54 Sphalerite Associated With Pyrrhotite-Chalcopyrite Ore Occurring in the Kotana Fe-Skarn Deposit

8/10/2019 54 Sphalerite Associated With Pyrrhotite-Chalcopyrite Ore Occurring in the Kotana Fe-Skarn Deposit

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Sphalerite Associated with Pyrrhotite-ChalcopyriteOre Occurring in the Kotana Fe-Skarn Deposit

(Giresun, NE Turkey): Exsolution or Replacement

EMN FT

stanbul echnical University, Faculty o Mines, Department o Geological Engineering,

Maslak, R34469 stanbul, urkey (E-mail: [email protected]) (E-mail: nezihi@ kocaeli.edu.tr)

Received 28 January 2010; revised typescripts receipt 13 July 2010 &07 October 2010; accepted 12 October 2010

Abstract:Te Kotana prospect is located about 30 km south o Giresun (NE urkey). Te ore mineralization is a Fe-skarn occurring within the low-grade pre-Lower Jurassic Pnarlar metamorphics, consisting o marble-phyllite intrudedby the Upper CretaceousEocene Aksu biotite monzogranite. Te principal primary ore minerals include pyrrhotite andmagnetite along with minor pyrite (I) and chalcopyrite, accompanied by trace sphalerite. Sphalerite is closely associatedwith chalcopyrite and to a lesser extent with hexagonal pyrrhotite. Secondary ore minerals include pyrite (II), marcasite,martite, hematite, goethite, lepidocrocite, and intermediate Fe-oxides-hydroxides. Gangue minerals are mainly calciteand quartz. Oxidation o the primary sulphides resulted in ormation o diverse secondary ore textures containing birdseye, martitic, spheroidal, colloorm, rim, and veinlets. Distinct crystal shapes o sphalerite are o particular interestto this investigation due mainly to their proposed ormation mechanisms. Tree alternative mechanisms or theirormation were considered: (i) quasi-exsolved bodies developed by hexagonal pyrrhotite replacement o chalcopyrite,(ii) interstitial ormation between coalescing pyrrhotite crystals during crystal growth, and (iii) as genuinely exsolvedbodies, and as such conict with previous experimental results. Although the general absence o solute mineral outsidethe solvent mineral suggests solid solution at high temperatures (avouring the third mechanism), textures, modal,microprobe and sulur-isotope data suggest that these are more likely to be pseudoexsolved bodies ormed as a result o

replacement o chalcopyrite by hexagonal pyrrhotite. Te 34

S values o pyrrhotite and chalcopyrite are between 5.23 and6.73 per mil (n= 12) and 2.29 and 3.26 per mil (n= 8), respectively, indicating continuous enrichment in heavy sulphurisotopes rom prograde stage to retrograde stage within the typical range or skarn-type mineralization. Fluid inclusionanalyses o calcite and quartz gangues indicate that the minimum homogenization temperature (T) averaged 40020C with salinities < 15 wt% NaCl equivalent.

Key Words:Eastern Pontides, exsolution, Fe-skarn, pseudoexsolution, pyrrhotite, replacement, sphalerite

Kotana Fe-Skarn Yata (Giresun-KD Trkiye)nda Bulunan Pirotit-

Kalkopirit ile ilikili Sfalerit: Eksolsyon(mu) veya Ornatm(m)

zet:Kotana sahas Giresun (KD rkiye)nin yaklak 30 km gneyinde bulunmaktadr. Cevher oluumu bir Fe-skarn

