www.geologia-croatica.hr ABSTRACT The Trepča Pb-Zn-Ag skarn deposit in Kosovo is spatially and temporarily related to the phreatomagmatic breccia of Oligocene age (~23Ma). The deposit shows features typical for skarn deposits worldwide, including a stage of isochemical metamorphism, a prograde stage of an anhydrous, low oxygen and low sulfur fugacity character, and a retrograde stage characterized by an increase in the water activity as well as by an increase in oxygen and sulfur fugacities. The mineralization is hosted by the recrystallized Upper Triassic limestone. The prograde mineralization consists mainly of Ca-Fe-Mn±Mg pyroxenes. The host recrystallized limestone at the contact with the prograde (skarn) mineralization has an increased content of Fe, Mn, Mo, As, Au, Cs, Ga, REE and Y suggesting their transport by infiltrating magmatic fluids. The decreased d13C and d18O values reflect the contribution of magmatic CO2. The retrograde mineral assemblage comprises ilvaite, magnetite, arsenopyrite, pyrrhotite, marcasite, pyrite, Ca-Fe-Mn±Mg carbonates and quartz. Hydrothermal ore minerals, mostly galena, sphalerite and pyrite, were deposited contemporaneously with the retrograde stage of the skarn development. Syn-ore and post-ore carbonates reflect the diminishing influence of magmatic CO2. Syn-ore carbonates are enriched in Fe, Mg, Mn, many chalcophile elements, including Ag, As, Bi, Cd, Cu, Pb, Sb and Zn, as well as in Au, Y and REE. The post-ore stage accompanied the precipitation of a significant amount of Ca-rich carbonates including travertine deposits at the deposit surface. The phreatomagmatic breccia was developed along a NW dipping contact between the ore bearing recrystallized limestone and the overlying schist. It has an inverted cone shape with vertical extension up to 800 m and a diameter of up to 150 m. The upper part of the diatreme (an underground segment of the phreatomagmatic breccia) is characterized by the presence of a hydrothermally altered rootless quartz-latite dyke surrounded by an unsorted polymict breccia mantle. Despite the alteration processes, the dyke has a preserved porphyritic texture. Partly preserved sanidine, accompanied with a mixture of muscovite and quartz, reflects a near-neutral to weakly acidic environment. The clasts of country rocks and skarn mineralization underwent intense milling and mixing due to repeated magmatic penetrations. Sericitization of the breccia matrix, locally accompanied with minor kaolinitization, point to an increased water activity under near-neutral to weakly acidic conditions. Large fragments originally composed of anhydrous skarn minerals (pyroxenes) are usually completely altered to a mixture of fibroradial magnetite, quartz and various amounts of carbonates suggesting an increase in oxygen fugacity. Their pyrite rims reflect that the increase in oxygen fugacity was followed by an increase in sulfur fugacity. The clast predominantly composed of Fe-sulfides and minor Bi-sulfides suggest that the increase in sulfur fugacity was locally sufficient to complete sulfidation of hedenbergite to pyrrhotite and/or pyrite. Although the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit does not carry significant amounts of ore mineralization, its formation was crucial for ore deposition. Phreatomagmatic explosions and formation of the breccia turned the system from the lithostatic to hydrostatic regime and triggered the retrograde stage increasing the water activity and oxygen fugacity in the system. In addition, cooling and decompression of the system contributed to more effective degassing of magmatic sulfur and increased the sulfur fugacity. doi:10.4154/gc.2016.10 Keywords: phreatomagmatic breccia, Pb-Zn- Ag skarn deposit, transition from lithostatic to