Oxidation of a Sulfide Body, Glove Mine, Santa Cruz County, Arizona

Home , Hydrozincite, Massicot, Plattnerite, Rosasite, Smithsonite, Wulfenite

Economic Geology Vol. 61, 1966, pp. 731-743

OXIDATION OF A SULFIDE BODY, GLOVE MINE, SANTA CRUZ COUNTY, ARIZONA

HARRY J. OLSON

ABSTRACT The Glove Mine is located on the southern extremity of an isolated syncllnalsedimentary block of Paleozoicand Cretaceous sediments on the southernflank of the Santa Rita Mountains in Santa Cruz County about forty miles southof Tucson, Arizona. Fluids probably associatedwith a Laramide (?) quartz monzonitein- trusive•havedeposited argentiferous galena, sphalerite, chalcopyrite, pyrite, and quartz along permeablezones causedby fault intersectionswithin a favorablelimestone bed of the Pennsylvanian-PermianNaco group. As a result of extensiveoxidation, only relics of the primary sulfidesexist in the minedportion of the deposit. Cerussite,and lesseramounts of anglesite, wulfenite,smithsonite, and other oxidationproducts of the primary sulfides have been conten{rated in solution caverns. The ore body can be divided into three general zoneson the basis of metalcontent and mineral assemblage. These zones are (A) the upper oxidizedand leachedzone, (B) the silver-enrichedintermediate zone, and .(C) the sulfidezone. The behaviorof individualmetals and minerals is dependentupon local Eh-pH conditionsas well as other environmental factorsaffecting mineral stability. In responseto changesin environment, mineraland metalassemblages vary not only betweenthe zonesbut within them as well.

INTRODUCTION THE GloveMine is a small,oxide, lead-silver-zinc deposit about 40 miles southof Tucson,Arizona. The mine is in the Tyndall Mining District in section30, T20S, R14E, on the southwesternflank of the Santa Rita Moun- tainsat an elevationof approximately4,200 feet (Fig. 1). The originalclaims of the Glovegroup were located in 1907. Production commencedin 1911and has continued intermittently under various operators until thepresent. The bulkof productiontook place from 1951to 1959under the managementof the SunriseMining Company,which produced from 20 to 25 tonsof lead-silverore per day. In all, morethan 21,000 tons of ore averaging7.6 ozssilver, 25.5% Pb, 4.1% Zn, and0.1% Cu perton and worth slightlymore than one million dollars have l•een produced.

GENERAL GEOLOGY The GloveMine is on the southernlimb of an isolatedsynclinal sedi- mentaryblock. Thisblock of Paleozoicand Cretaceous sediments may repre- sent a deformed remnant of the southwesternlimb of an anticline that was breachedby Laramide(?) quartz monzoniteintrusives (Harald Drewes, personalcommunication, 1965) which form the main massof the Santa Rita 731 732 HARRY ]. OLSON

Mountains. In the vicinityof the mine, the southernflank of the syncline is composedof limestones,siltstones, and shalesof the Naco groupof Penn- sylvanian-Permianage (1) whichstrike N75W-N60W anddip approximately 60ø northeast(Fig. 2). The limestonesare intruded by a latite porphyry sill that reachesa maximumobserved surface thickness of approximately30 feet severalhundred feeteast of the Gloveadit portal. This sill is discontinuous,and generally follows beddingtrends in the limestonenorth of the Glove fault. The Glovefault separatessediments of the Naco groupon the northfrom the quartzmonzonite to the south. This fault clearlyfollows an intrusivecon-

ARIZONA

FIG. 1. Index map. tact, which is roughlyconcordant with the beddingof the limestoneas to strike,but discordantas to dip. The intrusivenature of this contactis most vividlyillustrated in the areabetween the mainadit andthe 40-footshaft. Here, the quartz monzonitehas slicedinto the sediments,partitioning the limestoneinto thin alignedsepta. The contactis nearly vertical,generally dippingsteeply to the north. Minor showingsof lead-copperm•neralization crop out in the area of the Gloveworkings. Mineralization is in the limestone,generally associated with the quartz monzoniteor latite porphyry contacts,although some lead and coppershowings do occur in the limestonesome distance from thesecontacts. All mineralizedoutcrops are essentiallythe same. The limestoneis marbleized,but is only locally iron-stained. Lead mineralsoccur as small stringersand blebs in minorfracture zones. Cerussite,commonly with galena OXID,4TION OF .4 SULFIDE BODY 733

cores,is by far themost common lead mineral, although in particularlytight ground,tarnished galena is present.Evidence of coppermineralization is not readilyapparent, but small splotchesof copper"bloom" are sometimes noticeable. Sphaleriteor other zinc mineralswere not notedon the surface.

