2016, vol. 42 (1): 19–29 The paragenesis of silver minerals in the Pb-Zn Stan Terg deposit, Kosovo: an example of precious metal epithermal mineralization Joanna Kołodziejczyk1, Jaroslav Pršek1, Burim Asllani2, Feriz Maliqi3 1 AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Department of Economic Geology; al. A. Mickiewicza 30, 30-059 Krakow, Poland 2 E&E Experts LLC, 10000, Prishtina, Republic of Kosovo 3 Trepça – Enterprise under AKP Administration, Parku Industrial Mitrovicë, Mitrovicë, 40000, Republic of Kosovo © 2016 Authors. This is an open access publication, which can be used, distributed and reproduced in any medium according to the Creative Commons CC-BY 4.0 License requiring that the original work has been properly cited. Received: 9 February 2016; accepted: 12 April 2016 Abstract: This study reports silver mineral association found recently in the Stan Terg lead and zinc mine, locat- ed in the Vardar zone (in northern Kosovo). The described mineralization comprises pyrargyrite (Ag3SbS3), frei- eslebenite (AgPbSbS3), high-Ag bearing tetrahedrite and freibergite ((Ag4+2xCu2−2x)[(Cu,Ag)4(Fe, Zn)2]Σ6Sb4S12S1−x with (0 < x < 1)); as well as native compounds (Electrum, composition of those minerals was confirmed by the electron microprobe. The freibergite from native silver is native antimony). The Ag-minerals occur in vuggs and cracks in a massive galena ore and have signs of the latest minerals, which precipitated in the deposit. The chem- ical of the Stan Terg deposit reveals zonality and contains between 13.91–20.28% of Ag. The high concentration of Ag in solutions is also indicated by relatively high silver content in Au-Ag alloy (electrum), which is between 47.02% and 73.19% of Ag. The Ag association is supposed to be an epithermal equivalent of precious metal min- eralization, which could be located in the external part of the Stan Terg hydrothermal system. This association occurs in low temperatures, below 200°C. The Ag-minerals can be a part of epithermal veins from the external part of the Stan Terg hydrothermal system. Similarly to the other known Pb-Zn-Ag hydrothermal systems, the Ag association is related to the formation of the rhodochrosite banded ore and Ag-Au-Sb dominated mineralization. Keywords: Ag-minerals, pyrargyrite, freieslebenite, freibergite, Kosovo, Trepça mineral belt, Vardar zone INTRODUCTION Bi(Sb) + Ag vs 2Pb substitution (lillianite type). In high temperature conditions, silver could form Silver minerals are common ore minerals in vari- various groups of Ag-Pb-Bi(Sb) sulphosalts. In epi- ous types of ore mineralizations and deposits pri- thermal mineralization, silver commonly forms its marily in epithermal vein systems, but they can own sulphide minerals; e.g. pyrargyrite, stephan- be found also in skarn-, sedimentary-exhalative-, ite, proustite, argentite and/or native silver. sediment-hosted-, porphyry-types of mineraliza- Stan Terg is one of numerous Pb-Zn deposits tion (e.g. Pearson et al. 1988, Grossou-Valta et al. in the Vardar zone, located in the central part of 1990, Püttmann et al. 1991, Höller & Gandhi 1995, the Balkan Peninsula (Southern Europe). In an- Schalamuk et al. 1997, Zeng et al. 2000, Cheilletz cient times, mineral occurrences in the Balkan et al. 2002, Shalaby et al. 2004, Seifert & Sand- Peninsula were the main sources of Au and Ag. mann 2006). Silver in the ore deposits occurs pri- Mineralization is associated with Tertiary volcan- marily in solid solutions with galena in the form of ism and is related to hydrothermal activity. Silver http://dx.doi.org/10.7494/geol.2016.42.1.19 ISSN 299-8004 | e-ISSN 2353-0790 | Wydawnictwa AGH 20 Kołodziejczyk J., Pršek J., Asllani B., Maliqi F. mineralization is known from different base metal age are exposed on the surface. In addition a Cre- vein districts and deposits, for example the Pod- taceous complex occurs with carbonates, clastics, rinje Metallogenic District (Bosnia and Herzego- serpentinite, volcanics and volcanoclastic rocks vina), mainly from Srebrenica, where Ag-bearing of basaltic composition. Tertiary (Oligocene-Mi- tetrahedrite, stephanite, polybasite, pyrargyrite, ocene) volcanics of andesite, trachyte and latite argyrodite and native silver have been described composition are common in the area, and the sur- (Radosavljević et al. 2016). The Zletovo mining face is covered by felsic pyroclastic rocks (Hyseni district (Macedonia), freibergite, proustite, and et al. 2010, Strmić Palinkaš et al. 2013). pyrargyrite were described in sulphosalts par- Mineralization in the Stan Terg deposit is gen- agenesis (Serafimovski et al. 2006). In the territo- erally hosted in the Mesozoic carbonates, at the ry of Kosovo, pyrargyrite was reported by Smejkal contact with schists and the volcanic rocks of (1960), and Smejkal & Rakić (1957), in the Stan calc-alkaline affinity (Hyseni et al. 2010). The ore- Terg, Hajvalia, Kizhnica and Kopaonik deposits. bodies have an elongated shape of long mantos, or Berjaktarevic (1995) described the “Glama silver” huge veins (with diameters up to few hundreds of prospect, near Gjilan, with a