Cobalt , nickel , tungsten , cadmium , selenium , silver and gold-bearing mercurian tetrahedrite from the Saski Rad barite – siderite deposit in the Mid-Bosnian Schist Mts .

In the Saski Rad barite-siderite ore deposit, Hg-tetrahedrite is the main ore mineral, pyrite and some others are only accessories. Two tetrahedrite samples (fresh and weathered) have been analysed in detail: major and minor components, constituent trace elements, REE, and δSCDT values. The following microconstituents have been detected: Ni 71 ppm (in fresh sample) and 70 ppm (in weathered sample); Co 113 and 90 ppm; Cd 27 and 20 ppm; W 20 and 5 ppm, Bi 2500 and 1613 ppm; Se >100 and 72 ppm and Au 11 and 9 ppm. These values have been compared with the only currently available analysis of Hg-tetrahedrite from the Duboki Vagan near Kreševo in the Mid-Bosnian Schist Mts. (MBSM) carried out by JURKOVIĆ et al. (2010): Ni 266.2 ppm; Co 63.5 ppm, Cd 319.6 ppm; Bi 1466.0 ppm; Au 38.96 ppm which also agrees with our analysis of Hg-tetrahedrite from the Brixlegg barite deposit in Tyrol, Austria: Co 234.4 ppm; Cd 160.5 ppm; W 6.7 ppm; Sn 1.0 ppm; Bi 909.1 ppm; Se > 100 ppm and Au 2.3 ppm. The δSCDT isotope values of six tetrahedrites from the Saski Rad are on average –10.11‰, those of three tetrahedrites from the Duboki Vagan –10,05‰ and of the tetrahedrite from the Brixlegg deposit –1.60‰. The ΣREE content is lower in two analysed tetrahedrites from the Saski Rad deposit (10 ppm) compared to the tetrahedrite from Duboki Vagan (15 ppm) and the tetrahedrite from Brixlegg (17.4 ppm). The analysed barite sample from the Saski Rad deposit does not contain microconstituents typical of Hg-tetrahedrite. The distribution and genetic signifi cance of some trace elements, tetrahedrite microconstituents, REE and siderite isomorphic components in the seven most important genetic and paragenetic types of ore deposits in the MBSM and South-Eastern Bosnia have been commented upon.


INTRODUCTION
In the framework of the Variscan metallogeny in the Mid-Bosnian Schist Mts.(MBSM) and South-Eastern (SE) Bosnia, particular attention has been paid to the problem of tetrahedrites, the main ore minerals of numerous barite and barite-siderite ore deposits (JURKOVIĆ, 1956;JURKOVIĆ et al., 2010).
The analytical data obtained from these 16 tetrahedrite samples, demonstrate signifi cant differences resulting from a) the distance of the ore deposit from the long and deep Voljevac fault; b) the stratigraphic level (age) of the host rock; c) the type of the host rock (carbonates or metaclastics); d) being overprinted (or not) by ascending mercurybearing fl uids.
The average values of Hg, Fe, Zn and As in the tetrahedrite samples from the barite-siderite deposits of the four most important ore regions of the MBSM are represented in Table 1.Evidently, the mercury content in the tetrahedrite crystal lattice depends on the distance of the deposit from the Voljevac fault.The Maškara vein (No 6) and the Mračaj vein (No 46) are the biggest and the richest Hg-tetrahedrite ore deposits in the MBSM.The Maškara vein is 2 km and the Mračaj vein only 0.5 km away from the fi rst order Voljevac fault.The values of the same elements in tetrahedrites from the Gemericum (Slovakia) (CAMBEL-JURKOVSKY et al., 1985) and from the Brixegg, Tyrol (Austria) (LUKAS, 1971;GSTREIN, 1983;FRIMMEL and PAPESH, 1990) are included in Table 1 for comparison.
Our initial detailed study of the tetrahedrite genesis in the MBSM and SE Bosnia, demanded additional, more precise analytical methods which ensure the determination of Au intergrowths and microconstituents in the tetrahedrite samples such as Ni, Co, Cd, Sn, W, Se, Te, another 31 trace elements and 14 rare earth elements.The fi rst such determination has been done on Hg-tetrahedrite from the Duboki Vagan deposit (D-VAGT sample) in which the following microconstituents have been detected: 266 ppm Ni, 63.5 ppm Co, <0.5 ppm W, 313 ppm Cd, <1.0 ppm Sn, <0.5 ppm Se and 39 ppm Au (JURKOVIĆ et al., 2011).
In this paper, our objectives are to investigate in great detail the chemical composition of Hg-tetrahedrite from the smaller barite-siderite deposits Saski Rad and Rad.They present the south-eastern prolongation of the Maškara ore deposit, the biggest Hg-tetrahedrite deposit in the MBSM, located in the Silurian-Devonian (S,D) metaclastic rocks, 9 km SE of the town of Gornji Vakuf.In order to elucidate its genesis, Hg-tetrahedrites will be compared with Hg-tetrahedrite samples from other Maškara vein type deposits; the Duboki Vagan (Kreševo) and Brixlegg (Tyrol) barite deposits.