Descriptionof Rock Types QuartxMonxonite.--The quartz monzonite in the mine area has beende- scribedby Anthony (1) asthe "fine quartz monzonite" to distinguishit from a "coarsequartz monzonite," which occurs as isolatedmasses within it and as

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Scale mn ,7o o ,p •o,,,, •• about4,20•'aboveMSL. Fro. 2. Generalizedgeology of the GloveMine area. a largeintrusive mass to the northeast.The quartzmonzonite in the mine areavaries from fine- to medium-grain.It generallyweathers to a light orange-brownshade due to a finecoating of limonite.Anthony (1) from thin sectionanalysis quantitatively estimated the mineralconstituents of the quartzmonzonite to be (in percent):quartz, 50; microperthite,30; andesine- oligoclase(Ab6s-An32), 17; limonite,2; and unknownsilicate mineral, 1. Primary mafic silicateminerals are absentin all but one of the sections studied.This section contains about 25 percenthornblende which probably representsa local accumulation along the contact. LatitePorphyry.--The latite porphyry weathers greenish togreenish-gray andcontains abundant phenocrysts of chalky white plagioclase. In unaltered areasunderground, it has a moreuniform green appearance. The majority ofthe phenocrysts areplagioclase, although minor orthoclase and rare quartz phenocrystsarealso present. Primary quartz constitutes approximately 3 734 HARRY J. OLSON percentof thegroundmass. The remainderis largelyor{hoclase. There are no primary mafic silicate minerals. Opaque minerals constitute about 2 percent of the rock. NacoGroup.--The limestone sequence in which the Glove Mille is located has been identified as a portion of the Naco limestone,and included in the Naco group of Bryant (2). It consistsof alternatinglimestone and siltstone with minor interbeddedshale units. The limestonesweather white, pink, gray, and brown. The siltstonesand cherty layers generally weather to a shade of greenishbrown or black. Underground, the limestonebeds are generallywhite, althoughthey may be pink, gray, or variousshades of brown dependingupon the type and degreeof alteration. The siltstoneunits under- groundare generallysome shade of green,gray-green, or more rarely gray. The limestonebeds are mostly pure, although they may contain small amounts of silt-sized quartz. The siltstonebeds are composedchiefly of quartz, with small amounts of calcite and clay minerals. Chlorite also is presentin varying amounts,and was observedin almostall of the sections studied. Alteration Contact-metamorphiceffects producedby emplacementof the quartz monzoniteand latite porphyry are in general relatively minor. Near the contacts,the limestonehas been silicifiedand metamorphosedto a white to pinkishmarble, and chloriteis commonin the siltstoneand chertylayers. At increasingdistance from the contacts,these effects diminish and the marbles and chloritizedsiltstones grade into limestonesand siltstonesthat are typical of the Naco group. No continuoustactite zone has beendeveloped, and only two minor areas of sillcationcontaining epidote and garnetwere noted. Iron stainingis' common,but not strong,along the contact. The singleexception noted is a small ßkidney of specularhematite just to the eastof the 50-footshaft. In the vicinity of sulfidemineralization, the marbleizedlimestone is com- monlyintensely silicified. Silicificationgenerally takes the form of replacement by cryptocrystallinesilica suchas chalcedony,although it commonlyoccurs as euhedralquartz containingcalcite inclusions and relict structures. Sec- ondaryquartz in vugsand as vein filling is alsocommon. The extent to which the limestone is altered to dolomite, if at all, is un- known. Some replacementof the limestoneby sideriteand rhodochrosite, however,was observed. The quartzfragments of the siltstonebeds may be extensivelyveined by calcite,which was probablyreleased during the silicificationand marbleiza- tion of the limestone. Some of this calcite,however, may representmobilized calcitepresent in minoramounts in the siltstoneas a cementingmaterial. Most of the siltstonesare moderatelychloritized, which gives them a greenishcolor underground. The chloritizationof the siltstonesprobably oc- curred as a reactionof minor amountsof clay mineralsinherent in the rock, with possiblemagnesium and calcium introduction, in responseto the increased oXID,4TION OF .4 SULFIDEBODY 735 energy conditionsaccompanying metamorphism and emplacementof the ore minerals. The quartz monzoniteis unalteredexcept near the limestonecontact where it appears to be slightly silicified. Besides introduced silica, microscopic examinationshows the plagioclaseand orthoclasefeldspars to be partially alteredto sericiteand kaolinite. The plagioclasefeldspars also are alteredto calcite. Secondarymuscovite, which appears to be the same age as the sericite,is also presentbut not abundant,and may representmore intense local alteration. Chlorite is commonin some specimensas shredsreplacing the feldsparsor surroundingdisseminated pyrite. Limonite is almostuniver- sally present as stringers between mineral grains, and as fracture fillings. These alteration effects decrease with distance from the contact. At the surface, the latite porphyry appears megascopicallyto be only slightly altered. However, in thin section,the phenocrystsof plagioclase,as well as the groundmassmaterial with its high orthoclasecontent, are highly altered to sericite, kaolinite, and smaller amounts of calcite, muscovite,and chlorite. Secondarysilica derived from the alteration of the feldsparsas well as introducedsilica is present. This pattern of alterationcontinues down with uniformintensity at leastto the 300-levelof the mine, which is the lowest depthat whichthe sill hasbeen intersected.