base metal ore with meters). The orebodies stretch parallel to the con- increased Ag, Au and Sn contents. duit as columns. They split and join together in Silver in the Stan Terg deposit is linked most- a form of a huge stockwerk. ly with galena ore, as isomorphous substitution in The Stan Terg deposit has a large hydrothermal a lattice with Bi (Kołodziejczyk 2012), as well as in system with various mineralization styles, such as the form of its own minerals (Smejkal & Rakić 1957, skarns, skarn-free carbonate-replacements, veins Smejkal, 1960, Kołodziejczyk 2012). The Ag content and breccias (Féraud & Deshamps 2009, Hyseni et in ore from the Stan Terg mine is 70 g/Mg on aver- al. 2010, Strmić Palinkaš et al. 2013). Skarn miner- age, with Pb + Zn content around 10% (Féraud & als are observed primarily close to the central part Deshamps 2009, Trepça Mining Company internal of the deposit. According to Dangić (1993), part of documents). According to these works, most of the the ore mineralization could occur during skarn silver is linked to galena, and a minor part of it may formation; mainly magnetite, pyrite, pyrrhotite, belong to separate Ag-associations. chalcopyrite, sphalerite and galena. The skarns at The purpose of this study is to report the elec- Stan Terg are of Ca-type and consists of typical tron microprobe data of the epithermal, Ag-bear- contact-metamorphic assemblages, with garnet, ing mineral association from Stan Terg in the ex- hedenbergite, ilvaite and actinolite. Within the ternal part of the deposit. This association may skarn mineralization, Bi minerals were identified indicate the presence of an epithermal stage of (Kołodziejczyk et al. 2015). The Bi-assemblage is evolution in the Stan Terg hydrothermal system. also related to breccia mineralization, close to the central volcanic rocks. The main mineralization GEOLOGICAL SETTING at Stan Terg was formed during the hydrothermal stage and comprises several generations of py- The Stan Terg deposits and its hydrothermal sys- rite, galena, sphalerite, chalcopyrite, arsenopyrite, tem are located in Kosovo, within the Šumadi- marcasite and lead-antimony sulfosalts (Féraud & ja-Kopaonik ore district, known also as the Trepça Deshamps 2009). The gangue minerals are vari- mineral belt. It is a central part of the Vardar zone, ous Ca-Mn-Fe-Mg carbonates and quartz. Small in the vicinity of the Kopaonik granite massive veins and veinlets which run offset from the main (Hyseni et al. 2010). Stan Terg is the main Pb-Zn orebodies are observed in the external part of the deposit, surrounded by numerous smaller occur- deposit. The hydrothermal phase was divided into rences, of the same hydrothermal origin (Fig. 1). four sub-stages: “Zn + Pb” stage I, “Cu” stage II, The major lithologies in the area are fragments “Ag” stage III and “Sb” stage IV (Kołodziejczyk of Paleozoic crystalline schists and phyllites, with 2012), where galena and sphalerite precipitated unconformable overlying Triassic sediments, mostly during the first stage. According to this phyllites, volcanoclastic rocks and Upper Triassic classification, Ag-mineralization is postponed carbonates. In the broad surrounding of the de- only by the “Sb” stage comprising of boulangerite posit, ultrabasic rocks and serpentinites of Jurrasic and heteromorphite. https://journals.agh.edu.pl/geol The paragenesis of silver minerals in the Pb-Zn Stan Terg deposit, Kosovo: an example of precious metal epithermal mineralization 21 Fig. 1. Location and geological setting of the Stan Terg deposit (Kołodziejczyk et al. 2015) ANALYTICAL METHODS voltage 20 kV, current 10 nA, peak time 10 s, back- ground time 5 s, beam diameter was 3 μm. The fol- Silver minerals were found in samples collected lowing wavelengths were used: TeLα, SKα, PbMα, from the central part of 149e orebody. This ore- CuKα, BiMα, AgLα, SbLα, SeLα, AsLα. Natural body is localized in the external, northern part mineral standards (PbS, FeS2) and synthetic com- of the deposit. All of the described phases were pounds (Bi2Te 3, Cu, Ag, Sb, Se, InAs) were used for found in massive, fine-grained galena hand speci- the calibration. mens, with minor pyrite and siderite in the vuggs. For freieslebenite and tetrahedrite, operating Polished sections were examined by optical conditions were: accelerating voltage 20 kV, beam microscopy, and the chemical composition of the current 20 nA, peak time 20 s, background time minerals was determined by a JEOL JXA-8230 10 s and a beam diameter between 0 and 5 μm. Super Probe electron microprobe in the Criti- The following wavelengths were used: PbMα, cal Elements Laboratory at the Faculty of Geo- TeLα, BiMα, SbLα, SeLα, CdLα, InLα, ZnKα, logy, Geophysics and Environmental Protection, CuKα, SKα, SnLα, HgMα, FeKα, MnKα, AgLα, AGH University of Science and Technology in GaLα, GeLα, AsLα. Natural mineral standards Krakow. (PbS, ZnS, FeS2, Sb2S3, MnS) and synthetic com- The operating conditions for Ag-sulphosalts pounds (InAs, Cu, Bi, CdS, PbTe, Ag, HgTe, SnS, and native elements were as follows: accelerating Se, Ga) were used for the calibration.