www.geologia-croatica.hr ABSTRACT The Ljubija ore deposits are the loci typici of siderite-barite-polysulphide deposits within the Inner Dinarides, Gemerides and Eastern Alps. Numerous sites of ore outcrops, smaller or larger ore bodies of mineralization, consisting of Fe carbonates, sulphides, barite and fluorite are scattered over an area of 150 square km. The half billion tons of iron ore re- sources occur as replacement in dolostones and limestones, and as open-space fillings (veins, veinlets) in phyllites and sandstones. The genesis of the Ljubija ore deposits has been explained as (i) syngenetic sedimentary-exhalative, (ii) hydrothermal-metasomatic in Middle Triassic time or (iii) hydrothermal replacement of sedimentary carbonates in Permi- an time. Basically two alternatives Variscan or Alpine metallogeny, frame the time of gene- sis from the Middle Carboniferous to the Middle Triassic. Genetic interpretation of the Ljubija ore deposits required convincing arguments based on recent achievements of plate tectonics. This contribution presents a set of new data on ore petrology, geochemistry, geolo gy and time of formation. The Ljubija ore field could justifiably be termed the “Lju- bija geothermal field”, due to its areal extent and the thermal characteristics of numerous ore deposits and occurrences within the Sana-Una Palaeozoic terrain. The Ljubija geo- thermal field marks the first signs of thermal instability of Pangea, revealing its breakdown along the deep fractures and heralding incipient intracontinental rifting, the first phase of the new Alpine Wilson cycle. The research reveals novel data on the P-T-X characteristics of ore forming fluids (microthermometry, ion chromatography, Raman spectrometry), sul- phur isotopes, maturity of organic matter by vitrinite reflection, and age determination by 40Ar/39Ar and K-Ar methods. It adopts argumentatively all the estimated research parame- ters that constrain a justified genetic model. Keywords: Siderite-barite-polysulphide de- posits, Dinarides, Ljubija, Permian, zebra texture siderite, early intracontinental rift- ing, Pangea break-up, geothermometry, geo- chronology. Article history: Received December 07, 2015 Revised and accepted January 26, 2016 Avaliable online February 29, 2016 1. INTRODUCTION The Ljubija ore deposits are located in Northwest Bosnia and Herzegovina (44.55˚N, 16.3˚E; Fig. 1), at the margin of the Mesozoic carbonate platform, within the Sana-Una river Palaeo zoic terrain, a part of the Inner Dinarides. Numerous sites of ore outcrops represent smaller or larger bodies of mine- ralization, consisting of Fe carbonate, sulphide minerals, barite and fluorite over an area of 150 square km. According to written documents, iron ore excavation in this area began in the years before Christ. The first miners were Phoenicians and Illyrians. Romans excavated and smelted iron ore for over 400 years in Ljubija and they transported iron bars by road and the Sana, Una, Sava, and Danube rivers to places for further processing. In the middle ages, iron ore was smelted by the Turks, as confirmed by the remains of primitive smel- ting plants in this area. In 1916, during World War I., modern mining of iron was started by the Austro-Hungarian monarchy and the production of iron ore has been ongoing for 99 years intermittently under the changing geopolitical divisions in this part of the Balkans. The potential reserves of iron ore have been estimated at 500 million tonnes with an average Fe con- tent of 40-49 %. There are two types of iron ore, Fe-carbona- tes, siderites and ankerites, and secondary oxide ores with li- monite, in proportions of approx. 1:1 (CVIJIĆ, 2004). Modern industrial mining in the Ljubija ore field (Adamuša ore deposit) began however, as a lead-zinc mine, and was tem- porarily aimed at mining barite and fluorite as well (CVIJIĆ, 2001; CVIJIĆ, 2004; GRUBIĆ & CVIJIĆ, 2003). The Ljubija ore field includes four opencast mines (Adamuša, Tomašica, Omarska, and Vidrenjak) in an area of about 120 km2. Besides iron, several other commodities such as zinc, lead, barite, and fluorite were also exploited. The siderite ore occurs as a replacement in dolostones and limestones, and as open-space fillings (veins, veinlets) in phy- 3-30 26 Figs. 2 Tabs. doi: 10.4154/gc.2016.02 The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) Ladislav A. Palinkaš1, Sibila Borojević Šoštarić2, Sabina Strmić Palinkaš3, Walter Prochaska4, Zoltan Pécskay5, Franz Neubauer6 and Jorge E. Spangenberg7 1University of Zagreb, Faculty of Science, Institute of Mineralogy and Petrology, Horvatovac 95, HR-10000, Zagreb, Croatia (corresponding author: lpalinkas@geol.pmf.hr, phone: ++385 1 3361189) 2University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Department of Mineralogy, Petrology and Mineral Resources, Pierottijeva 6, Zagreb, Croatia 3University of Tromsø, Faculty of Science and Technology, Department of Geology, Dramsvegen 201, N-9037 Tromsø, Norway 4Institute für Geowissenschaften, Montanuniversität, Peter-Tunner-Strasse, A-8700, Leoben, Austria 5Hungarian Academy of Sciences, Institute of Nuclear Research, Bém tér 18/C, H-4001, Debrecen, Hungary 6University of Salzburg, Department of Geography and Geology, Hellbruner Str. 34, A-5020, Salzburg, Austria 7Institute of Earth Surface Dynamics, Bâtiment GEOPOLIS, CH-1015 Lausanne, Switzerland 4 Vol. 69/1 llites and sandstones, with rare chalcopyrite and pyrite. The replacement ore has occasionally a zebra texture, with rhyth- mic banding of dark fine-grained and light sparry siderite, ga- lena, sphalerite and quartz as open-space fillings. Large accu- mulation of limonite occurs as a secondary ore, named „brand“. The genesis of the Ljubija ore deposits has been explained by a few streams of thinking, (i) as a syngenetic sedimentary- exhalative, or as washouts of lateritic crusts in the sedimen- tary basin from a dry land area in Carboniferous time (JURKOVIĆ, 1961; JURIĆ, 1971; ŠARAC, 1981), as (ii) of hydrothermal-metasomatic origin in Middle Triassic time (CISSARZ, 1951; JANKOVIĆ, 1977), or as (iii) a hydrother- mal replacement of sedimentary carbonates in Permian time, recognized by KATZER (1925); and advocated by PALINKAŠ (1988; 1990), PALINKAŠ et al. (2003b) and co- workers BOROJEVIĆ ŠOŠTARIĆ (2004), STRMIĆ PALINKAŠ (2004), and STRMIĆ PALINKAŠ et al. (2009). The Ljubija deposits are the loci typici of the siderite-barite- polysulfide deposits within the Inner Dinarides, Gemerides and Eastern Alps. Previous studies connected the formation of the deposits either to the Variscan or to the Alpine metallogene- sis and considered the Middle Carboniferous or Middle Trias- sic time of formation, respectively. However, the application of modern plate tectonic aspects of ore genesis is necessary for clarifying these controversial views on the origon of the mine- ralisation. Variscan or Alpine metallogeny frame the time of genesis from the Middle Carboniferous to the Middle Triassic. Genetic interpretation of the Ljubija ore deposits required, however, convincing arguments based on the recent achievements of plate tectonics. A basic framework of Wilson cycles has been successfully established but difficulties have arisen from unre- solved problems such as the time and space boundary between Variscan and Alpine tectogenesis. It was a source of ambiguity in the fundamental research of Ljubija ore genesis. A proper genetic model depends substantially on understanding of the geological evolution of the Dinarides. This contribution pre- sents a set of new data on ore petrology, geochemistry and geo- logy of the Ljubija ore field, or justifiably termed the „Ljubija geothermal field“ in this wider sense of meaning, due to its areal extent and thermal characteristics of numerous ore de- posits and occurrences within it. This paper presents new data on the P-T-X characteristics of ore forming fluids (microthermometry, ionic chromatography, laser Raman spectrometry), sulphur isotopes, maturity of or- ganic matter by vitrinite reflection, and age determination by 40Ar/39Ar and K/Ar methods. It adopts argumentatively all the estimated research parameters which constrain a justified ge- netic model. Figure 1. Geological map of the Northwest- ern and Central Dinarides with the position of the siderite-barite-polysulphide depo- sits within the Upper Palaeozoic formation of the Inner Dinarides, Ljubija ore field, Trgovska gora, Petrova gora, Samoborska gora, Bistra Medvednica Mts. (accommo- dated on the map after PAMIĆ et al., 1998). (1) Palaeogene-Neogene overstep sequences (2) Palaeogene metamorphics and granitoids, (3) Upper Cretaceous and Palaeogene flysch, (4) Ophiolites, mostly mélange (5) Jurassic- Cretaceous sequences (6) Adriatic-Dinaridic carbonate platform, (7) Allochthonous Tria- ssic sequences, (8) Allochthonous Palaeo- zoic sequences and rhyolites, (9) Palaeozoic Hercynian metamorphic rocks and granitoids (10) Faults, (11) nappe, (12) Reverse faults, I Outer Dinarides, Ia Sava nappe, II Inner Dinarides, IIa Pannonian nappe, IIb Durmitor nappe, III Pannonian basin, IV Zagorje-Mid- Transdanubian zone, V Eastern Alps. Large faults: PL Periadriatic, ZZ Zagreb-Zemplin. 5 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) 2. SUMMARY OF PREVIOUS STUDIES ON THE GEOLOGY AND ORIGIN OF THE LJUBIJA ORE DEPOSITS The first description of the mineralization in the Ljubija basin came from KATZER (1910). He recognized the relationship between the Carboniferous limestone and siderite mineraliza- tion as a reaction contact, which was defined more precisely as a result of metasomatism, in his later work (KATZER, 1925). Thermal water enriched in iron bicarbonate, deposited siderite into the crevices of schists and limestones in the form of side- rite veins with some sulphides and quartz. The solutions circu- lating through the networks of interconnected fractures within schists and limestone filled them with siderite. Simultaneously, solutions caused metasomatism of the limestones into siderite and more distantly in fissures as ankerite. Later tectonics cut deposits into blocks and displaced them, into the present geo- logical structure. The only exception, suggesting syngenetic formation, was in Krivaja ore occurrences, in the Tomašica district. CISSARZ (1951) described the Ljubija mineral de- posits as hydrothermal deposits of Paleozoic age and related them to deep magmatism. All these descriptions are a short transposition of Katzer’s genuine obervations and interpreta- tions. NÖTH (1952) supposed an intrusive-hydrothermal origin and Upper Palaeozoic age for the siderite veins and irregular ore bodies. RAMOVIĆ (1957) distinguished three types of mineral de- posits in the Ljubija area: (i) siderite veins hosted by Palaeo- zoic schists and related to metasomatism of limestones interca- lated with smaller or larger quantities of clastic material, (ii) metasomatic ore bodies hosted by Palaeozoic limestones and (iii) secondary deposits formed by weathering. JURKOVIĆ (1961) described Ljubija as marine sedimen- tary deposits of Upper Carboniferous age. The Fe carbonates, siderite and ankerite, were deposited as mud, together with some contributory clastic detritus, with irregular sedimentary proportions. Iron carbonates were cryptocrystalline and pre- sent-day textures were recrystallized through diagenetic pro- cesses. JURIĆ (1971) supported a synsedimentary origin of the Ljubija mineral deposits. JANKOVIĆ (1987) emphasized the importance of Permo- Triassic intracontinental rifting, with a magmatic paroxysm in the Middle Triassic. This is also the period when volcano-sedi- mentary deposits, skarns, massive sulphides, mercury depo- sits, bedded ferromanganese oxides, and MVT deposits were formed in the Dinarides. There is no distinction, however, be- tween Permian early intracontinental rifting and Triassic ad- vanced rifting stages, so the Ljubija deposits remain in the vast group of Triassic deposits. Their subterrestrial nature and lack of contemporaneous magmatism in the area did not attract at- tention as an argument for genetic modelling and discrimina- tion from other Triassic deposits. PALINKAŠ et al. (1985, 1988, 1990, 2010) applied a wide spectrum of analytical methods to the siderite-barite-sulphides mineral deposits hosted by Upper Palaeozoic sedimentary complexes of the Inner Dinarides. Special attention was paid to the Ljubija ore deposits. On the basis of fluid inclusion studi es in quartz from three distinctive ore textures, e.g. dark massive siderite, zebra texture with dark and light siderite bands, and siderite veins in phyllites and meta-sandstones, the deposits were unambiguously ascertained to be hydrothermal in nature. Boiling of ore forming fluids