GEOLOGY OF THE ORE DEPOSIT

The metamorphosedlimestone beds in the undergroundworkings are cut by a seriesof faults that have approximatelythe sameattitude as the bedding. Thesefaults are, for the most part, tight, and showno evidenceof extensive movement. Solution by ground water aided by acids from the oxidation of the sulfides,especially in the zonesof brecciationdeveloped at fault inter- sections,has producedcavernous pipes which trend approximatelyS60E and plungeroughly 30 ø southeast. Three major faults are associatedwith the ore body. The Porphyry fault is probablythe masterfault of the mine area. It lies along the footwall side of the latite porphyrysill, and followsthe sameN'60-75W, 60N' attitude as the sill (Fig. 3). The Main fault "horsetails"off the Porphyry fault at approximatelythe 180~level,and assumesa more northwesterlystrike, although its dip remainsfairly constantat 60ø northeast(Fig. 4). The Southfault also "horsetails"off the Porphyry fault in the vicinity of the 180-level. At its intersectionwith the Main fault, (Fig. 4) the South fault has an attitude of approximatelyN'. 60E, 45-60S. Minor faults that "horsetail"off thesemajor faults are not commonin the upper levels,but becomemore abundantwith depth. Below the 180-level, they are importantas sitesfor ore deposition. A fault zonealong the hangingwall side of the sill produceda small ore pipe abovethe adit level (Fig. 3), but explorationon the 210-levelfailed to pick up the possibledownward projection of this pipe. A periodof minorpost-mineralization adjustment is evidencedby curving 736 HARRY J. OLSON

o_ •:./•_ J Smallmineralized pips;ith •' >C• - •'.• •/ oxideoreriles along •nging • ., 'x,,•, ,_ Ix >,. -, <' < • v...... r2 i L / / latitepoep yry '",,•.•^v • '• •ix\ ,•<'•>< Ix'•'•? v > '•rv ' "•-r.,_•s•, t.4•_, / J sill..---->

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Fro. 3. Generalizedgeology of the Glove Mine--adit level.