hydrostatic regime, fluid inclusions, stable isotopes, K/Ar dating Article history: Received September 24, 2015 Revised and accepted January 05, 2016 Avaliable online February 29, 2016 121-142 12 Figs. 4 Tabs. Origin and K-Ar age of the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit, Kosovo: Implications for ore-forming processes Sabina Strmić Palinkaš1,*, Ladislav Palinkaš2, Magda Mandić3, Zvjezdana Roller-Lutz4, Zoltan Pécskay5, Gani Maliqi6 and Vladimir Bermanec2 1University of Tromsø, Faculty of Science and Technology, Department of Geology, Dramsvegen 201, N-9037 Tromsø, Norway (*corresponding author, email: sabina.s.palinkas@uit.no) 2University of Zagreb, Faculty of Science, Geological Department, Horvatovac 95, HR-10000 Zagreb, Croatia 3Thermo Fisher Scientific, Hanna-Kunath-Straße 11, D-28199 Bremen, Germany 4University of Rijeka, Medical Faculty, Department of Physics, Braće Branchetta 20, HR-51 000 Rijeka, Croatia 5Institute of Nuclear Research, Hungarian Academy of Sciences, Bemtér 18/C, H-4001 Debrecen, Hungary 6Prishtina University, Faculty of Mines and Metallurgy, Mitrovica, Kosovo 122 Vol. 69/1 1. INTRODUCTION Breccia pipes have been recognized in different types of ore deposits, from porphyry to epithermal in their origin (e.g. the Acupan Au-Ag-Te epithermal deposit, Philippines (COOKE & BLOOM, 1990); the Roşia Montană Au-Ag epithermal de- posit, Romania (WALLIER et al., 2006); the Cerro de Pasco epithermal polymetallic deposit, Peru (BAUMGARTNER et al., 2008); the El Teniente Cu-Mo porphyry deposit, Chile (CANNELL et al., 2005; VRY et al., 2010)). At some locali- ties a genetic link between the breccia formation and ore min- eralization is evident (e.g. the Wau Au deposit, Papua New Guinea (SILLITOE et al., 1984); the Kelian Au deposit, Indo- nesia (DAVIES et al., 2008); the Galore Creek Cu-Au depo- sit, British Columbia, Canada (BYRNE & TOSDAL, 2014)), while at others it is more obscure. Also, at some localities breccia pipes host significant amounts of ore (e.g. the Au- bearing breccia pipe at Kidston, Queensland, Australia (BAKER & ANDREW, 1991); the Cu-bearing Donoso brec- cia pipe, Chile (SKEWES et al., 2003); the base metal-bear- ing breccia pipe at the Cerro de Pasco deposit, Peru (BAUMGARTNER et al., 2008)) whereas elsewhere they are mostly barren (the Aguablanca Ni-Cu magmatic deposit, Spain (TORNOS et al., 2001); the Copper Creek mining dis- trict, Arizona, USA (ANDERSON et al., 2009); the Blackbird Co-Cu-Au-Bi-Y-REE district, Idaho, USA (TRUMBULL et al., 2011)). The Trepča deposit in Kosovo (Fig. 1) is an example of the Pb-Zn-Ag skarn deposit spatially and temporarily related to the phreatomagmatic breccia (STRMIĆ PALINKAŠ et al., 2007; FÉRAUD et al., 2007; STRMIĆ PALINKAŠ et al, 2013). The deposit, with current reserves of 31 Mt of ore at 4.2 % of Pb, 3 % of Zn and 86 g/t of Ag, together with the past production of approximately 34 Mt of ore, represents an im- portant source of metals in the SE part of Europe. A nearly circular breccia pipe occurs at the contact between the minera- lized recrystallized limestone of Upper Triassic age and the barren schist (Fig. 2). Although the breccia does not host an economically significant amount of ore, we argue that the mechanism of its formation is a key factor for understanding ore forming processes in the Trepča deposit. The abandoned open pit and the active underground mine expose the breccia over a vertical interval of 800 m and allow access to various breccia lithofacies. The major aim of this study is to understand the origin of the phreatomagmatic breccia and its role in the ore-deposition processes at the Trepča Pb-Zn-Ag skarn deposit. The study combines descriptive features, mineralogy, stable isotope and fluid inclusion data obtained from the