olup, Erken Jura ncesi yal mermer-llitlerden oluan ve Ge KretaseEocene yal Aksu biyotitli monzogranitininsokulum yapt dk dereceli Pnarlar metamortleri ierisinde bulunmaktadr. Balca birincil cevher mineralleripirotit ve magnetit ile minr pirit (I), kalkopirit ve eser saleriti iermektedir. Salerit varl sk bir ekilde kalkopiritle,daha az olarak ta pirotitle birliktelik sunmaktadr. kincil cevher mineralleri pirit (II), markazit, martit, hematite, gtit,lepidokrosit ve ara Fe-oksit-hidroksitlerden olumaktadr. Gang mineraller esas olarak kalsit ve daha az olarak kuvarstanibarettir. Birincil slrlerin oksidasyonu, kugz, martitik, seroyidal, koloorm, ereve ve damarck gibi ok eitliikincil cevher dokularnn oluumunu sonulamtr. Saleritin zgn kristal ekilleri, bu almada, nerilen oluummekanizmalar nedeniyle zel bir nem tamaktadr. Oluumlar iin alternati mekanizma dikkate alnmtr: (i)hegzagonal pirotitin kalkopiriti ornatmas sonucu olumu olan yalanc kusma ktleleri olarak olumulardr, (ii) kristalbymesi sresince kaynaan pirotit kristalleri arasnda interstisiyal olarak olumulardr ve (iii) daha nceki deneyselbulgularn aksine bunlar gerek kusma (eksolsyon) yaplardr. Yksek scaklklarda solt mineralin solvent mineraldnda genel yokluu (nc mekanizmay avori klmaktadr), dokular, modal-mikroprob ve kkrt izotop verileribunlarn olaslkla kalkopiritin hegzagonal pirotit tarandan ornatlmasnn bir sonucu olarak oluan psydo-kusma

ktleleri olduunu nermektedir. Pirotit ve kalkopirite ait 34S deerleri srasyla 5.23 ve 6.73 per mil (n= 12) ve 2.29ve 3.26 per mil (n= 8) arasnda deimekte bu da, skarn yataklar iin tipik aralkta olmak zere, prograt saadan

urkish Journal o Earth Sciences (urkish J. Earth Sci.), Vol. 20, 2011, pp. 307320. Copyright BAKdoi:10.3906/yer-1001-26 First published online 12 October 2010


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Introduction

Many ore minerals undergo exsolution as they coolrom the temperatures o initial crystallization.Common examples o exsolution textures that mayoccur in diverse deposits are blebs (e.g., chalcopyritein sphalerite), lamellae (e.g., ilmenite in magnetite),ame-like (e.g., pentlandite in pyrrhotite), and

myrmekites (e.g., association o arsenic-antimony-stibarsen). Exsolution textures involving naturalpyrrhotite as host or guest are listed in able 1.

Te Fe-Zn-S system has the potential or use as ageothermometer and geobarometer to resolve manyproblems about genesis o an ore deposit providedthat the mineral phases ormed under requiredconditions. Many experimental studies deal withphase relations o this system over a large range otemperatures and applications o geothermometer

and geobarometer criteria with variable success(Vaughan & Craig 1997 and reerences therein).

A controversial micro-ore texture, observedbetween pyrrhotite-sphalerite-chalcopyrite in

the Kotana Fe-skarn deposit, in the Dereli area(Giresun, NE urkey; Figure 1) was studied.Initially the ore textures observed at Kotana wereinterpreted as conicting with the conclusions oexperimental studies (Barton & oulmin 1966;Barton & Skinner 1979). However, a single polishedsection showed a critical transormation between

pyrrhotite and chalcopyrite and is the ocus o thispaper. Tree probable mechanisms were discussed,based on the available data. It is ound that thereplacement mechanism produced an exsolution-like microtexture, and hence such textures occurringelsewhere should be interpreted cautiously.

Geological Framework

Te geological structure o the Eastern Pontides (NE

urkey) is the consequence o long-lived subduction,accretion and collision events associated with theclosure o the ethyan Ocean (Okay & ahintrk1997 and reerences therein).

retrograt saaya doru ar kkrt izotopunca srekli bir art gstermektedir. Kalsit ve kuvars ganglar zerindeyaplan sv kapanm analizleri, slr cevherlemesinin ana saasnda minimum oluum scaklnn ortalama 40020C olduunu ve tuzluluun < a. % 15 NaCl edeer olduunu gstermektedir.

Anahtar Szckler:Dou Pontitler, eksolsyon, Fe-skarn, psydo-eksolsyon, pirotit, ornatm, salerit

Table 1.Exsolution textures shown by pyrrhotite either as host or guest mineral.

