Canadian MineralogistVol. 25, pp.639-646 (1981)

A STUDY OF SPHALERITE FROM THE CARBONATE-HOSTED Pb-Zn SULFIDEDEPOSITS OF THE EASTERN CHALKIDIKI PENINSULA. NORTHERN GREECE

STAVROS I. KALOGEROPOULOS AND GEORGE S. ECONOMOUInstitute ol Geology & Mineral Exploration, Messoghion 70, Athens 115 27, Greece

ABSTRA T

A detailed textual and chemical study of sphalerite fromPb-Zn deposits in carbonate host-rocks from the ChalkidikiPeninsula, nofthern Greece, using doubly polished thin sec-tions, indicates a complex evolution of the ore-forming sys-tem. Single crystals that attain 1.5 cm show evidence offine growth-banding, leaching, and at least two stages ofbrecciation, "Chalcopyrite disease" has been detected alongfractures and along grain boundaries in sphalerite; itrepresents the initial s.ages of replacement rather than ex-solution. The proportion of FeS in the sphalerite is quitevariable, between 1.8 and l8.7mole Yo, amonggrains fromthe same sample, among samples from the same deposit,and among samples from the same mineralogical associa-tion in different deposits. This variability reflects variationsin 1) the activity of FeS in the fluid, 2) the physicochemi-cal conditions during precipitation (1.e.,/(S2), T), and 3)the "chalcopyrite disease" texture, or a combination of Iand 2 where that texture is absent, On the basis of temper-atures derived from fluid-inclusion data on sphalerite thatcoexists with pyrite and data on its composition (moleVoFeS), we infer a sulfur fugacity of 10-e.7 to 10-13 atm.during sphalerite depositron.

Keywords: sphalerite, chalcopyrite disease, growth band-ing, fugacity of sulfur, Pb-Zn deposit, carbonates,Chalkidiki Peninsula. Greece.

SOMMAIRE

Une €tude texturale et chimique de la sphal6rite de gise-ment Pb-Zn dans des roches h6tes carbonat6es dans lap6ninsule de Chalkidiki, dans le nord de la Grbce, effec-tuee sur lames minces doublement polies, rdvble unes6quence complexe de d6position des sulfures. Les mono-cristaux, qui atteignent 1.5 cm, montrent des fronts de crois-sance trbs fins, des signes d'un lessivage et d'au moins deuxstades de brdchification, On a ddcel6 la texture dite <maladiede la chalcopyrite> le long de fissures et en bordure desgrains de sphal6rite; ce ph6nomdne repr6senterait un rem-placement plut6t qu'une exsolution. La teneur en FeS decristaux uniques varie beaucoup, entre 1,8 et 18.790 (pro-portion molaire), d'un cristal d l'autre dans le m€me 6chan-tillon, d'un €chantillon d l'autre d'un seul gisement, et parmiles 6chantillons montrant les m€mes associations min6ra-logiques des divers gisements. Cette variabilit6 serait duel) aux changements en activit6 de FeS dans la phase fluide,2) aux variations dans les conditions physicochimiques depr6cipitation (i.e., flS), T), et 3) d la pr6sence de la tex-ture dite <<maladie de la chalcopyrite>, ou i la pr6sence desfacteurs I et 2 oi cette texture est absente. A la lumidredes temp6ratures obtenues de donn6es obtenues sur lesinclusions fluides dans la sphal6rite qui coexiste avec pyrite,

639

et de sa teneur en FeS, on en conclut que la fugacitd desoufre 6tait de l}e.'r i lll3 atm. pendant la d6position dela sphal6rite.

Clraduit par la R€daction)

Mots-clds: sphalerite, <<maladie de la chalcopyrite), frontsde croissance, fugacit6 de soufre, gisement Pb-Zn, car'bonates, pdninsule de Chalkidiki, Grbce.

INTRoDUCTIoN

The Olympias, Madem Laccos and Mavres PetresPb-Zn massive-sulfide ore deposits are located in theKerdylion Formation, Chalkidiki Peninsula, north-ern Greece (Fig. l). On the basis of available infor-mation, this formation represents the lowermost partof the stratigraphic column of the so-called Serbo-Macedonian Massif (SMM), whereas the uppermostmember is referred to as the Vertiskos Formation.

