GENESIS OF HIGH-SULFIDATION VINCIENNITE-BEARING … · Massive ores, with as much as 85–90% of sulfides, form lenticular or stock-like bodies, locally with highly variable morphol-ogy

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The Canadian MineralogistVol. 42, pp. 1501-1521 (2004)

GENESIS OF HIGH-SULFIDATION VINCIENNITE-BEARING Cu–As–Sn (±Au)ASSEMBLAGE FROM THE RADKA EPITHERMAL COPPER DEPOSIT,

BULGARIA: EVIDENCE FROM MINERALOGYAND INFRARED MICROTHERMOMETRY OF ENARGITE

KALIN KOUZMANOV§ AND CLAIRE RAMBOZ

Institut des Sciences de la Terre d’Orléans (ISTO–CNRS), 1A, rue de la Férollerie, F–45071 Orléans Cedex 2, France

LAURENT BAILLY

BRGM, REM/MESY, B.P. 6009, F–45060 Orléans Cedex 2, France

KAMEN BOGDANOV

Department of Mineralogy, Petrology and Economic Geology, Faculty of Geology and Geography,Sofia University “St. Kliment Ohridski”, 15 Tsar Osvoboditel Boulevard, 1000 Sofia, Bulgaria

ABSTRACT

The Radka deposit is one of the largest Cu–Au epithermal deposits related to Late Cretaceous volcanic arc-type magmaticactivity in the Panagyurishte ore region, central part of the Srednogorie zone, Bulgaria. The mineralogical and geochemicalfeatures of a vinciennite-bearing Cu–As–Sn (± Au) assemblage at Radka show very similar characteristics to those in othervinciennite-bearing high-sulfidation epithermal deposits worldwide. The assemblage consists of enargite, Cu-excess tennantite,chalcopyrite, gold, vinciennite, colusite, and minor covellite, within a gangue of barite, illite, and quartz. A detailed electron-microprobe study of vinciennite and associated minerals reveals the heterovalency of Cu and Fe. New data on the composition ofvinciennite sheds light on aspects of its crystal chemistry, such as incorporation of Cu2+ and Fe3+ and Sn4+ Ge4+ substitution,and leads us to propose a new empirical formula: Cu+

8Cu2+2Fe3+

3(Fe,Cu)2+(Sn,Ge)4+(As,Sb)5+S162–. Infrared microthermometry

of enargite-hosted fluid inclusions provides constraints on the conditions of deposition of this unusual assemblage in the contextof the evolution of the magma-related ore-forming system at Radka. The assemblage was formed by oxidized and slightly acidfluids, with a dominantly magmatic signature, high fugacity of sulfur and intermediate salinity (about 10 wt.% eq. NaCl) at atemperature of about 275°C. In view of the geology of the Radka deposit, its mineralogical and geochemical peculiarities, oretextures, type of hydrothermal alteration and the character of the fluids, we interpret the deposit as a deep part of a high-sulfidationepithermal mineralization, possibly genetically related to a porphyry copper system.

Keywords: vinciennite, enargite, mineralogy, infrared microthermometry, fluid inclusions, epithermal, Srednogorie, Radka,Bulgaria.

SOMMAIRE

Radka est un des plus gros gisements épithermaux de cuivre et or de la région minière de Panagyurishte, dans la partie centralede la zone de Srednogorie, en Bulgarie. Le développement de ce district métallogénique est lié à une activité magmatiquenéocrétacée de type arc insulaire. Les particularités minéralogiques et géochimiques de la paragenèse Cu–As–Sn (± Au) àvinciennite sont très semblables à celles décrites dans d’autres gisements de type épithermal acide. La paragenèse contient énargite,tennantite riche en cuivre, chalcopyrite, or, vinciennite, colusite et covellite en trace, dans une gangue de barite, illite et quartz.L’étude de la vinciennite et des phases associées à la microsonde électronique révèle que le cuivre et le fer dans ces minéraux sonthétérovalents. Les nouvelles données obtenues sur la composition de la vinciennite nous ont permis d’élucider certains aspects desa cristallochimie, tels que l’incorporation de Cu2+ et Fe3+ et la substitution Sn4+ Ge4+, et de proposer une nouvelle formulestructurale: Cu+

8Cu2+2Fe3+

3(Fe,Cu)2+(Sn,Ge)4+(As,Sb)5+S162–. L’étude microthermométrique des inclusions fluides dans l’énargite

au microscope infrarouge a permis de déterminer les conditions de formation de cette paragenèse inhabituelle dans le contexte del’évolution du système magmato-hydrothermal de Radka. La minéralisation a été formée par des fluides relativement oxydés et

§ Present address: Institute of Isotope Geochemistry and Mineral Resources, ETH Zentrum, NO F52.1, Sonneggstrasse 5, CH-8092 Zürich, Switzerland. E-mail address: [email protected]

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légèrement acides, avec une composante magmatique dominante, une fugacité du soufre élevée et une salinité intermédiaire(environ 10% poids équiv. NaCl) à une température de l’ordre de 275°C. Les particularités géologiques du gisement de Radka, sacomposition minéralogique et géochimique, ainsi que les textures du minerai, le type d’altération hydrothermale et le caractèredes fluides, nous ont permis de définir le gisement comme une partie profonde d’un système épithermal acide, tout en envisageantune relation génétique avec un système de type porphyre cuprifère en profondeur.

Mots-clés: vinciennite, énargite, minéralogie, microthermométrie infrarouge, inclusions fluides, épithermal, Srednogorie, Radka,Bulgarie.

portant ore-bearing igneous belt of calc-alkaline signa-ture within the Alpine – Balkan – Carpathian – Dinariderealm, defined as Banatitic Magmatic and Metallo-genetic Belt, BMMB (Berza et al. 1998, Ciobanu et al.2002) or Banat–Srednogorie Tectonic and MetallogenicZone, BSTMZ (Popov 1996). The Late Cretaceous in-

INTRODUCTION

The Radka deposit is one of the largest Cu–Auepithermal deposits in the Panagyurishte ore district,Bulgaria. The district is part of the Srednogorie zone(Fig. 1), which is the Bulgarian portion of the most im-

FIG. 1. a) Position of the Srednogorie zone and geology of the southern part of the Panagyurishte district with location of themajor mineral occurrences (modified from Bogdanov 1980). b) Cross-section of the Radka deposit (after Popov & Popov1997, Tsonev et al. 2000b).