was recognised in the Žune-Dolinac barite-fluorite ore body in the Ljubija ore field. It was used to reconstruct the depth of ore forming processes within one of numerous barite occurrences. Applied hydro- static pressure determines variable depths of formation around 100-200 m. Based on the plumbotectonic modeling, PALINKAŠ (1985), suggested a new genetic model with a subterrestrial, hydrothermal convection cell and suggested the Permian as the formation time, related to the early intraconti- nental rifting. The model leaned on the contemporary plate tectonic reconstructions by CHANNEL et al. (1979), HOR- VATH & D’ARGENIO (1985), KOVACS (1984), and PAMIĆ (1984), which convincingly linked similar deposits along the present day edge of the carbonate platform, Trgovska Gora, Petrova Gora, Samoborska Gora (Croatia; PALINKAŠ et al., 2000, 2001, 2003a, 2010; BOROJEVIĆ ŠOŠTARIĆ et al. (2004, 2009), Rudabanya (Hungary; SZAKALL, 2001), Rud- nyani (Slovakia, HURAI et al., 2002) and Erzberg (Austria, PROCHASKA et al., 1997) with an equivalent genesis in time and space. BOROJEVIĆ ŠOŠTARIĆ (2004), on the basis of fluid in- clusion studies, vitrinite reflection, 40Ar/39Ar and K-Ar dating supported a genetic model based on the subterrestrial hydro- thermal convection cell and Permian time of mineralisation related to early intracontinental rifting events. STRMIĆ PALINKAŠ et al. (2009) presented an extensive geochemical study of the ore and host rocks and made a sig- nificant breakthrough in the interpretation and confirmation of the previous studies. The study was focused on the stable iso- tope composition of barren and mineralized carbonates (δ13C and δ18O values), quartz (δ18O), and sulphur minerals (δ34S), the distribution of major and trace elements, including REE, in barren and mineralized carbonates and surrounding clastics, and organic geochemistry research (total organic carbon, hy- drocarbons distribution, isotopic composition of individual alkanes (δ13C), and kerogen (δ13C, δ15N) of barren and minera- lized samples. 3. GEOLOGICAL SETTING 3.1. REGIONAL GEOLOGICAL SETTING The orogenic belt of the Dinarides stretches 700 km along the north-eastern margin of the Adriatic microplates (DERCOURT et al., 1993). In the north, this highly complex folded, thrusted and imbricated belt merges with the Southern Alps and in the southeast it extends into the Hellenides (PAMIĆ et al., 1998). The general strike of the folds, thrusts and knappes in the Cen- tral Dinarides is NW–SE, and the transport direction is towards the SW. The main tectonstratigraphic units of the Central Di- narides display a regular zonal pattern from stable Adria to Tisia. The historical division to “External” and “Internal” Di- narides, predates the plate tectonic concept, but it is still useful to discriminate tectonostratigraphic elements belonging to the passive and active Tethyan continental margins, respectively. The Dinaridic Palaeozoic complexes (PCs) occur in the Exter- 6 Vol. 69/1 nal and Internal Dinarides. The PCs in the External Dinarides, close to or within the carbonate platform, acquired a compara- tively autochthonous position relative to their Mesozoic cover. Within the Sava knappe, PCs are disrupted and allochtonous. They can be correlated tectonostratigraphicaly with those in the Southern Alps, and could be related to the passive conti- nental margin of Gondwana. The Palaeozoic formations with- in a carbonate platform or adjacent to it, were not affected by high grade metamorphism. The PCs in the Sava knappe, in- cluding the Sana-Una PC, close to the ensialic Tisia block, however, underwent very low and low-grade metamorphism. The Dinaridic metallogenic province developed as a result of opening of the Vardar and Dinaridic branches of the Neo- Tethyan Ocean and its closure by convergence of the African and Eurasian plates. The northern boundary of the Dinarides is related to the northern African margin (Adria–Apulia). The Dinarides embrace well-developed and preserved tec- tonostratigraphic units related to the Alpine Wilson cycle, in contrast to the neighbouring Alps where the indentation of Adria obliterated or blurred their regular distribution as a re- sult of intensive tectono-metamorphic events (Fig. 1). The major stages of the cycle are: a) Permian early intra-conti- nental rifting, b) Triassic advanced rifting, c) Jurassic oceani- zation, d) Cretaceous subduction, e) Palaeogene collision; and f) Late Palaeogene/Neogene post collision and extension followed by orogenic collapse. The metallogeny of the Dinarides, based on the principles of plate tectonics, has been upgraded over recent decades. Each stage creates characteristic ore deposits related to spe- cific geological environments. Thermal events in the stage of early intra-continental rifting were in response to the high heat flow caused by thermal doming and thinning of the continental crust. It generated numerous hydrothermal cells in the thick piles of the postVariscan overstep successions. In addition, the incipient magmatism penetrated the Variscan basement of Pan- gea (PALINKAŠ et al., 2001; PALINKAŠ et al., 2010; ROT- TURA et al., 1998). This stage produced numerous hydrother- mal siderite-barite-polysulphide deposits, including the Ljubi- ja ore deposits. They are the loci typici among the other equiv- alent deposits within the Dinarides, Gemerides and Eastern Alps (Fig. 1), discriminated distinctly from the deposits of the advanced rifting stage occurring in the Middle Triassic (JANKOVIĆ, 1977, 1986; PETRASCHEK, 1977; PAMIĆ & JURKOVIĆ, 1997; HEINRICH & NEUBAUER, 2002; JURKOVIĆ, 2003). 3.2. THE SANA-UNA PALAEOZOIC TERRANE The Sana-Una PCs mostly consist of Carboniferous flysch se- quences (sensu KARAMATA et al., 1997). The flysch is overlain by bedded limestones with conodonts of late Viséan age. A new (“post-Variscan”) sedimentary cycle started with the accumula- tion of shallow water limestones (Stara Rijeka formation) of Bashkirian age, which rarely yield marine shallow water fossils and fusulinids. The overlying Eljdište formation (sandy and marly limestones) includes a rich brachiopod fauna. In the Una region, the Blagaj formation, covering the Carboniferous flysch, is an olistostromatic unit, termed “wild flysch“ sensu GRUBIĆ et Figure 2. A) Geological map and B) Stratigraphic column of the Sana-Una Palaeozoic formation (after CVIJIĆ, 2004). 7 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) al. (2000), with Devonian, Lower and Middle Carboniferous limestone clasts containing foraminifers, corals and conodonts, and is correlated with the “molasse” type Ivovik formation from the autochthonous Jadar Block Terrain. Disconformities between the Blagaj formation and the Carboniferous flysch have not been proven. These sequences are covered by Middle Permian clastic sediments (red breccias and conglomerates, sandstones, shales and evaporites) followed by Lower Triassic formations (Fig. 2) (PROTIĆ et al., 2000; GRUBIĆ & PROTIĆ, 2003; KRSTIĆ et al., 2005). 3.3. GEOLOGY OF THE ORE DEPOSITS The Ljubija ore deposits are placed within the Javorik flysch for- mation, which is well exposed within the Adamuša and the Tomašica opencast mines (GRUBIĆ et al., 2000; GRUBIĆ & CVIJIĆ, 2003). At Adamuša, the upper part of the lower flysch horizon contains irregular limestone blocks (olistostromes). Figure 4. A) Zebra siderite comprises dark siderite and light sparry si- derite bands. It contains cavities infilled with sparry ankerite, quartz, sulphides, represented mainly by galena and sphalerite (B) and altera- tion Li-phyllosilicates (C), Adamuša open-cast mine. Figure 3. Dark massive siderite and ankerite in contact with dark mas- sive limestones, the Tomašica open-cast mine. Figure 5. A) Siderite veins hosted by phyllites and metasandstones, Adamuša open-cast mine. B) Close lookup of the banded zebra tex- ture, dark siderite, light siderite and the central white ankerite band. A B 8 Vol. 69/1 stones, dolostones, Fe-enriched limestones, dark grey massive ankerite, and dark grey massive siderite locally weathered to po- rous limonite. 3.4. ORE MINERALIZATION The Ljubija ore field comprises the large iron ore deposits of Adamuša, Tomašica, Omarska, and Vidrenjak, and a number of smaller ones. Important reserves occur in the secondary haema- tite limonite ore, locally named “brand”, weathering products of carbonate ores. Beside iron ores important commodities are barite and fluorite occurrences, mined in the past, scattered over the whole Palaeozoic terrain. PALINKAŠ (1988) recognized three major types of primary iron ore textures: (1) dark massive siderite and ankerite, (2) ze- bra siderite composed of dark massive and light sparry siderite bands, and (3) sparry siderite veins hosted by phyllites and metasandstones (Figs. 3, 4, 5). A simplified stratigraphy for the paragenetic sequences of the Ljubija deposits is shown in (Fig. 6). Dark grey massive siderite and ankerite occur as replace- ments within limestone and dolostone blocks. The contacts be- tween Fe carbonates and host carbonates are obscure. All carbo- nates mentioned above are dark grey in colour due to the pre- sence of organic matter (STRMIĆ PALINKAŠ et al., 2009). A few millimetre thick white calcite veins, cross-cut dark grey limestones and are more abundant near Fe mineralisation. Simi- lar, siderite, quartz and white calcite veins locally intersect the dark grey siderite. White sparry ankerite rarely occurs at the contact with dark massive siderite. Zebra siderite is character- ized by the alternation of dark massive and light sparry siderite bands. Cavities infilled with white sparry ankerite, quartz, sul- phides, and secondary phyllosilicates are common. Sparry yel- lowish to brownish-ochre siderite veins, thick a few decimetres, hosted by phyllites and metasandstones, represent the latest phase of mineralization. The contact between siderite and fine-grained clastics is marked by the presence of sulphides, mainly chalcopyrite. In the eastern part of the Ljubija ore field, economically important quantities of galena, tetrahedrite, chalcopyrite, and sphalerite have been exploited in the past. Barite and fluorite ores are present mainly as E–W oriented veins that cross-cut the Palaeozoic dolostones. The Žune- Dolinac vein type deposit was the object of this study, and was described by JEREMIĆ, 1958; (Fig. 7). A barite vein is hosted by dolostone and phyllites, close to the Scytian shales and sand- stones. The vertical vein reaches 3-9 m in thickness. Barite in- corporates coarse fragments of the host rocks and fluorite and quartz accumulations close to the walls. The structure and tex- ture of the vein bears some elements of hydraulic fracturing, an important prerequisite for boiling of hydothermal fluid, as re- cognized in the fluid inclusion studies. 4. ANALYTICAL METHODS 4.1. MICROTHERMOMETRIC MEASUREMENTS Microthermometric measurements were performed on double polished 0.3 to 0.5 mm thick quartz wafers and 0.05 to 0.1 mm thick fluorite wafers using a Leitz-Wetzlar microscope coupled with a Chaixmeca cooling and heating stage, operating between -180 and +600°C. Objective lenses P25/0.50 were used for Figure 6. Stratigraphic column of the Adamuša open-cast (after GRUBIĆ et al., 2000). Side rite with a zebra texture and sparry ankerite occur mostly within the siderite-metaclastics horizon. The Javorik flysch for- mation at the Tomašica opencast mine is represented by six hori- zons. The siderite-limonite horizon contains dark-grey massive to yellowish coarse-grained siderite and gossan composed of po- rous limonite. The olistostrome horizon comprises a wide variety of carbonates including dark massive limestones, dolomitic lime- 9 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) freezing and UM 32/0.30 for heating runs. Microthermometric measurements on 0.1-0.2 mm thick siderite wafers were carried out using a Linkam THMS 600 freezing-heating stage mounted on an Olympus BX 51 microscope with 10x and 50x long-work- ing distance lenses. Pure H2O and H2O-CO2 synthetic fluid in- clusion standards (SYN FLINC) were used to calibrate the equipment. The precision of the systems was estimated at ±2°C for heating runs, and ±0.2°C in the temperature range between -60 and +10°C. Fluid inclusions were classified according to the criteria summarised by ROEDDER (1984) and SHEPHERD et al. (1985). The salinity of aqueous inclusions was calculated by temperatures of ice and hydrohalite melting using the FLUIDS computer program for NaCl-CaCl2 bearing aqueous solutions at low temperatures (BAKKER, 1999). Calculations are based on purely empirical best-fits, with no fundamental thermodynamic modelling involved (NADEN, 1996). Isochores were calculated by use of the computer program ISOC (BAKKER, 2003) using the equation of state by ZHANG & FRANTZ (1987) corrected for the volumetric properties of quartz (HOSIENI et al., 1985). The salinity of aqueous inclusions with the addition of CO2 at the vapour phase is calculated according to COLLINS (1979). Fluid inclusions are measured in: (i) quartz from quartz veins within dark metasomatic siderite (Adamuša locality), (ii) quartz and siderite from metasomatic zebra siderite (Adamuša locali- ty); (iii) quartz and siderite from vein-type siderite (Adamuša locality), and (iv) fluorite from fluorite-barite vein (Žune- Dolinac locality). 