breccia and wall rocks. The K/Ar data gained on whole rock and single grain separates revealed the age of the brecciation event. Figure 1. Geological setting of the Pb-Zn mineral deposits, including the Trepča Pb-Zn-Ag skarn deposit, within the Vardar zone, SE Eu- rope (simplified after KARAMATA et al. (2000) and DIMITRIJEVIĆ (2001)). External Vardar Zone: JB – Jadar Block and KB - Kopaonik Block; CVZ - Central Vardar Zone; IVZ - Internal Vardar Zone; DOB – Dinaride Ophiolite Belt; DIT – Drina-Ivanjica Terrain; PZ - Pelago- nian Zone; SMM - Serbo-Macedonian Massif. Figure 2. a. Cross section through the Trepča Pb-Zn-Ag skarn deposit; b. Local geological map of the Trepča Pb-Zn-Ag skarn deposit (after SCHUMACHER, 1950). 123 Strmić Palinkaš et al.: Origin and K-Ar age of the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit, Kosovo: Implications... 2. GEOLOGICAL SETTING The Trepča Pb-Zn-Ag skarn deposit is situated in the western part of the NW-SE trending Vardar zone that extends through- out the western part of the Balkan Peninsula between the Di- narides, the Drina-Ivanjica Terrain and the Pelagonian Zone to the west and the Serbo-Macedonian Massif to the east (Fig. 1). The Vardar zone represents the main suture zone along the contact between the Adriatic and the Euroasian plate with elements of both continental and oceanic lithologies (DIMITRIJEVIĆ, 2001; KARAMATA et al., 2000; ZELIĆ et al., 2010; ROBERT- SON et al., 2013). During the Late Permian to Middle Tri- assic the incipient rifting process affected metamorphosed Precambrian-Palaeozoic terrains separating the Pelagonian Zone and the Serbo-Macedonian Massif. Rifting was followed by the development of a sub- siding carbonate platform and formation of an oceanic crust during Late Triassic-Early Jurassic time (SHARP & ROBERTSON, 2006; DILEK et al., 2007; ROBERTSON et al., 2013). The Western (External) Var- dar Zone represents a complex zone that comprises ophiolites and ophiolitic mé- lange (KARAMATA et al., 1980). At seve- ral localities ophiolitic masses, composed of spinel lherzolite, harzburgite and dunite, have preserved evidence for metamorphic soles at their bases. The K/Ar age between 160 and 123 Ma (KARAMATA et al., 2000; MILOVANOVIĆ et al., 1995) and Ar/Ar age between 175 and 170 Ma (BOROJEVIĆ ŠOŠTARIĆ et al., 2014) obtained from the metamorphic soles suggest em- placement of ophiolites from the Middle Jurassic to the Early Cretaceous. The Jurassic-Cretaceous mélange of the Western Vardar Zone comprises mostly large blocks and fragments of Middle to Upper Triassic and Upper Jurassic limestones, ter- rigenous sediments (sandstone, greywacke), basalts, and Figure 3. a. Upper Palaeozoic schist intercalated with quartzite layers; b. Recrystallized Upper Triassic limestone with developed karst phe- nomena; c. Prograde skarn mineralization con- sisting mainly of pyroxenes; d. Retrograde skarn mineralization comprising a mixture of ilvaite, magnetite, quartz and Ca-Fe-Mn-Mg carbo- nates; e. Hydrothermal mineralization compris- ing ore (galena, sphalerite, pyrite) and gangue (carbonate, quartz) minerals; f. The principal ore minerals, galena and sphalerite, are accompa- nied by various amounts of pyrite; g. Travertine deposits at the surface of the Trepča Pb-Zn-Ag skarn deposit (835 m above mean sea level); h. Close view of the travertine deposit; i. Photo- micrographs of trachyte with typical porphyritic texture and altered sanidine phenocrysts (un- der crossed polarizers); j. Photomicrographs of quartz-latite with altered sanidine, plagioclases, amphiboles and quartz as principal phenocrysts (under crossed polarizers); k. Photomicrographs of andesite composed of plagioclase, amphi- boles and quartz phenocrysts embedded within a carbonized and silificated aphanitic groundmass. Mineral abbreviations: Hd – hedenbergite; Mt – magnetite, Ilv – ilvaite; Carb – Ca-Fe-Mn-Mg carbonates; Qtz – quartz; Sph – sphalerite; Gn – galena; Py – pyrite. 