THE RADKA HIGH-SULFIDATION EPITHERMAL COPPER DEPOSIT, BULGARIA 1503

trusive and volcanic rocks of the belt, including minortholeiitic and alkaline, but mostly calc-alkaline, high-Kcalc-alkaline to shoshonitic compositions (Stanisheva-Vassileva 1980, Berza et al. 1998) host two major stylesof ore deposits: porphyry copper, and “replacementmassive sulfide epigenetic” (Jankovic 1977, Bogdanov1980) or high sulfidation epithermal deposits (accord-ing to the modern classification: White & Hedenquist1990, Sillitoe 1999). The existence of these deposits isone of the unusual features of the BSTMZ because (a)the two types of mineralization are not only intimatelyspatially but also genetically related (Popov & Popov1997, Strashimirov et al. 2002), and (b) the epithermaldeposits show extremely varied and, in some cases,unusual mineralogical and geochemical features(Petrunov 1994, Tsonev et al. 2000b, Kouzmanov2001).

In this paper, we provide detailed information aboutthe mineralogical and geochemical features of avinciennite-bearing Cu–As–Sn (± Au) assemblage fromthe Radka deposit, Bulgaria. The mineral chemistry ofvinciennite and related minerals coupled with an infra-red (IR) microthermometric study of enargite-hostedfluid inclusions allow us to constrain the conditions ofdeposition of this unusual assemblage in the context ofthe evolution of the magma-related ore-forming systemat Radka.

GEOLOGICAL SETTING

The Radka deposit is located in the southeastern partof the Panagyurishte district, situated in the central partof the Srednogorie zone (Fig. 1a). The district is eco-nomically the most significant copper province in Bul-garia (more than 95% of the Bulgarian copper and goldproduction), with more than 10 deposits and numerousoccurrences of ore.

The Panagyurishte district is located at the inter-section of longitudinal subequatorial and diagonal N–NW-trending faults and has characteristics of amagmato-tectonic corridor with a rough northwesterlydirection, which covers an area of about 1500 km2. Thegeology consists of Precambrian (?) gneisses and Pa-leozoic granites overprinted by a Late Cretaceous vol-cano-plutonic complex (Fig. 1a). In some parts of thedistrict, these rocks are covered by Maestrichtianflyschoid sedimentary rocks and small outcrops of Pa-leogene and Neogene molasse (Bogdanov 1980). LateCretaceous magmatic activity, dated at 92.3 ± 1.4 Ma inthe northern part of the district to 82.25 ± 0.4 Ma in thesouthern part (U–Pb method on zircon; Von Quadt etal. 2001) and involving magmas calc-alkaline tosubalkaline in composition, is closely related to the twomain types of ore deposits: massive epigenetic Cu–S ±Ag–Au deposits of replacement origin (Krassen, Radkaand Elshitsa) and porphyry copper deposits (Assarel,Petelovo, Tsar Assen, Vlaykov Vruh and Popovo Dere(Fig. 1a; Bogdanov 1980, Popov & Popov 1997). Re-

cently, Tsonev et al. (2000a) defined the Radka depositas a transitional epithermal system with an intermediatesulfidation style of mineralization, closer to the highsulfidation type, in agreement with the original epige-netic theory of Dimitrov (1960) and consistent withcurrent genetic models of ore formation in the porphyry–epithermal environment (Hedenquist & Lowenstern1994, Hedenquist & Arribas 1999, Hedenquist et al.2000). Recent radiogenic and stable isotope data fromthe southern part of the Panagyurishte district confirmthat both metals and sulfur in the ore deposits are ofmagmatic origin (Kouzmanov 2001).

The official production from the Radka deposit overthe interval 1942–1995 was 6.39 million t of copper oregrading 1.06% Cu, and 0.28 million t of pyrite ore grad-ing 28.6% S, with a total production of 68,006 t of cop-per and 78,954 t of sulfur (Milev et al. 1996). Gold andsilver were extracted as a by-product from the pyrite andcopper concentrate. The mine closed in 1995. The de-posit consists of several steeply dipping, lenticular mas-sive orebodies with a halo of veinlets and disseminatedmineralization. Ore is confined to fault zones strikingwest–northwest and is hosted by felsic volcanic rocks(dacite lavas, tuffs and tuff breccias), cross-cut byrhyodacite dikes (Fig. 1b; Dimitrov 1960).

TYPES OF ORE, PARAGENETIC RELATIONSHIPS,HYDROTHERMAL ALTERATION AND FLUIDS AT RADKA

Two main types of ore exist at Radka. Massive ores,with as much as 85–90% of sulfides, form lenticular orstock-like bodies, locally with highly variable morphol-ogy. The complex history of hypogene mineralizationat Radka has been grouped into nine ore-forming stages.The mineralogical succession is summarized in Figure2. The main minerals in the massive ores are pyrite,chalcopyrite, bornite, tennantite, enargite, sphalerite,galena and chalcocite. Numerous subordinate and rareGe-, Ga-, In-, Sn-, Bi- and Te-bearing minerals also arepresent (Tzonev 1982, Kovalenker et al. 1986,Kouzmanov et al. 2000b; Fig. 2). Owing to their highpermeability, dacitic volcanic breccia and tuffs form themost favorable environment for metasomatic replace-ment and hydrothermal precipitation (Fig. 3a). Wallrockalteration is structurally and morphologically related toore-controlling faults. Radonova (1962) andChipchakova et al. (1981) described the zonation of al-teration from the orebodies outward consisting of quartz– white mica, quartz – chlorite – white mica andpropylitic assemblages. The second type of ore occursas veins, veinlets or dissemination of pyrite, chalcopy-rite and quartz at the periphery of massive bodies.

A particular feature of the Radka deposit is the pres-ence of clasts of massive fine-grained to colloform py-rite in a polymictic breccia affected by quartz – whitemica alteration (Fig. 3b; Bogdanov et al. 1970). Thepyrite from these clasts corresponds to the massive py-rite formed during the first stage of Fe (± As, Cu) min-


eralization (Fig. 2). Breccia occurs as dikes cross-cut-ting the massive dacite (Fig. 3c). Breccia clasts have apolymictic composition (dacite, dacitic tuffs, massivepyrite), are subrounded to rounded, and rarely are angu-lar in shape. Silt- and sand-sized clastic grains, ex-tremely altered to quartz – white mica ± argillicminerals, constitute the breccia matrix. The same tex-ture was observed under the microscope, affecting themassive orebodies (Fig. 3d). These macro- andmicrobreccia dikes indicate a process of fluidization ofrock and ore fragments in upward-escaping fluidchannelways that took place after the deposition of thefirst mineralized assemblage (Fig. 2). The fluidizedbreccias, together with the observed intense fracturing,in situ brecciation, and pebble-dike-like textures(Kouzmanov 2001), are very common characteristics ofmany hydrothermal systems formed in a porphyry toepithermal transitional environment (Sillitoe 1985,Corbett & Leach 1998).