Geology of the Gornji Vakuf area
The Gornji Vakuf area is situated in the middle part of the south-western Mid-Bosnian Schist Mts. (Fig. 1.a).Fig. 1.b presents a simplifi ed geological map, compiled from data published by SOFILJ & ŽIVANOVIĆ (1979) and SOFILJ et al. (1980).
The oldest rocks of the area are chlorite-sericite schists and sericite-chlorite-quartz schists, locally interlayered by metasandstones and, in the area of Gromilica, by quartzites.
Table 1: Average values (in wt.%) of Hg, Fe, Zn and As in the crystal lattices of tetrahedrite samples from the barite-siderite deposits located in the four most important regions of the Mid-Bosnian Schist Mountains (MBSM) (JURKOVIĆ et al., 1997).Abbreviations: lm = limestone; do = dolomite; sch = metaclastic rocks (phyllite, metasandstone); S = Silurian; D = Devonian; n = number of analysed tetrahedrite samples; nmrs = numerous; av = average value; rg = range; V. Fault = Voljevac Fault.In the Mt.Vranica area, the Silurian-Devonian complex is tectonically covered by Devonian limestones with subordinate dolomites.The lowest part, found only in the Suvodol valley, is built up by the fossiliferous Lower Devonian platy limestones (D 1 ).The Middle Devonian consists of zoogene, massive and rarely bedded limestones and subordinate dolomites (D 1 , 2 ).On the geological map, Prozor Sheet, Car bon iferous rocks have not been registered, although ŽIVA NOVIĆ (1972) presumes that younger parts of the Silurian-Devonian complex may belong to the Lower Carboniferous.
Shallow subvolcanic rhyolite (denoted as X in the Fig. 1.b) intrusions and extrusions are numerous.JURKOVIĆ et al. (2010) proved by 87 Sr/ 86 Sr ratio that they represent an S-type granitoid magma as previously assumed by MAJER & GARAŠIĆ, 2001.They are mostly transformed into meta- rhyolites (denoted as X' in the Fig. 1.b) by Variscan regional metamorphism.Keratophyres (nq), are much rarer, younger than (meta)rhyolites and belong to the Permian.
The Lower Triassic (T 1 ) is composed of siltstones and limestones, and the Middle Triassic (T 2 ) by limestones, dolomites and a volcanic-sedimentary formation.
2) Hydrothermal ore deposits (Nos 1-46 in Fig. 1.b): a) The Maškara vein type, containing siderite, barite and Hg-tetrahedrite, located SE of Gornji Vakuf in metapelites and metapsammites of the lower parts of the Silurian-Devonian complex (Nos 1-15); b) The Cvrče-Borova Ravan type, containing barite, siderite and Hg-tetrahedrite, located in metaclastic rocks of the higher parts of the Silurian-Devonian complex (Nos 16-24); c) The Sabiljine Pećine type, containing only barite, while Hg-tetrahedrite is a very subordinate or even accessory mineral.This type is located in the partly dolomitised Middle Devonian limestones, (Nos 25-43); and d) The Mračaj type, which is characterised by a barite-siderite-Hg-tetrahedrite paragenesis.This type is located along the Voljevac fault zone (the tectonic contact between the Upper Permian and Lower Palaeozoic) .
3) Metamorphogenic quartz deposit (No 47 in Fig. 1.b) The research here is restricted to ore occurrences situated in the triangular area between the western slopes of the Vrbas river, western banks of the river Desna and eastern banks of the river Dragučina, a western tributary of the Vrbas river.There are hydrothermal ore deposits of the Maškara paragenetic type (Nos 5-15 in Fig. 1.b) and the Cvrče-Borova Ravan paragenetic type (Nos 16-24) present in this (~60 km 2 ) area.
Taking into consideration two published detailed studies of the Maškara vein (KATZER, 1907;JURKOVIĆ, 1960), research samples were selected from the old medieval and Austrian mines Rad and Saski Rad, which are a prolongation of the Maškara vein.