124 Vol. 69/1 cherts with Carnian to Norian and Upper Jurassic radiolarians emplaced within an argillaceous to silty matrix (SUDAR & KOVACS, 2006; VASKOVIĆ & MATOVIĆ, 2010). In con- trast, the Eastern (Internal) Vardar Zone comprises the weakly metamorphosed mélange of Jurassic age with predominantly basaltic fragments (SUDAR & KOVACS, 2006, and refer- ences therein). The postcollisional magmatism of Oligocene to Miocene age (CVETKOVIĆ et al., 2004) was accompanied by wide- spread hydrothermal activity in the West- ern Vardar Zone, producing numerous skarn, hydrothermal replacement and vein type Pb-Zn-Ag deposits (Fig. 1; JANKOVIĆ, 1995; VESELINOVIĆ- WILLIAMS, 2011; BOROJEVIĆ ŠOŠTARIĆ et al., 2013; STRMIĆ PALINKAŠ et al., 2013). The Oligocene to Miocene magmatic rocks is represented mostly by trachytes, quartz-latites, ande- sites and pyroclastic deposits (CVETKOVIĆ et al., 2004; BOROJEVIĆ ŠOŠTARIĆ et al., 2012). 2.1. GEOLOGY OF THE DEPOSIT The basement of the Trepča Pb-Zn-Ag skarn deposit comprises a metamorphosed and folded Upper Palaeozoic to Triassic sedimentary complex composed predomi- nantly of schist and recrystallized lime- stone. The dark coloured schist occasiona- lly is intercalated with compact dense to coarse-grained quartzite layers (Fig. 3a). At the contact with the mineraliza- tion the schist is enriched in quartz and micas. The recrystal- lized limestone frequently exhibits developed karst phenome- na (Fig. 3b). The size of calcite grains varies from several millimetres at places spatially distal to the mineralization up to several centimeters along the contact with the ore bodies and the breccia pipe. According to the data obtained from co- nodont remains the limestone has been assigned to the Upper Figure 4. a. Pyroclastic rocks enclose euhedral calcite crystals, fragments of the country rocks and spheroid pumice lapillus. The leaves and plant root traces are also visible; b. Lateral dyke- like branches of the main breccia pipe sporadi- cally intrude the recrystallized Upper Triassic limestone; c. A gradual transition from the main breccia pipe into the brecciated schist; d. Hydro- thermally altered quartz-latite from the core of the main breccia pipe. White fine-grained ma- trix incorporates yellowish to greenish remains of sanidine phenocrysts, quartz phenocrysts and fragments of country rocks, predominantly the schist; e. Randomly oriented fragments of schist (S), recrystallized limestone (L) and magnetite- and pyrite-bearing clasts (M-P), the main brec- cia pipe, surface (835 m above mean sea level); f. Close view of the clast composed of a mag- netite core and pyritic rim; g. Photomicrographs of the clast composed of a fibroradial magnetite core and pyritic rim (plane-polarized light); h. Scanning electron photomicrograph of the clast composed of a magnetite core and pyritic rim reveals the presence of Bi-telluride and Bi- sulfide; i. Recrystallized limestone (L) fragment partly replaced with fibroradial arsenopyrite and magnetite (75 m above mean sea level); j. The clast composed of pyrite, pyrrhotite and minor Bi-sulfides. Mineral abbreviations: Mt – mag- netite; Py – pyrite; Po – pyrrhotite, Apy – arse- nopyrite; Carb – Ca-Fe-Mn-Mg carbonates; Qtz – quartz. 