4.2. IONIC CHROMATOGRAPHY, BULK CRUSH-LEACH ANALYSIS Bulk crush-leach analyses were performed by ion chromatogra- phy at Montanuniversität Leoben. Leachates were prepared ac- cording to the technique modified after BOTTRELL et al. (1988). A Dionex DX-500 system was used for halogen analy- ses. Cations were measured in the aliquots of the same solution using standard atomic absorption spectrometry. Bulk fluid inclu- sion composition is analysed in: (i) 3 quartz, (ii) 6 siderite, (iii) a single ankerite and (iv) galena sample from metasomatic zebra siderite (Adamuša locality); (v) 3 quartz, (vi) 4 siderite, (vii) 2 barite and (viii) 2 galena samples from vein-type siderite (Adamuša locality); (ix) 2 dark host limestone; (x) a single blad- ed calcite (Adamuša locality); (xi) 5 fluorite and (xii) 7 barite samples from fluorite-barite vein (Žune-Dolinac locality). Equilibration temperature between ore forming fluids and the host rocks was calculated using the equation of CAN (2002), GIGGENBACH (1988), FOURNIER & TRUESDELL (1973), and VERMA & SANTOYO (1997) for geothermometric pairs Na/K, K/Mg, Na/K/Ca and Na/Li. The evaporation trend of the sea water is taken from McCAFFERY et al. (1987), and Permian and recent water from HORITA et al. (1991). 4.3. RAMAN SPECTROSCOPY The Dilor LabRAM instrument equipped with double Nd-YAG 100 nW (532 nm) and HeNe (613 nm) lasers was used at the Institute für Geoswisssenschaften, Mountainuniversität, Leo- ben. The instrument is connected to an Olympus BX-40 equipped with Linkam THMSG 600 heating-freezing stage, ope rating between -180 and +600°C. Data were analysed using LABSPEC software. Laser Raman Spectroscopy was performed on fluorite samples from fluorite-barite vein (Žune-Dolinac lo- cality). 4.4. VITRINITE REFLECTION The analyses have been performed using a Leitz-MPV3 micro- scope-photometer, in oil, under magnification of 500× at the Or- ganic geochemistry laboratory, INA Oil Company, Zagreb. Samples are powdered, treated with HCl (3 days) and HF (3 days), washed and dried. Concentrated organic matter has been mixed with immersion oil and examined under the photometer. Synthetic spinel (R = 0.42 %) and garnets (R = 0.82 %; R = 1.76 %) are used for calibration. Mean random vitrinite reflectance (Rm in %) shows a strong correlation (r2=0.7, n>600) with maxi- mum burial temperature (Tmax in °C). These data are modelled after BERKER & PAWLEWITZ (1994) by the linear regression equation T = (lnRo + 1.68)/0.0124, Ro = degree of vitrinite reflec- tance. Vitrinite reflection is determined on (i) 6 host limestone samples; (ii) host siltstones (iii) host sediment containing sul- phides, and (iv) siderite samples from a metasomatic ore (all samples from Tomašica locality). 4.5. SULPHUR ISOTOPES Sulphur isotope analyses of sulphides and sulphates selected ex- clusively from the primary ore samples not from the sulfides in the host rocks, were performed at the University of Lausanne using a Carlo Erba 1108 elemental analyzer (EA) connected to a Thermo Fischer Delta S IRMS (EA/IRMS). The sulphur isotope values are reported relative to a Vienna-Cañon Diablo troilite standard (V-CDT). The reproducibility, assessed by replicate analyses of laboratory standards (pyrite, synthetic mercury sul- phide, working; barium sulphate), was better than ±0.2‰ (STRMIĆ PALINKAŠ et al., 2009). 4.6. GEOCHRONOLOGY K/Ar age dating K/Ar age dating of the whole rock samples, 21 samples of meta- clastic rocks and 7 samples of volcanic rocks, are performed at the Institute of nuclear physics, Debrecen, Hungary, after the procedure described by ODIN et al. (1982). Figure 7. The cross-section of Žune-Dolinac barite-fluorite body. 10 Vol. 69/1 Figure 8. A) Dark and light bands in the Zebra texture (photomicrographs, crossed polars). The dark band consists of nonplanar, closely packed anhedral siderite crystals with curved, lobate and serrated boundaries. The light band is made of saddle siderite characterized by curved crystal faces or crystals with sectorial growth. The sweeping extinction indicates a warped crystal lattice. The saddle texture forms under hydrothermal conditions in the voids, between dark bands; B) The void-filling process starts with saddle siderite lining the walls and succeeded by minerals in the following order: ankerite, sulphides and quartz, not necessarily with the presence of all the successive members. The residual zones in microgeodes on the photomicrographs are lined with curved saddle siderite crystals and those with sectorial growth are filled with quartz, the object of fluid inclusion study; C) Ankerite (blue-green) replaces micritic dark limestones (pinkish red) as a sharp ferritization front (crossed polars, the colour hues come from alizarin red-S and Kferricyanide tests. Detailed description of the staining method of WARNE, 1962); D) Metasomatic replacement of late diagenetic dolomite by Fe-carbonate. The late diagenetic unimodal, planar-e dolomite, is mimically replaced by non-planar, unimodal ankerite, with curved and serrated intercrystalline boundaries. The crystal boundaries of ankerite grains gradually fade into a shapeless mass of siderite (plain-polarized light), E) Advancing sideritization front in the greywacke sandstone, with sparry siderite, develops an exotic aggregation of detrital grains. The virtual, quartz-like shape of the detrital aggregation is framed and constrained by sparry siderite crystal faces; F) An advancing sideritization front pervades greywacke sandstone forming fine grained sideritic cement. Texturally im- mature greywacke contains poorly sorted, angular grains of quartz and lithic fragments mostly metamorphics, slates, cherts and quarzites, set in a compact clay-fine matrix and detrital carbonaceous matter. The greywacke sandstone and black shales, a part of the „wild flysch“, originated as a product of strong turbidity currents at the edges of the continental shelves. 11 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) Figure 9. A) Siderite veins were formed in the late stage of mineralization in which ore bearing fluids, penetrated into the clastics, along brittle fractures and deposited sparry siderite in the open veins. While the quartz teeth grow inward from the vein walls, sulphides, pyrite, chalcopyrite and traces of galena and sphalerite fill open-spaces in the vein centre; B) Void filling processes in the light band zebra siderite proceeds with increased concentration of metasomatically released ions, Ca2+, Mg2+, and silica leached from incorporated clay particles in dark bands. Increased sulphur fugacity is marked by co-precipitation of finegrained pyrite and traces of galena as a veneer within sparry siderite, the major sulphide phase; C) and D) Void-filling paragenesis in the light bands of the zebra siderite; E) The host rocks underwent pervasive sideritization followed by silicification, recognized by strain fringes and strain shadows around the pyrite crystals; F) Hydraulic fracturing of galena by silica rich fluids is evidenced by jig-saw-fit texture with fragments stuck together by silica cement. Absence of grain boundary migration and rotation, evidenced by near parallel cleavage among the galena grains, which already past static recrystal- lization (triplet junction), is a sign of low temperature recrystallization in the following mineralization history; G) Penetrative fabrics might have been developed by crystallization pressure in veins, evidenced by stylolites between sparry siderite grains, or as low grade metamorphism in the presence of water when pressure solution was dominant (MERINO et al., 2006). 12 Vol. 69/1 40Ar/39Ar analyses 40Ar/39Ar analyses were carried out at the ARGONAUT Labora- tory of the Division of General Geology and Geodynamics at the University of Salzburg. A single white mica concentrate from vein-type siderite was irradiated in the MTAKFKI reactor (Deb- recen, Hungary). 40Ar/39Ar analysis was carried out using a UHV Ar-extraction line equipped with a combined MERCHANTEK- TM UV/IR laser ablation facility and a VG-ISOTECHTM NG3600 Mass Spectrometer. Isotopic ratios, ages and errors for individual steps are calculated following suggestions by MC- DOUGALL & HARRISON (1999) and using decay factors re- ported by STEIGER & JÄGER (1977). Definition and calcula- tion of plateau ages was carried out using ISOPLOT/EX softwer (LUDWIG, 2001, 2005). 5. RESULTS 5.1. PETROGRAPHY Transmitted and reflected light microscopy supports the ge- netic interpretation of the ore textures (Figs. 8, 9). The three major type of textures are (i) dark grey massive siderite, (ii) zebra texture with dark and light siderite bands, and (iii) vein siderite. (i) Dark massive siderite was formed by volume-per- volume replacement of dolostones and limestones by Fe-satu- rated solution (Fig. 3). Metasomatizm is recongnized by the unimodal size of siderite grains, with nonplanar boundaries, non-mimical replacement of dolomite allochems, and traces of indigenous organic matter which still gives a dark colour to the bands. The nonplanar boundaries are characteristic of growth at elevated temperature and/or high supersaturation, as neo- morphism of a precursor dolostone or limestone (Fig. 8D) (SIBLEY & GREGG, 1987). (ii) Formation of the zebra texture is a combination of two different processes, replacement as simultaneous solution and deposition of siderite, in the manner of atom-per-atom, ex- pressed by reactions 1) and 2 ). 1) CaCO3 + Fe2+ = FeCO3 + Ca2+ ΔVreac = - 22%, ΔG reac 500 = -27.95 kJ log Kreac 500 = 2.91, T = 500 K ΔḠreac 500 = -27.95 + 9.59log aCa2+ - 9.59log aFe2+ 2) (Ca,Mg)CO3 + 2Fe2+ = 2 FeCO3 + Ca2+ + Mg2+ ΔVreac = -11% , ΔGr reac 500 = -43.7 kJ log Kreac 500 = 4.5, T = 500 K ΔḠreac 500 = - 43.7 + 9.59 (log aCa2+ + log aMg2+) – 19.18 log aFe2+ It is accompanied by a significant change of volume, ΔVreac %= -22% and -11%. A difference between the molar vo- lume of siderite and precursor limestone/dolomite, leaves open space for sparry siderite in the zebra texture. Replacement is sustained by infiltration of an iron rich hydrothermal fluid, rather than by restricted diffusion sensu KORZHINSKII (1968). The succeeding step was the crystallization of saddle style siderite in open voids from Fe-impoverished and Ca2+/Mg2+- enriched fluids. This highly variable concentration and compo- sition of the fluid is a cause for the growth of curved crystal faces and sweeping extinction of saddle siderite (Fig. 4A, 8B; 9D) (SAERL, 1989): 3) Fe2+ + CO3 = = FeCO3 ΔG reac 500 = -12.26 kJ log Kreac 500 = 1.27, T = 500 K ΔḠreac 500 = -12.26 – 9.59 log aFe2+ -9.59 log a CO = This is a typical of open space filling processes identified by many vugs and cavities, coarsening of minerals from the walls of the voids to their centre, comb structure or interdigitated vuggy zone, and symmetrical banding. The void-filling pro- cess starts with saddle siderite, lining the walls and proceeds in the following sequential mineral order: ankerite, quartz and sulphides, not necessarily with the presence of all the succes- sive members (Fig. 9B, 9D). Some thermodynamic consideration of the free energy change (ΔḠreac 500) at 500 K (227°C) confirms the prefe rence of reactions (1) and (2) during the early metasomatic phase, and the formation of dark bands. The increase of Ca2+/Mg2+ concentration increases ΔḠreac 500 and supports the tendency of reaction (3) to dominate during crystallization of light spar- ry siderite bands. The presence of CO2 (recognized at the trace level by Raman spectroscopy) is an irrelevant variable in the reactions (1) and (2) and equilibria is controlled by the Fe2+/ Ca2+Mg2+ratio. Reaction (3) proceeds under neutral and slight- ly alkaline conditions, buffered by carbonate host rocks and the dominant species are HCO3 - and CO3 =, and fugacity of CO2 is negligible. It is not the case in the silici clastic host rocks, during development of barite vein deposits, whereas liquid CO2 also participated in the control of pressure and boiling (BOROJEVIĆ ŠOŠTARIĆ et al., 2009). (iii) Siderite veins, another structural facet of the ores, were formed by mineralizing fluids, enriched in Fe-bicarbon- ate ions by widespread collateral metasomatic reactions (Fig.5). They penetrated into the shales, silts and sandstones, along planar discontinuities caused by fault slip events under brittle conditions and deposited sparry siderite in open veins with fuzzy boundaries (Fig. 9E). The host rocks underwent pervasive sideritization during the mineralization phase fol- lowed by silicification, recognized by antitaxial strain fringes and strain shadows around the rigid pyrite porphyroblasts. Characteristic dilatation sites were formed by silica rich fluids at low-temperature (200-300oC) and high fluid pressure (OLI- VER & BONS, 2001). Enrichment of the silica component in the fluids came from the alteration of phyllosilicates and re- sidual clay particles in the carbonate precursor. The best con- duits of the fluids were dark seams, composed of organic detri- tus, phyllosilicates, and insoluble material, deformed around a rigid object, e.g. a corroded detrital quartz grain (Fig. 9E). Hy- draulic fracturing of galena is another aspect of the high fluid pressure (Fig. 9F). The galena triple-junction system, forms a hexagonal network of recrystallized grains, which underwent fracturing, sustaining a jig-saw-fit texture with fragments stuck together with silica cement (lower corner of Fig. 9F). 