These formations consist of variable proportionsof biotite gneiss, two-mica gneiss, biotite-hornblendegneiss, microcline-plagioclase gneiss, amphibolites,marbles and pre-, sln- and postorogenic intrusivebodies (Kockel et al. 1977). Kockel el a/. assigneda probable Precambrian age for the SMM on thebasis of information existing for the similar geotec-tonic unit in Yugoslavia. The Serbo-MacedonianMassif has been subjected to at least three phasesof deformation. The first, most likely Hercynian, ischaracterized by isoclinal folding, with axes trend-ing and plunging to the north, whereas the other twoare Alpine. The first took place from the UpperJurassic to the Lower Cretaceous, with subisoclinalfolds of variable trends; the second, of Tertiary age,is characterized by open folds and intense thrusting(Moundrakis 1985). Regional metamorphism hasreached the almandine-amphibolite grade; the rockswere subsequently retrograded to the greenschistfacies along shear zones and near postorogenic intru-sive bodies (Demetriades 1974, Kockel et al. 1977,C. Kougoulis, pers. comm.). The metamorphic rocksof the SMM have been intruded by calc-alkalinepostorogenic granites of Tertiary a5e (e.9. Stratonigranodiorite, 29 Ma) that show a spatial associationwith manganese-bearing Pb-Zn sulfides. These intru-sive bodies are themselves ore-bearing (e.g., Skou-ries Cu-Au granodiorite porphyry) and have alsoaltered the surrounding rocks. Nicolaou & Kokonis(1980) suggested that this igneous activity has a

640 THE CANADIAN MINERALOGIST

O 3km

otl

o"/,

G R E E C Emv

Ul6oo

oa,

ffi

EEffi

Ftc. l. Location map of the Pb-Zn massive sulfide deposits in Chalkidiki Peninsula(from Kockel et al. 1977).

genetic relation to the Pb-Zn-Mn metallogeny in thearea.

The Pb-Zn sulfide ores referred to above occuralong the contact between a lower marble horizonand a biotite gneiss, as well as within the marbleKockel et ql. 1977, Nikolaou & Kokonis 1980). Themajor minerals present in these ores tre sphalerite,galena, pyrite, arsenopyrite and rhodochrosite,whereas the gangue mineralogy is represented by acombination of quartz and calcite.

These ore deposits are considered to be of metaso-matic origin, with the hydrothermal fluids derived

KERDIUON FORMATION-BOTITE GNEISS,BIOTITE -HORNBLENDEGNEISS, AMPHIBOLITE

UPPER A'{D LOIVER MARBLEHORTZONS

VERTISKOS FORMATION

2- MtcA GNE|SS,BOTITE 6NEISSAUGEN GNEISS,AMPHIBOLITE, SHISTOSE .GRANIIIC SILLS, PEGI4ATOIDS

E GRANrrolDs

from the Stratoni granodiorite (Fig. l; Nicolaou &Kokonis 1980). The present study is an attempt todeduce the relationship between the mineralizationevent and deformation associated with metamor-phism and to estimate certain geochemicalparameters of ore deposition by unravelling the tex-tural and geochemical features of the sphaleriteassociated with pyrite. This study forms part of acombined effort to gather information pertinent tothe development of a scientifically sound and gener-ally accepted genetic model for these Pb-Zn sulfidedeposits. Such a model will provide us with the most

SPHALERITE FROM A CARBONATE.HOSTED Pb.ZN DEPOSIT' GREECE 641

Frc. 2. Reflected (A,C) and corresponding transmitted (B,D) light photomicrographs of sphalerite (Olympias) (doublypolished thin section). Note the fine banding (B,D), which is also reflected in the chemistry.

suitable criteria for exploration for blind ores withinthe unexplored parts of the Kerdylion Formation.