125 Strmić Palinkaš et al.: Origin and K-Ar age of the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit, Kosovo: Implications... Triassic (SUDAR, 1986). The limestone-schist contact is marked by the presence of the breccia pipe (SCHUMACHER, 1950, 1954; FÉRAUD et al., 2007; STRMIĆ PALINKAŠ et al., 2013). The mineralization of the Trepča Pb-Zn-Ag skarn deposit is exclusively hosted by the recrystallized limestone (Fig. 2). The principal skarn minerals in the Trepča deposit are Ca-Fe- Mn±Mg silicates including pyroxenes, ilvaite and minor gar- nets. Accessory minerals are Ca-Fe-Mn±Mg carbonates and quartz. Paragenetic studies based on macro- and microtextures show that the skarn assemblage from the Trepča deposit was formed in several stages, similar to other skarns (MEINERT, 1992; MALO et al., 2000; MEINERT et al., 2005; CANET et al, 2011). The prograde stage has an anhydrous character with Ca-Fe-Mn±Mg pyroxenes as the major minerals (Fig. 3c). Ca- Fe garnets (andradite) occur rarely, exclusively in the upper- most levels of the deposit. The retrograde stage has a predom- inantly hydrous character with ilvaite, magnetite, carbonate and quartz as important products (Fig. 3d). The hydrothermal ore minerals commonly overprint the pyroxene-rich calcic skarn, although skarn mineralization free of the ore assem- blage as well as the ore mineralization without skarn precursor has been found (Fig. 3e). Black coloured sphalerite, galena and pyrite are the most abundant sulfide minerals (Fig. 3f). The deposit contains volumetrically minor, but mineralogi- cally diverse Bi-bearing minerals, including native Bi, bis- muthinite (Bi2S3), cosalite (Pb2Bi2S5), cannizzarite (Pb4Bi6S13), lillianite (Pb3Bi2S6), ikunolite (Bi4(S,Se)3), babkinite (Pb2Bi2(S,Se)3), joseite (Bi4(S,Te)3), heyrovskyite (Pb10Ag- Bi5S18) andizoklakeite (Pb27(Cu,Fe)2(Sb,Bi)19S57) (TERZIĆ et al., 1974; KOŁODZIEJCZYK et al., 2015). Travertine depo- sits locally occur as a top layer capping the deposit and mark- ing the preserved palaeosurface (Figs. 3g, h). During the Oligocene-Miocene, the Trepča area was a loca- tion of considerable volcanicactivity characterized by numer- ous lava flows and large masses of volcanoclastic rocks. The volcanic rocks are represented mostly by trachytes, quartz- latites and andesites. Trachytes are composed of a light gray matrix and sanidine phenocrysts (Fig. 3i). Quartz-latites are exposed at the Zvečan hill and occur as the core of the breccia pipe within the deposit. Beside sanidine they comprise signifi- cant amounts of quartz grains (Fig. 3j). The Ar/Ar age of the Zvečan hill quartz-latite spans between 24.8±0.2 Ma for K- feldspar and 25.8±0.3 Ma for amphibole (BOROJEVIĆ ŠOŠTARIĆ et al., 2012). Andesites are mainly light to medi- um gray in colour and porphyritic in texture. They are com- posed of plagioclase, hornblende, biotite, augite and bronzite (Fig. 3k). 2.2 THE BRECCIA GEOMETRY, COMPOSITION AND INTERNAL ORGANIZATION The breccia pipe exposed at the Trepča Pb-Zn-Ag skarn has an inverted cone shape characteristic for phreatomagmatic brec- cias elsewhere (e.g. SILLITOE, 1985; TAMAS & MILESI, 2002; LANDTWING et al., 2002; DAVIES et al., 2008). The diatreme (an underground segment of the phreatomagmatic breccia; LORENZ, 1973) extends vertically up to 800 m be- low the surface and has a diameter of approximately 150 m (Fig. 2). The partly preserved maar structure (a surface ex- pression of phreatomagmatic breccia; LORENZ, 1973) com- prises tuffaceous (Fig. 2; SCHUMACHER, 1950) and pyro- clastic deposits with common remnants of plant leaves and roots (Fig. 4a). The breccia pipe was emplaced along a NW dipping contact between the ore bearing recrystallized lime- stone and the overlying schist (Fig. 2). Contacts between the breccia and the recrystallized limestone are mostly sharp but locally cut by lateral dyke-like branches (Fig. 4b) infilled with rock flour (“milled matrix fluidized breccia”) or with angular fragments (“jigsaw-puzzle breccia”). In contrast, the contacts with the overlying schist are unclear, with a gradual transition from the breccia pipe into the brecciated schist (Fig. 4c). The upper