3 13 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) The quartz grain shows clear signs of dynamic recrystalliza- tion by development of subgrains and gradual bulging (STIPP et al., 2002). Beside fluid inclusion data, deformation lamellae in siderite crystals could be used as an approximate tempera- ture gauge of vein formation. Narrow straight twins (Fig. 9E, type I, BURKHARD, 1993) indicate temperatures bellow 170oC. The tabular thick twins, which can be optically resolved (Fig. 8C, type II, ˃1µm, FERRIL et al., 2004), dominate above 200 oC and up to 300oC. Penetrative fabrics which might be related to the crystallization pressure in veins, are evident by stylolites between sparry siderite grains (Fig. 9G, MERINO et al., 2006). The siderite walls of the vein include quartz-comb textures grown inward, accompanied by pyrite, chalcopyrite, traces of galena and sphalerite (Fig. 9A). Chert and schist frag- ments in the greywacke are inherited porphyroclasts from the Variscan high-grade metamorphic provenance, incorporated during the turbidite phase (Fig. 8F). 5.2. FLUID INCLUSION STUDY Fluid inclusion studies in quartz from quartz veins within the dark metasomatic siderite (Adamuša locality) Quartz veins are several mm to 10 cm thick containing milky white quartz. At several places open space cavities are found containing half-transparent idiomorphic quartz, several milli- metres in size. Fluid inclusion petrography shows the presence of primary and pseudosecondary liquid-rich inclusions of a uniform degree of fill. Eutectic melting occurs at temperature ranges from -39.4 to -21.0ºC. Ice melting in the temperature range from -23.9 to 1.5ºC shows salinities from 23.4 to 2.1 wt.% NaCl equiv. Homogenization by vapour disappearance occurs in a temperature range from 80 to 160ºC. Fluid inclusion study in quartz from cavities within metaso- matic zebra siderite (Adamuša locality) The investigated quartz follows precipitation of light zebra siderite, and precedes the precipitation of sulphides (galena, sphalerite, chalcopyrite, pyrite) within the cavities. Quartz crystals are idiomorphic, transparent up to 1 cm in size. They contain numerous fluid inclusions which are located within growth zones and classified as primary according to the crite- ria outlined by ROEDDER (1982): Type I; Liquid-rich four phase, aqueous inclusions containing a halite daughter mine- ral, also sometimes contain an unknown anisotropic daughter mineral, (L+V+Shal±SA); Type II; Liquid-rich three phase aqueous inclusions, containing an unknown anisotropic daugh- ter mineral (L+V±SA), high salinity; Type III; Inclusions con- tain immiscible liquids (L1+L2). Type IV; Monophase liquid Figure 10. Fluid inclusions in quartz from void-fillings in the zebra siderite, and meso- thermal siderite-quartz veins in the greywacke (Ljubija/Adamuša). a) „Zebra siderite“: primary (L+V+Shal), (L+V+SA) and (L+V) inclusions, Type I and II; b) Array of primary inclusions (L+V), Type II with the same degree of filling; c) Array of primary (L+V+Shal) inclusions; d) Primary (L+V) and (L+V+SA) inclusions, Type II; e) Primary inclusions with immiscible fluids (L1+L2), Type III; f) Primary inclusions (L+V+Shal), Type I. Mesothermal siderite- quartz veins: g) Quartz with marked primary (P), pseudosecondary (PS) and secondary (S) inclu- sions; h) Array of liquid inclusions, Type IV; j) Primary (L+V) and (L+V+SA) inclusions, Type III (see text). 14 Vol. 69/1 inclusions, liquid inclusions containing a halite daughter min- eral (L±V±Shal) and (V); Monophase gas inclusions (Fig. 10). The study was focused on a primary assemblage of aqueous inclusions. Within halite bearing inclusions eutectic melting occurs in a temperature range from -65.7º to -51.0ºC, followed by ice melting in the temperature range from -44.2º to -21.6ºC, and hydrohalite melting (transformation to halite) at a temper- ature range of -40.9º to +0.1 ºC. Under metastable conditions, hydrohalite exists up to 22ºC in a few inclusions. In addition, several inclusions show melting of an unknown, optically iso- tropic phase at a temperature range from -35.0º to 36.1ºC. To- tal homogenization occurs in the temperature range from 201ºC to 259 ºC, showing salinities from 35 to 39 wt.% NaCl equiv. During homogenization, inclusions show different be- haviours: (i) the disappearance of vapour follows the disap- pearance of halite; (ii) the disappearance of halite follows the disappearance of vapour, or (iii) halite and vapour disappear simultaneously. The case of simultaneous disappearance of vapour and ha- lite occurs at temperature ranging from 220º to 259ºC. The ex- istence of three and the disappearance of two phases (L+V+Shal→L) in the NaCl-H2O system (Th total), is univari- ant equilibria which enables determination of fluid pressure and salinity (32.9-35.3 wt.% NaCl equiv.). Thermochemical properties of the H2O-NaCl saturated solutions (HAAS, 1976) constrain the pressure at 16.5 bars or 32.7 bars, respectively. Halite undersaturated inclusions show eutectic melting at tem- peratures ranging from -60º to 51ºC, followed by hydrohalite melting at temperatures ranging from -27.5º to -20.8ºC. Ice melting in a range from -23º (undercooling below 21.2 ºC) to -2.5ºC, indicate salinities from 22.5 to 3.5 wt. % NaCl equiv. They all homogenized by vapour disappearance, in the tem- perature range of 11º - 210ºC. Figure 11. Histograms of microthermometric measurement for the inclusions from quartz in zebra siderite and quartz from mesothermal siderite veins. The histograms present frequency of A) Eutectic temperature (Te); B) Hydrohalvite melting temperature (Tm hyd); C) Final ice melting tem- perature (Tm ice); D) Salinity; and E) Total homogenization temperature (Th). 15 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) The extremely low eutectic temperature (Te) observed in some quartz samples could be interpreted as a metastable eu- tecticum in CaCl2-NaCl-H2O or MgCl2-NaCl-H2O systems (DAVIES et al. 1990), but can also be explained by the pres- ence of Li+ ions in ore bearing fluids as well. Fluid inclusion study in siderite from metasomatic zebra siderite (Adamuša locality) Fluid inclusions have been studied in siderite crystals separa- ted from light bands within metasomatic zebra ore. Most inclu- sions in siderite crystals are two-phase (L+V) and can be de- fined as primary. They acquire negative crystal, or irregular, three-dimensional shapes and are distributed irregularly within the crystals. Primary inclusions show consistent liquid–vapour (L/V) volume ratios, which indicate entrapment of a homoge- nous fluid. The eutectic temperature spans the range between -53° and -49.9°C, suggesting a CaCl2-NaCl-H2O system. Hy- drohalite melting occurs in the narrow range between -31.1° and -29.0°C. Ice melting temperatures recorded in an interval from -12.0° to -10.1°C corresponds to a salinity between 14.1 and 16.0 wt.% NaCl equiv. Total homogenization, always into the liquid phase, ranges between 147 and 164°C. Secondary two-phase (L-V) inclusions are recorded as well, but they have not been measured due to their small size. Fluid inclusion study in quartz from hydrothermal quartz- siderite veins (Adamuša locality) Vein-type siderite contains two types of quartz crystals: irregu- lar, milky white quartz which does not contain measurable FIs, and semi-transparent quartz-siderite intergrowth, containing Type III; Primary liquid-rich inclusions, with or without an anisotropic daughter mineral, (L+V±SA); Type IV; Pseudose- condary liquid-rich inclusions (sometimes with an anisotropic daughter mineral), (L±V±Shal) generating vapour bubbles after the freezing run. This is either a sign that our fluid inclusions were stretched during the freezing run or just metastability is affecting the re-apperance of the vapour phase after freezing. Primary inclusions show eutectic melting at tempera- tures ranging from -63ºC to -43ºC, followed by hydrohalite melting at temperatures from -31.0º to -21ºC. Salinities cal- culated from the ice melting temperatures (-17.7º to -7.1ºC) ranged from 20 to 11.5 wt.% (in those inclusions with the presence of a vapour phase at room temperature) NaCl equiv. Several inclusions show eutectic melting at -4.7ºC and gas hydrate melting at +10ºC, suggesting the pre sence of bicarbonates and CO2 hydrates. Homogenization was in the range from 97º to 250ºC. Pseudosecondary liquid-rich inclusions show eutectic melting at temperatures between -60º to -44ºC, followed by hydrohalite melting between -34º to 22ºC and ice melting between -7.1º to -1.4ºC. Calcu- lated salinities ranged from 2.0 to 9.0 wt.% NaCl equiv., whereas homogenization temperatures (by vapour disap- pearance) range from 90º to 133ºC. Fluid inclusion study in siderite from hydrothermal quartz-siderite veins (Adamuša locality) Several primary fluid inclusions have been recorded in sparry siderite crystals from siderite veins hosted by the Carboni ferous shale. A eutectic temperature around -52°C suggests a CaCl2NaCl-H2O system. Hydrohalite melting spans an interval between -29.5° and -21.0°C. Ice melting temperature recorded between -4.2° and -3.5°C points to a salinity between 5.7 and 6.7 wt.% NaCl equiv. Homogeni- zation into the liquid phase occurs in the range from 120° to 127°C. Results of microthermometric measurements on quartz from the three principal types of the Fe mineralisation in Ljubija/Adamuša are presented in Fig. 11. Figure 12. Ternary-component diagram NaCl-CaCl2-H2O for all mea- sured inclusions in Ljubija/Adamuša ore field. Shift of composition from NaCl-H2O line toward CaCl2-H2O line is a result of metasoma- tism. A wide variation of salinity points to the mixing of two contrast- ing fluids, high density FLUID 1with low density FLUID 2. Figure 13. Diagram of temperature of homogenization vs. sali- nity, Ljubija/Adamuša for fluid inclusions in the ore field Ljubija/ Adamuša, another confirmation of the mixing of two contrasting flu- ids, high salinity, high temperature FLUID 1 and low salinity, low temperature FLUID 2. 