Limited fluid-inclusion data for the Radka depositare available in Strashimirov & Kovachev (1992). Theyreported a homogenization temperature (Th) of 225°–245°C for inclusions in quartz from the early Fe (± As,Cu) assemblage, and Th between 180° and 230°C inanhydrite [late Ca (± Fe) assemblage]. We performedan extensive study of quartz-hosted, primary fluid in-clusions from the main Cu (± Bi, Te, Pb, As) stage(Kouzmanov et al. 2000a), and succeeded in identify-ing by micro-Raman spectrometry trapped kaolinite andwhite mica in these inclusions and CO2, H2 ± N2 in thevolatile phase. Microthermometric measurements indi-cate salinities ranging from 2.4 to 3.4 wt.% eq. NaClwith a mean of 2.8 ± 0.3 wt.% eq. NaCl. The inclusionshomogenize to the liquid between 218 and 260°C, witha mode at 250°C. The presence of kaolinite and illite astrapped minerals in these primary fluid inclusions indi-cates that they contain a mildly acidic fluid with a pH ofabout 4 at 250°C (Heald et al. 1987). The slight acidity

FIG. 2. Position of the Cu–As–Sn (± Au) assemblage within the mineralogical succession of the Radka ore deposit.


of the fluids during this stage is also confirmed by depo-sition of marcasite, which precipitates only at a pH lessthan 5 (Murowchick & Barnes 1986). Infrared micro-thermometry of pyrite-hosted fluid inclusions from theSi–Fe (± Co) stage in Radka suggests a late reheating ofthe system (Th up to 365°C) by low bulk-salinity fluids(3.5–4.6 wt.% eq. NaCl), interpreted as a magmaticvapor condensate (Kouzmanov et al. 2002). Sulfurisotopic data (�34S ≈ 0‰) for this generation of pyritesupport this interpretation (Kouzmanov 2001).

ANALYTICAL TECHNIQUES

Electron-microprobe analyses (EMPA) were per-formed with a CAMECA SX 50 electron microprobe(BRGM – CNRS – Université d’Orléans laboratory)operated at an acceleration potential of 20 kV, a probecurrent of 40 nA and with a beam diameter of 1 �m.Counting times were 10 s. We used K� lines for Fe, Cu,S, Zn, and V, L� lines for As, Sb, Ag, Se, Te, Au, Sn,and Ge, and the M� line for Bi. For standards, we used

pure metals for Cu, Ag, Se, Au, Bi, Te, Ge, and V, py-rite for Fe, S, stibnite for Sb, sphalerite for Zn, cassiter-ite for Sn, and synthetic GaAs for As. Apparentconcentrations were corrected for matrix effects with thePAP correction program (Pouchou & Pichoir 1984).

Selected samples, after reflected light microscopy,were examined using a JEOL JSM 6400 scanning elec-tron microscope (SEM) equipped with a KEVEX Deltaenergy-dispersion spectrometer (EDS) at the EcoleSupérieure de l’Energie et des Matériaux (Universitéd’Orléans).

Doubly polished sections (140–180 �m in thickness)were used for a fluid-inclusion study in enargite andquartz at the Infrared Microthermometry Laboratory ofthe BRGM in Orléans using a USGS gas-flow heating–freezing system mounted on an Olympus BHSM–IRmicroscope equipped with an infrared TV camera thatallows IR observations up to 2,500 nm (Lüders 1996).Synflinc standards and natural inclusions in fluoritewere measured for calibration using the IR equipmentand also in normal transmitted light.

FIG. 3. Ore textures from the Radka deposit. a) Selective replacement of dacitic tuffs by pyrite (Py), chalcopyrite (Ccp), bornite(Bn), sphalerite (Sp) and quartz (Qtz). b) Subrounded clast of massive fine-grained pyrite from the first stage of mineraliza-tion in fluidized breccia affected by intensive “quartz–sericite” alteration. Scale 2.5 cm. c) Fluidized breccia dike withsubrounded to rounded clasts of massive pyrite, dacitic tuffs and dacite, cross-cutting massive dacite. Both the breccia and thehost rock are affected by “quartz–sericite” alteration. d) “Micro breccia dike” structure with pyrite clasts cross-cutting themassive orebodies. Breccia matrix and host environment are replaced by later chalcopyrite, bornite and tennantite (Tn).Microphotograph in reflected light.


RESULTS: MINERALOGY

OF THE CU–AS–SN (± AU) ASSEMBLAGE

The Cu–As–Sn (± Au) assemblage formed duringthe third stage of mineralization at Radka (Fig. 2), oc-curs as pervasive replacement and in thin veins cross-cutting the massive pyrite ± chalcopyrite ore depositedduring the first two stages (Fig. 4a). The mineral assem-blage consists of enargite, tennantite, chalcopyrite, gold,vinciennite, colusite, and minor covellite, within agangue of barite, illite and very fine-grained silica.

Enargite, Cu3AsS4, is the dominant sulfide mineralprecipitating at the beginning of this stage. It forms poly-crystalline masses filling fractures and intergranularvoids within pyrite and chalcopyrite from the previousstages (Fig. 4b). The low-temperature polymorph ofCu3AsS4, luzonite, has not been observed in Radka. Thecomposition of enargite is close to being stoichiomet-ric. Its most significant feature is the presence of smallamounts of Sb (0.09–1.52 wt.%). Growth zoning inenargite, observed on BSE images (Figs. 5a, f), and IRtransmitted-light microphotographs (Figs. 6b, d), is dueto the substitution of Sb for As. Other trace elementsdetected by EMPA are minor Fe (300–5,800 ppm) andAg (800–1,800 ppm). The content of tin and zinc isbelow the detection limit, 400 and 700 ppm, respec-tively. Locally intergrown with the enargite is illite,whose composition has a phengitic character. Enargiteis partly replaced by a more abundant paragenesis withdominant tennantite, chalcopyrite and vinciennite.

Tennantite is the most common mineral in the as-semblage studied. It is intimately associated with chal-copyrite. Tennantite–chalcopyrite aggregates wereobserved as a replacement of enargite (Fig. 4c) as wellas forming a symplectitic intergrowth (Fig. 5e). Thetennantite is exceptionally rich in Cu [an average of 11atoms per formula unit (apfu) Cu for a total of 12 metalatoms; Table 1]. According to Marcoux et al. (1994), itcan be characterized as “Cu-excess” tennantite. Minor

Ag (up to 0.71 wt.%) and Bi (up to 0.51 wt.%) werealso recorded. The mineral is poor in Zn, Sn, Te and Se(Table 1). The tennantite is completely opaque in IRtransmitted light. This opacity could be due to the highFe content (as much as 4.30 wt.%, corresponding to 1.13apfu; Table 1), which is consistent with the interpreta-tion of Campbell et al. (1984) that one atom of Fe performula unit is the effective upper limit for IR transpar-ency of tennantite. Hall et al. (1974) obtained similarresults on synthetic samples of tetrahedrite, where onlythe Zn2 tetrahedrite end-member was transmitting in thered and near infrared. Comparable observations havebeen made by Charlat & Lévy (1974) on Fe-poor (<1wt.%) tetrahedrite. Recently, Lüders (1999) providednew data showing that the As-rich end-member of thetetrahedrite–tennantite solid-solution series is usuallyopaque in IR transmitted light, which limits the appli-cation of this technique to studies of fluid inclusions inthe Sb end-member only (i.e., tetrahedrite).