part of the diatreme hosts a hydrothermally altered quartz-latite dyke with the preserved porphyritic texture (Fig. 4d). The white fine-grained matrix comprises muscovite, quartz, and K-feldspars (Fig. 5). The sanidine phenocrysts are partly altered to a yellowish to greenish fine-grained mixture of muscovite and quartz (Fig. 5). The quartz phenocrysts are well preserved. Fragments of county rocks, especially schist, are embedded within the matrix too. The dyke occupies the pipe core and is surrounded by the unsorted polymict breccia mantle (Figs. 2, 4e). Figure 5. X-ray diffraction patterns reveal that a. hydrothermally altered quartz-latite matrix consists of K-feldspar, quartz and mus- covite; b. altered phenocrysts comprise sanidine remains as well as various micas and quartz. 126 Vol. 69/1 Sample Level Depth (m a.m.s.l.*) Description KM-10 surface 835 host limestone, barren, recrystallized P1 surface 835 pyroclastic deposit P2 surface 835 pyroclastic deposit P4 surface 835 travertine deposit TR-6 surface 835 quartz-latite TR-108 surface 835 hydrothermally altered quartz-latite core of the main breccia pipe KM7-1 surface 835 fragment composed of a magnetite core and a pyrite rim, the main breccia pipe KM8 surface 835 fragment composed of a magnetite core and a pyrite rim, the main breccia pipe KM9 surface 835 fragment composed of fractured pyrite, pyrrhotite and minor Bi-sulfides, the main breccia pipe TR-V-1 V 375 hydrothermal paragenesis TR-VII-7 VII 255 hydrothermal paragenesis TR-VIII-2 VIII 195 hydrothermal paragenesis TR-VIII-4 VIII 195 hydrothermal paragenesis T8 IX 135 hydrothermal paragenesis T8a IX 135 hydrothermal paragenesis T8-2 IX 135 hydrothermal paragenesis STS-0 X 75 host limestone, barren, recrystallized STS-1 X 75 hydrothermal paragenesis STS-2 X 75 hydrothermal paragenesis STS-3 X 75 hydrothermal paragenesis T1 X 75 clast composed of side- rite, quartz and dickite, the main breccia pipe T2 X 75 recrystallized limestone fragment, the main breccia pipe Sample Level Depth (m a.m.s.l.*) Description T2 X 75 recrystallized lime- stone fragment partly replaced by magnetite and aresenopyrite, the main breccia pipe T3 X 75 the recrystallized lime- stone in contact with the main breccia pipe T3a X 75 the recrystallized lime- stone in contact with the main breccia pipe T4 X 75 recrystallized limestone at the contact with lat- eral breccia branches T4a X 75 lateral breccia branch T5 X 75 hydrothermal paragenesis T6a X 75 skarn paragenesis T6b X 75 skarn paragenesis T6c X 75 skarn paragenesis T6d X 75 skarn paragenesis T6e X 75 skarn paragenesis T6f X 75 host limestone, barren, recrystallized T7-2 X 75 hydrothermal parage- nesis T7-3a X 75 hydrothermal paragenesis T7-4 X 75 recrystallized limestone at the contact with late- ral breccia branches T7-4a X 75 lateral breccia branch T7-5 X 75 hydrothermal paragenesis T9-1 X 75 skarn paragenesis T9-3 X 75 skarn paragenesis T9-4 X 75 skarn paragenesis T9-5 X 75 hydrothermal paragenesis T9-6 X 75 skarn paragenesis 148A X 75 hydrothermal paragenesis TR-XI-2 XI 15 hydrothermal paragenesis TR-XI-3 XI 15 hydrothermal paragenesis TR-XI-4 XI 15 hydrothermal paragenesis TR-XI-5 XI 15 hydrothermal paragenesis TR-XI-6 XI 15 hydrothermal paragenesis Table 1. Analyzed samples from the Trepča Pb-Zn-Ag skarn deposit. * a.m.s.l. – above mean sea level * a.m.s.l. – above mean sea level 127 Strmić Palinkaš et al.: Origin and K-Ar age of the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit, Kosovo: Implications... Clasts are angular to well-rounded ranging in size from less than a millimetre to several metres with no systematic distri- bution in fragment size and roundness. They occupy up to 90 vol.