici-

ficationwell beyond hat expected rom the break-

downof feldsparso sericite lus quartzplus alkali

ion appearscommon. Neither carbonatesnor an-

hydritewere dentifiedn the phyllic oneassemblage.

The phyllic assemblaget San Manuel-Kalamazoo

closely esembleshe quartz-sericite-pyritelteration

at Butte (Sales and Meyer, 1951), at Morenci

(Moolick and Durek, 1966), and at many other

southwestern orth Americanporphyrydeposits.

Contactsof the phyllic zone with the potassic

zone have beendescribed bove; hey are generally

gradationalover a hundred eet or so. Contactsof

the phylliczonewith the next outer most,argillic

zone are less definite.

Ar#illic Zone.--The argilliczoneat San Manuel-

Kalamazoos least well understood t this stage,

both mineralogicallynd distributionally. t is the

least well developed nd is the most likely to be

absentn any givenpenetrationf the ore deposit

symmetry. It is characterized y the conversion f

plagioclaseo either kaolin nearer the orebodyor

montmorilloniteartheraway rom the orebody en-

ter (Fig. 11). Kaolin is the more common eaction

product, radingoutward o sparse utlyingmont-

morillonite. Pyrite is commonbut much essabun-

dant than n the phylliczone. It is generally is-

tinctly veinlet controlled rather than disseminated.

Primarybiotitemay be essentiallynaffected,er-

sisting s shinyblackmegascopiclecks n a white,

earthyrock, or it may be in part converted long

cleavageo chlorite. The compositionalharacter-

isticsof this chloritehavenot yet beencompared

with thoseof the chloriteof the potassicnd deep

zones. K-feldspar howsminor fleckingwith seri-

cite and dustingwith kaolin,but it is generally ot

extensively ffected.

Propylitic Zone.--This zone contains the most

widely distributedand least distinctiveof the alter-

ation assemblages. lagioclase enerally emains

fresh (Fig. 12), although t is locallyribbedwith

eithermontmorillonite,aolin,or an apparentmix-

ture of the two minerals. Amorphousmineraloid

cloudinghe plagioclasesasnot conclusivelydenti-

fied but is suspectedn small amounts. Biotite is

replaced longcleavage y both chloriteand carbo-

nate, which generally decrease n abundanceout-

wardly. Epidote and calcite are common as fine

granulesn plagioclasend as coarser ggregates

with montmorilloniten amphibole ites. Bothalbite

andveinletK-feldspar ith minorcarbonate,uartz,

and epidoteare rare. Rock quartz is unaffected.

Chalcopyrites rare, but pyrite constitutes ne to

threepercent y volumeof the rock. The propylitic

assemblagerades nto argillicor phyllicphases t

the inner side over an interval of from 10 to 100

feetand s presumedo fadeoverperhapshousands

of feet in the outer reaches, lthough his has not

been proved.



$84 J. D. LOWELL AND J. M. GUILBERT

...

.

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--- •. %.z".-,. •.-' :'• .3'

a-?- :; , • .•%.... ::

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Figure 11

-.'7%• . ,;. : ::•,•.•"-•' i •*•.. •: :'• •. '":

• '•-':: •:. •' •: •.• • 4k : . .• • ..... ¾:-........ ß .•...•:

-.i ...... .;: '• • •.•' V • .•;• ': •-'•:,: • •::x;•.'.] • . • • ...... ..:•

'' .' • •--•-•'•-...-.."• '•:..'•2•"' ..i -*' : .... •--:..-•.'..•." • .D .'::.

;• ......'? :.: &. -•--.-?-:•m•.•..2.:.•.::'-:•-•'•½•:i•..-•.•;.:.•.•.:.;-7.-•.

":..•-i:/'' '..•-?• .:.:.•v'z-Tu-".•:'&.?'••k: .'.• .-: • ;"•.•'•

•' •.• ?-" , ' '•,:.•2...... .... •:-.•.... •;C•.,7'•.'2:'f;.•,

• ' '•. •' .. •.: -T."-.•:.- •' .::• • '.•::-:" .; : . ./' ';•-.•.'-' --e. '..•" .'--' -'• .

: •.• v• • _-.: &?:?•' z -- - ' - :•:.. '-•2-z- • ;•-.•;e--•- ' - '.:• :

•.:-:.,-L'3• • ':•' : ..•;•?---'_.•::•-...- '"•..•' •';::• .• •(•'- -•'

7•:••";.''?'• •-• ....":•--'-'-::•:......' • ........

L.:"2 •::•: "•;'-• i'5 • . .'? , .•:• :'• 5' • .: :• : ' ,'" . • '

.;;......... -• •-. .: g-,..' ..... ..,: ?,.. .'*•.:.;•'• : .....

. : ,:* .. ;'-:;;:•.- :.-.:.-.• ,.•' . .%.. . .• ...... :

'.,--;'• .• - ;•,. •'.1.?"..-1•...*,' --...,. . , :'-; .-.:...;•

..•" •.:.•: : .;. *•*., . .,-. • , • : . ..

':' 3;-...'"-;'-:•x' ':•, /';"' •' ,?-'" ' ":' ;• *:

Figure 12

...................... •:'-" * ' ' • :•" ;•;"':"::-'•::' •:;:=-;•';• ' .................. • ......... $•:,,:a-•,•:•?.•.•.•

FIG.10. Phyllic lterationf Oracle uartzmonzonite.hewhite ndgrayquartz nits reembeddedn plagioclase

andorthoclasenits,which ve been mpletely onvertedo sericite,uartz, ndpyrite blab). Perceptiblerienta-

tionof sericitendpyriteat bottome• denotesericitizediotite. Crossedimls,15X.

FI6. 11. Ar•lli•d T•e B potphys. Pl•lase in both ph•ocrysts nd •oun&ass •s beenconvert• to

weakly ffefringento1•, w•ch cont•s scattered•edsof sericiter hydromira. eeFig.6. S•rse pyrite, r•ci-

pally n pla•oclase henocrystites, s black. Crossed icols, 5X.

Fx6.12. Propylitizedype B porphyry.SeeFigs.6 and11. Plagoiclasenits repredominantlyhloritizedith

s• of epidotendcalcite visible s stipplingsn unitat lower ight). Biotite lade t upper ightandb•k at

le• center e c•oritized and pyriti•d. Pl•e light, 15X.




Deep Zones.--The deep zones at San Manuel-

Kalamazoo annotbe described ith certainty. Our

findingsare basedon only a few drill intercepts nd

may be modified n detailby further work and better

exposures. The grossrelationships re shown sche-

matically in Figure 2. A slight uncertainty,

especiallywith respect o chlorite-biotite elation-

ships, s introducedby the nearnessof the post-

Laramide an Manuel aultand ts pqssibleffects.

As shown n Figure 2, the propyliticassemblage

which rims the depositat moderatedepthsgrades

downward from propylitized Oracle quartz mon-

zonite nto a zone n which both rock feldspars re

dustedwith sericite. Biotite is largely chloritized,

and chloriteand epidote eplace mphibole. Quartz-

magnetite-minorpyrite veinletsup to « inch wide

are common and generally have narrow quartz-

sericite-chlorite elvages. The rocks are greenish

and free of alterationK-feldsparand biotite.

The phyllic zone is widest, possiblywith some

repetitionby steep aulting ust below the midpoint

of the orebody n the Kalamazoo ide,but is virtually

absent rom the deepest evels (Fig. 2). Moving

laterally toward the centerof the deposit t depth

(Fig. 3a), sericite ontent n alteredplagioclaseites

increases;magnetitecontentof the zone in veinlets

and as disseminations diminishes but does not dis-

appear. Narrow veinletsof chalcopyrite nd pyrite

occurWhich ack anhydrite ut have selvages f

nearly normal potassic lterationbut without biotite.

Neither typical argillic nor phyllic assemblagesre

discernible.The deepest enetrationnto the core

zone showsan assemblagen which K-feldspar and

sericite ustbothprimaryplagioclasend orthoclase;

in which veinletsof quartz-K-feldsparare flanked

and intergrownwith selvages f sericiteafter biotite

and plagioclase; nd in which magnetite,chalcopy-

rite, pyrite, and tracemolybdenite ccuras dissemi-

nationsand microveinlets.This deep-level spect

of the symmetryand characterof the Kalamazoo

assemblageesembles hat at Butte where alteration

envelopes lanking Main Stage veins decrease n

width at deepest evels with increasingly ommon

quartz-K-feldspar-sericite assemblages nd with

chlorite eplacing iotite (Meyer et al., 1969). No

real argillization s present n this deepzone at San

Manu•l-Kalamazoo.

Mineralization Zones

Concentric mineralization zones are coaxial with

the alterationzonesas shown n Figures 3a and 3b.

A plane normal to the axis of the depositat a

moderatedepth shows he followingzonesof min-

eralization.

Potassic one.--An innerzoneentirelywithin the

potassic lterationzoneaverages bout2,600 feet in

diameterndcontainsbout .3% Cualmostotally

as chalcopyrite. Total sulfide content is low and

pyrite-to-chalcopyriteatio s about :2; magnetite

•s rare or absent. Most sulfides are disseminated

grains. Surroundinghiszone Fig. 3b) is the ore

shellas defined y a 0.5% Cu cutoff ying n the

potassiconebut alsooverlappingnto the phyllic

zone. This ore shell averages bout 600 feet in

thicknessnd angesrom0.5%-1.0%Cu in grade

with a pyrite-to-chalcopyriteatio of 1:1. Pyrite

generallyormsstockworkeinlets; halcopyritec-

curs in disseminated rains.

Phyllic and ,4rgillic Zones.--There are three

rather distinct ypes of "ore" mineralizationn the

phyllicalteration one. The outerportionof the

ore shell, s ust mentioned,ies n the phyllic one.

Surroundinghe ore shelland entirelywithin he

phyllic zone s a zone about200 feet thick in which

coppermineralizationangesrom 0.1%-0.5% Cu,

with a pyrite-to-chalcopyriteatio of about 10:1.

Mostof both hepyriteandchalcopyriteorms ein-

lets. Surroundinghiszoneof marginalmineraliza-

tionbutstillentirely ithin hephyllic ndargillic

zonessa zone fpyritemineralizationhichanges

from1,000-1,500eet n widthandcontains%-

25% pyrite y weight.Pyriteoccurs ithquartz

in veinlets anging p to « inch hick.

Propyliticone.--Mineralizationn thepropylitic

zone onsistsf a fewsmall, igh-gradeilver, old,

chalcopyriteeins,and pervasive yrite n veinlets

whichconstitutes%-6% by weightof the rock.

Since he outeredgeof the propyliticonedoes ot

cropout t is uncertainhether isseminatedyrite

is coextensiveith propylitic lteration. The area

of pervasiveyrite einletsontains00-500 pm

copperwhich s apparentlyncludedn the pyrite

since iscreterimary opperminerals avenotbeen

found in this material.

Vertical Changesn Mineralization.--Totalsulfide

contentndcopperontentn the ow-gradeortion

of thephyllic onedecreaseithdepth. The char-

acterof the mineralizationppearslso o change

with depth rom inergrained isseminatedrains

to coarser rainedblebs. In the ore shell, here s

remarkablyittlechangen copperradewithdepth,but the chalcopyritegainchanges ownwardo a

predominantleb-type isseminatedccurrence.As

shown nFigure b,a progressivelyreater ortion

of theoreshell ccursn thepotassiclterationone

as depth ncreases. ittle changewith depth s

noted n the marginal oneexcepthat magnetite

substitutesor muchof the pyritenear the bottom

of the orebody.Similarly,magnetiteubstitutesor

mostof the pyrite n the zoneof peripheralyrite

mineralizationear the bottomof the orebody.

These elationshipsre alsoshownn Figure3a.



386 J. D. LOWELL AND J. M. GUlLBERT

Molybdenite and Bornire Distribution.--Molyb-

denum showsa tendency o be concentratedn the

middle two thirds of the ore shell (Fig. 3b) with

lower grade zonesat the upper and lower portions

of the ore shell. Within the 0.5% Cu zone,molyb-

denum grade in individual drill intercepts ends to

increasewith coppergrade and with thickness f the

ore shell. Higher grademolybdenum ccurs n both

the potassic nd phyllic zonesand doesnot seem o

be controlledby lateral alteration zoning, but from

the standpointof vertical zoning, molybdenumcon-

tent drops off at about the same level that deep

alterationassemblagesecome mportant (Fig. 3a).

Althoughonly a dozenor so bornite dentifications

were recorded in drill hole logging, bornite also

tends to occur in a short vertical column less than

half the total length of the column of copper min-

eralizationand nearly centeredbetween op and bot-

tom of the ore-gradecopper nterval. Most bornite

is found with potassic lteration but it occasionally

occursalso in phyllic and propylitic zones.

Comparison of Porphyry Deposits

The authors have used the San Manuel-Kalama-

zoo lateral and vertical zoning data as a framework

into which informationon zoning in other porphry

depositsmight be fit. Table 1 is a comparisonof

the geologiccharacteristics f 27 major North and

South American porphyry deposits or which de-

tailed information is available. The table summarizes

the descriptions s well as possible, lthough careful

interpretationwas required simply in selecting he

appropriatecolumn in which to enter information.