CHARACTERTSTICS oF THE ORE Dgposns

The ore deposits are stratabound (Nicolaou 1960,Nicolaou & Kokonis 1980) and generally composi-tionally banded. In addition, during recent visitsunderground at the Obrmpias mine, we noted thepresence of fault-controlled mineralization as well(N. Bitzios & S.I. Kalogeropoulos, unpubl. dato).Clastic ore commonly seen underground bears evi-dence of recrystallization. Two stages of brecciationmay be deduced from a study of polished slabs ofore. The first stage consists of fragments of pyriteand sphalerite that are cemented by quartz, whereasin the second stage, fragments of the compositeassemblage described above are cemented by sparrycalcite.

CHaRecrnntsrlcs oF THE SPHALERITE

The sphalerite exhibits a wide range of optical and

chemical variations; these can provide a wealth ofintbrmation concerning condrtions of deposition andsubsequent metamorphism of sulfide-bearing rocksand ores (Barton & Toulmin 1966, Scott & Barnes1971, Scott 1976). Uncovered doubly polished thinsections were used to decipher textural complexitiesand chemical variations in sphalerite (Figs. 2, 3)' Thechemical composition of the sphalerite in associa-tion with pyrite was determined by electron-microprobe analysis using the JEOL Superprobe 733'Operating conditions were as follows: 20 kV excita-tion voltige, 5 nA beam current, and 20 secondscounting iime. Mineral standards were used, andon-line ZAF corrections were carried out using aPDP-ll/04 computer. The error in the iron contentof the sphalerite does not exceed 0.2 mole 9o FeS'In most cases, the iron content varies widely withina single grain (Fig. 3A, Table l) and betwee! {aps(fig. :C). These properties, observed in sphaleriteirom the Olympias and Mavres Petres deposits' canalso be extended to that from the Madem Laccosdeposit, although our sampling in the latter was notsyitematic. Moieover, the internal texture in cefiain

642 THE CANADIAN MINERALOCIST

Ftc. 3. Transmitted (A,C) and reflected (B) light photomicrographs of the breccia fragments. Sphalerite-bearing brec-cia fragments (B and C) are of different origin. Note the banding and chemical zoning (mole 9o FeS) in the sphalerite.Numbers in parentheses (in A and C) indicate the number of analyses performed (Olympias).

Centre (z=5) lntemediate (r"3)

x 54 .94(0 .30) 58 .50(0 .78)e .88(0 .13) 7 .13(0 .15)

ZnFeCucdHnstotal

rcl eg FeS

o.zi(o.o)33.20(0 .50)98.06(0.85)17.36(o . te )

0 .33(0 .05)32.50(0 .36)98.46(0 .76)r2 .40(0 .26)

MaNin (r=3)

63.53(0 .28)2 .63(0 . r5 )

o.ei(o.os)0.23(0 .05)

33.10(0 .50)99.76(0 .95)4 .63(0 .20)

TABLE I. COMPOSITIONAL ZONINO IN A SINGLE CRAIN OF SPHALERITE, OLYMPTASPb-Zn SULFIOE DEPOSI.I, EASTERII CHALKIDIKI PENINSULA, I{ORTHERII GREECE

content. Since the host rocks have gone through atleast three stages of deformation, regional metamor-phism has reached the garnet-amphibolite facies, andthe sphalerite in our case does not show evidence ofdeformation twinning and of chemical homogeniza-'tion, it may be concluded that the deposition of theore postdates deformation and regional metamor-phism.

A study of the textural relationship betweensphalerite and chalcopyrite reveals that the latterappears along fractures and grain boundaries (so-called "chalcopyrite disease"). The grains ofsphalerite show a decrease in their iron content alongpreferred sites (Figs. 5, 6). This decrease may be dueto one or a combination of the following two possi-bilities: (i) decrease of temperature and concomitantincrease of the sulfur fugacity, and (ii) reaction ofcopper-bearing solutions with iron from sphalerite.Since the chalcopyrite primarily occurs cross-cuttingsphalerite that is finely zoned with respect to its ironcontent, we suggest that the second process is themore attractive explanation of the observed texture.

lllcroprobe analyses perfomed uslng energy dlsperslon. Nmbers lnparentheses represent one standard devlatJon. r number of analyses.

sphalerite grains suggests the occurrence ofhydrothermal leaching followed by redeposition(Fie.3A).