Host Guest Nature of Exsolution Pattern

pyrrhotite pentlandite lamellae/ame, myrmekitic

pyrrhotite chalcopyrite lamellae/ame

pyrrhotite magnetite platelets

pyrrhotite valleriite platelets

alabandite pyrrhotite blebs

hexagonal pyrrhotite monoclinic pyrrhotite curved lamellae/lenses

chalcopyrite pyrrhotite stars/crosses

pentlandite pyrrhotite emulsion

argentopyrite pyrrhotite uniorm network

sphalerite pyrrhotite blebs in rows

*pyrrhotite sphalerite star/stellar/crosses/irregular

*Reported in this study and also by Marignac (1989)


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Te Eastern Pontides rest generally on pre-Liassic composite basement rocks consisting o (i)high-temperature low-pressure metamorphic unitsintruded by Lower Carbonierous high-K I-typegranitoids (Okay 1996; opuz & Altherr 2004;opuz et al. 2004a, 2007, 2010), (ii) Permoriassic

low temperature high pressure metamorphic units(e.g., Okay & Gncolu 2004; opuz et al. 2004b),and (iii) molassic sedimentary rocks o PermoCarbonierous age (Okay & Leven 1996; apknolu2003). Te basement is overlain transgressively byLiassic volcanics and volcaniclastics, deposited in anextensional arc environment. Te volcanic memberso this sequence are represented by calc-alkaline totholeiitic basaltic to andesitic rocks (e.g., en 2007;Kandemir & Ylmaz 2009). Te Liassic volcanics and

volcaniclastics grade into Malmlower Cretaceouscarbonates (Okay & ahintrk 1997 and reerences

therein). Late Cretaceous time is represented by avolcano-sedimentary rock succession more than 2km thick in the north and by yschoid sedimentaryrocks with limestone olistoliths in the south. LateCretaceous volcanics compositionally range rombasalt to rhyolite (e.g., Ein & Hirst 1979; Manetti etal.1983; amur et al.1996; Arslan et al.1997; Okay &ahintrk 1997; Boztu & Harlavan 2008). Kuroko-type volcanogenic massive sulphide (VMS) depositsare widely associated with Late Cretaceous elsicvolcanics (ifi et al.2005 and reerences therein).Te Late Cretaceous magmatism occurred as a resulto northward subduction o the zmir-Ankara-Erzincan Neotethys ocean (e.g., engr & Ylmaz1981; Okay & ahintrk 1997; Ylmaz et al. 1997).Te collision between the Eastern Pontides and the

auride-Anatolide block to the south is constrainedto have occurred in the Paleocene to early Eocene

Figure 1. Location map o the study area.


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(e.g., Okay & ahintrk 1997; Okay & ysz 1999).Post-collisional Eocene volcanic and volcaniclasticsunconormably overlie the older units, and locallyseal the zmir-Ankara-Erzincan suture (Altherr et al.2008).

As a result o the long-lived subduction andcollisional events, the ages o granitoids in theEastern Pontides range rom Early Carbonierous toLate Eocene (e.g., Boztu et al.2004; 2005; opuz etal.2005, 2010; Arslan & Aslan 2006; Karsl et al.2007;Kaygusuz et al.2008; Kaygusuz & Aydnakr 2009).Tese granitoids are mostly shallow intrusions,and have well-developed contact aureoles, whichhave, however, ofen been neglected (aner 1977;

Sadklar 1993; opuz 2006). Within the contactaureoles and their vicinities, numerous skarn-typeore mineralizations o various size and elementcontents have developed (e.g., Kotana, zdil andDokumaclar) (Figure 1).