General characteristics of the Maškara vein type
From 15 ore occurrences (Nos 1-15) attributed to this paragenetic type, the biggest one is the Maškara vein (Nos 6).It is 250 to 350 m long, vertically over 110 m high, 0.1 to 1.0 m thick, dipping 75°/40-60°.This vein produced 8.0 tons of crude ore with 25% of Hg-tetrahedrite.The average content of Hg-tetrahedrite was 9-15 vol.% or 10-16 wt.% in barite crude ore and 20-60 vol.% or 15-65 wt.% in siderite crude ore (KATZER, 1907;JURKOVIĆ, 1960).The Rad (No 7) and Saski Rad (No 8) are ore occurrences which belong to the Maškara genetic type.The quantitative relationship of the main constituent elements in the Hg-tetrahedrite of the Rad and Saski Rad deposits is very similar to that in the Hg-tetrahedrite from the Maškara deposit, indicating that these deposits might represent the broken parts of the Maškara ore vein.The Maškara vein lies at the absolute altitudes of +820 to +930 m, the Rad deposit at an altitude of +1000 m, and the Saski Rad deposit at +1070 m.
On the western banks of the river Desna (a tributary of the Vrbas river), the other ore deposits belonging to the Ma š ka ra paragenetic type are located: Desna (No 9 in the Fig.In these deposits, siderite is the main mineral with single Hg-tetrahedrite grains, net-like aggregates or interrupted interlayers of tetrahedrite.Barite is abundant, but subordinate.Ore occurrences Nos 10 and 11 contain an increased quantity of quartz ± pyrite and a decreased amount of tetrahedrite (JURKOVIĆ et al., 1994).All these veined ore occurrences stretch NNE-SSW or NE-SW with a very steep dip.They are short, shallow and very thin veins (from 0.1 to 0.2 m thick).Their outcrops lie at altitudes of +1100 m, hosted by the rocks of the lower part of the Silurian-Devonian complex (phyllite and similar rocks).
In the Cvrče-Borova Ravan area, at altitudes of +1050-+1350 m, similar ore occurrences have been discovered, characterised by barite as the dominant ore mineral, whereas siderite ± quartz are subordinate minerals.Hg-tetrahedrite is scarce or very subordinate.The following ore deposits and occurrences belong to this paragenetic type: Ladina Voda ) is somewhat thicker (0.10-0.40 m).All ore occurrences are hosted by metasandstones and schists are attributed to the higher parts of the Silurian-Devonian complex.ŽIVANOVIĆ (1972) claims that these rocks belong to the Lower Carboniferous.
At Borova Ravan-Guvnanica (No 21) and Ričica (No 24) fragments of ore were only discovered in blocks and not in associated outcrops.
Mineralization of the Maškara vein type occurred inside a system of tensional fi ssures and joints of variable lengths, widths and depths.The ore occurrences strike mostly NNW-SSE and dips towards the ENE with very different angles.The other extensive system, 3.5 km long, has been registered between the Vrbas and Desna rivers (N-S strike, dip towards the E).
In higher levels of the ore deposits, barite predominates over subordinate Hg-tetrahedrite, whereas in the lower levels siderite and Hg-tetrahedrite (± quartz) predominate.
Within the geological column, a vertical zonation of the whole Silurian-Devonian complex was also observed.In the lower parts of the complex, siderite with subordinate barite and quartz are common, whereas in the higher parts, barite with subordinate siderite and tetrahedrite are common.
The relationships between tetrahedrite, barite and siderite in Maškara-Saski Rad vein described by KATZER (1907) are shown in Fig 2.

THE MAIN GENETIC AND PARAGENETIC TYPES OF MINERAL OCCURRENCES ESTABLISHED IN THE MBSM AND SE BOSNIA
The following main genetic and paragenetic types of mineral occurrences have been established in the MBSM and SE Bosnia: Ia) The oldest nonmetallic occurrences are numerous Variscan synorogenic and postorogenic sterile, monomineralic quartz veins and irregular quartz bodies located in the Busovača, Fojnica, Kiseljak, and Kreševo area (KATZER, 1926;JURKOVIĆ, 1956;HRVATOVIĆ, 1996).
II) The Vrtlasce ore deposit is a small, but paragenetically very interesting ore type, located east of the town of Fojnica.Siderite, ankerite and subordinate albite are the main minerals, but the pneumatolytic phase with cassiterite, stannite and molybdenite is clearly noticeable (JURKOVIĆ, 1956;1958).The hydrothermal phase with 0.02 wt.% Cu, 2.2 wt.% Pb, and 5.0 wt.% Zn is very well developed.This deposit having >300 ppm Ag was a very good supply of silver for the Saxon miners in the Middle Ages.Due to the reduction of Bi and Se, the content of gold was only 0.07 g/t.The silver bearing minerals were galena, boulangerite and other Pb-antimonides.
IV) The Bakovići gold-bearing pyrite veins with 10-20 wt.% SiO 2 , 5-10 wt.% of Mn-siderite and 50-75 wt.% of gold-bearing pyrite are the richest gold deposits in Bosnia and Herzegovina.The average gold content in the Bakovići ore deposit is 21 g/t Au and 13 g/t Ag.The source of gold in this deposit is presently unknown (JURKOVIĆ, 1995).
The position of the main genetic and paragenetic types of mineral occurrences are shown in Fig. 3.