The mole 9o FeS in sphalerite from the Olympiasore deposit 114.20j42(15); r:591 is not statisticallydifferent (/ test) from that of the Mavres Petressphalerite 19.4 ! 5.2(15); n=341. These data arepresented in Figure 4. In general, sphalerite fromdeformed and metamorphosed lead-zinc sulfidedeposits shows evidence of deformation twinning anda tendency to be homogeneous with respect to its iron

u . 1 4 , 2 o

oLYMPTAs | i u3 ' "R a n g e : 4 , 4 - 1 A , 7

M : 9 , 4 3S : 5 , 2 Ot t = 3 4

R a n g e : 3 , 2 - . l 8 , 3

M : 2 , 1 4

r.aro. r-accos l; 2'"uR a n g e : 1 . 5 - 2 4

SPHALERITE FROM A CARBONATE-HOSTED Pb-Zn DEPOSIT. GREECE

Mole o /o Fes

Frc. 4. Histogram of mole 9o FeS of sphalerite from Olympias, Madem Laccos andMavres Petres ore deposits. Mean (M), standard deviation (S), number of ana-lyses (n) and ranges are also shown.

643

(J2 1 2lrl:foIJ

.IO

EIL

q

This texture may have been produced according toone or both of the following reactions: 2 FeSsp +Cu2* (in solution) + CuFeS2 + F%2*(in solution),3FeSsp * FeS, + 2Cu2* (in solution) .. 2CuFeS2+ 2Fe+ (in solution). Where the second reactionis valid, replacement features are found in the pyrite.

CERTAIN PARAMETERS oF THE GEOCHEMICALENVIRoNMENT oF ORE DEPoSITIoN

We have chosen to present an overall estimate ofthe range of values of certain geochemical parametersof ore formation, for the following two main rea-sons: (i) it is not possible to statistically substantiatea correlation between fluid-inclusion data and ironcontents in certain growth-zones in single grains of

sphalerite (K. Doryforos & S.I. Kalogeropoulos, inprep.). (ii) We cannot be certain as to whether ornot each of these growth zones was in equilibriumwith pyrite. Utilizing both the geothermometric dataof fluid inclusions in sphalerite (not corrected forpressure) and its iron content, we can delineate theenvironment of ore deposition on anl(S) - T dia-gram (Fig. 7, Table 2), along with other geochemi-cal parameters. The sulfur fugacity obtained fromFigure 7 ranges from l0e'7 to 10-13 atm.

DISCUSSION

The Pb-Zn sulfide ore deposits of the easternChalkidiki Peninsula, northern Greece, which occur

644 THE CANADIAN MINERALOCIST

Frc. 5. Reflected (A) and transmitted light (B) photomicrographs of textures insphalerite. Note that the presence of chalcopyrite along grain boundaries is cou-pled with a bleaching and removal of iron in the sphalerite (B) (Olympias).

mainly within marble and along a lower marble -biotite gneiss contact (Kockel et ql. 1977, Nicolaou& Kokonis 1980), are fault-controlled, stratabound,and commonly stratiform. The host rocks havesuffered at least three phases of deformation andhave been regionally metamorphosed to the garnet-amphibolite facies. Along shear zones and Tertiaryigneous stocks, this prograde sequence was followedby a retrograde metamorphic event (greenschistfacies). The finely banded nature of single grains of

sphalerite, compositionally zoned with respect totheir iron content, combined with the lack of defor-mation twinning, both suggest that deposition of thesphalerite postdates deformation and regionalmetamorphism. The recrystallization featuresdetected are most likely due to the intermittent natureof the ore-forming hydrothermal activity. Duringsphalerite precipitation, this activity was dominatedby saline solutions (22-25wt.r/o eq NaCl), tempera-tures ranging from 220 to 250oC, and sulfur fugaci

SPHALERITE FROM A CARBONATE-HOSTED Pb-Zn DEPOSIT, GREECE

*ffsr - ._: E?tr .,--l

tP DN$f,ASI,,

,@;t

Ftc. 6. Reflected (A) and transmitted lieht (B) photomicrographs showing fracture-controlled fine "chalcopyrite disease" texture, which results in partly opaquesphalerite (Olympias).