Factual information, widdy known but not neces-

sarily in print, has also been judiciously ncluded.

Entries for most deposits ave beenreviewedby the

geologistsmost familiar with them. Abbreviations

used are listed on the page preceding he table.

The table first compares reorecontrolsand geo-

logic settingof the deposits--age, hape-size,ompo-

sition, sequence f intrusion,and mode of emplace-

merit of the igneous ost rock. Orebodies re con-

sidered n termsof shape, atureof externalbound-

aries, percentof ore in ore-stage gneous ocksand

preore rocks,dimensions,onnageand grade. More

significant,however,are the sectionson hypogene

alteration, hypogenemineralization,and sulfide oc-

currence.

The problem was approachedwith a model in

mind, but without assumptions oncerning ts cor-

rectness. This model assumed hat the porphyry

depositenvironment s one of coincident lteration

and mineralization involving silicate-sulfide-oxide

equilibria n a large, significantlyhree-dimensional

petrologic-mineralogic ystem. These assumptions

appear confirmedby the consistency f combined

depositdescriptions.

We adopt the four alteration assemblage ames

earlier defined. Twenty-fiveof the 27 deposits e-

scribedcontain a phyllic zone, so it serves as a

referencepoint in constructing he table. Other

alterationypeswereenteredwherever hey fell with

respect o that quartz-sericite-pyrite one according

to the descriptions.

At least 17 porphyriesapproach he form of a

steep-walledcylinder. Another seven, including

threemolybdenumeposits, howelements f stubby

cylindrical or inverted flatly conical form. The

chieflycylindricaldeposits re the most distinctly

zoned. The innermostor deepest nd/or generally

earliest one) is typicallypotassic;he next outward

zone s phyllic. Beyond hat is the commonlyhinner

and lesswell developed rgillic zone,and the outer-

most zone is propylitic. Ore mineral distribution

and sulfideoccurrenceroved o be consistentlye-

lated o alteration.A summary, olumn y column,

of the data entered n Table 1 is presented.

Deposit (Column1)

This columngives he namesand locations f the

deposits.

Preore Host Rock (Column 2)

This columncites ock typesand ages nto which

the igneous ost rocks of the respective eposits

havebeen ntruded. Thesepreore ocksmay be

mineralized,s at Bingham nd Safford, r the pre-

ore wall rocksmay be too remote,as at Butte. An

appraisalof the importance f preore rocks with

respect o ore control s given n Columns14 and 15

under Orebody." t is apparenthat igneousost

rocksmostcloselyelated o ore in time and space

are emplaced enerally igh n the geologic olumn.

Of the26 depositsor whichpreorewall rockages'

are available, deposits avepenetratednto late

Cretaceousreorematerials, are in older Mesozoic

sections, are in Paleozoic ocks,and 7 occur n

Precambrianocksonly. In several eposits,he

youngerectionsf thegeologicolumnanbe pro-

jectedover hemwithoutaddingmore han a few

thousandeetof capping bovehe top of the por-

phyry deposit. Probablymineralizationn mostof

the porphyrydeposits xtended pward o within

a few thousand feet of the surface.

Igneous ost Rock (Columns -11)

The third major sectionof Table 1 describeshe

igneous ost ocksof the porphyry eposits. he

names f Column apply o the intrusiveunitsmost

intimately associatedwith the orebodies n both

space nd time. Agescited n Column apply o

the intrusive osts ather han o the ore deposits



ALTERATION-MINERALIZATIONONING N PORPHYRYOREDEPOSITS' 387

TA•-•. 1. GeologicCharacteristicsf 27 Major PorphyryCopper nd Molybdenum eposits

ABBREVIATIONS-TABLE 1

Minerals rc rhodochrosite

ab albite rd rhodonite

Ag silver & silver minerals rt rutile

anh anhydrite ser sericite

ank ankerite sl sphalerite

ap apatite specspecularite

Au gold& goldminerals stb stibnite

bar barite tm tourmaline

bi bioti•te tn tennantite

bn bornite trem tremolite

cal calcite tt topaz

car carbonate V vanadiumminerals

cc chalcocite wf wolframite

cp chalcopyrite

chl chlorite zo zoisite

clzo clinozoisite

cs .cassiterite Rocks

alsk alaskite

cupcuprite And ndesite

cv covellite

apl aplite

dck dickite Dac dacite

dg .digenite Db diabase

dol 'dolomite Dio diorite

eh enargite gn gneiss

ep epdote G granite

feld feldspar Gd granodiorite

fl fluorite Iph lamprophyre

fm famatin'ite L. latite

gal galena Is lime•tone

gr garnet M monzonite

gyp gypsum p porphyry

hbl hornblende peg pegrnatite

hm hematite Qd quartzdiorite

hn 'huebnerite QI quartz atite

ill illire Qm quartzmonzonJte

kaolkaolin Qmp uartzmonzoniteorphyry

magmagnetite 'Qp' quartzorphyry'

mal malachite. qtzt quartzite

'mb molybdenite Rhy hyolite

mc marcasite sch schist

mn manganeseinerals seds ediments

montmontmorillonite sh shale

ss sandstone

py pyrite volc 'olcanics

prp pyrophyllite

pyx pyroxene

Q quartz

GeologicTime.

Lar Laramide

T Tertiary

K Cretaceous

Trias Triassic

Meso Mesozoic

Perm Permian

Penn Pennsylvanian

Pal Paleozoic

pC Precambrian

Alteration

Arg Argi c

Phyl Phyllic

Pot Potassic

Prop Propylitic

Mi scel laneou s

adv

bx

Cu

diss

fit

irreg

#vlt

Mo

mod

ND

repl

text

tr

vn

vlt

advanced

breccia

copper

disseminated

fault

irregular

microveinlet

molybdenum

moderate

no data

replacement

sulfide

texture

trace

vein

veinlet

weightpercent



388 J'.D. LOWELL AND J. M. GUILBERT

PREORE IGNEOUS HOST ROCK

D E P O S I T H O S T R O C K Age Controlling

Name (m.y.) Structures Shape

(1) (2) (3) (4) (S) (6)

Ajo pCgn;Meso(?) m; Cornelia uartz 63' steepNW ault elongate W

...... ?..n.•............................•..n..a:...t.•.....................m..o..n.?. .t..,............................................p..o..?.? .•.,...?.o..•..............r.r.e.• .•.•...................

Bagdad pC volcs, sch& G Bagdad tock 71 N 70 E[& N 30W its irregular

Arizona lenticular

Bethlehem Triassic volcanics GuichonQd &. 200 N-N 25 E fits irregular

....... .t .•.h....ce... •.•....................................................,..t.h...,.•.•..•?................................................................................m.• .t. .p. .:...p. •........

Bingham Penn Binghamtock 37 NE & NW its irregular, ipelike,

......u.•.h..............................q..t..t..>.....m..,..t..o.•?...................................................................................................................t..e.?..p........................

Elisbee pC sch; Pal Is, Sacramentotock 163 steepNW it; NI= its irregular

.......rj.•.o.•.........................[.,.:..•.a.•t..o.•.,..........................................................................................................................

elongate ¾,

Braden K-T And& teds brecciatedDac p mid-T (?) N-S & N 55 E fits circular&

.......C•.. . .e.....................................................................tock, d ß elongateikes

Butte Pal Is, sh, st; Boulder Batholith 72 NW & EW its batholith

Montana K And elongateNE

Cananea Pal teds; Lar volcs La ColoradoQp' 59 N & NW its irregular tocks,

Sonora & intrusive ocks plugs

CastleDome pC sch& pC G Lost GulchQm, 64 N40E fits irregular tock

.......r. •.o.•................................................................. .•..• .t.?...•.r.p..h.y..•.........................................................................................

Chuquicamata metaseds& volcs Chuquicamata Ear N & N l0 I= fits narrow,semicon-

......c...•. .'......................................................................•.p...................................................................................................,.•.o.•...u..j..s..•...•..,.

Climax PC sch Climax hyolite 30 N-S anticline circular,pipelike

........ce. .o..r.•.a..o...............................................................p?..r..p..h..y.?................................................p..o..?.. ?..n..t.•..o.............................................

CopperCities pC sch & pC granite Lost GulchQm, 60 N501 stockelo. gateNI=

........r.•.•.o.•.................................................................e..r..a.• .t.e....p..o.r..p.•.y..•.y......................................................................................

I:1 Salvador r( And, rhyolite I=1Salvador tock Lar(?) NI: & NW its elongateNI=

Chile

I:ly Pal Is, st, sh I:ly stock 109 I=-W its irregular

......u..:.¾.?..a..•...................................................................................................................................................................' .ø..n.•.t.'...•.,-..W...........

I:ndako early Meso eds TopIcyQm,alsk 139-143 NW& I:NI: fits irregular

British Columbia & volcanics & granite elongateNW

.....................................................................................................................................• ............f/C•i'•"g"h'"•'i•;•........';;'•'•'i•;...................

:speranza K fragmental& I:speranza tock

........r.•.•.o.•.........................w..,...a..,..a...•.•..•..q..t..•.t................................................................................................................[•r.•.,....•.•.•.k................

Inspiration PC sch, G, qtzt & Schultze uartz 60 N 50 I= fit irregular

Arizona Db monzonite large stock

.......r .•.o..n.•.........................m..,..t.?. S•.,..•.n..,. •.....................................................................•.W...?.•.t...........................•..W...........................

Mission-Pima Pal, K, I%cene 60 not recognized sill-like, tabular

Arizona sediments

Morenci pC G, Pal--•Aeso Morencistock Lar Pc NI:; K NW elongate

...... •.o.• ...........................•.,..•:.• ..............................................................................................................................

Ouesta Miocene(?)And, Questamine 30 N, NW its very irregular

........-•..•.,..x. .?.o...................•.t .t..,.:..•.•.y..o. .t,..............p.. .t..,...•..•.h..y...,.............................................................................•..m. •.[....................

Ray pC teds, metaseds, GraniteMt. Qm 63 I=NI schistosity irregularmasses

Arizona Db; Pal limestone NNW its in NI=belt

Safford K Qm,Qd, Rhy,QI, C) Weber eakdike 58 NW its & NI= shears dike swarm

........r. ?.• .........................:..•..a. .k..,.•.•..p. •..a•.... ..w.•.r..m............................................................................................,.. .o..n..?..,...•.•............

SanManueI-KalamazoaPC quartzmonzonite SanManuelMp 67 NE[& NW its irregular,mushroom.

Arizona shapedstock

Santa Rita PaI-Meso (K) teds Santa Rita'stock 63 NNW & NI= fits complex,elongate

New Mexico NW, domical

Silver Bell Pal & K teds Silver BeJl stock 63 NNW fit stock

......r •.o..n.•.............................................................................................................................................................,.[.o..•..a.•t..e....U..W............

Toquepala late K ?) Rhy,And, daciteporphyry 59 none ecognized irregular tock

Peru Dio elongate N-S

Typical Porphyry Pc-late K teds & Qmstock 65 NI= & NW its elongate

Copper metasediments irregular




iGNEOUS HOST ROCK-Continued

Size Modeof Stock- Sequence f Rock Types

(feet) F:mplacement Dike Intrusion Mineralized

(7) (8) (9) (10) (11)

3000x 10,000 passive stock Dio 4 Gd 4 Qm 4Qmp4 vfg Qm all

'"•'•6';Fg6'//6'..............................: ..................................................................................2 ......; ......................................................................

assive stock Rhy Gd Q Dio p-4 Dio p all

.......................................... -4Qmp

• 12,000x 5000 probably assive stock> dike Qd 4 Gd 4 Dacp .4 Lp .4 Rhy all

'"g'ci66';F•6i•..................................................................................................................•; ...............................................................................

assive> active stock> dike Qd Gd; /p, QIp all + seds

'"•iiti•i'•''6'6i•....................................................................................................................;'.........................................................................

assive> active stock 'Qp' 'feld Qp' all + seds

(both altered)

4000 x 4000 passive> active stock> dikes Qd 4 Dacp 4 I_p 4 Iph And, Qd, Dacp,

/p

150,000 350,000 passive batholith Qm apl, peg)-4Qmp all

8000 25,000 passive> ctive stock dike Dio,Gd,sy, G.4 QI• E•b all + seds

cluster

'"•J'l•'l•'•'•'•'•J•[.... passive stockdike Gd4Qm4Qmp4G 4Gp4Db Qm, p& Db

'"•'C•'•"•"(•J•J•J•'-•..... passiveactive(?) stock dike sodo d4Qd4Dio4Qm4 all(?)

......................................................................................................................................•.•.p.....o...a..•...a..p........................................................