ANALYTICAL METHODS
Numerous thick opaque polished sections of the tetrahedrite samples were studied using refl ected polarized light.Thinsections of barite and siderite samples were examined using transmitted polarized light.The information obtained enabled separation of the fresh and weathered samples.Selected samples were crushed, hand-picked under binocular microscope and powdered in an agate mortar for chemical analysis.
A relatively high Se content (>100 ppm) was determined for the fi rst time in the fresh Hg-tetrahedrite of the Saski Rad deposit in the MBSM.This led to similar analysis of the weathered Hg-tetrahedrite of Saski Rad deposit in order to confi rm a similar high Se content of Hg-tetrahedrite as a typical characteristic of this deposit.
Major and trace elements were analysed by inductively coupled plasma (ICP) mass spectrometry -in ACME Analytical Laboratories, (Vancouver) Ltd. in Canada.Sulphur and oxygen stable isotope compositions were determined at the Stable Isotope Laboratory of the University of Lausanne, using the Finnigan Mat Facility.
The Saski Rad No 7 tetrahedrite sample has been analyzed by atomic absorption spectrometry (AAS) and ICP-AES, after Br 2 HCL digestion, in the Croatian geological Institute in Zagreb (JURKOVIĆ et al., 1997), and Saski Rad No 8 tetrahedrite sample by PIXE method with scanning proton microprobe in the Institute Rudjer Bošković in Zagreb (JURKOVIĆ et al., 1997).
According to the analysis of the SAS-TET sample, the studied tetrahedrite represents a Cu-Sb-S tetrahedrite, in which Cu is isomorphically replaced by Fe (5.70 wt.%), Hg (3.81 wt.%), Zn (0.225 wt.%) and Ag (>0.03 wt.%) and also by minor elements (71 ppm Ni, 113 ppm Co, 20 ppm W and 27 ppm Cd).Additionally, Sb is replaced by As (5.02%) and Bi (0.25 %), whereas S is replaced by Se (>100 ppm).This represents the fi rst discovery of selenium in the MBSM and SE Bosnia tetrahedrite samples.Au (11 ppm) is present in microcavities and fi ssures of tetrahedrite.Only 9 trace elements (Cr, Mo, Tl, Cs, Rb, U, V, Zr and Y), among the 31 analysed, have been detected, accounting for 122.5 ppm in total.Among them Tl is the most abundant (91.9 ppm; accounting for 75% of the total).In the other analysed tetrahedrite samples from the MBSM, Tl was not detected.The REE values of the studied Hg-tetrahedrite are very low (10.16 ppm in total, Table 2).The δ 34 S CDT values of this Hg-tetrahedrite equal -10.60‰.There are six Hg-tetrahedrite samples from the Saski Rad deposit (Table 3), which have already been analysed for δ 34 S CDT values (three in this work).These values, ranging from -9.50‰ to -10.69‰ (average: -10.09‰), are in accordance with 18 other values obtained from 18 different Hg-tetrahedrite samples over the whole Mid-Bosnian Schist Mts.(JURKOVIĆ et al., 1997), which range from -5.50‰ to -15.40‰ (average: -10.40‰).

Analytical results of weathered Hg-tetrahedrite (SAS-41 sample)
Results of quantitative chemical analysis of one weathered Hg-tetrahedrite, grown inside the oxydised siderite from the Saski Rad deposit, are presented in Table 4.The elements V (15.00 ppm), Y (2.40 ppm), Rb (0.80 ppm), Zr (0.50 ppm) and U (0.40 ppm) have values barely above method determination limit (MDL).All other trace elements have been not detected.
The studied weathered Hg-tetrahedrite contains the following microconstituents: Ni (70 ppm), Ag (>300 ppm), Co (90 ppm), W (50 ppm), Cd (20 ppm) and Se (70 ppm), whereas Au (9175 ppb) is present in cavities and fi ssures of tetrahedrite.The discovery of selenium in the fresh tetrahedrite (>100 ppm Se) and also in the weathered tetrahedrite (70 ppm Se) from the Saski Rad ore deposit defi nitely confi rms the presence of selenium as a constitutive trace element in the tetrahedrite crystal lattice of the MBSM region.The REE values of the studied sample are very low (9.96 ppm in total), similar to the other Hg-tetrahedrites.