Chalcopyrite is intergrown with tennantite or fillsintergranular voids within enargite. In some samples, asecondary bornite – chalcocite – covellite assemblagealmost completely replaced the chalcopyrite (Figs. 4d,5a, c). The only trace element in chalcopyrite detectedby EMPA is As (500–5500 ppm). The composition ofchalcopyrite is nearly stoichiometric, with a slight ex-cess of Cu (Cu:Fe atomic ratio in the range from 1.04 to1.17).

Gold is a common mineral in this assemblage. It pre-cipitated at two intervals during the third mineralizingstage (Fig. 2). The gold, which appears as inclusions inenargite (Fig. 4d), is richer in Ag (11.8–12.8 wt.%) thanthe gold coprecipitated with tennantite (7.4–7.8 wt.%Ag). Both generations contain minor Cu (0.25–0.98wt.%), without any other trace element detectable byEPMA.

Lamellar crystals of covellite (length:width ratio inthe range 20–30) are fairly uncommon at Radka. Theyoccur as inclusions in barite (Fig. 5d) and in some re-


crystallized pyrite at the periphery of enargite–tennantiteveins. On the basis of textural relationships, we assumethat enargite and covellite precipitated almost contem-poraneously at the beginning of stage III of mineraliza-tion.

Tzonev (1982) described for the first time in Radkaan “orange-brown sulfide” with a composition Cu5.08Fe1.95Sn0.50As0.47Sb0.07S7.99. Three years later, Cesbronet al. (1985) defined vinciennite as a new mineral spe-cies, with an empirical formula Cu10Fe4Sn(As,Sb)S16,based on their study of samples from the Chizeuil andHuaron deposits (France and Peru, respectively).Kovalenker et al. (1986) confirmed the presence ofvinciennite at Radka. Vinciennite is the main tin-bear-ing mineral at Radka and occurs within the paragenesisreplacing enargite. It appears as amoeboid inclusions inchalcopyrite (Fig. 5b) and generally forms euhedralcrystals on the margin of patches of enargite (Figs. 4d,5c). Vinciennite grains reach 400 �m in size. They ap-pear to be zoned on BSE images (Fig. 5a). An extensiveEMPA study of vinciennite (Table 2) reveals the pres-ence of Sb (0.36–1.23 wt.%) and Ge (0.19–1.32 wt.%).All the analyses show slight cationic excess relative tothe ideal stoichiometric composition, with an average�cations:S ratio of 1.06 (Table 2). In near-IR transmit-ted light, vinciennite is opaque.

Colusite appears associated with vinciennite(Fig. 5c) or occurs as isolated inclusions in enargite (Fig.5f). Distinct zoning, in some cases observable even inreflected polarized light, is a very common feature ofcolusite from Radka. BSE images reveal a mosaic struc-ture in the central part of the crystals (Fig. 5f). Almostall microprobe analyses of colusite (Table 3) display theconstant presence of Fe (0.44–1.94 wt.%), Sb (1.22–3.92 wt.%) and Ge (0.22–1.14 wt.%).

MICROTHERMOMETRIC STUDY

IR microthermometry of enargite

Both primary and secondary fluid inclusions havebeen observed in enargite using the transmitted-light IRmicroscope (Fig. 6). Both types are two-phase and liq-uid-rich. Primary inclusions appear as isolated inclu-sions parallel to growth zones (Figs. 6b, d) or areattached to different solids trapped during the crystalgrowth of enargite (Figs. 6a, c). The latter feature iscommonly interpreted as a criterion for the primary ori-gin of fluid inclusions (Roedder 1984), e.g., fluid inclu-sions attached to chalcopyrite crystals trapped insphalerite (Sawkins 1964). These fluid inclusions,formed in the “shadow” of trapped solids, are generallyelongate, with their long axis parallel to the direction ofcrystal growth (Fig. 6a). Most primary inclusions inenargite are flat, tabular to isometric, rarely with stri-ated faces (Fig. 6b). They are small, with a diameterrarely exceeding 15 �m. Secondary inclusions decorate

healed fractures cross-cutting growth zones in enargite(Fig. 6e). They are isometric and small (<10 �m), regu-larly distributed along the fracture. Their degree of fill-ing (0.85–0.90) is similar to that of primary inclusionsand almost constant from one inclusion of the fractureto another.

No change in the IR-transparency of enargite wasobserved during heating runs. Freezing runs were per-formed before heating. Melting and homogenizationtemperatures, measured using the cycling technique(Goldstein & Reynolds 1994), are reproducible withinanalytical error. Microthermometric results for enargite-hosted fluid inclusions are summarized in Table 4. Ho-mogenization temperatures for primary inclusions arewithin the restricted range of 235°–252°C; only one in-clusion homogenized at 304°C. Secondary inclusionsyield slightly lower values of Th. It was not possible todetermine the first melting point of ice, either in pri-mary or in secondary inclusions. Clathrate formationwas not observed upon cooling. Final melting tempera-tures of ice (Tm ice), interpreted after Bodnar (1993),indicate salinities of 9.7–10.2 wt.% eq. NaCl for pri-mary inclusions. The salinities of two secondary inclu-sions fall in the same range. The small size of secondaryinclusions limited their suitability for microthermo-metric measurements.

Fluid inclusions in quartz phenocrysts

To complete the existing data on fluid inclusions atRadka, some microthermometric measurements wereperformed on trails of secondary fluid inclusion in quartzphenocrysts from the wallrock (mainly dacitic volcanicrocks). Two types of inclusions can be distinguished. Thedominant type includes liquid-rich, two-phase fluid in-clusions, with a vapor filling of 30–35% by volume(Fig. 7a). The second type consists of halite-saturated in-clusions, liquid–vapor–NaCl-filled at room temperature(Fig. 7b), with highly variable volume-proportions of thethree phases. The second type of inclusion is much lessabundant than the first. All fluid inclusions in magmaticquartz appear secondary, and the time relationships be-tween these two types of inclusion are unclear.