4- 3000 x 3000 active stock> dike Rhyp 4 apl p 4 Gp all

'"•/6•i'/i•';/"i'•i/i///'//'/•......;';';•i'•;•.............................................................................' ......; .........,"-;......; ..........................................

tock Qm apl alsk Db Gp all

'"/•/'•';•"i•;'6•///.................;';';';i'•;;............................................................................-;........; .........................................................

tock> clikes,sills Gd Gdp 'Qp' all

large,elongateEW passive stock dikes,sills M, Qmp omplex all + seds

'"¾//61iJiJii";,"i'•ii6i•;"c/6'6........;•';i;;;;¾.*'•...................................................................................• ........; ............; .........................................

tock> dike Qm.4 G alsk Q reid all

'";/•;'•i:i";,"•;/•i•i•......................"•;•.........................................................................................; ...............................................-•.....................

ass, stock> dike Qm.4 Dio Qmp.4Andp all seds&

voles

'"•/6/c•i:i';•...........................;;•';i'•;;.............................,';;'•'•;"•/ii•;.....................5i;"•;"'•'•'5':-;"i5i;....................................-7/•;';•;•;•i•....

0,000 all

'"•6///i';i'•///•..............................' ................................................................................................................................................

ass, e stock Qd 4 Qmp4 Qp' 4 Qp'+ Q Qmp 'C)p'

............................................................................................................................................................................p.2+...9................

+__4000 4000 passive sill > stock Qmp all + seds

'"•'¾i•;'666';•'b;'6'66............; ';' ; " •'•;i'• ...............i ; ii " "ili'l g ............•i'; ;"-7o;;;;"-75';,"-;6i;.....................'•;;' i ;..........

in wall

"i'•'6i:iii;,"•//ii•i•...............;';;';'i•;;.............................................................................................•;...............;;..........................................

tock dike Mp, Gp, bio G apl, apl d[l: voles

.....................................................................................................................................a...•..y....p..........................................................................

8000x 15,000 passive stocks dikes Qd 4 Db 4 Qmp4 And 4 Qmp4 all + metaseds

2000x 4000 passive dikeswarm QIp, Rhy,Dac,Qd,Gd 4 Dac 4 all + vales

...................................................................................................................................... ,...k,...a...•.y..................................................................

;4000 7000(?) passive stock dike Mp 4 Qmp4 Db all

'";/'66/i';F•//•.................................................................................................................•;....................................•;...........................................

ass,ve stock> dike Dio Qd+ hbl Gd & bi Gd Qd, Gd+ seds

..........................................................................................................m.•......................................................................

> 10,000NE passive stock si I > dike alsk 4 Dacp 4 Andp 4 Omp all + seds

30, oooNW

"i'g66'•"•'•'6'6'...................../:'ilk;;................................;;/'i;i'•';'•½"/li'i/g................•'g"/;...................................................;ii"•'i;;Fg"•,'g'i•;•"

4000x 6000 passive stock dikes Dio 4 Qm 4 Qmp4 Op' all + seds



390 .t. D. LOWELL AND .L M. GUILBERT

OREBOD'Y

D E P O S I T Outward hape Boundaries Percent n Percent n

IgneousHost Preore Rocks

(12) (13) (14) (15)

Aio oval, elongate W original& faults 80? 20?

Arizona

..................................................................................................................................................4:..................

longateoval original +_90 10

Arizona

"ifii;'d4 .......................................................................................................................................................................

teep, elliptical cylinder original -t-50 +50

British Columbia

Bingham pear-shaped,longateWSW original 75 25

Utah

................................................................................................................................................................'6'................

longateEW,oval original & faults + 30 +

Arizona (incl. bx)

Braden hollowcircularcylinder original& postore reccia 25 75

Chile pipe ..........................................

............ 0 .......... o .........................

Butte crudely omical original 100 0

Montana

Cananea pipelike originalbrecciapipe + 90 + 10

Sonora

,• ......................... 0,oo, .............................................................................................. o ..................................................................................................

Castle Dome oval, elongateNE original& NW ault 100 0

Arizona

...................... ............... .......................................................................

Chile

.0 ..... , ............... ,,,,o,0,, •o,,,, ...................... o ................. , ....................... • ............................................................................................ ,., ........... , ......... , ....

Climax nested, nverted ones original 40(?) 60(?)

Colorado

o0,•.o,•,, ........... ,.,,,,o,,0,,o.,00 .... ,o, o,.o ....... , ......................... 0 ............................................. • ......... , ..................... ,...•., ......... 0 ..... 0.,,,., ............................ ,,,o,.,

Copper ities oval, elongate W Original NE & N• faults 100 0

Arizona

.o[,,• ......... , ..... ,..,0 o..,,,o0,0 ..... , ...... , ..................... o .............................................................................................. ........................ , ........... •.,.o ................

El Salvador oval pipe, lowergrade original 70(?) 30(?)

Chile center

......... 0 ........... 0,.,, ..... 0 .............. • ..... • ............................................................................................................................ ,.,.0, ....... ,,., .................... 0 .........

Ely ?flat cylinder original with faults 80 20

Nevada above & below

......................... 0 ,,

Endako elongate val original 100 0

British. Columbia

.... 0, ............ ,o ................... ,,, ......................................................................................................................................................................................

Esperanza elongateNWoval original 60(?) 40(?)

Arizona

oo., ............... ,.0.o.o ..... • ................................................................................................................................................................................................

Inspiration flat cylinder original & fault 50 50

Arizona

.o ..... 0 ......... , ......... ,,,.o,,.,,o., ........

Mineral Park crescent, convex SW + 100 • 0

Arizona

,, ....... o ................. o ....... , ............. 0 ................ .................. .................. ... , ................. .................. ...... , ................. .................. ......... , ..... , ......... , ......... o ....

Mission-Pima oval original & fault + 10 +_90

Ari zo n a

.............................................................................................................................................................................................................

_ 70

orenci oval original + fault

Arizona

o.,,,o,o,0..,,.,.,,, o0.,...,.. ..... 0.0 ........................................ , ................................................................. o ........................................... 0 .......... 0 ......................

Questa irregular original 70(?) 30(?)

New Mexi co

,,..., 0,.0.,.,,0 ................... , ..... 0 ...... 0o. ............. , ..............................................................................................................................................................

Ra•rizon irregularval,longateW originalault 20 80

,0o,,,, ....... ,..,0,0,0.o,0 .o0 ........ , ...... , ..... , ............. , ....... 0 ........... , ................ .................. ................... ...... , ................. ... 0 ................. .................. ... , ........... 0 ....

Safford oval, dippingpipe original 20 80

Ari zon a

,,.0o, ..... , ........... ,,0 ........ 0 ................ .................. .................. ....... • ................ .................. .................. .................. .......... 0 ................. ............ 0., ...............

SanManuel-Kalamazoo hollowoval cylinder original 50 50

Arizona

,0 ................. , ...............

SantaRita oval• elongateNW original +_70 +_30

New Mexi co

....... , ...................

Silver Bell elongate val mineralbelt original 70 30

Arizona

o, .... , ........................... ,,,,0 ............................................. , .............................................................................. 0 ..... • ................ , ..................................

Toquepala oval, elongateNW original: brecciapipe 70 30 (walls

Typical Porphyry oval, pipelike original& postore aults 70 30

Copper



ALTERA TION-MINERALIZA TION ZONING IN PORPHYRY ORE DEPOSITS 391

0 R E BODY- Continued

Dimensions Total Ore Tonnoge Grade Grade

(feet) (million) Hypogene + Supergene Hypogene Only

(16) (17) (18) (19)

4000 x 7000 < 500 0.75% Cu 0.75% Cu

1000 x 5000 < 100 0.76% Cu + 0.5% Cu

+ 0..025% Mo + 0.025% Mo

2000 x 3000 < lr00 0.6% Cu 0.6% Cu

... •?..r.?.:..y............................................................................................................................................................

5000 x 7000 WSW > 500 0.75% Cu 0.75% Cu

0.05% Mo 0.05% Mo

2000 x 2000 < 100 0.81% Cu + 0.55% Cu

ñ 5000 x 5000 > 500 2.25% Cu 1.00% Cu

...•.o.).o...w...:..y. ?..4?..r..................................................................................O....O..5.•...a..o........................................0...O..5.•...a..O..................

5000 x 10,000 EW > 500 0.8% Cu 0.2% Cu

250 x 1200 > 500 0..8% Cu 0.5% Cu

....r.•.?..•.:•.s..a..p.. ......................................• ?. .:.t.?..................................................................................................................

•_ 1500 x 3000 < 100 + 0.70% Cu + 0.5% Cu (?)

2500 x 10,000 > 500 + 1.7%. + 1.2% Cu

"';ii:Ji:JiS'":ii:Sti/5...................................:'•6i:i......................................."6'.'•/qo'/,i•...................................•'i3•i•;i'qo"//•.................

1500 x 2000 < 100 + 0.60% Cu + 0.4% Cu

'"õiSi•ti',";/ti/5/5..................................................................................' .............................................................................

500 1.5% Cu N D

+ 1000 x 3000 x < 500 + 0.9% Cu + 0.1% Cu

........1..o..-...2..o.,..o..o..o................................................................................l...•.2.•...:.o...m..m...o.?.................................0.:.4..•...o..m...m..o.................

1200 x 6000 > 100 + 0.09% Mo •_ 0.09% Mo

ß

2300 x 4200 .( 100 0.51% Cu + 0.3% Cu

0.028% Mo 0.028% Mo

2500 x 8300 < 500 0.90% Cu 0.15-1.20% Cu

0.007% Mo

.... iJiS'•"•';i6• .....................................................................................................................................................................

100 0.5% Cu 0.1-0.15% Cu

0.04% Mo 0.04% Mo

5000NW x 7000NE ) 500 0.8% Cu 0.8% Cu

6000 x 13,000 ) 500 0.88% Cu 0.1-0.15% Cu

0.007% Mo

7000 x 7000 ) 500? 0.15-0.18% Mo 0.15-0.18% Mo

3000NS x 10,000 EW ( 500 0.80% Cu 0.10-0.80% Cu

+ 4000 x 5000 > 500 0.50% Cu + 0.2% Cu

cross section: 2500 x > 500 4- 0.75% Cu -t- 0.75% Cu

5000 x 4- 8000 high 0.015% Mo

5000 x 7000NNW < 500 0.97% Cu 0.1-0.2% Cu(intr)

0.8% Cu (tactite)

....2000x 2500& < 100 ............................................................J•':•'"6•l'•"E•'iig;i•...

.75% Cu

1500 x 2500 0.8% Cu (tactite)

4000WNW x 5000NNE • 500 0.9% Cu 0.3% Cu

3500 x 6000 150 0.80% Cu 0.45% Cu

0.015% Mo 0.015% Mo



392 .r. D. LOWELL AND .1. M. GUILBERT

HY POG EN E ALTERATION

D E P O S I T Known Extent

Beyond Ore (ft) Peripheral Zone Outer Zone Intermediate Zone

(20) (21) (22) (23)

Ajo + 5000 ?chl, ab, zo, ser, Q, ank

Arizona

Bagdad 500 + N D not reported not reported

Arizona

Bethlehem + 300 N D Q, chl, ep Q, kaol, mont

British Columbia

Bingham 3000 + chl, talc, kaol, ep, Q, chl, kaol, cal, ep

........u..t•..........................................................•.r..,..m..?..•.,...•..y..x....................................................................................................

Bisbee 7000? chl, ep, zo, cal, ser ? kaol, ser(?)

Arizona

...........................................4:•6i:3•..................•'i;'•37•};7•'•;•.......'•'i:;;;,7'•3; •i;•;•'•;•ii........,;•'"'"•'•,';;7;;,'i;•'•.................

raden

Chile tm

Butte 1000 + Q, chl, ep, cal Q, mont, kaol

Montana

Cananea 5000 chl, ep Q, ser, kaol

Sonora

Castle Dome 3000 chl, ept py, ser, cal & mont

Arizona c l zo

Chuquicamata few hundred chl, ep, cal, spec, hm, kaol ) ser

Chile TiOx

.............................................................................................................7'•i'i•i7•;'C.,'i..................';'•'•';'•'•'•................................

limax 2000?

Colorado

CopperCities 5000 + ep, cal, clzo, ser mont, Q

Ari zon a

..........................................................................................................................................................&';•;ii'ii•...................................l Salvador 1000 + py, chl

Chile

.............................................................................................................;-g•.•.ii¾i•;;•...............................................................

ly 2000

Nevada

..........................................................................................................................................................................................................

Endako 2000 + (?) kaol weak, Q, cal kaol moderate, Q, chl

British Columbia

Esperanza N D not reported Q, kao , mon

Arizona

.0ooo ........... , ..... , ................................................................................................................................................................... , ................

Inspiration 1500 + chl, ep Q, ser, kaol

Arizona

Mineral Park 10,000 chl, ep, clzo, Q, ser, 'clay' Q

.......•.r .z..o.?.?......................................................•.t?.•.t......................(.•.•. .•. •......................................................................

Mission-Pima up to 5000 skarn, tactitc, hornfels present

Ar i zo na

Morenci ) 5000 skarn on SE chl, ep Q, mont

Arizona

.........................................................................................................................................................................................................

Questa 2000 + (?) ser, car, kaol, ep, ser, Q, py -3_ al, kaol, ser, Q, py -3_ al, kaol, ill

New Mexico chl i l I, fl

...........................................................................................................................................................................................................