Analytical results of the barite (S-RAD sample)
Analysis of the barite, which occurs in paragenesis with tetrahedrite in the Rad ore deposit is presented in Table 5.In the fi rst group of trace elements, ranging from Be to Y, 4 elements (Hf, Rb, Ta and Y) were identifi ed accounting for only 12.20 ppm in total.
The second group of trace elements (Mo to Se) contains, among others, Cu (68.40 ppm), Sb (21.10 ppm), As (5.40 ppm), Hg (5.25 ppm), Zn (5.0 ppm), Ag (1.0 ppm) and Au (0.6 ppb), which are the major constituents of Hg-tetrahedrite.Microconstituent elements typical for Hg-tetrahedrite have not been identifi ed in this barite sample.Identical results were recorded in other studied barite samples taken from the various barite deposits throughout the MBSM.
The analysed barite sample is characterised by its extremely low content of REE (6.61 ppm in total), which is similar to the other analysed samples of barite from the MBSM and SE Bosnia.The values for Pr, Nd and Sm were below the MDL.

Analytical results of siderite
The content of the four major components (mol.and wt.%) of the siderite sample, representative of the Maškara-Saski Rad vein system, analysed by JURKOVIĆ et al. (1994), are presented in Table 6.Molar composition refl ects a hydrothermal fl uid system characterised by heightened temperature.

Analytical results of tetrahedrite and barite from neighbouring ore deposits
For the purpose of the comparison, the sulphur and oxygen isotope compositions of Hg-tetrahedrite and barite from the neighbouring Cvrče Village barite deposit (Fig. 1.b) were also determined within the scope of this work.These results, together with isotopic compositions and SrSO 4 content of barite from the Djamuš Brdo, Crvče/Zaganj and Borova Ravan barite deposits determinated by JURKOVIĆ et al. (1994) are presented in Table 7.All analyzed δ 34 S CDT values in tetrahedrites are negative (-1,20 to -10,69‰), whereas those in barites are positive (+15,10 to +18,48‰).

The problem of microconstituents in the tetrahedrite
According to RAMDOHR (1986) 1/4 of copper places in tetrahedrite must be replaced by Fe, Zn, Co, Ni, Ag and Hg; arsenic and antimony by Bi, Sn, W, Ge and Te, and sulphur by selenium.DUDA & REJL (1987) defi ned only Ni, Co, W, Cd and Se as trace elements in tetrahedrite.JOHNSON et al. (1988) and FOTT & HUGHES (2004) consider that copper can be replaced by Fe, Zn, Mn, Hg, Cd, and Ag; arsenic and antimony by Bi and Te; and sulphur by Se.They consider that the structure of tetrahedrite must be analo guous to the structure of the mineral sodalite.
The microconstituent elements can be inserted in tetrahedrite: (a) as micro-scale inclusions occupying defects in the structure; (b) as myrmekitic intergrowths of various fi neness, some of which originate through decomposition and (c) as exsolution textures.According to RAMDOHR (1986) exsolutions in tetrahedrite are exceptionally rare (only bismuthinite and questioned "goldfi eldite").The needles of bismuthinite (bi) oriented paralell to (111) (Fig. 3) and discs and needles of bis muthinite (Fig. 4) as exsolutions in tetrahedrite crystals (t) from the Trošnik, Fojnica deposit (MBSM) have been found by the fi rst author of this work during his postdoctoral study (1957) at the Geological Department of Heidelberg University.These results have been confi rmed by professor Ramdohr and published by JURKOVIĆ (1958).
Myrmekitic intergrowths of tetrahedrite (t) with one sulphide or sulphosalt (sl), the most probably Ag-mineral according to optical properties, have been also documented by JURKOVIĆ (1958) and are shown in Fig. 5.This texture most likely originated by decomposition of one rich silverbearing tetrahedrite containing 0.20 and 0.34 wt.% Ag (JURKOVIĆ et al., 1997).
According to our opinion, very often gold occurs mechanically inserted as micro-scale inclusions in tetrahedrite occuppying defect places in its structure.JURKOVIĆ (1958) took photomicrographs of gold also occurring as irregular masses of microscopic dimension (Fig. 6).

