Geochemical characteristics of mercurian tetrahedrite, barite and fluorite from the Duboki Vagan, Glumac and Dubrave-Dugi Dol barite deposits, south of Kresevo, Mid-Bosnian Schist Mts.

Headnote

ABSTRACT

The geochemical characteristics of tetrahedrite and barite of the Duboki Vagan barite deposit near the town of Kresevo in the MBSM (Mid-Bosnian Schist Mountains) have been determinated and correlated with the results of previously studied barite, from the adjacent Glumac deposit, and fluorite, from the Dubrave-Dugi Dol barite deposits. The studied tetrahedrite is characterized by a high content of Au (39 ppm) and Ag (>300 ppm), the presence of Co (63.5 ppm), Ni (266.2 ppm) and Cd (313,6 ppm) in the crystal lattice and negative δ^sup 34^S^sub CDT^ values (-11.80[per thousand]). On the plot of its C1 chondrite-normalized REE abundances, a slightly expressed positive Eu anomaly and high HREE concentrations are observed. The high content of SrSO^sub 4^ (2.33 to 3.42 wt.%) in the barite crystal lattice indicates hydrothermal parent solutions. The δ^sup 34^S^sub CDT^ values of the studied barite are +10.40[per thousand], which is typical for Permian seawater and its δ^sup 18^O^sub SMOW^ values range between 15.6 and 17.7[per thousand]. A distinct positive Eu anomaly is shown on the plot of the C1 chondrite- normalized REE abundances in barite. Geochemical characteristics of the studied tetrahedrite and barite of Duboki Vagan are very similar to those of previously investigated Glumac and Dubrave-Dugi Dol barite deposits. The fluorite from the Dubrave-Dugi Dol deposits displays a negative Eu anomaly and its Tb/La and Tb/Ca ratios indicate a quite different origin in relation to barite formation. This is all in the accordance with the possible existence of two different paragenetic types of barite deposits in the MBSM and SEB (Southeastern Bosnia), which signifi- cantly differ in the δ^sup 18^O^sub SMOW^ ranges of their barites and δ^sup 34^S^sub CDT^ values of their sulphides. The first type of barite deposits originated in the Late Variscan phase (Lower Permian). It is characterized by numerous Cu, Fe, Zn, Sb, As, Pb sulphides and Cu-Sb-tetrahedrite without mercury, all having positive δ^sup 34^S^sub CDT^ values (0 to +5 [per thousand]). Early intercontinental rifting took place between the uppermost Permian and Lower Triassic and enabled, in a great number of ba rite deposits, (especially in the MBSM), remobilization and partial fluidization of their Fe, Cu, Zn, Sb and Pb sulphides which reacted with ascended mercury, sulphur and fluorine rich mantle fluids and resulted in the formation of Hgtetrahedrite and octahedral fluorite. These processes caused the occurrence of the second paragenetic type of barite deposit with Hg-tetrahedrite as the main ore mineral, but characterized by strongly negative δ^sup 34^S^sub CDT^ values.

Keywords: Paleozoic, Mid-Bosnia, Hg-tetrahedrite, barite, fluorite, stable isotopes (S, C and O), trace elements, REE, genesis

1. INTRODUCTION

In the Mid-Bosnian Schist Mountains (MBSM) and Southeastern Bosnia (SEB) two completely different paragenetic types of barite deposits occur. Small amounts (<10%) of diverse sulphides (pyrite, chalcopyrite, sphalerite, galena, arsenopyrite and tetrahedrite without mercur) occur with barite in the first type. The second type of barite deposit is almost monosulphidic containing only Hg-tetrahedrite. There is a remarkable geochemical difference between the sulphides of these two types of barite deposits. All sulphides of the first type are characterized by positive δ^sup 34^S^sub CDT^ values (0 to +5[per thousand]), whereas the Hg-tetrahedrite of the second type contains negative δ^sup 34^S^sub CDT^ values (-4.95 to -15.40[per thousand]). Additionally, JURKOVIC et al. (2010), found that the δ^sup 18^O^sub SMOW^ values in barite of the first polysulphide type are significantly lower (+14.2[per thousand] to +15.6[per thousand]) than the δ^sup 18^O^sub SMOW^ values in barite from the second monosulphidic Hg-tetrahedrite type (+15.8[per thousand] to +22.4[per thousand]). Such differences can be explained by lower temperature and lower salinity of mineralisation in the first type of barite deposits JURKOVIC et al. (2010). These authors state that the first polysulphide paragenetic type of barite deposits originated in Late Variscan phase (Lower Permian). The second one originated in Post Variscan/Early Eoalpine phase due to the exposure of the first barite deposit type to the impact of early intercontinental rifting (JUR KOVIC et al., 2010).