Ray 1000-15,000 chl, ep, ab, cal, mont o

Arizona 20,000 x 30,000

Safford -3_ 2,000 ep, chl "chloritic"

Arizona

....g•'•'•'•'•'" •'•'•'•'•g ....5•5•5•5"'•'6'•6..............................................' •i4i';'•;',"fi•'i....................•7•fi•;'i•'gf;i.............................

Arizona

....•a'•"•i• ..................... 5000 tactite tactite ahl,ep (Argillic)

New Mexi co

.... ii•;•;"8'gl'•'.....................................• .....................................................................................................................................

3_ 2,00• 5000 chl, cal, ser, mont Q, ser, kaol

Arizona a Iteration zone tacti te tacti te

Toquepala m nor; <• 1000 mon

Peru

Typical Porphyry 2500 chl, ep, kaol, chl, ep, cal Q, kaol, ser, mont

Copper (skarn)



/ILTERATION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 393

HYPOGENE MIN ERAI-IZATION

D E P O S I T Peripheral Outer Intermediate Inner

Alteration Zone Alteration Zone Alteration Zone Alteration Zone

(28) (29) (30) (31)

Ajo spec, bar cp, py, bn, mb,mag,hm py cp= 1:4; py, cp

Arizona py:cp • 1

.... .............................•.;.•.•:x•.;.•.•...........................................................................................•..•.•..•..• ..........................

•ri zona

ß -•i•'• ........................;'•'•-;-•'•................;'•"•'•';'•'•'..............'•"•'•"•'• ......................."•"•'F•'• ............................

British Columbia

Bingham en, fm,gal, py py, cp, mb

.......u..t..•.............................. :.t..t......................................................................................................................................

Bisbee sl, gal, py, cp ND ND py, cp, bn, cc, mb,s I

.......• .•..o.•........................................................................................................................................y, •.p..•...]..0.•............................

Braden gal, sl, Ag, py py ) cp ) bn ) mb ) en

.......• .?.............................t.•:.•.y....................................................................................................m.•..•.•.n....................................

Butte Mn, Ag rc• sl, gal, rd py, bn• cp, tn py, cc, en•bn

Montana

ß ananea gal, sl, tt, Ag py, cp, bn, mb, sl, gal py, cp, bn, mb

Sonora

Castle Dome sl, gal, py, cp, py py • cp • mb py • cp • mb

........•: .•..o.,?.•..........................•.,...v..,..•.o.,...p.•....................................................................................................................

Chuquicamata minor sl, gal, py, cp en, cp, co, bn, py(?) en, cp, cc, py, bn(?), mb

........a,.. . .e............................• ................................................................................................................................

Climax gal, sl, Ag(?) py, tz, fl, hn,cs mb, cp

Colorado

Copper ities sl, gal, Ag py py• cp• mb py • cp mb

Arizona

Pl Salvador gal, sl, Ag py, spec ND py - cp

Chile

Ely Au.& base py, cp, high total sul

.........a..• ...........................t•. •. ..n..•.a.•.................................................................................... ?.•....s..-.. ..0........................

Pndako sl, gal, kg spec,cal mag,py, mb, py,mb,mag

.........•). ....ce..•.m.• ...........................................<..:..0•.•.•................<...0.... •.•.•.........................•..-. .:.0.•.•.............................

F:speranza gal, sl, kg py py > cp > mb py > cp > mb

Ari zon a

Inspiration cp, gal, sl, py • cp(?) py • cp py • cp • mb

Arizona mb, V, Mn '

MineralPark Au, Ag, gal, sl py, cp, sl, gal py, cp py, cp, mb

Arizona

....•i•i'•'"i•i;;;,'................';;i•'•i•"/,•...............i•;•;•;.........................F......................................................................

Arizona minerals' py, p,mb

Morenci gal, sl, Au, Ag py py:cp=-high;high py 3-8%; cp 9.3-0.5%;

.........• ..•.o..,.•..........................................................................................o..,•. .• .L.p..,. . .................•,..?.,..•.,.. ..........................

Questa py,mb,gal, sl py,mb, py,mb mb,py, cp,hn

.........•... •.o. ..................................................c..p.z.o.•.•..z•...........................................................................................

Ray gal, sl, py, cp, bn py, cp, bn py, cp, bn,mb

Ari zona

Safford Ag,cp Au, cp ND py, cp,mag, t, gal, sl

Arizona py 4-8%; cp +_0.4%

py:cp :- 10-20:1

.... a• ;,;•;;iz.'R•i•,• ....';'•'l';'•'i;..............,'•,"i'i'fo•'...................;•,"i'i'f•)'..............................;•," i'6'foi'i'• ;"ii•;'i"'•i•'i..........

Arizona Au, Ag mb(0-0,05%)

Santa ita sl, gal, Ag, py.4-8%; cp• 0.4% py 1-4%; cp 0.4-1%;

NewMexico spec,cp, 'inc py:cp= 40:1 mb;py:cp= 3:1

.... i'i•,•;"•i;;ii......................'•',"•'gi;';i...............'•';'•'•'i;';'(';/i...........;•;•;"'"•i'i........................;•;•'""i'•'i.............................

Arizona .

Toquepala minorcp,bar no py halo modpy:cp low py:cp;higher otal sul;

Peru low total sul py, cp, bn, sl, mb

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

y • cp • bn; mod py • cp • mb • bn; high

Copper total sul; py:cp=23:1 (10%) ot sul; py:cp= 13:1

.



394 I. D. LOWELL AND .1'.M. GUILBERT

H Y P 0 G E N E A b T E R AT I 0 N - Continued

Zoning Sequence Vertical Sequence

Inner Zone Innermost Zone from Center from Bottom

(24) (25) (26) (27)

(Q, ser, py)? Q, K reid, chl (anh) partial overlap

.........................................................................................................P.e.t...-..,..P.h•...-....•:.?..•..................................................................

Q, ser, K feld hi, ab, Q, K feld .Pat Phyl

Q, ser Phyl - Arg - Prop

Q, ser, K feld if_clays, Q, K feld, hi, ser Pot.- Ph•.l - Prop

chl

:•p', Q,dck,prp; adv.Arg& Phyl

........• .a...•.p..'.'..•..2:...s.•.r......................................................................r.g....•..•.r.o..p.........................................................................

Q, ser, hi, anh Q, ser, hi, anh Pot & Phyl - Arg - Prop Pot - Phyl

'" •';'';;' •,•)i'"6';'i i•"/,';•.........'"•"• •"i•i';' ;'i•i•¾ ..........l•'g;'""'/•i4•i'"'"•';•'""iu;•.......•';"-'"'l•'/,'•;i"'"'•;•'""'i•';•/•;....

.........g'l:......................................." •'i•' l•'i'•'•'i;/i.......................I•'L'•/'i'"'"•'•..................................................................

,,,,,0,,. 00o 0, •o,.,.,,, 0,0, ....... 0 ........... ,,,40.,.0,0 ...................... 0 .................... • ........... 0 ..... ,.0., ............................. ,•, ......... .,,00.,,,.0.0 ..... .0,, ...... ,.0..00 .....

Q, set, hydromica,K feld Phyl - Arg - Prop

.......................g;.............................................................................•'K•;i'"'"X;•'"'"i•';g•;.................•'i5..........................................

, K feld,

..... ................................................"'i•';;ii'•D....................................' .............................................................................

eld, Q, hi,' fl Q K feld - Q, py, ser Q - K feld - Q, py, ser

..........................................................................................................-;..5• :..•..............................................................................

Q• ser, py, hydromica Phyl - Arg - Prop

....;•"6';'ggL"•';'•........................"•;"•/;"/(igi•ii"L'L'L'•.................%';"'"'•i•{;i'i•'i""";•L'•'•'i'"'..... •g¾'"•'g•,'ii'.ff'"'•';•"".........

.........................................................................................................•.:• .........................................P..:•...............................general i ...........

•seri½iti½ •potassic • granitoid -p texture;

.............................................................................................................................................................•.?.:...-:...;.. ..*x......................

Q, ser, py, kaol Q, K feld, bi Pot - Phyl - Arg ND

Q, K feld Q, ser, K feld, bi Pot - Phyl - Arg(?) not reported

..........................................................•?,. ..•.?..,.:•..•.:.....................................................................................................

Q, ser, kaol K feld• hi, ser Pot - Phyl - Prop ND

Q• se• py Q, K feld (earliest) Pot - Phyl - Arg - Prop not reported

Q• ser• clay(?); skarn Q, K feld• ser• bil skarn Pot - Phyl - Arg -

•karn

,******•e•******•,****,,o.**,,,,,,,,,,,0,,,,,,,,, ,,,,,,,.,,,,,,,**,,,,,,,,•,,,,,.,,,,,,,,,,,•,,,,. ,,,, *************** **************** **************** ******

Q,set,py ND "J•'•,'i"""X;'•":"l•'ig'•.............ot eported

Q, K reid, bi • cal, Q, K reid (anh)

.... •b..•L•.............................................................................................................................................................

Q• •er • kaol bl• Q• ser• K feld Pot - Phyl - Arg - Prop ND

.... . 9.9.q:.•..].9.9.9.?................... •.•..•.9•.9. ...........................................................................................................................

Q, •er• py K feld• bi, Q, ser Pot - Phyl - Arg - Prop

""•;'•g)•'• ................................•;'"•"'g'l'•i"g'/;'B .....................•'gi":"• i":"•;•'"Z'•'g......g•":"O'g•'i•'fi........................

•,,,...,,,,,..,. ,...,,,,,.,, ,.,., ....... ..,,, .... 4 ........ ,.,,,.,. ......... ,,. ......... , .......... ,•..,,.,..,.,. ........................... ,,.,...,* ....... .-,....., ......... , ..... ,,.,,,,,**,,,,,,,,, ..... ,.

Q, set, py, tactitc Q, K reid, hi, plag, Pot - Arg - Phyl - Prop

........................................................•.•.b..m•L•.• .........................................................................................................

Q, ser• ta•i• Q, K feld, ser, Pot - Phyl - Arg - Prop ND

.......................................................• ............................

Q, ser• py Q, tm, hi, K feld poorlydeveloped anhydrite t depth

Q, ser• py Q, K reid, hi, ser (anh) Pot - Phyl - Arg - Prop Pot - Phyl(?)



,4LTER,4TION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 395

HY POGEN E MIN ERALIZATION-Continued

Innermost Overall Abundance Zoning Sequence Vertical Sequence

Alteration Zone Major Ore Minerals from Center from Bottom

(32) (33) (34) (35)

mag; cp; py, bn; cp• py• bn• mb(?) mb > cp -> py -> spec cp:bn decreases

low total sul

............................................... ... i. .............................................. ... ß ............................................ ........ i .......................................... . .....

cp•py• mb py•cp •mb cp -> py ND

............................................... ... i ............................... , ................. ß ................................................. ... i

cp•py•bn•mb bn -> cp ->-py ND

.................................................. i. ................................................. a .................................................... i. .............................. ß .....................

cp, bn, mb mb -> bn -> cp -> py ->

y•cp•bn•mb Cu to Pb-Zn in veins

...........................................................................................................•?..•:..•.. :..•:..•.?.................................................................

py> cp> bn> cc not reported less py upward

.................................................. • .................................................. i ................................................... i. ....................................................

py;:>'cp• n• mb• en py• cp• bn• mb• en (cp, py, bn, rob) > •(bn, p,mb) > (cp,bn,py, mb)

.................................................. (py, p) > gal, l, Ag) -> py, p,mb, n)

..... : ........................................... • ......................... , ......................... ,•,,.. ............. , ...................................

cp, py, mb py• cc•en•bn• cp mb-> p->py-> c->en-> mb-> p->py-> c->en->

..........................................................................................................•.?..•.r..a.•..• ............................:•.•.r..a.•..• .......................

py, cp, bn, mb py, cp) bn, sl, gal not reported ND

.............. 0 ............................................. ....................................... i ............................................... .... ß ........... 0 ............................. 0

py• cp• mb cp->py->sl, gal, Ag) cp->py(?)

................ ,.,,. ............................. i, ............................................. .... e ............................................... .... ,i ............................................. ........

en, py, cp, cc, bn(?), mb py> en> cp>bn> mb py->cp->py(?) ND

.... ;,'i;;•;;';•'•'..................................;;;'"'•;i•......................................•i;:;•'•':;'i;•'...............................i•;•';';•;;;•i;•...........................

.............................................................................................................................................................m.•.?•..-.•?.... ..........................

py) cp) mb cp->py-> sl, gal, Ag) py->cp(?)

.... F"•'•'•'•'" •'• ........................;•' •' •'•'• .........................•'•';'•'•'•' i•'; •'• •' ............';'•';'•'•'•'•;'• • .................

