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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
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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
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.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
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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
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.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
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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
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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.
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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.
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.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
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382 .t. D. LOWELL AND J'. M. GUILBERT
1• .-":4.
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.
.. •
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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-
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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.
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$84 J. D. LOWELL AND J. M. GUILBERT
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--- •. %.z".-,. •.-' :'• .3'
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Figure 10
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.
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ALTERATION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 385
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.
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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
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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
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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
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ALTERATION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 389
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
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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
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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
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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)
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/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
.
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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(?)
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,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)
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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
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.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
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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
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ALTERATION-MINERALIZATION ZONING IN PORPHYRY ORE DEPOSITS 399
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
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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-
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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-
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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-
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,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
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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.
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.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
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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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