Results of microthermometric measurements onquartz-phenocryst-hosted fluid inclusions are presentedin Table 4. The two-phase inclusions homogenize intoliquid in the temperature range between 296°C and323°C and have a low salinity (2.7–4.6 wt.% eq. NaCl),determined from the Tm ice using the equation of Bodnar(1993). Final homogenization of the three-phase fluidinclusions is taken as the higher of either the disappear-ance of the vapor bubble (Th L–V), or the dissolution ofhalite (Tm NaCl). The majority of the inclusions homog-enize by halite dissolution (Fig. 8). The salinities ofthese inclusions were determined from the dissolutiontemperatures of halite (Sterner et al. 1988) and arewithin the range of 31.2 to 46.0 wt.% eq. NaCl.


FIG. 4. Stage-III mineral assemblage. a) Tennantite – enargite ± barite vein cross-cutting massive pyrite ± chalcopyrite ore. Thered dotted line marks the vein margins. b) Tennantite (Tn) – enargite (En) association replacing massive pyrite (Py) withminor chalcopyrite (Ccp) from the second stage of mineralization. c) Tennantite and chalcopyrite replacing enargite. d) Gold(Au) associated with enargite and minor vinciennite (Vn). Secondary bornite (Bn) – chalcocite (Cc) – covellite (Cv) assem-blage replaces the chalcopyrite in interstices. Figures 4b, c and d are microphotographs taken in reflected light.

DISCUSSION

Mineral chemistry of vincienniteand associated minerals

Radka is one of the few ore deposits in the worldwhere vinciennite has been described; others include theChizeuil massive pyrite deposit, France, the Huaronepithermal polymetallic deposit, Peru (Cesbron et al.1985), the Maggie porphyry copper–molybdenum de-posit, British Columbia (Jambor & Owens 1987), theLayo epithermal deposit, southern Peru (Marcoux et al.1994), and the Kidd Creek volcanogenic massive sul-fide deposit, western Abitibi Subprovince, Canada(Hannington et al. 1999). Kovalenker (1982) describeda “stannoidite-like” mineral with a composition corre-sponding to vinciennite in a subvolcanic gold depositfrom the central Tien-Shan range in the former SovietUnion.

In most of these deposits, the vinciennite-bearingassemblage has very similar mineralogical andgeochemical (Cu–As–Sn) features. One of these featuresis the presence of “Cu-excess” tennantite as one of themost abundant minerals in the paragenesis. As a rule, inall deposits the tennantite is depleted in Zn and has morethan 10 apfu Cu for a total of 12 metal atoms. Giventhat the formula for the ideal end-member tennantite isCu10(Fe, Zn)2As4S13, the excess of Cu substituting for(Fe, Zn)2+ either indicates the presence of Cu2+, or ofCu+ in excess if the sum of metal atoms is over 12 for4[As + Sb] (Charnock et al. 1989, Marcoux et al. 1994).The importance of this variety of tennantite as an indi-cator for the oxidation state of Fe during the ore forma-tion was pointed out by Marcoux et al. (1994) andillustrated by them using the Cu*–Fe–(Zn + Hg) dia-gram of Charlat & Lévy (1974). Compositions of “Cu-excess tennantite” from Radka compared to othervinciennite-bearing deposits are reported on the same


FIG. 5. Mineralogy of the vinciennite-bearing Cu–As–Sn assemblage in the Radka deposit. a) Zoned crystal of vinciennite (Vn)in the interstice of an aggregate of enargite (En). Chalcopyrite (Ccp) is altered to chalcocite (Cc) and covellite (Cv). Back-scattered electron (BSE) image. b) Vinciennite crystals formed at the contact between tennantite (Tn) and chalcopyrite replac-ing enargite (En). Photomicrograph in reflected light (parallel nicols). c) Secondary assemblage of bornite (Bn) – chalcocite– covellite replacing chalcopyrite in association with enargite, tennantite, vinciennite and colusite (Col). Photomicrograph inreflected light (partly crossed nicols). d) Tabular crystal of covellite included in barite (Brt) surrounded by chalcopyrite andtennantite. Photomicrograph in reflected light (parallel nicols). e) Chalcopyrite–tennantite symplectitic intergrowth texture.BSE image. f) Inclusion of zoned colusite in enargite crystal. BSE image.


diagram (Fig. 9). Copper in excess, after substraction of10 Cu atoms, is presented as Cu*. The tennantite atRadka plots in two fields of the diagram. For one part ofthe tennantite samples, all Fe is as Fe3+, which is com-pensated by Cu+ (lower field on Figure 9). Most datapoints (>85%) plot in the upper part of the diagram,together with the tennantite from Layo, Chizeuil and twosamples from Huaron. The latter field corresponds totennantite with an excess of copper that is not compen-sated by Fe3+, thus indicating possible presence of Cu2+,which requires an absence of Fe2+. The possibility, men-tioned by Marcoux et al. (1994), that some Cu+ canoccupy interstitial sites in the structure on the basis ofthe low [As + Sb] total, is not acceptable for the Radkatennantite, where [As + Sb] is nearly stoichiometric (av-erage value of 3.99 apfu; Table 1).

Marcoux et al. (1994) suggested that in vinciennite,Cu10Fe4SnAsS16, iron is also in the Fe3+ state and someof the Cu atoms probably are divalent, thus transformingthe empirical formula to Cu+

9 Cu2+Fe3+4Sn4+As5+S2–

16.Jambor & Owens (1987) noted that not only Cu but alsoFe in vinciennite is probably heterovalent, suggestingthat at least one of the iron atoms is divalent. As thestructure of vinciennite has not been solved yet [Cesbronet al. (1985) described it as tetragonal P4122, or possi-bly P4/mmm, P422 or P4mm], its stoichiometry is stillspeculative. Spry et al. (1994) proposed the formulaCu11Fe4SnAsS16, rather than the original formula estab-

lished by Cesbron et al. (1985). They argued that thenew formula was in better agreement with the analyti-cal data; with this new formulation, the heterovalencyof Fe, claimed by Jambor & Owens (1987), is no longernecessary.

Electron-microprobe data for vinciennite from theRadka deposit, together with published data from otherlocalities, are reported on a Cu versus Fe diagram(Fig. 10a). The very good negative correlation betweenCu in excess after substraction of 10 Cu atoms and Fesuggests that at least one atom of Fe is divalent and sub-stitutes for one atom of Cu (most probably Cu2+). Theslight deviation from the theoretical trend of such a sub-stitution toward higher values (Fig. 10a) is consistentwith the slight cationic excess over the stoichiometriccomposition, already mentioned by previous investiga-tors. A particular feature of the vinciennite from Radkais the substitution of Ge for Sn (Fig. 10b) and of someminor Sb for As. On the basis of the new results con-cerning the crystal chemistry of vinciennite and in agree-ment with the original formula of Cesbron et al. (1985),calculated on the basis of 16 cations, we propose a newformula that best describes the substitutions invinciennite involving heterovalency of copper and iron:Cu+

8Cu2+2Fe3+

3(Fe,Cu)2+(Sn,Ge)4+(As,Sb)5+S2–16.