.......................................................................................................v..?.?..•.• .•..................................v.:.?•?.............................

py, cp, bn• mb py) cp)) •bn';mb (cp, bn, mb)->py-> ND

.... .x •.•. ..:....................................................................................•:.?.•.:.?.........................................................................

mag,mb•py •.15py mag•py•mb•cp mag->(py,mag,mb)-> ND

.........................................................................................................m...•:..?•..P...-t..P.•. •.P. ............................................................

py) cp) mb(?) py) cp)mb cp, mb-> y ND

cp• py• mb(?) py• cp• mb (cp, mb)-> y ND

.... ;,;;';•'i•';'•,'i................................';,;5''•;'•i• ...............................:•'•'•,'•'L;•;' ¾•'•'i;'; ..............•'5......................................

Ag,Au)-• (Au, Ag)

....;,;;'•;';•i•................................;;,;•'•'5'•';,'5'•,'•,'5'•'i...............;•;'•;,;;'•,'•'i•'¾;•'•'i;•;'•;•i;';i'i'/•'5......................................

....• •"'i•; :'•'i'•l'•"•' ?'..............." 5'•; :•;i5",•i;...................•;:'L'i:'•i:;i':;•'•,;......................,'L'";•;•g;;',',•...........................

.... .v.,..•,....m..,...•.............................................................................•. .,.• .,..•.,..•.u...................................................................

mb,py, cp, hn py) mb• cp, gal, sl mb-> cp, py)-> gal, sl, mb) not recognized

1000 ft

py, cp, bn, mb py> cp•bn• mb cp->py-> gal, sl) ND

............................................... ... • ............................................. .... a ................................................ .... • ........................................... .........

cp, py, bn, mb,mag,t, gal, py•cp•bn•mb ' (cp, mb)->py->Au mb at depth

sl; py 0.2-1%, cp 1-2%

.... . •.•..o.:. ................................................................................................................................................................

py (1%); cp (1-3%) py) cp) mb cp->py-> gal, sl, Au, Ag) cp->py

mb (0.01 -0.05%)

................................................ .. • .................................................. i .................................................. . •. .............................................. ......

low total sul; py•1%; py•cp•mb•bn low. grade center-> nnular py zone contracts& py:mag

py:cp= 10:1 ore zone & (cp, mb)->py-> increases

..........................................................................................................•.•..,..?.. ,..?.. .....................................................................

py, cp, bn, tt, mb,-sl py• cp• mb• bn• sl cp->py-> Ag, gal, sl) ND

Q, tm+minor sul py+__=p•bn, mb (Q, tm)->cp->py not observed

anhydrite at depth

py• cp?mb• bn; low 3%) py• cp•mb•bn (cp, mb)-•py-• (gal, sl, (cp, mb)-•py

tot sul; py:½p 3:1 Ag, Au)



396 .t. D. LOWELL AND J. M. GUILBERT

OCCURRENCE OF SULFIDES

D E P O S I T S Peripheral Outer Intermediate Inner

Alteration Zone Alteration Zone Alteration Zone Al•erati6n Zone

(36) (37) (38) (39)

AJ•rizon veinlets diss/•vlts diss/•vlts

Bagdad vns & massive vlts • diss diss • vlts

.......• .z..o.n.•........................r.•.p. •?.m..•?.t....................................................................................................................

Bethlehem veins veinlets veinlets veinlets

British Columbia

Bingham veins & vns, vlts, diss vlts, diss diss) vlts

........u..t•.•.................................•.• •.m..•?..t.............................................................................................................................

Bisbee vns, vlts, ND ND vns, vlts, diss

Arizona mass. repl.

Braden veins patches & vlts vlts & patches vlts • patches

Chile

Butte vn, vlt vn, vlt vn, vlt vlt, vn, diss

Montana

Cananea vein veinlets vlts, diss, mass. vlts• diss

So•ra

Castle Dome veins veinlets diss • vlts diss • vlts

Arizona

............................ , .......................................................................................................................................... 0 ..................................

Chuquicamata veins vns & vlts vlts • diss vlts • diss

Chile

.............. , ................. .................. .................. .................. .................. .................. .................. ................... .................. .................. .......

Climax vns & dikes vlts • diss vlts • diss

Colorado

................. , ....... , .................................................................................................... ,,.. ......................................................................

CopperCities veins veinlets di ss • vlts di ss • vlts

Arizona

"' •i"'•i•'•;•......................,'•i• .............................i';•5•'ii•"•'...................;i•'•';'•'ii•".•...................i'•"•;i¾•'...............

Chile

.............................. ,, ..................................................................................................................... , ...................................................

Ely diss • vlt diss • v.lt

Nevada

...................... , ....... , ................ , ..... , ............................................ .................................................. .. , ....... , .......... , ....... 0 ........................

Endako vlt • diss vlt • diss vlt •-- vlt

British Columbia

............... , ........... . ............................................................................................................................................................................

Esperanza veins vns & vlts vlts diss • vlts

Arizona

.,,., .......................................................................................................................................................................................................

Inspiration veins vns & vlts vlts •' diss vlts • diss

Arizona

.................... , ........... ,., ...... ,.. ........................... .., ................................................................. ß ...............................................................

Mineral Park veins vlts• vns, stkwk vlts• vns, stkwk vlts, vns• stkwk

.......•r. .z..o.?.?.................................................................Z.q.i..?..P.?.?. •..................:•.7...?.P.. ..•.."..•.................:•.'.•. ..P...?.•.?..•...........

Mission-Pima vn & vlt vlt, diss &

Arizona massive

.......................... ,.,.,o,o,,,0 ...... , ..... 0 ............. . ................................... . ................................... . ....................... 0 ........... , .............. ,,.,,..•0,.,0 .....

Morenci vns, Is repl. vlts • diss ND vns, vlts, diss

Ari zon a

...................................... . ..... , .................... . ................. ß .................................................. : .................................................................. ,..,

Questa veins paint vlts vns & vlts

New Mexi co

........................................................ ,., ........... . .............. , .......................................................................................................................

Ray veins vns, vlts, diss vns, vlts, diss vlts,, diss, vns

Arizona

.................................................................................................. 0 ......... 0 ..... . ............................................. , ............................................

Safford veins in shears, vns, in shears, vns, in veins, vlts, diss

........•..z..o.•?...................... eikes dikes

...... 0..,,, .,,0.....• ,.. o,,0.,,0 .... , ........ ....... ........ .o... .......... ,.., J .............. , ................................... , ............................

SanManuel-Kalamazoo veins vlts vlts • diss vlts • diss

Arizona

.................... , ..... . ............................ • ...................................... , .......... . .............................................................. , ........................ , ..........

SantaRita veins vns & vlts vns & vlts vlts,/•vlts• diss

New Mexico

......................................................................................................................... , .................. . ............................................... , ...............

& tactite & tactite vlts • di

ilver Bell vns vns ss vlts • diss

Arizona

...........................................................................................................................................................................ii'•'•'•:'•i¾•'...............

oquepala veins di ss • vlts

Peru bx vug fillings bx vug fillings

Typical orphyry veins vns& vlts veinlets vnlts diss

Copper



.4LTERATION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 397

OCCURRENCE OF SUL. FIDES-Continz•ed

Innermost

Alteratio0 Zone

(40)

diss •/•vlts

Breccia Pipes

(41)

not reported

Crackle Zones

(42)

beyond ore limit

SUPERGENE

SULFIDES

(43)

minor co, cv

diss • Its

.... i¾;"•;';1'/;';'...............................;;;; ;;:i'•,";,;'/;•';;;;;ii'•';,';i...........;'/ii-;•'f;;;';•';;;"•,';;;,'................,';';,';.....................................

...................................................... ..................................................................................

.... Ji'•'•'•";'i•;........................n gal,sl zone extendseyondal,sl co,cv

.......................................................p..,. ......................................................................................................................

important; 2 stages NE horsetail zone cc

vlts • patches postore with min. frag. present cc • cv

diss • vlt none horsetail zone cc, cv, dg

vlts• diss numerous& mineralized present co, cv

............. ............. .............. ............. ...... ; ............. ............. ............. i- ............ .............. ............. ......... .• .............. ............. ............. ......... ....,

present? present co, cv

vlts) diss large central pipe horsetail zone co, cv

irregular clots minor breccia, dikes present none

present present co, cv

diss,/J. lts deep, central, mineralized present cc • cv

diss) vlt present present co, ½v

.... . ........................................... .. • ................................................ .. • ................................ , ................. ß ............................................. .......

diss • vlt not reported present none

diss • vlt present present cv, cc

vlts • diss (?) not reported present cc

.................................................. • .................................................. • ................................................. ,• ............. , .....................................

vlts, vns, stockwork none present cc

.... ...................................................................................................................................................

vlt, diss & massive ore N-S dike; poorly developed cc• thin zone

.......................................................p.:...•..a. .,..?. :..t..t..................................................................................................................

breccia zones• in pit extensive co, cv

...................................... , ......... ,. ................................................ .. > .................................................. ß ........................................... . .........

vns & vlts present, important extensive none

...... , ................................... , ....... ............................................. ..... • .................................................. .................................................. ..

vlts• diss, vns present & mineralized present cc• cv

ß

.......... . ....................................... • ..................... , ............................ • .......... , ...................................... ,• .................................. . ..................

vns, vlts, diss present & mineralized present co, cv

.................................................. • ............................. , .................... • .................................................. ß .................................. , ................

diss • vlts not reported + 5000 ft diameter cc

................. ................... .............. • .................. .................. .............. • .................. .................. .............. ß ................ ................... ................

vlts•/J. lts, diss one 500x 2500 ft pipe• samearea.as intrusive cc • cv

mineralized

................. ................... .............. • ................. .................. ............... • .................. .................. .............. ß .................. .................. .................

ND none NW horsetail zone cc

......... , ................ ........... •, .............

.... •'•'•:¾•''•'Ji'i'•"•' •i'•'•...........•;•'•"•'•'J•i'•'J"•' •; .............'• •"•'•'•;•';,'•'•'•i'•' ..... cc

small mineralized

',; :• •:•;•::;:::: ::: :::: :: :::•: ::: ::::•:::•;;: ;:::J: '.:;•:: ::::: ::::::: :: ::•:: :: :::: :::,:: ::::: :::::: :J::::;: :::::::: :;: ;::: :::; ::•:; :::::: :: t.'::; '-:: :::: • :::: ::: ::;: :•: ::::: ::;: ::::: ', ::: •:::;::: •:: ::: :::: :.

diss )//vlts present& mineralized present cc) cv



398 I. D. LOWELL AND J. M. GUILBERT

associated with them, but evidence shows that ore

depositionwas essentially ontemporaneousith in-

trusion within the precisionof the I(-Ar technique.

Age dating of the Laramide-mid-Tertiary interval

in the Southwest eported by Damon and Mauger

(1966) has indicated wo distinct pulses, one of

Laramideplutonic ctivitybetween 0 and75 million

years ago and one of dominantlyextrusiveactivity

during mid-Tertiary time approximately 0 million

years ago.

Table 1 includes ges or depositsn British Co-

lumbia and South America as wall as southwestern

North America. Six of 27 depositsare of mid-

Tertiary age at 30-37 million years, 17 are probably

in the Laramide range of 59 to 72 million years, 3

are in the Jurassic ange of 122-143 million years,

and 1 deposithas a 200 million year Triassicdate.

Of the Southwestdeposits ncluded n Table 1, all

are of Laramideage except hree mid-Tertiary de-

posits (Climax, Questa, and Bingham) and two

Jurassic eposits Bisbeeand Ely), two of the mid-

Tertiary onesbeingporphyrymolybdenum eposits.

The pattern for porphyry dates emerging in

British Columbia eemso be one in which parallel,

overlapping, orthwest-trendingrits of mineraliza-

tion increasen age from west to east. The single

numerical age for a South American deposit n

Table 1 is for Toquepala, eru, at 59 millionyears.

However,geologicelationshipsnd recentdatingby

Chileangeologistsndicate hat many of the South

Americandeposits re of mid-Tertiary age.

Controllin#Structures (Column 5).--Column 5

lists attitudesof regional-scale tructures hought to

have controlled he emplacement f the stocksand

batholithsand hence the porphyry deposits hem-

selves. Considerationwas given to local structure

shownon publishedmine and district maps n pre-

paring Column 5, but many bounding aults shown

on thesemapsare of postoreage or of multiple age

such hat their preore importance annotbe deter-

mined. Greatereliance as hereforelaced pon

direct text statements han upon maps. Several

authors comment hat the specifics f controlling

structureswere obliteratedby the intrusionswhich

they guided.

Shapeand Size (Columns6 and 7).--The shapes

of intrusions (Column 6), like determinations f

their size (Column 7), are difficult to establish

meaningfully,sinceboth have been affectedby in-

ternal and externalvariables. Exposureof a pluton

is certainly affectedby original depth and by post-

intrusion ectonic nd erosional istory. The Boulder

batholithhas been exposed or tens of miles, and a

large southernArizona batholith (Ettlinger, 1928)

has been inferred from the distributionof cupolas.

The shape nd sizeof porphyryhost ntrusions eem

to be related o contemporaneousnd younger ault-

ing and uplift. Table 1 shows hat most of the host

igneousbodiesare somewhat longateand that dis-

tricts with strong structuralcontrol tend to include

pronouncedlyelongate stocks.