The aim of this work is to investigate the geochemical characteristics of the tetrahedrite and barite of the Duboki Vagan barite deposit near Kresevo in the MBSM, correlate them with the results of previously studied barite from the adjacent Glumac deposit and fluorite from the Dubrave-Dugi Dol barite deposits. In addition a broad comparison of these results with geochemical characteristics of the other barite deposits in the MBSM and SEB will be made.

2. GEOLOGY AND PARAGENESIS OF THE BARITE DEPOSITS

2.1. Geology

The Duboki Vagan, Glumac and Dubrave-Dugi Dol barite deposits occur in the area which surrounds the town of Krese vo and belongs to the Mid-Bosnian Schist Mountains (MBSM). According to JOVANOVIC et al. (1977, 1978), rocks of Palaeozoic and Triassic age have been recognized in this area. The lowermost part of the Palaeozoic sequences includes chlorite and muscovite schists, phyllites and argillaceous schists, quartzites and lidites. The overlying dolomites, dolomitic limestones and marbles are found to be Devonian in age (SOFILJ et al., 1980). Magmatic rocks occur as porphyrites forming sills within chlorite and muscovite schists, and as quartz porphyry and keratophyre extrusions being situated on the verge of the Devonian carbonate complex (JURKOVIC, 1987). The youngest Palaeozoic sediments consist of conglomerates, sandstones, phyllites with Permian flora and brecciated limestones (JURKOVIC, 1987). The Lower Triassic is represented by sandstones, clay-like schists, marls and rare limestones, while the Middle Triassic is composed of dolomites and limestones. The lower Ladinian horizons consist of sandstones, hornstones, marls, claylike schists and rare limestones, whereas limestones dominate in upper Ladinian horizons (JURKOVIC, 1987). The geological relationships between the Lower Palaeozoic metamorphic complex and the overlying (<300 m thick) carbonate complex are not clear. The occurrence of barite deposits is exclusively related to the Upper Silurian - Devonian metaclastites and dolomites (Fig. 1).

2.2. Duboki Vagan

The northern border of the Duboki Vagan ore deposit runs 1 km south of the town of Kresevo and its southern limit is 4 km south of Kresevo (Fig. 1). The Duboki Vagan lies at absolute altitudes of +800 to +1000 m. Barite is the main ore mineral (50-75% of the ore mass), while pyrite and Hg-tetrahedrite (2-3%) are subordinate ore minerals. Quartz is the main gangue mineral (25-33% of the ore mass), followed by subordinate siderite (which is strongly oxidized into goethite). Octahedral fluorite is an accessory mineral. The deposit is hosted by the Devonian dolomite, intruded by a large mass of metarhyolite (1-2 km2) which crystallized from an S-type granitoid magma (JURKOVIC et al., 2010).

The Duboki Vagan deposit lies in a large, 20 m deep karstified depression. The bottom of the depression is filled with rubble and blocks of siliceous barite which represented gangue from an earlier time. Part of this material comes from mining operations, but part is the residue leftby the weathering and leaching out of the ore-bearing Devonian dolomite. The ancient miners removed only cinnabar, which was necessary for the amalgamation of gold from Hg-tetrahedrite, and limonite used in the production of iron.

In recent times the old dumps and elluvial deposits have been worked over and barite recovered. This clearing up has afforded a better view of the morphology of the Duboki Vagan barite deposit. The ore bodies are irregular seams running NW-SE, 1-1.5 m thick, dipping towards the NE, but there are also satellite barite veins. Recently, MIKO performed a quantitative chemical analysis of one Hg-tetrahedrite sample from the Duboki Vagan deposit (JURKOVIC & MIKO, 1997) which determined the weight % composition of: 37.53 Cu; 1.09 Fe; 4.69 Zn; 0.129 Ag; 2.45 Hg; 1.41 As; 24.25 Sb; 0.20 Bi; 25.03 Ws; 154.50 ppm Au (Σ = 97.70 wt.%).