% of the breccia. Fragments of the country rocks, lime- stones and schists, together with Ca-Fe-Mn±Mg silicate-, magnetite- and sulfide-bearing fragments represent the princi- pal types of clasts. The upper portion of the diatreme is chara- cterized by the extreme mixing of the rock fragments of vari- ous origin but besides the country rock fragments, the fra- gments composed of the magnetite core and pyrite-enriched rim are the most frequent. Magnetite occurs in the form of fi- broradial to spherulitic aggregates (Fig. 4f) with minor masses of pyrite, Bi-sulfides, Bi-tellurides, carbonates and quartz em- placed between magnetite grains (Figs. 4g, h). The rim com- prises fresh pyrite accompanied by carbonates and quartz (Figs. 4f, g). Fragments of pyroclastic rocks and fragments with lacustrine plant remains have been found at various depths suggesting collapse events (McCALLUM, 1985; BAKER et al., 1986). In the deeper part of the breccia pipe, magnetite and over- printing fibroradial arsenopyrite are found to be embedded within recrystallized limestone fragments (Fig. 4i). The clasts composed of fractured pyrite, pyrrhotite and minor Bi-sulfides are common at various depths of the breccia pipe. The space between sulfide grains is filled with a fine-grained mixture of carbonates and quartz (Fig. 4j). Quartz-latite (juvenile) frag- ments occur as well. The breccia matrix comprises a fine- grained rock flour that has been affected by various types of hydrothermal alterations, including sericitization, kaolinitiza- tion, pyritization and carbonatization. 3. SAMPLES AND METHODS A total of forty-nine hand-picked rock samples were collected from existing underground works and from the surface of the Trepča Pb-Zn-Ag skarn deposit. We sampled various types of breccia fragments, wall rocks as well as mineral parageneses (Table 1). Paragenetic relationships were studied in thin sections by transmitted polarized light microscopy. Ore minerals were ex- amined in polished thick sections by reflected light microsco- py. X-ray powder diffraction (XRD) analysis was conducted at the University of Zagreb on a Philips PW 3040/60 X’Pert PRO powder diffractometer (45 kV, 40 μA), with CuKα- monochromatized radiation (λ = 1.54056 Å) and θ-θ geome- try. The area between 4 and 63° 2θ, with 0.02° steps, was mea- sured with a 0.5° primary beam divergence. Compound iden- tifications were based on a computer program X’Pert high score 1.0B and literature data. The textural features and semi- quantitative analyses of breccia fragments were examined by a Tescan Scanning Electron Microscope (SEM) equipped with an INCA 250 analyzing system and Oxford detectors at the University of Zagreb. The analyses were performed on car- bon-coated polished thin sections using the following operat- ing conditions: 3-40 mm beam, accelerating voltage 20 kV, current 10 nA and counting time of 200 seconds. Bulk chemi- cal compositions of 14 selected samples were prepared in an agate ball mill and analyzed at Acme Analytical Laboratories (Vancouver, Canada) after lithium metaborate or tetraborate fusion using inductively coupled plasma (ICP) for major ele- ments and inductively coupled plasma-mass spectrometry (ICP-MS) for trace elements. Microthermometric measurements of fluid inclusions with- in transparent minerals (calcite, quartz) were performed at the University of Zagreb. Double polished, ~0.5-mm-thick, trans- parent mineral wafers were used. Measurements were carried out on a Linkam THMS 600 stage mounted on an Olympus BX 51 microscope using 10× and 50× Olympus long-working distance objectives for visible light. Two synthetic fluid inclu- sion standards (SYN FLINC; pure H2O and mixed H2O-CO2) were used to calibrate the equipment. The precision of the sys- tem was ±2.0°C for homogenization temperatures, and ±0.2°C in the temperature range between –60° and +10°C. Microther- mometric measurements were made on carefully defined fluid inclusion assemblages, representing groups of inclusions that were trapped simultaneously. The fluid inclusion assemblages were identified based on petrography prior to heating and freezing. If all of the fluid inclusions within the assemblage showed similar homogenization temperatures, the inclusions were assumed to have trapped the same fluid and to have not been modified by leakage or necking; these fluid inclusions thus record the original trapping conditions (GOLDSTEIN & REYNOLDS, 1994; GOLDSTEIN, 2001; BODNAR, 2003). Carbon and oxygen isotope analyses of carbonates from the wall rocks and breccia fragments as well as analyses of car- bonates associated with the ore mineralization were performed at the University of Rijeka. Carbonate powder was extracted from hand-picked samples using a dentist’s drill. A mass of 250 μg of powder has been loaded in sealed reaction vessels, then flushed with helium gas and reacted at 72°C with phos- phoric acid. The evolved carbon dioxide was sampled using a Thermo Finnigan Gas-Bench and isotope ratios were mea- sured in continuous flow mode using a Thermo Finnigan Del- taplus XPmass spectrometer. The data was extracted into an EXCEL file by using the ISODAT NT EXCEL export utility and further calculation steps were carried out using a pre- defined EXCEL worksheet. Linearity corrections were ap- Figure 6. The post-Archean Australian shale (PAAS) normalized plots of the recrystallized limestone at the contact with the main brec- cia pipe and the recrystallized limestone clast from the main breccia pipe (75 m above mean sea level). The data for the schist and barren limestone are adopted from STRMIĆ PALINKAŠ et al. (2013). 128 Vol. 69/1 Table 2. Chemical composition of carbonates from the Trepča Pb-Zn-Ag skarn deposit. SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O TiO2 P2O5 MnO Cr2O3 % ppm Barren recrystallized limestone STS-0* Recrystallized limestone 0.22 0.07 0.07 0.41 55.69 0.01 0.04 0.01 0.01 0.01 0.001 KM10* Recrystallized limestone 0.13 0.03 0.07 0.08 56.77 0.01 0.04 0.01 0.01 0.03 0.001 T6f* Recrystallized limestone 0.06 0.03 0.09 0.11 56.24 0.01 0.04 0.01 0.01 0.10 0.001 Recrystallized limestone at contact with the breccia T7-4* Contact with the milled matrix breccia 0.14 0.03 0.09 0.15 55.91 0.01 0.04 0.01 0.01 0.09 0.001 T-3A Contact with the main breccia pipe 0.35 0.03 0.54 0.3 54.37 0.01 0.04 0.01 0.03 0.92 0.001 Recrystallized limestone clast from the breccia T-2 Recrystallized limestone clast 0.23 0.08 0.31 0.34 55.18 0.01 0.04 0.01 0.01 0.27 0.001 Recrystallized limestone at con- tact with the mineralization T6e* Recrystallized limestone at contact with skarn mineral assemblage 0.16 0.03 0.74 0.11 52.92 0.01 0.04 0.01 0.01 3.67 0.001 T9-5* Recrystallized limestone at contact with hydrothermal mineral assemblage 0.08 0.03 0.16 0.23 55.75 0.01 0.04 0.01 0.01 0.47 0.001 Syn-ore carbonates T6a-1* Syn-ore carbonates, Skarn mineral assemblage 0.04 0.03 13.69 4.54 35.03 0.01 0.04 0.01 0.01 5.72 0.001 T9-5 (4)-1* Syn-ore carbonates, Hydrothermal mineral assemblage 0.09 0.03 9.45 5.79 34.14 0.01 0.04 0.01 0.01 10.32 0.001 Post-ore carbonates T6a-2* Post-ore carbonates, Skarn mineral assemblage 0.04 0.03 0.85 0.23 53.66 0.01 0.04 0.01 0.01 2.46 0.001 T7-2* Post-ore carbonates, Hydrothermal mineral assemblage 0.05 0.03 0.16 0.22 54.04 0.01 0.04 0.01 0.01 2.88 0.001 T8a* Post-ore carbonates, Hydrothermal mineral assemblage 0.04 0.03 0.74 0.25 53.29 0.01 0.04 0.01 0.01 3.19 0.001 T9-5 (4)-2* Post-ore carbonates, Hydrothermal mineral assemblage 0.10 0.03 0.36 0.30 54.54 0.01 0.04 0.01 0.01 2.77 0.001 Mo Cu Pb Zn Ni As Cd Sb Bi Ag Hg % ppm Barren recrystallized limestone STS-0* Recrystallized limestone