Within the deposits from the Panagyurishte district,colusite has been described in the porphyry copper de-posits of Medet (Strashimirov 1982) and Assarel

FIG. 6. Enargite-hosted fluid inclusions from the Radka deposit. Microphotographs in infrared transmitted light. a) Isometricand channel-like primary fluid inclusions attached to solids (S) trapped in growth zones (GZ) of enargite. The small arrowindicates direction of crystal growth (see text for explanation). b) Flat elongate primary fluid inclusion parallel to growthzone. c) Primary fluid inclusion attached to solid in the central part of enargite crystal. d) Isolated primary inclusion parallelto growth zone. e) Secondary fluid inclusion plane cross-cutting a growth zone. Note the same vapor:liquid ratio in differentinclusions from this plane.


(Petrunov et al. 1991), and in the high-sulfidation cop-per–gold deposit of Chelopech (Terziev 1966, Petrunov1994). A specific aspect of the colusite from the Cu–As–Sn assemblage in Radka is its Ge content (Fig. 11).As in vinciennite, iron and copper are probably divalentin colusite from Radka. Vanadium is replaced by Fe3+,for a total of 2 [V + Fe3+] atoms, and the rest of the iron(most likely Fe2+) substitutes for Cu2+ (Table 3).Kovalenker et al. (1984) suggested a similar scheme ofsubstitution for nekrasovite, the tin end-member of thecolusite series: Cu+

18(Cu,Fe,Zn)2+8(V,Fe)3+

2(Sn4+,As5+,Sb5+)6S2–

32.The mineral chemistry of the main ore minerals from

the vinciennite-bearing Cu–As–Sn (± Au) assemblageat Radka implies very particular conditions of ore for-mation, comparable with those in the Layo epithermal

deposit (Marcoux et al. 1994). The precipitation of Asas As5+ in enargite, vinciennite and colusite, and As3+

in tennantite, and the deposition of minor covellite atthe beginning of the stage, indicate generally high ac-tivity of sulfur in the fluid phase (Hayba et al. 1985),which is decreasing with time (enargite to tennantitetransformation). Fluids were mildly acidic, with a pHof 4.5–5.5 based on illite stability at 250°C (Heald et al.1987). The high activity of sulfur probably also favoredthe fixation of Fe exclusively as Fe3+ in tennantite,vinciennite and colusite. The fluids were completelydepleted in Zn, but slightly enriched in Ge, which wasincorporated as a trace element in vinciennite andcolusite. These two elements, together with Sb and Ag,were deposited during the later stages of mineralization,especially stages IV and V (Fig. 2). Such an evolution


of the hydrothermal system with time is characteristicof some classic examples of late-magmatic mineraliza-tion related to porphyry copper systems (Einaudi 1977).As tin is an element commonly enriched in porphyry-type deposits (Sillitoe et al. 1975), the Sn signature ofthe assemblage studied is another argument in favor ofa possible genetic link with a porphyry system at Radka.

Fluid evolution at Radka

Suitable hosts for fluid-inclusion studies are scarcein high-sulfidation epithermal deposits, as the gangueminerals are typically fine-grained (Arribas 1995). Themost reliable data on the ore-forming fluids are obtainedusing infrared microscopy directly on ore minerals suchas enargite (Campbell et al. 1984). Microthermometricstudies on enargite-hosted fluid inclusions from several


high-sulfidation deposits [Lepanto, Philippines:Mancano & Campbell (1995); Julcani, Peru: Deen et al.(1994); Chelopech, Bulgaria: Moritz et al. (2002)]strongly support the idea that hydrothermal solutionsresponsible for the enargite precipitation are the resultof mixing between two end-member fluids: a) a high-temperature and high-salinity parent magmatic fluid,and b) a low-temperature, low-salinity fluid, most likelygroundwater (Arribas 1995).

Most genetic models for high-sulfidation epithermaldeposits (e.g., Hedenquist et al. 1998, Shinohara &Hedenquist 1997) stress an early stage of advancedargillic alteration (quartz–alunite ledge formation) as-sociated with the absorption of high-pressure magmaticvapor by deep meteoric water, resulting in the forma-tion of highly reactive acidic waters in an environmentshallower than the porphyry one. On the basis of stud-ies of active high-sulfidation epithermal systems [e.g.,White Island: Hedenquist et al. (1993); SatsumaIwojima: Hedenquist et al. (1994)] and their fossil ana-logues [e.g., Lepanto: Hedenquist et al. (1998)],Hedenquist and his colleagues proposed that the mostwidespread low-salinity (2–4 wt.% equiv. NaCl) fluidsin these deposits are related to the relatively later stageof alteration to white mica, usually formed after the for-mation of advanced argillic alteration lithocaps in thecentral parts of the magmatic–hydrothermal system, andthat they are the main ore-precipitating fluids. As re-ported by Hedenquist & Richards (1998), “sericitic”alteration forms from waters that have a magmatic sig-nature, with variable isotopic compositions rangingfrom >90% end-member magmatic to about 3:1 mix-tures of magmatic and meteoric water.

Muntean & Einaudi (2001) proposed an alternativescenario for the fluids responsible for the high-sulfidation epithermal mineralization in the Maricungabelt, northern Chile. They assumed that both enargite-bearing ore and surrounding quartz–alunite alterationformed at essentially the same time from a latesupercritical magmatic fluid with a salinity of 10 wt.%NaCl (salinity considered appropriate for supercriticalmagmatic fluids; cf. Hedenquist et al. 1998). The fluidcooled below its critical temperature without enteringthe two-phase liquid + vapor field. Upon crossing intothe brittle regime (<400°C) at depths of about 2 to 3km, the fluid underwent abrupt decompression andboiled along the liquid + vapor curve under hydrostatic

FIG. 7. Fluid inclusions in quartz phenocrysts. a) Two-phase (L–V) fluid inclusions. b) Three-phase (L–V–NaCl) inclusion.

FIG. 8. Halite dissolution temperatures (Tm NaCl) versus tem-perature of vapor bubble disappearance (Th L–V) for indi-vidual halite-saturated inclusions in quartz phenocrystsfrom dacitic host-rock at Radka. The Th L–V = Tm NaCl lineseparates inclusions that undergo final homogenization byhalite dissolution from those that homogenize by disappear-ance of vapor bubble.


pressure. Such a boiling did not generate a hypersalineliquid, but caused a progressive and moderate increasein the salinity of the liquid phase (Fournier 1987). Orewas deposited from the liquid phase, while the conden-sation of magmatic volatiles (e.g., SO2, HCl) into shal-low meteoric water above the ascending liquid resultedin “sericitic” alteration at depth and quartz–alunite andvuggy quartz near the surface (Muntean & Einaudi2001).