2.3. Dubrave-Dugi Dol

Dubrave-Dugi Dol barite deposits are located ~ 1 km southeast of Meduvrsje summit (+1195 m) and 3 km southeast of Kresevo. According to JURKOVIC & MIKO (1997), the ore is hosted in dolomite of Devonian age and occurs as irregular nests, lense-shaped veins, networks of veinlets or as breccias in tectonically dislocated dolomites. These authors also noted significant allochtonous residual barite deposits on a karstified dolomite relief. A detailed description of the mineral paragenesis was given by JURKOVIC (1987). He pointed out that the main mineral is barite, Hg-tetrahedrite is the most frequent sulphide at 1-5 wt.%, whereas pyrite, chalcopyrite I and II, and two unidentified copper sulphosalts, colloform pyrite and goethite are accessories. Hg-tetrahedrite replaces barite grains along margins and fine fissures (JURKOVIC, 1987). Quartz I and II occur as gangue minerals, as does transparent fluorite, being violet or colourless, and scarce leaves of sericite and rutile (JURKOVIC, 1987). Quantitative chemical analyses of the Hg-tetrahedrite sample from the Dubrave-Dugi Dol ore deposits, performed by MIKO (JURKOVIC & MIKO, 1997), is expressed (wt%) as: 40.62 Cu; 2.63 Fe; 3.81 Zn; 0.29 Ag; 0.33 Hg; 1.98 As; 25.44 Sb; 0.06 Bi; 24.78 S; 8.30 ppm Au (Σ = 99.94 wt.%).

2.4. Glumac

The Glumac barite deposits are situated at elevations of 800 to 920 metres above sea level on the northern side of Me duvrsje mountain and ~1 km south of Kresevo. Ore bodies occur in different forms (nests, veins, irregular bodies, ore breccias), and are usually very irregular (JURKOVIC, 1987). The main mineral is barite, whereas calcite, ankerite, fluorite, neodolomite, Hg-tetrahedrite, pyrite and quartz are subordinate (JURKOVIC, 1987). Chemical analysis of the Hgtetrahedrite sample from Glumac-Vidici location, which is a part of Glumac barite occurrences, indicated the following composition (wt%): 40.26 Cu; 4.15 Fe; 1.22 Zn; 0.20 Ag; 1.83 Hg; 2.73 As; 24.89 Sb; trace Bi; 24.22 S; 0.20 LOI; 13.40 ppm Au, Σ = 99.70 wt.% (JURKOVIC, 1987).

3. RESEARCH HISTORY

The first data on ore deposits and mining works in the area of Duboki Vagan come from WOLF (1847). These deposits were later investigated by CONRAD (1870), HERBICH (1880, 1880a), VOGT (1880), WALTER (1887), KATZER (1907), JURKOVIC et al. (1951), JURKOVIC (1956, 1958), JEREMIC (1963), MIKOLJI (1969), JOVANOVIC et al. (1977), JURKOVIC (1987, 1988), JURKOVIC et al. (1997) and JURKOVIC & MIKO (1997).

JURKOVIC (1956, 1988) produced the first detailed ore paragenesis from the Duboki Vagan deposit and identified the genetic position of this type of ore deposit in the MBSM. He established hypogenic and hypergenic parageneses. The hypogenic paragenesis includes barite, quartz I, siderite, pyrite, ankerite, Hg-tetrahedrite, sericite, kaolinite (?), fluorite and quartz II. The hypergenic paragenesis consists of goethite, lepidocrocite, "basic sulphates", cinnabar, malachite, azurite, elemental gold, manganomelane, pyrolusite and chal cedony.

Examination of the waste heaps and elluvial material has revealed that barite is the main mineral, with significant quantities of quartz, lesser amounts of pyrite, significantly less Hg-tetrahedrite (exploited by Roman and medieval miners), and a considerable quantity of Au-Ag-bearing limonite.

KATZER (1907) determined the approximate relationship of the main minerals: 40.2% barite, 32.6% quartz, 2.4% tetrahedrite, 0.8% Cu and 24.8% soluble matter what is equal 100.8% in total.

JURKOVIC et al. (1997) presented the first geochemical data of barite and tetrahedrite from the Duboki Vagan barite deposit (see Tables 1 and 3).

4. ANALYTICAL METHODS

The quantitative chemical analysis of Hg-tetrahedrite (DVAGT sample) was performed by Acme Analytical Laboratories, Vancouver Ltd., Canada (Table 1). The trace element content of Hg-tetrahedrite (D-VAGT sample) and barites (VAG and DUV samples) was analysed by inductively coupled plasma (ICP) mass spectrometry in the same laboratory (Tables 2 and 3).

The isotope composition of sulphur in the Hg-tetrahedrite (D-VAGT), oxygen in barite (VAG) and sulphur and oxygen in barite (DUV) were determined in the Stable Isotope Laboratory of the University of Laussane, Swiss, using a Finnigan Mat Facility (Table 4).

The chemical composition of Hg-tetrahedrite from the Duboki Vagan barite deposit was determined by Slobodan MIKO (in JURKOVIC & MIKO, 1997) by atomic absorption spectrometry (AAS) and by ICF-AES after Br-HCl digestion (Table 1).