645

ties ranging from l0-e'7 to l0r3 atm. The temporaland spatial association of sulfide ore deposition andpostkinematic igneous activity in the easternChalkidiki Peninsula does not necessarily imply thatthe sulfide ores represent a peripheral manifestationof ore-forming hydrothermal activity due to ema-nations from the nearby igneous stocks. This doesnot preclude the existence of predeformationalmineralization which is now completely redistributedand reconcentrated through a Tertiary geothermalsystem set up by the post-kinematic igneous activity(e.g., near the Stratoni granodiorite).

RrFsnsNces

BanroN, P.8., Jn. (1978): Some ore textures involvingsphalerite from the Furutobe mine, Akita Prefec-ture, Japan. Mining Geol, ?.8,293-300.

Tourrr,uN, P., III (1966): Phase relationsinvolving sphalerite in the Fe-Zn-S system. .Ecor.Geol. 61,815-849.

CzaueNsre, G.K. (1974): The FeS content ofsphalerite along the chalcopyrite-plrite-bornite sul-fur fugacity buffer. Econ. Geol. 69,1328-1334.

646

PAMIIETER

Tsperature

S a l i n J t y

!hle? FeSin sphaler i tef(s2) (atn. )

RANCE220 - 270"c

235 - 387"C

22 - 25 vt."l

1 . 8 - 1 8 . 7

l0 -e .7 _ 10-13

THE CANADIAN MINERALOGIST

200 250 300 400

T E M p E R A T u R E ' C

Ftc. 7. LoglS2 - T ("C) diagram for the Fe-Zn-S systemshowing the mole 9o FeS of the sphalerite in equilibriumwith pyrite and pyrrhotite (Czamanske 1974). Note theoutline on the field of sphalerite deposition.

TABLE 2, PARAI€TERS 0F oRE pEposlTloN, oLyl,tpIAS pb-Zn DEP0SIT

DrMErnreoEs, S. (1974): Petological Studies of theMigmatitic Gneisses and Amphibolites from theRedino - Asprovalta Areas. Ph.D. thesis, Univ.Thessaloniki, Thessaloniki, Greece.

Karocenopoulos, S.I. (1984): Composit ion ofarsenopyrite from the Olympias Pb-Zn massive sul-fide deposit, Chalkidiki Peninsula, N. Greece. NeaesJahrb. Mineral. Monatsh., 296-300.

Kocrar F., Mor n, H. & Werrnpn, H. (1977): Erkiu-terungen zur Geologischen Karte der Chalkidhikiund angrenzender Gebiete l:100.000 (Nord-Griechenland). Hannover, Germany.

Mouonerrs, D. (1985): Geology of Greece. Univ. Stud.Press, Thessaloniki, Greece.

Nrcoreou, M. (1960): L'intrusion granitique dans lar6gion de Stratoni - Olympiade et sa relation avecla metallogendse. Annales Gdol. Pays Hell4n. ll,2t4-265.

KoroNrs, D. (1980)l Geology and develop-ment of Olympias mine, eastern Chalkidiki,Macedonia, Greece..Ir Complex Sulfide Ores (J.M.Jones, ed.). Inst. Mining Metallurgy, London.

Scorr, S.D. (1976): Application of the sphaleritegeobarometer to regionally metamorphosed ter-ranes. Amer. Mineral. 61,661-670.

& BeRNEs, H.L. (1971): Sphalerite geother-mometry and geobarometry. Econ, Geol. 66,653-669.

Received April 9, 1986, revised manuscript March 6,1987.

SOURCE OF INFORI4ATION

f l u l d i n c l u s l o n s l nsphaler l te (Doryforos &

Kalogeropoulos, ln prep. )arsenopyrl te geothemonetry

(Kalogeropoulos 1984)f l u J d J n c l u s l o n s

(Doryforos &Kalogeropoulos, in prep. )

thts study

thJs study