16 Vol. 69/1 A ternary diagram NaCl-CaCl2-H2O (Fig. 12) for all types of FIs in the Ljubija/ Adamuša deposit shows a shift of data points from the NaCl-H2O line toward the CaCl2-H2O according to the dominant meta- somatic process. The diagram also empha- sizes the wide distribution of salinity from very low to very high. An explanation is suggested by the diagram Th vs. salinity (Fig. 13). The diagram shows a wide range of high to low salinity, and a narrow but de- clining trend of Th, from high to low, which suggests the mixing of the two types of con- trasting fluids. The high temperature, high salinity, Type I, true evaporitic brine, and the low temperature, low salinity Type II, indicating that the sea water not only evolved by evaporation. Mixing happened a few hundred metres close to the topogra- phic surface. A P-T diagram with isochores calculated by the ISOC computer program is presented in Figure 14. Fluid inclusion study in fluorite from a fluorite-barite vein (Žune-Dolinac locality) Purple fluorite crystals with well developed growth zones were selected for the fluid in- clusion analysis. The petrography revealed the presence of various inclusion types, classified as primary: type I; Liquid-rich aqueous inclusions containing a halite daughter mineral and an unknown anisotro- pic daughter mineral, high salinity (L+V+Shal±SA) (Fig. 15B), Type II; Liquid- rich aqueous inclusions containing an anisotropic daughter mineral, high salinity (L+V±SA), (Fig. 15B), Type III; Liquid-rich aqueous inclusions (L+V), low to moderate salinity, (Fig.15D), Type IV; Vapour rich aqueous inclusion (V+L±SA), low to mode- rate salinity, possibility of leaking (Fig. 15), Type V; Vapour rich with halite daughter mineral (V±L+Shal) (Figs. 15E,F), Type VI; Two immiscible liquids (L1+L2), no sign of fluorescence, neither freezing, Type VII; Vapour inclusions (V) (Fig. 15F), Type VIII; Solid inclusions (SA) (Fig. 15C), anisotropic mineral present in the Types I, II, and IV. Type IX; Liquid inclusions (L), (Fig. 15D), (important note that all num- bered types coexist within one single grain, Fig. 16). Fluid inclusion study was performed on liquid rich and vapour rich inclusions with or without daughter minerals. Halite satu- rated aqueous inclusions (± unknown aniso- tropic daughter mineral) Type I and II show first melting at temperatures from -66.4º to 49.0ºC, followed by ice melting in the tem- Figure 14. A) Isochores for the end members (L+V+Shal±SA) inclusions Type I, and (L+V±SA) Type II in the quartz from zebra siderite, and B) end members inclusions (L+V±SA) Type III and IV in quartz from the mesothermal siderite veins. Figure 15. Fluid inclusions in fluorite in the barite-fluorite vein ore body Žune-Dolinac; A) Array of primary inclusions in the central part of the fluorite crystal; B) Primary FI-s (L+V+Shal+SA), Type I and (L+V) Type III; C) Boiling effects – array of Fis with differ- ent degrees of filling (L+V), (V+L), (L+V+Shal+SA) and (L+V+SA), Type II, III, IV, V; D) Boiling effect – array of primary FIs (L), (L+V), (V+L), Type III, IV and IX; E) coex- istance of (L+V) and (L+V+Shal) Fis Type I and II; F) Boiling effects – array of primary (L+V), (L+V+Shal), (V), Fis Type I, II and VII; G) Primary (L+V+SA) FI Type II; and H) Primary (V+L) FI Type IV. Important note, the listed types of fluid inclusions coexists within one single grain. Graphical presentation of fluid inclusions depicting the great vari- ability in salinity, density, number of phases, different solids, indicate a boiling system, and are presented in the drawing Fig. 16. 17 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) perature range from -41.2 to -21.6ºC and hydrohalite melting/ transformation between -35.5º to -1.2ºC. During heating, within the majority of the inclusions, the vapour phase disap- peared first, followed by halite dissolution in the temperature range between 125º - 297ºC. A single inclusion melted sylvite at 129ºC followed by halite melting at 139ºC. Several inclu- sions melted halite in the temperature range from 8.1 to 11.4ºC, followed by the disappearance of the vapour phase at temperatures between 145 - 238ºC. Salinities are between 26.0 and 41.7 wt% NaCl equiv. Halite undersaturated aqueous inclusions (L+V), Type III; show similar eutectic tempera- tures (Te = -65.0º to -49.0 ºC), followed by hydrohalite melt- ing (Thyd = -35.6º to -21.0ºC). Salinities are calculated from ice melting temperatures (Tice = -21.1 to -1.2 ºC) and range from 25 to 3.5 wt% NaCl equiv. Homogenization into a liquid phase was in a temperature range from 175 to 275ºC. Type IV, vapour rich aqueous inclusions show eu- tectic melting in a temperature range from -56º to - 48ºC, followed by hydrohalite melt- ing (Thyd = -44º to -21ºC) or ice melting (Tice = -38º to -3.1ºC). Salinities range from 33.4 to 5.1 wt% NaCl equiv, whereas homogeniza- tion to a vapour phase occurred in the range from 125º to 245ºC. Several inclusions de- crepitated during heating procedure (Fig. 17). The co-existence of liquid rich inclusions Type II, (L+V+Shal), of high salinity from 25 to 42 wt% NaCl equiv, and Type IV, vapour rich (V+L) with very low salinity between 0.4 to 5 wt% NaCl equiv, homogenizing in the same temperature interval between 125 and 245 ºC, corroborate the indication of boiling. The inclusions with halite as the last ho- mogenization phase after (L+V+Shal)→(L+ Shal) →(L) at 300ºC, and vapour rich inclu- sions with halite crystals (V+Shal), and those with solid halite inclusions (Shal) are the pro- duct of a distillation (boiling evaporation) process in a semiclosed system with variable pressure, communicating with the open space on the earth surface followed by hete- rogeneous trapping. However, the behaviour of these high salinity and low salinity FI-s, especially the type (V+Shal), and solid inclu- sion (Shal) cannot be explained by one single episode of boiling. This impressive collection of fluid inclusion types, (more than 9 in one single crystal) requires multistage episodes of boiling producing a mixture of liquid water and bubbles, suspension of crystalls, halite, sylvite, and unknown solids, trapped into one single crystal. It represents repeated boiling episodes under changable pressure, due to a change in hydraulic head, water table, pres- sure of gases (suspected hydrocarbon liquids in inclusions), breakage of sealing, or maybe the intrusion of hot superheated water or steam from below into low salinity meteoric water, causing the rise of vapour and boiling, etc. The ternary diagram NaCl-CaCl2-H2O (Fig. 18), also indicates the boiling process. The Th vs. salinity dia- gram also confirms boiling and the separation of high salinity liquids from low salinity vapour (Fig. 19). In this plethora of FI-s types and disequilibrium conditions, there was an at- tempt to determine the pressure of boiling by coexisting in- clusions in one crystal, 33.4 wt% NaCl equiv. (L+V), and 0.4 wt% NaCl equiv. (V+L), and homogenization at the same temperature, (Th), at 245ºC which yields 36.1 bars. Applying hydrostatic pressure, the depth of boiling would be 361 m (HAAS, 1976, 1971). Figure 16. Selection of fluid inclusion types in one single crystal of fluorite, Žune- Dolinac locality (PALINKAŠ, 1988). 18 Vol. 69/1 5.3. LASER RAMAN SPECTROSCOPY Laser Raman spectroscopy was performed on fluid inclusions from fluorite (fluorite-barite vein, Žune-Dolinac locality) on the four-phase, (L+V+Shal±SA) Type I; the three-phase, (L+V±SA) Type II; two-phase (L+V) Type III. Liquid-rich aqueous inclusions containing halite daughter minerals, with high salinity. At room temperature they are composed of aque- ous liquid (broad shoulder at around 3400 cm-1) and aqueous gas and/or traces of CO2 (peaks at 1278 and 1383 cm-1). Other volatiles were not detected. At -21ºC fluid inclusions contain ice (a broad peak at 3100 cm-1) and hydrohalite (a doublet around 3418 cm-1 and a sharp peak at 3543 cm-1). 5.4. BULK CRUSH-LEACH ANALYSES Bulk crush-leach analysis by ionic chromatography was per- formed on quartz, siderite, ankerite and galena from metaso- matic zebra-type siderite; quartz, siderite, barite and galena samples from vein-type siderite, dark host limestone; bladed calcite (Adamuša locality) and fluorite and barite samples from a fluorite-barite vein (Žune-Dolinac locality, Table 1). Recalculated bromine contents from leachates in quartz from metasomatic zebra siderite are elevated and vary between 535 and 685 ppm, whereas within vein-type siderite varies be- tween 165 and 256 ppm (according to the procedure outlined by CHANNER et al. (1999). The recalculated bromine con- centration in fluorite from the Žune-Dolinac locality is similar to the quartz from the metasomatic zebra-type siderite, ranging from 430 ppm to 605 ppm. A high concentration of bromide is registered in the dark limestone and barite as well. Na+, Ca2+, K+, and Mg2+are major cations, while the domi- nant anion is Cl– followed by SO4 2-. These data correspond to the observed low eutectic temperature and depression of hy- drohalite melting, both indicating the presence of divalent cat- ions within the fluids, with the exception of Mg2+ which is Figure 17. Histograms of microthermometric meas- urement for the inclusions in the fluorite in the Žune-Dolinac barite-fluorite vein deposit. A) Eutec- tic temperature (Te); B) Hydrohalite melting tem- perature (Tm hyd); C) Final ice melting temperature (Tm ice); D) Salinity; and E) Total homogenization temperature (Th). 19 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) below the detection limit within quartz zebra siderite. It ex- plains the precipitation of ankerite in the middle of the light bands, and the formation of saddle siderite crystals. High Ca2+ and Mg2+ concentrations are the direct results of intensive metasomatic ankeritization and sideritization. Concentration of sulphate is between 0.1 wt % and 0.3 wt % within quartz from the zebra type minerallisation and between 0.3 wt % and 0.7 wt % within vein type quartz, whereas within fluorite samples (Žune-Dolinac locality) it is between 0.4 and 0.5 wt %. Maximum SO4 2- values up to 30,000 ppm (3 wt.%), were observed within a single fluorite sample. This very high concentration level, not confirmed by presence of gypsum or anhydrite in the fluid inclusions, (due to high Ca concentra- tion), is most likely attributed to contamination (e.g., solid in- clusions of barite) since barite is frequently found in the para- genesis. However, it also points to a significant change in the fluid chemistry responsible for the genesis of barite deposits, decreased depth of formation, and the increased contribution of sea water. A deficit of cations is observed in the vein-type quartz. This can be attributed to the presence of Fe2+ within the fluids, which was not measured during the procedure or to the absorption of divalent cations to the quartz powder during the crushing procedure. The lithium content is highly elevated within zebra-type quartz and varies between 366 ppm and 2300 ppm, whereas for the vein type quartz it is in the range between 60 ppm and 150 ppm. Fluorite samples have uniform lithium concentra- tions varying between 325 ppm and 405 ppm. The presence of Li in the ore fluids was suspected by the extremely low eutec- tic temperature in quartz fluid inclusions from the zebra side- rite down to -90 ºC. High Li concentration in the leachates and the presence of dio-trioctachedral chlorites from the donbassite-tosudite- cookeite solid solution and (LiAl4(Si3Al)O10(OH)8 (Fig. 4C, SLOVENEC & PALINKAŠ, 2003) in the same cavity, con- firms the high Li concentration in evaporitic bitter brines tak- ing part in siderite genesis. This is one piece of evidence which connects evolved sea water from Permian evaporitic basins or lagoons with the ore forming process. High Li and B concen- trations are common components in evaporitic bitter brines elsewhere (STEVEN & ZVI, 2011; 209 ppm, LIPPMANN et al.,1999). An additional contribution of Li may come from leaching of the surrounding host rocks, shales and sandstones. (McCAFFREY et al., 1987). CÉCILE et. al. (2002) consider high-salinity fluids, derived from sedimentary basins, respon- sible for the Li enrichment in FI-s in the barren quartz from the Spanish Central System (Sierra de Guadarrama). According to KRAUSKOPF (1982), the average shale contains 60 ppm of Li, twice that of the average granite. Diagram Na/Cl vs. Cl/Br follows the sea water evaporation line. The measured ratios are the result of sea water evapora- tion rate between 12 and 36 % (Fig. 20A). It confirms the evapo ration trend on all samples of zebra siderite, vein side- rite, ankerite, quartz in siderite veins, vein barite and dark limestone. Galena exhibits very variable ratios. Galena asso- ciated with zebra siderite has Na+ around the sea water compo- sition, and in the vein siderite, above sea water on the evapo- ration line. It means a possible contribution of halite dissolu- tion from evaporites. It should be mentioned that sulphide paragene sis in the cavities within zebra siderite is the last phase in the succession of dark siderite-light siderite-quartz- sphalerite-galena which suggests a prolonged time-span of ore formation. The Caexcess vs. Nadeficiency diagram (Fig. 20B) shows a wide spectrum of contemporaneous ore forming processes which follow concurrently the metasomatism of Carboniferous lime- stones and dolostones by hydrotherms. The major trends are: (i) Caexces increases by metasomatism of carbonates, ankeritiza- tion and sideritization, and (ii) albitization of plagioclases (1 mole of Na for 1 mole of Ca). The temperature of fluids was also calculated on the basis of geothermometric pairs: Na/K = 210-258 ºC (mean 184ºC); K/ Mg = 261-443 ºC (mean 355ºC); Na/K/Ca = 280-441ºC (mean 328ºC); and Na/Li = 124-589ºC (mean 329ºC). The use of tra- ditional geothermometric pairs which includes Ca and Mg, obtains unreliably high values. Their use is provided for water/ fluid equilibria in the common aquifer rocks, while in the Lju- bija geothermal field metasomatism excessively predominates other equilibrium processes. In contrast, the Na/K geother- mometer gives reasonable temperature, although in geother- mal and epithermal enviroments this geothermometer reflects the deep reservoir fluid/rock equilibration rather than the fluid inclusion entrapment temperature (SIMPSON et al., 2015). 