Two clear fluorite crystals from the Dubrave-Dugi Dol barite deposits were analysed 15 years ago by INAA (Instrumental Neutron Activation Analysis) in the Institute for Petrology and Geochemistry, Karlsruhe University, Germany (PALINKAS & JURKOVIC, 1994).

5. RESULTS

5.1. Hg-tetrahedrite

The analysed Hg-tetrahedrite (sample D-VAGT) from Duboki Vagan was very fine-grained, densely dispersed in the gangue consisting of barite, quartz and calcite. Tetrahedrite grains were carefully handpicked under a binocular microscope. The chemical analysis revealed that it is a mercurybearing Cu-Sb-Zn tetrahedrite, strongly weathered, containing ~ 2.73 wt.% of mechanically admixed barite, (which has 3.425 wt.% SrSO^sub 4^ built into its crystal lattice), calcite and galena (Table 1). Co (63.5 ppm), Ni (266.2 ppm) and Cd (313.6 ppm) were detected in the crystal lattice of the tetrahedrite for the first time in the MBSM (Table 1). These elements, together with Bi, W, Sn and Se, are constituent elements in the tetrahedrite crystal lattice (DUDA et al., 1987). Their concentrations so far in analysed barite samples, (7 from the MBSM and 6 from the SEB), were mostly below minimal detection limits (MDL) and only rarely around MDL. This suggests that the presence of admixed barite in the analysed sample could only inconsiderably influence the abundance and distribution of trace elements in the Hg-tetrahedrite.

Very high values of Au (39 ppm) and Ag (>300 ppm) were found in this tetrahedrite (Table 1).

Standard trace element analysis including 22 elements shows the presence of only 10 elements (Rb, Ta, U, Zr, Y, Mo, Pb, Bi, Sr and Ba) in tetrahedrite, while 12 of them (Be, Sc, Cs, Ga, Hf, Nb, Sn, Th, V, W, Tl and Se) were below MDL (Table 2).

The total sum of the rare earth elements (REE) in the studied tetrahedrite is only 15.03 ppm although all 14 REE were analysed (Table 3). La shows by far the highest concentration (10.6 ppm) and the ratios of LaN/YbN (27.11) and ΣLREE / ΣHREE (5.530) indicate enrichment of the total LREE against the total HREE. But, excluding La, the LREEN are depleted with regard to the HREEN as clearly shown in the plot of REE normalized to CI chondrite values (SUN & McDONOUGH, 1989) presented in Fig. 2. The REE pattern is characterized by a pronounced positive Eu anomaly (Eu/ Eu* = 2.48) and expressed as a negative Ce anomaly (Ce/ Ce* = 0.220).

The δ^sup 34^S^sub CDT^ value of the investigated tetrahedrite sample is strongly negative: -11.8[per thousand]. (Table 4).

5.2. Barite

Table 2 presents the values of 30 analysed trace elements of both barite samples (VAG and DUV) taken from the Duboki Vagan barite deposit.

The group of elements between Be and Y consist of 17 elements but only Ni, Hf, Ta, W and Y were detected in both barite samples. Additionally, Ga, U and Zr were also found in the VAG sample. The values of 8 other trace elements of this group (Be, Co, Sc, Cs, Nb, Sn, Thand V) were below the MDL. The total content of the Be-Y trace element group is very low in both barite samples (<24.8 ppm in the VAG sample and <16.2 ppm in the DUV sample).

In the second group of 13 trace elements between Mo and Se only 5, (Cu, Zn, As, Sb and Hg) were detected in analyses of both barite samples. Pb and Tl were only found in the VAG sample, while Au (0.9 ppb) is present only in the DUV sample. There were 5 trace elements (Mo, Cd, Bi, Ag and Se) below the MDL. The total sum of the trace elements of the Mo-Se group in the VAG sample is <102.41 ppm where As (87.8 ppm) dominates. In the DUV sample the total sum of the same elements is <84.58 ppm, but here Cu (66.0 ppm) dominates.

The analysed REE in barite are characterized by extremely low values: 7.77 ppm in total in the VAG sample and 7.98 ppm in total in the DUV sample (Table 3). The LaN/YbN ratio in the VAG sample corresponds to 7.18, and the ΣLREE / ΣHREE ratio is 0.63, whereas in the DUV sample the same ratios are 47.03 and 1.58 respectively. The values for Nd and Sm in both samples, and also the value of Dy in the DUV sample, were below the MDL. Therefore the values of the Eu anomaly (Eu/Eu*) could not be calculated. However, it is obvious from the plot of the REE pattern normalized to CI chondrite (SUN & McDONOUGH, 1989) that both samples have pronounced positive Eu anomalies because of the extremely low concentration of Sm (Fig. 3). The expressed negative Ce/Ce* anomaly is visible in both samples (where Ce/Ce* = 0.220 in the VAG sample and 0.440 in the DUV sample).