Heinrich et al. (1999) suggested another possibilityfor the accumulation of low-salinity (< ~10 wt.%) flu-ids in the high-sulfidation epithermal environment. Theyproposed cooling of a magmatic vapor at elevated pres-sure or its condensation into nonmagmatic water atlower temperature in the deeper part of the magmatic–hydrothermal system, transitional between the porphyryand the epithermal zone, without additional input ofsuperficial meteoric waters. This hypothesis is based onthe preferential enrichment of Cu, Au, As and S intolow-density inclusions of magmatic vapor relative to

coexisting brine inclusions, observed by LA–ICP–MSmicro-analysis in the Grasberg porphyry Cu–Au de-posit, in the Irian Jaya Mountains of Indonesia. Thus,the vapor-like low- to intermediate-salinity fluids couldbe the prime agent for selective transfer of ore metalsinto the high-sulfidation epithermal deposits. Recently,Heinrich (2003) provided thermodynamic constraints onthe mechanism of transport of ore metals by low-den-sity magmatic fluid, and demonstrated that such a fluidoriginating either by direct exsolution from a silicatemelt or by separation of vapor from a high-temperaturebrine (>400°C), can cool and condense to an aqueousliquid without further phase transition.

Data on fluid-inclusion microthermometry for theRadka deposit are summarized in Figure 12. The halite-saturated solution in the secondary inclusions in quartzphenocrysts may be derived from either of two pro-cesses, injection of an exotic magmatic brine into theshallow part of the system, or entrapment during almostcomplete (up to 99%) vaporization of a deeply derived,

FIG. 9. Compositions of Cu-excess tennantite in association with vinciennite from differ-ent localities plotted in the Cu–Fe–Zn system (apfu). Cu* is Cu in excess after substrac-tion of 10(Cu + Ag) atoms for a total of 12 metal atoms. Lower field (Cu* = Fe3+)includes compositions where excess Cu is compensated by Fe3+. Upper field includescompositions where Cu* is not compensated by Fe3+ (Cu* > Fe3+), which is an indica-tion of Cu2+, requiring an absence of Fe2+.


high-sulfidation epithermal deposits (e.g., Moritz et al.2002), but does not fit very well with the very restrictedrange of salinities and Th registered for the enargite-hosted fluid inclusions at Radka. Both scenarios favorthe dominantly magmatic signature of the fluid respon-sible for the formation of the Cu–As–Sn assemblage.The salinity of the “diluted” fluids at Radka is restrictedto 3 to 5.5 wt.% equiv. NaCl, thus supporting the “mag-matic vapor condensation” model (Heinrich 2003) un-der lithostatic pressure (see below), or more importantmixing between magmatic fluid and deep groundwater(Arribas 1995). However, to be able to quantify cor-rectly the magmatic input to the ore-forming fluids inthe Radka deposit, further stable isotopic analyses ofinclusion fluids are needed, especially in sulfide miner-als, such as enargite and pyrite, which are not suscep-tible to 18O exchange between fluid-inclusion watersand host (cf. Deen et al. 1994).

An important feature of the fluid evolution at Radkais the increase of Th, up to 365°C, registered for a nearlyconstant salinity of the fluids for the late quartz–pyritevein assemblage [Si–Fe (± Co) stage VI, Fig. 12]. Apossible explanation for this process consists of latepulses of high-pressure magmatic vapor ascending fromand condensing above a deeper porphyry system(Kouzmanov et al. 2002). Sulfur isotope data (�34S ≈0‰) for the late cobalt-bearing pyrite are in agreementwith such a hypothesis. The late anhydrite-bearing (Ca± Fe) assemblage was formed by oxidized and coolerfluids at 230–180°C (Strashimirov & Kovachev 1992).

FIG. 10. a) Cu** versus Fe diagram (apfu) showing vinciennite compositions from various localities. Cu** is Cu in excess aftersubtraction of 10 Cu atoms for a total of 16 cations. The black line corresponds to the theoretical trend of substitution of 1 Cuexcess atom for 1 Fe atom. b) Sn versus Ge diagram (apfu) showing vinciennite compositions from Radka. The line corre-sponds to the theoretical substitution trend of Ge for Sn.

dilute thermal water, as has been proposed by Simmons& Browne (1997) for secondary saline fluid inclusionsin sphalerite from the Broadlands–Ohaaki geothermalsystem. A sedimentary origin of these brines can beexcluded because there are no evaporite sequenceswithin the Panagyurishte ore zone that may explain thesaline nature of such fluids.

The restricted ranges of Th and salinity of theenargite-hosted fluid inclusions characterize the Cu–As–Sn assemblage at Radka as a single hydrothermalevent, differing from the other stages of mineralization.We believe that the enargite-precipitating fluid had anintermediate position between the hypothetical mag-matic brines, represented by NaCl-saturated inclusionsin quartz phenocrysts, and the most widespread rela-tively low-salinity (3–5 wt.% equiv. NaCl) fluids, de-termined for the main stages of mineralization at Radka(Fig. 12). Two alternative scenarios are possible to ex-plain the intermediate salinity of enargite-precipitatingfluids. The first one (path A, Fig. 12) consists in a directmagmatic input to the hydrothermal system at Radka,either by a supercritical magmatic fluid, as proposed byMuntean & Einaudi (2001) for the deposits of theMaricunga belt, in Chile, or by a condensed magmaticvapor-like fluid, as proposed by Heinrich (2003). Thesalinity of ~10 wt.% NaCl of the enargite-forming flu-ids strongly supports either hypothesis. The second sce-nario (path B, Fig. 12) involves a mixture of hotmagmatic brine and low-salinity water. This scenario ismore consistent with the mixing trends observed in other


The vinciennite-bearing Cu–As–Sn assemblagein the high-sulfidation epithermal environment:metallogenic implications

Most of the ore deposits in which a vinciennite-bear-ing assemblage has been described show features ofhigh-sulfidation epithermal systems (i.e., Lemiere et al.1986, Marcoux et al. 1994). Jambor & Owens (1987)described vinciennite from quartz – pyrite – tennantiteveinlets peripheral to the main ore zone at the Maggieporphyry copper – molybdenum deposit in British Co-lumbia, corresponding probably to the transition zoneto the epithermal part of the magmatic–hydrothermalsystem (Hedenquist et al. 1998).