Kotana Skarn Mineralization

Te study area is located in the central portion othe northern zone, but very close to the boundary

between the northern and southern zones othe Eastern Pontides, according to the classicaldivision in terms o rock associations (Figure 1).Basement rocks in the area consist o pre-JurassicPnarlar metamorphics and overlying post-Jurassic

volcaniclastics intruded by the upper CretaceousEocene Aksu monzogranite (78.31.5 Ma (Mooreet al.1980; Ylmaz & Boztu 1996; Sara 2003). Asa consequence, contact metasomatic assemblageswere developed locally within the marbles. TeKotana deposit occurs within the marbles o themetamorphic basement, which are generally white,but green in skarns. Hornelsic rocks are generallygreen and contain abundant clinopyroxene, garnetand calcite visible to the naked eye. Te Kotana skarnis a calcic exso-skarn. Although it does not covera large area and occurs as discontinuous massesbetween the ore zone and marble, three distinct zonesbased on the mineral assemblages were distinguished

(Figure 3a): (i) garnet-clinopyroxene, (ii) epidote-garnet-clinopyroxene-calcite, and (iii) epidote;although garnet, clinopyroxene, calcite, scapolite,amphiboles (erroactinolite, magnesian hornblende,errohornblende) micas, quartz, and albite occurin all three zones in varying quantities. Occasionalpyritization was also observed.

Although the exact size o the ore body has notbeen determined, its height and thickness appearto be constant at about 30 m and 15 m, respectively

(Figure 3a). Te length o the ore body is not knownbecause o aulting, but is estimated at about 0.6kilometres based on eld observations and a numbero geological sections. Te ore mineralization appearsto be a concordant layer with an arcuate shape (Figure

Figure 2. Major contact metasomatic occurrences and associated lithological units along the Eastern Pontide tectonicbelt (updated and moded rom Aslaner et al.1995).


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3b, c). Te ore exhibits a somewhat gradual transitionrom the ootwall rocks, but it is cut off sharply atthe contact with the hanging-wall rocks. It laterallyterminates gradually in one direction and sharplyby a ault in the other direction. Proven reserves areabout hal a million tons with a possible reserve o 1million tons (Van 1977).

Analytical Methods

Samples examined, considered to be representativeor the major ore types o the deposit, were collected

rom an exploration trench. Polished sections wereprepared or both reected-light microscopy andElectron Probe Microanalysis (EPMA). o obtainthe bulk chemical compositions, modal analysesand electron microprobe analyses were carried outusing polished sections. Modal analyses were carriedout on pyrrhotite and chalcopyrite, both containingsphalerite skeletal inclusions. Digital images wereevaluated using SCION image processing sofware.Pyrrhotite, sphalerite, and chalcopyrite crystals were

analyzed or selected elements through point andline analyses by wavelength dispersive X-ray analysis

probable fault

Figure 3. Simplied geological map o the study area (a) along with a SWNE through section (b) and acolumnar section (c)(modied rom Van 1977 and ifi & Vcl 2003) (size o the ore deposit in allthree gures exaggerated).


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using a CAMECA SX50 electron microprobe. Anaccelerating voltage o 15 kV was used. Te beamcurrent and counting time or major elements were 20nA and 20 seconds, respectively. race elements wereanalyzed at a beam current o 100 nA and a countingtime o 30 seconds. Te accuracy o the EPMAanalyses was monitored using reerence samples osimilar composition (sphalerite, chalcopyrite andpyrrhotite).

On the same polished samples, pyrrhotite andchalcopyrite crystals selected or sulphur isotopicanalysis were drilled using a 0.75-mm carbidebit. Mineral powders and a small amount o V

2O

5

were loaded into tin capsules and analyzed usingElemental Analyzer-Continuous Flow IsotopeRatio Mass Spectrometry on a Finnigan MA252isotope ratio mass spectrometer (Indiana University,Bloomington, Indiana). Analytical precision is betterthan 0.05%.

Analytical results are listed in ables 2 to 3.Sulphur isotopic compositions are reported instandard notation relative to Vienna Canyon Diabloroilite (VCD). Listed sulphide analyses are romhomogenous crystals through point analyses. Line

analysis on a pyrrhotite crystal replacing chalcopyritewas carried out at intervals o 50 micrometers.

Te microscope used or uid inclusions studyis a Nikon Optiphot, with x10 oculars, x5, x10, andx40 long working distance lenses. Te microscope isully equipped with transmitted white light. Attached

to this microscope is a modied USGS heating andreezing stage, designed by Fluid Inc. USA. Tis allowsmicrothermometry to be perormed on inclusions,by passing heated air over the sample; inclusions canbe heated to 700 C. By passing nitrogen gas passedthrough liquid nitrogen over the sample, inclusionscan be cooled down to 190 C.