Distribution of the most important tetrahedrite microconstituents as trace elements in the ore deposits located in the MBSM and SE Bosnian areas
The distribution of Co, Ni, Sn, W, Ag, Au, Hg, Bi and Se in the seven main genetic types of ore deposits (Chapter 3) is presented in the Table 8.
Cobalt is the most abundant element in the oldest phase (Mačje Jame, 78 ppm) and in the youngest phase of mineralisation (Maškara-Saski Rad veins, 113 ppm).One unindentifi ed mineral with optical characteristics very similar to a    Co-Ni-arsenide was discovered using a polarised microscope, but only from the Mačje Jame deposit.
Nickel is most abundant in the Mačje Jame deposit (105 ppm) then in the Vrtlasce deposit (78 ppm) and in the Maškara-Saski Rad tetrahedrite veins (71 ppm).
Tin has been found optically as cassiterite and stannite minerals by JURKOVIĆ (1956JURKOVIĆ ( , 1958a) ) in the Vrtlasce deposit (average 429 ppm Sn; maximal 900 ppm) and in the Mačje Jame (115 ppm Sn).JURKOVIĆ & HRVATOVIĆ (manuscript) found tin in the Vranjska Rijeka deposit.These three ore deposits are characterized by a well developed pneumatolytic phase.In the hydrothermal phase (Hg-tetrahedrite) tin is very rare and hardly measurable.
Tungsten as the mineral ferberite (Fe,Mn)WO 4 was discovered by RAMOVIĆ (1956), in the silver-bearing sphalerite-antimonite quartz vein named "Main vein" and "NW Čemernica" veins (W = >100 ppm).Small contents of W we found in the Mačje Jame deposit (26 ppm) and in the Maškara-Saski Rad Hg-tetrahedrite veins (20 ppm).The majority of tungsten was consumed earlier by formation of mineral wolframite.
Bismuth and selenium are closely genetically related.Their presence was fi rst observed in the Mačje Jame deposit (Bi = 15 and Se = 14 ppm), but they are most abundant in the Vranjska Rijeka deposit (230 ppm Bi and 20 ppm Se), as the minerals cosalite and elemental bismuth (JURKOVIĆ & HRVATOVIĆ, in press).The Vranjska Rijeka deposit contains 0.33 g/t of gold, the Vrtlasce deposit contains 0.07 g/t and there is less in the Mačje Jame deposit at 0.01 g/t.The occurrence of Bi and Se simultaneously with gold in these three deposits indicates their clear positive correlation.
The best positive correlation between Bi, Se and Au has been established in the Hg-tetrahedrite deposits, Maškara-Saski Rad and Kreševo types.The element Bi, having usually microelement status, becomes a very important major element (0.20-0.25 wt.%; max.0.58 wt.%), whereas the abundance of Se exceedes 100 ppm.Tetrahedrites with such contents of Bi and Se, contain 8 to 62 g/t of Au and between 300 ppm and 0.34 wt.% of Ag (JURKOVIĆ et al., 1997).
In Hg-tetrahedrite, gold is in pronounced positive correlation with mercury which in the Hg-tetrahedrite also be-comes a major element (on average 3.0 wt.%) for the fi rst time.In the earlier mineralization phases, mercury was only a trace element.The occurrence of scarce cinnabar in the Čemernica deposit is an exception, but in our opinion, this phenomenon is only a younger overprint.
Silver is characterized by a positive correlation with Pb-Sb sulphides and sulphosalts in the Vrtlasce and Čemernica deposits.In the Middle Ages, these two groups of silverbearing deposits were rich suppliers of silver ore for the Saxon miners.
The second bearers of silver are small, but numerous polymetallic barite ± siderite ± calcite ± quartz veins and replacement bodies, and are best developed in SE Bosnia.They are rare in the MBSM.Ag is linked with Fe, Cu, Zn, Pb, and Sb sulphides and sulphosalts, particularly with PbS and Pbantimonides.The silver content is moderate (some tenths of a gram/t) and gold only occurs as a trace element.
The third, youngest silver mineralization phase is genetically related to the occurrences of Hg-Bi-tetrahedrite in the monosulphide barite-siderite Maškara-Saski Rad veins, and in the barite ± fl uorite replacement bodies of the Kreševo type.These deposits contain Hg-tetrahedrite, in which the Ag content ranges between 300 ppm and 3400 g/t, whereas its Au content varies from 8 to 62 g/t.The Bakovići deposit also has a high content of gold (21 g/t) but only 13 g/t Ag.
Cadmium isomorphically supstitutes zinc in the crystal lattice of sphalerite and zinc in the Hg-tetrahedrite.
Tellurium in the Hg-tetrahedrite from the MBSM has not, so far, been investigated by chemical analyses.Optical investigations of polished sections of Maškara Hg-tetrahedrites under polarized microscope revealed some minute minerals, with optical characteristics very similar to Au-telluride (JURKOVIĆ, 1960).This suggests that there should be a positive correlation between gold and tellurium.
Thalium with an increased content of 91.9 ppm has been only been discovered in one out of more than fi fty analysed samples.
Comparison of the microconstituents of studied Hg-tetrahedrite from the Saski Rad vein deposit, with those of the Hg-tetrahedrite samples taken from the Duboki Vagan de-  Rash reduction of total REE content during the subsequent phase of mineralization (Vrtlasce deposit) is the result of crystallization of some lanthanide minerals in the earlier phase.These were most probably minerals of the bastnaesite group, as described by RADVANEC et al. (2004) in the similar Slovakian ore deposit.