5.5. VITRINITE REFLECTANCE Nine of seventeen samples from the Tomašica locality are se- lected for vitrinite reflection: (i) 6 host limestones; (ii) phyllite (aleurolite, frequently used in the literature on Sana-Una. Pa- laeozoic lithology); (iii) siderite, and (iv) sulphide rich sedi- ment, which all contained >0.5% of organic carbon. According to petrography, most of the samples are composed of amorphous organic matter (99-100%) with traces of vitrinite and rarely py- robitumene. The exception is the sample composed of 70% amorphous organic matter and 30 % vitrinite. All samples show a high thermal alteration index (TAI ~ 4). The degree of vitrinite Figure 18. Ternary-component diagram NaCl-CaCl2-H2O for all types of inclusions in fluorite from the Žune-Dolinac barite-fluorite vein deposit, Ljubija ore field. Shift of composition from NaCl-H2O line toward CaCl2-H2O line is a result of metasomatism. Differentiation of high salinity and low salinity inclusions, however, could be attributed to the extensive boiling processes determined in the deposit. 20 Vol. 69/1 Sample Mineralogy Mineralisation type Li+ (meq/l) Na+ (meq/l) K+ (meq/l) Mg2+ (meq/l) Ca2+ (meg/l) F- (meg/l) Cl- (meg/l) Br- (meq/l) I- (meq/l) NO3 2- (meq/l) SO4 2- (meq/l) Na (mol/l) LJ 010/1 Quartz Siderite, Zebra type 96 7481 609 1139 472 7584 22 119 145 325 Lj 011/1 Quartz Siderite, Zebra type 22 10392 823 315 7 11119 42 162 75 452 Lj 014/1 Quartz Siderite, Zebra type 103 10377 660 806 2 11425 43 74 451 PR-LJ-12 Quartz Siderite, Vein type 11 5336 476 683 12465 34 9344 47 0.5 4318 1341 232 PR-LJ-13 Quartz Siderite, Vein type 12 4391 452 581 12659 30 8381 27 0.6 998 454 191 PR-LJ-14 Quartz Siderite, Vein type 16 3081 249 363 11748 9 5496 20 0.5 465 327 134 Lj 008/2 Siderite Siderite, Zebra type 157 9834 544 2343 9419 32 14136 71 33 860 428 Lj 010/2 Siderite Siderite, Zebra type 314 14459 863 3763 11172 27 23017 258 65 90 629 Lj 011/2 Siderite Siderite, Zebra type 196 10099 761 4297 10995 33 15760 147 74 208 439 Lj 013/2 Siderite Siderite, Zebra type 246 11236 732 3899 8741 27 18174 149 31 489 Lj/014/2 Siderite Siderite, Zebra type 256 10226 570 4452 6635 7 16224 122 40 445 Lj 015/2 Siderite Siderite, Zebra type 209 10527 505 4418 7271 19 16665 123 29 458 PR-LJ-1 Siderite Siderite, Vein type 101 12534 544 6535 6337 145 30458 192 0.9 321 206 545 PR-LJ-4 Siderite Siderite, Vein type 188 8812 1844 5275 16245 62 20489 231 0.6 196 3527 383 PR-LJ-5 Siderite Siderite, Vein type 67 14884 856 741 1995 56 26356 114 1.7 820 <20 647 PR-LJ-9 Siderite Siderite, Vein type 417 10468 458 7720 12683 43 25633 338 0.7 196 1129 455 Lj 009/2 Ankerite Siderite, Zebra type 280 20159 735 10602 25392 20 31845 110 28 138 877 Lj S-4 Calcite Hydrothermal calcite 216 46 268 16406 4 166 72 238 9 PR-LJ-3 Dark limestone Host rock 62 3775 5269 2197 19779 227 6620 36 10.8 308 1358 164 PR-LJ-8 Dark limestone Host rock 26 3032 436 1507 25951 121 4744 68 6.9 177 19065 132 PR-LJ-6 Barite Siderite, Vein type 16 4943 319 616 14378 9658 50 0.8 118 3965 215 PR-LJ-7 Barite Siderite, Vein type 3 3877 325 682 22685 46 8630 34 0.6 174 20654 169 Lj 012/3 Galena Siderite, Zebra type 3 4659 293 178 1624 13 6673 8 114 1492 203 PR-LJ-2 Galena Siderite, Vein type 4 5869 352 571 8487 126 10701 26 0.1 168 409 255 PR-LJ-11 Galena Siderite, Vein type 1455 96 315 1711 31 2034 <0,1 163 2243 63 ŽUNE/DOLINAC Naziv Mineral Opis Li+ (meq/l) Na+ (meq/l) K+ (meq/l) Mg2+ (meq/l) Ca2+ (meg/l) F- (meg/l) Cl- (meg/l) Br- (meq/l) I- (meq/l) NO3 2- (meq/l) SO42- (meq/l) Na (mol/l) DZ 1/I Fluorite Barite-fluorite vein 34 6316 1073 1256 9490 7351 11896 58 683 564 275 DZ 3/II Fluorite Barite-fluorite vein 40 8281 421 382 9626 7040 15072 52 308 701 360 DZ 3/III Fluorite Barite-fluorite vein 49 10793 825 306 9260 7703 19137 88 185 651 469 DZ 3/I Fluorite Barite-fluorite vein 53 8928 297 381 21709 6841 16199 50 156 494 388 DZ 3/II Fluorite Barite-fluorite vein 36 11963 436 277 8631 7895 13612 64 134 3343 520 DZ 100 Barite Barite-fluorite vein 281 125 568 10824 982 257 269 10352 12 DZ 101 Barite Barite-fluorite vein 373 167 169 3708 371 823 230 2815 16 DZ 102 Barite Barite-fluorite vein 369 192 1839 130 779 197 2723 16 DZ 103 Barite Barite-fluorite vein 15 9234 781 195 2374 52 18092 120 241 2133 402 PR-LJ-10 Barite Barite-fluorite vein 395 47035 1353 14662 33533 60 76299 467 32.3 192 562 2046 PR-LJ-10A Barite Barite-fluorite vein 336 72 1358 21291 11 146 0.1 202 18953 15 LJ-10/A Barite Barite-fluorite vein <1 57 24 <2000 12160 35 102 1.0 84 16698 2 DZ 106 Quartz Barite-fluorite vein 10 5065 537 262 5088 8 5804 27 609 823 220 DZ 107 Quartz Barite-fluorite vein 3272 448 2248 8 3367 15 545 1109 142 Table 1. Ljubija/Adamuša reflection within the limestones is represented by Ro of 4.0 – 4.6%. Using the diagram T-Ro-t (time of effective heating, max- imum temperature, vitrinite reflectance) gives a temperature of 200-210 ºC (BOSTICK et al., 1979) and 247-258 ºC after (BERKER & PAWLEWITZ, 1994); The sample of limestone with pyrobitumen has an Ro of 4.6%, which appropriates to a temperature of 210 ºC and 258 ºC, respectively. Within phyllites with 30% vitrinite, Ro of 4.8 %, gives T of 215 ºC and 262 ºC, by two methods. Sediments with sulphides, where Ro = 3.7%, appropriate to T of 193 ºC and 228 ºC. A siderite sample with Ro 3.2% gives T of 193ºC and 228ºC. The temperatues obtained are in good agreement with the fluid inclusion data, Tboiling 240ºC, and Na/K, where T is 210-258 ºC. 5.6. SULPHUR ISOTOPES Sulphur isotope compositions were determined on sulphides and sulfates. Sulfur isotopic data are presented in Table 2 (STRMIĆ PALINKAŠ, 2004). The δ34S values of the sulphides increases in order to 3.0 ‰) ≤ chalcopyrite ≤ (-0.8 to +2.3 ‰) ≤sphalerite (+0.4 to +4.4 ‰) < pyrite (+5.4 to +8.5 ‰). There was no distinction perceived between sulphides separated from dark siderite and zebra ore. The δ34S values of barite sam- ples (+9.2 to ± 0.2 ‰ V-CDT) fall within the range of the latest Permian marine evaporites (HOLSER & KAPLAN, 1966). The temperature of cogenetic geothermometric pairs was calculated by the constants given by OHMOTO & RYE (1979). The calculated temperature suggests the absence of isotopic equilibria. The reasonable temperature of 245ºC was 21 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) Cl (mol/l) Br (mol/l) Ca (mol/l) Na/Br (mol) evapor. (%) Cl/Br (mol) evapor. (%) GEOT. Na/K (oC) GEOT. K2/Mg (oC ) GEOT. Na/K/ Ca b=1/3 (oC ) GEOT. Na/Li Cl<0.3M (oC ) GEOT. Na/Li Cl>0.3M (oC ) Ca/Na Mg/Na Caex (meq/l) Nadef (meq/l) 214 0.28 28.42 1162 0.0 764 0.0 188.9 373.4 177.0 373.2 0.2 49.7 -142.1 314 0.53 7.87 857 0.0 595 12.0 186.7 407.7 64.6 190.0 0.0 5.2 -183.3 322 0.54 20.11 838 0.0 598 12.0 171.6 364.6 156.1 337.8 0.1 29.4 -175.2 264 0.59 311.03 393 15.0 446 15.1 195.8 392.0 330.2 64.0 189.1 2.3 0.1 613.2 -6.2 236 0.34 315.86 558 9.0 690 0.0 207.6 394.6 337.4 77.1 209.6 2.9 0.1 623.8 11.6 155 0.24 293.12 549 9.0 635 0.0 188.3 364.3 305.2 113.5 267.5 3.8 0.1 581.0 -1.2 399 0.89 235.03 481 10.7 449 15.5 163.0 352.6 309.2 195.6 405.2 1.0 0.2 456.7 -86.0 649 3.23 278.76 195 23.6 201 35.0 167.6 370.3 325.3 225.7 458.0 0.8 0.3 535.7 -72.5 445 1.83 274.34 239 20.4 242 26.8 183.2 355.0 336.5 214.4 438.1 1.1 0.4 533.8 -58.3 513 1.87 218.09 262 20.0 275 24.0 173.2 355.8 329.5 226.3 459.0 0.8 0.3 419.0 -49.4 458 1.53 165.56 290 19.0 299 23.0 163.4 332.1 316.3 240.6 484.7 0.6 0.4 315.8 -52.6 470 1.54 181.41 296 19.0 304 23.1 154.8 323.7 302.3 216.7 442.0 0.7 0.4 347.1 -55.0 859 2.40 158.12 227 21.0 358 20.1 149.6 315.4 300.8 141.2 313.0 0.5 0.5 287.4 191.1 578 2.89 405.34 133 30.0 200 35.0 281.4 422.3 441.0 223.6 454.3 1.8 0.6 791.3 112.0 743 1.43 49.78 454 12.0 521 12.0 165.3 443.4 350.9 103.2 251.0 0.1 74.6 -10.3 723 4.23 316.46 108 36.0 171 40.4 150.0 298.3 286.4 297.1 589.0 1.2 0.7 608.7 164.3 898 1.38 633.57 636 0.0 651 10.5 141.2 319.4 280.0 183.6 384.5 1.3 0.5 1237.0 -107.1 5 409.35 284.3 261.6 308.1 76.0 1.2 818.5 -5.4 187 0.45 493.51 367 15.0 417 16.4 198.6 410.4 5.2 0.6 980.7 -4.2 134 0.85 647.52 155 27.0 157 44.8 239.0 352.4 346.6 145.1 319.5 8.6 0.5 1290.5 -17.2 272 0.63 358.76 341 16.0 432 16.3 172.6 363.1 296.5 85.6 223.0 2.9 0.1 708.4 18.5 243 0.43 566.03 393 14.9 567 12.0 191.0 360.4 305.4 27.6 133.2 5.9 0.2 1123.9 40.0 188 0.10 40.52 2009 0.0 1866 0.0 170.9 408.8 325.0 20.9 123.0 0.3 0.0 74.7 -41.3 302 0.33 211.76 775 0.0 916 0.0 167.9 374.2 302.7 21.5 124.0 1.4 0.1 413.4 3.4 57 42.70 174.3 301.1 294.2 1.2 0.2 83.5 -14.1 MEAN: 184.7 355.3 328.1 148.7 329.5 4.8 0.4 ŽUNE/DOLINAC Cl (mol/l) Br (mol/l) Ca (mol/l) Na/Br (mol) evapor. (%) Cl/Br (mol) evapor. (%) GEOT. Na/K (oC) GEOT. K2/Mg (oC ) GEOT. Na/K/ Ca b=1/3 (oC ) GEOT. Na/Li Cl<0.3M (oC ) GEOT. Na/Li Cl>0.3M (oC ) Ca/Na Mg/Na Caex (meq/l) Nadef (meq/l) 336 0.73 236.80 379 14.0 463 15.1 257.0 439.6 411.4 113.5 267.7 1.5 0.2 462.3 12.8 425 0.65 240.18 551 9.0 650 10.5 158.1 407.1 296.5 107.3 257.5 1.2 466.1 4.2 540 1.10 231.06 428 13.2 492 13.2 184.2 486.8 343.0 103.5 251.4 0.9 444.0 -6.8 457 0.63 541.67 617 0.0 726 0.0 137.2 376.8 254.1 120.0 278.2 2.4 1068.0 3.2 384 0.80 215.37 651 0.0 480 13.2 141.2 425.4 280.5 80.5 214.9 0.7 417.9 -191.3 7 270.08 390.1 298.8 399.8 38.6 2.0 539.9 -6.0 23 92.52 391.0 362.9 434.7 10.0 0.5 184.3 3.7 22 45.89 5.0 91.0 2.8 510 1.50 59.22 268 19.0 340 20.4 191.7 506.6 371.8 52.5 171.2 0.3 101.3 35.7 2152 5.85 836.68 350 15.0 368 20.5 131.2 352.1 279.9 143.7 317.2 0.7 0.3 1601.2 -201.5 4 531.24 284.3 241.6 317.5 63.3 4.0 1062.3 -11.1 3 303.42 379.8 333.7 212.4 606.7 -0.0 164 0.33 126.94 661 0.0 491 13.2 210.3 448.9 361.0 60.4 183.5 1.0 0.1 248.4 -80.0 95 0.19 56.10 757 0.0 505 13.0 234.2 388.3 0.7 109.0 -60.9 MEAN: 237.7 395.1 344.0 97.7 242.7 24.2 1.2 obtained by galena-sphalerite pair from cavities in the zebra siderite calculated by the equation of KIYOSU (1973) and FRIEDMAN & O’NEIL (1977). The Δ34Ssulphide-sulphatevs. δ34Ssulphide diagram enabled determination of the δ34S∑S, R = XSO4/XH2S by the equation after OHMOTO (1986). A determined value of +9.2 ‰ V-CDT supports the evolution of Permian sea water by evaporation as the main sulphur source. Sulphur isotope values of sulphates were not affected by thermochemical reduction, it explains a low fugacity of sulfur and small quantity of sulfides including pyrite in the overall area. Some contribution from the decomposition of organically-bound sulphur and oxidation of pyrite from the sedimenary host rocks, dark coloured clas- tics, are not excluded (Fig. 21). 5.7. GEOCHRONOLOGY K/Ar dating K/Ar dating was performed on the following samples: (i) 5 phyllites from the Trnava locality; (ii) 6 phyllites from the Blagaj locality; (iii) 6 phyllites from the Adamuša locality, 4 of them are fragments associated within vein-type siderite mine- ra lization; (iv) a single phyllite sample from the Tomašica lo- cality; (v) single phyllite sample from Jezero locality; (vi) limestone undissolved residuum from the Adamuša locality, and (vii) 9 samples of rhyolite rocks from the Trnava locality. Whole rock phyllite samples (4 samples) from the Trnava locality contain between 1.3 and 3.6 % of potassium and gave an age between 171.3±6.6 and 195.4±7.5 Ma, whereas a single Table 1. Ljubija/Adamuša 22 Vol. 69/1 (4.2 % of potassium) gave an age of 188.7±7.1 and 193.7±7.3 Ma. Two whole rock phyllite samples (1.2 and 4.0 % of potas- sium) gave ages of 290.0±11.0 Ma and 283.4±10.6 Ma, respec- tively. Additional 4 whole rock phyllites associated with vein- type siderite mineralization (0.7 to 3.6 % of K) yielded ages between 200.0±9.0 and 236.0±9.0 Ma. A whole rock phyllite sample from the Tomašica locality contains 1.5 % of K and gave an age of 238.7±9.2 Ma, whereas a whole rock phyllite sample from the Jezero locality (3.9 % of K) yielded an age of 132.9±5.1 Ma. Whole rock analysis of the undissolved residu- um of the limestone of the Adamuša locality (2.1 % of K) gave an age of 220±10.0 Ma. Whole rock rhyolite samples (9 samples) of the Trnava lo- cality contain from 0.1 to 2.0 % potassium with an age range from 56.6±4.3 to 237.0±9.5 Ma. Wide spectrum of data from 56 Ma to 290 Ma on phyllites and volcanics shows different degrees of loss of radiogenic Ar, due to long-term tectonism and associated thermal events in the polyphase metamorphic evolution of the Dinarides (PALINKAŠ & PECSKAY, 1996, unpublished, Fig. 22). The first group (i), (283-290 Ma), belongs to the post-Va- riscan thermal event in Lower Permian time, connected with an incipient intra-continental rifting stage. It corresponds to the post-Variscan ages determined in the Mid-Bosnian Schists Mts. (PAMIĆ et al., 2004). The group (ii) varies widely (175-238 Ma) and represents disturbed ages by the later tectono-thermal events, as indicated by the 40Ar/39Ar dating. The third group (iii) with a Lower Cretaceous overprint (98-132 Ma) is most likely a result of later resetting in a tectonically active zone. It has a regional significance and marks obduction related tectonism and metamorphism, traditionally named the Eoalpine, which started 130 Ma ago (HSÜ, 1989). This Lower Cretaceous over- print is recognized on the Silurian-Devonian metamorphic complex on the Medvednica Mts. ( 110-122 Ma), (BELAK et al., 1996), on the Drina-Ivanjica Palaeozoic block in Serbia (129-139), (MILOVANOVIĆ, 1984), and in the metarhyolites in the Mid-Bosnian Schist Mts. (92-121), (PAMIĆ et al., 2004). The group (iv), younger Palaeocene overprint (56-64 Ma) de- termined on volcanics, corresponds to the Palaeocene early col- lision stage between Africa (Adria) and Euroasia (Tisia-Moe- sia), the cause of the Dinaride uplift in the Eocene. PAMIĆ & PÉCSKAY (1996) reported Late Cretaceous K/Ar ages of 94.3 and 85.4 Ma from basalt and diabase from the northwestern side of the Medvednica Mts. 40Ar/39Ar analysis 40Ar/39Ar analysis is performed on the low potassium white mica concentrate (paragonitic white mica), from phyllite fragments associated with the vein type of mineralization. The white mica concentrate yields a strongly disturbed pattern. The low-energy steps of the age spectrum show signi- ficant excess argon and an age of 340 Ma, whereas high ener- gy steps gave a plateau-type of age at 275 Ma constituting together 96.7 percent of 39Ar (steps 2-4, Fig. 23; BOROJEVIĆ ŠOŠTARIĆ, 2009). 