In order to determine the zinc content o typicalore, a representative ore sample was also analyzed byInductively Coupled Plasma (ICP-ES & MS) (AcmeLabs/Canada): a 15 g sample was digested in 90 mL2-2-2 HCl-HNO

3-H

20 at 95C or one hour, was

diluted to 300 mL, and then analyzed by employingICP-ES & MS.

Ore Mineralogy and Micro Ore-textures

Major ore minerals observed in this deposit arehexagonal pyrrhotite (based on PXRD pattern)and magnetite. Chalcopyrite and pyrite locallybecome signicant. Sphalerite and covellite occurin trace quantities. Te ormer is associated mainlywith chalcopyrite and, to a lesser extent, hexagonalpyrrhotite. Te association o sphalerite with

chalcopyrite appears to occur through exsolution;although its association with pyrrhotite is probablydue to replacement o chalcopyrite containingexsolved sphalerite by pyrrhotite. A secondgeneration o pyrite, typically ne-grained andintimately intergrown with ne-grained marcasitewas also observed and is considered to be a product o

Table 2. EPMA results or selected elements in sphalerite, pyrrhotite and chalcopyrite crystal (results in wt%).

Element Sphalerite Pyrrhotite Chalcopyrite

w/Po w/Cp w/Sl w/o Sl w/Sl w/o Sl

Fe 9.074 8.524 58.727 60.978 29.582 29.856Cu 0.180 0.842 0.017 0.008 36.048 34.989S 33.180 33.112 38.739 37.085 34.547 34.178Zn 58.001 58.293 0.034 0.017 0.134 0.105As 0.008 0.015 0.033 0.064 0.023 0.018Ni 0.003 0.006 nd 0.021 nd 0.017Co 0.011 0.012 nd 0.003 nd ndBi nd nd 0.01 0.136 nd ndCd 0.220 0.200 nd nd 0.002 ndMn 0.017 0.008 nd nd nd nd

*nd: not detected


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exsolution rom sulphur-rich pyrrhotite. In contrast,the rst generation o pyrite occurs as euhedral tosubhedral crystals. Martite, hematite, lepidocrocite,and goethite are the principal secondary Fe-oxides,occurring with unidentied intermediate Fe-oxide-hydroxide phases. Quartz and calcite are the majorgangue minerals. Te presence o twelve more mainlyCa-Fe-Mg-silicates were reported by ifi & Vcl(2003).

Microscopic examination o ore textures indicatedthat the primary sulphide phases (Stage-I sulphidesin Figure 5) show mainly simple granular and mosaicore microtextures, whereas secondary ore texturesare much more complicated and varied. During rapid

cooling hexagonal pyrrhotite converts to monoclinicpyrrhotite as a stage in the ormation o ne-grained pyrite-marcasite mixtures. Where supergenealteration is intense, pyrrhotite alters directly to iron-oxides/hydroxides, which occur as rims surrounding,and veins crosscutting pyrrhotite crystals. Since ne-grained pyrite and marcasite spheroids are especiallyprone to oxidation, alternating pyrite, marcasite,and iron-oxides-hydroxide layers orm concentricspheroids or concentrically grown bands. Marginal

weathering o monoclinic pyrrhotite to pyrite andmarcasite also resulted in the ormation o the so-called birds eye texture (Figure 4e, h). Figure 5 showsthe suggested mineral paragenesis or the deposit.