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Fro. 4. Generalizedgeology of the Glove Mine--240 level. OXIDATION OF A SULFIDE BODY 737 cleavagefaces in the galena. ttowever, no evidenceof any post-oreoffsets was noted. Ore Bodies The main-stopecomplex, which has been mined from the surfaceto the 360-level, is in the form of a seriesof coalescingpipes that are irregular in planand section(Fig. 5). Thesepipes developed along zones of permeability formedby faultsand fault intersectionswithin the favorablelimestone. Ore

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FIG. 5. Generalizedview of the Glove ore body.

fluidsascending along these permeable zones replaced the limestoneforming stringersand bandsof massivesulfide and someminor sulfidedisseminations. Later, acidsfrom oxidation of the sulfidesfurther leachedthe limestone, forming a complicatedsystem of cavernscontrolled largely by the original permeablezones and the sulfidepipes. As the cavernsenlarged, they were filled with the oxidationproducts of the sulfideminerals, along with quantities of wad, calcite,gypsum, and minor silica. Bouldersof limestoneand marble that collapsedfrom the backsduring the leachingof the cavernare scattered 738 HARRY J. OLSON

throughoutthis cavern fill, andother limestone boulders and partitionsrepre- sentremnants of undissolvedcountry rock. Most of the presentoxide-filled pipes apparently were sitesof primary nfineralization.However, many of thesmaller and shorter pipes appear to be post-mineralcaverns leached in barrenlimestone and subsequentlyfilled with the oxidationproducts derived from neighboringsulfide zones. The leachingof the limestoneand the downwardmigration of the metals hasenriched the ore bodyconsiderably within the zoneof oxidationincreasing a possibleprimary lead-zinc grade of perhaps20 percentto as muchas 40 percent or more in certain areas.

Ore Controls The lead-zinc-silvermineralization at the Glove Mine is primarily lime- stonereplacement although some fissure-filling occurs. Althoughthe min- eralizationis post-intrusion,the ore-bearingfluids are probablyassociated with the emplacementof the quartzmonzonite and the latite porphyrysill. Sulfidedeposition appears to have beencontrolled by permeablezones of brecciationand fissuringcaused by faults and fault intersectionswithin a favorablelimestone bed. The controlis mainlyphysical and relatedto the permeabilityof the rock, but is also chemicalin that a "favorable"limestone was replaced. Smallerfaults that convergeupward into the larger fault zones probablychanneled the mineralizingfluids into the main ore zones. The zone of brecciation at the intersection of the Main and South faults is the locusof ore depositionin the main stopearea from the 180- to the 360- level. However,in the lower levels,the Southfault appearsto haveexerted an increasingamount of controlover ore deposition. Below the 240-level, the latite porphyrysill seemsto have had no effectupon sulfide deposition. However, above the 240- and 180-1eveIswhere the Main and South faults are captured by the Porphyry fault, the sill appears to have acted as an impermeabledeflecting barrier that channeledthe ascendingfluids along the Porphyry fault on its footwall side. This prevented,to a large extent, the spreadingof the mineralizingfluids into the limestonesto the north, and explainswhy only one small mineralizedpipe existson the hangingwallside of the sill. Abovethe 180-level,the Porphyryfault is the dominantcontrol of ore deposition. Host rock alterationmay representa more subtleform of control. The favorablelimestone bed is relatively pure carbonate,and the underlying siltstoneis largely quartz. The limestoneassociated with the ore pipesap- pearsto havebeen slightly silicified, whereas areas of more intensesilicification seemto havebeen bypassed as sitesof sulfidedeposition. It thusappears that pure or only moderatelysilicified limestone were favorableto ore deposition, whereasthe siltstoneand the intenselysilicified limestone were unfavorable.

Sulfide Mineralization Hypogenemetallization is quite simple. It consistsof minor amountsof pyrite and chalcopyriteassociated with galena and sphalerite. OXIDATION OF A SULFIDE BODY 739'