40Ar/39Ar released spectra could be inter- preted in another way. The plateau age of 340 Ma might be an inherited Variscan age (Lower Carboniferous) of the sedi- Figure 19. Temperature of homogenization (Th) vs. salinity diagram for the inclusions in the fluorite from the Žune-Dolinac barite-fluorite vein deposit. The span of Th and salinities reflects the evolution of P-T-X condition during boiling. Table 2. Sulphur isotope data of sulphides and sulphates from the Ljubija ore deposits. Sample Mineralogy δ34S (‰ V-CDT) JS-LJ-100-1 Galena -0.5 JS-LJ-101-1 Pyrite 7.6 JS-LJ-104-1 Sphalerite 0.8 JS-LJ-104-2 Chalcopyrite 2.3 JS-LJ-104-3 Chalcopyrite 1.2 JS-LJ-105-1 Pyrite 6.5 JS-LJ-106-1 Pyrite 8.5 JS-LJ-106-4 Pyrite 6.7 JS-LJ-107-1 Galena -1.3 JS-LJ-107-2 Barite 9.3 JS-LJ-108-1 Galena -0.4 JS-LJ- 109-1 Sphalerite 4.4 JS-LJ-109-2 Barite 9.2 JS-LJ-109-3 Galena 3 JS-LJ-112-1 Sphalerite 0.8 JS-LJ-113-1 Sphalerite 0.4 JS-LJ-113-4 Galena -2.3 JS-LJ-113-5 Chalcopyrite -0.8 mica concentrate (4.2 % of potassium) gave an age of 212.0±8.0 Ma. Whole rock phyllite samples (4 samples) from the Blagaj locality (1.2 to 3.6 % of potassium) gave an age between 214.2±8.3 and 233.1±9.4 Ma, whereas two mica concentrates 23 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) ment, precursor of phyllite, overprinted by a Lower Permian thermal event. A white mica concentrate from the phyllite, sample LJUB 1, from the Palaeozoic Sana-Una Unit yielded a plateau age of 335.1 ± 23.1 Ma comprising 96.8 percent of 39Ar released. The inverse isochrone plots show a slightly disturbed initial 40Ar/36Ar ratio of 322± 27 Ma, and an age of 327±30 Ma, to- gether constituting 100 percent of 39Ar released (BOROJEVIĆ ŠOŠTARIĆ, 2012). 6. ORE GENESIS Genesis of the Ljubija ore deposits was a subject of controversy. The basic interpretation models have two approaches (i) a syn- sedimentary stratiform type with an obscure origin of iron, and the alternative (II) hydrothermal replacement and epigenetic vein type. To solve the dilemma, in the past decades a number of analytical procedures and methodologies have been applied in building a convincing genetic model. There was a number of ambiguities which obscured the solution, and paved the ground for unsupported genetic hypotheses. The objective approach re- quires resolution of the following particularities: textural-struc- tural characteristics, time of formation, source of metal, pressure, temperature and chemistry of the ore forming fluids, alterations, and not least, the metallogenic affiliation to the equivalent de- posits in the frame of plate tectonic divisions and reconstruction of the Dinarides, and the wider area within the Neotethyan do- main. 6.1. TEXTURAL-STRUCTURAL CHARACTERISTICS The Fe mineralisation in the Ljubija ore field comprises strata- bound siderite and ankerite bodies hosted by Carboniferous limestones, and siderite-sulphide veins placed within organic rich shales. PALINKAŠ (1988) recognized three major types of primary iron ore textures: (1) dark massive siderite and ankerite, and (2) zebra siderite composed of dark massive and light sparry siderite bands, and (3) sparry siderite veins hosted clastics (Figs. 3, 4, 5). Ore microscopy and transmitted light microscopy offer a vi- sual observation of metasomatic processes (Figs. 8, 9). The tex- tural type (1) was formed by the metasomatic replacement of dark massive limestone by dark massive siderite. The differences between massive siderite (1) and zebra siderite texture (2) were the result of chemical kinetics controlled by temperature, acidity buffered by the host rocks, and salinity. All these parameters have been reasserted by the research data (PALINKAŠ et al., 2003b; STRMIĆ PALINKAŠ, 2004, 2009; BOROJEVIĆ ŠOŠTARIĆ, 2004). When the dissolution volumetric rate of calcite was equal to the precipitation volumetric rate of siderite, the primary texture was retained, i.e. dark metasomatical Fe-carbonate was precipi- tated. In contrast, when the volumetric rate of dissolution was higher than the rate of precipitation, cavities are formed and the primary texture is lost. Further supply of mineralizing fluid caused crystallization of light sparry siderite directly from solu- tion (STRMIĆ PALINKAŠ, 2004). The genesis of three textural types has been ascertained by the chemistry of metasomatic processes, (STRMIĆ PALINKAŠ, 2004; STRMIĆ PALINKAŠ et al., 2009) through the following contributions: (i) Variations in δ13C values of the barren and mine ralized carbonates suggest the progressive replacement, and depositional character of vein siderite; (ii) The δ18O values of siderite and the calcite vein from dark massive siderite give a value of isotope equilibrium temperature, Tisotope = 224 ºC; (iii) The δ18O values of siderite and quartz pairs from siderite veins give Tisotope = 168 ºC; (iv) The δ34S values of sphalerite and galena pairs from zebra ore give Tisotope = 245 ºC; (v) The δ34S value of barite falls within the range of contemporaneous Permian sea water; (vi) Barren massive limestones have a negative CeN anomaly and negative EuN typical of marine carbonates;(vi) Posi tive EuN in siderite indicates precipitation in a low-tempera- ture environment (<250 ºC) from fluid which received their REE signature during fluid/rock interactions in a high temperature en- vironment. A combination of positive EuN and negative CeN anomalies is inconceivable in sedimentary siderite; (vii) Vein siderite has a negative EuN due to its precipitation from fluids depleted from Eu; (viii) The pristine/phitane ratio higher than 1 Figure 20. A) Diagram showing Na/Cl/Br variation of fluids extracted as leachates from the ore and host minerals. Most of data follow the evaporation trend, and only a few the trend of halite dissolution, the Ljubija/Adamuša ore deposit; B) Diagram Ca access vs. Na deficiency with theoretical trends of fluid evolution. Legend: HDL halite dissolution line; BLF line of basinal fluids; zebra siderite, banded texture; vein mesothermal siderite; dark limestones, footwall of the ore mineralization. 24 Vol. 69/1 Figure 23. The 40Ar/39Ar analyses, performed on the low potassium white mica concentrate from phyllite fragments associated with the vein type of mineralization, yielded two ages, the low energy step of 340 Ma, and a high energy step with a plateau age of 275 Ma (Fig. 23B). The first, Variscan age of 340 Ma, is overprinted by an Early Permian tectono-thermal event dated at 275 Ma. These pairs of ages bear regional significance and are repeated steadily in the neighbouring area of the Sana-Una Palaeozoic, in the Trgovska gora and Petrova gora ore districts hosted by the Carboniferous sediments. 40Ar/39Ar released spectra show Variscan plateau ages at 332.8±3.1 Ma and 342.9±3.3 Ma, overprinted by a thermal event at ca. 265.6±6.2 to 274.2±3.1 Ma, interpreted as a maximum age of the hydrothermal activity (Fig. 23A, BOROJEVIĆ-ŠOŠTARIĆ et al., 2009). in the barren and mineralized samples points to an oxic deposi- tional environment for the host rock carbonates, an inconvenient condition for the synsedimentary deposition of siderite ore. A reducing environment during diagenesis, controlled by indige- nous organic matter, however, is a prerequisite for epigenetic metasomatic sideritization. 6.2. TEMPERATURE AND CHEMISTRY OF FLUIDS Study of fluid inclusions in quartz from three textural siderite types and within the siderite itself from the ore deposit Adamuša/ Ljubija, and fluorite from the fluorite-barite deposit Žune- Dolinac supported by crush-leach analysis and vitrinate reflec- tance, paved the way to substantial information on ore forming fluids, their temperature and composition. The ore forming fluids with highly variable salinities (2-39 wt% NaCl equiv., Adamuša/Ljubija; 5-33.4 wt% NaCl equiv., Žune-Dolinac), are essentially modified sea water derived through different degrees of evaporation in lagoons, up to the point of halite precipitation (the evaporation line on the diagram Na/Cl vs Cl/Br). Boiling phenomena, observed and determined on fluid inclusions, contributed to the variable salinity of fluids, which underwent distillation (boiling evaporation), at the top- most position of the cell, near the land surface. The boiling tem- perature was controlled by hydrostatic pressure at depths of 100- 200 m below the land surface. The hydrothermal solution in fluid inclusions is primarily rep- resented by NaCl-H2O and NaCl-CaCl2±MgCl2-H2O systems. Ca2+ and Mg2+ ions are evidence of the widespread metasomatic replacement of limestones and dolomites by Fe2+ (Caexcess vs. Nadeficiency diagram). The high concentration of Li+ ions in leachates, and the pres- ence of cookeite, (LiAl4(Si3Al)10(OH)8) as an alteration mineral, confirm the engagement of chloride rich evaporitic sea water, responsible for the mobilization of metasomatic Fe2+ from shale, but some proportion comes from leaching of Li-rich mica. The SO4 2- ion, recorded in leachates, was essential for deposition of the ubiquitous barite deposits. In spite of a slight variation, the δ34S values of barite around +9.2%0 V-CDT, the δ34Sbarite value bears witness to Permian sea water as a dominant water supplier in the circulation cell. The minor thermochemical reduction of sulphate was the source of HS- for sulphide deposition. Thermal characteristics of the ore forming fluids are con- firmed by the study of fluid inclusions (Th, 100-275ºC), Na/K ratio in leachates (141-281ºC), vitrinite reflectance (210-260ºC) and stable isotope geothermometers (164-224ºC). This overall range of temperatures could be more specific in a sketch presen- Figure 21. Δ34Ssulphide-sulphate vs. δ34Ssulphide digram for coexisting sul- phates and sulphides. The measured value at +9.2 ‰ V-CDT sug- gests an evaporative-evolved Permian sea water as the main sulphur source. Figure 22. The range of 40Ar/39K values determined on 21 samples of phyllites and 7 samples of volcanics from the Sana-Una Palaeozoic area (PALINKAŠ & PECSKAY, 1996, unpub.). A B 25 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) tation of thermal distribution in the hydrothermal circulation cell (Fig. 24). The shape of the circulation cells, formed over the foci of high heat flow, at the Adamuša/Ljubija deposit, is defined by the posi- tion of isotherms reconstructed by the temperature of mineral formation. The chemical zonation is accompanied by thermal zonation. The highest trapping temperature and salinities are reg- istered at the lower position of the cell, in the quartz of the zebra metasomatic siderite (salinity 35-39 wt% NaCl equiv., Th 215- 275ºC). The lowest temperature and salinity are measured in the quartz in siderite veins in the uppermost part of the cell (salinity 2-9 wt% NaCl equiv., Th 100-250ºC). The plume of heat con- trols the shape and the character of fluids from high salinity bitter brines at deeper parts of the cell, to the diluted aliquots, with lower salinity, supplied by normal sea or meteoric water. The wide range of temperatures suggest mixing of hot-high salinity water FLUID 1 and cold-low salinity waters FLUID 2 (Fig. 13, diagram Th vs. salinity). The Žune-Dolinac barite-fluorite deposit (like the other nu- merous barite deposits in the Ljubija geothermal field) experi- enced intensive boiling due to their near-surface setting. 