Column7 lists the size of igneoushost rock out-

crops for each district, the numbers having been

taken from texts or measured rom geologicmaps.

These dimensions re in part subject o the same

uncertainties s the descriptionsn Column 6. The

dimensionsndicate that the porphyry copper de-

positenvironment ascommonly evelopedn stocks

or cupolaswith crosssections f well under a square

mile at the elevationof ore deposition. There ap-

pear to be two host-rock izepopulations, ne group

less than a mile squareand another smallergroup

of very large dimensions.

Mode of Eraplacement Column 8).---These en-

tries adopt the terminology nd tend to confirm he

conclusions f Stringham (1966) regarding mode

of emplacement. Stringham'scriteria are extended

to include the additionalporphyry copper deposits

described ere. Emplacement f the porphyrycop-

per deposithost rocks s shown o be almost otally

passive. This passivitysuggestshat replacement,

stoping,and assimilationwere more importantpro-

cesseshan shouldering sideor other manifestations

of forceful intrusion,and it also suggestshe likeli-

hood hat both lateral and verticalpetrologic oning

might be more common han has been recognized.

Comparison f Column 8 with Columns41 and 42,

the latter reporting brecciation nd shatteringspe-

cificallywithin the orebodies,eveals hat brecciation

or shatteringare associatedwith ore deposition n

every porphyrydeposit,even where emplacement f

the host stocks s passive. This disparity suggests

that brecciation nd shattering re themselves pas-

sive," and that they can commonly e expected o

be "blind," as they are at many southwestern orth

Americanporphyrydeposits nd prospects.Force-

ful intrusionand active, even explosivebrecciation

as at Toquepalaand Braden are apparentlyrare.

Extensivemagmaticstoplng, ssimilation, nd meta-

somatism ppearmechanically nd kinetically ncon-

sistent with extremely shallow emplacement, ut

moderatelyshallowenvironmentsmay be indicated.

Porphyry molybdenum epositsseem to show

more evidenceof forceful emplacementhan do por-

phyry coppersn general. This evidence onsists f

ring and radial dikes and doming of the layered

rocks which sometimes verlie the deposits.

Stock-Dike (Column 9).--Column 9 indicates

that stocks and stocks with subordinate associated

dikes are far more typical of porphyrycopperde-

posits han are dikes,dike swarms, r breccias lone.

This same dationshipwas indicatedn Column6




where porphyry depositswere shownto be equi-

dimensional to oval rather than tabular or linear

bodies. Twenty-fourof the 27 depositsnvolve m-

portant stock development nd a high ratio of stock

to dike forms.

Sequenceof Intrusions and Rock Types Mineral-

ized (Columns10 and //).--The sequences f in-

trusion shown n Column 10 reinforceearly observa-

tions (Buddington,1933) of the association f cop-

per deposits ith intermediateo felsic gneous ocks.

Except for generally late diabasedikes, no rocks

more mafic than diorite occur in the intrusions as-

sociatedwith porphyry copperdeposits. Granodi-

orite and quartz monzoniteand their aphaniticand

hypabyssalequivalentsoccur in almost all of the

porphyry copperdeposits,with more felsic variants

common to the porphyry molybdenumdeposits.

Most papers consulted n preparing Table 1 give

specificsequences f intrusive events and igneous

rock compositions,ut uncertain ield relationships

coupledwith paucityof radiometric ge determina-

tions seldom ermit unequivocaldentification f the

beginning nd endingof the magmatic pisode hat

involved ore mineralization. Much older and much

younger ocks,as describedn the appropriate efer-

ences, are excluded. Column 11 shows that all of

the intrusive rocks of Column 10 are mineralized

in 22 of the 27 depositsabulated nd the youngest

intrusiveunit is mineralized n 2 of the remaining5.

Columns 10 and 11 show that the sequences

generally from dioritic to monzonitic ocks, com-

monly with late latitic to rhyolitic or "quartz por-

phyry" intrusions. Typically, all of theseare min-

eralized, showing hat mineralization ither accom-

panied or briefly succeededhe emplacement f in-

trusive rocks. The association f porphyrycopper

depositswith intermediate lutonic ocks s impres-

sive but not as consistent as the association with

porphyry n all 27 districts isted. There has been

discussionn recent years as to whether the name

"porphyrycopper" s appropriate or the group of

deposits escribedn this paper. The writers be-

lieve that this associations genetic ather than co-

incidentaland feel that "porphyry copper" is an

excellentdescriptivename for this unique and im-

portant group of ore deposits.

The lamprophyreor "late diabase"event is less

commonn the porphyry oppershan hasbeenpre-

viously thought (Spurr, 1925). Late diabasehas

been reported in only 5 of the 27 districts. The

general trend, clearly, is from dioritic plutonic to-

ward more felsic hypabyssal ocks with all rock

types usuallymineralized. The degree o which the

shift from dioritic through granodioritic o monzo-

nitic rocks may reflect K-feldspar enrichmentby

means of potassicalteration (Peters et al., 1966)

will be considered elow. Dioritic rockscommonly

occur at intrusionmargins,as at Ajo and Mineral

Park, with progressively ore K-feldspathic ocks

inward, a relationshipnot apparent in the table.

This distribution s consistentwith apparent elsic-

component nrichment ccompanyingotassic lter-

ation near the central portions of some porphyry

copperdeposits.

Orebody (Columns12-19)

Outward Shape (Column /2).--The porphyry

copperdeposits lmost ll havecircularor oval cross

sections.At least our deposits aveclearlydefined

low-gradecentersproducinga ringlike orebody n

plan. The vertical dimensionsof hypogenemin-

eralization n most depositsare unknown; however,

the tabulatedhypogenemineral bodiesseem o fall

into three general configurations.

1. Seventeendepositshave a steep-walledcylin-

drical shape. Two deposits Cananeaand Toque-

pala) approximately oincidewith brecciapipes.

2. Sevendepositshave stubbycylindricalor flat,

conical orms,as do all three of the porphyrymolyb-

denurndeposits.

3. Three deposits Inspiration,Ely, and Safford)

have a gently dipping, abular shape,perhaps epre-

sentinga depositsimilar to (2) following a preore

structure r postore isplacement,r they may repre-

sent a separate type.

Boundaries Column 13).--In all of the deposits

studied, he orebodyboundaries re at least in part

gradationalor "assaywall" boundaries. All have

been ntersected y a postoreerosionsurface. Eleven

are boundedby at least one postore fault. Two

coincidecloselywith brecciapipes which are preore

or contemporaneous ith ore, and one deposit

(Braden) forms a crude cylindricalshell surround-

ing a postorebrecciapipe.

Percent in I#neous Host and Preore Rocks

(Columns 14 and 15).--In several deposits,100

percentof the ore mineralizations in igneoushost

rocks (Butte, Castle Dome, Copper Cities, Endako,

and Mineral Park). All contain someore in igne-

ous host rocks, but most ore at Bisbee, Braden, Mis-

sion, and Ray is in wall rocks. Somethingike 30

percentof all ore mineralizationassociated ith por-

phyriesoccurs n wall rocks,again suggesting upola

or at least high-levelenvironment or the porphyry

deposition.

DimensionsColumn16) .--Horizontal dimensions

of the tabulateddeposits ange from 250 x 1,200

feet for the La Colorada ipe at Cananeao 6,000 x

13,000 feet for the Morenci deposit. Fringes of the

difficult-to-limitButte district may reach to dimen-

sionson the order of 20,000 x 50,000 feet (only the

"porphyryequivalent" or Butte is cited in Column



400 ]. D. LOWELL AND J. M. GUILBERT

16). The averagedepositsize deducedrom pub-

lisheddescriptionsnd maps s a perhapssurpris-

ingly small 3,500 x 5,000 feet.

Total Ore Tonnageand Grade (Columns 17, 18,

and 19.)--Of the 27 depositsabulated, 3 are esti-

mated to containover 500,000,000 ons of ore, 6 fall

between 100,000,000 and 500,000,000 tons, and 8

contain ess than 100,000,000 ons. These tonnage

estimates ust be considerednly approximate.

Included in these figures are several deposits

whose ore grade dependson secondary halcocite

enrichment. Averagegradeof copperore is 0.80%

Cu, and averagegrade of hypogenemineralization,

where this information is available, s 0.45% Cu.

Twelve copperdeposits ontainat least 0.5% Cu in

hypogenemineralizationand 10 contain less than

0.5% Cu. Molybdenumdepositsaverage 0.17%

Mo in grade.

Hypogene dlteration Columns20-27)

The next three sections,Hypogene Alteration

(Columns20 through27), HypogeneMineralization

(Columns 28 through 35), and Occurrenceof Sul-

fides (Columns36 through 42), have parallel or-

ganization so that the columns for each zone in a

given deposithave denticalheadings. For example,

the innermost alteration zone at San Manual-Kala-

mazoo consistsof quartz, K-feldspar, biotite, and

minor anhydrite Column25), and the ore minerals

(with amounts) are pyrite, chalcopyrite,molyb-

denite, and trace bornite (Column 32). The sul-

fides occur more commonlyas disseminationshan

as veinlets (Column 40).

It should be restated here that the table is based

as completely s possibleupon publisheddescrip-

tions, and these are hardly uniform in approach,

detail,or even erminology.Severaldeposit escrip-

tions were based on temporal rather than spatial

relationships;hesedepositswere enteredas earliest

equals nnermost,and so on outward. Several de-

posit descriptionsnvolved separateand poorly re-

lated descriptions f alteration, mineralization,and

occurrence. We have made every effort to match

appropriatespatial and mineralogicaldata. Ques-

tion marks in the table generallydenoteuncertainty

of placementof the information rather than un-

certainty in the data.

The problemof distinguishingetween upergene

and hypogene ffects s important. Hemley and

Jones 1964) curves ndicatesericitestabilityonly

at moderately igh K+/H + ratios at low tempera-

tures, an environment onsistentwith (but not re-

quiring) high pH. The extremdy low pH pre-

sumed or activesupergene nrichment onesargues

against mportantdevelopment f supergene ericite

and indicate he kaolin minerals o be stablesuper-

genesilicatealterationphases. Nonetheless,uper-

gene sericitehas been reported. Supergene ffects

havebeeneliminated rom Table 1 whereveroriginal

authors rovided escriptionshichwouldpermit t.

Known Extent BeyondOre (Column 20).--Col-

umn 20 records the stated or mapped extent of

alteration eyond he outerboundary f the orebody

itself. These distances are somewhat uncertain since

differentobservers rew the outer line on differing

criteria. External alteration is narrow around the

Bethlehem, .C., deposit, characteristicf many

of the Canadianporphyrydeposits. Other deposits

show alteration extending housands f feet, aver-

aging approximately ,500 feet. The higher num-

bers probably represent merging of hydrothermal

with low-rankregionalmetamorphic ffects, he two

being distinguishedonly with difficulty. Signifi-

cantly,detectablelteration xtendsaterallyan aver-

age of half a mile beyond he orebodies, erhaps

more, since some authors drew the outer limit on

the basisof "bleaching" nd the presence f sericite,

phenomena hat probably do not mark the true

outer limit.

PeripheralZone (Column 21) .--Alteration is de-

scribed n this zone for only five deposits. It is

generallyalongwell-developed tructures nd is sel-

dom well describedwith respect o associatedmin-

eralization. Where alteration mineralogy s given

it is of mixed affinity, dominantlypropylitic, with

sericitementioned t Questa. Skarn is describedn

this zone at Morenci and Santa Rita. Skarn or

tactite developments not as well reported n the

literature as are hydrous silicate alteration assem-

blages. It is well known that skarn zonesproject

into and apparentlydistort more normal zoning re-

lationships, nd that many porphyrydepositsmight

also be describedas contact-metamorphic eposits.

Skarn can also apparentlypersist to the centersof

orebodies.

Outer Zone (Column 22).--Mineralogic notation

is given for 20 of the 27 deposits,with "propylitic"

cited for Ely, Nevada. Of these,18 includechlorite,

17 epidote, and 13 a carbonate (calcite in 11).

Quartz is cited 7 times, sericite6, zoisite-clinozoisite

5, kaolin 3, specularite2, montmorillonite2, and

albite,hematite,magnetite,ourmaline, nd ruffle(?)

once each. By far the most commonassemblages

chlorite-epidote--calcite. ention s seldommadeof

the replacedminerals,but the chief onesare amphi-

bole,biotite,and plagioclaseFig. 12). This assem-

blage has affectedby far the largestvolume of rock.

The chlorite-epidote-calciteropyliticassemblages

alwaysoutside he ore zone and beyond he phyllic

and argillic zoneswhere theseare present. Sericite

is commonly eported even in outermostalteration

assemblages.Whether this mineral varies import-



ALTERATION-MINERALIZATION ONING N PORPHYRYORE DEPOSITS 40i

antly in composition,nd hence n stability ield and

distribution, s yet to be shown. It has been ob-

served, however, in amountsranging from trace to

moderate, nd chiefly replacingplagioclase,n some

outer zonesnot reported n Table 1. The distribu-

tion with respecto vertical oningwill be discussed

below.