OXIDATION OF PRIMARY SULFIDES

The oxide portion of the Glove Mine is wholly above the water table• During periodsof high seasonalrainfall, surfacerunoff is capturedby open fracturesand cavernouszones in the limestone,which providefor entry and downwardpercolation of ground water. The oxidizing environmentof the lead-zincsulfides has been,then, one of alternatingperiods of moistnessand dryness,with perhapssome intervals of flooding. Water in this oxidizing environmentis constantlyreceiving atmospheric oxygen as the dissolvedoxy- gen is beingconsumed by the oxidationof the sulfides. In the oxide portion of the ore body in areasof unrestrictedground water and atmosphericmovement, as in the cavernsof the main ore body, solu- tionswould tend to havea high pI-I becauseof their frequentif not constant contactwith the limestones. However, in stagnantbackwash areas of re- strictedcirculation, the oxidationproducts of the sulfidescan effectivelyinsu- late the ground water solutionsfrom extensivecontact with the limestones, and therebypermit lower pH conditions. Therefore,it appearsthat in the oxide zoneabove the water table,the pH of the vadosewater solutionsis partially a functionof circulation. The ore bodycan be dividedinto threegeneral zones on the basisof metal contentand mineral assemblage.These zonesare: (A) the upper oxidized and leachedzone, (B) the silver enrichedintermediate zone, and (C) the sulfide zone. The upperoxidized and leachedzone (A) roughlyextends from the surfaceto the 300-level. Alongwith abundantiron oxides,wad, and gypsum, this zonecontains remnants of all sulfideminerals, cerussite, anglesite, and wulfenite. Cerussiteis the dominantlead mineral. Zinc valuesare present in the orderof 5 percentor less. Silvervalues are alsolow, andaverage less than 5 ouncesper ton. The Ag:Pb ratio variesbetween 0.2 and 0.3. The Zn: Pb ratiois low andis nearlyconstant at 0.1. The intermediatezone (B) extendsfrom the 300- to aboutthe 360-level. It hasa raggedinterface with the underlyingsulfide zone (C). In addition to all the mineralscommon to zone(A), the intermediatezone contains abundant encrustationsof "dry bone" smithsonite. Cerussiteremains the domi- nant lead mineral. Wulfenite becomes much less abundant and smaller in crystalsize. Averagezinc values rise to 13 percent,and the zoneis enrichedin silver,which averages approximately 13 ouncesper ton. The Ag: Pb ratio is high,varying between 0.4 and0.7, and the Zn:Pb ratioincreases with depth until a ratio of 0.6 is reached. The sulfidezone (C) extendsbelow the 360-level:andcontains approxi- matelyequal amounts of galenaand sphalerite, and smaller amounts of pyrite. Chalcopyriteis presentas minor disseminationsand as exsolutionblebs in the sphalerite.Minor amountsof supergenecovellite commonly replace the hypogenesulfides. Silver values are intermediatebetween zones (A) and (B) andaverage about 8 ouncesper ton. The Ag: Pb ratiois constantat 0.4 and the Zn: Pb ratio reaches 1:1. The behaviorof the individualmetals present in the mineis dependent ?40 HARRY J. OLSON upon the local environment and varies not only between the zones but within them as well. This is illustratedgraphically in Figure 6. Galenaexists in all three zones. It is leastabundant in the upperoxide and leachedzone and increasesin abundancedownward until it representsapproximately 50 percent of the metal sulfidesin the sulfidezone. In the upper portionsof the mine, it exists in areas of tight ground where the effectsof oxidationhave not reached and as remnant cores in lead carbonate and sulfate aggregates.

Fro. 6. Ore gradeand metal ratios 1956through 1960. The plotson the graphrepresent the averagemonthly ore gradeand the metal ratios (calculatedto the nearest0.1) as computedfrom smelterreturns. Ship- mentsto the smelterwere not made in everymonth of the periodpresented, so each year is not necessarilyrepresented by 12 figures. During period"A" the upper oxidized and leachedzone was mined. Silver and zinc values are low; the Ag:Pb ratio rangesbetween 0.2 and 0.3; and the Zn:Pb ratio is low. The zinc anomalies representthe mining of large amountsof smithsoniteon the 300-level. During period "B" the silver-enrichedintermediate zone was mined. Silver values are high, zinc valuesincrease, the Ag:Pb ratio is high, and the Zn:Pb ratio increases. During period"C" substantialamounts were minedfrom the sulfidezone. Silver values decrease,zinc values increase,the Ag:Pb ratio is intermediate,and the Zn:Pb ratio reaches 1:1.