The geology of the Radka deposit, its mineralogicaland geochemical particularities, ore textures, type ofhydrothermal alterations and the character of the fluids,allow us to define the deposit as a deep part of a high-sulfidation epithermal system, possibly related to a por-phyry copper system (Hedenquist & Lowenstern 1994,

Sillitoe 1999). Another argument supporting this con-clusion is the maximum depth of formation of the Radkadeposit, estimated to be ~2 km, based on the micro-thermometry study of fluid inclusions in pyrite(Kouzmanov et al. 2002).

The mineralogical and geochemical features of thevinciennite-bearing Cu–As–Sn (± Au) assemblage in theRadka deposit are very similar to those at Layo(Marcoux et al. 1994) and Chizeuil (Cesbron et al.1985). The high activity of sulfur and the oxidized andslightly acidic character of the fluids are other points incommon. In Radka, the IR microthermometry ofenargite-bearing fluid inclusions allowed us to deter-mine the temperature of formation of this assemblage.If the measured Th of 250°C of fluid inclusions with asalinity of 9.9 wt.% equiv. NaCl is corrected for an es-timated maximum pressure of trapping of 430 bar atRadka (Kouzmanov et al. 2002), we obtain a tempera-ture of formation of about 275°C. This temperature isvery close to 280°C, the lowest temperature of stabilityof Sb-free enargite (the high-temperature modificationof Cu3AsS4; Maske & Skinner 1971, Posfai & Buseck1998). At Radka, the low-temperature modification,luzonite, which is stable below 280°C, was not ob-served. The enargite contains minor Sb (up to 1.5 wt.%),which increases slightly the temperature of the phasetransition (Posfai & Buseck 1998).

Paragenetic relations in the Cu–As–Sn assemblagestudied at Radka indicate an evolution to a lowersulfidation state with time, from enargite to tennantite–chalcopyrite deposition. This tendency is preserved dur-ing the stages 4 and 5, when a base-metal mineralizationformed, accompanied by Au (Fig. 2). The paragenesisat Radka is similar to that in the Chelopech high-sulfidation epithermal deposit, in the northern part ofthe Panagyurishte district (Petrunov 1994). The shift toa lower sulfidation state with time is accompanied byless acidic conditions and an increase in the oxidationstate of the fluids, illustrated by massive formation ofanhydrite veins during the latest Ca ± Fe stage of min-eralization.

Copper, sulfur and arsenic are the characteristicmajor elements determining the geochemical signaturenot only of the studied vinciennite-bearing assemblage,but also of the Radka deposit in general. In a porphyryenvironment, as demonstrated by Heinrich et al. (1999),these elements are preferentially concentrated into thevapor phase during separation of the parental magmaticfluid to give a liquid brine and a low-density vapor. Thelow-density magmatic gas-like fluids have a significantmetal-transporting capacity (e.g., Lowenstern et al.1991, Williams-Jones et al. 2002) and could play a sub-stantial role in the formation of high-sulfidation oredeposits, as proposed by Heinrich (2003).

FIG. 11. Compositions of colusite from the Radka deposit,projected in the As–Sn–Sb–Ge diagram.


FIG. 12. Temperatures of final homogenization versus salinity diagram for fluid inclu-sions in Radka. a) Measurements on single fluid inclusions. Data are from (a)Kouzmanov (2001), (b) Kouzmanov et al. (2000a), (c) Kouzmanov et al. (2002), andthis study. b) Interpretive diagram for the origin of enargite-precipitating fluid at Radka.Data points correspond to modal values for different stages of mineralization presentedin a). Error bars indicate the range of data. The paths labeled A and B refer to theproposed two fluid paths responsible for the formation of the Cu–As–Sn assemblage inRadka, as explained in the text. The critical curve is from Driesner & Heinrich (2002),and the solubility curve (L + V + NaCl) is from Sourirajan & Kennedy (1962).


CONCLUSIONS

Our systematic mineralogical, trace element andfluid-inclusion study of the vinciennite-bearing Cu–As–Sn (± Au) assemblage from the Radka copper epi-thermal deposit, Bulgaria, reveals physicochemicalparameters of formation very similar to those inferredfor analogous deposits in other parts of the world. Thisassemblage was formed by oxidized and slightly acidicfluids, with a high fugacity of sulfur and an intermedi-ate salinity at a temperature of about 275°C, typicalfeatures for high-sulfidation epithermal systems(Hedenquist & Arribas 1999, Hedenquist et al. 2000).The geology of the Radka deposit, its geochemical pe-culiarities, ore textures and patterns of hydrothermal al-teration, complemented by the new results about themineralogical features and the nature of the hydrother-mal fluids, allow us to interpret the deposit as a deeppart of a high-sulfidation epithermal system, possiblyrelated to a porphyry copper system, which is consis-tent with the close spatial and genetic relationship be-tween epithermal and porphyry-copper deposits in thePanagyurishte ore region (Popov & Popov 1997,Strashimirov et al. 2002).

The detailed electron-microprobe study of vincien-nite and associated minerals at Radka reveals theheterovalency of Cu and Fe in minerals from this as-semblage. The tennantite associated with vinciennite, asa rule, corresponds to “Cu-excess” tennantite (Marcouxet al. 1994). New data on the composition of vincienniteled us to elucidate some aspects of its crystal chemistry(such as incorporation of Cu2+ and Fe3+ and Sn4+ Ge4+ substitution), obviously strongly dependent on thephysicochemical parameters of formation. Thusvinciennite, a rare Sn-bearing sulfide, with only sevenknown occurrences in the world, forms in a geologicalenvironment typical of the transition zone between por-phyry to epithermal deposits, in particular, conditionswithin a uniform mineral assemblage including enargite,Cu-excess tennantite, chalcopyrite and additional Sn-bearing minerals.

ACKNOWLEDGEMENTS

The authors thank Dimitar Tsonev for providingsome samples from the deep levels of exploitation inthe Radka deposit, Vsevolod Kourtchatov for giving usaccess to the collection of the Mineralogy and Petrogra-phy Museum of the University of Sofia, Annick Gentyfor her assistance during the scanning electron micros-copy, and Olivier Rouer for his help with the electron-microprobe analyses. We are indebted to Yves Moëlo,Robert Moritz, Ivan Bonev and Chris Heinrich for fruit-ful discussions and advice. We thank Volker Lüders andRobert Moritz for helpful reviews of the manuscript.The study was supported by ISTO–CNRS Orléans,BRGM Orléans and a grant to KK by the Ministère desAffaires Etrangères, France. This is a contribution to the

GEODE (European Science Foundation) program“Geodynamics and Ore Deposit Evolution of the Alpine– Balkan – Carpathian – Dinaride Province”.

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Received December 5, 2002, revised manuscript acceptedJune 13, 2003.

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GENESIS OF HIGH-SULFIDATION VINCIENNITE-BEARING … · Massive ores, with as much as 85–90% of sulfides, form lenticular or stock-like bodies, locally with highly variable morphol-ogy