Intermediate Zone (Column 23).--This column

describes redominantlyrgillicassemblages. ilici-

fication is clearly more important here than in the

outer zone, and the dominant minerals are quartz,

kaolin, montmorillonite, and sericite. Argillic as-

semblagesre discerniblen 22 of the 27 deposits,

if quartz-sericite-kaolinite4 occurrences) e in-

cluded as argillic. Quartz is cited first in most

assemblages. aolin is cited singlyor beforemont-

morillonite in 17 of the 22 assemblagesor which

dataare given. Three deposits avemontmorillonite

zonally beyondkaolin, and 7 involve sericite. No

argillic assemblages reported n 5 deposits.

Inner Zone (Column 24).--Most of the quartz-

sericite (and pyrite) assemblages,he chief ore

bearersof the porphyrycopperdeposits,all in this

inner zone column. The zone is reportedunequi-

vocally to have a pervasivequartz-sericite ssem-

blageat 19 porphyrydistricts, quartz-majorseri-

cite-minorK-feldspar rray at 3 more,and a quartz-

major sericite-minorkaolin assemblage t 3 more.

At Braden a quartz-sericite-biotite-anhydritenner-

zone assemblagerades nto strongersecondary io-

tite in the innermostzone. Only at Esperanza s

a quartz-K-feldspar air reported onallyoutsideof

an unusual quartz-K-feldspar-biotite assemblage.

Creasey (1966) indicates hat K-feldspar can be

part of his quartz-muscovite ssemblageound at

Bagdad, Bingham, and Chuquicamata. Creasey

states 1966, p. 62) "quartz-sericite-pyritewithout

either a clay mineral or K-feldspar associateds a

commonassemblagehat doesnot fit into any of the

three previouslydescribed lteration types. If clay

were present [as at Endako, Inspiration, and Mis-

sion-Pima,where kaolin s reported], he assemblage

wouldbelong o the argillic alteration,and if K-feld-

spar were present [as at Bagdad, Bingham, and

Chuquicamata], t would belong to the potassic."

Since he assemblageppears y far mostcommonly

as quartz-sericite-pyrite,he term "phyllic" s herein

urged as a specific erm. Advancedargillic alter-

ation, involving chiefly pyrophyllite,dickite, and

topaz (Meyer and Hemley, 1968), is associated ith

phyllic assemblagest Butte and Bisbee. It is not

reportedelsewhere ut may have escaped etection.

The phyllicassemblagef Column24 is the inner-

most exposedalterationassemblagen at least six

districts.

Innermost Zone (Column 25).--This column is

perhaps he most surprisingof the hypogenealter-

ation data block. Potassicalteration, though rela-

tively subordinaten the literature, occursat most of

the porphyrydeposits s either an early or an inner-

most assemblage r both. It is reportedas simple

quartz, K-feldspar,and biotite(?) only at Endako;

as quartz, K-feldspar,biotite,and sericiteat 7 de-

posits,and as quartz, K-feldspar,biotite with chlor-

ite, albite, fluorite, anhydrite, or tourmaline at 8

more. Quartz, K-feldspar,and sericiteare reported

at Silver Bell, and quartz with only K-feldsparoc-

curs at Mineral Park and Questa. Quartz, phlogo-

pite, and tourmalineoccurat Cananea,but the zone

may not be innermost here. Quartz, sericite,bio-

tite, and anhydriteoccurat Braden. Anhydrite at

several ocales s given in parenthesesn Table 1

where t hasnot beendescribedn print. Specimens

of anhydrite rom Esperanza,Questa,San Manuel-

Kalamazoo, and Santa Rita have been observed to

swell the published occurrences t Butte, E1 Sal-

vador, Toquepala,Ajo, and Braden.

The commonoccurrence f anhydrite n the po-

tassiczone indicates hat (1) redox potentialsare

considerablyhigher in the late magrnatic-deuteric

fluids han the prevalence f unoxidized ulfur spe-

cies would indicate; (2) a high percentage f the

total sulfur n the porphyrysystemmay be present

as sulfate; and (3) high-temperature ydrothermal

reactions involving silicates, oxides, and sulfides

must concern hemselveswith equilibria involving

higher total sulfur than the net sulfide contents

would indicate. It is also noteworthy hat the con-

clusionof Lutton (1959) concerningdepositional

continuum rom pegrnatoidnto "porphyry"condi-

tions are supported nd that the elementsgrouped

by Ringwood 1955) as "complex ormers"of high

ionic potential are precisely hose found in major

and trace minerals n the porphyry base-metalde-

posits,especiallyn the potassic lterationzone.

Other characteristicsof the potassic zone are

briefly described y Meyer and Hemley (1963) and

Guilbertand Lowell (1968). Ore commonly ccurs

at the interfacebetweenpotassicand phyllic alter-

ation zones. The potassic one is generallycentral

or deepest, r if a time sequences discernible,t is

earliest.

Zoning Sequencerom Center and Bottom (Col-

umns26 and27).---The upwardzoningand outward

zoningof alteration ssemblagesre seldom eported

as such,but their systematic ntry by description r

from map or diagram evealsa significant equence.

Seven,possiblyeight (the positionof phyllic al-

teration at E1 Salvador is uncertain), of the de-

positsshow alterationassemblagesn the sameout-

ward sequence: otassic,phyllic, argillic, and pro-



402 1. D. LOWELL AND ]. M. GUiLBERT

pylitic. Even wherecertainassemblagesre not re-

ported, the remainingassemblagesall in the same

order. Two deposits,possibly hree, show only

potassic nd phyllic zones, our lack only argillic,

and six start with phyllic and includeargillic and

propylitic. For a few depositshe sequences un-

known.

Vertical sequence f zonation s generallymuch

less well known, so assignmentsan be made in

Column27 only for Butte, Climax,E1 Salvador, nd

San Manuel-Kalamazoo.Except for uncertainty t

E1 Salvador, the order is consistent with lateral

zoning. Outwardand upwardzoningof the 27 de-

posits s mostconsistent ith the sequencef potas-

sic,phyllic, rgillic, ndpropylitic ssemblages.

An alterationassemblageas been noted n sev-

eral localitieswhich consists f K-feldspar,biotite,

coarsesericite,chlorite,and albite, accompaniedy

moderate pyrite and chalcopyritemineralization.

This groupdoesnot readily it the classificationut-

lined n Table 1, nor do the deposits enerally each

ore grade. The writers are of the opinion hat this

represents deep assemblage hose elationshipo

the main porphyrysystem asnot beenexposedor

study because f the geometryand large vertical

dimensions involved.

HypogeneMineralization Columns 8-35)

As has long beenknown,hypogene ulfide-oxide

mineralassemblagesre closely elated n time and

spacewith silicate lterationmineralassemblagesn

porphyrydeposits. The designation f pyrite and

magnetite as ore minerals rather than alteration

minerals, or example,appears o be largely arbi-

trary.

In Table 1, sulfide-oxide ineralassemblagesave

been described in Columns 28-35 with reference to

the same alteration zones as are described in Col-

umns20-27. The consistentequencehrougheach

zone and from one assemblageo another outward

from the center s again significant.

PeripheralAlteration Zone (Column 28).roThis

column describes metal occurrences that form a dis-

continuousing normallynear the outer edgeof the

propyliticzone. The deposits end to be small to

medium size, although arge lead-zincdepositswith

or without preciousmetals occur in this zone at

Santa Rita, Bingham, and Butte. At least minor

peripheralmineralizations found n all 27 deposits

studied. Arcuateclusters f minesor prospectsur-

round 23 deposits. Minerals common n this zone

are sphalerite, alena,silver,chalcopyrite, old, and

pyrite, and less commonly,specularite,enargite,

famatinite, etrahedrite,barite, various sulfosalts, nd

manganese nd vanadium minerals.

Outer Alteration Zone (Column 29).--This zone

generally corresponds o the propylitic alteration

zone, and mineralization s generally restricted o

pyrite, although sparse chalcopyrite s generally

present along with variable amounts of bornite,

molybdenite,magnetite, specularite, hodochrosite,

sphalerite, alena,and rhodonite.

Intermediate Alteration Zone (Column 30).--

This correspondsoughly to the argillic alteration

zone,and the bulk of mineralizations usuallypyrite

with highpyrite-to-chalcopyriteatioswhichaverage

23:1 in deposits or which figures are available.

Variableamounts f bornite,molybdenite,ennantite,

sphalerite, alena,enargite,chalcocite, nd huebner-

ite have been found in this zone. Hypogeneore-

grademineralizationmay overlap nto this zone,but

generally his zone s outside he orebody.

Inner Alteration Zone (Column 31).--This zone

commonly orrespondso the phyllic alterationzone

and typicallycontains bundant yrite and high total

sulfidesogetherwith pervasive ericitization.Pyrite

content s not reportedquantitatively or most de-

positsbut it appears o average bout 10 percentby

weight for the 27 deposits, r about 16 percent,ex-

cluding he porphyrymolybdenumroup,whichare

relatively low in pyrite. Pyrite-to-chalcopyrite

ratiosaverage12.5:1. This zonecommonly onsti-

tutes the ore zone, especiallyn those deposits n

which chatcocite enrichment has occurred. The

principal"ore" mineral s pyrite, which occurswith

chalcopyrite, olybdenite,nd variable ut generally

small amounts of bornite, chalcocite,sphalerite,

enargite,and magnetite.

Innermost lteration one (Column 2).roThis

zone s generallyequivalento the potassic lteration

zone and is usually he central zone. Total sulfide

content s low to moderatewith an averagepyrite

content of about one percent and a pyrite-to-chal-

copyrite atio of 3:1 in the depositsabulated. This

zonemay reachore gradeand probablyaccountsor

most ore in solelyhypogene re deposits. It also

forms he "low-grade enter" n five deposits.The

sulfidemineral assemblages chalcopyrite, yrite,

and molybdenite.

Overall Abundance ol Major Ore Minerals

(Column 33).•In the porphyry coppers,pyrite is

by far the most commonsulfide, ollowed n order

by chalcopyrite, ornite, enargite,and molybdenite.

Molybdenite s present n all 27 deposits, fact not

previously ecognized.

Zoning Sequencerom Center (Column 34) and

from Bottom Column35).•Grading outward rom

the centerof the deposit, he typical ateral minerali-

zation sequence ppears o be the assemblages1)

chalcopyrite,yrite,bornite,molybdenite; 2) pyrite,

chalcopyrite, olybdenite, ornite; (3) pyrite, chal-



,4LTERATION-MINERALIZATIONONING N PORPHYRY REDEPOSITS 403

copyrite; and (4) sphalerite,galena, silver, gold.

Apparent reversalswere noted in only three camps.

Information as to vertical zoning is extremely

limited. Most deposits ave beenexploredby mine

openingsor drill holes only to depths which are

shallowas comparedwith the probableoriginal ver-

tical dimensions. Tentative evidence from 13 de-

positssuggestshat typicallya pyrite-chalcopyrite-

molybdenite ssemblage radesupward into pyrite.

An apparent eversalof this order has been eported

in two deposits.

Occurrence l Sulfides (Columns36-42)

Hypogenesulfides n porphyry deposits ypically

form veinlets or disseminated rains. This habit

is probably elated to the fact that cracklebrecciation

is present hroughout he volumeof mineralization.

Broadly, he porphyries eem o be masses f homo-

geneous ock penetratedby reticulate racturesand

mineralizedby fluids which soaked he massrather

than beingconstrictedo tabularmasses r replace-

ments.

Occurrence f Sulfidesby Zones (Columns36-

40) .--A progressive radation n sulfidedistribution

is noted in almost every deposit abulated. This

sequenceprogresses rom veins in the peripheral

zone o veinlets n the outer zone,veinletsand minor

disseminatedrains in the intermediate one,vein-

lets approximately qual to disseminationsn the

inner zone, and predominantdisseminationsn the

innermost one. The tendency or the increasing

importance f disseminationowards he core may

result from metasomatismr recrystallization f the

rock and healingof veinlets. The absence f promi-

nentveins n mostalteration onesmay ndicatehat

a crackle recciationonebehaves s an incompetent

masswhich can not support hrough-goingissures

and veins.

BrecciaPipes and CrackleZones (Columns41

and 42).--Breccia pipesare present n 20 and are

mineralizedn 18 deposits.Toquepala nd Cananea

are mineralized recciapipes n whichore limits are

nearly coextensive ith the pipes. Toquepala,n

particular,showsevidencehat the surrounding l-

terationzoneshavebeen elescopednto a relatively

thin halo,and alteration ssemblagesithin the ore-

body' verlap. The Bradenorebody pparently on-

sistsof a verticalcylindrical epositwhichhasbeen

penetratedlong ts verticalaxis by a postore reccia

pipe.

A well-developedracklezone is present n 26

deposits ut is largely absent n the skarn of the

Mission-Pima rebody. Cracklezonesare usually

circular n outline and are always arger than the

orebodies,ypically adingout in the zoneof propyl-

itic alteration. Crackle texture is often less distinct

near the center,particularlyf a potassic lteration

zone is present.