Galenaalters directly to cerussiteor anglesite.In the oxidezone, in areasin which the ground water has a high CO2 contentand unrestrictedmovement (conditionsfavorable for high pH), galenaalters directly to cerussite.These conditionsare typical of the cavernsof the main ore complexand explain the predominanceof cerussitein these areas. Cerussiteis the main ore mineral and has been mined as massivebodies, encrustations, and "sand car- OXIDATION OF A SULFIDE BODY 741

bonate" associatedwith other oxide productsof the cavern fill from the surfaceto the top of the sulfidezone on the 360-level. The environmentsof stabilityof anglesiteand cerussiteare quite different. In the presenceof CO2and the carbonateion, anglesiteis stablein an acid environmentwhereas cerussite is stablein mildly acidic to basicconditions (4). Anglesiteis not as commonas cerussite.This is as wouldbe expected becausecirculating acid water would be quicklyneutralized by contactwith the limestonehost rock producingan environmentin which cerussiteis the stable mineral. However, in stagnantareas of limited circulationaway from the main zonesof groundwater circulation,oxidation of the sulfidescould pro- ducea low pH environmentand would provide a sulfateion source. Anglesite is foundin suchenvironments at the Glove,and as suchexists throughout the extent of the oxide zone from the surface to the 360-level. The lead oxides plattnerite (PbOz), massicot(PbO), and miniurn (Pb•O4) werenot noted and if present,are probably quite rare. Wulfenite(PbMoO4) is common,and existsas fine crystalsthroughout theentire oxide body and as spectacularcrystalline aggregates along the backs and sidesof numerouscaverns above the 300-level. In one stope,between the 180-and 210-1eveIs, it was the principallead ore. Molybdenitewas not notedin polishedsection in or aroundany of the sulfideminerals. Examinationof polishedsections under vertical and ob- lique illuminationfailed to revealany galenaaltering directly. to wulfenite. If molybdenumwere presentin the galena, direct alterationto wulfenite would be expectedas wulfeniteis the stableoxidized lead mineral in the presenceof the molybdateion (4). Cerussitewill be stableand form only afterall themolybdate ions have been combined. In theabsence of a molyb- date ion source,wulfenite becomesunstable and is removedin solutionto be reprecipitatedlater by the presenceof a largelead ion concentrationor by evaporationof the solution. Sphaleritewas not recognizedabove the 300-level,but at that levelbecame fairlyabundant. Smithsonite was also first recognized at thislevel, although zincvalues of 5 percenthad beenencountered in miningfrom the surface. Zincabove the 300-levelis finelydisseminated throughout the oxidezone, and its mineralform is notknown. The absenceof zincvalues equal to thoseof leadin the upperoxide zone is probablydue to the greatersolubility of the zincminerals, and their migration and later precipitationon the lowerlevels. In an oxidizingaqueous solution smithsonite is the least solubleof the supergenezinc minerals, and hence the moststable mineral in the pH range 6.2 to 8.1 (4). This suggeststhat smithsonite might also be the zincmineral disseminatedthroughout the upperoxide zone. However,in the absenceof a plentifulsupply of groundwater in a dry environment,the carbondioxide concentrationmay be solow that hydrozincite(ZZnCOa'3Zn(OH) 2) would be morestable than smithsonite(4). In this event,a portionof the zinc valuesabove the 300-level could quite well be present as hydrozincite. Belowthe 300-level,in the intermediateoxide zone, zinc valuesincrease to the orderof 15 to 20 percentas veinsand encrustations of "dry bone" smithsoniteand as sphaleriteremnants associated with galena. At thetop 742 HARRY J. OLSON of the sulfidezone, near the 360-level,sphalerite and galenaoccur in approximately equal amountsin stringersand grains scatteredthroughout the calcite of the ore zone. Minor chalcopyrite,corellite, and pyrite are associatedwith the sphaleriteand galenaas inclusions,replacements and separategrains. Silver valuesare approximatelycovariant with leadvalues (Fig. 6). The rdative concentrationof silveris highestin anglesite,intermediate in galena,and lowestin cerussite. In the upper levelsof the mine, silver valueshave aver- agedapproximately 4.5 ouncesper ton. The amountof silverslowly increases with depth,and the greatestconcentration of silveris just abovethe 360-level. This high silverzone occurs as an irregularblanket just abovethe raggedinterface between the sulfide and intermediate oxide zones. In this zone, silver valueshave been as high as 27 ouncesper ton,wiih 13 ouncesper tonas a fair approximationof the average. The silvercontent drops to approximately 8 ouncesper ton in the sulfidezone. Silver in the form of primary argentitenor any of the secondarysilver mineralswere recognizedin polishedsection. Primary silverprobably exists as ions"admitted" into the galenacrystal structure. Evidentlythere is in- sufficientmaterial, such as a chlorideion sources,to immediatelyfix the silver ionsreleased by the oxidationof galena. Silver ionsapparently enter into solution and are washed down to the zone of increased sulfide content at and slightlyabove the top of the sulfidezone. Upon contactwith the sulfides, theyprobably precipitate to formsecondary argentite or reactwith the oxides to form suchminerals as argentiferousplumbojarosite and argentojarosite. Continuedleaching and downwardmigration of the silver from the upper oxidizedzone would thus tend to form the irregularblanket of increasedsilver valuesthat is foundin the intermediatezone just abovethe top of the sulfide zone.