Experimental Results

Mineral and Bulk Chemistry

A representative ore sample was analyzed or bulkchemistry: Fe (46.6%), Cu (0.098%), Zn (0.04%), Mn

(0.02%), Ni (0.003%), Co (0.024%). As, Cd, and Sbwere also present, (%69 liquid +%69 vapour +


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Figure 4. (AD) Buttery-lke exsolved sphalerte bodes n pyrrhotte and chalcopyrte hosts, (B)pyrrhotte pseudomorph afer chalcopyrte through a complete replacement, (C) ncompletereplacement o pyrrhotte afer chalcopyrte attestng that replacement occurred (E)concentrcgrowth bands ormed by pyrte and marcaste accompaned by varous Fe-oxd es-hydroxdes,(F) brds eye texture depeloped by pyrte as a result o pyrrhottes lateral weatherng, (G)rm texture resulted rom pyrhotte weatherng to Fe-oxdes, (H) close-up vew o growthbands contanng a repeatng successon o pyrte, marcaste, and Fe-oxdes (Py pyrte; Cp

chalcopyrte; Sl sphalerte; Mc marcaste; Po pyrrhotte; Poh hexagonal pyrrhotte (Fgure4a s reproduced through scannng and enlargng rom ifi & Vcl 2003).


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Discussion

Micrometer-sized grains o sphalerite in chalcopyriteand pyrrhotite hosts orm stellate shapes (Figure4ac). Micrometer-sized sphalerite exsolution bodiesoccur as rosettes, star or stellar orms, associatedwith chalcopyrite as a result o unmixing. Such

associations can also come about as a result o a localsupersaturation in sphalerite at the growing rontso chalcopyrite at lower temperatures (e.g.,


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Te converse, namely chalcopyrite in sphalerite(chalcopyrite disease) is one o the most commonassociations in unmetamorphosed epithermal andmassive sulphide deposits (Barton & Bethke 1987).In act, chalcopyrite inclusions in sphalerite are verycommon and represent, under various circumstances,exsolution and co-precipitation, as well asreplacement. Tere are also reported occurrences opyrrhotite orming exsolved bodies within sphalerite(Craig & Vaughan 1994; Picot & Johan 1982; Lepetitet al. 2003). Te reverse association, in the ormo sphalerite apparently exsolved rom pyrrhotite,is very unusual, although Uytenbogaart & Burke(1985) reported the presence o sphalerite inclusions

within pyrrhotite and oriented intergrowths betweenpyrrhotite and sphalerite, and Ramdohr (1980, p. 602)mentioned the presence o thin plates o a sphalerite-like mineral in pyrrhotite. Te underlying reasonis that the solubility o zinc sulphide in pyrrhotiteis very low. However, despite the observation oBarton & oulmin (1966) o limited Zn solubility inpyrrhotite and ability o pyrrhotite to dissolve lessthan 0.1% ZnS (Barton & Skinner 1979; p. 366), theore microtextures strongly suggest that sphaleriteexsolved rom pyrrhotite (Figure 4a, b). Tus, thisparticular texture presents a contradiction.

Ore microscopy indicated that sphalerite occurredonly in chalcopyrite and pyrrhotite. In principle,complex sphalerite crystal outlines can be producedthrough a number o combinations o coalescingpyrrhotite crystals as shown in Figure 6. However,the sphalerite association with pyrrhotite would beexpected irrespective o the presence o chalcopyrite,in such a hypothetical scenario. Ore microscopy studyruled out the possibility o this mechanism, because

chalcopyrite was always part o the occurrence.

A second and more probable mechanism thatcould produce such a texture is replacement o theoriginal host chalcopyrite by pyrrhotite. Troughreplacement, exsolved sphalerite bodies originallywithin chalcopyrite could be preserved even thoughthe parent mineral, chalcopyrite, was completelyreplaced. EPMA analyses o pyrrhotite crystals withand without sphalerite masses indicated that the onlysignicant difference is in Cu and Zn contents, which

were enriched in pyrrhotite containing sphaleritebodies (able 2) that were originally chalcopyrite

(Figure 4b). Line analyses crossing the chalcopyrite-pyrrhotite interace show a gradual decrease in Cuas the replacement ront advanced. Te advancelef behind the exsolved sphalerite as a record othe process. Some o the ractures in chalcopyritecontinue into replacing pyrrhotite, whereas reverseoccurrence was not observed, thereby indicatingthe pseudomorphous replacement o chalcopyrite(Figure 7) resulting in the ormation o quasi-exsolved bodies o sphalerite in pyrrhotite. Figures4c and 7 both show the sphalerite stars straddlingthe chalcopyrite-pyrrhotite boundary that could beconsidered as another indication o the process.