Supergene ulfides Column43)

Twenty-threeepositsontain upergeneulfides,

and secondarynrichment as required o reach

marginalore grade n 10. Supergenehalcocite

(andprobablylsosecondaryigenite nddjurleite)

is presentwherever econdaryulfides ccurand

alwaysconstituteshe chief enrichmentmineral.

Covellite s reported n 12 deposits, enerallyow

in the enrichment blanket.

Porphyry Deposit Genesis

The data of Table 1 and the inferences drawn

from them, from the field, and from the detailed

geologyof the San Manuel-Kalamazoo epositap-

pear to support he orthomagmatic odeldescribed

earlier, although he nature of the data and the

scale actorsare not suchthat the problemscan be

conclusivelyesolved. The formationalmodelwhich

appearsmost generallyapplicables one of a dif-

ferentiationcontinuumas suggestedmany years ago

by W. H. Emmons (1933) in his descriptionof

cupola ormation. Near-surfacentrusionof a melt

whichproducesocksof intermediate ranitoidcom-

position s either a passive ntrusion as at Butte,

Santa Rita, and Ajo, or a dike swarm as at San

Manuel-Kalamazoo nd Safford. Response f wall

rocks o this intrusiondepends pon their composi-

tion, their structural fabric, and the nature of the

intrusive melt. Cooling begins from the surface

downward,and gentle thermal gradientsare estab-

lished from higher temperatures t depth to slightly

lower ones nearer to the surface and outward. Min-

eralization and alteration chemistries are established

with respect o thesegradients, hemistrieshat re-

flect essentially euteric o late magmatic onditions,

with potassicalteration yielding upward and out-

ward through the phyllic zones (or the "zone of

feldspar destruction," Robertson, 1962) into the

zones of more typical hydrothermal alteration re-

sponses. These gentle gradients presumablyhave

a direct bearing on the large dimensionsof the

porphyriesand the coarselygradationalalteration-

mineralizationboundarieswhich they show.

We thus reaffirm on the basis of the published

record that the porphyry copper depositsare the

results of a physical-geochemicalontinuum from

low-temperaturemagmatic o "conventional" ydro-

thermal conditions. The gradientsare reachedas a

result of cooling in an intrusive mass, and the

alteration-mineralizationonal boundary interfaces

appear to have been established s standing orms



404 .r. D. LOWELL AND J. M. GUILBERT

rather than as upward and outward advancingmega

envelopes. Application of the Hemley-Jonesmodel

of potassiumsilicate stabilities and alteration, as

modified by Fournier (1967) and Meyer and

Hemley (1968), permits passage rom essentially

magmaticconditionsat depth to areas of higher

hydrogen on concentration nd lower K+/H + and

lower temperatures ither with time at a given point

deep in the systemor through spaceupward and

outward at a given time. It is important o note,

however, that an inner zone need not have been

precededby the mineralogyand assemblagesf an

outer zone in a systemof decline,of lowering tem-

peratures, or of shallow upward gradients. Vari-

ation in the differentiation index of the intrusion

may well dictate whether copper or molybdenum

predominatesn the ultimate deposit,molybdenite

tending to be associatedwith more silicic variants.

Conclusions

The foregoing summary forcefully demonstrates

that the porphyry copper-molybdenumeposits is-

play important unifying geologiccharacteristicsn-

cluding various lateral and vertical zones. The fact

of zoning s not new, but several mportant aspects,

such as sulfide species,detailed alteration assem-

blages,and the characteristic ccurrences f the sul-

fides, is far more widespread han has previously

been realized. Indeed, a "typical" porphyrycopper

depositcan be hypothesizedrom Table 1 and is

includedalong the bottom of the table.

It is especially oteworthy hat many,and perhaps

most, porphyry depositshave coaxially cylindrical

alterationzones. Factors hat limit the development

of discernible ymmetry n porphyrydepositsnclude

the following:

1. Regional or local structural fabric that may

produce asymmetry in alteration and mineral ore

zones.

2. Heterogeneous nd contrastingcomposition f

preore rocks, especially he presenceof sedimentary

"screens."

3. Dislocationsof the original geometryby fault

displacement r by postore ntrusions.

4. Exposureof the porphyry system aterally and

at depth.

The vertical dimension nterpreted for the San

Manuel-Kalamazoosystem s on the order of 8,000-

10,000 feet. No definiteevidencesuggestshat this

vertical dimension s either typical or normal, but

the mineral assemblagesypical of different vertical

zones n San Manuel-Kalamazooappear to be use-

ful in estimating he depth of formation of several

deposits. These "depth levels" of presentexposure

surfaces or several porphyry copper depositsare

shown n Figure 13. Morenci is placedhigh in the

hypotheticalvertical section becauseof the wide

exposureof the phyllic zone without exposureof

potassicassemblages. Several aspectsof Morenci

geologymbreccia ones, the broad-scalealteration

symmetry, and the occurrenceand distribution of

sulfides•suggest hat potassic lterationwill be en-

countered t depth under the existing open pit.

It is also noteworthyhere that phyllic zone alter-

ation assemblages,ith their high pyrite contentand

their profusion of veinlets and microveinlets,are

chiefly responsibleor the extensivedevelopment f

supergeneoxidation, leaching, and enrichment of

southwesternNorth American deposits. This high

level of exposureappears o be the most common,

especially n supergene-enrichedeposits.

Recentpublications n the Chino deposit t Santa

Rita, New Mexico, show hat an island of low-grade

material is being left in the center of the northern

portion of the pit area. This island of low grade

is symmetrically nd centrally disposedwith respect

to secondary -feldspar,chalcopyrite, nd pyrite dis-

tribution as reportedby Nielson (1968, Figs. 6, 7,

and 9). This "low grade island" may represent

the croppingout of a low-grade barren zone analo-

gous to the central core at San Manuel-Kalamazoo.

Lastly, Gilluly's (1946) descriptionof the Ajo de-

posit involves much the same K-feldspar-biotite-

chlorite-sericiteand magnetite-chalcopyrite ssem-

blagesand zonal characteristics s those encountered

at depth in San Manuel-Kalamazoo. It appears

possible, herefore, o assigna third dimension o

at least several deposits,and many others may be

assigneddepth parametersas further information

develops. For example,brecciation nd ring diking

may have significancen regard to depth of forma-

tion.

It alsoappears ignificanthat the major porphyry

depositsof British Columbia (for example, the

Bethlehemand Lornex deposits) occur in quartz

diorite, and the K-feldspathic ock types reportedat

Ajo yield outward to a quartz diorite composition

(Wadsworth, 1968). The evidence oncerningarge-

scalemetasomatismf rocks,generallywith attendant

enrichment in K-feldspar and quartz as described

at BinghamCanyonby Stringham 1956), may well

prove to be more general han is now realized. The

alterationassemblages, ineralization haracteristics,

and occurrence of sulfides at Bethlehem and Lornex

are consistent ith deep exposure, nd we may see

now exposeda relatively deep-seated orphyry en-

vironment. The fact that thesedeposits lso nvolve

quartz diorites rather than granodioriteor quartz

monzonitesmay be another manifestationof the

vertical dimension n porphyry depositgenesis.



.dLTERATION-MINERALIZATIONONINGN PORPHYRYRBDEPOSITS 405

SAN MANUEL

KALAMAZOO•1

EGMENT

ARGILLIC

Q- Kool-

Chl

ChI-Ser-

Epi-eg

FAULT

SAN MANUEL•

SEGM NT.._•?•

PROPYLITIC •

ChlEpi- arb •

AdulAIb

PHYLLIC••'--.,.••--,'•-MORENCl,UTTE

Ser-py

/ • \ MINERAL PARK,

\ • SILVERELL

POTASSIC •

Q- K- fe•l•- Bi -

+ser + onh

t

t

t

BINGHAM, SANTA

ADO,(BETHLEHEM )

RITA

Fro. 13. Schematic rawingof San Manuel-Kalamazoo howingexposureevelsof several orphyry opper eposits. Other

deposits ould be added,but these ew serve to show a vertically developed imension.

A growing body of data indicates hat the por-

phyry deposit minerals may form at depths as

shallowas 5,000-10,000 feet. Facts supporting his

conclusionre (1) the occurrence f porphyryrocks

in all 27 deposits f Table 1; (2) the cutting of all

deposits y postoreerosionsurfaces; 3) the wide-

spread occurrenceof brecciation even though the

host intrusions are usually passively emplaced);

(4) the location of 14 deposits n Cretaceousor

youngerpreorerockswhile the intrusions hemselves

are of late Cretaceous r youngerage; (5) regional

structural-stratigraphiconsiderations; nd (6) the

common occurrenceof porphyry-ore-formingen-

vironments n cupola-like tocks ess han one square

mile in area at the ore-forming elevation.

Deposits seem o range from "wet" types having

high pyrite-to-chalcopyriteatios and surrounded y

enormous alos of pyrite-sericite-quartz ydrother-

mal alteration o "dry" depositswith relatively ow

sericite-pyrite ontent. Althoughperhaps he terms

are too casual, "wet" and "dry" refer to the net

apparent bundance,nvolvement, nd permeation f

a mineralizing-alteringluid. Concentric oning is

also present n "dry" deposits, ut it is telescoped

laterally into a small fraction of the halo thickness

of the "wet" type. The "wet" type is represented

by mostof the Southwest eposits,uchas Bingham

and 7Morenci, nd includesmost of the large por-

phyry copper deposits. The "dry" type is repre-

sentedby many of the British Columbiadeposits,

suchas Bethlehem, nd includesmany of the hypo-

gene ore-gradeporphyry coppers.

The most distinctive eature of the porphyry de-

posits s simply heir huge size as comparedwith



406 .L D. LOWELLAND J'.M. GUILBERT

other hydrothermalre deposits. ncludingore-

grademineralizationnd surroundinglteration nd

mineralization,hey assume imensions ore com-

monly ssociatedith stockshanwith ore deposits.

Thebulkshape f porphyry epositseflectsarge-

scalestructural ontrolof mineralizationnd may

also be related o the originaldepth of formation.

Flat-tabular, one,and flat-dippingube-type e-

positsmay represent elativelyshallowdepth of

formation heresteep nvironmentalradients re-

vail. Steep,columnar eposits ith long vertical

dimensions and little brecciation seem to indicate

relativelygreat depthof formation nd gentleen-

vironmentalgradients.

Brecciapipe deposits, uch as Toquepala,with

only thin alteration halos and with evidenceof vio-

lent emplacement,re clearly representativef a

different enesisn which he mineralizers ay have

evolved uddenlyn a more or lessopenvent with

relatively steeppressuregradients. Examplesof

blind mineralized recciapipesat Cananea, ilares,

and elsewhere ndicate, however, that mineralized

breccia ipesneednot necessarilye eitheropen o

the surface r emplacedt shallow epth.

Porphyry deposits end to have either elongate,

vertical, columnarshapes San Manuel-Kalamazoo

and Bingham) or foreshortened olumnar, almost

discoldshapes Climax or Ray). These shapes

suggest hat migration of hydrothermal luids was

controlled y nearlyverticalgradients nd that fluids,

however derived, migrated upward across arge

areas, up to tens of thousandsof feet in diameter.

It appears ikely that the mineralizersoriginatedas

a separation f fluids at the point of crystallization

of the "host intrusive body." It should be noted

that the "overhang"effect or beet shape of San

Manuel-Kalamazoo could also be consistent with an

influx of deeplycirculating, xternallyderived,per-

hapscoolerwater, although oth he depthand wall

rocks nvolvedmake his explanation eemunlikely.

Many characteristicsdescribed n Table 1 and

systematizedn Figure 13 are consistentwith one

another. Variations in the character of sulfide oc-

currence, or example, appear best explained by

considering that dissemination extures are com-

patible with a model involving crystallizationof

rock-formingsilicates i.e., the potassic one) such

that the sulfides,whichare really igneous ccessory

minerals,are deposited ither as truly includedmin-

erals or in fracturesand microfracturesn newly

competent ocks which are subsequently ealed by

localcrystallization.

The San Manuel-Kalamazooeposithusappears

to be typicaland illustrativeof porphyrycopperand

molybdenum eposits. We suggest n conclusion

that the integratedmodelof verticaland lateral sili-

cate-oxide lteration, ulfidemineralization,nd sul-

fide occurrenceharacteristicsn the porphyry e-

positsmay be useful o economiceologistsoth

explorationallynd scientifically.

Acknowledgments

The writerswish o expressheir appreciationo

their many colleagueswhose discussion nd com-

ments have contributed o this paper, to L. B.

Gustafson,ames'Gilluly,ndT. W. Mitcham ho

reviewed he manuscript, nd to H. R. Hauck, M.

T. Wolf, and B. Townsend for their assistance n

preparing he manuscript nd illustrations.

5211 N. ORACX.E,

TucsoN, ARIZONA,

AND

DEPARTMENTFGEOLOGY,

UNIVERSITY FARIZONA,

TUCSON,ARIZONA,

December19, 1969; March 16, 1970

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lowell guilbert on porphyry cu (36 pags)

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