The wt.% of SrSO^sub 4^ in barite varies in the VAG sample from 2.51 to 3.42 (thin fine grained and thick tabular coarse grained habits of barite crystals of the same sample) and in DUV sample equates to 2.33 (Table 4).

The δ^sup 34^S^sub CDT^ value of barite (DUV sample) is +10.4[per thousand], while the δ^sup 18^O^sub SMOW^ values of barite in the VAG and DUV samples are +15.6 and +17.3[per thousand] respectively (Table 4).

6. DISCUSSION

In this section, these results will be compared with those from previously published papers concerning fluid inclusion studies (PALINKAS, 1988; PALINKAS & JURKOVIC, 1994), sulphur, carbon and oxygen isotope compositions (SIFTAR, 1988; JURKOVIC et al., 1997; JURKOVIC & PALINKAS, 2002; JURKOVIC et al., 2010) and REE analysis (PALINKAS & JURKOVIC, 1994; JURKOVIC et al., 2010) in barite deposits of the MBSM and SEB.

6.1. Hg-tetrahedrite

Hg-tetrahedrite from the Duboki Vagan and Dubrave-Dugi Dol barite deposits is mercury-bearing Cu-Sb-Zn tetrahedrite, characterized by strongly negative δ^sup 34^S^sub CDT^ values (Table 4). Similar δ^sup 34^S^sub CDT^ values (-12,82; -10,18; -7.91; -9.50; -10.69; -9.68; -12.77; -11.00; -12.40; -10.92; -6.96; -11.43; -5.50; -10.91; -8.20; -8.79; -15.40; -13.74 [per thousand]) corresponding to an average of -10.49 [per thousand] have been found in all studied samples of Hg-tetrahedrite in the MBSM (JURKOVIC et al., 1997). In the SEB, only one Hg-tetrahedrite has been analyzed (Focanska Jabuka) and its δ^sup 34^S^sub CDT^ value equates to -4.95[per thousand] (HALAMIC et al., 1987; JURKOVIC et al., 2010).

Very high values for gold and silver were determined in the studied Hg-tetrahedrite, where 39 ppm Au and >300 ppm Ag is a typical, genetically very important characteristic of all MBSM Hg-tetrahedrites (JURKOVIC et al., 1997; JURKOVIC et al., 2010). In a tetrahedrite sample from the Duboki Vagan deposit analysed earlier (JURKOVIC et al., 1997), 1290 ppm Ag was obtained (Table 1). Comparing the analyses of both Duboki Vagan tetrahedrite samples, (the first analysed in 1997 and the second from the present study), it is obvious that they are very similar in Cu, Fe, Zn and As values. The analysis performed here demonstrates that Sb, Hg and S are the most rapid weathering components of Hgtetrahedrite (Table 1).

The analysed tetrahedrite displays the pronounced positive Eu anomaly (Eu/Eu* = 2.480). According to BAU (1991), BILAL (1991) and BAU & MÖLLER (1992) such a positive Eu anomaly indicates REE mobilisation by a F-, OH- and CO3 2-fluid in a high-temperature regime. Such regimes have already been proven in the MBSM by PALINKAS & JURKOVIC (1994), JURKOVIC & PALINKAS (2002) and JURKOVIC et al. (2010). The Eu3+/Eu2+ ratio in aqueous solutions depends on pressure, pH and REE speciation, but the most important parameter is temperature (SVJERENSKY, 1984; WOOD, 1990, 1990a; BAU, 1991; HENDERSON, 1984, 1996; GIERÉ, 1996). In natural aqueous systems the occurrences of Eu anomalies are due to the redox reaction: 2Eu3+ + 2OH- = 2Eu2+ + H2O + 0.5O2 (BAU & MÖLLER, 1992).

In general, negative Ce anomalies are characterized by oxidizing conditions. A negative Ce anomaly appears to be a function of O2 and pH, but is more sensitive to pH than to O2. In natural aqueous systems, the occurrences of Ce anomalies are due to the redox reaction: 2Ce3+ + 0.5O2 + 3H2O = 2CeO2 + 6H+ (BAU & MÖLLER, 1992). The generation of Ce anomalies in a high-temperature environment seems unlikely, because with increasing temperature, the Ce4+/Ce3+ redox equilibrium shifts toward higher fO2. According to WOOD (1990, 1990a), with increasing temperature both the Ce4+/Ce3+ ratio and the Ce complex formation constants increase.