6.3. TIME OF MINERALIZATION Age determination relied on indirect methods, available during research, (i) 39K/40Ar, (ii) 40Ar/39Ar, and (iii) origin of sulphur in the ore mineralization implied through its isotope signature. The K/Ar blocking temperatures, determined on phyllites, in- dicate four significant thermal events. The group (i), (283-290 Ma), belongs to the post-Variscan thermal event in Lower Permian time, connected with the incipient intra-continental rift- ing stage. The group varies widely (175-238 Ma) and represents disturbed ages by the later tectono-thermal events. The third group (iii) with a Lower Cretaceous overprint (98-132 Ma) is most likely a result of later resetting in a tectonically active zone. The group (iv), younger Palaeocene overprint (56-64 Ma) deter- mined on the volcanics, corresponds to a Palaeocene early colli- sional stage between Africa (Adria) and Eurasia (Tisia-Moesia). The first group (i) on the Carboniferous phyllites is of primordial significance in the polyphase metamorphic history of the Tethys (Fig. 22). (ii) The 40Ar/39Ar analyses, performed on the low po- tassium white mica concentrate from phyllite fragments associ- ated with the vein type of mineralization, yielded two ages, the low energy step of 340 Ma, and a high energy step with a plateau age of 275 Ma. The first, Variscan age of 340 Ma, is overprinted by an Early Permian tectono-thermal event dated at 275 Ma. These pairs of ages bear regional significance and are repeated steadily in the neighbouring area of the Sana-Una Palaeozoic, in the Trgovska gora and Petrova gora ore districts hosted by the Carboniferous sediments. 40Ar-39Ar released spectra show Va- riscan plateau ages at 332.8±3.1 Ma and 342.9±3.3 Ma, over- printed by a thermal event at ca. 265.6±6.2 to 274.2±3.1 Ma, interpreted as a maximum age of the hydrothermal activity (Fig. 23). The Middle Permian age of mineralisation is corroborated by the following arguments: (i) The mineralisation is hosted ex- clusively within Carboniferous to Early Permian units. (ii) Sul- phur isotopes show a Permian seawater signature, while the in- creased bromine content of the leachates points to evaporated seawater not to the evaporites themselves, as a source of sul- phates. (iii) The 40Ar/39Ar spectra recorded thermal overprints at 265.6±6.2 and 274.2±3.1 Ma for Petrova gora and at 298.0±4.2 Ma for Trgovska gora, superimposed exclusively onto the Va- riscan ages of the host rock. 6.4. LJUBIJA GEOTHERMAL FIELD The Ljubija ore deposits were formed within the Ljubija geother- mal field which extends into the Trgovska gora and Petrova gora Palaeozoic terrains. The Ljubija geothermal field deserves the term “geothermal field” by because of the areal extension of its ore deposits of several hundred square kilometres over the Sana- Una Palaeozoic. The Ljubija geothermal field incorporates a huge accumulation of Fe-carbonate, sulphide, barite and fluorite A B Figure 24. Metasomatic-hy- drothermal genetic model of the Ljubija mineral deposits based on inorganic and organic geochemical data. Shape of iso- therms depict local heat foci and fluid flow in a geothermal field. 26 Vol. 69/1 Figure 25. Palinspastic sketch shows the North Hungarian Triassic units, with spe- cial regard to Ladinian palaeogeography (not to scale), KOVÁCS (1984). The sketch depicts advanced rifting in progress toward the Northwest (present geographi- cal orientation), dissecting Pangea into the Gondwanian and Eurasian continental blocks. Early rifting formations and phe- nomena, including Permo-Carboniferous geothermal fields, were covered by newly formed Dinaridic and Moesian carbon- ate platforms,. Tectonic evolution, uplift, napping, thrusting and erosion uncovered their mineral load to the present exposed situation. Abbreviations: R.-M. Lj Ljubi- ja, Tg Trgovska gora, Pg Petrova gora, Sg Samoborska gora, Rud Rudabánya. mineralisation, with almost half a billion tonnes of Fe ore, at the Adamuša/Ljubija, Tomašica, and Omarska ore districts. The chemistry, pressure and temperature of the thermal waters en- riched in Ca, Mg, Na, chloride and bromine, are common in rifting-related fluids elsewhere (e.g., HARDI, 1990; ROW- LAND & SIBSON, 2004; SIMPSON et al., 2015). The general characteristics of the Ljubija geothermal field corresponds in many aspects to the Salton sea geothermal field, an active rifting environment, regarding composition and temperature of Ca rich brines, metaliferous sediments, etc. (CRAIG, 1966; SKINNER et al., 1967). Due to the initial phase of rifting, the crust in the passive mar- gin was thinner than adjacent crust, and geothermal systems de- veloped at high heat flow foci along an elongated rifting zone and fractures controlled convection circulation systems. Here the geothermal water had been circulating to considerable depth (> 1 km), through mostly vertical fractures, to extract the heat from the rocks. SAEMUNDSSON (2009) classified geothermal systems on the basis of geological setting, reservoir temperature and enthal- py: (i) Low-temperature systems with reservoir temperatures at 1 km depth below 150°C; (ii) Medium-temperature systems with reservoir temperature at 1 km depth between 150- 200°C; (iii) High-temperature systems with reservoir temperature at 1 km depth above 200°C, with reservoir fluid enthalpies greater than 800 kJkg-1. The pressure-temperature characteristics of the Ljubija geo- thermal field are closer to the (iii) High temperature system. The Ljubija geothermal field was water dominated, and at places, to varying degrees, vapour dominated. The enthalpy content in the two-phase boiling system in Žune-Dolinac was close to 982 kJkg-1 for the liquid phase and 2877 kJkg-1 for the developing vapour phase (data for the temperature of 245°C and salinity of 33 wt. % NaCl). Carboniferous and Permian formations were cap rocks (to- tal thickness of 600-800 m), a blanketing seal of the geother- mal system and their rock formation were the object of meta- somatic sideritization. The rifting fault zones provided con- duits for fluid flow and heat flow, and hydraulic pressure forces fluids to the surface forming hot springs, fumaroles, etc., in the boiling zone, at places were the temperature and pressure fol- lowed the boiling point curve and where steam and water co- existed. The barite-fluorite vein deposit of Žune/Dolinac is a feeder zone of one of the many hot springs. Thermal gradients calcu- lated on the basis of hot hydrothermal water, issuing on the surface, and colder Permo-carboniferous host rocks are not a convenient place to calculate a regional geothermal gradient. A proper geothermal gradiant, providing the thermal water, is in the aquifer reservoir below the Carboniferous and Permian formations. As initial rifting proceeded, listric fault systems formed and further subsidence resulted in the creation of a Red sea type basin, developed by the formation of the Neo-Tethyan ocean crust. Equivalent types of huge siderite-barite-polysulfide mine ralisations are situated within the similar geotectonic en- vironment, however, with a much more complex tectono-ther- mal history in the course of the Alpine orogeny. The siderite mineralisation with similar characteristics, in low to medium grade metamorphic Variscan basement units, has been studied in the Western Carpathians and Eastern Alps (GRECULA et al.,1995; HURAI et al., 2002, 2008a; RADVANEC et al., 2004; URBAN et al., 2006; HURAI et al., 2008b, b; POHL, 1986; LAUBE et al., 1995; PROCHASKA & HAFELLNER, 1994), EBNER et al. (1999). The origin and age of this mine- ralisation is still under discussion. As a corollary, the Ljubija geothermal field is a herald for the birth of the Tethyan Ocean and the onset of the new Alpine Wilson cycle. 27 Palinkaš et al.: The Ljubija geothermal field: A herald of the Pangea break-up (NW Bosnia and Herzegovina) Reconstruction of the opening scenario which loosely de- fines space, time and related geotectonic events is depicted on the palinspastic sketch of the North Hungarian Triassic units, with special reference to Ladinian palaeogeography (not to scale!), (Fig. 25, KOVÁCS, 1984). The sketch portrays ad- vanced rifting in progress toward the northwest (present geo- graphical orientation) dissecting Pangea into the Gondwana and Eura sian continental blocks. Early rifting formations and Permo-Carboniferous geothermal fields, were covered by newly growing Dinaridic and Moesian carbonate platforms on the opposite sides of divergent, drifting continental margins (PALINKAŠ et al., 2016, this publication). Tectonic evolution, uplift, napping, thrusting and erosion uncovered their mineral load to the present exposed situation. 7. SUMMARY The Ljubija ore deposits are situated within the thick Upper Palaeozoic sequence of the allochthonous Sana-Una Palaeo- zoic complex of the Inner Dinarides. The primary ore occurs as stratabound metasomatic bodies of iron carbonates within Car- boniferous limestones and dolostones, and siderite veins with- in the Carboniferous phyllites and metasandstones. Primary mineralization consists of siderite-ankerite-barite- polysulphides with three textural types, dark massive siderite, zebra siderite, alternation of dark and light siderite bends with sulphide cavities, and open space fillings in the veins. The shape of the cell is defined by isotherms based on mineral for- mation temperature, tentatively. The most influential processes in the formation of chemical components of fluids are metaso- matic sideritization and ankeritization. The ore forming fluids are dominantly NaCl-CaCl2-H2O, with highly variable salinity (0.4 to 39 wt% NaCl equiv.) and Th between 100 and 310ºC. The hydrothermal fluids are a mixture of high-temperature- high-salinity Permian evaporitic sea water, diluted by low- temperature-low-salinity sea or meteoric waters. Boiling of near-surface hydrothermal reservoirs contributed to the high variability of temperature and salinity of the fluids. Sulphur isotopes confirm Permian sea water as the major source of sul- phates (δ34S +9.2 ‰ V-CDT) for barite formation. Thermal reduction of marine sulphates supplies HS- for the precipitation of sulphides, which were deposited out of equilibria, with the exception of the cogenetic pair galena-sphalerite, formed at 245ºC. The temperature of formation determined by oxygen isotopes on calcite-siderite-quartz cogenetic mineral pairs is in the range between 164º to 224ºC. Temperatures of the cation geothermometer (Na/K) matches those obtained from fluid in- clusion, vitrinite reflectance and isotope thermometry. The age determination recorded two prominent tectono- thermal events, Variscan (332.8±3.1 Ma and 342.9±3.3 Ma), overprinted by a thermal post-Variscan event at ca. 265.6±6.2 to 274.2±3.1 Ma, and interpreted as the maximum age of hy- drothermal activity in the Middle Permian. The ages and thermal features coincide well with those in the neighbouring deposits in the Palaeozoic of Trgovska gora and the Petrova gora Mts., its counterparts in space and time, announcing the future break-up of Pangea and the birth of Te- thys (Fig. 26). Acknowledgement This study was mostly supported by the Croatian Ministry of Sciences, Technology and Sports (Projects 119-0982709-1175). We are grateful to Tamara TROSKOT and Darko ŠPANIĆ (INA oil company) for valuable vitrinite reflection analyses, Prof. Ronald J. BAKKER (Montanuniversität, Leoben, Austria) for Figure 26. A simplified genetic model of the Per- mian siderite-barite-polysulphide deposits, Ljubija, Trgovska gora, Petrova gora, Samoborska gora, Bis- tra-Medvednica, presently placed along the Dinaridic carbonate platform, within the Palaeozoic of the In- ner Dinarides. As initial rifting proceeded and listric fault systems formed, further subsidence resulted in the creation of a Red sea type basin, developing into the Tethyan oceanic crust in Late Triassic time. The high heat flow in the early rifting structures created an array of circulating hydrothermal cells. 28 Vol. 69/1 providing access to the Raman spectrometry facilities, to Štefica KAMPIĆ for assistance in the lab work, to Nenad RAKOVIĆ and Zorana SLJEPČEVIĆ (ArcelorMittal, Ljubija mining com- pany) for the field assistance during numerous visits with or without students. 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