Problem of lanthanides (REE)
Only partial analytical data is available for the Čemernica type deposit and the later Bakovići ore type mineralisation phase, and therefore they could not be included in Table 10.
Numerous analytical values have been obtained from the fi fth phase of mineralization.The highest content of total REE characterizes the siderite from SE Bosnia (33.0 ppm).Lower contents have been found in siderite from the Trošnik ore deposit (15.6 ppm), in the Hg-tetrahedrite from the Maškara-Saski Rad deposit (9.2 ppm) and in barite from the Maškara-Saski Rad deposit (8.4 ppm), whereas barite from the SE Bosnia contains only 5.1 ppm of total REE.Fluorite from the Dubrava (Kreševo) ore deposit is the mineral containing the least REE.Its two analyses contain 0.427 and 0.406 ppm of total REE.These fl uorites belong to the latest phase of mineralisation in the MBSM.Analyses of fl uorites were performed by INAA facilities in the Institute for Petrology and Geochemistry, Karlsruhe University (PALINKAŠ & JURKOVIĆ, 1994).
The evidence suggests a successive decrease of total REE contents, not only because of the formation of new REE minerals, but also due to insertion of REE in the vacant defect places of the crystal lattices of other minerals, especially siderite, ankerite, barite and tetrahedrite.Evidence suggests that mixed hydrothermal fl uids played a specifi c role in this process during the last mineralization phase.The development of REE from the oldest to the youngest ore deposits indicates gradual reestablishment of a uniform and unique hydrothermal system in the MBSM area.

Composition of FeCO 3 , CaCO 3 , MgCO 3 and MnCO 3 isomorphic components of siderite in the diff erent genetic and paragenetic types of ore deposits in the MBSM and SE Bosnia
Table 11 shows six siderite chemical analyses belonging to the six most important genetic and paragenetic ore types from the MBSM deposits: Mačje Jame, Vranjska Rijeka, Vrtlasce, Trošnik, Maškara-Saski Rad and Bakovići-Čemer- nica.The paragenesis and some PT conditions of these deposits are described in Chapter 3. Table 11 demonstrates the clear interdependence of the composition of Fe-carbonates and PT conditions during their genesis.