6.2. Barite

The SrSO^sub 4^ content in the barite crystal lattice ranges between 2.33 and 3.42 wt.%. The SrSO^sub 4^ contents of two barite samples obtained from the Duboki Vagan deposit by SIFTAR (1988) and JURKOVIC et al. (1997) were 4.4 and 3.6 wt.%. Barite from the Glumac deposit (K-GLU sample) contained 3.03 wt.% (JURKOVIC et al., 2010), while barite from the Dubrave-Dugi Dol barite deposits has 4.4 and 6.1 wt.% SrSO^sub 4^, and barite from the Glumac-Vidici deposit is composed of 6.60 and 5.70 wt.% SrSO^sub 4^ (JURKOVIC et al., 1997) (Table 4). Such SrSO^sub 4^ values in analysed barites are in accordance with the other 108 previously analysed barite samples from the MBSM, which contain on average 4.22 wt.% SrSO^sub 4^ and are of hydrothermal origin (JURKOVIC & PALINKAS, 1999).

So far, only one REE analysis was performed on the MBSM barites, which was the analysis of the K-GLU sample from the Glumac barite (JURKOVIC et al., 2010). The two new REE analyses performed here on the Duboki Vagan barite samples (VAG and DUV) produced almost identical results, despite the fact that there are small differences in mineral paragenesis.

It has to be stressed that the δ^sup 34^S^sub CDT^ value obtained from the analyzed barite (+10.40[per thousand]) corresponds well with earlier published data of δ^sup 34^S^sub CDT^ values in barite (+10.11[per thousand] on average) and is typical for Permian seawater (Table 4).

The analyzed δ^sup 18^O^sub SMOW^ values (n=3) in the barites of Duboki Vagan (+15.6 and +17.3[per thousand]) together with the previously published δ^sup 18^O^sub SMOW^ value (19.70[per thousand]) in the barite of Glumac (JURKOVIC et al., 2010) illustrate that heightened δ^sup 18^O^sub SMOW^ values are typical for Hg-tetrahedrite and octahedral fluorite-bearing barite deposits located in the MBSM (JURKOVIC et al., 2010).

6.3. Fluorite

In order to compare the REE distribution pattern in barite and tetrahedrite analysed here with those in fluorite published by PALINKAS & JURKOVIC (1994) in the Dubrave- Dugi Dol barite deposits, the plot of REE distribution in fluorite normalized to CI chondrite is shown in Fig. 4.

The fluorite crystals (DD-FA and DD-FB) studied by PALINKAS & JURKOVIC (1994), show extremely low REE values of 0.427 and 0.406 ppm respectively. Such fluorites, with a total REE content of about only half that of chondrites, were reported by MÖLLER & MORTEANI (1983) and EPPINGER & CLOOS (1990) from limestones in the Alps, Spain, Morrocco and the USA. MÖLLER & MORTEANI (1983) maintain that these fluorites have been formed under hypersaline conditions or in evaporating basins. SCHNEIDER et al. (1975), investigating fluorite in the Northern Calcareous Alps, also reported extremely low total REE values of 0.17, 0.57 and 0.72 ppm.

The LaN/YbN ratios of the fluorite samples from the Dubrave- Dugi Dol barite deposits (0.112 and 0.139 respectively), reflect an enrichment of the HREE over LREE (Table 4, Fig. 4). According to EKAMBARAN et al. (1986), and EPPINGER & CLOOS (1990), such a REE pattern indicates the late-stage formation of fluorites.

The formation of barite and fluorite took place under opposing environmental conditions. The Ce anomalies, although less pronounced, are also of opposite character.

The increased Sm values and decreased Tm values in the TmN/SmN ratios are, according to BOWERS & HELGESON (1983) and WENDLANDT & HARRISON (1979), usual for fluids supersaturated with respect to CO2 and halides.

SCHNEIDER et al. (1975, 1977), and MÖLLER et al. (1976), distinguish fluorite of hydrothermal and sedimentary origin, on the basis of the Tb/Ca atom ratio and the TbN/LaN ratios. TbN/LaN-Tb/Ca ratios for the fluorites from the Dubrave- Dugi Dol barite deposits (PALINKAS & JURKOVIC, 1994), plot into the "sedimentary field" according to SCHNEIDER et al. (1975, 1977). In contrast, barites, as evidenced by their 87Sr/86Sr ratios are of hydrothermal origin. These data support the idea that barite on the one hand, and Hg-tetrahedrite (±octahedral fluorite) on the other, have been formed at different times and in dissimilar environments. A Tb/La ratio >1.0 indicates late stage formation from a mineralization solution. The enrichment of the MREE and HREE relative to the LREE may have been due to the formation of their stable F- and CO3 2- complexes.