A signicant portion o dissolved copper would

be expected to precipitate as copper rich speciesrequiring less sulphur, although due to decreasingtemperature and sulphur ugacity, some o thatcopper may probably have lef the system. However,minor to trace malachite could account or someo the copper produced during the replacementprocesses. Te replacement might have been drivenby introduction o Fe2+in a reaction such as

CuFeS2+ Fe+++ 0.5 H

2= 2 FeS + Cu++ H+

but the real reaction must be more complex to allowor pyrrhotite o Fe

(1x)S composition and also to

accommodate volume changes during replacement.Furthermore, declining temperature and sulphurugacity are scarcely the primary drivers here.

Te only signicant difference in the mineralchemistry between chalcopyrite with and withoutsphalerite was in copper content and, to lesser extent,contents o zinc and cadmium. Chalcopyrite withoutsphalerite was comparatively low in copper since someo the copper ions were substituted by zinc. However,

in chalcopyrite with sphalerite, zinc was exsolved assphalerite, leaving copper sites in chalcopyrite lledonly by copper, resulting in chalcopyrite enriched incopper. Zinc and cadmium contents were also higherin chalcopyrite containing sphalerite masses. Tis isbecause Cd preers sphalerite as a host; thereore, assphalerite exsolves the Cd goes into the sphalerite.Line analyses also showed that points closer tosphalerite bodies are signicantly low or nil in zinccontent.

However, many convincing data came rom theEPMA o sphalerite bodies in both pyrrhotite and


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chalcopyrite. Te chemistry was strikingly similar

(able 2, Figure 8) avouring the scenario whereinchalcopyrite crystallized during prograde stage Iand exsolved sphalerite under conditions that weremore magmatic (as indicated by the sulphur isotopedata). Pyrrhotite was subsequently deposited duringretrograde stage II under low sulphur ugacity andmore dilute conditions with respect to source osulphur, under conditions that become suitable ormassive magnetite deposition later in the retrogradestage. Te modal analyses o pyrrhotite containingskeletal sphalerite yielded very similar results (< 4

vol%) to those acquired rom the chalcopyrite. Tisruled out the possibility o sphalerite being real

exsolved bodies in pyrrhotite (the third mechanism).

Micro-analytical data with ore microscopy indicatedthat this particular texture was brought about as aresult o pyrrhotite replacement o chalcopyrite thatalready contained exsolved sphalerite bodies, thusorming the exsolution-like ore texture.

Acknowledgement

Tis project was unded by the Scientic andechnological Research Council o urkey(BAK; Project Code: 2219). Te author

thanks Paul B. Barton (USGS), Richard D. Hagni(Missouri University o Science and echnology,

Figure 6. Simplied sketch o coalescing pyrrhotite crystals (1 through 5) that could entrapintergranular sphalerite that would lead to exsolution-like textures (constructed throughpersonal communication with M. Vcl).


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USA), . Kuu (Mula University), and Dr. G. opuz(stanbul echnical University) or their careulreading o the manuscript and comments on theore textures and the regional geology, respectively.Teir contributions and constructive criticisms

signicantly improved the manuscript. I am alsoindebted to Edward M. Ripley and Chusi Li (Indiana

University, Bloomington, USA) or their kind helpor EPMA and sulphur isotope analysis carried out attheir acilities and to N. Hanili (stanbul University)or his help on interpretation o uid inclusion dataand to M. Vcl (Karadeniz echnical University) or

sample acquisition and or constructing Figure 6.

Figure 7. BSE image o incomplete replacement o chalcopyrite by pyrrhotite and microanalysis along selected 3 lines.Dark solid dots indicate micropoints analyzed. Along three lines within the darker phase (pyrrhotite), coppercontent decreases as the replacement ront advances.

Figure 8. EPMA values o major and common elements o sphalerite hosted both by chalcopyrite and pyrrhotite.


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54 Sphalerite Associated With Pyrrhotite-Chalcopyrite Ore Occurring in the Kotana Fe-Skarn Deposit

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