CONCLUSIONS
a) Both fresh and weathered Hg-tetrahedrite samples from the Saski Rad deposit have been examined concerning their microconstituents.W (20 ppm) and Se (>100 ppm) have been detected for the fi rst time in the MBSM Hg-tetrahedrite.
There is an interesting correlation of the Se content between the Saski Rad and Brixlegg deposits.The Au content of the Saski Rad Hg-tetrahedrite is relatively high (11 ppm), four times lower than in the Duboki Vagan tetrahedrite, but four times higher than in the Brixlegg Hg-tetrahedrite.
b) The low content of total REE (10 ppm) and strong negative δ 34 S CDT values (average: -10.09‰) in the Hg-tetrahedrite samples of the Saski Rad vein deposit are in accordance with 18 other previously analysed Hg-tetrahedrite samples from the whole of the Mid-Bosnian Schist Mts.
c) The quantitative relationship of the main constituents in the studied tetrahedrite is very similar to that in the tetrahedrite of the Maškara deposit, confi rming the earlier assumption that the Saski Rad vein deposit represents the broken part of the Maškara ore vein.
d) The Co, Ni, Sn, W, Ag, Au, Hg, Bi and Se distribution in the seven most important paragenetic types of the MBSM and SE Bosnia ore deposits is signifi cant in several ways.Optical studies suggest that Co and Ni, are most probably present as Co-Ni arsenides in the oldest iron deposits (Mačje Jame and Vranjska Rijeka), and also occur as microconstituents in Hg-tetrahedrite.Sn is completely consumed in the pneumatolytic-hydrothermal Pb, Zn and Cu sulphide deposits as cassiterite and stannite.The fi rst Sn occurrence is detected in the Mačje Jame deposit.W, as the mineral ferberite, was found in the silver-bearing Čemernica sphaleriteantimonite deposit.Bi with 230 ppm and Se with 20 ppm drew attention to the fi rst gold (0.33 ppm) presence in the Vranjska Rijeka copper (0.7 % Cu) deposit.The second very strong occurrence of Bi (with 0.25-0.58wt.%) and Se (with >100 ppm) is observed in the last hydrothermal Hg-tetrahedrite-bearing barite ± siderite phase.Hg (average 3.07 wt.%), occurs in association with Bi and Se as a major constituent, whereas in all other deposits it is absent or present only as a trace element.There is a positive correlation between Bi, Se, Hg and Au, Ag presence in studied ore deposits.e) A review of numerous previous scientifi c investigations of parageneses, isotope composition (C, O, S, Sr, Pb), fl uid inclusion, trace elements, and REE data analysis, suggests that the seven main paragenetic and genetic types of the MBSM and SE Bosnia ore deposits are generated dominantly from metamorphogenic fl uids.The important masses of (meta)-rhyolites and keratophyres are formed by anatexis, as evidenced by Sr isotope data.Palaeozoic protoliths, metamorphosed by several stages of Variscan progressive and retrograde metamorphism, are the sources of hydrothermal fl uids.A similar opinion concerning the genesis of siderite ± barite deposits of Rudnány (Slovakia) was published by GRECULA et al. (1989);ŽAK et al. (1950) and RADVAN EC et al. (2004).
The most convincing evidence of the metamorphogenic origin of the hydrothermal fl uid is the strong similarity of total REE and the dominant La, Ce and Nd elements in the meta-rhyolite and their pellitic and psammitic metamorphosed protoliths on one hand and the oldest Mačje Jame and Vranska Rijeka iron ore deposits on the other (Table 10).f) Previous investigations of the MBSM and SE Bosnia ore deposits established unexpected contrasting parageneses that indicate several different hydrothermal fl uids and PT conditions.The best example is Čemernica, an important rich silver-bearing deposit containing >150 g/t Ag, only traces of Au and >100 ppm W, in relation to the richest goldbearing pyrite deposit Bakovići having 11 g/t Au and only 13 g/t Ag, but without W.
g) The composition of FeCO 3 , CaCO 3 , MgCO 3 and MnCO 3 isomorphic components of sideritic gangue in the MBSM and SE Bosnia ore deposits are dependent upon PT conditions and the hydrothermal fl uid system.
0-6.0)LUKAS (1971),GSTREIN (1983),FRIMMEL & PAPESH (1990) In the area of the Cvrče Village and in the Desna Valley younger rocks and slates occur.The area near Krugljača is characterised by the occurrence of sandy sericite-chlorite schists and schistose sandstones.Limestone and dolomite lenses are very rare.All these rocks are attributed to the Silurian-Devonian metamorphic rocks of greenschist facies (S,D in Fig. 1.b).

Table 3 :
Sulphur isotope composition of six mercurian tetrahedrites from the Saski Rad deposit.

Table 5 :
Trace element and REE contents of the barite sample (S-RAD) from the Saski Rad deposit.

Table 8 :
The distribution of Co, Ni, Sn, W, Ag, Au, Hg, Bi and Se in the seven main genetic types of ore deposits.

Table 8 .
There is an interesting correspondence in the content of Se between Saski Rad and Brixlegg deposits.The Au content in the Saski Rad and Duboki Vagan tetrahedrites is several times higher than that of Brixlegg tetrahedrite.Furthermore, the Saski Rad and Duboki Vagan tetrahedrite have higher Ni and Bi content compared to the Brixlegg tetrahedrite.However, the Brixlegg tetrahedrite contains more Co and Cd than the Saski Rad tetrahedrite.

Table 10 :
The contents of the total REE and the values of the three dominant lanthanides (La, Ce, and Nd) in the (meta)-rhyolite and keratophyre of the Kreševo (KRE) and Busovača (BUS) regions compared with those of some important ore deposits in the MBSM and SE Bosnia.

Table 11 :
Interdependence between the composition of siderite and its genetic ore type (PT conditions).