The fluid inclusion study of fluorite suggets a very high homogenization temperature (Th=250-330°C) with noticeable evidence of boiling and high salinity, (over 20 wt.% NaCl equivalent). Massive decrepitation started above 330°C (PALINKAS & JURKOVIC, 1994). In the fluorite-barite deposit of Zune, Ljubija, NW Bosnia, fluid inclusions in fluorites distinguish even clear boiling processes and high salinity (PALINKAS, 1988).

6.4. Origin of barite deposits in the MBSM and SEB

According to JURKOVIC et al. (2010), two paragenetic types of barite deposits have been formed in the MBSM and SEB during two mineralization phases.

The first, (older) phase, took place during the early Permian (Cisuralian), and produced veiny and metasomatic barite deposits with subordinate or scarce Fe, Cu, Zn, Pb and Sb sulphides and sulphosalts. These had positive δ^sup 34^S^sub CDT^ values (±0 to +5[per thousand]), with some siderite and quartz as gangue minerals. This paragenetic type of barite deposits formed throughout the MBSM and also in the Praca-Foca region of the SEB, and in the Jajce-Jezero region (the outermost NNW part of the MBSM). The best example of this type of barite deposit is the thoroughly studied Trosnik ore deposit near Fojnica (MBSM), which formed as irregular metasomatic bodies and veins within the Lower Palaeozoic dolomite (JURKOVIC, 1958; JURKOVIC et al., 1997). Quartz, siderite and barite are the main gangue minerals. Pyrite and chalcopyrite are the main ore minerals, whereas tetrahedrite is subordinate. All sulphides are characterized by positive δ^sup 34^S^sub CDT^ values. Three tetrahedrite samples from the Trosnik ore deposit produced +3.24[per thousand] and +3.73[per thousand] (KUBAT et al., 1979/80) and +4.00[per thousand] values (JURKOVIC et al., 2010). Tetrahedrite from the Trosnik deposit contains only traces of mercury (<0.20% and 0.03% according to JURKOVIC et al., 1997), and is formed by hydrothermal fluid from the same sulphur source, as for pyrite and chalcopyrite in the same paragenesis. This fact indicates that the Trosnik ore deposit has suffered a negligible overprint during a later phase.

The second (younger) mineralization phase took place at the end of the Permian (Permian-Triassic boundary), when Early Intracontinental Rifting started. This period was characterized by heating, dilatation and fracturing of the greater part of the MBSM, enabling the rise of mercury, fluorine and H2S from the upper mantle. KARAMATA et al. (1995), published the highest concentration of mercury in the Dinarides which occurred in the Lower and Middle Triassic. The sulphides and sulphosalts formed during the first mineralization phase were regenerated, remobilized, partly and/or completely fluidized and reacted with ascending mercury and sulphur from the new source. These processes led to formation of the only Hg-tetrahedrite characterized by negative δ^sup 34^S^sub CDT^ values, ranging between -4.95[per thousand] and -15.4[per thousand] and also of high-temperature octahedral fluorite. The rifting overprint (impact metasomatism) occurred very irregularly and with very differing intensity in various parts of the MBSM, SEB and Jajce-Jezero areas. The most strongly affected areas were probably fault zones of the first and second order, and zones warmed by magmatic eruptions. The most intensive processes and overprinting took place in the Rostovo, Gornji Vakuf and Kresevo areas, whereas a very weak overprint occurred in SE Bosnia.

Barite formed during the first mineralization phase underwent strong heating and a change of pressure and f(O2) in the environment during the later second phase. These events are reflected in the shiftof δ^sup 18^O^sub SMOW^ values toward higher values, and δ^sup 34^S^sub CDT^ values toward lower values in barite (JURKOVIC et al., 2010). Sulphide-bearing barites from SEB which are weakly overprinted, and have δ^sup 18^O^sub SMOW^ values within a narrow range (+14.6[per thousand] to +15.6[per thousand]), whereas barite samples with Hg-tetrahedrite and fluorite from the MBSM, reveal higher δ^sup 18^O^sub SMOW^ values ranging from +15.6 to +22.4[per thousand]. The sulphur isotopes (δ^sup 34^S^sub CDT^) in the barites from the SEB span a range from +11.6 to +17.7[per thousand] (mean +16.4[per thousand]). Barites from the MBSM also display a narrow range of δ^sup 34^S^sub CDT^ values between +10.1[per thousand] to +16.8[per thousand], but with a significantly lower mean value of +11.8[per thousand] (JURKOVIC et al., 2010). The most pronounced result is a very expressive positive Eu anomaly in all the overprinted barite samples, which suggests a high-temperature mineralizing fluid.