PARAGENETIC SEQUENCE Hydrothermalmineralization began after the intrusionof the quartz monzoniteand the latite porphyry,and the fracturingof the limestones. Quartz and possiblypyrite were introducedfirst, followedby sphalerite, chalcopyrite,and galena. Subsequentoxidation of the primaryminerals re- sulted in the breakdown of sulfides and the formation of corellite and the variety of oxide mineralsfound in the mine. The generalparagenetic sequence as developedfrom geologicrelations andpolished section study is given in Figure7. Thelist of supergeneminerals is by no meanscomplete; the mineralassemblage is complex and varied, and is complicatedby mechanicalmixing. Manyof the mineralsare exceedingly fine-grained,and cannot be identifiedby generalmegascopic or opticaltech- niques. It is recognizedthat a supergeneparagenetic sequence has little meaning unlessrelated to a particularEh-pH environment(3). In many instances, suchan environmentalone has little meaning,as, for example,the amount of dissolvedcarbon dioxide may bear a controllingrelationship to mineral stability.The mineralsare in constantinteraction with oneanother, and mineralsuites vary with changesin environment.Different mineral suites OXIDATION OF A SULFIDE BODY 743

Paragenetic Sequence Hypogene $upergene Quartz Pyr•te $phaler•te Chalcapyrite Galena Fracturing Covetlite Malachttl Chry$ocolla Rosasite Corusslte .Anglesite Wutfenite Van odinitc - Mimctite $mithsanite Mangerote Pyrotucite Housmannite Psllomelane L•monite Hlmatltl Calcste Gypsum Chalcedony FIc. 7. Parageneticsequence. are stable at different levels of the mine. One mineral may form and re- main stableat onelocation, but be highlyunstable in an adjacentenvironment. Therefore,the supergeneminerals are placedon the diagramas being con- temporaneous,asindeed they are.

ACKNOWLEDGMENTS

I would like to thank Professors•[. W. Anthony,W. C. Lacy, E. B. Mayo, and S. R. Titley of the University of Arizona for assistanceand guidancein the collectionof the data, and to J. A. Hansuld,D. L. Mathias,It. T. Schass- berger,and R. •[. Wright of AmericanMetal Climax, Inc. for criticalreading. Acknowledgmentis dueto the SunriseMining Companyfor employmentwhile collectingthe data and for permissionto publishthe results. AMERICANMETAL CLIMAX, INC., DENVER,COLORADO, Dec. 27, 1965

REFERENCES

1. Anthony, J. W., 1951, Geology of the Montosa-CottonwoodCanyons area, Santa Cruz County, Arizona: Univ. Arizona unpubl. master's thesis. 2. Bryant, D. L., 1955, Stratigraphy of the Permian System in Southern Arizona: Univ. Arizona unpubl. doctoral thesis. 3. Sato, M., 1960, Oxidation of sulfide ore bodies, I, geochemical environments in terms of Eh and pH: EcoN. G•.or,., v. 55, p. 928-961. 4. Takahashi, T., 1960, Supergene alteration of zinc and lead deposits in limestone: EcoN. G•.or,., v. 55, p. 1083-1115.