In the Focanska Jabuka deposit (SEB), two different mineralization phases are very clearly distinguished in time. In the older (Lower Permian) phase, barite, quartz, siderite deposits formed with pyrite, chalcopyrite and galena ore minerals KUBAT et al. (1979/1980) found that the δ^sup 34^S^sub CDT^ values of sulphides are +2.80[per thousand] in pyrite, +2.49[per thousand] in chalcopyrite and +3.04[per thousand] in galena. JURKOVIC et al. (2010) determined δ^sup 34^S^sub CDT^ (+17.7%o) and δ^sup 18^O^sub SMOW^ (+15.1[per thousand]) values in barite. The ore body is transected by a younger barite vein containing even younger Hg-tetrahedrite veinlets characterized by a strongly negative δ^sup 34^S^sub CDT^ value -4.95[per thousand] in a later mineralization phase (HALAMIC et al., 1987).

7. CONCLUSION

A broad comparison of geochemical data was undertaken of barite deposits associated with subordinate or scarce Fe, Cu, Zn, As and Sb sulphides and sulphosalts, characterized by a positive δ^sup 34^S^sub CDT^ value (±0 to +5[per thousand]) with barite deposits where Hg-tetrahedrite, as the only sulphide mineral, was characterized by negative δ^sup 34^S^sub CDT^ values (-4.95 to -15.4[per thousand]) and which is locally associated with high-temperature octahedral fluorite.

The following facts and data were established as a result:

1) Both paragenetic barite types are contemporaneous and have an epigenetic hydrothermal origin. They also share almost the same 87Sr/86Sr ratio, (the difference is only 0.0041), and very similar REE contents (on average 7.1 and 8.3 ppm respectively). The most pronounced difference between the two paragenetic types is observed in the oxygen isotopic com position of the barites. Polysulphide-bearing barites show a δ^sup 18^O^sub SMOW^ value within a narrow range (+14.6[per thousand] to +15.6[per thousand]), whereas Hg-tetrahedrite bearing barites have δ^sup 18^O^sub SMOW^ values ranging from +15.6 to +22.4[per thousand]. Differences in the sulphur isotope composition have also been noted, but are inexplicable.

2) A new sulphur source was vital for formation of the Hg-tetrahedrite (schwazite). Most probably, it was H2S that ascended from the upper mantle during early intercontinental rifting and/or organic sulphur being formed in the ores and rocks of completely different sedimentary environments.

3) The octahedral, high temperature fluorite occurs only in the Hg-tetrahedrite-bearing barite deposits. It is characterized by extremely low REE contents, a low LaN/YbN ratio indicating a very distinct enrichment of HREE and late stage formation of fluorite.

4) A very low REE (0.4 to 0.45 ppm) content indicates the formation of fluorite under hypersaline conditions or in evaporating basin. Increased values for Sm and decreased values for Tm in the SmN/TmN ratios, characterize fluids supersaturated with respect to CO2 and halides.

5) TbN/LaN-Tb/Ca atom ratios of fluorites from the Dubrave- Dugi Dol barite deposits plot in the sedimentary field of SCHNEIDER et al. (1975, 1977), while all barites have a hydrothermal origin. This indicates great differences in the timing and environmental circumstances of barite and fluorite formation.

6) All the described events are effects of the early intercontinental rifting which took place between the uppermost Permian and Lower Triassic. Concerning the strength and intensity of this geological event, it affected separate parts of the MBSM and SEB in very different ways. The most important event was the ascension of mercury, fluorine, boron and sulphur from the upper mantle, and very strong heating and tectonization. These circumstances enabled remobilization and partial fluidization of primary Fe, Cu, Zn, Sb and Pb sulphides and their reaction with the ascended mercury and sulphur, followed by formation of octahedral fluorite, tourmalinization and large, local masses of calcite. In a single case (Focanska Jabuka) a new barite body was formed in this younger phase containing one even younger Hg-tetrahedrite vein, characterized by a strongly negative δ^sup 34^S^sub CDT^ value -4.95[per thousand].

7) The Duboki Vagan barite deposit, together with in this work compared the Glumac and Dubrave-Dugi Dol barite deposits originated in the Late Variscan (Lower Permian). Early intercontinental rifting in the Post Variscan (Early Eoalpine phase), triggered processes that caused the shiftof barite δ^sup 18^O^sub SMOW^ values, remobilization and partial fluidization of primary polysulphides and formation of Hg- tetrahedrite as the only ore mineral with octahedral fluorite.

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Manuscript received July 02, 2010

Revised manuscript accepted December 15, 2010

Available online February 22, 2011